Diazepam induces mitotic arrest at prometaphase by inhibiting centriolar separation

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.

The ability of the mouse lymphoma TK assay to detect aneugens

There is some evidence that the mouse lymphoma TK assay (MLA) can detect aneugens, and this is accepted in the current International Conference on Harmonisation guidance for testing pharmaceuticals. However, whether or not it can be used as a reliable screen for aneugenicity has been the subject of debate. Consequently, aneugens with diverse mechanisms of action were tested in the MLA using 24-h exposure. No evidence of increased mutant frequency was seen with noscapine, diazepam or colchicine and increases were seen with taxol, carbendazim, econazole and chloral hydrate only at high levels of toxicity (for all but one taxol concentration survival reduced to ≤10% of control). None of these agents would be unequivocally classified as positive using currently accepted criteria. The largest increases in mutant number were seen with taxol and carbendazim; therefore, trifluorothymidine (TFT)-resistant clones resulting from treatment with them were cultured and analysed for chromosome 11 copy number using fluorescent in situ hybridisation (FISH) and loss of heterozygosity (LOH). High concentrations of these aneugens induced LOH at all loci examined indicating only one chromosome 11 was present but, perhaps surprisingly, all were found to have two copies of chromosome 11 using FISH. This would be consistent with loss of the tk(+) chromosome 11b with concomitant duplication of chromosome 11a, which has been proposed as a likely mechanism for induction of TFT-resistant clones. However, it was also surprising that analysis of centromere size showed that almost all the clones had both small and large centromeres, i.e. suggesting the presence of both chromosomes 11a and 11b. In conclusion, it appears that the TFT-resistant mutants resulting from treatment with toxic concentrations of some aneugens such as taxol and carbendazim have undergone complex genetic changes. However, these data show that the MLA cannot be used as a routine screen to detect aneugens.

Cytogenetic activity of diazepam in normal human lymphocyte cultures

INTRODUCTION

Diazepam (DZ) belongs to benzodiazepines, a group of drugs used for sedation, for the relief of anxiety, and in the treatment of epilepsy. It has been found that DZ influences cytotoxic activity and diminishes antiviral and antitumor reactions in human natural killer cells in vitro. It has also been demonstrated that DZ causes a significant increase in the frequency of chromosomal aberrations in human lymphocytes in vitro.

MATERIALS AND METHODS

In the present research the cytogenetic effects of DZ have been studied in normal human lymphocyte cultures of peripheral blood at 17.6-211.2 microM (final concentrations). Sister chromatid exchanges (SCEs), one of the most sensitive methods reflecting instability in DNA or a deficiency in DNA repair mechanisms, and proliferation rate index (PRI), a valuable indicator for cytostatic activity, have been evaluated.

RESULTS

After 72-h incubation, DZ was found to cause a dose-dependent, statistically significant increase of SCE frequency (p < 0.001), followed by an equally significant decrease of PRI (p < 0.001).

CONCLUSION

Our results suggest that DZ's administration presents cytogenetic effects in normal human lymphocyte cultures.

Carbamazepine induces mitotic arrest in mammalian Vero cells

We reported recently that the anticonvulsant drug carbamazepine, at supratherapeutic concentrations, exerts antiproliferative effects in mammalian Vero cells, but the underlying mechanism has not been elucidated. This motivates us to examine rigorously whether growth arrest was associated with structural changes in cellular organization during mitosis. In the present work, we found that exposure of the cells to carbamazepine led to an increase in mitotic index, mainly due to the sustained block at the metaphase/anaphase boundary, with the consequent inhibition of cell proliferation. Indirect immunofluorescence, using antibodies directed against spindle apparatus proteins, revealed that mitotic arrest was associated with formation of monopolar spindles, caused by impairment of centrosome separation. The final consequence of the spindle defects induced by carbamazepine, depended on the duration of cell cycle arrest. Following the time course of accumulation of metaphase and apoptotic cells during carbamazepine treatments, we observed a causative relationship between mitotic arrest and induction of cell death. Conversely, cells released from the block of metaphase by removal of the drug, continued to progress through mitosis and resume normal proliferation. Our results show that carbamazepine shares a common antiproliferative mechanism with spindle-targeted drugs and contribute to a better understanding of the cytostatic activity previously described in Vero cells. Additional studies are in progress to extend these initial findings that define a novel mode of action of carbamazepine in cultured mammalian cells.

Caspase-independent apoptosis is activated by diazepam-induced mitotic failure in HeLa cells, but not in human primary fibroblasts

DZ, a benzodiazepine known to affect centrosome separation at prophase, leads to a higher degree of mitotic arrest in HeLa cells than in primary human fibroblasts. In fact, differently from fibroblasts, which undergo a transient block in prophase-to-prometaphase transition, a high proportion of tumor cells attempt to escape from the DZ-imposed mitotic block, fail to undergo complete mitosis and die by mitotic failure. DZ-treated samples showed certain biochemical hallmarks of apoptosis, such as induction of the proapototic Bax protein, mitochondrial alterations assessed by JC-1 staining and TEM analysis, PARP cleavage, and DNA fragmentation. However, in DZ-treated cells, we observed a very low or absent caspase activation as shown by immunofluorescence and immunoblot experiments with antibodies directed to activated caspases and by staining with the pancaspase inhibitor FITC-VAD-FMK. Experiments on mitochondrial depolymerization and apoptosis induction carried out in the presence of specific inhibitors of caspase-2 and caspase-3/7 indicated a caspase-independent apoptotic process induced by DZ. Accordingly, TEM analysis of treated cells revealed ultrastructural features resembling those reported for caspase-independent apoptosis. In conclusion, we hypothesize that HeLa cells override the prophase block imposed by DZ, producing a high rate of aberrant pro-metaphases, which, in turn, activates caspase-independent, apoptosis-like mitotic catastrophe.

