32P-postlabeling analysis of DNA adducts in rats during estrogen-induced hepatocarcinogenesis and effect of tamoxifen on DNA adduct level

Decreased Diethylnitrosamine-induced Liver Preneoplastic Lesions by Estradiol-3-benzoate Treatment

To clarify whether inhibitory effect of estrogen on liver tumor is associated with cell proliferation, we investigated its role in diethylnitrosamine (DEN)-induced rat preneoplastic lesions, with time sequenced manners. F344 male rats (n = 90) were divided into three groups at 5 weeks of age. The mini-osmotic pumps providing a continuous infusion of DEN was implanted into the abdominal cavity of each animal in group 1, 2 and 3 at 6 weeks of age. To see the effect of estrogen, pellet containing 1 or 10 μg of estradiol- 3-benzoate (EB) was implanted subcutaneously in the animals of groups 2 or 3, respectively, one week prior to DEN treatment. Ten animals of each group were euthanized at 10, 14 and 18 weeks after DEN treatment. Liver tissues at each time point were fixed in 10% phosphate-buffered formalin and were processed and embedded in paraffin and 5 μm sections mounted on a silanized slide. Glutathione S-transferase placental form (GST-P) positive foci and 5-bromo-2-deoxyuridine (BrdU) labeling cells were detected at each time point. Area of GST-P positive foci in DEN+EB 1 or 10 μg group was significantly decreased compared to DEN alone at 14 weeks (p < 0.01 or p < 0.05, respectively) an at 18 weeks (p < 0.05 or p < 0.01, respectively). BrdU index in DEN+EB 1 or 10 μg groups was significantly decreased compared to DEN alone at 14 weeks and at 18 weeks (p < 0.01). Taken together, we conclude that EB treatment decrease the DEN-induced liver preneoplastic lesions and this may be associated with decrease of cellular proliferation.

Glycine soya diet synergistically enhances the suppressive effect of tamoxifen and inhibits tamoxifen-promoted hepatocarcinogenesis in 7,12-dimethylbenz[α]anthracene-induced rat mammary tumor model

There is increasing interest in phytoestrogens as potential alternatives to synthetic selective estrogen receptor modulators (SERMs) in the prevention and therapy of breast cancer. The present study is aimed at determining whether dietary glycine soya (Glycine max seeds; GS), which is rich in phytoestrogens, can enhance the anti breast cancer efficacy of the SERM tamoxifen (TAM) and the effect of TAM and GS, either alone or in combination, on DMBA-initiated hepatocarcinogenesis in rat. For determination of enhancing effect, rats bearing palpable 7, 12-dimethylbenz[α] anthracene (DMBA)-induced mammary tumors were treated with TAM (10 mg kg(-1)/day) while being fed AIN-93G diet with or without added GS (3×10(4) mg kg(-1)), and the tumor growth was monitored up to 5 weeks of treatment. For determining the effect on hepatocarcinogenesis, DMBA-initiated rats were exposed to TAM and dietary GS as above for 6 weeks during promotion stage in a medium-term bioassay, and the development of placental form of glutathione-S-transferase (GST-P)-expressing preneoplastic liver lesions was quantified. Exposure to both TAM and dietary GS enhanced the anti tumor efficacy of TAM via a combination of tumor cell apoptosis (determined by TUNEL) and inhibition of tumor cell proliferation (determined by PCNA immunostaining) and suppressed the growth of GST-P-positive liver lesions. The findings show that dietary GS enhances the therapeutic efficacy of TAM against mammary tumors and minimizes TAM's hepatocarcinogenesis promotion potential.

Role of sex steroid receptors in pathobiology of hepatocellular carcinoma

The striking gender disparity observed in the incidence of hepatocellular carcinoma (HCC) suggests an important role of sex hormones in HCC pathogenesis. Though the studies began as early as in 1980s, the precise role of sex hormones and the significance of their receptors in HCC still remain poorly understood and perhaps contribute to current controversies about the potential use of hormonal therapy in HCC. A comprehensive review of the existing literature revealed several shortcomings associated with the studies on estrogen receptor (ER) and androgen receptor (AR) in normal liver and HCC. These shortcomings include the use of less sensitive receptor ligand binding assays and immunohistochemistry studies for ERα alone until 1996 when ERβ isoform was identified. The animal models of HCC utilized for studies were primarily based on chemical-induced hepatocarcinogenesis with less similarity to virus-induced HCC pathogenesis. However, recent in vitro studies in hepatoma cells provide newer insights for hormonal regulation of key cellular processes including interaction of ER and AR with viral proteins. In light of the above facts, there is an urgent need for a detailed investigation of sex hormones and their receptors in normal liver and HCC. In this review, we systematically present the information currently available on androgens, estrogens and their receptors in normal liver and HCC obtained from in vitro, in vivo experimental models and clinical studies. This information will direct future basic and clinical research to bridge the gap in knowledge to explore the therapeutic potential of hormonal therapy in HCC.

