The thermosensory transient receptor potential vanilloid 1 channel (TRPV1) is a polymodal receptor activated by physical and chemical stimuli. TRPV1 activity is drastically potentiated by proinflammatory agents released upon tissue damage. Given the pivotal role of TRPV1 in human pain, there is pressing need for improved TRPV1 antagonists, the development of which will require identification of new pharmacophore scaffolds. Uncompetitive antagonists acting as open-channel blockers might serve as activity-dependent blockers that preferentially modulate the activity of overactive channels, thus displaying fewer side effects than their competitive counterparts. Herein we report the design, synthesis, biological evaluation, and SAR analysis of a family of triazine-based compounds acting as TRPV1 uncompetitive antagonists. We identified the triazine 8aA as a potent, pure antagonist that inhibits TRPV1 channel activity with nanomolar efficacy and strong voltage dependency. It represents a new class of activity-dependent TRPV1 antagonists and may serve as the basis for lead optimization in the development of new analgesics.

We have characterized the effect of triazine derivatives on neuronal nicotinic receptors expressed in Xenopus oocytes. All triazines investigated inhibit the current of α7 and α3β4 neuronal nicotinic receptors elicited by acetylcholine. The effect is concentration dependent, reversible, and noncompetitive. In contrast, some derivatives have a dual effect on α4β2 receptors, by potentiating the currents at intermediate concentration and causing inhibition at higher concentrations. Triazine derivatives also affect the macroscopic kinetics of the heteromeric receptors α3β4 and α4β2 accelerating the rise and decay time course of the currents, but have no significant effect on the kinetics of homomeric α7 receptors. Two simple kinetic models are presented. The first reproduces the effects of different concentrations of triazines both on the peak currents and on the macroscopic kinetics of α7 with a simple inhibitory result. The second model describes the behavior of α4β2 receptors involving a more complex dual action.