| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Experimental Therapeutics, Preclinical Pharmacology |
Developmental Therapeutics Department, Medicine Branch, National Cancer Institute [R. W. R., W. Y. M-P., K. N., K. M., T. L., S. E. B.], and Molecular Therapeutics Unit, Oral and Pharyngeal Cancer Branch, National Institute of Dental and Craniofacial Research, NIH, Bethesda, Maryland 20892 [T. L., A. M. S.], and University of Maryland Greenebaum Cancer Center and Department of Medicine, University of Maryland School of Medicine, and Baltimore Veterans Medical Center, Department of Veterans Affairs, Baltimore, Maryland 21201 [D. D. R.]
 |
ABSTRACT |
|---|
 Top ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
|
INTRODUCTION |
|---|
|
TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
As the clinical development of flavopiridol is pursued, it becomes important to evaluate mechanisms of cellular resistance. Although a number of resistance mechanisms are possible, we focused on the ABC family of transporter proteins that may mediate efflux of anticancer agents, thereby reducing intracellular drug concentrations. Pgp and MRP are two of the most extensively studied ABC transporters and are known to confer resistance to a wide variety of structurally unrelated cytotoxic agents (10 , 11) . The newly described mitoxantrone resistance protein, MXR or ABCG2, is an ABC half-transporter that is thought to dimerize to function and has been shown to confer resistance to mitoxantrone, anthracyclines, and to the camptothecins topotecan and SN-38 (12, 13, 14, 15, 16) . Except for minor sequence differences, MXR is identical to BCRP reported by Doyle et al. (13) and to the placental ABC protein (ABCP1), which was reported by Allikmets et al. (17) and is expressed in high levels in the placenta. The Human Gene Nomenclature Committee has suggested that MXR/BCRP/ABCP1 be renamed ABCG2,4 and such terminology will be used hereafter.
Recent studies have shown that flavopiridol is able to inhibit MRP-mediated transport and increase MRP-related ATPase activity in membrane vesicles and MRP-overexpressing cells; however, little cross-resistance to flavopiridol attributable to this mechanism was observed (18 , 19) . Moreover, bladder cancer cells overexpressing Pgp were not found to have increased flavopiridol resistance (20) . A flavopiridol-resistant ovarian carcinoma cell line has also recently been described that spontaneously developed resistance to flavopiridol as well as cisplatin after prolonged passage in tissue culture, although no transporter was implicated as a cause for the resistance (21) . Schlegel et al. (22) also recently reported in abstract form that cells which overexpress ABCG2 were resistant to flavopiridol, and that the dipyridimol analogue, BIB-E, was able to reverse this resistance.
In the present study, we sought to characterize the interactions of flavopiridol with these three members of the ABC-transporter family. The ability of flavopiridol to block MRP-mediated transport was confirmed, and it was demonstrated that the novel ABC half-transporter, ABCG2, is able to confer resistance to flavopiridol. We also describe a flavopiridol-resistant human breast cancer subline, MCF-7 FLV1000, which is maintained in 1000 nM flavopiridol. This subline was shown to overexpress the ABCG2 gene, thus implicating ABCG2 as a mechanism of resistance for flavopiridol.
|
MATERIALS AND METHODS |
|---|
|
TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Cell Lines.
The MCF-7 FLV25, FLV100, FLV250, FLV500, and FLV1000 cells were
selected by exposing MCF-7 cells to increasing concentrations of
flavopiridol. The Pgp-overexpressing SW620 Ad300 cell line was derived
from SW620 colon cancer cells and is maintained in 300 ng/ml Adriamycin
(23)
. The human colon carcinoma cell line S1 and its
ABCG2-overexpressing subline S1-M1-3.2 were obtained from Dr. Lee M.
Greenberger (Wyeth-Ayerst; Ref. 24
). The S1-M1-80 subline
was generated by exposing the S1-M1-3.2 subline to increasing
concentrations of mitoxantrone (12)
. The S1-M1-3.2 and
S1-M1-80 subline were maintained in 3.2 and 80 µM of
mitoxantrone, respectively. The Pgp-overexpressing subline S1-B1-20,
which is maintained in 20 µM bisantrene, was also
obtained from Dr. Greenberger (25)
. The
ABCG2-overexpressing MCF-7 subline MCF-7 AdVp3000 was maintained in
3000 ng/ml Adriamycin and 5 µg/ml verapamil (26)
. The
MRP-overexpressing subline MCF-7/VP was provided by Dr. Kenneth
Cowan (University of Nebraska Medical Center, Omaha, NE) and is
maintained in 4 µM etoposide (27)
. The
ABCG2-transfected cell line, MCF-7/BCRP, and the empty
vector-transfected cell line, MCF-7/pcDNA3, were kindly provided by Dr.
