Ultragenyx and Kyowa Hakko Kirin Say FDA Accepted Application on XLH Therapy

Rare Disease Staff

Ultragenyx Pharmaceutical and Kyowa Hakko Kirin said that the U.S. Food and Drug Administration has accepted the Biologics License Application for burosumab, an experimental treatment for pediatric and adult patients with X-linked hypophosphatemia, a rare genetic disorder that causes abnormal bone formation and bone weakness.

The FDA has granted burosumab Priority Review status, which is available to drugs that treat a serious condition and, if approved, would provide a significant improvement in safety or effectiveness. The agency previously granted burosumab Breakthrough Therapy designation from the FDA for the treatment of X-linked hypophosphatemia in pediatric patients one year and older.

X-linked hypophosphatemia has an estimated prevalence of 3,000 pediatric and 9,000 adult patients in the United States. The symptoms, which usually manifest themselves when a child begins to bear weight on his or her legs, includes bowing and/or twisting of the lower legs, or knock-knees. Teeth may be slow to appear, and the child may be very small for his or her age. Most cases are diagnosed during childhood, however, the diagnosis is sometimes not made until adulthood because of the variety and severity of symptoms that can occur.

“XLH is a debilitating disease and there are no current treatment options that address the underlying cause,” said Emil Kakkis, president and CEO of Ultragenyx. “We are pleased that the FDA has granted priority review and are looking forward to working with the agency in the coming months with the goal of bringing this potential new treatment to patients as quickly as possible.”

Burosumab is an experimental recombinant fully human monoclonal antibody discovered by Kyowa Hakko Kirin. It acts against the phosphaturic hormone fibroblast growth factor 23, or FGF23. FGF23 is a hormone that reduces serum levels of phosphorus and active vitamin D by regulating phosphate excretion and active vitamin D production by the kidney.

Burosumab is designed to bind to and thereby inhibit the biological activity of FGF23. By blocking excess FGF23 in patients, burosumab is intended to increase phosphate reabsorption from the kidney and increase the production of vitamin D, which enhances intestinal absorption of phosphate and calcium.

Ultragenyx, Kyowa Hakko Kirin and Kyowa Kirin International, a wholly owned subsidiary of Kyowa Hakko Kirin, have been collaborating on the development and commercialization of burosumab globally.

The FDA previously designated burosumab as a drug for a rare pediatric disease, enabling issuance of a priority review voucher if burosumab is approved. The voucher is potentially lucrative because it is transferrable and can be used to accelerate the approval of any drug. That could give the holder faster access to mutibillion markets. In the past, such vouchers have sold for as much as $350 million.

The agency is expected to act on the application by April 17, 2018. It has not yet said whether it will hold an advisory committee meeting to discuss the application.

October 10, 2017