Progesterone receptor-B enhances estrogen responsiveness of breast cancer cells via scaffolding PELP1- and estrogen receptor-containing transcription complexes

Progesterone and estrogen are important drivers of breast cancer proliferation. Herein, we probed ER-alpha and PR cross-talk in breast cancer models. Stable expression of PR-B in PR-low/ER+ MCF7 cells increased cellular sensitivity to estradiol and IGF1, as measured in growth assays performed in the absence of exogenous progestin; similar results were obtained in PR-null/ER+ T47D cells stably expressing PR-B. Genome-wide microarray analyses revealed that unliganded PR-B induced robust expression of a subset of estradiol-responsive ER-target genes, including CathepsinD (CTSD). Estradiol-treated MCF7 cells stably expressing PR-B exhibited enhanced ER Ser167 phosphorylation and recruitment of ER, PR, and the proline, glutamate and leucine rich protein 1 (PELP1) to an estrogen response element (ERE) in the CTSD distal promoter; this complex co-immunoprecipitated with IGF1R in whole cell lysates. Importantly, ER/PR/PELP1 complexes were also detected in human breast cancer samples. Inhibition of IGF1R or PI3K blocked PR-B-dependent CTSD mRNA upregulation in response to estradiol. Similarly, inhibition of IGF1R or PR significantly reduced ER recruitment to the CTSD promoter. Stable knockdown of endogenous PR or onapristone treatment of multiple unmodified breast cancer cell lines blocked estradiol-mediated CTSD induction, inhibited growth in soft agar, and partially restored tamoxifen-sensitivity of resistant cells. Further, combination treatment of breast cancer cells with both onapristone and IGF1R tyrosine kinase inhibitor AEW541 was more effective than either agent alone. In summary, unliganded PR-B enhanced proliferative responses to estradiol and IGF1 via scaffolding of ERalpha/PELP1/IGF1R-containing complexes. Our data provide a strong rationale for targeting PR in combination with ER and IGF1R in patients with luminal breast cancer.

Abstract ES04-1: Basic science 101 – Targeting cell signaling in breast cancer

Since normal cells require extracellular signals to proliferate, it seems likely that some transformed breast cancer cells can still respond to these signals. This premise is now well established; disruption of estrogen receptor function, important in normal mammary gland biology, by estrogen deprivation (ovarian suppression or aromatase inhibition) or selective estrogen receptor modulators demonstrated the clinical value of interrupting these key signaling pathways. Further advances have included the disruption of the human epidermal growth factor 2 (HER2) by monoclonal antibodies and tyrosine kinases. These successes have generated greater enthusiasm for identifying mechanism of action of cell signaling with the hope of identifying new therapeutic targets. The intracellular signaling pathways that transduce proliferative signals is becoming better understood. Activation of the phosphatidyl 3-kinase (PI3K) and the mitogen activated protein kinase (MAPK) pathways are required for normal and malignant cell growth. Multiple strategies and drugs have been developed to target these pathways and are in clinical trial. It is also evident that co-targeting of new or established pathways also have utility over targeting only one molecule. For example, the demonstration that estrogen receptor targeting and mTOR inhibition has clinical value has revealed the potential for the inhibition of multiple pathways. Similar advances have been made in targeting HER2 by both trastuzumab and pertuzumab. These clinical strategies have value as combination therapy may more fully suppress cell signaling than single agent therapy. Additional concepts and strategies will be discussed based on the established targets of estrogen receptor and HER2.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr ES04-1.

Analysis of intraprostatic therapeutic effects in prostate cancer patients using [(11)C]-choline pet/ct after external-beam radiation therapy

PURPOSE

The objective of the present study was to analyze, with relatively high sensitivity and specificity, uptake properties of [(11)C]-choline in prostate cancer patients by means of positron-emission tomography (pet)/computed tomography (ct) imaging using objectively defined pet parameters to test for statistically significant changes before, during, and after external-beam radiation therapy (ebrt) and to identify the time points at which the changes occur.

METHODS

The study enrolled 11 patients with intermediate-risk prostate cancer treated with ebrt, who were followed for up to 12 months after ebrt. The [(11)C]-choline pet scans were performed before treatment (baseline); at weeks 4 and 8 of ebrt; and at 1, 2, 3, 6, and 12 months after ebrt.