Douglas Ross and have been described previously (13)
. The
MCF-7 and derivative sublines were cultured in Iscove’s modified
Eagle’s medium, and the SW620 and S1 cells and derivative lines were
cultured in RPMI 1640. Both were supplemented with 2
mM L-glutamine, 100 units/ml penicillin, and
100 µg/ml streptomycin. All cells were maintained in the selecting
drug at the indicated concentrations at 37°C in 5%
CO2. Cells were placed in drug-free medium 7–14
days prior to assay.
Cytotoxicity Assays.
Assays were performed in 96-well plates using the colorimetric method
described by Skehan et al. (28)
. Cells were
seeded in 96-well plates at a density of 2000 cells/well and allowed to
attach overnight. Subsequently, drug was added at the desired
concentrations, and the cells were incubated 4 days at 37°C, fixed in
50% trichloroacetic acid, then stained in 0.4% sulforhodamine B
dissolved in 1% acetic acid. After washing, bound dye was solubilized
with 10 mM unbuffered Tris base (pH 10.5).
Cell density was determined by measuring the absorbance at 570
nm.
Efflux Assays.
The rhodamine 123, calcein, and mitoxantrone efflux assays were
performed as described previously (29
, 30)
. Briefly, a
suspension of log-phase cells was obtained by trypsinization. Cells
were incubated in 0.5 µg/ml rhodamine 123, 0.5 µM
calcein AM, or 20 µM mitoxantrone with or without FTC,
flavopiridol, probenecid, or PSC 833 at the desired concentration in
complete medium (phenol red-free Iscove’s modified Eagle’s medium
with 10% FCS) at 37°C in 5% CO2 for 30 min.
The cells were washed once with cold complete medium and then
resuspended in complete medium with or without FTC, flavopiridol,
probenecid, or PSC 833 for a 60-min efflux period at 37°C. Cells were
then washed in ice-cold Dulbecco’s PBS, placed in Dulbecco’s PBS at
4°C, and kept in the dark until flow cytometric analysis. A FACSort
flow cytometer with a 488-nm argon laser and 530 nm bandpass filter was
used to read the fluorescence of rhodamine and calcein, whereas a
FACSCalibur flow cytometer equipped with a 635-nm red diode laser and
670-nm bandpass filter was used to read the fluorescence of
mitoxantrone. At least 10,000 events were collected. Debris was
eliminated by gating on forward versus side scatter, and
dead cells were excluded based on propidium iodide staining.
Northern Blot and PCR Analysis.
RNA was prepared using RNA STAT-60 according to the manufacturer’s
instructions (Tel-Test, Inc., Friendswood, TX). Northern blotting was
performed as described previously (12)
. Quantitative PCR
analysis was performed as described previously (31)
using
the following primers: MDR1 5' primer, 5'-GCC TGG CAG CTG GAA GAC AAA
TAC ACA AAA TT-3'; MDR1 3' primer, 5'-CAG ACA GCA GCT GAC AGT CCA AGA
ACA GGA CT-3'; MRP1 5' primer, 5'-CGG AAA CCA TCC ACG ACC CTA ATC C-3';
MRP1 3' primer, 5'-ACC TCC TCA TTC GCA TCC ACC TTG G-3'; ABCG2 3'
primer, 5'-TGC CCA GGA CTC AAT GCA ACA G-3'; and ABCG2 5' primer,
5'-GAC TGA AGG GCT ACT AAC C-3'.
Western Blot Analysis.
Microsomal membrane fractions were prepared by nitrogen cavitation,
subjected to electrophoresis on a premade 8% SDS-polyacrylamide gel,
and electrotransferred onto polyvinylidene difluoride membranes. The
blots were blocked with 5% nonfat dry milk and probed with a
polyclonal anti-ABCG2 antibody, 87405, which was raised against a
region of the ATP-binding site of ABCG2, a polyclonal anti-Pgp antibody
(Calbiochem, San Diego, CA), or a monoclonal anti-MRP antibody, MRPm5
(Kamiya Biomedical, Seattle, WA). The blots were then incubated with a
secondary antirabbit or antimouse horseradish peroxidase-conjugated
antibody (Amersham Pharmacia Biotech, Piscataway, NJ), followed by
enhanced chemiluminescence detection (DuPont NEN, Boston, MA) and
subsequent exposure to Kodak X-OMAT AR film.
Fluorescence Immunohistochemistry.
