The overall goal of project 4 is to develop novel approaches distinct from ATP mimetics to overcome resistance to BRAF inhibitors for treatment of melanoma. This project will focus on two mechanisms of resistance;BRAF dimerization leading to paradoxical MAPK activation and STATS activation which is downstream of a number of parallel signaling pathways that are activated in BRAF inhibitor resistant cells as well as in BRAF^'"^ cells. We will also determine if combination of BRAF inhibitors with the inhibition of broad cellular biological properties that sustain survival of resistant tumor cells, specifically the stress response or autophagy, can kill melanomas and prevent the emergence of drug resistance. Together, we hypothesize that targeting these pathways will overcome therapeutic resistance in a large subset of BRAF mutant melanomas, and possibly other melanoma genotypes.
The Specific Aims of the proposal are to (1) Develop inhibitors that selectively target RAF dimers. Since BRAF inhibition can lead to paradoxical MAPK activation through RAF dimers in both normal tissues and in resistant melanoma tumors, we hypothesize that targeting RAF dimers will be more effective for melanoma therapy than targeting monomeric mutant BRAF. We will employ two complementary inhibitor design strategies to target RAF dimers and evaluate the biological activity of the resulting inhibitors. (2) Develop novel STAT3 inhibitors. STATS is activated in a high proportion of melanomas and is upregulated in response to BRAF and MEK inhibition. In preliminary studies, we have developed a family of quinolol/naphthol compounds that are low-micromolar inhibitors of STATS activation through the apparent binding to the SH2 phospho-binding domain of STATS. We will now use structure-based design and medicinal chemistry to prepare more potent and selective inhibitors and evaluate the biological activity of inhibitors alone and in combination with BRAF inhibitors. (3) Determine if combination of BRAF inhibitors with HSP70 or autophagy antagonists can kill melanomas and prevent the emergence of drug resistance. HSP70 is overexpressed in BRAF mutant melanoma and HSP70 inhibitors have shown promising pre-clinical efficacy in melanoma. High autophagy levels are also common in melanoma and correlate with poor response to chemotherapy and shortened overall survival;and BRAF inhibitors can induce autophagy as a survival mechanism. We hypothesize that dual inhibition of BRAF and HSP70 or autophagy will be an effective therapeutic strategy for melanoma. Together, we anticipate that these studies will provide novel and attractive avenues to overcome resistance to BRAF inhibition in melanoma in order to provide effective long-lasting therapies for melanoma patients.
In melanoma, the elevated activity of mutant BRAF kinase accounts for ~50% of malignant tumors. BRAF mutant selective inhibitors have extended the survival of patients in the clinic, however, most patients develop drug resistance causing the cancer to return. There is therefore a critical unmet need for novel approaches to overcome resistance to BRAF inhibitors. The goal of project 4 is to develop novel approaches to overcome resistance to BRAF inhibitors for treatment of melanoma. We anticipate that these studies will provide novel and attractive avenues to overcome resistance to BRAF inhibition in melanoma in order to provide effective long-lasting therapies for melanoma patients.
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