A genomic change associated with the development of resistance to hycanthone in Schistosoma mansoni.

Ribosomal gene probes were used to investigate the genetic basis of drug resistance in schistosomes in a model where resistance to the anthelmintic hycanthone (HC) is generated by exposing immature worms to the drug. Two strains of Schistosoma mansoni, JHU and NMRI, were used. Drug resistance could be produced in the JHU strain by treatment with HC, but was also found to occur spontaneously. In contrast, it was not possible to detect or produce resistance to HC in the NMRI strain. A genomic alteration accompanied the development of resistance. The change was evidence by the occurrence of restriction fragment length polymorphisms (RFLPs) when Southern blots of genomic DNA from HC-resistant worms were hybridized with the ribosomal probe pSM389, which contains part of the small rRNA gene plus non-transcribed spacer (NTS) sequence. The most reliable marker of HC-resistance was a 3.6-kb BamHI fragment which was present and heritable in 7 drug-resistant lines derived from the JHU strain but absent from the parent JHU population and from NMRI parasites. The universal absence of the 3.6-kb RFLP in HC-sensitive individuals and its presence in the drug-resistant progeny suggest that resistance results from an induced change in the population rather than from selection of HC-resistant parasites. The rRNA gene sequence responsible for detecting the 3.6-kb RFLP appears to be localized either to the NTS or to the 5' end of the small rRNA gene, since hybridization to a probe containing sequence from the rRNA gene contiguous and downstream from the insert of pSM389 failed to reveal the RFLP. These results show that the development of resistance to HC is accompanied by a genomic rearrangement.

Effects of oltipraz, BHA, ADT and cabbage on glutathione metabolism, DNA damage and lipid peroxidation in old mice.

Eighteen-month-old female mice were fed defined diets for 2 weeks which contained 0.05% or 0.10% oltipraz, 0.10% anethole dithione (ADT), 0.10% butylated hydroxyanisole (BHA) or 20% lyophilized cabbage. All diets resulted in significant increases in hepatic reduced glutathione (GSH) content. Glutathione reductase and glutathione S-transferase activities were also significantly higher than the control values. All diets produced significant decreases in hepatic DNA damage (single strand breaks) and lipid peroxidation (malondialdehyde content). In general, similar effects were produced by the two dithiolthiones, oltipraz and ADT. More pronounced effects were produced by oltipraz and ADT than by BHA or cabbage in the diet. Diets high in antioxidants may be effective in retarding free radical reaction processes associated with aging and cancer.

Clinical evaluation of amoscanate in healthy male volunteers.

Single oral doses of amoscanate (4-isothiocyanato-4'-nitrodiphenylamine), an experimental antiparasitic agent, are highly effective in animals against the four major species of schistosomes which infect humans. Two prospective, randomized, double blinded, placebo controlled Phase I studies were designed to evaluate the tolerance and safety of the 5% aqueous suspension of 2-mu particles of amoscanate administered to healthy male volunteers. In addition to routine safety monitoring, particular attention was directed toward detecting hepatic, neurological, cardiovascular or ocular toxicity. Three of four men who received 3.5 mg/kg of amoscanate developed mild, reversible hepatotoxicity, which could not be unequivocably attributed to the drug. In the second study, of 1 mg/kg amoscanate, there was no statistically significant evidence of hepatotoxicity, although 1 of 12 drug recipients developed transient liver chemistry changes. Despite intensive monitoring, there was no evidence in either study of significant symptomatic complaints, or of neurological, cardiovascular or ocular toxicity. No mutagenic activity attributable to amoscanate was detectable in the urine. These results suggest that this formulation of amoscanate, at 1 mg/kg, is sufficiently well tolerated and safe to justify evaluation for efficacy in patients with schistosomiasis.

Inhibitory effects of 5-(2-pyrazinyl)-4-methyl-1,2-dithiol-3-thione (Oltipraz) on carcinogenesis induced by benzo[a]pyrene, diethylnitrosamine and uracil mustard.