Cells were grown on eight-well chamberslides (Nunc, Roskilde,
Denmark) for 3 days before analysis. The samples were fixed in
methanol:ethanol (1:1) for 1 min and then washed in PBS with 2% human
type AB serum (Sigma) three times for 10 min. The primary antibody,
anti-ABCG2 polyclonal rabbit, 87405, was added at a 1:3000 dilution and
incubated for 2 h at room temperature. After washing three times
for 10 min with PBS with 2% human AB serum, the secondary antibody,
FITC-conjugated pig antirabbit (DAKO, Glostrup, Denmark) at a
dilution of 1:50 was added for 1 h. The samples were washed four
times for 10 min in PBS, and a coverslip was mounted with a drop of
Antifade (Molecular Probes, Leiden, Denmark). Antibody binding
was detected by confocal microscopy with a Zeiss LSM410, exciting FITC
at 488 nm (Ar-Kr laser), and measuring emission through a 515–540 nm
bandpass filter.
|
RESULTS |
|---|
|
TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
. The MCF-7 AdVp3000 and S1-M1-80 cells, which express the newly
identified ABC half-transporter, ABCG2, were approximately 36- and
6-fold resistant to flavopiridol, respectively. Little cross-resistance
was observed in the two Pgp-overexpressing lines, S1-B1-20 or SW620
Ad300 (0.87- and 1.5-fold, respectively), or in the MRP-overexpressing
MCF-7/VP cells (1.1-fold).
|
A shows 10 µM flavopiridol
(dashed line) was almost as effective as 5
mM probenecid (dotted line) in
preventing MRP-mediated calcein efflux (solid line) in the
MRP-overexpressing MCF-7/VP cell line. Probenecid has been shown
previously to prevent MRP-mediated transport in MRP-overexpressing cell
lines (32)
.
|
B. The effect of
the Pgp inhibitor PSC 833 is shown for comparison (dotted
line). With PSC 833, intracellular accumulation of rhodamine was
restored to the levels seen in parental cells in both sublines.
Characterization of a Flavopiridol-resistant Subline.
To explore the potential contribution of ABC transporters to
flavopiridol resistance, MCF-7 human breast cancer cells were exposed
to increasing concentrations of flavopiridol. The resulting sublines,
MCF-7 FLV25, FLV100, FLV250, FLV500, and FLV1000, were maintained in
25, 100, 250, 500, and 1000 nM flavopiridol, respectively.
The cross-resistance profile of the MCF-7 FLV1000 subline was
evaluated, and the results are summarized in Table 2
. The MCF-7 FLV1000 cells were found to be 24-fold resistant to
flavopiridol and were highly cross-resistant to topotecan (423-fold),
mitoxantrone (675-fold), and SN-38 (950-fold), the active metabolite of
irinotecan, and less so to paclitaxel (3.6-fold) and 5-FU (10-fold). As
the mitoxantrone and camptothecin resistance profile was similar to
that of cells that overexpress the ABCG2 protein, cytotoxicity assays
with and without 5 µM FTC were performed. FTC, an extract
of Aspergillus fumigatus, is known to inhibit transport
mediated by ABCG2 (24
, 33)
. As seen in Fig. 2
A, FTC was able to sensitize the cells to flavopiridol as
well as to topotecan, mitoxantrone, and SN-38. FTC was not able to
restore sensitivity to 5-FU or paclitaxel in the MCF-7 FLV1000 cells,
suggesting that another resistance mechanism is responsible for the low
levels of cross-resistance observed in these cells. In Fig. 2
B, the ABCG2-transfected cell line, MCF-7/BCRP, was also
found to be resistant to flavopiridol (3.75-fold, average of two
independent experiments), again confirming the role of ABCG2 in
flavopiridol resistance.
|
|
shows, FTC (dashed line) is able to increase intracellular
mitoxantrone fluorescence, which reflects the intracellular
mitoxantrone concentration, in the MCF-7 FLV250, MCF-7 FLV500, and
MCF-7 FLV1000 cells. Mitoxantrone fluorescence in MCF-7 FLV1000 cells
is reduced to levels comparable with those in the ABCG2-overexpressing
MCF-7 AdVp3000 cells, which are shown for comparison. In early steps of
selection, small decreases in mitoxantrone fluorescence were also
noted, suggesting that low levels of ABCG2 may be present in these
cells.
|
that neither Pgp nor MRP overexpression confers
flavopiridol resistance.
Northern analysis was performed to evaluate ABCG2 expression levels in
the flavopiridol-resistant sublines. Fig. 4
A shows a dose-dependent increase in the expression of ABCG2
at the RNA level in MCF-7 FLV250, MCF-7 FLV500, and MCF-7 FLV1000
cells. High levels were found in the MCF-7 FLV1000 cells but were
slightly lower than those in the S1-M1-80 cells, which are shown for
comparison.
|
B. Additionally, the cells were found not to
overexpress MRP or Pgp, which correlates with results obtained from
flow cytometry analysis. MCF-7 AdVp30000 cells served as a positive
control for ABCG2, MCF-7/VP cells for MRP, and S1-B1-20 cells for Pgp
in Fig. 4
B. Immunofluorescence studies with the polyclonal
antibody 87405 also showed increased ABCG2 expression in MCF-7 FLV1000
cells. Confocal images of MCF-7 parental cells incubated with 87405
show that the level of ABCG2 is below the limits of detection (Fig. 4
C), whereas increased expression is detected in the MCF-7
FLV1000 cell line (Fig. 4
D). PCR analysis revealed a 48-fold increase in ABCG2 expression and a 1.3-fold increase in MRP expression in MCF-7 FLV1000 cells versus MCF-7 parental cells; MDR-1 levels were undetectable in both the parental and resistant line (data not shown).
