PT-141 (INN: Bremelanotide; brand name Vyleesi) is a synthetic cyclic heptapeptide with the sequence cyclo-[Nle4, Asp5, D-Phe7]-α-MSH(4-10). It is registered under CAS number 189691-06-3 and has a molecular formula of C₅₀H₆₈N₁₄O₁₀ with a molecular weight of 1025.17 g/mol. PT-141 was derived from Melanotan II (MT-II), a cyclic analogue of α-MSH, through structural optimization aimed at improving selectivity and pharmacokinetic properties.

PT-141 acts as a non-selective agonist of melanocortin receptors, with activity at MC1R, MC3R, MC4R, and MC5R. The melanocortin system is a complex neuroendocrine signaling network that regulates diverse physiological processes including skin pigmentation (MC1R), energy homeostasis and inflammation (MC3R), autonomic function and energy balance (MC4R), and exocrine gland function (MC5R). The broad receptor profile of PT-141 makes it a useful research tool for studying melanocortin system biology.

PT-141 received FDA approval in 2019 under the brand name Vyleesi for the treatment of hypoactive sexual desire disorder (HSDD) in premenopausal women — making it one of the few research peptides to have achieved regulatory approval. This regulatory history provides a clinical pharmacology data package that supports its use as a research tool for studying MC4R-mediated central nervous system pathways.

Research applications for PT-141 include studies of melanocortin receptor pharmacology, central nervous system melanocortin signaling, and the downstream effects of MC4R activation on autonomic function and behavior in preclinical models. In vitro applications include receptor binding assays, cAMP accumulation assays in cells expressing individual melanocortin receptor subtypes, and studies of receptor internalization and trafficking.