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

• Published in: Clinical cancer research 2013-11, Vol.19 (22), p.6163-6172
• Main Authors: SKOR, Maxwell N, WONDER, Erin L, KOCHERGINSKY, Masha, GOYAL, Anju, HALL, Ben A, YI CAI, CONZEN, Suzanne D
• Format: Article
• Language: English
• Subjects: Animals; Anti-Inflammatory Agents - therapeutic use; Antineoplastic agents; Antineoplastic Agents, Phytogenic - therapeutic use; Antineoplastic Combined Chemotherapy Protocols - therapeutic use; Apoptosis - drug effects; Biological and medical sciences; Caspase 3 - metabolism; Cell Line, Tumor; Dexamethasone - therapeutic use; Drug Resistance, Neoplasm; Dual Specificity Phosphatase 1 - biosynthesis; Female; Gene Expression - drug effects; Gynecology. Andrology. Obstetrics; Hormone Antagonists - therapeutic use; Humans; Immediate-Early Proteins - biosynthesis; Mammary gland diseases; Medical sciences; Mice; Mice, SCID; Mifepristone - therapeutic use; Multiple tumors. Solid tumors. Tumors in childhood (general aspects); Neoplasm Recurrence, Local; Neoplasm Transplantation; Paclitaxel - therapeutic use; Pharmacology. Drug treatments; Poly(ADP-ribose) Polymerases - metabolism; Protein Serine-Threonine Kinases - biosynthesis; Receptors, Estrogen - metabolism; Receptors, Glucocorticoid - antagonists & inhibitors; Receptors, Glucocorticoid - metabolism; Signal Transduction - drug effects; Transplantation, Heterologous; Triple Negative Breast Neoplasms - drug therapy; Tumors
• ISSN: 1078-0432; 1557-3265
• DOI: 10.1158/1078-0432.ccr-12-3826

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 TNBC's 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. 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. 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. These results suggest that mifepristone pretreatment could be a useful strategy for increasing tumor cell apoptosis in chemotherapy-resistant GR+ TNBC.