Intermittent energy restriction inhibits tumor growth and enhances paclitaxel response in a transgenic mouse model of endometrial cancer

OBJECTIVE

Overweight/obesity is the strongest risk factor for endometrial cancer (EC), and weight management can reduce that risk and improve survival. We aimed to establish the differential benefits of intermittent energy restriction (IER) and low-fat diet (LFD), alone and in combination with paclitaxel, to reverse the procancer effects of high-fat diet (HFD)-induced obesity in a mouse model of EC.

METHODS

Lkb1fl/flp53fl/fl mice were fed HFD or LFD to generate obese and lean phenotypes, respectively. Obese mice were maintained on a HFD or switched to a LFD (HFD-LFD) or IER (HFD-IER). Ten weeks after induction of endometrial cancer, mice in each group received paclitaxel or placebo for 4 weeks. Body and tumor weights; tumoral transcriptomic, metabolomic and oxylipin profiles; and serum metabolic hormones and chemocytokines were assessed.

RESULTS

HFD-IER and HFD-LFD, relative to HFD, reduced body weight; reversed obesity-induced alterations in serum insulin, leptin and inflammatory factors; and decreased tumor incidence and mass, often to levels emulating those associated with continuous LFD. Concurrent paclitaxel, versus placebo, enhanced tumor suppression in each group, with greatest benefit in HFD-IER. The diets produced distinct tumoral gene expression and metabolic profiles, with HFD-IER associated with a more favorable (antitumor) metabolic and inflammatory environment.

CONCLUSION

In Lkb1fl/flp53fl/fl mice, IER is generally more effective than LFD in promoting weight loss, inhibiting obesity-related endometrial tumor growth (particularly in combination with paclitaxel), and reversing detrimental obesity-related metabolic effects. These findings lay the foundation for further investigations of IER as an EC prevention and treatment strategies in overweight/obesity women.

FGFR1 Signaling Facilitates Obesity-Driven Pulmonary Outgrowth in Metastatic Breast Cancer

Survival of dormant, disseminated breast cancer cells contributes to tumor relapse and metastasis. Women with a body mass index greater than 35 have an increased risk of developing metastatic recurrence. Herein, we investigated the effect of diet-induced obesity (DIO) on primary tumor growth and metastatic progression using both metastatic and systemically dormant mouse models of breast cancer. This approach led to increased PT growth and pulmonary metastasis. We developed a novel protocol to induce obesity in Balb/c mice by combining dietary and hormonal interventions with a thermoneutral housing strategy. In contrast to standard housing conditions, ovariectomized Balb/c mice fed a high-fat diet under thermoneutral conditions became obese over a period of 10 weeks, resulting in a 250% gain in fat mass. Obese mice injected with the D2.OR model developed macroscopic pulmonary nodules compared with the dormant phenotype of these cells in mice fed a control diet. Analysis of the serum from obese Balb/c mice revealed increased levels of FGF2 as compared with lean mice. We demonstrate that serum from obese animals, exogenous FGF stimulation, or constitutive stimulation through autocrine and paracrine FGF2 is sufficient to break dormancy and drive pulmonary outgrowth. Blockade of FGFR signaling or specific depletion of FGFR1 prevented obesity-associated outgrowth of the D2.OR model.

IMPLICATIONS

Overall, this study developed a novel DIO model that allowed for demonstration of FGF2:FGFR1 signaling as a key molecular mechanism connecting obesity to breakage of systemic tumor dormancy and metastatic progression.

Tirzepatide attenuates mammary tumor progression in diet-induced obese mice

We report for the first time an anticancer benefit of tirzepatide-a dual glucagon-like peptide 1 and glucose-dependent insulinotropic polypeptide receptor agonist-in a model of obesity and breast cancer in female mice. Long-term tirzepatide treatment induced weight loss, mitigated obesity-driven changes in circulating metabolic hormone levels, and suppressed orthotopic E0771 mammary tumor growth. Relative to tirzepatide, chronic calorie restriction, an established anticancer intervention in preclinical models, promoted even greater weight loss, systemic hormonal regulation, and tumor suppression. We conclude that tirzepatide represents a promising pharmacologic approach for mitigating the procancer effects of obesity. Moreover, strategies promoting greater weight loss than achieved with tirzepatide alone may augment the anticancer benefits of tirzepatide.

Calorie restriction outperforms bariatric surgery in a murine model of obesity and triple-negative breast cancer

Obesity promotes triple-negative breast cancer (TNBC), and effective interventions are urgently needed to break the obesity-TNBC link. Epidemiologic studies indicate that bariatric surgery reduces TNBC risk, while evidence is limited or conflicted for weight loss via low-fat diet (LFD) or calorie restriction (CR). Using a murine model of obesity-driven TNBC, we compared the antitumor effects of vertical sleeve gastrectomy (VSG) with LFD, chronic CR, and intermittent CR. Each intervention generated weight and fat loss and suppressed tumor growth relative to obese mice (greatest suppression with CR). VSG and CR regimens exerted both similar and unique effects, as assessed using multiomics approaches, in reversing obesity-associated transcript, epigenetics, secretome, and microbiota changes and restoring antitumor immunity. Thus, in a murine model of TNBC, bariatric surgery and CR each reverse obesity-driven tumor growth via shared and distinct antitumor mechanisms, and CR is superior to VSG in reversing obesity's procancer effects.

Regulation of IGF1R by MicroRNA-15b Contributes to the Anticancer Effects of Calorie Restriction in a Murine C3-TAg Model of Triple-Negative Breast Cancer

Calorie restriction (CR) inhibits triple-negative breast cancer (TNBC) progression in several preclinical models in association with decreased insulin-like growth factor 1 (IGF1) signaling. To investigate the impact of CR on microRNAs (miRs) that target the IGF1/IGF1R pathway, we used the spontaneous murine model of TNBC, C3(1)/SV40 T-antigen (C3-TAg). In C3-TAg mice, CR reduced body weight, IGF1 levels, and TNBC progression. We evaluated the tumoral expression of 10 miRs. CR increased the expression of miR-199a-3p, miR-199a-5p, miR-486, and miR-15b. However, only miR-15b expression correlated with tumorigenicity in the M28, M6, and M6C C3-TAg cell lines of TNBC progression. Overexpressing miR-15b reduced the proliferation of mouse (M6) and human (MDA-MB-231) cell lines. Serum restriction alone or in combination with low levels of recombinant IGF1 significantly upregulated miR-15b expression and reduced Igf1r in M6 cells. These effects were reversed by the pharmacological inhibition of IGFR with BMS754807. In silico analysis using miR web tools predicted that miR-15b targets genes associated with IGF1/mTOR pathways and the cell cycle. Our findings suggest that CR in association with reduced IGF1 levels could upregulate miR-15b to downregulate Igf1r and contribute to the anticancer effects of CR. Thus, miR-15b may be a therapeutic target for mimicking the beneficial effects of CR against TNBC.

You complete me: tumor cell-myeloid cell nuclear fusion as a facilitator of organ-specific metastasis

Every cancer genome is unique, resulting in potentially near infinite cancer cell phenotypes and an inability to predict clinical outcomes in most cases. Despite this profound genomic heterogeneity, many cancer types and subtypes display a non-random distribution of metastasis to distant organs, a phenomenon known as organotropism. Proposed factors in metastatic organotropism include hematogenous versus lymphatic dissemination, the circulation pattern of the tissue of origin, tumor-intrinsic factors, compatibility with established organ-specific niches, long-range induction of premetastatic niche formation, and so-called "prometastatic niches" that facilitate successful colonization of the secondary site following extravasation. To successfully complete the steps required for distant metastasis, cancer cells must evade immunosurveillance and survive in multiple new and hostile environments. Despite substantial advances in our understanding of the biology underlying malignancy, many of the mechanisms used by cancer cells to survive the metastatic journey remain a mystery. This review synthesizes the rapidly growing body of literature demonstrating the relevance of an unusual cell type known as "fusion hybrid" cells to many of the hallmarks of cancer, including tumor heterogeneity, metastatic conversion, survival in circulation, and metastatic organotropism. Whereas the concept of fusion between tumor cells and blood cells was initially proposed over a century ago, only recently have technological advancements allowed for detection of cells containing components of both immune and neoplastic cells within primary and metastatic lesions as well as among circulating malignant cells. Specifically, heterotypic fusion of cancer cells with monocytes and macrophages results in a highly heterogeneous population of hybrid daughter cells with enhanced malignant potential. Proposed mechanisms behind these findings include rapid, massive genome rearrangement during nuclear fusion and/or acquisition of monocyte/macrophage features such as migratory and invasive capability, immune privilege, immune cell trafficking and homing, and others. Rapid acquisition of these cellular traits may increase the likelihood of both escape from the primary tumor site and extravasation of hybrid cells at a secondary location that is amenable to colonization by that particular hybrid phenotype, providing a partial explanation for the patterns observed in some cancers with regard to sites of distant metastases.

Intermittent fasting interventions to leverage metabolic and circadian mechanisms for cancer treatment and supportive care outcomes

Intermittent fasting entails restricting food intake during specific times of day, days of the week, religious practice, or surrounding clinically important events. Herein, the metabolic and circadian rhythm mechanisms underlying the proposed benefits of intermittent fasting for the cancer population are described. We summarize epidemiological, preclinical, and clinical studies in cancer published between January 2020 and August 2022 and propose avenues for future research. An outstanding concern regarding the use of intermittent fasting among cancer patients is that fasting often results in caloric restriction, which can put patients already prone to malnutrition, cachexia, or sarcopenia at risk. Although clinical trials do not yet provide sufficient data to support the general use of intermittent fasting in clinical practice, this summary may be useful for patients, caregivers, and clinicians who are exploring intermittent fasting as part of their cancer journey for clinical outcomes and symptom management.

Abstract 4235: Obesity drives inflammation and metabolic reprogramming in an orthotopic mouse model of early colon cancer

Obesity is strongly associated with colon cancer incidence and, in animal models, promotes colon cancer growth and progression. Mounting evidence indicates that circulating growth factors and chronic inflammation are procancer factors likely mediating this relationship. While obesity blunts antitumor immunity in many cancer types, how obesity-driven inflammation and reduced antitumor immunity may cooperate to promote colon cancer progression is not yet clear. Here we used a murine syngeneic orthotopic transplantation model of colon cancer to profile changes driven by diet-induced obesity (DIO) in the immune and cancer cell compartments of the tumor using digital spatial profiling and RNA sequencing. 7-9-week-old male and female C57BL/6 mice remained on either a 10 kcal% fat diet (control, n=34) or a 60 kcal% fat diet (DIO, n=27) for at least 19 weeks. 700 Apc-null;KrasG12D/+;Trp53-null;Smad4-null;tdTomato (i.e., AKPS) organoids were transplanted into the colonic wall of control and DIO mice via colonoscopy-guided injection. Tumors were excised after four weeks of growth, an early time point to assess changes between diet groups independent of tumor size differences or weight loss associated with tumor growth. RNA sequencing was performed on RNA extracted from tumoral CD45+ and EpCAM+ cell fractions isolated using Milltenyi MicroBeads. DIO mice weighed more than controls (males: controls 37.0 g ± 5.1 vs. DIO 47.4 g ± 4.3; females: controls 26.4 g ± 3.7 vs. DIO 45.9 g ± 9.7) and had more mesenteric fat surrounding the colon (males: controls 388 mg ± 217 vs. DIO 577 mg ± 185; females: controls 201 mg ± 143 vs 1176 mg ± 589). Leptin, resistin, and plasminogen activator inhibitor-1 were significantly elevated in the serum of DIO mice relative to control mice. Tumor weight did not differ between groups. Gene set enrichment analysis demonstrated that tumor cells from DIO mice were significantly enriched for pathways related to inflammation (INFLAMMATORY_RESPONSE, IL6_JAK_STAT3_SIGNALING), glucose and lipid metabolism (GLYCOLYSIS, FATTY_ACID_METABOLISM), and proliferation (E2F_TARGETS, G2M_CHECKPOINT). Within the CD45+ transcriptomic profiles, Tumor Immune Estimation Resource (TIMER2.0) indicated an increase in M0- and M1-like macrophages and B cells in tumors from DIO compared with control mice. Analysis of whole tumor sections from DIO mice showed significantly reduced CD3+ cells by immunofluorescence and more Ki67+ CD45+ immune cells by digital spatial profiling relative to tumors from control mice. Taken together, obesity drives an inflammatory profile in both the immune and epithelial cell populations of AKPS murine tumors, which is associated with increased markers of proliferation. Future studies will address whether inflammatory signals from the mesenteric fat adjacent to the colon tumors may contribute to obesity-driven tumor inflammation, and thereby to colon cancer progression.

Citation Format: Elaine M. Glenny, Babak Mirminachi, Tori L. McFarlane, Jatin Roper, Stephen D. Hursting. Obesity drives inflammation and metabolic reprogramming in an orthotopic mouse model of early colon cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4235.

