Abstract 1680: ARHI-induced autophagy enhances chemosensitivity to cisplatin in ovarian cancer cell lines and xenografts.

Autophagy can protect or kill tumor cells depending upon the context. Our group has found that autophagy and tumor dormancy can be regulated by an imprinted tumor suppressor gene, ARHI (DIRAS3), which is downregulated in 60% of ovarian cancers. Re-expression of ARHI induces autophagy by inhibiting PI3K and mTOR signaling, displacing Bcl-2 from Beclin to form the autophagy initiating complex, inducing ATG4 and decorating the autophagosome membrane, co-localizing with LC3II. Re-expression of ARHI in cell culture produces cell death within 72 hours, whereas re-expression of ARHI in xenografts produces cell growth arrest and tumor dormancy. When ARHI levels are reduced after 6 weeks of induction, xenografts grow promptly. Outgrowth can be delayed if dormant cancers are treated with chloroquine, a functional inhibitor of autophagy, suggesting that autophagy is a survival mechanism in this context. Our current experiments were designed to determine whether autophagic cells could be eliminated more or less readily by treatment with cisplatin with or without chloroquine. In short-term or long-term cell culture, induction of ARHI enhanced the cytotoxic effect of cisplatin and tumor cell killing was further enhanced by the addition of chloroquine. In xenografts, treatment with cisplatin slowed the outgrowth of dormant autophagic ovarian cancer cells, but the addition of chloroquine did not further inhibit xenograft growth. In cell culture, caspase 3/8 release and Anexin V expression on the surface of ovarian cancer cells can account for enhancement of caspase dependent apoptosis observed when autophagic ovarian cancer cells are treated with cisplatin. Treatment of ARHI-induced autophagic ovarian cancer cells with chloroquine and cisplatin downregulated the expression of survivin, XIAP and Bcl-2. Re-expression of ARHI induced caspase dependent apoptosis and autophagic cell death in the absence of cisplatin. ARHI-induced apoptosis and autophagic cell death could be blocked by Z-VAD that inhibits caspase mediated apoptosis and by stable knockdown of ATG5 that inhibits autophagy. In this context, induction of autophagy enhanced platinum toxicity. Additional treatment with chlorooquine produced additional cancer cell cytotoxicity in cell culture, but not in dormant xenografts. These preclinical studies do not support the addition of chloroquine to platinum based chemotherapy for ovarian cancer in the clinic, but do support the association of “autophagic” cell death with apoptosis. Citation Format: Michele N. Washington, Grace Suh, Aaron F. Orozco, Maojie Yang, Yan Wang, Neely Atkinson, Warren Liao, Zhen Lu, Robert Bast. ARHI-induced autophagy enhances chemosensitivity to cisplatin in ovarian cancer cell lines and xenografts. [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 1680. doi:10.1158/1538-7445.AM2013-1680