Antagonism of ABCG2-mediated Mitoxantrone Transport by
Flavopiridol.
Because flavopiridol appears to be a substrate for ABCG2, its ability
to inhibit ABCG2-mediated drug efflux was assessed, because many
transporter substrates are known to act as inhibitors as well
(34)
. We incubated S1-M1-80, MCF-7 FLV1000, MCF-7
AdVp3000, and MCF-7/BCRP cells in mitoxantrone with 1, 10, and 100
µM flavopiridol. Flavopiridol at a concentration of 100
µM (dashed line) was indeed able to antagonize
mitoxantrone transport from all four cell lines, as seen in Fig. 5
. The ABCG2 blocker FTC at a concentration of 10
µM (dotted line) is also shown for
comparison. In the ABCG2-transfected cell line MCF-7/BCRP, flavopiridol
was as effective as 10 µM FTC in preventing
mitoxantrone efflux, but this may be attributable to the fact that this
cell line expresses a low level of ABCG2. Flavopiridol fluorescence was
found to be negligible under these conditions (data not shown).
|
|
DISCUSSION |
|---|
|
TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
The interactions of flavopiridol with members of the ABC-transporter family were also characterized. Pgp was not found to confer resistance to flavopiridol in Pgp-overexpressing cell lines, nor was flavopiridol able to appreciably prevent Pgp-mediated rhodamine transport in these cells. This is in agreement with Chien et al. (20) , who also demonstrated little cross-resistance to flavopiridol in Pgp-overexpressing, drug-selected bladder cancer cells. In contrast, flavopiridol was able to prevent MRP-mediated calcein efflux from MRP-overexpressing cells, which is consistent with the findings of Hooijberg et al. (19) , who demonstrated increased daunorubicin accumulation in MRP-overexpressing cells in the presence of flavopiridol. Our observation that ABCG2 is able to confer resistance to flavopiridol parallels that of a preliminary report by Schlegel et al. (22) , who demonstrated increased resistance to flavopiridol in ABCG2-overexpressing cells.
Another flavopiridol-resistant subline was recently reported by Bible et al. (21) . The ovarian carcinoma cell line, OV202 hp, spontaneously developed drug resistance after long-term culture and was found to be 5-fold resistant to flavopiridol as well as 3-fold resistant to cisplatin. Although decreased intracellular flavopiridol concentrations were noted, Bible et al. (21) conclude that neither Pgp nor MRP were responsible for drug transport based on the fact that no cross-resistance to known substrates was observed. They did not test for the presence of ABCG2. However, Bible et al. (21) did not find enhanced resistance to mitoxantrone or topotecan, two cytotoxics that are readily transported by ABCG2 (12, 13, 14, 15, 16) . Thus, it does not appear that resistance to flavopiridol is attributable to ABCG2 in the OV202 hp cell line.
Interestingly, we found the S1-M1-80 cell line to be 6-fold resistant to flavopiridol, whereas the MCF-7 AdVp3000 cell line was 36-fold resistant. This difference could be explained by the structure of the ABCG2 protein. Because it is thought to dimerize for function, it is possible that ABCG2 homodimerizes in one cell line and heterodimerizes in the other cell line, leading to differing substrate specificity, much as in the case of the Drosophila white protein (35) . Alternatively, polymorphisms in ABCG2 could result in differing substrate affinities. A splice variant of the human Tap2 gene, Tap2iso, was shown recently to encode for a protein having differing substrate specificities from the normal Tap2 gene product (36) .
Flavopiridol was also found to prevent ABCG2-mediated mitoxantrone efflux in ABCG2-overexpressing cells, albeit at a relatively high concentration. The mechanism of inhibition is unknown. This could be attributable to competitive inhibition, much like the classic paradigm for Pgp where a Pgp substrate may also function as an antagonist if used at sufficiently high concentrations (34) . Alternatively, as flavopiridol does compete for the ATP-binding site of cdks (2) , it is possible that flavopiridol is able to compete for the ATP-binding site of ABCG2.
We conclude from these studies that ABCG2 is able to confer resistance to flavopiridol. One solution that has been proposed to the problem of drug resistance is to develop agents that are not substrates for P-glycoprotein and thereby circumvent drug resistance. However, it could be argued that this strategy is flawed because there appears to be enough genetic diversity among transporters to suggest that most compounds may be a substrate for some transporter. As flavopiridol enters Phase II trials, it becomes important to examine which mechanisms of resistance may emerge as a result of drug treatment. With the expanding number of ABC transporters described, it will become important to identify which transporters may play a role in resistance to drugs in the clinic and developing strategies to prevent or thwart this resistance.
|
ACKNOWLEDGMENTS |
|---|
|
FOOTNOTES |
|---|
1 Funded in part by Grant RO1-CA77545 from the
National Cancer Institute, NIH and a Merit Review Grant from the
Department of Veterans Affairs (to D. D. R.). 
