Biomedical subjects

Y M Rustum

Publications and source records attributed to Y M Rustum.

At least 109 records · Page 6Linked to original sources

PubMed1992

Pharmacologic rationale for fluoropyrimidine-leucovorin combination: biochemical mechanisms.

Fluoropyrimidines, 5-fluorouracil (5-FU), and 5-fluorodeoxyuridine (FdUrd) are effective inhibitors of DNA synthesis. Inhibitory action is potentiated both in vitro and in vivo by the addition of leucovorin (LV; either the natural [6S] isomer or the mixture of the unnatural and natural [6R,S] isomers). The inhibition of DNA is subsequent to thymidylate synthase inhibition mediated by the formation of a covalently bound ternary complex consisting of 5-fluorodeoxyuridine monophosphate, 5,10-methylenetetrahydrofolate, and thymidylate synthase. In vitro exposure of cells to varying concentrations of [6R,S]LV or [6S]LV increases intracellular pools of the reduced folate cofactor. The effect of [6S]LV is both dose and time dependent. The in vitro effective concentration of [6S]LV is approximately 1 to 10 mumol/L, depending on cell type. While HCT-8 cells demonstrated optimal modulation of 5-FU and FdUrd cytotoxicity with 1 mumol/L of [6S]LV for 5 hours, the SE cells required higher doses of LV and longer exposure time. Thus, dependent on the cell type, higher concentration (10 mumol/L) and duration of exposure (greater than 5 hours) may be essential for an effective modulation of fluoropyrimidine action. Clinically, to achieve the concentration and conditions found optimal in an in vitro system, a dose of 500 mg/m2 by 5-hour infusion appears to be the present optimal dose and schedule of [6R,S]LV administration in combination with 5-FU.

Cecal Neoplasms↗

PubMed1992

Modulation of fluoropyrimidines: role of dose and schedule of leucovorin administration.

The biochemical modulation of 5-fluorouracil (5-FU) and 5-fluoro-2'-deoxyuridine (FdUrd) by leucovorin (LV) has resulted in a significant improvement of the antitumor activity in a variety of malignancies. Although this combination is frequently used, the optimal dose and schedule of LV remains to be determined. In vitro studies with human colon carcinoma (HCT-8) and renal carcinoma (SE) cells show that the increase of intracellular folate pools by LV is dose and time dependent and varies significantly between cell lines. While HCT-8 cells showed optimal modulation of FdUrd cytotoxicity with 1 mumol/L [6S]LV for 5 hours, SE cells required 10 mumol/L [6S]LV for 5 days. Clinical data indicate that low doses of [6R,S]LV (20 mg/m2) might be equivalent to higher doses (200 to 500 mg/m2) when 5-FU is given on 5 consecutive days, whereas doses of 200 mg/m2 might be necessary when 5-FU chemotherapy is given once weekly. Unless biochemical assays to assess a patient's individual needs of LV become available, the use of higher (200 to 500 mg/m2) doses might offer the best chance to effectively modulate 5-FU clinically.

Clinical Trials as Topic↗

PubMed1992

Mechanisms of resistance to fluoropyrimidines.

The fluoropyrimidines fluorouracil (5-FU) and 5-fluoro-2'-deoxyuridine (FdUrd) have shown activity in a variety of malignancies. Nevertheless, even in initially responsive tumors, the development of resistance is a frequent problem. To understand the biochemical basis for acquired resistance, two pairs of cell lines were investigated. MCF7/Adr cells were obtained from the breast cancer cell line MCF7 by incubation with increasing concentrations of Adriamycin (doxorubicin; Adria Laboratories, Columbus, OH). These cells are resistant to Adriamycin (200- to 600-fold) and cross-resistant to 5-FU (25-fold) and FdUrd (67-fold). The resistant cells showed significantly increased levels of thymidylate synthase, the target enzyme of the fluoropyrimidines' active metabolite, 5-fluoro-2'-deoxyuridine-5'-monophosphate (FdUMP). Other biochemical characteristics, including folate pools, drug uptake, metabolism, and retention, were unchanged. Fd9XR cells have been selected from a human colon cancer cell line (HCT-8) by exposure to FdUrd. These cells are resistant to FdUrd (1,000-fold) but not 5-FU. Biochemical evaluations show that the resistant cells are deficient of thymidine kinase and are thus unable to convert FdUrd to FdUMP. This understanding of the various biochemical mechanisms is essential for the design of specific modulations to overcome resistance to fluoropyrimidines.

