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P J Tofilon

Publications and source records attributed to P J Tofilon.

At least 73 records · Page 4Linked to original sources
PubMed1986

cis-Diamminedichloroplatinum(II)-induced sister chromatid exchange: an indicator of sensitivity and heterogeneity in primary human tumor cell cultures.

The effect of cis-diamminedichloroplatinum(II) (cPt) on sister chromatid exchange (SCE) induction was determined in 13 human primary tumor cell cultures. Primary cultures were derived from surgical specimens of solid tumors composed of a variety of histologies. Three to 16 days after biopsy, depending on the growth rate, cultures were treated with graded concentrations of cPt for 1 h and the SCE assay was performed. SCE dose-response curves (SCEs induced per chromosome versus cPt concentration) showed a wide range in cPt sensitivities that was not dependent on histology. SCE frequency histograms showed that several of the primary cultures contained both cPt-sensitive and -resistant cells. For six of the cultures, the SCEs induced per chromosome at 15 microM cPt were plotted versus the IC90 determined from a survival assay. A line fit to those points yielded a correlation coefficient of -0.74. These results show a relationship between the activity of cPt in the SCE assay and in the survival assay, which suggests that SCE analysis may be useful for predicting cPt sensitivity. In addition, characterization of cellular heterogeneity in cPt sensitivity using the SCE assay may provide additional information useful in the prediction of tumor response to treatment.

Cell Survival↗
PubMed1986

Prediction of human tumor cell chemosensitivity using the sister chromatid exchange assay.

The sister chromatid exchange (SCE) assay has been used to predict the chemosensitivity to 1,3-bis(2-chloroethyl)-1-nitrosourea of various neoplastic cell subpopulations in eight cell lines derived from human brain tumors. Because the SCE assay is based on analysis of individual cells, data obtained can be plotted as frequency histograms of SCEs per chromosome, and the range of chemosensitivities of cell subpopulations can be identified easily. Results suggest that the SCE assay has predictive value as a clinical assay for drugs for which a strong correlation between cell kill and induction of SCEs has been established.

Brain Neoplasms↗
PubMed1985

Comparative study of the effects of hyperthermia and BCNU on BCNU-sensitive and BCNU-resistant 9L rat brain tumor cells.

1,3-Bis(2-chloroethyl)-1-nitrosourea (BCNU)-sensitive and BCNU-resistant 9L rat brain tumor cells were treated with BCNU at graded temperatures between 37 and 44 degrees C. The cytotoxic effects of hyperthermia alone on both cell lines were the same. Treating both cell lines with BCNU at temperatures above 37 degrees C caused a progressive increase in cell kill. All survival curves for drug-sensitive cells had shoulders followed by a region of exponential cell kill; dose enhancement ratios calculated at the 10% survival level ranged from 1.7 to 3.0. Survival curves for drug-resistant cells were exponential without a shoulder; dose enhancement ratios ranged from 3.3 to 8.4. For each cell line, a similar amount of the increased cell kill could be explained on the basis of the increases concentration of reactive species produced by hydrolysis of BCNU at elevated temperatures. The amount of cell kill that cannot be explained on this basis, however, suggests that factors other than an increase in the concentration of reactive species at higher temperatures are involved in the enhanced cell killing. Possible mechanisms include a heat-induced change in the structure of DNA chromatin and the effect of isocyanate deactivation of repair enzymes, both of which could lead to an increase in the number of crosslinks formed and therefore to an increase in cytotoxicity.

Animals↗
PubMed1985

Effects of hyperthermia on DNA interstrand crosslinking after treatment with BCNU in 9L rat brain tumor cells.

The effects of hyperthermia (42 degrees C) on 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU)-mediated DNA interstrand crosslink formation were investigated in 9L rat brain tumor cells using the technique of alkaline elution. When cells were treated with 60 microM BCNU for 1 hr at 37 degrees C and incubated for 6 hr in drug-free medium at 42 degrees C, there was a 50% increase in crosslinking; and when cells were treated at 42 degrees C and incubated at 37 degrees C, there was a 45% increase in crosslinking compared with the results for cells treated and incubated at 37 degrees C. When cells were treated and incubated at 42 degrees C, there was a 129% increase in DNA crosslinking. The same relative order of results was found for cell survival. These results suggest that hyperthermia can increase DNA interstrand crosslink formation and the consequent cell death through two independent mechanisms: an increase in the amount of initial alkylation because of the increased rate of hydrolysis of BCNU at higher temperatures, and the effect of heat on DNA structure that leads to an increase in the number of crosslinks formed.

