The novel hybrid agonist HyNDA-1 targets the D3R-nAChR heteromeric complex in dopaminergic neurons

n this paper, we designed, synthesized and tested a small set of three new derivatives potentially targeting theD3R-nAChR heteromer, a receptor complex recently identified and characterized as the molecular entity that, indopaminergic neurons, mediates the neurotrophic effects of nicotine. By means of a partially rigidified spacer ofvariable length, we incorporated in the new compounds (1a-c) the pharmacophoric substructure of a known?2-subunit-containing nAChR agonist (A-84543) and that of the D2/D3R agonist drug ropinirole. All the compoundsretained the ability to bind with high affinity both?2-subunit-containing nAChR and D3R. Compound1a, re-namedHyNDA-1, which is characterized by the shortest linker moiety, was the most interesting ligand. Wefound, in fact, thatHyNDA-1significantly modulated structural plasticity on both mice and human dopami-nergic neurons, an effect strongly prevented by co-incubating this ligand with either nAChR or D3R antagonists.Moreover, the neurotrophic effects ofHyNDA-1were specifically lost by disrupting the complex with specificinterfering peptides. Interestingly, by using the Bioluminescence Resonance Energy Transfer 2 (BRET2) assay inHEK-293 transfected cells, we also found thatHyNDA-1has the ability to increase the affinity of interactionbetween nAChR and D3R. Overall, our results indicate that the neurotrophic effects ofHyNDA-1are mediated byactivation of the D3R-nAChR heteromeric complex specifically expressed on dopaminergic neurons