Disc Medicine has announced a significant step forward in the development of bitopertin, a potential treatment for the rare and debilitating skin condition erythropoietic protoporphyria (EPP). Following constructive discussions with the U.S. Food and Drug Administration (FDA), the company is now eyeing a potential accelerated approval pathway for the drug, contingent on existing clinical data and the successful completion of the upcoming Phase III APOLLO trial.
This development offers hope for individuals with EPP and X-linked protoporphyria (XLP), genetic disorders characterized by the buildup of phototoxic heme precursors in red blood cells. These conditions lead to extreme sensitivity to visible light, causing severe pain and burn-like injuries after even brief sun exposure.
Regulatory Path and Clinical Endpoints
The FDA's agreement on the Phase III APOLLO trial design is a crucial milestone. The agency has indicated that existing clinical data could support an accelerated approval application, with the APOLLO trial serving as a confirmatory study. A key aspect of this agreement is the acceptance of protoporphyrin IX (PPIX) reduction as a surrogate marker for efficacy.
The APOLLO trial will evaluate the safety and efficacy of a 60mg dose of bitopertin over a six-month period. The primary endpoint will measure the average monthly time patients can spend in sunlight without pain during the final month of treatment. Secondary outcome measures include PPIX levels, phototoxic reactions, cumulative pain-free sunlight exposure, and patient global impression of change.
John Quisel, CEO of Disc, expressed enthusiasm about the potential for accelerated approval, highlighting the significance of using PPIX reduction as a surrogate endpoint.
APOLLO Trial Design and Patient Population
The Phase III APOLLO study is planned to commence by mid-2025. It will be a single, randomized, double-blind, placebo-controlled trial involving patients aged 12 and older diagnosed with EPP or XLP. This design aims to provide robust evidence of bitopertin's efficacy and safety.
Bitopertin's Mechanism and Prior Clinical Data
Bitopertin is designed to reduce levels of protoporphyrin IX (PPIX), the phototoxic compound that accumulates in the blood of EPP and XLP patients. By lowering PPIX levels, the drug aims to decrease sensitivity to sunlight and improve patients' quality of life.
Data from a Phase II trial demonstrated that once-daily doses of bitopertin (20mg and 60mg) were well-tolerated over 24 weeks in 22 patients. Notably, no serious adverse events were reported during the study. Participants also had the option to continue in an open-label extension for an additional 24 weeks, showing continued positive outcomes.
Current Treatment Landscape and Unmet Needs
Currently, only one treatment is approved for EPP: afamelanotide (Scenesse) by Clinuvel Pharmaceuticals. Scenesse increases skin pigmentation and has anti-inflammatory properties, offering protection against light-induced skin damage. Clinical trial data (NCT01605136) showed that Scenesse allowed patients to spend an average of 20 additional minutes in sunlight daily without pain, compared to placebo.
Despite the availability of Scenesse, there remains an unmet need for additional therapies that can effectively manage EPP and XLP. Bitopertin, with its distinct mechanism of action, could provide a valuable alternative for patients.
Ethical Considerations in EPP Trials
Clinical trials in EPP present unique ethical challenges. As highlighted at the Outsourcing in Clinical Trials (OCT) DACH 2024 conference, the potential for phototoxic burns in participants randomized to control groups raises concerns. Additionally, patient selection bias may occur, as more severely affected patients might hesitate to participate due to the risk of experiencing burns during the trial.
Financial Support
Disc Medicine recently secured $225.5 million through an upsized public offering to advance its pipeline, including bitopertin. This financial boost underscores the company's commitment to developing innovative therapies for rare diseases.
