CALR regulates the chemosensitivity of BC cells. (A) NTC (Left) and shCALR-1 (Right) subclones of MDA-MB-231 cells were cultured for 4 d in the presence of the indicated concentration of DOX, and viable cell numbers were determined by CCK-8 assay. (B) Data are presented according to DOX concentration (mean ± SEM, n = 3; *P < 0.05 vs. NTC; **P < 0.01 vs. NTC; ***P < 0.001 vs. NTC). (C) In total, 5 × 105 cells of each MDA-MB-231 subclone were implanted into the mammary fat pad. When tumors were palpable (day 0), mice were treated with saline or 2.5 mg/kg of DOX every 7 d. Tumor volumes were determined weekly (mean ± SEM, n = 4 in the NTC + saline and shCALR-1 + saline groups, n = 5 in the NTC + DOX and shCALR-1 + DOX groups; *P < 0.05; **P < 0.01). (D and E) On day 35, tumors were excised, (D) photographed, and (E) weighed (mean ± SEM, n = 4 in the NTC + saline and shCALR-1 + saline groups, n = 5 in the NTC + DOX and shCALR-1 + DOX groups; **P < 0.01; n.s., not significant).