Cancerogene alkylierende Substanzen

Dimethyl Sulfate as Methylation Agent and Solvent in Highly Regioselective Synthesis of Methyl Salicylate Using Sodium Bicarbonate as a Base

Methyl salicylate (MS), the principal constituent of wintergreen oil, was obtained from salicylic acid (SA) by regioselective methylation of the carboxyl group. A new procedure involved exclusive capture of carboxylic hydrogen (-CO2H) through the use of the selective base, NaHCO3, and methylation via an SN2 mechanism employing the previously formed carboxylate as a nucleophile and the dimethyl sulfate [DMS] as the electrophilic reagent or substrate in a solvent-free reaction process. SA and NaHCO3 were added, followed by DMS after 30 min, and the reaction mixture was stirred at 90 °C for 90 min. The reaction was accompanied by thin-layer chromatography and gas chromatography. The conversion rate via GC was 100%, and the MS yield was 96%. The DMS used in excess was transformed into MeOH and H2SO4 when the mixture was washed with water. The MeOH was stored, and H2SO4 was transformed in Na2SO4 by neutralization with NaOH. The simplicity of the procedure, ready availability of MS, short reaction times, excellent yields, and mild reaction conditions are other advantages of this protocol. MS is being biologically tested as an antibacterial and antitumor agent. The focus of the study is on the search for drugs with greater selectivity for tumor cells so as to reduce adverse effects on normal cells because MS is rarely reported in the literature for this application. Cytotoxicities of 50 and 64% for cultured S. aureus and metastatic melanoma cells, respectively, were observed for a concentration of 0.6 mg/mL of the MS produced, whereas no cytotoxicity against nontumor cells was observed at this concentration. This is considered to be the optimum concentration.

Strain a Mouse Lung Tumor Bioassay

This report summarizes data on the testing of 228 chemicals for carcinogenic activity by the strain A mouse lung adenoma bioassay. The assay is of six months duration and can distinguish two-fold dose differences in carcinogenic potential of compounds from a variety of chemical classes. Most compounds that induced lung tumors in strain A mice have also evoked a neoplastic response in other experimental animal bioassays and/or demonstrated mutagenic activity in various short-term tests. Recommendations are made for future studies on the: (a) distribution and metabolism of chemicals in strain A mouse lung tissue and in specific lung cell types, (b) ability of the lung adenoma bioassay to detect promoting agents, and (c) use of the bioassay to investigate the interactions of more than one chemical.

The selective cytotoxicity of the alkenyl glucosinolate hydrolysis products and their presence in Brassica vegetables

Cruciferous vegetable consumption correlates with reduced risk of cancer. This chemopreventative activity may involve glucosinolates and their hydrolysis products. Glucosinolate-derived isothiocyanates have been studied for their toxicity and chemopreventative properties, but other hydrolysis products (epithionitriles and nitriles) have not been thoroughly examined. We report that these hydrolysis products differ in their cytotoxicity to human cells, with toxicity most strongly associated with isothiocyanates rather than epithionitriles and nitriles. We explored mechanisms of this differential cytotoxicity by examining the role of oxidative metabolism, oxidative stress, mitochondrial permeability, reduced glutathione levels, cell cycle arrest and apoptosis. 2-Propenylisothiocyanate and 3-butenylisothiocyanate both inhibited cytochome P450 1A (CYP1A) enzyme activity in CYP expressing MCL-5 cells at high cytotoxic doses. Incubation of MCL-5 cells with non-cytotoxic doses of 2-propenylisothiocyanate for 24h resulted in a dose-dependent inhibition of ethoxyresorufin O-deethylase, yet failed to affect CYP1A1 mRNA expression indicating interference with enzyme activity rather than inhibition of transcription. Increased reactive oxygen species (ROS) production was observed only for 2-propenylisothiocyanate treatment. 2-Propenylisothiocyanate treatment lowered reduced glutathione levels whereas no changes were noted with 3,4-epithiobutylnitrile. Cell cycle analysis showed that 2-propenylisothiocyanate induced a G2/M block whereas other hydrolysis products showed only marginal effects. We found that 2-propenylisothiocyanate and 3-butenylisothiocyanate induced cell death predominantly via necrosis whereas, 3,4-epithiobutylnitrile promoted both necrosis and apoptosis. Thus the activity of glucosinolate hydrolysis products includes cytotoxicity that is compound-class specific and may contribute to their putative chemoprotection properties.

A bifunctional dimethylsulfoxide substitute enhances the aqueous solubility of small organic molecules

An oxetane-substituted sulfoxide has demonstrated potential as a dimethylsulfoxide substitute for enhancing the dissolution of organic compounds with poor aqueous solubilities. This sulfoxide may find utility in applications of library storage and biological assays. For the model compounds studied, significant solubility enhancements were observed using the sulfoxide as a cosolvent in aqueous media. Brine shrimp, breast cancer (MDA-MB-231), and liver cell line (HepG2) toxicity data for the new additive are also presented, in addition to comparative IC(50) values for a series of PKD1 inhibitors.

