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A Tomida

Publications and source records attributed to A Tomida.

33 records · Page 2Linked to original sources
PubMed1996

Glucose-regulated stresses induce resistance to camptothecin in human cancer cells.

The glucose-regulated stress response in mammalian cells is characterized by the increased synthesis of glucose-regulated proteins (GRPs). In this study, we found that GRP-inducing conditions in culture led to induction of resistance to the topoisomerase I-targeted drug camptothecin in human colon cancer HT-29 and ovarian cancer A2780 cells. The induction of camptothecin resistance was accompanied by decreased levels of camptothecin-induced cleavable complexes, as measured by a topoisomerase I band depletion assay. However, topoisomerase I protein levels were the same in both stressed and non-stressed cells. Furthermore, when isolated nuclei from stressed and non-stressed cells were treated with camptothecin, similar levels of cleavable complexes were obtained, suggesting that the activity of topoisomerase I did not change in stressed cells. In contrast, intracellular accumulation of camptothecin decreased in stressed cells. Our results indicate that stress-induced camptothecin resistance could be explained by reduced camptothecin accumulation, leading to decreased numbers of cleavable complexes, without quantitative or qualitative changes in topoisomerase I levels. In addition, cell cycle analysis revealed that the GRP-inducing treatments resulted in an accumulation of G1/G0-phase cells. As camptothecin shows an S-phase-specific cytotoxicity, the G1/G0-phase accumulation is another mechanism for camptothecin resistance. Since a glucose-regulated response is produced by hypoxia and nutrient deprivation that occur naturally in solid tumors, the resistance observed here can occur in some solid tumors and can be an obstacle to chemotherapy.

Antineoplastic Agents, Alkylating↗
PubMed1996

DT-diaphorase as a critical determinant of sensitivity to mitomycin C in human colon and gastric carcinoma cell lines.

Mitomycin C (MMC), a known cytotoxic agent, requires cellular enzyme-mediated activation for effective antitumor activity. To study the bioreductive enzymes responsible for MMC activation in tumor cells, we examined the enzyme activities of DT-diaphorase (DTD) and NADPH:cytochrome P-450 reductase in 13 colon and gastric carcinoma cell lines and then compared these activities to the respective cellular MMC sensitivity. We found that cell lines with nonexistent or marginal DTD activity, such as St-4 and MKN7, showed resistance to MMC, in comparison to cell lines with DTD activity ranging from 210 to 1420 nmol/min/mg protein. No correlation was found between NADPH:cytochrome P-450 reductase activity and MMC sensitivity in these cell lines. To confirm the role of DTD in cellular MMC sensitivity, we constructed an expression vector containing NQO1, a gene that codes for DTD, and transfected the vector into St-4 cells expressing no DTD activity. Several transfectant clones with DTD activity from 144 to 2085 nmol/min/mg protein were obtained. All of the transfectants showed 5-10-fold higher sensitivity to MMC compared to the parental St-4 cells. Consistent with the MMC sensitivity, we also found that MMC-DNA adduct was formed more extensively in the NQO1 transfectants than in the St-4 cells. These results indicate that DTD activity is required for effective cytotoxicity of MMC in colon and gastric carcinoma cells.

Antibiotics, Antineoplastic↗
PubMed1996

Increased expression of thioredoxin/adult T-cell leukemia-derived factor in cisplatin-resistant human cancer cell lines.

Thioredoxin (TRX) is a widely distributed Mr 13,000 protein with a redox-active dithiol/disulfide in the active site. The TRX system, consisting of TRX, TRX reductase, and NADPH, has an intracellular reducing capacity. Another reducing capacity, glutathione (GSH), can be associated with cis-diaminedichloroplatinum (cDDP) resistance. Therefore, we examined the involvement of TRX in cDDP resistance using two cell lines designated St/DDP and HT/DDP, which were established from the human gastric cancer cell line St-4 and the colon cancer cell line HT-29. St/DDP and HT/DDP were seven and five times as resistant to cDDP as their parental lines, and the expression of TRX in these variants was increased by 2.5- and 2-fold, respectively. The expression of TRX in the complete revertant cells of St/DDP was reduced as low as that in St-4 cells. TRX reductase activity was also increased in St/DDP and HT/DDP, suggesting that activation of the TRX system was associated with in vitro-acquired cDDP resistance. Because cDDP is the first-line drug against ovarian cancer, we examined the expression of TRX in 11 human ovarian cancer cell lines not treated with cDDP in vitro. Positive correlation between TRX expression and cDDP resistance was observed in these cell lines (r = 0.76, P = 0.007). This correlation was comparable to that between GSH content and cDDP resistance (r = 0.69, P = 0.019). These results suggest a possible involvement of TRX, as well as GSH, in cDDP resistance.

Antineoplastic Agents↗
PubMed1995

Multidrug resistance.

