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.
Novartis Pharma K.K., Tsukuba Research Institute, Ibaraki, Japan.
T
T
Watanabe
N
N
Uchiyama
I B
IB
Roninson
D
D
Cohen
P
P
Atadja
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