Chromosomal effects of methotrexate on cultured human lymphocytes

Ameliorative effect of metformin on methotrexate-induced genotoxicity: An in vitro study in human cultured lymphocytes

Methotrexate is a folic acid antagonist that has been shown to be genotoxic to normal healthy cells. Metformin is an insulin-sensitizing agent, with multiple potential pharmacodynamic profiles. The aim of the present study was to evaluate the genotoxic effect of methotrexate on DNA and the potential ameliorative effect of metformin on chromosomal damage induced by methotrexate. The present study was performed in vitro, and the frequency of chromosomal aberrations (CAs) and sister chromatid exchanges (SCEs) in human cultured lymphocytes were measured. Blood samples from five non-smoking healthy men aged 20-35 years were donated and used in the present study. Treatment of cultured blood cells with methotrexate significantly increased the number of cells with CAs (P<0.0001) and the frequency of SCEs (P<0.0001). The chromosomal injury induced by methotrexate was significantly reduced by pretreatment of the samples with metformin (P<0.0001). Importantly, the treatment of the cells with metformin alone did not affect the frequency of SCEs compared with the control group (P>0.05). Additionally, methotrexate and metformin alone, and combined, induced significant decreases in the proliferative index compared with the control group (P<0.05). In conclusion, metformin ameliorated the genotoxicity induced by methotrexate in cultured human lymphocytes.

The Protective Effect of Cilostazol in Genotoxicity Induced by Methotrexate in Human Cultured Lymphocytes

BACKGROUND

Methotrexate is an antagonist of folic acid that has been shown to be genotoxic to healthy body cells via induction of oxidative stress. Cilostazol is a phosphodiesterase III inhibitor and a potent antioxidant drug.

OBJECTIVE

To evaluate the potential protective effect of cilostazol on methotrexate genotoxicity.

METHODS

The genotoxic effect of methotrexate by measuring the frequency of chromosomal aberrations (CAs) and sister chromatid exchanges (SCEs) in human cultured lymphocytes was studied.

RESULTS

Methotrexate significantly increased the frequency of CAs and SCEs (p < 0.0001) as compared to control cultures. This chromosomal damage induced by methotrexate was considerably decreased by pretreatment of the cells with cilostazol (P < 0.01). Moreover, the results showed that methotrexate resulted in a notable reduction (P < 0.01) in cells kinetic parameters, the mitotic index (MI) and the proliferative index (PI). Similarly, cilostazol significantly reduced the mitotic index, which could be related to the anti-proliferative effect (P < 0.01).

CONCLUSION

Methotrexate is genotoxic, and cilostazol could prevent the methotrexate-induced chromosomal damage with no modulation of methotrexate-induced cytotoxicity.

Chlorophyll derivative mediated PDT versus methotrexate: an in vitro study using MCF-7 cells

BACKGROUND

Breast cancer is the most common cause of cancer deaths among women worldwide. Although chemotherapy is a standard method for the treatment of breast cancer, the photodynamic therapy (PDT) is a recent promising modality for cancer diagnosis and treatment. Its major advantages over chemotherapy are better selectivity of tumour tissue destruction and lack of severe local and systemic complications. This work is directed towards evaluation of the efficacy of Photodynamic therapy using chlorophyll derivative (CHL) as a photosensitizer in treatment of breast cancer. It also aims at investigation of the genetic safety of chlorophyll mediated PDT in comparison to the conventional chemotherapy.

METHODS

Both methotrexate (MTX) and light activated chlorophyll derivative were used to target MCF-7 breast cancer cell line. Standard karyotyping and alkaline single cell microgel electrophoresis assay (Comet assay) were applied on normal human peripheral blood lymphocytes (HPL) in order to investigate the respective possible mutagenic and genotoxic side effects that might result from application of each therapeutic modality.

RESULTS

Results obtained from this study showed that 50% of MCF-7 tumour cell death (LC(50)) was reached by using a concentration of chlorophyll derivative that is 138 times lower than MTX. Moreover, chlorophyll derivative exerted no genetic side effects as compared to MTX that resulted into several types of chromosomal breakages.

CONCLUSIONS

Compared to MTX, light activated chlorophyll derivative proved to be a better candidate for breast cancer cell toxicity, referring to its higher efficacy at tumour cells killing, safety to normal cells and simple method of extraction.

Biological dosimetry after radiosynoviorthesis with rhenium-186 sulphide and erbium-169 citrate

Radiosynoviorthesis (RSO) with the nuclides rhenium-186 sulphide (186Re) and erbium-169 citrate (169Er) is an established concept for the treatment of persistent synovitis of medium and small sized joints. THE AIM of the present studies was to investigate the biological radiation effect based on analysing chromosome aberrations.

