PGAM1 inhibition sensitizes BRCA-proficient breast cancer toward PARP inhibitors. (A) Clonogenic assay. MDA-MB-231 shPGAM1#1 or scramble (Scr) cells were treated with Olaparib at indicated concentrations for 14 d. (B and C) Cell apoptosis assay. Cells were exposed to Olaparib (30 µM) for 48 h, and apoptotic cells were detected by Annexin V–PI dual staining. (B) MDA-MB-231 shPGAM1#1 cells. (C) MDA-MB-231 shPGAM1#1 cells transfected with empty vector (EV), WT, or mutant PGAM1 for 24 h. (D) Cell viability assay. MDA-MB-231 cells were treated with Olaparib alone or in combination with PGMI-004A (20 µM) for 72 h. Cell viability was measured by Sulforhodamine B assay. (E–I) Tumor growth inhibition in vivo. Mice bearing indicated tumors were dosed with Olaparib (50 mg/kg) alone or in combination with PGMI-004A (50 mg/kg) daily for 14 d (n = 6). Tumor volume was measured every other day, and tumor growth inhibition at endpoint was measured (E and H). Tumor tissues collected at 2 h after the last dosing were subjected to immunoblotting (F and I) or immunohistochemistry (G) analysis. Bar, 20 µm. **, P < 0.01; ***, P < 0.001; n.s., not significant.