Targeting the MAPK/Hippo Interactions in Melanoma

Melanoma is the most lethal type of skin cancer with increasing incidence and low survival rates in advanced stages of the disease. Despite treatment advances for melanoma patients over the past decade, the development of treatment resistance is almost inevitable. Additionally, patients with melanoma driven by an NRAS mutation that represent around 20% of melanoma patients, have limited benefits from current treatment strategies. Work from our group and others have described kinase independent functions for the MAPK protein RAF-1, where it is able to regulate and inhibit pro-apoptotic signalling in cancer. In this study, we hypothesize that disrupting the anti-apoptotic kinase independent interactions of RAF-1 could be a novel targeted therapy option in melanoma. We addressed the aims of this study using molecular, computational and in vivo approaches. First, we defined the role of RAF-1 in melanoma cell lines with different driver mutations and assessed its impact on apoptosis and its regulation of the pro-apoptotic Hippo pathway. Next, we utilised small molecule disruptors that inhibit the RAF-1/Hippo interactions to investigate the role of RAF-1’s kinase independent activities under the different oncogenes. We then moved to generate an in vivo zebrafish melanoma model to facilitate our understanding of the regulation of the Hippo pathway downstream BRAF and NRAS mutations. Finally, we generated multi-omics datasets from zebrafish tumours that guided our analysis of patient data obtained from the TCGA. The data presented in this study confirms that the disruption of the RAF kinase independent interactions reactivates the Hippo pathway and triggers apoptosis in a cell dependent manner. Moreover, our findings in the zebrafish tumour analysis were further substantiated by the analysis of patient data, which have shown that the impairment of the Hippo pathway results in perturbations in vital cellular processes that contribute towards melanoma progression. Finally, our study demonstrates a proof of concept that describes the possible benefits associated with targeting the RAF-1 kinase independent interactions to reactivate central pro-apoptotic pathways in melanoma.