Since we found verapamil as a multidrug resistance (MDR) reversing agent in 1981, many MDR reversing compounds have been reported. This type of drug must have strong effects with little side effects. We recently found MS-209 and PSC-833 as reversing agents. These two compounds interacted directly with P-glycoprotein, and showed a good MDR reversing effect in vitro and in vivo. MRK16, an antibody against P-glycoprotein, also showed a good therapeutic effect against drug resistant human tumors. MS-209, PSC-833 and the antibody against P-glycoprotein are interesting candidates for clinical use in the future.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1995

Acute induction of adriamycin-resistance in human colon carcinoma HT-29 cells exposed to a sublethal dose of adriamycin.

To study the mechanisms of the acute induction of drug resistance in cancer cells, we have established a model system in which adriamycin (ADM) induces immediate drug resistance. In this system, human colon carcinoma HT-29 cells were pretreated for 1 h with a subtoxic dose of ADM (0.3 micrograms/ml) and incubated for 24 h in drug-free medium. Then the cells were treated for 1 h with ADM, and the cell survival was determined in terms of colony-forming ability. The survival of the pretreated cells was increased up to 100-fold, as compared with that of untreated cells. Such increased survival, however, was observed only after high doses of ADM (2 to 8 micrograms/ml); more than 99% of the cells were killed. These results indicate that only a small fraction of ADM-pretreated cells acquire the ADM-resistant phenotype. Similar induced resistance was observed in five of seven subclones isolated from HT-29 cells by limiting dilution, suggesting that the majority of cells in the parental HT-29 population could acquire the ADM-resistant phenotype. In the subclone HT-29T9, the ADM pretreatment induced concomitant resistance to daunomycin, VP-16, and VM-26 but not to agents other than topoisomerase II inhibitors. The ADM-induced drug resistance did not accompany MDR1 gene expression and could not be overcome by verapamil, a P-glycoprotein inhibitor. The present system could be useful to study the acute induction mechanism(s) of ADM-resistance, which could be relevant to clinical resistance in patients.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1995

Glucose-regulated stresses confer resistance to VP-16 in human cancer cells through a decreased expression of DNA topoisomerase II.

Glucose-regulated proteins (GRPs) are induced in cells by a variety of stress conditions such as treatment with 2-deoxyglucose, glucosamine, or the calcium ionophore A23187. We found that resistance to topoisomerase II (topo II) inhibitors, VP-16 and adriamycin, was induced by these treatments in human colon cancer HT-29 cells. Similar VP-16 resistance occurred in human ovarian cancer A2780 and breast cancer MCF-7 cells. The VP-16 resistance was reversible, since the sensitivity of the cells to VP-16 recovered within 24 h after the stresses were removed. Western blotting analysis showed that under these stress conditions the cellular contents of topo II alpha were decreased. The decreased expression of topo II was reversed to control levels within 24 h following removal of the stresses. The decrease in topo II levels under the stress conditions correlated well with the induction of GRP78 and 94. The close correlation between topo II and GRPs suggests that topo II is a protein sensitive to the glucose-regulated stresses. Since hypoxia and nutrient deprivation, which are also GRP-inducing conditions, could occur naturally in the solid tumors, the stress-associated cellular resistance through decrease in topo II levels may be a mechanism of the natural resistance of the solid tumors to topo II-directed chemotherapy.

Antineoplastic Agents, Phytogenic↗
PubMed1994

Resistance to antitumor agent-induced apoptosis in a mutant of human myeloid leukemia U937 cells.

Human monocytic leukemia U937 cells underwent apoptosis when the cells were treated with a variety of antitumor drugs. We isolated and characterized a mutant, UK711, that was resistant to apoptosis induced by antitumor agents. When U937 cells were treated with etoposide (VP-16), an inhibitor of DNA topoisomerase II, apoptosis occurred in a large number of cells, and flow-cytometric analysis revealed that the majority of cells in S phase underwent apoptosis within 2 h of the end of treatment. Such treatment, however, induced apoptosis in only a few UK711 cells. The levels of protein-DNA covalent links and DNA double-strand breaks caused by VP-16 were similar in both cell lines, indicating that the initial DNA damage caused by VP-16 were comparable, whereas the following cellular responses that resulted in apoptosis differed between these cell lines. UK711 cells also showed resistance to apoptosis induced by such antitumor agents as 1-(beta-D-arabinofuranosyl) cytosine (Ara-C), adriamycin, mitomycin C, camptothecin, and by cytotoxic stimuli such as staurosporine, cycloheximide, and uv irradiation. UK711 cells, however, were sensitive to apoptosis induced by tumor necrosis factor (TNF), as were U937 cells. In accordance with resistance to apoptosis induced by antitumor agents, UK711 cells showed significant actual drug resistance to these antitumor agents. The present results indicate that UK711 cells acquired resistance to apoptosis induced by a variety of cytotoxic stimuli resulting in actual anticancer drug resistance. This cell line may be useful in studying the mechanism of apoptosis induced by cytotoxic agents.

