Biogen announces enrollment completion of phase III gene therapy study of timrepigene emparvovec to treat choroideremia.

Biogen Inc.has announced the enrollment of the last patient in the global Phase III STAR clinical study which is evaluating the investigational gene therapy timrepigene emparvovec (BIIB111/AAV2-REP1) for the treatment of choroideremia (CHM). CHM is a rare, degenerative, X-linked inherited retinal disorder that leads to blindness.

STAR is a randomized, masked, prospective, parallel-controlled group Phase III study that enrolled 170 adult males with CHM. The study is evaluating the safety and efficacy of a single subretinal injection of timrepigene emparvovec. The primary endpoint is the proportion of patients with an improvement of at least 15 letters from baseline in best corrected visual acuity (BCVA) at 12 months post treatment as measured by the Early Treatment Diabetic Retinopathy Study (ETDRS) visual acuity protocol. The STAR study was initiated based on proof-of-concept data from Phase 1/II studies, which indicated that at month 24, over 90 percent of patients treated with timrepigene emparvovec via targeted subretinal injection maintained visual acuity instead of experiencing the natural decline in BCVA expected in this degenerative disease. In a subset of treated patients with moderate to severe visual acuity loss, 21 percent experienced a gain in visual acuity of at least 15 ETDRS letters from baseline as compared to one percent of untreated patients in a natural history study.

Choroideremia primarily affects males and is caused by a loss of function in the CHM gene which encodes the Rab escort protein-1 (REP-1). The REP-1 protein plays a role in intracellular protein trafficking, and the loss of function in the CHM gene leads to abnormal intracellular protein trafficking and impaired elimination of waste products from the retinal pigment epithelium and photoreceptors. Initially, patients with CHM experience poor night vision and over time, progressive visual loss ultimately leads to blindness.