5-(2-Pyrazinyl)-4-methyl-1,2-dithiol-3-thione (Oltipraz) was studied for its capacity to inhibit carcinogen-induced neoplasia in female ICR/Ha mice. When administered by oral intubation 48 h prior to benzo[a]pyrene (BP), also given by oral intubation, Oltipraz inhibited the occurrence of pulmonary adenomas and tumors of the forestomach. The ratio of the number of tumors occurring in the mice receiving Oltipraz to that of the corresponding controls was: lung, 0.36 and forestomach 0.38. Inhibition also occurred when Oltipraz was given p.o. 24 h prior to BP. In other experiments, oral administration of Oltipraz 48 h prior to p.o. administration of diethylnitrosamine or uracil mustard inhibited pulmonary adenoma formation but to a lesser extent than with BP as the carcinogen. The low toxicity of Oltipraz found previously, coupled with evidence of protective effects against chemically diverse carcinogens, suggests that this compound should be studied further for its possible use as an agent for the chemoprevention of neoplasia.

1,2-Dithiol-3-thione analogs: effects on NAD(P)H:quinone reductase and glutathione levels in murine hepatoma cells.

The 1,2-dithiol-3-thiones are a class of five-membered cyclic sulfur compounds which have chemotherapeutic and chemoprotective properties. The parent 1,2-dithiol-3-thione nucleus and a series of six substituted analogs all induced NAD(P)H: quinone reductase (EC 1.6.99.2) activity and elevated glutathione levels in Hepa 1c1c7 murine hepatoma cells in culture thereby enhancing detoxification potential. These analogs included monosubstituted derivatives with phenyl, p-methoxyphenyl or 2-pyrazinyl groups at C-4 or C-5, and disubstituted compounds bearing phenyl or 2-pyrazinyl moieties at C-5 and an additional methyl group at C-4. This system can be used as an in vitro model for the study of the specificity and mechanism of action of the 1,2-dithiol-3-thiones as already demonstrated for several other classes of chemoprotective agents. The 1,2-dithiol-3-thiones also elevated quinone reductase and glutathione levels in the Hepa 1c1c7 cell mutants (BPrc1 and TAOBPrc1) that are defective in aryl hydrocarbon receptor functions. We conclude that the 1,2-dithiol-3-thiones are largely concerned with the stimulation of metabolic inactivation of electrophiles.

Biochemical effects of dithiolthiones.

Administration of dithiolthiones to mice in single intragastric doses (2-4 mmol/kg body weight) or in the diet (0.5% for 14 days), and to rats in the diet (0.1% for 14 days) was found to increase glutathione levels and the activities of a number of enzymes in various tissues including the liver and lung. The enzymes affected were glutathione transferases (with chlorodinitrobenzene or dichloronitrobenzene), quinone and glutathione reductase, and glucose-6-phosphate and 6-phosphogluconate dehydrogenase, all of which are involved directly or indirectly in the detoxication of xenobiotics, including carcinogens. The dithiolthiones tested in mice were oltipraz, ADT, 116L and 129L, and in rats, oltipraz. Intragastric administration of dithiolthiones (oltipraz, ADT or 116L; two doses each of 1 g/kg body weight) did not increase glutathione levels or enzyme activities in murine mammary adenocarcinoma transplants. Increases in glutathione levels and enzyme activities similar to those found with dithiolthiones were observed when a semi-synthetic diet containing 10-40% lyophilized cabbage was fed to mice for 30 days. Dithiolthiones that are present in cabbage may play a role in the protective actions of diets high in vegetables against the toxic actions of xenobiotics. The biochemical effects of dithiolthiones reported here may account for the protective actions of these compounds.

Effects of anethole dithiolthione and 2(3)-tert-butyl-4-hydroxyanisole on schistosome granuloma formation.

Administration of the antioxidants 2(3)-tert-butyl-4-hydroxyanisole (BHA) or 5-(P-methoxyphenyl)-3H-1,2-dithiol-3-thione (ADT) to female CD-1 mice starting 4 weeks after infection with 70 cercariae of Schistosoma mansoni resulted in a decrease in the size of the inner fibrotic region of the hepatic granuloma. The cellular composition of the granuloma was not altered by treatment with these two compounds. The administration of the specific superoxide scavenger copper diisopropylsalicylate (CuDIPS) resulted in a similar decrease in granuloma size, suggesting a role of superoxide radicals in the granulomatous response.

