Figure 3

Induction of P-gp expression and its involvement in tumor growth in mice. Panel a. Dox pretreatment before tumor xenograft inhibited the therapeutic efficiency of Dox therapy. Athymic mice were pretreated for 15 days with either NaCl (group III) or Dox (group IV). Injection of MDA-MB-435 cells was performed subcutaneously in each mouse and the treatment (NaCl for group III and Dox for group IV) was administered for 25 days. Panel b. Therapeutic efficiency was observed in Dox-treated mice who had not received Dox pretreatment. The same experiment was performed without the 15-day pretreatment in mice receiving only NaCl (group V) or Dox (group VI). Results are expressed as the mean ± SEM of 10 mice per group. Significant difference in tumor growth rates was found between groups V and VI (*p < 0.05), but not between groups III and IV. Panel c: Presence of endothelial P-gp in the organs of Dox-treated mice. Livers, kidneys, and tumors from the six groups of treated athymic mice were removed. Following digestion with collagenase, cell suspensions were filtered and washed in PBS-BSA. Endothelial cells were isolated and characterized by flow cytometry using 10 μg/ml of control IgG or C219 antibody. The histograms represent the percentage of endothelial cells positive for P-gp. Results are expressed as the mean ± SEM with 10 mice in each group and the experiments were repeated at least 3 times. * : P < 0.05 in comparison to the control groups I or III without Dox treatment; ** : p < 0.05 between group IV versus group VI. Panel d: Immunochemical staining of P-gp on the tumor sections. Red arrows indicate endothelial cells with lumen within the tumors. The tumors were obtained and sectioned at the end of the experiments as described in above panels.