Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “resistant”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 397 records · Page 22Linked to original sources
PubMed2001

Differentiation of resistance phenotypes among erythromycin-resistant Pneumococci.

Laboratory differentiation of erythromycin resistance phenotypes is poorly standardized for pneumococci. In this study, 85 clinical isolates of erythromycin-resistant (MIC > or = 1 microg/ml) Streptococcus pneumoniae were tested for the resistance phenotype by the erythromycin-clindamycin double-disk test (previously used to determine the macrolide resistance phenotype in Streptococcus pyogenes strains) and by MIC induction tests, i.e., by determining the MICs of macrolide antibiotics without and with pre-exposure to 0.05 microg of erythromycin per ml. By the double-disk test, 65 strains, all carrying the erm(AM) determinant, were assigned to the constitutive macrolide, lincosamide, and streptogramin B resistance (cMLS) phenotype, and the remaining 20, all carrying the mef(E) gene, were assigned to the recently described M phenotype; an inducible MLS resistance (iMLS) phenotype was not found. The lack of inducible resistance to clindamycin was confirmed by determining clindamycin MICs without and with pre-exposure to subinhibitory concentrations of erythromycin. In macrolide MIC and MIC-induction tests, whereas homogeneous susceptibility patterns were observed among the 20 strains assigned to the M phenotype by the double-disk test, two distinct patterns were recognized among the 65 strains assigned to the cMLS phenotype by the same test; one pattern (n = 10; probably that of the true cMLS isolates) was characterized by resistance to rokitamycin also without induction, and the other pattern (n = 55; designated the iMcLS phenotype) was characterized by full or intermediate susceptibility to rokitamycin without induction turning to resistance after induction, with an MIC increase by more than three dilutions. A triple-disk test, set up by adding a rokitamycin disk to the erythromycin and clindamycin disks of the double-disk test, allowed the easy differentiation not only of pneumococci with the M phenotype from those with MLS resistance but also, among the latter, of those of the true cMLS phenotype from those of the iMcLS phenotype. While distinguishing MLS from M resistance in pneumococci is easily and reliably achieved, the differentiation of constitutive from inducible MLS resistance is far more uncertain and is strongly affected by the antibiotic used to test inducibility.

Anti-Bacterial Agents↗
PubMed1984

The effects of chlorate- and streptomycin-resistance mutations on nitrofurantoin resistance in Escherichia coli K-12.

Chlorate-resistant mutants with none of the usual pleiotropic effects such as defective nitrate reductase activity were isolated from Escherichia coli K-12. These chlorate-resistant mutants (designated chlHW) did not yield strains with a high level of nitrofurantoin resistance following selection with nitrofurantoin. The chlorate-resistance mutation reduced the nitrofurantoin resistance of high-level mutants to an intermediate level. Further mutation to resistance to streptomycin and other aminoglycoside antibiotics suppressed the effect of chlHW on the level of nitrofurantoin resistance. Other chlorate-resistance genes examined did not have the same effect on nitrofurantoin resistance as chlHW. The gene was cotransducible (Pl) with intermediate-level nitrofurantoin resistance and proC. It is suggested that the chlHW mutation may enhance the accumulation of nitrofurantoin inside the cell since it is known that a multiple aminoglycoside-resistance mutation with pleiotropic effects on the cell membrane can also confer high-level resistance to nitrofurantoin.

Chlorates↗
PubMed1992

Multifactorial resistance to antineoplastic agents in drug-resistant P388 murine leukemia, Chinese hamster ovary, and human HeLa cells, with emphasis on the role of DNA topoisomerase II.

