Dissociation Rates as One of the Differentiating Factors for Hyperthermic and Non-Hyperthermic TRPV1 Antagonists

Abstract

In addition to pain sensation, both thermal regulation and thermosensation are thought to be influenced by TRPV1 channel functioning. Involvement of TRPV1 in these latter physiological functions became clear during pharmaceutical development of selective TRPV1 antagonists for the treatment of chronic painful conditions. The majority of TRPV1 antagonists that have been progressed into clinical trials were reported to increase body temperature (hyperthermia) in healthy humans. Currently, hyperthermia is a major concern in pharmaceutical development of TRPV1 antagonists. We therefore sought of an in-vitro method to identify compounds with a low hyperthermic potential early in the drug discovery process. Using whole-cell patch clamp electrophysiology on human TRPV1 expressing CHO cells, we performed kinetic measurements of dissociation from the receptor of known hyperthermic (AMG517 and ABT102) and non-hyperthermic (SB705498) TRPV1 antagonists. We found that AMG517 and ABT102, two hyperthermic compounds, exhibited slow off- (dissociation) rates when channels were activated by capsaicin. Conversely, the non-hyperthermic compound SB705498, showed a significantly faster rate of dissociation from the receptor. Finally, we assessed an in-house proprietary antagonist V116517 which demonstrated significant separation between analgesic efficacy and hyperthermia. Once again, this compound displayed a faster off-rate as compared to the hyperthermic compounds.With these initial findings we hypothesize that the dissociation rate of an antagonist from the TRPV1 channel is an important parameter in determining a compound's effect on thermal regulation and thermosensation. Antagonists with a fast off-rate may allow endogenous ligands to interact with the TRPV1 channel and thereby fulfil its physiological role in body temperature regulation while still effectively modifying pain signaling. In conclusion, our findings suggest that in vitro kinetic measurements early in the drug discovery process may be a useful means of identifying non-hyperthermic TRPV1 antagonists.