Abstract
The human multidrug resistance gene MDR1 encodes a membrane-bound transporter P-glycoprotein (Pgp) that confers the drug resistance of cancer cells by mediating an ATP-dependent drug efflux transport. We and others have reported a number of functionally significant MDR1 variants, including G1199A and G1199T, that modulate cancer drug resistance and intracellular levels of antivirals. In this report, we describe a novel G571A variant of MDR1 detected in 6.4% of leukemia patients. Because this nucleotide modification gives rise to an amino acid change from Gly to Arg at the 191 amino acid position of Pgp, we have developed and characterized the functional affect of the G571A variant in stable, recombinant cells. Using six chemotherapeutic drugs, doxorubicin HCl, daunorubicin HCl, vinblastine sulfate, vincristine sulfate, taxanes (paclitaxel), and epipodophyllotoxin (etoposide, VP-16), we found that the MDR1571A variant selectively reduced the degree of Pgp-mediated resistance in drug-dependent manner. Although there was a minimal effect on doxorubicin and daunorubicin, the MDR1-dependent resistance on vinblastine, vincristine, paclitaxel, and etoposide was reduced by approximately 5-fold. The increased drug sensitivity in MDR1571A, compared with MDR1wt, paralleled the intracellular drug levels. These data suggest that individuals with this novel MDR1 variant, the 571A genotype, may be more sensitive to the specific anticancer drugs that are Pgp substrates.
Footnotes
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This work was supported in part by the National Institutes of Health (Grants GM62883, AI52663, and NS 39178), the Milo Gibaldi Endowment Fund, and the University of Washington Center for DNA Sequencing and Gene Analysis.
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.108.138313.
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ABBREVIATIONS:MDR1 or ABCB1, the human multidrug resistance gene; Pgp, a membrane-bound transporter P-glycoprotein that confers the drug resistance of cancer cells; SNP, single nucleotide polymorphism; MDS, myelodysplasia; AML, acute myelogenous leukemia; HEK, human embryonic kidney; GF120918, Elacridar, [N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl) ethyl]-phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide]; DMEM, Dulbecco's modified Eagle's medium; RT, reverse transcriptase; PCR, polymerase chain reaction; R123, rhodamine 123; PBS, phosphate-buffered saline; DPBSG, Dulbecco's phosphate-buffered saline plus glucose containing medium.
- Received March 6, 2008.
- Accepted August 21, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
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