Alkylating potential of oxetanes

Small, highly strained heterocycles are archetypical alkylating agents (oxiranes, beta-lactones, aziridinium, and thiirinium ions). Oxetanes, which are tetragonal ethers, are higher homologues of oxiranes and reduced counterparts of beta-lactones, and would therefore be expected to be active alkylating agents. Oxetanes are widely used in the manufacture of polymers, especially in organic light-emitting diodes (OLEDs), and are present, as a substructure, in compounds such as the widely used antimitotic taxol. Whereas the results of animal tests suggest that trimethylene oxide (TMO), the parent compound, and beta,beta-dimethyloxetane (DMOX) are active carcinogens at the site of injection, no studies have explored the alkylating ability and genotoxicity of oxetanes. This work addresses the issue using a mixed methodology: a kinetic study of the alkylation reaction of 4-(p-nitrobenzyl)pyridine (NBP), a trap for alkylating agents with nucleophilicity similar to that of DNA bases, by three oxetanes (TMO, DMOX, and methyloxetanemethanol), and a mutagenicity, genotoxicity, and cell viability study (Salmonella microsome test, BTC E. coli test, alkaline comet assay, and MTT assay). The results suggest either that oxetanes lack genotoxic capacity or that their mode of action is very different from that of epoxides and beta-lactones.

In vitro induction of micronuclei by monofunctional methanesulphonic acid esters

Six monofunctional alkylating methanesulphonates of widely varying structures were investigated in the in vitro micronucleus assay with Syrian hamster embryo fibroblast cells. The results were compared with the alkylating activities measured in the 4-(nitrobenzyl)pyridine test (NBP-test) and the N-methyl mercaptoimidazole (MMI-test) as measures for S(N)2 reactivity as well as in the triflouoroacetic acid (TFA) solvolysis and the hydrolysis reaction as measures for S(N)1 reactivity in order to provide insights into the role of alkylation mechanisms on induction of micronuclei. Moreover we compared the results of micronucleus assay with those of the Ames tests in strain TA 100 and TA1535 and with those of the SOS chromotest with the strains PQ37, PQ243, PM21 and GC 4798. The potency of methanesulphonates to induce micronuclei depended only to a certain degree, on the total alkylating activity (S(N)1 and S(N)2 reactivity). An inverse, significant correlation between the Ames test and the micronucleus assay was observed and an inverse correlation between the micronucleus assay and the SOS chromotest with the different strains. The results indicate that the primary mechanism leading to induction of micronuclei is not O-alkylation in DNA as it is the case in the Ames test with the hisG46 strains TA1535 and TA100 and not N-alkylation as with the SOS chromotest. There is evidence that protein alkylation, e.g. in the spindle apparatus in mitosis is decisive for induction of micronuclei by alkylating compounds. The structurally voluminous methanesulphonates 2-phenyl ethyl methanesulphonate and 1-phenyl-2-propyl methanesulphonate show a clear higher micronuclei inducing potency than the other tested though the bulky methanesulphonates possess a lower total alkylating activity than the others. This effect can be explained by a higher disturbance during mitosis after alkylation of the spindle apparatus with the structurally more bulky methanesulphonates.

DNA methylation, cell proliferation, and histopathology in rats following repeated inhalation exposure to dimethyl sulfate

Dimethyl sulfate (DMS) is an alkylating agent that is carcinogenic to the respiratory tract of rodents. DNA adducts, cell proliferation, and histopathology were assessed in rats to better understand the molecular dosimetry and tissue dynamics associated with repeated inhalation exposure to DMS. For DNA methylation, rats were exposed to DMS vapor 6 h/day for up to 10 days to 0.0, 0.1, 0.7 and 1.5 ppm. N7-Methylguanine and N3-methyladenine were detected in neutral thermal hydrolysates of DNA isolated from respiratory tract tissues by high-performance liquid chromatography (HPLC) using fluorescence and ultraviolet (UV) detection. DNA methylation was greatest in DNA isolated from nasal respiratory mucosa, less in olfactory, and little was found in lung. N7-Methylguanine levels in respiratory mucosa approached steady-state levels by day 5, and N7-methylguanine persistence following exposure for 5 consecutive days was also determined. Loss of N7-methylguanine from respiratory and olfactory mucosa appeared to follow first-order kinetics. N3-Methyladenine levels were at or below detection limits in all samples. The effect of DMS on histopathology and cell proliferation in the nasal epithelium was also investigated. Rats were exposed nose-only for 2 wk to DMS vapor at concentrations of 0, 0.1, 0.7, or 1.5 ppm. Inhalation exposure to DMS induced degenerative and inflammatory changes in nasal epithelium at >or=0.7 ppm. Cell proliferation evaluations showed a trend towards an increased response at 1.5 ppm. These experiments demonstrate that DMS can induce cytotoxic and proliferative effects and is a potent methylating agent of the nasal mucosa in vivo. These experiments will provide data for the development of dosimetry models useful for risk extrapolation.

