Abstract 2121: Studies on antitumor effects of bithionol on ovarian cancer cells.

Introduction: ‘Drug Repurposing’ promises to be a successful concept for the treatment of many diseases. We focused on Bithionol (BT), a clinically approved antiparasitic drug for use as a therapeutic agent against ovarian cancer. BT has been shown to inhibit solid tumor growth in several preclinical cancer models by targeting autotaxin (ATX). Methods: In the present study, we determined the anti-tumor effect of BT and its mechanism of action against a panel of ovarian cancer cell lines. First, we studied the cytotoxic effect of BT against a panel of ovarian cancer cell lines (A2780 & A2780-CDDP OVACAR-3, SKOV-3, IGROV-1, and IGROV-1CDDP). We identified the type of cell death i.e. apoptotic vs. necrosis, and examined markers of apoptosis and necrosis. Mechanism(s) of action were studied in terms of reactive oxygen species (ROS) generation, autotoxin (ATX) inhibition and MAPK signaling. In addition, we studied the sensitizing effect of BT on cisplatin cytotoxicity. Results: Our results have shown that BT causes dose dependent cytotoxicity against all the cell lines tested with IC 50 values ranging from 20μM - 60μM. The order of ranking in terms of sensitivity to BT is A2780 > SKOV-3 > OVACAR-3>, IGROV-1. Cisplatin resistant variants of A2780 and IGROV-1 have shown almost similar IC 50 values to their sensitive variant. Apoptotic cell death was observed at low concentration and early time points whereas necrosis was observed at high concentrations and later time points. Apoptotic cell death was shown by expression of caspases 3,7, increased homogenous caspases 3/7 activity, loss of mitochondrial potential, cPARP expression, DNA condensation, up-regulation of p38 and down regulation of XIAP. At higher concentrations, BT caused down-regulation of caspases3/7 activity and increased LDH activity indicative of necrosis. Sensitization studies with BT showed that pre-treatment of ovarian cancer cell lines with BT for 24 hrs enhanced cisplatin cytotoxicity by 20 - 80%. Interestingly, cisplatin resistant variants of A2780 and IGROV-1 were more sensitive to cisplatin upon BT pre-treatment as compared to their sensitive variants. The order of ranking in terms of enhanced sensitivity to cisplatin upon BT pre-treatment was A2780-CDDP > A2780 > OVCAR-3 > IGROV-1CDDP > IGROV-1 >SJOV-3. BT treatment resulted in increased ROS generation. Treatment with antioxidant ascorbic acid resulted in partial restoration of cell viability. In addition, dose and time dependent inhibition of ATX was observed. Conclusions: Our results demonstrate the cytotoxic effect of BT on various ovarian cancer cells and the mechanism of actions appears to be partly via ROS generation and inhibition of ATX. Pre-treatment with BT resulted in enhanced cytotoxicity to cisplatin especially in cisplatin resistant variants. In view of these results, BT can be an effective adjunct agent along with cisplatin for ovarian cancer treatment. Citation Format: Vijayalakshmi N. Ayyagari, Laurent Brard. Studies on antitumor effects of bithionol on ovarian cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2121. doi:10.1158/1538-7445.AM2013-2121