The role of DNA topoisomerase II in multifactorial resistance to antineoplastic agents is reviewed. We have previously observed that in Adriamycin (ADR) resistant P388 murine leukemia cells, DNA topoisomerase II enzyme content and cleavage and catalytic activities were all reduced and correlated with drug sensitivity. A subsequent study provided evidence for an allelic mutation of the gene for DNA topoisomerase II as a possible molecular mechanism underlying the enzyme alterations. To ascertain how universal were these observations, a study was undertaken of DNA topoisomerase II (topo II) in other cell lines resistant either to ADR or another topo-II-interactive drug, mitoxantrone. In ADR-resistant Chinese hamster ovary (CHO) cells, topo II cleavage and catalytic activities and the gene product were all reduced; however, only cleavage activity correlated with drug sensitivity. No differences were noted between ADR-sensitive and -resistant CHO cells by Northern or Southern blot analysis, raising the possibility that the enzyme in resistant cells may be regulated at a posttranscriptional level. Findings on a gel retardation or immunoblot band depletion assay showed that the enzyme in CHO/ADR-1 cells failed to bind to the DNA-drug-enzyme complex, suggesting a qualitative as well as quantitative enzyme alteration in those cells. Mitoxantrone-resistant HeLa cells (Mito-1) displayed not only a lower level of cleavage activity but also of enzyme content and catalytic activity, relative to the parental drug-sensitive HeLa cells. As with the CHO cells, no differences were noted between mitoxantrone-sensitive and -resistant HeLa cells on Northern and Southern blot analyses, suggesting that enzyme regulation in these resistant cells may also be at a posttranscriptional level. There was no evidence of enzyme binding to DNA-drug-enzyme complex in resistant HeLa/Mito-1 cells, once again suggesting the presence of a qualitative enzyme alteration. The findings in both ADR-resistant CHO cells and mitoxantrone-resistant HeLa cells do not exclude the possibility that subtle changes in the topoisomerase II gene, such as point mutations, may account for these enzyme changes. The apparent qualitative changes observed in enzyme may result from posttranslational modifications such as phosphorylation.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2000

Correlated insecticide cross-resistance in azinphosmethyl resistant codling moth (Lepidoptera: Tortricidae).

Resistance to several classes of insecticides was correlated with azinphosmethyl resistance in codling moth, Cydia pomonella (L.), in California. In tests of laboratory and field populations, cross-resistance was positively correlated with azinphosmethyl and two organophosphates (diazinon, phosmet), a carbamate (carbaryl), a chlorinated hydrocarbon (DDT), and two pyrethroids (esfenvalerate and fenpropathrin). Additionally, negatively correlated cross-resistance was identified between azinphosmethyl and two other organophosphates, chlorpyrifos and methyl parathion. Patterns of resistance observed in laboratory colonies were confirmed with field bioassays. In bioassays of field populations, azinphosmethyl resistance was observed to increase from 1991 to 1993, although levels of resistance remained < 13-fold. Because orchards with azinphosmethyl resistance have had difficulties with suppression of codling moth, and cross-resistance was found for all tested classes of insecticides, strategies for managing resistance will need to be developed so as to protect current and future control tactics. The two insecticides with negatively correlated cross-resistance are discussed as potential tools for resistance management.

Animals↗
PubMed2001

Fitness consequences of malathion-specific resistance in red flour beetle (Coleoptera: Tenebrionidae) and selection for resistance in the absence of malathion.

Malathion resistance in the red flour beetle, Tribolium castaneum (Herbst), is a worldwide problem and is very stable once it becomes widespread in natural populations. In the absence of insecticide the proportion of resistant phenotypes may rapidly decline but the development of resistance does not always involve reduced fitness. Malathion-specific resistance in T. castaneum seems not to involve any loss of fitness in laboratory or field conditions. Susceptible beetles were in competition with resistant beetles at different initial frequencies and modifications of susceptible gene frequency were estimated in these laboratory populations over 10 generations. A significant decrease in susceptible gene frequency was observed in Tribolium populations over time. The selection coefficient of the susceptible allele was estimated and the fitness of susceptible alleles in all tests was observed to range from 0.89 to 0.93 compared with the fitness of resistant genotypes, which was assumed to be 1. Data provided evidence that the resistant strains exhibited fitness advantages in the absence of malathion. We also compared the biotic potential (fecundity and developmental time) of the susceptible strain, the homozygous malathion-specific resistant strain, and their hybrids. Malathion-specific resistant strains showed an 8 -23% increase in biotic potential relative to the susceptible strain. These findings are consistent with those of malathion-specific resistance in T. castaneum; the fitness of the insects seems independent of the genetic background and the fitness of the resistant insects is not affected by this resistance mechanism.