Pronucleotides: toward the in vivo delivery of antiviral and anticancer nucleotides

To overcome the many hurdles preventing the use of antiviral and anticancer nucleosides as therapeutics, the development of a prodrug methodology (i.e., pronucleotide) for the in vivo delivery of nucleotides has been proposed as a solution. The ideal pronucleotide should be non-toxic, stable in plasma and blood, capable of being i. v. and/or orally dosed, and intracellularly convertible to the corresponding nucleotide. Although this goal has yet to be achieved, many clever and imaginative pronucleotide approaches have been developed, which are likely to be important pharmacological tools. This review will discuss the major advances and future directions of the emerging field of antiviral and anticancer pronucleotide design and development.

Developmental toxicity of dimethyl sulfate by inhalation in the rat

Dimethyl sulfate (DMS; CAS No. 77-78) is a colorless, oily liquid which is used as a chemical intermediate and as a reactant in producing polyurethane resins. In this study, groups of pregnant Crl:CD BR rats were exposed, nose-only, to either 0.1, 0.7 or 1.5 ppm DMS by inhalation for 6 hr/day from Days 7 through 16 of gestation (day in which copulation plug was detected was designated Day 1G). A control group of pregnant rats was exposed simultaneously to air only. All female rats were euthanized on Day 22G and the fetuses were examined. A suppression of both food consumption and the rate of body weight gain was seen in the 0.7 and 1.5 ppm groups. No unusual clinical signs were seen in rats exposed to DMS. None of the reproductive parameters was altered in any of the groups and no statistically significant fetal effects were detected. DMS is not a developmental toxin in the rat following inhalation exposures up to 1.5 ppm during the period of major organogenesis.

Mechanisms of carcinogenicity of methyl halides

Methyl chloride, bromide, and iodide are used as methylating agents. These compounds are mutagenic in short-term tests and do not require activation by exogenous S9 mix. In DNA-binding studies performed in rats and mice, 14C-labeled methyl chloride was given by inhalation, and methylation of DNA bases was examined. The compound did not lead to specific DNA adducts. In particular, methylation of DNA bases was not observed. In contrast, methyl bromide and methyl iodide, upon oral and inhalation administration to rats and mice, caused systemic DNA methylation. Specifically, 3-methyl-adenine, 7-methyl-guanine, and O6-methyl-guanine were formed. Long-term inhalation bioassays have been performed in rats and mice with methyl chloride and methyl bromide. Methyl chloride induced renal tumors, but only in male mice at the highest concentration tested (1000 ppm). Under these special conditions, a number of secondary effects occur subsequent to glutathione depletion in the target tissue, resulting in DNA damage (DNA-protein cross-links and probably DNA single-strand breaks). The particular coincidence of secondary high-dose effects precludes a risk extrapolation to man. Methyl bromide did not induce tumors in rats and mice when administered by inhalation. However, experimental data point to a possible local carcinogenic effect on the rat forestomach when the compound is given by gavage. A factor that accounts for the discrepancy between systemic DNA methylation and apparent noncarcinogenicity upon inhalation might be the preference of 7-N over O6 methylation of guanine. An extrapolation of the negative rodent inhalation bioassay of methyl bromide to man might be problematic because rodents metabolize methyl bromide very quickly whereas in humans there is a particular subpopulation that only poorly metabolizes the compound ("nonconjugators"). Such individuals can be characterized by incubation of erythrocytes with methyl chloride or methyl bromide and measurement of the substrate decline. Methyl iodide has been tested, with positive outcome, in early carcinogenicity bioassays not based on modern methodology. However, these results, along with the proven systemic methylating potency of methyl iodide, argue in favor of a carcinogenic effect of the compound.

Micronucleated reticulocyte induction by ethylating agents in mice

Six model ethylating agents were tested for clastogenic potency by means of a new technique of the micronucleus assay with mouse peripheral blood cells using acridine orange (AO)-coated slides, to evaluate the test. The alkylating agents were: N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG), N-ethyl-N-nitrosourea (ENU), diethylsulfate (DES), ethyl methanesulfonate (EMS), epichlorohydrin (ECH) and ethylene dibromide (EDB). The animals were given a single intraperitoneal injection of the following doses of the chemicals: ENNG and ENU, 25, 50 and 100 mg/kg; EMS and DES, 100, 200 and 400 mg/kg body weight. For EDB and ECH, the doses were 50, 100 and 200 mg/kg, given twice, 24 h apart. Before and after the injection, blood samples were taken from the tails at 24-h intervals up to 72 h and preparations were made on AO-coated slides. For each dose group, 4 animals were used and 1000 reticulocytes were examined per slide for the presence of micronuclei. At the optimum induction time of 48 h, ENU induced micronucleated reticulocytes (MNRETs) at all 3 doses. ENNG and EMS induced MNRETs significantly at 2 dose levels each and DES only at the highest dose. ECH and EDB failed to induce MNRETs. On the basis of the dose of chemical needed to double the spontaneous frequency, the order of clastogenic potency was ENU greater than ENNG greater than EMS greater than DES. The results obtained compared favorably with those from other in vivo methods. The present technique proves to be simple, flexible and relatively sensitive. Shifts in the optimum induction peak in individual animals and by some chemicals can be picked up easily which is important when testing weak mutagens and chemicals with an unknown mechanism of action.

