Hot on the heels of a clinical hold, Arrowhead torches its clinical pipeline, slashes staff

Just three weeks after Arrowhead Pharmaceuticals $ARWR was forced to put its lead program on clinical hold, the biotech is torching everything related to its EX1 delivery vehicle, wiping out three RNAi treatments — all of its clinical-stage work — and eliminating close to a third of its staff in a reorganization.

The unexpected news, which stunned a few analysts on Tuesday evening, eliminates its ARC-520, ARC-521 and ARC-AAT efforts. Its stock was eviscerated, losing 60% of its value on the news.

The biotech says it had little choice in the matter. Regulators forced the hold due to non-human primate deaths in a tox study. And they’ve been making it clear that all the work related to EX1 would be put in limbo while they sorted out the cause. Still, it’s extraordinarily rare for a company to abandon trials this quickly as investigators try to nail down the cause for concern.

The company also tried to give it a positive spin, saying that they’ve learned a considerable amount about their drug technology which should give them an edge on the second generation products. But that’s likely to be cold comfort for anyone following the setback today.

The RNAi field has gone through some extreme highs and lows over the years. While work on a number of programs has finally reached late-stage studies, even some of the most promising treatments have been plagued by safety fears, as Alnylam $ALNY rediscovered for itself recently when it deep-sixed one of its top late-stage programs — revusiran — after tracking a higher death rate in the drug arm. And Arrowhead itself grabbed Novartis’ RNAi portfolio last year after the pharma giant decided to abandon its work in the field.

Pasadena, CA-based Arrowhead had this to say in a statement on Tuesday:

The company believes it is prudent to focus its development resources entirely on its subQ and extra-hepatic pipeline, which includes programs in HBV, AAT, Factor 12, HIF-2alpha, and other unannounced programs. In addition to its own pipeline, Arrowhead is also focused on providing full resources to support its partnership with Amgen and potential future partnerships for its subQ and extra-hepatic delivery systems.

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