Arrowhead Pharmaceuticals-

Arrowhead Pharmaceuticals is at University Research Park, Madison.

Arrowhead Pharmaceuticals is getting a $25 million milestone payment from Janssen Pharmaceuticals, and the payment is coming sooner than expected.

Arrowhead is headquartered in Pasadena, California, but its main employment base is in Madison, at 502 S. Rosa Road. The firm has begun administering doses of its chronic hepatitis B drug to patients in a trial that’s been tweaked.

The new study looks at how Arrowhead’s JNJ-3989 — formerly known as ARO-HBV — works in combination with two other drugs chosen by Janssen but not publicly identified.

Janssen bought the rights to the hepatitis B drug last October in a deal that gave Arrowhead $250 million at the outset — $175 million from Janssen and a $75 million investment from Johnson & Johnson Innovation. The next milestone payment was supposed to amount to $50 million when the second phase of clinical trials began. Instead, Arrowhead is getting half of that, or $25 million, with the addition of this mid-stage trial and will receive the rest at a later point.

The drug candidate is based on RNA interference, a process known as gene silencing. It aims to reduce the messenger RNA that directs production of proteins tied to a disease.

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Studies so far have shown JNJ-3989 has been effective at lowering the presence of the hepatitis B virus after three doses, according to results released in April.

“With this type of therapeutic, this is the best antigen reduction that’s been published,” said Tao Pei, Arrowhead senior director of chemistry.

The current clinical trial involves more than 100 patients and is expected to be completed by the end of January 2020.

Under the deal with Janssen, Arrowhead could eventually receive as much as $3.7 billion if the hepatitis B drug and additional drugs aimed at up to three more disease targets are successful.

Arrowhead has more than 100 employees in Madison, where its research and development is handled, and about 20 employees in Pasadena.

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