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 199 records · Page 11Linked to original sources
PubMed2001

The changing nature of aminoglycoside resistance mechanisms and prevalence of newly recognized resistance mechanisms in Turkey.

OBJECTIVE: To determine the most frequently occurring individual and combined resistance mechanisms in Gram-negative bacteria resistant to any of the clinically available aminoglycosides in Turkey, and to compare these mechanisms with those found in smaller, earlier studies. METHODS: Aminoglycoside resistance mechanisms in Gram-negative isolates resistant to either gentamicin, tobramycin, netilmicin or amikacin collected in different regions of Turkey were evaluated both phenotypically and genotypically using 12 aminoglycosides and up to 22 aminoglycoside resistance gene probes. RESULTS: Among 696 aminoglycoside-resistant Gram-negative bacteria, resistance rates were very high for gentamicin (94.5%), tobramycin (82.4%), netilmicin (53.6%), and amikacin (49.7%). Although isepamicin was the most active aminoglycoside against Gram-negative bacteria, increased resistance (29.7%) was found and resistance rates were higher than those in most of the other countries surveyed in earlier studies. The most common aminoglycoside resistance mechanisms (AAC(3)-II (GTN), AAC(6')-I (TNA), and ANT(2")-I (GT)) in the earlier studies were also found in the present isolates of Klebsiella spp., Enterobacter spp. and Escherichia coli, with increased complexity. In addition to these old mechanisms, two new aminoglycoside resistance mechanisms, namely AAC(6')-III (TNAI) and AAC(6')-IV (GTNA), were also found at significant frequencies (11.9% and 26.9%, respectively) in these isolates of Enterobacteriaceae (n = 435). Among the isolates of Pseudomonas spp. (n = 150), in addition to the increased complexity of enzymatic resistance mechanisms (AAC(3)-I (16.6%), AAC(6')-II (29.3%), AAC(6')-III (19.3%), ANT(2")-I (40%)), permeability resistance seemed to be responsible for the high rates of resistance to aminoglycosides. CONCLUSION: The results of this study indicated increased resistance to clinically available aminoglycosides, including isepamicin, even though it was the most active, as a result of both the presence of new aminoglycoside resistance mechanisms and the increased complexity of all mechanisms, including permeability resistance, particularly in Pseudomonas in Turkey.

Aminoglycosides↗
PubMed2001

Investigation of cross-resistance to a range of photosensitizers, hyperthermia and UV light in two radiation-induced fibrosarcoma cell strains resistant to photodynamic therapy in vitro.

Two distinct photodynamic therapy-resistant variants of the murine radiation-induced fibrosarcoma (RIF) cell line have been isolated. One strain displayed relative resistance over the parental RIF-1 strain to treatment with the porphyrin-based compound, polyhaematoporphyrin (PHP), whereas the other strain displayed relative resistance over the RIF-1 strain to treatment using the cationic zinc (II) pyridinium-substituted phthalocyanine (PPC). The PHP-resistant strain did not display cross-resistance to PPC-mediated treatment, and vice versa. In both PDT-resistant strains, the increased resistance could not be attributed to altered cellular growth rate, antioxidant capacity or intracellular sensitizer localization. The PHP-resistant strain displayed resistance to treatment with both short (1 h) and extended (16 h) sensitizer incubation periods, which may indicate that in this strain, the resistance has arisen through an alteration in a membrane component. Conversely, the PPC-resistant strain only displayed increased resistance over the parental cells to treatment involving the short drug incubation, which is likely to reflect the existence of a threshold effect caused by the alteration of an individual cellular target. Each resistant strain has been compared to the parental strain in terms of cellular sensitivity to treatment with a range of other photosensitizers, hyperthermia, UV light and the anticancer agent cis-diamminedichloroplatinum. The PHP-resistant strain exhibited crossresistance to photosensitization treatment using exogenously added protoporphyrin IX, and also to treatment with the anionic phthalocyanine sensitizers, zinc (II) tetrasulfonated phthalocyanine and zinc (II) tetraglycine-substituted phthalocyanine. The PPC-resistant strain did not display cross-resistance to any of the treatment strategies employed in this investigation. The results of this investigation indicate that there are at least two distinct mechanisms of PDT resistance in RIF cells, and that the mechanism of PHP resistance may, to some extent depend, upon the physical nature of the sensitizer molecule.

Animals↗
PubMed1995

Multidrug resistance proteins and other drug transport-related resistance to natural product agents.

