Dr. Zaks on the JAK2 Inhibitor SAR302503 in Myelofibrosis

Tal Zaks, MD, PhD, vice president and head of development at Sanofi Oncology, details a phase II randomized study of the JAK2 inhibitor SAR302503 in patients with intermediate-2 or high-risk primary myelofibrosis (MF), post-polycythemia vera MF, or post-essential thrombocythemia MF.

The purpose of the study, Zaks says, was to correlate doses and effect of SAR302503 on the inhibition of the JAK2 pathway and the patient's symptoms. Patients in the study were randomized to receive 300 mg, 400 mg or 500 mg once daily in consecutive 28-day cycles until the disease progressed or toxicity was unacceptable. The study found that as exposure to SAR302503 increased, the ability to inhibit JAK2 also increased, Zaks says. With regards to symptoms, median percentage reductions in spleen volume vs baseline at the end of cycle 3 were 26% in the 300 mg group, 31% in the 400 mg group, and 38% in the 500 mg group. At the end of cycle 3, 30% of patients in the 300 mg group, 50% of patients in the 400 mg group, and 64% of patients who received 500 mg saw spleen response.

Zaks says that, based on responses, the appropriate range of doses for SAR302503 has been identified and will be confirmed in a phase III trial. Further, this study shows a strong linkage between the ability to have an exposure to the drug modulates the biological pathways as well as impact the ability to affect patient symptoms. The pharmacological properties (long half-life and once daily dosing) were also positive.