Animals↗
PubMed1985

Prediction of in vivo tumor response to chemotherapeutic agents by the in vitro sister chromatid exchange assay.

The ability of the in vitro sister chromatid exchange (SCE) assay to predict in vivo tumor drug sensitivity was investigated using a spontaneous hepatocarcinoma in C3Hf/Kam mice and 3 chemotherapeutic agents: melphalan; cis-platinum; and 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). For hepatocarcinoma cells grown in monolayer culture, melphalan was the most efficient at inducing SCEs, and BCNU, the least. cis-Platinum induced a range in SCEs that overlapped those of BCNU and melphalan, suggesting that hepatocarcinoma is not a homogeneous population with intermediate sensitivity, but is a mixture of cis-platinum-sensitive and -resistant cells. According to in vitro cell survival curves, hepatocarcinoma was most sensitive to melphalan, less sensitive to cis-platinum, and essentially resistant to BCNU. The relative antineoplastic effects of melphalan, cis-platinum, and BCNU in vivo were compared by the response of artificial and spontaneous pulmonary metastases and solid tumors to these agents. For artificial metastases, there was a dose-dependent decrease in the number of lung nodules in mice treated with melphalan or cis-platinum, with melphalan being the more effective. BCNU had no effect. Spontaneous pulmonary metastases generated from hepatocarcinoma leg tumors were reduced in those mice treated with melphalan, unaffected by cis-platinum, and increased by BCNU. In hepatocarcinoma leg tumors (5 to 6 mm in diameter), melphalan induced the longest growth delay, and BCNU the least. Therefore, the relative effects produced by these three drugs in vivo were the same as predicted by SCE induction in vitro. The SCE assay may thus have potential clinical application.

Animals↗
PubMed1984

Effect of cell-cell interactions on drug sensitivity and growth of drug-sensitive and -resistant tumor cells in spheroids.

Multicellular spheroids were grown from mixtures of rat brain tumor cells sensitive (9L) and resistant (R3) to 1,3-bis(2-chloroethyl)-1-nitrosourea. Percentages of each cell subpopulation in these spheroids were estimated with the sister chromatid exchange assay and were found to be approximately the same as those used to initiate spheroids. Spheroids grown from 9L cells alone had a higher growth rate than spheroids grown from R3 cells alone. However, the growth rate of mixed-cell spheroids was essentially the same as that of pure 9L spheroids and was independent of the percentages of R3 cells in mixed-cell spheroids. The sensitivity of 9L cells in mixed-cell spheroids treated with 1,3-bis(2-chloroethyl)-1-nitrosourea, estimated by changes in the number of sister chromatid exchanges per metaphase induced by treatment, decreased as the percentage of R3 cells increased. These effects are probably the result of an interaction between the two cell subpopulations held in three-dimensional contact, a situation similar to that in tumors in situ. The results suggest why one cell subpopulation of tumors does not become dominant during growth and indicate that interactions between cell subpopulations can influence the sensitivity of one subpopulation to 1,3-bis(2-chloroethyl)-1-nitrosourea.

Animals↗
PubMed1984

Prediction of the relative in vitro sensitivity of 9L rat brain tumor cells to nitrosoureas by the sister chromatid exchange assay.

In an earlier study we showed that there is a good correlation between sister chromatid exchange induction and cell kill in 9L cells treated with certain nitrosoureas. In the study reported here, we treated four 9L cell lines that have different sensitivities to chloroethylnitrosoureas with 1,3-bis (2-chloroethyl)-1-nitrosourea, chlorozotocin, and ethylnitrosourea and determined the number of sister chromatid exchanges induced. Cell lines that were most sensitive to the drugs with respect to cell kill were also most sensitive to induction of sister chromatid exchanges for a given drug, and the assay based on sister chromatid exchange is therefore predictive of the relative sensitivity of these cells to the drugs used.

Animals↗
PubMed1984

Detection of heterogeneity in the chemosensitivity of 9L brain tumor cell lines to 1,3-bis (2-chloroethyl)-1-nitrosourea by the sister chromatid exchange assay.

To investigate the potential use of the sister chromatid exchange assay to analyze the heterogeneity of drug response among tumor cell subpopulations, mixtures of 1,3-bis (2-chloroethyl)-1-nitrosourea-sensitive (9L) and -resistant (9L2) rat brain tumor cells were treated in vitro with 2 microM 1,3-bis (2-chloroethyl)-1-nitrosourea. When data were plotted as histograms representing the number of cells vs sister chromatid exchanges/metaphase, two regions corresponding to the 9L and 9L2 populations were obtained. The approximate percentages of 9L and 9L2 in each mixture could be predicted from these histograms. While these results were obtained with a limited model chosen for its simplicity, they suggest that the sister chromatid exchange assay may be useful in the analysis of heterogeneity in drug sensitivity among cell subpopulations in a tumor.