The term multidrug resistance is defined in this article as cellular resistance to anticancer agents due to a decreased concentration of active drug at the target sites that is caused by increased metabolism or altered transport or routing of the active drug species. Resistance related to alterations in the drug targets or apoptotic pathways is not discussed. Until recently multidrug resistance was associated almost exclusively with p-glycoprotein (Pgp)-overexpression. However, other non-Pgp-related mechanisms have been tracked down. It has been shown that transfection of the gene that encodes a novel drug transport protein, the multidrug resistance protein, induces cross-resistance for many multidrug resistance drugs as well as active transport of daunorubicin from tumor cells. Surprisingly, it has also been found that multidrug resistance protein mediates transport of negatively charged species that are not classic multidrug resistance drugs, such as leukotriene C4 and other glutathione conjugates as well as negatively charged dyes. It was therefore suggested that multidrug resistance protein is identical with the multispecific organic anion transporter. The transport rate of several positively charged drugs (vincristine, rhodamine-123, daunorubicin) by multidrug resistance protein appeared to be dependent on the cellular glutathione levels. Multidrug resistance protein seems to be constitutively expressed in normal tissues at a low level with few tissues having higher expression. Multidrug resistance protein overexpression in in vitro-selected MDR cell lines occurs relatively frequently in lung cancer and leukemia cell lines and often precedes Pgp overexpression. Differential expression has been demonstrated in tumor samples, which suggests a role in resistance to chemotherapy in at least certain tumor types. Modulation studies of multidrug resistance protein activity are still scarce. Other non-Pgp, non-multidrug resistance protein multidrug resistance mechanisms probably exist but have not been identified at the molecular level as yet.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

Incidence, distribution, and spread of tetracycline resistance determinants and integron-associated antibiotic resistance genes among motile aeromonads from a fish farming environment.

A collection of 313 motile aeromonads isolated at Danish rainbow trout farms was analyzed to identify some of the genes involved in high levels of antimicrobial resistance found in a previous field trial (A. S. Schmidt, M. S. Bruun, I. Dalsgaard, K. Pedersen, and J. L. Larsen, Appl. Environ. Microbiol. 66:4908-4915, 2000), the predominant resistance phenotype (37%) being a combined oxytetracycline (OTC) and sulphadiazine/trimethoprim resistance. Combined sulphonamide/trimethoprim resistance (135 isolates) appeared closely related to the presence of a class 1 integron (141 strains). Among the isolates containing integrons, four different combinations of integrated resistance gene cassettes occurred, in all cases including a dihydrofolate reductase gene and a downstream aminoglycoside resistance insert (87 isolates) and occasionally an additional chloramphenicol resistance gene cassette (31 isolates). In addition, 23 isolates had "empty" integrons without inserted gene cassettes. As far as OTC resistance was concerned, only 66 (30%) out of 216 resistant aeromonads could be assigned to resistance determinant class A (19 isolates), D (n = 6), or E (n = 39); three isolates contained two tetracycline resistance determinants (AD, AE, and DE). Forty OTC-resistant isolates containing large plasmids were selected as donors in a conjugation assay, 27 of which also contained a class 1 integron. Out of 17 successful R-plasmid transfers to Escherichia coli recipients, the respective integrons were cotransferred along with the tetracycline resistance determinants in 15 matings. Transconjugants were predominantly tetA positive (10 of 17) and contained class 1 integrons with two or more inserted antibiotic resistance genes. While there appeared to be a positive correlation between conjugative R-plasmids and tetA among the OTC-resistant aeromonads, tetE and the unclassified OTC resistance genes as well as class 1 integrons were equally distributed among isolates with and without plasmids. These findings indicate the implication of other mechanisms of gene transfer besides plasmid transfer in the dissemination of antibiotic resistance among environmental motile aeromonads.

Aeromonas↗
PubMed1990

Cyromazine resistance in the house fly (Diptera: Muscidae): genetics and cross-resistance to diflubenzuron.

Larvae of a house fly, Musca domestica L., strain collected in a chicken house near Pittsburg, Tex, after a control failure with the poultry feedthrough insecticide cyromazine showed 6.5-fold resistance to cyromazine and 10-fold resistance to diflubenzuron. Adults of the strain showed high levels of resistance to carbaryl, DDT, and diazinon; moderate resistance to cypermethrin and permethrin; and low resistance to dieldrin. In contrast, no resistance to cyromazine was observed in eight laboratory house fly strains with resistance to four groups of conventional insecticides. When the genetics of cyromazine resistance was investigated in crosses to susceptible strains with visible mutant markers, results indicated cyromazine resistance was incompletely dominant over susceptibility and the resistance gene was on chromosome V. The same or a closely linked gene conferred resistance to diflubenzuron. A strain containing only chromosome V from the original resistant strain was resistant to cyromazine and diflubenzuron, but not to other insecticides except for low level resistance to DDT and carbaryl. Resistance to the latter insecticides appeared to be due to a linked, but distinct, gene. Therefore, resistance to cyromazine and probably diflubenzuron appears to be genetically distinct from other types of insecticide resistance.

Animals↗
PubMed1977

Mucidin resistance in yeast. Isolation, characterization and genetic analysis of nuclear and mitochondrial mucidin-resistant mutants of Saccharomyces cerevisiae.

