(A) H&E staining and immunolabeling of pimonidazole on consecutive sections of MDA-MB-231 tumors implanted in athymic nu/nu mice. White areas without tissue correspond to sites where punch biopsies were taken for molecular analysis. Scale bar: 2 mm. (B) Correlation of mouse Angpt2 and Pecam1 transcript levels on various biopsies obtained from 4 different tumors (n = 4 mice). Pearson’s r correlation coefficient and significance levels are presented. (C and D) Analysis of cancer cell–derived human ANGPT2 and endothelial cell–derived murine Angpt2 transcript levels in each PDX. Human ANGPT2 is normalized to human TBP (C) and murine Angpt2 (D) is normalized to Pecam1. Data are presented as dCT. (E) Representative images of FFPE tumor sections obtained from murine (mu) Angpt2^High and mu Angpt2^Low PDX models immunolabeled for CD31, desmin, and PDGFRβ. The bottom row shows digitally zoomed images. Perivascular cells that have direct contact with CD31⁺ cells and are positive for each marker are quantified. Scale bar: 100 μm. (F) Quantification of murine Angpt2 expression in mu Angpt2^High and mu Angpt2^Low. Groups are divided based on median value of dCT (Supplemental Table 4). Box-and-whiskers plots show median (line within box), upper and lower quartile (bounds of box), and minimum and maximum values (bars). (G) Representative images of pimonidazole immunolabeling of FFPE tumor sections obtained from mu Angpt2^High and mu Angpt2^Low PDX models. Scale bar: 2 mm. (H) Quantification of the percentage of hypoxic area based on the pimonidazole staining in G. (I) Quantification of relative vascular density (number of CD31⁺ cells). (J) Quantification of the relative percentage of desmin⁺ pericytes associated with CD31⁺ vessels. (K) Quantification of the relative percentage of PDGFRβ⁺ desmin^– pericytes associated with CD31⁺ vessels. The red dot identifies BCX042 (C, D, and H–K). Experimental n numbers were as follows: mu Angpt2^High, n = 9; mu Angpt2^Low, n = 8. Unless otherwise stated, the data are represented as the mean ± SD, and unpaired 2-tailed t test was used to determine statistical significance. *P < 0.05, **P < 0.01.