Aneugenic potential of the nitrogen mustard analogues melphalan, chlorambucil and p-N,N-bis(2-chloroethyl)aminophenylacetic acid in cell cultures in vitro

Centrosome amplification in cancer and cancer-associated human diseases

Accumulated evidence from genetically modified cell and animal models indicates that centrosome amplification (CA) can initiate tumorigenesis with metastatic potential and enhance cell invasion. Multiple human diseases are associated with CA and carcinogenesis as well as metastasis, including infection with oncogenic viruses, type 2 diabetes, toxicosis by environmental pollution and inflammatory disease. In this review, we summarize (1) the evidence for the roles of CA in tumorigenesis and tumor cell invasion; (2) the association between diseases and carcinogenesis as well as metastasis; (3) the current knowledge of CA in the diseases; and (4) the signaling pathways of CA. We then give our own thinking and discuss perspectives relevant to CA in carcinogenesis and cancer metastasis in human diseases. In conclusion, investigations in this area might not only identify CA as a biological link between these diseases and the development of cancer but also prove the causal role of CA in cancer and progression under pathophysiological conditions, potentially taking cancer research into a new era.

Role of aneuploidy in the carcinogenic process: Part 3 of the report of the 2017 IWGT workgroup on assessing the risk of aneugens for carcinogenesis and hereditary diseases

Aneuploidy is regarded as a hallmark of cancer, however, its role is complex with both pro- and anti-carcinogenic effects evident. In this IWGT review, we consider the role of aneuploidy in cancer biology; cancer risk associated with constitutive aneuploidy; rodent carcinogenesis with known chemical aneugens; and chemotherapy-related malignant neoplasms. Aneuploidy is seen at various stages in carcinogenesis. However, the relationship between induced aneuploidy occurring after exposure and clonal aneuploidy present in tumours is not clear. Recent evidence indicates that the induction of chromosomal instability (CIN), may be more important than aneuploidy per se, in the carcinogenic process. Down Syndrome, trisomy 21, is associated with altered hematopoiesis in utero which, in combination with subsequent mutations, results in an increased risk for acute megakaryoblastic and lymphoblastic leukemias. In contrast, there is reduced cancer risk for most solid tumours in Down Syndrome. Mouse models with high levels of aneuploidy are also associated with increased cancer risk for particular tumours with long latencies, but paradoxically other types of tumour often show decreased incidence. The aneugens reviewed that induce cancer in humans and animals all possess other carcinogenic properties, such as mutagenicity, clastogenicity, cytotoxicity, organ toxicities, hormonal and epigenetic changes which likely account for, or interact with aneuploidy, to cause carcinogenesis. Although the role that aneuploidy plays in carcinogenesis has not been fully established, in many cases, it may not play a primary causative role. Tubulin-disrupting aneugens that do not possess other properties linked to carcinogenesis, were not carcinogenic in rodents. Similarly, in humans, for the tubulin-disrupting aneugens colchicine and albendazole, there is no reported association with increased cancer risk. There is a need for further mechanistic studies on agents that induce aneuploidy, particularly by mechanisms other than tubulin disruption and to determine the role of aneuploidy in pre-neoplastic events and in early and late stage neoplasia.

A vibrational spectroscopy study on 3-aminophenylacetic acid by DFT calculations

In this study, in which the group vibrations of 3-aminophenylacetic acid were investigated by electronic structure calculations based on Density Functional Theory (DFT), the possible stable conformers of the molecule were searched through a relaxed "potential energy surface scan" carried out at B3LYP/6-31G(d) level of theory. The corresponding equilibrium geometrical and vibrational spectral data for each of the determined stable conformers and for their possible dimer structures were obtained through "geometry optimisation" and "frequency" calculations carried out at B3LYP/6-31G(d) and B3LYP/6-311G++(d,p) levels of theory. The obtained results confirmed that anharmonic wavenumbers calculated at B3LYP/6-311G++(d,p) level generally quite well agree with the experimental wavenumbers, however, harmonic wavenumbers calculated at both levels of theory need an efficient refinement for a satisfactory agreement with experiment. In particular, the harmonic wavenumbers, IR and Raman intensities refined within Scaled Quantum Mechanical Force Field (SQM FF) methodology constituted the primary data set in the interpretation of the experimental FT-IR, FT-Raman and dispersive Raman spectra of 3-aminophenylacetic acid. By the help of these refined spectral data, the effects of conformation and intermolecular hydrogen bonding on the fundamental bands observed in the experimental spectra could be correctly predicted.

