Stapling Amantadine to Melanostatin Neuropeptide: Discovery of Potent Positive Allosteric Modulators of the D 2 Receptors.

This work describes the synthesis and pharmacological and toxicological evaluation of melanostatin (MIF-1) bioconjugates with amantadine (Am) via a peptide linkage. The data from the functional assays at human dopamine D 2 receptors ( h D 2 R) showed that bioconjugates 1 (EC 50 = 26.39 ± 3.37 nM) and 2 (EC 50 = 17.82 ± 4.24 nM) promote a 3.3- and 4.9-fold increase of dopamine potency, respectively, at 0.01 nM, with no effect on the efficacy ( E max = 100%). In this assay, MIF-1 was only active at the highest concentration tested (EC 50 = 23.64 ± 6.73 nM, at 1 nM). Cytotoxicity assays in differentiated SH-SY5Y cells showed that both MIF-1 (94.09 ± 5.75%, p < 0.05) and carbamate derivative 2 (89.73 ± 4.95%, p < 0.0001) exhibited mild but statistical significant toxicity (assessed through the MTT reduction assay) at 200 μM, while conjugate 1 was found nontoxic at this concentration.