Magnetization transfer ratio in the delayed-release dimethyl fumarate DEFINE study

We measured changes in brain magnetization transfer ratio (MTR) as a potential indicator of myelin density in brain tissue of patients with relapsing-remitting multiple sclerosis (RRMS) treated with delayed-release dimethyl fumarate (DMF) in the Phase 3 DEFINE study. DEFINE was a randomized, double-blind, placebo-controlled study in which patients with RRMS were randomized 1:1:1 to 2 years of treatment with delayed-release DMF 240 mg twice daily (BID) or three times daily (TID) or placebo. MTR was analyzed in whole brain and normal-appearing brain tissue (NABT) at baseline, week 24, 1 year, and 2 years in a subset of patients. MTR data from 392 patients were analyzed. Mean percentage reduction from baseline to 2 years in median whole brain MTR was -0.386 % in the placebo group vs increases of 0.129 % (p = 0.0027) and 0.096 % (p = 0.0051) in the delayed-release DMF BID and TID groups, respectively. Similarly, mean percentage reduction from baseline in median NABT MTR was -0.392 % with placebo vs increases of 0.190 % (p = 0.0006) and 0.115 % (p = 0.0029) with delayed-release DMF BID and TID, respectively. Post hoc analysis of data from patients with no new or enlarging T2 lesions (n = 147), or who experienced no relapses (n = 238), yielded similar results. In this analysis, increases in MTR in brain tissue most likely reflect increases in myelin density in response to delayed-release DMF. These data in patients with RRMS are consistent with preclinical studies that indicate a potential for cytoprotection and remyelination with delayed-release DMF treatment.