Multidrug-resistant Cancer Cell Lines Research Articles

Reduced topoisomerase II activity in multidrug-resistant human non-small cell lung cancer cell lines: Eijdems EWHM, De Haas M, Timmerman AJ, Van Der Schans GP, Kamst E, De Nooij J et al. Division of Molecular Biology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam. Br J Cancer 1995;71:40–47

Reduced topoisomerase II activity in multidrug-resistant human non-small cell lung cancer cell lines: Eijdems EWHM, De Haas M, Timmerman AJ, Van Der Schans GP, Kamst E, De Nooij J et al. Division of Molecular Biology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam. Br J Cancer 1995;71:40–47

Expression of multidrug resistance-associated protein (MRP), MDR1 and DNA topoisomerase II in human multidrug-resistant bladder cancer cell lines

The acquisition of the multidrug resistance phenotype in human tumours is associated with an overexpression of the 170 kDa P-glycoprotein encoded by the multidrug resistance 1 (MDR1) gene, and also with a 190 kDa membrane ATP-binding protein encoded by a multidrug resistance-associated protein (MRP) gene. Human bladder cancer is a highly malignant neoplasm which is refractory to anti-cancer chemotherapy. In order to understand the mechanism underlying multidrug resistance in bladder cancer, we established three doxorubicin-resistant cell lines, T24/ADM-1, T24/ADM-2 and KK47/ADM, and one vincristine-resistant cell line, T24/VCR, from human bladder cancer T24 and KK47 cells respectively. Both T24/ADM-1 and T24/ADM-2 cells which had elevated MRP mRNA levels showed both a cross-resistance to etoposide and a decreased intracellular accumulation of etoposide. T24/VCR cells which had elevated levels of MDR1 mRNA and P-glycoprotein but not of MRP mRNA, showed cross-resistance to doxorubicin. On the other hand, KK47/ADM cells, which had elevated levels of both MRP and MDR1 mRNA and a decreased level of topoisomerase II mRNA, were found to be cross-resistant to etoposide, vincristine and a camptothecin derivative, CPT-11. Our present study demonstrates a concomitant induction of increased levels of MRP mRNA, decreased levels of topoisomerase II mRNA and decreased drug accumulation during development of multidrug resistance in human bladder cancer cells. The enhanced expression of the MRP gene is herein discussed in a possible correlation with the decreased expression of the topoisomerase II gene.

Reduced topoisomerase II activity in multidrug-resistant human non-small cell lung cancer cell lines

Multidrug-resistant (MDR) cell lines often have a compound phenotype, combining reduced drug accumulation with a decrease in topoisomerase II. We have analysed alterations in topoisomerase II in MDR derivatives of the human lung cancer cell line SW-1573. Selection with doxorubicin frequently resulted in reduced topo II alpha mRNA and protein levels, whereas clones selected with vincristine showed normal levels of topo II alpha. No alterations of topo II beta levels were detected. To determine the contribution of topo II alterations to drug resistance, topo II activity was analysed by the determination of DNA breaks induced by the topo II-inhibiting drug 4'-(9-acridinylamino)methane-sulphon-m-anisidide (m-AMSA) in living cells, as m-AMSA is not affected by the drug efflux mechanism in the SW-1573 cells. The number of m-AMSA-induced DNA breaks correlated well (r = 0.96) with in vitro m-AMSA sensitivity. Drug sensitivity, however, did not always correlate with reduced topo II mRNA or protein levels. In one of the five doxorubicin-selected clones m-AMSA resistance and a reduction in m-AMSA-induced DNA breaks were found in the absence of reduced topo II protein levels. Therefore, we assume that post-translational modifications of topo II also contribute to drug resistance in SW-1573 cells. These results suggest that methods that detect quantitative as well as qualitative alterations of topo II should be used to predict the responsiveness of tumours to cytotoxic agents. The assay we used, which measures DNA breaks as an end point of topo II activity, could be a good candidate.

