810 Topical application of self-delivering RNAi (sd-rxRNA®) compounds for reduction of hyperpigmentation

Abstract

Metastatic melanoma is a deadly skin cancer with limited therapeutic options. Although targeted-and immuno-therapeutics led to a paradigm shift in melanoma management, resistance to these drugs necessitates identifying new targets. We demonstrated that constitutive activation of NLRP inflammasome is responsible for autoinflammation in human melanoma. Autoinflammation has been linked to tumorigenesis and drug resistance in cancers. Among NLRP proteins, NLRP1 is unique because it contains the caspase recruitment domain (CARD), a homotypic protein interaction motif. Knocking down NLRP1 revealed a tumor promoting property of NLRP1 in metastatic melanoma in vitro and in vivo. While NLRP1 did not affect cell cycle, it inhibited caspase-2,-9, and-3/7 activities and apoptosis in melanoma cells. NLRP1, caspase-2 and-9 all contain a CARD which facilitates protein binding through CARD homodimerization. Co-IP confirmed the interaction of NLRP1 with caspase-2 and-9 in melanoma. We activated NLRP1 inflammasome because its activation has been reported to induce apoptosis and pyroptosis in macrophages. Whereas NLRP1 inflammasome activation increased caspase-2,-9 and-3/7 activities and induced pyroptosis and apoptosis in monocytic THP-1 cells, it reduced apoptotic caspase activities and provided protection against cell death in melanoma cells. To understand the differential effects of active NLRP1 inflammasome on apoptosis, we evaluated cellular localization of NLRP1. Unlike THP-1 with prominent nuclear localization of NLRP1, melanoma cells expressed NLRP1 mainly in the cytoplasm where NLRP1 inflammasome is assembled with inflammatory caspase-1, and NLPR1 interacts with apoptotic caspase-9. Thus, we demonstrated that melanoma NLRP1 has an anti-apoptotic activity, leading to tumor promotion and cell survival in metastatic melanoma.