Modification of aflatoxin B1 binding to DNA in vivo in rats fed phenolic antioxidants, ethoxyquin and a dithiothione.

The effects of dietary administration of 3,5-di-tert-butyl-4-hydroxytoluene (BHT), 2(3)-tert-butyl-4-hydroxyanisole (BHA), ethoxyquin (EQ) and 5-(2-pyrizinyl)-4-methyl-1,2-dithiol-3-thione (oltipraz) on aflatoxin B1 (AFB1) - DNA adduct formation in vivo in livers and kidneys of rats were investigated. Male F344 rats were treated with 1 mg/kg AFB1 by i.p. administration and nucleic acids isolated 2 h post dosing. Animals were fed a semipurified diet supplemented with either 0.5% EQ, 0.45% BHT, 0.45% BHA or 0.1% oltipraz for 2 weeks prior to AFB1 treatment. Analysis of nucleic acid bases by h.p.l.c. showed that several AFB1 metabolite-DNA adducts were formed in both tissues. The principal and related adducts of 8,9-dihydro-8-(N7-guanyl)-9-hydroxyaflatoxin B1 represented approximately 80-90% of all adducts in both tissues and in all treatment groups. However, inclusion of the antioxidants in the diet resulted in substantial reductions in overall AFB1 modified DNA levels. EQ, BHT, BHA and oltipraz reduced the covalent binding of AFB1 to liver DNA by 91, 85, 65 and 76% and to kidney DNA by 80, 35, 62 and 64%, respectively. Concordantly, the specific activities of hepatic enzymes of presumed importance to AFB1 detoxification, epoxide hydrase, and glucuronyl and glutathione transferases were significantly elevated by all antioxidants. Reduced glutathione levels were unchanged except by oltipraz, although activities of enzymes contributing to the maintenance of reduced glutathione pools, glutathione reductase and glucose-6-phosphate dehydrogenase, were elevated in most treatment groups. An excellent correlation (r = 0.95) was observed between the degree of inhibition of DNA binding by AFB1 and the induction of hepatic glutathione S-transferase activities by the four antioxidants.

Carcinogenicity of the antischistosomal nitrofuran trans-5-amino-3-[2-(5-nitro-2-furyl)vinyl]-1,2,4-oxadiazole.

The antischistosomal and antitrypanosomal drug trans-5-amino-3-[2-(5-nitro-2-furyl)vinyl]-1,2,4-oxadiazole [(SQ18506) CAS: 28754-68-9; (E)-amino-3-(2-(5-nitro-2-furyl)-vinyl)-1,2,4-oxadiazole] was carcinogenic for both male and female CD-1 mice when it was administered either in the diet or by gastric intubation. Dose-dependent increases in tumors of the forestomach and lymphatic tissues were observed in all groups receiving SQ18506 including mice infected with Schistosoma mansoni. The predominant tumor observed was squamous cell carcinoma of the forestomach. The presence or absence of schistosome infection did not appear to alter the incidence or distribution of tumors at comparable doses of SQ18506. The incidence of bladder tumors was positively correlated with the dose in gastric intubation studies and inversely correlated with the dose in dietary studies. The carcinogen N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide (CAS: 24554-26-5) was fed to male and female CD-1 mice in the diet as a positive control. The predominant tumor observed in these groups was transitional cell carcinoma of the bladder. These data indicate that SQ18506 is unsuitable for use in the treatment of parasitic diseases.

Effects of multiple putative anticarcinogens on the carcinogenicity of trans-5-amino-3-[2-(5-nitro-2-furyl)vinyl]-1,2,4-oxadiazole.

