Abstract 2567: DIM regulates anoikis through sonic hedgehog in ovarian cancer cells

Abstract

Abstract Ovarian cancer is the second leading gynecological cancer with poor prognosis. By the time of detection, it usually metastasizes to peritoneum or organs such as stomach and liver. Detachment of a cell from extracellular matrix (ECM) allows the cells to travel and lodge at metastatic site. Anoikis is an emerging form of cell death that is associated with the apoptosis of cells detached from ECM. Normal or immortal epithelial cells are sensitive to anoikis. However, carcinomas are generally associated with resistance to anoikis. Hence, induction of anoikis is an important step in preventing metastasis. We have recently shown that diindolylmethane (DIM), a compound present in cruciferous vegetables reduces the survival of ovarian cancer cells by inducing apoptosis. Here, we evaluated the effect of DIM in inducing anoikis in ovarian cancer cells. A2780, SKOV-3 and OVCAR-429 cells were grown on low attachment plates and treated with various concentrations of DIM for 24 hours and analyzed. Our results show that DIM treatment resulted in the concentration-dependent anoikis in all the cell lines. For example, anoikis induction was approximately 50-70% in all the cell lines treated with 75µM DIM. Furthermore, Integrin Linked Kinase 1 (ILK-1), an important regulator of anoikis was significantly down-regulated by DIM treatment. Western blotting revealed cleavage of caspase-3 and PARP by DIM treatment, confirming anoikis induction in our model. Few recent studies showed that Sonic Hedgehog (Shh) pathway is activated in ovarian tumors. Shh pathway is also associated with metastasis of various cancers. We therefore next determined whether Shh pathway was involved in anoikis induction by DIM. Our results demonstrated that DIM treatment reduced the expression of Shh and Gli1 in a concentration-dependent manner. Moreover, Shh secretion as well was reduced by DIM treatment in ovarian cancer cells. Importantly, Shh pretreatment significantly inhibited DIM-induced anoikis in A2780 ovarian cancer cells. Treatment of cells with Shh also reduced the cleavage of caspase-3 or PARP induced by DIM treatment indicating the involvement of Shh pathway in anoikis. Taken together, these results suggest that DIM induces anoikis in ovarian cancer cells by regulating sonic hedgehog signaling. Further in-depth mechanistic studies are in progress to establish anoikis induction by DIM and to validate it in an in vivo model. [Supported in part by R01 grants CA 1065953 and CA 129038 awarded to S.K.S by National Cancer Institute, NIH] Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2567. doi:1538-7445.AM2012-2567