Abstract 161: The role of mTOR in the cisplatin resistant phenotype in ovarian cancer lineage

Abstract

Background Ovarian cancer (OVCA) is the second cause of gynecological-cancer deaths in Brazil, being frequently associated to chemotherapy resistance, a characteristic usually associated to PI3K/Akt/mTOR. We herein present data concerning the role of mTORC2 in cisplatin-resistant phenotype acquisition by OVCA cells. Methods Antineoplastic efficacy of cisplatin, doxorubicin, paclitaxel, and rapamycin was accessed, in different combinations, in the OVCA lineage OVCAR3 (cisplatin-resistant, advanced serous OVCA), through cellular metabolic viability (CMV) (MTT method). Cells were cultured in RPMI media supplemented with 10% (v/v) FBS and antibiotics until subconfluence. To characterize the role of mTORC1 or mTORC2 in OVCAR3 MCV, 1.5x105 cells/well were treated according to: EA1) Inhibition of mTORC1: Drugs at IC50 for 24h; EA2) Inhibition of mTORC1 and mTORC2: Rapamycin 100nM for 72h, followed by drugs at IC50 for 24h. Modulation of MTOR expression by PKA, PKC, and PI3K was investigated by real time RT-PCR. Statistical analysis was performed using PrismaGraphPad version 5.1. Findings OVCAR3 CMV was not significantly changed by cisplatin (IC50 0,08mM) nor paclitaxel (IC50 0,06nM) or rapamycin (IC50 0,02nM) (CMV 95%, 100%, 100%, respectively), but by doxorubicin (IC50 0,02nM) (CMV 60%), especially in combination with cisplatin (CMV 31%), following EA1. Considering the irreversible doxorubicin-induced cardiotoxicity, we pursued with EA2. Intriguingly, OVCAR3 cisplatin sensitivity was, at least partially, recovered (CMV 65%). No addictive effect was observed with cisplatin/doxorubicin following EA2 (CMV 60%), suggesting that OVCA-resistant patient might benefit from less toxic rapamycin-based chemotherapy, leaving doxorubicin for palliative final-staged disease management. Finally, neither PKA nor PI3K modulate MTOR expression; however, PKC suppresses its transcription by 4.42-fold. Interpretation Altogether, our data suggest that mTORC2, but not mTORC1, might influence cisplatin sensitivity in OVCA. Moreover, PKC inhibits the expression of MTORC in cisplatin-resistant OVCA. We propose that the inhibition of mTORC2 followed by cisplatin treatment might lead to a conjunction of autophagic cell death and apoptosis in OVCA. Of remarkable clinical interest, we point to the urge of better design clinical trials, in which not only novel drugs are tested, but also the chronological order of drugs administration to the patient is seen as crucial for treatment efficacy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 161. doi:1538-7445.AM2012-161