Abstract 656: Suppression of pyruvate carboxylase drives tumor microenvironment immunosuppression

Metabolic reprogramming and immune evasion are established hallmarks of the tumor microenvironment (TME). Tumor metabolic dysregulation is a key mediator of tumor immune evasion. High levels of lactate produced by the tumor potently suppress antitumor immunity in the TME. Pyruvate carboxylase (PC), the enzyme responsible for the anaplerotic conversion of pyruvate to oxaloacetate, is required for lung metastasis in triple negative breast cancer (TNBC). Moreover, PC may be dispensable in some cells within the TME, and loss of PC expression is associated with immunosuppression. Here we test whether PC suppression in two murine models of TNBC alters tumor metabolism and promotes immunosuppression. C57BL6/J mice were orthotopically injected with E0771 or M-Wnt tumor cells bearing shRNA either targeting PC or a scramble control (n=3-6/group for each experiment). Tumor growth was monitored by digital calipers. RNA isolated from tumors was used for transcriptomic profiling using Affymetrix Clariom D microarray. Gene set enrichment analysis was used to identify pathways and processes enriched in each condition, as well as to define a hypoxia signature associated with PC expression. Immunohistochemistry was performed using an anti-CD3 antibody to identify T cell infiltration. Untargeted metabolomics, extracellular flux analysis and high resolution respirometry were used to assay metabolic effects of PC suppression. We found that suppression of PC in multiple animal models promotes primary tumor growth (~2 fold increase in size) and alters metabolic, transcriptomic and immunohistochemical markers of tumor immunosurveillance. Specifically, suppression of PC drove reduction of OCR, which was restored when exogenous malate was provided to ensure anaplerosis was non-limiting. Simultaneously, lactate production was elevated by PC suppression, as was in vitro sensitivity to inhibition of lactate metabolism. Critically, we identified that loss of immunosurrveilance following PC suppression could be restored by inhibition of lactate transport. Finally, we demonstrated that PC expression is markedly lower in tumors of patients whose transcriptomic profile indicated higher levels of hypoxia, and confirmed in vitro that hypoxia can directly suppress PC. Taken together, these data demonstrate hypoxia-driven PC suppression may be a key mechanism through which primary tumors limit antitumor immunity in part via enhanced lactate production. Thus, these data highlight that PC-directed tumor metabolism is a nexus of tumor progression and antitumor immunity. Ongoing work will examine the immune profile of the TME from PC suppressed tumors, and identify if PC overexpression is sufficient to enhance antitumor immunity.

Citation Format: Michael F. Coleman, Eylem Kulkoyluoglu Cotul, Alexander J. Pfeil, Emily N. Devericks, Muhammad H. Safdar, Hao Chen, Violet A. Kiesel, Dorothy Teegarden, Stephen D. Hursting, Michael K. Wendt. Suppression of pyruvate carboxylase drives tumor microenvironment immunosuppression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 656.

Abstract 3030: Effect of 6 months of bazedoxifene and conjugated estrogen on measures of insulin resistance in postmenopausal women at increased risk for breast cancer

Background: Bazedoxifene 20 mg (BZA) + Conjugated estrogen 0.45 mg (CE) as Duavee™ is FDA approved for treatment of hot-flashes and prevention of osteoporosis. We are investigating 6 months of BZA + CE vs wait list control in a multisite Phase IIB trial for primary prevention of breast cancer in high-risk peri-and postmenopausal women with vasomotor symptoms. Primary endpoints are change in mammographic fibroglandular volume and normal breast epithelial proliferation as assessed by Ki-67. Menopause transition is marked by an increase in insulin resistance and incidence of metabolic syndrome which in turn are implicated in the development of breast cancer. Tamoxifen can induce insulin resistance due to effects on small adipocytes, pancreatic beta cells, and hepatic lipid accumulation. In contrast, preclinical studies suggest that BZA + CE may have favorable effects on insulin resistance, particularly in obese animals. Consequently, we are exploring effects of BZA + CE on measures of insulin resistance in our clinical trial.

Methods: Fasting plasma was assessed for insulin and glucose in a CLIA laboratory the same day as drawn. HOMA-IR (insulin resistance) was computed as insulin (µU/ml) × glucose (mg/dl)]/405) and HOMA-%S (measure of insulin sensitivity) as 100/HOMA-IR. HOMA-IR ≥ 1.9 is considered an indication of early insulin resistance and HOMA-IR >2.8 significant insulin resistance. HOMA-%S values of ≥100% are considered an indication of insulin sensitivity.

Results: 21 women have been randomized in the initial 10 months of accrual at the University of Kansas Cancer Center with 8 women completing the 6 -month randomized period to date. Median age was 53 (48-56), and median BMI was 25 kg/m2 (22-35 kg/m2). All women were normoglycemic. However, 2 women (1 each BZA + CE and wait list) had baseline evidence of insulin resistance by HOMA IR (≥1.9). In the woman randomized to BZA + CE, HOMA-IR improved from 2.29 at baseline to 1.0 at 6 months and HOMA-%S improved from 44 to 100%. There was little change in insulin resistance measures in the woman with baseline insulin resistance randomized to wait list. HOMA-IR was 2.83 at baseline and 2.76 at 6 months and HOMA-%S 35% at baseline and 36% at 6 months. Another waitlist participant with normal baseline HOMA-%S of 141% dropped to 71% at 6 months. Results will be available for 20 study participants at the meeting.

Summary: In our initial accrual group there is no indication that 6 months of BZA +CE is associated with development of insulin resistance. Funded in part by NIH grant CA249437 and Breast Cancer Research Foundation grants BCRF-21-049 and BCRF-22-049.

Citation Format: Carol J. Fabian, Erin D. Giles, Katherine L. Cook, Kandy Powers, Christy Altman, Amy Kreutzjans, Teresa Phillips, Adrian Zelenchuk, Krystal Pittman, Stephen D. Hursting, Bruce Kimler. Effect of 6 months of bazedoxifene and conjugated estrogen on measures of insulin resistance in postmenopausal women at increased risk for breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3030.

Translating energy balance research from the bench to the clinic to the community: Parallel animal-human studies in cancer

Advances in energy balance and cancer research to date have largely occurred in siloed work in rodents or patients. However, substantial benefit can be derived from parallel studies in which animal models inform the design of clinical and population studies or in which clinical observations become the basis for animal studies. The conference Translating Energy Balance from Bench to Communities: Application of Parallel Animal-Human Studies in Cancer, held in July 2021, convened investigators from basic, translational/clinical, and population science research to share knowledge, examples of successful parallel studies, and strong research to move the field of energy balance and cancer toward practice changes. This review summarizes key topics discussed to advance research on the role of energy balance, including physical activity, body composition, and dietary intake, on cancer development, cancer outcomes, and healthy survivorship.

Separate and combined effects of advanced age and obesity on mammary adipose inflammation, immunosuppression and tumor progression in mouse models of triple negative breast cancer

Introduction

Advanced age and obesity are independent risk and progression factors for triple negative breast cancer (TNBC), which presents significant public health concerns for the aging population and its increasing burden of obesity. Due to parallels between advanced age- and obesityrelated biology, particularly adipose inflammation, we hypothesized that advanced age and obesity each accelerate mammary tumor growth through convergent, and likely interactive, mechanisms.

Methods

To test this hypothesis, we orthotopically transplanted murine syngeneic TNBC cells into the mammary glands of young normoweight control (7 months), young diet-induced obese (DIO), aged normoweight control (17 months), and aged DIO female C57BL/6J mice.

Results

Here we report accelerated tumor growth in aged control and young DIO mice, compared with young controls. Transcriptional analyses revealed, with a few exceptions, overlapping patterns of mammary tumor inflammation and tumor immunosuppression in aged control mice and young DIO mice, relative to young controls. Moreover, aged control and young DIO tumors, compared with young controls, had reduced abundance ofcytotoxic CD8 T cells. Finally, DIO in advanced age exacerbated mammary tumor growth, inflammation and tumor immunosuppression.

Discussion

These findings demonstrate commonalities in the mechanisms driving TNBC in aged and obese mice, relative to young normoweight controls. Moreover, we found that advanced age and DIO interact to accelerate mammary tumor progression. Given the US population is getting older and more obese, age- and obesity-related biological differences will need to be considered when developing mechanism-based strategies for preventing or controlling breast cancer.

Obesity and Breast Cancer Metastasis across Genomic Subtypes

BACKGROUND

Obese women have higher risk of aggressive breast tumors and distant metastasis. However, obesity has rarely been assessed in association with metastasis in diverse populations.

METHODS

In the Carolina Breast Cancer Study Phase 3 (2008-2013), waist-to-hip ratio (WHR), body mass index (BMI), and molecular subtype [PAM50 risk-of-recurrence (ROR) score] were assessed. Obesity measures were evaluated in association with metastasis within five years of diagnosis, overall and stratified by race and ROR score. Absolute risk of metastasis and risk differences between strata were calculated using the Kaplan-Meier estimator, adjusted for age, grade, stage, race, and ER status. Relative frequency of metastatic site and multiplicity were estimated in association with obesity using generalized linear models.

RESULTS

High-WHR was associated with higher risk of metastasis (5-year risk difference, RD, 4.3%; 95% confidence interval, 2.2-6.5). It was also associated with multiple metastases and metastases at all sites except brain. The 5-year risk of metastasis differed by race (11.2% and 6.9% in Black and non-Black, respectively) and ROR score (19.5% vs. 6.6% in high vs. low-to-intermediate ROR-PT). Non-Black women and those with low-to-intermediate ROR scores had similar risk in high- and low-WHR strata. However, among Black women and those with high ROR, risk of metastasis was elevated among high-WHR (RDBlack/non-Black = 4.6%, RDHigh/Low-Int = 3.1%). Patterns of metastasis were similar by BMI.

CONCLUSIONS

WHR is associated with metastatic risk, particularly among Black women and those with high-risk tumors.

IMPACT

Understanding how risk factors for metastasis interact may help in tailoring care plans and surveillance among patients with breast cancer.

Reversing the Genomic, Epigenetic, and Triple-Negative Breast Cancer-Enhancing Effects of Obesity

The reversibility of the procancer effects of obesity was interrogated in formerly obese C57BL/6 mice that lost weight via a nonrestricted low-fat diet (LFD) or 3 distinct calorie-restricted (CR) regimens (low-fat CR, Mediterranean-style CR, or intermittent CR). These mice, along with continuously obese mice and lean control mice, were orthotopically injected with E0771 cells, a mouse model of triple-negative breast cancer. Tumor weight, systemic cytokines, and incidence of lung metastases were elevated in the continuously obese and nonrestricted LFD mice relative to the 3 CR groups. Gene expression differed between the obese and all CR groups, but not the nonrestricted LFD group, for numerous tumoral genes associated with epithelial-to-mesenchymal transition as well as several genes in the normal mammary tissue associated with hypoxia, reactive oxygen species production, and p53 signaling. A high degree of concordance existed between differentially expressed mammary tissue genes from obese versus all CR mice and a microarray dataset from overweight/obese women randomized to either no intervention or a CR diet. Assessment of differentially methylated regions in mouse mammary tissues revealed that obesity, relative to the 4 weight loss groups, was associated with significant DNA hypermethylation. However, the anticancer effects of the CR interventions were independent of their ability to reverse obesity-associated mammary epigenetic reprogramming. Taken together, these preclinical data showing that the procancer effects of obesity are reversible by various forms of CR diets strongly support translational exploration of restricted dietary patterns for reducing the burden of obesity-associated cancers.

PREVENTION RELEVANCE

Obesity is an established risk and progression factor for triple-negative breast cancer (TNBC). Given rising global rates of obesity and TNBC, strategies to reduce the burden of obesity-driven TNBC are urgently needed. We report the genomic, epigenetic, and procancer effects of obesity are reversible by various calorie restriction regimens.

Weight Loss and/or Sulindac Mitigate Obesity-associated Transcriptome, Microbiome, and Protumor Effects in a Murine Model of Colon Cancer

Obesity is associated with an increased risk of colon cancer. Our current study examines whether weight loss and/or treatment with the NSAID sulindac suppresses the protumor effects of obesity in a mouse model of colon cancer. Azoxymethane-treated male FVB/N mice were fed a low-fat diet (LFD) or high-fat diet (HFD) for 15 weeks, then HFD mice were randomized to remain on HFD (obese) or switch to LFD [formerly obese (FOb-LFD)]. Within the control (LFD), obese, and FOb-LFD groups, half the mice started sulindac treatment (140 ppm in the diet). All mice were euthanized 7 weeks later. FOb-LFD mice had intermediate body weight levels, lower than obese but higher than control (P < 0.05). Sulindac did not affect body weight. Obese mice had greater tumor multiplicity and burden than all other groups (P < 0.05). Transcriptomic profiling indicated that weight loss and sulindac each modulate the expression of tumor genes related to invasion and may promote a more antitumor immune landscape. Furthermore, the fecal microbes Coprobacillus, Prevotella, and Akkermansia muciniphila were positively correlated with tumor multiplicity and reduced by sulindac in obese mice. Coprobacillus abundance was also decreased in FOb-LFD mice. In sum, weight loss and sulindac treatment, alone and in combination, reversed the effects of chronic obesity on colon tumor multiplicity and burden. Our findings suggest that an investigation regarding the effects of NSAID treatment on colon cancer risk and/or progression in obese individuals is warranted, particularly for those unable to achieve moderate weight loss.

PREVENTION RELEVANCE

Obesity is a colon cancer risk and/or progression factor, but the underlying mechanisms are incompletely understood. Herein we demonstrate that obesity enhances murine colon carcinogenesis and expression of numerous tumoral procancer and immunosuppressive pathways. Moreover, we establish that weight loss via LFD and/or the NSAID sulindac mitigate procancer effects of obesity.

