The heterogenous cytotoxic response of colon cancer cells is unrelated to phenotypic differentiation characteristics

Six colon cancer cell lines segregated into three groups with distinct biological properties (i.e., morphological differentiation, DNA content, carcinoembryonic antigen production, etc.) were treated with ten antitumor drugs. Cytotoxic responses were heterogenous and not associated to biological grouping, in fact, for some drugs, the response of one member of the group resembled that of a member of another group rather than its group counterpart. Thus the most common phenotypic characteristics that identify colon cancer cells did not predict the cytotoxic response and do not appear useful for stratifying patients into categories with distinct responses to currently available chemotherapeutic agents.

Stage-related induction of chromosomal aberrations and SCE in mouse embryos treated transplacentally during organogenesis with MMC and DMBA

During organogenesis, mouse embryos were treated transplacentally with MMC and DMBA. The clastogenic and SCE-inducing effects of MMC and the clastogenic effects of DMBA were analyzed in metaphases from whole embryo suspensions. Positive effects were observed on all the days of pregnancy on which the embryos were analyzed, i.e., on days 10, 11, 12, and 13. Whereas the MMC-induced SCE-frequencies did not change significantly during the tested period, the clastogenic effects of MMC and DMBA varied drastically. Extremely high aberration rates were observed in embryos on day 11; on the other days the aberration rates were much lower. Factors that might have given rise to these stage-related effects are discussed.

Caffeine post-treatment causes a shift in the chromosome aberration types induced by mitomycin C, suggesting a caffeine-sensitive mechanism of DNA repair in G2

Human lymphocytes were exposed in G1 to mitomycin C (2.5 microM for 2 h) and harvested at 3-h intervals from 48 to 84 h after stimulation. All cultures were also post-treated in G2 with caffeine (2 mM). Different types of chromosomal aberrations were scored in the first division metaphases. Caffeine increases all chromosome aberration types by promoting a premature mitosis of damaged cells. However, when the frequency of damaged cells is not affected by the caffeine post-treatment, a reduction of the frequency of the exchange-type aberrations was shown. The possibility that caffeine interferes with some mechanism of G2 repair is discussed.

Teratogenic interactions between methylmercury and mitomycin-C in mice

Pregnant mice were given p.o. various nonteratogenic doses (0, 2.5, 5 and 10 mg/kg) of methylmercuric chloride on day 9 of pregnancy, and then injected i.p. with a teratogenic dose (4 mg/kg) of mitomycin-C on day 10. Major malformations produced by mitomycin-C alone were cervical rib and vertebral anomaly, polydactyly of the hindlimb and tail anomaly. Combined treatment significantly increased the incidence of these malformations, showing the dose-effect relationship of methylmercury, whereas methylmercury alone is known not to produce such malformations. When mitomycin-C treatment alone was performed on day 9.5 of pregnancy, only vertebral anomalies increased in incidence. Therefore, mitomycin-C teratogenicity in terms of the manifestation of cervical rib, polydactyly and tail anomaly, but not vertebral anomaly, was suggested to be enhanced by methylmercury. A considerable number of foetuses showed cleft palate involvement following combined treatments, but not by either chemical alone. Cleft palate is known to be a major malformation in mice that is caused by methylmercury, and mitomycin-C also induces cleft palate. Therefore, the two chemicals might have affected foetuses additively and thereby induced cleft palate.

The search for more active and less toxic mitomycin and etoposide analogs

Mitomycin C has broad-spectrum activity, but clinical utility is limited by cumulative myelosuppression. VP-16 also has broad-spectrum activity and, although myelosuppression is the dose-limiting toxicity, unlike mitomycin C it is predictable and reversible. Using toxicity reduction as a target for analog selection with mitomycin C has not yet resulted in a more clinically effective agent. Another goal would be to look for more rapid recovery and reversibility of myelosuppression, or compounds with greater antitumor activity or a different antitumor profile. With VP-16, analog evaluation is in an early stage, but selection based upon increased activity not reduced toxicity appears to be the avenue of choice and has resulted in the preliminary identification of analogs which in initial studies have superior activity to the parent compound.