Enhancement by estradiol 3-benzoate in thioacetamide-induced liver cirrhosis of rats

As part of an investigation on the role of estrogen in liver disease, we tested the effects of estradiol-3-benzoate (EB) in the thioacetamide (TAA)-induced rat liver cirrhosis model. Male F344 rats (n = 100) were divided into six groups. Animals of groups 1-4 received TAA (0.03% in drinking water) for 12 weeks, and groups 5 and 6 served as controls without TAA. For the exposure period, EB pellets were implanted subcutaneously to give doses of 0 (groups 1 and 5), 1 (group 2), 10 (group 3), and 100 mug (groups 4 and 6) simultaneously. All animals were sacrificed at week 12. Significant increase of liver cirrhosis, liver weight, collagen content, and lipid peroxidation in the livers was evident in groups 3 and 4 (p < 0.05) compared with group 1. Formation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) was significantly elevated in group 4 (p < 0.01), along with expression of alpha-smooth muscle actin (alpha-SMA) and stellate cell activation-associated protein (STAP), as determined by RT-PCR analysis (p < 0.01). However, there were no differences in liver weight, collagen content, lipid peroxidation, 8-OHdG formation, and alpha-SMA and STAP mRNA expression between groups 5 and 6. We conclude that EB treatment enhances TAA-induced cirrhosis, associated with increase of oxidative stress and activation of hepatic stellate cells.

Genotoxic potential of ethinylestradiol in cultured mammalian cells

Ethinylestradiol, a steroidal estrogen, is widely used with various progestogens in oral contraceptives formulations. There are sufficient evidences for the carcinogenicity of ethinylestradiol in experimental animals. The reports on the genotoxic potential of ethinylestradiol are contradictory. Here in the present study we have tested the genotoxicity of ethinylestradiol in human lymphocytes using chromosomal aberrations (CAs), mitotic index (MI) and sister chromatid exchanges (SCEs) as a parameter. The study was carried out in the absence, as well as in the presence, of rat liver microsomal fraction, with and without NADP. Ethinylestradiol was studied at three different concentrations (1, 5 and 10 microM) and was found non-genotoxic in the absence of metabolic activation (S9 mix) and in S9 mix without NADP. Ethinylestradiol was found to be genotoxic at 5 and 10 microM in the presence of S9 mix with NADP. To study the possible mechanism of the genotoxicity of ethinylestradiol, superoxide dismutase (SOD) and catalase (CAT) were used separately and in combination along with 10 microM of ethinylestradiol at different doses. SOD treatment increased CAs and SCEs and decreases MI as compared with treatment with 10 microM of ethinylestradiol alone in the presence of S9 mix with NADP at both of the tested doses. CAT treatment decreased the frequencies of CAs and SCEs and increased MI, as compared with treatment with 10 microM of ethinylestradiol alone in the presence of S9 mix with NADP. CAT treatment in combination with SOD also decreased the frequencies of CAs and SCEs and increased MI suggesting a possible role of reactive oxygen species for the genotoxic damage.

Genotoxicity of hormonal steroids

Hormonal steroids have a widespread use in medicine and their side effects are continuously debated. The possible genotoxic activity of steroids has been the subject of many investigations. The natural estrogens estradiol, estrone and estriol are generally negative in the ICH core battery of tests, but several positive results have been obtained when using additional endpoints of genotoxicity. The genotoxic activity of the 4-hydroxy metabolites of estradiol and estrone is well established. The synthetic steroidal estrogens have a comparable profile of negative and positive test results. Cyproterone acetate and some of its analogues have a special position within the group of progestins. Their genotoxic potential has been established. Other progestins are generally negative in the routine tests. Anti-glucocorticoids, anti-progestins, corticosteroids, androgens, anabolics and anti-androgens appear to be devoid of genotoxic activities. The genotoxic potential of estradiol, estrone and cyproterone acetate with its analogues may play no role under normal physiological and therapeutic conditions. The metabolic conditions that are needed for the formation of DNA-reactive metabolites and oxygen radicals may not be present in humans. Epidemiological cancer data seem to support this view. The importance of thresholds in the dose-effect-relationship of genotoxicity data and their use in risk assessment is discussed.

Evaluation of the Tg.AC transgenic mouse assay for testing the human carcinogenic potential of pharmaceuticals--practical pointers, mechanistic clues, and new questions

Transgenic mouse strains with genetic alterations known to play a role in the multistage process of carcinogenesis are being used increasingly as models for evaluating the human carcinogenic potential of chemicals and pharmaceuticals. The Tg.AC transgenic mouse is one of the strains currently being used in such alternative short-term carcinogenicity testing protocols. This review is focused on recent data from studies designed to evaluate this model's ability to discriminate carcinogens from noncarcinogens. Details relating to protocol design that can significantly impact study outcome are described. Data relating to mechanisms of chemical tumor induction in the Tg.AC model are reviewed, and questions have been formulated to encourage research to further guide appropriate future applications of this model.

