Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “KB Cells”

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 217 records · Page 12Linked to original sources
PubMed1980

Hydroxyurea: protection of KB cells against the toxic effect of N-methyl-N'-nitro-N-nitrosoguanidine.

This report shows that hydroxyurea (HU) protected KB cells specifically against the toxic effect of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). It appears unlikely that this action was due to stimulation of DNA repair since HU neither protected the cells when added after removal of MNNG, nor shielded them against the toxicity of other DNA damaging agents. Similarly, it seems difficult to account for HU protection by its specific effect as an inhibitor of DNA synthesis, because cell protection was found to be maximal when the proliferative activity of the cultures was minimal, and because much higher doses of HU were required to ensure cell protection than to inhibit DNA synthesis. In fact, the shift of the MNNG dose-response curves in the presence of increasing HU concentrations suggests that HU might interfere with the MNNG-molecule. This was confirmed by our finding that HU enhanced the decomposition rate of MNNG, as did other substances like cysteine or ascorbic acid, which also appeared able to protect the cells against the toxic effect of MNNG.

Ascorbic Acid↗
PubMed1977

Thermal behavior of HeLa and KB cells in suspension and attached to glass.

HeLa S-3 and KB cells were grown in a LKB Batch Microcalorimeter under a variety of nutrient medium conditions amd mixing intervals. These conditions produced rather large apparent endothermic and exothermic responses on mixing that could be correlated with the presence of suspended cells (unattached) as well as cells attached to the glass calorimeter vessel. Cells capable of being resuspended upon mixing of the calorimeter vessel produces first an endothermic followed by an exothermic signal while attached cells produced only an apparent endothermic response. The exothermic response is believed to be associated with increased metabolic heat on suspending the cells followed by partial suppression of the steady state metabolic heat on cell settling. Rates of cell settling correlated well with the rate of decay of the exothermic signal. The rapid appearance of endothermicity on mixing suggests it is associated with rapid events such as binding of nutrients to cell surfaces. The response in the endothermic direction on mixing is discussed in terms of the disruption of mechanisms which tend to exclude nutrients from the surface of the cell.

Calorimetry↗
PubMed1984

Demonstration of a herpes simplex virus type 2-induced deoxyuridine triphosphate nucleotidohydrolase in infected KB cells and in biochemically transformed HeLa cells.

The deoxyuridine triphosphate nucleotidohydrolase (dUTPase) activity which is induced in KB cells infected with herpes simplex virus type 2 (HSV-2) and expressed in biochemically transformed HeLa cells was separated from the host dUTPase activity using either gel filtration or chromatofocusing chromatography. The HSV-2-induced dUTPase differed from the host dUTPase activity in its molecular weight (53000 versus 46000) and isoelectric point (pI 5 X 9 versus 6 X 4). However, it was similar to the host enzyme in that only dUTP served as a substrate for the enzyme.

Cell Transformation, Viral↗
PubMed1981

Purification and characterization of DNA-dependent ATP phosphohydrolases from KB cells.

DNA-dependent ATPases have been purified from logarithmically growing KB cells by chromatography on single-stranded DNA cellulose and phosphocellulose. Phosphocellulose resolved the DNA-dependent ATPases into three activities designated ATPase I, II and III, respectively. From gel filtration and sedimentation analysis ATPases II and III were found to be very similar, both with calculated molecular weights of 78,000. Due to the extreme lability these enzymes were not purified further. The molecular weight of ATPase I determined by gel filtration and sedimentation analysis was calculated to be 140,000. ATPase I was further purified by gradient elution on ATP-agarose, revealing two peaks of activity (IA and IB), and by sucrose gradient sedimentation. Analysis of the fractions from the sucrose gradient by sodium dodecylsulphate gel electrophoresis revealed only one broad polypeptide band co-sedimenting with both ATPase IA and ATPase IB. This band was composed of four closely spaced polypeptides with apparent molecular weights of 66,000, 68,000, 70,000 and 71,000. Comparison of the native molecule weight (140,000) with these results suggests that ATPase I is a dimer. ATPase IA and IB were indistinguishable in their structural and enzymatic properties and presumably represent the same enzyme. The purified enzyme has an apparent Km of 0.5 mM for ATP producing ADP + Pi. A maximum activity of 2,100 molecules of ATP hydrolyzed per enzyme molecular per minute was found. Hydrolysis of ATP requires the presence of divalent cations (Mg2+ greater than Ca2+ greater than Mn2+ greater than Co2+). A broad pH optimum (pH 6--8) was observed. The enzyme uses ATP or dATP preferentially as a substrate, while other deoxyribonucleoside or ribonucleoside triphosphates were inactive. ATPase I prefers denatured DNA as cofactor. The activity with native DNA is 40% of that with denatured DNA.

