Background: The vast majority of breast cancers express the androgen receptor (AR) with ∼80% of ER+ and 30% to50% of ER− tumors being positive for AR by immunohistochemistry (IHC). Approximately 30% of breast cancer patients with estrogen receptor positive (ER+) tumors do not respond to tamoxifen or aromatase inhibitors and AR signaling has been implicated as a possible mechanism of this insensitivity. AR overexpression has also been associated with resistance to either tamoxifen or aromatase inhibitors in cell line models. Hypothesis: ER+ breast cancers can switch from estrogen to androgen-dependent growth as they become resistant to traditional endocrine therapies and AR can serve as a therapeutic target in AR+ breast cancers, irrespective of ER status. Methods: The proliferative effect of dihydrotestosterone (DHT) and estradiol (E2) in the presence enzalutamide (formerly MDV3100) was examined in vitro and in xenograft studies using models of both ER+ and ER− breast cancer that express AR. Furthermore, AR and ER were examined by IHC in clinical specimens from breast cancer patients treated with neoadjuvant exemestane and adjuvant tamoxifen. Tumor tissue was compared to adjacent normal breast epithelium. Results: In ER+ models, bicalutamide and enzalutamide both inhibited DHT-mediated proliferation, while enzalutamide uniquely inhibited E2-mediated proliferation. In vivo, enzalutamide significantly reduced estrogen- and androgen-mediated growth of MCF7 (ER+/AR+) xenograft tumors. Remarkably, enzalutamide demonstrated an anti-proliferative effect comparable to tamoxifen. in vitro, enzalutamide inhibits E2-stimulated tumor cell proliferation and E2 bound ER activation of genes such as PR and SDF-1, despite no observed binding of enzalutamide to ER alpha or beta. In ER−/AR+ MDA-MB-453 xenografts, enzalutamide treatment resulted in decreased nuclear AR localization, increased apoptosis and tumor growth inhibition. Conclusions: Enzalutamide demonstrated significant anti-tumor activity in preclinical models of breast cancers that express AR, regardless of ER status. When enzalutamide opposes DHT, it functions by excluding AR from the nucleus, thereby reversing the anti-apoptotic effect of AR. In contrast, when opposing E2, it causes a decrease in tumor cell proliferation. Profiling of ER+ xenografts is underway to further elucidate the mechanism by which this occurs. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P2-14-02.

A conflict of interest disclosure statement: The authors do not have any conflict of interest. Translational relevanceMany rare ovarian cancers lack effective management strategies and are resistant to the standard platinum-and taxane-based chemotherapy. Thus, for a rare ovarian cancer subtype like small cell carcinoma of the ovary, hypercalcemic type (SCCOHT) -an aggressive malignancy affecting young women in their twenties, effective targeted therapeutics are urgently needed. We used global proteomics to identify a deficiency in arginosuccinate synthase (ASS1) as a common feature among some rare ovarian cancer subtypes. Using in-vitro and in-vivo models, we demonstrated that the arginine-depriving investigational agent ADI-PEG20 effectively inhibited cell growth in ASS1 deficient ovarian cancers including SCCOHT, establishing it as a potential therapeutic agent for rare ovarian cancer subtypes deficient in ASS1. Further clinical investigation is warranted. AbstractPurpose: Many rare ovarian cancer subtypes such as small cell carcinoma of the ovary, hypercalcemic type (SCCOHT) have poor prognosis due to their aggressive nature and resistance to standard platinum and taxane based chemotherapy. The development of effective therapeutics has been hindered by the rarity of such tumors. We sought to identify targetable vulnerabilities in rare ovarian cancer subtypes. Experimental Design: We compared the global proteomic landscape of six cases each of endometrioid ovarian cancer (ENOC), clear cell ovarian cancer (CCOC), and SCCOHT to the most common subtype high grade serous ovarian cancer (HGSC) to identify potential therapeutic targets. Immunohistochemistry of tissue microarrays were used as validation of ASS1 deficiency. The efficacy of arginine-depriving therapeutic ADI-PEG20 was assessed in vitro using cell lines and patient derived xenograft mouse models representing SCCOHT. Results: Global proteomic analysis identified low ASS1 expression in ENOC, CCOC, and SCCOHT compared to HGSC. Low ASS1 levels were validated through IHC in a large patient cohort. The lowest levels of ASS1 were observed in SCCOHT, where ASS1 was absent in 2/15 cases, and expressed in less than 5% of the tumor cells in 8/15 cases. ASS1 deficient ovarian cancer cells were sensitive to ADI-PEG20 treatment regardless of subtype in vitro. Furthermore, in two cell line mouse xenograft models and one patient derived mouse xenograft model of SCCOHT, once a week treatment of ADI-PEG20 (30mg/kg and 15mg/kg) inhibited tumor growth in vivo. Conclusions: Preclinical in vitro and in vivo studies identified ADI-PEG20 as a potential therapy for patients with rare ovarian cancers including SCCOHT. Author's contributions Conception and design:

Background: Approximately 5-10% of all breast cancers are hereditary and the majority of these arise due to germline mutations in the BRCA1 and BRCA2 tumour suppressor genes. BRCA1 is involved in multiple cellular pathways including DNA damage signalling, DNA repair, cell cycle regulation, protein ubiquitination, chromatin remodelling, transcriptional regulation and apoptosis. Several distinct pathological features can be used to estimate the likelihood of the presence of a BRCA1 mutation, however, it is not yet possible to fully categorise a BRCA1 mutated tumour. BRCA1-associated breast cancers are generally defined as being ER (Estrogen Receptor) negative and indeed triple negative for ER, PR and HER2. However, approximately 10-36% of BRCA1 mutated breast cancers are, in fact, ER positive. These tumours less frequently demonstrate the characteristics more commonly associated with BRCA 1 -associated breast cancers. Initial molecular evidence also suggests that there is heterogeneity within BRCA1-associated breast tumours and this is dependent on the presence or absence of the estrogen receptor. The aims of this study are to investigate the underlying biology of BRCA1-mutated (ER positive) and BRCA1-mutated (ER negative) breast tumours. Methods: Extensive gene expression profiling and data analysis was performed on a cohort of 70 FFPE (Formalin Fixed Paraffin Embedded) derived BRCA1 mutated breast tumours and matched sporadic controls using the ALMAC Breast Cancer DSA™ research tool. Within this dataset we have generated molecular profiles of: (1) BRCA 1 -mutated ER positive and (2) BRCA1-mutated ER negative breast cancer. Functional analysis was performed using DAVID and METACORE. Validation of gene targets was performed by qRT-PCR and Western blotting. Results: A list of differentially expressed transcripts was derived from the comparison of 35 BRCA1 mutant breast tumours and 35 matched sporadic controls. Further analysis based on the presence and absence of ER identified a set of transcripts defining BRCA1-mutated (ER positive) and BRCA1-mutated (ER negative) breast cancer. Functional analysis of these two datasets has identified the main pathways and processes that are deregulated. Specifically, BRCA1-deficiency in the absence of ER was associated with deregulation of pathways implicated in immune response whereas BRCA 1 deficiency in the presence of ER was associated with pathways implicated in cell adhesion and cytoskeletal remodelling. Validation of the key genes underlying these two BRCA1-deficient breast cancer subtypes has been performed. Discussion: This approach has revealed significant heterogeneity within BRCA1 mutated breast cancer based on the presence or absence of ER. Significant differences in the transcripts and molecular processes underlying BRCA1-mutated (ER positive) and BRCA1-mutated (ER negative) breast tumours have been identified. The ability to identify BRCA 1 -deficiency by gene expression profiling from FFPE derived breast tissue may also have significant clinical application. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P6-04-14.

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