Optimum conditions for detecting hepatic micronuclei caused by numerical chromosome aberration inducers in mice

To ascertain an optimum condition for detecting micronuclei in the liver caused by numerical aberration inducers, either carbendazim (125-1000mg/kg, p.o.), colchicine (0.375-1.5mg/kg, i.v.), cytochalasin B (2.5-20mg/kg, i.v.), diazepam (3.13-25mg/kg, i.v.), noscapine (7.8-62.5mg/kg, i.v.), paclitaxel (1-100mg/kg, i.v.) or trichlorfon (18.75-150mg/kg, i.v.) was administered once to male Slc:ddY mice 1 day before or after partial hepatectomy (PH, Day 1). Five days after PH (on Day 6), hepatic micronuclei were determined in conjunction with classifications of the main nuclei and relative liver weights as a proliferative indicator or a dysfunction marker of cell division. Additionally, hepatocyte proliferation index (HPI) was calculated by using mono-, bi- and multinucleated cell counts. Treatment of mice with six compounds, except for colchicine, after PH showed higher incidence of micronucleated hepatocytes (MNH) than that before PH, and also increases in binucleated and multinucleated cells. Especially for carbendazim, diazepam, noscapine and trichlorfon, the dosing after PH was essential for the detecting numerical aberration. Colchicine evidently increased HPI and decreased relative liver weights without MNH induction on Day 6. On Day 8 when HPI and relative liver weights almost returned to the basal range, a significant increase in MNH was noted. This implied that the strong inhibition of colchicine on hepatocyte proliferation may obstruct the induction of MNH on Day 6. In conclusion, to detect the potential numerical aberration, exposure of mice to test chemicals should be performed 1 day after PH, during which enhanced proliferation of hepatocytes was seen, and it would be better to analyze the liver specimens on Day 6 or more post-PH.

Ovarian follicle bioassay reveals adverse effects of diazepam exposure upon follicle development and oocyte quality

A mouse ovarian follicle bioassay was used to study folliculogenesis and oocyte quality in vitro. Diazepam (DZ) was chosen as test compound to evaluate the system for its ability to detect possible effects of chemicals on reproduction. The bioassay is suitable to analyze the influence of DZ on each of the follicular components at any stage of development. A dose finding study revealed that follicle growth, differentiation and steroidogenesis were significantly disturbed by > or =5 microg/ml DZ. A transient exposure procedure was used to examine stage-specific sensitivities of oogenesis to DZ. The oocyte appeared to be most vulnerable during its growth process within the follicle. Resumption of meiosis was disturbed dose-dependently with reduced oocyte quality after chronic exposure to > or =2.5 microg/ml DZ. The bioassay is a highly efficient and informative tool to assess the hazards of chemical compounds for female fertility and to elucidate their mechanisms of action.

Diazepam and propofol used as anesthetics during open-heart surgery do not cause chromosomal aberrations in peripheral blood lymphocytes

Diazepam is a benzodiazepine with anticonvulsant, anxiolytic, sedative and muscle-relaxing properties. Many aspects of its toxicity have been investigated, including genotoxic and carcinogenic effects in various model systems. However, it is still unclear whether diazepam is in fact a genotoxic agent. Propofol is a rapid-onset, short-acting intravenous anesthetic agent. It is used widely for the induction and maintenance of anesthesia as well as for long-term sedation in intensive care units. There is limited information in the literature on its genotoxic effects. Both drugs are commonly used as anesthetic in patients undergoing open-heart surgery. Therefore, we investigated the possible genotoxic effects of propofol and diazepam in those patients, using a chromosomal aberration (CA) assay. Peripheral blood samples were collected from 45 patients before induction of anesthesia and at the end of the anesthesia with diazepam or propofol. In Group I (n=24), anesthesia was induced with 0.2 mg kg(-1) diazepam and 10 microg kg(-1) fentanyl. In Group II (n=21), anesthesia was induced with 1 mg kg(-1) propofol and 10 microg kg(-1) fentanyl. Pancuronium bromide (0.1 mg kg(-1)) was administered for skeletal muscle relaxation in both groups. Anesthesia was maintained by diazepam administration at 5 mg kg(-1) in Group I or by continuous propofol administration at 2-4 mg (kg h)(-1) in Group II. All patients received 0.02 mg kg(-1) pancuronium and 5 microg kg(-1) fentanyl boluses at 30-40 min intervals for anesthesia maintenance. Body temperature was controlled during bypass in the two groups. We found that the mean frequency of CAs in both groups before and at the end of the anesthesia were not statistically significantly different. Our analysis also indicated that age, smoking habit and gender were not confounding factors. In conclusion, our results indicate that diazepam and propofol do not exert genotoxic effects in blood cells during open-heart surgery.

Stuck in division or passing through: what happens when cells cannot satisfy the spindle assembly checkpoint

Cells that cannot satisfy the spindle assembly checkpoint (SAC) are delayed in mitosis (D-mitosis), a fact that has useful clinical ramifications. However, this delay is seldom permanent, and in the presence of an active SAC most cells ultimately escape mitosis and enter the next G1 as tetraploid cells. This review defines and discusses the various factors that determine how long a cell remains in mitosis when it cannot satisfy the SAC and also discusses the cell's subsequent fate.

Diazepam enhances etoposide-induced cytotoxicity in U-87 MG human glioma cell line

Various approaches might be employed in an effort to increase efficacy of the chemotherapeutic treatment of cancer. Recently, various modulators of anticancer therapy effectiveness have been studied. Antiproliferative effects of peripheral benzodiazepine receptor (PBR) ligands might be exploited to enhance cytotoxic effect of a chemotherapeutic drug towards cancer cells. In this work, we sought to enhance cytotoxic effect of etoposide (VP-16) by a PBR ligand, diazepam (DZ) in U-87 MG human glioma cells. Cytotoxicity of VP-16, DZ and their combinations was assessed by using the microculture MTT assay. Cell survival, effective concentrations (EC) and the onset of cytotoxic effect were determined. After 72 h of cultivation, survival of U-87 MG cells was reduced to 57 +/- 7% in the presence of VP-16 at 12.5 microg/mL alone, whereas DZ at 10-4 mol/L alone caused 28 +/- 6% reduction in cell survival. Coincubation of VP-16 at 12.5 microg/mL with DZ at 10-4 mol/L led to a further decrease in cell survival to 45 +/- 6%. Furthermore, DZ at 10-4 mol/L significantly decreased effective concentrations, EC10, EC30 and EC50, of VP-16 and the dose-response curves were shifted to the left. Addition of DZ at 10-4 mol/L to VP-16 also facilitated the onset of its cytotoxic effect. The same decrease in survival was thus achieved approximately 30 h earlier in comparison with VP-16 alone. However, DZ at 10-9 mol/L failed both to exert any effect on glioma cells survival and enhance cytotoxic effect of VP-16. DZ at 10-4 mol/L was capable of both reducing U-87 MG glioma cells survival when applied alone and also enhancing the cytotoxic effect of VP-16. No such observation was made for the lower concentrations of DZ. Potential implementation of diazepam in the antiglioma/anticancer armamentarium awaits further experimentation but phase I and phase II clinical trials could be suggested.

