Altered lipid metabolism in APC-driven colorectal cancer: the potential for therapeutic intervention

Altered lipid metabolism is a well-recognized feature of solid cancers, including colorectal cancer. In colorectal cancer, upregulation of lipid metabolism contributes to initiation, progression, and metastasis; thus, aberrant lipid metabolism contributes to a poor patient outcome. The inactivating mutation of APC, a vital tumor suppressor in the Wnt signaling pathway, is a key event that occurs early in the majority of colorectal cancer cases. The potential crosstalk between lipid metabolism and APC-driven colorectal cancer is poorly understood. This review collectively highlights and summarizes the limited understanding between mutations in APC and the upregulation of Wnt/beta-catenin signaling and lipid metabolism. The interconnection between APC inactivation and aberrant lipid metabolism activates Wnt/beta-catenin signaling which causes transcriptome, epigenetic, and microbiome changes to promote colorectal cancer initiation and progression. Furthermore, the downstream effects of this collaborative effort between aberrant Wnt/beta-catenin signaling and lipid metabolism are enhanced stemness, cellular proliferation, prooncogenic signaling, and survival. Understanding the mechanistic link between APC inactivation and alterations in lipid metabolism may foster identification of new therapeutic targets to enable development of more efficacious strategies for prevention and/or treatment of colorectal cancer.

Inflammation and cardiometabolic diseases induced by persistent organic pollutants and nutritional interventions: Effects of multi-organ interactions

The development and outcome of inflammatory diseases are associated with genetic and lifestyle factors, which include chemical and nonchemical stressors. Persistent organic pollutants (POPs) are major groups of chemical stressors. For example, dioxin-like polychlorinated biphenyls (PCBs), per- and polyfluoroalkyl substances (PFASs), and polybrominated diphenyl ethers (PBDEs) are closely associated with the incidence of inflammatory diseases. The pathology of environmental chemical-mediated inflammatory diseases is complex and may involve disturbances in multiple organs, including the gut, liver, brain, vascular tissues, and immune systems. Recent studies suggested that diet-derived nutrients (e.g., phytochemicals, vitamins, unsaturated fatty acids, dietary fibers) could modulate environmental insults and affect disease development, progression, and outcome. In this article, mechanisms of environmental pollutant-induced inflammation and cardiometabolic diseases are reviewed, focusing on multi-organ interplays and highlighting recent advances in nutritional strategies to improve the outcome of cardiometabolic diseases associated with environmental exposures. In addition, advanced system biology approaches are discussed, which present unique opportunities to unveil the complex interactions among multiple organs and to fuel the development of precision intervention strategies in exposed individuals.

The role of perfluorooctane sulfonic acid (PFOS) exposure in inflammation of intestinal tissues and intestinal carcinogenesis

PFAS (per- and polyfluoroalkyl substances) are organofluorine substances that are used commercially in products like non-stick cookware, food packaging, personal care products, fire-fighting foam, etc. These chemicals have several different subtypes made of varying numbers of carbon and fluorine atoms. PFAS substances that have longer carbon chains, such as PFOS (perfluorooctane sulfonic acid), can potentially pose a significant public health risk due to their ability to bioaccumulate and persist for long periods of time in the body and the environment. The National Academies Report suggests there is some evidence of PFOS exposure and gastrointestinal (GI) inflammation contributing to ulcerative colitis. Inflammatory bowel diseases such as ulcerative colitis are precursors to colorectal cancer. However, evidence about the association between PFOS and colorectal cancer is limited and has shown contradictory findings. This review provides an overview of population and preclinical studies on PFOS exposure and GI inflammation, metabolism, immune responses, and carcinogenesis. It also highlights some mitigation approaches to reduce the harmful effects of PFOS on GI tract and discusses the dietary strategies, such as an increase in soluble fiber intake, to reduce PFOS-induced alterations in cellular lipid metabolism. More importantly, this review demonstrates the urgent need to better understand the relationship between PFOS and GI pathology and carcinogenesis, which will enable development of better approaches for interventions in populations exposed to high levels of PFAS, and in particular to PFOS.

Glycolytic Regulation of Intestinal Stem Cell Self-Renewal and Differentiation

BACKGROUND AND AIMS

The intestinal mucosa undergoes a continual process of proliferation, differentiation, and apoptosis. An imbalance in this highly regimented process within the intestinal crypts is associated with several intestinal pathologies. Although metabolic changes are known to play a pivotal role in cell proliferation and differentiation, how glycolysis contributes to intestinal epithelial homeostasis remains to be defined.

METHODS

Small intestines were harvested from mice with specific hexokinase 2 (HK2) deletion in the intestinal epithelium or LGR5+ stem cells. Glycolysis was measured using the Seahorse XFe96 analyzer. Expression of phospho-p38 mitogen-activated protein kinase, the transcription factor atonal homolog 1, and intestinal cell differentiation markers lysozyme, mucin 2, and chromogranin A were determined by Western blot, quantitative real-time reverse transcription polymerase chain reaction, or immunofluorescence, and immunohistochemistry staining.

RESULTS

HK2 is a target gene of Wnt signaling in intestinal epithelium. HK2 knockout or inhibition of glycolysis resulted in increased numbers of Paneth, goblet, and enteroendocrine cells and decreased intestinal stem cell self-renewal. Mechanistically, HK2 knockout resulted in activation of p38 mitogen-activated protein kinase and increased expression of ATOH1; inhibition of p38 mitogen-activated protein kinase signaling attenuated the phenotypes induced by HK2 knockout in intestinal organoids. HK2 knockout significantly decreased glycolysis and lactate production in intestinal organoids; supplementation of lactate or pyruvate reversed the phenotypes induced by HK2 knockout.

CONCLUSIONS

Our results show that HK2 regulates intestinal stem cell self-renewal and differentiation through p38 mitogen-activated protein kinase/atonal homolog 1 signaling pathway. Our findings demonstrate an essential role for glycolysis in maintenance of intestinal stem cell function.

Abstract 2308: Inhibition of fatty acid synthesis and concurrent lipid deprivation decreases neuroendocrine cancer cell proliferation and colony formation

Introduction. Gastroenteropancreatic neuroendocrine tumors (GEP-NETs), the second most common digestive cancer in terms of prevalence, can be particularly challenging to treat due to resistance to current clinical regimens. Lipid metabolism provides an important energy source for cancer cells; cells increase lipid supply by endogenous synthesis or exogenous uptake. Both processes can become dysregulated in cancer, but little is known about the role of either pathway in neuroendocrine tumors (NETs). The goal of this project was to determine whether inhibition of lipid synthesis with concurrent lipid deprivation affects NET cell proliferation and survival.

Methods. (i) Expression and localization of fatty acid synthase (FASN) in NET patient samples (n=39) and human cell lines (BON, QGP-1, and NT-3) were examined with immunohistochemistry and immunoblotting, respectively. (ii) NET neutral lipid stores were determined with immunofluorescent analysis of Bodipy 493/503 staining. (iii) To study the role of lipid synthesis and lipid uptake on colony formation, NET cells were treated with TVB-3664 with or without FA depletion for 10d. Colonies were visualized with sulforhodamine B (SRB) dye staining and quantified with photospectrometry. (iv) To study the effect of lipid synthesis and uptake on proliferation, NET cells were treated with TVB-3664 with or without FA depletion for 72h, 96h, and 120h. Cellular growth was determined with SRB assays. (v) The effect of TVB-3664 on cyclin D1 and β-catenin expression in NET cells was determined with immunoblotting.

Results. (i) FASN was detected in the cytoplasm of all 39 NET primary and metastatic tissue samples; scores of 5 or 6 indicated robust expression in 38/39 samples. Among cell lines, FASN expression was highest in BON cells followed by similar levels in QGP-1 and NT-3 cells. (ii) TVB-3664 treatment or lipid deprivation for 5d reduced neutral lipid storage in BON cells; combined TVB-3664 treatment with FA depletion for 5d fully depleted BON lipid stores. (iii) TVB-3664 treatment, but not FA deprivation, reduced NET colony formation by ~25% in BON cells and ~50% in QGP-1 cells. TVB-3664 treatment with FA deprivation reduced colony formation by ~65% in BON cells and ~75% in QGP-1 cells. (iv) TVB-3664 treatment or FA deprivation reduced NET cell proliferation at 72h, 96h, and 120h. (v) TVB-3664 treatment reduced cyclin D1 expression in BON and QGP-1 cells and β-catenin levels in BON cells.

