Smith, Gregg

Abstract Abstract 3849 Background: CYT387 is a potent JAK-1/2 inhibitor. The maximum tolerated dose (MTD) and preliminary safety and efficacy of once daily dosing of CYT387 were determined in a single center Phase I/II study. Previously reported results from the first 60 subjects enrolled in this study determined a MTD of 300 mg QD and demonstrated improvements in splenomegaly and constitutional symptoms as well as in RBC transfusion requirements. The study was expanded into a multicenter study with planned accrual of 165 subjects at 6 study sites and a twice daily dosing arm was added. The preliminary safety and efficacy results from this expanded multicenter study will be presented. Methods: Subjects with high or intermediate-risk primary myelofibrosis (PMF) and post-polycythemia vera (post-PV) or post-essential thrombocythemia (ET) myelofibrosis were enrolled. In the core expansion study, oral CYT387 was administered either once daily at 150 mg or 300 mg or twice daily at 150 mg for 9 months. Patients who maintained at least stable disease were permitted to continue CYT387 treatment beyond 9 months in an extension phase of the study. Responses were assessed by International Working Group (IWG) Criteria. Results: At present, 163 subjects have been enrolled across the 6 study sites. The diagnoses of enrolled subjects include 64% PMF, 14% post-ET MF and 22% post-PV MF; 67% of the patients were JAK2V617F positive. Starting doses of CYT387 in the dose escalation, confirmation and expansion phases of the study are shown in Table 1. The median duration (range) of treatment was 6.6 months (0.25 to 20.4 months). Patient characteristics were as follows: median age 68 years, 58% male, 87% were spleen evaluable at baseline per IWG criteria (median spleen length was 18 cm by palpation). Sixty three percent (63%) of subjects were anemia evaluable at baseline per IWG criteria; 46% were transfusion dependent. Previous JAK inhibitor and IMiD therapy was reported for 11% and 8% of enrolled subjects, respectively. Reductions in spleen size, improvements in constitutional symptoms and the achievement of transfusion independence were observed in subjects in the expanded multicenter study. CYT387 was well tolerated. Based on currently available data, 73% of subjects reported treatment-related adverse events, with the majority reported as Grade 1. The most common Grade 3–4 treatment related adverse events included thrombocytopenia (16%), and hyperlipasemia (3%). New onset treatment-related Grade 3–4 anemia remains rare (<1%). Grade 1 toxicities included peripheral sensory neuropathy whose incidence and natural history is currently being studied. Twenty-five of 163 subjects (15%) have discontinued from the 9 month core study giving a retention rate of 85%. Conclusions: When examined in an expanded, multicenter study, CYT387 continues to show substantial clinical activity in myelofibrosis, with improvements in splenomegaly, constitutional symptoms and anemia. It appears to be well tolerated when administered in either a once or twice daily dosing regimen. CYT387 continues to demonstrate an ability to induce durable anemia responses in a subset of subjects. Detailed analyses of safety and efficacy will be available at the time of the meeting. Disclosures: Gupta: Incyte: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Smith:YM Biosciences: Employment, Equity Ownership. Bavisotto:YM Biosciences: Consultancy. Kowalski:YM Biosciences: Employment, Equity Ownership.

