Dual 5-HT6 and D3 Receptor Antagonists in a Group of 1H-Pyrrolo[3,2-c]quinolines with Neuroprotective and Procognitive Activity.

In light of the multifactorial origin of neurodegenerative disorders and some body of evidence indicating that pharmacological blockade of serotonin 5-HT6 and dopamine D3 receptors might be beneficial for cognitive decline, we envisioned (S)-1-[(3-chlorophenyl)sulfonyl]-4-(pyrrolidine-3-yl-amino)-1H-pyrrolo[3,2-c]quinoline (CPPQ), a neutral antagonist of 5-HT6R, as a chemical template for designing dual antagonists of 5-HT6/D3 receptors. As shown by in vitro experiments, supported by quantum chemical calculations and molecular dynamic simulations, introducing alkyl substituents at the pyrrolidine nitrogen of CPPQ, fulfilled structural requirements for simultaneous modulation of 5-HT6 and D3 receptors. The study identified compound 19 ((S)-1-((3-chlorophenyl)sulfonyl)-N-(1-isobutylpyrrolidin-3-yl)-1H-pyrrolo[3,2-c]quinolin-4-amine), which was classified as a dual 5-HT6/D3R antagonist (Ki(5-HT6) = 27 nM, Ki(D3) = 7 nM). Compound 19 behaved as a neutral antagonist at Gs signaling and had no influence on receptor-operated, cyclin-dependent kinase 5 (Cdk5)-dependent neurite growth. In contrast to the well characterized 5-HT6R antagonist intepirdine, compound 19 displayed neuroprotective properties against astrocyte damage induced by doxorubicin, as shown using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium (MTT) staining to assess cell metabolic activity and lactate dehydrogenase (LDH) release as an index of cell membrane disruption. This feature is of particular importance considering the involvement of loss of homeostatic function of glial cells in the progress of neurodegeneration. Biological results obtained for 19 in in vitro tests, translated into procognitive properties in phencyclidine (PCP)-induced memory decline in the novel object recognition (NOR) task in rats.