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 derivative, with human Pglycoprotein (P‐gp) was analyzed from the viewpoint of cellular pharmacokinetics, i.e. by means of [(3)H]azidopine photoaffinity labeling, cellular accumulation and transcellular transport experiments. In this study, P‐gp‐overexpressing LLC‐GA5‐COL150 cells, porcine kidney epithelial LLC‐PK(1) cells transformed with human MDR1 cDNA, were used, since this cell line constructs monolayers with tight junctions, and would provide sufficient information for analyzing the cellular pharmacokinetics. 3‐(4,5‐Dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) assay revealed that the growth‐inhibitory effect of KRN5500 in LLC‐GA5‐COL150 cells was comparable to that in LLC‐PK(1) cells (IC(50)= 79.4 and 72.7 nM, respectively), but the inhibition of [(3)H]azidopine binding by KRN5500 was concentration‐dependent in the membrane fraction of LLC‐GA5‐COL150 cells. The cellular accumulation of [(14)C]KRN5500 after its basal application in LLC‐GA5‐COL150 cells was slightly lower than that in LLC‐PK(1) cells, and was restored by the multidrug resistance (MDR) modulator SDZ PSC 833. The basal‐to‐apical transport of [(14)C]KRN5500 in LLC‐GA5‐COL150 cells was also slightly higher than that in LLC‐PK(1) cells, and was inhibited by SDZ PSC 833. However, the basal‐to‐apical transport of [(14)C]KRN5500 in LLC‐GA5‐COL150 cells was only a little higher than the apical‐to‐basal transport. Consequently, these results demonstrated that KRN5500 interacted with, but was hardly transported via, P‐gp. These observations suggested that KRN5500 may be useful even for the treatment of tumors exhibiting P‐gp‐mediated MDR.