It’s been one thing after another for rusfertide from Protagonist Therapeutics Inc. for the past year. Now the U.S. FDA has told the company it wants to rescind the breakthrough designation, a relatively rare occurrence, based on observed malignancies in a follow-up to September’s clinical hold.
Shares of Protagonist Therapeutics Inc. (NASDAQ:PTGX) fell 62% to $17.53 on Sept. 17 after it reported finding malignant skin tumors in a mouse model test of its most advanced candidate, rusfertide for blood disorders. After the company notified the FDA, the regulator put the program on a clinical hold, leading dosing of patients in all ongoing trials of rusfertide to be halted for now. The development could impact Protagonist's ability to start phase III testing of the candidate in polycythemia vera (PV) early in 2022, as well as efforts to expand its development to a third indication beyond PV and hereditary hemochromatosis (HH) by the end of this year, as it has planned.
“All along our guidance has been that, look, we are doing multiple open-label studies with the intent of picking a winner,” said Protagonist Therapeutics Inc. CEO Dinesh Patel during a conference call with investors. “Today, we have picked a winner by a huge margin” in the shape of PTG-300, an injectable hepcidin mimetic for the rare blood cancer polycythemia vera (PV).