A new perspective in melanoma treatment: Melanocortin receptor 4 antagonist in association with B-Raf inhibitor Vemurafenib

The melanocortin receptor subtype 4 (MC4R) is expressed in various human cells such as skin melanocytes, astrocytes, and neural progenitor cells1.Our aim is to evaluate the role of MCR4 as a novel target in melanoma therapy, using a selective antagonist ML00253764 (ML) alone and in combination with the B-Raf V600E inhibitor Vemurafenib.We employed the human melanoma B-Raf mutated A-2058 and WM 266-4 cell lines, while the CRISPR/Cas9 system was used to eliminate the MCR4 gene in the A-2058 cell line (MCR4 null).MC4R protein expression in melanoma cells was then tested though immunohistochemistry, immunofluorescence, and western blotting, while BCL-XL and ERK1/2 phosphorylation were assessed via western blotting.For the in vivo experiments, Athimic nude-Foxn1nu male mice were utilised, weights and tumour dimensions were checked every 2-3 days. The mice were then divided in 3 groups: ML, Vemurafenib and their combination. Tumour slices were stained, and necrosis and mitotic indices were calculated, and DNA damage (Comet and Cytome assays).The results show the expression of functional MC4R in human melanoma cell lines and in tissue samples. The selective antagonist ML induces apoptosis via the decrease of ERK1/2 phosphorylation and a decline in BCL-XL. Moreover, the combination of Vemurafenib and ML caused a synergistic antiproliferative effect in vitro and in vivo, without any presence of weight loss or genotoxicity.These data open yet unexplored fields in antineoplastic research for tumours derived from cells that normally express functional MCR4, such as human skin melanocytes.Reference:Giuliani et.al, Prog. Neurobiol. 2017https://doi.org/10.1016/j.pneurobio.2016.11.004