Afamelanotide

Overview

Afamelanotide is a linear tridecapeptide analog of alpha-MSH ([Nle4, D-Phe7]-alpha-MSH). The substitutions increase resistance to degradation and prolong receptor activation, making it far more potent than endogenous alpha-MSH at driving melanogenesis.

Erythropoietic protoporphyria is caused by accumulation of protoporphyrin IX, which produces severe, painful phototoxic reactions on light exposure and drastically limits patients' time outdoors. By activating the melanocortin-1 receptor (MC1R) on melanocytes, afamelanotide increases production of eumelanin, the pigment that absorbs and scatters visible and ultraviolet light and provides antioxidant protection. In the pivotal randomized trials, afamelanotide implants significantly increased the duration of pain-free sun exposure and improved quality of life, leading to its approval (EMA 2014/2016, FDA 2019) as the first approved therapy for EPP.

Afamelanotide is a controlled-release implant inserted subcutaneously roughly every two months. Because it is a melanocortin agonist, it darkens the skin generally; nausea, headache, and injection-site effects can occur, and skin monitoring is advised.

Mechanism of Action

Binding of afamelanotide to MC1R raises intracellular cAMP, upregulating tyrosinase and other melanogenic enzymes to shift pigment production toward photoprotective eumelanin. The resulting increase in skin pigmentation attenuates light penetration and mitigates reactive-oxygen-species damage triggered by protoporphyrin IX accumulation. Its enhanced potency and metabolic stability versus native alpha-MSH, combined with slow-release implant delivery, sustain this photoprotective pigmentation over roughly a two-month interval.

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