Interspecies comparison of liver carcinogenesis: implications for cancer risk assessment

The morphology of hepatocellular carcinoma is similar among mice, rats and humans, and the cellular pathogenesis shows features that are both similar and divergent among these species. However, major elements of etiology, molecular pathogenesis, and natural history differ between humans and rodents. As a reflection of these species-determined differences, rodents appear to be neither highly sensitive nor highly specific surrogates for detecting agents that are potential causes of hepatocellular cancer in humans. Results of tests of chemical carcinogenicity in rodents are likely to include a significant number of both false-positive and false-negative risks for humans.      

Comparison of oral ftorafur and intravenous 5-fluorouracil in patients with advanced cancer of the stomach, colon or rectum

In this prospective randomized study the effect of oral Ftorafur was compared with that of intravenous 5-fluorouracil in patients with advanced adenocarcinoma of the stomach, colon or rectum. Forty-five patients were evaluable. The overall response rates were 26.9% in the 5-fluorouracil group, 26.7% in the Ftorafur group. The median duration of response was 6 months in both groups. Survival in the 5-fluorouracil group was slightly better than in the Ftorafur group, but the difference was not statistically significant. The myelosuppressive effect of 5-fluorouracil was significantly stronger than that of Ftorafur. Gastrointestinal side effects were more pronounced in the Ftorafur group, but the difference was not statistically significant.     

Metallothionein modulates the carcinogenicity of N-butyl-N-(4-hydroxybutyl)nitrosamine in mice.

We examined the carcinogenicity of N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) in transgenic mice deficient in the metallothionein (MT) I and II genes and in control (129/Sv) mice. Both strains of mice were given BBN for 8 weeks with or without Zn treatment. All mice were killed at 12 weeks after the cessation of BBN administration. BBN induced bladder tumors in 75% of MT null mice and in 43% of 129/Sv mice. The average number of bladder tumors per mouse was significantly higher in MT null mice (1. 18 +/- 0.27) than in 129/Sv mice (0.43 +/- 0.20). Zn treatment suppressed the carcinogenicity of BBN in 129/Sv mice but not in MT null mice. Histopathological examination of the tumors revealed that the malignant potential of bladder tumors in 129/Sv mice was greater than that in MT null mice. These results indicate that MT is an important modulator of carcinogenicity of BBN in the bladder of mice.     

Reporter gene transgenic mice as a tool for analyzing the molecular mechanisms underlying experimental carcinogenesis

Carcinogenic compounds are classified into 2 categories, genotoxic and non-genotoxic, which are basically judged from in vitro genotoxicity data. However, it is well documented that genotoxicants do not necessarily exert in vivo carcinogenicity in rodents, partly because of a discrepancy between in vitro and in vivo mutagenicities. Recently, transgenic animal models with reporter genes such as lacI, lacZ and gpt have been developed as a tool for assessing in vivo mutagenicity as well as carcinogenicity. In this article, data using lacI transgenic mice and gpt delta mice are presented and their application is discussed. In lacI transgenic mice, dimethylnitrosamine (DMN) treatment significantly increased lacI mutant frequency (MF) in the liver, kidenys and lungs, but not in other non-target organs. Repeated dose ip administration of DMN was more effective than single dose treatment in the induction of lacI MF. The spectrum of mutant plaques induced by DMN was characterized by deletions as well as GC to AT base transitions. The remaining mice receiving DMN proved to have liver adenomas at a high frequency after 78 weeks. Meanwhile, dietary 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MelQx) significantly increased lacI and gpt MFs in the liver and colon. The characteristic spectrum of mutant plaques induced by MeIQx was a GC to TA base transversion in both the lacI and gpt mutations. Our results thus strongly suggest that these reporter gene transgenic animal models could offer a useful tool for analyzing molecular mechanisms underlying experimental carcinogenesis and for assessing the carcinogenic risk of environmental chemicals.     

Ftorafur, adriamycin, cyclophosphamide and BCG in the treatment of metastatic breast cancer.

