On October 30, 2017 Mateon Therapeutics, Inc. (OTCQX:MATN), a biopharmaceutical company developing investigational drugs for the treatment of orphan oncology indications, reported updated data from the fifth dose cohort of OX1222, a phase 1b dose-ranging study of OXi4503 in combination with cytarabine in patients with relapsed/refractory acute myeloid leukemia (AML) or myelodysplastic syndromes (MDS) (Press release, Mateon Therapeutics, OCT 30, 2017, View Source [SID1234521300]).

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Mateon previously reported that two of four patients in this cohort of the study had morphological complete remissions following one cycle of treatment with OXi4503. A morphological complete remission occurs when an AML patient has fewer than 5% AML blasts in the bone marrow count following treatment and has no significant hematologic abnormalities or other evidence of disease.

One of the patients showing disease remission discontinued the study due to an unrelated adverse event. The other patient continued to receive treatment with an additional two cycles of OXi4503 and remains in complete remission with a cytogenetic complete response. A cytogenetic complete response occurs when testing shows eradication of chromosomal abnormalities following treatment.

"We continue to see encouraging signs of safety and efficacy for OXi4503 in Study OX1222, including complete remissions at very low doses and evidence of a dose-response as we progressively increase the dose of OXi4503 in the trial," said William D. Schwieterman, M.D., President and Chief Executive Officer of Mateon. "OXi4503 represents a completely new way to treat AML – by both killing tumor cells directly and by destroying their protective environment in the bone marrow. Based on the results seen to date, we are excited about the enormous potential for this compound in relapsed/refractory AML, especially in older patients unable to tolerate the high levels of chemotherapy typically needed to see a response. There is a huge unmet medical need in these patients and they specifically appear to benefit from treatment with OXi4503."

Summarized initial efficacy data generated to date from OX1222 in relapsed/refractory AML or MDS are as follows:

Cohort (Dose) n CR% PR% ORR%
Cohort 1 (3.75 mg/m2) 6 17% 0% 17%
Cohort 2 (4.68 mg/m2) 4 25% 0% 25%
Cohort 3 (6.25 mg/m2) 4 25% 25% 50%
Cohort 4 (7.81 mg/m2) 3 0% 33% 33%
Cohort 5 (9.76 mg/m2) 4 50% 0% 50%
n: number of patients
CR: complete remission
PR: partial remission
ORR: overall response rate (sum of partial and complete)
OXi4503 continues to have a favorable safety profile. The most common adverse events (AEs) of any grade across all cohorts include neutropenia, fever, nausea, anemia and diarrhea. Grade 3 or above AEs which were related to treatment include anemia (32%), decreased platelet count (27%), decreased neutrophil count (23%) and decreased white blood cell count (18%).

Mateon is in the process of expanding the size of future, higher-dose cohorts to 10 patients to increase the utility of the data generated. The company is also continuing discussions to secure a partner or otherwise obtain additional capital prior to initiating treatment in the sixth cohort of Study OX1222.

About Acute Myeloid Leukemia
A devastating form of cancer of the blood and bone marrow, AML is the most common type of acute leukemia in adults and accounts for the greatest number of leukemia deaths in the United States. There is no standard regimen of care for patients who relapse following front-line treatment or have refractory disease. According to the NIH’s National Cancer Institute Surveillance, Epidemiology and End Results (SEER) program, there are an estimated 21,380 new cases of AML and 10,590 deaths expected in 2017 in the United States. AML arises from a clonal hematopoietic stem cell and is characterized by accumulation of malignant myeloblasts in the bone marrow and results in ineffective hematopoiesis. AML often responds initially to front-line treatment of conventional cytotoxic chemotherapy, but it often relapses and long-term disease-free survival is low, posing a significant challenge to treat relapsed and/or refractory disease.

About OXi4503
OXi4503 has received Fast Track designation from the U.S. Food and Drug Administration for the treatment of AML. It disrupts tumor vasculature residing within bone marrow while simultaneously targeting malignant myeloid cells. Preclinical data show that OXi4503 disrupts bone marrow endothelial cells which normally protect AML cells from exposure to chemotherapeutic agents. In human xenograft animal models of AML, OXi4503 has demonstrated almost complete elimination of leukemic cells. In other animal models, the combination of OXi4503 and cytarabine has shown a much greater effect against AML than either agent alone.