Enhancing effect of tetrandrine on sister-chromatid exchanges induced by mitomycin C and cigarette-smoke condensate in mammalian cells

The enhancing effect of tetrandrine, an antisilicosis, antitumor and antiinflammatory drug, on the genotoxic activity of two known mutagens, mitomycin C (MMC) and cigarette-smoke condensate (CSC), has been studied using cultured Chinese hamster lung (V79) cells. The sister-chromatid exchange (SCE) was used as genetic endpoint to measure genotoxicity. One-day cultured cells were exposed to the test chemicals for 3 h with or without metabolic activation. The results show that the frequencies of SCE induced by MMC or CSC were enhanced by tetrandrine. The percent of enhancement was dependent on the concentration of tetrandrine.

Myeloprotective effect of diethyldithiocarbamate treatment following 1,3-bis(2-chloroethyl)-1-nitrosourea, adriamycin, or mitomycin C in mice

The effect of diethyldithiocarbamate (DDTC) on myelotoxicity induced by 1,3-bis(2-chloroethyl)-1-nitrosourea, Adriamycin, or mitomycin C in C57BL/6J x DBA/2J mice is reported here. All drugs were administered i.v. Myelotoxicity was assessed, 24 h after administration of the myelotoxic drug, using bone marrow stem cell (spleen colony-forming unit) and granulocyte/macrophage progenitor cell (granulocyte/macrophage colony-forming unit in culture) clonogenic assays. Administration of DDTC alone had no effect on spleen colony-forming units or granulocyte/macrophage colony-forming units in culture. 1,3-Bis(2-chloroethyl)-1-nitrosourea showed a dose-dependent toxicity for both cell types, and subsequent treatment with DDTC (300 mg/kg i.v. 3 h after 1,3-bis(2-chloroethyl)-1-nitrosourea) ameliorated this toxicity. The same dosing regimen of DDTC ameliorated Adriamycin-induced toxicity to bone marrow stem cells at the two higher doses tested. However, the myelosuppressive effects of mitomycin C were not altered by DDTC administration (300 mg/kg i.v. 3 h after or 30 min before mitomycin C). These results demonstrate that DDTC ameliorates myelotoxicity induced by several, but not all, chemotherapeutic agents and suggest a broad role for DDTC in cancer chemotherapy.

Repair analysis of mitomycin C-induced DNA crosslinking in ribosomal RNA genes in lymphoblastoid cells from Fanconi's anemia patients

The repair of mitomycin C (MMC)-induced DNA crosslinking was analyzed by denaturation-renaturation gel electrophoresis in ribosomal RNA genes in lymphoblastoid cell lines from 4 patients with Fanconi's anemia (FA). In comparison to normal lymphoblastoid cell lines, 2 lines of FA cells belonging to complementation group A clearly exhibited higher sensitivity to MMC and an almost identical deficiency in the removal of DNA crosslinking. A complementation group B cell line, HSC 62, exhibited a lower sensitivity than group A cells and a lesser deficiency in crosslink repair. Another 'non-A' group cell line, HSC 230, reproducibly exhibited even higher sensitivity to MMC than group A cells. The results on MMC crosslinkage removal at the molecular level correlated well with cell survival. The observed subtle differences of repair among the 4 FA cell lines might represent possible genetic differences in the respective FA complementation groups.

Characterization of mitomycin C-induced gastrointestinal damage. II. In vitro everted sac experiment

The everted gut sac technique was employed to clarify the effects of preadministration of mitomycin C (MMC) on intestinal transport of various drugs. Loss of intestinal tissue weight and increase in mucosal-to-serosal fluxes of passively absorbed drugs were noted in the case of MMC pretreatment, although the extent of the latter effect varied according to the inherent absorbability of each drug. The maximal effect of MMC on intestinal tissue weight and transport of sulfanilamide, a model of a passively absorbed drug, was observed 48 hr after pretreatment. The increase in the transfer of sulfanilamide correlated well with the MMC-induced decrease in intestinal tissue weight. These phenomena may result from the shortened transfer distance from mucosal to serosal fluid and impaired barrier function of the intestinal mucosa. On the other hand, transport of actively absorbed 3-O-methyl-D-glucose was not influenced by MMC pretreatment, which could be explained by an increment in the passive permeation counterbalancing the decrement in the active permeation. The present study also suggested that the measurement of transport of drugs through everted gut sacs might be useful as a simple and qualitative index of gastrointestinal mucosal damage.