Conclusions. Our findings indicate that FASN is robustly expressed in NET patient samples and cell lines. Inhibition of endogenous lipid synthesis with concurrent lipid deprivation reduces colony formation and proliferation of NET cells. Importantly, our findings show that lipid metabolism promotes NET cell growth and that targeting de novo lipogenesis may be a potential treatment strategy for advanced GEP-NETs.

Citation Format: Jeremy Johnson, Yekaterina Y. Zaytseva, Jennifer Castle, B. Mark Evers, Piotr Rychahou. Inhibition of fatty acid synthesis and concurrent lipid deprivation decreases neuroendocrine cancer cell proliferation and colony formation [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 2308.

Diaminobutoxy-substituted Isoflavonoid (DBI-1) Enhances the Therapeutic Efficacy of GLUT1 Inhibitor BAY-876 by Modulating Metabolic Pathways in Colon Cancer Cells

Cancer cells undergo significant "metabolic remodeling" to provide sufficient ATP to maintain cell survival and to promote rapid growth. In colorectal cancer cells, ATP is produced by mitochondrial oxidative phosphorylation and by substantially elevated cytoplasmic glucose fermentation (i.e., the Warburg effect). Glucose transporter 1 (GLUT1) expression is significantly increased in colorectal cancer cells, and GLUT1 inhibitors block glucose uptake and hence glycolysis crucial for cancer cell growth. In addition to ATP, these metabolic pathways also provide macromolecule building blocks and signaling molecules required for tumor growth. In this study, we identify a diaminobutoxy-substituted isoflavonoid (DBI-1) that inhibits mitochondrial complex I and deprives rapidly growing cancer cells of energy needed for growth. DBI-1 and the GLUT1 inhibitor, BAY-876, synergistically inhibit colorectal cancer cell growth in vitro and in vivo. This study suggests that an electron transport chain inhibitor (i.e., DBI-1) and a glucose transport inhibitor, (i.e., BAY-876) are potentially effective combination for colorectal cancer treatment.

Upregulation of CD36, a Fatty Acid Translocase, Promotes Colorectal Cancer Metastasis by Increasing MMP28 and Decreasing E-Cadherin Expression

Altered fatty acid metabolism continues to be an attractive target for therapeutic intervention in cancer. We previously found that colorectal cancer (CRC) cells with a higher metastatic potential express a higher level of fatty acid translocase (CD36). However, the role of CD36 in CRC metastasis has not been studied. Here, we demonstrate that high expression of CD36 promotes invasion of CRC cells. Consistently, CD36 promoted lung metastasis in the tail vein model and GI metastasis in the cecum injection model. RNA-Seq analysis of CRC cells with altered expression of CD36 revealed an association between high expression of CD36 and upregulation of MMP28, a novel member of the metallopeptidase family of proteins. Using shRNA-mediated knockdown and overexpression of CD36, we confirmed that CD36 regulates MMP28 expression in CRC cells. siRNA-mediated knockdown of MMP28 decreases invasion of CRC cells, suggesting that MMP28 regulates the metastatic properties of cells downstream of CD36. Importantly, high expression of MMP28 leads to a significant decrease in active E-cadherin and an increase in the products of E-cadherin cleavage, CTF1 and CTF2. In summary, upregulation of CD36 expression promotes the metastatic properties of CRC via upregulation of MMP28 and an increase in E-cadherin cleavage, suggesting that targeting the CD36-MMP28 axis may be an effective therapeutic strategy for CRC metastasis.

Abstract 2880: CD36, a fatty acid translocase, promotes metastasis in CRC

Altered fatty acid metabolism, a hallmark of cancer, is an attractive target for therapeutic intervention. Fatty acid translocase (CD36), a multifunctional glycoprotein, has an important role in fatty acid metabolism: it serves as a fatty acid transporter. We have previously shown the importance of CD36 in promotion of colorectal cancer (CRC) cell proliferation and tumorigenesis and its role in compensation of de novo fatty acid synthesis inhibition. CD36 also plays important roles in migration, invasion and metastasis in gastric, ovarian and oral carcinomas. Cell lines with higher metastatic potential express higher levels of CD36; however, the role of CD36 in CRC metastasis has not been previously studied. The purpose of our study is (i) to determine the functional effect of CD36 on CRC metastasis, and (ii) to delineate the mechanistic pathways in which CD36 may regulate CRC metastasis.

Methods: In this study we utilized HCT116 and HT29 CRC cell lines. The HT29 LuM3-GFP-Luc cell line was established from HT29 cells and has an increased propensity to metastasize to mouse lungs. The increase in metastatic capacity of HT29 LuM3 is associated with an increase in the expression of CD36. We utilized parental HT29-GFP-Luc and HT29 LuM3-GFP-Luc to overexpress and knockdown CD36, respectively, and we used a CD36 neutralizing antibody to block the activity of CD36 in HCT116 and HT29 LuM3 cells. To measure colonization, migration and invasion in vitro, we used soft agar colony formation assays, a wound healing assay, and spheroid and trans-well invasion assays. In vivo, we utilized the tail-vein injection model to study tumor cell colonization in mouse lungs, and the cecum injection model to study liver metastasis from the primary tumor. We analyzed samples with qRT-PCR, western blot and immunohistochemistry.

Results: Knockdown of CD36 significantly reduced CRC cell invasion and colony formation in HCT116 and HT29 LuM3 in vitro. CRC cell invasion and colony formation increased with overexpression of CD36 in HCT116 cells. Overexpression of CD36 in established CRC cell lines increased markers of survival and invasion, such as phospho-Akt, P-Met, and MMP28. Most importantly, knockdown of CD36 in HT29 LuM3-GFP-Luc cells significantly reduced lung metastasis in vivo.

Conclusions: CRC cells that have a higher propensity to initiate metastasis in vivo express higher levels of CD36. We showed that this upregulation of CD36 represents a unique advantage for CRC cells to initiate tumor colonies, migrate and invade both in vitro and in vivo. Thus, our study highlights the potential of CD36 as a viable target for metastatic disease in CRC patients.

Citation Format: James Michael Drury, Piotr Rychahou, Heidi L. Weiss, Yekaterina Y. Zaytseva. CD36, a fatty acid translocase, promotes metastasis in CRC [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 2880.

Upregulation of CPT1A is essential for the tumor-promoting effect of adipocytes in colon cancer

Colon tumors grow in an adipose tissue-enriched microenvironment. Locally advanced colon cancers often invade into surrounding adipose tissue with a direct contact with adipocytes. We have previously shown that adipocytes promote tumor growth by modulating cellular metabolism. Here we demonstrate that carnitine palmitoyltransferase I (CPT1A), a key enzyme controlling fatty acid oxidation (FAO), was upregulated in colon cancer cells upon exposure to adipocytes or fatty acids. In addition, CPT1A expression was increased in invasive tumor cells within the adipose tissue compared to tumors without direct contact with adipocytes. Silencing CPT1A abolished the protective effect provided by fatty acids against nutrient deprivation and reduced tumor organoid formation in 3D culture and the expression of genes associated with cancer stem cells downstream of Wnt/β-catenin. Mechanistically, CPT1A-dependent FAO promoted the acetylation and nuclear translocation of β-catenin. Furthermore, knockdown of CPT1A blocked the tumor-promoting effect of adipocytes in vivo and inhibited xenograft tumor initiation. Taken together, our findings identify CPT1A-depedent FAO as an essential metabolic pathway that enables the interaction between adipocytes and colon cancer cells.

Inhibition of Fatty Acid Synthase Upregulates Expression of CD36 to Sustain Proliferation of Colorectal Cancer Cells

Fatty acid synthase, a key enzyme of de novo lipogenesis, is an attractive therapeutic target in cancer. The novel fatty acid synthase inhibitor, TVB-3664, shows anti-cancer activity in multiple cancers including colorectal cancer; however, it is unclear whether uptake of exogeneous fatty acids can compensate for the effect of fatty acid synthase inhibition. This study demonstrates that inhibition of fatty acid synthase selectively upregulates fatty acid translocase (CD36), a fatty acid transporter, in multiple colorectal cancer models including colorectal cancer cells with shRNA mediated knockdown of fatty acid synthase and genetically modified mouse tissues with heterozygous and homozygous deletion of fatty acid synthase. Furthermore, human colorectal cancer tissues treated with TVB-3664 show a significant and selective upregulation of CD36 mRNA. shRNA-mediated knockdown of CD36 and inhibition of CD36 via sulfosuccinimidyl oleate, a chemical inhibitor of CD36, decreased cell proliferation in vitro and reduced tumor growth in subcutaneous xenograft models. Isogenic cell populations established from patient derived xenografts and expressing high levels of CD36 show a significantly increased ability to grow tumors in vivo. The tumor-promoting effect of CD36 is associated with an increase in the levels of pAkt and survivin. Importantly, combinatorial treatment of primary and established colorectal cancer cells with TVB-3664 and sulfosuccinimidyl oleate shows a synergistic effect on cell proliferation. In summary, our study demonstrates that upregulation of CD36 expression is a potential compensatory mechanism for fatty acid synthase inhibition and that inhibition of CD36 can improve the efficacy of fatty acid synthase-targeted therapy.