Genotoxic potency of monofunctional alkylating agents in E. coli: comparison with carcinogenic potency in rodents

A quantitative correlation between carcinogenicity and genotoxicity was investigated by a comparison between the carcinogenic potency in rodents and the mutagenic (M), recombinogenic (R) and SOS-inducing (I) potencies in a bacterial test (E. coli multitest) for 9 monofunctional alkylating agents: N-nitroso-N-methylurethane, N-nitroso-N-ethylurea, epichlorohydrin, N-nitroso-N-methylurea, N-nitroso-N-methyl-N'-nitroguanidine, methyl methanesulfonate, diethylsulfate, dimethylsulfate, ethyl methanesulfonate. A significant positive correlation between the carcinogenic potency and the product of the mutagenic and recombinogenic potencies was found for all tested compounds. Thus, the E. coli multitest may be used as a simple test to search for correlations between carcinogenicity and genotoxicity of DNA-damaging agents.

Nucleophilic selectivity as a determinant of carcinogenic potency (TD50) in rodents: a comparison of mono- and bi-functional alkylating agents and vinyl chloride metabolites

Using published data, the carcinogenic potency (TD50) in rodents of a series of monofunctional alkylating agents, bifunctional antitumor drugs and the vinyl chloride (VC) metabolites chloroethylene oxide (CEO) and chloroacetaldehyde (CAA) was compared to their nucleophilic selectivity (Swain and Scott's constant s or initial ratio of 7-/O6-alkylguanine in DNA). A positive correlation between the log of TD50 estimates and the s values for a series of 14, mostly monofunctional, alkylating agents was observed. This linear relationship also included 2 bifunctional chloroethylnitrosoureas, although their carcinogenic potency was compared to their initial 7-/O6-alkylguanine ratio rather than their s values (n = 16, r = 0.91, p less than 0.005). In addition, the carcinogenic potency of 2 alkyl sulfates, which is not yet known accurately, may correlate with their nucleophilic selectivity through the same relationship. By contrast, 2 methyl halides and 5 bifunctional antitumor drugs (nitrogen mustards and azyridinyl derivatives) did not follow this linear relationship: at similar nucleophilic selectivity, they were more potent carcinogens than the above 18 alkylating agents; this may hold true for CEO and CAA too, although further carcinogenicity experiments are needed to calculate their precise TD50 values. The possible molecular mechanisms involved in tumor induction by these agents are discussed on the basis of these findings. Comparison of the estimated TD50 for CEO, CAA and VC in rodents confirms that CEO is the ultimate carcinogenic metabolite of VC and suggests that only a very small proportion of metabolically generated CEO is available for DNA alkylation in vivo.

Genotoxicity of monofunctional methanesulphonates in the SOS chromotest as a function of alkylation mechanisms. A comparison with the mutagenicity in S. typhimurium TA100

17 monofunctional methanesulphonates of widely varying structures were investigated in the SOS chromotest using the E. coli strain PQ37. All compounds tested were positive in this assay. The monofunctional methanesulphonates in general possess low SOSiP values. Five of the compounds tested i.e. iBMS, NpMS, 2 PhPMS, PkMS and 1,3-DC12PMS (for abbreviations see Table 1) did not show increasing beta-galactosidase activity and both the positive induction factors and the positive SOSiP values resulted from the toxicity correction as performed according to Quillardet and Hofnung (1985). In general methanesulphonates with a higher SN1 reactivity, in particular the secondary compounds, showed clear genotoxic activities whereas those possessing low SN1 reactivities (primary compounds) induced a low SOS repair indicating that the alkylation of O-atoms in the DNA bases contributes more to the induction of SOS repair in strain PQ37 than N-alkylations. The only exception was methyl methanesulphonate (MMS) which possessed a very high SN2 reactivity but a rather low SN1 reactivity. It had the highest SOSiP value of all tested methanesulphonates. No dependence of the genotoxicity on the SN2 reactivity could be found in this series. In general the phenyl-substituted methanesulphonates showed higher SOSiP values, which is presumably due to their relatively high SN1 reactivities and their relatively long life times in aqueous systems. There is a clear relationship between SN1 reactivities and the SOSiP values: the SOSiP values increase with rising SN1 reactivities reaching a maximum at iPMS after which the genotoxicities decrease due to the decreasing life times. The compounds with very high SN1 reactivities also possess very high hydrolysis rates. A good correlation could be established between the mutagenicities in S. typhimurium TA100 and the SOS chromotest (strain PQ37). Only 4 small deviations from this correlation could be found. The reasons for these deviations are discussed.

