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J Cloos

Publications and source records attributed to J Cloos.

30 records · Page 2Linked to original sources
PubMed1996

Influence of the antioxidant N-acetylcysteine and its metabolites on damage induced by bleomycin in PM2 bacteriophage DNA.

Bleomycin is considered to be a useful model compound for studying environmental carcinogenesis, due to its broad spectrum of DNA damaging properties. In addition, bleomycin is a useful antitumor drug because of its cytotoxic properties. To investigate the influence of the antioxidant N-acetylcysteine and its metabolites glutathione and cysteine on bleomycin-induced DNA damage and more importantly to gain insight into the biological relevance of such damage, PM2 DNA was exposed to Cu(2+)-bleomycin in the presence and absence of the thiols N-acetylcysteine, glutathione and cysteine. It was found that the presence of these thiols led to a considerable enhancement of bleomycin-induced single- and double-strand breaks and a concomitant decrease in the biological activity of PM2 DNA in a dose-dependent way. A similar observation was made when ascorbic acid was used. Bleomycin showed no DNA damaging activity when PM2 DNA was pretreated with the strong Fe ion chelator desferal and its activity was strongly inhibited by the addition of Cu2+ ions or under hypoxic (N2) conditions. Cu(2+)-bleomycin under our conditions is not active by itself, but most probably after binding to DNA exchanges Cu2+ for Fe3+ bound to DNA. Fe(3+)-bleomycin is then reduced to Fe(2+)-bleomycin, a process potentiated by the added antioxidants, and subsequently activated by O2. The contribution to biological inactivation of bleomycin alone or in the presence of ascorbic acid is only approximately 15%. The contribution to lethality in the presence of thiols is higher. These results indicate that ascorbic acid only enhances the DNA damaging properties of bleomycin, whereas the thiol compounds in addition influence the type of DNA damage. The remainder of the biological inactivation is probably caused by double damage, such as single-strand breaks with closely opposed alkali-labile sites or base damage.

Acetylcysteine↗
PubMed1996

Lack of effect of daily N-acetylcysteine supplementation on mutagen sensitivity.

The European Organization for Research and Treatment of Cancer multicenter Euroscan trial was set up to prevent the occurrence of second primary tumors in the upper aerodigestive and respiratory tract in patients cured for early stage head and neck squamous cell carcinoma. One randomized group of patients receive daily N-acetylcysteine, an antioxidant that may be protective especially in the early steps of carcinogenesis. Mutagen sensitivity, measured as sensitivity to bleomycin in peripheral blood lymphocytes, has been found to be increased in head and neck squamous cell carcinoma and is hypothesized to reflect cancer susceptibility. The aim of this study was to investigate whether mutagen sensitivity is influenced by oral N-acetylcysteine supplementation and can therefore be used as intermediate end point in chemoprevention. Patients (n = 19) who had various periods of N-acetylcysteine supplementation (600 mg daily for 3-9 months) were analyzed. In addition, a patient group (n = 14) that did not receive N-acetylcysteine supplementation was analyzed for comparison. Our results show no evidence that administration of N-acetylcysteine did influence the mutagen sensitivity level. The only explanatory variable in the analysis of the difference between two samples of one person was the b/c value of the first measurement. Moreover, the variability in these repeated measurements (coefficient of variation of 14%) indicates that additional studies should be performed to minimize this variability and to optimize the testing of mutagen sensitivity to accurately identify individual patients at high risk for the development of multiple primary tumors.

Acetylcysteine↗
PubMed1995

The effect of different routes of administration of 5-fluorouracil on thymidylate synthase inhibition in the rat.

A rat colon tumour model of liver metastases was used to administer 5-fluorouracil (5FU) by intraperitoneal (i.p.) bolus injection (50 mg/kg), isolated liver perfusion (ILP, 150 mg/kg) and hepatic artery infusion (HAI, 50 mg/kg). The biochemical effect of 5FU, delivered by different routes, on its target enzyme thymidylate synthase (TS) was studied in both tumour and normal tissues of the rat. In tumour tissue, only small differences were observed in the extent of TS inhibition. A pronounced inhibition of TS was observed 3 h after 5FU administration by all routes, but was followed by a recovery of TS activity within 24 and 48 h. Effects of 5FU on normal tissues were diverse. In liver, TS activity increased 6-fold after ILP and HAI administration of 5FU, and a 2-fold increase of FdUMP binding to TS was seen for all routes of administration. In intestinal mucosa, both induction of TS activity (by ILP) and inhibition of TS activity (by HAI) were observed, while i.p. injection did not cause major changes. TS activity and FdUMP binding to TS in bone marrow was strongly inhibited after administration of 5FU by all routes, but administration by ILP seemed slightly advantageous, since a smaller extent of TS inhibition was observed compared to the other routes of administration. 5FU given by ILP had a small antitumour effect in this colon tumour model, while HAI administration had no antitumour activity. Since this difference in antitumour activity could not be related to differences in TS inhibition in the tumour, the RNA-directed mechanism of action of 5FU could be involved. Focusing on the effects of TS, we may conclude that the ILP administration of 5FU offered the important advantage of a lack of severe TS inhibition in normal tissues, which corresponds with the low systemic toxicity observed.