The P-glycoprotein-related gene family in Leishmania

P-glycoprotein gene amplification has been described in several drug-resistant parasitic protozoa. The first P-glycoprotein related gene described in Leishmania was ltpgpA, a gene frequently amplified in arsenite resistant Leishmania. Hybridization experiments indicated that ltpgpA was part of a gene family. In addition to ltpgpA, four novel genes were cloned that are present in two loci: ltpgpB and ltpgpC tandemly linked to ltpgpA on a 800-kb chromosome; and ltpgpD and ltpgpE closely linked on a chromosome ranging from 950 kb to 1400 kb, depending on the Leishmania species. Another P-glycoprotein gene, homologous to the more recently described ldmdrl, was linked to ltpgpD and ltpgpE. Nucleotide sequencing of ltpgpB and ltpgpE revealed that the Leishmania P-glycoprotein-related genes have diverged considerably from the main branch of P-glycoproteins and are more homologous to the recently described multidrug resistance-associated protein found in multidrug-resistant human lung cancer cell lines. Cross-resistance studies and gene transfection experiments indicated that under the conditions tested only ltpgpA and ldmdrl are involved in resistance to arsenite and antimonials or hydrophobic drugs such as vinblastine respectively.

Utilization of multiple polyadenylation signals in the human RHOA protooncogene

Little is known regarding the regulation of expression of the RHOA protooncogene, a member of the family of genes encoding Ras-related GTP-binding proteins. We have previously reported that the 3′ untranslated region ( UTR) of RHOA was contained within a genomic sequence which flanked the 5′ end of the human glutathione peroxidase 1-encoding gene [J.A. Moscow et al. J. Biol. Chem. 267 (1992) 5949–5958]. Our previous studies revealed the presence of multiple (1.8 and 1.5kb) RHOA mRNA species in breast cancer cell lines and of three putative polyadenylation signals in the RHOA 3′ UTR. In this report, we have isolated several RHOA cDNAs from a multidrug-resistant MCF-7 human breast cancer cell line. Sequence analyses of these RHOA cDNA clones indicate that multiple polyadenylation signals are used to terminate RHOA transcripts. RNase-protection analysis demonstrated that all three polyadenylation signals are utilized in breast cancer cell lines and RNA stability studies demonstrated that RHOA RNA species with different 3′ ends have equivalent stability. Since little is known about the RNA expression of RHOA in human tumors, and since both activated and non-activated RHOA genes possess transformation potential, we analyzed RHOA mRNA in lung and colon tumors by Northern blot and RNase-protection analyses. In all eight lung tumors examined, RHOA RNA levels were decreased relative to the level in normal surrounding tissue, whereas RHOA expression was decreased in only two of six colon tumors. We also found that lovastatin-induced cell cycle arrest resulted in increased RHOA RNA expression in breast cancer cell lines. RNase-protection analysis of RHOA RNA from these tumor and cell line specimens demonstrated that the relative abundance of RNA transcripts utilizing these three polyadenylation signals did not vary with total RHOA mRNA levels.

Reversible transcriptional activation of mdr1 by sodium butyrate treatment of human colon cancer cells.

We investigated the mechanism of sodium butyrate (NaB)-mediated induction of mdr1 mRNA in parental (wild type) and multidrug-resistant (Ad1000) SW620 colon cancer cell lines. NaB treatment resulted in reversible, time-dependent increases in nuclear run-on transcription of endogenous mdr1 in these cell lines that paralleled the reversible increases of mdr1 mRNA in both timing and magnitude. In contrast, NaB treatment had no effect on mdr1 mRNA stability. Thus, the effects of NaB on mdr1 mRNA levels are fully attributable to altered mdr1 transcription. Furthermore, NaB induces the expression of transiently transfected chloramphenicol acetyltransferase reporter plasmids that are under the transcriptional control of the mdr1 promoter (mdrCAT vectors). Transfections using mdrCAT vectors modified by deletion and site-directed mutagenesis of the mdr1 promoter indicate that NaB-mediated induction of these vectors is at least partially dependent upon sequences present in the basal mdr1 promoter between -89 and +11 relative to the start site of transcription. The Y-box motif located between -82 and -73 contributes to NaB inducibility of mdrCAT vector expression in Ad1000 SW620 cells.