Obesity genetics in mouse and human: back and forth, and back again

Obesity is a major public health concern. This condition results from a constant and complex interplay between predisposing genes and environmental stimuli. Current attempts to manage obesity have been moderately effective and a better understanding of the etiology of obesity is required for the development of more successful and personalized prevention and treatment options. To that effect, mouse models have been an essential tool in expanding our understanding of obesity, due to the availability of their complete genome sequence, genetically identified and defined strains, various tools for genetic manipulation and the accessibility of target tissues for obesity that are not easily attainable from humans. Our knowledge of monogenic obesity in humans greatly benefited from the mouse obesity genetics field. Genes underlying highly penetrant forms of monogenic obesity are part of the leptin-melanocortin pathway in the hypothalamus. Recently, hypothesis-generating genome-wide association studies for polygenic obesity traits in humans have led to the identification of 119 common gene variants with modest effect, most of them having an unknown function. These discoveries have led to novel animal models and have illuminated new biologic pathways. Integrated mouse-human genetic approaches have firmly established new obesity candidate genes. Innovative strategies recently developed by scientists are described in this review to accelerate the identification of causal genes and deepen our understanding of obesity etiology. An exhaustive dissection of the molecular roots of obesity may ultimately help to tackle the growing obesity epidemic worldwide.

Cinnamic acid induces apoptotic cell death and cytoskeleton disruption in human melanoma cells

Anticancer activities of cinnamic acid derivatives include induction of apoptosis by irreversible DNA damage leading to cell death. The present work aimed to compare the cytotoxic and genotoxic potential of cinnamic acid in human melanoma cell line (HT-144) and human melanocyte cell line derived from blue nevus (NGM). Viability assay showed that the IC₅₀ for HT-144 cells was 2.4 mM, while NGM cells were more resistant to the treatment. The growth inhibition was probably associated with DNA damage leading to DNA synthesis inhibition, as shown by BrdU incorporation assay, induction of nuclear aberrations and then apoptosis. The frequency of cell death caused by cinnamic acid was higher in HT-144 cells. Activated-caspase 3 staining showed apoptosis after 24 hours of treatment with cinnamic acid 3.2 mM in HT-144 cells, but not in NGM. We observed microtubules disorganization after cinnamic acid exposure, but this event and cell death seem to be independent according to M30 and tubulin labeling. The frequency of micronucleated HT-144 cells was higher after treatment with cinnamic acid (0.4 and 3.2 mM) when compared to the controls. Cinnamic acid 3.2 mM also increased the frequency of micronucleated NGM cells indicating genotoxic activity of the compound, but the effects were milder. Binucleation and multinucleation counting showed similar results. We conclude that cinnamic acid has effective antiproliferative activity against melanoma cells. However, the increased frequency of micronucleation in NGM cells warrants the possibility of genotoxicity and needs further investigation.

