Abstract 88: Targeting Bcl-XL enhances arsenic-induced cell death in ovarian cancer cells

Abstract

Abstract Autophagy is an evolutionary conserved process in which long-lived proteins and damaged organelles are digested under physiological conditions including starvation. Autophagy has also been shown to act as a programmed cell death mechanism (type II PCD) and considered as caspase independent cell death. Several studies showed that autophagy has been triggered by anti-cancer treatments, such as chemo and hormonal therapy and radiotherapy and growth factor deprivation, function either as a protective survival pathway or cellular death mechanism. Arsenic trioxide (ATO), which is a FDA approved drug and used as a treatment in acute promyelocytic leukemia, has been reported to induce autophagic and/or apoptotic cell death in leukemia, glioblastoma and also ovarian cancer cells, we have previously found that ATO induces autophagy in ovarian cancer cells. Here, we investigated the role of antiapoptotic protein Bcl-Xl, which inhibits autophagy by binding beclin-1, an essential autophagy promoting protein, in arsenic induced apoptosis and determined the effects of ATO/Bcl-XL RNA interference combination therapy in ovarian cancer. We found that ATO induces dose dependant growth inhibition in MTS proliferation assay. ATO treatment (2-4 uM) induced apoptosis in A2780 (40-50 %) and SKOV3 (20-25 %) cells, detected by annexin V staining and flow cytometric (FACS) analysis and by caspase 9 and PARP cleavage (Western blotting). ATO induced marked autophagy in A2780 (60-70 %) and in SKOV3 (15-20 %) as indicated by LC3-II, a marker for autophagy, formation autophagic vacuoles detected by acridine orange staining and FACS and by transmission electron microscopy. ATO induced Bcl-XL protein expression in ovarian cancer cells. We also found expression of high levels of Bcl-XL in all ovarian cancer cell lines including drug (i.e., cisplatin and paclitaxel) resistant cells. Inhibition of Bcl-XL expression by Bcl-XL siRNA induced growth inhibition (40-60 %), apoptosis (40-60 %) and autophagy (50-60% in A2780 and 15-25 % in SKOV3 ovarian cancer cell line). Furthermore, combination of ATO with Bcl-XL siRNA led to 90 % cell death and 70 % apoptosis in both A2780 and SKOV3 cells. Overall, our results suggest that combination of ATO and Bcl-XL induced predominantly apoptosis, although each of them induced autophagy. In conclusion we provided first evidence that inhibition of Bcl-XL induces autophagy in ovarian cancer cells and sensitizes them to ATO that may be a promising treatment regimen for ovarian cancer patients. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 88.