Inhibition of P-glycoprotein by D-alpha-tocopheryl polyethylene glycol 1000 succinate (TPGS).
OBJECTIVE
To investigate whether d-alpha-tocopheryl polyethylene glycol 1000 succinate (TPGS) functions as an inhibitor of P-glycoprotein (P-gp), the multidrug resistance transporter.


METHODS
Two assays were used to measure the function of TPGS on P-gp function. First, we examined the ability of TPGS to modulate the cytotoxicity of established, cytotoxic, P-glycoprotein substrates. Parental NIH 3T3 cells and NIH 3T3 cells transfected with the human MDR1 cDNA (G185) were exposed to doxorubicin, paclitaxel, colchicine, vinblastine and 5-fluorouracil (5FU) in the presence or absence of TPGS. Cytotoxicity was assessed with the MTT assay. Second, polarized transport of the P-gp substrates rhodamine 123 (R123), paclitaxel and vinblastine was measured using the human intestinal HCT-8 and Caco-2 cell lines grown in Transwell dishes. Drug flux was measured by liquid scintillation counting or fluorescence spectroscopy of the media.


RESULTS
G185 cells were 27-135 fold more resistant to the cytotoxic drugs doxorubicin, vinblastine, colchicine and paclitaxel than the parental NIH 3T3 cells. In contrast 5FU, which is not a P-gp substrate, is equally cytotoxic to parental and G185 cells. Co-administration of TPGS enhanced the cytotoxicity of doxorubicin, vinblastine, paclitaxel, and colchicine in the G185 cells to levels comparable to the parental cells. TPGS did not increase the cytotoxicity of 5FU in the G185 cells. Using a polarized epithelial cell transport assay, TPGS blocked P-gp mediated transport of R123 and paclitaxel in a dose responsive manner.


CONCLUSIONS
These data demonstrate that TPGS acts as a reversal agent for P-glycoprotein mediated multidrug resistance and inhibits P-gp mediated drug transport. These results suggest that enhanced oral bioavailability of drugs co-administered with TPGS may, in part, be due to inhibition of P-glycoprotein in the intestine.
Dintaman
J M
JM
Division of Drug Transport, AvMax, Inc. Berkeley, California 94710, USA.
Silverman
J A
JA
D016475:3T3 Cells; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors*; D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology; D000972:Antineoplastic Agents, Phytogenic / Q000378:metabolism; D015153:Blotting, Western; D002470:Cell Survival / Q000187:drug effects; D004396:Coloring Agents; D016572:Cyclosporine / Q000378:metabolism; D005472:Fluorouracil / Q000633:toxicity; D007166:Immunosuppressive Agents / Q000378:metabolism; D051379:Mice; D008823:Micelles; D017239:Paclitaxel / Q000378:metabolism; D011092:Polyethylene Glycols; D020112:Rhodamine 123; D014747:Vinblastine / Q000378:metabolism; D014810:Vitamin E / Q000031:analogs & derivatives* / Q000494:pharmacology
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000964:Antimetabolites, Antineoplastic; D000972:Antineoplastic Agents, Phytogenic; D004396:Coloring Agents; D007166:Immunosuppressive Agents; D008823:Micelles; D014810:Vitamin E; D020112:Rhodamine 123; D011092:Polyethylene Glycols; D014747:Vinblastine; D016572:Cyclosporine; C014225:tocophersolan; D017239:Paclitaxel; D005472:Fluorouracil