RESULTS

Analysis of [(11)C]-choline uptake in prostate tissue before treatment resulted in a maximum standardized uptake value (suvmax) of 4.0 ± 0.4 (n = 11) at 40 minutes after injection. During week 8 of ebrt, the suvmax declined to 2.9 ± 0.1 (n = 10, p < 0.05). At 2 and 12 months after ebrt, suvmax values were 2.3 ± 0.3 (n = 10, p < 0.01) and 2.2 ± 0.2 (n = 11, p < 0.001) respectively, indicating that, after ebrt, maximum radiotracer uptake in the prostate was significantly reduced. Similar effects were observed when analyzing the tumour:muscle ratio (tmr). The tmr declined from 7.4 ± 0.6 (n = 11) before ebrt to 6.1 ± 0.4 (n = 11, nonsignificant) during week 8 of ebrt, to 5.6 ± 0.03 (n = 11, p < 0.05) at 2 months after ebrt, and to 4.4 ± 0.4 (n = 11, p < 0.001) at 12 months after ebrt.

CONCLUSIONS

Our study demonstrated that intraprostatic [(11)C]-choline uptake in the 11 analyzed prostate cancer patients significantly declined during and after ebrt. The pet parameters SUVmax and tmr also declined significantly. These effects can be detected during radiation therapy and up to 1 year after therapy. The prognostic value of these early and statistically significant changes in intraprostatic [(11)C]-choline pet avidity during and after ebrt are not yet established. Future studies are indicated to correlate changes in [(11)C]-choline uptake parameters with long-term biochemical recurrence to further evaluate [(11)C]-choline pet changes as a possible, but currently unproven, biomarker of response.

Abstract P1-14-11: Assessing Prognosis and Therapy Response in Primary Systemic Therapy of Breast Cancer with Magnetic Resonance Spectroscopy

PURPOSE: We have previously reported results of a pilot study in patients with locally advanced breast cancer receiving primary systemic chemotherapy (PST) showing that a decrease in tumor choline concentration ([tCho]) measured one day after starting treatment was associated with clinical response based on MRI. In this follow-up study with a larger cohort, we assessed whether early changes in [tCho] were associated with clinical response, based on both MRI and pathology, and survival.

METHODS AND MATERIALS: Women with locally advanced breast cancer scheduled for PST were scanned using a high-field MRI/MRS protocol prior to treatment, day 1 after treatment, and at the end of the first course of chemotherapy. MRI/MRS was performed on a 4 T Varian system with unilateral transmit/receive breast coils. MRI consisted of contrast-enhanced T1-weighted 3D gradient echo scans with one-minute temporal resolution. A single-voxel MR spectrum was acquired from the index lesion after MRI, and the concentration of total choline compounds ([tCho]) was quantified using water as an internal reference. Clinical response was assessed using RECIST criteria for measuring the longest diameter (LD) of the index lesion, and by pathologic complete response (pCR) at definitive surgery. Overall survival (OS) and invasive disease free survival (IDFS) were assessed by retrospective review of clinical records and the social security death index. The associations of change in [tCho] with pCR/LD response and with IDFS/OS were assessed using logistic/Cox regression, respectively, adjusted for node positivity and pCR status.

RESULTS: Of the 74 women enrolled in the trial, 51 women (ages 28–71, median 47 years) were scanned at all time points and included in the final analysis. Of these, 17 subjects had a partial or complete imaging RECIST response based on a ≥30% decrease of the LD of the index lesion. Pathologic complete response, defined as no detectable invasive disease in the breast, was observed in 13/51 overall subjects and in 6/35 hormone receptor positive (ER+ or PR+) subjects. Median follow-up time for survival analysis was 64 months (range 11–102 months). Linear models showed no significant association between change in [tCho] and either pCR or RECIST response. An increase in [tCho] between the pretreatment scan and day 1 after treatment was found to be associated with reduced likelihood of both OS and IDFS. We found no association between pCR status and either OS or IDFS when considering all subjects and in the HR+ cohort (see Table 1). No results could be reported for the HR- group (14 subjects) due to an insufficient number of events.

