Maxwell N. Skor

Glucocorticoid Receptor Antagonism as a Novel Therapy for Triple-Negative Breast Cancer

Purpose: Triple-negative breast cancer (TNBC) accounts for 10% to 20% of newly diagnosed invasive breast cancer. Finding effective targets for chemotherapy-resistant TNBC has proven difficult in part because of TNBCs molecular heterogeneity. We have previously reported that likely because of the antiapoptotic activity of glucocorticoid receptor (GR) in estrogen receptor (ER)-negative breast epithelial and cancer cells, high GR expression/activity in early-stage TNBC significantly correlates with chemotherapy resistance and increased recurrence. We hypothesized that pretreatment with mifepristone, a GR antagonist, would potentiate the efficacy of chemotherapy in GR+ TNBCs by inhibiting the antiapoptotic signaling pathways of GR and increasing the cytotoxic efficiency of chemotherapy. Experimental Design: TNBC cell apoptosis was examined in the context of physiologic glucocorticoid concentrations, chemotherapy, and/or pharmacologic concentrations of mifepristone. We used high-throughput live microscopy with continuous recording to measure apoptotic cells stained with a fluorescent dye and Western blot analysis to detect caspase-3 and PARP cleavage. The effect of mifepristone on GR-mediated gene expression was also measured. TNBC xenograft studies were performed in female severe combined immunodeficient (SCID) mice and tumors were measured following treatment with vehicle, paclitaxel, or mifepristone/paclitaxel. Results: We found that although mifepristone treatment alone had no significant effect on TNBC cell viability or clonogenicity in the absence of chemotherapy, the addition of mifepristone to dexamethasone/paclitaxel treatment significantly increased cytotoxicity and caspase-3/PARP cleavage. Mifepristone also antagonized GR-induced SGK1 and MKP1/DUSP1 gene expression while significantly augmenting paclitaxel-induced GR+ MDA-MB-231 xenograft tumor shrinkage in vivo. Conclusions: These results suggest that mifepristone pretreatment could be a useful strategy for increasing tumor cell apoptosis in chemotherapy-resistant GR+ TNBC. Clin Cancer Res; 19(22); 6163–72. ©2013 AACR.

Chronic Social Isolation Is Associated with Metabolic Gene Expression Changes Specific to Mammary Adipose Tissue

Chronic social isolation is linked to increased mammary tumor growth in rodent models of breast cancer. In the C3(1)/SV40 T-antigen FVB/N (TAg) mouse model of “triple-negative” breast cancer, the heightened stress response elicited by social isolation has been associated with increased expression of metabolic genes in the mammary gland before invasive tumors develop (i.e., during the in situ carcinoma stage). To further understand the mechanisms underlying how accelerated mammary tumor growth is associated with social isolation, we separated the mammary gland adipose tissue from adjacent ductal epithelial cells and analyzed individual cell types for changes in metabolic gene expression. Specifically, increased expression of the key metabolic genes Acaca, Hk2, and Acly was found in the adipocyte, rather than the epithelial fraction. Surprisingly, metabolic gene expression was not significantly increased in visceral adipose depots of socially isolated female mice. As expected, increased metabolic gene expression in the mammary adipocytes of socially isolated mice coincided with increased glucose metabolism, lipid synthesis, and leptin secretion from this adipose depot. Furthermore, application of media that had been cultured with isolated mouse mammary adipose tissue (conditioned media) resulted in increased proliferation of mammary cancer cells relative to group-housed–conditioned media. These results suggest that exposure to a chronic stressor (social isolation) results in specific metabolic reprogramming in mammary gland adipocytes that in turn contributes to increased proliferation of adjacent preinvasive malignant epithelial cells. Metabolites and/or tumor growth-promoting proteins secreted from adipose tissue could identify biomarkers and/or targets for preventive intervention in breast cancer. Cancer Prev Res; 6(7); 634–45. ©2013 AACR.

Serum and glucocorticoid-regulated kinase 1 (SGK1) activation in breast cancer: requirement for mTORC1 activity associates with ER-alpha expression.