Metabolic inactivation of mutagens in Drosophila melanogaster

The route of administration of a drug is a pharmacological factor to be reckoned with. In Drosophila, a whole-animal object for mutagenicity studies, the way in which a mutagen is applied can also be of crucial importance. In this study the mutagenicity of a number of directly acting agents was determined after feeding or injection of the mutagen. Methyl-p-toluenesulphonate (Me-Tos), ethyl-p-toluenesulphonate (Et-Tos) and nor-nitrogen mustard (NNM) were not mutagenic in a sex-linked recessive lethal test when fed to the adult flies. Injection, however, did produce significant mutagenicity. The absence of mutagenicity after oral application is not caused by chemical instability but is the result of metabolic de-activation, presumably in the gut and the fat body. Feeding of these compounds in combination with the inhibition of cytochrome P-450 by 1-phenylimidazole (PhI) allowed sufficient quantities of the mutagen to reach the gonads and to produce significant genetic damage. This resembles what is known in pharmacology as a 'first-pass effect'. Formaldehyde (FA) mutagenicity, which also is only observed after injection and not in feeding experiments, was not affected by either iproniazid (Ipr) or PhI pretreatment. Aspecific enhancement of mutagenicity is excluded as this effect was not observed with mutagens that are structurally related to the tosylates, such as methyl methanesulphonate (MMS), ethyl methanesulphonate (EMS) or hycanthone methanesulphonate (HyMS). A number of other inhibitors of metabolism did not influence metabolic de-activation in Drosophila.

Headspace gas chromatographic-mass spectrometric analysis of light hydrocarbons and volatile organosulphur compounds in reduced-pressure cultures of Clostridium

A static headspace gas chromatographic method for the simultaneous separation of trace light hydrocarbons and volatile organosulphur compounds in gases of nineteen Clostridium cultures at reduced pressure is described. The separation was achieved on n-octane-Porasil C after sampling of the gaseous compounds in a PTFE loop without any pretreatment. Most peaks were identified by gas chromatography-mass spectrometry. The presence of methane and ethylene sulphide among Clostridium volatiles is confirmed and 3-methyl-1-butene, 2-methyl-2-butene, dimethyl trisulphide and S-methyl thioacetate are reported for the first time in the Clostridium group.

Effect of benzyl chloride on rat liver functions

Benzyl chloride (BCL) is extensively used in industry for the manufacture of dyes, perfumes, and pharmaceutical products. A previous study from this laboratory revealed the presence of liver steatosis of the microvesicular type and central focal inflammation in rats following the inhalation of BCL. This study was conducted to investigate the hepatotoxicity of intravenous (iv) BCL in rat. BCL (250, 25, and 0 micrograms/kg) was administered (iv) to rats, and serum enzyme tests were used to evaluate hepatic injury. After 10 min from BCL administration, serum glutamic-pyruvic transaminase and lactic dehydrogenase activities were significantly increased compared to the control group, while the values returned to normal within 1 h from the administration of BCL. Also, ornithine carbamyltransferase enzyme activity was significantly increased and reached a maximum as early as 0.5 h from the administration of BCL. Hepatic excretory function was investigated by the clearance of bromosulfophthalein (BSP) after 0.5 and 24 h from the administration of BCL. The clearance of BSP in both treatments was significantly slower compared to control group throughout the 24 h studied. Furthermore, BCL significantly decreased liver and blood glutathione values. This study revealed that BCL has the potential to cause hepatomalfunction.

Increase of nicotinamide methyltransferase and N1-methyl-nicotinamide oxidase activities in the livers of the rats administered alkylating agents

Twenty four hours after intraperitoneal injection of alkylating agents, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), N-methyl-N-nitrosourea (MNU) and methyl methanesulfonate (MMS), into rats, an increase in nicotinamide (Nmd) methyltransferase and N1-methylnicotinamide (1-CH3Nmd) oxidase activities in the liver was found. Since activities of these enzymes in the liver extracts were not stimulated directly by these agents in vitro, it is postulated that the increases in these enzyme activities are due to the induction of each enzyme.

