Targeting Lineage-specific MITF Pathway in Human Melanoma Cell Lines by A-485, the Selective Small-molecule Inhibitor of p300/CBP

Metastatic melanomais responsible for approximately 80 percent of deaths from skin cancer. Microphthalmia-associated transcription factor(MITF) is a melanocyte-specific transcription factorthat plays an important role in the differentiation, proliferation and survival of melanocytes as well as in melanomaoncogenesis. MITF is amplified in approximately 15% of metastatic melanomapatients. However, no small molecule inhibitors of MITF currently exist. MITF was shown to associate with p300/CBP, members of the KAT3 family of histone acetyltransferase(HAT). p300/CBP regulate a wide range of cellular events such as senescence, apoptosis, cell cycle, DNA damage response and cellular differentiation. p300/CBP act as transcriptional co-activators for multiple proteins in cancers, including oncogenic transcription factorssuch as MITF. In this study, we showed that our novel p300/CBP catalytic inhibitor, A-485, induces senescence in multiple melanomacell lines, similar to silencing expression of EP300(encodes p300) or MITF. We did not observe apoptosis and increase invasiveness upon A-485 treatment. A-485 regulates the expression of MITF and its downstream signature genes in melanomacell lines undergoing senescence. In addition, expression and copy number of MITF is significantly higher in melanomacell lines that undergo A-485-induced senescence than resistant cell lines. Finally, we showed that A-485 inhibits histone-H3acetylation but did not displace p300 at promoters of MITF and its putative downstream genes. Taken together, we provide evidence that p300/CBP inhibition suppressed the melanomadriven transcription factor, MITF and could be further exploited as a potential therapy for treating melanoma.