Reducing methylmercury accumulation in the food webs of San Francisco Bay and its local watersheds

San Francisco Bay (California, USA) and its local watersheds present an interesting case study in estuarine mercury (Hg) contamination. This review focuses on the most promising avenues for attempting to reduce methylmercury (MeHg) contamination in Bay Area aquatic food webs and identifying the scientific information that is most urgently needed to support these efforts. Concern for human exposure to MeHg in the region has led to advisories for consumption of sport fish. Striped bass from the Bay have the highest average Hg concentration measured for this species in USA estuaries, and this degree of contamination has been constant for the past 40 years. Similarly, largemouth bass in some Bay Area reservoirs have some of the highest Hg concentrations observed in the entire US. Bay Area wildlife, particularly birds, face potential impacts to reproduction based on Hg concentrations in the tissues of several Bay species. Source control of Hg is one of the primary possible approaches for reducing MeHg accumulation in Bay Area aquatic food webs. Recent findings (particularly Hg isotope measurements) indicate that the decades-long residence time of particle-associated Hg in the Bay is sufficient to allow significant conversion of even the insoluble forms of Hg into MeHg. Past inputs have been thoroughly mixed throughout this shallow and dynamic estuary. The large pool of Hg already present in the ecosystem dominates the fraction converted to MeHg and accumulating in the food web. Consequently, decreasing external Hg inputs can be expected to reduce MeHg in the food web, but it will likely take many decades to centuries before those reductions are achieved. Extensive efforts to reduce loads from the largest Hg mining source (the historic New Almaden mining district) are underway. Hg is spread widely across the urban landscape, but there are a number of key sources, source areas, and pathways that provide opportunities to capture larger quantities of Hg and reduce loads from urban runoff. Atmospheric deposition is a lower priority for source control in the Bay Area due to a combination of a lack of major local sources. Internal net production of MeHg is the dominant source of MeHg that enters the food web. Controlling internal net production is the second primary management approach, and has the potential to reduce food web MeHg in some habitats more effectively and within a much shorter time-frame. Controlling net MeHg production and accumulation in the food web of upstream reservoirs and ponds is very promising due to the many features of these ecosystems that can be manipulated. The most feasible control options in tidal marshes relate to the design of flow patterns and subhabitats in restoration projects. Options for controlling MeHg production in open Bay habitat are limited due primarily to the highly dispersed distribution of Hg throughout the ecosystem. Other changes in these habitats may also have a large influence on food web MeHg, including temperature changes due to global warming, sea level rise, food web alterations due to introduced species and other causes, and changes in sediment supply. Other options for reducing or mitigating exposure and risk include controlling bioaccumulation, cleanup of contaminated sites, and reducing other factors (e.g., habitat availability) that limit at-risk wildlife populations.

Dosimetry study of [I-131] and [I-125]- meta-iodobenz guanidine in a simulating model for neuroblastoma metastasis

The physical properties of I-131 may be suboptimal for the delivery of therapeutic radiation to bone marrow metastases, which are common in the natural history of neuroblastoma. In vitro and preliminary clinical studies have implied improved efficacy of I-125 relative to I-131 in certain clinical situations, although areas of uncertainty remain regarding intratumoral dosimetry. This prompted our study using human neuroblastoma multicellular spheroids as a model of metastasis. 3D dose calculations were made using voxel-based Medical Internal Radiation Dosimetry (MIRD) and dose-point-kernel (DPK) techniques. Dose distributions for I-131 and I-125 labeled mIBG were calculated for spheroids (metastases) of various sizes from 0.01 cm to 3 cm diameter, and the relative dose delivered to the tumors was compared for the same limiting dose to the bone marrow. Based on the same data, arguments were advanced based upon the principles of tumor control probability (TCP) to emphasize the potential theoretical utility of I-125 over I-131 in specific clinical situations. I-125-mIBG can deliver a higher and more uniform dose to tumors compared to I-131 mIBG without increasing the dose to the bone marrow. Depending on the tumor size and biological half-life, the relative dose to tumors of less than 1 mm diameter can increase several-fold. TCP calculations indicate that tumor control increases with increasing administered activity, and that I-125 is more effective than I-131 for tumor diameters of 0.01 cm or less. This study suggests that I-125-mIBG is dosimetrically superior to I-131-mIBG therapy for small bone marrow metastases from neuroblastoma. It is logical to consider adding I-125-mIBG to I-131-mIBG in multi-modality therapy as these two isotopes could be complementary in terms of their cumulative dosimetry.

