OXi4503 induced regression of systemic AML in bone marrow. Irradiated NOG mice were transplanted with human AML of differing subtypes (M1/2, M4, and M5) including a primary human AML specimen that harbored a high-risk FLT3 ITD mutation and after verification of leukemia engraftment were randomly assigned to 1 of 4 treatment cohorts. (A) Six weeks after AML transplant, NOG mice were treated with bevacizumab, OXi4503, combination (OXi4503+Bev), or controls. After 2 weeks of treatment, bone marrow showed persistence of AML in control and bevacizumab-treated mice. However, incidences of AML engraftment were significantly decreased with OXi4503 (1/8 positive) and combination treatment (1/11 positive) in comparison to controls. Shown are representative flow cytometric plots showing leukemic engraftment in control and bevacizumab-treated mice and no leukemic engraftment in Oxi4503 and combination-treated mice. (B) Quantification of AML engraftment by flow cytometry showed significantly decreased engraftment in OXi4503 and combination-treated animals versus controls. (C) PCR analysis for FLT3 ITD AML revealed molecular remissions (*) of high-risk FLT3 ITD⁺ AML in 40% of OXi4503 and combination-treated animals. (D-E) TUNEL staining showed no detectable apoptotic response to bevacizumab (D); however, a hypoxia-mediated reaction was observed upon HIF-1α staining (E). CD45⁺ cells were observed throughout bone marrow sections (scale bar: 100 μm). Values represent mean ± SEM. Gating was established using appropriate isotype controls.