Mammalian target of rapamycin (mTOR) is an attractive target for cancer treatment. While rapamycin and its derivatives (e.g., everolimus) have been shown to inhibit mTOR signaling and cell proliferation in preclinical models of breast cancer, mTOR inhibition has demonstrated variable clinical efficacy with a trend toward better responses in estrogen receptor alpha positive (ERα+) compared to ERα negative (ERα−) tumors. Recently, serum- and glucocorticoid-regulated kinase 1 (SGK1) was identified as a substrate of mTOR kinase activity. Previous studies have alternatively suggested that either mTORC1 or mTORC2 is exclusively required for SGK1’s Ser422 phosphorylation and activation in breast cancer cells. We investigated the effect of rapamycin on the growth of several ERα+ and ERα− breast cancer cell lines and examined differences in the phosphorylation of mTOR substrates (SGK1, p70S6K, and Akt) that might account for the differing sensitivity of these cell lines to rapamycin. We also examined which mTOR complex contributes to SGK1-Ser422 phosphorylation in ERα+ versus ERα− breast cell lines. We then assessed whether inhibiting SGK1 activity added to rapamycin-mediated cell growth inhibition by either using the SGK1 inhibitor GSK650394A or expressing an SGK1 shRNA. We observed sensitivity to rapamycin-mediated growth inhibition and inactivation of insulin-mediated SGK1-Ser422 phosphorylation in ERα+ MCF-7 and T47D cells, but not in ERα− MDA-MB-231 or MCF10A-Myc cells. In addition, either depleting SGK1 with shRNA or inhibiting SGK1 with GSK650394A preferentially sensitized MDA-MB-231 cells to rapamycin. Finally, we found that rapamycin-sensitive SGK1-Ser422 phosphorylation required ERα expression in MCF-7 derived cell lines. Therefore, targeting SGK1 activity may improve the efficacy of rapamycin and its analogs in the treatment of ERα− breast cancer.

Glucocorticoid receptor activation inhibits chemotherapy-induced cell death in high-grade serous ovarian carcinoma

OBJECTIVES To test the hypothesis that glucocorticoid receptor (GR) activation increases resistance to chemotherapy in high-grade serous ovarian cancer (HGS-OvCa) and that treatment with a GR antagonist will improve sensitivity to chemotherapy. METHODS GR expression was assessed in OvCa cell lines by qRT-PCR and Western blot analysis and in xenografts and primary human tumors using immunohistochemistry (IHC). We also examined the effect of GR activation versus inhibition on chemotherapy-induced cytotoxicity in OvCa cell lines and in a xenograft model. RESULTS With the exception of IGROV-1 cells, all OvCa cell lines tested had detectable GR expression by Western blot and qRT-PCR analysis. Twenty-five out of the 27 human primary HGS-OvCas examined expressed GR by IHC. No cell line expressed detectable progesterone receptor (PR) or androgen receptor (AR) by Western blot analysis. In vitro assays showed that in GR-positive HeyA8 and SKOV3 cells, dexamethasone (100nM) treatment upregulated the pro-survival genes SGK1 and MKP1/DUSP1 and inhibited carboplatin/gemcitabine-induced cell death. Concurrent treatment with two GR antagonists, either mifepristone (100nM) or CORT125134 (100nM), partially reversed these effects. There was no anti-apoptotic effect of dexamethasone on chemotherapy-induced cell death in IGROV-1 cells, which did not have detectable GR protein. Mifepristone treatment alone was not cytotoxic in any cell line. HeyA8 OvCa xenograft studies demonstrated that adding mifepristone to carboplatin/gemcitabine increased tumor shrinkage by 48% compared to carboplatin/gemcitabine treatment alone (P=0.0004). CONCLUSIONS These results suggest that GR antagonism sensitizes GR+ OvCa to chemotherapy-induced cell death through inhibition of GR-mediated cell survival pathways.

Mammary Adipose Tissue-Derived Lysophospholipids Promote Estrogen Receptor–Negative Mammary Epithelial Cell Proliferation