Detection of aneuploidy in rodent and human sperm by multicolor FISH after chronic exposure to diazepam

Aneuploidy induction in male germ cells of mice and men after chronic exposure to diazepam (DZ; CAS 439-14-5; Valium was assessed by multicolor fluorescence in situ hybridization (FISH). DZ, a widely administered sedative and muscle relaxant, was proposed to act as an aneugen by disturbing spindle function in various assay systems. Male mice were treated by oral intubation with 3mg/kg DZ once or daily for 14 consecutive days. At 22 days after the last treatment, epididymal sperm were collected from the caudae epididymes. Evaluation of aneuploid and diploid sperm (10,000 sperm per animal) was performed by multicolor FISH employing DNA probes specific for chromosomes X, Y, and 8 simultaneously. We found a significant increase in the frequency of disomy 8 in subchronically DZ-treated mice when compared to the concurrent solvent control group (2.4-fold; P<0.01), while no increase was detected for sex-chromosome hyperhaploidies. No effect was seen when mice were treated with a single dose (3mg/kg DZ). In a parallel human approach, two men were evaluated who chronically ingested >0.3mg/kg/d DZ for more than 6 months. Multicolor FISH was applied to human sperm probing for chromosomes X, Y, and 13. Frequencies for sperm with disomy 13, disomy X, and total sex-chromosomal disomies were found to be elevated among the two subjects after chronic DZ-exposure compared to control subjects. In conclusion, the results indicate that diazepam acts as an aneugen during meiosis in male spermatogenesis, both in mice and humans. The quantitative comparison indicates that humans may be at least 10 times more sensitive than mice for aneuploidy induction by DZ during male meiosis.

Centrosome reduction during Rhesus spermiogenesis: gamma-tubulin, centrin, and centriole degeneration

Centrosome reduction during spermiogenesis has been studied using anti-gamma-tubulin and anti-centrin antibodies and electron microscopy in nonhuman primates. Rhesus spermatids possess apparently normal centrosomes comprising a pair of centrioles associated with gamma-tubulin and centrin. However, they do not nucleate detectable microtubules. The spermatids discard gamma-tubulin in the residual bodies during the spermiation stage. Mature sperm do not have any detectable gamma-tubulin. About half of the centrin associated with the distal centriole degenerates during spermiogenesis and the remainder is intimately bound to the centriolar microtubules. The mature sperm possess highly degenerated distal centrioles. The centriolar microtubules degenerate in the rostral region and the ventral side of the sperm. The study indicates that the centrosome is reduced during rhesus spermiogenesis, but not completely as in mice.

Increased expression of peripheral benzodiazepine receptors and diazepam binding inhibitor in human tumors sited in the liver

The peripheral benzodiazepine receptor system triggers intracellular metabolic events and has been associated with cell proliferation. Its endogenous ligand, the diazepam binding inhibitor, contributes to steroidogenesis by promoting cholesterol delivery to the inner mitochondrial membrane. The present study was undertaken to verify whether this system is altered in tumors sited in the liver. Peripheral benzodiazepine receptors and diazepam binding inhibitor were studied using immunocytochemistry and in situ hybridization in 9 human tumors sited in the liver, in liver hyperplasia, cirrhotic nodular regeneration, intestinal adenocarcinoma and in surrounding non-tumoral tissue. Immunocytochemical staining and in situ hybridization demonstrated that peripheral benzodiazepine receptors and diazepam binding inhibitor were more prominently expressed in neoplastic cells than in non-tumoral tissue. They were present in the same cells, suggesting that diazepam binding inhibitor may act in an intracrine manner in these cells. Higher peripheral benzodiazepine receptors and diazepam binding inhibitor expression in tumor cells suggest an implication of this system in the metabolism of neoplastic cells. Furthermore the evaluation of peripheral benzodiazepine receptor and diazepam binding inhibitor expression might be useful in evaluating malignancy and in diagnostic approaches of tumors in liver tissue.

The mammalian interphase centrosome: two independent units maintained together by the dynamics of the microtubule cytoskeleton

In mammalian cells the centrosome or diplosome is defined by the two parental centrioles observed in electron microscopy and by the pericentriolar material immunostained with several antibodies directed against various centrosomal proteins (gamma-tubulin, pericentrin, centrin and centractin). Partial destabilization of the microtubule cytoskeleton by microtubule-disassembling substances induced a splitting and a slow migration of the two diplosome units to opposite nuclear sides during most of the interphase in several mammalian cell lines. These units relocated close together following drug removal, while microtubule stabilization by nM taxol concentrations inhibited this process. Cytochalasin slowed down diplosome splitting but did not affect its relocation after colcemid washing. These results account for the apparently opposite effects induced by microtubule poisons on centriole separation. Moreover, they provide new information concerning the centrosome cycle and stability. First, the centrosome is formed by two units, distinguished only by the number of attached stable microtubules, but not by pericentrin, gamma-tubulin, centrin and centractin and their potency to nucleate microtubules. Second, the centrosomal units are independent during most of the interphase. Third, according to the cell type, these centrosomal units are localized in close proximity because they are either linked or maintained close together by the normal dynamics of the microtubule cytoskeleton. Finally, the relocalization of the centrosomal units with their centrioles in cells possessing one or two centrosomes suggests that their relative position results from the overall tensional forces involving at least partially the microtubule arrays nucleated by each of these entities.

Up-regulation of peripheral benzodiazepine receptor system in hepatocellular carcinoma

Increased number of peripheral benzodiazepine receptors (PBRs) have been found in some tumors outside the liver. The present study was to verify whether the PBR system is altered in hepatocellular carcinoma (HCC). The levels of endogenous benzodiazepine-like compounds (BZDs), measured by radioreceptor binding technique after HPLC purification and the endogenous ligand for PBRs, termed diazepam binding inhibitor (DBI), measured by radioimmunoassay utilizing a specific antibody for human DBI, were studied in the blood of 15 normal subjects, 12 liver cirrhosis and 10 patients with HCC. The levels of BZDs in serum were increased hundred fold in liver cirrhosis patients and slightly elevated in HCC patients. DBI was found to be increased in HCC patients. The binding recognition sites for PBRs (Bmax) were increased 4 to 7 fold in HCC tissue in comparison with that found in non-tumoral liver tissue (NTLT). On the contrary the concentrations of DBI were found to be significantly decreased in HCC tissue in comparison with the respective NTLT. These results seem to suggest an implication of PBRs and of their putative endogenous ligands in the metabolism of these neoplastic cells and possibly in their proliferation. The up-regulation of PBRs found in HCC tissue seems to indicate an increased functional activity of these receptors and opens up the possibility of new pharmacological and diagnostic approaches while the changes in the circulating endogenous ligands for the above receptors might be envisaged as early markers of tumorigenesis in liver cirrhosis.

