Effects of OXi4503 and bevacizumab on subcutaneous leukemic chloromas. NOD/scid/IL2Rγ^−/− (NOG) mice were subcutaneously inoculated with KG-1 human acute myelogenous leukemia (AML) cells. After chloromas were palpable mice were treated with intraperitoneal injections of bevacizumab, OXi4503, combination (OXi+Bev), or controls. Leukemia growth was measured every other day. (A) OXi4503 alone decreased leukemia growth in comparison to controls. Combination Oxi4503+Bev treatment resulted in regression of cancer size. Bevacizumab alone had no effect on tumor growth. (B) Comprehensive staining of chloromas was performed for: H&E (scale bar: 200 μm), TUNEL/MECA-32 (scale bar: 100 μm), (TUNEL/CD45 (scale bar: 50 μm), and CD45/VEGF-A (scale bar: 100 μm). Sections showed that OXi4503 monotherapy led to chloromas with central cores made up mainly of nonvascularized, TUNEL⁺ apoptotic cells and viable rims (outlined by dotted lines) containing MECA-32⁺ blood vessels at the periphery of leukemias. VEGF-A expression was also observed in viable rims. Combination therapy eliminated the viable rim resulting in widespread apoptosis and a lack of intact blood vessels throughout the tumor mass. Bevacizumab-treated tumors showed no difference in staining compared with controls. (C) Quantification of microvessels based on MECA-32⁺ blood vessels revealed decreased density within leukemic cores of mice treated with OXi4503 and combination therapy in comparison to bulk control tumors. Blood vessels within viable leukemia rims are increased after OXi4503 treatment but significantly decreased with additional bevacizumab treatment. Values represent mean ± SEM. *P < .05.