Mutants of Saccharomyces cerevisiae resistant to the antibiotic mucidin, a specific inhibitor of electron transport between cytochrome b and c, were isolated and divided into three phenotypic groups, as follows. Class 1 mutants were cross-resistant to a variety of mitochondrial inhibitors and exhibited no resistance at the mitochondrial level. Class 2 mutants were specifically resistant to mucidin exhibiting resistance also at the level of isolated mitochondria. Biochemical studies indicated that the mucidin resistance in class 2 mutants involved a modification of mucidin binding of inhibitory sites on the mitochondrial inner membrane without a significance change in the sensitivity of mitochondrial oxygen uptake to antimycin A, 2-heptyl-4-hydroxyquinoline-N-oxide, and 2,3-dimercaptopropanol. Class 3 was represented by a mutant which showed a high degree of resistance to mucidin and was cross-resistant to a variety of mitochondrial inhibitors at the cellular level but exhibited only a resistance to mucidin at the mitochondrial level. Genetic analysis of mucidin-resistant mutants revealed the presence of both nuclear and mitochondrial genes determining mucidin resistance/sensitivity in yeast. Resistance to mucidin in class 1 mutants was due to a single-gene nuclear recessive mutation (mucPR) whereas that in class 2 mutants was caused by mutations of mitochondrial genes. Resistance in class 3 mutant was determined both by single-gene nuclear and mitochondrial mutations. In the mitochondrial mutants the mucidin resistance segregated mitotically and the resistance determinant was lost upon induction of petite mutation by ethidium bromide. Allelism tests indicated that the mucidin resistance mutations fell into two genetic loci (MUC1 and MUC2) which were apparently not closely linked in the mitochondrial genome. Recombination studies showed that the two mitochondrial mucidin loci were not allelic with other mitochondrial loci RIB1, RIB2 and OLI1. An extremely high mucidin resistance at the cellular level was shown to arise from synergistic interaction of the nuclear gene mucPR and the mitochondrial mucidin-resistance gene (MR) in a cell. The results suggest that at least two mitochondrial gene products, responsible for mucidin resistance/sensitivity in yeast, take part in the formation of the cytochrome bc1 region of the mitochondrial respiratory chain.

Adenosine Triphosphatases↗
PubMed2006

Population genetics study of isoniazid resistance mutations and evolution of multidrug-resistant Mycobacterium tuberculosis.

The molecular basis for isoniazid resistance in Mycobacterium tuberculosis is complex. Putative isoniazid resistance mutations have been identified in katG, ahpC, inhA, kasA, and ndh. However, small sample sizes and related potential biases in sample selection have precluded the development of statistically valid and significant population genetic analyses of clinical isoniazid resistance. We present the first large-scale analysis of 240 alleles previously associated with isoniazid resistance in a diverse set of 608 isoniazid-susceptible and 403 isoniazid-resistant clinical M. tuberculosis isolates. We detected 12 mutant alleles in isoniazid-susceptible isolates, suggesting that these alleles are not involved in isoniazid resistance. However, mutations in katG, ahpC, and inhA were strongly associated with isoniazid resistance, while kasA mutations were associated with isoniazid susceptibility. Remarkably, the distribution of isoniazid resistance-associated mutations was different in isoniazid-monoresistant isolates from that in multidrug-resistant isolates, with significantly fewer isoniazid resistance mutations in the isoniazid-monoresistant group. Mutations in katG315 were significantly more common in the multidrug-resistant isolates. Conversely, mutations in the inhA promoter were significantly more common in isoniazid-monoresistant isolates. We tested for interactions among mutations and resistance to different drugs. Mutations in katG, ahpC, and inhA were associated with rifampin resistance, but only katG315 mutations were associated with ethambutol resistance. There was also a significant inverse association between katG315 mutations and mutations in ahpC or inhA and between mutations in kasA and mutations in ahpC. Our results suggest that isoniazid resistance and the evolution of multidrug-resistant strains are complex dynamic processes that may be influenced by interactions between genes and drug-resistant phenotypes.

Alleles↗
PubMed2004

Adaptive resistance to biocides in Salmonella enterica and Escherichia coli O157 and cross-resistance to antimicrobial agents.

