Altered activity of MDR-reversing agents on KB3-1 cells transfected with Gly(185)-->Val human P-glycoprotein.
P-glycoprotein (P-gp) is a transmembrane glycoprotein that confers multidrug resistance (MDR). It has been demonstrated that the Gly185 residue within the cytoplasmic loop between predicted transmembrane portions 2 and 3 plays an important role in substrate specificity of human P-gp. Derivatives of cyclosporin interact with and reverse the ability of P-gp to act as a drug efflux pump. To determine if the Gly185 residue of human P-gp is also important for the interaction of P-gp with closely related cyclosporin derivatives, we examined the effect of PSC-833 and CsA on P-gp in KB3-1 cells transfected with human wild-type P-gp (GSV-2) or with the mutant P-gp (VSV-1) that habored the Gly185-->Val substitution. While the ability of CsA to sensitize VSV-1 cells to anticancer agents was enhanced, no changes in the potency of PSC-833 against cells transfected with either the wild-type or mutant P-gp were observed. In addition, VSV-1 transfected cells were more sensitive to CsA inhibition of verapamil-stimulated ATPase activity than cells transfected with wild-type P-gp. Furthermore, the intracellular accumulation of CsA was low in GSV-2 P-gp-expressing cells, compared with its accumulation in VSV-1 cells and it was found to be as high as in non-P-gp expressing KB3-1 cells. These results indicated an enhanced sensitivity of Val185-P-gp expressing cells to CsA that correlated with increased intracellular accumulation in these cells. In contrast, no significant difference in the accumulation of PSC-833 was observed among the parental, wild-type or resistant cells. Since PSC-833 was found to be more potent than CsA, these studies provided insight into the effects of the structure of MDR modulators in mediating sensitivity to anticancer drugs.
Watanabe
T
T
Novartis Pharma K.K., Tsukuba Research Institute, Ibaraki, Japan.
Uchiyama
N
N
Roninson
I B
IB
Cohen
D
D
Atadja
P
P
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D000251:Adenosine Triphosphatases / Q000378:metabolism; D019943:Amino Acid Substitution; D000970:Antineoplastic Agents / Q000378:metabolism*; D001693:Biological Transport, Active / Q000187:drug effects; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002294:Carcinoma, Squamous Cell / Q000473:pathology; D003078:Colchicine / Q000378:metabolism; D016572:Cyclosporine / Q000494:pharmacology*; D003524:Cyclosporins / Q000494:pharmacology*; D003630:Daunorubicin / Q000378:metabolism; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D006801:Humans; D009363:Neoplasm Proteins / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D017239:Paclitaxel / Q000378:metabolism; D017354:Point Mutation; D013329:Structure-Activity Relationship; D014162:Transfection; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D014700:Verapamil / Q000494:pharmacology; D014747:Vinblastine / Q000378:metabolism
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000970:Antineoplastic Agents; D002121:Calcium Channel Blockers; D003524:Cyclosporins; D009363:Neoplasm Proteins; D014747:Vinblastine; D016572:Cyclosporine; D014700:Verapamil; D000251:Adenosine Triphosphatases; D017239:Paclitaxel; C070272:valspodar; D003078:Colchicine; D003630:Daunorubicin