TRPV1 is a cation channel activated by a range of noxious stimuli and highly expressed in nociceptive fibres. TRPV1 receptors are involved in pain and sensitisation associated with tissue injury and inflammation; hence, TRPV1 antagonists are potentially useful for the treatment of such pain states. SB-705498 is a potent, selective and orally bioavailable TRPV1 antagonist with demonstrated efficacy in a number of preclinical pain models. In this first-time-into-human study, we have investigated the pharmacodynamic and antihyperalgesic activity of SB-705498. The compound was safe and well tolerated at single oral doses up to 400 mg. In a cohort of 19 healthy volunteers, we used a randomised placebo-controlled single-blind cross-over design to assess the effects of SB-705498 (400 mg) on heat-evoked pain and skin sensitisation induced by capsaicin or UVB irradiation. Compared with placebo, SB-705498 reduced the area of capsaicin-evoked flare (P = 0.0047). The heat pain threshold on non-sensitised skin was elevated following SB-705498 (estimated difference from placebo [95% confidence intervals]: 1.3 °C [0.07, 2.53], P = 0.019). Following capsaicin sensitisation, the heat pain threshold and tolerance were similar between SB-705498 and placebo. However, SB-705498 increased heat pain tolerance at the site of UVB-evoked inflammation (estimated difference from placebo: 0.93 °C [0.25, 1.6], P = 0.0054). The magnitude of the pharmacodynamic effects of SB-705498 appeared to be related to plasma concentration. These results indicate that SB-705498, at a clinically safe and well-tolerated dose, has target-specific pharmacodynamic activity in humans. These data provide the first clinical evidence that a TRPV1 antagonist may alleviate pain and hyperalgesia associated with inflammation and tissue injury.
aClinical Pharmacology and Discovery Medicine, GlaxoSmithKline, Cambridge and Harlow, UK
bBiomedical Data Sciences, GlaxoSmithKline, Harlow, Essex, UK
*Corresponding author. Address: GlaxoSmithKline, Addenbrooke’s Centre for Clinical Investigation, Addenbrooke’s Hospital, Box 128, Hills Road, Cambridge CB2 2GG, UK. Tel.: +44 1223 296048; fax: +44 1223 296063.
Submitted December 15, 2006; received in revised form April 10, 2007; accepted June 5, 2007.