Spermine synthase and MYC cooperate to maintain colorectal cancer cell survival by repressing Bim expression

Dysregulation of polyamine metabolism has been linked to the development of colorectal cancer (CRC), but the underlying mechanism is incompletely characterized. Here, we report that spermine synthase (SMS), a polyamine biosynthetic enzyme, is overexpressed in CRC. Targeted disruption of SMS in CRC cells results in spermidine accumulation, which inhibits FOXO3a acetylation and allows subsequent translocation to the nucleus to transcriptionally induce expression of the proapoptotic protein Bim. However, this induction is blunted by MYC-driven expression of miR-19a and miR-19b that repress Bim production. Pharmacological or genetic inhibition of MYC activity in SMS-depleted CRC cells dramatically induces Bim expression and apoptosis and causes tumor regression, but these effects are profoundly attenuated by silencing Bim. These findings uncover a key survival signal in CRC through convergent repression of Bim expression by distinct SMS- and MYC-mediated signaling pathways. Thus, combined inhibition of SMS and MYC signaling may be an effective therapy for CRC.

Polyamine metabolism is frequently dysregulated in cancers. Here, the authors show that a polyamine biosynthetic enzyme, spermine synthase, is overexpressed in colorectal cancers and cooperates with MYC to prevent cancer cell apoptosis by repression of proapoptotic protein, Bim.

Novel chemotherapeutic agent, FND-4b, activates AMPK and inhibits colorectal cancer cell proliferation

Colorectal cancer (CRC) is the second leading cause of cancer deaths in the US with the majority of deaths due to metastatic disease. Current chemotherapeutic regimens involve highly toxic agents, which limits their utility; therefore, more effective and less toxic agents are required to see a reduction in CRC mortality. Novel fluorinated N,N’-diarylureas (FND) were developed and characterized by our group as potent activators of adenosine monophosphate-activated kinase (AMPK) that inhibit cell cycle progression. The purpose of this study was to determine the effect of a lead FND compound, FND-4b, either alone or combined with PI-103 (a dual PI3K/mTOR inhibitor) or SN-38 (active metabolite of irinotecan) on cell cycle arrest and apoptosis of CRC cell lines (both commercially-available and novel lines established from our patient population). Treatment with FND-4b for 24h resulted in a marked induction of phosphorylated AMPK expression and a concomitant reduction in markers of cell proliferation, such as cyclin D1, in all CRC cell lines. Apoptosis was also notably increased in CRC cells treated with FND-4b. Regardless of the genetic profile of the CRC cells, FND-4b treatment alone resulted in decreased cell proliferation. Moreover, the combination of FND-4b with PI-103 resulted in increased cell death in all cell lines, while the combination of FND-4b with SN-38 resulted in increased cell death in select cell lines. Our findings identify FND-4b, which activates AMPK at micromolar concentrations, as a novel and effective inhibitor of CRC growth either alone or in combination with PI-103 and SN-38.

N-glycosylation-defective splice variants of neuropilin-1 promote metastasis by activating endosomal signals

Neuropilin-1 (NRP1) is an essential transmembrane receptor with a variety of cellular functions. Here, we identify two human NRP1 splice variants resulting from the skipping of exon 4 and 5, respectively, in colorectal cancer (CRC). Both NRP1 variants exhibit increased endocytosis/recycling activity and decreased levels of degradation, leading to accumulation on endosomes. This increased endocytic trafficking of the two NRP1 variants, upon HGF stimulation, is due to loss of N-glycosylation at the Asn150 or Asn261 site, respectively. Moreover, these NRP1 variants enhance interactions with the Met and β1-integrin receptors, resulting in Met/β1-integrin co-internalization and co-accumulation on endosomes. This provides persistent signals to activate the FAK/p130Cas pathway, thereby promoting CRC cell migration, invasion and metastasis. Blocking endocytosis or endosomal Met/β1-integrin/FAK signaling profoundly inhibits the oncogenic effects of both NRP1 variants. These findings reveal an important role for these NRP1 splice variants in the regulation of endocytic trafficking for cancer cell dissemination.

De Novo Fatty Acid Synthesis-Driven Sphingolipid Metabolism Promotes Metastatic Potential of Colorectal Cancer

Metastasis is the most common cause of death in colorectal cancer patients. Fatty acid synthase (FASN) and sphingosine kinase-1 and -2 (SPHK1 and 2) are overexpressed in many cancers, including colorectal cancer. However, the contribution of FASN-mediated upregulation of sphingolipid metabolism to colorectal cancer metastasis and the potential of these pathways as targets for therapeutic intervention remain unknown. This study determined that sphingosine kinases (SPHK) are overexpressed in colorectal cancer as compared with normal mucosa. FASN expression significantly correlated with SPHK2 expression in data sets from The Cancer Genome Atlas (TCGA) and a colorectal cancer tumor microarray. FASN, SPHK1, and SPHK2 colocalized within invadopodia of primary colorectal cancer cells. Moreover, FASN inhibition decreased SPHK2 expression and the levels of dihydrosphingosine 1-phosphate (DH-S1P) and sphingosine 1-phosphate (S1P) in colorectal cancer cells and tumor tissues. Inhibition of FASN using TVB-3664 and sphingolipid metabolism using FTY-720 significantly inhibited the ability of primary colorectal cancer cells to proliferate, migrate, form focal adhesions, and degrade gelatin. Inhibition of the FASN/SPHK/S1P axis was accompanied by decreased activation of p-MET, p-FAK, and p-PAX. S1P treatment rescued FASN-mediated inhibition of these proteins, suggesting that FASN promotes metastatic properties of colorectal cancer cells, in part, through an increased sphingolipid metabolism. These data demonstrate that upregulation of the FASN/SPHK/S1P axis promotes colorectal cancer progression by enhancing proliferation, adhesion, and migration. IMPLICATIONS: This study provides a strong rationale for further investigation of the interconnection of de novo lipogenesis and sphingolipid metabolism that could potentially lead to the identification of new therapeutic targets and strategies for colorectal cancer.

Erbin Suppresses KSR1-Mediated RAS/RAF Signaling and Tumorigenesis in Colorectal Cancer

Erbin belongs to the LAP (leucine-rich repeat and PDZ domain) family of scaffolding proteins that plays important roles in orchestrating cell signaling. Here, we show that Erbin functions as a tumor suppressor in colorectal cancer. Analysis of Erbin expression in colorectal cancer patient specimens revealed that Erbin was downregulated at both mRNA and protein levels in tumor tissues. Knockdown of Erbin disrupted epithelial cell polarity and increased cell proliferation in 3D culture. In addition, silencing Erbin resulted in increased amplitude and duration of signaling through Akt and RAS/RAF pathways. Erbin loss induced epithelial-mesenchymal transition, which coincided with a significant increase in cell migration and invasion. Erbin interacted with kinase suppressor of Ras 1 (KSR1) and displaced it from the RAF/MEK/ERK complex to prevent signal propagation. Furthermore, genetic deletion of Erbin in Apc knockout mice promoted tumorigenesis and significantly reduced survival. Tumor organoids derived from Erbin/Apc double knockout mice displayed increased tumor initiation potential and activation of Wnt signaling. Results from gene set enrichment analysis revealed that Erbin expression associated positively with the E-cadherin adherens junction pathway and negatively with Wnt signaling in human colorectal cancer. Taken together, our study identifies Erbin as a negative regulator of tumor initiation and progression by suppressing Akt and RAS/RAF signaling in vivoSignificance: These findings establish the scaffold protein Erbin as a negative regulator of EMT and tumorigenesis in colorectal cancer through direct suppression of Akt and RAS/RAF signaling. Cancer Res; 78(17); 4839-52. ©2018 AACR.

