Abstract 1647: Role of Sirt1 histone deacetylase in melanoma: A target for melanoma management via its inhibition

Abstract

Abstract Melanoma is one of the most aggressive skin cancers that rapidly metastasizes and is often lethal, if not diagnosed early. The available preventive strategies and treatment options have not been able to effectively manage melanoma. Therefore, novel mechanisms and target-based approaches are needed to combat this deadly neoplasm. A detailed understanding of genetic controls of cellular proliferation and cell division may provide the basis for the rational design of specific targets and therapeutic strategies for melanoma management. This study was designed to test the hypothesis that Sirt1 is differentially expressed in melanoma and could be used as a target for designing novel approaches for the management of this neoplasm. Sirt1 is the most well studied member of the Sirtuin (Sir2) family enzymes, which are nicotinamide adenine dinucleotide-dependent class III histone deacetylases, and have been shown to deacetylate lysine residues on various proteins. Sirt1 has been shown to be involved in a number of cellular processes including gene silencing, DNA repair, recombination, and stress response. Sirt1 also regulates the tumor suppressor p53 and FoxO transcription factors to favor cell survival. To test and support our hypothesis, we determined the expression of Sirt1 in a variety of melanoma cell lines (A375, Hs294T and G361) and normal human epidermal keratinocytes (NHEKs) and normal human melanocytes (NHEMs). We found that compared to normal NHEK and NHEM, Sirt1 was significantly overexpressed at protein (immunoblot analysis) as well as mRNA levels (Real-Time PCR analysis) in all melanoma cell lines tested. In order to determine the functional significance of Sirt1 in human melanoma cells, we determined the effect of Sirt1 knockdown on melanoma cells employing two distinct approaches viz. i) chemical knockdown of Sirt1 enzyme via small molecule inhibitors, and ii) genetic knockdown of Sirt1 gene via short hairpin RNA (shRNA)-mediated RNA interference. We found that shRNA-mediated knockdown as well as small-molecule-mediated activity inhibition resulted in a significant decrease in the viability and growth of melanoma cells. In addition, Sirt1 inhibition was also found to result in a significant decrease in clonogenic survival of melanoma cells. Taken together, our study suggested that i) Sirt1 overexpression could be a contributing factor in human melanoma development and/or progression, and ii) Sirt1 could serve as a potential target towards developing novel strategies for the management of this lethal skin cancer. However, future studies in appropriate in vitro and in vivo systems are needed to substantiate our findings and to define the mechanism(s) by which Sirt1 imparts a growth advantage to melanoma cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1647. doi:10.1158/1538-7445.AM2011-1647