Studying the genotoxicity of vincristine on human lymphocytes using comet assay, micronucleus assay and TCR gene mutation test in vitro

Genotoxicity, DNA damage and sperm defects induced by vinblastine

BACKGROUND

The treatment with chemotherapy may develop secondary tumors as a result of chemo genotoxicity. Sperm defects is another complication associated with chemo treatment. In this study the genotoxicity of vinblastine (VB) was estimated in both somatic and germ cells.

MATERIALS

85 mice were taken. Four single doses of VB at 3, 4.5, 6 and 10 mg/kg and three successive doses at 3, 4.5 and 6 mg/kg were taken for estimation of chromosomal aberrations (CAs). Four single doses of VB were involved in estimating the DNA fragmentation, and comet assay. For sperm abnormalities mice were injected with three successive doses of VB at 3, 4.5, and 6 mg/kg.

RESULTS

The results demonstrated a significant frequency of DNA fragmentation in spleen cells and in the percentage of CAs in bone marrow. Numerical and structural aberrations were recorded with a pronounced number of polyploidy metaphases which reached (11.60%) after treatment with 6 mg/kg for three successive days vs zero for control. VB also induced a significant percentage of CAs in spermatocytes in the form of univalent. Sperm defects in the form of coiled tail, absence of acrosome and shapeless head and a significant DNA damage in the testes were recorded. The frequency of sperm abnormalities reached 11.06 ± 0.14 after treatment with highest tested dose (6 mg/kg) vs 3.04 ± 0.19 for control.

CONCLUSION

VB is genotoxic in somatic and germ cells. Sperm defects induced by VB are of serious concern to future generations and may affect the fertility of cancer survivors.

Overview of biological mechanisms of human carcinogens

This review summarizes the carcinogenic mechanisms for 109 Group 1 human carcinogens identified as causes of human cancer through Volume 106 of the IARC Monographs. The International Agency for Research on Cancer (IARC) evaluates human, experimental and mechanistic evidence on agents suspected of inducing cancer in humans, using a well-established weight of evidence approach. The monographs provide detailed mechanistic information about all carcinogens. Carcinogens with closely similar mechanisms of action (e.g. agents emitting alpha particles) were combined into groups for the review. A narrative synopsis of the mechanistic profiles for the 86 carcinogens or carcinogen groups is presented, based primarily on information in the IARC monographs, supplemented with a non-systematic review. Most carcinogens included a genotoxic mechanism.

Assessment of genotoxicity of vincristine, vinblastine and vinorelbine in human cultured lymphocytes: a comparative study

Vincristine (VCR), vinblastine (VBL) and vinorelbine (VRL) are anticancer agents from the Vinca alkaloid family that have the potential to induce genotoxic effect. The aim of the present study was to compare the genotoxic effect of VCR, VBL and VRL. Levels of 8-hydroxy-2-deoxy guanosine (8-OHdG) and sister chromatid exchanges (SCEs) were measured in cultured human blood lymphocytes treated with VCR, VBL and VRL at concentrations of 0.01 and 0.1 μg/mL. Results showed that VCR, VBL and VRL significantly increased the 8-OHdG levels (p <0.05), whereas it did not cause a significant increase in the frequencies of SCEs in human blood lymphocytes as compared to controls. On the other hand, all three agents significantly increased cells mitotic index (p <0.05). At both tested concentrations, the magnitude of the increase in 8-OHdG was VBL>VCR>VRL. In conclusion, VCR, VBL and VRL induce DNA damage as indicated by the increase in the 8-OHdG biomarker but with different magnitude.

Stem Cell Hierarchy and Clonal Evolution in Acute Lymphoblastic Leukemia

Cancer is characterized by a remarkable intertumoral, intratumoral, and cellular heterogeneity that might be explained by the cancer stem cell (CSC) and/or the clonal evolution models. CSCs have the ability to generate all different cells of a tumor and to reinitiate the disease after remission. In the clonal evolution model, a consecutive accumulation of mutations starting in a single cell results in competitive growth of subclones with divergent fitness in either a linear or a branching succession. Acute lymphoblastic leukemia (ALL) is a highly malignant cancer of the lymphoid system in the bone marrow with a dismal prognosis after relapse. However, stabile phenotypes and functional data of CSCs in ALL, the so-called leukemia-initiating cells (LICs), are highly controversial and the question remains whether there is evidence for their existence. This review discusses the concepts of CSCs and clonal evolution in respect to LICs mainly in B-ALL and sheds light onto the technical controversies in LIC isolation and evaluation. These aspects are important for the development of strategies to eradicate cells with LIC capacity. Common properties of LICs within different subclones need to be defined for future ALL diagnostics, treatment, and disease monitoring to improve the patients' outcome in ALL.

