Ionis, Arrowhead file dueling patent lawsuits over genetic-disorder drug

Ionis Pharmaceuticals

11/09/2025 20:12

Corrects paragraph 7 to clarify that Ionis is not seeking to block Arrowhead drug sales

By Blake Brittain

Sept 11 (Reuters) - Ionis Pharmaceuticals IONS.O sued biotech rival Arrowhead Pharmaceuticals ARWR.O for patent infringement in California federal court on Thursday over Arrowhead's planned competitor to Ionis' drug Tryngolza.

Ionis' lawsuit said that Arrowhead copied its patented messenger RNA (mRNA) technology to develop its drug for familial chylomicronemia syndrome (FCS), a genetic disorder that prevents the body from breaking down fats.

Pasadena, California-based Arrowhead filed a separate lawsuit against Ionis in Delaware federal court on Wednesday, seeking to invalidate Ionis' patent. Arrowhead said in a press release on Thursday that its drug was "based entirely on work developed internally at Arrowhead, which Ionis was not involved with and provided no contribution to whatsoever.”

Ionis said in a statement that it was "confident in our IP around FCS and will vigorously defend our patent position," and that it was "not seeking to block patient access to this potential new therapy."

The U.S. Food and Drug Administration approved Ionis' Tryngolza in December, the company's first wholly owned drug and the United States' first approved treatment for FCS. The disorder prevents the body from breaking down triglycerides, which cause pancreatic inflammation when they accumulate in the blood.

The company's shares jumped by 34% earlier this month after Tryngolza was shown to significantly reduce patients' triglyceride levels in clinical trials, with analysts estimating that Tryngolza sales could peak near $2.5 billion annually.

Ionis said in its lawsuit that Arrowhead applied for FDA approval of its "copycat" drug plozasiran in January. The complaint said that Arrowhead intends to sell plozasiran to treat FCS "in blatant disregard for Ionis’s patent rights." Ionis asked the California court for an unspecified amount of monetary damages.

Arrowhead said in its Delaware complaint that Ionis' allegations were baseless and meant to obstruct Arrowhead's launch of its competing drug.

The cases are Ionis Pharmaceuticals Inc v. Arrowhead Pharmaceuticals Inc, U.S. District Court for the Central District of California, No. 2:25-cv-08609 and Arrowhead Pharmaceuticals Inc v. Ionis Pharmaceuticals Inc, U.S. District Court for the District of Delaware, No. 1:25-cv-01130.

For Ionis in California: Jessamyn Berniker, Thomas Fletcher and Kathryn Kayali of Williams & Connolly

For Arrowhead in Delaware: Susan Morrison, Louis Fogel, Megan Chacon and Madelyn McCormick of Fish & Richardson

Read more:

US FDA approves Ionis Pharma's genetic disorder drug

Ionis shares surge after drug to lower blood fat shows promise in trials

 (Reporting by Blake Brittain in Washington)