Altered drug distribution and elevated expression of a novel transporter gene (MRP) in a multidrug resistant lung cancer cell line : Cole SPC, Mirski SEL, Bhardwaj G, Almquist KC, Deeley RG. Cancer Research Laboratories, Queen's University, Kingston, Ontario K7L 3N6, Canada

Altered drug distribution and elevated expression of a novel transporter gene (MRP) in a multidrug resistant lung cancer cell line : Cole SPC, Mirski SEL, Bhardwaj G, Almquist KC, Deeley RG. Cancer Research Laboratories, Queen's University, Kingston, Ontario K7L 3N6, Canada

Peripheral blood mononuclear cells express antigens associated with multidrug resistance in a small cell lung cancer cell line : Krebes KA, Mirski SEL, Pross HF, Cole SPC. Cancer Research Laboratories, RM 331 Botterell Hall, Queen's University, Kingston, Ont K7L 3N6. Anticancer Res 1993;13:317–21

H69AR is a multidrug resistant small cell lung cancer (SCLC) cell line that does not overexpress P-glycoprotein, the plasma membrane drug efflux pump usually associated with this type of resistance. Monoclonal antibodies (MAbs) were previously raised against H69AR cells, and three of these MAbs, 2.54, 3.50, and 3.186, cross-reacted with peripheral blood mononuclear cells. T cells (CD3+), B cells (CD19+), NK cells (CD16+) and monocytes (CD14+) expressed each of the three antigens, but to differing degrees. Immunoprecipitation and partial proteolytic mapping experiments demonstrated that the antigens detected by MAbs 2.54 and 3.186 are identical in H69AR cells and PBMCs. SCLC cells are known to express many hematopoietic antigens; however, this is the first report of SCLC multidrug resistance-associated antigens being expressed on hematopoietic cells.

Energy-dependent processes involved in reduced drug accumulation in multidrug-resistant human lung cancer cell lines without P-glycoprotein expression : Versantvoort CHM, Broxterman HJ, Pinedo HM, De Vries EGE, Feller N, Kuiper CM et al. Department of Medical Oncology, Free University Hospital, BR 232, De Boelelaan 1117, 1081 HV Amsterdam. Cancer Res 1992;52:17–23

Mechanisms contributing to reduced cytotoxic drug accumulation were studied in two multidrug-resistant (MDR) human lung cancer cell lines without P-glycoprotein expression. In these (non-small cell) SW-1573/2R120 and (small cell) GLC4/ADR MDR cells, the steady-state accumulation of [14C]daunorubicin was 30 and 12%, respectively, of that in the parent cells. When cells, at steady state, were permeabilized with digitonin, the amount of daunorubicin binding increased only in the resistant cells. The reduced accumulation of daunorubicin in the SW-1573/2R120 and GLC4/ADR cells was accompanied by a lower initial (2 min) uptake rate of this drug. No difference in initial efflux rate of daunorubicin from preloaded cells could be detected between sensitive and resistant SW-1573 cells. However, daunorubicin was extruded 5-fold faster from GLC4/ADR cells than from the parental cells. In the presence of the energy metabolism inhibitors sodium azide and deoxyglucose, the reduced daunorubicin accumulations in the SW-1573/2R120 and GLC4/ADR MDR cells were (almost) completely reversed. The effects of these inhibitors on drug uptake were already apparent during the earliest measured time points (less than 15 s). Also, the enhanced efflux of daunorubicin from GLC4/ADR cells was inhibited. In ATP-depleted cells, the intracellular pH was lowered by approximately 0.3 units in resistant as well as in sensitive cells. The lower intracellular pH, however, could not account for the increase in daunorubicin accumulation in the resistant cells. Also, for vincristine and etoposide, the increases in drug accumulation under energy-deprived conditions were more pronounced in the resistant SW-1573/2R120 cells than in the parent SW-1573 cells. These results suggest that accumulation of drugs in the non-P-glycoprotein MDR human lung carcinoma cell lines SW-1573/2R120 and GLC4/ADR is reduced by an energy-dependent drug export mechanism which prevents efficient transport of drug to the target. Since P-glycoprotein expression in lung tumors is generally low, these MDR lung cancer cell lines can be used as a model to study alternative mechanisms leading to multidrug resistance in this tumor type.