Centrosome structure and function is altered by chloral hydrate and diazepam during the first reproductive cell cycles in sea urchin eggs

This paper explores the mode of action of the tranquillizers chloral hydrate and diazepam during fertilization and mitosis of the first reproductive cell cycles in sea urchin eggs. Most striking effects of these drugs are the alteration of centrosomal material and the abnormal microtubule configurations during exposure and after recovery from the drugs. This finding is utilized to study the mechanisms of centrosome compaction and decompaction and the dynamic configurational changes of centrosomal material and its interactions with microtubules. When 0.1% chloral hydrate or 350-750 microM diazepam is applied at specific phases during the first cell cycle of sea urchin eggs, expanded centrosomal material compacts at distinct regions and super-compacts into dense spheres while microtubules disassemble. When eggs are treated before pronuclear fusion, centrosomal material aggregates around each of the two pronuclei while microtubules disappear. Upon recovery, atypical asters oftentimes with multiple foci are formed from centrosomal material surrounding the pronuclei which indicates that the drugs have affected centrosomal material and prevent it from functioning normally. Electron microscopy and immunofluorescence studies with antibodies that routinely stain centrosomes in sea urchin eggs (4D2; and Ah-6) depict centrosomal material that is altered when compared to control cells. This centrosomal material is not able to reform normal microtubule patterns upon recovery but will form multiple asters around the two pronuclei. When cells are treated with 0.1% chloral hydrate or 350-750 microM diazepam during mitosis, the bipolar centrosomal material becomes compacted and aggregates into multiple dense spheres while spindle and polar microtubules disassemble. With increased incubation time, the smaller dense centrosome particles aggregate into bigger and fewer spheres. Upon recovery, unusual irregular microtubule configurations are formed from centrosomes that have lost their ability to reform normal mitotic figures. These results indicate that chloral hydrate and diazepam affect centrosome structure which results in the inability to reform normal microtubule formations and causes abnormal fertilization and mitosis.

Genetic toxicology of four commonly used benzodiazepines: a review

Benzodiazepines are a group of drugs which have been extensively used for their activities as an anti-anxiety, sedative, muscle relaxant and anti-convulsant. Benzodiazepines at present are the most commonly prescribed drugs. Some of these drugs are teratogenic and also carcinogenic in experimental animals. The wide human exposure to this group of drugs throughout the world is of great concern for human health. In the present review, we have attempted to evaluate and update the mutagenic and genotoxic effects of four of the most commonly used benzodiazepines, i.e., chlordiazepoxide (CDZ), diazepam (DZ), nitrazepam (NZ) and oxazepam (OZ) based on available literature.

A new aspect of the antiproliferative action of peripheral-type benzodiazepine receptor ligands

Ro 5-4864 (4-chlorodiazepam), PK 11195 (1-(2-chlorophenyl)-1,3-dihydro-1-methyl-propyl)isoquinoline carboxamide) and diazepam inhibit, in a concentration-dependent way, the proliferation of V79 Chinese hamster lung cells (IC50 values were: 65.0 +/- 3.73 microM, 57.70 +/- 4.75 microM and 106.80 +/- 8.89 microM, respectively) without being cytotoxic. This antiproliferative effect is mediated by mitosis arrest in the G2 + M stage without affecting DNA synthesis and seems unrelated to a specific interaction of these drugs with the peripheral-type benzodiazepine receptor.

Antimicrotubule effects of the novel antitumor benzoylphenylurea derivative HO-221

The antitumor action of HO-221, a novel benzoylphenylurea derivative, was studied. The in vitro cytotoxic strength of HO-221 was investigated, as measured by IC50 values, compared with those of other drugs with different action mechanisms, using Chinese hamster lung (CHL) cells, mouse leukemia L1210 cells and human promyelocytic leukemia HL-60 cells. Morphological alterations following treatment were observed under a phase contrast microscope, and the mitotic index was determined at regular intervals to check for accumulation of metaphase cells. HO-221 was found to have a very strong toxic effect on all cell types, equal to that of the spindle poisons used as controls. HO-221 also produced the same specific morphological changes as the spindle poisons, with a significant accumulation of metaphase cells. A chromosome analysis of treated cells showed that HO-221 frequently induced polyploid and aneuploid cells, but without accompanying chromosome-breaking activity. An in vivo mouse bone marrow micronucleus assay was also carried out. The assay allowed the in vivo identification of a chromosome breaker or a spindle poison through the measurement of the relative sizes of micronuclei produced and erythrocytes. HO-221 was found frequently to induce relatively large micronuclei, an action regarded as specific to spindle poisons. It was thus demonstrated that HO-221 acts as a spindle poison both in vitro and in vivo. In order to investigate the mechanism of this action, a study of tubulin assembly using purified calf brain tubulin was carried out, which demonstrated clearly that HO-221 inhibits microtubule assembly. A detailed investigation of the action mechanism of HO-221 as a spindle poison is now called for.

The effects of diazepam on mitosis and the microtubule cytoskeleton. I. Observations on the diatoms Hantzschia amphioxys and Surirella robusta

The effects of diazepam (DZP) on mitosis and the microtubule (MT) cytoskeleton in the live diatoms Hantzschia amphioxys and Surirella robusta were followed using time-lapse video microscopy. Similarly treated cells were fixed and later examined for immunoflouresence staining of MTs or for transmission electron microscopy. DZP treatment (250 microM) had no effect on interphase cells but affected mitosis, resulting in the majority of prometaphase and metaphase chromosomes releasing from one or both spindle poles and collecting irregularly along the central spindle. Chromosomes remaining attached to one pole continued to display slight prometaphase oscillations; however, this activity was never observed in metaphase spindles. Following removal of DZP, some chromosomes still bipolarly attached, immediately released elastically from one pole. Within the first 2 minutes of recovery, all chromosomes recommenced spindle attachment, exhibiting normal prometaphase oscillations and proceeded through mitosis. DZP treatment during anaphase had no detectable effect on chromosome motion or cell cleavage. These results suggest that DZP acts as an anti-MT agent, selectively affecting polar MTs at prophase, prometaphase and metaphase, and thereby weakening kinetochore connection to the poles. From these and other results (unpublished), its mode of action is different to that of most anti-MT agents.

