Melanotan 2

Melanotan 2 (MT-2) is a synthetic cyclic heptapeptide analog of alpha-melanocyte-stimulating hormone (α-MSH), developed at the University of Arizona by Hruby and Hadley. Unlike the linear Melanotan 1, MT-2 is a lactam-bridged cyclic peptide with a constrained conformation that gives it broad melanocortin receptor activity, agonizing MC1R, MC3R, MC4R, and MC5R. This non-selective melanocortin receptor profile results in multiple biological activities: MC1R activation promotes melanogenesis (pigmentation), MC4R activation has been associated with sexual function and appetite modulation, and MC3R activation influences energy homeostasis. MT-2’s development at Arizona led to the creation of bremelanotide (PT-141), a related compound approved by the FDA for hypoactive sexual desire disorder. MT-2 is more potent on a molar basis than MT-1 at several melanocortin receptors and has a different pharmacological profile due to its cyclic structure and broader receptor activity.

Melanotan 2 has been investigated for its non-selective agonist activity across multiple melanocortin receptors. At MC1R, MT-2 activates Gs-coupled cAMP signaling in melanocytes, promoting eumelanin synthesis through MITF and tyrosinase induction. At MC4R, expressed in the paraventricular nucleus and other CNS regions, MT-2 activates pathways involved in sexual arousal and erectile function — researchers observed that MC4R signaling stimulates oxytocinergic neurons that project to spinal centers controlling erectile tissue. At MC3R, MT-2 modulates energy homeostasis signaling in hypothalamic neurons. The cyclic lactam bridge between Asp and Lys residues constrains MT-2 into a beta-turn conformation that optimizes binding across melanocortin receptors. Studies suggest that this broad receptor profile accounts for the multiple reported effects of MT-2, including melanogenesis, appetite modulation, and sexual function changes. The non-selectivity of MT-2 was a key motivation for developing more selective melanocortin receptor agonists like bremelanotide.

Development and Characterization

Al-Obeidi et al. (1989) described the design and synthesis of Melanotan 2, characterizing its cyclic structure and enhanced potency at melanocortin receptors compared to linear α-MSH analogs [1].

Sexual Function Research

Wessells et al. (1998) investigated MT-2 in male subjects and observed dose-dependent changes in erectile function parameters. This study established MC4R-mediated sexual function as a key pharmacological activity of non-selective melanocortin agonists [2].

Melanogenesis

Dorr et al. (1996) characterized MT-2’s melanogenic activity in human subjects, demonstrating increased skin pigmentation following subcutaneous administration [3].