Melanotan II (MT-2)
The cyclic lactam heptapeptide analogue of alpha-MSH as freeze-dried powder in a sealed vial. Every lot is tested in the manufacturer’s own laboratory and ships with a lot certificate.
| Compound | Melanotan II (acetate) Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH₂; supplied as the acetate salt, values quoted for the free peptide |
|---|---|
| CAS number | 121062-08-6 |
| Molecular formula | C50H69N15O9 |
| Theoretical mass | 1024.2 Da |
| Sequence / structure | Ac-Nle-cyclo[D-H-[D-Phe]-R-W-K]-NH₂ (7 residues; Asp–Lys side-chain lactam; N-acetyl; C-terminal amide) |
| Label claim | 10 mg/vial |
| Form | Lyophilized (freeze-dried) powder or cake in a sealed glass vial with a rubber stopper and aluminium crimp cap |
| Storage, sealed | −20 °C, desiccated, dark |
| Purity specification | 99.0% or higher by RP-HPLC |
| Format | Lyophilized powder, sealed vial |
Sizes and lots
- 10 mg · 1 vial — $57.50 · lot PL-2609-066, certificate PL-26-00066
- 10 mg · Kit of 10 — $519.00 · lot PL-2609-066, certificate PL-26-00066
Melanotan II (MT-2) is a cyclic heptapeptide analogue of alpha-melanocyte-stimulating hormone, Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2, closed by a lactam bridge between the aspartate and lysine side chains. This listing is a sealed vial of 10 mg freeze-dried melanotan II, supplied as the acetate salt. Its literature covers receptor pharmacology, preformulation chemistry, two small human studies reported in 1996 and 2000, case reports linked to unregulated products and a laboratory analysis of vials bought online.
Which molecule is in this vial
Three related peptides are easy to confuse. Melanotan II, in this vial, ends in a C-terminal amide: formula C50H69N15O9, theoretical mass 1024.2 Da for the free peptide. Bremelanotide, sold as PT-141, has the same ring but ends in a free carboxylic acid, which makes it about one dalton heavier at 1025.2 Da. Melanotan I is a different molecule altogether, the linear 13-residue analogue at 1646.9 Da. The LC-MS identity result on the certificate is the figure to check against 1024.2 Da.
The peptide is supplied as its acetate salt, and the formula and mass on the certificate are those of the free peptide. On that basis 10 mg corresponds to about 9.8 µmol. The melanotan 1 vs melanotan 2 guide sets the three side by side.
What the research covers
Structure and receptors
Dorr and colleagues described melanotan II as a lactam-bridged cyclic heptapeptide analogue of alpha-MSH, Ac-Nle4-Asp5-His6-D-Phe7-Arg8-Trp9-Lys10 alpha-MSH4-10-NH2, with superpotent melanotropic activity in vitro1. The numbering comes from the parent hormone: the peptide keeps residues 4 to 10 of alpha-MSH, with norleucine at position 4 and D-phenylalanine at position 7. Wessells and colleagues later described it as a non-selective melanocortin receptor agonist2, so an effect seen with it may come from more than one receptor.
Physical chemistry
Preformulation work by Lan and colleagues in 1994 estimated the pKa of the histidine at 6.54 and of the arginine at 11.723. They measured the apparent partition coefficient at three pH values, with an octanol value of 2.82 at pH 7.35, and together with a bioavailability of 4.6% observed in the rat the authors judged the peptide a possible candidate for oral delivery3. No oral product followed in the literature cited here.
Human studies
The first human study was a pilot phase I trial in three healthy men, single-blind and placebo-controlled, with saline as the comparator1. Pigmentation was measured by quantitative reflectance and by eye; two of the three men had increased pigmentation of the face, upper body and buttock one week after the study ended1. Recorded side effects included mild nausea at most levels, somnolence and fatigue in one man, and a stretching and yawning complex that coincided with spontaneous erections1.