Cecal Neoplasms↗

PubMed1992

Quantitation of dihydrofolate reductase and thymidylate synthase mRNAs in vivo and in vitro by polymerase chain reaction.

Rapid and quantitative polymerase chain reaction (PCR) assays based upon the competitive template technique have been developed for human dihydrofolate reductase (DHFR; E.C.1.5.1.3) and thymidylate synthase (TS; E.C.2.1.1.45) mRNAs. In various tumor cell lines and clinical tumor biopsies, TS mRNA levels correlated with TS levels as determined by [3H]-fluorodeoxyuridylate binding. Levels of DHFR and TS mRNAs, determined by PCR, correlated with mRNA quantitation by conventional dot blot methodology. The ratio of TS/DHFR mRNAs in a number of human carcinoma cell lines varies from 0.4 to 9.9 but ranges from 1 to greater than 1.5 x 10(3) in a number of tumor samples. Differences in the TS/DHFR mRNA ratio in tumors as compared with cultured cells reflects low levels of DHFR mRNA in some tumors. In patients treated with a combination of 5-fluorouracil and leucovorin, mRNA levels for TS increased approximately an order of magnitude in tumor samples 4 and 24 hr after drug treatment, whereas TS levels decreased. These results have significance for the biochemical pharmacology of antifolates and fluorinated pyrimidines in vivo and the relevance of cell culture models for antifolate chemotherapy and drug resistance.

Base Sequence↗

PubMed1991

Effects of diastereoisomers of 5-formyltetrahydrofolate on cellular growth, sensitivity to 5-fluoro-2'-deoxyuridine, and methylenetetrahydrofolate polyglutamate levels in HCT-8 cells.

We investigated the biological activities of the natural and unnatural diastereoisomers of 5-formyltetrahydrofolate [(6S)- and (6R)-5-HCO-H4PteGlu, respectively, both 99.99% pure], using a human ileocecal carcinoma cell line (HCT-8). Optimal cell growth could be supported by (6S)-5-HCO-H4PteGlu at concentrations as low as 1 nM. (6R)-5-HCO-H4PteGlu did not support growth. Modulation of the in vitro cytotoxicity of 5-fluoro-2'-deoxyuridine (FdUrd) and intracellular (6R)-5,10-methylenetetrahydrofolates [(6R)-CH2H4PteGlun] pools by (6S)- and (6R)-5-HCO-H4PteGlu was determined with cells growing in 1 nM (6S)-5-HCO-H4PteGlu. For the control cells, the concentration of FdUrd inhibiting growth by 50% was 179 nM and the total (6R)-CH2H4PteGlun was 2.3 pmol/10(6) cells. When cells were treated with (6S)-5-HCO-H4PteGlu for 24 h, the 50% inhibition concentration of FdUrd decreased with increasing concentrations of (6S)-5-HCO-H4PteGlu, and reached a plateau of 36 nM when (6S)-5-HCO-H4PteGlu was greater than or equal to 1 microM. The total (6R)-CH2H4PteGlun pools were augmented by (6S)-5-HCO-H4PteGlu dose dependently up to 6.8 pmol/10(6) cells at 1 microM (6S)-5-HCO-H4PteGlu. (6S)-5-HCO-H4PteGlu at 10 microM did not further increase the total (6R)-CH2H4PteGlun, but induced a marked shift in the polyglutamate chain length distribution, with an increase in tri- and tetra-, and a decrease in penta-, hexa-, and heptaglutamate. The down-shift of (6R)-CH2H4-PteGlun polyglutamate chain length observed after (6S)-5-HCO-H4PteGlu treatment did not impair the modulation of FdUrd cytotoxicity. Thus shorter chain (6R)-CH2H4PteGlua (n = 3-4) function as well as longer ones (n = 5-7). (6R)-5-HCO-H4PteGlu, at 200 microM, had no effect on the cytotoxicity of FdUrd, the total (6R)-CH2H4PteGlun level, or chain length distribution in the presence or absence of additional (6S)-5-HCO-H4PteGlu. These results suggest that the high plasma (6R)-5-HCO-H4PteGlu concentrations (up to 200 microM) achieved in patients following i.v. administration of high doses of (6R,S)-5-HCO-H4PteGlu probably do not have adverse effects on the modulation of antitumor activity of FdUrd or 5-fluorouracil. Since the optimal dose and schedule of (6S)-5-HCO-H4PteGlu for modulation of fluoropyrimidines may vary from one cell type to another, introducing high doses of (6R,S)-5-HCO-H4PteGlu in patients so that the plasma concentration of the natural isomer reaches 10 microM is still recommended.