Effect of tumor promoter TPA on spontaneous and mitomycin C induced mitotic recombination in Drosophila melanogaster

It has been proposed that mitotic recombination is involved in tumor promotion. To test this idea, we investigated the effect of a tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), on spontaneous and mitomycin C (MMC)-induced mitotic recombination in Drosophila melanogaster. The test system used was the wing-spot assay. Third instar larvae (mwh+/+flr) were treated with MMC (0-0.3 mM) for 6 h and fed media containing TPA (0-10 micrograms/ml), and the wings of surviving adults were analyzed for the presence of mutant spots. The results are: (1) MMC induced twin spots as well as single spots dose dependently (0.03-0.3 mM). (2) TPA itself did not induce twin spots or single spots in the range of doses examined (0.1-10 micrograms/ml). (3) TPA did not enhance the frequencies of twin or single spots induced by MMC. These results indicate that TPA induced neither mitotic recombination nor mutations under these experimental conditions. Thus the results would not support the mitotic recombination theory in tumor promotion. Rather, in this study, TPA posttreatment resulted in reduced frequencies of mutant single spots induced by MMC.

Mouse strain differences in the induction of micronuclei by polycyclic aromatic hydrocarbons

The frequency of micronucleated erythrocytes (MNE) in 3 inbred mouse strains and 2 of their hybrids (C57BL/6, BALB/c, DBA/2, BDF1 and CDF1) were examined after polycyclic aromatic hydrocarbons (PAHs; 7,12-dimethylbenz[a]anthracene (DMBA), 3-methylcholanthrene (3-MC), benzo[a]pyrene (BaP), benzo[e]pyrene (BeP) and anthracene (ANT] were injected i.p. PAHs are thought to form active metabolites after being administered to mammals. In mouse strains with inducible PAH activating enzymes, such as C57BL/6 or BALB/c, MNE were significantly induced, as compared to control mice, 48 h after DMBA, BaP, or 3-MC was injected. No increase in the frequency of MNE occurred in the DBA/2 strain which cannot induce the activating enzymes. BeP and ANT did not increase the frequency of MNE in any mouse used. The levels of MNE induction in BDF1 or CDF1 hybrids were similar to those in C57BL/6 or BALB/c. These results support the view that the genetic capacity to metabolize PAHs is strongly associated with micronucleus induction as in the case of PAH carcinogenesis.

Effects of the mode of administration of mitomycin on tumor and marrow response and on the therapeutic ratio

The antineoplastic and toxic effects of mitomycin (MC) administered as a single pulse injection were compared with the effects of MC given as infusions over 2, 5, or 24 hours and with the effects of the drug administered in fractionated regimens incorporating 2-20 injections. The antineoplastic effects of MC were assessed using EMT6 mouse mammary tumors implanted in BALB/c mice; tumor response was assessed using both cell survival and tumor growth assays. The host toxicity of MC was assessed by measuring the survival of bone marrow stem cells (CFU-S) and by determining LD50/30's (which reflect primarily marrow injury). The survival curve for cells from tumors treated with varying doses of MC was exponential, with no shoulder which might suggest accumulation of sublethal lesions. No evidence was found that the tumor cells repaired MC damage when left in situ for up to 24 hours after treatment (repair of potentially lethal damage) or that the tumor repaired sublethal damage during times of up to 24 hours between drug treatments or during drug infusions. The responses of tumors treated with single injections of MC, with infusions over 2, 5, and 24 hours, with two injections separated by 5 or 24 hours, and with five daily injections were all similar. The survival curve for CFU-S from mice treated with varying doses of MC was exponential, with no shoulder which might suggest accumulation of sublethal lesions. LD50/30's were the same whether MC was administered as single injections, as infusions over 2, 5 or 24 hours, or as five daily fractions. Longer fractionated regimens, in which mice received daily injections, 5 days per week, for up to 4 weeks, produced less host toxicity but also less antineoplastic effect; the therapeutic ratio for the most protracted regimen tested was lower than that for single injections. The therapeutic ratios achieved with infusions and fractionated regimens were never greater than that obtained with a large single dose, confirming clinical impressions that infrequent, large doses of MC are an optimal method of treatment with this drug.

