4D Molecular Therapeutics announced that the U.S. Food and Drug Administration (FDA) has granted Fast Track Designation for 4D-125 for treatment of patients with inherited retinal dystrophies due to defects in the RPGR gene, including X-linked Retinitis Pigmentosa (XLRP). 4D-125 is a targeted and evolved R100-based product candidate, which was invented at 4DMT for efficient intravitreal delivery, and is designed to deliver a functional copy of the RPGR gene to photoreceptors in the retina. The FDA's Fast Track process is designed to accelerate the development and review of treatments for serious and life-threatening diseases where no treatment exists or where the treatment in discovery may provide advantages over what is currently available.

A drug candidate that receives Fast Track designation is eligible for more frequent communication with the FDA throughout the drug development process and a rolling and/or priority review of its marketing application if relevant criteria are met. 4D-125 is 4DMT's targeted and evolved R100-based product candidate for XLRP and is designed to deliver a functional copy of the RPGR gene to photoreceptors in the retina. 4DMT is currently enrolling patients in an on-going Phase 1/2 clinical trial.

The study employed a standard 3+3 dose-escalation design, followed by dose expansion. In dose-escalation, patients were enrolled in one of two dose cohorts: 3E11 vg/eye and 1E12 vg/eye. The dose expansion phase of the study is enrolling patients at the 1E12 vg/eye dose.

The primary objectives of this trial are to evaluate the safety and maximum tolerated dose of 4D-125. Secondary endpoints include assessments of clinical activity, including both visual function and anatomical endpoints. XLRP is a rare inherited X-linked recessive genetic disorder that causes progressive vision loss and blindness in boys and young men.

There are currently no approved therapies for XLRP. 70% of cases are caused by mutations in the retinitis pigmentosa GTPase regulator (“RPGR”) gene. The estimated worldwide prevalence of XLRP due to RPGR variants is approximately one in 25,600 people, which represents approximately 24,000 patients in the United States, and France, Germany, Italy, Spain and the United Kingdom (together, EU-5).

It is characterized by dysfunction and degeneration of photoreceptors in the retina. Symptoms of XLRP are initially characterized by night blindness, followed by loss of peripheral visual field, decreasing visual acuity and eventually blindness.