Liu, Feng

7110 Background: Abnormal cytokine expression may represent an inflammatory response that contributes to the clinical phenotype of MF. Some constitutional symptoms (eg. fever, fatigue, pruritus, cachexia) are thought to be caused by elevated cytokines. In phase I/II studies, SAR302503 reduced splenomegaly and constitutional symptoms in patients with MF. Here, we report the effects of SAR302503 on the expression of 97 cytokines in MF patients enrolled in a Phase II study (NCT01420770) and the relationship to clinical response (spleen size), pharmacokinetic (PK) exposure, and body weight changes. Methods: Thirty-one patients were randomized to receive 300, 400, or 500 mg of SAR302503 orally, once daily, continuously in 4-week cycles. Plasma cytokines were measured at baseline and at the end of 4, 8, and 12 weeks of treatment using a microsphere-based immuno-multiplex assay (Rules Based Medicine). Results: Complete sample sets were available for 29/31 patients. A total of 28 cytokines predominantly involved in immune/inflammation pathways were regulated ≥1.5-fold (ANOVA P<0.05) and of these, 19 were regulated at all time points, indicating rapid and sustained modulation by JAK2 inhibition. At 4 weeks, 16 cytokines were down-regulated, including TNFα, IL-1RA, and IL-18, and 6 were up-regulated, including leptin, EPO, and adiponectin. Hierarchical clustering of the 22 regulated cytokines enriched patients into spleen responder (≥35% reduction in spleen volume by MRI) and non-responder groups, suggesting a link between cytokine modulation and clinical response. Moderate correlations (P<0.05) with spleen volume reduction at the end of week 12 were seen for a subset of regulated cytokines, including adiponectin and TNFα. Levels of the majority of the regulated cytokines tended to correlate with steady state PK exposure at week 4. A positive association with weight changes at week 24 were observed for leptin and adiponectin at week 4 (P<0.05). Conclusions: This analysis shows that SAR302503 treatment modulated the expression of circulating cytokines in MF patients in association with changes in clinical activity, PK exposure, and symptom improvement (weight gain). Clinical trial information: NCT01420770.