Quality-of-life outcomes in high-risk prostate cancer patients treated with helical tomotherapy in a hypofractionated radiation schedule with long-term androgen suppression

PURPOSE

We examined the impact of hypofractionated radiation therapy and androgen suppression therapy (AST) on quality of life (QOL) in high-risk prostate cancer patients.

METHODS

Between March 2005 and March 2007, 60 patients with high-risk prostate cancer were enrolled in a prospective phase ii study. All patients received 68 Gy (2.72 Gy per fraction) to the prostate gland and 45 Gy (1.8 Gy per fraction) to the pelvic lymph nodes in 25 fractions over 5 weeks. Of the 60 patients, 58 received ast. The University of California-Los Angeles Prostate Cancer Index questionnaire was used to prospectively measure QOL at baseline (month 0) and at 1, 6, 12, 18, 24, 30, and 36 months after radiation treatment. The generalized estimating equation approach was used to compare the QOL scores at 1, 6, 12, 18, 24, 30, and 36 months with those at baseline.

RESULTS

We observed a significant decrease in QOL items related to bowel and sexual function. Several QOL items related to bowel function were significantly adversely affected at both 1 and 6 months, with improvement toward 6 months. Although decreased QOL scores persisted beyond the 6-month mark, they began to re-approach baseline at the 18- to 24-month mark. Most sexual function items were significantly adversely affected at both 1 and 6 months, but the effects were not considered to be a problem by most patients. A complete return to baseline was not observed for either bowel or sexual function. Urinary function items remained largely unaffected, with overall urinary function being the only item adversely affected at 6 months, but not at 1 month. Urinary function returned to baseline and remained unimpaired from 18 months onwards.

CONCLUSIONS

In our study population, who received hypofractionated radiation delivered using dynamic intensity-modulated radiotherapy with inclusion of the pelvic lymph nodes, and 2-3 years of ast prescription, QOL with respect to bowel and sexual function was significantly affected; QOL with respect to urinary function was largely unaffected. Our results are comparable to those in other published studies.

P4-02-11: Insulin-Like Growth Factor I Promotes Estrogen Receptor Positive Breast Cancer Cell Proliferation, in Part, through CYP1A1 Signaling

Activation of the transmembrane tyrosine kinase insulin-like growth factor 1 receptor (IGF-1R) contributes to breast cancer progression. Nonetheless, the mechanisms by which the IGF-1R contributes to breast cancer progression need to be better characterized to further develop therapeutic strategies that target this pathway. It is known that cytochrome P450 monooxygenases synthesize metabolites from endogenous and exogenous sources that promote breast cancer proliferation. Here we propose that activity of the IGF-1R modulates the activity of CYP1A1 to promote breast cancer cell proliferation. We have found that IGF-IR activation by treatment with IGF1 (5nM ) for 4hrs induces cytochrome P450 1A1 (CYP1A1) mRNA levels in estrogen receptor (ER) positive line T47D-CO, but not ER negative line MDA-MB-231. Treatment with IGF1 promotes the proliferation of ER positive lines T47D-CO and MCF7. Interestingly, we found that treatment with IGF1 only partially compensates the growth-inhibition induced by CYP1A1 knock down by siRNA, suggesting that IGF1 requires CYP1A1 for full promotion of cell growth. These preliminary data suggest that IGF-1 signaling functions, in part, through CYP1A1 to promote ER positive breast cancer cell proliferation. The mechanism of IGF-1 signaling through CYP1A1 is novel and may represent an effector mechanism for IGF-1. Further understanding the role of CYP1A1 downstream of the IGF-1R may allow novel approaches for inhibition of breast cancer cell proliferation downstream of the IGF-1R.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P4-02-11.

