Children whose dwarfism stems from achondroplasia have had few treatment choices other than surgeries to address spinal or limb complications. A drug is now available that could head off some of those problems in the first place. The FDA has approved a BioMarin Pharmaceutical therapy that addresses the genetic mutation at the root of the inherited disorder.
The regulatory nod for the drug, vosoritide, covers children 5 and older who have achondroplasia and still have open growth plates. The decision comes three months after the European Commission awarded marketing authorization for the drug, which is sold under the name “Voxzogo,” for children from age 2 until their growth plates close.
San Rafael, California-based BioMarin said in an investor presentation that as the first approved medicine that addresses the underlying cause of achondroplasia, Voxzogo has the potential to become a blockbuster seller. Chief Commercial Officer Jeff Ajer said he expects the drug will eclipse sales of the company’s enzyme replacement therapy Vimizan, which accounted for $544.4 million in sales last year.
“What I believe is Voxzogo has the biggest long term revenue potential, relative to the products that have been approved before it, including Vimizan, which is our largest marketed product to date,” Ajer said during a conference call Friday.
Bone development is regulated by several proteins. Achondroplasia is caused by a mutation to the gene responsible for producing fibroblast growth factor receptor 3 (FGFR3), a protein that down-regulates bone growth. The mutation leads to overactivity of this protein, which in turn results in people who have short limbs and an average height of about 4 feet. While achondroplasia does not typically impair mental abilities, it can require surgeries to correct spinal deformities or to straighten bowed legs, according to the National Organization for Rare Disorders.
FGFR3 is counterbalanced in the body by a peptide called C-type natriuretic peptide (CNP). Voxzogo is an analog of that peptide. FDA approval of the BioMarin drug is based on the results of a Phase 3 study enrolling 121 children 5 and older. Those participants were randomly assigned to receive either a once-daily injection of the study drug or a placebo. The goal of the study was to measure annualized growth velocity, which is the rate of height growth, after one year of treatment.
Study results showed that children who received the BioMarin drug grew an average of 1.57 centimeters taller compared to those who were given a placebo. Side effects included injection site reactions, vomiting, and decreased blood pressure. Decrease in blood pressure is listed as a warning on the drug’s label.
BioMarin estimates that 21,000 children worldwide — about 3,000 of them in the U.S.— have achondroplasia and are eligible for treatment with Voxzogo. The company has set a wholesale price of $899 per vial, which Ajer said is in line with wholesale pricing in France and Germany. One vial represents one daily dose of Voxvogo, and at the wholesale price, the annual cost of therapy tops $320,000. With rebates and discounts, BioMarin calculates that the average revenue it will draw per U.S. patient will be about $240,000 annually. Voxzogo is still under regulatory review in Japan, Brazil, and Australia.
Other companies are aiming to challenge BioMarin in achondroplasia. A peptide drug from Ascendis Pharma is in mid-stage clinical development. Pfizer has a mid-stage biologic drug candidate via its $340 million acquisition of Therachon in 2019. Tyra Biosciences raised nearly $173 million from its September IPO to fund development of its small molecule inhibitor of FGFR3. Though that biotech’s focus is blocking FGFR3’s role in cancer, it also plans to develop its lead drug candidate for achondroplasia.
Friday’s FDA approval of Voxzogo was made under the agency’s accelerated approval pathway, which permits earlier approval of drugs for serious conditions with limited treatment options. These speedier decisions, based on a surrogate endpoint — an indication that a drug might be working – require a post-marketing study to confirm patient benefit. To fulfill that requirement, BioMarin plans to use the ongoing open-label extension studies, which will compare participants to the available natural history of patients who have had the condition. The main goal will be to assess final adult height.
Hank Fuchs, BioMarin’s president of worldwide research and development, said BioMarin’s post-marketing study plans put the company in a good position to gather the adult height data needed to convert the accelerated approval to a full approval, helping to fend off would-be competitors. Fuchs explained that after BioMarin secures full approval, annualized growth velocity will no longer be available as a surrogate endpoint for accelerated approval. That means subsequent achondroplasia drugs will need to meet the same adult height threshold BioMarin must show for full FDA approval.
“I think the expectation is that in the future hundreds of patients will be required to cross the finish line at final adult height before any followers can enter into this market,” Fuchs said. “We feel really good about the post-marketing requirement because it establishes a fairly high bar for subsequent approvals.”
BioMarin said Voxzogo will become available to U.S. patients by late December, if not sooner.
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