The novel anticancer drug KRN5500 interacts with, but is hardly transported by, human P-glycoprotein

The interaction of the novel anticancer drug KRN5500, a spicamycin derivati ve, with human P-glycoprotein (P-gp) was analyzed from the viewpoint of cel lular pharmacokinetics, i,e, by means of [H-3]azidopine photoaffinity label ing, cellular accumulation and transcellular transport experiments, in this study, P-gp-overexpressing LLC-GA5-COL150 cells, porcine kidney epithelial LLC-PK1, cells transformed with human MDR1 cDNA, were used, since this cel l line constructs monolayers with tight junctions, and would provide suffic ient information for analyzing the cellular pharmacokinetics, 3-(4,5-Dimeth ylthiazol-2-yl)-2,5-diphenyltetrabromide (MTT) assay revealed that the grow th-inhibitory effect of KRN5500 in LLC-GA5-COL150 cells was comparable to t hat in LLC-PK1 cells (IC50 = 79.4 and 72.7 nM, respectively), but the inhib ition of [H-3]azidopine binding by KRN5500 was concentration-dependent in t he membrane fraction of LLC-GA5-COL150 cells. The cellular accumulation of [C-14]KRN5500 after its basal application in LLC-GA5-COL150 cells was sligh tly loner than that in LLC-PK1 cells, and was restored by the multidrug res istance (MDR) modulator SDZ PSC 833, The basal-to-apical transport of [C-14 ]KRN5500 in LLC-GA5-COL150 cells was also slightly higher than that in LLC- PK1 cells, and was inhibited by SDZ, PSC 833, However, the basal-to-apical transport of [C-14]KRN5500 in LLC-GA5-COL150 cells was only a little higher than the apical-to-basal transport. Consequently, these results demonstrat ed that KRN5500 interacted with, but was hardly transported via, P-gp, Thes e observations suggested that KRN5500 may be useful even for the treatment of tumors exhibiting P-gp-mediated MDR.