Cell Division↗

PubMed1991

Extrachromosomal chromatin: novel target for bleomycin cleavage in cells and solid tumors.

The preference of bleomycin, a DNA strand scission antitumor agent, to damage extrachromosomal (episomal) DNA was investigated. These episomes contain transcriptional promoters, replication origins, and oncogenes from MMTV, BPV, and v-Ha-ras and confer a neoplastic phenotype to a mouse fibroblast cell line. We found that bleomycin induces dose-dependent single- and double-stranded cleavage of intracellular episomes as measured by topological forms conversion. Bleomycin scission of episomes occurs within 1 min, and upon drug removal, damaged episomes are as rapidly repaired. By expressing the episomal and genomic damage as breaks per nucleotide, bleomycin has a 30-50-fold cleavage preference for episomal chromatin compared to genomic DNA. The episomes have preferred regions of the bleomycin-induced damage, particularly within the MMTV LTR and BPV origin of replication. Also, it is possible to assess bleomycin action on episomes in solid tumors in mice. Single intravenous injections of BLM into tumor-bearing mice result in single- and double-stranded cleavage of episomes that are dose related and occur within 1 min. Specific double-stranded breaks occur in the same regulatory regions of episomes in solid tumors and in cultured cells. Finally, we observe that damage to the episomal drug target occurs at therapeutic doses in mice.

Animals↗

PubMed1991

Modulation of fluoropyrimidines by leucovorin: rationale and status.

In recent years the concept of metabolic modulation of fluoropyrimidines by leucovorin has been introduced clinically in patients with advanced colorectal cancer, breast cancer, gastric cancer and head and neck cancer among others. The concept of metabolic modulation was developed in the laboratory and employed clinically. Leucovorin is a noncytotoxic compound used to increase the therapeutic efficacy of 5-fluorouracil. Following 5-fluorouracil activation to 5-fluorodeoxyuridine monophosphates, its binding to thymidylate synthase is stabilized by the active cofactor, 5,10 methylene tetrahydrofolate and its polyglutamate forms. Under these conditions, both the extent and duration of inhibition of thymidylate synthase and consequently, DNA synthesis are more pronounced. The results of clinical trials (phase II and III) indicate that the response rates to 5-fluorouracil/leucovorin modulation are significantly higher than that of fluorouridine alone.

Antineoplastic Combined Chemotherapy Protocols↗

PubMed1991

In vitro study of the interaction of doxorubicin, thiotepa, and mitomycin-C, agents used for intravesical chemotherapy of superficial bladder cancer.

Several cytotoxic agents have been identified as effective in the treatment of superficial transitional cell carcinoma of the bladder, including doxorubicin, thiotepa and mitomycin-C. An in vitro study was conducted to assess the interactions of these three drugs against a well differentiated human bladder tumor cell line, RT-4, to identify and evaluate synergistic combinations among these agents. Cytotoxicity was evaluated by a colorimetric assay based on the capacity of viable cells to metabolize a tetrazolium dye, MTT, to produce a colored formazan product. The analyses of drug interactions were done by the isobolographic method (construction of isoeffect plots). The combination of doxorubicin and thiotepa was found to be the most synergistic, followed by the combination of doxorubicin and mitomycin-C. The combination of mitomycin C and thiotepa demonstrated an unpredictable effect. These findings suggest the combination of doxorubicin and thiotepa has potential advantage for chemotherapy of superficial bladder tumors.

Antineoplastic Agents↗

PubMed1991

A model for mimicking the pharmacokinetics of chemotherapy drugs for evaluation of drug effects in a soft agar colony formation assay system.