Variegated clonality and rapid emergence of new molecular lesions in xenografts of acute lymphoblastic leukemia are associated with drug resistance

The use of genome-wide copy-number analysis and massive parallel sequencing has revolutionized the understanding of the clonal architecture of pediatric acute lymphoblastic leukemia (ALL) by demonstrating that this disease is composed of highly variable clonal ancestries following the rules of Darwinian selection. The current study aimed to analyze the molecular composition of childhood ALL biopsies and patient-derived xenografts with particular emphasis on mechanisms associated with acquired chemoresistance. Genomic DNA from seven primary pediatric ALL patient samples, 29 serially passaged xenografts, and six in vivo selected chemoresistant xenografts were analyzed with 250K single-nucleotide polymorphism arrays. Copy-number analysis of non-drug-selected xenografts confirmed a highly variable molecular pattern of variegated subclones. Whereas primary patient samples from initial diagnosis displayed a mean of 5.7 copy-number alterations per sample, serially passaged xenografts contained a mean of 8.2 and chemoresistant xenografts a mean of 10.5 copy-number alterations per sample, respectively. Resistance to cytarabine was explained by a new homozygous deletion of the DCK gene, whereas methotrexate resistance was associated with monoallelic deletion of FPGS and mutation of the remaining allele. This study demonstrates that selecting for chemoresistance in xenografted human ALL cells can reveal novel mechanisms associated with drug resistance.

Genomic instability in human lymphocytes from male users of crack cocaine

Recent research suggests that crack cocaine use alters systemic biochemical markers, like oxidative damage and inflammation markers, but very few studies have assessed the potential effects of crack cocaine at the cellular level. We assessed genome instability by means of the comet assay and the cytokinesis-block micronucleus technique in crack cocaine users at the time of admission to a rehabilitation clinic and at two times after the beginning of withdrawal. Thirty one active users of crack cocaine and forty control subjects were evaluated. Comparison between controls and crack cocaine users at the first analysis showed significant differences in the rates of DNA damage (p = 0.037). The frequency of micronuclei (MN) (p < 0.001) and nuclear buds (NBUDs) (p < 0.001) was increased, but not the frequency of nucleoplasmic bridges (NPBs) (p = 0.089). DNA damage decreased only after the end of treatment (p < 0.001). Micronuclei frequency did not decrease after treatment, and nuclear buds increased substantially. The results of this study reveal the genotoxic and mutagenic effects of crack cocaine use in human lymphocytes and pave the way for further research on cellular responses and the possible consequences of DNA damage, such as induction of irreversible neurological disease and cancer.

Factors influencing heterogeneity of radiation-induced DNA-damage measured by the alkaline comet assay

Background

To investigate whether different conditions of DNA structure and radiation treatment could modify heterogeneity of response. Additionally to study variance as a potential parameter of heterogeneity for radiosensitivity testing.

Methods

Two-hundred leukocytes per sample of healthy donors were split into four groups. I: Intact chromatin structure; II: Nucleoids of histone-depleted DNA; III: Nucleoids of histone-depleted DNA with 90 mM DMSO as antioxidant. Response to single (I-III) and twice (IV) irradiation with 4 Gy and repair kinetics were evaluated using %Tail-DNA. Heterogeneity of DNA damage was determined by calculation of variance of DNA-damage (V) and mean variance (Mvar), mutual comparisons were done by one-way analysis of variance (ANOVA).

Results

Heterogeneity of initial DNA-damage (I, 0 min repair) increased without histones (II). Absence of histones was balanced by addition of antioxidants (III). Repair reduced heterogeneity of all samples (with and without irradiation). However double irradiation plus repair led to a higher level of heterogeneity distinguishable from single irradiation and repair in intact cells. Increase of mean DNA damage was associated with a similarly elevated variance of DNA damage (r = +0.88).

Conclusions

Heterogeneity of DNA-damage can be modified by histone level, antioxidant concentration, repair and radiation dose and was positively correlated with DNA damage. Experimental conditions might be optimized by reducing scatter of comet assay data by repair and antioxidants, potentially allowing better discrimination of small differences. Amount of heterogeneity measured by variance might be an additional useful parameter to characterize radiosensitivity.

