Melanotan II

Melanotan II is a synthetic cyclic lactam analog of alpha-melanocyte stimulating hormone (α-MSH), developed at the University of Arizona. It was designed with increased potency and prolonged activity compared to the linear native hormone. The peptide is a non-selective melanocortin receptor agonist, activating MC1R, MC3R, MC4R, and MC5R with varying affinities.

It was developed in photoprotection research. Because it also activates MC3R and MC4R, it is used to study central melanocortin pathways as well as pigmentation, a broader profile than more selective analogs.

Melanotan II acts through multiple melanocortin receptors:

MC1R Activation (Pigmentation) The primary mechanism for melanogenesis. MC1R activation on melanocytes triggers a cAMP-dependent cascade that increases tyrosinase activity and melanin production. This shifts the melanin ratio toward eumelanin (brown/black pigment) rather than pheomelanin (red/yellow).

MC4R Activation (Central Pathways) Activation in the hypothalamus and limbic regions affects central melanocortin signalling. Work on this receptor led to the more selective analog PT-141.

MC3R/MC4R (Appetite/Metabolism) These receptors in the hypothalamus are involved in energy homeostasis. Their activation is studied in models of food intake and energy balance.

Prolonged Activity The cyclic lactam structure and amino acid substitutions (notably D-Phe and Nle) protect against enzymatic degradation, extending the duration of action compared to native α-MSH.