Characterization of mitomycin C-induced gastrointestinal damage. I. In situ recirculation experiment

The effects of mitomycin C (MMC), an anti-tumor agent, on the intestinal absorption of various drugs in rats were investigated. Based on microscopic observations, preadministration of a single intravenous dose of MMC (3 mg/kg) caused serious degeneration of epithelial cells, villous atrophy, and mitotic arrest in crypts at 48 hr after pretreatment. At this time point, absorption of sulfanilamide, salicylic acid, cephalexin, and L-tryptophan was shown to be significantly decreased by means of an in situ recirculation technique. The histological changes and the decrease in absorption of sulfanilamide, a model for passively absorbed drugs, were shown to depend on the timing of MMC pretreatment. Maximal effects were observed 48 hr after dosing. The MMC-induced reduction in the absorption of drugs was not a result of differences between treated and control animals with respect to pH of the drug solution, binding of drugs with intraluminal macromolecules, or intestinal mucosal blood flow. The absorption of sulfanilamide from the small intestine in the in situ system correlated well with the wet weight of the small intestine regardless of pretreatment dose or route. This suggests that the change in absorptive surface area of the intestinal mucosa may play a major role in the MMC-induced decrease in absorption capacity of the intestine.

Chromosomal hypersensitivity in mutant MCN-151 mouse cells exposed to mitomycin C

After exposure to mitomycin C, the mouse lymphoma cell mutant MCN-151, previously shown to be sensitive to the toxic effect of the drug, demonstrates higher frequencies of chromatid-type aberrations and of aberrant cells in comparison to L5178Y cells. At any given dose of mitomycin C, the frequencies of chromosomal aberrations increased with time reaching a plateau in both cell strains, with the mutant in all cases being more sensitive than normal cells.

DNA damage, cytotoxicity and free radical formation by mitomycin C in human cells

Mitomycin C (MMC), a quinone-containing antitumor drug, has been shown to alkylate DNA and to form DNA cross-links. The ability of MMC to alkylate O6-guanine and to form interstrand cross-links (ISC) has been studied using Mer+ and Mer- human embryonic cells. Mer+ (IMR-90) cells have been reported to contain an O6-alkylguanine transferase enzyme and are, in general, more resistant to alkylating agents than the Mer- (VA-13) cell line, which is deficient in the repair of O6-lesions in DNA. Studies reported here show that MMC is more cytotoxic to VA-13 cells compared to IMR-90 cells. The alkaline elution technique was used to quantify MMC-induced ISC, and double strand breaks (DSB) in these cells. The drug-dependent formation of DSB was significantly lower in IMR-90 cells than in VA-13 cells. In contrast, no significant difference in cross-linking could be detected at the end of 2-h drug treatment. Although a small increase in cross-link frequency was observed in the VA-13 cell line relative to the IMR-90 cell line 6 h post drug treatment, it is not clear whether monoalkylated adducts at the O6-position are formed, and contribute to cross-link formation for differential cytotoxicity in VA-13 cells. Electron spin resonance and spin-trapping technique were used to detect the formation of hydroxyl radical from MMC-treated cells. Our studies show that MMC significantly stimulated the formation of hydroxyl radical in VA-13 cells, but not in the IMR-90 cells. The formation of the hydroxyl radical was inhibited by superoxide dismutase (SOD) and catalase. In addition, the presence of these enzymes partially protected VA-13 cells from MMC toxicity but not IMR-90 cells. Further studies indicated that the decreased free radical formation and resistance to MMC may be due to the increased activities of catalase and glutathione transferase in the IMR-90 cell line. These results suggest that MMC-dependent DNA damage (alkylation and DNA DSB) and the stimulation of oxy-radical formation may play critical roles in the determination of MMC-induced cell killing.

