A placebo response rate of 33.3% should have been the first warning sign: when nearly one-in-three patients on sugar pills meet your primary hemoglobin endpoint, differentiation becomes nearly impossible, and that is exactly what killed tebapivat’s future in sickle cellsickle cell disease. Agios disclosed topline Phase 2 results Monday, and the numbers tell a straightforward story. Across three once-daily dose levels of the oral pyruvate kinase (PK) activator, hemoglobin response rates (defined as a gain of at least 1.0 g/dL from baseline averaged over weeks 10 through 12) ranged from 29.4% to 47.1%, producing no meaningful separation from placebo and no dose-response signal worth chasing.
The trial enrolled 59 participants aged 16 and older, randomized across 2.5 mg, 5.0 mg, and 7.5 mg tebapivat arms or placebo over a 12-week double-blind period. The design was explicitly built to answer one clinical question: does tebapivat produce a differentiated profile relative to other PK activators? The answer was no. Hemoglobin improvements and reductions in hemolysis were present across all active arms, confirming that the mechanism works, but the magnitude and consistency were indistinguishable from what the class already delivers. Safety presented no new signals. Agios has discontinued development in this indication, a clean and unsentimental call given the data.
The deeper consequence lands on mitapivat, Agios’s lead PK activator, which is now carrying the full weight of the company’s sickle cell ambitions. Its supplemental NDA is under FDA Priority Review, with a PDUFA date of November 1, 2026. The Phase 3 RISE UP trial gave mitapivat a 40.6% hemoglobin response rate against a pre-specified threshold, supporting the accelerated approval application. Tebapivat’s failure does not undermine that filing, but it does strip away any optionality Agios had if the FDA’s review of mitapivat encounters friction. The company was implicitly running two horses in the PK activation space for sickle cell; now it is running one.
The single marker worth tracking is the complete response data package Agios submits in support of the mitapivat Priority Review, specifically whether the RISE UP hemoglobin response rates hold up across subgroups that regulators flag during review. If the FDA requests additional analyses or raises questions about the accelerated approval pathway, Agios now has no backup PK program to point toward, and that changes its negotiating position considerably heading into the November decision window.
Jon Napitupulu is Director of Media Relations at The Clinical Trial Vanguard. Jon, a computer data scientist, focuses on the latest clinical trial industry news and trends.