Ftorafur is a 5-fluorouracil analogue which is slowly metabolized to 5-FU, resulting in prolonged therapeutic levels of this latter drug. Ninety-one evaluable patients with metastatic breast cancer were treated with Ftorafur, Adriamycin, cyclophosphamide, and BCG (ACFTOR-BCG), in an attempt to increase the effectiveness of the program or decrease its myelosuppressive toxicity. The results of this trial were compared to those previously reported with the combination of 5-FU, Adriamycin, cyclophosphamide, and BCG (FAC-BCG). Overall objective response rates were 65% and 76% for ACFTOR-BCG and FAC-BCG, respectively. Durations of response were 12 months and 14 months for ACFTOR-BCG and FAC-BCG (p = 0.53). The median survival of responders was 22 and 23.9 months, respectively. Substantial toxicity was observed with Ftorafur: nausea and vomiting severe enough to cause weight loss was observed in a substantially higher fraction of the patients treated with this drug than with 5-FU. Other side-effects, which were not observed with the 5-FU combination, were somnolence, dizziness, personality changes, tremor, ataxia, and confusion. No differences in myelosuppressive toxicity were observed between the two combinations, and the incidence of infectious complications was identical. The combination of Ftorafur, Adriamycin, cyclophosphamide and BCG did not offer any advantages with respect to increased effectiveness or reduced toxicity over the FAC-BCG regimen in breast carcinoma.     

左旋咪唑与呋喃氟脲嘧啶伍用对小鼠抗肿瘤及免疫功能的影响

本文采用呋喃氟脲嘧啶(FT-207)与增效减毒剂左旋咪唑(LMS)伍用来提高FT-207的疗效。结果伍用对小鼠S-180肉瘤的抑制作用与LMS的剂量有关,以低剂量的LMS(1mg/kg)抑瘤最佳,并能拮抗FT-207所致小鼠白细胞下降,增加小鼠胸腺和脾脏重量,促进小鼠腹腔内巨噬细胞吞噬功能,提高小鼠脾脏中NK细胞活性。     

In vitro biological evaluation of the R and S isomers of 1-(Tetrahydrofuran-2-yl)-5-fluorouracil.

The S isomer of Ftorafur was synthesized and the ability of the latter to inhibit growth of cultured human fibroblasts was determined relative to both the R isomer and the racemic mixture (Ftorafur) that is presently used clinically. No significant difference in the cytotoxic effects or the relative abilities to prevent an increase in cell numbers was observed with the three forms. Inhibition of DNA synthesis in murine L1210 leukemia cells by either isomer was observed only after prolonged (18-hr) exposure. The data suggest that Ftorafur is a repository form of 5-fluorouracil and that activity is manifested equally by both isomers.     

Assessment and Validation of US EPA's OncoLogic® Expert System and Analysis of Its Modulating Factors for Structural Alerts

OncoLogic® is a software program able to screen chemical compounds for toxicological effects. The software predicts the potential carcinogenicity of chemicals by applying rules of structure activity relationship (SAR) analysis. To validate the predictivity of OncoLogic® (Version 7.0), 123 compounds tested with the long-term carcinogenicity bioassay on rodents were extracted from the ISSCAN database and were analyzed. The concordance between the OncoLogic® SAR analysis and the bioassay results was high. To better understand the strength of the SAR science in OncoLogic®, we investigated the influence of a select group of modulating factors on the predictions by the structural alerts.     

Identification of trihalomethanes in drinking water and assessment of their toxicity, mutagenicity and carcinogenicity

Dichlorobromomethane (DCMB) and dibromochloromethane (DBCM) isolated from chlorinated drinking water were tested for toxicity, mutagenicity and carcinogenicity. Both agents proved mutagenic in a "dessicator" modification of the Ames test using Salmonella typhimurium TA98 and TA100 in the presence of exogenous metabolic activation. In aquarium Danio rerio fish tests, LD50/30 was 250 mg/l for both compounds. Both agents induced hepatocellular carcinoma in fish: DCMB--in 11 out of 29 animals (at 16.5 weeks) and DBCM--in 3 out of 16 (at 26.5 weeks). These data merit further investigation of the agents' carcinogenicity in chronic experiments in rodents.     

Phase I-II study of ftorafur and methyl-CCNU in advanced colorectal cancer.

The combination of Ftorafur (NSC-148958) and methyl-CCNU (NSC-95441) was evaluated in 36 patients with advanced colorectal cancer. The principle toxicities encountered were myelosuppression, gastrointestinal, and neurological. There were no complete responses and only 5/34 (14.7%) patients achieved a partial response. Methyl-CCNU and Ftorafur does not appear to be an effective combination in advanced adenocarcinoma of the colon and rectum.     