Quantitative comparison of carcinogenicity, mutagenicity and electrophilicity of 10 direct-acting alkylating agents and of the initial O6:7-alkylguanine ratio in DNA with carcinogenic potency in rodents

The quantitative relationship between carcinogenicity in rodents and mutagenicity in Salmonella typhimurium was examined, by using 10 monofunctional alkylating agents, including N-nitrosamides, alkyl methanesulfonates, epoxides, beta-propiolactone and 1,3-propane sultone. The compounds were assayed for mutagenicity in two S. typhimurium strains (TA1535 and TA100) and in plate and liquid assays. The mutagenic activity of the agents was compared with their alkylating activity towards 4-(4'-nitrobenzyl)pyridine and with their half-lives (solvolysis constants) in an aqueous medium. No correlations between these variables were found, nor was mutagenic activity correlated with estimates of carcinogenicity in rodents. There was a positive relationship between carcinogenicity and the initial ratios of 7-:O6-alkylguanine formed or expected after their reaction with double-stranded DNA in vitro. The results suggest that alkylation of guanine at position O6 (or at other O atoms of DNA bases) may be a critical DNA-base modification that determines the overall carcinogenicity of these alkylating agents in rodents.

The biological activity of 4-chloromethylbiphenyl, benzyl chloride and 4-hydroxymethylbiphenyl in 4 short-term tests for carcinogenicity. A report of an individual study in the UKEMS genotoxicity trial 1981

4-Chloromethylbiphenyl (4CMB), benzyl chloride (BC) and 4-hydroxymethyl-biphenyl (4HMB) were tested for biological activity in the following assays: (i) the Salmonella/microsome assay; (ii) a bacterial 'fluctuation' assays; (iii) a DNA repair assay in Hela cells, and (iv) a mouse lymphoma mutation assay. 4CMB was active in assays (i), (ii) and (iii) but not in (iv); BC was active in assays (i), (ii), (iii) but not in (iv) while 4HMB was inactive in all assays. Where biological activity was seen this did not require addition of a liver S9 preparation. 4CMB was more active than BC in all the test systems in which a positive response was obtained. The implication of these results for a test battery approach to in vitro testing is discussed.

Toxicity, tissue distribution, and excretion of benzyl chloride in the rat

The tissue distribution and excretion of [14C]benzyl chloride was investigated in adult male and female Fischer 344/N rats after administration of a single oral dose of [14C]benzyl chloride in corn oil at 25 mg/kg, data was correlated with histopathologic and toxicity findings elicited from a 27-37-wk repeated-dose oral toxicity study of benzyl chloride. Radioactivity was detected in all tissues selected for examination. Elimination of the isotope occurred predominantly in the urine. Female rats excreted the isotope at a faster rate than the males and also maintained slightly lower tissue concentrations (with the exception of the blood and kidneys). Isotope recovery was achieved at 90% in the urine and feces of female rats at 24 h, compared with an 80% recovery rate in males. Concentrations of radioactivity were high in the gastrointestinal tract, reflecting the route of administration; however, the squamous stomach and the small intestine consistently retained higher concentrations of isotope than the glandular stomach. Results of acute toxicity and organ histopathology studies in animals dosed with benzyl chloride for 27-37 wk are compatible with the organ distribution and excretion of [14C]benzyl chloride. Histopathologic findings included severe acute and chronic gastritis, hyperkeratosis and hyperplasia of the squamous stomach, and progressive lesions of the heart ranging from proliferation of interstitial cells to acute necrosis of myocardial fibers. Both of these studies suggest that the squamous stomach is a target organ for benzyl chloride or one of its metabolites.

Potential carcinogenic and mutagenic industrial chemicals. I. Alkylating agents

A variety of alkylating agents, acylating agents, peroxides, halogenated derivatives, and nitrogen derivatives have been reviewed, principally in terms of their synthesis, areas of utility, stability, distribution, reactivity, levels of exposure, population at risk, metabolism, carcinogenicity, and mutagenicity.

Determination of reaction rate constants for alkylation of 4-(p-nitrobenzyl) pyridine by different alkylating agents

The rate constants have been determined for the reaction between some different alkylating agents and 4-(p-nitrobenzyl) pyridine (NBP) in methanol. These constants have been compared with those for alkylation of aniline in water. All the constants were lower in methanol than in water but in different degrees. The rate constants of the different alkylating agents have been calculated at a nucleophilic strength n=2. The genetic risk defined as the degree of alkylation of a nucleophile (n=2) is equivalent to the rate constant kn=2 and the target dose. The dependence of the genetic risk on the rate constant (kn=2) is discussed.

Dimethyl and monomethyl sulfate: presence in coal fly ash and airborne particulate matter

Dimethyl sulfate and its hydrolysis product monomethyl sulfate have been found at concentrations as high as 830 parts per million in fly ash and in airborne particulate matter from coal combustion processes. This discovery poses a new environmental problem because of the mutagenic and carcinogenic properties of these compounds.