Colony formation assay systems are an important part of in vitro drug evaluation. It would be useful if the in vitro drug cytotoxicity could be carried out under conditions mimicking those employed clinically. We have developed an individual colony formation assay system that would allow monitoring and quantitation of the growth of individual colonies (9) in the presence of the drug under conditions of continuous and/or short-term exposure, after plating of the cells in the agarose. In this brief report, we established the pharmacokinetic profile of four drugs, cytosine arabinoside (araC), Doxorubicin (Dox), 5-fluorouracil (5-FUra) and 5-fluoro-2'-deoxyuridine (FdUrd) in agarose mimicking those that are achieved when these agents were administered in vivo as an i.v. push. The results show that short-term treatment in agarose is possible and that the washing procedure of the drugs decreased the drug concentrations 3-4 logs over 44 hours.

Antineoplastic Agents↗

PubMed1991

Rational basis for the metabolic modulation of 5-fluorouracil by leucovorin and interferon alpha.

Although 5-fluorouracil (FUra) has been the drug of choice for the treatment of patients with advanced colorectal carcinoma, the response rates are in the range of 15% and the median survival times do not exceed 9 months. Interferon alpha (IFN alpha) has limited antitumour activity in this disease. Recent clinical trials have demonstrated that both the response rate and the survival time of patients with advanced colorectal cancer can be significantly improved by the addition of leucovorin (CF) to FUra. In a randomized phase III trial, the median response to FUra and CF was about 30% with a range of 20-55%, dependent on the dose and schedule of administration of CF. Due to multiplicity of mechanisms of action postulated for IFN alpha, the role of IFN alpha in the modulation of the cytotoxicity and therapeutic efficacy of FUra alone and in combination with CF has been evaluated in patients with advanced colorectal cancer and also in a variety of human cell lines in culture, including human colorectal cell lines, HCT-8, human bladder cell line RT-4 and leukaemia CEM cells. The results obtained in patients demonstrated that indeed the antitumour activity of FUra can be improved by the addition of IFN alpha with a response range from 26% to 76%. The initial clinical use of this combination, however, has been limited in some cases by the severe host toxicity. In vitro results demonstrated that: (1) in vitro cytotoxicity potentiation by IFN alpha is cell-type dependent; (2) in these cells where modulation was possible, alpha IFN was used as a low and noncytotoxic doses (10-50 micrograms/ml for 3-5 d exposure), and (3) the cytotoxicity of IFN alpha was dose dependent, indicating a direct antiproliferative cellular effect.

Antineoplastic Combined Chemotherapy Protocols↗

PubMed1991

Comparative DNA strand breakage induced by FUra and FdUrd in human ileocecal adenocarcinoma (HCT-8) cells: relevance to cell growth inhibition.

Although several mechanisms of 5-fluorouracil (FUra) and 5-fluoro-2'-deoxyuridine (FdUrd) cytotoxicity have been postulated, their effects on cellular DNA integrity have not been fully investigated. Cytotoxicity and the induction of DNA single and double strand breaks (SSB and DSB) were evaluated in the human ileocecal adenocarcinoma cell line, HCT-8, following 2 hr of exposure to these agents. Alkaline and neutral elution techniques were utilized to quantitate the amounts of DNA SSB and DSB induced by FdUrd and FUra. FdUrd, but not FUra, induced a high level of DNA SSB and DSB. These effects were concentration and time dependent, reaching a maximum at 10 microM FdUrd and at 12 hr post-treatment. Minimal amounts of DNA damage were observed in HCT-8 cells exposed to FUra, even at a concentration of 300 microM that produced greater than 99% inhibition of cell growth. In order to delineate the mechanisms associated with the effects observed following FUra and FdUrd treatment of HCT-8 cells, the effects of thymidine and leucovorin were evaluated. DNA SSB and DSB induced by FdUrd were reversed by thymidine. The effects of thymidine were time dependent. Complete reversal of DNA damage and cytotoxicity was achieved when 10 microM thymidine was added at up to 12 hr after treatment, the time of appearance of maximum DNA damage. These results suggest that the extensive DNA damage induced by FdUrd (but not by FUra) was an important determinant of FdUrd cytotoxicity in HCT-8 cells.

Adenocarcinoma↗

PubMed1990

Topoisomerase II-mediated DNA damage of episomes in tumor-bearing mice.