A mode-of-action approach for the identification of genotoxic carcinogens

Distinguishing between clastogens and aneugens is vital in cancer risk assessment because the default assumption is that clastogens and aneugens have linear and non-linear dose-response curves, respectively. Any observed non-linearity must be supported by mode of action (MOA) analyses where biological mechanisms are linked with dose-response evaluations. For aneugens, the MOA has been well characterised as disruptors of mitotic machinery where chromosome loss via micronuclei (MN) formation is an accepted endpoint used in risk assessment. In this study we performed the cytokinesis-block micronucleus assay and immunofluorescence mitotic machinery visualisation in human lymphoblastoid (AHH-1) and Chinese Hamster fibroblast (V79) cell lines after treatment with the aneugen 17-β-oestradiol (E₂). Results were compared to previously published data on bisphenol-A (BPA) and Rotenone data. Two concentration-response approaches (the threshold-[Td] and benchmark-dose [BMD] approaches) were applied to derive a point of departure (POD) for in vitro MN induction. BMDs were also derived from the most sensitive carcinogenic endpoint. Ranking comparisons of the PODs from the in vitro MN and the carcinogenicity studies demonstrated a link between these two endpoints for BPA, E₂ and Rotenone. This analysis was extended to include 5 additional aneugens, 5 clastogens and 3 mutagens and further concentration and dose-response correlations were observed between PODs from the in vitro MN and carcinogenicity. This approach is promising and may be further extended to other genotoxic carcinogens, where MOA and quantitative information from the in vitro MN studies could be used in a quantitative manner to further inform cancer risk assessment.

The mechanism of guanine alkylation by nitrogen mustards: a computational study

The thermodynamics and kinetics for the monofunctional binding of nitrogen mustard class of anticancer drugs to purine bases of DNA were studied computationally using guanine and adenine as model substrates. Mechlorethamine and melphalan are used as model systems in order to better understand the difference in antitumor activity of aliphatic and aromatic mustards, respectively. In good agreement with experiments that suggested the accumulation of a reactive intermediate in the case of mechlorethamine, our model predicts a significant preference for the formation of corresponding aziridinium ion for mechlorethamine, while the formation of the aziridinium ion is not computed to be preferred when melphalan is used. Two effects are found that contribute to this difference. First, the ground state of the drug shows a highly delocalized lone pair on the amine nitrogen of the melphalan, which makes the subsequent cyclization more difficult. Second, because of the aromatic substituent connected to the amine nitrogen of melphalan, a large energy penalty has to be paid for solvation. A detailed study of energy profiles for the two-step mechanism for alkylation of guanine and adenine was performed. Alkylation of guanine is ∼6 kcal mol(-1) preferred over adenine, and the factors contributing to this preference were explained in our previous study of cisplatin binding to purine bases. A detailed analysis of energy profiles of mechlorethamine and melphalan binding to guanine and adenine are presented to provide an insight into rate limiting step and the difference in reactivity and stability of the intermediate in both nitrogen mustards, respectively.

Comparison of the aneugenic properties of nocodazole, paclitaxel and griseofulvin in vitro. Centrosome defects and alterations in protein expression profiles

We have comparatively investigated the aneugenic activity of two anticancer drugs, nocodazole (NOC) and paclitaxel (PTX), and the antifungal griseofulvin with promising role in cancer treatment (GF), which affect microtubule dynamics in different ways. The comparison was achieved in HFFF2 human fibroblasts, MCF-7 human breast cancer cells and C2C12 mouse myoblasts, and focused on three issues: (i) induction of chromosome delay by estimation of MN frequency using CREST analysis; (ii) disturbance of spindle organization with Aurora-A/β-tubulin immunofluorescence; and (iii) alterations in the expression of Aurora-A, β- and γ-tubulin by western blotting. They induced chromosome delay, provoked metaphase arrest and promoted microtubule disorganization, reflecting their common characteristic of generating aneuploidy. In particular, NOC induced mainly monopolar metaphases, although PTX induced only multipolar metaphases. GF generated different types of abnormal metaphases, exhibiting cell specificity. Additionally, NOC decreased the expression of Aurora-A and β-tubulin, while the opposite held true for PTX and GF. γ-Tubulin expression was not modulated owing to NOC treatment, whereas PTX and GF increased γ-tubulin expression. Our findings throw a light on the manifestation of the aneugenicity of the studied compounds through centrosome proliferation/separation and protein expression, reflecting their different effects on microtubule dynamics.

