FDA hits pause on Protagonist’s blood cancer med after mouse study turns up skin tumors

FDA hits pause on Protagonist’s blood cancer med after mouse study turns up skin tumors

Protagonist Therapeutics’ treatment for a rare, slow-growing blood cancer is under an FDA clinical hold after the company reported safety concerns in a nonclinical mouse study.

The mice in the study developed benign and malignant skin tumors, the company announced in a statement Friday. The FDA verbally told the company about the hold, Protagonist said.

Shares of the California biotech plummeted 56% to $19.98 in premarket trading Friday, compared to a prior close of $46.13.

Protagonist is testing the drug, rusfertide, in several phase 2 trials. These include two studies in polycythemia vera (PV), a slow-growing blood cancer in which the body makes too many red blood cells, and one study in hereditary hemochromatosis, a group of rare disorders in which iron builds up in organs such as the liver, heart and pancreas.

“Patient safety is our absolute top priority,” said Protagonist President and CEO Dinesh Patel, Ph.D., in the statement. “We are fully committed to working closely with the FDA in understanding and evaluating potential clinical risks and determining next steps for the development of rusfertide.”

The company will provide more safety reports, update brochures and forms related to its clinical studies and make necessary changes to study protocols, Protagonist said in the statement.

Rusfertide is a synthetic form of the hormone hepcidin, which controls the production of red blood cells thanks to the role it plays in the absorption, storage and distribution of iron in the body.

Current treatments for PV include having one’s blood drawn in a process called phlebotomy to reduce the volume of red blood cells in the body. Many patients will also receive medicines that tamp down on the formation of blood cells in the bone marrow, such as the chemo drug hydroxyurea, and drugs like aspirin to lower the risk of blood clots. In 2014, the FDA approved Incyte’s JAK inhibitor Jakafi for PV patients for whom hydroxyurea does not work.

The FDA hold comes three months after Protagonist snagged a breakthrough therapy tag for rusfertide and presented data for the drug at the European Hematology Association’s Virtual Congress.

It comes six months after the company unveiled plans to start a phase 3 trial for rusfertide in 200 to 250 adult patients with PV, following feedback from the FDA and the European Medicines Agency.

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