2 To whom requests for reprints should be
addressed, at Medicine Branch, National Cancer Institute, NIH, Building
10, Room 12N226, 9000 Rockville Pike, Bethesda, MD 20892. Phone:
(301) 496-4916; Fax: (301) 402-0172; E-mail: sebates{at}helix.nih.gov
3 The abbreviations used are: cdk,
cyclin-dependent kinase; ABC, ATP-binding cassette; Pgp,
P-glycoprotein; MRP, multidrug resistance-associated protein; BCRP,
breast cancer resistance protein; ABCP1, placental ABC protein 1; FTC,
fumitremorgin C; 5-FU, 5-fluorouracil.
4 Internet address:
http://www.gene.ucl.ac.uk/users/hester/abc.html.
Received 5/18/00; revised 9/13/00; accepted 9/15/00.
|
REFERENCES |
|---|
|
TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
This article has been cited by other articles:
|
|
 |
|
  S. Shukla, R. W. Robey, S. E. Bates, and S. V. Ambudkar Sunitinib (Sutent, SU11248), a Small-Molecule Receptor Tyrosine Kinase Inhibitor, Blocks Function of the ATP-Binding Cassette (ABC) Transporters P-Glycoprotein (ABCB1) and ABCG2 Drug Metab. Dispos., February 1, 2009; 37(2): 359 - 365. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 K. K. W. To, Z. Zhan, T. Litman, and S. E. Bates Regulation of ABCG2 Expression at the 3' Untranslated Region of Its mRNA through Modulation of Transcript Stability and Protein Translation by a Putative MicroRNA in the S1 Colon Cancer Cell Line Mol. Cell. Biol., September 1, 2008; 28(17): 5147 - 5161. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 Z. Liao, R. W. Robey, J. Guirouilh-Barbat, K. K. W. To, O. Polgar, S. E. Bates, and Y. Pommier Reduced Expression of DNA Topoisomerase I in SF295 Human Glioblastoma Cells Selected for Resistance to Homocamptothecin and Diflomotecan Mol. Pharmacol., February 1, 2008; 73(2): 490 - 497. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 K. K.W. To, O. Polgar, L. M. Huff, K. Morisaki, and S. E. Bates Histone Modifications at the ABCG2 Promoter following Treatment with Histone Deacetylase Inhibitor Mirror Those in Multidrug-Resistant Cells Mol. Cancer Res., January 1, 2008; 6(1): 151 - 164. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. J. Henrich, R. W. Robey, H. R. Bokesch, S. E. Bates, S. Shukla, S. V. Ambudkar, M. Dean, and J. B. McMahon New inhibitors of ABCG2 identified by high-throughput screening Mol. Cancer Ther., December 1, 2007; 6(12): 3271 - 3278. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C.-P. Wu, S. Shukla, A. M. Calcagno, M. D. Hall, M. M. Gottesman, and S. V. Ambudkar Evidence for dual mode of action of a thiosemicarbazone, NSC73306: a potent substrate of the multidrug resistance linked ABCG2 transporter Mol. Cancer Ther., December 1, 2007; 6(12): 3287 - 3296. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Shukla, C.-P. Wu, K. Nandigama, and S. V. Ambudkar The naphthoquinones, vitamin K3 and its structural analogue plumbagin, are substrates of the multidrug resistance linked ATP binding cassette drug transporter ABCG2 Mol. Cancer Ther., December 1, 2007; 6(12): 3279 - 3286. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 Z. Shi, X.-X. Peng, I.-W. Kim, S. Shukla, Q.-S. Si, R. W. Robey, S. E. Bates, T. Shen, C. R. Ashby Jr., L.-W. Fu, et al. Erlotinib (Tarceva, OSI-774) Antagonizes ATP-Binding Cassette Subfamily B Member 1 and ATP-Binding Cassette Subfamily G Member 2 Mediated Drug Resistance Cancer Res., November 15, 2007; 67(22): 11012 - 11020. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. P. Lopez, J. Wang-Rodriguez, C. Chang, J. S. Chen, F. S. Pardo, J. Aguilera, and W. M. Ongkeko Gefitinib Inhibition of Drug Resistance to Doxorubicin by Inactivating ABCG2 in Thyroid Cancer Cell Lines Arch Otolaryngol Head Neck Surg, October 1, 2007; 133(10): 1022 - 1027. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. Glavinas, E. Kis, A. Pal, R. Kovacs, M. Jani, E. Vagi, E. Molnar, S. Bansaghi, Z. Kele, T. Janaky, et al. ABCG2 (Breast Cancer Resistance Protein/Mitoxantrone Resistance-Associated Protein) ATPase Assay: A Useful Tool to Detect Drug-Transporter Interactions Drug Metab. Dispos., September 1, 2007; 35(9): 1533 - 1542. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. W. Robey, S. Shukla, K. Steadman, T. Obrzut, E. M. Finley, S. V. Ambudkar, and S. E. Bates Inhibition of ABCG2-mediated transport by protein kinase inhibitors with a bisindolylmaleimide or indolocarbazole structure Mol. Cancer Ther., June 1, 2007; 6(6): 1877 - 1885. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. S. Lee, H.-E. Jeong, J.-M. Yi, H.-J. Jung, J.-E. Jang, E.-Y. Kim, S.-J. Lee, and J.-G. Shin Identification and Functional Assessment of BCRP Polymorphisms in a Korean Population Drug Metab. Dispos., April 1, 2007; 35(4): 623 - 632. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. G. Turner, J. L. Gump, C. Zhang, J. M. Cook, D. Marchion, L. Hazlehurst, P. Munster, M. J. Schell, W. S. Dalton, and D. M. Sullivan ABCG2 expression, function, and promoter methylation in human multiple myeloma Blood, December 1, 2006; 108(12): 3881 - 3889. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. Chen, V. Gandhi, and W. Plunkett A Sequential Blockade Strategy for the Design of Combination Therapies to Overcome Oncogene Addiction in Chronic Myelogenous Leukemia. Cancer Res., November 15, 2006; 66(22): 10959 - 10966. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. A. Seamon, C. A. Rugg, S. Emanuel, A. M. Calcagno, S. V. Ambudkar, S. A. Middleton, J. Butler, V. Borowski, and L. M. Greenberger Role of the ABCG2 drug transporter in the resistance and oral bioavailability of a potent cyclin-dependent kinase/Aurora kinase inhibitor. Mol. Cancer Ther., October 1, 2006; 5(10): 2459 - 2467. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
W. Chearwae, S. Shukla, P. Limtrakul, and S. V. Ambudkar Modulation of the function of the multidrug resistance-linked ATP-binding cassette transporter ABCG2 by the cancer chemopreventive agent curcumin. Mol. Cancer Ther., August 1, 2006; 5(8): 1995 - 2006. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A Mohan, M Kandalam, H L Ramkumar, L Gopal, and S Krishnakumar Stem cell markers: ABCG2 and MCM2 expression in retinoblastoma Br. J. Ophthalmol., July 1, 2006; 90(7): 889 - 893. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. Nakanishi, K. J. Bailey-Dell, B. A. Hassel, K. Shiozawa, D. M. Sullivan, J. Turner, and D. D. Ross Novel 5' Untranslated Region Variants of BCRP mRNA Are Differentially Expressed in Drug-Selected Cancer Cells and in Normal Human Tissues: Implications for Drug Resistance, Tissue-Specific Expression, and Alternative Promoter Usage. Cancer Res., May 15, 2006; 66(10): 5007 - 5011. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. W. Robey, Z. Zhan, R. L. Piekarz, G. L. Kayastha, T. Fojo, and S. E. Bates Increased MDR1 Expression in Normal and Malignant Peripheral Blood Mononuclear Cells Obtained from Patients Receiving Depsipeptide (FR901228, FK228, NSC630176) Clin. Cancer Res., March 1, 2006; 12(5): 1547 - 1555. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. A. Rudek, M. Zhao, N. F. Smith, R. W. Robey, P. He, G. Hallur, S. Khan, M. Hidalgo, A. Jimeno, A. D. Colevas, et al. In vitro and In vivo Clinical Pharmacology of Dimethyl Benzoylphenylurea, a Novel Oral Tubulin-Interactive Agent Clin. Cancer Res., December 1, 2005; 11(23): 8503 - 8511. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 U. Henriksen, J. U. Fog, T. Litman, and U. Gether Identification of Intra- and Intermolecular Disulfide Bridges in the Multidrug Resistance Transporter ABCG2 J. Biol. Chem., November 4, 2005; 280(44): 36926 - 36934. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. Ahmed-Belkacem, A. Pozza, F. Munoz-Martinez, S. E. Bates, S. Castanys, F. Gamarro, A. Di Pietro, and J. M. Perez-Victoria Flavonoid Structure-Activity Studies Identify 6-Prenylchrysin and Tectochrysin as Potent and Specific Inhibitors of Breast Cancer Resistance Protein ABCG2 Cancer Res., June 1, 2005; 65(11): 4852 - 4860. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. Richard, D. Matthews, W. Duivenvoorden, J. Yau, P. S. Wright, and J. P.H. Th'ng Flavopiridol Sensitivity of Cancer Cells Isolated from Ascites and Pleural Fluids Clin. Cancer Res., May 1, 2005; 11(9): 3523 - 3529. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 U. Henriksen, U. Gether, and T. Litman Effect of Walker A mutation (K86M) on oligomerization and surface targeting of the multidrug resistance transporter ABCG2 J. Cell Sci., April 1, 2005; 118(7): 1417 - 1426. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Zhou, Y. Zong, P. A. Ney, G. Nair, C. F. Stewart, and B. P. Sorrentino Increased expression of the Abcg2 transporter during erythroid maturation plays a role in decreasing cellular protoporphyrin IX levels Blood, March 15, 2005; 105(6): 2571 - 2576. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
