Hypoxia is increased in tumors treated with YW152F. TC71 cells were subcutaneously injected in nude mice. Mice were treated with YW152F or IgG as described in “YW152F treatment in vivo.” Before killing, mice were injected with Hypoxyprobe-1 to identify hypoxic cells. (A) Hypoxic regions (red) were identified by immunohistochemical analysis using anti–Hypoxyprobe-1. Nuclei were identified using Sytox Green (green). (B) The ratio of the total number of hypoxic cells to nuclei was determined using Simple PCI software for 5 fields per tumor, and the average values were calculated. Blue diamonds represent average hypoxia/nuclei ratios for IgG-treated tumors, and pink squares represent YW152F-treated tumors. Black bars show mean values.