Animals↗
PubMed2001

Different cross-resistance patterns in the diamondback moth (Lepidoptera: Plutellidae) resistant to Bacillus thuringiensis toxin Cry1C.

Two strains of the diamondback moth, Plutella xylostella (L.), were selected using Cry1C protoxin and transgenic broccoli plants expressing a Cry1C toxin of Bacillus thuringiensis (Bt). Both strains were resistant to Cry1C but had different cross-resistance patterns. We used 12 Bt protoxins for cross-resistance tests, including Cry1Aa, Cry1Ab, Cry1Ac, Cry1Bb, Cry1C, Cry1D, Cry1E, Cry1F, Cry1J, Cry2Ab, Cry9Aa, and Cry9C. Compared with the unselected sister strain (BCS), the resistance ratio (BR) of one strain (BCS-Cry1C-1) to the Cry1C protoxin was 1,090-fold with high level of cross-resistance to Cry1Aa, Cry1Ab, Cry1Ac, Cry1F, and Cry1J (RR > 390-fold). The cross-resistance to Cry1A, Cry1F, and Cry1J in this strain was probably related to the Cry1A resistance gene(s) that came from the initial field population and was caused by intensive sprayings of Bt products containing Cry1A protoxins. The neonates of this strain can survive on transgenic broccoli plants expressing either Cry1Ac or Cry1C toxins. The other strain (BCS-Cry1C-2) was highly resistant to Cry1C but not cross-resistant to other Bt protoxins. The neonates of this strain can survive on transgenic broccoli expressing Cry1C toxin but not Cry1Ac toxin. The gene(s) conferring resistance to Cry1C segregates independently from Cry1Ac resistance in these strains. The toxicity of Cry1E and Cry2Ab protoxins was low to all of the three strains. The overall progress of all work has resulted in a unique model system to test the stacked genes strategy for resistance management of Bt transgenic crops.

Animals↗
PubMed1999

Camptothecin resistance: role of the ATP-binding cassette (ABC), mitoxantrone-resistance half-transporter (MXR), and potential for glucuronidation in MXR-expressing cells.

The mitoxantrone resistance (MXR) gene encodes a recently characterized ATP-binding cassette half-transporter that confers multidrug resistance. We studied resistance to the camptothecins in two sublines expressing high levels of MXR: S1-M1-80 cells derived from parental S1 colon cancer cells and MCF-7 AdVp3,000 isolated from parental MCF-7 breast cancer cells. Both cell lines were 400- to 1,000-fold more resistant to topotecan, 9-amino-20(S)-camptothecin, and the active metabolite of irinotecan, 7-ethyl-10-hydroxycamptothecin (SN-38), than their parental cell lines. The cell lines demonstrated much less resistance to camptothecin and to several camptothecin analogues. Reduced accumulation and energy-dependent efflux of topotecan was demonstrated by confocal microscopy. A significant reduction in cleavable complexes in the resistant cells could be observed after SN-38 treatment but not after camptothecin treatment. In addition to topotecan and SN-38, MXR-overexpressing cells are highly resistant to mitoxantrone and epirubicin. Because these compounds are susceptible to glucuronidation, we examined UDP-glucurono-syltransferase (UGT) activity in parental and resistant cells by TLC. Glucuronides were found at equal levels in both parental and resistant colon cancer cell lines for epirubicin and to a lesser extent for SN-38 and mitoxantrone. Low levels of glucuronidation could also be detected in the resistant breast cancer cells. These results were confirmed by analysis of the UGT1A family mRNAs. We thus conclude that colon and breast cancer cells have a capacity for glucuronidation that could contribute to intrinsic drug resistance in colon cancer cells and may be acquired in breast cancer cells. The lack of selection for higher levels of UGT capacity in the colon cells suggests that high levels of expression of MXR alone are sufficient to confer resistance to the camptothecins.