PATIENTS, METHODS

Immediately before and 17 to 19 days (186Re) or 45 to 50 (169Er) days after RSO with 186Re or 169Er colloid and subsequent immobilisation of the treated joint, blood samples of a total of 23 patients were collected. The yield of dicentric chromosomes in lymphocytes was determined exclusively in metaphases of the first cell cycle in vitro. In addition, for 186Re the activity leakage was measured three days after RSO by whole-body scintigraphy.

RESULTS

No statistically significant increase in the number of dicentric chromosomes (40 and 88 before and 59 and 105 after treatment with 186Re and 169Er, respectively) in a total of 47017 cells analysed from 46 blood samples could be found as a result of RSO. For 186Re an activity leakage of 3.9%±7% with a maximum of 23.4% corresponding to an effective dose of 2.8±4.5 mSv , respectively 13.8 mSv, was determined. Also in the case of the maximum leakage no significant increase of dicentric chromosomes were detected.

CONCLUSIONS

No significant biological radiation effect can be detected after RSO with 186Re and 169Er, also in cases of high leakage. Therefore, RSO can be classified as a save therapeutic procedure without a relevant radiation risk.

Comparison of in vitro micronucleus and gene mutation assay results for p53-competent versus p53-deficient human lymphoblastoid cells

The high frequency of false or irrelevant positive results in in vitro mammalian cell genotoxicity tests is a critical concern for regulators. Here, we tested whether such results may be due to the mammalian cells used in the tests being deficient in p53, which is involved in the maintenance of genomic stability. We compared the in vitro responses of two human lymphoblastoid cell lines derived from the same progenitor cell-p53-competent (TK6) and p53-deficient (WTK-1) cells-in a micronucleus (MN) test and a thymidine kinase gene (TK) mutation assay. We tested 14 chemicals including three mutagens and 11 clastogens and spindle poisons. The three mutagens evoked clear positive responses in both assays in both cell lines. The responses to the clastogens and spindle poisons, on the other hand, depended on the assay endpoint and/or the cell line. Most of clastogens and spindle poisons were positive in the MN test in both cell lines. In the TK mutation assay, on the other hand, WTK-1 cells but not TK6 cells detected spindle poisons, which may have been due to the disturbance of the spindle checkpoint and lack of apoptosis in the p53-deficient cells. Some chemicals that induced chromosome aberrations in rodent cells were negative in both TK6 and WTK-1 cells, indicating that a species-specific factor rather than p53 status was associated with the response. In conclusion, the p53 status did not seriously influence the MN test results but it did influence the TK mutation assay results.

Formaldehyde as a potential human leukemogen: an assessment of biological plausibility

The International Agency for Research on Cancer (IARC, 2004) recently reevaluated the epidemiological data on formaldehyde and concluded that there was "strong but not sufficient evidence for a causal association between leukaemia and occupational exposure to formaldehyde." This conclusion was tempered since a mechanism for leukemia induction could not be identified. Chemically induced leukemia is a well-studied phenomenon with benzene and a number of cancer chemotherapeutic drugs recognized as capable of causing this effect. Abundant in vitro and in vivo data in animals and humans demonstrate that exposure to sufficient doses of these recognized leukemogens can initiate a cascade of events leading to hematopoietic toxicity and the subsequent development of leukemia. This review addresses the biological plausibility that formaldehyde might be capable of causing any type of leukemia by providing a broad overview of the scientific data that must be considered in order to support or refute a conclusion that a particular substance might be leukemogenic. Data on benzene and selected chemotherapeutic cancer drugs are used as examples and are briefly summarized to demonstrate the similar biological events thought to result in leukemogenesis. These data are compared and contrasted with the available data on formaldehyde in order to judge whether they fulfill the criteria of biological plausibility that formaldehyde would be capable of inducing leukemia as suggested by the epidemiological data. Based on the epidemiological data, it is reasonable to expect that if formaldehyde was capable of inducing leukemia, in vivo and in vitro data would offer supporting evidence for biological plausibility. In particular, there is (1) no evidence to suggest that formaldehyde reaches any target organ beyond the site of administration including the bone marrow, (2) no indication that formaldehyde is toxic to the bone marrow/hematopoietic system in in vivo or in vitro studies, and (3) no credible evidence that formaldehyde induces leukemia in experimental animals. As discussed in this review, based on the key biological events that occur in the process of chemically induced leukemia, there is inadequate biological evidence currently available to corroborate existing weak epidemiological associations. This provides an insufficient database to conclude that there is a causal relationship for formaldehyde and leukemia risk.