Observations of cells in culture have demonstrated that, for many antitumor agents, topoisomerase II-mediated DNA damage relates to cytotoxicity. However, there is no evidence in tumor-bearing animals to suggest that such agents induce topoisomerase II-mediated damage of DNA in solid tumors or that such damage reflects inhibition of tumor growth. To address this question, a mouse fibroblast cell line neoplastically transformed by an episomal element containing the v-Ha-ras and bovine papillomavirus genes was utilized to measure topoisomerase II-induced DNA damage and growth inhibition of solid tumors derived from this line. Using the topoisomerase II inhibitor amsacrine, the episomal element was found to be a sensitive indicator of topoisomerase II-mediated damage in vivo. The DNA breaks induced by single i.v. injections of amsacrine were protein linked and occurred preferentially in episomal regulatory regions. A strong correlation between suppression of tumor growth and topoisomerase II-mediated damage of the episome was demonstrated.

Amsacrine↗

PubMed1990

Application of a new approach for the quantitation of drug synergism to the combination of cis-diamminedichloroplatinum and 1-beta-D-arabinofuranosylcytosine.

This report describes the application of a new approach, the universal response surface approach, to the quantitative assessment of drug interaction, i.e., the determination of synergism, antagonism, additivity, potentiation, inhibition, and coalitive action. The specific drug combination and experimental growth system for this introductory application was that of 1-beta-D-arabinofuranosylcytosine (ara-C) and cisplatin with simultaneous drug exposure (1, 3, 6, 12, or 48 h) against L1210 leukemia in vitro. To quantitate the type and degree of drug interaction, a model was fitted using nonlinear regression to the data from each separate experiment, and parameters were estimated (K. C. Syracuse and W. R. Greco, Proc. Biopharm. Sect. Am. Stat. Assoc., 127-132, 1986). The parameters included the maximum cell density over background in absence of drug, the background cell density in presence of infinite drug, the 50% inhibitory concentrations and concentration-effect slopes for each drug, and a synergism-antagonism parameter, alpha. A positive alpha indicates synergism, a negative alpha, antagonism, and a zero alpha, additivity. Maximal synergy was found with a 3-h exposure of ara-C + cisplatin, with alpha = 3.08 +/- 0.96 (SE) and 2.44 +/- 0.70 in two separate experiments. Four different graphic representations of the raw data and fitted curves provide visual indications of goodness of fit of the estimated dose-response surface to the data and visual indications of the intensity of drug interaction. The universal response surface approach is mathematically consistent with the traditional isobologram approach but is more objective, is more quantitative, and is more easily automated. Although specifically developed for in vitro cancer chemotherapy applications, the universal response surface approach should prove to be useful in the fields of pharmacology, toxicology, epidemiology, and biomedical science in general.

Animals↗

PubMed1990

A phase II trial of 5-fluorouracil, doxorubicin, mitomycin C, and leucovorin in advanced gastric carcinoma.

To determine the feasibility and toxicity of combining leucovorin (CF) with a 5-fluorouracil (5-FU) combination chemotherapy regimen currently accepted by many as standard treatment for gastric cancer, CF (500 mg/m2) was administered in combination with the Georgetown 5-FU, doxorubicin, and mitomycin C (FAM) regimen. Thirty-two patients with advanced adenocarcinoma of the stomach were evaluable for toxicity and 26 patients with measurable disease were evaluable for response. Fifty-four percent of patients were previously treated with chemotherapy or radiation therapy. The response rate was 38% (95% confidence interval, 21% to 59%). The median duration of response was 6 months (range, 2 to 23+ months). The estimated median survival time was 6.8 months for patients with measurable disease and 11.5 months for all 32 patients. Although diarrhea is dose limiting when 5-FU and CF are administered weekly for 6 of 8 weeks, diarrhea occurred rarely on this combination regimen with 5-FU and CF administered only 4 of every 8 weeks. The dose-limiting toxicity of FAM-CF was cumulative myelosuppression, which also occurs with the standard FAM regimen. As a result, the administered dose intensity of 5-FU decreased as patients continued on study. Thus, a randomized comparison of FAM with FAM-CF would not determine whether CF modulation increases the efficacy of 5-FU when it is administered in optimal doses to patients with gastric cancer.

Adult↗

PubMed1990

The determination of growth rates of individual colonies in agarose using high-resolution automated image analysis.

