BridgeBio's Growth Disorder Drug Excels in Phase II Update

BridgeBio Pharma's investigational therapy infigratinib has yielded promising results in the Phase II PROPEL 2 study, aimed at treating children with achondroplasia. This rare genetic disorder causes abnormal bone growth, resulting in dwarfism with disproportionately short limbs. The study's findings exceeded expectations, particularly in Cohort 5, where children received the highest dose of the oral FGFR3 inhibitor at 0.25 mg/kg per day.

At the 12-month mark, the treatment resulted in a mean annualized height velocity (AHV) increase of 2.51 cm/year from baseline. This improvement remained consistent, showing a 2.50 cm/year increase at 18 months. Analysts, like Salim Syed of Mizuho Securities, had anticipated only a 2-cm rise in AHV, making these results notably impressive. Syed commented that this "best-in-class" data should put to rest any discussions about the drug's potential, particularly highlighting its magnitude of effect.

Moreover, the study revealed significant improvements in body proportions. By the 18th month, the ratio between the upper and lower body segments improved markedly, with a mean ratio declining from 2.02 at baseline to 1.88. This is a critical finding because, in a similar 52-week study, children treated with BioMarin Pharmaceutical's Voxzogo (vosoritide) did not show significant improvements in body segment ratios. Voxzogo, a once-daily injection, was first approved in 2021 after showing an AHV increase of 1.57 cm/year compared to placebo. Its label was expanded last October to include children under five. The body proportionality data from the PROPEL 2 study might therefore provide a competitive edge for infigratinib in investor discussions.

Another encouraging aspect of infigratinib's profile is its clean safety record. Throughout the study, there were no treatment-related adverse events in Cohort 5, and no incidents of hyperphosphatemia or hypergrowth were reported. This safety profile is an essential factor in the drug's overall evaluation and future use.

Currently, BridgeBio has initiated a Phase III registrational study named PROPEL 3, which is actively recruiting participants and is expected to reach full enrollment by the end of the year. If successful, this trial could pave the way for infigratinib's approval and subsequent commercial availability. Mizuho Securities estimates that infigratinib could achieve peak sales of $1.2 billion for the treatment of achondroplasia, reflecting the high expectations and market potential for this therapy.

In summary, the latest data from the PROPEL 2 study showcase infigratinib as a highly effective and safe treatment option for children with achondroplasia, particularly in improving height velocity and body proportions. The drug’s promising results, combined with its favorable safety profile, position it as a strong competitor against existing treatments like BioMarin's Voxzogo. With the ongoing Phase III PROPEL 3 study, infigratinib is well on its way to potentially becoming a significant player in the treatment landscape for achondroplasia.