Impact of Endogenous DOPA Signaling on Melanocyte Homeostasis and Melanoma Susceptibility

点击翻译按钮获取中文摘要

Abstract The risk of melanoma is substantially higher in people with lightly pigmented skin, compared to those with darkly pigmented skin. While this discrepancy is traditionally attributed to the ultraviolet radiation shielding effect of melanin pigment, there is accumulating evidence suggesting that this may not account for the totality of these differences. Our preliminary data show that high levels of baseline pigmentation in melanocytes correlates with inhibited proliferation and limited tumorigenic potential. This effect appears to result not from melanin itself, but rather, from the melanin synthesis intermediate dihydroxyphenylalanine (DOPA). In light melanocytes and melanoma cells, addition of exogenous DOPA induced a more differentiated cell state as defined by increased expression of well-established melanocyte differentiation antigens, increased pigment production, decreased proliferative capacity, and decreased expression of c-Myc and FOXM1, which are critical proliferation-associated transcription factors that are overexpressed in many cancers. Our results indicate that DOPA likely inhibits the cholinergic receptor muscarinic 1 (CHRM1), which is a Gq coupled G Protein-Coupled Receptor that seems to promote melanoma proliferation. Genetic ablation of CHRM1 blocked DOPA’s anti-proliferative effect, while overexpression of CHRM1 in melanoma cell lines with low baseline CHRM1 promoted and also rendered cells newly sensitive to DOPA. In Aim 1 we will validate pilot data suggesting that CHRM1 mediates DOPA effects in primary melanocytes and melanoma, and use a new bioluminescence resonance energy transfer (BRET) biosensor platform to define the signaling mechanisms by which CHRM1 and DOPA impact melanocyte function and melanoma proliferation. In Aim 2 will we will use medically relevant preclinical melanoma models to test the idea that pharmacologic CHRM1 antagonism inhibits melanoma in vivo, both as monotherapy, and in combination with standard of care immune and targeted melanoma therapeutics. For this we will use stemically delivered DOPA/carbidopa, a currently FDA-approved drug combination for Parkinson’s disease, which in pilot studies was well tolerated and effectively inhibited melanoma growth mouse models. Together this work will define a mechanistic link between skin pigmentation, melanoma risk, DOPA and CHRM1, and is likely to provide critical preclinical in vivo data that would support new human trials to test the efficacy of repurposing a Parkinson’s disease drug as a melanoma therapeutic.