Comparison of the aneugenic activity of diazepam in mouse oocytes and other mammalian cells

Previous studies have reported that diazepam (DZ) is capable of inducing mitotic-meiotic arrest and increasing the frequency of aneuploidy in mammalian cells both in vitro and in vivo. We now report that DZ failed to induce either meiotic arrest or aneuploidy in mouse oocytes. In fact, doses of 0, 50, 100, or 150 mg/kg DZ administered at the same time as human chorionic gonadotropin did not induce the ovulation of metaphase I oocytes or of hyperploid metaphase II oocytes. A reduction in the number of ovulated oocytes was observed in the treated groups relative to controls, but this reduction was only significant (p < 0.01) at the highest dose. These findings indicate that different results are found among the assays used for detecting chemically induced aneuploidy. Determining the factors responsible for these differences is an important area for future research.

The cytochalasin-B micronucleus/kinetochore assay in vitro: studies with 10 suspected aneugens

An in vitro micronucleus assay in low passage Chinese hamster Luc2 cells capable of detecting numerical and structural chromosome changes was developed. Chromosome loss was inferred by indirect visualisation of human CREST antikinetochore antibodies bound to centromeres in chemically-induced micronuclei of cytochalasin-B arrested binucleated cells. The assay was used to evaluate 10 chemicals which had been selected for their known or suspected effects upon various components of the cell-division apparatus. These chemicals were colchicine (COL), vinblastine (VBL), thiabendazole (TBZ), chloral hydrate (CH), thimerosal (TM), diazepam (DZ), pyrimethamine (PYR), hydroquinone (HQ), cadmium chloride (CdCl2) and econazole nitrate (EZ). Mitomycin-C (MMC) was used as a positive control for the induction of micronuclei. 8 of the core chemicals induced micronuclei in Chinese hamster Luc2 cells. 4 of the chemicals (COL, VBL, TBZ, CH) increased levels of micronuclei which were positive for kinetochore antibody labelling and hence chromosome loss. 3 of the chemicals (DZ, PYR, HQ) and the positive control (MMC) increased the levels of Mn which were negative for kinetochore antibody labelling. The results with TM were equivocal and EN was negative. The results of these studies suggest that the cytochalasin-B Mn/k assay is a cost-effective, simple and rapid alternative to classical cytogenetic assays for the detection of chemically induced aneuploidy.

Induction of mitotic aneuploidy using Chinese hamster primary embryonic cells. Test results of 10 chemicals

Using primary Chinese hamster embryonic cells, 10 known or suspected aneugens supplied as a part of the EC 4th Environmental Research and Development Programme were evaluated by the technique described by Dulout and Natarajan (1987). The chemicals included cadmium chloride, chloral hydrate, colchicine, diazepam, econazole, hydroquinone, pyrimethamine, thiabendazole, thimerosal and vincristine. All chemicals except pyrimethamine gave clearly positive effect at most of the doses tested. The ease with which the assay is performed and reproducible results that are obtained with the suspected compounds indicate that this in vitro test using primary embryonic fibroblasts is a promising one for routine screening.

A comparison of two in vitro mammalian cell cytogenetic assays for the detection of mitotic aneuploidy using 10 known or suspected aneugens

Two in vitro cytogenetic assays were evaluated for their ability to detect aneugenic and polyploidy-inducing agents using a battery of 10 known or suspected aneugens supplied as part of the EEC 4th Environmental Research and Development Programme. The compounds tested were colchicine, vinblastine, chloral hydrate, thiabendazole, hydroquinone, thimerosal, cadmium chloride, econazole nitrate, pyrimethamine and diazepam. The cell division aberration assay employed a differential chromosome/spindle staining procedure to detect perturbations of the mitotic division apparatus. This assay was carried out in two pulmonary-derived Chinese hamster cell lines; the immortal DON:Wg3h culture and a low passage LUC2 culture. The second assay involved quantification of metaphase chromosomes, for which only the LUC2 cell line was used, due to the stability of its diploid karyotype. All the chemicals induced spindle disturbances in the immortal line. In addition, all the compounds except cadmium chloride yielded positive results in the LUC2 culture, although many were not as potent. In the low passage line, 8 of the compounds (colchicine, vinblastine, chloral hydrate, thiabendazole, thimerosal, econazole nitrate, pyrimethamine and diazepam) induced aneuploidy and/or tetraploidy. Cadmium chloride was negative in the chromosome enumeration assay and hydroquinone yielded inconclusive results. The study of cell division aberrations was much less time-consuming and technically complex than the counting of metaphase chromosomes. In addition, it provided a degree of mechanistic understanding of the mode of action of some aneugenic and polyploidy-producing agents. However, the enumeration of chromosomes provides a more definitive data set for the evaluation of a chemical's aneugenic potential.

The detection and assessment of the aneugenic potential of environmental chemicals: the European Community Aneuploidy Project

Within the framework of its' Environment Research and Development Programme, the European Communities (EC) Directorate General (DG) XII has supported a research project aimed at developing and validating assay systems for the detection and evaluation of chemicals capable of inducing numerical chromosome changes such as aneuploidy and polyploidy. A range of test chemicals were selected, which include a core set comprising; colchicine, econazole nitrate, chloral hydrate, hydroquinone, diazepam, thiabendazole, cadmium chloride, thimerosol, pyrimethamine and vinblastine sulphate. These test chemicals were used to evaluate the ability of test systems ranging from tubulin polymerisation, fungal cultures, cultured mammalian cells and intact rodents to detect chemical aneugens and to assess the significance of such activity to exposed human populations.

In vivo studies on chemically induced aneuploidy in mouse somatic and germinal cells

Within the context of a coordinated program to study aneuploidy induction sponsored by the European Community, nine chemicals were tested in mouse bone marrow and spermatocytes after intraperitoneal injection. In somatic cells, cell progression delay, hyperploidy, polyploidy induction and induction of micronucleated polychromatic erythrocyte (MnPCE) were studied. In germ cells hyperploidy induction was evaluated. The chemicals selected were: colchicine (COL), econazole (EZ), hydroquinone (HQ), thiabendazole (TB), diazepam (DZ), chloral hydrate (CH), cadmium chloride (CD), pyrimethamine (PY) and thimerosal (TM). Using literature data on c-mitotic effects in bone marrow as a reference, the same doses were tested in somatic and germ cells in order to compare the effects induced. Bone marrow cells were sampled 18 or 24 h after treatment. Germ cells were sampled 6, 8 or 18 h after treatment. Effects of COL and HQ in bone marrow have been reported elsewhere. Somatic effects were induced by CH (hyperploidy and cell cycle lengthening), TB (MnPCEs and cell cycle lengthening) and by PY (MnPCEs). EZ, DZ, CD and TM did not induce any kind of somatic effects. An increase in the incidence of hyperploid spermatocytes was induced by COL, at three dose levels, and by one dose of HQ and TB. All the other chemicals did not induce germinal aneuploidy at any dose or time tested. The hyperploidy control frequency ranged between 0.4 and 1.0% in somatic cells and from 0.3 to 0.9% in germ cells. In both somatic and germ cells, the maximum yield of induced hyperploidy did not exceed 3.5%. The time period of target cell sensitivity is probably restricted and this, associated with the heterogeneity and the asynchrony of cellular maturation processes, may account for our data. Under these circumstances, the negative data should be interpreted with some caution, particularly in germ cells, where additional indicators of chemical-cell interaction and cell cycle effects were not provided by standardized approaches. The possibility of increasing the size of analyzed cell samples could be considered in the light of automatic scoring procedures.

