Sanofi is confident that its JAK2 inhibitor for myelofibrosis will become a key player in a market where currently only one drug is approved, Incyte/Novartis' Jakafi.

The French drugmaker has unveiled Phase II data at the American Society of Hematology meeting in Atlanta, showing that treatment with SAR302503 reduced spleen size and improved symptoms in patients with MF at both 400mg and 500mg doses. MF is a rare, life-threatening disease characterised by abnormal blood cell production and fibrosis within the bone marrow. The spleen and liver try to produce and store extra blood cells, which can cause these organs to become enlarged.

Specifically, the data revealed that spleen volume was reduced by 33% and 42% in the 400mg and 500mg doses, respectively, while those who achieved a greater than or equal to 35% reduction was 50% and 63.6%. The proportion of patients who achieved greater than or equal to 50% reduction in a sum of six key constitutional symptoms (night sweats, itching, abdominal discomfort, abdominal pain, bone pain, early satiety), the figures were 50% for 400mg and 44% for 500mg. The most common serious adverse event was anaemia (30% and 55%, respectively).

Incyte's Jakafi (ruxolitinib), soon to be launched by Novartis in Europe as Jakavi, was approved in the USA in November last year. The drug is a JAK 1 and JAK 2 inhibitor but Tal Zaks, head of oncology development at Sanofi, told PharmaTimes World News that this remains an area of unmet medical need, as some patients are resistant or intolerant to Jakafi.

He noted that specifically targeting the JAK2 enzyme appears to be the most promising approach, saying that SAR302503 also enjoys the benefit of once-daily dosing. Jakafi is a twice-daily pill and concerns have been raised concerning lack of survival benefit data and its side effects (Incyte and Novartis are presenting new long-term data at ASH,including information on these issues, but after PT went topress. We will report on the findings later this week).

A Phase III trial of the Sanofi drug finished recruiting in August, with 289 patients being enrolled over nine months and top-line results are expected in the second quarter of 2013. A Phase II trial evaluating SAR302503 in patients previously treated with Jakafi was initiated in April 2012 but is not expected to complete until 2019.