Abstract A23: Induction of the unfolded protein response in ovarian cancer cells exposed to cytostatic concentrations of antiprogestin/antiglucocorticoid mifepristone

Ovarian cancer is rare; yet, it is the deadliest gynecologic malignancy with a 5-year survival rate that has only improved 9% in the past 30 years and a dismal overall survival rate that has remained stagnant for over 50 years. Although most patients diagnosed with advanced disease undergo remission after optimal surgical cytoreduction and platinum (Pt)-based chemotherapy, microscopic foci of cells defined as minimal residual disease (MRD) manage to survive within the peritoneal cavity and recreate the disease (recurrence) that develops a more aggressive phenotype for which current therapies almost always fail. Thus, it is critical to take advantage of the time the patient is in remission to attack the cells constituting the MRD by disengaging their repopulation capacity. Evidence suggests the feasibility of this consolidation therapeutic approach using cytostatic agents. Previously, we demonstrated that the repopulation of cells escaping Pt or Pt-taxane chemotherapy can be abrogated using steroids with antiprogestin/antiglucocorticoid activity, such as mifepristone (MF). We found that MF (i) blocks ovarian cancer cell growth by inducing G1 cell cycle arrest mediated by the up-regulation of cyclin dependent kinase inhibitors p21 and p27, leading to the blockage of the activity of cyclin dependent kinase 2 (Cdk2) and, consequently, lack of DNA synthesis and S phase progression; (ii) induces cell death in combination with blockage of the PI3K/Akt survival pathway; and (iii) it does not require progesterone receptors to exert its anti-growth effect. To further elucidate the cytotoxic mechanism triggered by MF in ovarian cancer cells, we performed genomic and proteomic screenings using ovarian cancer cell lines of different genetic backgrounds and sensitivities to Pt. We exposed OV2008 (wt p53, Pt sensitive), OV2008/C13 (wt p53/Pt resistant), or SK-OV-3 (null p53, Pt semi-resistant) cells to cytostatic concentrations of MF for 24, 48 or 72 h. Total RNAs and whole protein extracts were subjected to cDNA microarray analysis and two-dimensional nano-liquid chromatography (2D-nanoLC)-mass spectrometry (MS/MS), respectively. The combined use of cDNA microarray and 2D nanoLC-MS/MS to discover mRNAs and proteins differentially regulated by MF led to the identification of key proteins involved in the regulation of the unfolded protein response (UPR), which were further validated by Western blotting. We identified the master ER chaperone glucose regulated protein (GRP) 78 (also referred to as BiP/HSPA5) highly up-regulated by MF. Also the ER stress sensors protein kinase RNA-like ER kinase (PERK) and inositol-requiring kinase 1 (IRE1alpha) were up-regulated by MF. Activation of PERK and IRE1alpha signaling pathway usually leads to attenuated global protein synthesis thus contributing to cell cycle arrest. We found the translation repressor protein 4E-BP1 augmented by MF suggesting reduced protein translation capability. We also found highly up-regulated the transcription factor C/EBP homologous protein (CHOP), the induction of which is usually linked to cell death. In summary, we identified the UPR as a target for MF activity. We hypothesize that the UPR integrates the cytotoxicity of MF towards ovarian cancer cells when used as monotherapy or in combination therapies triggering, respectively, cell cycle arrest (cytostasis) or cell death (lethality) depending on the degree of cellular stress generated. Citation Format: Maria B. Hapon, Carlos D. Gamarra-Luques, Alicia A. Goyeneche, Eduardo A. Callegari, Kathleen M. Eyster, Carlos M. Telleria. Induction of the unfolded protein response in ovarian cancer cells exposed to cytostatic concentrations of antiprogestin/antiglucocorticoid mifepristone. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: From Concept to Clinic; Sep 18-21, 2013; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2013;19(19 Suppl):Abstract nr A23.