The mechanisms by which bacteria resist killing by antibiotics and biocides are still poorly defined, although repeated exposure to sublethal concentrations of antibacterial agents undoubtedly contributes to their development. This study aimed both to investigate the potential of Salmonella enterica and Escherichia coli O157 for adaptive resistance to commonly used biocides and to determine any cross-resistance to antibiotics. Strains were repeatedly passaged in media containing increasing concentrations of a biocide or antibiotic until adaptive resistance was obtained. A wide panel of antimicrobial agents was then screened by using the adapted strain to determine cross-resistance, if any. Adaptive resistance was readily achieved for both S. enterica and E. coli O157. Cross-resistance in adaptively resistant S. enterica varied with the serotype; Salmonella enterica serovar Enteritidis expressed cross-resistance to chloramphenicol, whereas Salmonella enterica serovar Typhimurium expressed cross-resistance to chlorhexidine. Benzalkonium chloride-resistant Salmonella enterica serovar Virchow showed elevated resistance to chlorhexidine; however, chlorhexidine-resistant Salmonella serovar Virchow did not demonstrate reciprocal cross-resistance to benzalkonium chloride, suggesting specific rather than generic resistance mechanisms. E. coli O157 strains acquired high levels of resistance to triclosan after only two sublethal exposures and, when adapted, repeatedly demonstrated decreased susceptibilities to various antimicrobial agents, including chloramphenicol, erythromycin, imipenem, tetracycline, and trimethoprim, as well as to a number of biocides. These observations raise concern over the indiscriminate and often inappropriate use of biocides, especially triclosan, in situations where they are unnecessary, whereby they may contribute to the development of microbial resistance mechanisms.

Adaptation, Physiological↗
PubMed2005

Resistance development and insecticide susceptibility in Culex quinquefasciatus against selection pressure of malathion and permethrin and its relationship to cross-resistance towards propoxur.

To determine resistance level and characterize malathion and permethrin resistance in Culex quinquefasciatus, two methods were used namely: WHO procedures of larval bioassay to determine the susceptibility of lethal concentration (LC) and adult bioassay to determine the lethal time (LT) which are resistant to malathion and permethrin. These mosquito strains were bred in the Insectarium, Division of Medical Entomology, IMR. Thousands of late fourth instar larvae which survived the selection pressure to yield 50% mortality of malathion and permethrin were reared and colonies were established from adults that emerged. Larvae from these colonies were then subjected to the subsequent 10 generations in the test undertaken for malathion resistant strain (F61 - F70) and permethrin resistant strain (F54 - F63). Selection pressure at 50% - 70% mortality level was applied to the larvae of each successive generation. The rate of resistance development and resistance ratio (RR) were calculated by LC5 0 for larval bioassay and LT50 value for adult bioassay. The lab bred Cx. quinquefasciatus was used as a susceptible strain for comparison purpose. The adult bioassay test was carried out by using diagnostic dosages of malathion 5.0%, permethrin 0.75% and with propoxur 0.1%. All bioassay results were subjected to probit analysis. The results showed that LC5 0 for both malathion (F61 - F70) and permethrin (F54 - F63) resistant Cx. quinquefasciatus increased steadily to the subsequent 10 generations indicating a marked development of resistance. The adult female malathion resistant strain have developed high resistance level to malathion diagnostic dosage with resistance ratio 9.3 to 9.6 folds of resistance. Permethrin resistance ratio remained as 1.0 folds of resistance at every generation. It was obvious that malathion resistance developing at a higher rate in adult females compared to permethrin. Female adults exposed to 2 hours of exposure period for propoxur 0.1% showed presence of cross-resistance among the both strains of mosquitoes towards propoxur and it was indicated by 70%-100% mortality at 24 hours post-recovery period.

Animals↗
PubMed1990

Human tumor cell line resistance to chemotherapeutic agents does not predict resistance to natural killer or lymphokine-activated killer cell-mediated cytolysis.

Cancer cells selected for resistance to natural product chemotherapeutic agents typically display cross-resistance to a variety of structurally and mechanistically diverse agents, a phenomenon known as multidrug resistance. Preliminary studies involving cells selected for multidrug resistance in vitro have suggested that the development of resistance to these agents might simultaneously confer resistance to some forms of immunotherapy. Using human tumor cell line models, we have investigated the relationship between either intrinsic or selected multidrug resistance and sensitivity to natural killer (NK) or lymphokine-activated killer (LAK) cell-mediated cytolysis. We compared the NK and LAK cell susceptibility of three human tumor cell lines displaying distinct mechanisms of selected drug resistance with that of the parental drug-sensitive lines. We also evaluated the NK and LAK susceptibility of five established renal cell carcinoma lines, all of which were found to be intrinsically resistant to doxorubicin and vinblastine. The drug-resistant cell lines were variably sensitive to NK-mediated lysis. In contrast, all drug-resistant cell lines tested were LAK cell sensitive. The NK and LAK cell-mediated cytolytic sensitivities of the drug-resistant cell lines correlated well with those of the drug-sensitive parental lines, suggesting that susceptibility to lysis was related intrinsically to each tumor type, and not to the resistance phenotype. We attempted to correlated the NK sensitivity of these cells with the cell surface expression of Class I or II histocompatibility antigens, or the presence or absence of the membrane inhibitor of complement-mediated reactive lysis. None of these phenotypic markers were found to predict NK resistance. We therefore conclude that these cells, which are either spontaneously resistant to commonly utilized antitumor agents or are multidrug resistant as a result of drug exposure in vitro, remain sensitive to LAK cell-mediated cytolysis. Our studies suggest that interleukin 2-induced LAK cells may be useful in the therapy of some chemotherapy-resistant cancers.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1989

Sequential amplification of dihydrofolate reductase and multidrug resistance genes in Chinese hamster ovary cells selected for stepwise resistance to the lipid-soluble antifolate trimetrexate.

