GlaxoSmithKline (GSK) and XenoPort, Inc. announced an exclusive agreement to co-develop and commercialise XP13512, a unique prodrug of gabapentin that improves its bioavailability, in the US and other countries worldwide, excluding certain Asian countries.

XP13512 is currently in phase III development for Restless Legs Syndrome (RLS) and in phase II development for neuropathic pain. Prior clinical trial results have been encouraging.

XP13512 is a patented, new chemical entity that is designed to improve upon the clinical utility of gabapentin by taking advantage of high-capacity transport mechanisms in the gut to improve absorption.

Under the terms of the agreement, XenoPort is entitled to receive an up-front cash payment of £40 million. XenoPort is also eligible to receive aggregate milestone payments of up to £34 million for development activities leading up to the NDA filing for RLS, up to £111million in other potential development and regulatory milestone payments and up to £153million in potential sales milestone payments based on successful commercialization of XP13512 for RLS and neuropathic pain.

In addition to royalties on sales outside the US, XenoPort is entitled to receive tiered, double-digit royalty payments on US sales of XP13512 unless XenoPort elects to co-promote XP13512 with GSK in the US, in which case it will be entitled to participate in a net profit share for XP13512 in the US. If XenoPort decides to co-promote XP13512 in the US, it is also entitled to detail REQUIP products currently in development by GSK, provided they are approved in the US. GSK will have an exclusive right to develop, manufacture and commercialise XP13512 in the US and all countries worldwide except certain Asian countries previously licensed by XenoPort to Astellas Pharma Inc.

In the US, XenoPort will complete the ongoing studies to support RLS development. Subject to positive Phase III clinical data, GSK will file the NDA for RLS for FDA approval. GSK will lead development and registration of XP13512 for all other indications, including neuropathic pain. GSK will also be solely responsible for the manufacture of XP13512 to support its development and commercialization within the licensed territories.

The agreement is subject to review by the US Government under the Hart-Scott-Rodino Act and will become effective after clearing review.

Moncef Slaoui, chairman of R&D, GSK, commented, "This is another important late-stage programme addition to GSK's R&D pipeline. We are pleased to work with XenoPort toward bringing a new treatment alternative for the management of these two important disease areas of RLS and neuropathic pain where there is still such a large unmet need."

Ronald W. Barrett, Ph.D., XenoPort's chief executive officer, stated, "GSK has demonstrated leadership and innovation in educating doctors and patients about the debilitating aspects of RLS and has helped improve the lives of many patients with RLS. We are excited to be collaborating with GSK to advance the development and commercialization of XP13512 and, most importantly, to be creating a new treatment for patients with RLS and neuropathic pain."