Differential effects of mitogen-activated protein kinase pathway inhibitors on P-glycoprotein activation

The aim of this study was to evaluate the effects of the mitogen-activated protein kinase (MAPK) pathway inhibitors SB203580, CMPD-1, SB239063, SP600125, and FR180204 on the activity of P-glycoprotein (P-gp) and to assess whether the MAPK pathway affects P-gp directly. Changes in the fluorescence of residual rhodamine 123, a marker of P-gp activity, in the apical region of Caco-2 cells were measured in the presence of MAPK pathway inhibitors using time-lapse confocal laser scanning microscopy at 0, 10, 20, 30, and 60 min. Significant differences were observed between the fluorescence levels of control cells and cells treated with SB203580 for 20, 30, or 60 min. However, no significant change was observed in the residual rhodamine 123 fluorescence of cells treated with CMPD-1, SB239063, SP600125, or FR180204. Among the p38-MAPK pathway inhibitors investigated, CMPD-1 and SB239063 showed no detectable effect on the activity of P-gp. Further, JNK 1, 2, 3-MAPK pathway (SP600125) and ERK1/2 pathway (FR180204) inhibitors did not affect P-gp activity. However, SB203580 enhanced the transfer of rhodamine 123 across the apical cell membrane. Thus, SB203580 activated P-gp, although not through the p38-MAPK pathway. Importantly, the MAPK pathway did not affect P-gp activity shortly after treatment.