ATP-Binding Cassette Transporters↗
PubMed1999

Expression of multidrug resistance protein-3 (multispecific organic anion transporter-D) in human embryonic kidney 293 cells confers resistance to anticancer agents.

Multidrug resistance-associated protein (MRP)1 and canalicular multispecific organic anion transporter (cMOAT)/MRP2 are ATP-binding cassette (ABC) transporters that confer resistance to natural product cytotoxic drugs. We recently described the complete coding sequences of four human MRP/cMOAT subfamily members and found that, among these proteins, MRP3/MOAT-D is most closely related to MRP1 (58% identity; M. G. Belinsky and G. D. Kruh, Br. J. Cancer, 80: 1342-1349, 1999). In the present study, we sought to determine whether MRP3 is capable of conferring resistance to cytotoxic drugs. To address this question, human embryonic kidney 293 cells were transfected with an MRP3 expression vector, and the drug resistance phenotype of the transfected cells was analyzed. The MRP3-transfected cells displayed approximately 4-fold resistance to etoposide and approximately 2-fold resistance to vincristine, compared with control transfected cells. In addition, approximately 1.7-fold resistance was observed for the antimetabolite methotrexate. Increased resistance was not observed for several other natural product agents, including anthracyclines and Taxol. The MRP-transfected cells exhibited reduced accumulation of radiolabeled etoposide, consistent with the operation of a plasma membrane efflux pump. These results indicate that MRP3 confers resistance to some anticancer agents but that its resistance pattern is distinct from the resistance patterns of other ABC transporters involved in resistance to natural product chemotherapeutic agents.

ATP-Binding Cassette Transporters↗
PubMed2000

Methotrexate cross-resistance in a mitoxantrone-selected multidrug-resistant MCF7 breast cancer cell line is attributable to enhanced energy-dependent drug efflux.

Cellular resistance to the antifolate methotrexate (MTX) is often caused by target amplification, uptake defects, or alterations in polyglutamylation. Here we have examined MTX cross-resistance in a human breast carcinoma cell line (MCF7/MX) selected in the presence of mitoxantrone, an anticancer agent associated with the multidrug resistance (MDR) phenotype. Examination of protein expression and enzyme activities showed that MCF7/MX cells displayed none of the classical mechanisms of MTX resistance. They did, however, exhibit an ATP-sensitive accumulation defect accompanied by reduced polyglutamylation. Although the kinetics of drug uptake was similar between parental and resistant cells, the resistant cells exhibited increased energy-dependent drug efflux. This suggested the involvement of an ATP-binding cassette (ABC) transporter. However, cells transfected with the breast cancer resistance protein (BCRP)-the ABC transporter known to be highly overexpressed in MCF7/MX cells and to confer mitoxantrone resistance (D. D. Ross et al., J. Natl. Cancer Inst. 91: 429-433, 1999)-were not MTX resistant, which suggested that this transporter is not involved in MTX cross-resistance. Moreover, members of the MRP protein family of transport proteins, which had previously been implicated in MTX resistance, were not found to be overexpressed in the MCF7/MX cells. Thus, our data suggest that a novel MTX-specific efflux pump may be involved in this unusual cross-resistance phenotype.

ATP Binding Cassette Transporter, Subfamily G, Mem↗
PubMed2002

Drug resistance. Navigating resistance pathways.

