Insmed pointed to a strong placebo response as the reason for the trial’s failure.
Insmed’s oral drug Brinsupri did not ease the burden of sinus symptoms in a mid-stage study of chronic rhinosinusitis without nasal polyps, forcing the New Jersey biotech to discontinue its program in this indication.
Writing to investors on Thursday, analysts at Guggenheim Partners called the mid-stage miss a “rare disappointment” for Insmed—but one that nevertheless sent its shares tumbling 16% to $166.55 apiece at market close.
“Based on our conversation with management, the BiRCh trial was well-conducted and delivered clear results, but the patients on placebo performed much better than expected,” Guggenheim noted.
In the Phase IIb BiRCh study, Insmed enrolled nearly 290 patients who were randomly assigned to receive 10-mg Brinsupri, 40-mg Brinsupri or placebo, on top of their usual daily mometasone furoate nasal spray background therapy. Data presented on Thursday showed that at 24 weeks, patients given the respective doses of Brinsupri saw a 2.2- and 2.33-point decrease in the Sinus Total Symptom Score (sTSS), a tool used to measure rhinitis symptoms.
While these changes indicated improvements due to treatment, there was also improvement in patients in the placebo arm, whose sTSS scores dropped 2.44 points at the same time point.
In conversation with Guggenheim, Insmed management indicated that the BiRCh readout came earlier than expected. “Results were so unequivocal that they needed minimal time to process the results and decide to discontinue all further work in this indication,” the analysts said.
Still, Guggenheim projects that the effects of Thursday’s rhinosinusitis fail will be “limited,” particularly given Brinsupri’s bright market prospects in non-cystic fibrosis bronchiectasis (NCFB). “We continue to see Brinsupri having ~$9Bn in peak sales potential in NCFB alone,” the analysts wrote.
The BiRCh readout comes months after Insmed in June announced that its trepostinil palmitil inhalation powder (TPIP) aced a Phase IIb study in pulmonary arterial hypertension. Data presented at the time showed that TPIP led to a 35% improvement in pulmonary vascular resistance, a key measure of heart function, and to better six-minute walk distance.
In its third quarter report, Insmed said that it would start a Phase III trial for TPIP in pulmonary arterial hypertension early next year. The biotech is also testing TPIP for pulmonary hypertension associated with interstitial lung disease, for which it expects to launch a late-stage study before the year ends.
On Thursday, Guggenheim pointed to TPIP as one of the main reasons for its optimism about Insmed’s business. “We believe the Street continues to significantly underappreciate the potential for TPIP to become the preferred treprostinil across multiple large indications,” the analysts wrote.
