Oncogenic signalling in BRAF/RAS wild type melanoma

Selective inhibition of the mitogen-activated protein kinase (MAPK) pathway has significantly improved the survival of patients with BRAF V600 - mutant advanced melanoma. However, BRAF / RAS wild type (WT) melanomas have no known actionable mutations, and immune checkpoint inhibitors remain the only effective therapy for patients with this melanoma subtype. In this PhD project, we explored the signalling activity and response of BRAF / RAS WT melanomas to combination small molecule inhibitors. In Chapter 2, we investigated MAPK dependency in 23 melanoma cell lines, including 10 BRAF V600 - mutant and 13 BRAF / RAS WT (seven NF1 - mutant and six triple WT) melanomas. Melanoma cell lines were treated with the MEK inhibitor trametinib, and the impact of MEK inhibition on cell survival and proliferation were examined. We showed that BRAF / RAS WT melanomas had variable responses to MEK inhibition; 23% were highly sensitive, indicating dependency on MAPK signalling for survival and proliferation, whereas 38% were resistant, and this was commonly associated with high mutation burden and loss - of - function mutation s in NF1. We demonstrated that NF1 loss conferred MEK inhibitor resistance in BRAF V600 - mutant cells but not in BRAF / RAS WT melanomas. The mutational profiles of BRAF / RAS WT melanomas revealed concurrent mutations in RASopathy genes, and enrichment of TP53 mutations. In Chapter 3, we explored the precise contribution of p53 loss to MEK inhibitor resistance in our panel of melanoma cells. We also examined the efficacy of a p53 activator in combination with MEK inhibition on suppressing melanoma proliferation. Finally, in Chapter 4, the activity of oncogenic signalling pathways in BRAF/RAS WT melanoma cell lines was examined and the activity of combination inhibitors targeting activated cascades w as tested .