Effects of potential aneuploidy inducing agents on microtubule assembly in vitro

The present study was carried out with the 10 known or suspected spindle poisons of the Commission of the European Communities program to study aneuploidy induction. We have investigated these substances on the assembly of isolated bovine microtubules at 10, 100 and 1000 microM and studied morphology by electron microscopy. The substances could be grouped into two categories, strong and weak inhibitors. Colchicine, vinblastine and thimerosal were strong inhibitors; cadmium chloride, thiabendazole, chloral hydrate, hydroquinone, diazepam and econazole were weak inhibitors, the latter three causing aberrant forms visible on electron microscopy. Pyrimethamine did not inhibit the assembly of microtubules, but produced aberrant forms.

Cytogenetic effects of diazepam in peripheral lymphocytes of self-poisoned persons

The frequencies of chromosomal aberrations and of micronuclei were determined in lymphocyte cultures of 25 patients who attempted suicide with diazepam, 6-12 h, 72 h and 30 days after self-poisoning. These data were compared with those of healthy controls. The frequencies of numerical aberrations showed a significant increase immediately after self-poisoning. However, this effect could not be detected on the 3rd and 30th days after self-poisoning.

Clorazepate synchronizes cultured rat C6 glioma in the early G1 phase of the cell cycle

A water soluble benzodiazepine, clorazepate, has been used to establish the point of benzodiazepine proliferative arrest in the rat C6 glioma. Clorazepate inhibited C6 proliferation in a dose-dependent manner with an IC50 value of 280 microM, as judged by a nuclei counting procedure. Release of cells from a 48 h exposure to 350 microM clorazepate, at which over 70% of the cells were arrested, resulted in a synchronous entry into S phase 8-9 h later, as evidenced by a sharp increase in the incorporation of [3H]thymidine. This restriction point was demonstrated to be 2-3 h into the G1 phase by measuring the length of G1 in synchronized populations of C6 cells obtained by selection of mitotic figures from an asynchronous culture. Synchronous arrest of C6 by clorazepate required an exposure period of 24-36 h, approximately twice the doubling time of the cell line. A morphological study confirmed an early G1 point of proliferative arrest. Clorazepate synchronized cells exhibited a uniform morphology with the majority of cells assuming a configuration representative of anchorage-dependent cells in an early phase of attachment. The majority of cells were somewhat rounded and attached to the substratum by cytoplasmic 'skirts' with punctate structures which may represent focal adhesion points.

Effects of the tumor inhibitor IKP-104, a 4(1H)-pyridinone derivative, on cytoskeletal microtubules of cultured tumor cells

The effects of IKP-104, a 4(1H)-pyridinone derivative, on the mitotic profile and cytoskeletal microtubule dynamics of cultured B16 melanoma cells were examined in order to investigate the mechanism of its antitumor activity. The exposure to IKP-104 caused accumulation of cells in abnormal metaphase with chromosomes scattered within the cytoplasm and induced polyploid and multinucleate cells as detected by differential staining microscopy with brilliant blue R and safranin O. An immunofluorescence study with monoclonal anti-alpha-tubulin antibody revealed that IKP-104 diminished cytoskeletal microtubules of both interphase and mitotic cells, resulting in induction of a few fragments resembling "microtubular bundles" induced by vinblastine (VLB). These results indicated that IKP-104 arrests cells in the mitotic phase by inhibition of polymerization and induction of depolymerization of cytoskeletal microtubules, similarly to VLB.

In vitro screening for anticonvulsant-induced teratogenesis: drug alteration of cell adhesivity

Anticonvulsant-induced alteration in C6 glioma cell adhesivity has been evaluated in two independent in vitro assay systems. A centrifugal shear assay was employed to determine drug-induced change in cell-substratum adhesivity. Valproate and clonazepam were found to significantly increase cell-substratum adhesivity when cells were cultured at concentrations which were within twice their therapeutic plasma level. A second assay evaluated change in affinity for concanavalin A lectin coated surfaces to determine change in cell surface glycoconjugate expression. Valproate and clonazepam and, to a lesser extent, diazepam significantly decreased drug-exposed C6 glioma cell affinity for concanavalin A lectin coated surfaces. Valproate and clonazepam had approximate IC50 values of 0.75 mM and 75 microM, respectively. These findings are compared and discussed in relation to those obtained with an anti-proliferative assay which has been suggested to predict teratogen potential.

Detection of induced mitotic chromosome loss in Saccharomyces cerevisiae--an interlaboratory assessment of 12 chemicals

Induced mitotic chromosome loss was assayed using diploid yeast strain S. cerevisiae D61.M. The test relies upon the uncovering and expression of multiple recessive markers reflecting the presumptive loss of the chromosome VII homologue carrying the corresponding wild-type alleles. An interlaboratory study was performed in which 12 chemicals were tested under code in 2 laboratories. The results generated by the Berkeley and the Darmstadt laboratories were in close agreement. The solvents benzonitrile and methyl ethyl ketone induced significantly elevated chromosome loss levels. However, a treatment regime that included overnight storage at 0 degree C was required to optimize chromosome loss induction. Hence, these agents are postulated to induce chromosome loss via perturbation of microtubular assembly. Fumaronitrile yielded inconsistent results: induction of chromosome loss and respiratory deficiency was observed in both laboratories, but the response was much more pronounced in the Darmstadt trial than that observed in Berkeley. The mammalian carcinogens, benzene, acrylonitrile, trichloroethylene, 1,1,1-trichloroethane and 1,1,1,2-tetrachloroethane failed to induce chromosome loss but elicited high levels of respiratory deficiency, reflecting anti-mitochondrial activity. Trifluralin, cyclophosphamide monohydrate, diazepam and diethylstilbestrol dipropionate failed to induce any detectable genetic effects. These data suggest that the D61.M system is a reproducible method for detecting induced chromosome loss in yeast.

