Ultragenyx, Kyowa Hakko Kirin plan a date with the FDA after positive PhIII for X-linked hypophosphatemia

Emil Kakkis

Shares of Ultragenyx surged about 10% after the biotech reported clearly positive Phase III data for their Kyowa Hakko Kirin-partnered drug for X-linked hypophosphatemia. And now they plan to hustle that data package to regulators at the FDA and EMA.

Researchers recruited 134 patients for the study, and found that 94% of the patients treated with burosumab achieved normal serum phosphorus levels, compared to only 8% in the placebo arm. The drug also hit on a couple of secondary endpoints, rating improvements in stiffness and physical function, but missed statistical significance on the pain score.

Kyowa Hakko Kirin discovered this antibody, which targets phosphaturic hormone fibroblast growth factor 23, or FGF23, which limits serum levels of phosphorus and active vitamin D. The drug is also in development for tumor-induced osteomalacia, which is also characterized by excess levels of FGF23.

These two companies struck a development deal for this drug back in 2013, with Ultragenyx leading development efforts in the XLH indication and a split on the development costs. If the drug is approved, Ultragenyx and KHK will share commercial responsibilities and profits in the US and Canada. KHK will commercialize the therapy alone in the EU while Ultragenyx will develop and commercialize KRN23 in Mexico, Central and South America.

“These data demonstrate a clinical improvement in patients treated with burosumab and support the potential for treatment of adults,” said Ultragenyx CEO Emil Kakkis in a statement. “When combined with a favorable safety profile and a strong serum phosphorus response, we believe these clinical data should support regulatory submissions in adults with XLH, and we look forward to discussing our filing plans with the U.S. FDA.”

Ditto the executive crew at partner Kyowa Hakko Kirin.

“This study provides valuable additional placebo controlled data to that already obtained from the global clinical development program for pediatric and adult patients with XLH.” said Mitsuo Satoh, VP and R&D chief at Kyowa Hakko Kirin. “I believe burosumab has the potential to be an effective treatment option for patients with XLH.”

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