P2-03-02: An IGF1R Antibody Does Not Inhibit Growth of Tamoxifen Resistant MCF-7 Cells

The role of the insulin-like growth factor (IGF) system in breast cancer has been well defined, and inhibitors of this pathway are currently in clinical trials. The majority of anti-IGF1R clinical trials are in estrogen receptor-positive patients who have progressed on prior endocrine therapy with some early reports showing no benefit for addition of IGF1R inhibitors to endocrine therapy. The effect in endocrine-resistant models, mimicking the clinical trial scenario, has not been adequately investigated. To examine the effectiveness of IGF1R inhibitors in vitro, tamoxifen-resistant (TamR) cells were generated by culturing MCF-7L cells in the presence of 4-hydroxy-tamoxifen for more than 1 year. TamR cells had diminished levels of IGF1R with unchanged levels of insulin receptor (IR), and enhanced phosphorylation of Akt. Further, TamR cells failed to further respond to IGF-I-induced Akt activation while retaining responsiveness to both insulin and IGF-II. Additionally, IGF-I failed to enhance the proliferation and anchorage-independent growth of TamR cells; however, both insulin and IGF-II stimulated proliferation and anchorage-independent growth. An IGF1R antibody (dalotuzumab) was able to inhibit IGF-I-mediated Akt phosphorylation, proliferation, and anchorage-independent growth in parental MCF-7L cells and had minimal effect on insulin and IGF-II stimulation. In TamR cells, dalotuzumab failed to inhibit proliferation or anchorage-independent growth in response to either insulin or IGF-II. An IGF1R tyrosine kinase inhibitor, (AEW 541) with equal potency for the IGF1R and IR, inhibited IGF-I-, IGF-II-, and insulin-stimulated Akt phosphorylation, proliferation, and anchorage-independent growth in MCF-7L parental cells. Interestingly, AEW 541 also inhibited insulin- and IGF-II-stimulated Akt phosphorylation, proliferation, and anchorage-independent growth in MCF-7L TamR cells. We conclude that cells selected for tamoxifen resistance in vitro have downregulated IGF1R making antibodies directed against this receptor ineffective. Preliminary studies in vivo, suggest that initial co-treatment with tamoxifen plus dalotuzumab was more effective than either drug alone. In contrast, acquired tamoxifen resistance might require dual inhibition of IGF1R and PI3K targets to completely suppress IGF system signaling as currently under study in the clinic. Alternatively, IGF1R tyrosine kinase inhibitors may be effective by inhibiting both IGF1R and IR signaling in cells selected for tamoxifen resistance.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P2-03-02.

P4-01-14: Fulvestrant Regulates Epidermal Growth Factor (EGF) Ligands and Induces EGF Receptor Activation in MCF-7 Breast Cancer Cells

Selective Estrogen Receptor Modulators (SERMs) 4 Hydroxy Tamoxifen (4-HT) and fulvestrant (fulv) inhibit estrogen receptor a (ER) positive breast cancer growth. We have observed that treatment (24 to 48 hours) of fulv in MCF-7 cells induced a 190kDa tyrosine phosphorylated band, which was blocked by EGFR and HER-2 tyrosine kinase inhibitors erlotinib and lapatinib. Immunoprecipitation showed EGFR, HER-2, and HER-3 were all phosphorylated after fulv treatment. 4-HT and estradiol did not cause this phosphorylation. No changes in receptor level after fulv treatment were noted. Downstream MAPK signaling was also blocked by erlotinib and lapatinib. Fulv induced activation of EGFR was ER dependent, since fulv treatment in C4-12, an ER negative cell line derived from MCF-7 cells, did not induce EGFR activation. Co-treatment with estradiol and fulv prevented EGFR activation. To explore the possibility that fulv enhanced ligand expression, we collected conditioned media (CM) from MCF-7 cells after 48 hours of treatment. pEGFR was lost when CM was removed, but recurred within 30 minutes. Cycloheximide abolished the ability of fulv to activate EGFR suggesting autorcine production of EGFR ligands was induced by fulv. To detect specific EGFR ligands, we used qPCR to measure various EGFR ligand mRNA levels in MCF-7 and C4-12 cell at 1, 4, 24 and 48 hours after fulv treatment. TGF-α and HB-EGF mRNAs were upregulated over 48 hours, which correlated well with pEGFR activation. 4-HT did not affect mRNA levels of these ligands. In contrast, amphiregulin (AREG) mRNA levels were substantially reduced 48 hours after fulv treatment. A similar trend was seen for AREG mRNA levels in 4HT treated cells but to a much lesser extent. There was no change in any EGFR ligand mRNA levels in ER negative C4-12 cells. These qPCR data suggested differential regulation of EGFR ligands by fulv treatment contributed to EGFR family member activation and was dependent on ER expression. Upon fulv treatment, levels of ER were diminished with decreased detection of S167 and S118 ER phosphorylation sites. Monolayer cell growth analysis showed that while fulv treatment in SFM reduced MCF-7 cell numbers compared to control treatment, erlotinib plus fulv significantly reduced cell numbers below the level of cells maintained in fulv alone. In conclusion, we show that fulv, but not E2 or 4-HT, activates EGFR family members accompanied by upregulation of ligands. Since SERM resistance has been associated with EGFR family member activation, differential control of EGFR ligand gene expression by ER may contribute to the development of fulvestrant resistance in breast cancer.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P4-01-14.

