Abstract 1833: A large-scale synthetic lethal RNAi screening identifies unique sensitizing targets for anti-inflammatory CDDO-Me in metastatic melanoma

Abstract

Abstract Metastatic melanoma is the most lethal form of skin cancer strongly associated with the inflammatory process by secreting high levels of proinflammatory cytokines and producing reactive oxygen and nitrogen species. Chronic inflammation is considered as a major factor to promote the tumor microenvironment in advantage of resistance to radiation, chemotherapy, and biotherapy for metastatic melanoma. CDDO-Me, a novel synthetic triterpenoid, has been shown to exert potent anti-inflammatory and antitumor activity by decreasing oxidative stress and the production of pro-inflammatory molecules, such as Nrf2 and iNOS, in several tumor models. CDDO-Me is presently under evaluation in clinical studies for chronic kidney disease and pancreatic cancer. Here, we used CDDO-Me as a primary agent to inhibit metastatic melanoma growth. In order to improve CDDO-Me response in melanoma cells, we utilized a large-scale synthetic lethal RNAi screen with 24,000 siRNAs targeting ∼6,000 human druggable genes to identify targets that when silenced would sensitize melanoma cells to CDDO-Me. Results from the screens identified twenty of siRNA pools that significantly potentiated the growth inhibitory effects of CDDO-Me in A375 cells. We selected five unique genes, GNPAT, SUMO1, SPUNT2, FLI1, and SSX1, which have not been addressed as drug targets in melanoma before, for target validation and functional analysis in four metastatic melanoma and control cell lines. Specific siRNA against each of these five genes could substantially sensitize four tested melanoma cells to CDDO-me by increasing the growth inhibition and induction of apoptosis, while treatment with nontarget siRNA resulted in no change compared to the treatment with CDDO-Me only. Further studies of downstream signaling revealed that these five genes involved in regulating melanoma cell proliferation and cell death. We identified for the first time that the levels of phosphorylated Erk1/2, Akt, GSK-2, and PRAS40, were dramatically decreased by individual siRNA against GNPAT, SUMO1, SPUNT2, FLI1, and SSX1. Our findings indicate that GNPAT, SUMO1, SPUNT2, FLI1, and SSX1 may play critical roles in synergy with inflammation pathways in modulating melanoma cell survival, which could serve as sensitizing targets to enhance CDDO-Me efficacy in melanoma. Supported by MDACC SPORE in Melanoma P50CA093459. 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 1833. doi:1538-7445.AM2012-1833