Animals↗
PubMed1984

BCNU-induced sister chromatid exchanges are increased by X irradiation.

We have studied the effect on sister chromatid exchange (SCE) induction in 9L rat brain tumor cells caused by combination treatment with BCNU and X rays. Over the dose and concentration ranges used in these experiments, BCNU induced relatively large numbers of SCEs, while X rays induced few SCEs. When cells were X irradiated immediately after BCNU treatment, the number of SCEs induced was greater than the number of SCEs expected by adding the number of SCEs induced by each agent alone; the number of SCEs induced as a result of this BCNU-X-ray interaction increased as the concentration of BCNU and/or dose of X rays increased. When the addition of bromodeoxyuridine was delayed from 0 to 16 hr after BCNU treatment, the number of SCEs induced declined to control levels by 16 hr. If X irradiation was delayed for up to 16 hr after BCNU treatment the same pattern of decrease was observed; the number of SCEs induced at each time point, however, was greater than that induced by BCNU and X rays alone. X irradiation from 0-16 hr before BCNU treatment produced the same number of SCEs as that produced by BCNU alone. Thus the SCE assay is capable of detecting a drug-X-ray interaction in mammalian cells and provides a sensitive means of studying the sequencing and timing that leads to the interaction.

Animals↗
PubMed1984

The effects of X rays on BCNU-induced DNA crosslinking.

We have used the technique of alkaline elution to study DNA interstrand crosslinking in 9L rat brain tumor cells treated with combinations of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and X rays. Irradiation with doses as low as 50 rad of X rays immediately or 6 hr after a 1-hr treatment with 60, 80, or 100 microM BCNU produced a significant increase in BCNU-induced DNA interstrand crosslinking. If cells were irradiated before BCNU treatment, the amount of crosslinking was not affected compared with BCNU alone. Cell survival experiments using 600 rad of X rays and 1-hr treatments with 0-30 microM BCNU were also performed. As found in the crosslinking studies, irradiation immediately or 6 hr after the BCNU treatment produced enhanced cell kill, but irradiation 6 hr before BCNU treatment did not produce enhanced cell kill. Therefore, the X-ray-mediated increase in BCNU-induced DNA interstrand crosslinking may be the mechanism through which cell kill is increased by combination treatment with the agents.

Animals↗
PubMed1983

alpha-Difluoromethylornithine-induced polyamine depletion of 9L tumor cells modifies drug-induced DNA cross-link formation.

Depletion of intracellular levels of polyamines, which are believed to have a role in the intranuclear stabilization of DNA, alters the cytotoxicity of 1,3-bis(2-chloroethyl)-1-nitrosourea and cis-diamminedichloroplatinum II in 9L rat brain tumor cells. Alkaline elution techniques were used to show that polyamine depletion alters the number of DNA cross-links formed by these cytotoxic agents.

Animals↗
PubMed1983

Differential potentiation of 1,3-bis(2-chloroethyl)-1-nitrosourea by alpha-difluoromethylornithine in chloroethylnitrosourea-sensitive and -resistant 9L rat brain tumor cells in vitro.

alpha-Difluoromethylornithine, an enzyme-activated, irreversible inhibitor of ornithine decarboxylase, inhibited the growth of both chloroethylnitrosourea-sensitive and -resistant 9L rat brain tumor cells in vitro. After 48 hr of treatment with 10 mM alpha-difluoromethylornithine, the putrescine and spermidine contents of both resistant and sensitive cells were less than 5% of control levels, but the spermine level was slightly elevated. The cytotoxicity of 1,3-bis(2-chloroethyl)-1-nitrosourea, as measured by a colony-forming efficiency assay, was significantly increased in alpha-difluoromethylornithine-pretreated sensitive cells but not in resistant cells treated with this polyamine inhibitor. With the sister chromatid exchange assay, we found that alpha-difluoromethylornithine pretreatment increased 1,3-bis(2-chloroethyl)-1-nitrosourea-induced damage to chromosomes in sensitive but not in resistant cells.

Animals↗
PubMed1983

Comparison of the sister chromatid exchange and cell survival assays as a measure of tumor cell sensitivity in vitro to cis-diamminedichloroplatinum (II).

