Abstract 4722: Targeted inhibition of SIRT1 histone deacetylase by small-molecule inhibitor Tenovin-1 imparts significant anti-proliferative effects in human melanoma cells
Authors: Singh Chandra K. , Wilking Melissa J. , Nihal Minakshi , Ahmad Nihal 
Published: August 2012

Abstract
Melanoma, one of the most lethal forms of skin cancer, remains resistant to available treatments. Unfortunately, current treatment options are insufficient for preventing the rapid metastasis and death associated with this disease. Thus, additional target-based approaches are needed for the management of this neoplasm. SIRT1, a member of mammalian sirtuin-family and a class III histone deacetylase has been implicated in several cancers. SIRT1 plays an important role in cell survival, as it is involved in DNA repair and inhibits apoptosis and cellular senescene in response to oxidative stress and DNA damage. It also favors cell survival through its regulation of the FOXO transcription factors and the tumor suppressor gene p53. Previous studies from our laboratory have demonstrated that i) histone deacetylase SIRT1 is expressed at much higher levels in melanoma cells than in normal human epidermal melanocytes, and ii) inhibition of SIRT1 through shRNA-mediated RNA interference or sirtinol-mediated activity inhibition resulted in decreased growth, viability, and clonogenic survival of melanoma cells (Nihal et al; In: AACR Annual Meeting: Proceedings; 2011 Apr 2-6, Orlando, FL Abstract # 1647). Here, in order to determine if SIRT1 is a viable target for melanoma management, we extended our studies to determine the effects of Tenovin-1, which is a more specific and efficient small molecule inhibitor of SIRT1, in multiple melanoma cell lines, representing different stages of disease progression. For this purpose, we employed i) A375 (primary and vertical-growth tumorigenic) and HS294T (metastatic and tumorigenic), both of which are amelanotic cell lines, and ii) G361 (metastatic and tumorigenic) melanin-producing cell line. We determined the effects of Tenovin-1 on the expression levels of SIRT1 protein in melanoma cells. Our data demonstrated that Tenovin-1 treatment resulted in a dose dependent decrease in the level of SIRT1 protein in all the melanoma cell lines tested. Further, we found that Tenovin-1 treatment resulted in a concentration dependent decrease in the growth and viability of melanoma cells, as shown by Trypan blue exclusion and MTT analyses. Furthermore, we found that Tenovin-1 caused an increase in protein level of the tumor suppressor p53 in a concentration-dependent fashion. Taken together, our results suggested that Tenovin-1 reduces melanoma cell growth via inhibition of SIRT1 and subsequent increase in p53 activity. However, additional studies are needed to confirm our results and to further establish the mechanism of how Tenovin-1 mediated SIRT1 inhibition leads to melanoma cell death. This includes the evaluation of other known SIRT1 targets such as the FOXO transcription factors. Finally, in vivo studies are also required to further determine the clinical relevance of our findings.
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 4722. doi:1538-7445.AM2012-4722