Abstract
Ixabepilone is the first epothilone to be approved for clinical use. Current data suggest the epothilones have a role in treating taxane-resistant cancers and ixabepilone is unaffected by at least some of the mechanisms underlying chemoresistance. Here, we report a series of cytotoxicity and transport studies to assess the potential role of P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) in ixabepilone resistance. A significant decrease in ixabepilone-mediated cytotoxicity was observed in Madin-Darby canine kidney cells transfected with human multidrug resistance 1 (MDR1) comparative with the parental cells (IC50 > 2000 nM versus 90 nM). Overexpression of P-gp also resulted in significantly decreased cell susceptibility to docetaxel, paclitaxel, and vinblastine. Bidirectional transport of ixabepilone across monolayers of porcine kidney-derived cells expressing human MDR1 showed a significantly increased efflux ratio relative to the parental cells. A BCRP-overexpressing cell line was developed by transfecting human embryonic kidney (HEK)-293 cells with BCRP cDNA and confirmed by immunoblotting and bodipy prazosin and mitoxantrone uptake. Neither P-gp nor multidrug resistance protein 2 was detected in the cells by corresponding polyclonal antibodies. This HEK-BCRP cell line demonstrated resistance to docetaxel, paclitaxel, vinblastine, and mitoxantrone, in comparison with the parental cell line (7.3, 4.3, 2.9, and 11.9 resistance factor, respectively). Transport inhibition by BCRP inhibitor fumitremorgin C and broad efflux inhibitor 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 (GF120918) restored drug sensitivity. In contrast, ixabepilone was far less susceptible to BCRP-mediated resistance, resulting in a resistance factor of only 1.2-fold. In summary, these results suggest that P-gp could cause resistance to ixabepilone in tumors and affect the disposition of the drug, but it is unlikely that BCRP mediates any drug resistance to ixabepilone.
Footnotes
This study was supported by Bristol-Myers Squibb.
Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
doi:10.1124/jpet.110.175604.
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ABBREVIATIONS:
- ABC
- ATP-binding cassette
- P-gp
- P-glycoprotein
- BCRP
- breast cancer resistance protein
- MRP2
- multidrug resistance protein 2
- HEK
- human embryonic kidney
- MDCK
- Madin-Darby canine kidney
- LLC-PK1
- Lilly laboratory cell for porcine kidney 1
- FTC
- fumitremorgin C
- MDR
- multidrug resistance
- RR
- relative resistance
- BP
- bodipy prazosin
- PBS
- phosphate-buffered saline
- HPBS
- PBS containing 10 mM HEPES, pH 7.4
- RT
- reverse transcription
- PCR
- polymerase chain reaction
- LC/MS/MS
- liquid chromatography/tandem mass spectrometry
- ER
- efflux ratio
- FRT
- Flp recombination target
- A → B
- apical to basal
- B → A
- basal to apical
- GF120918
- 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
- MK-571
- 3-[[[3-[(1E)-2-(7-chloro-2-quinolinyl)ethenyl]phenyl][[3-(dimethylamino)-3-oxopropyl]thio]methyl]thio]propanoic acid
- XTT
- sodium 3′-[1-(phenylaminocarbonyl)-3,4-tetrazolium]-bis(4-methoxy-6-nitro)benzene sulfonic acid hydrate.
- Received September 27, 2010.
- Accepted January 21, 2011.
- Copyright © 2011 by The American Society for Pharmacology and Experimental Therapeutics
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