Strain A mouse pulmonary tumor test results for chemicals previously tested in the National Cancer Institute carcinogenicity tests

Sixty-five chemicals were coded and examined for their ability to induce lung tumors in strain A/St (laboratory A) or strain A/J (laboratory B) mice. Thirty-five chemicals were tested in laboratory A only, 6 in laboratory B only, and 24 in both laboratories. Two-year carcinogenicity test results as well as genotoxicity test data are available for most of these chemicals. There was poor interlaboratory agreement in strain A test results for the 24 chemicals tested in both laboratories. In addition, there was poor agreement between strain A test results from either laboratory and 2-year carcinogenicity test results or genotoxicity results. Possible explanations for these findings include selection of a large number of aromatic amines in the group of chemicals submitted for strain A testing, differences in strain A testing protocols and in statistical analysis of results from the two laboratories, low sensitivity of the strain A/St mice used in this particular study, and general problems inherent in comparing any relatively short-term animal tumor model with 2-year carcinogenicity tests. Since there is no absolute reference for carcinogenicity, no one test system is better than another. Carcinogenicity test data are relevant only to the test model employed.     

The problem of carcinogenic hazard evaluation for new chemicals: general considerations about the carcinogenic process

We discuss the problem of oncogenic hazard evaluation for new chemicals. In the recent past, assessment of global carcinogenicity in rodents was considered the most significant type of information. It has recently emerged that this type of information is not adequate to distinguish initiation and genotoxicity from promotion-like effects. In this report we suggest that hazards from initiating agents and hazards from promoting agents should be treated separately. In this perspective, longterm experiments for carcinogenicity in rodents should still play an important role but a less central one. Initiation-promotion experiments in different target organs are recommended. We suggest a strategy of hazard evaluation related to the initiating potential as distinct from overall carcinogenicity. The problem of utilizing not only the qualitative component of the available information, but also the quantitative component, is considered. Finally, we discuss a possible hazard evaluation for promoting effects, but conclude that this area is very much in its infancy. Possible contributions of computer science technology to the problem of oncogenic hazard evaluation are briefly introduced.     

On the contribution of polycyclic aromatic hydrocarbons to the carcinogenic impact of automobile exhaust condensate evaluated by local application onto mouse skin

The objective of this investigation was to identify the substances chiefly responsible for the carcinogenicity of automobile exhaust condensate using topical application onto the skin of mice. This was performed by comparing the carcinogenic effect of various fractions with that of an unseparated sample of automobile exhaust condensate, tested in 3 different doses. The probit and Weibull analysis of the result shows: (a) The condensate, emitted from a gasoline-driven automobile provokes local tumors after long-term application to the dorsal skin of mice. The tumor incidence demonstrates a clear cut dose-response relationship. (b) The fraction of polycyclic aromatic hydrocarbons (PAH) containing more than 3 rings accounts for about 84-91% of the total carcinogenicity of automobile exhaust condensate. This fraction represents only about 3.5% by wt of the condensate. (c) The content of benzo[a]pyrene (BaP) (0.414 mg/g) accounts for 6-7.6% of the total carcinogenicity of automobile exhaust condensate, 15 selected PAHs for about 41%. (d) Regarding the minor effect of the PAH-free fraction (about 83% by wt), no hints for a cocarcinogenic activity were observed.     

Enhanced accumulation of 5-Fluorouracil in human tumors in athymic mice by co-administration of Ftorafur and Uracil

Human colonic tumors grown in athymic mice were tested for the effect of coincident uracil (U) and Ftorafur (FT) exposure versus FT alone on 5-Fluorouracil (5-FU) metabolism. Serum and tumor FT and 5-FU levels were studied as a function of time after FT +/? U injections. The combination of U + FT led to significantly higher tumor/serum 5-FU ratios than FT alone. The data indicate that the metabolism of 5-FU released from FT can be modulated by coincident U exposure in human tumor cells in vivo. Such combinations may be of use in the development of oral 5-FU pro-drugs for applications using 5-FU as an out-patient non-invasive radiosensitizer.     

Species correlation in long-term carcinogenicity studies

Species correlation in neoplastic response was examined for 266 long-term toxicology and carcinogenicity studies. The overall concordance between rats and mice exposed to the same chemical was 74% (198/266). Within a species, the results for males and females were also highly correlated (87% concordance for rats and 89% for mice). Had only male rats and female mice been utilized in these experiments, the same conclusions regarding carcinogenicity would have been reached in 96% of the studies (255/266). The high interspecies correlation shown in these studies supports the view that extrapolation of carcinogenicity outcomes to other species, including humans, is appropriate.     

Effects of repeated applications of two semi-permanent hair dyes to the skin of A and DBAf mice

Two proprietary semi-permanent hair dyes were tested for carcinogenicity in A and DBAf mice by repeated topical applications in aqueous acetone. Mice of both strains developed lymphoid tumours but experimental differences were marked only in DBAf mice. A number of tumours of the ovary and uterus, and some skin papillomas near the penis, occured in dye-treated but not in control DBAf mice. As many hair-dye constituents are known mutagens, adequate carcinogenicity testing of these substances, and epidemiological study of exposed human populations, are needed for evaluating possible health hazard from hair dyeing.     