We describe the development of resistance to trimetrexate and piritrexim (BW 301U) by a stepwise selection protocol in Chinese hamster ovary cells. Selection in trimetrexate resulted in initial resistance as a result of dihydrofolate reductase gene amplification. Several trimetrexate-resistant variants that display 250-340-fold and 25-50-fold resistance to lipophilic and hydrophilic antifolates, respectively, were established. Increased antifolate resistance was associated with a prominent overexpression of dihydrofolate reductase as determined from the elevated folate reductase activity, cellular labeling with fluorescein-methotrexate, and steady-state mRNA levels as a result of a consistent dihydrofolate reductase gene amplification. However, upon subsequent incremental increases in trimetrexate, further resistance was also associated with amplification of the multidrug resistance gene. This resulted in overexpression of P-glycoprotein and a subsequent 20-50-fold collateral resistance to pleiotropic drugs such as adriamycin, actinomycin D, vinca alkaloids, etoposide, and colchicine. In contrast, initial resistance following selection with low piritrexim concentrations resulted from an unknown mechanism(s) not involving overproduction of either dihydrofolate reductase or P-glycoprotein. This piritrexim resistance was shared with trimetrexate but not with methotrexate. Upon further selection with piritrexim, resistant variants emerge with amplified dihydrofolate reductase but not with multidrug resistance genes. These variants were subsequently resistant to both hydrophilic and lipophilic folate antagonists but retained sensitivity to pleiotropic drugs. The pattern of resistance with methotrexate, trimetrexate, and piritrexim shared a common mechanism, dihydrofolate reductase gene amplification, but differed regarding the additional amplification of the multidrug resistance gene in trimetrexate-resistant cells as well as the emergence of an additional unknown mechanism(s) of resistance to lipid-soluble antifolates upon initial selection in piritrexim.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1988

Combined modalities of resistance in etoposide-resistant human KB cell lines.

The alkaloid derivative 4'-demethylepipodophyllotoxin 9-(4,6-O-ethylidene)-beta-D-glucopyranoside (etoposide, VP-16) is believed to exert cytotoxicity by causing double-stranded DNA breaks through interruption of the breaking-resealing reaction of topoisomerase II (topo II). Thus it was conceivable that cells could become resistant to VP-16 by a decrease in topo II enzyme level, since this would lead to fewer DNA breaks. As well, given the structure of VP-16, it was also possible that a pleiotropic mechanism of resistance could decrease sensitivity to this drug. To study these possibilities, a series of VP-16-resistant human KB cell lines was established by stepwise selection. The concentrations of VP-16 required to inhibit cell proliferation by 50% in the parent line and KB/1c, KB/7d, KB/20a, and KB/40a lines were, respectively, 0.16, 4.7, 24, 31, and 47 microM. These cell lines expressed cross-resistance to 4'-(9-acridinylamino)methanesulfon-m-anisidide, doxorubicin, vincristine, and methotrexate, although the pattern of relative drug sensitivity was quite different from that of pleiotropic resistant cell lines reported elsewhere. The resistance to vincristine and methotrexate did not increase above the level of the KB/1c cells, and resistance to VP-16, doxorubicin, and especially vincristine was unstable in VP-16-resistant cells cultured in the absence of drug. Although the drug resistance marker Mr 180,000 glycoprotein could not be detected in any of our cell lines, cellular accumulation of [3H]VP-16 was reduced 50-75% in the resistant lines compared with parent KB. With increasing VP-16 resistance, the level of topo II protein, detected by antibody staining, decreased at each step of selection, concomitant with a general decrease in topo II unknotting activity. Sensitivity of the topo II unknotting assay to inhibition by VP-16 was the same for the parent and all resistant cell lines. The level of topo I activity and enzyme increased slightly in the resistant cells. Thus, these cell lines are resistant to VP-16 by virtue of at least two mechanisms: (a) reduced levels of topo II, which confers cross-resistance to other compounds which are topo II-dependent cytotoxic agents; and (b) reduced accumulation of drug, which is likely also responsible for vincristine and methotrexate resistance. However, the possible existence of other mechanisms of resistance cannot be ruled out.

DNA Damage↗
PubMed1987

Reciprocal cross-resistance in human rhabdomyosarcomas selected in vivo for primary resistance to vincristine and L-phenylalanine mustard.