Cytotoxic effects of treating RIF-1, EMT6, and 9L tumor cell lines with cis-diamminedichloroplatinum(II) were measured with the sister chromatid exchange assay and compared to results obtained with the colony-forming efficiency assay. The greatest number of sister chromatid exchanges was induced in RIF-1 cells, fewer in EMT6 cells, and the least in 9L cells. Cell survival data obtained with the colony-forming efficiency assay paralleled data obtained with the sister chromatid exchange assay. These studies suggest that the sister chromatid exchange assay may be a useful method with which to determine the in vitro sensitivity of tumor cells to some antineoplastic agents.

Animals↗
PubMed1983

Nitrosourea-induced sister chromatid exchanges and correlation to cell survival in 9L rat brain tumor cells.

The ability of various nitrosoureas to induce sister chromatid exchanges (SCEs) in 9L rat brain tumor cells was investigated. Treatment of cells for 1 hr with the alkylating and cross-linking agents 1,3-bis(2-chloroethyl)-1-nitrosourea or chlorozotocin produced concentration-dependent increases in SCEs; elevations above controls were detected at concentrations of 1 microM or more. Above 0.25 mM, the alkylating agent ethylnitrosourea produced a dose-dependent increase in SCEs. Treatment with the carbamoylating agent 1,3-bis(trans-4-hydroxycyclohexyl)-1-nitrosourea did not induce SCEs. The maximum drug concentration at which SCEs are readily scored kills approximately 50% of cells. When accurate cell survival data in this dose range were obtained, a direct correlation between nitrosourea-induced cell kill, measured by a colony-forming efficiency assay, and SCE induction was found. Thus, analysis of the levels of SCE production may provide information about the efficacy of antineoplastic drugs.

Animals↗
PubMed1982

2,3,7,8-Tetrachlorodibenzo-p-dioxin-mediated depression of rat testicular heme synthesis and microsomal cytochrome P-450.

Exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) produces hirsutism, alopecia, and chloracne, symptoms that suggest a possible alteration of endocrine function. Therefore, the effects of TCDD on rat testicular cytochrome P-450 content were investigated. Forty-eight hours after a single, oral dose of TCDD (25 microgram/kg) testicular microsomal cytochrome P-450 levels were depressed by approximately 24%. Microsomal cytochrome P-450 continued to decrease to 62% of control levels at 4 days and remained at approximately the same levels 7 days following treatment. Testicular microsomal heme content exhibited a similar pattern after administration of TCDD. No alterations in testicular delta-aminolevulinic acid (ALA) synthase were detected. The incorporation of [14C]ALA into microsomal heme was decreased to approximately 36% of control values at 24 hr after TCDD administration. Testicular weights were not altered during the 7-day experimental period. These data suggest that TCDD depresses cytochrome P-450 levels in the rat testis through an inhibition of the synthesis of testicular heme.

5-Aminolevulinate Synthetase↗
PubMed1982

Inhibition of rat testicular heme synthesis and depression of microsomal cytochrome P-450 by estradiol benzoate.

Twenty-four hours after a single dose (50 microgram, s.c.) of estradiol benzoate (EB), rat testicular microsomal heme and cytochrome P-450 were decreased to 72 and 76% of control levels respectively. Treatment of rats with human chorionic gonadotropin (hCG) resulted in elevated levels of microsomal heme and cytochrome P-450 and increased activity of delta-aminolevulinic acid (ALA) synthase (EC 2.3.1.37). However, the hCG-mediated elevations of testicular microsomal heme and cytochrome P-450 content failed to occur in animals treated with EB. To investigate the possibility that the observed effect of EB was mediated through the pituitary, studies were conducted with hypophysectomized animals. The increased microsomal heme and cytochrome P-450 content mediated by hCG in hypophysectomized animals was again prevented by administration of EB. The elevated activity of testicular mitochondrial ALA synthase produced by hCG in both intact and hypophysectomized animals was not affected by EB. Incorporation of [14C]ALA into microsomal heme was depressed 60% 12 hr following a single dose of EB (50 microgram, s.c.). These data suggest that EB depresses testicular microsomal heme and cytochrome P-450 content by inhibiting the synthesis of heme at an enzymatic reaction other than ALA synthase.

5-Aminolevulinate Synthetase↗
PubMed1982

Polyamine depletion influences drug-induced chromosomal damage.

Polyamines have been implicated in the intracellular stabilization of DNA. Depletion of intracellular polyamines influences the cytotoxicity of 1,3-bis(2-chloroethyl)-1-nitrosourea and cis-diamminedichloroplatinum II. By means of the sister chromatid exchange assay, it was found that intracellular polyamine depletion can also alter the induction of chromosomal damage by these cytotoxic agents.

Animals↗