Fig 1: Talazoparib (Tal)-resistant tumors show increased VEGFR2 (KDR) and PGF expression but only modest sensitization to Tal upon VEGFR2 depletion.(A) Representative images of immunohistochemistry (IHC) for CD31 on talazoparib-sensitive (“Sen”) and -resistant (“Res”) tumors from the Brca1-def and Bard1-def models described in Fig. 1. Arrows mark a few examples of endothelial cells, identified by both CD31+ immunostaining and morphology. Scale bars, 20 µm. (B) Immunostained tumor sections from (A) were quantified using automated QuPath software to identify positively stained cells. n = 4 Sen and Res tumors for both models. Data were presented as mean values ± SEM. P values were determined by a two-tailed, unpaired, Mann–Whitney test. * indicates P = 0.0286 for both models. (C–F) Representative images of IHC for VEGFA (C) or PGF (E) on Sen and Res tumor sections from the Brca1-def and Bard1-def models are described in Fig. 1. Scale bars, 20 µm. Immunostained tumor sections from (C) or (E) were quantified using automated QuPath software to identify positively stained cells (D, F). For both VEGFA and PGF in the Brca1-def model, n = 5 tumors for both Sen and Res, and for the Bard1-def model, n = 5 Sen tumors, and n = 4 Res tumors. Data were presented as mean values ± SEM. P values were determined by a two-tailed, unpaired, Mann–Whitney test. * indicates P = 0.0317 for the Bard1-def model (VEGFA) in (D); ns; not significant. For PGF staining in (F), ** indicates P = 0.0079 for the Brca1-def model, and * indicates P = 0.0159 for the Bard1-def model. (G) Representative images of IHC for VEGFR2 (KDR) on Sen and Res tumor sections from the Brca1-def and Bard1-def models described in Fig. 1. Arrows show a few examples of VEGFR2+ endothelial cells. Scale bars, 20 µm. (H) Immunostained tumor sections from (G) were quantified using automated QuPath software to identify positively stained cells. n = 4 tumors for both Sen and Res for both models. Data were presented as mean values ± SEM. P values were determined by a two-tailed, unpaired, Welch’s t-test. *** indicates P = 0.0003 for the Brca1-def model, and * indicates P = 0.0249 for the Bard1-def model. (I) Schematic representation of the experimental design to test the effect of in-vivo inhibition of VEGFR2 in Res tumors from the Brca1-def and Bard1-def models. For the Brca1-def model, Res tumor cells were injected in mice, and 2 weeks later, randomized tumor-bearing mice received one of the following four treatments: (1) isotype control antibody + vehicle (“Isotype + Veh”), (2) isotype + Tal, (3) anti-mouse VEGFR2 antibody (“Anti-VEGFR2”) + Veh, and (4) anti-VEGFR2 + Tal. Brca1-def mice were then euthanized for tumor collection at 4 weeks post Res-cancer-cell injection. For the Bard1-def model, mice started receiving treatments at 1 week post Res-cancer-cell injection and were euthanized at 3 weeks post Res-cancer-cell injection. (J) Tumor growth curves for the Res-tumor-bearing mice described in (I). For the Brca1-def model, n = 4 mice for the Isotype + Veh group, n = 4 mice for the Isotype + Tal group, n = 4 mice for the Anti-VEGFR2 + Veh group, and n = 5 mice for the Anti-VEGFR2 + Tal group. For the Bard1-def model, n = 3 mice for the Isotype + Veh group, n = 6 mice for the Isotype + Tal group, n = 3 mice for the Anti-VEGFR2 + Veh group, and n = 7 mice for the Anti-VEGFR2 + Tal group. Data were presented as mean values ± SEM. P values were determined by a two-tailed, unpaired, Student’s t-test, comparing endpoint tumor volumes between the Isotype + Tal and Anti-VEGFR2 + Tal groups. For the Brca1-def model, * at 4 weeks indicates P = 0.0174. For the Bard1-def model, * at 3 weeks indicates P = 0.0306. (K) Representative images of tumors following the treatment regimens from (I). Source data are available online for this figure.