Mutation at the APRT locus in Friend erythroleukaemia cells. 2. Sensitivity to mitomycin C induced cytogenetic damage

Clone 707 of the Friend cell was compared with an APRT-deficient subclone for sensitivity to cell killing and the induction of cytogenetic aberrations by mitomycin C (MMC). Two 16-h doses of MMC were used, 0.1 and 0.15 microgram/ml and cells were scored for aberrations at 16, 33 and 44 h post-treatment. The APRT-deficient subclone showed increased cell killing, a higher frequency of aberrations and a higher frequency of cells with severe cytogenetic damage. It is proposed that APRT may play a role in balancing deoxyribonucleoside triphosphate pools for DNA-repair processes.

Baseline and mutagen-induced sister-chromatid exchanges in cultures of human whole blood and purified fresh or frozen lymphocytes

Baseline and mutagen-induced levels of sister-chromatid exchanges were evaluated in 10 normal individuals. Cultures with whole blood or purified lymphocytes, either freshly isolated or after 1 or 6 months of cryopreservation, were analyzed to determine whether frozen lymphocytes are suitable for SCE studies. Whole blood and freshly isolated lymphocytes were cultured from samples taken at the beginning of the study (Time 0) and 6 months later (Time 6). Cryopreserved lymphocytes were recovered after 1 month (Time 1) and 6 months (Time 6) of cryopreservation and then challenged with mutagens in culture. The mutagens used were mitomycin C, 4-nitroquinoline-1-oxide, and N-methyl-N'-nitro-N-nitrosoguanidine. Purified lymphocytes had consistently and significantly higher baseline SCE frequencies than cells from whole blood cultures and were more sensitive to N-methyl-N'-nitro-N-nitrosoguanidine and 4-nitroquinoline-1-oxide. The response to mitomycin C was similar in all culture types. There was, overall, no consistent effect of freezing on baseline or induced sister-chromatid exchange frequencies in the purified lymphocytes. This suggests that purification and cryopreservation of human lymphocytes does not alter the baseline or mutagen-induced sister-chromatid exchange response and in certain epidemiological, occupational and monitoring situations may have logistical and technical advantages over the use of fresh whole blood.

Studies of gene transfer and reversion to mitomycin C resistance in Fanconi anemia cells

As a first step to the cloning of the Fanconi anemia (FA) gene, we have attempted to correct the sensitivity of FA cells to DNA crosslinking agents by the introduction of wild-type DNA. The protocol involved the introduction of both genomic and pRSVneo DNA, selection for G418-resistant colonies and the subsequent selection of mitomycin C-resistant cells from the latter. Preliminary experiments indicated that untransformed FA cells were not suitable recipients for the introduction of foreign DNA, so all experiments were performed with an SV40-transformed FA cell line. Approximately 40,000 G418-resistant colonies were obtained in 5 separate experiments at an overall frequency of about 5 X 10(-4). These were then selected in mitomycin C and 15 colonies were recovered. Colonies were obtained with wild-type DNA (both human and rodent) and with FA DNA at about the same frequency of 2 X 10(-7). Colonies were isolated and shown to have a stable, partial (from 25 to 90% of wild-type) resistance to mitomycin C. One colony was also shown to be partially resistant to two other DNA crosslinking agents, diepoxybutane and nitrogen mustard. This clone also had an intermediate level of spontaneous and MMC-induced chromosome aberrations. pRSVneo, but not rodent, DNA could be demonstrated in the high molecular weight fraction of several colonies. Thus, it is likely that these colonies represent partial revertants rather than transfectants. These mitomycin C-resistant FA cells should be useful for the biochemical analysis of the FA mutation.

Response of mammalian ADP-ribosyl transferase to lymphocyte stimulation, mutagen treatment and cell cycling