Abstract 1443: Overexpression of CD36 promotes tumorigenesis in colorectal cancer

Fatty acid translocase (CD36), a multifunctional glycoprotein, has an important role in fatty acid metabolism as a fatty acid receptor and transporter. The presence of CD36 positive metastasis-initiating cells correlates with a poorer prognosis in glioblastoma and oral carcinoma. Fatty acid synthase (FASN), a critical enzyme involved in de novo lipogenesis, is upregulated and associated with poorer prognosis in many cancers including colorectal cancer (CRC). The role of CD36 in primary and metastatic CRC as well as its relation to de novo fatty acid synthesis is not understood. The purpose of our study was: (i) to determine the role of CD36 in primary and metastatic CRC, and (ii) to delineate the association of CD36 expression with FASN as a possible mechanism of resistance to FASN inhibition.

METHODS. Expression of CD36 and FASN was assessed in a CRC tumor microarray (matched normal colon and primary tumor; 56 cases) as well as matched normal colon, primary and metastatic tumors (liver [n=12] and lung metastasis [n=5]) by immunohistochemistry. CD36 expression was analyzed in control and FASN shRNA knockout CRC cells and tissues from APC/FASN/CRE mouse models by western blot. Cell proliferation was assessed in primary CRC cells established from patient derived xenografts (PDX) treated in combination with Sulfo-N-succinimidyl oleate (SSO), an irreversible inhibitor of CD36, and FASN inhibitor TVB-3664. CD36 expression levels in primary and metastatic PDX derived CRC cells were analyzed via western blot and immunofluorescence imaging.

RESULTS. CD36 is overexpressed in primary tumors as compared to normal colon mucosa and its expression positively correlates with expression of FASN. Cell proliferation was significantly reduced when CD36 was inhibited by SSO and a further reduction in cell proliferation was observed when SSO treatment was combined with TVB-3664. Treatment with SSO induced apoptotic markers such as cleaved capspase-3 and decreased survivin. Western blot analysis of primary and metastatic CRC cells showed an upregulation of CD36 expression in the metastatic CRC cells. Additionally, FASN shRNA knockdown of FASN in CRC cells and Cre recombinase-mediated intestinal deletion of FASN in an APC/FASN/CRE mouse model led to an induction of CD36 expression. Immunofluorescence imaging of primary CRC treated with TVB-3664 showed an upregulation of membrane bound CD36.

CONCLUSION. CD36 upregulation is associated with CRC progression and inhibition of CD36 decreases proliferation and survival of primary CRC cells. Correlation between expression of CD36 and FASN suggests an interconnection between CD36 and de novo lipid synthesis. Furthermore, a decrease in FASN expression is associated with an induction of CD36, suggesting a possible mechanism of resistance to FASN inhibition. Better understanding the role of CD36 may provide new therapeutic approaches for treatment of CRC patients.

Citation Format: James M. Drury, Naser Jafari, B Mark Evers, Yekaterina Y. Zaytseva. Overexpression of CD36 promotes tumorigenesis in colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1443.

Deptor Is a Novel Target of Wnt/β-Catenin/c-Myc and Contributes to Colorectal Cancer Cell Growth

Activation of the Wnt/β-catenin signaling pathway drives colorectal cancer growth by deregulating expression of downstream target genes, including the c-myc proto-oncogene. The critical targets that mediate the functions of oncogenic c-Myc in colorectal cancer have yet to be fully elucidated. Previously, we showed that activation of PI3K/Akt/mTOR contributes to colorectal cancer growth and metastasis. Here, we show that Deptor, a suppressor of mTOR, is a direct target of Wnt/β-catenin/c-Myc signaling in colorectal cancer cells. Inhibition of Wnt/β-catenin or knockdown of c-Myc decreased, while activation of Wnt/β-catenin or overexpression of c-Myc increased the expression of Deptor. c-Myc bound the promoter of Deptor and transcriptionally regulated Deptor expression. Inhibition of Wnt/β-catenin/c-Myc signaling increased mTOR activation, and the combination of Wnt and Akt/mTOR inhibitors enhanced inhibition of colorectal cancer cell growth in vitro and in vivo Deptor expression was increased in colorectal cancer cells; knockdown of Deptor induced differentiation, decreased expression of B lymphoma Mo-MLV insertion region 1 (Bmi1), and decreased proliferation in colorectal cancer cell lines and primary human colorectal cancer cells. Importantly, our work identifies Deptor as a downstream target of the Wnt/β-catenin/c-Myc signaling pathway, acting as a tumor promoter in colorectal cancer cells. Moreover, we provide a molecular basis for the synergistic combination of Wnt and mTOR inhibitors in treating colorectal cancer with elevated c-Myc.Significance: The mTOR inhibitor DEPTOR acts as a tumor promoter and could be a potential therapeutic target in colorectal cancer. Cancer Res; 78(12); 3163-75. ©2018 AACR.

Downregulation of SREBP inhibits tumor growth and initiation by altering cellular metabolism in colon cancer

Sterol regulatory element-binding proteins (SREBPs) belong to a family of transcription factors that regulate the expression of genes required for the synthesis of fatty acids and cholesterol. Three SREBP isoforms, SREBP1a, SREBP1c, and SREBP2, have been identified in mammalian cells. SREBP1a and SREBP1c are derived from a single gene through the use of alternative transcription start sites. Here we investigated the role of SREBP-mediated lipogenesis in regulating tumor growth and initiation in colon cancer. Knockdown of either SREBP1 or SREBP2 decreased levels of fatty acids as a result of decreased expression of SREBP target genes required for lipid biosynthesis in colon cancer cells. Bioenergetic analysis revealed that silencing SREBP1 or SREBP2 expression reduced the mitochondrial respiration, glycolysis, as well as fatty acid oxidation indicating an alteration in cellular metabolism. Consequently, the rate of cell proliferation and the ability of cancer cells to form tumor spheroids in suspension culture were significantly decreased. Similar results were obtained in colon cancer cells in which the proteolytic activation of SREBP was blocked. Importantly, knockdown of either SREBP1 or SREBP2 inhibited xenograft tumor growth in vivo and decreased the expression of genes associated with cancer stem cells. Taken together, our findings establish the molecular basis of SREBP-dependent metabolic regulation and provide a rationale for targeting lipid biosynthesis as a promising approach in colon cancer treatment.

Colorectal cancer lung metastasis treatment with polymer-drug nanoparticles

Colorectal cancer (CRC) is the second leading cause of cancer deaths in the United States; the predominant cause for mortality is metastasis to distant organs (e.g., lung). A major problem limiting the success of chemotherapy in metastatic CRC is the inability to target tumor tissues selectively and avoid severe side effects to normal tissues and organs. Here, we demonstrate polymeric nanoparticles (PNPs) entrapping chemotherapeutic agents provide a new therapeutic option for treating CRC that has metastasized to the lung. PNPs assembled from FDA approved biocompatible block copolymer accumulated predominantly in lung tissue. PNPs showed negligible accumulation in liver, spleen and kidneys, which was confirmed by fluorescent nanoparticle imaging and analysis of PI3K inhibition in the organs. PNPs entrapping PI3K inhibitors (i.e., wortmannin and PX866) suppressed CRC lung metastasis growth, and SN-38-loaded PNPs completely eliminated CRC lung metastasis. Our results demonstrate that polymer-drug nanoparticles offer a new approach to reduce toxicity of cancer therapy and has the potential to improve outcomes for patients with lung metastasis.

Abstract 452: Activation of Akt pathway and autophagy promotes resistance to FASN inhibition in colorectal cancer patient-derived xenograft models