P5-13-05: Non-Invasive In Vivo 1H Magnetic Resonance Spectroscopy (MRS) Monitoring of Breast Tumor Response to IGF1R Targeted Therapy

Drugs targeting IGF1R are in clinical trials for breast cancer therapy. To date no suitable biomarkers of response have been identified for this therapy. It is important to select patients with tumors sensitive to disruption of IGF1R signaling. In addition, predicting response in patients quickly following initial treatment would also assist in the development of these strategies. While expression of IGF1R must be a minimum requirement for enrolling patients in trials with IGF1R agents, the mere expression of IGF1R is not necessarily sufficient for IGF-driven biology. We have previously shown that monitoring levels of total choline-containing compounds (tCho) non-invasively in breast cancer patients with locally advanced breast cancer is a useful predictor of response to primary systemic therapy. The tCho measured in these studies included choline, phosphocholine (pCho) and glycerophosphocholine (GPC). In this study, we examined if changes in tCho could be used as a marker of response to anti-IGF1R therapy. We tested the effect of two antibodies against IGF1R on intratumoral tCho levels in vivo. Mice bearing MCF-7 xenografts were subjected to MR imaging (MRI) and spectroscopy (MRS) to measure baseline tCho levels. MRI was performed at 4.7 Tesla (200 mHz) with a transceive surface coil. Single-voxel 1H spectroscopy was performed using water suppression and TE-averaging. A fully relaxed, unsuppressed water spectrum from the same voxel was acquired and tCho signal was referenced against the tissue water signal and expressed as mmol/kg water. The next day, mice were treated with 500 μg of scFv-Fc or phosphate buffered saline, or 800 μg EM164 or isotype-matched control antibody. 24 hours post-treatment, tCho was measured. The percent change in tCho 24h after treatment (% tCho24) was determined using the formula 100[(tCho24-tCho0)/tCho0]. In 9 out 10 mice treated with scFv-Fc, % tCho24 ranged from −26 to −81% of baseline levels while in mice treated with PBS the change was from 0% to +46%. EM164 treatment also caused decrease in tCho levels in 3 out of 3 mice while the control antibody did not. tCho was also monitored for a period of 2 weeks during the course of treatment with EM164 or control antibody; EM164 caused a decrease in tCho with % tCho of −35% while the control antibody treated mice showed % tCho of +43% over the two-week treatment. To further delineate the precise choline species regulated by IGF signaling, MCF-7 cells were treated in vitro with IGF-I for 24h and cell extracts subjected to MRS at 14.1 Tesla using a NMR scanner. IGF-I enhanced levels of pCho compared to choline and GPC. We next investigated if there is a mechanistic link between IGF signaling and choline metabolism. MCF-7 cells were treated with IGF-I for 10 minutes or 24h and levels of choline kinase (ChoK), the rate-limiting enzyme that converts choline to pCho and then phosphatidylcholine were examined. Surprisingly, IGF-I signaling enhanced ChoK levels. Our data show that decrease in tCho could be a surrogate marker of early response to anti-IGF1R therapy. Thus, MRS to measure tCho levels could be included in the design of clinical trials with such reagents to quickly identify patients whose tumors are sensitive to inhibition of IGF1R.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P5-13-05.