K. F. K. Ejendal and C. A. Hrycyna Differential Sensitivities of the Human ATP-Binding Cassette Transporters ABCG2 and P-Glycoprotein to Cyclosporin A Mol. Pharmacol., March 1, 2005; 67(3): 902 - 911. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. Ozvegy-Laczka, G. Varady, G. Koblos, O. Ujhelly, J. Cervenak, J. D. Schuetz, B. P. Sorrentino, G.-J. Koomen, A. Varadi, K. Nemet, et al. Function-dependent Conformational Changes of the ABCG2 Multidrug Transporter Modify Its Interaction with a Monoclonal Antibody on the Cell Surface J. Biol. Chem., February 11, 2005; 280(6): 4219 - 4227. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P.L. R. Ee, X. He, D. D. Ross, and W. T. Beck Modulation of breast cancer resistance protein (BCRP/ABCG2) gene expression using RNA interference Mol. Cancer Ther., December 1, 2004; 3(12): 1577 - 1584. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. Gupta, Y. Zhang, J. D. Unadkat, and Q. Mao HIV Protease Inhibitors Are Inhibitors but Not Substrates of the Human Breast Cancer Resistance Protein (BCRP/ABCG2) J. Pharmacol. Exp. Ther., July 1, 2004; 310(1): 334 - 341. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. Ozvegy-Laczka, T. Heged""s, G. Varady, O. Ujhelly, J. D. Schuetz, A. Varadi, G. Keri, L. Orfi, K. Nemet, and B. Sarkadi High-Affinity Interaction of Tyrosine Kinase Inhibitors with the ABCG2 Multidrug Transporter Mol. Pharmacol., June 1, 2004; 65(6): 1485 - 1495. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Zhang, X. Yang, and M. E. Morris Flavonoids Are Inhibitors of Breast Cancer Resistance Protein (ABCG2)-Mediated Transport Mol. Pharmacol., May 1, 2004; 65(5): 1208 - 1216. [Abstract] [Full Text]
|
|
|
|
|
|
R. W. Robey, K. Steadman, O. Polgar, K. Morisaki, M. Blayney, P. Mistry, and S. E. Bates Pheophorbide a Is a Specific Probe for ABCG2 Function and Inhibition Cancer Res., February 15, 2004; 64(4): 1242 - 1246. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. L. R. Ee, S. Kamalakaran, D. Tonetti, X. He, D. D. Ross, and W. T. Beck Identification of a Novel Estrogen Response Element in the Breast Cancer Resistance Protein (ABCG2) Gene Cancer Res., February 15, 2004; 64(4): 1247 - 1251. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. Nakanishi, L. A. Doyle, B. Hassel, Y. Wei, K. S. Bauer, S. Wu, D. W. Pumplin, H.-B. Fang, and D. D. Ross Functional Characterization of Human Breast Cancer Resistance Protein (BCRP, ABCG2) Expressed in the Oocytes of Xenopus laevis Mol. Pharmacol., December 1, 2003; 64(6): 1452 - 1462. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. M. Incles, C. M. Schultes, L. R. Kelland, and S. Neidle Acquired Cellular Resistance to Flavopiridol in a Human Colon Carcinoma Cell Line Involves Up-Regulation of the Telomerase Catalytic Subunit and Telomere Elongation. Sensitivity of Resistant Cells to Combination Treatment with a Telomerase Inhibitor Mol. Pharmacol., November 1, 2003; 64(5): 1101 - 1108. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
E. L. Volk and E. Schneider Wild-Type Breast Cancer Resistance Protein (BCRP/ABCG2) is a Methotrexate Polyglutamate Transporter Cancer Res., September 1, 2003; 63(17): 5538 - 5543. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. Nakanishi, J. E. Karp, M. Tan, L. A. Doyle, T. Peters, W. Yang, D. Wei, and D. D. Ross Quantitative Analysis of Breast Cancer Resistance Protein and Cellular Resistance to Flavopiridol in Acute Leukemia Patients Clin. Cancer Res., August 1, 2003; 9(9): 3320 - 3328. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Z.-S. Chen, R. W. Robey, M. G. Belinsky, I. Shchaveleva, X.-Q. Ren, Y. Sugimoto, D. D. Ross, S. E. Bates, and G. D. Kruh Transport of Methotrexate, Methotrexate Polyglutamates, and 17{beta}-Estradiol 17-({beta}-D-glucuronide) by ABCG2: Effects of Acquired Mutations at R482 on Methotrexate Transport Cancer Res., July 15, 2003; 63(14): 4048 - 4054. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 K. Shimano, M. Satake, A. Okaya, J. Kitanaka, N. Kitanaka, M. Takemura, M. Sakagami, N. Terada, and T. Tsujimura Hepatic Oval Cells Have the Side Population Phenotype Defined by Expression of ATP-Binding Cassette Transporter ABCG2/BCRP1 Am. J. Pathol., July 1, 2003; 163(1): 3 - 9. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. Summer, D. N. Kotton, X. Sun, B. Ma, K. Fitzsimmons, and A. Fine Side population cells and Bcrp1 expression in lung Am J Physiol Lung Cell Mol Physiol, July 1, 2003; 285(1): L97 - L104. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. Janvilisri, H. Venter, S. Shahi, G. Reuter, L. Balakrishnan, and H. W. van Veen Sterol Transport by the Human Breast Cancer Resistance Protein (ABCG2) Expressed in Lactococcus lactis J. Biol. Chem., May 30, 2003; 278(23): 20645 - 20651. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. Ozvegy, A. Varadi, and B. Sarkadi Characterization of Drug Transport, ATP Hydrolysis, and Nucleotide Trapping by the Human ABCG2 Multidrug Transporter. MODULATION OF SUBSTRATE SPECIFICITY BY A POINT MUTATION J. Biol. Chem., December 6, 2002; 277(50): 47980 - 47990. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
I. Gojo, B. Zhang, and R. G. Fenton The Cyclin-dependent Kinase Inhibitor Flavopiridol Induces Apoptosis in Multiple Myeloma Cells through Transcriptional Repression and Down-Regulation of Mcl-1 Clin. Cancer Res., November 1, 2002; 8(11): 3527 - 3538. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
E. L. Volk, K. M. Farley, Y. Wu, F. Li, R. W. Robey, and E. Schneider Overexpression of Wild-Type Breast Cancer Resistance Protein Mediates Methotrexate Resistance Cancer Res., September 1, 2002; 62(17): 5035 - 5040. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. M. van der Kolk, E. Vellenga, G. L. Scheffer, M. Muller, S. E. Bates, R. J. Scheper, and E. G. E. de Vries Expression and activity of breast cancer resistance protein (BCRP) in de novo and relapsed acute myeloid leukemia Blood, May 15, 2002; 99(10): 3763 - 3770. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T. K. Bera, C. Iavarone, V. Kumar, S. Lee, B. Lee, and I. Pastan MRP9, an unusual truncated member of the ABC transporter superfamily, is highly expressed in breast cancer PNAS, May 14, 2002; 99(10): 6997 - 7002. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. D. Allen and A. H. Schinkel Multidrug Resistance and Pharmacological Protection Mediated by the Breast Cancer Resistance Protein (BCRP/ABCG2) Mol. Cancer Ther., April 1, 2002; 1(6): 427 - 434. [Full Text] [PDF]
|
|
|
|
|
|
C. W. Scharenberg, M. A. Harkey, and B. Torok-Storb The ABCG2 transporter is an efficient Hoechst 33342 efflux pump and is preferentially expressed by immature human hematopoietic progenitors Blood, January 15, 2002; 99(2): 507 - 512. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
V. Smith, F. Raynaud, P. Workman, and L. R. Kelland Characterization of a Human Colorectal Carcinoma Cell Line with Acquired Resistance to Flavopiridol Mol. Pharmacol., November 1, 2001; 60(5): 885 - 893. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G. Schmitz, T. Langmann, and S. Heimerl Role of ABCG1 and other ABCG family members in lipid metabolism J. Lipid Res., October 1, 2001; 42(10): 1513 - 1520. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y. Honjo, C. A. Hrycyna, Q.-W. Yan, W. Y. Medina-Perez, R. W. Robey, A. van de Laar, T. Litman, M. Dean, and S. E. Bates Acquired Mutations in the MXR/BCRP/ABCP Gene Alter Substrate Specificity in MXR/BCRP/ABCP-overexpressing Cells Cancer Res., September 1, 2001; 61(18): 6635 - 6639. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Cancer Research | Clinical Cancer Research |
| Cancer Epidemiology Biomarkers & Prevention | Molecular Cancer Therapeutics |
| Molecular Cancer Research | Cancer Prevention Research |
| Cancer Prevention Journals Portal | Cancer Reviews Online |
| Annual Meeting Education Book | Meeting Abstracts Online |
, 
) and MCF-7 FLV1000 cells (
, •) were
incubated for 4 days with flavopiridol, topotecan, mitoxantrone, SN-38,
5-FU, and paclitaxel in the presence (•, 