The inhibitors of the nuclear enzyme ADP-ribosyl transferase (ADPRT) had been shown to block the stimulation of quiescent lymphocytes with mitogens suggesting the involvement of the enzyme in the control of gene expression and cell differentiation. By means of the activity-gel assay we have analysed the intensity and the molecular mass of the catalytic bands of the enzyme at early and late times after stimulation of human lymphocytes by phytohemagglutinin. We observed that the increase in the activity of ADPRT is concurrent with the onset of DNA synthesis and is maintained for up to 10 days after lymphocyte stimulation, when DNA replication is over but the capacity to perform repair synthesis is still elevated. The analysis of ADPRT in stimulated lymphocytes by Western blots indicated that the increase in enzyme activity is due to the de novo synthesis of enzyme protein. The response of ADPRT to the treatment of human lymphocytes with DNA-damaging agents was studied at various dose-ranges, using the activity-gel technique. The results obtained indicate that dimethyl sulfate is 10 times as active as methyl methane sulfonate in stimulating ADPRT activity and that, at very high doses, the activity band of the enzyme tends to disappear. Very similar observations were obtained when Chinese hamster ovary cells were treated with the same agents, although the concentrations of the mutagens eliciting maximal ADPRT activation were 10 times higher than in human lymphocytes. When analysed by Western blots, no significant difference of the protein band of the enzyme was observed in comparing control and treated cells. This suggests that the activity-gel system can detect two different phenomena: the increase in enzyme protein, as in the case of stimulated lymphocytes, and the enzyme-activating effect of DNA-damaging agents, which occurs without changing the number of enzyme molecules. Of particular interest is the observation that mitomycin C is capable of activating ADPRT in human lymphocytes, thus suggesting that cross-linking agents are involved in promoting ADP-ribosylation reactions. We have also analysed the variations of the enzyme throughout the cell cycle in HeLa cells synchronized in S phase or in mitosis. No significant changes in the levels of the enzyme activity were revealed by the activity-gel assay during the progression of the cycle, although an overall increase of active polypeptides of larger size in concomitance with the S period was observed.

Extrapolation from in vitro tests to human risk: experience with sodium fluoride clastogenicity

Genotoxic effects observed in vitro, only at high doses or high levels of cytotoxicity, will be false positives if such conditions are not achieved or cannot be tolerated in vivo. However, for such effects to be disregarded there must be a threshold dose or level of cytotoxicity below which genotoxicity is absent. Sodium fluoride (NaF) has previously been shown to be clastogenic in vitro in Syrian hamster cells and human fibroblasts. We have extended these studies in human fibroblasts and included a positive control (mitomycin C, MMC) which is clastogenic in vivo and carcinogenic, and a chemically related control (NaCl). Cytotoxicity was measured as mitotic inhibition and cell death (loss of clonogenicity). The results are used to illustrate the problems associated with quantitative extrapolation from in vitro tests to human risk, as follows. (1) There appears to be a threshold response (clastogenicity vs. dose) with NaF at around 10 micrograms/ml (48 h exposure) but a more definitive conclusion must await elucidation of the mechanisms of clastogenicity. (2) NaCl is weakly clastogenic at 1000 times the threshold dose for NaF. The mechanisms are unlikely to be similar. (3) No clastogenicity was detected with NaF below about 30% mitotic inhibition but the relationship between clastogenicity and mitotic inhibition was similar for NaF and MMC. (4) There was no obvious threshold in the relationship between clastogenicity and cell killing with NaF. MMC was less clastogenic than NaF at equitotoxic doses. Observations 3 and 4 preclude the possibility of regarding the clastogenicity of NaF as a false positive by virtue of associated cytotoxicity.

The pR plasmid: a tool for discriminating between DNA lesions induced by different types of cytotoxic agents in cultured mammalian cells

The LA-D cells, obtained by cotransformation of LTA mouse cells (tk- aprt-) with pR plasmid and with tk gene as selective marker, are significantly more resistant to UV light and 4-nitroquinoline-N-1-oxide than LTA control cells. In this work, we report that the LA-D cells exhibit different degrees of response to various DNA-damaging agents: wild-type survival to mitomycin, increased sensitivity to bleomycin, cis-diamminedichloroplatinum and N-methyl-N'-nitro-N-nitrosoguanidine. The pR plasmid could, therefore, play an important role in the DNA-repair mechanisms that modulate the cytotoxic effect of the DNA-inhibitory agents. The possible interactions between pR plasmid products and the different repair enzymes involved are discussed.