Fatty Acid Synthase (FASN), a key enzyme of de novo lipogenesis, is upregulated in many cancers including colorectal cancer (CRC); increased FASN expression is associated with poor prognosis. Potent FASN inhibitors developed by 3-V Biosciences demonstrate anti-tumor activity in vitro and in vivo and a favorable tolerability profile in a Phase I clinical trial in solid tumor patients. However, CRC characteristics associated with responsiveness to FASN inhibition are not fully understood. The purpose of our study was: (i) to determine the effect of FASN inhibition on tumor growth in CRC patient-derived xenografts (PDXs); (ii) to identify potential biomarkers associated with CRC responsiveness to FASN inhibition; and (iii) to explore new combination strategies with FASN inhibitors. METHODS. Tumor growth was assessed in 9 PDXs established in NSG mice using freshly resected specimens. Once the xenografts grew to ~100 mm3, mice were randomized into two groups (n=5) to receive either vehicle or TVB-3664 or four groups (n=10) for TVB-3664 treatment in combination with either MK2206 or Chloroquine (CQ). Tumor volume and animal weights were measured weekly. Western blot analysis and immunohistochemistry staining were used to identify FASN-mediated changes in signaling pathways. Changes in metabolites and lipids were analyzed by nuclear magnetic resonance and mass spectrometry in plasma and tumor tissues. Next Generation Sequencing was used to assess the mutation profile of 198 oncogenes in patient tumors and PDXs. RESULTS. PDXs showed a wide range of sensitivity to FASN inhibition: TVB-3664 treatment attained significant response (reduced tumor volume) in 3 PDXs, significant response followed by developed resistance in one PDX, and no response in 5 PDXs. Activation of Akt and AMPK pathways was associated with resistance to FASN inhibition and combination of TVB-3664 with either MK2206 or CQ led to a significant reduction in tumor volume as compared to either drug alone. Moreover, TVB-3664 treatment significantly decreased the total palmitate level in plasma and the levels of triglycerides, diglycerides, phosphatidylserines, phosphatidylethanolamines, and phosphatidylcholines in tumor tissues. Furthermore, a significant decrease in the levels of AXP-1, AXP-2 and myo-Inositol-2 was observed in tumors responsive to FASN inhibition. CONCLUSIONS. Our studies demonstrate that TVB-3664 shows anti-tumor activity in CRC. Importantly, our results suggest that activation of Akt and autophagy are major mechanisms of resistance to FASN inhibition and demonstrate that combine inhibition of these pathways and FASN may be a new therapeutic approach in CRC. Ongoing studies of correlation between mutation and metabolic profiles of tumors and tumor response to FASN inhibition aim to identify a subset of CRC patients that are likely to respond to FASN-targeted therapy.

Citation Format: Yekaterina Y. Zaytseva, Piotr G. Rychahou, Anh-Thu Le, Robert M. Flight, Timothy L. Scott, Jennifer W. Harris, Sally Hodges, Brent J. Hallahan, Dana L. Napier, Jinpeng Liu, Chi Wang, Manjula Sunkara, Andrew Morris, Ji Tae Kim, Sivakumaran Theru Arumugam, Andrew Lane, Teresa W. Fan, Hunter Moseley, Tianyan Gao, Eun Y. Lee, Heidi L. Weiss, Timothy S. Heuer, George Kemble, B Mark Evers. Activation of Akt pathway and autophagy promotes resistance to FASN inhibition in colorectal cancer patient-derived xenograft models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 452. doi:10.1158/1538-7445.AM2017-452

Abstract 1010: Evaluation of small-molecule FASN inhibitors in preclinical models of colorectal cancer

Fatty Acid Synthase (FASN), a key enzyme of de novo lipid synthesis, is upregulated in many cancers including colorectal cancer (CRC); increased FASN activity is associated with decreased survival and increased disease recurrence. Recently, a first-in-class, oral FASN inhibitor (TVB-2640) entered a Phase I clinical trial (3V2640-CLIN-002) in solid tumor patients demonstrating a favorable tolerability profile with no significant adverse events; however, tumor characteristics that would indicate responsiveness to FASN inhibition are not fully understood. The purpose of our study was: (i) to determine the effect of novel, selective and reversible FASN inhibitors on proliferation of primary CRC cell cultures, established CRC cell lines, and CRC patient-derived xenografts (PDXs); and (ii) to identify potential biomarkers associated with CRC responsiveness to FASN inhibition. METHODS. The effect of TVB-3166, TVB-3664, and TVB-3693 (all developed by 3-V Biosciences) on the proliferation of primary cells (established from 1st generation PDX tumors) and CRC cell lines was assessed by cell count; apoptosis was assessed by Cell Death ELISA. In addition, tumor growth was assessed in PDX models established in NOD SCID gamma mice using freshly resected CRC specimens (either primary CRC or metastasis) from our patient population. Once the xenografts grew to ∼100 mm3, mice were randomized into two groups (n = 5) to receive either vehicle or TVB-3664 (3mg/kg) by gavage daily. Tumor volume and animal weights were measured weekly. Western blot analysis, immunohistochemistry and immunofluorescent staining were used to identify FASN-mediated changes in β-catenin, Akt and AMPK pathways. RESULTS. TVB compounds tested showed similar efficacy in primary and established CRC cells with a wide range of sensitivity to FASN inhibition. The 5 cell lines that were most responsive to FASN inhibition demonstrated a low basal level of pAMPK and pAkt as compared to the 5 least responsive cells. Moreover, we noted that increased FASN protein expression was also associated with increased sensitivity to FASN inhibition. Inhibition of proliferation by TVB compounds was associated with decreased expression of active β-catenin, c-MYC, pAkt, and survivin, while an increase in apoptosis was noted by induction of PARP cleavage. Consistent with our in vitro studies, TVB-3664 treatment significantly reduced tumor volume in vivo with no weight changes or toxicity observed. CONCLUSIONS. Our studies show that the novel FASN inhibitors, as a single agent, significantly inhibit CRC growth both in vitro and in vivo. Importantly, our results suggest that basal activation of AMPK and Akt may be predictive of responsiveness to FASN inhibition and may function as potential biomarkers to allow a more personalized treatment approach.

Citation Format: Yekaterina Y. Zaytseva, Piotr G. Rychahou, Tianyan Gao, Eun Y. Lee, Heidi L. Weiss, Timothy S. Heuer, George Kemble, B. Mark Evers. Evaluation of small-molecule FASN inhibitors in preclinical models of colorectal cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1010.

Increased expression of fatty acid synthase provides a survival advantage to colorectal cancer cells via upregulation of cellular respiration

Fatty acid synthase (FASN), a lipogenic enzyme, is upregulated in colorectal cancer (CRC). Increased de novo lipid synthesis is thought to be a metabolic adaptation of cancer cells that promotes survival and metastasis; however, the mechanisms for this phenomenon are not fully understood. We show that FASN plays a role in regulation of energy homeostasis by enhancing cellular respiration in CRC. We demonstrate that endogenously synthesized lipids fuel fatty acid oxidation, particularly during metabolic stress, and maintain energy homeostasis. Increased FASN expression is associated with a decrease in activation of energy-sensing pathways and accumulation of lipid droplets in CRC cells and orthotopic CRCs. Immunohistochemical evaluation demonstrated increased expression of FASN and p62, a marker of autophagy inhibition, in primary CRCs and liver metastases compared to matched normal colonic mucosa. Our findings indicate that overexpression of FASN plays a crucial role in maintaining energy homeostasis in CRC via increased oxidation of endogenously synthesized lipids. Importantly, activation of fatty acid oxidation and consequent downregulation of stress-response signaling pathways may be key adaptation mechanisms that mediate the effects of FASN on cancer cell survival and metastasis, providing a strong rationale for targeting this pathway in advanced CRC.

An obligatory role for neurotensin in high-fat-diet-induced obesity

Obesity and its associated comorbidities (e.g., diabetes mellitus and hepatic steatosis) contribute to approximately 2.5 million deaths annually¹ and are among the most prevalent and challenging conditions confronting the medical profession^2,3. Neurotensin (NT), a 13-amino acid peptide predominantly localized in specialized enteroendocrine (EE) cells of the small bowel⁴ and released by fat ingestion⁵, facilitates fatty acid (FA) translocation in rat intestine⁶, and stimulates growth of various cancers⁷; the effects of NT are mediated through three known NT receptors (NTR1, 2 and 3)⁸. Increased fasting plasma levels of pro-NT (a stable NT precursor fragment produced in equimolar amounts relative to NT) are associated with increased risk of diabetes, cardiovascular disease and mortality⁹; however, a role for NT as a causative factor in these diseases is unknown. Here, we show that NT-deficient mice demonstrate significantly reduced intestinal fat absorption and are protected from obesity, hepatic steatosis and insulin resistance associated with high fat consumption. We further demonstrate that NT attenuates the activation of AMP-activated protein kinase (AMPK) and stimulates FA absorption in mice and in cultured intestinal cells, and that this occurs through a mechanism involving NTR1 and NTR3/sortilin. Consistent with the findings in mice, expression of NT in Drosophila midgut EE cells results in increased lipid accumulation in the midgut, fat body, and oenocytes (specialized hepatocyte-like cells) and decreased AMPK activation. Remarkably, in humans, we show that both obese and insulin-resistant subjects have elevated plasma concentrations of pro-NT, and in longitudinal studies among non-obese subjects, high levels of pro-NT denote a doubling of the risk of developing obesity later in life. Our findings directly link NT with increased fat absorption and obesity and suggest that NT may provide a prognostic marker of future obesity and a potential target for prevention and treatment.

