A Phase II Randomized Dose-Ranging Study of the JAK2-Selective Inhibitor SAR302503 in Patients with Intermediate-2 or High-Risk Primary Myelofibrosis (MF), Post-Polycythemia Vera (PV) MF, or Post-Essential Thrombocythemia (ET) MF.

Abstract 2837 Introduction: Treatment with the JAK2 selective inhibitor SAR302503 reduced spleen size, disease-related symptoms, and the JAK2 V617F allele burden, with an acceptable safety profile in patients with primary MF, post-PV MF, or post-ET MF in a Phase I/II study (J Clin Oncol 2011;29:789, ASH 2011; Abs 3838). The objective of this Phase II study is to assess the efficacy, safety, pharmacokinetics (PK), and pharmacodynamics (PD) of 3 doses of SAR302503. Methods: Patients with intermediate-2 or high-risk primary MF, post-PV MF, or post-ET MF were randomized to 1 of 3 dose groups of SAR302503 (300, 400, or 500 mg per day). Eligibility criteria included age ≥18 years, ECOG PS 0–2, and an enlarged spleen (length ≥5 cm). SAR302503 was taken orally, once a day, in consecutive 28-day cycles until disease progression or unacceptable toxicity. The primary endpoint is the absolute change in spleen volume at the end of cycle 3 assessed by MRI with independent central review. Secondary endpoints include spleen response (≥35% reduction in spleen volume vs baseline), safety, symptom response (MPN-SAF), PK, and PD (changes in leukocyte pSTAT3). Results: From August–December 2011, at total of 31 patients were enrolled (n=10 in the 300 and 400 mg groups; n=11 to 500 mg). Risk status (intermediate-2 vs high) was balanced in the 400 mg and 500 mg groups (∼50%), whereas the 300 mg group had more high-risk patients (70%). The majority of patients (88% to 91%) had the JAK2 V617F mutation and most (∼80%) were blood transfusion independent. Mean (median) percentage reductions in spleen volume vs baseline at the end of cycle 3 were 30% (26%) in the 300 mg group, 33% (31%) with 400 mg, and 42% (38%) with 500 mg. A spleen response at the end of cycle 3 was seen in 30% of patients (3/10) in the 300 mg group, 50% (5/10) in the 400 mg group, and 64% (7/11) in the 500 mg group. Patients with constitutional symptoms at baseline in all groups reported a symptom response at the end of cycle 3, with at least a 2-point improvement in or resolution of night sweats in 93% (14/15) of patients, itching in 71% (10/14), early satiety in 56% (10/18), abdominal pain in 56% (10/18), and abdominal discomfort in 50% (10/20). Safety was evaluated in all patients. The most common grade 3–4 hematological adverse event (laboratory) was anemia, with rates across the 300, 400, and 500 mg doses of 33%, 30%, and 55%, respectively. Rates of grade 3–4 thrombocytopenia were 20%, 0, and 9%. There was no grade 3–4 neutropenia. Most common grade 3–4 nonhematological events were diarrhea (10%, 20%, 0), nausea (10%, 10%, 0), and vomiting (10%, 10%, 0). Adverse events in the 300 mg group led to discontinuation in 2 patients: 1 patient had grade 3 anemia, and 1 patient with pre-existing intermittent mild transaminase elevations and polyarthritis had hepatic failure, but completely recovered after discontinuation. No other grade 3–4 increases of AST, ALT, or bilirubin were observed. No deaths were due to an adverse event. Following repeated once-daily oral doses, SAR302503 exposure increased in a dose-dependent manner, with a median time to maximum plasma concentration of 2 to 3 hours. Steady state was achieved by cycle 1 day 15 (C1D15), with a 2.95- to 3.88-fold accumulation of drug. Time-dependent pSTAT3 inhibition was observed at all doses, with the highest mean percentage decreases from baseline (range) occurring at C1D15 (44% to 52%) and C2D1 (40% to 51%). The relationship between PK and PD pSTAT3 suppression can be described by an Emax model. There was also a correlation between percentage of pSTAT3 inhibition and spleen response rate at C1D15 and C2D1 and evidence of a steady state exposure-response relationship for spleen volume reduction at the end of cycle 3. Conclusions: In this Phase II trial, treatment with SAR302503 was associated with clinically meaningful reductions in splenomegaly and improvements in constitutional symptoms. SAR302503 was generally well tolerated in this trial and adverse events were consistent with the known safety profile. Time-dependent decreases in pSTAT3 and exposure-response correlations can be demonstrated across the three doses tested. Sponsored by Sanofi (NCT01420770) Disclosures: Talpaz: Novartis: Research Funding, Speakers Bureau; BMS: Research Funding; ARIAD: Research Funding; Deciphera: Research Funding. Gabrail:Sanofi: Research Funding. Lebedinsky:Sanofi: Employment, Equity Ownership. Gao:Sanofi: Employment, Equity Ownership. Liu:Sanofi: Employment, Equity Ownership. Pardanani:YM BioSciences: Clinical trial support, Clinical trial support Other; BMS: Clinical trial support, Clinical trial support Other; Sanofi: Clinical trial support Other.