Persistence of micronuclei in the marine mussel, Mytilus galloprovincialis, after treatment with mitomycin C

The frequency of micronuclei induced by mitomycin C (MMC) in cells of the gill tissue of the marine mussel, Mytilus galloprovincialis Lmk., was determined over a long period (up to 40-52 days) following treatment. Two doses of MMC (0.5 X 10(-7) and 10(-7) M) were tested at 13 degrees C and 23 degrees C, temperatures representative of the winter and summer thermic conditions of the Mediterranean Sea. In all cases, the frequency of micronuclei was significantly increased by MMC and declined after treatment until it reached a plateau level, significantly higher than the control value. This persisted for a very long time. The frequency of micronuclei induced by a second treatment with MMC performed on the 28th day, did not differ significantly from that produced by the first treatment at the same dose. Temperature did not influence the pattern of the described phenomena to a significant extent. The reason for the persistence of an increased frequency of micronuclei is discussed, and a system is proposed for evaluating the genotoxicity of water pollutants present long before sampling.

Single-dose and multiple-dose intravenous toxicity studies of BMY-25282 in rats

Single-dose and multiple-dose (daily X 5 and weekly X 5) intravenous toxicity studies in rats were conducted to determine the possible acute and delayed toxicity of BMY-25282 (7-N-(dimethylaminomethylene) mitomycin C), a potential anticancer drug. Rats in the single-dose study received either 0.05, 0.25, or 0.50 mg/kg (0.3, 1.5, or 3.0 mg/m2) of BMY-25282; rats in the daily X 5 multiple-dose study received doses of 0.005, 0.025, or 0.050 mg/kg (0.03, 0.15, and 0.3 mg/m2) of BMY-25282 once each day for 5 days; and rats in the weekly X 5 multiple-dose study received 0.05 mg/kg of BMY-25282. All doses were in 0.1% Pluronic F-68 diluent. Acute toxicities included gastrointestinal epithelial necrosis, myelosuppression, and splenic lymphoid depletion in the high and intermediate dose groups in the single-dose study and myelosuppression in the high dose group of the daily X 5 multiple-dose study. One death in a high dose male of the single-dose study was attributed to acute gastrointestinal and lymphoid toxicity. Between the interim necropsy on Day 5 or 9 and termination of the 9-week dose-free observation period, 9/20 rats of the high and intermediate dose groups of the single-dose study and 4/10 high dose rats in the daily X 5 multiple-dose study died, primarily due to hydrothorax and congestive heart failure caused by delayed, drug-related myocardial degeneration. The most prominent drug-related histopathologic changes observed in rats of both the single-dose study and the daily X 5 studies were myocardial degeneration (cardiomyopathy), glomerulopathy with tubular degeneration, and necrotizing arteritis. These three changes, observed at 0.5 and 0.25 mg/kg in the single-dose study and at 0.05 mg/kg/day in the multiple-dose (daily X 5) study, were delayed in onset and irreversible. Drug-related tubular degeneration and slight glomerulopathy were observed in male BMY-25282-treated rats in the weekly X 5 study, but cardiotoxicity, pulmonary arteritis, hydrothorax, and lethality were not observed. The diluent, Pluronic F-68, was not associated with any morphologic or clinico-pathologic changes. A single-dose of 0.05 mg/kg or 5 daily doses of 0.025 and 0.005 mg/kg of BMY-25282 were considered nontoxic doses in rats. A cumulative dose of 0.25 mg/kg, which caused cardiotoxicity in the daily X 5 study, was not cardiotoxic in the weekly X 5 study. These results indicate that the delayed cardiotoxicity of BMY-25282 is schedule dependent.

On the localization of mitomycin C-induced aberrations in normal human and Fanconi's anaemia cells

This paper summarizes the results of a series of experiments with primary cultures of normal human fibroblasts and lymphocytes designed to investigate chromatid aberration 'break-point' localization after a 1-h pulse of mitomycin C. For discontinuities and interchanges, 60-70% of the inferred 'break-points' were localized to defined paracentric heterochromatin and the centromeric regions (i.e. approximately 21% by length of the normal karyotype), irrespective of 'dose', aberration frequency, sample time or cycle sub-phase as determined by replication banding. Chromatid intrachanges are non-(or negatively) localized because of an inescapable scoring bias. SCE in fibroblasts show no such localization. Cells from a number of Fanconi's anaemia subjects were examined. In poorly growing cultures, localization was as high as in normal cells but in vigorous cultures localization was reduced to approximately 30%. It is suggested that the enhanced aberration sensitivity of this syndrome could arise because non-localized aberrations, usually eliminated before division in normal cells, are allowed to reach mitosis in FA cells.