Oral Ftorafur Versus Intravenous 5-Fluorouracil: A comparative study in patients with colorectal cancer

The toxicities of ora] Ftorafur (1 g/m²/day 1-21) and intravenous 5-fluorouracil (5-FU) (500 mg/m²/day 1-5) were compared in a prospective randomized study in patients with colorectal cancer. The treatment courses were repeated every 6th week. Leu-copenia was more common after 5-FU. Leucocyte nadir in connection with first treatment cycle was on average seen on day 15 in patients receiving 5-FU and on day 28 in patients receiving Ftorafur. Significantly more patients on 5-FU developed stomatitis. There was no difference in the number of patients with diarrhea or nausea/vomiting. Median survival and response rates were not significantly different after the two treatment schedules.     

Quantification of DNA and hemoglobin adducts of 3,4-epoxy-1,2-butanediol in rodents exposed to 3-butene-1,2-diol

1,3-Butadiene (BD) is a confirmed rodent carcinogen and a suspect human carcinogen that forms mutagenic epoxide metabolites during biotransformation. Species differences in the roles of individual DNA reactive intermediates in BD mutagenicity and carcinogenicity are not completely understood. Evidence suggests that 1,2:3,4-diepoxybutane (DEB) is responsible for the mutagenic effect induced by exposures to low concentrations of BD in mice and that metabolites of 3-butene-1,2-diol (BD-diol) are involved in the mutagenicity at high exposures in both mice and rats. Two reactive metabolites, 3,4-epoxy-1,2-butanediol (EB-diol) and hydroxymethylvinyl ketone (HMVK), are formed during the biotransformation of BD-diol and could potentially be involved in BD-diol associated mutagenicity. To examine the role of EB-diol in BD-diol mutagenicity we have evaluated the dosimetry of N7-(2,3,4-trihydroxybutyl)guanine (THB-Gua) and N-(2,3,4-trihydroxybutyl)valine (THB-Val) in female B6C3F1 mice and female F344 rats exposed by inhalation to 0, 6, 18 and 36 p.p.m. BD-diol for 4 weeks (6 h/day x 5 days/week). Results showed higher levels of both THB-Gua and THB-Val in mice than in rats. An evaluation of THB-Gua adducts showed virtually no differences between liver and lung for either species, suggesting that EB-diol is stable and is freely circulated. The data also indicated that THB adduct formation began to plateau around 18 p.p.m. in both species. Most importantly, the shape of the dose-response curve for THB adduct formation mimicked the one observed for hypoxanthine-guanine phosphoribosyltransferase (Hprt) mutation frequency. This showed that THB adducts, which are not thought to be responsible for causing the mutations, are good quantitative indicators of mutagenicity in rodents exposed to BD-diol. Although the potential contribution of HMVK still needs to be evaluated, the data suggest that EB-diol is responsible, at least in part, for BD-diol associated mutagenicity in rodents.     

Thiophene analogues of the carcinogens benzidine and 4-aminobiphenyl: evaluation in vitro.

A biologically active molecule with one or more aromatic rings often retains its activity when one of these rings is replaced by an isosteric and/or isoelectronic aromatic ring. Consideration has been given to whether this effect can be expected to apply to aromatic organic carcinogens. The literature relevant to this topic has been reviewed and the thiophene analogues of the carcinogens benzidine and 4-aminobiphenyl have been synthesized and evaluated for potential carcinogenicity. The compounds prepared were 5-p-acetamidophenyl-2-thiophenamine hydrochloride (XIII), 5-phenyl-2-thiophenamine hydrochloride (XIV), N-(5-p-acetamido-phenylthiophen-2-yl)acetamide (XV) and N-(5-phenylthiophen-2-yl)-acetamide (XVI) (see Chart for structures). Each compound was evaluated in the Salmonella reverse-mutation assay of Ames and the cell-transformation assay of Styles. The activity profiles observed for these compounds in vitro were consistent with their known chemistry, and indicate potential carcinogenicity. However, their overall chemical and biological behaviour casts doubt upon whether they would be capable of eliciting tumours in vivo. Because it is important to establish the degree of reliance which can be placed upon in vitro predictions of potential carcinogenicity generated for structurally new compounds, one of the thiophene derivatives, N-(5-phenylthiophen-2-yl)acetamide ((XVI), is currently being evaluated for carcinogenicity in mice.