Melanotan 2 (MT-II): A Cyclic Melanocortin Receptor Agonist Studied in Pigmentation, Appetite, and Sexual-Behaviour Models

Research summary. Melanotan 2 (MT-II) is a synthetic cyclic heptapeptide analogue of α-melanocyte-stimulating hormone (α-MSH). It was developed in the 1980s at the University of Arizona during a research programme exploring melanocortin receptor pharmacology and photoprotective pigmentation. Compared with native α-MSH, MT-II is more metabolically stable, more potent, and broadly active across the melanocortin receptor family — it is therefore a non-selective agonist, which explains both its broad activity profile and its broad side-effect profile in research models.

Molecular profile

• Sequence: Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH₂ (lactam-bridged cyclic heptapeptide)
• Molecular formula: C₅₀H₆₉N₁₅O₉
• Molecular weight: ~1024.2 g/mol
• PubChem CID: 92432
• CAS Number: 121062-08-6
• Class: Non-selective melanocortin receptor agonist (MC1R, MC3R, MC4R, MC5R)

Mechanism of action

MT-II is a non-selective agonist at the melanocortin receptor family, with appreciable activity at MC1R, MC3R, MC4R, and MC5R. Each receptor is associated with a distinct downstream phenotype:

• MC1R (melanocytes): activation drives eumelanin synthesis, the basis of MT-II's well-known pigmentation activity.
• MC3R / MC4R (CNS, hypothalamus): activation modulates feeding behaviour, energy expenditure, and sexual-behaviour circuits.
• MC5R (exocrine tissues): activation is associated with sebaceous and sweat-gland output in research models.

The cyclic-lactam architecture confers proteolytic resistance and extended duration of action compared with native α-MSH. Because MT-II is non-selective, it is generally distinguished in the research literature from MC4R-selective agonists (e.g. bremelanotide, the closely related linear analogue marketed as PT-141 for hypoactive sexual desire disorder under the brand Vyleesi) and from MC1R/MC4R-targeted clinical agents (e.g. afamelanotide).

Preclinical research highlights

Pigmentation. The original development programme demonstrated that MT-II drives melanogenesis in cell culture and in rodent models. This activity has been the most consistently reproduced finding across the literature and has motivated continued interest in melanocortin agonists as research tools in photoprotection studies.

Feeding and energy balance. Preclinical research has reported that central MT-II administration suppresses food intake and increases energy expenditure in rodent models, with effects attributed primarily to MC4R activation. MC4R knockout animals are largely resistant to these effects, which has been used as a control in mechanistic studies.

Sexual-behaviour circuits. Rodent studies have reported that MT-II administration produces pro-erectile responses in male animals and increases proceptive behaviours in females, again primarily through MC4R-mediated CNS pathways. This line of work led to the development of the MC4R-preferring linear analogue bremelanotide (PT-141), which has been studied more extensively in human trials.

Cardiovascular and autonomic effects. Research has reported transient pressor responses, yawning, flushing, and gastrointestinal effects in animal models, most consistent with broad melanocortin receptor activation rather than a single-receptor effect.

Limitations and safety considerations in research

The non-selective melanocortin pharmacology of MT-II is associated with a wider side-effect profile in research models than its more selective successors. Concerns reported in case-report literature on non-research use of MT-II products include atypical naevi, eruptive melanocytic lesions, and rhabdomyolysis. These are not findings drawn from controlled clinical trials of MT-II — there is no approved clinical formulation of MT-II for any indication.

Current research status

MT-II is an investigational research peptide with no FDA-approved status for any indication. The compound is widely studied as a tool molecule in melanocortin receptor pharmacology and continues to appear in mechanistic preclinical work. Clinical-stage development has shifted toward more selective melanocortin agonists (afamelanotide for erythropoietic protoporphyria, bremelanotide for hypoactive sexual desire disorder, setmelanotide for rare MC4R-pathway obesity syndromes).

For research-supplier contexts, MT-II is supplied as a research-grade reference peptide and is not intended for self-administration.

Key takeaways for researchers

• MT-II is a cyclic heptapeptide α-MSH analogue with non-selective activity across MC1R, MC3R, MC4R, and MC5R.
• Reported preclinical effects span pigmentation, feeding suppression, and modulation of CNS sexual-behaviour circuits.
• The non-selective receptor profile yields a correspondingly broad side-effect profile in research models.
• More selective melanocortin agonists (afamelanotide, bremelanotide, setmelanotide) are the agents that have advanced into approved or late-stage clinical use; MT-II itself remains investigational.
• MT-II is not an FDA-approved drug.

References

1. Hadley ME, Dorr RT. Melanocortin peptide therapeutics: historical milestones, clinical studies and commercialization. Peptides. 2006;27(4):921–930.
2. Schiöth HB, Mutulis F, Muceniece R, Prusis P, Wikberg JE. Discovery of novel melanocortin4 receptor selective MSH analogues. Br J Pharmacol. 1998;124(1):75–82.

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This article is provided for educational and research purposes only. Melanotan 2 is a research peptide. It is not an approved drug or therapeutic agent and is not intended for human consumption, diagnosis, treatment, cure, or prevention of any disease or condition. All work involving this peptide should be conducted by qualified personnel within an appropriate research setting and in compliance with applicable institutional and regulatory requirements.