Phenylarsine oxide induces apoptosis in Bax and Bak deficient cells through upregulation of Bim Running title: PAO induces Bax/Bak-independent apoptosis

Purpose: Bax and Bak are regarded as key mediators for cytochrome c release and apoptosis. Loss of Bax or Bak is often reported in human cancers and renders resistance of these cancerous cells to chemotherapy. Here we investigated that phenylarsine oxide (PAO) could induce Bax/Bak-independent apoptosis. Experimental Design: Annexin V/PI staining, TUNEL staining and Caspase activation assays were performed to detect apoptosis in Bax/Bak deficient MEFs and HCT116 bax colorectal cancer cells. Cytochrome c release and Bim expression were assessed by Western blotting and immunostaining. Bim was stably knocked down by shRNA. Immunoprecipitation was applied to detect the interaction between Bim and Bcl-2. Both subcutaneous and colorectal orthotopic tumor implantation models were used in nude mice to investigate the effect of PAO in vivo. Results: PAO triggered cytochrome c release and apoptosis in a Bax/Bak-independent manner. Bim and Bcl-2 were both involved in this process. PAO augmented the expression of Bim and strengthened the interaction between Bim and Bcl-2. Furthermore, PAO attenuated the growth of Bax deficient cancer cells in vivo. Conclusions: Our results demonstrated that PAO induced apoptosis in chemotherapy-resistant cancer cells, which suggests that PAO has the potential to serve as a chemotherapeutic agent for Bax and Bak deficient cancers. Translational Relevance It has been well known that both bax and bak genes are frequent targets for mutation in a subset of human tumors. Loss or inactivation of Bax or Bak is considered as a mechanism of protection of cancer cells against apoptosis, and these cancers are largely resistant to chemotherapy. We demonstrated in this study that PAO induced apoptosis in Bax deficient colorectal cancer cells which are drug resistant. PAO also attenuated the growth of these cells in subcutaneous and orthotopic xenograft tumors without significant converse effects on nude mice. These all indicate that PAO has potential value for development in the therapy of Bax/Bak inactivation cancers. Bim and Bcl-2 were both involved in this process, which provides new targets in overcoming drug resistance during cancer therapy. Research. on April 28, 2017. © 2011 American Association for Cancer clincancerres.aacrjournals.org Downloaded from Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. Author Manuscript Published OnlineFirst on November 2, 2011; DOI: 10.1158/1078-0432.CCR-10-3450