Aneugenic potential of the anticancer drugs melphalan and chlorambucil. The involvement of apoptosis and chromosome segregation regulating proteins

Previous findings showed that the anticancer drugs p-N,N-bis(2-chloroethyl) amino-l-phenylalanine (melphalan, MEL) and p-N,N-bis(2-chloroethyl)aminophenylbutyric acid (chlorambucil, CAB) belonging to the nitrogen mustard group, in addition to their clastogenic activity, also exert aneugenic potential, nondisjunction and chromosome delay. Their aneugenic potential is mainly mediated through centrosome defects. To further investigate their aneugenicity we (a) studied whether apoptosis is a mechanism responsible for the elimination of damaged cells generated by MEL and CAB and (b) investigated if proteins that regulate chromosome segregation are involved in the modulation of their aneugenic potential. Apoptosis was studied by Annexin-V/Propidium Iodide staining and fluorescence microscopy. The involvement of apoptosis on the exclusion of cells with genetic damage and centrosome disturbances was analyzed by DAPI staining and immunofluorescence of β- and γ-tubulin in the presence of pan-caspase inhibitor. The expressions of Aurora-A, Aurora-B, survivin and γ-tubulin were studied by western blot. We found that (a) apoptosis is not the mechanism of choice for selectively eliminating cells with supernumerary centrosomes, and (b) the proteins Aurora-A, Aurora-B and survivin are involved in the modulation of MEL and CAB aneugenicity. These findings are important for the understanding of the mechanism responsible for the aneugenic activity of the anticancer drugs melphalan and chlorambucil.

Genotoxicity of all-trans retinoic acid (ATRA) and its steroidal analogue EA-4 in human lymphocytes and mouse cells in vitro

The aim of our study is to: (a) investigate whether ATRA and its steroidal analogue EA-4 enhance micronucleation in human lymphocytes and mouse cells in vitro and clarify the micronucleation mechanism by FISH and CREST analysis respectively, and (b) analyze their effect on spindle organization by immunofluorescence of β- and γ-tubulin in mouse cells. We found that they: (a) induce micronucleation mainly via chromosome breakage and chromosome delay in a lesser extent, (b) disturb microtubule network, chromosome orientation and centrosome duplication/separation, (c) accumulate cell cycle at ana-telophases, which exert micronucleation, multiple γ-tubulin signals, nucleoplasmic bridges and multinucleation, and (d) generate multinucleated and multimicronucleated interphase cells.

Fluorescence in situ hybridization in combination with the comet assay and micronucleus test in genetic toxicology

Comet assay and micronucleus (MN) test are widely applied in genotoxicity testing and biomonitoring. While comet assay permits to measure direct DNA-strand breaking capacity of a tested agent MN test allows estimating the induced amount of chromosome and/or genome mutations. The potential of these two methods can be enhanced by the combination with fluorescence in situ hybridization (FISH) techniques. FISH plus comet assay allows the recognition of targets of DNA damage and repairing directly. FISH combined with MN test is able to characterize the occurrence of different chromosomes in MN and to identify potential chromosomal targets of mutagenic substances. Thus, combination of FISH with the comet assay or MN test proved to be promising techniques for evaluation of the distribution of DNA and chromosome damage in the entire genome of individual cells. FISH technique also permits to study comet and MN formation, necessary for correct application of these methods. This paper reviews the relevant literature on advantages and limitations of Comet-FISH and MN-FISH assays application in genetic toxicology.

Comparative study of genetic activity of chlorambucil's active metabolite steroidal esters: the role of steroidal skeleton on aneugenic potential