Elevated expression of annexin II (lipocortin II, p36) in a multidrug resistant small cell lung cancer cell line.

The doxorubicin-selected multidrug resistant small cell lung cancer cell line, H69AR, is cross-resistant to the Vinca alkaloids and epipodophyllotoxins, but does not overexpress P-glycoprotein, a 170 kDa plasma membrane efflux pump usually associated with this type of resistance. Monoclonal antibodies were raised against the H69AR cell line and one of these, MAb 3.186, recognises a peptide epitope on a 36 kDa phosphorylated protein that is membrane associated, but not presented on the external surface of H69AR cells (Mirski & Cole, 1991). In the present study, in vitro translation and molecular cloning techniques were used to determine the relative levels of mRNA corresponding to the 3.186 antigen. In addition, a cDNA clone containing an insert of approximately 1.4 kb was obtained by screening an H69AR cDNA library with 125I-MAb 3.186. Fragments of this cloned DNA hybridised to a single mRNA species of approximately 1.6 kb that was 5 to 6-fold elevated in H69AR cells. Partial DNA sequencing and restriction endonuclease mapping revealed identity of the cloned DNA with p36, a member of the annexin/lipocortin family of Ca2+ and phospholipid binding proteins.

Doxorubicin selected multidrug-resistant small cell lung cancer cell lines characterised by elevated cytoplasmic Ca2+ and resistance modulation by verapamil in absence of P-glycoprotein overexpression

Sublines from the small cell lung cancer (SCLC) cell lines U1285 and U1690, denoted U1285-100, U1285-250, U1690-40 and U1690-150, were adapted to grow in the continuous presence of 100, 250, 40 and 150 ng ml-1 doxorubicin (Dox), respectively. The Dox resistance was accompanied by cross-resistance to vincristine (Vcr), Vp-16 and for U1285-100 also to cisplatinum. Sublines of U1690-40 and U1285-100, cultured in absence of Dox for 4 months were only partially reversed with respect to Dox resistance. Neither the parental nor the most Dox resistance sublines had detectable levels of mdr 1 RNA but a small fraction of cells in all cell lines stained weakly positive for P-glycoprotein (P-gp). Verapamil (Ver) at 5 microM reversed the Dox resistance completely and partly in the U1690 and U1285 sublines, respectively, but did not increase the cellular accumulation of Dox. The cytoplasmic free Ca2+ concentration (Ca2+i) was close to 100 nM in both parental cell lines but elevated in the U1285-100 and U1690-40 sublines by 21 and 44%, respectively, and in U1285-250 and U1690-150 by 51 and 91%, respectively. The partly reverted sublines still showed significant but smaller elevations in Ca2+i of 10-30%. Ver was without acute or long term effects of Ca2+i in the U1285-100 and U1690-40 sublines. Selection for Dox resistance in SCLC may thus result in atypical multidrug-resistance characterised by absence of P-gp overexpression and atypical cross-resistance. Although Ver did not seem to affect Dox accumulation it may still work as a resistance modulator.(ABSTRACT TRUNCATED AT 250 WORDS)

Selenium-dependent glutathione peroxidase expression is inversely related to estrogen receptor content of human breast cancer cells.