Abstract Abstract 460 Background: CYT387 is a potent JAK-1/2 inhibitor that suppresses the in vitro growth of cells harboring JAK2V617F (Leukemia 2009;23:1441) and was effective in a murine model of myeloproliferative neoplasms (MPN) (Blood 2010;115:5232). Aims/Methods: To assess the safety, tolerability, and pharmacokinetic behavior of CYT387 in a Phase I dose-escalation study in patients with high- or intermediate-risk primary myelofibrosis (PMF) and post-PV or post-essential thrombocythemia (ET) myelofibrosis. The secondary objective was evaluation of preliminary efficacy. CYT387 was administered orally once daily in 28-day cycles. Once dose-limiting toxicity (DLT) was identified, a dose-confirmation cohort initiated treatment at the maximum tolerated dose (MTD) or lower. Result: Thirty six subjects (median age 64 years) have been enrolled (targeted accrual 120); 18 each in the dose escalation and dose confirmation phases. Twenty-three subjects had PMF, 8 post-PV MF, and 5 post-ET MF; 81% were JAK2V617F-positive. Median palpable spleen size was 18 cm and 20 subjects (56%) were red cell transfusion-dependent at study entry. Prior treatment included JAK inhibitors (9 and 1 subjects with INCB018424 and TG101348, respectively) and pomalidomide in 9 patients. The median treatment duration to date is 15 weeks (range 4–38). Dose-linear plasma exposures were observed up to 300 mg/day, with mean elimination T1/2 at steady state ranging from 3.9 to 5 hours across doses. Toxicity: All 36 subjects were evaluable for toxicity. At 400 mg/day, 2 of 6 subjects experienced DLT (1 each with asymptomatic grade 3 hyperlipasemia and grade 3 headache that were reversible upon holding drug); consequently, the MTD was declared at 300 mg/day. In the dose-confirmation phase, subjects were started at one of 2 dose levels that were deemed clinically effective: 150 mg/day (n=15) and 300 mg/day (n=3). Thirty-five subjects are currently on active therapy: 100 mg/day (n=2), 150 mg/day (n=20), 300 mg/day (n=10), and 400 mg/day (n=3). CYT387 was well tolerated. No grade 4 non-hematological toxicities were observed. Grade 3 non-hematologic adverse events were infrequent and included increased transaminases (n=2), increased alkaline phosphatase (n=2), headache/head pressure (n=2), increased lipase (n=1), and QTc prolongation (n=1). Thirteen (36%) subjects experienced “first-dose effect” characterized by grade 1 lightheadedness and hypotension; this phenomenon was self-limited and generally resolved within 3–4 hours with rare recurrence. Grade 3/4 thrombocytopenia was seen in 8 (22%) subjects, and treatment-emergent grade 3 anemia was seen in 1 subject only (3%). Treatment-emergent grade 3/4 neutropenia was not observed. Efficacy: Thirty two of 36 subjects who completed at least 1 cycle were eligible for response assessment: Anemia: Twenty two subjects were evaluable for anemia response (baseline Hgb <10 g/dL or red cell transfusion-dependent). Of these, 9 subjects (41%) achieved the threshold of response for “Clinical Improvement (CI)” per the International Working Group for MPN Research and Treatment (IWG-MRT) criteria, including 2 of 4 subjects who were previously treated with INCB018424. An additional 5 subjects experienced a >50% reduction in transfusion requirement, thus increasing the total anemia response rate to 63%. Splenomegaly: Thirty of 32 evaluable subjects had splenomegaly at baseline: median 20 cm; range 10–32 cm. Twenty nine subjects (97%) had some degree of spleen size reduction (median 9 cm; range 2–18 cm): 11 (37%) patients have achieved a minimum 50% decrease in palpable spleen size, thus qualifying them for a CI, including 3 of 8 subjects (38%) who were previously treated with INCB018424. Constitutional symptoms: The proportion of patients with the following symptoms at baseline, are: fatigue (97%), pruritus (22%), night sweats (38%), cough (13%), bone pain (28%), and fever (16%). At last follow up, improvement (complete resolution) in these symptoms was reported by 68% (16%), 86% (57%), 83% (75%), 75% (50%), 78% (44%), and 100% (100%), respectively. Conclusion: CYT387 is first-in-class of the JAK inhibitors with a significant response rate in anemia in myelofibrosis patients. The drug also shows substantial activity in reducing spleen size and controlling constitutional symptoms. CYT387 is well tolerated, and treatment responses have been seen both at (300 mg/day) and below (150 mg/day) the MTD. Disclosures: Pardanani: Cytopia Inc.: Research Funding. Off Label Use: Clinical trial data for CYT387 use in Myelofibrosis. Fida:YM Biosciences Australia: Employment, Equity Ownership. Burns:YM Biosciences Australia: Employment, Equity Ownership. Smith: YM Biosciences Australia: Employment, Equity Ownership.