Treatment failure due to the rise of drug-resistant viral strains remains a serious problem confronting HIV treaters and patients alike. Among patients receiving antiretroviral therapy for HIV infection, new mutations associated with drug resistance continue to emerge, as do new patterns of cross-resistance and multidrug resistance. Drug-resistant HIV variants are now becoming so widespread that an increasing number of patients are experiencing "primary" resistance, having been infected with drug-resistant and sometimes multidrug-resistant strains. Drug-specific resistance mutations, in some cases, show resistance to a number of anti-retroviral drugs in the same class. Recent data have shown that there is more cross-resistance among the nucleoside reverse transcriptase inhibitors than initially thought. The growing complexity of the HIV-1 resistance spectrum calls for more sophisticated testing and clinical expertise, in addition to more effective drugs.

Anti-HIV Agents↗
PubMed2003

Natural killer resistance of a drug-resistant leukemia cell line, mediated by up-regulation of HLA class I expression.

BACKGROUND AND OBJECTIVES: Drug-resistant leukemia cells may exhibit cross-resistance towards immunological effector mechanisms by alterations of apoptosis pathways. This is particularly relevant in allogeneic bone marrow transplantation for leukemia, where the graft-versus-leukemia effect acts on cells pretreated with cytostatic drugs. Here, we clarify the mechanism underlying cross-resistance of drug-resistant variants of the T-leukemia cell line CEM towards natural killer cells. DESIGN AND METHODS: We determined the sensitivity of different CEM sublines to natural killer (NK) cytotoxicity, and separately analyzed the components of the killing machinery by detection of granzyme B-induced caspase cleavage and HLA class I-dependent recognition mechanisms. Furthermore, we studied regulation of HLA class I expression comparing CEM with other cell lines. RESULTS: We found that CEM cells resistant to cytostatic drugs or CD95 were cross-resistant towards NK cells from a variety of donors. Granzyme B-induced caspase and PARP cleavage in the sensitive and resistant cells were comparable, indicating that downstream apoptosis pathways were not altered in the drug-resistant cells. HLA class I molecules were upregulated in the resistant cells, inhibiting NK cells at the level of killer/target recognition. HLA class I upregulation was not found in other leukemia cell lines. INTERPRETATION AND CONCLUSIONS: This is the first description of HLA class I-mediated NK cross-resistance in drug-resistant cells. This finding may have a clinical impact since it may be considered as a possible reason for resistance to a graft-versus-leukemia approach in allogeneic bone marrow transplantation

Antineoplastic Agents↗
PubMed1992

Collateral resistance or sensitivity of human larynx carcinoma HEp2 cells resistant to cis-dichlorodiammineplatinum (II) or vincristine sulfate.

Human larynx carcinoma HEp2 cells in tissue culture were repeatedly treated with two chemotherapeutic agents which exhibit distinct mechanisms of action and which differ in mechanisms underlying resistance: cis-dichlorodiammineplatinum (II) (cis-DDP) and vincristine sulfate (VCR). Two schedules of resistance development were used: Acute (cells repeatedly treated with drug for 1 hour in serum-free medium: CA15 and VA15 cells), and continuous (repeatedly treated for 24 hours in complete medium: CK15 and VK15 cells). The sensitivity of cis-DDP resistant (CA15 and CK15 cells) and VCR resistant (VA15 and VK15 cells) sublines to cis-DDP VCR, methotrexate (MTX) and gamma rays was determined by survival assay. The results showed that all sublines became resistant to MTX. Cis-DDP resistant cells became cross-resistant to VCR too. Of VCR resistant sublines, only VK15 cells changed (increased) their sensitivity to cis-DDP. Resistant sublines (except CA15) became sensitive to gamma rays. The degree of resistance or collateral resistance/sensitivity depended on the chemotherapeutic agent used for selection and on the schedule of resistance development. The present data support the idea of complexity of resistance phenomenon. They also emphasize the difficulty and importance of judicious choice of agents that should be given in combined therapy of tumors.

Cell Survival↗
PubMed2006

[Primary drug-resistance is the main cause of drug-resistant tuberculosis].