The absence of estrogen receptors (ER) in human breast tumors has been associated with a poorer prognosis compared to patients with ER positive breast cancer. Previous studies from our laboratory have shown that a multidrug resistant human breast cancer cell line selected for resistance to Adriamycin (ADR) exhibited markedly increased expression of both the pi class glutathione S-transferase (GST-pi) and the selenium-dependent glutathione peroxidase. These studies also revealed that the ER status was inversely related to the expression of GST-pi in six human breast cancer cell lines and primary tumor specimens. In the present study, we have examined the relationship between ER status and several biological properties of these cells, including their levels of glutathione peroxidase (GSH-Px) and catalase expression, their capacity to generate toxic hydroxyl radicals (degrees OH) by redox cycling of ADR, and their sensitivities to the cytotoxic effects of ADR and the oxidant, H2O2. Our results show that expression of GSH-Px, but not catalase, is inversely related to the ER status in these cell lines. Formation of the degree OH induced by treatment of cells with ADR was inversely proportional to the GSH-Px activity in these cell lines, and thus directly related to the ER status. Sensitivity of these cells to ADR or to H2O2, however, was not consistently related to ER status, GSH-Px, or catalase activity, or to ADR induced degree OH radical formation. These results indicate that these parameters are not predictive of cellular susceptibility to oxidative damage in these cell lines under the conditions studied.

Multidrug resistance-associated antigens on drug-sensitive and -resistant human tumour cell lines

In this paper the biochemical properties of the antigens detected by six murine monoclonal antibodies (MAbs) are described. These MAbs react selectively with the multidrug-resistant small cell lung cancer (SCLC) cell line, H69AR, compared to its sensitive parent cell line, H69 (Mirski & Cole, 1989). Because H69AR cells do not overexpress P-glycoprotein, the antigens detected by these MAbs may be markers for non-P-glycoprotein-mediated mechanisms of resistance. We found that the 36 kDa protein precipitated by MAb 3.186 is phosphorylated and has a pI of approximately 6.7. The 55 kDa protein precipitated by MAb 3.50 is also phosphorylated and has a pI of approximately 5.7. Several observations suggest that MAbs 3.80, 3.177 and 3.187 recognise the same 47 kDa molecule and hence only MAb 3.187 was characterised further. This MAb precipitates an acidic protein which runs as a streak on isoelectric focusing gels. The 25 and 22.5 kDa cell surface proteins precipitated by MAb 2.54 both have a pI of approximately 7.6. Treatment of immunoprecipitates with glycosidase F indicated that none of the proteins detected by MAbs 2.54, 3.187, 3.50 and 3.186 have large N-linked carbohydrates. The peptide nature of the epitopes detected by MAbs 2.54 and 3.186 was unequivocally demonstrated by precipitation from in vitro translation products of H69AR RNA. The antigens detected by MAbs 3.50 and 3.187 were not detectable in immunoprecipitates of translation products but the epitopes are probably peptides because they were destroyed by boiling in sodium dodecyl sulphate. When the reaction of the MAbs with a panel of 15 paired drug-sensitive and -resistant cell lines was examined in a cell enzyme-linked immunosorbent assay, only a few resistance associated reactions were observed. Most of the reactions were either negative or not resistance-associated. When tested with three SCLC cell lines, MAb 3.187 reacted in a manner consistent with the relative resistance of the cell lines. Antigens that had similar electrophoretic mobility to those from H69AR cells were precipitated from extracts of five human cell lines of various tumour types. These data indicate that the cross-reactivities of the MAbs are due to antigens shared among the cell lines and not just the expression of common epitopes on different proteins. Resistance-associated proteins with the biochemical properties of the antigens described in this paper have not been reported previously and they remain potential markers for the as yet to be determined mechanisms of drug resistance in SCLC and other human malignancies.

Glutathione depletion in human and in rat multi-drug resistant breast cancer cell lines

