Pfizer and OPKO's Growth Hormone Deficiency Drug Denied by FDA

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Shares of Opko Health plunged more than 16% in premarket trading after the U.S. Food and Drug Administration rejected the once-weekly human growth hormone somatrogon the company co-developed alongside Pfizer for the treatment of growth hormone deficiency (GHD) in pediatric patients.

The FDA issued a Complete Response Letter for the Biologics License Application for somatrogon. However, in its brief announcement, Pfizer and OPKO did not elaborate on the reasons for the regulatory agency’s rejection. The larger pharma company is still evaluating the FDA’s comments and plans to work with the agency in order to determine a path forward. 

Somatrogon is an investigational biologic product that is “glycosylated and comprises the amino acid sequence of human growth hormone and one copy of the C-terminal peptide (CTP) from the beta chain of human chorionic gonadotropin (hCG) at the N-terminus and two copies of CTP (in tandem) at the C-terminus,” according to Pfizer.

Brenda Cooperstone, chief development officer of Rare Diseases for Pfizer Global Product Development, said they remain confident in the potential treatment benefits for somatrogon. 

We will work closely with the FDA to determine the best path forward to bring this important once-weekly treatment option to pediatric growth hormone deficiency patients and their families,” Cooperstone said in a statement.

Growth hormone deficiency is a rare disease that is characterized by the inadequate production of somatropin, the hormone that regulates growth from the pituitary gland. The condition can be caused by genetic mutations or acquired after birth. The disease affects one in 4,000 to 10,000 children.

Pfizer and OPKO’s BLA was based on Phase III trial data that compared somatrogon to Pfizer’s previously-approved Genotropin (somatropin), a once-per-day treatment. Top-line data from the study showed that growth was slightly greater in patients who received somatrogon than Genotropin, 10.12 centimeters per year compared to 9.78 centimeters per year. Additionally, change in height standard deviation scores at 6 and 12 months, key secondary endpoints, were higher in the somatrogon dosed once-weekly cohort in comparison to the somatropin dosed once-daily cohort.

Genotropin has been approved for GHD in children and adults, as well as for treatment of Prader-Willi syndrome and Turner syndrome. 

Pfizer and OPKO, who have partnered since 2014 on the development of somatrogon, hoped their treatment would have become a contender with Ascendis Pharma’s Skytrofa (lonapegsomatropin-tcgd), which was approved for children one year and older who have growth failure from inadequate secretion of endogenous growth hormone (GH).

Pfizer and OPKO are also seeking regulatory approval of somatrogon across the globe. Last week, somatrogon was approved in Japan and will be marketed under the branded name Ngenla. It has also been approved in Canada and Australia. The European Commission is expected to make a decision later this year. 

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