Yeast DEL assay detects clastogens

Chromosomal rearrangements, including DNA deletions are involved in carcinogenesis. The deletion (DEL) assay scoring for DNA deletions in the yeast Saccharomyces cerevisiae is able to detect a wide range of carcinogens. Among approximately 60 compounds of known carcinogenic activity, the DEL assay detected 86% correctly whereas the Ames Salmonella assay detected only 30% correctly [R.J. Brennan, R.H. Schiestl, Detecting carcinogens with the yeast DEL assay, Methods Mol. Biol. 262 (2004) 111-124]. Since the DEL assay is highly inducible by DNA double strand breaks, this study examined the utility of the DEL assay for detecting clastogens. Ten model compounds, with varied mechanisms of genotoxicity, were examined for their effect on the frequency of DNA deletions with the DEL assay. The compounds tested were: actinomycin D, camptothecin, methotrexate and 5-fluorodeoxyuridine, which are anticancer agents, noscapine and furosemide are therapeutics, acridine, methyl acrylate and resorcinol are industrial chemicals and diazinon is an insecticide. The in vitro micronucleus assay (IVMN) in CHO cells, a commonly used tool for detection of clastogens, was performed on the same compounds and the results of the two assays were compared. The results of our study show that there is 70% concordance in the presence of metabolic activation (rat liver S9) and 80% concordance in the absence of metabolic activation between the DEL assay and the standard in vitro micronucleus assay. The lack of cytotoxicity observed for four of the ten compounds examined indicates limited diffusion of lipophilic compounds across the yeast cell wall. Thus, the development of a more permeable yeast tester strain is expected to greatly improve concordance of the DEL assay with the IVMN assay. The yeast DEL assay is inexpensive, amenable to automation and requires less expertise to perform than the IVMN. Thus, it has a strong potential as a robust, fast and economical screen for detecting clastogens in vitro.

A de novo, apparently balanced reciprocal translocation in a child with developmental delay whose mother was being treated with low-dose methotrexate at the time of conception

BACKGROUND

Methotrexate is a proven teratogen and its use periconceptually is strongly advised against. Concerns about possible chromosomal effects in the offspring of women treated with this agent have been raised, but they have not been reported. In vivo and in vitro studies have supported this possibility, however.

CASE

A 32-year-old primigravida was treated with low-dose methotrexate for rheumatoid arthritis from prior to conception until six weeks postconception. Her child was born without congenital malformations but subsequently developed seizures and was diagnosed with developmental delay. He was found to have a de novo, apparently balanced, reciprocal translocation between chromosomes 5 and 20 (46,XY,t(5:20)(q15;p12)). Other investigations failed to reveal another cause for his developmental delay.

CONCLUSIONS

The possible association between maternal methotrexate exposure and a de novo chromosomal anomaly in an offspring supports the recommendation that women should be advised to cease taking this drug for at least six months prior to conception.

In vitro micronucleus assay with Chinese hamster V79 cells - results of a collaborative study with in situ exposure to 26 chemical substances

A collaborative study with 10 participating laboratories was conducted to evaluate a test protocol for the performance of the in vitro micronucleus (MN) test using the V79 cell line with one treatment and one sampling time only. A total of 26 coded substances were tested in this study for MN-inducing properties. Three substances were tested by all 10 laboratories and 23 substances were tested by three or four laboratories in parallel. Six aneugenic, 7 clastogenic and 6 non-genotoxic chemicals were uniformly recognised as such by all laboratories. Three chemicals were tested uniformly negative by three laboratories although also clastogenic properties have been reported for these substances. Another set of three clastogenic substances showed inconsistent results and one non-clastogenic substance was found to be positive by one out of three laboratories. Within the study, the applicability of the determination of a proliferation index (PI) as an internal cytotoxicity parameter in comparison with the determination of the mitotic index (MI) was also evaluated. Both parameters were found to be useful for the interpretation of the MN test result with regard to the control of cell cycle kinetics and the mode of action for MN induction. The MN test in vitro was found to be easy to perform and its results were mainly in accordance with results from chromosomal aberration tests in vitro.

Inhibitors of thymine nucleotide biosynthesis: antimetabolites that provoke genetic change via primary non-DNA targets

Folate antagonists and direct-acting inhibitors of thymidylate synthase are potent genotoxic antimetabolites. These agents induce genetic change not by attacking DNA, but by interfering with the control of DNA precursor metabolism. This review surveys the genetic effects attributable to selected representatives of this class of antimetabolites.

International Commission for Protection Against Environmental Mutagens and Carcinogens. Deoxyribonucleoside triphosphate levels: a critical factor in the maintenance of genetic stability

DNA precursor pool imbalances can elicit a variety of genetic effects and modulate the genotoxicity of certain DNA-damaging agents. These and other observations indicate that the control of DNA precursor concentrations is essential for the maintenance of genetic stability, and suggest that factors which offset this control may contribute to environmental mutagenesis and carcinogenesis. In this article, we review the biochemical and genetic mechanisms responsible for regulating the production and relative amounts of intracellular DNA precursors, describe the many outcomes of perturbations in DNA precursor levels, and discuss implications of such imbalances for sensitivity to DNA-damaging agents, population monitoring, and human diseases.