The effects of GSH depletion in a human breast cancer cell line and a multi-drug resistant subline (ADRr) were determined in a number of experimental conditions. The ADRr cells contained lower GSH concentration which cannot be explained solely on the basis of differences in cell kinetics, and yet the rate-limiting synthetic enzyme gamma-glutamylcysteine synthetase was increased 2-fold. Inhibition of GSH synthesis by BSO resulted in more rapid and more pronounced GSH depletion in ADRr compared to the wild-type cells, suggesting that enhanced GSH utilization and efflux in the resistant cells account for the lowered basal concentration. In addition, the gamma-glutamyl moiety salvage enzyme gamma-glutamyltranspeptidase was reduced markedly in the ADRr cell line. Since these cells have overexpression of the efflux pump protein P-glycoprotein, we examined the effects on cellular GSH of inhibition of the pump's function by verapamil. We found that verapamil significantly depleted cellular GSH. In a rat mammary carcinoma cell line selected in Adriamycin for multi-drug resistance, a similar molecular phenotype has been described including diminished cellular GSH concentration. Verapamil treatment of these cells also resulted in significant depletion of cellular GSH. These results are consistent with the recent report that combined treatment of BSO and verapamil has an additive effect on cytotoxicity. It is likely that decreased basal GSH concentration is due to oxidation and conjugation of it in reactions catalyzed by the enhanced peroxidase and GST found in these cells.

Flow cytometric double labeling technique for screening of multidrug resistance

We investigated the capabilities of flow cytometry in the analysis of a multidrug resistant (MDR) human ovarian cancer cell line 2780AD and its drug sensitive parental A2780. A functional assay using daunorubicin (DNR) as a fluorescent probe was combined with an immunofluorescence assay of P-glycoprotein (P-gp) using the monoclonal antibody MRK-16. Functionally MDR could be demonstrated by the lower DNR-content of MDR cells compared to DNR-content of drug sensitive cells. When incubation was performed with DNR in the presence of verapamil, DNR-content increased in the MDR cells. However the content of the A2780 cells was never attained. Differences in DNR-content were not related to differences in DNA-content. In experimental cell lines immunofluorescence data were inversely related with those of DNR-content: MDR cells had high levels of P-gp expression and low levels of DNR-content (and vice versa in drug sensitive cells). Both assays can be easily combined in a multiparametric flow cytometric procedure to evaluate both parameters simultaneously in the same cells. Analysis of clinical samples demonstrates the existence of aberrant subpopulations which would not be detected by using a single parameter assay.

Antigens associated with multidrug resistance in H69AR, a small cell lung cancer cell line : Mirski SEL, Cole SPC. Department of Oncology, Queen's University, Kingston, Ont. K7L 3N6. Cancer Res 1989;49:5719-24

In a previous study (S.E.L. Mirski et al., Cancer Res., 47: 2594-2598, 1987), we described the derivation of a multidrug-resistant small cell lung cancer cell line, H69AR. The H69AR cell line does not over-express P-glycoprotein and is therefore a useful model for the investigation of alternate mechanisms of drug resistance. In this paper we report the production and preliminary characterization of six murine monoclonal antibodies (MAbs) which react selectively with the H69AR cell line compared to its drug-sensitive parent cell line, NCI-H69. One of these antibodies, MAb 2.54, detects a cell surface epitope and reacts with multiple proteins of molecular weight 24,500-34,500 on immunoblots. Non-cell surface membrane-associated epitopes are detected by the other five antibodies, MAbs 3.50, 3.80, 3.177, 3.187, and 3.186. MAbs 3.50 and 3.186 immunoprecipitate antigens of molecular weight 55,000 and 36,000, respectively, while MAbs 3.80, 3.177, and 3.187 all precipitate a molecular weight 47,000 protein, suggesting that they may detect epitopes on the same antigen. The epitopes detected by all six antibodies are present on greater than 80% of H69AR cells, as determined by flow cytometry. With the exception of MAb 2.54, the MAbs cross-react in an enzyme-linked immunosorbent assay with the multidrug-resistant human fibrosarcoma cell line HT1080/DR4. Thus, these MAbs react with two drug-resistant cell lines derived from different tumor types in which overexpression of P-glycoprotein is undetectable. These MAbs may detect novel markers for drug resistance and thus may have potential diagnostic or therapeutic value.

Altered regulation of P-450IA1 expression in a multidrug-resistant MCF-7 human breast cancer cell line.

