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C Lipschultz

Publications and source records attributed to C Lipschultz.

7 recordsLinked to original sources
PubMed1995

Enhanced glutathione peroxidase expression protects cells from hydroperoxides but not from radiation or doxorubicin.

Both radiation and anthracycline antibiotics may produce reactive oxygen species to cause cytotoxicity, and it has been suggested that some cellular antioxidant enzymes may be important for resistance to these agents. The human breast adenocarcinoma cell line MCF-7WT has a low level of glutathione peroxidase (GPX) activity. We have transfected MCF-7WT cells with a plasmid that contains the cDNA for human GPX under the transcriptional control of the human metallothionein IIA promoter. One transfected clone, MCF-GPX-6, contained multiple copies of GPX cDNA/cell and, after exposure to heavy metals, expressed a level of GPX enzyme activity that was 40-fold higher than that present in MCF-7WT cells and comparable to the GPX activity contained in the doxorubicin-resistant MCF-7DOX cell line. No differences in levels of glutathione, catalase, superoxide dismutase, glutathione S-transferase, or glutathione reductase were noted in MCF-GPX-6 cells compared to MCF-7WT cells. MCF-GPX-6 cells were relatively resistant to hydrogen peroxide and tert-butylhydroperoxide compared to MCF-7WT cells, e.g., exposure of both cell lines to 750 microM H2O2 for 1 h resulted in a relative surviving fraction of 0.07 for MCF-7WT and 0.35 for MCF-GPX-6 cells. However, no difference in sensitivity to either radiation or doxorubicin was noted between MCF-7WT and MCF-GPX-6 cells. These results suggest that GPX is not important for the development of cellular resistance to either radiation or doxorubicin.

Antibiotics, Antineoplastic↗
PubMed1994

The influence of Cremophor EL on the cell cycle effects of paclitaxel (Taxol) in human tumor cell lines.

We have performed DNA flow analysis, mitotic index studies, time-lapse photography, and paclitaxel uptake studies of human tumor cell lines exposed to paclitaxel. DNA flow analysis demonstrated that cells began accumulating in G2/M within 6 hrs of exposure to paclitaxel; by 12 hrs over 50% of cells accumulated in G2/M at all concentrations tested. After 24 hrs of exposure to 10 nM paclitaxel, cells underwent non-uniform mitotic division resulting in multinucleated cells. Of cells treated with 30 nM to 1000 nM paclitaxel, 75% to 85% remained blocked in G2/M for up to 72 hrs. Although a large proportion of cells treated with higher concentrations of paclitaxel (10,000 nM) was blocked in G2/M, a significant proportion (10% to 40%) of these cells was also in G1. Cells exposed to lower concentrations of paclitaxel (10 nM to 1000 nM) in medium containing 0.135% (v/v) Cremophor EL also had a relatively large proportion in G1. Mitotic index studies demonstrated that the paclitaxel-induced G2/M block was initially a mitotic block and that cells remained in mitosis for up to 24 hrs. With additional time of exposure to paclitaxel, mitotic index and time-lapse studies indicated that cells attempted to complete mitosis; however, cytokinesis was inhibited and cells became multinucleated. Time-lapse photography revealed that paclitaxel markedly prolonged the time in mitosis from 0.5 hr to 15 hr. High levels of Cremophor EL (0.135% v/v) markedly reduced the number of cells in mitosis but did not alter the mitotic delay induced by paclitaxel. 3H-paclitaxel uptake studies revealed that high concentrations of Cremophor EL did reduce the rate of uptake of paclitaxel into cells but had little effect on total paclitaxel accumulation. These results confirm that paclitaxel has striking effects on the cell cycle and show that high concentrations of Cremophor EL are capable of inducing a cell cycle block distinct from the mitotic block seen with paclitaxel. These results also demonstrate that cells exposed to paclitaxel for longer than 24 hours attempt to complete mitosis but the process of cytokinesis is inhibited. Together with cytotoxicity data, these results indicate that entry into and exit out of mitosis are prerequisites for paclitaxel cytotoxicity.