Administration, Topical↗
PubMed1995

[Determination of genetic susceptibility for development of squamous epithelial carcinomas of the had and neck with bleomycin-induced chromosome instability].

BACKGROUND: Cigarette smoking is a well established risk factor for head and neck squamous cell carcinoma. However, data on smoking history are not sufficient to predict which patients are at high risk for the development of multiple primary tumors. It is hypothesized that both exposure to carcinogens and individual susceptibility determine cancer risk. The aim of this study was to investigate whether a possible individual susceptibility for head and neck squamous cell carcinoma was related to the outcome of the mutagen sensitivity assay, which was adopted from Hsu and colleagues. METHODS: Cultured peripheral blood lymphocytes were treated for five hours with 30 mIU/ml of bleomycin, and sensitivity was estimated by the mean number of chromatid breaks per cell scored in 100 metaphases of duplicate cultures. RESULTS: It was shown that using this standard mutagen sensitivity assay, a person's sensitivity can be reproducibly measured. Age had a significant but small contribution, whereas gender and tobacco and alcohol use had no influence on the outcome of the assay. Therefore, we consider this sensitivity for the DNA damaging effect of bleomycin constitutional. A retrospective study showed that the breaks per cell in head and neck squamous cell carcinoma patients (0.96 +/- 0.31; n = 52) were significantly higher (p < 0.001) than in control persons (0.77 +/- 0.19; n = 50). In addition, head and neck cancer patients who had already developed multiple primary tumors had a break per cell level (1.20 +/- 0.47; n = 20) which was even significantly higher (p < 0.025) than in patients with one primary tumor. CONCLUSION: We hypothesize that mutagen sensitivity reflects an individual's sensitivity vor DNA damaging agents. The extremely high sensitivity in patients with multiple primary tumors suggests that mutagen sensitivity is a phenotype reflecting a person's susceptibility to head and neck cancer. We postulate that mutagen sensitivity in combination with smoking history can be used to identify those patients at highest risk for the development of multiple primary tumors.

Adult↗
PubMed1995

Screening of colon tumor cells and tissues for folylpolyglutamate synthetase activity.

Polyglutamylation of (anti)folates catalyzed by folylpolyglutamate synthetase (FPGS) determines the retention of these compounds in the cell. This feature is essential for the activity of folates (e.g., folinic acid) and antifolates (e.g., methotrexate) in the treatment of cancer. A FPGS assay was developed using murine liver and was based on published methods, but had a novel analytic procedure. Tritiated glutamate and aminopterin served as substrates for FPGS, and after the reaction the mixture of substrates and products was separated by thin-layer chromatography. Results were verified by standard anion-exchange high performance liquid chromatography for folates. The assay was applied to measure the activity of FPGS in several cancer cell lines and human and murine (tumor) tissues. Cancer cell lines had a much higher activity (varying from 82 to 656 pmol diglutamate formed per hour per 10(6) cells) than murine bone marrow cells (35 pmol/h/10(6) cells). Murine gut mucosa had a very low FPGS activity compared to murine liver (7 vs. 24 pmol diglutamate/h/g wet weight), but the activity in murine colon tumors was comparable to or higher than that in liver (28-52 pmol diglutamate/h/g wet weight). A screening of 11 human colon tumors or metastases demonstrated that there was a large variation in FPGS activity in this tumor type, but overall the activity was higher in tumor tissue than in normal colon mucosa. The latter feature may increase the selectivity of antifolate-based chemotherapy of colon tumors. The FPGS assay described in this paper allows large-scale screening of cell lines and tissues, because of its rapid separation procedure by thin-layer chromatography.

Animals↗
PubMed1994

Increased mutagen sensitivity in head-and-neck squamous-cell carcinoma patients, particularly those with multiple primary tumors.

Mutagen sensitivity is a constitutional factor which may be used to identify head-and-neck squamous-cell carcinoma (HNSCC) patients at high risk for the development of multiple primary tumors (MPT). In this retrospective study, mutagen sensitivity was measured in HNSCC patients with a single primary tumor (SPT), HNSCC patients who have already developed MPT and control subjects with no tumor history. In vitro, lymphocytes were challenged with bleomycin and chromosomal damage was quantified by scoring chromatid breaks of 100 cells. A significant difference in the mean number of breaks per cell (b/c) was found between SPT patients and controls. Patients with MPT showed a significantly higher mean b/c value than SPT patients. This increase in mutagen sensitivity in HNSCC patients was not related to well-known cancer risk factors such as age, or life-style factors such as smoking and alcohol drinking habits. In addition, tumor site but not tumor stage was found to be related to mutagen sensitivity. On the basis of our findings, we propose that mutagen sensitivity is not an independent risk factor but a constitutional factor which reflects the way in which genotoxic compounds are dealt with and is thereby directly related to cancer risk.

Aged↗
PubMed1994

Effects of the modulating agent WR2721 on myelotoxicity and antitumour activity in carboplatin-treated mice.