Suppression of x-ray induced transformation by Valium and aspirin in mouse C3H10T1/2 cells

Two commonly used drugs, Valium (diazepam) and Aspirin (acetylsalicyclic acid), were shown to suppress X-ray induced transformation in mouse C3H/10T1/2 cells. Valium was studied in an ethanol solution. Aspirin, which is soluble in both water and ethanol, was active only in the ethanol solution. Both drugs were effective only when present throughout the entire assay period.

Formation of the astral mitotic spindle: ultrastructural basis for the centrosome-kinetochore interaction

The formation of the astral mitotic spindle is initiated at the time of nuclear envelope breakdown from an interaction between the replicated spindle poles (i.e. centrosomes) and the chromosomes. As a result of this interaction bundles of microtubules are generated which firmly attach the kinetochores on each chromosome to opposite spindle poles. Since these kinetochore fibers are also involved in moving the chromosomes, the mechanism by which they are formed is of paramount importance to understanding the etiology of force production within the spindle. As a prelude to outlining such a mechanism, the dynamics of spindle formation and chromosome behavior are examined in the living cell. Next, the properties of centrosomes and kinetochores are reviewed with particular emphasis on the structural and functional changes that occur within these organelles as the cell transits from interphase to mitosis. Finally, a number of recent observations relevant to the mechanism by which these organelles interact are detailed and discussed. From these diverse data it can be concluded that kinetochore fiber microtubules are derived from dynamically unstable astral microtubules that grow into, or grow by and then interact laterally with, the kinetochore. Moreover, the data clearly demonstrate that the interaction of a single astral microtubule with one of the kinetochores on an unattached chromosome is sufficient to attach the chromosome to the spindle, orient it towards a pole, and initiate poleward motion. As the chromosomes move into the region of the forming spindle more astral microtubules become incorporated into the nascent kinetochore fibers and chromosome velocity decreases dramatically. During this time the distribution of spindle microtubules changes from two overlapping radial arrays to the fusiform array characteristic of metaphase cells.

Antiproliferative action of benzodiazepines in cultured brain cells is not mediated through the peripheral-type benzodiazepine acceptor

The benzodiazepines, Ro 5-4864, diazepam, clonazepam, and also PK-11195, inhibited, at micromolar concentrations, the proliferation of rat C6 glioma and mouse neuro-2A neuroblastoma cells in culture. The cells possessed high levels of "peripheral-type" high-affinity benzodiazepine binding sites as judged by binding assays and displacement potencies. However, the different potencies and specificities of compounds for the antiproliferative actions and binding affinities for the binding site suggest that the antiproliferative actions were not mediated through the peripheral-type binding site. In support of this, these compounds have also been shown to inhibit proliferation of some nonneuronal cultured cell lines, e.g., mouse SP2/O-Ag 14 hybridoma and rat NCTC epithelial cells, which have no detectable high-affinity peripheral-type benzodiazepine binding sites.

The effects of 1,6-dinitropyrene on spindle morphology in transformed human cells

The effects of 1,6-dinitropyrene (1,6-DNP) on the fidelity of cell division were studied in the transformed human fibroblast cell line MRC5VA. Over a dose range of 0.1-10 micrograms/ml of 1.6-DNP, we observed significant increases in the levels of abnormal division stages, associated with damage to the spindle apparatus of the cell. Qualitative changes in spindle morphology and a quantitative decrease in pole-to-pole spindle length were also observed with increasing doses of 1.6-DNP. Such changes in the size and morphology of the spindle corresponded with an accumulation of cells blocked at metaphase. The presence of catalase did not modify the response, suggesting that the effects on the spindle apparatus and cell division were not caused by the generation of radicals but by the direct action of 1.6-DNP.

Interactions between anticancer drugs and other clinically used pharmaceuticals. A review

Drug interactions are increasingly common, since clinical practice is getting more complex with the flood of new drugs. Simultaneously, the increased life expectancy of the population increases the number of individuals likely to receive multiple prescriptions. Cytotoxic drugs generally have a narrow therapeutic index, and are delivered at doses close to toxic levels. Consequently, a slight increase in biological activity caused by an interaction with other concomitantly administered drugs could be deleterious to the patient. Interactions between drugs can sometimes also be used in a positive way, i.e. to increase the therapeutic ratio and overcome drug resistance. Interactions between different cancer treatment modalities have attracted considerable interest. However, much less interest has been devoted to interactions between anticancer drugs and other pharmaceuticals. The purpose of this review is to summarize data about the interactions between anticancer drugs and other clinically used drugs with regard to effects on tumor and toxicity.

Teratogenic effects of benzodiazepine use during pregnancy

Eight children exposed in utero to benzodiazepines had characteristic dysmorphic features, growth aberrations, and central nervous system abnormalities from birth. Their dysmorphic characteristics resembled those of the fetal alcohol syndrome, although they had greater focal involvement of cranial nerves, with a sullen and expressionless face, and they more often had impairment of vitality at birth. One infant died and at autopsy had varying degrees of distortion of neuronal migration, with concomitant heterotopias. Five of the eight mothers had regularly consumed benzodiazepines, and the three remaining mothers had blood samples during pregnancy revealing benzodiazepine concentrations indicative of regular use. Our findings indicate that maternal consumption of benzodiazepines may be teratogenic in humans.

The effects of benzodiazepines upon the fidelity of mitotic cell division in cultured Chinese hamster cells

4 benzodiazepine sedatives, namely diazepam, medazepam, midazolam and bromazepam were investigated for their effects upon the fidelity of cell division in both low passage number and immortalised Chinese hamster cell lines. The study revealed substantial differences in the effect of these structurally related drugs upon mitosis, which may reflect different mechanisms of action of the drugs in cultured cells. Diazepam and medazepam exposure of immortal and low passage number cells resulted in the formation of monopolar mitotic spindles and subsequent metaphase arrest. The production of these spindles may be explained by the inhibition or centriole separation . In contrast, midazolam and bromazepam failed to produce observable changes in spindle structure. All 4 benzodiazepines produced significant toxicity in low passage number cells whereas, immortalised cells were more resistant to their toxic effects. They all induced metaphase chromosome dislocations in immortalised cells, whereas only diazepam and medazepam produced such effects in the low passage number cell line. In general, immortal cells appeared to be less sensitive to the toxic effects of benzodiazepines than the low passage number cells.

