Tysabri is approved in more than 65 countries, including the US, as a monotherapy for relapsing forms of MS, generally for patients who have had an inadequate response to, or are unable to tolerate an alternative MS therapy.
A Study to Characterise the Efficacy of Natalizumab on Disability (ASCEND) trial is a double-blind placebo-controlled study with SPMS patients, who are randomised to receive either Tysabri 300 mg or placebo intravenously every four weeks for 96 weeks.
The Phase 3b study is expected to enroll approximately 850 patients between the ages of 18 and 58 with a diagnosis of SPMS for at least two years, an Expanded Disability Status Scale (EDSS) score between 3.0 and 6.5, MS Severity Score of 4 or higher, confirmed evidence of disease progression, independent of clinical relapses during the one-year prior to enrollment and naïve to Tysabri treatment.
ASCEND advisory board member Aaron Miller said the trial is investigating whether treatment with Tysabri may prevent worsening in walking, hand movement and daily functioning in SPMS patients.
Imperial College, London Cellular Neuroscience professor Richard Reynolds said preliminary data suggest that Tysabri may hinder the inflammation in the brain and reduce SPMS-related disease progression.
In the trial, the primary endpoint is to investigate whether treatment with Tysabri slows the accumulation of disability not related to relapses in subjects with SPMS.
Earlier Phase 3 Affirm trial showed that after two years, Tysabri treatment led to a 68% relative reduction in the annualised relapse rate when compared with placebo and reduced the relative risk of disability progression by 42-54%.