Wessells and colleagues then reported a double-blind, placebo-controlled crossover study in 20 men with psychogenic or organic erectile dysfunction, with penile rigidity monitored for six hours by RigiScan and sexual desire and side effects recorded by questionnaire2. The authors reported erectile responses, and nausea and yawning were frequent side effects2.
Unregulated products and case reports
Much of the recent literature concerns melanotan II sold online. Breindahl and colleagues developed and validated LC-UV and LC-MS/MS methods and applied them to vials from three online shops, each labelled 10 mg: the vials held 4.32 to 8.84 mg of melanotan II, and products from two of the shops carried 4.1 to 5.9% unknown impurities4. A 2017 review of unregulated melanotan I and II collected case reports of changes in existing moles, new dysplastic naevi and four melanomas arising from existing moles, while stating that conclusive evidence of a link was lacking5. One such melanoma was reported in a 20-year-old woman with Fitzpatrick skin type II who had combined melanotan II with sunbed tanning6.
What is not established
The controlled human data come to two small studies by overlapping authors1,2. Case reports cannot separate the peptide from sun and sunbed exposure, and the 2017 review judged the evidence for a link inconclusive5. No study in these references isolated which receptor drives each effect in people. None of the work used SCALE Performance material.
Frequently asked questions
Is MT-2 the same as bremelanotide (PT-141)?
No, though they are close. Both are cyclic seven-residue alpha-MSH analogues with the same lactam ring, but melanotan II ends in an amide and bremelanotide in a free acid, about one dalton apart (1024.2 against 1025.2 Da). SCALE Performance sells them as separate products.
How is melanotan II different from melanotan I?
Melanotan I is linear, 13 residues and 1646.9 Da; melanotan II is a seven-residue lactam ring of 1024.2 Da. A 2017 review described afamelanotide, the melanotan I molecule, as the only alpha-MSH analogue approved for use, and then in a limited number of medical indications. Melanotan II has no such status.
How should the vial be stored?
Sealed at −20 °C, desiccated and protected from light. Bring the vial to room temperature before opening so moisture does not condense on the powder. The safety data sheet gives 2 to 8 °C, away from light, for reconstituted solutions, kept for a period your laboratory has established.
What does the research on melanotan II leave open?
A great deal. The controlled human data are a three-man pilot study from 1996 and a 20-man crossover reviewed in 2000. Most later papers are case reports of products bought online, which cannot establish cause, and an analysis of online vials that found less peptide than labelled.
References
- Dorr RT, Lines R, Levine N, et al. Evaluation of melanotan-II, a superpotent cyclic melanotropic peptide in a pilot phase-I clinical study. Life Sci. 1996;58(20):1777-84. DOI · PubMed
- Wessells H, Levine N, Hadley ME, et al. Melanocortin receptor agonists, penile erection, and sexual motivation: human studies with Melanotan II. Int J Impot Res. 2000;12 Suppl 4:S74-9. DOI · PubMed
- Lan EL, Ugwu SO, Blanchard J, et al. Preformulation studies with melanotan-II: a potential skin cancer chemopreventive peptide. J Pharm Sci. 1994;83(8):1081-4. DOI · PubMed
- Breindahl T, Evans-Brown M, Hindersson P, et al. Identification and characterization by LC-UV-MS/MS of melanotan II skin-tanning products sold illegally on the Internet. Drug Test Anal. 2015;7(2):164-72. DOI · PubMed
- Habbema L, Halk AB, Neumann M, et al. Risks of unregulated use of alpha-melanocyte-stimulating hormone analogues: a review. Int J Dermatol. 2017;56(10):975-980. DOI · PubMed
- Hjuler KF, Lorentzen HF. Melanoma associated with the use of melanotan-II. Dermatology. 2014;228(1):34-6. DOI · PubMed
For laboratory research use only. Not for human or veterinary consumption. Products have not been evaluated by the U.S. Food and Drug Administration and are not intended to diagnose, treat, cure or prevent any disease.