In an attempt to dissociate the chemotherapeutic from the carcinogenic properties of the antischistosomal and antitrypanosomal nitrovinylfuran trans-5-amino-3-[2-(5-nitro-2-furyl)vinyl]1,2,4-oxadiazole [(SQ18506) CAS: 28754-68-9; (E)-5-amino-3-(2-(5-nitro-2-furyl)vinyl)-1,2,4-oxadiazole], potential inhibitors of carcinogenesis were administered to female outbred CD-1 mice before and during exposure to SQ18506. The compounds tested were ascorbic acid, etretinate, butylated hydroxyanisole (BHA), cysteamine hydrochloride, cysteine hydrochloride, dimercaprol, disulfiram, 1,4-dithiothreitol, reduced glutathione, and spermidine phosphate. The primary types of tumors observed were squamous cell carcinomas of the stomach and thymic and nonthymic lymphomas. BHA reduced the incidence of malignant tumors to control levels, whereas cysteine hydrochloride, spermidine phosphate, and disulfiram reduced the incidence of chemically induced tumors by 42, 34, and 32%, respectively. Although cysteamine hydrochloride and disulfiram had no or only a modest effect on the overall incidence of tumors, the data suggested possible tissue-specific anticarcinogenic properties for these agents. Of the 8 antioxidants tested, only 1 had marked anticarcinogenic properties against SQ18506. These data indicate that antioxidant properties alone cannot account for the anticarcinogenic activity of the compounds tested. Coadministration of the anticarcinogen BHA with SQ18506 also blocked the chemotherapeutic effects of this agent on female CD-1 mice infected with Schistosoma mansoni.

Chemoprotective effects of two dithiolthiones and of butylhydroxyanisole against carbon tetrachloride and acetaminophen toxicity.

Administration of tert-butyl-4-hydroxyanisole or of two dithiolthiones to female CD-1 mice protected against the acute toxic effects of two hepatotoxic agents, acetaminophen and carbon tetrachloride. Reduced mortality of mice was observed following pretreatment with tert-butyl-4-hydroxyanisole or dithiolthiones. Pretreatment reduced or prevented hepatic glutathione depletion produced by these two hepatotoxic agents. Liver damage, i.e., as determined by serum transaminase and sorbitol dehydrogenase activities, was less after pretreatment with tert-butyl-4-hydroxyanisole or dithiolthiones. Administration of dithiolthiones resulted in increased (from four- to over six-fold) activities of liver glutathione-S-transferases.

Efficacy of amoscanate against experimental schistosomal infections in monkeys.

The antischistosomal activity of oral doses of amoscanate (4-isothiocyanato-4'-nitrodiphenylamine) was determined in infected Cebus apella (capuchin monkeys) and Macaca mulatta (rhesus monkeys). In C. apella infected with Schistosoma japonicum or S. mansoni an initial dose of 10 mg/kg body weight did not alter fecal egg counts, but a subsequent dose of 25 mg/kg markedly reduced both egg counts and worm burdens; in animals infected with S. haematobium, a single dose of 25 mg/kg of amoscanate was similarly effective. Comparable schistosomicidal effects were also produced in S. japonicum- and S. mansoni-infected M. mulatta by single oral doses of 20 and 35 mg/kg, respectively. In both C. apella and M. mulatta the coadministration of single oral doses of 50 or 75 mg/kg of erythromycin attenuated the appearance of mutagenic metabolites of amoscanate in the urine but did not interfere with the antischistosomal action of amoscanate. In non-infected monkeys single oral doses of 75 mg/kg of amoscanate with or without erythromycin (50 mg/kg in C. apella or 75 mg/kg in M. mulatta) did not cause any major organ toxicity as revealed by gross and histopathologic examination, hematology, blood chemistry, electrocardiograms and urinalysis. The data indicate that in C. apella and M. mulatta, amoscanate is a relatively non-toxic antischistosomal agent effective orally against a broad spectrum of schistosome species.

Identification and quantitation of a metabolite of anethol dithiolthione in rat and mouse urine using high-performance liquid chromatography.

Urine samples from rats and mice fed anethol dithiolthione (ADT) [3-(p-methoxyphenyl)-1,2-dithiol-3-thione] were analyzed using reversed-phase high-performance liquid chromatography. Urine was introduced directly on the liquid chromatograph which was modified by replacing the sample loop with a guard column. Highly polar urine components were washed off the guard column prior to chromatography. A major metabolite and the parent compound (ADT) were separated and detected using the chromatographic conditions described in this study. The metabolite was identified as desmethyl ADT. The identification was based on co-chromatography on two columns using two mobile phases and peak height ratios of the metabolite and the reference standard. Data pertaining to the pattern of excretion of ADT and desmethyl ADT in the animals studied are reported.