Brain cancer in petrochemical workers: a case series report

Eighteen primary brain cancer deaths among male workers at one Texas petrochemical plant from 1965-1980 are reported. Federal officials from OSHA and NIOSH are performing with company cooperation an historical prospective cohort mortality study, a case-control study, and neuropathological case confirmation. Average age at death was 53 (range 30-66). Median employment was 21 years and median latency was 24 years. 15/18 tumors were glioblastoma multiforme, an unusual histologic distribution. A preliminary estimate reveals a plant-wide excess brain cancer risk twice expected among 6,800 white males at the plant since 1941. Brain cancer mortality rates in surrounding counties are in the median range for US counties from 1950-1969. Ten recognized or suspected carcinogens are present in quantities greater than 10(6) lbs/yr. To date no common chemical exposures or work assignments have been identified among the cases. Data on 26 experimental brain carcinogens and relevant epidemiological studies are provided.

Genetic effects of dimethyl sulfate, diethyl sulfate, and related compounds

DMS and DES are monofunctional alkylating agents that have been shown to induce mutations, chromosomal aberrations, and other genetic alterations in a diversity of organisms. They have also been shown to be carcinogenic in animals. As an alkylating agent, DMS is a typical SN2 agent, attacking predominantly nitrogen sites in nucleic acids. DES is capable of SN1 alkylations as well as SN2 and thereby causes some alkylation on oxygen sites including the O6-position of guanine which is thought to be significant in mutagenesis by direct mispairing. The mutagenicity of DMS is better explained in terms of indirect, repair-dependent processes. With respect to both alkylating activity and genetic effects, striking similarities are found between DMS and MMS and between DES and EMS. In most systems where they have been tested, both DMS and DES are mutagenic. Results of many of the mutagenesis studies involving these compounds and other alkylating sulfuric acid esters are summarized in Tables 6, 7, 8, 9 and 10 of this review. Most data are consistent with these agents acting primarily as base-pair substitution mutagens. In the case of DES, strong specificity for G.C to A.T transitions has been reported in some systems but has not been clearly supported in some others. Low levels of frameshift mutations of the deletion type are also likely. In addition to the induction of mutations, recombinogenic and clastogenic effects have been described.

[Carcinogenic activity of benzyl-nitrosourea (BzNH) in BD-rats (author's transl)]

Chronic weekly oral and subcutaneous administration of N-Benzyl-N-nitrosourea induced carcinomas of the forestomach and local s.c. sarcomas respectively in BD-rats. This confirms a local carcinogenic effect of the compound. In prenatal experiments in BD-rats no carcinogenic effect of BzNH could be found.

On the reaction kinetics in water of 1,3-propane sultone and 1,4-butane sultone: a comparison of reaction rates and mutagenic activities of some alkylating agents

To determine correlations between the biological action pattern and chemical reactivity of alkylating agents, the rate constants for reactions of 1,3-propane sultone and 1,4-butane sultone with a series of nucleophiles at 37 degrees C have been determined. Previously published data on the mutagenicity of the two sultones and of some alkyl methanesulfonates and dialkyl sulfates towards Schizosaccharomyces pombe have been used in the evaluation of the dependence of mutagenic effectiveness on chemical reactivity. It is of interest to note that the mutagenic effectiveness of the two sultones, if expressed per alkylating event at a certain low nucleophilicity is the same as that of e.g. methyl methanesulfonate and ethyl methanesulfonate.

Tissue distribution and mode of DNA methylation in mice by methyl methanesulphonate and N-methyl-N' -nitro-N-nitrosoguanidine: lack of thymic lymphoma induction and low extent of methylation of target tissue DNA at 0-6 of guanine

The methylating agents methyl methanesulphonate (MMS) and N-methyl N'-nitro-N-nitrosoguanidine (MNNG), administered by single i.p. injection in mice failed to yield thymic lymphoma at doses around 60% of the LD50 values, in contrast to MNUA which gives a high yield of tumours by this route. Comparison of the tissue distribution and mode of DNA methylation by these agents showed a positive correlation with ability to methylate the 0-6 atom of guanine in DNA of the target tissues thymus and bone marrow and tumorigeneis. MMS gave a low yield of this product due to its relatively low Sn1 reactivity but was able to methylate DNA extensively at other sites in the target tissues and other organs examined. MNNG despite its ability to methylate 0-6 of guanine in DNA in vitro to the same relative extent as the potent carcinogen MNUA, methylated DNA of thymus and bone marrow to a very small extent in vivo but was able to methylate DNA in certain other tissues nearer the site of i.p. injection. These findings contrast with the general relatively extensive methylation of 0-6 of guanine in DNA of the target tissues and other organs by N-methyl-N-nitrosourea (MNUA).

Methylation of DNA in various organs of C57B1 mice by a carcinogenic dose of N-methyl-N-nitrosourea and stabiltty of some methylation products up to 18 hours

Female 6-8-week-old (57B1 mice were injected i.p. with N-methyl-N-nitrosourea (MNUS) (14C or 3H-methyl-labelled) in saline (80 mg/kg) and DNA was isolated from bone marrow, small bowel, kidneys, liver, lungs, spleen and thymus at various times thereafter up to 18 h. Methylation of DNA was found in all organs examined, and by analyses using column or paper chromatography of DNA hydrolysates, the extent of methylation of DNA purines was determined. Methylated guanine residues (at N-3, N-7 and 0-6 positions) were stable in DNA up to 18 h, but methylated adenines (at N-3 or N-7) were removed from DNA of all organs examined; the overall half-life of methyladenines was about 3 h, but removal appeared to occur in a biphasic manner, with a proportion of methyladenine remaining relatively stable. This relative stability was somewhat more marked in bone marrow than in other organs.