Differential effects of calorie restriction and rapamycin on age-related molecular and functional changes in skeletal muscle

Aging is a multifactorial process associated with progressive degradation of physiological integrity and function. One of the greatest factors contributing to the deleterious effects of aging is the decline of functional ability due to loss of muscle mass, strength, and function, a condition termed sarcopenia. Calorie restriction (CR) has consistently been shown to extend lifespan and delay the onset and progression of various age-related diseases, including sarcopenia. Additional anti-aging interventions that are receiving scientific attention are CR mimetics. Of these pharmacological compounds, rapamycin has shown similar CR-related longevity benefits without the need for diet restrictions. To investigate the potential role of rapamycin as an anti-sarcopenic alternative to CR, we conducted a study in male and female C57BL/6 J mice to assess the effects of rapamycin on age-related gene expression changes in skeletal muscle associated with loss of muscle mass, strength, and function, relative to control. We hypothesize that the effects of rapamycin will closely align with CR with respect to physical function and molecular indices associated with muscle quality. Our results indicate CR and rapamycin provide partial protection against age-related decline in muscle, while engaging uniquely different molecular pathways in skeletal muscle. Our preclinical findings of the therapeutic potential of rapamycin or a CR regimen on geroprotective benefits in muscle should be extended to translational studies towards the development of effective strategies for the prevention and management of sarcopenia.

Hypoxia-Mediated ATF4 Induction Promotes Survival in Detached Conditions in Metastatic Murine Mammary Cancer Cells

Regions of hypoxia are common in solid tumors and drive changes in gene expression that increase risk of cancer metastasis. Tumor cells must respond to the stress of hypoxia by activating genes to modify cell metabolism and antioxidant response to improve survival. The goal of the current study was to determine the effect of hypoxia on cell metabolism and markers of oxidative stress in metastatic (metM-Wntlung) compared with nonmetastatic (M-Wnt) murine mammary cancer cell lines. We show that hypoxia induced a greater suppression of glutamine to glutamate conversion in metastatic cells (13% in metastatic cells compared to 7% in nonmetastatic cells). We also show that hypoxia increased expression of genes involved in antioxidant response in metastatic compared to nonmetastatic cells, including glutamate cysteine ligase catalytic and modifier subunits and malic enzyme 1. Interestingly, hypoxia increased the mRNA level of the transaminase glutamic pyruvic transaminase 2 (Gpt2, 7.7-fold) only in metM-Wntlung cells. The change in Gpt2 expression was accompanied by transcriptional (4.2-fold) and translational (6.5-fold) induction of the integrated stress response effector protein activating transcription factor 4 (ATF4). Genetic depletion ATF4 demonstrated importance of this molecule for survival of hypoxic metastatic cells in detached conditions. These findings indicate that more aggressive, metastatic cancer cells utilize hypoxia for metabolic reprogramming and induction of antioxidant defense, including activation of ATF4, for survival in detached conditions.

The obesity-breast cancer link: a multidisciplinary perspective

Obesity, exceptionally prevalent in the USA, promotes the incidence and progression of numerous cancer types including breast cancer. Complex, interacting metabolic and immune dysregulation marks the development of both breast cancer and obesity. Obesity promotes chronic low-grade inflammation, particularly in white adipose tissue, which drives immune dysfunction marked by increased pro-inflammatory cytokine production, alternative macrophage activation, and reduced T cell function. Breast tissue is predominantly composed of white adipose, and developing breast cancer readily and directly interacts with cells and signals from adipose remodeled by obesity. This review discusses the biological mechanisms through which obesity promotes breast cancer, the role of obesity in breast cancer health disparities, and dietary interventions to mitigate the adverse effects of obesity on breast cancer. We detail the intersection of obesity and breast cancer, with an emphasis on the shared and unique patterns of immune dysregulation in these disease processes. We have highlighted key areas of breast cancer biology exacerbated by obesity, including incidence, progression, and therapeutic response. We posit that interception of obesity-driven breast cancer will require interventions that limit protumor signaling from obese adipose tissue and that consider genetic, structural, and social determinants of the obesity–breast cancer link. Finally, we detail the evidence for various dietary interventions to offset obesity effects in clinical and preclinical studies of breast cancer. In light of the strong associations between obesity and breast cancer and the rising rates of obesity in many parts of the world, the development of effective, safe, well-tolerated, and equitable interventions to limit the burden of obesity on breast cancer are urgently needed.

Abstract 3507: β-Hydroxy-β-methylbutyrate (HMB) sensitizes murine pancreatic ductal adenocarcinoma (PDAC) to immunotherapy

Background: Pancreatic cancer is the fourth leading cause of cancer-related death in the United States. PDAC often presents at advanced tumor stages, resulting in poor survival rates. Immunotherapies such as inhibition of programmed death 1 (PD1) are effective in many cancers, but not in PDAC. HMB is a leucine metabolite that reduces PDAC progression and cachexia in association with enhanced antitumor immune responses. The purpose of this study was to determine if HMB treatment enhances immunotherapeutic response in PDAC.

Methods: C57BL/6J mice bearing subcutaneously transplanted PANC02 tumors were fed either a control (AIN93G) or HMB (1% w/w) supplemented diet. Once tumors were palpable, mice were randomized for treatment with vehicle or anti-PD1 immunotherapy (n=12-13/group). Tumors were harvested and global transcriptomic analysis was performed.

Results: Both HMB and anti-PD1 interventions alone were insufficient to reduce tumor growth. However, the combination of HMB and anti-PD1 resulted in significantly smaller tumors than the anti-PD1 alone group, indicating that HMB was able to stimulate PDAC response to ICI. Transcriptomic analysis revealed limited transcriptional effects attributable to immunosurveillance following treatment with either HMB or anti-PD1 alone; however, the combination produced a robust antitumor immune response. Digital cytometry analysis revealed altered immune cell composition in the tumor microenvironment.

Conclusion: The combination of HMB with anti-PD1 treatment elicited significant antitumor responses in a murine model of PDAC progression. Given that immunotherapy trials in PDAC have not yet proven effective, even when combined with cytotoxic chemotherapy, our preclinical findings support clinical evaluation of combined ICI and HMB regimens as a therapeutic strategy against PDAC.

Citation Format: Suhas K. Etigunta, Michael F. Coleman, Kristyn A. Liu, Alex J. Pfeil, Zhengrong Cui, Stephen D. Hursting. β-Hydroxy-β-methylbutyrate (HMB) sensitizes murine pancreatic ductal adenocarcinoma (PDAC) to immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3507.

Abstract 1336: Characterization of a novel transplantable model of obesity-driven basal-like breast cancer

Introduction: Breast cancer (BC) is a leading cause of cancer-related death in women, with the poorest prognosis found in the basal-like subtype. Although obesity is an established risk factor for basal-like BC, existing mouse models to study the interaction of basal-like BC and diet-induced obesity (DIO) are limited. The C3(1)/SV40 large T-antigen (TAg) transgenic mouse is an established, human-relevant basal-like mammary cancer model developed on an obesity-resistant FVB genetic background. The goal of this study was to create and characterize a transplantable C3TAg model on an obesity-sensitive C57BL/6J (B6) genetic background.

Methods: Male C3TAg transgenic FVB mice were backcrossed with female wild-type B6 mice for 10 generations. Spontaneous mammary tumors from these female B6:C3TAg mice were dissociated and subcloned, generating 4 distinct cell lines differing in their expression of metabolic genes. A pilot orthotopic transplant study using the 4 candidate cell lines (at 3 cell concentrations of each line) in 96 B6 mice identified cell line 2.51 as an attractive model for further evaluation based on in vivo growth characteristics and initial genomic analyses. To assess the impact of DIO in this model, 61 female B6 mice were randomized to receive either control (n=30) or DIO (n=31) diet regimens for 24 weeks, then were orthotopically injected into the 4th mammary fat pad with cell line 2.51 (2.5x105 cells/mouse). The mice continued on their respective diets, were monitored for tumor development, and were euthanized 4 weeks post-injection. Tumors were collected, weighed and flash frozen for genomic, immunologic and biochemical analyses.

Results: All 4 cell lines tested in the pilot study generated basal-like mammary tumors when orthotopically transplanted. Tumor gene expression profiling (via Affymetrix microarray) revealed inflammation and stem-like gene expression profiles discordant between cell lines tested, with tumors induced by cell line 2.51 showing striking enrichment in immune signatures relative to the other cell lines. DIO, relative to control diet, significantly accelerated transplanted 2.51 cell tumor progression, as indicated by increased tumor mass in mice from DIO relative to control diet-fed animals. Genomic, biochemical, and immunological assessment of the tumor-enhancing effects of DIO in this model are ongoing.

Conclusions: Herein, we report the development and characterization of a novel transplantable C3TAg mammary tumor model in C57BL/6J mice, highly responsive to energy balance. This work represents a promising new tool for preclinical studies of the interactions between diet, obesity, immunity and basal-like breast cancer.

Funding: This work was supported by R35CA197627 to SDH.

Citation Format: Meredith S. Carson, Elaine M. Glenny, Violet A. Kiesel, Ashlee Taylor, Daniel Roth, Jody Albright, Melissa VerHague, John E. French, Michael F. Coleman, Stephen D. Hursting. Characterization of a novel transplantable model of obesity-driven basal-like breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1336.

Abstract 3010: Targeting metabolic pathways through pharmacological and chemotherapeutic interventions to improve triple-negative breast cancer therapy

Triple-negative breast cancers (TNBCs) lack targeted therapies, leaving surgery and systemic chemotherapy as current standard approaches for treatment. However, chemotherapy resistance is a major clinical challenge. Stimulation of receptor tyrosine kinases such as insulin receptor (IR) and insulin-like growth factor 1 receptor (IGF-1R) activates the protein kinase A (PKA), mitogen-activated protein kinase (MAPK), and phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling cascades. Activation of these pathways is observed in the majority of TNBC tumors and promotes pro-proliferative signaling. Thus IGF-1R/IR are potential therapeutic targets in TNBC, but clinical trials of anti-IGF-1R/IR therapies have consistently shown minimal and often heterogeneous therapeutic responses. Our objective was to determine whether metabolic reprogramming achieved by combination regimens, specifically the IGF-1R/IR inhibitor BMS-754807 and/or treatment with the platinum-based chemotherapeutic agent, carboplatin, promotes autophagy induction and sensitizes cancer cells to autophagy inhibition. Cytotoxicity of BMS-754807, alone or in combination with carboplatin and/or the autophagy inhibitor, hydroxychloroquine, was assessed in murine (E0771, metM-Wntlung, B6C3TAg 2.51) and human (MDA-MB-231, MDA-MB-468) models of TNBC using MTT assays. Analysis of mitochondrial mass was measured in cells stained with MitoTracker Green FM using flow cytometry. Autophagic flux was measured with an mCherry-EGFP-LC3B tandem fluorescent protein. BMS-754807 (10μM) significantly induced 22-51% cytotoxicity in all cell lines tested, with E0771 cells showing the strongest response. Treatment with BMS-754807 (2.5µM) significantly increased mitochondrial mass (31%) compared to untreated cells. In addition, co-treatment with BMS-754807 and carboplatin further suppressed cell viability and regulated phosphorylation of the double-stranded DNA damage response proteins γ;-H2AX and Chk2. Co-treatment with BMS-754807 and carboplatin also altered the GFP/RFP ratio in LC3-expressing cells, suggesting modulation of autophagic flux. Finally, the addition of the autophagy inhibitor hydroxychloroquine further induced cytotoxicity when coupled with BMS-754807 and carboplatin. This work indicates that IGF-1R/IR inhibition remodels metabolism in TNBC cells, potentially synergizing with carboplatin to induce double stranded DNA damage. Moreover, the combination of IGF-1R/IR and carboplatin can further collaborate with autophagy inhibition to strongly suppress TNBC cell growth. We conclude that inhibiting nutrient-sensing metabolic pathways such as IGF-1R/IR in combination with chemotherapy and/or autophagy inhibition warrants additional study as a strategy to improve therapeutic responses in women with TNBC.

Citation Format: Alyssa N. Ho, Violet A. Kiesel, Scott P. Connelly, Michael F. Coleman, Stephen D. Hursting. Targeting metabolic pathways through pharmacological and chemotherapeutic interventions to improve triple-negative breast cancer therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3010.

Abstract 1627: Metabolic links between obesity and ferroptosis in a murine model of breast cancer

Background Obesity is an established risk factor for post-menopausal triple negative breast cancer (TNBC). Multiple aspects of fatty acid metabolism, including fatty acid synthesis, are upregulated in white adipose tissue during obesity development. The enzyme pyruvate carboxylase (PC), a supportive player in fatty acid synthesis, is relied upon for metastasis of murine TNBC particularly in models of obesity- further elucidating the importance of fatty acid metabolism to breast cancer progression in those with obesity. Ferroptosis, a method of cell death induced by peroxidation of phospholipid fatty acyl chains, is a recently discovered and rapidly developing mechanistic target in multiple cancer types. While several cancers, including breast cancer, are sensitive to ferroptosis induced by different mechanisms, the metabolic vulnerabilities and consequent therapeutic potential of ferroptosis are just beginning to be explored. This study aims to determine whether obesity-driven reprogramming of fatty acid metabolism exacerbates breast cancer progression via altered sensitivity to ferroptosis

Methods The relationship between obesity, breast cancer and lipid peroxidation was investigated in vitro via proliferation assays, qPCR, Western blot and flow cytometry using multiple murine models of breast cancer treated with erastin and RSL3. PC was suppressed using shRNA introduced via lentiviral transduction. In vivo tumor growth in lean and obese mice was determined following treatment with erastin, RSL3, or a vehicle control.

