Fig. 5

Ivermectin decreased P-gp expression by inhibiting the EGFR activation. a The expression levels of the proteins in the VCR-resistant/sensitive HCT-8 cells treated with 25 nM VCR and/or 3 μM IVM for 48 h were detected. b-i The expression levels of the proteins (b-e) and the cell viability (f-i) of the VCR-resistant HCT-8 cells untransfected (b, d, f, and h) or transfected with the plasmid pcDNA3.1(+)-EGFR (c and g) or siRNA for EGFR (e and i), treated with 25 nM VCR and/or 3 μM IVM in the presence or absence of 8 nM EGF (b and f) or 1 μM lapatinib (LAP), an EGFR inhibitor (d and h), for 48 h were determined. Cell viability was detected by MTT assay and the protein expression levels were detected by Western blotting analysis using GAPDH as internal control. Cells treated with vehicle, or transfected with empty vector pcDNA3.1(+) (mock)/control siRNA (siCtrl) serve as control. Abbreviations: EGF, epidermal growth factor; IVM, ivermectin; VCR, vincristine; S, vincristine-sensitive HCT-8 cells; R, vincristine-resistant HCT-8 cells. Data in a-e are the representative of two independent experiments. Data in f-i represent the percentage of respective control values (mean ± SD, n = 5). Statistical significances in f-i were determined using one-way ANOVA followed by Dunnett’s test. ^*P < 0.05 and ^**P < 0.01, compared with the respective controls; ^#P < 0.05 and ^##P < 0.01, comparison between the two columns