p-N,N-bis(2-chloroethyl)aminophenylacetic acid (PHE), a nitrogen mustard analogue and chlorambucil's active metabolite used as chemotherapeutic agent, has been shown that, in addition to its clastogenic activity, induces chromosome delay. In the present study an efford has been made (a) to investigate if the steroidal analogues of PHE (EA-92, EA-97, AK-333, AK-409 and AK-433) exert the same genetic activity as the parent compound, (b) to further analyze the aneugenic activity of nitrogen mustard analogues, (c) to investigate the mechanism by which they exert aneugenic potential and (d) to correlate the genetic activity with chemical structure. For this purpose the Cytokinesis Block Micronucleus (CBMN) assay was conducted in human lymphocytes in vitro and the micronucleus (MN) frequency was determined to investigate their genetic activity. The mechanism of micronucleation was determined in combination with Fluorescence In Situ Hybridization (FISH) using pancentromeric DNA probe. Since one of the mechanisms that chemicals cause aneuploidy is through alterations in the mitotic spindle, we also investigated the effect of the above compounds on the integrity and morphology of the mitotic spindle using double immunofluorescence of beta- and gamma-tubulin in C(2)C(12) mouse cell line. We found that PHE and its steroidal analogues, EA-92, EA-97, AK-333, AK-409 and AK-433, affect cell proliferation in human lymphocytes and C(2)C(12) mouse cells. All studied compounds are capable of inducing chromosome breakage events, as indicated by the enhanced C(-)MN frequencies. The less lipophilic compounds are the most genetically active molecules. PHE and only two of the studied analogues, AK-409 and AK-433, the most hydrophilic ones, showed aneugenic potential, by increasing the frequencies of MN containing a whole chromosome. The aneugenic potential of the above referred analogues is associated with amplification of centrosome number, since they caused high multipolar metaphase frequencies.

The in vitro genotoxicity of ethanol and acetaldehyde

Ability of ethanol to produce chromosomal changes has been controversial in past many years; nevertheless many recent studies have shown that ethanol itself produces genotoxic effects like acetaldehyde. This study was carried out to evaluate the ability of ethanol and its metabolite acetaldehyde to induce chromosomal changes using in vitro CBMN assay (Cytokinesis Blocked Micronucleus assay) in conjunction with immunofluorescent labeling of kinetochores. Kinetochore staining was used with a view to differentiate, between the genotoxic effects of both chemicals, and ascertain the mechanisms of genotoxicity induction by ethanol and acetaldehyde. Both ethanol and acetaldehyde produced statistically significant (P<0.05) dose dependent increase in MN induction as compared with the controls over the dose range tested. Kinetochore analysis proved that the MN induced in ethanol were originated by an aneugenic mechanism, whereas in the case of acetaldehyde most of the MN had originated by a clastogenic mechanism. This not only confirms the ability of ethanol to produce DNA damage in vitro but it also establishes the efficacy of CBMN assay to detect and differentiate between the genotoxic effects of different genotoxins. Here we report that ethanol is itself genotoxic, at least in vitro, and produces genotoxic effects mainly through an aneugenic mechanism whereas its metabolite acetaldehyde is a clastogen.

In vitro genotoxic assessment of xenobiotic diacylglycerols in an in vitro micronucleus assay

Xenobiotic diacylglycerols (DG) may induce pathological disorders by causing abnormal chromosomal segregation, which could be aneuploid. In this study, seven xenobiotic-diacylglycerols (four of drug origin and three of pesticide origin) were evaluated for their ability to induce aneuploidy in mammalian cultures using in vitro cytokinesis blocked micronucleus (CBMN) assay coupled with kinetochore labeling and interphase fluorescent in situ hybridization. Out of seven xeno-DGs, two (ibuprofen-DG and fenbufen-DG) induced statistically significant (P < 0.001) and dose-dependent increase in micronucleus induction, but this apparent micronucleus induction was very weak in case of fenbufen-DG. These MN were produced predominantly by aneugenic and clastogenic mechanisms, respectively, confirmed by immunofluorescent labeling of kinetochores. Fluorescent in situ hybridization analysis revealed that ibuprofen-DG induced significantly higher nondisjunction for chromosomes 10, 17, and 18. Other xenobiotic diacylglycerols (indomethacin-DG, salicylic acid-DG, 4-(2-methyl-4-chlorophenoxy) butanoic acid-DG (MCPB-DG), 2-(2-methyl-4-chlorophenoxy) propanoic acid-DG (MCPP-DG) and 2-(4-dichlorophenoxy)-butanoic acid-DG (2,4 DB-DG) did not induce micronuclei, but the concentrations tested did not reach levels that caused the marked growth suppression typically required for testing for regulatory testing purposes. However, the levels of growth suppression achieved were similar to that seen with ibuprofen-DG, which was positive. This study shows that xeno-DGs, which have been neglected in the past for their possible link to any pathological disorders, need serious assessment of their mutagenic potential.

