Astellas Pharma and XenoPort submitted an NDA for Japanese regulatory approval of ASP8825/XP13512 (gabapentin enacarbil) as a treatment for restless legs syndrome (RLS). Acceptance of the filing triggered a $5 million milestone payment from Astellas to XenoPort, which originally discovered XP13512.
A transported prodrug of gabapentin, XP13512 is in clinical development as a potential treatment for RLS, post-herpetic neuralgia, painful diabetic neuropathy, and migraine prophylaxis. Astellas has exclusive rights to develop and commercialize the drug in Japan, Korea, the Philippines, Indonesia, Thailand, and Taiwan. GSK and XenoPort are collaborating on development of the drug (also known as GSK1838262) in the rest of the world, and XenoPort has an option to co-promote the drug in the U.S.
GSK1838262 is currently undergoing FDA review for the RLS indication in the U.S. In September, GSK reported positive topline results from a Phase IIb trial evaluating the safety and efficacy of GSK1838262 in adult patients with neuropathic pain associated with post-herpetic neuralgia.
All doses of GSK1838262 demonstrated statistically significant improvements over placebo on the primary endpoint, defined as the change from baseline to the end of maintenance treatment in the 24-hour average pain intensity score.