Effect of a single treatment with the alkylating carcinogens dimethynitrosamine, diethylnitrosamine and methyl methanesulphonate, on liver regenerating after partial hepatectomy. I. Test for induction of liver carcinomas

A single injection of dimethylnitrosamine (DMN), 12.0-15.6 mg-kg, given to 100 g female rats 24 h after partial hepatectomy, induced hepatocellular carcinoma. No animals receiving DMN without partial hepatectomy developed liver carcinomas. Previous evidence had suggested that the incidence of tumours was highest when DMN was administered during the wave of DNA replication which follows partial hepatectomy. The present experiments made this suggestive evidence statistically significant. A single treatment with diethylnitrosamine (DEN) induced liver cell cancer when given to intact or to partially hepatectomised rats. No tumors developed when another alkylating carcinogen, methyl methanesulphonate (MMS), was administered after partial hepatectomy. The significance of these results in relation to the mechanism of initiation of carcinogenesis is discussed.

The specificity of different classes of ethylating agents toward various sites of HeLa cell DNA in vitro and in vivo

The sites and extent of ethyl products of neutral ethylation of HeLa cell DNA by [14-C]diethyl sulfate, [14-C]ethyl methanesulfonate, and [14-C]ethylnitrosourea have been determined in vitro and in vivo, and found to differ significantly depending on the ethylating agents. Diethyl sulfate and ethyl methanesulfonate ethylate the bases of HeLa cell DNA in the following order: 7-ethylguanine greater than 3-ethyladenine greater than 1-ethyladenine, 7-ethyladenine greater than 3-ethylguanine, 3-ethylcytosine, O-6-ethylguanine. Ethyl bases accounted for 84-87% of the total ethyl groups associated with HeLa cell DNA. Ethylnitrosourea, in contrast, has particular affinity for the O-6 position of guanine. It ethylates the bases of HeLa cell DNA in the following order: O-6-ethylguanine, 7-ethylguanine greater than 3-ethyladenine greater than 3-ethylguanine, 3-ethylthymine greater than 1-ethyladenine, 7-ethyladenine, 3-ethylcytosine. Ethylation of the bases only accounts for 30% of the total ethylation in the case of ethylnitrosourea. The remaining 70% of the [14-C]ethyl groups, introduced in vivo and in vitro, are in the form of phosphotriesters which after perchloric acid hydrolysis are found as [14-CA1ethanol and [14-C]ethyl phosphate. In contrast, phosphotriesters amounted to only 8-20% of total ethylation in in vivo or in vitro diethyl sulfate and ethyl methanesulfonate treated HeLa cell DNA, and 25% of the total methylation in in vitro methylnitrosourea treated HeLa cell DNA. Alkylation at the N-7 and N-3 positions of purines in DNA destabilizes the glycosidic linkages. Part of 7-ethylguanine and 3-ethyladenine are found to be spontaneously released during the ethylation reaction. Incorporation of the 14-C of the alkylating agents into normal DNA bases of HeLa cells can be eliminated by performing the alkylations, in the presence of cytosine arabinoside, for 1 hr.

Hybridization of ribosomal RNA labeled to high specific radioactivity with dimethyl sulfate

RNA radioactively methylated with dimethyl sulfate has the advantage of relatively low background noise level when utilized in DNA saturation hybridization employing the membrane filter technique. In addition, the RNA can be methylated with either 3H- or 14C-labeled methyl groups. However, the low specific radioactivity usually obtained with dimethyl sulfate has limited the use of this labeling technique. We describe a detailed characterization of the methylation of rRNA with dimethyl sulfate giving specific radioactivities on the order 10-5 cpm/mug. Kinetics and optimum conditions for the methylation reaction of rRNA were studied. The methylation did not cause excessive degradation of RNA in neutral aqueous solution, and the methyl derivative of RNA was stable under normal hybridization conditions. Specific radioactivitiy of the methylated RNA was found to be a linear function of the product of RNA concentration and specific radioactivity of the dimethyl sulfate in the reaction mixture at a constant incubation time. The methylated bases of the RNA lowered the thermal stability of the DNA-RNA hybrids by 1 degree in Tm per 1.6 per cent methylated RNA bases. rRNA gene dosage values using high specific radioactive methylated RNA were found to be 81 and 180 genes/haploid genome, respectively. Dissociation constants of the hybridization reaction ranged from 0.90 times 10-10 to 2.37 times 10-10 M.