Adenosine Triphosphatases↗
PubMed2006

Cytotoxic activity toward KB cells of 2-substituted naphtho[2,3-b]furan-4,9-diones and their related compounds.

We investigated the cytotoxic activity of 2-substituted naphtho[2,3-b]furan-4,9-diones. We have previously synthesized 33 types of 2-substituted and related compounds, and the cytotoxic activity of these compounds was then examined by a KB cell culture assay. 2-(3-Furanoyl)benzoic acids and 1,4-naphthoquinones had no activity. 2-Acetyl-4,9-dimethoxynaphtho[2,3-b]furan 4 showed low activity. However, parent naphtho[2,3-b]furan-4,9-dione 2 and most 2-substituted derivatives exhibited cytotoxic activity. The parent structure was therefore for cytotoxicity. 2-Formylnaphtho[2,3-b]furan-4,9-dione 11 had particularly potent activity (ED50=0.09 microg/ml).

Cell Proliferation↗
PubMed1974

Solubilization and fractionation of glycoproteins and glycolipids of KB cell membranes.

1. A fraction enriched in plasma membranes of human tumour KB cell line, a permissive cell for adenovirus type 5, was obtained. 2. Electrophoresis of the membranes in polyacrylamide gels with buffers containing sodium dodecyl sulphate showed that the membranes after reduction with 2-mercaptoethanol contained over 20 polypeptide species. Three polypeptides were glycosylated and had apparent mol.wts. of 92000, 72000 and 62000. 3. The glycoproteins and the specific receptors responsible for adenovirus adsorption to the membranes were readily extracted into solutions containing low concentrations of Triton X-100. Glycolipids and proteins were also made soluble. A membranous residue obtained after Triton X-100 extraction was enriched in several proteins that appeared to consist of polypeptides of lower molecular weight than the average of KB membrane polypeptides. 4. Sphingomyelin, cholesterol and triglycerides were similarly concentrated in the insoluble residue remaining after successive extractions of KB membranes with Triton X-100. Further, ceramide trihexoside was significantly less easily extracted from KB membranes than lactosyl ceramide. 5. The differences noted in the ease of extraction of membrane components are discussed. 6. The components of membranes made soluble by detergent extraction and containing the large part of the KB membrane glycoproteins were subjected to chromatography on Sepharose 6B and DEAE-cellulose and to isoelectric focusing in the presence of buffers containing Triton X-100. In general, the degree of separation into fractions enriched in individual glycoproteins was disappointing. Possible reasons for the poor fractionation of membrane components by chromatographic systems conveniently used for purification of proteins and glycoproteins of non-membranous origin are briefly discussed.

Adenoviridae↗
PubMed1987

Isolation of human KB cell lines resistant to epidermal growth factor-Pseudomonas exotoxin conjugates.

Mutants of the human KB carcinoma cell line resistant to a cytotoxic conjugate of epidermal growth factor (EGF) and Pseudomonas exotoxin (PE) were selected. EGF-PE and the drug verapamil, which enhanced EGF-PE cytotoxicity, were used in the selection process. These mutants also showed some cross-resistance to PE. All of the EGF-PE resistant variants displayed lower levels of 125I-EGF binding, 20-50% of parental KB levels, without altered affinity for EGF and grew at a slower rate than the parental cell line KB-3-1. These results indicate that EGF-PE resistant KB cells have a complex phenotype which includes a reduction in the number of EGF receptors and reduced sensitivity to unconjugated PE. Resistance to toxin-conjugates, although pleiotropic, is specific and does not lead to resistance to multiple other anticancer drugs, nor are independently selected multidrug resistant KB lines resistant to PE. These results argue that protocols for cancer treatment could effectively use specifically designed cytotoxic toxin conjugates as an adjunct to conventional chemotherapy.

Bacterial Toxins↗
PubMed1979

Characterization of virus DNA synthesized in KB cells infected with two temperature-sensitive mutants of adenovirus type 5.