Lysophosphatidic acid (LPA), acting in an autocrine or paracrine fashion through G protein–coupled receptors, has been implicated in many physiologic and pathologic processes, including cancer. LPA is converted from lysophosphatidylcholine (LPC) by the secreted phospholipase autotaxin (ATX). Although various cell types can produce ATX, adipocyte-derived ATX is believed to be the major source of circulating ATX and also to be the major regulator of plasma LPA levels. In addition to ATX, adipocytes secrete numerous other factors (adipokines); although several adipokines have been implicated in breast cancer biology, the contribution of mammary adipose tissue–derived LPC/ATX/LPA (LPA axis) signaling to breast cancer is poorly understood. Using murine mammary fat-conditioned medium, we investigated the contribution of LPA signaling to mammary epithelial cancer cell biology and identified LPA signaling as a significant contributor to the oncogenic effects of the mammary adipose tissue secretome. To interrogate the role of mammary fat in the LPA axis during breast cancer progression, we exposed mammary adipose tissue to secreted factors from estrogen receptor–negative mammary epithelial cell lines and monitored changes in the mammary fat pad LPA axis. Our data indicate that bidirectional interactions between mammary cancer cells and mammary adipocytes alter the local LPA axis and increase ATX expression in the mammary fat pad during breast cancer progression. Thus, the LPC/ATX/LPA axis may be a useful target for prevention in patients at risk of ER-negative breast cancer. Cancer Prev Res; 9(5); 367–78. ©2016 AACR.

Glucocorticoid receptor ChIP-sequencing of subcutaneous fat reveals modulation of inflammatory pathways.

To identify glucocorticoid receptor (GR)‐associated chromatin sequences and target genes in primary human abdominal subcutaneous fat.

Hsp90 Inhibition Results in Glucocorticoid Receptor Degradation in Association with Increased Sensitivity to Paclitaxel in Triple-Negative Breast Cancer.

Targetable molecular drivers for triple-negative breast cancer (TNBC) have been difficult to identify; therefore, standard treatment remains limited to conventional chemotherapy. Recently, new-generation small-molecule Hsp90 inhibitors (e.g., ganetespib and NVP-AUY922) have demonstrated improved safety and activity profiles over the first-generation ansamycin class. In breast cancer, clinical responses have been observed in a subset of TNBC patients following ganetespib monotherapy; however, the underlying biology of Hsp90 inhibitor treatment and tumor response is not well understood. Glucocorticoid receptor (GR) activity in TNBC is associated with chemotherapy resistance. Here, we find that treatment of TNBC cell lines with ganetespib resulted in GR degradation and decreased GR-mediated gene expression. Ganetespib-associated GR degradation also sensitized TNBC cells to paclitaxel-induced cell death both in vitro and in vivo. The beneficial effect of the Hsp90 inhibitor on paclitaxel-induced cytotoxicity was reduced when GR was depleted in TNBC cells but could be recovered with GR overexpression. These findings suggest that GR-regulated anti-apoptotic and pro-proliferative signaling networks in TNBC are disrupted by Hsp90 inhibitors, thereby sensitizing TNBC to paclitaxel-induced cell death. Thus, GR+ TNBC patients may be a subgroup of breast cancer patients who are most likely to benefit from adding an Hsp90 inhibitor to taxane therapy.

Abstract P2-16-21: A randomized phase I trial of nanoparticle albumin bound paclitaxel (nab-paclitaxel, Abraxane®) with or without mifepristone for advanced breast cancer