Primary resistance to vincristine (VCR) has been selected in rhabdomyosarcoma xenograft HxRh12 by sequential administration of VCR at 1.5 and subsequently 3 mg/kg/passage. The resistant tumor (HxRh12/VCR-3) was approximately 4-fold resistant to VCR and resistance was stable in the absence of selecting pressure (greater than 2 yr). HxRh12/VCR-3 was 2- to 3-fold cross-resistant to L-phenylalanine mustard (L-PAM) but only slightly cross-resistant to ifosfamide. To determine whether selection for primary resistance to L-PAM conferred cross-resistance to VCR we selected an L-PAM-resistant subline of rhabdomyosarcoma xenograft HxRh28 (HxRh28/L-PAM-13). This tumor was 2- to 3-fold resistant to L-PAM and 3-(p-fluorophenyl)-L-alanyl-3-[m-bis-(2-chloroethyl)-aminophenyl]-L- alanyl-L-methionine ethoxyhydrochloride, cross-resistant to cyclophosphamide and ifosfamide, and completely resistant to VCR under in vivo conditions. Pharmacokinetic studies in HxRh12/VCR-3 showed decreased retention of [G-3H]VCR but not alteration in metabolism. Expression of mdr1, a gene that encodes P-glycoprotein, associated with the multiple drug resistance phenotype, was examined. Expression of mdr1 was detected in both HxRh12 and HxRh28 tumors, sensitive to VCR, but there was no increase in expression in tumors selected for primary resistance to VCR or L-PAM. Data suggest that mechanisms other than those associated with "classical" multiple drug resistance confer resistance in these tumors. In clinical evaluation against childhood rhabdomyosarcoma, L-PAM has demonstrated only slight activity in patients relapsing on conventional therapy (including VCR) but demonstrated marked activity in patients with advanced previously untreated disease. It appears likely, therefore, that cross-resistance between VCR and L-PAM as demonstrated in this model may have clinical significance.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1986

Resistance to adriamycin: relationship of cytotoxicity to drug uptake and DNA single- and double-strand breakage in cloned cell lines of adriamycin-sensitive and -resistant P388 leukemia.

Cloned lines of Adriamycin (ADR)-sensitive and -resistant P388 leukemia have been established from single cell cultures. A marker chromosome M1 was found in all cells in the heterogeneous resistant P388/ADR parental line as well as in the cloned resistant lines P388/ADR/3 and P388/ADR/7; a different marker chromosome M2 was present in the heterogeneous sensitive P388 parental line as well as the cloned sensitive line P388/4. Dose-survival studies showed that D0, the dose of Adriamycin reducing survival to 1/e (i.e., 37% of the initial population), was 33 +/- 5 (SE) nM for sensitive P388/4 cells, 169 +/- 17 nM for resistant P388/ADR/3 cells, and 336 +/- 28 nM for the more resistant P388/ADR/7 cells. Drug uptake in sensitive P388/4 cells was 1.6-fold greater than in resistant P388/ADR/3 cells and 2.1-fold greater than in resistant P388/ADR/7 cells. The number of DNA single-strand breaks produced per microM Adriamycin was 131 +/- 9 rad equivalents in sensitive clone 4 cells, 41 +/- 8 rad equivalents in resistant clone 3 cells, and 33 +/- 11 rad equivalents in resistant clone 7 cells. The number of DNA double-strand breaks per microM Adriamycin was 1721 +/- 126 rad equivalents in sensitive cells, 117 +/- 36 rad equivalents in resistant P388/ADR/3 cells, and 194 +/- 16 rad equivalents in resistant P388/ADR/7 cells. Differences in drug uptake were insufficient to explain the higher incidence of DNA single- and double-strand breaks in sensitive cells. These findings strongly support the concept that resistance to Adriamycin in P388 leukemia cells is multifactorial; however, this study did not resolve whether these changes arise from a single pleiotropic mutation or from multiple mutations. In sensitive P388/4 cells the number of DNA single-strand breaks formed could all be attributed to double-strand breaks. However, in both resistant cell lines the level of induction of single-strand breaks was in excess of that due to double-strand breaks, and this excess of single-strand breaks appeared to vary directly with the degree of resistance, being greater in the more resistant clone 7 cells than in the less resistant clone 3 cells. In both sensitive and resistant cell lines the ratio of true single- to double-strand breaks varied inversely with the concentration of Adriamycin. Finally, the cytotoxic activity of Adriamycin appeared to correlate more closely with formation of DNA double-strand breaks than with single-strand lesions.

Animals↗
PubMed1983

Patterns of cross-resistance to the antifolate drugs trimetrexate, metoprine, homofolate, and CB3717 in human lymphoma and osteosarcoma cells resistant to methotrexate.