[Cytotoxicity of mitomycin C in rabbit eyes]

The cytotoxic effects of mitomycin C (MMC) on intact rabbit eyes were studied using light microscopy and transmission electron microscopy. A volume of 0.1 ml MMC solution (0.4 mg/ml) was given to rabbits subconjunctivally once a day. The eyes were enucleated at 1, 2, 3, and 4 weeks after subconjunctival injection. MMC showed considerable cytotoxicity in most tissues of the rabbit eyes, such as the cornea, the iris, especially to the choroid and the ciliary body. However, MMC cytotoxicity in the sclera was slight. Based on the above results it is concluded that MMC should not be used when the cornea or sclera is invaded, for example after pterygial resection, and scleral necrosis due to MMC could occur due to the damage of alimentary vessels of the sclera.

Preclinical toxicity study of mitomycin C infused into the internal carotid artery of beagle dogs

Young adult male and female beagle dogs were infused with single doses of 0.5 (2 dogs) or 0.25 mg (5 dogs) Mitomycin C (MMC)/kg body weight directly into the internal carotid artery. Serial hematology and serum chemistry profiles, electrocardiograms and physical observations were made, the animals necropsied at varying times after dosage, and the major organs examined histologically. Results indicate that the dose limiting toxicity of this treatment regimen is myelosuppression. No ocular or neurologic toxicity was detected in any test animal. The findings suggest that infusion of MMC can be safely attempted in humans for the treatment of brain tumors that derive their blood supply from the internal carotid artery.

Reversible inhibition of mammalian tubulin assembly in vitro and effects in Saccharomyces cerevisiae D61.M by mitomycin C

Gaulden reported a novel and unexpected mitomycin C (MMC) effect, namely a pronounced retardation of very late prophase and loss of chromosome orientation in neuroblasts of the grasshopper Chortophaga viridifasciate. Because this effect may be due to interactions of MMC with non-DNA targets, MMC was tested for its interaction with porcine brain tubulin assembly in vitro and for the induction of chromosomal malsegregation in the diploid yeast Saccharomyces cerevisiae strain D61.M. A reversible dose-dependent inhibition of tubulin assembly was observed. Since no biological activation system was present in the incubation mixture this inhibition seems to result from an interaction of unactivated MMC with the assembly process. The possible chemical activation of MMC by reduction with 1,4-dithioerythritol (DTE) was investigated by omission of this compound during isolation and polymerization of tubulin. The absence of DTE resulted in a strong reduction of the net tubulin assembly. Also under these conditions MMC led to a dose-dependent inhibition of the assembly, indicating that the effect of MMC on tubulin assembly is independent of a reductive chemical modification. In S. cerevisiae D61.M, MMC did not induce chromosome loss, but induced other genetic events (possibly mutations, deletions or mitotic recombination) as was detected by an increase of the total number and of the frequency of cycloheximide-resistant colonies. This effect could be observed with and without the addition of rat liver S9 as an exogenous activation system.

Synaptonemal complex damage as a measure of genotoxicity at meiosis

Synaptonemal complex aberrations can provide a sensitive measure of chemical-specific alterations to meiotic chromosomes. Mitomycin C, cyclophosphamide, amsacrine, ellipticine, colchicine, vinblastine sulfate, and cis-platin exposures in mice have been shown to cause various patterns of synaptonemal complex structural damage and synaptic irregularity. These effects are suggestive of abnormal homologue pairing/synapsis/recombination effects which, theoretically, could be implicated in mechanisms leading to aneuploidy and other potentially heritable chromosomal disorders.

[Mitomycin C induced structural changes in heterochromatic regions of human chromosomes 1, 9, 16 and Y]

Aberrations and variations in the heterochromatic blocks of chromosomes 1, 9, 16 and Y were found under the influence of mitomycin C in cultured lymphocytes of peripheral human blood. Lymphocytes were cultured during 96 hours, mitomycin C in final concentration of 0.3 mkg/ml was present in the culture during the latest 24 hours of culturing. Different changes in the heterochromatic regions of chromosomes were found in approximately 30% of cells: in 6.3% of cells mitotic chiasmata were indicated. In 9.5% of cells isolocus breaks were observed in heterochromatic region of chromosome 1 in segment 1q11. In the latter case this may be a fragile site detected under the influence of mitomycin C on the lymphocytes.