KB cells were infected with H5ts36 or H5ts125, two adenovirus type 5 (Ad5) mutants with a temperature-sensitive synthesis of virus DNA. Infection was started at the nonpermissive temperature and at 16 h p.i. the temperature was shifted down to the permissive temperature. Shortly after the shift-down H5ts125-infected cells showed an accumulation of purely single-stranded DNA of virus origin, which was not observed in H5ts36-infected cells. This single-stranded DNA has been characterized by hybridization and sedimentation analysis. It was found that the single-stranded DNA was derived from both complementary strands and consisted of short fragments. The observation that the single-stranded DNA accumulates in H5ts125-infected cells under conditions in which the amount of DNA binding protein is reduced, suggests that the DNA-binding protein is not only involved in initiation, but also in elongation of nascent strands.

Adenoviruses, Human↗
PubMed1994

Characterization of a hydroxyurea-resistant human KB cell line with supersensitivity to 6-thioguanine.

Hydroxyurea (HU) is currently used in the clinic for the treatment of chronic myelogenous leukemia, head and neck carcinoma, and sarcoma. One of its drawbacks, however, is the development of HU resistance. To study this problem, we developed a HU-resistant human KB cell line which exhibits a 15-fold resistance to HU. The characterization of this HU-resistant phenotype revealed a gene amplification of the M2 subunit of ribonucleotide reductase (RR), increased levels of M2 mRNA and protein, and a 3-fold increase of RR activity. This HU-resistant cell line also expressed a "collateral sensitivity" to 6-thioguanine (6-TG), with a 10-fold decrease in the dose inhibiting cell growth by 50% as compared to the KB parental line. The mechanism responsible for this supersensitivity to 6-TG is believed to be related to an increasingly efficient conversion of 6-TG to its triphosphate form, which is subsequently incorporated into DNA. After passage of the resistant cells in the absence of HU, the cell line reverts. The revertant cells lose their resistance to HU and concomitantly their sensitivity to 6-TG. This phenomenon is due to the return of RR to levels comparable to that of the KB parental cell line. These observations and their relevance to cancer chemotherapy will be discussed in this paper. Our results suggest that a clinical protocol could be designed which would allow for a lower dose of 6-TG to be used by taking advantage of the increased RR activity in HU-refractory cancer patients. Two drugs which display collateral sensitivity are known as a "Ying-Yang" pair. Alternate treatment with two different Ying-Yang pairs is the rationale for the "Ying-Yang Ping-Pong" theory in cancer treatment. This rationale allows for effective cancer chemotherapy with reduced toxicity.

Animals↗
PubMed1993

Rapid stimulation of rhodamine 123 efflux from multidrug-resistant KB cells by progesterone.

Rhodamine 123 is a mitochondrial dye that is retained for prolonged periods by carcinoma cells. While investigating causes of retention of this dye, we found that 10 microM progesterone caused a rapid stimulation of efflux of rhodamine 123 within 15 min from KB V20C cells, which overexpress the multidrug resistance pump. Progesterone did not stimulate efflux from KB cells that do not overexpress the pump, and verapamil blocked rhodamine 123 efflux in the presence or absence of progesterone, indicating that rhodamine 123 is removed from KB V20C cells by the multidrug resistance pump. Progesterone, however, is unlikely to stimulate rhodamine 123 efflux by simply increasing pump activity for two reasons: (1) progesterone inhibited the efflux of daunomycin from KB V20C cells, so it did not stimulate efflux of all drugs, and (2) progesterone inhibited efflux of rhodamine 123 from L1210/VMDRC cells and had little effect on Adr MCF7 cells; both overexpress the multidrug resistance pump. In the experiments with KB V20C cells, progesterone was the most active steroid tested. At 10 microM, progesterone caused a 70-fold stimulation, desoxycorticosterone, testosterone, promegestone and estradiol about 20-fold, and others had little or no effect. Progesterone may act by a non-genomic mechanism to decrease intracellular binding of rhodamine 123, making the dye accessible to the multidrug resistance pump.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1994

Derivatives of a novel cyclopeptolide. 2. Synthesis, activity against multidrug resistance in CHO and KB cells in vitro, and structure-activity relationships.

