Sponsor: Else-Kröner Fresenius Stiftung

Metastatic malignant melanoma is a highly aggressive and chemoresistant skin cancer with poor clinical outcome. Significant breakthroughs in the treatment of this devastating disease have been achieved in the recent years. Small molecule inhibitors against the mutated BRAF or MEK kinases and antibody-mediate blockade of negative immune checkpoint molecules like CTLA-4 and PD-1/PD-L1 prolong overall survival rates, but acquired resistance to these targeted therapies is the major obstacle for long-term remissions despite profound initial responses. Recent studies including ours identified diverse mechanisms of resistance to signaling inhibitors and immunotherapies in melanoma. We found that phenotypic plasticity of melanoma cells caused by a proinflammatory tumor microenvironment represents a critical route to resist a targeted T-cell immunotherapy directed against melanocytic antigens through reversible dedifferentiation without the need for acquired secondary hardwired genetic aberrations (Landsberg, , Hölzel, Tüting. Nature 2012). In this project we aim to scrutinize our central hypothesis that rational multimodal regimens combining targeted signaling inhibition with immunotherapeutic approaches represent a strategy to combat genetic and non-genetic tumor heterogeneity to achieve more durable responses in melanoma.To accomplish this goal we exploited oncogene addiction to the MET receptor tyrosine kinase in our HgfxCdk4R24C murine melanoma model and implemented CRIPSR/Cas9 genome engineering to establish a rapid modular pipeline to probe clinically relevant determinants of responsiveness to multimodal immunotherapeutic regimens. We hypothesize that targeted inhibition of oncogenic MET signaling synergizes with a T-cell therapy directed against the gp100 melanocytic antigen and we will explore how phenotypic plasticity and genetically engineered gp100 loss variants interplay to resist this immunotherapy. We expect to provide novel insight into the dynamic evolution of genetic and non-genetic melanoma heterogeneity in a preclinical therapeutic in vivo model of combined MET signaling inhibition and immunotherapy. Our long-term goal is to delineate new strategies that can be translated to improved clinical care. As MET plays a critical role in other cancers like hepatocellular carcinoma and lung cancer, we are convinced that our findings will have implications beyond melanoma.