Antineoplastic Agents↗
PubMed1993

Enhancement of cellular accumulation of cyclosporine by anti-P-glycoprotein monoclonal antibody MRK-16 and synergistic modulation of multidrug resistance.

BACKGROUND: Drug resistance is a major obstacle to successful cancer chemotherapy. P-glycoprotein, which transports certain antitumor agents out of resistant tumor cells, is known to be a major factor in some types of multidrug resistance. Studies have shown that verapamil and the immunosuppressors cyclosporine and FK-506 can reverse multidrug resistance in vitro and in vivo and that the P-glycoprotein monoclonal antibody MRK-16 increases drug toxicity in multidrug-resistant tumors. PURPOSE: The purpose of this in vitro study was to establish effective treatment modalities for overcoming multidrug resistance. We assessed the synergistic effects of verapamil, cyclosporine, or FK-506 in combination with MRK-16 and antitumor agents. METHODS: Human myelogenous leukemia K562 cells and multidrug-resistant K562/ADM cells were treated with vincristine or doxorubicin combined with MRK-16 and cyclosporine alone or together; MRK-16 and verapamil alone or together; or MRK-16 and FK-506. The effects of MRK-16 and cyclosporine or verapamil on the accumulation of vincristine and doxorubicin were examined in K562/ADM cells, and the mechanisms of action were analyzed. RESULTS: MRK-16 and cyclosporine synergistically enhanced the antitumor effects of vincristine and of doxorubicin in K562/ADM cells. However, the combined use of MRK-16 with verapamil or FK-506 did not show such synergistic effects in these cells. Studies of the effect of MRK-16 on cellular accumulation of cyclosporine and verapamil revealed that MRK-16 substantially increased accumulation of cyclosporine in K562/ADM cells, but did not increase accumulation of verapamil. CONCLUSIONS: MRK-16 and cyclosporine synergistically enhanced the antitumor effects of vincristine and doxorubicin because MRK-16 increased cellular accumulation of cyclosporine. IMPLICATIONS: These results, together with our previous finding that intravenous administration of MRK-16 induced regression of multidrug-resistant subcutaneous tumors in athymic mice, support the hypothesis that the combined use of MRK-16 and cyclosporine might increase the efficacy of antitumor agents against multidrug-resistant tumors expressing P-glycoprotein. Clinical phase I trials of MRK-16 in the treatment of multidrug-resistant tumors are under consideration.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1993

Enhancement of reversing effect of cyclosporin A on vincristine resistance by anti-P-glycoprotein monoclonal antibody MRK-16.

The synergistic effect of MRK-16, a monoclonal antibody against P-glycoprotein, and cyclosporin A (CsA) on the modulation of vincristine resistance was studied by isobologram analysis in three different, highly multidrug-resistant tumor cells. In all cell lines, the synergistic effect was demonstrated at various concentrations of MRK-16 and CsA. While MRK-16 alone did not enhance the sensitivity of the moderately resistant KB-8-5 cells to vincristine, it increased two-fold the reversing effect of cyclosporin A at 1 microM, an achievable blood concentration. Since MRK-16 alone showed therapeutic effects against multidrug-resistant tumors, the combined use of MRK-16, CsA and antitumor agents should provide therapeutic benefits for the treatment of resistant tumors.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1991

Novel mechanism of N-solanesyl-N,N'-bis(3,4-dimethoxybenzyl)ethylenediamine in potentiation of antitumor drug action on multidrug-resistant and sensitive Chinese hamster cells.

The mechanism of the synthetic isoprenoid N-solanesyl-N,N'-bis(3,4-dimethoxybenzyl)ethylenediamine (SDB-ethylenediamine) in potentiating antitumor drug action against multidrug-resistant cells was comparatively studied with other potentiators such as verapamil and cepharanthine. SDB-ethylenediamine increased the accumulation of [3H]daunorubicin (DNR) in Chinese hamster V79 (V79/S) and its multidrug-resistant mutant (V79/ADM) cells. Even after SDB-ethylenediamine was removed from the medium, its effect continued. But when verapamil was removed from the medium, its effect disappeared immediately. Unlike verapamil and cepharanthine, SDB-ethylenediamine did not greatly inhibit the efflux of [3H]DNR from V79/ADM, the binding of [3H]vinblastine to membrane vesicles of V79/ADM, or the binding of [3H]azidopine to P-glycoprotein in the cytoplasmic membrane of V79/ADM. It did stimulate the influx of [3H]DNR into the ATP-depleted cells of V79/S and V79/ADM. Thus, SDB-ethylenediamine uniquely potentiates antitumor drugs. The increased intracellular accumulation of antitumor drugs in the presence of SDB-ethylenediamine is due not only to the inhibition of active efflux but also to the stimulation of the influx of antitumor drugs.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1990

Synergistic effect in culture of bleomycin-group antibiotics and N-solanesyl-N,N'-bis(3,4-dimethoxybenzyl)ethylenediamine, a synthetic isoprenoid.