Up to 40% of breast cancers have been shown to express the glucocorticoid receptor (GR), and activation of the GR is associated with poor prognosis in ER-negative breast cancer. We hypothesize that GR activation in breast cancer cells initiates anti-apoptotic signaling contributing to chemotherapy resistance. Based on our compelling preclinical data demonstrating that GR antagonism with mifepristone (mif) increases paclitaxel (pac) induced breast cancer cell death in vitro and in vivo, we conducted the first clinical trial of the combination of anti-GR therapy and chemotherapy in patients (pts) with metastatic breast cancer (MBC). Because the combination of mif and nab-paclitaxel (nab) had not previously been administered to pts, and because nab can result in cumulative neurotoxicity, a randomized, placebo-controlled, phase I design was used. Mif is known to inhibit CYP2C8, an enzyme involved in the metabolism of pac, thus plasma pac levels were monitored to evaluate for significant changes in clearance. A 3+3 dose escalation scheme was planned, with an initial nab dose of 100mg/m2 weekly and a mif dose of 300 mg/d for 2 days (day prior to and of nab infusion). For each dose level (DL), patients were randomized 3:2 to mif:placebo (p) for cycle 1 (C1). After C1, pts randomized to p were crossed over to receive mif at their assigned DL for the duration of study treatment. DL1 was deemed intolerable due to neutropenia, so the nab dose was decreased to 80 mg/m2 for DL2, and dose escalation of mif beyond 300 mg was halted. Serum cortisol and ACTH levels—biomarkers of effective GR blockade—were measured before and after mif treatment. Archival tumor was collected to determine tumor GR expression, and peripheral blood lymphocytes (PBLs) were collected to evaluate GR-target gene expression after mif. 9 pts were enrolled. Median age was 56 yrs (range 47-74). Median number of prior therapies for MBC was 2 (range 0-3). 8 pts had triple-negative breast cancer (TNBC), and 1 had ER+ disease. 8 of 9 pts had recurred after taxane-based therapy. 1 pt had a CR, 4 pts a PR, and 4 pts POD. 4 of 5 pts who responded to nab plus mif had previously relapsed after taxane-based therapy. 4 pts were treated at DL1 (2 mif, 2 p). Both pts randomized to mif experienced a dose-limiting toxicity (DLT) of neutropenia during C1. 5 pts were treated at DL2 (3 mif, 2 p), and 2 of the 3 pts randomized to mif for C1 experienced a DLT (neutropenia). Plasma pac levels were consistent with delayed clearance of nab when co-administered with mif for most pts. All pts were found to have a 2-fold or greater rise in their serum cortisol levels, demonstrating effective adrenal GR inhibition. Mif delays clearance of nab in most pts, and results in DLT. Given the inter-patient variability in delay of nab clearance by mif, co-administration produces unpredictable toxicity. However, given the responses seen in taxane-pretreated TNBC pts, GR antagonism is a promising approach for treating aggressive TNBCs. As neither carboplatin nor gemcitabine are metabolized, mif is unlikely to affect clearance of these agents. As they are widely used for advanced TNBC, both agents represent attractive chemotherapy partners for future clinical investigation. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P2-16-21.

Metabolism of megestrol acetate in vitro and the role of oxidative metabolites

Abstract 1. There is limited knowledge regarding the metabolism of megestrol acetate (MA), as it was approved by FDA in 1971, prior to the availability of modern tools for identifying specific drug-metabolizing enzymes. We determined the cytochrome P450s (P450s) and UDP-glucuronosyltransferases (UGTs) that metabolize MA, identified oxidative metabolites and determined pharmacologic activity at the progesterone, androgen and glucocorticoid receptors (PR, AR and GR, respectively). 2. Oxidative metabolites were produced using human liver microsomes (HLMs), and isolated for mass spectral (MS) and nuclear magnetic resonance (NMR) analyses. We screened recombinant P450s using MA at 62 μM (HLM Km for metabolite 1; M1) and 28 μM (HLM Km for metabolite 2; M2). UGT isoforms were simultaneously incubated with UDPGA, nicotinamide adenine dinucleotide phosphate (NADPH), CYP3A4 and MA. Metabolites were evaluated for pharmacologic activity on the PR, AR and GR. CYP3A4 and CYP3A5 are responsible for oxidative metabolism of 62 μM MA. 3. At 28 μM substrate concentration, CYP3A4 was the only contributing enzyme. Mass spectral and NMR data suggest metabolism of MA to two alcohols. After oxidation, MA is converted into two secondary glucuronides by UGT2B17 among other UGTs. MA, M1 and M2 had significant pharmacologic activity on the PR while only MA showed activity on the AR and GR.

Gene expression of peripheral blood cells reveals pathways downstream of glucocorticoid receptor antagonism and nab-paclitaxel treatment.

Objectives Whereas paclitaxel treatment is associated with leukopenia, the mechanisms that underlie this effect are not well-characterized. In addition, despite the importance of glucocorticoid signaling in cancer treatment, the genomic effects of glucocorticoid receptor antagonism by mifepristone treatment in primary human cells have never been described. Methods As part of a randomized phase 1 clinical trial, we used microarrays to profile gene expression in peripheral blood cells sampled from each of four patients at baseline, after placebo/nanoparticle albumin-bound paclitaxel (nab-paclitaxel) treatment (cycle 1), and after mifepristone/nab-paclitaxel treatment (cycle 2). Results We found that 63 genes were differentially expressed following treatment with nab-paclitaxel, including multiple genes in the tubulin pathway. We also found 606 genes that were differentially expressed in response to mifepristone; genes downregulated by mifepristone overlapped significantly with those previously identified as being upregulated by dexamethasone. Conclusion These results provide insights into the mechanisms of paclitaxel and glucocorticoid receptor inhibition in peripheral blood cells.