Scientists created double‑headed versions of a short melanin‑stimulating peptide and found they stick to a specific brain receptor better than the single‑headed version, but the work is purely laboratory‑based and doesn’t give any usable tips for people looking to take or dose melanotan‑I.

We demonstrate the potential utility of multivalent ligands as targeting agents for cancer imaging or therapy by determining the binding of homobivalent ligands to their corresponding receptors. This manuscript details the synthesis and evaluation of a series of bivalent ligands containing two copies of the truncated heptapeptide version of [Nle4-D-Phe7]-alpha-melanocyte stimulating hormone (NDP-alpha-MSH), referred to as MSH(7). These were connected with various semirigid linkers containing Pro-Gly repeats, with or without flexible poly(ethylene glycol) (PEGO) moieties at their termini. Modeling data suggest a distance of 20-50 A between the ligand binding sites of two adjacent G-protein coupled receptors, GPCRs. These bivalent ligands were observed to bind with higher affinity compared to their monovalent counterparts. Data suggest these ligands may be capable of cross-linking adjacent receptors. An optimal linker length of 25 +/- 10 A, inferred from these ligands, correlated well with the inter-receptor distance estimated through modeling. Although there was no difference in maximal binding affinities between the ligands constructed with the Pro-Gly repeats versus those constructed with the PEGO inserts, the PEGO-containing ligands bound with high affinities over a greater range of linker lengths.