Like bleomycin and peplomycin, libromycin, a newly developed bleomycin-group antibiotic, was potentiated 130-fold against Chinese hamster V79 cells (V79/S) and 47-fold against its multidrug-resistant mutant (V79/ADM) by N-solanesyl-N,N'-bis(3,4-dimethoxybenzyl)ethylenediamine (SDB-ethylenediamine) at 10 and 3 micrograms/ml, respectively. But neocarzinostatin, known to cause DNA strand scission as bleomycins do, was potentiated only twofold. This suggests that the high potentiation by SDB-ethylenediamine is unique to the bleomycin-group antibiotics. Isobologram analysis revealed that the combined effect of peplomycin and SDB-ethylenediamine was highly synergistic. SDB-ethylenediamine did not increase the intracellular accumulation of [3H]peplomycin in V79/S cells. Analyses by an alkaline elution method demonstrated that single strand scission in DNA of intact V79/S cells caused by 1-h incubation with peplomycin was greatly stimulated by pre- and co-existence of SDB-ethylenediamine, but DNA strand breaks in isolated nuclei were not affected. Apparently some cytoplasmic constituent(s) is involved in the potentiation mechanism. SDB-ethylenediamine did not block the DNA repair which occurred after the removal of peplomycin from the medium. Two fragments of SDB-ethylenediamine, solanesol (polyprenoid moiety) and a diamine component (verapamil-like moiety), were not synergistic with peplomycin, even when they were mixed together. This indicates that the steric conformation of the intact SDB-ethylenediamine molecule is important for the activity.

Animals↗
PubMed1990

Cytocidal activity of a synthetic isoprenoid, N-solanesyl-N,N'-bis(3,4-dimethoxybenzyl)ethylenediamine, and its potentiation of antitumor drugs against multidrug-resistant and sensitive cells in vitro.

A synthetic isoprenoid, N-solanesyl-N,N'-bis(3,4-dimethoxybenzyl)ethylenediamine (SDB-ethylenediamine), inhibited the colony formation of multidrug-resistant mutant cell lines derived from Chinese hamster V79 (V79/ADM) and human hepatoma PLC/PRF/5 (PLC/COL) cells to a greater extent than that of the parental cells. When combined with other clinically useful antitumor agents, it potentiated the cytotoxic activity of almost all kinds of drugs tested including adriamycin (ADM), actinomycin D, vincristine, cytosine arabinoside, and 5-fluorouracil (5-FU), and the potentiation ratios were higher against V79/ADM cells than against V79/S cells. Among the antitumor agents tested, the activities of bleomycin-group antibiotics were more strongly enhanced by SDB-ethylenediamine and the potentiation was higher in the parental cells than in V79/ADM cells. SDB-ethylenediamine enhanced the uptake of ADM and daunorubicin into V79/ADM and its parental cells, but it did not increase the uptake of 5-FU or peplomycin, indicating that different mechanisms operate for potentiation in the cases of the latter drugs, i.e., not simply an increase of intracellular drug uptake. Two fragments of SDB-ethylenediamine, solanesol (polyprenoid moiety) and the diamine component (verapamil-like moiety), showed neither cytotoxic activity nor potentiator activity, even if they were mixed together, indicating that the steric conformation of intact SDB-ethylenediamine molecule is important for these two activities.

Animals↗
PubMed1990

Resorthiomycin, a novel antitumor antibiotic. III. Potentiation of antitumor drugs and its mechanism of action.

Resorthiomycin suppressed the clonogenic activity of a multidrug-resistant mutant cell line of Chinese hamster V79 cells more potently than its parental cells. Moreover, resorthiomycin at 40 micrograms/ml potentiated the cytotoxic activity of vincristine and actinomycin D on V79 cells over 3-fold. Uptake of [3H]actinomycin D into V79 cells was stimulated 2-fold by 40 micrograms/ml of resorthiomycin during 2 hours incubation. On the other hand, incorporation of [3H]thymidine and [3H]uridine into mouse leukemia L5178Y cells was inhibited in a dose-dependent manner at resorthiomycin concentrations ranging from 5 to 40 micrograms/ml. In ATP-depleted L5178Y cells, membrane transport of [3H]thymidine and 2-[3H]deoxyglucose was strongly suppressed by resorthiomycin. These results suggest that resorthiomycin acts on the plasma membrane and perturbes some membrane function.

Animals↗