Intrathecal administration of AS1928370, a transient receptor potential vanilloid 1 antagonist, attenuates mechanical allodynia in a mouse model of neuropathic pain

Transient receptor potential vanilloid 1 (TRPV1) is primarily expressed in central and peripheral terminals of non-myelinated primary afferent neurons. We previously showed that AS1928370, a novel TRPV1 antagonist that can prevent ligand-induced activation but not proton-induced activation, ameliorates neuropathic pain in rats without hyperthermic effect. In this study, we investigated its analgesic profile in mice. AS1928370 showed good oral bioavailability and high penetration into the brain and spinal cord in mice. The mean plasma-to-brain and plasma-to-spinal cord ratios were 4.3 and 3.5, respectively. Pretreatment with AS1928370 significantly suppressed both capsaicin-induced acute pain and withdrawal response in hot plate test at 10-30 mg/kg per os (p.o.). At lower oral doses (0.3-1.0 mg/kg), AS1928370 improved mechanical allodynia in mice undergoing spinal nerve ligation. Intrathecal administration of AS1928370 (30 μg/body) also significantly suppressed mechanical allodynia. In addition, AS1928370 showed no effect on locomotor activity up to 30 mg/kg p.o. These results suggest that spinal TRPV1 has an important role in the transmission of neuropathic pain and that the central nervous system (CNS) penetrant TRPV1 receptor antagonist AS1928370 is a promising candidate for treating neuropathic pain.