Abstract 4028: ARHI plays a critical role in ovarian cancer tumor dormancy by inhibition of angiogenesis switch
Authors: Lu Zhen , Mao Weiqun , Wang Yan , Levine Douglas A. , Bast Robert C. 
Published: August 2015

Each year in the US, more than 22,000 women develop ovarian cancer. Despite progress in surgery and chemotherapy, the disease still proves lethal in 70% of cases. One of the most important factors contributing to poor outcomes is the ability of drug resistant ovarian cancer cells to remain dormant for years after treatment, only to grow progressively and kill their host. Judging from sites of recurrence, most dormant ovarian cancer cells are found on the surface of the peritoneal cavity, often in small, poorly vascularized collagenous scars observed at “second look” operations. 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 associated with necroptosis, whereas re-expression of ARHI in xenografts produces cell growth arrest and tumor dormancy. Our current experiments were designed to determine whether ARHI inhibition of angiogenesis could play an important role in tumor dormancy in ovarian cancer. By analysis of cell culture lysates from SKOv3-ARHI ovarian cancer cells with antibody array, we confirmed that induction of ARHI reduces VEGF, bFGF and TIMP1 pro-angiogenic protein expression and increases anti-angiogenic TSP-1. In line with this, co-culture of human ovarian SKOv3-ARHI cells with 2H11 murine endothelial cells stimulated the formation of murine endothelial tubes. Addition of exogenous bFGF enhanced endothelial tube formation, while induction of ARHI markedly decreased tube formation associated with a decrease in bFGF. Furthermore, by immunohistochemical staining dormant (DOX) SKOv3-ARHI xenografts, we demonstrated that Induction of ARHI in human cancer xenografts was associated with lower Ki 67 and MVD. Similarly, Ki67 and MVD were measured in primary human ovarian cancers and in matched positive second look specimens from archival clinical specimens (Memorial Sloan Kettering Cancer Center). Second look specimens exhibited significantly lower Ki-67 (P&lt;0.0001) and MVD (P&lt;0.0001) than did primary cancers. Altogether, our data suggested that ARHI plays a critical role in ovarian cancer tumor dormancy by inhibition of angiogenesis switch. Our better understanding of tumor cell dormancy will lead to novel detection techniques in the clinic and therapeutic options to prevent deadly tumor recurrence and metastasis.

Citation Format: Zhen Lu, Weiqun Mao, Yan Wang, Douglas A. Levine, Robert C. Bast. ARHI plays a critical role in ovarian cancer tumor dormancy by inhibition of angiogenesis switch. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4028. doi:10.1158/1538-7445.AM2015-4028