Effects of a superpotent melanotropic peptide in combination with solar UV radiation on tanning of the skin in human volunteers

Objective: Three phase 1 clinical trials of a superpotent melanotropic peptide, metanotan-1 (MT-1, or [Nle⁴-D-Phe⁷] α-melanocyte-stimulating hormone) were performed to demonstrate safety for MT-1 therapy combined with UV-B light or sunlight. Design: Open-label studies at 2 dose levels of MT-1 combined with small doses of UV-B to the neck or buttock or full sunlight to half of the back. Setting: Dermatology clinics at the Arizona Health Sciences Center, Tucson. Interventions: The first study randomized 4 subjects to MT-1 (0.08 mg/kg per day subcutaneously) and 4 subjects to injections of isotonic sodium chloride (9%) solution for 10 days, followed by neck irradiation with 3 times the minimal erythema dose (MED) of UV-B light. In the next study (n = 12), the MT-1 dosage was increased to 0.16 mg/kg per day for 10 days, with UV-B radiation (0.25-0.75 MED) given to a buttock site for 5 days during (n = 7) or after (n = 5) MT-1 administration. A final study randomized 8 subjects to 3 to 5 days of sunlight to half of the back or to sunlight plus 0.16 mg/kg of MT-1 for 5 days per week for 4 weeks. Results. Tanning in the first study was achieved in 3 of 4 subjects receiving MT-1, and these subjects also had 47% fewer sunburn cells at the irradiated neck site. More skin sites darkened with the higher dose of MT-1 in the second study. In the third study, there was significantly enhanced tanning of the back in the MT-1 group, and this was maintained at least 3 weeks longer than the tanning in the sunlight-only controls, who required 50% more sun-exposure time for equivalent tanning. Main Outcome Measure: There were no pathologic findings at any UV-B or sun-exposed sites in any subject. Toxic effects due to MT-1 were minor, consisting of nausea and transient facial flushing. Conclusion: Melanotan-1 can be safely combined with UV-B light or sunlight and appears to act synergistically in the tanning response to light.