A series of derivatives of the novel cyclopeptolide 1 was prepared, and their ability to chemosensitize multi drug resistant CHO and KB cells in vitro was evaluated. In contrast to the parent compound, several of the derivatives were found to be highly active. In particular, conversion of the R-lactic acid residue of 1 into its S-isomer via lactone ring cleavage and recyclization with inversion resulted in a marked enhancement of activity. Some of these derivatives (e.g., 15a, SDZ 280.446) belong to the most potent resistance modulating compounds known so far.

Amino Acid Sequence↗
PubMed1995

alpha-Interferon potentiates epidermal growth factor receptor-mediated effects on human epidermoid carcinoma KB cells.

The molecular mechanisms underlying the growth inhibition of human tumor cells induced by recombinant interferon-alpha (IFN alpha) are mostly unknown. It has been proposed that this effect could be related to down-regulation and/or impaired function of peptide growth factor receptors (PGF-Rs) in tumor cells exposed to IFN alpha. However, we have previously described that IFN alpha-induced growth inhibition of human epidermoid carcinoma cells is paralleled by up-regulation of epidermal growth factor receptor (EGF-R). Here we report that an increase in EGF-R synthesis is detectable after 3 hr of exposure to cytostatic concentration of IFN alpha in epidermoid KB tumor cells. In these experimental conditions IFN alpha does not depress and even potentiates EGF-R function. IFN alpha-treated KB cells retain sensitivity to the cytotoxic activity of the anti-EGF-R 225 monoclonal antibody (MAb), which acts through receptor blockade, and are sensitized to the growth-promoting effect of EGF. EGF-induced tyrosine (tyr) phosphorylation both of total cellular protein extracts and of the immunoprecipitated EGF-R is increased in IFN alpha-treated cells. We conclude that a cross-talk between IFN alpha and EGF occurs in KB cells since IFN alpha, at cytostatic concentration, potentiates the effects mediated by the EGF-R.

Antibodies, Monoclonal↗
PubMed1994

Regulation of folate-binding protein gene expression by DNA methylation in methotrexate-resistant KB cells.

Folate-binding protein (FBP) is responsible for the cellular transport of folate and methotrexate (MTX) in human KB (nasopharyngeal epidermoid carcinoma) cells. The levels of membrane-associated FBP and FBP mRNA are decreased 70-80% in an MTX-resistant KB subline (KB1BT) (Hsueh C-T and Dolnick BJ, Oncol Res 4: 497-505, 1992). Southern blot analysis did not reveal any differences in FBP gene organization or copy number between KB1BT and KB cells. However, there was a 70% decrease in the FBP gene transcription rate and no change in FBP mRNA stability in KB1BT cells. Assessing genomic DNA methylation by MspI and HpaII restriction analysis suggested that the FBP gene in KB1BT cells was more methylated than in KB cells. These alterations in the expression, transcription rate and DNA methylation state of the FBP gene did not change when KB1BT cells were grown in the absence of MTX for 8 months (MTX-free KB1BT). When MTX-free KB1BT cells were exposed to 2.5 microM 5-aza-2'-deoxycytidine for 72 hr, the FBP gene became hypomethylated and the levels of membrane-associated FBP and FBP mRNA increased by 2- to 3-fold. These data indicate that decreased FBP gene expression in KB1BT cells results from increased DNA methylation.

Azacitidine↗
PubMed1985

Characterization of dihydrofolate reductase-related DNA and RNA from human KB cell subclones containing different amounts of enzyme.

The present study was aimed to characterize dihydrofolate reductase (DHFR)-related DNA and RNA in a series of human KB cell sublines and to further understand the mechanisms of DHFR regulation. We used two probes, one which could recognize the 5' flanking sequence (p5') of the human DHFR gene and one derived from mouse complementary DNA (pDHFR 26) which contains the coding sequence for DHFR, to identify the DHFR-related DNA and RNA. Our results revealed no major differences in DNA gene structure as the copy number increases. The recognizable fragments of DHFR gene were similar including the 5' flanking sequence upstream from the first exon. We observed that all DHFR mRNA species identified were present in the subclones. The content of cytoplasmic DHFR mRNA does not always correlate with the relative gene copy number in these cell lines. Furthermore, we were able to detect high-molecular-weight RNA related to DHFR which might be the precursors of the DHFR mRNAs. Finally, using different RNA extraction procedures, we observed that different patterns of cytoplasmic DHFR mRNA can be obtained, which is probably due to differential breakdown of RNA species during extraction procedures.

Base Sequence↗