US drugmaker Spectrum Pharmaceuticals has said it plans to developa biosimilar version of Roche and Biogen Idec's cancer and arthritis drug Mabthera/Rituxan(rituximab), with the help of Canadian partner Viropro.

While specific financial aspects of the agreement have not beenrevealed, Viropro said it is a "multimillion" dollar contract andthat it stands to receive milestone payments over a period of three years, aswell as royalties on eventual sales.

Rituxan is Roche's second biggest-selling product with sales of almost$6 billion a year in indications including non-Hodgkin's lymphoma, chroniclymphocytic lymphoma and rheumatoid arthritis. In the past Roche has claimedpatent protection for the drug until at least 2015 and possibly 2018 in the USAand 2013 elsewhere, and Spectrum has indicated only that it plans to enter themarket on "patent expirations for rituximab over the coming years."

The US cancer specialist has no heritage in biosimilars. Its twocommercialised products were bought-in from other companies, and it has apipeline of novel oncology drugs both developed in-house and in-licensed. Itcan however offer specialist sales and marketing network in oncology, while Viroprobrings its expertise in cell culture and bioprocessing technologies to thealliance.

Indeed, Viropro has made no secret of its desire to findcommercial partners for its biosimilar cell lines and manufacturing processes,and its president and chief executive Dr. Rajiv Datar said the Spectrumalliance was "an importantbreakthrough for us in the North American market."

The announcement comes a few months after Israeli generics giantTeva Pharmaceutical Industries said it had started clinical testing of its ownbiosimilar version of rituximab.

Teva is expected to put in a strong bid in the emerging biosimilarmarket given its two-year-old alliance with contract manufacturer Lonza. Thatsaid, Spectrum would likely have to capture only a small percentage ofRituxan's market share in order to recoup a healthy return on its investment.

With over $30 billion-worth of biologic drugs losing patentprotection within the coming years, analysts have estimated that biosimilarscould quickly become a $10 billion category.

A number of biosimilar products are already in the market inEurope, notes Spectrum, and since the enactment of the Biologics PriceCompetition and Innovation Act of 2009 an abbreviated approval pathway forbiosimilars has been created in the USA.