Interaction of forskolin with the P-glycoprotein multidrug transporter.
Forskolin and 1,9-dideoxyforskolin, an analogue that does not activate adenylyl cyclase, were tested for their ability to enhance the cytotoxic effects of adriamycin in human ovarian carcinoma cells, SKOV3, which are sensitive to adriamycin and express low levels of P-glycoprotein, and a variant cell line, SKVLB, which overexpresses the P-glycoprotein and has the multidrug resistance (MDR) phenotype. Forskolin and 1,9-dideoxyforskolin both increased the cytotoxic effects of adriamycin in SKVLB cells, yet had no effect on SKOV3 cells. Two photoactive derivatives of forskolin have been synthesized, 7-O-[[2-[3-(4-azido-3- [125I]iodophenyl)propionamido]ethyl] carbamyl]-7-deacetylforskolin, 125I-7-AIPP-Fsk, and 6-O-[[2-[3-(4-azido-3- [125I]iodophenyl)propionamido]ethyl]carbamyl]forskolin, 125I-6-AIPP-Fsk, which exhibit specificity for labeling the glucose transporter and adenylyl cyclase, respectively (Morris et al., 1991). Both photolabels identified a 140-kDa protein in membranes from SKVLB cells whose labeling was inhibited by forskolin and 1,9-dideoxyforskolin. There was no specific labeling of proteins in membranes from the SKOV3 cells. The overexpressed 140-kDa protein in SKVLB membranes was identified as the P-glycoprotein by immunoblot analysis and immunoprecipitation using anti-P-glycoprotein antiserum. Total inhibition of photolabeling of the P-glycoprotein was observed with verapamil, nifedipine, diltiazem, and vinbalastine, and partial inhibition was observed with colchicine and cytochalasin B. Forskolin was less effective at inhibiting the photolabeling of the P-glycoprotein than 1,9-dideoxyforskolin or a lipophilic derivative of forskolin. The data are consistent with forskolin binding to the P-glycoprotein analogous to that of other chemosensitizing drugs that have been shown to partially reverse MDR.(ABSTRACT TRUNCATED AT 250 WORDS)
Molecular Pharmacology Laboratory, Food and Drug Administration, Bethesda, Maryland 20892.
D I
DI
Morris
L A
LA
Speicher
A E
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Ruoho
K D
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Tew
K B
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Seamon
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000345:Affinity Labels; D000595:Amino Acid Sequence; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000737:chemistry; D005576:Colforsin / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D004317:Doxorubicin / Q000633:toxicity; D004347:Drug Interactions; D004351:Drug Resistance; D005260:Female; D006801:Humans; D008562:Membrane Glycoproteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009363:Neoplasm Proteins / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000345:Affinity Labels; D002352:Carrier Proteins; D008562:Membrane Glycoproteins; D009363:Neoplasm Proteins; D005576:Colforsin; D004317:Doxorubicin; C047983:1,9-dideoxyforskolin