A Phase 1 Study Of TH-302, An Investigational Hypoxia-Targeted Drug, In Patients With Advanced Leukemias

TH-302 is a 2-nitroimidazole prodrug of the DNA alkylator bromo-isophosphoramide mustard designed to be selectively activated in hypoxic conditions. Preclinical data in mice with acute lymphoblastic leukemia (ALL) have demonstrated marked expansion of hypoxia in areas of marrow leukemia infiltrates (Benito et al., PLoS One 2011). TH-302 also exhibited specific hypoxia-dependent cytotoxicity when tested against primary ALL and acute myelogenous leukemia (AML) samples in vitro (Benito et al., ASH 2012). Based on these findings, a phase 1 study of TH-302 was designed for advanced leukemias.

Eligible patients had ECOG ≤ 3, relapsed/refractory leukemias for which no standard therapy options were available, and acceptable hepato-renal function. A standard 3+3 dose-escalation design was used with 40% dose increments. TH-302 was administered IV over 30-60 min daily, either by 30 min-bolus administration or as a continuous infusion on days 1-5 of a 21-day cycle. The objectives were to determine the maximum tolerated dose (MTD) and pharmacokinetic (PK) profile of TH-302 with these schedules and to assess preliminary clinical activity of TH-302.

A total of 49 patients with previously treated AML (n=39), ALL (n=9) or CML in blast phase (n=1) received TH-302 at bolus doses of 120 (n=4), 170 (n=4), 240 (n=3), 330 (n=3), 460 (n=20), 550 (n=4) mg/m² or continuous doses of 330 (n=8) or 460 (n=3) mg/m². Two of 3 evaluable patients treated with bolus TH-302 (550 mg/m²) experienced DLTs of grade 3 esophagitis; bolus administration MTD was established at 460 mg/m². Two of 3 patients treated with continuous infusion of TH-302 (460 mg/m²) experienced DLTs of grade 3 mucositis or grade 3 hyperbilirubinemia; continuous administration MTD was established at 330 mg/m². Thirteen patients received greater than 1 cycle. Generally, a significant rapid cytoreduction was evident early in the cycle, but was not maintained prior to initiation of the next cycle. Two AML patients who received 550 mg/m² bolus TH-302 had complete resolution of leukemia cutis. One AML patient at 550 mg/m² bolus TH-302 had a complete response with incomplete platelet recovery (CRp), and one AML patient at 440 mg/m² bolus TH-302 had a CR.

In patients with advanced leukemias, MTDs were established for daily bolus infusion and 5-day continuous infusion of TH-302 at 460 mg/m² and 330 mg/m², respectively. Increased incidence of skin and mucosal toxicity were observed at higher dose levels with both administration schedules. Clinical activity of single-agent TH-302 has been noted with a few objective responses, but the majority of cytoreductions were transient.

Konopleva:Threshold Pharmaceuticals: Research Funding. Handisides:Threshold Pharmaceuticals: Employment, Equity Ownership. Kroll:Threshold Pharmaceuticals: Employment, Equity Ownership. Kantarjian:Ariad: Research Funding; Novartis: Research Funding; Pfizer: Research Funding; BMS: Research Funding.