FDA puts the brakes on another gene therapy trial

Sept. 7, 2021

BioMarin Pharmaceutical announced this week that the FDA has placed a clinical hold on its trial for a gene therapy targeting patients with phenylketonuria (PKU).

According to the company, the trial pause stems from concerns over liver tumors found in mice during a preclinical study. Interim safety data from the study revealed that six out of seven mice given the treatment — BMN 307 — at the highest dose were found to have the tumors when autopsied 52 weeks after dosing. The mice were predisposed to develop malignancy, and it is unclear how transmissible the same trend would be in humans. 

The company’s head of R&D noted that more than 3,000 patients have received the treatment at a lower dose in the ongoing phase 1/2 trial and so far, there have been no reports of cancer. 

PKU is a very rare condition that hinders a patient’s ability to metabolize an essential amino acid found in most protein-rich foods, which can lead to toxicities in the brain. 

BM 307 is one of four drugs in BioMarin’s clinical pipeline, and the company has successfully launched a number of products aimed at treating mucopolysaccharidosis (MPS), a group of inherited metabolic diseases. 

The company suffered a setback last year, however, when its gene therapy for severe hemophilia A was given a complete response letter from the FDA. 

This latest clinical hold is also the latest in a string of trial pauses impacting gene therapies in the last year. Just last week, Astellas announced that it is pausing a gene therapy study due to abnormal liver function tests in a trial participant.