Sanofi has suffered a setback in the clinic and discontinued development of fedratinib, a JAK2 inhibitor that was in Phase III for myelofibrosis.

The French drugmaker has halted all clinical trials and cancelled plans for regulatory filings for fedratinib following recent reports of cases consistent with the brain disorder Wernicke’s encephalopathy in patients participating in studies.

The US Food and Drug Administration told Sanofi to put all fedratinib trials on clinical hold while the company thoroughly investigated the cases. The firm says it took "immediate action requesting that study investigators discontinue fedratinib treatment for patients in the trials".

This is quite a blow given that Sanofi had high hopes for the drug in MF, a rare, but serious blood disease. In particular it was hoping to gain market share with patients who are either resistant or intolerant to Novartis' already-approved Jakafi/Jakavi (ruxolitinib).  
Tal Zaks, interim head of Sanofi oncology, said that "we are deeply disappointed to have to discontinue development of fedratinib, especially given the needs of this difficult-to-treat patient population and the earlier promise shown for this therapy". However, he added, "patient safety is our top priority and drove this decision".