ABCG2 and neoplasm: We implanted U87 cells into mouse brains and found that the tumor fluorescence intensity of the ABCG2 knockout group was lower than that of the empty vector group when the mice were treated with TMZ (2 mg/kg) and reared under normoxic conditions, but the tumor fluorescence intensity of the ABCG2 overexpression group was greater than that of the empty vector group when the mice were treated with TMZ (2 mg/kg) and reared under HBO conditions (Figure 6G).