Enhanced susceptibility of mouse embryos heterozygous for oligosyndactyly (Os/+) to mitomycin C-induced skeletal abnormalities

The mouse mutation, oligosyndactyly (Os), results in syndactyly, muscle anomalies, and deficiency of nephrons in heterozygous animals and early embryonic lethality in homozygotes. Since the homozygous lethality results from mitotic arrest with intact spindles at the time of implantation, we have hypothesized that the heterozygous manifestations may result from impairment of cell proliferation in regions with high proliferative rates. To test this hypothesis, Os/+ and +/+ mouse embryos at 6.5 days of gestation were exposed to mitomycin C (MMC), an agent that causes a high degree of embryonic cell death which is "compensated" for by a period of rapid cell proliferation. 17.9% of MMC-treated +/+ fetuses had fused vertebrae, a significant increase over untreated fetuses, and this frequency was further increased to 33.6% in MMC-treated Os/+ fetuses. Saline treated Os/+ and +/+ fetuses showed the same low rate (0-3%) of vertebral fusion. These results indicate that Os/+ embryos have an increased sensitivity to the vertebral fusion-inducing effect of MMC at 6.5 days of gestation, a finding compatible with the hypothesis that rapid cell proliferation may be impaired in Os/+ embryos and fetuses.

Enhanced anticancer efficacy by use of mitomycin C adsorbed on small activated carbon particles in mice

A new dosage form of mitomycin C (MMC-CH) was tested for toxicity and therapeutic efficacy against intraperitoneally inoculated cancer cells in mice. MMC-CH is a suspension comprising 7.16 mg/ml of activated carbon particles, 1 mg/ml of mitomycin C (MMC) and 20 mg/ml of polyvinylpyrrolidone in saline. The LD50 value determined by means of the Litchfield-Wilcoxon method after intraperitoneal administration was 2.29 times higher for MMC-CH than for MMC aqueous solution. Mice were inoculated intraperitoneally with 2 X 10(5) P388 leukemia cells and given an intraperitoneal injection of 10 to 1.25 mg/kg of MMC in the form of MMC-CH or MMC aqueous solution 24 hr after the inoculation. The median survival time was prolonged to 270.5%, 223.0% or 168.3% by MMC-CH at the dose equivalent to 10, 5 or 2.5 mg/kg of MMC, respectively, while it was prolonged to 182.7%, 139.6% or 155.4% by MMC aqueous solution at the dose of 5, 2.5 or 1.25 mg/kg of MMC, respectively, as compared with the median survival time in the non-treated group. MMC-CH prolonged the survival time to more than 120% as compared with the same dose of MMC given as MMC aqueous solution, and was less toxic.

Antineoplastic drug cytotoxicity in a human bladder cancer cell line: implications for intravesical chemotherapy

The clonogenic survival of MGH-U1 human bladder carcinoma cells treated with melphalan, cisplatin, mitomycin-C, adriamycin, vincristine and 5-fluorouracil was measured to determine the relative contribution of drug concentration and duration of exposure to cytotoxicity and to measure the relative cytotoxic effects of these agents used in intravesical chemotherapy. The survival curves were plotted as a function of log (C X T) and were fitted using a linear least squares analysis. The survival was the same for any given C X T whether this was determined by varying concentration or by varying the duration of exposure in the cases of melphalan, cisplatin, adriamycin, mitomycin-C and 5-fluorouracil. However, duration of exposure was more important than was drug concentration in the case of vincristine cytotoxicity. By utilizing the slope of the log (survival fraction) as a function of log (C X T), the relative cytotoxicity of each agent was determined. Mitomycin C, melphalan, adriamycin and cisplatin had comparable activity in this cell line, whereas vincristine and 5-fluorouracil demonstrated much lower cytotoxicity. We conclude that: mitomycin-C, adriamycin and melphalan were the agents with the greatest cytotoxic efficacy; determination of survival as a function of C X T can be used to separate the relative importance of concentration and of duration of exposure. the cytotoxicity of 5/6 drugs studied was equal when the C X T was kept constant but concentration and exposure times were varied.