Results In vitro data reveals that TNBC cells are highly sensitive to treatment with the ferroptosis-inducing molecules erastin and RSL3. Erastin treatment transcriptionally induces PC expression in several murine models of TNBC in vitro. Suppression of PC at baseline (without ferroptosis induction) is sufficient to induce transcription of glutathione peroxidase-4 (a critical regulator of ferroptosis). While Affymetrix array data of untreated metastatic M-WntLung primary tumors showed a decrease in PC and associated genes in tumors from obese mice relative to lean mice, treatment with erastin increased PC expression specifically in tumors from obese mice. Tumors from obese mice relative to control mice have an altered response to treatment with the ferroptosis inducing molecules erastin and RSL3.

Conclusion These data indicate that obesity-associated dysregulation of lipid metabolism and regulation of PC may be key determinants of sensitivity to induction of ferroptosis. Future work will delineate the relationship between breast cancer, ferroptosis, and fatty acid metabolism utilizing in vivo models to determine whether ferroptosis-specific mechanisms are exacerbated with PC suppression to further impede obesity-exacerbated tumor growth.

Citation Format: Emily Devericks, Michael F. Coleman, Hannah Malian, Violet Kiesel, Dorothy Teegarden, Stephen D. Hursting. Metabolic links between obesity and ferroptosis in a murine model of breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1627.

Abstract 1321: Effects of sulindac on inflammatory and cellular responses in mammary tumors from obese mice

Background: Breast cancer is the second leading cause of cancer-related death in US women. Obesity (BMI &gt; 30 kg/m2) promotes breast cancer incidence, progression, and mortality in women of all ages. The prevalence of obesity in the US has increased dramatically over recent decades and continues to rise. Although obesity is associated with increased adipose tissue inflammation and metabolic dysfunction the exact mechanisms regulating obesity-exacerbated tumor growth are relatively unknown. Nonsteroidal anti-inflammatory drugs (NSAIDs), like sulindac, inhibit cyclooxygenase-1 and cyclooxygenase-2 and modulate the secretion of pro-inflammatory cytokines. The purpose of this study was to investigate the mechanisms underlying the anticancer effects of sulindac in our E0771 mouse model of obesity and mammary tumor growth.

Methods: C57BL/6J mice were fed either a high-fat diet (n=16) or a low-fat control diet (n=12) for 15 weeks. Half of the control (n=6) and DIO (n=8) mice were then treated with 140 ppm sulindac in their respective diets for 4 weeks prior to orthotopic injection of 20,000 E0771 cells. Tumors were harvested and weighed, and serum was collected 4 weeks following injection. Bulk transcriptional profile analysis was performed on E0771 tumors from untreated control and DIO mice relative to sulindac-treated control and DIO mice using Affymetrix microarrays followed by gene set enrichment analysis (GSEA) to identify significantly enriched gene sets. Serum cytokine levels were measured in all mice using the Bio-Plex Pro mouse chemokine panel 33-plex; multiple linear regression was conducted to determine cytokines associated with mammary tumor size, independent of diet or treatment group assignment.

Results: DIO mice had increased tumor weight relative to control mice, while sulindac decreased tumor weight in DIO but not control mice. GSEA analysis revealed only one gene set upregulated in the DIO tumors relative to control or DIO sulindac tumors. Immune-related gene sets were commonly enriched in tumors from control and DIO sulindac relative to DIO mice, suggesting that sulindac restored immune signaling in tumors from DIO mice. Leading edge analysis of the significantly enriched gene sets showed that: 1) the reversal of DIO-mediated immunosuppression by sulindac occurred via principally overlapping genes; and 2) cytokine and immune genes predominate the transcriptional effects of sulindac treatment in DIO mice. Sulindac also modified circulating serum cytokine levels, but multiple linear regression showed that cytokine levels were not independently predictive of tumor weight in our study.

Conclusions: The study suggests that sulindac can reverse transcriptional changes in mammary tumors from obese mice and restore immunosurveillance. Sulindac, or potentially other NSAIDs, may protect against obesity–driven mammary tumor growth via remodeling of antitumor immune function.

Citation Format: Morgan E. Cody, Shannon B. McDonell, Qing Shi, Elaine M. Glenny, Michael F. Coleman, Stephen D. Hursting. Effects of sulindac on inflammatory and cellular responses in mammary tumors from obese mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1321.

Abstract 3128: Paracrine adipocyte signaling promotes colorectal cancer growth in vitro

Purpose: To identify candidate mediators of paracrine signaling between adipocytes and colorectal cancer cells contributing to the obesity-cancer link.

Background: The worldwide prevalence of obesity has nearly tripled over the last few decades and is a major public health concern. Obesity-associated inflammation in adipose tissue correlates with colorectal tumorigenesis and tumor proliferation. The altered secretome of obesity-associated adipose tissue also affects colon cancer growth and development. Hence, we sought to determine the role of adipocyte-derived secreted factors in mediating the tumor-promoting paracrine signaling observed in obesity.

Methods: Adipocytes were isolated from the gonadal fat pad of C57BL/6J male mice fed either a low-fat (10 kcal% fat) or high-fat (60 kcal% fat) diet and cultured for 24 hours. Cytokine production from the cultured adipocytes was quantified using the Bio-Plex Pro mouse chemokine 33-plex panel. To determine if adipocyte-derived metabolites or growth factors promote cancer cell proliferation, human SW620 colon cancer cells were grown for 24 hours in conditioned media and cell viability was assessed using the MTT assay. To test whether a subset of these cytokines directly impacted cancer cell growth, SW620 cells were cultured with or without the addition of 20 ng/mL recombinant IL-6 or 50 ng/mL CCL5 to the culture media. Proliferation was measured using the MTT assay and gene expression was assessed via qPCR.

Results: Adipocyte-conditioned media contained 19 detectable cytokines, with CCL2, CCL7, and CCL5 being the most abundant. IL-6, CCL12, CCL11, and CXCL16 were all significantly elevated (p&lt;0.05, fold enrichment &gt;2.0) in adipocyte-conditioned media from obese relative to lean mice. SW620 cells demonstrated a &gt;20% increase in proliferation when grown in conditioned media from adipocytes isolated from either low-fat or high-fat fed mice. CCL5 stimulation for 24 hours resulted in a ~17% increase in SW620 cell viability when cultured under replete (10% FBS) growth factor conditions, but a ~8% decrease under reduced (0.5% FBS) growth factor conditions. IL-6 stimulation did not impact SW620 cell growth. To understand the downstream cell signaling effects of IL-6 and CCL5 stimulation, we performed qPCR analysis on EMT and Wnt signaling markers in SW620 cells after 4-hour cytokine stimulation in media without growth factors (0% FBS). IL-6-stimulated cells exhibited a significant increase in SOCS3 and PTHLH while CCL5-stimulated cells exhibited a significant decrease in TCF7L1.

Conclusions: Overall, these data indicate tumor-promoting paracrine signaling from adipose tissue may potentiate colon cancer growth in part via adipocyte-derived cytokine production. Further work to delineate the mechanisms through which such paracrine signaling acts will be important to develop interventions to reduce the growing burden of obesity-driven colon cancer.

Citation Format: Nivetha S. Ramasamy, Elaine M. Glenny, Qing Shi, Stephen D. Hursting. Paracrine adipocyte signaling promotes colorectal cancer growth in vitro [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3128.

Abstract 2376: Pyruvate carboxylase regulates mammary tumor microenvironment composition via central carbon metabolism

Introduction: Metastatic triple-negative breast cancer (TNBC) is one of the deadliest cancers amongst women in the US, with a 5-year survival rate of 12%. Due to a lack of targeted therapies, investigation into the metabolic drivers of TNBC progression at both the primary and secondary site is vital to direct future treatment strategies. Pyruvate carboxylase (PC) is an anaplerotic enzyme vital for TNBC metastasis to the lungs, though its expression is commonly suppressed in the primary tumor compared to normal tissue. In this study, we investigated the role of PC expression in the metabolic reprogramming of TNBC cell lines and how its reduced expression in vivo may support primary tumor progression.

Methods: Modulation of PC expression in M-Wnt cell lines was achieved through lentiviral-mediated transduction of PCx-targeting short hairpin RNAs (ShPC). In vitro metabolic alterations to central carbon metabolism following PC suppression were assessed via intracellular lactate and NAD+/NADH assays. Functional shifts in mitochondrial metabolism were assessed via extracellular flux analysis in various substrate conditions. Electron transport chain (ETC)-intrinsic dysfunction was assessed via high-resolution respirometry (HRR) and qPCR analysis of ETC gene expression. C57BL/6J mice were injected with ShPC M-Wnt cells and the resulting tumors were harvested after 4 weeks following injection. Metabolomic analysis, mass cytometry, and HRR were conducted with samples from excised tumors.

Results: PC knockdown in vitro results in reduced oxygen consumption and a gene expression profile indicative of mitochondrial dysfunction. Genes encoding subunits of ETC complexes such as ND4FA10, SDHB, and ATP5c1 were downregulated while markers of mitochondrial biogenesis were upregulated following suppression of PC. Intracellular lactate and cell proliferation assays revealed enhanced flux through lactate dehydrogenase and sensitization of PC knockdown M-Wnt cells to lactate metabolism inhibitors. PC knockdown in vivo resulted in enhanced primary tumor growth and an immunosuppressed tumor microenvironment, as indicated by downregulated cytokine signaling and reduced cell fractions of critical anti-tumor immune cells.

Conclusions: Suppression of PC in vitro results in mitochondrial dysfunction, manifesting in a metabolic phenotype characterized by enhanced production of lactate and reduced oxidative phosphorylation. In vivo, PC knockdown resulted in enhanced primary tumor growth and a tumor immune landscape indicative of immunosuppression. We conclude that PC knockdown promotes distinct metabolic reprogramming of the primary mammary tumor microenvironment associated with immune evasion and enhanced tumor progression.

Funding: This study was supported by grants from the National Cancer Institute (R35 CA197627 to SD Hursting, and RO1 CA232589 to SD Hursting and D. Teegarden)

Citation Format: Alexander J. Pfeil, Michael F. Coleman, Eylem Kulkoyluoglu-Cotul, Violet Kiesel, Emily Devericks, Suhas K. Etigunta, Dorothy Teegarden, Michael K. Wendt, Stephen D. Hursting. Pyruvate carboxylase regulates mammary tumor microenvironment composition via central carbon metabolism [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2376.

Abstract 1995: β-Hydroxy-β-methylbutyrate promotes immunotherapy response and pro-inflammatory macrophage polarization in a mouse model of pancreatic cancer

Background: Pancreatic ductal adenocarcinoma (PDAC) continues to represent a critical unmet therapeutic need in the US, and is exacerbated by obesity. Current chemotherapeutic regimens poorly control PDAC progression, and immunotherapy has yet to be widely successful against PDAC. Obesity promotes a potently protumor PDAC microenvironment including suppression of antitumor immune response. The purpose of our studies was to test whether dietary supplementation with β-hydroxy-β-methylbutyrate (HMB), shown to be safe and well tolerated in cancer patients, could offset obesity-mediated exacerbation of PDAC and promote antitumor immunosurveillance.

Methods: Lean and obese C57BL/6 mice were treated with HMB alone or in combination with anti-PD1 immunotherapy following subcutaneous injection of Panc02 PDAC cells. Bone marrow-derived macrophages (BMDM) were treated with HMB in vitro with or without lipopolysaccharide (LPS). Tumor/macrophage transcriptomic analysis using Affymetrix arrays followed by gene set enrichment was performed, and tumor microenvironment immune cell composition was determined by mass cytometry.

Results: a) HMB cooperates with obesity and immunotherapy to reduce PDAC progression, as indicated by reduced tumor growth with the combination regimen of HMB + anti-PD1 relative to obese or anti-PD1 immunotherapy treated mice without HMB supplementation; b) HMB mitigates PDAC immunosuppression and promotes tumor immune surveillance, as demonstrated by induction of an antitumor immune-related gene expression profile in response to HMB supplementation; c) HMB promotes pro-inflammatory polarization of tumor-associated macrophages and BMDM, as shown by increased CD38 positivity and reduced Arg1 positivity in tumor-associated macrophages from HMB supplemented mice relative to control. Further, BMDM transcriptional response to HMB alone or HMB in combination with LPS paralleled that of BMDM treated with LPS relative to untreated LPS.

Conclusion: Overall, our findings suggest HMB is an adjuvant for antitumor immune responses in PDAC. Moreover, HMB promotes immune surveillance in PDAC, synergizing with immunotherapy. Hence, HMB-induced suppression of PDAC tumor growth and promotion of immune surveillance may offer significant synergy with chemotherapies or immunotherapies in PDAC.

Funding: This work was supported by R35CA197627 to SDH.