Mitomycin C-induced meiotic crossing-over on the interstitial segments in the Chinese hamster heterozygous for a reciprocal translocation

Using Chinese hamsters heterozygous for T(2;10)3Idr and T(1;3)8Idr reciprocal translocations, the authors studied mitomycin C (MMC)-induced crossing-over on the interstitial segments. Marker chromosomes with unequal-length chromatids resulting from crossing-over were clearly detectable, and the frequencies of such marker chromosomes were constant among individual males which were heterozygous for the same reciprocal translocation. The frequency of MMC-induced crossing-over on the interstitial segments increased roughly with increase in dose. These findings, therefore, indicated that marker chromosomes with unequal-length chromatids in translocation heterozygotes may be a useful indicator for detection of the cytogenetic effects of environmental mutagens on germ cells.

Glutathione monoethyl ester can selectively protect liver from high dose BCNU or cyclophosphamide

Normal Swiss Webster mice were treated with monocrotaline or high doses of three antitumor alkylating agents (BCNU, cyclophosphamide, or mitomycin C), all of which have been connected with hepatic veno-occlusive disease at our clinic. Prior administration of WR-2721 did not improve the survival of monocrotaline-treated animals. Glutathione (GSH) improved the survival of these animals to a small degree. Glutathione monoethyl ester (GSHet) almost completely protected animals from the toxicity of monocrotaline. Pretreatment with WR-2721 produced moderate increases in survival at the highest doses of BCNU, and at the lower BCNU doses none of the animals pretreated with WR-2721 died before they were killed on day 150. Pretreatment with GSHet gave good protection from BCNU toxicity at the highest dose of the drug, and there were no deaths in the groups of animals treated with GSHet 1 hour before BCNU. On a multiple dose schedule, GSH provided some protection from cyclophosphamide toxicity; GSHet gave a very good level of protection from cyclophosphamide. In none of these treatment groups were lesions suggestive of hepatic or pulmonary venoocclusive disease identified. In all three experimental protocols (monocrotaline, BCNU, and cyclophosphamide), there was a consistent decrease in hepatic toxicity after GSHet pretreatment; this was not observed in GSH- or WR-2721-pretreated animals. There was no evidence of protection of the FSaIIC fibrosarcoma growing in C3H mice as assayed by tumor growth delay or tumor cell survival in groups treated with two different doses of GSHet 1 hour before each drug injection compared to those treated with the BCNU or cyclophosphamide alone, or BCNU with cyclophosphamide. Pretreatment with GSHet did not alter the toxicity of these drugs to bone marrow. GSHet appears to be an effective protector of critical normal tissue and does not appear to protect tumor.

Relative efficacy of short-term tests in detecting genotoxic effects of cadmium chloride in mice in vivo

The ability of intraperitoneally administered cadmium chloride (0.42-6.75 mg/kg) to induce genotoxic damage in somatic and germ cells of mice was evaluated using chromosomal aberrations, sister-chromatid exchanges (SCE), micronuclei and sperm-head abnormalities as end-points. A significant increase in the frequency of chromosomal aberrations and SCEs was observed in almost all treated series when compared to the negative control. Micronucleus formation in polychromatic erythrocytes was not affected significantly except at the highest concentration used (6.75 mg/kg). Significant differences were observed in the frequency of sperm with abnormal head morphology at all concentrations tested except the lowest one. The clastogenic effects of cadmium chloride in both somatic and germinal cells are found to depend directly on the concentrations used.

Pharmacokinetics and toxicity of mitomycin C in rodents, given alone, in combination, or after induction of microsomal drug metabolism

The pharmacokinetics of mitomycin (MMC) was studied in Wistar rats. Up to five half-lives, the plasma concentration-time curve was biphasic. The AUC changed linearly with increasing doses between 0.5 and 7.5 mg/kg, which corresponds to 0.2 and 3 times the LD50 value in rats. Most of the drug was metabolized, and only 1%-2% and 10%-15% of the dose was eliminated unchanged by biliary and urinary excretion, respectively. The AUC of MMC at the LD50 is slightly less than that reported for the human MTD. Inoculation of MMC together with 5-fluorouracil and doxorubicin did not change the terminal half-life of MMC but decreased the total body clearance and the volume of distribution. The lack of significant influence of phenobarbital and 3-methylcholanthrene pretreatment on the terminal elimination half-life suggests that microsomal drug-metabolizing enzymes inducible by these compounds do not play a decisive role in the in vivo biotransformation of MMC.