P3-16-03: Enhancing Anti-IGF Directed Therapeutics by Co-Targeting Autophagy

Autophagy (macroautophagy) is a cellular mechanism that maintains homeostasis and cell growth by regulating the turnover of damaged proteins. Autophagy has a critical role in maintaining cellular viability during nutrient starvation and metabolic stress by recycling intracellular proteins for nutrient reallocation. Whether the autophagy pathway utilized by breast cancer cells has a survival mechanism or is a feature of cell death is not fully understood. Since the IGF/insulin signaling maintains cellular growth, nutrient utilization, and survival, increased autophagy or autophagic flux might be induced with IGF-I inhibitors as a compensatory survival mechanism. In breast cancer cells treated with anti-IGF1R kinase inhibitors, we observed an increase in autophagic flux; similar to levels induced by nutrient deprivation.

Objective: In this study, we examined whether IGF1R inhibitor -induced autophagy is cytoprotective or cytotoxic. If autophagy has a protective role in nutrient-depleted conditions it could reduce the long term efficacy of IGF1R inhibition by making cells refractory to blockade of this signaling system. In this study, we hypothesized that blocking autophagy in combination with anti-IGF1R therapies (antibodies or small molecules) would further enhance growth inhibition in a panel of breast cancer cells types (luminal and basal-like/triple negative).

Results: We initially examined whether autophagy inhibitors (chloroquine or bafilomycin A1) had a differential growth effect on breast cancer cells that varied in their sensitivity to IGF1R stimulated growth. We found that low-to-moderate IGF growth dependent MDA-MB-231 and MDA-MB-435A breast cancer cells were more sensitive to chloroquine alone. However, sensitivity to bafilomycin A1 differed between breast cancer cell lines compared to chloroquine. In conditions of cellular stress when autophagy is normally triggered, co-treatment with IGF inhibitor (OSI-906) and chloroquine, increased growth inhibition in all breast cancer cell lines. Further, basal-like breast cancer cells (i.e. low-to-moderate IGF growth dependent cells) had a higher baseline autophagic flux compared to luminal MCF-7L breast cancer cells (i.e. highly IGF-I dependent). Using MCF-7L cells selected for long-term resistance to IGF1R kinase inhibitor (AEW-541), we found that these cells were not sensitivite to chloroquine or Bafilomycin A1 compared to wild type MCF-7Ls. Inhibiting autophagy in combination with anti-IGF therapies could offer benefit over single therapy alone if autophagy inhibitors are given together with IGF1R inhibitors, but not in IGF1R inhibitor resistant cancers. Additionally, targeting autophagy as a single agent therapy may be more beneficial in triple negative breast cancer compared to other subtypes of breast cancer.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P3-16-03.

P2-03-03: An Insulin-Like Growth Factor I (IGF-I)-Induced Gene, Solute Carrier Family 7 Member 11 (SLC7A11)/xCT, Mediates IGF-I-Induced Biological Behaviors in Breast Cancer Cells

Our laboratory studied the gene expression profiles of a series of T47D variant cell lines with differential insulin receptor substrate (IRS) adaptor protein expression to develop predictive IGF-I pathway biomarkers. We identified an IGF-I-induced gene, SLC7A11 (or xCT), which is specifically regulated through IRS-1. xCT encodes the cystine/glutamate transporter subunit of the heterodimeric amino acid transport system xc- which is a major plasma membrane transporter for the cellular uptake of cystine in exchange for intracellular glutamate. xCT is involved in the regulations of proliferation, metastasis, and drug resistance in various cancers. However, to date, the linkage between xCT and the IGF-I signaling pathway has not been described. To study the role for xCT in mediating IGF-I-induced biology in breast cancer cell lines, we examined xCT mRNA expression upon IGF-I stimulation in two breast cancer cell lines; the MCF-7 (IRS-1 activated) and MDA-MB-231 (IRS-2 activated) cells. Significant increased xCT expression was observed only in MCF-7 cells after IGF-I treatment. Immunoblots showed that xCT protein expression was elevated after IGF-I treatment and induced glutamate/cystine exchange in MCF-7 cells. shRNA was used to downregulate xCT in MCF-7 and MDA-MB-231 cells. In MCF-7, IGF-I-stimulated cell monolayer growth was suppressed by xCT shRNA or by the xCT inhibitor sulfasalazine (SASP). In MDA-MB-231 cells, xCT downregulation did not affect IGF-mediated Boyden chamber migration. Thus, IGF-I induction of cellular xCT levels is associated with cell growth in the IRS-1 activated MCF-7 cells, while MDA-MB-231 cells were not affected by downregulation of this gene. Therefore, our data imply that xCT may mediate IGF-I induced biological functions in breast cancer cell lines through an IRS-1 dependent pathway.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P2-03-03.

