AstraZeneca has signed a deal that could be worth almost $1.25 billion to get the rights to Rigel Pharmaceuticals’ late-stage rheumatoid arthritis drug fostamatinib.

The drug, also known as R788, is the furthest developed oral spleen tyrosine kinase (Syk) inhibitor. This is a new class of treatment which is thought to block the intracellular signaling of various immune cells implicated in the destruction of bone and cartilage that is characteristic of RA.

Under the terms of the agreement, AstraZeneca will make an upfront payment of $100 million and up to $345 million more payable depending on regulatory and first sale milestones being met. Rigel is also eligible to receive up to an additional $800 million and double-digit royalties.

The Anglo-Swedish drugmaker will design a global Phase III programme, anticipated to begin in the second half of 2010, with regulatory filings to follow in 2013. Fostamatinib is being developed for RA patients who have failed to respond adequately to a traditional disease modifying anti-rheumatic drug such as methotrexate, where add-on treatment with tumour necrosis factor inhibitors would currently be considered.

The clinical progress of fostamatinib has not always been smooth. Two Phase II trials comparing the drug to methotrexate produced promising data but a smaller study, which included 219 patients who had failed biologic therapies did not meet its primary endpoint, although there was some evidence of efficacy.

Nevertheless, AstraZeneca clearly has high hopes for the drug and development chief Anders Ekblom, said that given the debilitating effect this disease can have on patients, the firm looks forward to working with Rigel to continue development of “this innovative investigational compound.” He added that collaborations such as this one “demonstrate the key role externalisation continues to play in AstraZeneca's strategy."