Citation Format: Michael F. Coleman, Kristyn A. Liu, Alexander J. Pfeil, Suhas K. Etigunta, Xiaohu Tang, Laura M. Lashinger, Zhengrong Cui, Stephen D. Hursting. β-Hydroxy-β-methylbutyrate promotes immunotherapy response and pro-inflammatory macrophage polarization in a mouse model of pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1995.

Abstract 14: Resolution of obesity-driven proinflammatory adipose signaling by weight loss or an NSAID is associated with reduced tumor burden in a mouse model of colon cancer

Obesity increases the incidence and progression of colon cancer. The chronic low-grade inflammation that often accompanies obesity is purported to promote these adverse outcomes. In obesity, remodeling of visceral white adipose tissue contributes to an inflammatory state via increased immune cell recruitment and production of proinflammatory cytokines. The aim of this study in a mouse model of obesity and colon carcinogenesis was to compare the effects of weight loss versus treatment with a nonsteroidal anti-inflammatory drug (sulindac) on tumor development and adipose and tumoral transcriptional changes. Azoxymethane (10 mg/kg) was intraperitoneally injected weekly into FVB/N male mice for 5 weeks to induce colon tumors. Mice were then randomized to an ad libitum 10 kcal% fat diet (control, n=20) or 60 kcal% fat diet to promote diet-induced obesity (DIO, n=55). After 15 weeks, DIO mice were randomized again to receive for an additional 7 weeks either: a) DIO diet (n=18); b) DIO diet supplemented with 140ppm sulindac (DIO+Su, n=19), or c) 10 kcal% fat control diet to generate formerly obese (FOb-LFD) mice (n=18). Mesenteric fat and colon tumors were collected for an Affymetrix Clariom D mouse gene expression microarray (n=5-6/group). FOb-LFD mice, but not DIO+Su mice, lost significant body weight and body fat. Relative to DIO mice, tumor burden and multiplicity were lower in control, DIO+Su, and FOb-LFD mice. Gene set enrichment analysis (GSEA) using the Hallmark gene sets revealed strikingly concordant transcriptional changes in the control, DIO+Su, and FOb-LFD mesenteric fat depots compared with DIO mice. Of the 8 immune related gene sets, 7 were uniformly suppressed (Normalized enrichment score (NES) &gt;1.66, FDR q&lt;0.05) across all groups relative to DIO. Moreover, compared with DIO, metabolism gene sets (e.g., FATTY_ACID_ METABOLISM, GLYCOLYSIS) were significantly enriched (NES &gt;1.45, FDR q&lt;0.05), and none were suppressed in control, DIO+Su, and FOb+LFD tumors. Tumor transcriptional changes were less coherent with EPITHELIAL_MESENCHYMAL_TRANSITION and COAGULATION being the only gene sets commonly suppressed across all groups relative to DIO. A leading-edge analysis revealed that Lum, Pthlh, Sfrp4, Mmp8, and Serpine1 were commonly suppressed amongst tumors from groups other than DIO mice. Both weight loss and sulindac impeded the effects of chronic obesity on colon tumorigenesis. GSEA analyses of immune related gene sets indicated that weight loss and sulindac effectively suppressed inflammation in the adipose tissue but not in the tumor. The conserved immunological and metabolic transcriptional programs in the adipose tissue relative to the tumor suggests the possibility that paracrine signaling from the adipose to the tumor may underpin the observed beneficial effects of these interventions on obesity-driven colon tumor growth.

Citation Format: Elaine M. Glenny, Laura W. Bowers, Michael F. Coleman, Jatin Roper, Stephen D. Hursting. Resolution of obesity-driven proinflammatory adipose signaling by weight loss or an NSAID is associated with reduced tumor burden in a mouse model of colon cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 14.

Abstract 612: Microbial determinants of immune checkpoint inhibition response in a murine model of obesity and metastatic basal-like breast cancer

Introduction: Breast cancer (BC) is the second leading cause of cancer-related mortality among American women and is exacerbated by obesity. The basal-like (BL) subtype accounts for 10-15% of all BCs and is a particularly aggressive disease due to its extreme intrinsic diversity compared with other subtypes. Paradoxically, obesity promotes immune checkpoint inhibition (ICI) response in some cancers. Further, obesity promotes altered intestinal microbial composition, and recent clinical studies of fecal microbiota transplants suggest causal links between the microbiome and immunotherapy responses. Hence, we evaluated the correlation of tumoral and cecal microbiota with anti-Programmed Cell Death Protein 1 (PD1) immunotherapy response in a murine model of BLBC and obesity.

Methods: In an initial study, normoweight female C57BL/6J mice (n=8/group) received orthotopic injection of one of two novel C3TAg BLBC cell lines (1.02 and 2.51) syngeneic to C57BL/6J derived from a spontaneous tumor excised from B6-C3TAg transgenic mice. Gene expression profiling (Affymetrix arrays) with Gene Set Enrichment Analysis (GSEA) was performed on the resulting transplanted tumors. In a second study, female C57BL/6J mice were divided into a diet-induced obesity (DIO) group (n=30), promoted by high-fat diet feeding, and a lean control group (n=30). After 24 weeks, 2.51 cells were orthotopically injected into the fourth mammary fat pad of all mice, followed by treatment with anti-PD1 or IgG control antibodies (n=15/diet group). Tumor and cecal DNA was extracted and subjected to 16S rRNA amplicon sequencing.

Results: GSEA from the initial study revealed that orthotopically transplanted line 2.51 tumors, relative to line 1.02 tumors, had lower levels of stromal remodeling as indicated by significant enrichment of gene sets related to extracellular matrix proteoglycans, collagen chain trimerization, and collagen biosynthesis and modification. Gene sets related to insulin and IGF-1 signaling were also lower in line 2.51 tumors than line 1.02 tumors. The in-life portion of the second study revealed a heterogeneous response to ICI therapies among lean and obese mice. To understand this diversity of response, 16S rRNA sequencing analysis of tumoral and cecal microbiota in response to DIO and ICI therapy is underway.

Discussion: These data reveal striking differences in tumor microenvironment and nutrient sensing as being potentially important determinants of differential tumor growth in BLBC. Ultimately, this research may contribute to the development of precision nutrition approaches using pro-/pre-biotics to promote microbial communities, targeting the tumor microenvironment, which may improve immunotherapy response and disrupt the obesity-associated exacerbation of breast cancer.

Financial Support: This work was supported by R35CA197627 to SDH.

Citation Format: Tori L. McFarlane, Meredith S. Carson, Elaine M. Glenny, Violet A. Kiesel, Ashlee Taylor, Daniel Roth, Jody Albright, Melissa VerHague, John E. French, Michael F. Coleman, Stephen D. Hursting. Microbial determinants of immune checkpoint inhibition response in a murine model of obesity and metastatic basal-like breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 612.

Increased Ammonium Toxicity in Response to Exogenous Glutamine in Metastatic Breast Cancer Cells

Several cancers, including breast cancers, show dependence on glutamine metabolism. The purpose of the present study was to determine the mechanistic basis and impact of differential glutamine metabolism in nonmetastatic and metastatic murine mammary cancer cells. Universally labeled 13C5-glutamine metabolic tracing, qRT-PCR, measures of reductive-oxidative balance, and exogenous ammonium chloride treatment were used to assess glutamine reprogramming. Results show that 4 mM media concentration of glutamine, compared with 2 mM, reduced viability only in metastatic cells, and that this decrease in viability was accompanied by increased incorporation of glutamine-derived carbon into the tricarboxylic acid (TCA) cycle. While increased glutamine metabolism in metastatic cells occurred in tandem with a decrease in the reduced/oxidized glutathione ratio, treatment with the antioxidant molecule N-acetylcysteine did not rescue cell viability. However, the viability of metastatic cells was more sensitive to ammonium chloride treatment compared with nonmetastatic cells, suggesting a role of metabolic reprogramming in averting nitrogen cytotoxicity in nonmetastatic cells. Overall, these results demonstrate the ability of nonmetastatic cancer cells to reprogram glutamine metabolism and that this ability may be lost in metastatic cells.

Concurrent Inhibition of IGF1R and ERK Increases Pancreatic Cancer Sensitivity to Autophagy Inhibitors

The aggressive nature of pancreatic ductal adenocarcinoma (PDAC) mandates the development of improved therapies. As KRAS mutations are found in 95% of PDAC and are critical for tumor maintenance, one promising strategy involves exploiting KRAS-dependent metabolic perturbations. The macrometabolic process of autophagy is upregulated in KRAS-mutant PDAC, and PDAC growth is reliant on autophagy. However, inhibition of autophagy as monotherapy using the lysosomal inhibitor hydroxychloroquine (HCQ) has shown limited clinical efficacy. To identify strategies that can improve PDAC sensitivity to HCQ, we applied a CRISPR-Cas9 loss-of-function screen and found that a top sensitizer was the receptor tyrosine kinase (RTK) insulin-like growth factor 1 receptor (IGF1R). Additionally, reverse phase protein array pathway activation mapping profiled the signaling pathways altered by chloroquine (CQ) treatment. Activating phosphorylation of RTKs, including IGF1R, was a common compensatory increase in response to CQ. Inhibition of IGF1R increased autophagic flux and sensitivity to CQ-mediated growth suppression both in vitro and in vivo. Cotargeting both IGF1R and pathways that antagonize autophagy, such as ERK-MAPK axis, was strongly synergistic. IGF1R and ERK inhibition converged on suppression of glycolysis, leading to enhanced dependence on autophagy. Accordingly, concurrent inhibition of IGF1R, ERK, and autophagy induced cytotoxicity in PDAC cell lines and decreased viability in human PDAC organoids. In conclusion, targeting IGF1R together with ERK enhances the effectiveness of autophagy inhibitors in PDAC.

SIGNIFICANCE

Compensatory upregulation of IGF1R and ERK-MAPK signaling limits the efficacy of autophagy inhibitors chloroquine and hydroxychloroquine, and their concurrent inhibition synergistically increases autophagy dependence and chloroquine sensitivity in pancreatic ductal adenocarcinoma.

4-(N)-Docosahexaenoyl 2', 2'-difluorodeoxycytidine induces immunogenic cell death in colon and pancreatic carcinoma models as a single agent

PURPOSE

Docosahexaenoyl difluorodeoxycytidine (DHA-dFdC) is an amide with potent, broad-spectrum antitumor activity. In the present study, DHA-dFdC's ability to induce immunogenic cell death (ICD) was tested using CT26 mouse colorectal cancer cells, an established cell line commonly used for identifying ICD inducers, as well as Panc-02 mouse pancreatic cancer cells.

METHODS

The three primary surrogate markers of ICD (i.e., calreticulin (CRT) surface translocation, ATP release, and high mobility group box 1 protein (HMGB1) release) were measured in vitro. To confirm DHA-dFdC's ability to induce ICD in vivo, the gold standard mouse vaccination studies were conducted using both CT26 and Panc-02 models. Additionally, the effect of DHA-dFdC on tumor response to anti-programmed cell death protein 1 monoclonal antibody (anti-PD-1 mAb) were tested in mice with pre-established Panc-02 tumors. RNA sequencing experiments were conducted on PANC-1 human pancreatic cancer cells treated with DHA-dFdC, dFdC, or vehicle control in vitro.

RESULTS

DHA-dFdC elicited CRT surface translocation and ATP and HMGB1 release in both cell lines. Immunization of mice with CT26 or Panc-02 cells pretreated with DHA-dFdC prevented or delayed the development of corresponding secondary live challenge tumor. DHA-dFdC enabled Panc-02 tumors to respond to anti-PD-1 mAb. RNA sequencing experiments revealed that DHA-dFdC and dFdC differentially impacted genes related to the KRAS, TP53, and inflammatory pathways, and DHA-dFdC enriched for the unfolded protein response (UPR) compared to control, providing insight into DHA-dFdC's potential mechanism of inducing ICD.

CONCLUSION

DHA-dFdC is a bona fide ICD inducer and can render pancreatic tumors responsive to anti-PD-1 mAb therapy.

Rapid Escalation of High-Volume Exercise during Caloric Restriction; Change in Visceral Adipose Tissue and Adipocytokines in Obese Sedentary Breast Cancer Survivors

Simple Summary

Aerobic exercise reduces risk for developing breast cancer or for breast cancer recurrence. In obese women exercise can significantly augment the effects of caloric restriction on visceral fat, reducing metabolic abnormalities and cancer. Women who are older, obese, and sedentary, especially those who have been treated for breast cancer, find it difficult to initiate and achieve the minimum or optimum levels of exercise. In a two-part pilot we found that by providing older, obese, sedentary breast cancer survivors 12 weeks of twice weekly personal training sessions, they could safely increase exercise to ≥200 min/week by 9 weeks during caloric restriction. At 24 weeks, high levels of exercise were still observed with continued behavioral support and study-provided exercise facility. Substantial improvement in visceral fat and breast cancer risk biomarkers were observed with this affordable intervention that is readily exportable to the community.

