Defining and targeting the epigenetic programs involved in melanoma development

Ultraviolet radiation (UVR) exposure has long been linked to melanoma development, with clear correlations seen between latitude and the incidence of melanoma, particularly in individuals with fair skin and a poor ability to tan. As such, sporadic cutaneous melanoma has one of the highest mutational burdens of all cancers. The high mutational burden following UVR exposure is associated with increased neoantigen load and greater immune recognition. These observations suggest that the melanocytes that initiate melanoma survive UVR induced stress/cell damage and then avoid immune recognition. Unrelated studies in our lab focused on BRAF inhibitor resistance in melanoma identified a stress-activated epigenetic program mediated through histone deacetylase (HDAC)-8 that allowed escape from both cell death and immune recognition through transcriptional reprogramming. The objective of this proposal is to develop novel melanoma prevention strategies that target the epigenetic programs required for UVR-damaged melanocytes to avoid cell death and immune recognition. We will test the hypothesis that UVR-induced HDAC8 activation allows melanocytes to avoid cell death and immune attack, allowing cells with pathogenic mutations to survive and later develop into melanoma. This proposal is conceptually innovative in seeking to define the role of HDAC8 in the epigenetic reprogramming of melanocytes that experience UVR-induced stress and DNA damage. We will further address the role of immune evasion in the development of melanoma precursor lesions and will use unique mouse models, single cell RNA-Seq, and multi-Omics approaches to identify core pathways and regulators involved in the persistence of UVR-damaged melanocytes that constitute the precursor lesions for melanoma development. In Aim 1, we will define how HDAC8 modulates the transcriptional profile of melanocytes following UV-irradiation and will determine how this contributes to increased cell survival and reduced immunogenicity. We will then use our recently developed HDAC8 mouse model to demonstrate the role for HDAC8-induction in melanoma development and will perform single cell RNA-Seq and immune profiling to characterize how HDAC8 activation in melanocytes modulates the immune microenvironment of the skin. In Aim 2, we will determine whether inhibition of HDAC8 using genetic silencing or small molecule HDAC8 inhibitors reverses the survival and immune escape transcriptional programs that are activated in melanocytes following UVR exposure. In vivo studies will evaluate whether HDAC8 inhibitors or silencing of HDAC8 in mouse skin melanocytes are sufficient to delay the initiation of melanoma development in our BRAF mutant/PTEN-silenced melanoma model, and the role of the immune system in this response. At completion of this work we expect to have demonstrated the proof-of-principle for the development of HDAC8 inhibitors as a novel melanoma prevention strategy.