[Effect and mechanism of silibinin on the inhibition of ALK positive NSCLC cells by sensitizing crizotinib]

Objective: To explore the synergistic effect of silibinin combined with crizotinib on anaplastic lymphoma kinase positive (ALK+ ) non-small cell lung cancer (NSCLC) cells and its mechanism. Methods: H2228 and H3122 cells were treated with silibinin, crizotinib alone or in combination. Cell proliferation was measured by 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay and colony formation assay. Migration or invasion ability was tested by wound healing assay or transwell assay, respectively. Expressions of E-Cadherin and vimentin protein were examined by immunofluorescence staining. The protein expressions of ALK, p-ALK, E-Cadherin and Vimentin were detected by western blotting.The anti-cancer effect of silibinin combined with crizotinib in vivo was determined by subcutaneously injecting 2×10(6) H2228 cells into immunodeficient nude mice. Results: The result of MTT assay showed that the cell viability of H2228 or H3122 treated with 100 μmol/L silibinin was (88.38±4.10)% or (72.27±3.62)%, respectively, marginally decreased compared with that of the control. The 50% inhibitory concentration (IC(50)) of H2228 cells treated with crizotinib alone or combined with 100 μmol/L silibinin was (917.10±7.75) nmol/L or (238.73±7.67) nmol/L, respectively. The IC(50) of H3122 cells treated with crizotinib alone or combined with 100 μmol/L silibinin was (472.50±15.70) nmol/L or (206.10±12.01) nmol/L, respectively. The IC(50s) of H2228 and H3122 cells were significantly decreased by combined treatment of crizotinib and silibinin compared to crizotinib treatment alone (P<0.01). When compared with the control group, colony forming ratios of H2228 cells were (83.34±2.72)% in 100 μmol/L silibinin treatment group, (69.42±3.06)% in 400 nmol/L crizotinib treatment group and (27.32±1.42)% in combined treatment group. When compared with the control group, colony forming ratios of H3122 cells were (84.45±5.67)% in 100 μmol/L silibinin treatment group, (45.02±5.83)% in 400 nmol/L crizotinib treatment group and (17.43±3.83)% in combined treatment group. Silibinin combined with crizotinib treatment significantly inhibited the colony formation ability of H2228 and H3122 cells (P<0.01). Migration and invasion results showed that combined treatment of crizotinib and silibinin markedly inhibited the migration and invasion ability of H2228 cells (P<0.01). Western blot results indicated that treated with silibinin alone or in combination of crozitinib for 48 hours, the protein level of E-cadherin in H2228 cells was upregulated, while the expressions of p-ALK and vimentin were downregulated, without obvious alteration of ALK protein expression. In the xenograft model, the mean tumor weight was (9.40±2.58)g in crizotinib treatment group and (4.58±1.07)g in the combined treatment group. The inhibitory effect of tumor growth in vivo of combined treatment was significantly superior to that of crizotinib treatment alone (P<0.05). Conclusion: Silibinin enhances the inhibitory effect of crizotinib on ALK positive NSCLC cells, which may be associated with suppression of ALK activity and mesenchymal-epithelial transition.