YM BioSciences Reports Updated 12-Week Phase I/II Results for its JAK1/JAK2 Inhibitor CYT387

YM BioSciences Inc. has reported updated interim results for the first 60 patients with high/intermediate-risk myelofibrosis who have completed a minimum of three cycles of treatment (12 weeks) in its ongoing Phase I/II multi-center study.

"In addition to reducing spleen volumes and improving constitutional symptoms, CYT387 continues to demonstrate the ability to induce durable anemia responses in a significant number of patients with transfusion dependency associated with myelofibrosis," said Dr. Nick Glover, President & CEO of YM BioSciences.

These results were submitted to the 2011 Annual Meeting of the American Society of Clinical Oncology (ASCO) as an abstract in February 2011. Study Investigators will present additional updated information from the study in a poster session at ASCO on June 3rd from 2:00-6:00pm. CYT387 was administered orally once daily in 28-day cycles.

Responses were assessed by International Working Group (IWG) criteria. Forty-two of the 60 patients were evaluable for anemia response per IWG criteria (Blood 2006;108:1497) and 33 of these were red cell transfusion-dependent.

In the latter group, anemia response required a transfusion-free period of ≥12 weeks, while on protocol drug therapy, and capped by a hemoglobin level of ≥8 g/dL.

Efficacy Results:

• The anemia response rate was 50% overall and 58% in transfusion-dependent patients.

• At the time the abstract was submitted, the median duration of anemia response was 20 weeks (range 12-54 weeks) and only two (11%) of the 19 patients who achieved transfusion-independency required single episodes of PRBC transfusions. As previously announced, at the First Annual Florence Meeting on Myeloproliferative Neoplasms held in Florence, Italy on April 16, 2011 an updated median duration of transfusion independence was reported by Study Investigators to be six months (range 4-15 months).

• Responses in anemia were not affected by leukocyte count (p=0.39), platelet count (p=0.35), circulating blast count (p=0.35), circulating CD34 cell count (p=0.78), karyotype (p=0.67) or JAK2V617F mutational status (p=0.17).

• Spleen response rate by IWG criteria was approximately 45%.

• The majority of patients experienced resolution of constitutional symptoms including pruritus, night sweats and bone pain.

Safety Results:

• The study retention rate after a median treatment duration of 6.4 months was 92%.

• Grade 3/4 hematologic and non-hematologic adverse events were infrequent with the exception of thrombocytopenia, which occurred in approximately 25% of patients (platelet inclusion criteria: 50,000/µl).

• About half of the patients experienced a first-dose effect (transient lightheadedness and Grade 1 hypotension), which was self-limited and generally resolved within hours with rare recurrence.

Enrollment in the trial has currently exceeded the initial target of 140 patients and is expected to close in calendar Q2 2011 and include approximately 155 patients. YM anticipates that more mature data from the full trial will be reported by the end of calendar 2011.