Amgen hits a snag in its plot to challenge AbbVie's blockbuster Humira

Amgen ($AMGN), at work on a biosimilar of AbbVie's ($ABBV) best-selling treatment, got an unfavorable decision from U.S. regulators that could delay the launch of its take on Humira.

The U.S. Patent and Trademark Office declined to review a pair of AbbVie patents that Amgen contends are invalid, Reuters reports. Amgen isn't giving up, promising to challenge AbbVie's intellectual property in court in hopes of launching its Humira knockoff in 2017.

For its part, AbbVie has said its patent protection should keep the treatment safe from biosimilar competition untill 2022, according to Reuters.

Amgen submitted its take on AbbVie's injection, the top-selling medicine in the world, for FDA review in November, touting Phase III results in which version matched up to Humira in more than 500 patients with rheumatoid arthritis. Humira, approved for a range of autoimmune diseases, brought in about $12.5 billion for AbbVie last year, accounting for more than 60% of the drugmaker's total revenue.

Humira is one of the major targets for companies around the globe developing biosimilars. Trailing Amgen is Merck ($MRK), working with Samsung Bioepis, plus Novartis ($NVS) and partners Baxalta ($BXLT) and Momenta Pharmaceuticals ($MNTA).

For Amgen, setting sites on Humira is in part an effort to dull the blow of mounting biosimilar competition for its own top products. Novartis' Sandoz business launched the U.S.'s first biosimilar last year with a version Amgen's Neupogen, marketed as Zarxio. And a host of contenders are targeting Amgen's Humira rival, the blockbuster autoimmune treatment Enbrel, but the company believes it has secured patents that will protect that drug in the U.S. through 2029.

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