MCF-7 human breast cancer cells, selected for resistance to adriamycin (AdrR), exhibit the phenotype of multidrug resistance (MDR). Previous studies have shown that resistance in AdrR MCF-7 cells is associated with several biochemical changes that are similar to those induced in rat hyperplastic nodules, preneoplastic liver lesions which display broad spectrum resistance to carcinogens and hepatotoxins. In this report, we show that these changes in the AdrR MCF-7 cells are also associated with the development of cross-resistance to the procarcinogen benzo(a)pyrene (BP) and are associated with a marked defect in the conversion of BP to its cytotoxic, carcinogenic metabolites by AdrR cells. Since aryl hydrocarbon hydroxylase is the principle enzyme activity which converts benzo(a)pyrene to toxic hydroxylated forms, the regulation of cytochrome P-450IA1 expression, the gene encoding this enzyme activity in MCF-7 cells, was examined. Incubation with 100 nM 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) for 24 h results in a marked increase in aryl hydrocarbon hydroxylase activity in wild type (WT) but not AdrR MCF-7 cells. The alteration in aryl hydrocarbon hydroxylase expression in the AdrR cells is not overcome by incubation either with higher concentrations of TCDD (1 microM) or for longer periods of time (4 days). Northern blot analysis indicates that this defect in AdrR MCF-7 cells involves a regulatory defect at the level of P-450IA1 RNA. Following transfection of a construct containing the normal mouse P-450IA1 promoter fused to a reporter gene (bacterial chloramphenicol acetyltransferase) into WT and AdrR MCF-7 cells, TCDD induced chloramphenicol acetyltransferase activity in WT MCF-7 cells only. Furthermore, TCDD also induces both DT-diaphorase and UDP-glucuronyltransferase activities in WT, but not AdrR cells. These data suggest that the defect in the AdrR MCF-7 cells is not due to a structural P-450IA1 gene mutation, but rather involves a product regulating the polycyclic hydrocarbon-inducible expression of several drug-metabolizing enzyme activities. This defect in the AdrR MCF-7 cells is also associated with the development of resistance to ellipticine, an anticancer agent which is converted to more toxic hydroxylated species by aryl hydrocarbon hydroxylase or a similar mixed function oxidase. The WT and AdrR MCF-7 cells represent a useful model to study the regulation of the P-450IA1 gene in human cells.

A multidrug-resistant MCF-7 human breast cancer cell line which exhibits cross-resistance to antiestrogens and hormone-independent tumor growth in vivo.

MCF-7 human breast cancer cells provide a useful in vitro model system to study hormone-responsive breast cancer as they contain receptors for estrogen and progesterone, and estrogen both induces the synthesis of specific proteins in these cells and increases their rate of proliferation. An MCF-7 cell line which was selected for resistance to adriamycin (MCF-7/AdrR) exhibits the phenotype of multidrug resistance (MDR), and displays multiple biochemical changes. MDR in MCF-7/AdrR is also associated with a loss of mitogenic response to estrogen and the development of cross-resistance to the antiestrogen 4-hydroxytamoxifen. In addition, while the parental MCF-7 cell line responds to estrogen with increased levels of progesterone receptors and the secretion of specific proteins, these estrogen responses are lost in MCF-7/AdrR. Furthermore, while the formation of tumors in nude mice by wild-type MCF-7 cells is dependent upon the presence of estrogen, MCF-7/AdrR cells form tumors in the absence of exogenous estrogen administration. These changes in hormonal sensitivity and estrogen-independent tumorigenicity of the multidrug-resistant MCF-7 cell line are associated with a loss of the estrogen receptor and a concomitant increase in the level of receptors for epidermal growth factor. Thus, in MCF-7/AdrR cells, the development of MDR is associated with alterations in the expression of both cytosolic and membrane receptors, resulting in resistance to hormonal agents and the expression of hormone-independent tumor formation.

Cyclosporin A and its analogues as modifiers of adriamycin and vincristine resistance in a multi-drug resistant human lung cancer cell line.

Cyclosporin A and its analogues as modifiers of adriamycin and vincristine resistance in a multi-drug resistant human lung cancer cell line