Mitomycin C toxicity and pharmacokinetics in mice given sulfur nucleophiles

The sulfur nucleophiles, sodium thiosulfate (Na2S2O3) and N-acetylcysteine (NAC) given in maximally tolerated doses did not reduce the hematologic toxicity of high dose mitomycin C (MMC) in normal mice. In addition, neither sulfur nucleophile significantly altered the antileukemic activity of MMC. Pharmacokinetic studies of MMC in normal mice, demonstrated rapid plasma elimination (T1/2 beta = 0.53 hrs) and substantial drug distribution to the bone marrow which was enhanced by NAC. These results demonstrate a lack of MMC antidotal activity for Na2S2O3 and NAC.

Microbial mutagenicity of chlorambucil, its half-mustard and mitomycin C: a modified screening strategy for genetic toxicology of bis-alkylating anti-tumour drugs

Early assessment of the genetic toxicology of anti-tumour drugs often employs microbial assays, particularly a group of specially developed Salmonella typhimurium strains (uvrB-) which are DNA repair-deficient due to a defective uvrB gene. While such strains are more sensitive than the wild-type to the mutagenic effects of many classes of compound, the DNA cross-linking agent chlorambucil (which is a known human carcinogen) has been shown to be toxic but non-mutagenic in this assay. The mutagenic activities of chlorambucil, its half-mustard analogue and another cross-linking agent (mitomycin C) were thus evaluated in a DNA-proficient strain of the yeast Saccharomyces cerevisiae and also in two isogenic sets of four S. typhimurium strains differing in uvrB gene and plasmid pKM101 presence. In yeast, all three compounds were effective mutagens and recombinogens, while in bacteria the two cross-linking agents were significantly mutagenic in the uvrB+ (DNA repair-proficient) but not in the uvrB- strains. By comparison, the half-mustard was mutagenic in both the uvrB- and uvrB+ strains. This work suggests that it is unwise to rely on results from the commonly used S. typhimurium bacterial strains for evaluating the mutagenicity of DNA cross-linking agents destined as clinical anti-tumour drugs. The use of yeast plus at least one of the sets of four strains employed in this study would provide information more directly relevant to mammalian cells, which are DNA repair-proficient. In addition, a comparison of the patterns of bacterial mutagenicity and toxicity provides evidence for the mode of action (DNA cross-linking or monoadduct formation) of compounds within a series.

Mitomycin C-induced organ toxicity in Wistar rats: a study with special focus on the kidney

Two studies were performed to investigate acute and chronic organ toxicity after Mitomycin C (MMC) administration in Wistar rats. Six rats received 2.5 mg/kg MMC i.p. once and were followed for 5 consecutive days. The alanine aminopeptidase (AAP)/creatinine ratio increased significantly, compared to a control group receiving saline. Four groups of rats were injected i.p. weekly for 5 weeks; 6 control rats with saline, 7 rats with 1.7 mg/kg of MMC, 7 rats with 10 mg/kg 5-fluorouracil (5-FU) and 7 rats with MMC as well as 5-FU. The latter two groups were included to study possible toxicity synergism between the two drugs. A significant decrease in AAP excretion in the MMC group, as well as a nonsignificant decrease in the MMC/5-FU group were the most remarkable observations. Light microscopy did not show renal changes, but did not show alveolar septal congestion after repeated MMC injections. It is concluded that MMC causes tubular damage in Wistar rats, with acute leakage of enzyme from the cells, followed by enzyme depletion during chronic treatment. Also MMC induces pulmonary changes in Wistar rats. To what extent these changes represent early stages of toxicity remains to be elucidated.

