A Tanning Peptide That Accidentally Became Much More
In the late 1980s, researchers at the University of Arizona had a straightforward goal: create a peptide that would stimulate skin pigmentation without requiring UV exposure. A sunless tan in a vial. What they got was Melanotan II — a compound that does trigger tanning, but also activates sexual arousal pathways, suppresses appetite, and modulates fat metabolism. Sometimes the side effects are the story.
MT-2 is a synthetic cyclic heptapeptide analog of alpha-melanocyte-stimulating hormone (α-MSH). The cyclic structure — a lactam bridge between positions 4 and 10 — makes it more stable and gives it a broader receptor binding profile than its linear cousin Melanotan I (afamelanotide). That broader profile is exactly why MT-2 does so many things: it hits multiple melanocortin receptor subtypes, each governing different biological functions.
This compound is supplied exclusively for in vitro and preclinical research. It is not intended for human consumption, therapeutic application, or diagnostic use.
The Melanocortin Receptor System: Five Receptors, Five Different Jobs
MT-2’s diverse effects make sense when you understand the receptor family it targets. There are five melanocortin receptors (MC1R through MC5R), each with distinct tissue distribution and function:
- MC1R (skin): Drives melanogenesis — the tanning response. This was the original target.
- MC2R (adrenal): The ACTH receptor. MT-2 has minimal affinity here, thankfully.
- MC3R (brain, gut): Involved in energy homeostasis and nutrient partitioning. MT-2 binds here.
- MC4R (brain): Regulates sexual arousal, appetite, and energy balance. This is where the “side effects” come from. MT-2 is a potent MC4R agonist, which is why PT-141 was developed as a more selective MC4R compound.
- MC5R (exocrine glands): Sebaceous gland function and other exocrine roles.
MT-2 activates MC1R, MC3R, MC4R, and MC5R. That multi-receptor profile is both its strength (broad research utility) and its complexity (multiple concurrent effects to untangle).
The Tanning Research
MT-2’s original purpose was photoprotection through induced melanogenesis. The published data confirms it works — MT-2 stimulates eumelanin production (the dark, protective pigment) through MC1R activation. The signaling cascade runs through cAMP → CREB → MITF → tyrosinase — the same pathway UV exposure triggers, but without the DNA damage that UV causes.
Early human studies (Dorr et al., 1996) demonstrated visible increases in skin pigmentation after MT-2 administration, with the tanning response occurring even in individuals with naturally fair skin who typically burn rather than tan. This was the proof-of-concept that a peptide could drive melanogenesis independently of UV.
Sexual Arousal: The Unexpected Finding
During early research, subjects receiving MT-2 reported spontaneous arousal — a central, desire-driven response distinct from the vascular effects of PDE5 inhibitors. This observation, mediated by MC4R activation in hypothalamic circuits, led directly to the development of PT-141 (bremelanotide) as a more targeted compound for this pathway.
The mechanism: MC4R activation in the hypothalamus triggers dopaminergic and oxytocinergic signaling pathways that mediate the psychological experience of arousal. This is brain-first pharmacology — desire circuitry, not plumbing.
Appetite and Body Composition
MC3R and MC4R are both deeply involved in appetite regulation and energy homeostasis. MC4R knockout mice are severely obese, establishing the critical role of this receptor in body weight regulation. MT-2’s agonism at both receptors has been studied for:
- Reduced food intake in animal models (centrally mediated appetite suppression)
- Altered substrate utilization — shifts toward fat oxidation
- Changes in feeding behavior patterns
These effects add complexity to MT-2 research protocols but also make it a valuable tool for studying melanocortin involvement in metabolic regulation.
Structural Advantages: Why the Cyclic Form Matters
MT-2’s lactam bridge between Asp⁴ and Lys¹⁰ isn’t just a stability modification — it constrains the peptide into a conformation that optimizes melanocortin receptor binding. Key structural features:
- D-Phenylalanine at position 7: The D-amino acid provides protease resistance and positions the pharmacophore (His-D-Phe-Arg-Trp) for optimal receptor interaction
- Norleucine at position 1: Replaces the oxidation-prone methionine found in α-MSH, improving chemical stability
- Cyclic structure: Reduces conformational flexibility, which typically enhances binding affinity and selectivity
These modifications give MT-2 an estimated half-life significantly longer than native α-MSH, which is rapidly degraded by serum proteases.
Product Specifications
- Sequence: Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH₂
- Molecular Weight: 1,024.18 g/mol
- CAS Number: 121062-08-6
- Physical Form: Sterile lyophilized white powder
- Purity: ≥99% (verified by HPLC)
- Solubility: Freely soluble in bacteriostatic water
Key References
- Hadley ME, Dorr RT. Melanocortin peptide therapeutics: historical milestones, clinical studies and commercialization. Peptides. 2006;27(4):921-930.
- Dorr RT, et al. Effects of Melanotan II on tanning. Life Sci. 1996;58(17):1485-1491.
- Hruby VJ, et al. Cyclic lactam α-melanotropin analogues of Ac-Nle4-c[Asp5,D-Phe7,Lys10]α-MSH(4-10)-NH₂. J Med Chem. 1995.
Browse Melanotan II 10mg with verified COA from Janoshik Analytical. For the selective MC4R agonist, see PT-141. Explore our full catalog.