In vitro effects of benzodiazepines on ciliogenesis in the quail oviduct

Immature oviduct implants from quails stimulated by estrogen to induce ciliogenesis were submitted to the in vitro action of benzodiazepines in organotypic culture. Diazepam and medazepam were added to the culture medium for 24 or 48 hours and tissues were examined by transmission and scanning electron microscopy for alterations in ciliary differentiation. Ciliogenesis was inhibited by both diazepam and medazepam, which affected mainly the migration of the basal bodies. Assembly of basal bodies was achieved normally in the cytoplasm, but their separation from generative complexes and migration toward the apical membrane were prevented. They remained in clusters around a deuterosome or eventually anchored to the close lateral plasma membrane. Furthermore, the drugs affected mature beating cilia, which then appeared lying tangentially to the cell surface. Relation between basal bodies and cortical cytoskeleton seemed to be altered by the drugs, which implies that the bearing of cilia and probably the ciliary beating movement were modified. Microvillus development was also altered by the action of these drugs.

The antimitotic activities of some benzodiazepines

Among 9 benzodiazepines, tested on the proliferation of synchronously dividing flagellate cells, only diazepam and medazepam can induce an accumulation of abnormal mitotic figures after 24 h of treatment. It seems that there is not a direct relation between the activity of benzodiazepines on the central nervous system and their ability to inhibit mitosis.

Mitotic inhibition and aneuploidy induction by naturally occurring and synthetic estrogens in Chinese hamster cells in vitro

We used a predominantly diploid Chinese hamster cell line to test a number of naturally occurring and synthetic estrogens for their ability to arrest cells at metaphase, their potential for allowing anaphase recovery, and their capability of inducing aneuploid progeny. The chemicals employed included diethylstilbestrol, dienestrol, hexestrol, beta-estradiol, ethynylestradiol and estriol. We also tested progesterone, estrone and testosterone in this regard. Only estrogens and their synthetic analogs caused mitotic arrest and aneuploidy, while progesterone, estrone and testosterone did not cause mitotic disturbances. Among the estrogens, DES was the most effective arrestant on a comparative molar basis, whereas dienestrol was most potent over a wide range of concentrations. Estriol was the least potent as an arrestant but was an effective inducer of aneuploidy. The addition of a metabolic activator (S9) did not alter the ability of DES to arrest mitosis. Following the removal of the drugs, cells were able to quickly reorganize a spindle apparatus and enter anaphase. Diethylstilbestrol, dienestrol, hexestrol, beta-estradiol, ethynylestradiol and estriol caused significant increase in aneuploidy within a narrow range of high concentrations in recovering cell populations. Aneuploidy was induced in a non-random manner. Immunofluorescence studies with anti-tubulin antibody indicate that estrogens may have a mechanism of mitotic arrest similar to that of colchicine and colcemid, viz inhibiting the polymerization of tubulin to form microtubules. These data suggest that the interaction between estrogens and microtubules may mediate the induction of aneuploidy in somatic cells. Aneuploidy induction by DES and similar compounds may be related to their carcinogenic potential.

Chemically induced aneuploidy in mammalian cells in culture

Our objectives were to assess whether there exist useful aneuploidy tests in vitro, to identify chemicals that showed potential for mitotic aneuploidy induction, and to recommend some features of suitable protocols for such testing. From over 100 papers we selected 24 for review. The acceptable studies examined hyperdiploidy at metaphase, had concurrent negative controls with low background rates of hyperdiploidy, used a fixation time sufficient for cells to complete more than one cell cycle after treatment and had multiple dose levels with at least 100 cells scored per point. We judged that 12 compounds were positive, 7 inconclusive, and 4 negative with the reservation that 2 of the 4 compounds had not been tested up to toxic doses. Many of the positive compounds are also known to cause structural chromosome aberrations. We separately reviewed qualitative reports of 'C-mitotic' effects, anaphase lagging, multipolar mitoses, or altered DNA content, since these effects may sometimes by associated with aneuploidy induction. No well-validated in vitro aneuploidy assay exists, and much research is required to develop tests, perhaps using chromosome counts, DNA content, or effects on cell organelles necessary for mitosis. In test protocol development we should carefully consider choice of cell sample size, use of in vitro metabolic activation systems, and selection of doses, especially with regard to the problem of whether cytotoxic concentrations should be used.

Chemically induced aneuploidy in mammalian cells: mechanisms and biological significance in cancer

A growing body of evidence from human and animal cancer cytogenetics indicates that aneuploidy is an important chromosome change in carcinogenesis. Aneuploidy may be associated with a primary event of carcinogenesis in some cancers and a later change in other tumors. Evidence from in vitro cell transformation studies supports the idea that aneuploidy has a direct effect on the conversion of a normal cell to a preneoplastic or malignant cell. Induction of an aneuploid state in a preneoplastic or neoplastic cell could have any of the following four biological effects: a change in gene dosage, a change in gene balance, expression of a recessive mutation, or a change in genetic instability (which could secondarily lead to neoplasia). To understand the role of aneuploidy in carcinogenesis, cellular and molecular studies coupled with the cytogenetic studies will be required. There are a number of possible mechanisms by which chemicals might induce aneuploidy, including effects on microtubules, damage to essential elements for chromosome function (ie, centromeres, origins of replication, and telomeres), reduction in chromosome condensation or pairing, induction of chromosome interchanges, unresolved recombination structures, increased chromosome stickiness, damage to centrioles, impairment of chromosome alignment, ionic alterations during mitosis, damage to the nuclear membrane, and a physical disruption of chromosome segregation. Therefore, a number of different targets exist for chemically induced aneuploidy. Because the ability of certain chemicals to induce aneuploidy differs between mammalian cells and lower eukaryotic cells, it is important to study the mechanisms of aneuploidy induction in mammalian cells and to use mammalian cells in assays for potential aneuploidogens (chemicals that induce aneuploidy). Despite the wide use of mammalian cells for studying chemically induced mutagenesis and chromosome breakage, aneuploidy studies with mammalian cells are limited. The lack of a genetic assay with mammalian cells for aneuploidy is a serious limitation in these studies.

Improved technique for the expression of fragile-X in cultured amniotic fluid cells

An improved technique for inducing fra(X) expression in cultured cells was obtained by using diazepam for mitotic arrest and 5-fluorodeoxyuridine (FUdR) for the induction of fra(X) expression. The method was developed using cultured fibroblast and urinary cells from fra(X) patients. Prenatal studies were performed on cultured amniotic fluid cells in five pregnancies at risk for fra(X). In two cases the cultured cells showed a 46,XY, fra(X) karyotype. One of the pregnancies was terminated and the diagnosis was confirmed by chromosome studies on several fetal tissues including chorionic villi and by histopathologic changes in the lymphatic vessels of the fetal testes. The fra(X) was also demonstrated in chorionic villi in a case in which amniotic fluid cells were not studied. Chorionic villi were isolated after a spontaneous abortion, the cultured cells had a 45,X karyotype and in addition 5% of the cells were fra(X) positive.