A simplified protocol for the mouse bone marrow micronucleus assay

Complex and expensive protocols involving multiple sampling times have been proposed and recommended for the in vivo mouse bone marrow micronucleus assay. The purpose of this study was to determine whether a simplified procedure employing two identical exposures and a single sampling time would be equally effective at detecting chemical clastogens. Furthermore, the utility of the protocol was investigated for both intraperitoneal and oral routes of administration. The results obtained from a group of chemicals spanning the known time range for maximum frequency of micronucleus induction prove the effectiveness of this simplified protocol.

Alteration of rat Kupffer cell function following mitomycin-C administration

Cancer chemotherapeutic agents modify the human immune system in diverse ways including both immunosuppression and immunostimulation. We evaluated the effects of mitomycin-C on rat Kupffer cell phagocytosis, C3b receptor binding, and lysosomal enzyme activity. Kupffer cell cultures were greater than 95% pure. Phagocytosis of IgG-coated sheep red blood cells was demonstrated by 84% of control cells but by only 25% of cells isolated two weeks following mitomycin-C administration (p less than 0.0005). This depression in phagocytic ability had returned to control levels by four weeks posttreatment. Similarly, C3b receptor binding of IgM and complement coated sheep red blood cells was observed in 88% of control Kupffer cells, but declined to 47% at two weeks after drug administration (p less than 0.005) and returned to normal after four weeks. Lysosomal enzyme activity was not impaired by mitomycin-C. Histologically severe ulceration of the colon of treated animals was seen one and two weeks after drug administration, but healed by four weeks post-mitomycin-C treatment. Depression of macrophage function as a consequence of cancer chemotherapy may have important clinical consequences in host defense against bacteria and tumor metastases.

The mutagenicity of urine fractions from patients administered antineoplastic therapy

A concern among hospital personnel is their exposure to mutagenic drugs and in the incidental exposures that could occur in caring for the patients. In a recent published study the mutagenicity of urine from patients administered antineoplastic drugs was determined and techniques were developed to chemically inactivate the mutagenicity. A question still remained as to what components of the excreted urine were mutagenic. Urine samples from patients receiving mutagenic drugs were fractionated by high pressure liquid chromatography (HPLC) to then assay by the Ames test the collected and concentrated fractions to determine what were the mutagenic compounds in the urine. Urine samples from patients on single agent cancer treatment with cisplatin, cyclophosphamide, doxorubicin and mitomycin C were assayed. In general, all urine samples containing the cytotoxic agents studied were mutagenic because of the presence of the parent compound, except cyclophosphamide which requires activation and therefore an active metabolite was the major mutagenic constituent in the urine sample. This data indicates that the mutagenicity of urine from patients receiving these antineoplastic agents is the result of the parent compound or a single major metabolite.

Cell fusion-mediated improvement in transfection competence for repair-deficient mutant of mouse T cell line

A multiple mutagen-sensitive mutant (XUM1) of mouse T-cell lymphoma line, L5178Y, is hypersensitive to ionizing radiation, ultraviolet (UV) light, and cross-linking agents (such as mitomycin C). The frequency of transfection for XUM1 cells after exposure to calcium phosphate-coprecipitated pSV2neo DNA was more than 10(4)-fold less effective than that for Ltk-aprt- (LTA) cells. Other transfection methods (DEAE-dextran and polybrene-DMSO) were not effective for L5178Y and XUM1 cells. The transfection-proficient trait of LTA cells was demonstrated to be genetically dominant by examining the the transfection frequency in hybrid clones constructed between XUM1 and LTA cells. To circumvent the problem with XUM1, the LTA genes necessary for transformation processes were introduced into XUM1 cells by constructing hybrids between XUM1 and LTA cells irradiated with X-rays which causes directional chromosome elimination for hybrid cells. Four of 194 hybrid clones tested were transfection-proficient and hypersensitive to UV (XL102, XL107, XL215, and XL216). All four clones were not hypersensitive to X-rays or mitomycin C. The frequencies of transfection for XL102 and XL216 were nearly the same level as that for LTA cells. The efficiency of transfection for XL107 and XL215 was 10 to 100-fold lower than that for LTA cells.