Methotrexate (MTX)-resistant sublines of malignant human cells were selected in vitro by stepwise increase in drug concentration in the medium. By this procedure a subline of Burkitt's lymphoma cells (RAJI) was made 290-fold resistant (RAJI/MTX-R), T-cell leukemia cells (CCRF-CEM) were obtained 210-fold resistant (CEM/MTX-R), and 3 MTX-resistant human osteosarcoma lines were selected: TE-85/MTX-R (19-fold resistant; relative to wild-type); MG-63/MTX-R (8-fold resistant); and SAOS-2/MTX-R (200-fold resistant). We also studied a B-cell lymphoblastoid line, WI-L2/m4, that was 13,000-fold resistant. Assay of cellular dihydrofolate reductase (DHFR) showed the following pattern of activity in resistant cell lines, relative to parental cell activity: RAJI/MTX-R, 550-fold increased; CEM/MTX-R, unchanged; TE-85/MTX-R, 4-fold increased; MG-63/MTX-R, 6-fold increased; SAOS-2/MTX-R, unchanged; and WI-L2/m4, 110-fold increased. Measurement of MTX membrane transport showed decreased uptake in CEM/MTX-R and SAOS-2/MTX-R, relative to parental cell lines. The other DHFR-overproducing cells all gave normal initial MTX uptake rates but increased total uptake. The DHFR-overproducing lines all had significant cross-resistance to both metoprine and trimetrexate; the two lines with defective MTX transport were not cross-resistant, and the CEM/MTX-R cells showed collateral sensitivity to these agents. Only minor cross-resistance to homofolic acid was found in all MTX-resistant lines. The highly MTX-resistant RAJI/MTX-R and WI-L2/m4 cells showed minor cross-resistance to the dual inhibitor of thymidylate synthetase and DHFR, CB3717 (5- and 15-fold, respectively). These studies demonstrated that, depending upon the mechanism of resistance, MTX-resistant human tumor cells may be effectively killed by antifolates with different routes of uptake into cells, or with a different enzyme target. Thus, there are at least three functionally distinct classes of folate antagonist with antitumor activity.

Antineoplastic Agents↗
PubMed1984

[Development of ACNU-resistant meningeal gliomatosis models: establishment of resistant rat glioma subline against ACNU].

Induction in vivo of resistance of C6 rat glioma and 9L rat glioma to ACNU [1-(4-amino-2-methyl-5-pyrimidinyl) methyl-3-(2-chloroethyl)-3-nitrosourea hydrochloride] was studied and ACNU-resistant rat meningeal gliomatosis models were developed by using these resistant glioma sublines. Rapid acquisition of resistance to the agent was present at 2nd transplant generation in both glioma lines. Cellular resistance to ACNU remained unchanged in the absence of drug over 5 transplant generations in vivo in spite of the fact that the drug treatment was discontinued at the 5th generation after a complete resistance was induced. On the other hand, the degree of resistance of 9L resistant subline established by only once ACNU treatment was found to be decreased after 5 transplant generations in vitro. Degree of resistance at the cellular level was observed with each subline by in vitro technique and compared with each other. Each subline was found to have different degree of resistance: 9L resistant subline showed higher resistance than C6 resistant subline, and the differences in degree of resistance between 9L resistant subline and C6 resistant subline were approximately 750 and 20, respectively, when they were expressed as ratios of IC50 (drug concentration for 50% growth inhibition) for the resistant subline to the original one.

Animals↗
PubMed1997

In vitro cross-resistance and collateral sensitivity in seven resistant small-cell lung cancer cell lines: preclinical identification of suitable drug partners to taxotere, taxol, topotecan and gemcitabin.

The acquisition of drug-resistant tumour cells is the main problem in the medical treatment of a range of malignant diseases. In recent years, three new classes of anti-cancer agents, each with a novel mechanism of action, have been brought forward to clinical trials. These are the topoisomerase I (topo I) poisons topotecan and irinotecan, which are both camptothecin derivatives, the taxane tubulin stabilizers taxol and taxotere and, finally, the antimetabolite gemcitabin, which is active in solid tumours. The process of optimizing their use in a combination with established agents is very complex, with numerous possible drug and schedule regimens. We describe here how a broad panel of drug-resistant small-cell lung cancer (SCLC) cell lines can be used as a model of tumour heterogeneity to aid in the selection of non-cross-resistant regimens. We have selected low-fold (3-10x) drug-resistant sublines from a classic (NCI-H69) and a variant (OC-NYH) SCLC cell line. The resistant cell lines include two sublines with different phenotypes towards alkylating agents (H69/BCNU and NYH/CIS), two sublines with different phenotypes against topo I poisons (NYH/CAM and NYH/TPT) and three multidrug resistant (MDR) sublines (H69/DAU, NYH/VM, and H69/VP) with combinations of mdr1 and MRP overexpression as well as topoisomerase II (topo II) down-regulation or mutation. Sensitivity to 20 established and new agents was measured in a standardized clonogenic assay. Resistance was highly drug specific. Thus, none of the cell lines was resistant to all drugs. In fact, all resistant cell lines exhibited patterns of collateral sensitivity to various different classes of drugs. The most intriguing pattern was collateral sensitivity to gemcitabin in two cell lines and to ara-C in five drug-resistant cell lines, i.e. in all lines except the lines resistant to topo I poisons. Next, all sensitivity patterns in the nine cell lines were compared by correlation analysis. A high correlation coefficient (CC) for a given pair of compounds indicates a similar pattern in response in the set of cell lines. Such data corroborate the view that there is cross-resistance among the drugs. A numerically low coefficient indicates that the two drugs are acting in different ways, suggesting a lack of cross-resistance between the drugs, and a negative correlation coefficient implies that two drugs exhibit collateral sensitivity. The most negative CCs (%) to the new drug leads were: taxotere-carmustine (BCNU) (-75), taxol-cisplatin (-58), ara-C-taxol (-25), gemcitabin-doxorubicin (-32), camptotecin-VM26 (-41) and topotecan-VP16 (-17). The most negative correlations to the clinically important agent VP-16 were: cisplatin (-70); BCNU (-68); camptothecin (-38); bleomycin (-33), gemcitabin (-32); ara-C (-21); topotecan (-17); melphalan (-3); and to the other main drug in SCLC treatment cisplatin were: doxorubicin (-70); VP-16 (-70); VM-26 (-69); mAMSA (-64); taxotere (-58); taxol (-58). Taxol and taxotere were highly correlated (cross-resistant) to VP-16 (0.76 and 0.81 respectively) and inversely correlated to cisplatin (both -0.58). Similarly, camptothecin and topotecan were correlated to cisplatin but inversely correlated to VP-16 and other topo II poisons. From the sensitivity data, we conclude that collateral sensitivity and lack of cross-resistance favours a cisplatin-taxane or topo I-topo II poison combination, whereas patterns of cross-resistance suggest that epipodophyllotoxin-taxane or topo I poison-cisplatin combinations may be disadvantageous.