Abstract

Aerobic exercise reduces risk for breast cancer and recurrence and promotes visceral adipose tissue (VAT) loss in obesity. However, few breast cancer survivors achieve recommended levels of moderate to vigorous physical activity (MVPA) without supervision. In a two-cohort study, feasibility of 12 weeks of partially supervised exercise was started concomitantly with caloric restriction and effects on body composition and systemic risk biomarkers were explored. In total, 22 obese postmenopausal sedentary women (including 18 breast cancer survivors) with median age of 60 and BMI of 37 kg/m² were enrolled. Using personal trainers twice weekly at area YMCAs, MVPA was escalated to ≥200 min/week over 9 weeks. For cohort 2, maintenance of effect was assessed when study provided trainer services were stopped but monitoring, group counseling sessions, and access to the exercise facility were continued. Median post-escalation MVPA was 219 min/week with median 12-week mass and VAT loss of 8 and 19%. MVPA was associated with VAT loss which was associated with improved adiponectin:leptin ratio. In total, 9/11 of cohort-2 women continued the behavioral intervention for another 12 weeks without trainers. High MVPA continued with median 24-week mass and VAT loss of 12 and 29%. This intervention should be further studied in obese sedentary women.

Designing Relevant Preclinical Rodent Models for Studying Links Between Nutrition, Obesity, Metabolism, and Cancer

Diet and nutrition are intricately related to cancer prevention, growth, and treatment response. Preclinical rodent models are a cornerstone to biomedical research and remain instrumental in our understanding of the relationship between cancer and diet and in the development of effective therapeutics. However, the success rate of translating promising findings from the bench to the bedside is suboptimal. Well-designed rodent models will be crucial to improving the impact basic science has on clinical treatment options. This review discusses essential experimental factors to consider when designing a preclinical cancer model with an emphasis on incorporating these models into studies interrogating diet, nutrition, and metabolism. The aims of this review are to (a) provide insight into relevant considerations when designing cancer models for obesity, nutrition, and metabolism research; (b) identify common pitfalls when selecting a rodent model; and (c) discuss strengths and limitations of available preclinical models. Expected final online publication date for the Annual Review of Nutrition, Volume 41 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Psychometrics of the Balance Beam Functional Test in C57BL/6 Mice

Aging is associated with a progressive decline in physical function characterized by decreased mobility, which is an important risk factor for loss of independence and reduced quality of life. Functional testing conducted in animals has advanced our understanding of age-related changes in physical ability and contributed to the development of physiologic measurements that can be used to assess functional changes during aging. The balance beam test is one assessment tool used to measure age-related changes in balance and coordination. The goal of this study is to provide analytical examples and psychometric support of a protocol that has been analyzed to show how the number of successive test runs, foot slips, pauses, and hesitations affect the reliability of the primary outcome measure, which is the time to cross the beam. Our results suggest that conducting more than 1 training session, consisting of greater than or equal to 3 successful training runs, followed by at least one test session with no less than 2 successful runs (that is, runs without pauses or hesitations) provides a psychometrically sound outcome. The data presented here indicate that a psychometric approach can improve protocol design and reliability of balance beam measures in mice.

Change in Blood and Benign Breast Biomarkers in Women Undergoing a Weight-Loss Intervention Randomized to High-Dose ω-3 Fatty Acids versus Placebo

The inflammation-resolving and insulin-sensitizing properties of eicosapentaenoic (EPA) and docosahexaenoic (DHA) fatty acids have potential to augment effects of weight loss on breast cancer risk. In a feasibility study, 46 peri/postmenopausal women at increased risk for breast cancer with a body mass index (BMI) of 28 kg/m² or greater were randomized to 3.25 g/day combined EPA and DHA (ω-3-FA) or placebo concomitantly with initiation of a weight-loss intervention. Forty-five women started the intervention. Study discontinuation for women randomized to ω-3-FA and initiating the weight-loss intervention was 9% at 6 months and thus satisfied our main endpoint, which was feasibility. Between baseline and 6 months significant change (P < 0.05) was observed in 12 of 25 serum metabolic markers associated with breast cancer risk for women randomized to ω-3-FA, but only four for those randomized to placebo. Weight loss (median of 10% for trial initiators and 12% for the 42 completing 6 months) had a significant impact on biomarker modulation. Median loss was similar for placebo (-11%) and ω-3-FA (-13%). No significant change between ω-3-FA and placebo was observed for individual biomarkers, likely due to sample size and effect of weight loss. Women randomized to ω-3-FA exhibiting more than 10% weight loss at 6 months showed greatest biomarker improvement including 6- and 12-month serum adiponectin, insulin, omentin, and C-reactive protein (CRP), and 12-month tissue adiponectin. Given the importance of a favorable adipokine profile in countering the prooncogenic effects of obesity, further evaluation of high-dose ω-3-FA during a weight-loss intervention in obese high-risk women should be considered. PREVENTION RELEVANCE: This study examines biomarkers of response that may be modulated by omega-3 fatty acids when combined with a weight-loss intervention. While focused on obese, postmenopausal women at high risk for development of breast cancer, the findings are applicable to other cancers studied in clinical prevention trials.

Abstract 2357: Anticancer effects of calorie restriction in a murine C3-TAg model of triple-negative breast cancer: the role of miR-15b

Calorie restriction (CR) has an antitumorigenic effect against triple-negative breast cancer (TNBC). A key mitogenic pathway modulated by CR involves insulin-like growth factor (IGF)-1, which plays a central role in local and systemic growth and cell survival by activating the PI3K/AKT/mTOR pathway downstream of the IGF-1 receptor (IGF-1R). Although multiple miRNAs that target components of the IGF-1 signaling pathway have been identified, the impact of CR on IGF-1-related miRNA expression has not been addressed. We hypothesize that CR-induced decreases in TNBC development and progression involve miRNA's regulating IGF-1 signaling, we used C3(1)/SV40 T-antigen (C3-TAg) mice (a TNBC model), a C3-Tag progression series of cell lines (M28, M6, and M6C), and human TNBC cell line (MDA-MB-231). The expression of miRNAs previously reported to target components of the IGF-1 and/or mTOR pathways was evaluated by real-time PCR. Hormone levels were measured using the mouse Luminex Screening Assay. To mimic CR in vitro, and to test the effects of miRNA manipulation, the C3-Tag series of TNBC cell lines were treated (separately and in combination) with serum restriction, BMS754807 (inhibitor of IGF1-R), and various levels of recombinant IGF-1 as well as manipulated levels of miRNA's associated with IGF-1/mTOR signaling. We also conducted in silico analysis using Metabric, TCGA, TargetScan, and miRTarBase data sets to identify genes and pathways associated with specific miRNAs expression related to the PI3K/Akt/mTOR pathway. Our results confirm that CR maintains lower body weight, reduces circulating levels of IGF-1, and slows spontaneous TNBC development and progression in mice. CR also significantly increased the expression of miR-15b and miR-486. In vitro studies showed miR-15b and miR-486 expression decreased with increasing tumorigenicity of the C3-tag series of TNBC progression. Treatment of mouse and human TNBC cells with low IGF-1 induced miR-15b expression and inhibited proliferation. Moreover, miR-15b overexpression inhibited cell proliferation and decreased IGF-1R expression (mRNA and protein). Consistent with these results, the in silico analysis shows that the amplification of miR-15b correlates with downregulation of pathways involved in tumor growth and IGF1-R signaling. Together these findings suggest that reduced circulating IGF-1 levels in response to CR leads to the upregulation of miR-15b, which correspondingly targets and downregulates IGF-1R, both at the mRNA and protein levels. This combination of reduced IGF-1 ligand and miR-15b-induced IGF-1R downregulation contributes to the potent anticancer effects of CR and reveals potential targets for pharmacologically mimicking those effects. This research is supported by R35CA197627.

Citation Format: Ximena Minerva Bustamante-Marin, Kaylyn L. Devlin, Om Dave, Jenna L. Merlino, Shannon B. McDonell, Michael F. Coleman, Stephen D. Hursting. Anticancer effects of calorie restriction in a murine C3-TAg model of triple-negative breast cancer: the role of miR-15b [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2357.

Abstract 2325: Hypoxia-mediated ATF4 induction promotes survival in detached conditions in metastatic murine mammary cancer cells

Regions of hypoxia are common in solid tumors and drive changes in gene expression that increase risk of cancer metastasis. Tumor cells must respond to the stress of hypoxia by activating genes to modify cell metabolism and antioxidant response to improve survival. The goal of the current studies was to determine the effect of hypoxia on cell metabolism and markers of oxidative stress in non-metastatic M-Wnt compared to metastatic metM-Wntlung murine mammary cancer cell lines. We show that hypoxia increased expression of genes involved in antioxidant response in metastatic compared to non-metastatic cells, including glutamate cysteine ligase catalytic and modifier subunits and malic enzyme 1. Further, hypoxia induces a greater suppression of glutamine to glutamate conversion in metastatic cells (15% in metastatic cells compared to 9% in non-metastatic cells). Interestingly, hypoxia increased the mRNA level of the transaminase glutamic pyruvic transaminase 2 (Gpt2, 7.7-fold) only in metM-Wntlung cells. The change in Gpt2 expression was accompanied by transcriptional (4.2-fold) and translational (6.5-fold) induction of the integrated stress response effector protein activating transcription factor 4 (ATF4), which mediated survival of hypoxic metastatic cells in detached conditions, as shown by genetic ATF4 depletion. These data indicate that more aggressive, metastatic cancer cells rely on metabolic reprogramming and induction of antioxidant defense, including activation of ATF4, in hypoxia for survival in detached conditions.

Citation Format: Violet A. Kiesel, Stephen D. Hursting, Dorothy Teegarden. Hypoxia-mediated ATF4 induction promotes survival in detached conditions in metastatic murine mammary cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2325.

Abstract 2700: Sulindac reverses an immunosuppressive tumor microenvironment associated with metastatic mammary tumors in obese mice

Obesity is an established risk factor for several breast cancer (BC) subtypes. Obese BC patients also show poorer response to therapy, increased metastases, and increased mortality. While high levels of inflammation are thought to be a driver for BC metastasis, it is unknown how chronic exposure to low levels of obesity-associated inflammation contributes to BC progression and metastasis. We previously showed that treatment with the non-steroidal anti-inflammatory drug (NSAID) Sulindac (140 ppm mixed into control [10% kcal/fat] or diet induced obesity [DIO, 60% kcal/fat] diets) offset both the pro-growth and pro-metastatic effects of obesity on BC using three different mouse models of metastatic BC - basal-like E0771, and claudin-low metM-Wntlung and metM-Wntliver. To determine the effect of Sulindac treatment on the tumor microenvironment, we conducted gene expression microarray analysis on tumors from mice in all four diet groups (Control, Control+Sulindac, DIO, and DIO+Sulindac). Ingenuity Pathway Analysis revealed significant decreases (q&lt;0.01) in several pathways relating to immune function in DIO tumors that was restored in DIO+Sulindac tumors. Specifically, CD28 signaling and dendritic cell activation were significantly downregulated in DIO tumors compared to all other diet groups, while markers of T cell exhaustion were up in DIO tumors. To further explore Sulindac-associated effects on immune and cancer cell gene expression, we performed single-cell RNA-seq on E0771 tumors. Preliminary analyses showed marked differences in both tumor and immune populations between control, DIO, and DIO+Sulindac mice. Of the top 10 significant (q&lt;0.01) genes upregulated in DIO vs Control tumor cells, 7 have been previously shown to be drivers of breast cancer progression or metastasis. Similarly, 7 of the top 10 genes upregulated in DIO+Sulindac compared to DIO tumor cells have been previously shown to have tumor suppressive functions or limit progression of cancer. Immune analyses showed fewer immune cells in DIO tumors, specifically myeloid (CD11b+) and CD8+ T cells, which were both partially restored in the DIO+Sulindac tumors. Finally, T cell receptor (TCR) analysis showed decreased TCR diversity in DIO T cells compared to control that was restored in DIO+Sulindac T cells. Taken together, these preclinical findings indicate that obesity-driven mammary tumor progression and metastatic burden are associated with an immunosuppressive tumor microenvironment that is largely reversed by Sulindac treatment. This suggests treatment with NSAIDs like Sulindac should be further assessed as a possible strategy for decreasing immunosuppression and improving outcomes in obese breast cancer patients.

This research was supported by R35CA197627 to S.D. Hursting and T32LM012420 and F30CA225142 to S.B. McDonell.

Citation Format: Shannon B. McDonell, Lydia K. Eisenbeis, Andrea N. Walens, Alyssa J. Cozzo, Stephen D. Hursting. Sulindac reverses an immunosuppressive tumor microenvironment associated with metastatic mammary tumors in obese mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2700.

Abstract 2022: Palmitate promotes breast cancer progression in vitro through induction of a senescent-like phenotype in fibroblasts

Background: Obesity confers a worse breast cancer prognosis, including an increased risk of recurrence and mortality. While the causative mechanisms have yet to be fully uncovered, emerging evidence implicates palmitate, increased in the obese state, in development of cellular senescence, an inflammatory state associated with breast tumorigenesis in preclinical models. However, studies are warranted to corroborate the impact of palmitate on induction of a cohesive senescent-like phenotype as well as the extent to which palmitate-induced senescence impacts breast tumorigenesis either in vitro or in vivo. This said, we hypothesize that palmitate exposure induces a senescent-like phenotype in fibroblasts, contributing to measures of breast cancer progression.