Cytogenic analysis of dominant lethal effects of mitomycin C and ethyl methanesulfonate

To gain further insight into the mechanism of induction of dominant lethal mutations, the relationship between chromosome aberrations in bone marrow and in male germ cells after treatment with mitomycin C (MMC) and ethyl methanesulfonate (EMS) was examined. In addition, we obtained fertilized eggs from the oviducts of crossbred female mice in the same way as in the dominant lethal mutation test, and examined chromosome aberrations in male pronuclei. MMC 2.5 and 5.0 mg/kg, EMS 175 and 350 mg/kg were given subcutaneously to slc-ICR mice. It was concluded that MMC causes a decrease in the sperm count by killing germ cells, which in turn causes an increase in the number of unfertilized eggs and preimplantation egg loss. MMC seems also to cause invisible damages in the chromosomes of spermatocytes which lead to dominant lethality. EMS induced chromosome damage in the post-meiotic germ cells, and this damage, in turn, produced chromosome aberrations in the eggs, resulting in a high incidence of dominant lethality.

Mutagenicity tests of the antithyroid agent thiamazole. Cytogenetic studies on male mice

The mutagenic potential of thiamazole, an antithyroid agent, was investigated by an in vivo cytogenetic test and was compared with those of mitomycin C and vincristine. These drugs were subcutaneously injected into slc-ICR male mice either as a single dose or as multiple doses for 5 successive days. Thiamazole (90 or 180 mg/kg) did not increase the number of micronuclei in bone marrow cells. This drug also did not induce chromosomal aberrations in spermatogonium, spermatocyte, or bone marrow cells. On the other hand, mitomycin C (3.0 mg/kg) increased the appearance of chromosomal aberrations and micronuclei. Vincristine (0.2 mg/kg) induced bone marrow cells with a so called large micronucleus (d greater than or equal to D/4). These results suggest that thiamazole may not have significant effects on the genetic systems of mice.

Measurement of micronuclei by cytokinesis-block method in cultured Chinese hamster cells: comparison with types and rates of chromosome aberrations

The cytokinesis-block method of Fenech and Morley (1985) has been tested for the enumeration and characterization of micronuclei in exponentially growing Chinese hamster cells in culture. The consistent dose-response relations were obtained in cultures treated with mitomycin C, caffeine and colcemid. Comparison with the chromosome aberration frequencies indicated that approximately 30% of the acentric chromosomes are expressed as micronuclei in the mitomycin C and caffeine treated cells. The size distribution of the micronuclei suggested that the base-line frequency of micronuclei is mainly a reflection of mitotic dysfunctions rather than chromosome structural aberrations.

Synaptonemal complex damage as a measure of chemical mutagen effects on mammalian germ cells

As heritable chromosome anomalies are implicated in a variety of human disabilities, their induction in germ cells by environmental chemicals is viewed as a threat to health (National Research Council, 1982; Hook, 1983). Synaptonemal complex (SC) analysis is a novel approach for the detection of germ-line chromosomal damage. This sensitive cytological procedure reveals induced structural damage and pairing abnormalities in SCs of meiotic prophase chromosomes, together with other germ-line toxic effects, in the testes of rodents treated with mitomycin C and cyclophosphamide. Our results demonstrate the effectiveness of SC analysis as a rapid and practical in vivo germ-line mutagen assay that lacks many of the short-comings of existing tests.

Toxicity and pathological effects of a new dosage form of mitomycin C for carcinomatous peritonitis

A new dosage form (MMC-CH) of mitomycin C (in a suspension of activated carbon adsorbing mitomycin C in saline), designed for intracavitary use in carcinomatous peritonitis, was studied for its toxicity and pathological effects in rats. The LD50 values determined with the Litchfield-Wilcoxon's method in three types of MMC-CH were 7.6 (100 micrograms/ml MMC and 0.5 mg/ml activated carbon in saline), 16.5 (100 micrograms/ml MMC and 0.75 mg/ml activated carbon in saline), and more than 25 mg/kg (100 micrograms/ml MMC and 1 mg/ml activated carbon in saline), while in mitomycin C solution the value was 3.05 mg/kg. The lethal toxicity decreased with the change of dosage form. Studies on survival, symptoms of intoxication and macroscopic and microscopic examinations of autopsied animals revealed that there was no evidence of any additional side effects produced by the change of dosage form.