Cardiac safety of fordadistrogene movaparvovec gene therapy in Duchenne muscular dystrophy: Initial observations from a phase 1b trial

Fordadistrogene movaparvovec (FM; PF-06939926) is a recombinant adeno-associated virus serotype-9 gene-replacement construct containing a mini-dystrophin transgene, in development for Duchenne muscular dystrophy (DMD). We present findings of cardiac safety assessments in DMD participants during a 1-year follow-up from an ongoing, phase 1b, multicenter, single-arm, open-label trial of low- and high-dose FM. Cardiac troponin-I (cTn-I) levels and cardiac magnetic resonance imaging (cMRI) measures were obtained from 19 ambulatory participants (n=3, low-dose; n=16, high-dose; median age 8.8 years), and three non-ambulatory participants (high-dose; median age 15.1 years). Six ambulatory and three non-ambulatory participants had cTn-I levels above the upper limit of normal (ULN) at baseline. Of these, one ambulatory participant and two non-ambulatory participants had cTn-I levels >3x the baseline level during the first year following infusion. At 1-year post-infusion, mean (±SD) change from baseline in left ventricular ejection fraction (LVEF) was -0.9%±4.0% in ambulatory participants, and −3.1%±1.8% in non-ambulatory participants. One 16-year-old non-ambulatory DMD participant experienced fatal cardiogenic shock 6 days after high-dose of FM. With the exception of participants with DMD with advanced cardiac fibrosis, assessments of cTn-I, LVEF by cMRI, and progression of late gadolinium enhancement suggest low cardiac toxicity from FM in ambulatory DMD participants in this study.