P4-02-09: Estrogen-Related Receptor a Mediates Insulin-Like Growth Factor-I Dependent Migration in Breast Cancer Cells

The orphan nuclear estrogen-related receptors (ERR) have homology to steroid hormone receptors. Unlike classical steroid hormone receptors, ERRs do not have known ligands but are transcriptionally activated upon binding to nuclear receptor coregulators such as PGC1α, PGC1β, and PPRC1. ERRs regulate energy metabolism and are accordingly expressed in tissues that require high energy production. ERRs recognize their own ERRE (estrogen-related receptor response element) gene promoters, but can also activate transcription via ERE (estrogen receptor response element) promoters, representing the ability of ERRs to cross participate in ERα regulatory pathways in the absence of estrogen. Of the three family members (α,β,γ), ERRα is the most highly expressed in breast tissue. ERRα expression was found to be increased in ERα negative breast cancers and associated with poor prognoses. ERRα and its coactivators can increase the expression of a critical mediator of breast tumor angiogenesis and metastasis, VEGFA. We have previously shown that VEGFA is regulated by insulin and IGF receptor activation and hypothesized that ERRα may be a mediator of this finding. We therefore explored whether ERRα and its coactivators are necessary for IGF-I/insulin dependent regulation of VEGFA and cell migration. ERRα was expressed in breast cancer cell lines, but no correlation was observed with breast cancer subtypes. Reducing endogenous ERRα levels by shRNA reduced IGF-I dependent migration in MDA-MB-231 cells. These results were confirmed using an ERRα specific inverse agonist (XCT-790), which also inhibited MDA-MB-231 cell migration. Modulating ERRα mRNA levels via shRNA resulted in decreased VEGFA mRNA levels in MCF7L cells and increased VEGFA mRNA levels in MDA-MB-231 cells, while the inverse agonist XCT-790 caused an increase in VEGFA mRNA levels in both cell lines. Reducing ERRa levels did not affect the expression of the IGF1R, InsR, IRS-1, IRS-2, PI-3K-Akt-mTOR dependent signaling pathway. Neither ERRα protein nor mRNA levels were modulated by IGF-I or insulin. We conclude that ERRα is important for mediating IGF-I dependent migration, but have shown that ERRα is not directly regulated by the IGF signaling. We will next explore the role of ERRα's coregulators (PGC1α, PGC1β, and PPRC1) in the regulation of VEGFA by the IGF/insulin pathway given their central role in regulating ERRα's function.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P4-02-09.

Application of machine learning methodology for PET-based definition of lung cancer

We applied a learning methodology framework to assist in the threshold-based segmentation of non-small-cell lung cancer (nsclc) tumours in positron-emission tomography–computed tomography (pet–ct) imaging for use in radiotherapy planning. Gated and standard free-breathing studies of two patients were independently analysed (four studies in total). Each study had a pet–ct and a treatment-planning ct image. The reference gross tumour volume (gtv) was identified by two experienced radiation oncologists who also determined reference standardized uptake value (suv) thresholds that most closely approximated the gtv contour on each slice. A set of uptake distribution-related attributes was calculated for each pet slice. A machine learning algorithm was trained on a subset of the pet slices to cope with slice-to-slice variation in the optimal suv threshold: that is, to predict the most appropriate suv threshold from the calculated attributes for each slice. The algorithm’s performance was evaluated using the remainder of the pet slices. A high degree of geometric similarity was achieved between the areas outlined by the predicted and the reference suv thresholds (Jaccard index exceeding 0.82). No significant difference was found between the gated and the free-breathing results in the same patient. In this preliminary work, we demonstrated the potential applicability of a machine learning methodology as an auxiliary tool for radiation treatment planning in nsclc.