Chromosome aberrations and telomere length modulation in bone marrow and spleen cells of melphalan-treated p53+/- mice

The p53 gene regulates cell cycle and apoptotic pathways after induction of DNA damage. Telomeres, capping chromosome ends, are involved in maintaining chromosome stability; alterations of their length have been related to increased levels of chromosomal aberrations. To study a possible interaction between chromosome aberrations, telomere dysfunction, and p53, we investigated via painting analysis the induction and persistence of chromosome aberrations in bone marrow and spleen cells of p53+/- (and wild type) mice exposed for 4, 13, or 26 weeks to 2 mg/kg melphalan (MLP), a chemotherapeutic agent with carcinogenic potential. In addition, telomere length was evaluated in bone marrow cells by quantitative fluorescence in situ hybridization (Q-FISH). Chromosome aberrations were significantly increased in both tissues after MLP treatment. The p53 genotype did not influence the response of spleen cells, whereas a slight but significant increase of the aberration frequency was measured in the bone marrow of p53+/- mice exposed to MLP for 13 weeks with respect to the level detected in the matched wild-type group. The main finding of our still preliminary results on telomere length modulation was again a difference between the two genotypes. In bone marrow cells of wild-type mice, MLP treatment was associated with telomere shortening, while in p53+/- mice telomere elongation was the prevalent response to MLP exposure. In agreement with previous literature data, our in vivo study suggests that even the lack of a single functional copy of the p53 gene might have an impact on the quantity and quality of chromosome alterations induced in cycling cells by a clastogenic exposure.

In vitro micronucleus assay scored by flow cytometry provides a comprehensive evaluation of cytogenetic damage and cytotoxicity

This laboratory has previously reported on the development of a flow cytometry-based method for scoring in vitro micronuclei in mouse lymphoma (L5178Y) cells [S.L. Avlasevich, S.M. Bryce, S.E. Cairns, S.D. Dertinger, In vitro micronucleus scoring by flow cytometry: differential staining of micronuclei versus apoptotic and necrotic chromatin enhances assay reliability, Environ. Molec. Mutagen. 47 (2006) 56-66]. With this method, necrotic and mid/late stage apoptotic cells are labeled with the fluorescent dye ethidium monoazide. Cells are then washed, stripped of their cytoplasmic membranes, and incubated with RNase plus a pan-nucleic acid dye (SYTOX Green). This process provides a suspension of free nuclei and micronuclei that are differentially stained relative to chromatin associated with dead/dying cells. The current report extends this line of investigation to include the human cell line TK6. Additionally, methods are described that facilitate simultaneous quantitative analysis of cytotoxicity, perturbations to the cell cycle, and what we hypothesize is aneuploidization. This comprehensive cytogenetic damage assay was evaluated with the following diverse agents: etoposide, ionizing radiation, methyl methanesulfonate, vinblastine, ethanol, and staurosporine. Cells were harvested after 30h of continuous treatment (in the case of chemicals), or following graded doses of radiation up to 1Gy. Key findings include the following: (1) Significant discrepancies in top dose selection were found for five of the six agents studied when relative survival measurements were based on Coulter counting versus flow cytometry. (2) Both microscopy- and flow cytometry-based scoring methods detected dose-dependent micronucleus formation for the four genotoxic agents studied, whereas no significant increases were observed for the presumed non-genotoxicants ethanol and staurosporine when top dose selection was based on flow cytometric indices of cytotoxicity. (3) SYTOX and ethidium monoazide fluorescence signals conveyed cell cycle and cell death information, respectively, and appear to represent valuable aids for interpreting micronucleus data. (4) The frequency of hypodiploid nuclei increased in response to each of the genotoxic agents studied, but not following exposure to ethanol or staurosporine. Collectively, these results indicate that a comprehensive assessment of genotoxicity and other test article-induced toxicities can be acquired simultaneously using a simple two-color flow cytometry-based technique.