Methods: HCA2, IMR-90, and human mammary fibroblasts were exposed to bovine serum albumin or palmitate in media supplemented with 2% charcoal-stripped fetal bovine serum, after which the cells were measured through qPCR for expression of IL-1a, IL-6 and IL-8, some of the most prominent members of the senescence-associated secretory phenotype. Palmitate-exposed fibroblasts were also stained for senescence-associated beta-galactosidase and BrdU incorporation, well-established senescence markers. Experiments were then repeated with administration of eicosapentaenoic and docosahaexanoic acids to evaluate the potential of omega-3 fatty acids to limit the effects of palmitate on fibroblast senescence. Finally, we assessed the tumor-promoting potential of these palmitate-exposed fibroblasts by culturing MCF-7 and T47D breast cancer cells in their conditioned media and assessing changes in carcinogenic measures.

Results and Conclusions: Palmitate induced pro-inflammatory gene expression and SA-beta-gal positivity and decreased proliferation in fibroblasts, while omega-3 fatty acid supplementation reversed these effects. These palmitate-exposed fibroblasts also appeared to be of pathological impact, as exposure to their CM increased proliferation in breast cancer cells. These findings are important in that they support emerging evidence implicating obesity-associated factors in the exacerbation of breast cancer progression as well as indicate the potential of omega-3 fatty acids to improve outcome.

Citation Format: Brittany Susanne Harlow, Albert R. Davalos, Andrew J. Brenner, Christopher Jolly, Stefano Tiziani, Stephen D. Hursting, Linda A. deGraffenried. Palmitate promotes breast cancer progression in vitro through induction of a senescent-like phenotype in fibroblasts [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2022.

Abstract 2575: Intermittent calorie restriction reverses the adverse effects of obesity and advanced age on tumor growth in a mouse model of breast cancer

Advanced age and obesity are two major risk factors for breast cancer (BC) mortality. This presents a significant public health concern as the number of older individuals and incidence of obesity are increasing worldwide. In our mouse models of BC, we have demonstrated that, similar to obesity, advanced age accelerates mammary tumor growth. Mechanistically, obesity and advanced age suppress tumor gene expression relating to antitumor immunity and reduce tumoral abundance of cytotoxic CD8+ T cells. Thus, advanced age- and obesity-related enhancement of mammary tumor growth is explained, in part, through the development of an immunosuppressive tumor microenvironment. Given the aging of our populations and the increasing prevalence of obesity, interventions capable of reversing the tumor-promoting effects of advanced age and obesity are needed. We have previously demonstrated that weight loss by intermittent calorie restriction (ICR), in which mice are placed on a 5:2 calorie restriction (CR) regimen (5 days 14% CR, 2 nonconsecutive days 70% CR per week), attenuates tumor growth and immunosuppression in formerly obese mice. This project tests if ICR will provide similar benefit to aged and aged obese mice. Cohorts of young control (5 mos), young diet-induced obese (DIO; 5 mos), aged control (15 mos), and aged DIO (15 mos) mice were generated and subsequently randomized to either remain on their baseline diet or switch to the ICR intervention. Following 9 weeks on ICR or baseline diet, serum samples were collected and then tumor development induced by orthotopic transplantation of E0771 cancer cells into the 4th mammary fat pad of mice. At tumor endpoint mammary tumors were collected and weighed. To determine if ICR alters systemic inflammation in each experimental group, cytokine levels were measured in serum samples collected prior to tumor inoculation. Multiple inflammatory cytokines were downregulated following ICR intervention in young DIO, aged control, and aged DIO mice, including CCL7, CCL10, and CCL24. Downregulation of inflammatory cytokines was correlated with decreased tumor burden in young DIO, aged control, and aged DIO mice placed on ICR, compared with their respective non-intervention controls. Ongoing analyses are investigating if ICR increases the abundance of cytotoxic CD8+ T cells within the tumor microenvironment of young DIO, aged control, and aged DIO mice. These findings demonstrate that ICR may be effective in reversing obesity- and advanced age-related enhancement of mammary tumor growth in mouse models of breast cancer. More research is needed to test if these preclinical findings translate to obese and aged humans with BC. Identifying dietary interventions that may attenuate obesity- and age-related tumor growth has the potential to improve both patient outcomes and quality of life. This research was supported by R35CA197627 to S. Hursting.

Citation Format: Dalton M. Craven, Laura A. Smith, Michael F. Coleman, Elaine M. Glenny, Stephen D. Hursting. Intermittent calorie restriction reverses the adverse effects of obesity and advanced age on tumor growth in a mouse model of breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2575.

Abstract 2256: A population-based mouse model for an experimental basal-like mammary cancer

The prevalence of obesity, an established risk and prognostic factor for basal-like breast cancer (BLBC), has risen dramatically in the US and many other countries over the past 4 decades. Obesity is also associated with increased resistance to several classes of cancer chemotherapeutic agents used for advanced BLBC. Unfortunately the mechanisms underlying chemotherapy resistance, and the inter-individual differences driving resistance, are poorly understood. Population-based experimental mouse models for determining inter-individual genetic differences in chemotherapy pharmacokinetics and treatment-related efficacy or resistance in mammary gland cancer are not well-defined. Our aim is to develop a population-based experimental model based on outcrosses between 30 different Collaborative Cross line females and hemizygous male B6.FVB-Tg(C3-1-TAg) (greater than N15) congenic mice to produce 30 Collaborative Cross (CC) recombinant inbred line intercross (CC RIX) mouse lines to investigate the interactive effects between diet-induced obesity (DIO) and genetic susceptibility to chemotherapy in a genetically heterogeneous mouse model of BLBC. We report here that thirty genetically-different CCRIL X hemizygous B6.FVB-Tg(C3-1-TAg) congenic female and male CC RIX mice observed longitudinally for occurrence of basal-like mammary tumors showed significant differences in both age at first mammary tumor observation and the fraction of females and males in each RIX bearing tumors. Litter size and the number of females and males of each RIX varied across the 30 CC RIX line. The study was well-powered, with at least X males and Y females for each CC RIX line evaluated longitudinally. We observed that 25 of 30 female CC RIX lines presented with BLMC, with distinct times-to-tumor with each CC RIX. The penetrance of the fraction of each CC RIX line (birth cohort) presenting with BLMC varied greatly in females (25-100%). Surprisingly, 11 of 30 male CC RIX lines presented with BLMC, with penetrance of BLMC varying in males between 10-75%. In conclusion, we present preliminary data to support development of an experimental mouse model for BLBC based on the random mating of 8 genetically-diverse homozygous inbred founder lines followed by in-breeding to greater than 95% homozygosity carrying 45 million single-nucleotide and structural variants. Studies are underway using these CC RIX lines to evaluate the genetic underpinnings of obesity-associated resistance to carboplatin in C3-TAg-driven mammary tumors.

Citation Format: John Edgar French, William Pressel, Jody Albright, Melissa VerHague, Stephen D. Hursting. A population-based mouse model for an experimental basal-like mammary cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2256.

Abstract 2323: Mammary tumor microenvironment reprogramming in response to pyruvate carboxylase modulation

Introduction: Breast cancer (BC) is the second deadliest cancer amongst women in the US, with metastatic breast cancer being particularly deadly. Pyruvate carboxylase (PC) catalyzes the conversion of pyruvate to oxaloacetate for anaplerotic refilling of TCA intermediates, feeding numerous energetic and biosynthetic pathways. Upregulation of PC is an important contributor to metabolic reprogramming in both primary and metastatic BC. In this study, we investigate whether suppression of PC alters metabolism and drives microenvironmental adaptation in a primary tumor model of BC.

Methods: C57/Bl6 mice were injected with M-Wnt cells transduced with doxycycline-inducible ShRNA targeting PC. Doxycycline treatment began once tumors were palpable. Tumors were harvested 4 weeks following injection. Tumor transcriptomic analysis was conducted via GSEA and enrichment mapping. Digital cytometry using CIBORSORTx was conducted to determine tumor microenvironment immune cell composition. In vitro metabolic adaptation to PC suppression in BC cell lines following knockdown of PC was analyzed. Perturbations of mitochondrial metabolism and respiration were assessed by extracellular flux analysis. Assays of extracellular lactate and glucose concentrations determined changes in the production and utilization of carbon sources in the context of loss of PC

Results: Metabolic assays revealed that cells with PC knockdown export more lactate into their environment and respire less efficiently, without consuming additional glucose. This indicates potential mitochondrial dysfunction with loss of PC-derived anaplerosis. In vivo suppression of PC resulted in increased tumor mass and volume relative to control. Gene expression data from PC knockdown tumors revealed distinct transcriptomic profiles between groups. GSEA analysis further showed profound suppression of immunological pathways following loss of PC, indicating that PC knockdown resulted in a diminished immune response. Digital cytometry supported this finding with PC suppression resulting in decreased proportions of critical innate and adaptive immune cell populations.

Conclusion: Metabolic assays revealed increased flux through lactate production with a decrease in mitochondrial respiration, suggesting that diminished PC-mediated anaplerosis is altering the fate of carbon sources and contributing to metabolic reprogramming. Suppression of PC resulted in tumors with distinct transcriptomic profiles versus control, with immune response signatures being diminished in response to loss of PC. We conclude that PC knockdown promotes a metabolically altered tumor microenvironment associated with immunosuppression, tumor progression, and increased metastatic potential. This work was supported by R35CA197627 to S. Hursting, and R01CA232589 to D. Teegarden and S. Hursting.

Citation Format: Michael F. Coleman, Alexander J. Pfeil, Violet Kiesel, Suhas K. Etigunta, Michael K. Wendt, Dorothy Teegarden, Stephen D. Hursting. Mammary tumor microenvironment reprogramming in response to pyruvate carboxylase modulation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2323.

Abstract 2577: Metaboendocrine and inflammatory correlates of tumor growth following caloric restriction and vertical sleeve gastrectomy in a mouse model of breast cancer

Breast cancer is the second leading cause of cancer-related deaths in women living in the United States, and obesity is a well-established breast cancer risk and progression factor. Identifying interventions that effectively break the obesity-cancer link is therefore of great importance. This preclinical project aims to compare circulating cytokine and metaboendocrine hormone levels in formerly obese mice following dietary and surgical weight loss to identify serum markers potentially contributing to differential tumor mass outcomes. 20 control female C57BL/6 mice were maintained on a 10 kcal% fat diet throughout the study. All other mice were placed on a 60 kcal% diet for 15 weeks to promote diet-induced obesity (DIO), then randomized to receive either: a) vertical sleeve gastrectomy (VSG) with concurrent switch to control diet (16 mice); b) sham surgery and continuation of DIO regimen (18 mice); c) sham surgery with switch to a chronic calorie restricted (CCR; 30% daily calorie reduction) regimen (16 mice); or d) sham surgery with switch to an intermittent calorie restricted (ICR; 14% calorie reduction 5 days per week, 70% calorie reduction 2 non-consecutive days per week) regimen (19 mice). Following 10 weeks of weight loss interventions, serum from fasted animals was collected, and glucose (by glucometer), cytokines (by BioRad Mouse Cytokine 23-plex panel on a BioRad MAGPIX Instrument), and hormones (BioRad Mouse Diabetes 8-plex panel) were analyzed to characterize the systemic metaboendocrine and inflammatory environment immediately prior to orthotopic transplantation of E0771 mammary cancer cells. Surgical or dietary weight loss reduced serum cytokines that are classically induced by obesity, including interleukin 6 (IL-6), interleukin 2 (IL-2), and tumor necrosis factor alpha (TNFα), compared with DIO mice. Compared with VSG mice, only circulating chemokine ligand 13 (CXCL13) was significantly lower in serum from both CCR and ICR mice. Moreover, CCR and ICR mice displayed significantly lower fasting blood glucose levels and circulating plasminogen activator inhibitor-1 (PAI-1) compared with VSG mice. Therefore, these data suggest that decreased circulating CXCL13, PAI-1 and/or decreased fasted blood glucose may contribute to the superior antitumor effects of CCR and ICR versus VSG.

This research was supported by R35CA197627 to S. Hursting.

Citation Format: Tori L. McFarlane, Kristina Kalevas Camp, Elaine M. Glenny, Erika Rezeli, Michael F. Coleman, Stephen D. Hursting. Metaboendocrine and inflammatory correlates of tumor growth following caloric restriction and vertical sleeve gastrectomy in a mouse model of breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2577.

Abstract 2567: Duavee® improves metabolic health without increasing cancer risk: findings from a preclinical model of obesity and postmenopausal breast cancer

Introduction: Many women at high risk for breast cancer will not take standard selective estrogen receptor modulators (SERMs) for cancer prevention due to concern of side effects, especially vasomotor symptoms. Duavee®, a tissue selective complex of the SERM bazedoxifene (BZA; 20mg) + conjugated estrogen (CE; 0.45mg), is FDA approved for relief of hot-flashes. Preclinical and early phase human studies suggest Duavee® has potential for breast cancer prevention, with favorable change in mammographic fibroglandular volume and proliferation. Given the &gt;40% incidence of obesity in postmenopausal women, and that obesity increases breast cancer risk, the current study was aimed at identifying the effects of obesity on response to Duavee® in a rodent model of obesity and postmenopausal breast cancer.

