On December 6, 2016 Mateon Therapeutics, Inc. (Nasdaq:MATN), a biopharmaceutical company developing vascular disrupting agents (VDAs) for the treatment of orphan oncology indications, reported the poster presentation of data from its on-going phase 1b OX1222 study of OXi4503 in combination with cytarabine in patients with Acute Myeloid Leukemia (AML) or Myelodysplastic Syndrome (MDS) (Press release, Mateon Therapeutics, DEC 6, 2016, View Source [SID1234516953]).

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OXi4503 is one of Mateon’s two VDAs currently in clinical development. OX1222 is a dose-ranging study of OXi4503 combined with cytarabine in relapsed/refractory AML and MDS. The poster presented at the 58th Annual Meeting of the American Society of Hematology (ASH) (Free ASH Whitepaper) describes results from the initial two cohorts of OX1222, which represent the lowest doses of OXi4503 in the study.

The first cohort enrolled 6 patients at a dose of 3.75 mg/m2 of OXi4503 in combination with an intermediate dose (1g/m2/day x 5 days) of cytarabine. The second cohort enrolled 4 patients at a dose of 4.68 mg/m2 of OXi4503 in combination with the same intermediate dose of cytarabine. Patients enrolled into OX1222 were treatment-resistant, end-stage AML/MDS patients who had on average four prior therapy failures before entering the study.

In total 2 of 10 (20%) patients achieved a complete remission (CR) on treatment and currently remain in CR without further treatment – one at 6 months and the other at 3 months. One patient of six (17%) responded in the 3.75 mg/m2 dose cohort, and one patient of four (25%) responded in the 4.68 mg/m2 dose cohort. The study is currently enrolling patients in the third cohort at 6.25 mg/m2 of OXi4503.

OXi4503 was generally well tolerated in the first two cohorts of the study. The adverse event profile remains similar to that seen in the monotherapy Phase 1b portion of the trial, with coagulopathies and hematological adverse events the most significant events. The most common drug-related SAEs were anemia (30%), neutropenia (30%), D-dimer increase (20%), thrombocytopenia (20%), and AST increase (20%). One patient in the 3.75 mg/m2 cohort experienced a dose-limiting toxicity of hypofibrinogenemia with no clinical evidence of bleeding, which resolved with treatment.

"I am very excited to see two complete remissions out of the ten patients treated to date, as these were heavily pre-treated patients," stated Tara L. Lin, MD, Associate Professor, Division of Hematologic Malignancies & Cellular Therapeutics, University of Kansas Cancer Center. "Our poster presentation at ASH (Free ASH Whitepaper) concluded that OXi4503 in combination with cytarabine demonstrated preliminary evidence of activity in heavily pretreated relapsed/refractory AML patients and that this combination was generally well tolerated through cohorts 1 and 2. I greatly look forward to seeing the results from additional cohorts as the optimal dose of OXi4503 in combination with cytarabine has yet to be determined."

The poster presentation was entitled "A Phase 1b (OX1222) Dose-Finding Study of OXi4503 Combined with Cytarabine in Patients with Relapsed/Refractory Acute Myeloid Leukemia or Myelodysplastic Syndrome" and was presented by Justin M. Watts, MD, Assistant Professor of Clinical Medicine at the University of Miami.