Fig. 3.

Tumor endothelial cells are the major targets of the engineered anthrax lethal toxins in tumor therapy. (A–C) B16-BL6 melanoma-bearing mice with various CMG2 genotypes were treated intraperitoneally with 30 µg of PA-L1 plus 15 µg of LF at the days indicated by arrows. Cmg2^EC, CMG2 receptor expressed solely in endothelial cells; Cmg2^SM, CMG2 receptor expressed solely in vascular smooth muscle cells; Cmg2(EC)^−/−, endothelial cell-specific CMG2-null; ns, nonsignificant different. (D) B16-BL6 melanoma-bearing endothelial cell-specific CMG2-null mice and myeloid-specific CMG2-null mice (Cmg2(Mye)^−/−) and their littermate controls were treated intraperitoneally with 30 µg of IC2-PA (15 µg of PA-L1-I207R plus 15 µg of PA-U2-R200A) plus 10 µg of LF or PBS at the days indicated by the arrows. (E) B16-BL6 melanoma-bearing WT mice were treated intraperitoneally with 30 µg of PA-L1 plus 15 µg of LF, 30 µg of PA-L1 without LF, or PBS at the days indicated by the arrows. (F) B16-BL6 tumor-bearing mice were treated with PA-L1/LF (30 µg/15 µg) or PBS (n = 3 for each group) at days 0 and 2, and tumors were collected 24 h later, fixed, sectioned, and stained as indicated. Tumors were also costained for CD31 (red fluorescence) and TUNEL (green fluorescence). (Magnification: 200×.) Blood vessel densities were expressed as the means ± SE of CD31⁺ vasculatures in 10 fields from each group. Tumor volumes (means ± SE). One-way ANOVA was used to evaluate tumor size differences. In A, Cmg2^+/+ PBS vs. Cmg2^+/+ PA-L1/LF, P < 0.01; Cmg2^−/− PBS vs. Cmg2^EC PA-L1/LF, P < 0.01; Cmg2^−/− PBS vs. Cmg2^−/− PA-L1/LF or Cmg2^SM PA-L1/LF, P > 0.05.