Ultragenyx Pharma (RARE) Completes Successful End-of-Phase 2 Meeting with FDA and Finalizes Phase 3 Study Design for DTX301 Ornithine Transcarbamylase Gene Therapy Program

April 22, 2021 8:33 AM EDT

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Ultragenyx Pharmaceutical Inc. (NASDAQ: RARE), a biopharmaceutical company focused on the development and commercialization of novel therapies for rare and ultra-rare diseases, today announced the successful completion of an End-of-Phase 2 (EOP2) meeting with the U.S. Food and Drug Administration (FDA) for the DTX301 ornithine transcarbamylase (OTC) deficiency gene therapy program. The meeting focused on the discussion of the Phase 1/2 data and alignment on Phase 3 design and endpoints.

Based on the outcome of this meeting, Ultragenyx has finalized the Phase 3 study design, which will include a 64-week primary efficacy analysis period and enroll approximately 50 patients 12 years of age and older, randomized 1:1 to DTX301 (1.7 x 10^13 GC/kg dose) or placebo. The co-primary endpoints are change in 24-hour plasma ammonia levels and the percent of patients who achieve a response as measured by discontinuation or reduction in baseline disease management. Ultragenyx previously completed an initial Scientific Advice process with the European Medicines Agency (EMA) and this design incorporates the scientific advice.

The Phase 3 study is expected to begin dosing as planned in the second half of 2021. Following the initial 64-week study period, all patients who received placebo will be eligible to receive DTX301.

“Alignment with the FDA on our Phase 3 plan provides additional clarity on our development pathway for DTX301, and we are rapidly moving ahead toward initiation of the study in the second half of this year,” said Eric Crombez, M.D., Chief Medical Officer of the Ultragenyx Gene Therapy development unit. “We expect that the results from this 64-week Phase 3 study coupled with the longer-term data from the ongoing Phase 1/2 study should provide a robust data package to support the durable effect of DTX301 to establish the normal metabolism of ammonia and improve the lives of patients living with OTC.”

The increase in study duration from 48 to 64 weeks will allow more time for weaning of scavenger medications and dietary protein restrictions which will help assure success in the co-primary endpoint of baseline treatment reduction. Given the strong results in the Phase 1/2 study showing total discontinuation of all scavenger medications and diet in responders, this co-primary endpoint is designed to demonstrate clinically meaningful reduction in baseline disease treatment and is well-powered with the 50-patient, 1:1 randomized design.

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