The selective modulation of carboplatin [diammine(1,1-cyclo-butanedicarboxylato)platinum(II)]-induced myelotoxicity was investigated in mice, using the protective agent WR2721 [S-2-(3-aminopropylamino)ethyl-phosphorothioic acid, ethiofos]. In female BALB/c mice, WR2721 (200 mg/kg intraperitoneally, i.p.) partly prevented the reduction of in vitro proliferation of whole bone marrow cells and non-adherent cells when administered at different time points relative to 90 mg/kg carboplatin (i.p.). Protection was highest when WR2721 was administered 5 min prior to carboplatin. In vitro proliferation of whole bone marrow cells and non-adherent cells in liquid culture increased from 15% of control for carboplatin alone to 45% when WR2721 was administered 5 min prior to carboplatin. However, WR2721 did not significantly prevent the loss in clonogenic capacity of early hematopoietic progenitors in the bone marrow, as determined by a bilayered soft agar colony forming units assay. In nude mice, bearing well-established subcutaneous human ovarian carcinoma xenografts OVCAR-3, WR2721 (200 mg/kg i.p.) 5 min prior to intravenous carboplatin allowed a 1.5-fold increase in the maximum tolerated dose of carboplatin as determined by overall weight loss. WR2721 alone did not affect tumour growth. However, WR2721 had a potentiating effect on the tumour growth inhibition of a standard dose of carboplatin in this model. Minimal tumour volume compared to control (T/C) decreased from 9.4% with carboplatin alone to 2.2% with WR2721 5 min prior to the same dose of carboplatin. Specific growth delay (SGD) increased from 7.4 to 10.3. With the 1.5-fold increased, equitoxic dose of carboplatin in combination with WR2721, the antitumour activity was only slightly further increased (T/C = 1.4%, SGD = 10.5).

Amifostine↗
PubMed1993

Association between bleomycin genotoxicity and non-constitutional risk factors for head and neck cancer.

Sensitivity of phytohaemagglutinin-stimulated lymphocytes to bleomycin clastogenicity is increased in patients with tumours in organs and tissues that are in direct contact with the external environment, such as the mucosa of the head and neck. Sensitivity to bleomycin may reflect a genetically determined hypersensitivity to certain genotoxicants and therefore may be important in the carcinogenic process. In this study the applicability of bleomycin genotoxicity was investigated in cultured lymphocytes of forty individuals without a tumour history. No correlations were observed with increasing age or the well-known head and neck cancer risk factors alcohol and tobacco consumption. Since inter-individual variation in sensitivity greatly exceeded intra-individual variation, our results suggest that an elevated bleomycin clastogenicity score may identify individuals who have a constitutional hypersensitivity towards certain genotoxicants and may show an increased cancer susceptibility.

Alcohol Drinking↗
PubMed1992

Effect of folinic acid on fluorouracil activity and expression of thymidylate synthase.

Folinic acid (leucovorin, [LV]) can potentiate the growth inhibitory effects of fluorouracil (5-FU) in vitro and in vivo. LV is a precursor for 5,10-methylene-tetrahydrofolate (CH2-THF). Sufficient levels of CH2-THF enhance the inhibition of the enzyme thymidylate synthase by the 5-FU metabolite FdUMP. This study describes the effects of 5-FU and LV in two murine (C26-10, C38-1) and two human (WiDr, HT-29) colon carcinoma cell lines and in two murine tumors (Colon 26 and Colon 38). In vitro, only C38-1 was more sensitive for the combination of LV/5-FU compared with 5-FU alone. This effect was not dose or schedule dependent. l-LV, a purified stereo-isomere of LV, is thought to be the biological active form. Tests with this compound in vitro did not show a better effect than the mixture of d- and l-LV. In vivo, dl-LV could potentiate 5-FU antitumor effect in two murine colon tumors (Colon 26, Colon 38). This effect was clearly schedule dependent. dl-LV administered 1 hour before and together with 5-FU was much better than only simultaneous or posttreatment, but there was no dose dependency, while like in vitro l-LV effect was comparable to dl-LV. TdR was used to study the role of TS inhibition in the growth inhibitory effect of 5-FU with and without LV. TdR can reverse growth inhibition caused by TS inhibition due to 5-FU. In vitro, a partial reversal of growth inhibition of 5-FU and 5-FU/LV was observed, but in vivo there was no reversal. In vivo, TdR combinations led to high toxicity. Measurements of TS amounts in cells and tumors showed that those of human origin had much lower TS than the murine. C38-1 and Colon 38 with low TS were more sensitive to 5-FU than Colon 26 with higher TS amounts. TS inhibition was studied in the two murine colon tumors at several time points after weekly 5-FU or LV and 5-FU administration. LV did not increase the extent or retention of TS inhibition due to 5-FU during the first week. After three courses of treatment a fourfold increase of TS levels was seen in Colon 26 after 5-FU therapy. This resulted in a less effective TS inhibition after this treatment. Tumors treated with 5-FU and LV also showed an increase of TS, but to a lower extent, while the effect on TS inhibition remained the same.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