OBJECTIVE: To investigate the main cause of drug-resistant tuberculosis. METHODS: Clinic isolates of Mycobacterium tuberculosis from 1996 to 2004 in Shanghai were analyzed and the proportion of isolates from new cases (the proxy of primary drug-resistance) and retreatment cases (the proxy of acquired drug-resistance) were calculated. Mycobacterial interspersed repetitive units (MIRU) genotyping was performed and analyzed on pairs of isolates of Mycobacterium tuberculosis from 16 recurrent patients with drug-resistant tuberculosis. RESULTS: Of all 8 120 isolates of Mycobacterium tuberculosis from new cases, 707 isolates (8.7%) were drug resistant. Of all 610 isolates from retreatment cases, 150 isolates (24.6%) were drug resistant. Primary drug resistance accounted for 82.5% (707/857) of all drug resistant isolates. Based on the MIRU genotypes, 13 of all 16 recurrent drug-resistant patients were reinfected with new drug-resistant strain of Mycobacterium tuberculosis. CONCLUSION: Primary drug-resistance is the main cause of drug-resistant tuberculosis.

Antitubercular Agents↗
PubMed2006

[Characterization of Salmonella typhimurium multidrug resistance and the reversal of antimicrobial resistance].

Salmonella typhimurium 17Y, isolated from one diseased pig that was clinically diagnosed as pig salmonellosis, was a multiresistance strain with resistance to 14 antibiotics among tested 19 antibiotics. In this study, the resistance to 11 antimicrobials was reversed by high temperature and high concentration (0.5%) of SDS, resulting in the sensitive strain 17S1. PCR results showed that the resistant genes BlaTEM, blaOXA-1, cat 1, tet (B), aacC2 located on the plasmid. Furthermore, PCR detected the class I integron which carries dhfrX II for trimethoprim resistance, aadA18b for aminoglycoside resistance and sull for sulfamethoxazole resistance. The integron was identified to exist in the plasmid. Because the target genes gyrA and parC for quinolone category were detected by PCR from both resistant and sensitive strains, it was determined that the genes gyrA and parC were located in the bacterial genome. The gene sequencing of gyrA and parC revealed that a point mutation AAC --> GAC resulting in one amino acid replacement of N87D in gyrA occurred for the sensitive strain 17S1. It was demonstrated that the amino acid 87 was a hot point for mutation in quinolone resistance determining region (QRDR). The finding suggests that the amino acid replacement of N87D is responsible for the quinolone susceptibility. In addition, the 100 continuous passages of the sensitive strain showed that the drug sensitive status was stable. However, when the drug pressure maintained for a long time, the resistance was induced again. Meanwhile, 6 salmonella plasmid virulence genes (spvA-D, R and rck) were eliminated with the resistance reversal, indicating that the virulence plasmid was cured. Reasonably, the bacterial virulence decreased shown by 10- fold increase of LD50 for the sensitive strain, and the statistical significant decline of in vivo spread and growth (P < 0.05) in mice. Taken altogether, the multidrug resistance of Salmonella typhimurium was determined by its plasmid. The plasmid elimination with SDS reversed most of the resistance (11/14) and decreased the bacterial virulence. Therefore, strategy to eliminate the plasmids would be an effective way to deal with the multiresistance issue. However, drug control in routine clinical practice would not be neglected at any time.

Animals↗
PubMed1991

Protein kinase C activity and multidrug resistance in MOLT-3 human lymphoblastic leukemia cells resistant to trimetrexate.

