Tryptamine-based derivatives as Transient Receptor Potential Melastatin type-8 (TRPM8) channel modulators

Pharmacological modulation of the transient receptor potential melastatin type 8 (TRPM8) is currently under investigation as a new approach for the treatment of pain and other diseases. In this study, a series of N-substituted tryptamines was prepared to explore the structural requirements determining TRPM8 modulation. Using a fluorescence-based screening assay, we identified two compounds acting as an activator (2-(1H-indol-3-yl)-N-(4-phenoxybenzyl) ethanamine, 21) or an inhibitor (N,N-dibenzyl-2-(1H-indol-3-yl) ethanamine, 12) of calcium influx in HEK293 cells. In patch-clamp recordings, compound 21 displayed a significantly higher potency (EC50 = 40±4 µM) and a similar efficacy when compared to menthol; by contrast, compound 12 produced a concentration-dependent inhibition of menthol-induced TRPM8 currents (IC50=367±24 nM). Molecular modelling studies using a homology model of a single rat TRPM8 subunit identified a putative binding site located between the VSD and the TRP box, disclosing differences in the binding modes for the agonist and the antagonist.