Abstract 1151: Overexpression of Fatty Acid Synthase is associated with inhibition of autophagy under conditions of metabolic stress in colorectal cancer cells

Fatty Acid Synthase (FASN), a key enzyme of de novo lipid synthesis, is significantly up regulated in colorectal cancer (CRC) and its activity is associated with poor prognosis. Recent studies suggest that FASN plays a crucial role in the survival of cancer cells by reprogramming metabolic pathways to maintain energy homeostasis under conditions of metabolic stress. However, the mechanisms of metabolic adaptation of cancer cells regulated by FASN to promote their survival are not yet fully understood. Cancer cells use autophagy as one of the survival strategies under metabolic stress. The purpose of our study was to determine the role of aberrant activation of FASN in regulation of autophagy in vitro and in human CRC.

METHODS. Expression of p62 and LC3 (autophagy markers), pAMPK, and Cyclin D was assessed in CRC cell lines with altered expression of FASN cultured in normal, serum free medium and/or detached conditions by Western blot and confocal microscopy. Human specimens, including matching cancer, normal colon and liver metastasis tissues from 19 patients were analyzed for expression of FASN, p62, and pAMPK by immunohistochemistry (IHC).

RESULTS. We demonstrated that under metabolic stress conditions overexpression of FASN is associated with a decrease in autophagy as shown by accumulation of p62, a marker of inhibition of autophagy, and a decrease in LC3A, an autophagosome marker, in CRC cell lines. Under energy stress conditions, overexpression of FASN is also associated with an increase in Cyclin D and a decrease in activation of pAMPK. Statistical analysis of IHC staining showed that expression of FASN, p62, and pAMPK is significantly higher in cancer and metastatic tissues as compared to normal colon tissues. Using Spearman's rank correlation, we determined moderate correlation between expression of FASN and p62 in human primary CRC and liver metastasis. Similar results were obtained using Western blot analysis on human normal colon and matching cancer tissues.

CONCLUSIONS. Our data suggest that overexpression of FASN is protective during metabolic stress conditions by shifting metabolism towards higher energy production as indicated by activity of pAMPK. Furthermore, we have identified a novel link between FASN and p62, and showed that, under metabolic stress conditions, overexpression of FASN is associated with inhibition of autophagy. However, further studies are require to understand how FASN-mediated up regulation of p62 contributes to tumorigenesis.

The differential expression of FASN in normal versus cancer cells makes de novo lipogenesis a desirable target for therapeutic intervention. Understanding the role of FASN in regulation of survival and aggressive behavior of cancer cells will uncover new therapeutic approaches in CRC.

Citation Format: Yekaterina Y. Zaytseva, Jennifer W. Harris, Ji Tae Kim, Tianyan Gao, Eun Y. Lee, Heidi L. Weiss, B Mark Evers. Overexpression of Fatty Acid Synthase is associated with inhibition of autophagy under conditions of metabolic stress in colorectal cancer cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1151. doi:10.1158/1538-7445.AM2015-1151

Neurotensin, a novel target of Wnt/β-catenin pathway, promotes growth of neuroendocrine tumor cells

Wnt/β-catenin signaling plays a pivotal role in regulating cell growth and differentiation by activation of the β-catenin/T-cell factor (TCF) complex and subsequent regulation of a set of target genes that have one or more TCF-binding elements (TBEs). Hyperactivation of this pathway has been implicated in numerous malignancies including human neuroendocrine tumors (NETs). Neurotensin (NT), an intestinal hormone, induces proliferation of several gastrointestinal (GI) cancers including cancers of the pancreas and colon. Here, we analyzed the human NT promoter in silico and found at least four consensus TBEs within the proximal promoter region. Using a combination of ChIP and luciferase reporter assays, we identified one TBE (located ∼900 bp proximal from the transcription start site) that was immunoprecipitated efficiently by TCF4-targeting antibody; mutation of this site attenuated the responsiveness to β-catenin. We also confirmed that the promoter activity and the mRNA and protein expression levels of NT were increased by various Wnt pathway activators and decreased by Wnt inhibitors in NET cell lines BON and QGP-1, which express and secrete NT. Similarly, the intracellular content and secretion of NT were induced by Wnt3a in these cells. Finally, inhibition of NT signaling suppressed cell proliferation and anchorage-independent growth and decreased expression levels of growth-related proteins in NET cells. Our results indicate that NT is a direct target of the Wnt/β-catenin pathway and may be a mediator for NET cell growth.

Activation of c-Met and upregulation of CD44 expression are associated with the metastatic phenotype in the colorectal cancer liver metastasis model

BACKGROUND

Liver metastasis is the most common cause of death in patients with colorectal cancer. Despite extensive research into the biology of cancer progression, the molecular mechanisms that drive colorectal cancer metastasis are not well characterized.

METHODS

HT29 LM1, HT29 LM2, HT29 LM3 cell lines were derived from the human colorectal cancer cell line HT29 following multiple rounds of in vivo selection in immunodeficient mice.

RESULTS

CD44 expression, a transmembrane glycoprotein involved in cell-cell and cell-matrix adhesions, and cancer cells adhesion to endothelial cells was increased in all in vivo selected cell lines, with maximum CD44 expression and cancer cells adhesion to endothelial cells in the highly metastatic HT29 LM3 cell line. Activation of c-Met upon hepatocyte growth factor (HGF) stimulation in the in vivo selected cell lines is CD44 independent. In vitro separation of CD44 high and low expression cells from HT29 LM3 cell line with FACS sorting confirmed that c-Met activation is CD44 independent upon hepatocyte growth factor stimulation. Furthermore, in vivo evaluation of CD44 low and high expressing HT29 LM3 cells demonstrated no difference in liver metastasis penetrance.

CONCLUSIONS

Taken together, our findings indicate that the aggressive metastatic phenotype of in vivo selected cell lines is associated with overexpression of CD44 and activation of c-MET. We demonstrate that c-Met activation is CD44 independent upon hepatocyte growth factor stimulation and confirm that CD44 expression in HT29 LM3 cell line is not responsible for the increase in metastatic penetrance in HT29 LM3 cell line.

Cancer cell-associated fatty acid synthase activates endothelial cells and promotes angiogenesis in colorectal cancer

Upregulation of fatty acid synthase (FASN), a key enzyme of de novo lipogenesis, is associated with metastasis in colorectal cancer (CRC). However, the mechanisms of regulation are unknown. Since angiogenesis is crucial for metastasis, we investigated the role of FASN in the neovascularization of CRC. The effect of FASN on tumor vasculature was studied in orthotopic CRCs, the chick embryo chorioallantoic membrane (CAM) and Matrigel plug models using immunohistochemistry, immunofluorescent staining and confocal microscopy. Cell secretion was evaluated by ELISA and antibody arrays. Proliferation, migration and tubulogenesis of endothelial cells (ECs) were assessed in CRC-EC coculture models. In this study, we found that stable knockdown of FASN decreased microvessel density in HT29 and HCT116 orthotopic CRCs and resulted in 'normalization' of tumor vasculature in both orthotopic and CAM models. Furthermore, FASN regulated secretion of pro- and antiangiogenic factors, including vascular endothelial growth factor-A (VEGF-A). Mechanisms associated with the antiangiogenic activity noted with knockdown of FASN included: downregulation of VEGF(189), upregulation of antiangiogenic isoform VEGF(165b) and a decrease in expression and activity of matrix metalloproteinase-9. Furthermore, conditioned medium from FASN knockdown CRC cells inhibited activation of vascular endothelial growth factor receptor-2 and its downstream signaling and decreased proliferation, migration and tubulogenesis of ECs as compared with control medium. Together, these results suggest that cancer cell-associated FASN regulates tumor vasculature through alteration of the profile of secreted angiogenic factors and regulation of their bioavailability. Inhibition of FASN upstream of VEGF-A and other angiogenic pathways can be a novel therapeutic strategy to prevent or inhibit metastasis in CRC.

Cotargeting the PI3K and RAS pathways for the treatment of neuroendocrine tumors

BACKGROUND

The precise involvement of the PI3K/mTOR and RAS/MEK pathways in carcinoid tumors is not well defined. Therefore, the purpose of our study was to evaluate the role these pathways play in carcinoid cell proliferation, apoptosis, and secretion and to determine the effects of combined treatment on carcinoid tumor inhibition.

