Setmelanotide

Grehlin and other hunger signals from the gastrointestinal tract stimulate orexigenic neurons, stimulating the release of agouti-related protein. Agouti-related protein inhibits melanocortin 4 receptor (MC4R) activation until satiety signals such as insulin or leptin stimulate anorexigenic neurons. Insulin and leptin stimulate production of the POMC-derived melanocortin peptide α-melanocyte simulating hormone, which is a ligand of MC4R.

Orexigenic and anorexigenic neurons contain prohormone convertase 1/3 (PC1/3), which is encoded by the gene proprotein subtilisin/kexin type 1. PC1/3 preforms activation cleavage of a number of peptide hormone precursors, including α-melanocyte simulating hormone.

Setmelanotide is a pro-opiomelanocortin derived peptide that is an agonist of MC4R. It is an approximately 20-fold more potent agonist of MC4R than endogenous α-melanocyte stimulating hormone, with an EC50 of 0.27 nM. By directly agonizing MC4R, upstream genetic deficiencies in the MC4R signalling pathway cannot inhibit satiety, food intake is decreased, and weight loss is achieved.

MC4R is a 332 amino acid G-protein coupled receptor (G-PCR). Although the lack of cardiovascular adverse effects with setmelanotide treatment are not well understood, it is believed that earlier MC4R antagonists activated multiple G-protein signalling pathways. Earlier drugs that targeted G-PCRs either bound with high affinity to the highly conserved orthosteric binding site, or with high specificity to less conserved allosteric sites. Setmelanotide is an atypical bitopic ligand that interacts with both the orthosteric and putative allosteric binding site, allowing for both high affinity and specificity.