Adenocarcinoma↗
PubMed1993

Glutathione depletion by L-buthionine sulfoximine antagonizes taxol cytotoxicity.

Taxol is a naturally occurring chemotherapeutic agent that is active against a variety of tumors. Taxol is believed to act by binding tightly to microtubules and preventing their disaggregation. Others have shown that depletion of cellular glutathione results in the disaggregation of microtubules, presumably by allowing the oxidation of some or all of the cysteine residues in tubulins. We studied the effect of glutathione (GSH) depletion by L-buthionine sulfoximine (L-BSO) on taxol cytotoxicity in two human tumor lines. After a 24-h incubation in 5 mM L-BSO, the breast adenocarcinoma line MCF-7 and the lung adenocarcinoma line A549 were exposed to varying concentrations of taxol for 24 h. GSH levels were undetectable in cells treated with L-BSO. At the highest concentrations of taxol (50 nM), control MCF-7 cells had 10% cell survival and control A549 cells had only 1% cell survival as assessed by clonogenic assay. Pretreatment with 5 mM L-BSO resulted in a 3-fold increase in survival of MCF-7 cells and a 10-fold increase in survival of A549 cells. Pretreatment with L-BSO had no effect on taxol uptake into A549 or MCF-7 cells, as assessed by measurement of binding of [3H]taxol to cells. Following exposure to 37 nM taxol for 24 h, both cell lines had over 80% of their population in G2/M and bromodeoxyuridine labeling showed that taxol markedly reduced the percentage of cells in S phase. L-BSO pretreatment had no effect on the cell cycle in either cell line in the absence of taxol. However, in cells treated with taxol, L-BSO increased the percentage of cells in S phase by 3-fold in both cell lines. We conclude that depletion of cellular GSH by L-BSO results in resistance to taxol in MCF-7 and A549 cells. Resistance to taxol mediated by GSH depletion is not due to alterations in cellular uptake of taxol by L-BSO. L-BSO increased the S-phase fraction of taxol-treated cells in both cell lines. These data suggest that GSH depletion interferes with cell cycle changes induced by taxol. The alteration in taxol-induced cell cycle effects may account for the resistance to taxol produced by L-BSO.

Buthionine Sulfoximine↗
PubMed1993

Cytotoxic studies of paclitaxel (Taxol) in human tumour cell lines.

The cytotoxicity of paclitaxel against eight human tumour cell lines has been studied with in vitro clonogenic assays. The fraction of surviving cells fell sharply after exposure for 24 h to paclitaxel concentrations ranging from 2 to 20 nM; the paclitaxel IC50 was found to range between 2.5 and 7.5 nM. Increasing the paclitaxel concentration above 50 nM, however, resulted in no additional cytotoxicity after a 24 h drug exposure. Cells incubated in very high concentrations of paclitaxel (10,000 nM) had an increase in survival compared with cells treated with lower concentrations of the drug. Prolonging the time of exposure of cells to paclitaxel from 24 to 72 h increased cytotoxicity from 5 to 200 fold in different cell lines. Exponentially growing cells were more sensitive to paclitaxel than were cells in the plateau phase of growth. Cremophor EL, the diluent in which the clinical preparation of paclitaxel is formulated, antagonised paclitaxel at concentrations of 0.135% (v/v). These data suggest that paclitaxel will be most effective clinically when there is prolonged exposure of tumour to the drug. Further, it appears that modest concentrations (i.e., 50 nM) should be as effective as higher concentrations of paclitaxel. Finally, we have noted that Cremophor EL is a biologically active diluent and, at high concentrations (0.135% v/v), can antagonise paclitaxel cytotoxicity.

Adenocarcinoma↗
PubMedDate not supplied

The silent deceiver.

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Decision Making, Organizational↗