Conversion of amoscanate to a mutagenic metabolite in gnotobiotic mice implanted with Streptococcus equinus.

Recent in vitro studies indicate that intestinal bacteria convert amoscanate (4-nitro-4'-isothiocyanodiphenylamine), an antischistosomal drug, to a potent mutagen. The present study indicates that the implantation of germfree mice with Streptococcus equinus, isolated from the small intestine of conventional mice, restores the mutagenic activation of amoscanate in vivo.

The antischistosomal activity of oltipraz.

Administration of a single oral dose of oltipraz (5-(2-pyrazinyl)-4 methyl-1,2 dithiol-3-thione) to mice infected with Schistosoma mansoni resulted in the elimination of the parasites. Oltipraz is a slow-acting drug and approximately 2 months are required until its full schistosomicidal effect becomes evident. One of the earliest effects of the drug is a reduction of the glutathione stores of the worms. The antischistosomal activity of oltipraz is lowered when drug metabolism is stimulated by pretreatment with phenobarbital or butyl-hydroxyanisole (BHA). By contrast, administration of L-cysteine is synergistic with the antischistosomal effect of oltipraz. Evaluation of a limited number of oltipraz analogs revealed among dithiolthiones rather stringent structural requirements for antischistosomal activity.

Granuloma formation around exogenous eggs of Schistosoma mansoni and Schistosoma japonicum in mice.

Hepatic granulomata which were qualitatively and quantitatively similar to those seen in infections established with cercariae were induced by surgical injection of exogenous eggs of Schistosoma mansoni and Schistosoma japonicum via the mesenteric veins of previously unexposed albino mice. Thereafter, their comparative histopathologic studies were made. The maximum mean sizes of granulomata were attained on Day 32 with viable eggs of these parasite species. Although S. mansoni eggs produced significantly larger lesions (368.4 +/- 21.5 microns) than eggs of S. japonicum (205.8 +/- 18.6 microns) at the peak period, the difference in the mean granulomal size showed no correlation with either the time of onset or the severity of pathologic changes produced. Thus, eggs of S. japonicum with smaller granulomata, evoked pathologic changes which were earlier in onset and more severe than those produced by the same quantity of S. mansoni eggs. Since the most obvious variables (the quantity of eggs, the sequence of their arrival in the liver, the timing of observation, and the strain of experimental animals) were controlled, it was concluded that the most severe and fatal effects produced by eggs of S. japonicum, as previously suggested, are largely due to differences in the cytotoxic and antigenic peculiarities of this species.

An evaluation of the host-mediated assay and body fluid analysis. A report of the U.S. Environmental Protection Agency Gene-Tox Program.

The methodologies and status of the Host-Mediated Assay were reviewed using the published literature available up to June 1980. The Working Group reviewed 274 documents, including abstracts, research articles, review articles, and publicly available contracts and grant final reports. From this group, abstracts and reviews were rejected from critical evaluation. 77 documents were accepted and reviewed by the Working Group and the test results summarized. These selected documents yielded 208 chemicals that were evaluated in th host-mediated assay. Of these chemicals, 133 were mutagenic in this assay with one or more indicators. 76 chemicals, several of which are not considered to be carcinogenic, were not detected by any of the indicators. Of the 208 chemicals, 125 had been tested in carcinogenicity assay in rodents. 90, or 71%, of the carcinogens were detected as mutagens in the Host-Mediated Assay. In several cases, those carcinogens not detected may have been negative because of improper selection of the indicator. The Working Group concluded that the Host-Mediated Assay is an important test in mutagenicity/carcinogenicity research and that, by proper selection of protocols and indicators, valuable information can be gained that otherwise would be overlooked strict, in vitro assays.

Metabolic requirements of schistosomes.

In adult Schistosoma mansoni and S. japonicum carbohydrate utilization, formation of lactic acid and ATP levels were the same under aerobic and anaerobic conditions. Therefore, these parasites exhibited no pasteur effect. When the metabolic requirements of the parasites were raised by 5-hydroxytryptamine-(5-HT)-induced stimulation of the worm's motor activity, aerobic conditions did not reduce the rate of carbohydrate utilization nor the ATP levels of the worms. Therefore, these parasites do not derive metabolic energy from respiration.