Localization of breakpoints in the karyotype of workers professionally exposed to benzene

Cytogenetic analysis was carried out on peripheral blood lymphocytes of 33 workers professionally exposed to benzene for 10-26 years. In the examined group structural chromosome aberrations were found in 147 metaphases (4.7%). Statistical analysis has shown that the distribution of breakpoints was not random. Chromosomes 2, 4 and 9 are almost twice as susceptible to breaks, while chromosomes 1 and 2 are almost twice as susceptible to gaps, as would be expected based on a random distribution of damage among chromosomes.

Cytogenetic effects of dacarbazine on mouse bone marrow cells in vivo

The mutagenicity of dacarbazine was assayed in an in vivo test utilizing mouse bone marrow cells. The dose rates used in the experiments were computed according to the standard surface area of the mouse and were proportional to the human dose rate. These were 0.27, 0.44 and 0.60 mg/30 g body weight, each given twice daily at an interval of not less than 6 h. The duration of drug treatment was 24, 48 and 72 h. This alkylating agent proved to be mitodepressive and produced a 3-fold reduction in the mitotic index. The drug also induced chromosome anomalies mainly in the form of chromatid gaps and breaks. These anomalies were proportional to dose rate and duration of drug treatment.

Electrochemistry of the anticancer agents methotrexate and alpha-difluoromethylornithine in iminium form

The electrochemical characteristics of the antitumor agents methotrexate and alpha-difluoromethylornithine were determined as their iminium derivatives. Iminium formation from methotrexate is accomplished in vivo via protonation by enzyme. The requisite imine precursor is generated from alpha-difluoromethylornithine by condensation with enzyme containing pyridoxal phosphate. Electroreduction occurs in the range of -0.2 to -0.6 V. The relationship of reduction to structure is discussed. A possible mode of anticancer action involving electron transfer is presented.

Comparison of synchronized Chinese hamster ovary cells obtained by mitotic shake-off, hydroxyurea, aphidicolin, or methotrexate

Synchronized cell populations are necessary to study many aspects of cell biology. We have developed a method to obtain highly synchronized Chinese hamster ovary cell populations in S phase or G2 phase by utilizing mitotic selection followed by incubation with either hydroxyurea, aphidicolin, or methotrexate for 12 h. Flow cytometry analysis shows that the coefficient of variation in the spread of the cell population in S phase is as low as 6%. Drug toxicity studies compare the effects of the various drugs on G1 and S phase cells. The use of aphidicolin or hydroxyurea results in the most highly synchronized cell populations, but methotrexate yields inadequate synchronization. These results demonstrate that both aphidicolin and hydroxyurea are useful drugs for obtaining highly synchronized cell populations after an initial synchrony in mitosis. Aphidicolin is perhaps the best choice because of less toxicity to S phase cells when used in low concentrations.

The most common fragile site in man is 3p14

In man a common fragile site is known to occur at 3p14. We studied the expression of this fragility in a group of 70 normal healthy subjects. Chromosome breaks, chromatid breaks and gaps at 3p14 could be observed in every examined individual, and in a total of 7000 metaphases they were seen in a mean of 4% of cells. Fluorescence studies in ten persons with chromosome No. 3 polymorphism showed that in all cases both Nos. 3 were about equally liable to breakage. A considerable variation in the fra 3p14 expression was found between individuals as well as in repeated cultures from the same person. Neither sex nor age influences could be detected. Cultures with a high percentage of lesions at 3p14 tended to have also a high number of lesions at other sites. Methotrexate and fluorodeoxyuridine markedly enhanced the expression of fra 3p14 and other fragilities. It is concluded that the chromosomal region at 3p14 represents man's most common fragile site, the expression of which seems to be influenced by environmental and heritable factors.

Comparison of prometaphase chromosome techniques with emphasis on the role of colcemid

Six different techniques were evaluated to define better those technical factors that are most critical for obtaining prometaphase cells for banding analysis. Our results demonstrate: colcemid exposures of 30 min or less have no effect on increasing the yield of prometaphase cells, colcemid exposures of greater than 0.1 microgram/ml can be toxic, methotrexate depresses the mitotic index significantly and seems to increase the incidence of prometaphase cells only because it suppresses later forms; and (d) the optimum number of cytogenetically satisfactory prometaphase cells can be obtained with a 4-h exposure to a combination of low concentration actinomycin D (0.5 microgram/ml) and colcemid (0.1 microgram/ml). This technique inhibits chromosome condensation while permitting prometaphase cells to accumulate for 4 h.