Polycythemia vera (PV) and essential thrombocytosis (ET) are clonal hematopoietic stem cell disorders characterized by the over production of phenotypically normal circulating blood cells. Most PV and approximately half of ET patients harbor the activating mutation JAK2 V617F. CEP-701 is an orally available, potent low nanomolar inhibitor of both the wild-type and mutated JAK2 tyrosine kinase, with its inhibitory effect demonstrated both in enzymatic and cellular assays and in vivo, where CEP-701 significantly inhibited the growth of JAK2 V617F-positive HEL.92 xenografts in mice. These findings suggest that CEP-701 is an attractive candidate for clinical evaluation in JAK2 V617F-positive myeloproliferative disorders. The purpose of this study is to test the safety and efficacy of CEP-701 administration in JAK2 V617F positive ET and PV patients. The primary endpoint is reduction in JAK2 V617F neutrophil allele burden; secondary endpoints are reduction in phlebotomy rates, improvement in hemoglobin, white cell and platelet counts, reduction in hydroxyurea (HU) dose, and reduction in spleen size. The secondary endpoints include the pharmacokinetics and pharmacodynamics of CEP-701 and the safety of CEP-701 treatment in patients with JAK2 V617F-positive PV and ET. This is a multicenter study with an anticipated enrollment of 40 PV and ET patients. Inclusion criteria include JAK2 V617F-positive PV and ET patients; patients with PV either have a neutrophil count greater than 7,000/ul or are receiving HU, while ET patients are receiving concomitant HU. Other inclusion criteria include an ECOG performance status of 0, 1 or 2, and 18 years of age or older. Exclusion criteria include the active use of anegrelide or interferon, or a recent history of venous or arterial thrombosis. This is an 18 week trial with an optional 1 year extension period; doses will escalate from 80 mg twice daily to a maximum of 120 mg twice daily. To date, 20 subjects, 11 PV and 9 ET, comprised of 11 females and 9 males, ages 34 to 74, have enrolled. Approximately 27% of the PV patients were taking HU. The most common adverse events have been gastrointestinal (GI) and constitutional in nature. No related serious adverse events have been observed. Five patients have discontinued study participation, all for adverse events: 1 due to disease progression, 1 leg cramps, and 3 GI. To date, 7 patients have completed 18 weeks of therapy and 6 of these patients will continue to receive CEP-701 on the extension phase of the trial. Five of 8 subjects with splenomegaly have responded with reductions in spleen size evident within 6 weeks of therapy initiation. Updated results on current and future patients will be presented at the meeting.

Disclosures: Carroll:Sanofi Aventis: Research Funding. Bensen-Kennedy:Cephalon: Employment.

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