On August 17, 2018 Mateon Therapeutics, Inc. (OTCQB:MATN), a biopharmaceutical company developing investigational drugs for the treatment of orphan oncology indications, reported that the U.S. Food and Drug Administration (FDA) placed a partial clinical hold on Study OX1222 during a telephone conversation held with the Company on August 16, 2018 (Press release, Mateon Therapeutics, AUG 17, 2018, View Source [SID1234528963]). OX1222 is the Company’s clinical trial of OXi4503 in combination with cytarabine for the treatment of relapsed/refractory acute myeloid leukemia and myelodysplastic syndromes. The partial clinical hold applies to the 12.2 mg/m2 dose of OXi4503. The FDA is allowing the study to continue to treat and enroll patients using a dose of 9.76 mg/m2 of OXi4503, which the Company previously tested in cohort 5 of Study OX1222.

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The partial clinical hold follows two potential dose-limiting toxicities (DLTs) observed at the 12.2 mg/m2 dose level that was being evaluated in cohort 6 of Study OX1222. These DLTs consist of one patient experiencing hypotension shortly following initial treatment with OXi4503, and another patient experiencing acute hypoxic respiratory failure approximately two weeks after receiving OXi4503 and cytarabine. Both events were deemed "possibly-related" to OXi4503, and both patients recovered following treatment. The protocol for Study OX1222 generally defines a DLT as any grade 3 serious adverse event (SAE) where a relationship to OXi4503 cannot be ruled out. The FDA has indicated that additional data on patients receiving 9.76 mg/m2 of OXi4503 must be evaluated before the Company resumes dosing at 12.2 mg/m2.

"Although it is disappointing that we are not currently continuing with the higher dose of OXi4503, we look forward to gathering more safety and efficacy data at the previous dose level, where we observed two complete remissions in the four patients that we treated," said William D. Schwieterman, M.D., Chief Executive Officer of Mateon.