Splicing Factors And The Role Of Navitoclax In Drug-Resistant Ovarian Cancer

Alternative RNA splicing allows processing of a pre-mRNA into various mature mRNAs. In this way multiple protein products can be derived from a single gene. In cancer it is known that specific splice variants may facilitate malignant transformation and therapeutic resistance. Our current studies focus on the problem of drug resistance in ovarian cancer and we have approached this in a variety of ways. Following sequencing analysis of a panel of ovarian cancer cell lines we identified the RNA splicing factors TCERG and SRSF2 as being reduced in drug resistant ovarian cancer cell lines, compared with their drug sensitive counterpart. TCERG is important in regulating the splicing of variant forms of the BClx gene: BClx L (long form) and BClx s (short form). There are clear implications for drug resistance whereby low TCERG results in reduced BClx splicing to yield the pro-apoptotic BClx s form. In the SKOV-3 human ovarian cancer cell line panel both paclitaxel resistant SKOV-3TaxR and SKOV-3CR carboplatin resistant cells showed reduced levels of TCERG mRNA using qPCR analysis. In addition, qPCR analysis for BClx l and BClx s levels indicated increased ratio of long:short form with drug resistance: SKOV-3 parent line ratio 1.0; SKOV-3TaxR 1.8; SKOV-3CR 1.65. Western immunoblotting showed relatively decreased levels of Bax protein in drug resistant versus drug sensitive cell line in line with a reduced apoptotic reduced. We then explored the use of Navitoclax (ABT0263), the small-molecule Bcl-2 family protein inhibitor for Bcl-xL, Bcl-2 and Bcl-w in our cell line panel. Navitoclax in combination with paclitaxel for 48h gave rise to significantly increased apoptotic response in drug-resistant versus drug sensitive ovarian cancer cell line counterparts, using the Annexin V assay with PI, indicative of re-sensitisation to paclitaxel. Synergistic effects were also seen for the parental cell line but the effects were more marked for the resistant cell lines. Our future work will also involve the use of clinical biopsies of ovarian cancer cases. Citation Format: Helen M. Coley, Laura Lattanzio, Ornella Garrone, Marco Merlano, Daniela Vivenza, Cristiana Lo Nigro, Nelofer Syed, Alistair Thompson, Bhavya Rao, Tim Crook. Splicing factors and the role of Navitoclax in drug-resistant ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3197. doi:10.1158/1538-7445.AM2017-3197