This paper describes the evaluation of a colony formation assay using automated image analysis, which permits the tracking of growth at the individual colony level, such that a growth rate can be estimated for each colony followed. In principle, this will permit quantitative characterization of cellular heterogeneity in growth rate and cellular heterogeneity in response to proliferation-modifying agents. In addition, we have demonstrated the possibility of using correlative microscopy to relate growth rate to other parameters, using metabolic viability as an example. This should be useful for determining cellular characteristics associated with proliferative behavior and response to proliferation-modifying agents.

Adenocarcinoma↗

PubMed1990

Enhancement of the antitumor effects of 5-fluorouracil by folinic acid.

Although 5-fluorouracil (FUra) is one of the most effective cytotoxic agents in the treatment of various solid tumors (carcinomas of the gastro-intestinal tract, breast, head and neck), remissions occur in only 20-30% of cases and usually are of short duration. Recently, preclinical studies have shown that the antitumor activity of FUra can be potentiated by modulating the metabolism of this drug by using other substances, in particular 5-formyltetrahydrofolate (folinate, LV). Reduced folates (LV and 5-methyltetrahydrofolate) at concentrations greater than or equal to 1 microM can, by raising the intracellular levels of 5,10-methylenetetrahydrofolate, increase and prolong the inhibition of the target enzyme, thymidylate synthase, with formation of a stable ternary complex formed by the enzyme, the folate coenzyme and the fluoropyrimidine inhibitor (5-fluorodeoxyuridylate). After phase II clinical trials reported encouraging results with the combination LV-FUra in the treatment of patients with various solid tumors, randomized controlled studies in patients with colorectal carcinoma have documented an increase in the response rate of the combination compared to treatment with FUra alone. The integration of the LV-FUra combination into multidrug regimens is now under investigation for the treatment of carcinomas of the breast, stomach, and head and neck.

Animals↗

PubMed1990

Biochemical rationale for the 5-fluorouracil leucovorin combination and update of clinical experience.

Although 5-fluorouracil has been the drug of choice for the treatment of patients with advanced adenocarcinoma of the colon, the reported response rate dose not exceed 20% with a median survival time less than 9 months. Mechanisms of sensitivity to this agent include: 1) inhibition of thymidylate synthase by FdUMP, the active metabolite of 5-fluorouracil; 2) incorporation of FUTP into cellular RNA; and 3) incorporation of FdUTP into cellular DNA. Recent laboratory preclinical results suggest that the major site of action of 5-fluorouracil when combined with 5-formyltetrahydrofolate (folinic acid, leucovorin) is thymidylate synthase resulting in pronounced and prolonged inhibition of DNA synthesis. This effect is primarily due to the stabilization of FdUMP binding to thymidylate synthase by the reduced folate cofactor, N5, N10-methylenetetrahydrofolate. In this paper, the rationale for the modulation of 5-fluorouracil by leucovorin, the clinical pharmacology and the clinical experience of this combination will be reviewed.

Animals↗

PubMed1990

Generation and characterization of a low-degree drug-resistant human tumor cell line.

A 2780 human ovarian cancer cells, obtained from an untreated patient, have been exposed to a relatively low, clinically maintainable dose (10 nmol/l) of the anthracycline doxorubicin (DX) to derive a low-degree (5-fold) drug-resistant subline (A2780-DX1). Compared to parental cells, these DX-resistant cells have increased size (+60% of cell volume) and contain a greater number of cytoplasmic vacuoles as determined by electron microscopy. When exposed to several other antiproliferative drugs, A2780-DX1 cells were highly cross-resistant (greater than 10-fold) to epirubicin, mafosfamide and cisplatin and slightly cross-resistant (2- to 3-fold) to navelbine and bleomycin, while they retained the original sensitivity to vinblastine, Ara-C and fluorouracil. Gel electrophoresis of cytoplasmic membrane proteins showed differences between the pattern of parental A2780 sensitive and A2780-DX1 cells as far as low-molecular-weight proteins (less than 45 kD) are concerned, while no clear overexpression of P-glycoprotein (P-170) could be detected. Membrane modifications yielding a decrease of both DX uptake and retention, increased content of intracellular glutathione (+32%) and reduced DNA double-strand breaks seem to be involved in the resulting multidrug-resistant phenotype of A2780-DX1 cells.

Antineoplastic Agents↗