Genetic damage induced by organic extract of coke oven emissions on human bronchial epithelial cells

Coke oven emissions are known as human carcinogen, which is a complex mixture of polycyclic aromatic hydrocarbon. In this study, we aimed to clarify the mechanism of action of coke oven emissions induced carcinogenesis and to identify biomarkers of early biological effects in a human bronchial epithelial cell line with CYP1A1 activity (HBE-CYP1A1). Particulate matter was collected in the oven area on glass filter, extracted and analyzed by GC/MS. DNA breaks and oxidative damage were evaluated by alkaline and endonucleases (FPG, hOGG1 and ENDO III)-modified comet assays. Cytotoxicity and chromosomal damage were assessed by the cytokinesis-block micronucleus cytome (CBMN-Cyt) assay. The cells were treated with organic extract of coke oven emissions (OE-COE) representing 5, 10, 20, 40μg/mL extract for 24h. We found that there was a dose-effect relationship between the OE-COE and the direct DNA damage presented by tail length, tail intensity and Olive tail moment in the comet assay. The presence of lesion-specific endonucleases in the assays increased DNA migration after OE-COE treatment when compared to those without enzymes, which indicated that OE-COE produced oxidative damage at the level of pyrimidine and purine bases. The dose-dependent increase of micronuclei, nucleoplasmic bridges and nuclear buds in exposed cells was significant, indicating chromosomal and genomic damage induced by OE-COE. Based on the cytotoxic biomarkers in CBMN-Cyt assay, OE-COE may inhibit nuclear division, interfere with apoptosis, or induce cell necrosis. This study indicates that OE-COE exposure can induce DNA breaks/oxidative damage and genomic instability in HBE-CYP1A1 cells. The FPG-comet assay appears more specific for detecting oxidative DNA damage induced by complex mixtures of genotoxic substances.

A core in vitro genotoxicity battery comprising the Ames test plus the in vitro micronucleus test is sufficient to detect rodent carcinogens and in vivo genotoxins

In vitro genotoxicity testing needs to include tests in both bacterial and mammalian cells, and be able to detect gene mutations, chromosomal damage and aneuploidy. This may be achieved by a combination of the Ames test (detects gene mutations) and the in vitro micronucleus test (MNvit), since the latter detects both chromosomal aberrations and aneuploidy. In this paper we therefore present an analysis of an existing database of rodent carcinogens and a new database of in vivo genotoxins in terms of the in vitro genotoxicity tests needed to detect their in vivo activity. Published in vitro data from at least one test system (most were from the Ames test) were available for 557 carcinogens and 405 in vivo genotoxins. Because there are fewer publications on the MNvit than for other mammalian cell tests, and because the concordance between the MNvit and the in vitro chromosomal aberration (CAvit) test is so high for clastogenic activity, positive results in the CAvit test were taken as indicative of a positive result in the MNvit where there were no, or only inadequate data for the latter. Also, because Hprt and Tk loci both detect gene-mutation activity, a positive Hprt test was taken as indicative of a mouse-lymphoma Tk assay (MLA)-positive, where there were no data for the latter. Almost all of the 962 rodent carcinogens and in vivo genotoxins were detected by an in vitro battery comprising Ames+MNvit. An additional 11 carcinogens and six in vivo genotoxins would apparently be detected by the MLA, but many of these had not been tested in the MNvit or CAvit tests. Only four chemicals emerge as potentially being more readily detected in MLA than in Ames+MNvit--benzyl acetate, toluene, morphine and thiabendazole--and none of these are convincing cases to argue for the inclusion of the MLA in addition to Ames+MNvit. Thus, there is no convincing evidence that any genotoxic rodent carcinogens or in vivo genotoxins would remain undetected in an in vitro test battery consisting of Ames+MNvit.

Assessing cytogenotoxicity of cigarette smoke condensates using three in vitro assays

Cigarette smoke condensates (CSCs) are complex mixed compounds that contain both direct and indirect mutagens/carcinogens. To detect genotoxicity of CSCs in vitro, a combination of various enzymes (e.g. activation and detoxification enzymes) called S9 is usually added. However, as S9 may induce cytotoxicity in target cells, it is unclear whether the addition of S9 can impact CSC-induced toxicity. Here, differences in cytogenotoxicity between CSCs in the presence or absence of S9 were studied using three in vitro assays (neutral red uptake assay, comet assay, and TCR gene mutation test) in human peripheral lymphocytes, which were exposed to CSCs at doses of 25, 50, 75, 100 and 125 microg/ml for 4 h. Assay results showed that both CSCs + S9 or CSCs - S9 could induce a dose-dependent elevation of cytogenotoxic effects in human lymphocytes with some differences between the two groups. The cytogenotoxicity induced by CSCs - S9 was significantly higher than that induced by CSCs + S9 in all three assays. The comet and NRU assays revealed that a dose-response relationship of cytogenotoxicity induced by CSCs + S9 was less typical than that induced by CSCs - S9, possibly due to specific cytogenotoxic agents in CSCs and enzymes contained in the S9 mixture. Thus, the three in vitro assays used in the present study are suitable for detecting cytogenotoxic effects in human lymphocytes induced by CSCs. Furthermore, the cytogenotoxicity induced by both CSCs + S9 and CSCs - S9 should be measured simultaneously when assessing and comparing the biological activity of different CSCs.