How Melanotan 2 was discovered

Melanotan 2 grew out of a long partnership at the University of Arizona in Tucson between the peptide chemist Victor Hruby and the physiologist Mac Hadley, later joined by the pharmacologist Robert Dorr. Their question was easy to ask and hard to answer: which parts of α-MSH really matter, and could a smaller, tougher molecule do the same job?

Frog and lizard skin as a test bench

Before the human melanocortin receptors were cloned in the early 1990s, potency was measured on pieces of frog and lizard skin, whose pigment cells visibly darken when an α-MSH-like compound binds. These simple bioassays let the Tucson group compare dozens of analogues side by side.

1980: a mirror-image amino acid

In 1980 the team reported that exchanging methionine for norleucine and the usual phenylalanine for its D-form produced [Nle4, D-Phe7]-α-MSH. It resisted serum enzymes and acted far longer than the natural hormone. This linear peptide later became known as Melanotan 1 and, decades on, as the medicine afamelanotide.

1989: closing the ring

Using molecular dynamics simulations to estimate the hormone's active shape, Fahad Al-Obeidi and colleagues next designed short cyclic fragments held together by a lactam bridge. One of the most potent, about 90 times stronger than α-MSH on lizard skin, kept only residues 4 to 10 of the hormone. That cyclic heptapeptide is the molecule now known as Melanotan 2.

A first look in people

In the mid-1990s the Arizona group ran a pilot phase 1 study in three healthy male volunteers to check tolerability. The paper recorded mild nausea at most dose levels, sleepiness and fatigue at the highest level, bouts of stretching and yawning, spontaneous erections and increased skin pigmentation. The unexpected erectile effect would later send part of the research in a separate direction.

Two branches, two medicines

From there the work divided. The linear Melanotan 1 was developed as afamelanotide, a slow-release implant tested in erythropoietic protoporphyria, a rare disorder in which sunlight causes severe pain. It was approved in the EU in 2014 and in the US in 2019. A close variant of the cyclic peptide with a free acid end became bremelanotide (PT-141), developed by another company. Melanotan 2 itself was never taken forward to approval.

Laboratory tool and grey-market product

Meanwhile, Melanotan 2 became a workhorse in laboratories studying the melanocortin system of the brain, as the research page describes. From the mid-2000s it was also sold online as an unlicensed product, which led to the regulator warnings covered on the rules and safety page.

Key dates

• 1980: [Nle4, D-Phe7]-α-MSH, the future Melanotan 1, is described in Tucson.
• 1989: cyclic lactam analogues are designed with molecular dynamics; the α-MSH(4-10) ring becomes Melanotan 2.
• Early 1990s: the receptors MC3R, MC4R and MC5R are cloned, giving MT-II new targets to be profiled against.
• 1995: the naphthylalanine variant SHU9119 is reported as an MC3R/MC4R antagonist.
• 1996: results of the three-volunteer pilot phase 1 study are published.
• 1997: MT-II and SHU9119 help show that brain melanocortin signalling restrains feeding in mice.
• 2008 onwards: medicines regulators in the UK, Denmark and elsewhere warn the public about unlicensed Melanotan products.
• 2014 and 2019: afamelanotide is approved in the EU and then the US; bremelanotide is approved in the US in 2019.
• 2024: a review lists MT-II among the recommended tool compounds for melanocortin receptor research.