Methods: This study used our well-characterized rat model of diet-induced obesity and postmenopausal ER-positive breast cancer. Rats were injected with N-methylnitrosourea (MNU, 50 mg/kg) at 7 weeks of age to induce mammary tumors and fed a high fat diet (HF; 46% kcal fat) to promote obesity. Lean and obese rat were selected based on % body fat at 16 weeks. Tumors were monitored by manual palpation weekly and measured using digital calipers. Tumor-bearing rats were ovariectomized (OVX) when a tumor reached 0.7cm3. Rats were then maintained on ad libitum HF diet or HF diet plus a daily oral dose of Duavee® (3mg BZA+ 0.07mg CE/kg body weight) for 8 weeks. Body composition was analyzed biweekly (qMR) and fat pads weighed at study end to determine regional fat distribution.

Results: Like menopause in women, OVX induces weight gain in this model. Duavee® significantly blunted the OVX-induced weight gain in both lean (-65%, p&lt;0.001) and obese (-88%, p&lt;0.001) rats compared to controls. Similarly, Duavee®-treated rats gained less body fat after OVX vs controls (-50% lean; -97% obese, p&lt;0.001). Duavee® administration was associated with reduction in glucose in obese rats after 2 weeks and in lean and obese rats after 8 weeks (-11% vs controls, p=0.03). The effects of Duavee® on regional fat deposition varied by adiposity. Obese Duavee®-treated rats had significantly lower pericardial fat (-17%, p&lt;0.05) and tended to have lower mammary fat (-19%, p=0.08); lean rats had less gonadal fat (-20%, p&lt;0.05), while deposition in this region was not altered by Duavee® in obese rats. At 8 weeks there was no evidence that Duavee® promoted tumor development or growth in lean or obese OVX rats.

Conclusions: These data suggest that Duavee® may provide beneficial effects on body composition and metabolism in obese OVX animals without promotion of tumor growth. Further analyses will include study of direct effects of Duavee® on tumors, the tumor microenvironment, and systemic markers of insulin resistance and mammary cancer risk in our rat model of pre-and postmenopausal obesity and breast cancer.

Citation Format: Karen A. Corleto, Tara N. Mahmood, Danilo Landrock, Stephen D. Hursting, Carol J. Fabian, Bruce F. Kimler, Erin D. Giles. Duavee® improves metabolic health without increasing cancer risk: findings from a preclinical model of obesity and postmenopausal breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2567.

Abstract 2918: Characterization of a novel transplantable C3TAg breast cancer model in C57BL/6J mice

Introduction: In women in the United States, breast cancer (BC) is the second leading cause of cancer-related death. BC is a heterogeneous disease, characterized by several subtypes based on molecular markers including several hormone receptors. Transcriptomic analysis further stratifies the disease. The basal-like subtype, often triple-negative for hormone receptors, has the poorest prognosis partially due to the absence of targeted therapies. Obesity, a preventable cause of cancer, is an established risk factor for breast cancer, including basal-like breast cancers. Mouse models to study the interaction of BC and obesity, particularly the more aggressive basal-like BC, are crucial. The C3(1)/SV40 large T-antigen (TAg) transgenic mouse model is an established model of basal-like mammary cancer that recapitulates several key features of human breast cancer. However, this model was generated in FVB mice, which is not an ideal genetic background for studying obesity, immunology and other aspects of cancer research. The goal of this study was to develop and characterize a C3TAg transgenic mouse model on a C57BL/6 background. Therefore, the current study backcrossed C3TAg transgenic FVB mice with C57BL/6 mice, a model most commonly used to study obesity, for 10 generations to create a transplantable C3TAg model in C57BL/6 mice.

Methods: Cell Line Generation: C3TAg transgenic FVB mice were backcrossed with C57BL/6 mice for 10 generations. Tumors from 6-month-old heterozygous female mammary tissue were harvested, dissociated, and subcloned by limited dilution. A total of 156 clonal lines were established from which a subset of 12 lines displaying differences in morphology, growth and expression of metabolic and EMT genes (by qPCR). In vivo: 96 female C57BL/6J mice were randomized into 12 groups (n=8/group) and orthotopically injected with three different cell densities (5*104, 1.5*105, 5*105 cells/mouse) from one of the four selected lines. Mice tumor growth was assessed using electronic calipers. In vitro: Proliferation and cellular respiration were assessed and molecular subtyping was conducted using Affymetrix microarray data.

Results: All tested cell lines formed tumors in vivo, with macroscopic characteristics of basal-like tumors including central necrosis. In vitro growth and metabolism of tested lines showed modest dissimilarity; in contrast, tumor growth rates and metastatic outgrowth were starkly dissimilar among the tested lines. Transcriptomic data clustered these cell lines with human BC tumors.

Conclusions: Here we report for the first time a transplantable C3TAg model in C57BL/6 mice with highly effective tumor engraftment and growth, and with variable phenotypes for tumor growth and metastasis. Thus, this model may serve as an attractive model for the study of the interactions of basal-like breast cancer and obesity. This work was supported by R35CA197627 to SH.

Citation Format: Meredith S. Carson, Michael F. Colman, Daniel Roth, Jody Albright, Melissa VerHague, John E. French, Stephen D. Hursting. Characterization of a novel transplantable C3TAg breast cancer model in C57BL/6J mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2918.

Abstract 2579: Links between obesity and secreted frizzled-related protein 4 (Sfrp4) in a murine model of colon cancer

Obesity is a well-established risk factor for colon cancer and the effect of obesity-mediated inflammation is particularly pronounced in colon carcinogenesis. An incomplete understanding of the biology underlying this strong obesity-colon cancer association has hampered efforts to identify effective colon cancer prevention strategies. The current study aims to identify novel colon tumor intrinsic targets that mediate critical inflammatory signals underlying the obesity-colon cancer connection. To induce colon tumors, FVB/N male mice were treated weekly with azoxymethane (10 mg/kg intraperitoneally) for 5 weeks. Mice were then randomized to either continue receiving 10 kcal% fat diet (control) or were switched to a 60 kcal% fat diet to promote diet-induced obesity (DIO) over a 15-week period. DIO mice were then randomized to either receive 0ppm (DIO) or 140ppm sulindac (DIO+Su), a non-steroidal anti-inflammatory drug, for 7 additional weeks. At the end of the 27-week study, colonic tumors were collected for histology and global transcriptomic analysis using Affymetrix Clariom D mouse gene expression microarrays. DIO increased tumor multiplicity and burden in AOM-treated mice. Moreover, long-term administration of dietary sulindac was sufficient to reduce inflammatory signals, tumor multiplicity, and tumor burden in DIO-Su versus DIO mice. Principal component analysis and hierarchical clustering based on the 1,000 most differentially expressed genes revealed distinct gene expression profiles in tumors from control, DIO, and DIO+Su mice. To determine the biological processes most up- or down-regulated in tumors from DIO mice, gene set enrichment analysis was run using the hallmark gene sets. Epithelial-mesenchymal-transition (EMT) was the most upregulated gene set in tumors from DIO mice compared with tumors from control mice (normalized enrichment score 2.00; adjusted p=0.0002) and compared with tumors from DIO+Su mice (normalized enrichment score 1.78; adjusted p=0.009), suggesting that obesity drives EMT via an inflammatory mechanism. Based on a leading-edge analysis, secreted frizzled-related protein 4 (Sfrp4) expression was significantly enriched in the EMT gene set. Sfrp4 is of biological interest given its biphasic modulation of Wnt signaling and association with poor prognosis in aggressive prostate cancer. We confirmed via immunofluorescence that Sfrp4 is produced by AOM-treated colonic intestinal epithelial and submucosal cell populations and observed by qPCR that it is expressed across multiple human colon cancer cell lines. Hence, Sfrp4 may be a novel target to mitigate obesity-induced exacerbation of colon tumorigenesis. Future work will determine the role of Sfrp4 in colon cancer cell-adipose interactions and whether ablation of Sfrp4 is sufficient to impede colon tumor growth. This research was supported by R35CA197627 to S. Hursting.

Citation Format: Elaine M. Glenny, Laura W. Bowers, Diana Li, Jatin Roper, Stephen D. Hursting. Links between obesity and secreted frizzled-related protein 4 (Sfrp4) in a murine model of colon cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2579.

Abstract 1565: β-hydroxy-β-methylbutyrate enhances anti-PD1 immunotherapy in a mouse model of pancreatic ductal adenocarcinoma

Background: Pancreatic ductal adenocarcinoma (PDAC) has a five year survival rate in single digits.This is driven by a number of factors including limited effective therapeutic options for the management of PDAC. Immunotherapies such as inhibition of programmed death 1 (PD1) have provided dramatic benefit to cancers with historically poor treatment options such as melanoma. However, PDAC has thus far proven unresponsive to immunotherapies. It is well understood that the development of effective anti-tumor immunity is in part limited by the metabolically hostile tumor microenvironment. β-Hydroxy-β-Methylbutyrate (HMB) is a leucine metabolite which has been shown to reduce cancer cachexia and tumor progression. We sought to determine if HMB treatment would alter immunotherapy response in PDAC via reduction of metabolic competition.

Methods: C57BL/6 mice were injected with PANC02 cells subcutaneously to generate PDAC tumors, then fed either a control (AIN93G) or HMB supplemented diet. Once tumors were palpable, mice were further randomized for treatment with anti-PD1 immunotherapy or a vehicle control. Tumors were collected, measured and weighed; RNA isolated; and cDNA synthesized for global transcriptomic analysis. Gene set enrichment analysis followed by enrichment mapping was used to determine the pathway activation induced by HMB, anti-PD1, or the combination. CIBERSORTx deconvolution was used to determine microenvironment immune cell composition.

Results: As anticipated, neither HMB nor anti-PD1 therapies alone were sufficient to reduce tumor growth. The combination of HMB and anti-PD1; however, resulted in significantly smaller tumors than the anti-PD1 treated group, indicating that HMB was sufficient to enable PDAC response to immunotherapy. Transcriptomic analysis demonstrated only moderate immunomodulatory effects of HMB or anti-PD1 alone; however, the combination potently induced putatively anti-tumor immune response. Deconvolution analysis indicated that the combination of HMB and anti-PD1 increased the abundance of anti-tumor immune cell types. HMB treatment, as expected, was very well tolerated by all animals with no adverse effects detected. Overall, HMB promotes efficacy of anti-PD1 immunotherapy in a model of PDAC.

Discussion: Here, we report that the combination of HMB with anti-PD1 elicited significant anti-tumor response, without the need for the prior induction of immunological cell death via chemotherapy or radiation. This is particularly remarkable as many PDAC immunotherapy trials with or without other treatments did not result in significant benefit. HMB has been well tolerated in numerous cancer cachexia clinical trials and is both cheaply and commonly available. Thus, this combination is a highly promising avenue for the advancement of immunotherapy in PDAC. This research was supported by R35CA197627 to S. Hursting.

Citation Format: Suhas K. Etigunta, Michael F. Coleman, Alex J. Pfeil, Laura M. Lashinger, Zhengrong Cui, Stephen D. Hursting. β-hydroxy-β-methylbutyrate enhances anti-PD1 immunotherapy in a mouse model of pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1565.

Metabolic Response of Triple-Negative Breast Cancer to Folate Restriction

Background: Triple-negative breast cancers (TNBCs), accounting for approximately 15% of breast cancers, lack targeted therapy. A hallmark of cancer is metabolic reprogramming, with one-carbon metabolism essential to many processes altered in tumor cells, including nucleotide biosynthesis and antioxidant defenses. We reported that folate deficiency via folic acid (FA) withdrawal in several TNBC cell lines results in heterogenous effects on cell growth, metabolic reprogramming, and mitochondrial impairment. To elucidate underlying drivers of TNBC sensitivity to folate stress, we characterized in vivo and in vitro responses to FA restriction in two TNBC models differing in metastatic potential and innate mitochondrial dysfunction. Methods: Metastatic MDA-MB-231 cells (high mitochondrial dysfunction) and nonmetastatic M-Wnt cells (low mitochondrial dysfunction) were orthotopically injected into mice fed diets with either 2 ppm FA (control), 0 ppm FA, or 12 ppm FA (supplementation; in MDA-MB-231 only). Tumor growth, metabolomics, and metabolic gene expression were assessed. MDA-MB-231 and M-Wnt cells were also grown in media with 0 or 2.2 µM FA; metabolic alterations were assessed by extracellular flux analysis, flow cytometry, and qPCR. Results: Relative to control, dietary FA restriction decreased MDA-MB-231 tumor weight and volume, while FA supplementation minimally increased MDA-MB-231 tumor weight. Metabolic studies in vivo and in vitro using MDA-MB-231 cells showed FA restriction remodeled one-carbon metabolism, nucleotide biosynthesis, and glucose metabolism. In contrast to findings in the MDA-MB-231 model, FA restriction in the M-Wnt model, relative to control, led to accelerated tumor growth, minimal metabolic changes, and modest mitochondrial dysfunction. Increased mitochondrial dysfunction in M-Wnt cells, induced via chloramphenicol, significantly enhanced responsiveness to the cytotoxic effects of FA restriction. Conclusions: Given the lack of targeted treatment options for TNBC, uncovering metabolic vulnerabilities that can be exploited as therapeutic targets is an important goal. Our findings suggest that a major driver of TNBC sensitivity to folate restriction is a high innate level of mitochondrial dysfunction, which can increase dependence on one-carbon metabolism. Thus, folate deprivation or antifolate therapy for TNBCs with metabolic inflexibility due to their elevated levels of mitochondrial dysfunction may represent a novel precision-medicine strategy.