Ability of a Specific ERK Signal-Pathway Inhibitor to Reverse P-Glycoprotein-Mediated Vincristine Resistance in Colon Cancer Cell Lines

OBJECTIVE To investigate the effect of a specific inhibitor PD098059 of the extracellular-signal regulated protein kinase (ERK) pathway on the P-glycoprotein (P-gp)-mediated resistance of colon cancer cell lines SW480/ VCR and CoLo205/VCR.

METHODS SW480/VCR and CoLo205/VCR cells were generated by exposuring SW480 and CoLo205 cells to vincristine (VCR) (30 ng/ml) for 72 h, which resulted in a comparatively higher level of P-gp expression. Western blotting was used to analyze P-gp, MRP, LRP, GST-π and TOPOII expression after exposuring the SW480 and CoLo205 cells to VCR (30 ng/ml) for 72 hrs. P-gp and pERK1/2 expressions was analyzed in SW480/VCR and CoLo205/VCR cells treated with or without the specific inhibitor of MEK, PD098059. The MTT assay was used to determine the susceptibility of SW480/VCR and CoLo205/VCR cells to VCR, treated with or without PD098059.

RESULTS The results showed that VCR induced a comparatively higher level of P-gp expression in the cell lines, but not that of MRP, LRP, GST-π or TOPOII. P-gp expression levels were depressed significantly in SW480/ VCR and COLO205/VCR cells by the specific inhibitor of MEK, PD098059. The IC50 (248 ±19.6 and 215 ±10.7 ng/ml) to VCR of SW480/VCR and CoLo205/VCR cells exhibited a 2.16 and 2.03-fold higher resistance compared to the negative control group (SW480 and CoLo205 cells)(115± 15.6 and 106 ±11.9 ng/ml), but a 1.35 and 1.21-fold higher resistance than the group treated with VCR (30 ng/ml) + PD098059 (184 ± 21.8 and 177± 19.4 ng/ml).

CONCLUSION This study shows that the expression of P-gp can be induced by exposuring cells to VCR, and that this induction can be reversed by inhibiting the ERK signaling pathway at the point of MEK by its specific inhibitor, PD098059. The ERK signal-transduction pathway may play a role in modulating mdr1 expression in colon cancer.