FDA Rejects Protalix’s Enzyme Replacement Therapy for Rare Genetic Disease

April 28th, 2021 – Earlier today, Protalix BioTherapeutics, Inc. announced the FDA’s rejection of its investigational enzyme replacement therapy for Fabry disease. Since the news, the Israel-based biopharma’s shares dropped more than 43% in pre-market trading.

“While disappointing, we remain confident in the strength of our data and in the depth of our program,” said Dror Bashan, President and CEO of Protalix. “We remain committed to the program and to working with the FDA and Chiesi toward the approval of PRX‑102.”

Enzyme Replacement Therapy

Fabry disease is a rare inherited disorder caused by the mutation of the GLA gene that produces the α-Galactosidase-A enzyme. A lack of this enzyme results in the accumulation of a type of fat in the body leading to complications like heart attacks, stroke, or kidney damage.

Diagnosis usually involves measuring the levels of this enzyme in the patient. Common treatments include pain killers that provide symptomatic relief or medications that prevent the symptoms from becoming life-threatening. At present, the FDA has approved two enzyme replacement therapies for this condition–Sanofi Genzyme’s Fabrazyme (agalsidase beta) and Amicus Therapeutics’ Galafold (migalastat). Fabrazyme was the first enzyme replacement therapy to be approved for this condition in 2004 and has become a standard of care.

Protalix’s PRX‑102 or pegunigalsidase alfa is a chemically modified, stabilized version of the recombinant α-Galactosidase-A enzyme produced by the company’s proprietary ProCellEx® plant cell-based protein expression system. In 2017, Protalix entered into a collaboration with Chiesi Farmaceutici S.p.A. to commercialize the therapy outside of the US. A year later, it expanded the partnership to give commercialization rights to Chiesi within the US market as well.

FDA’s Complete Response Letter

In May 2020, both companies submitted the BLA for PRX‑102 through the FDA’s accelerated approval pathway program. The document included data from the Phase 1/2 trials, NCT01678898 and NCT01769001, and interim data from the ongoing Phase 3 BRIDGE trial, NCT03018730.

Although the FDA has provided a complete response letter today, there were no concerns about the potential safety or efficacy of PRX–102, Protalix said in a statement. Rather, the agency required an inspection of Protalix’s manufacturing facility in Carmiel, Israel, before it arrived on a decision. Due to COVID-19 related travel restrictions, the inspection was not possible during the review period.

The FDA has also noted that Fabrazyme was recently converted to full approval. Therefore, this fact must be addressed in any potential resubmission of the BLA for PRX–102.

“We thank the patients and clinicians participating in our completed and ongoing clinical studies evaluating PRX-102. We are continuing to coordinate closely with the FDA to address and quickly resolve the deficiencies contained in the CRL.” said Giacomo Chiesi, Head of Chiesi Global Rare Diseases

“Based on extensive clinical data including results from the Phase 3 BRIDGE clinical trial of PRX-102 for the proposed treatment of Fabry disease, we continue to feel strongly that PRX‑102 is an important option for the treatment of Fabry disease in adult patients, and we are continuing with our efforts to make this therapy available to patients,” added Chiesi.

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