METHODS

The human neuroendocrine cell lines BON (pancreatic carcinoid), NCI-H727 (lung carcinoid), and QGP-1 (somatostatinoma) were treated with either the pan-PI3K inhibitor, BKM120, or the dual PI3K-mTOR inhibitor, BEZ235, alone or in combination with the MEK inhibitor, PD0325901; proliferation, apoptosis, and protein expression were assessed. Peptide secretion was evaluated in BON and QGP-1 cells. The antiproliferative effect of BEZ235, alone or combined with PD0325901, was then tested in vivo.

RESULTS

Both BKM120 and BEZ235 decreased proliferation and increased apoptosis; combination with PD0325901 significantly enhanced the antineoplastic effects of either treatment alone. In contrast, neurotensin peptide secretion was markedly stimulated with BKM120 treatment, but not BEZ235. The combination of BEZ235 + PD0325901 significantly inhibited the growth of BON xenografts without systemic toxicity.

CONCLUSIONS

Both BKM120 and BEZ235 effectively inhibited neuroendocrine tumor (NET) cell proliferation and stimulated apoptosis. However, inhibition of the PI3K pathway alone with BKM120 significantly stimulated neurotensin peptide secretion; this did not occur with the dual inhibition of both PI3K and mTOR using BEZ235 suggesting that this would be a more effective treatment regimen for NETs. Moreover, the combination of BEZ235 and the MEK inhibitor PD0325901 was a safe and more effective therapy in vivo compared with single agents alone.

Novel small interfering RNA cotargeting strategy as treatment for colorectal cancer

BACKGROUND

RNA interference has the potential to be more selective than small molecule inhibitors and can be used to target proteins, such as Ras, that are currently undruggable. The purpose of our study was to determine the optimal cotargeting strategy of the commonly mutated PI3K/AKT/mTOR and Ras pathways by a selective RNA interference approach in colorectal cancer cell lines possessing coexistent PIK3CA and KRAS mutations.

METHODS

Human colorectal cancer cell lines HCT116 and DLD-1 were treated with a panel of small interfering RNAs directed against the PI3K/AKT/mTOR and Ras pathways; proliferation, apoptosis, and protein expression were assessed. Combined treatment with small interfering RNA and 5-fluorouracil was then evaluated.

RESULTS

PIK3CA and KRAS small interfering RNAs were most effective as single treatments; combined treatments with PIK3CA and KRAS small interfering RNA resulted in a more pronounced inhibition of colorectal cancer cell proliferation. Either KRAS small interfering RNA alone or combined PIK3CA and KRAS small interfering RNA treatments increased apoptosis in HCT116 cells but not in the DLD-1 cell line. Inhibition of 4E-BP1 phosphorylation correlated with increased apoptosis. In addition, small interfering RNA treatment combined with 5-fluorouracil further inhibited colorectal cancer cell proliferation.

CONCLUSION

Combined PIK3CA and KRAS small interfering RNA treatments offer an effective therapy against colorectal cancer cells with coexisting mutations in both pathways. Decreased 4E-BP1 phosphorylation correlates with increased apoptosis and may provide a biomarker indicative of treatment success. In addition, small interfering RNA directed to PIK3CA and KRAS may be used to enhance the effects of current chemotherapy.

Sorafenib enhances the therapeutic efficacy of rapamycin in colorectal cancers harboring oncogenic KRAS and PIK3CA

Activation of phosphatidylinositol 3-kinase (PI3K)/Akt signaling is associated with tumorigenesis and metastasis of colorectal cancer (CRC). The mammalian target of rapamycin (mTOR) kinase, a downstream effector of PI3K/Akt signaling, regulates tumorigenesis and metastasis of CRCs, indicating that mTOR inhibition may have therapeutic potential. Notwithstanding, many cancers, including CRC, demonstrate resistance to the antitumorigenic effects of rapamycin. In this study, we show that inhibition of mTORC1 with rapamycin leads to feedback activation of PI3K/Akt and Ras-MAPK signaling, resulting in cell survival and possible contribution to rapamycin resistance. Combination with the multikinase inhibitor, sorafenib, abrogates rapamycin-induced activation of PI3K/Akt and Ras-MAPK signaling pathways. Combination of rapamycin with sorafenib synergistically inhibits proliferation of CRC cells. CRCs harboring coexistent KRAS and PIK3CA mutations are partially sensitive to either rapamycin or sorafenib monotherapy, but highly sensitive to combination treatment with rapamycin and sorafenib. Combination with sorafenib enhances therapeutic efficacy of rapamycin on induction of apoptosis and inhibition of cell-cycle progression, migration and invasion of CRCs. We demonstrate efficacy and safety of concomitant treatment with rapamycin and sorafenib at inhibiting growth of xenografts from CRC cells with coexistent mutations in KRAS and PIK3CA. The efficacy and tolerability of combined treatment with rapamycin and sorafenib provides rationale for use in treating CRC patients, particularly those with tumors harboring coexistent KRAS and PIK3CA mutations.

Inhibition of fatty acid synthase attenuates CD44-associated signaling and reduces metastasis in colorectal cancer

Fatty acid synthase (FASN) and ATP-citrate lyase, key enzymes of de novo lipogenesis, are significantly upregulated and activated in many cancers and portend poor prognosis. Even though the role of lipogenesis in providing proliferative and survival advantages to cancer cells has been described, the impact of aberrant activation of lipogenic enzymes on cancer progression remains unknown. In this study, we found that elevated expression of FASN is associated with advanced stages of colorectal cancer (CRC) and liver metastasis, suggesting that it may play a role in progression of CRC to metastatic disease. Targeted inhibition of lipogenic enzymes abolished expression of CD44, a transmembrane protein associated with metastases in several cancers including CRC. In addition, inhibition of lipogenic enzymes and reduced expression of CD44 attenuated the activation of MET, Akt, FAK, and paxillin, which are known to regulate adhesion, migration, and invasion. These changes were consistent with an observed decrease in migration and adhesion of CRC cells in functional assays and with reorganization of actin cytoskeleton upon FASN inhibition. Despite the modest effect of FASN inhibition on tumor growth in xenografts, attenuation of lipogenesis completely abolished establishment of hepatic metastasis and formation of secondary metastasis. Together, our findings suggest that targeting de novo lipogenesis may be a potential treatment strategy for advanced CRC.

Abstract 4251: Inhibition of membrane bound and soluble VEGF receptor-2 activity enhances the proliferation of the BON carcinoid cell line

There is a growing interest in using angiogenesis inhibitors to treat neuroendocrine tumors. Previously, we detected the expression of vascular endothelial growth factor receptor-2 (VEGFR-2) and its soluble isoform (sVEGFR-2) in the epithelial component of carcinoid tumors and in the BON carcinoid cell line. Recent studies have demonstrated that VEGF inhibitors transiently inhibit tumor growth, followed by increased tumor invasion and metastasis. Also, we have reported that shRNA reduction of VEGFR-2 increases BON cell proliferation and invasion. Thus, the purpose of our current study was to: i) assess the effect that the VEGF signaling inhibitors bevacizumab, an antibody against VEGF-A, or sunitinib, a small molecule inhibitor of VEGFR-2, have on BON cell proliferation and, ii) evaluate the effect of knockdown and overexpression of sVEGFR-2 on BON cell proliferation. Methods. i) BON cells were cultured in media supplemented with bevacizumab (50 ng/ml), sunitinib (50 ng/ml), or vehicle control for two weeks. Media was replaced every other day, and cell lysates for western blot and RNA analysis were collected after one and two weeks. After two weeks, cell proliferation was measured using a cell counting kit-8 assay. ii) Knockdown or upregulation of sVEGFR-2 was achieved by transfecting BON cells with shRNA to sVEGFR-2 or a cDNA plasmid expressing the sVegfr2 gene, respectively. Proliferation following sVEGFR-2 knockdown or upregulation was determined and compared to cells transfected with the appropriate controls. Results. i) BON cell proliferation was significantly increased in cells treated with bevacizumab or sunitinib compared to vehicle control. Western blot analysis demonstrated an increase in phospho-ERK and phospho-Akt following treatment with bevacizumab. Interestingly, there were no observed changes in activation of ERK or Akt following treatment with sunitinib. However, sunitinib treatment increased protein and mRNA expression of VEGFR-2, as assessed by western blot and qRT-PCR, respectively. ii) BON cells with reduced expression of sVEGFR-2 demonstrated increased proliferation at 24 h, 48 h, 72 h, 96 h, and 120 h following plating. Conversely, BON cells transfected with plasmid cDNA encoding sVEGFR-2 displayed reduced proliferation at the aforementioned time points compared to cells transfected with empty plasmid. Conclusions. We have demonstrated that the VEGF inhibitors bevacizumab and sunitinib can enhance the proliferation of BON cells in vitro and that sVEGFR-2 inhibits BON cell proliferation, possibly by sequestering VEGF ligands. While VEGF inhibitors have been shown to effectively inhibit angiogenesis, they may also enhance the aggressiveness of surviving tumor cells, suggesting that a multimodal treatment plan is warranted in carcinoid patients.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4251. doi:10.1158/1538-7445.AM2011-4251

The effect of PTEN on serotonin synthesis and secretion from the carcinoid cell line BON

BACKGROUND

Carcinoid tumors are associated with the carcinoid syndrome, a set of symptoms resulting from the peptide and amine products, including serotonin, secreted from the cancer cells. The purpose of this study was to investigate the relationship between the phosphatidylinositol-3-kinase/protein kinase B (PI3K/Akt) inhibitor PTEN (phosphatase and tensin homolog deleted on chromosome ten) and serotonin synthesis and secretion in the carcinoid cancer cell line BON.

