As election storm gathered, Arrowhead drops word about a clinical hold

As everyone’s attention was being commanded by the big presidential vote Tuesday night, Arrowhead Pharmaceuticals $ARWR chose to put out word that its lead program has been put on hold by the FDA.

The Pasadena, CA-based biotech says that regulators clamped down on the Phase II for ARC-520, its treatment for hepatitis B, after the deaths of primates in an ongoing toxicology study. That study involved higher doses than what is being used in human studies, using its EX1 delivery vehicle. Arrowhead did not explain how many of the primates died, but said investigators did not know what caused the deaths, which are under investigation.

The clinical hold will put the brakes on a study involving 12 patients as Arrowhead researchers respond to regulators’ queries.

The biotech emphasized that it has only gathered evidence of serious adverse reactions from three out of hundreds of patients treated with EX1. And across the work done on ARC-520, ARC-521 and ARC-AAT investigators have not seen the kind of issues reported in the primate trial.

The drug — billed as a potential cure — uses small interfering RNA, siRNA, to slash levels of HBV proteins as well as the RNA template required to produce viral DNA. Arrowhead shares are down 17% in pre-market trading.

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