It has been suggested that protein kinase C (PKC) plays a role in multidrug resistance (MDR). In this study we assayed PKC activity in MOLT-3 human acute lymphoblastic leukemia cells and found an approximately 50% decrease in activity in MDR sublines made resistant to the lipophilic antifolate trimetrexate, when compared with trimetrexate-sensitive parent cells. The PKC activity of a methotrexate-resistant subline without MDR (MOLT-3/MTX10,000) was identical to that of parent cells. Although a downward trend was noted in PKC activity in the membrane fraction of cells with increasing trimetrexate resistance, there was no absolute correlation between the degree of MDR and the relative decrease in PKC activity. Using the same method, we also confirmed an over 6-fold increase in PKC activity in the MDR human breast cancer subline MCF-7/DOXR when compared with the sensitive parent cell line, MCF-7/WT. Because of this divergent relationship between relative PKC activity and MDR, we tested the effect of PKC inhibition and activation on drug resistance. The PKC inhibitor staurosporine, at both subtoxic and toxic concentrations as well as at concentrations shown to be inhibitory to PKC, failed to increase drug resistance of parent and resistant MOLT-3 cells and decrease drug resistance of MCF-7/WT and MCF-7/DOXR cells. Short-term exposure to 3-phorbol-12-myristate-13-acetate, which activated PKC 7.0-fold and 4.7-fold, respectively, in the membrane of MOLT-3 and resistant cells, resulted in small (1.3- to 1.8-fold), approximately equivalent, increases (rather than decreases) in resistance to doxorubicin, whereas for vincristine no consistent trend was observed. Identical results were also obtained with phorbol-12,13-dibutyrate. These results indicate that PKC activity can be decreased and increased in MDR cells. Both staurosporine inhibition and phorbol ester activation failed to produce changes in drug resistance that would be considered consistent with the resulting degree of PKC activity. Short-term phorbol ester exposure can change the sensitivity of the cells to doxorubicin without changing the relative drug resistance. PKC activity in these cells may then be unrelated to MDR.

Alkaloids↗
PubMed1990

Characterization of adriamycin-resistant human breast cancer cells which display overexpression of a novel resistance-related membrane protein.

Development of multidrug resistance due to overexpression of P-glycoprotein (Pgp), a cell membrane drug efflux pump, occurs commonly during in vitro selections with adriamycin (Adr). Pgp-mediated drug resistance can be overcome by the calcium channel blocker verapamil (Vp), which acts as a competitive inhibitor of drug binding and efflux. In order to identify other mechanisms of Adr resistance, we isolated an Adr-resistant subline by selecting the human breast cancer cell line MCF-7 with incremental increases of Adr in the presence of 10 microgram/ml verapamil. The resultant MCF-7/AdrVp subline is 900-fold resistant to Adr, does not overexpress Pgp, and does not exhibit a decrease in Adr accumulation. It exhibits a unique cross-resistance pattern: high cross-resistance to the potent Adr analogue 3'-deamino-3'-(3-cyano-4-morpholinyl)doxorubicin, lower cross-resistance to the alkylating agent melphalan, and a sensitivity similar to the parental cell line to vinblastine. The levels of glutathione and glutathione S-transferase are similar in the parental line and the Adr-resistant subline. Topoisomerase II-DNA complexes measured by the potassium-sodium dodecyl sulfate precipitation method shows a 2-3 fold decrease in the resistant subline. The MCF-7/AdrVp cells overexpress a novel membrane protein with an apparent molecular mass of 95 kDa. Polyclonal antibodies raised against the P-95 protein demonstrate a correaltion between the level of expression and Adr resistance. Removal of Adr but not verapamil from the selection media results in a decline in P-95 protein levels that parallels a restoration of sensitivity to Adr. Immunohistochemistry demonstrates localization of the P-95 protein on the cell surface. The demonstration of high levels of the protein in clinical samples obtained from patients refractory to Adr suggests that this protein may play a role in clinical drug resistance.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1989

Characteristics of bleomycin-resistant phenotypes of human cell sublines and circumvention of bleomycin resistance by liblomycin.