MATERIALS AND METHODS

PTEN was inhibited by pharmacological and molecular approaches, and the resultant secretion of serotonin and expression of tryptophan hydroxylase 1 (TPH1), the rate-limiting enzyme in serotonin synthesis, was assessed.

RESULTS

Inhibition of PTEN in vitro, with concomitant increased Akt signaling, resulted in decreased secretion of serotonin, as well as decreased serotonin synthesis, as confirmed by reduced expression of TPH1. Inhibition of PTEN in BON cells in an animal model resulted in decreased serum serotonin.

CONCLUSION

By inhibiting signaling through Akt, PTEN indirectly promotes serotonin synthesis and secretion.

The PPARgamma antagonist T0070907 suppresses breast cancer cell proliferation and motility via both PPARgamma-dependent and -independent mechanisms

BACKGROUND

Peroxisome proliferator-activated receptor gamma (PPARγ) is overexpressed in many types of cancer, including breast cancer, and it is regulated by ligand binding and post-translational modifications. It was previously demonstrated that endogenous transactivation promotes an aggressive phenotype of malignant breast cells. This study examines whether selective antagonism of PPARγ with T0070907 is a potential strategy for breast cancer therapy.

MATERIALS AND METHODS

PPARγ activation was inhibited using both pharmacological and molecular approaches and proliferation, apoptosis, migration and invasion were measured in MDA-MB-231 and MCF-7 breast cancer cells.

RESULTS

T0070907 treatment inhibited proliferation, invasion and migration but did not significantly affect apoptosis. Molecular inhibition using a dominant negative (Δ462) receptor yielded similar results. T007 also mediated a dose-dependent decrease in phosphorylation of PPARγ, and its ability to bind to DNA, and may directly affect mitogen-activated protein kinase signaling.

CONCLUSION

These data indicate that inhibiting endogenous PPARγ signaling may be a promising new approach to breast cancer therapy.

Targeting the peroxisome proliferator-activated receptor gamma one in the treatment of breast cancer

Abstract #3055

Peroxisome proliferator-activated receptor gamma 1 (PPARγ1) is a member of the nuclear hormone receptor superfamily and is over expressed in breast cancer compared to human mammary epithelial cells (HMEC). Although synthetic ligands of PPARγ have been reported to mediate differentiation, inhibit proliferation, and induce apoptosis of cancer cells in culture it remains unclear whether these are mediated through PPARγ or by off target effects. Furthermore, the controversial nature of these studies and the disappointing results from clinical trials raise questions about the efficacy of these drugs in treating breast cancer. Recent work from our lab and others suggests that targeting the expression or endogenous transactivation of PPARγ represents a novel strategy in the treatment of breast cancer. We have previously demonstrated that the increase in PPARγ1 expression in seen in breast cancer cells is driven by a tumor-specific promoter. Furthermore, we have identified the myc-associated zinc finger protein (MAZ) as a critical mediator of PPARγ1 expression in these cells. In this study, we further demonstrated the significance of MAZ in the transcriptional regulation of PPARγ1 and confirmed that high expression of PPARγ1 in MCF-7 breast cancer cells is MAZ dependent. Additionally, using RNA interference (RNAi) techniques to knockdown PPARγ1 or MAZ or driving the expression of a dominant negative form of PPARγ1 in MCF-7 breast cancer cells, we demonstrated that blocking the expression of either protein resulted in reduced cellular proliferation and enhanced apoptosis. These findings suggest that in the absence of any exogenous ligand an increase in PPARγ1 signaling, driven at least in part by MAZ, contributes to an imbalance between proliferation and apoptosis, and may be an important mediator or of breast cancer progression. These results also highlight the need to understand the molecular mechanisms that drives tumor specific expression of PPARγ1 and development pure antagonist as a therapeutic treatment of this devastating disease.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 3055.

Down-regulation of PPARgamma1 suppresses cell growth and induces apoptosis in MCF-7 breast cancer cells

BACKGROUND

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a member of the nuclear hormone receptor superfamily and is highly expressed in many human tumors including breast cancer. PPARgamma has been identified as a potential target for breast cancer therapy based on the fact that its activation by synthetic ligands affects the differentiation, proliferation, and apoptosis of cancer cells. However, the controversial nature of current studies and disappointing results from clinical trials raise questions about the contribution of PPARgamma signaling in breast cancer development in the absence of stimulation by exogenous ligands. Recent reports from both in vitro and in vivo studies are inconsistent and suggest that endogenous activation of PPARgamma plays a much more complex role in initiation and progression of cancer than previously thought.

RESULTS

We have previously demonstrated that an increase in expression of PPARgamma1 in MCF-7 breast cancer cells is driven by a tumor-specific promoter. Myc-associated zinc finger protein (MAZ) was identified as a transcriptional mediator of PPARgamma1 expression in these cells. In this study, using RNA interference (RNAi) to inhibit PPARgamma1 expression directly or via down-regulation of MAZ, we report for the first time that a decrease in PPARgamma1 expression results in reduced cellular proliferation in MCF-7 breast cancer cells. Furthermore, we demonstrate that these changes in proliferation are associated with a significant decrease in cell transition from G1 to the S phase. Using a dominant-negative mutant of PPARgamma1, Delta462, we confirmed that PPARgamma1 acts as a pro-survival factor and showed that this phenomenon is not limited to MCF-7 cells. Finally, we demonstrate that down-regulation of PPARgamma1 expression leads to an induction of apoptosis in MCF-7 cells, confirmed by analyzing Bcl-2 expression and PARP-1 cleavage.

CONCLUSION

Thus, these findings suggest that an increase in PPARgamma1 signaling observed in breast cancer contributes to an imbalance between proliferation and apoptosis, and may be an important hallmark of breast tumorigenesis. The results presented here also warrant further investigation regarding the use of PPARgamma ligands in patients who are predisposed or already diagnosed with breast cancer.

Transactivation of ERalpha by Rosiglitazone induces proliferation in breast cancer cells

In the present study, we demonstrate that Rosiglitazone (Rosi), a thiazolidinedione and PPARgamma agonist, induces ERE (Estrogen Receptor Response Element) reporter activity, pS2 (an endogenous ER gene target) expression, and proliferation of ER positive breast cancer (MCF-7) cells. By performing a dose-response assay, we determined that high concentrations of Rosi inhibit proliferation, while low concentrations of Rosi induce proliferation. Using the anti-estrogen ICI, ER negative breast cancer (MDA-MB-231) cells, and a prostate cancer cell line (22Rv1) deficient in both ERalpha and PPARgamma, we determined that Rosiglitazone-induced ERE reporter activation and proliferation is through an ERalpha dependent mechanism. Rosiglitazone-induced ERE activation is also dependent on activation of the Extracellular Signal-Regulated Kinase-Mitogen Activated Protein Kinase (ERK-MAPK) pathway, since it is inhibited by co-treatment with U0126, a specific inhibitor of this pathway. We also demonstrate that when ERalpha and PPARgamma are both present, they compete for Rosi, inhibiting each others transactivation. To begin to unravel the pharmacological mechanism of Rosi-induced ER activation, sub-maximally effective concentrations of E(2) were used in combination with increasing concentrations of Rosi in luciferase reporter assays. From these assays it appears that E(2) and Rosi both activate ERalpha via similar pharmacological mechanisms. Furthermore sub-maximally effective concentrations of E(2) and Rosi additively increase both ERE reporter activity and MCF-7 cell proliferation. The results of this study may have clinical relevancy for Rosi's use both as an anti-diabetic in post-menopausal women and as an anti-cancer drug in women with ER positive breast cancer.