Antineoplastic Combined Chemotherapy Protocols↗
PubMedDate not supplied

Cytosine arabinoside (ara-C) resistance confers cross-resistance or collateral sensitivity to other classes of anti-leukemic drugs.

The major limitation of treatment with antimetabolite drugs is that they produce resistant clones both in vitro and in patients who either do not respond to treatment or relapse soon after response has been documented. To better understand the phenomenon of cross-resistance, we developed seven CEM/ara-C-resistant leukemic clones from the CEM/0 (wt) cell line. These clones ranged from 4- to 3.5 x 10(8)-fold more resistant to ara-C than the wt CEM/0 cell line. Using this model, we determined IC50 concentrations to several chemotherapeutic agents and gamma radiation, and we also studied pro- (p53) and anti-apoptotic (bcl-2) proteins, as well as P-glycoprotein (P-gp) and multidrug resistance related protein (MRP). The cell viability assays showed that these clones were cross-resistant to 6-thioguanine (6-TG) or 6-mercaptoguanosine (6-TGuo) from 1.1- to 8.8-fold with ara-C; cross-resistance to vincristine (VCR) was from 200- to 1 x 10(4)-fold with ara-C. Taxotere (TXR) showed cross-resistance with ara-C from 1.39- to 3.03 x 10(3)-fold; dexamethasone (DEX) also showed a significant degree of cross-resistance from 27.4- to 3.87 x 10(7)-fold. Gamma radiation treatments from 0.77 Gy to 12.3 Gy showed a radiation dose-dependent cross-resistance with ara-C from 1.43- to 2.93-fold. Idarubicin was collaterally sensitive with ara-C from 4.6- to 1 x 10(9)-fold in these cell lines. The CEM/ara-C/G resistant cell line was 3-fold more sensitive to 6-TG or VCR than CEM/0 (wt), and 5-fold more sensitive to 6-TGuo. This cell clone expressed p53 and did not overexpress bcl-2 protein. All of the cell lines studied, CEM/0 (wt) and the ara-C resistant clones, showed functional p53 protein. The cell treatment with 0.1, 1 and 10 microM ara-C for 48 hours showed increased p53 protein expression in most of these lines. No increase in bcl-2 protein expression was seen in the wt cell line after ara-C treatment for 48 hours. Three cell lines resistant to ara-C (CEM/ara-C/B, CEM/ara-C/D and CEM/ara-C/I) showed an important increased expression of bcl-2 protein after treatment with 1 microM ara-C, but not after 10 microM. This alteration may lead to resistance to apoptosis and enhanced cell survival. The ratio of bcl-2 to p53 was increased significantly in these three clones, thus favoring an anti-apoptotic drive. All of the cell lines examined were negative for MRP expression and only two, CEM/ara-C/B and CEM/ara-C/J, were positive for MRP functional activity. However, three ara-C resistant cell clones, CEM/ara-C/7A, CEM/ara-C/B and CEM/ara-C/G, were positive for P-gp expression and functional activity. It is apparent that selection for ara-C resistance confers cross-resistance to many other classes of drugs and gamma radiation, probably due to bcl-2 protein overexpression or P-gp and MRP expression, as independent mechanisms.

ATP Binding Cassette Transporter, Subfamily B, Mem↗