Three bleomycin (BLM)-resistant sublines were isolated from a human head and neck squamous cell carcinoma cell line (A-253); these sublines (C-10, D-10, and G-11) were 4-, 9-, and 21-fold resistant to BLM A2, respectively. These sublines were selectively resistant to other members of the BLM class, namely BLM B2, peplomycin, talisomycin S10b, and bleomycinic acid; none of the sublines displayed cross-resistance to vincristine, doxorubicin, cis-diamminedichloroplatinum or melphalan; only one subline (G-11) was cross-resistant to X-irradiation. None of the BLM-resistant cell lines demonstrated resistance to the novel BLM analogue liblomycin, which contains a lipophilic terminal amine. The cell cycle distributions of the clonally derived BLM-resistant cell populations were similar to the distribution of the parental cell population. In vitro BLM hydrolase activity in homogenates of D-10 and G-11 BLM-resistant cell lines was two- to threefold higher than that in homogenates of A-253 or C-10 cells. Nonetheless, no deamido BLM A2 was found associated with any cell type or in the culture medium and more than 80% of the radioactivity in all cells appeared as unmetabolized BLM A2 by high pressure liquid chromatography. Thus, the appearance of large quantities of the deamido BLM metabolite was not a prominent feature of acquired resistance to BLM in these human tumor cells. The cellular accumulation of radiolabeled BLM A2 by C-10 and G-11 cells during a 1-h incubation with [3H]BLM A2 was 1/2 that seen with A-253 and D-10 cells. C-10 cells maintained a lower nuclear content of radioactivity than A-253, G-11, or D-10 cells. Initial single strand DNA damage, based upon alkaline elution analysis, also was lower in C-10 cells compared to A-253 cells. D-10 cells, in contrast, exhibited high initial genomic DNA damage but demonstrated a greater repair rate than either A-253 or C-10 cells. Thus, multiple BLM-resistant phenotypes can be obtained from a population of human squamous carcinoma cells, and modification of the terminal amine in the BLM molecule can produce compounds capable of circumventing all of these BLM-resistant phenotypes. Liblomycin, which appears to be a nonclassical BLM, may be a useful therapeutic agent with a spectrum of activity distinct from other members of the BLM class.

Antineoplastic Agents↗
PubMed1989

Characterization of an amsacrine-resistant line of human leukemia cells. Evidence for a drug-resistant form of topoisomerase II.

HL-60/AMSA is a human leukemia cell line that is 100 times more resistant to the cytotoxic actions of the antineoplastic, topoisomerase II-reactive DNA intercalating acridine derivative amsacrine (m-AMSA) than is its parent HL-60 line. HL-60/AMSA cells are minimally resistant to etoposide, a topoisomerase II-reactive drug that does not intercalate. Previously we showed that HL-60 topoisomerase II activity in cells, nuclei, or nuclear extracts was sensitive to m-AMSA and etoposide, while HL-60/AMSA topoisomerase II was resistant to m-AMSA but sensitive to etoposide. Now we show that purified topoisomerase II from the two cell lines exhibits the same drug sensitivity or resistance as that in the nuclear extracts although the magnitude of the m-AMSA resistance of HL-60/AMSA topoisomerase II in vitro is not as great as the resistance of the intact HL-60/AMSA cells. In addition HL-60/AMSA cells are cross-resistant to topoisomerase II-reactive intercalators from the anthracycline and ellipticine families and the pattern of sensitivity or resistance to the cytotoxic actions of the various topoisomerase II-reactive drugs is paralleled by topoisomerase II-reactive drug-induced DNA cleavage and protein cross-link production in cells and the production of drug-induced, topoisomerase II-mediated DNA cleavage and protein cross-linking in isolated biochemical systems. In addition to its lowered sensitivity to intercalators, HL-60/AMSA differed from HL-60 in 1) the susceptibility of its topoisomerase II to stimulation of DNA topoisomerase II complex formation by ATP, 2) the catalytic activity of its topoisomerase II in an ionic environment chosen to reproduce the environment found within the living cell, and 3) the observed restriction enzyme pattern on a Southern blot probed with a cDNA for human topoisomerase II. These data indicate that an m-AMSA-resistant form of topoisomerase II contributes to the resistance of HL-60/AMSA to m-AMSA and to other topoisomerase II-reactive DNA intercalating agents. The drug resistance is associated with additional biochemical and molecular alterations that may be important determinants of cellular sensitivity or resistance to topoisomerase II-reactive drugs.

Adenosine Triphosphate↗