Identification of estrogen-modified nucleosides from calf thymus DNA reacted with 6-hydroxyestrogen 6-sulfates

Two estrogen sulfates, pyridinium 3-methoxyestra-1,3, 5(10)-trien-6alpha-yl sulfate (3MeE-6alpha-S) and its 6beta-isomer (3MeE-6beta-S), synthesized as model compounds to demonstrate the carcinogenesis of estrogen, were found to react with calf thymus DNA to produce steroid-modified DNA adducts. Digestion of the DNA by nuclease P1 and phosphodiesterase I followed by alkaline phosphatase gave a deoxyribonucleoside fraction, of which N2-[3-methoxyestra-1,3, 5(10)-trien-6alpha-yl]deoxyguanosine, N2-[3-methoxyestra-1,3, 5(10)-trien-6beta-yl]deoxyguanosine, N6-[3-methoxyestra-1,3, 5(10)-trien-6beta-yl]deoxyadenosine, and N6-[3-methoxyestra-1,3, 5(10)-trien-6alpha-yl]deoxyadenosine (identified as a base adduct) were identified using HPLC by comparing them with authentic specimens prepared by reacting dG and dA with both sulfates. No steroid-dC adduct was detected in the digestion products of the DNA adduct, although dC reacted with the sulfates to form N4-[3-methoxyestra-1,3,5(10)-trien-6beta-yl]deoxycytidine. These results mean that estrogen 6-sulfate has an ability to modify DNA via the amino group of a guanine or adenine residue in DNA. The present studies imply that a sequential metabolism (hydroxylation and sulfation) at the C6-position of the estrogen molecule causes damage to DNA.

Tamoxifen in treatment of hepatocellular carcinoma: a randomised controlled trial. CLIP Group (Cancer of the Liver Italian Programme)

BACKGROUND

Results from small randomised trials on tamoxifen in the treatment of hepatocellular carcinoma (HCC) are conflicting. We studied whether the addition of tamoxifen to best supportive care prolongs survival of patients with HCC.

METHODS

Patients with any stage of HCC were eligible, irrespective of locoregional treatment. Randomisation was centralised, with a minimisation procedure accounting for centre, evidence of disease, and time from diagnosis. Patients were randomly allocated best supportive care alone or in addition to tamoxifen. Tamoxifen was given orally, 40 mg per day, from randomisation until death.

RESULTS

496 patients from 30 institutions were randomly allocated treatment from January, 1995, to January, 1997. Information was available for 477 patients. By Sept 15, 1997, 119 (50%) of 240 and 130 (55%) of 237 patients had died in the control and tamoxifen arms, respectively. Median survival was 16 months and 15 months (p=0.54), respectively. No differences were found within subgroups defined by prognostic variables. Relative hazard of death for patients receiving tamoxifen was 1.07 (95% CI 0.83-1.39).

INTERPRETATION

Our findings show that tamoxifen is not effective in prolonging survival of patients with HCC.

Endocrine treatment of hepatocellular carcinoma. Any evidence of benefit?

In the past 20 years, a number of studies have investigated the relationship between sex hormones and liver cancer. Experimental studies indicate that a dynamic process, with sequential modifications in the pattern of sex hormones in the serum and of sex hormone receptors in the liver, occurs progressively during hepatocarcinogenesis. Overall, it seems that both androgens and oestrogens may enhance liver carcinogenesis, while androgens may also support the growth of established liver tumours. Unfortunately, clinical studies of endocrine treatment of hepatocellular carcinoma (HCC) have not adequately tested the suggestions from biological studies. So far, no clinical trial has been performed to test the efficacy of endocrine manipulation for the chemoprevention of HCC in cirrhotic patients nor in preventing relapse after radical resection of primary HCC. Anti-oestrogens have been the most studied agents for the endocrine treatment of established HCC, although the rationale that supports their use is weaker than for anti-androgens. Studies with anti-androgens have produced prevalently negative results, due to either a lack of activity or excessive toxicity. The use of chemical castration, which theoretically could enhance the activity of antihormonal compounds, yielded no benefit at all. In summary, there is, as yet, no definitive evidence that endocrine treatment favourably affects the outcome of patients with HCC.

Chemicals with carcinogenic activity in the rodent liver; mechanistic evaluation of human risk

A wide variety of chemicals, both naturally occurring and synthetic, have exhibited carcinogenic activity in rodent liver. Some are clearly DNA reactive whereas others produce only epigenetic effects. Hepatocarcinogens are categorized according to these properties and the characteristics of examples of both types are reviewed. DNA-reactive rodent hepatocarcinogens represent human cancer risk even at non-toxic exposures, whereas epigenetic agents pose either no risk because their effects are specific to rodents, or a risk only at high exposures at which they produce the same cellular effects in humans that are the basis for their carcinogenic activity in rodents.

DNA adduct formation by hormonal steroids in vitro

We examined the binding of various steroid hormones to DNA in vitro by means of 32P-postlabeling. Seventeen steroid hormones and cholesterol (CS) were incubated with human liver DNA at 37 degrees C for 1 h under aerobic conditions in the absence of catalysis. The reaction mixtures were analyzed by the nuclease P-1 version of 32P-postlabeling. The results showed that cortexolone (CX), prednisolone (PS), cortisone (CN), cortisol (CL), tetrahydrocortisol (TC), corticosterone (CC), 11-deoxycorticosterone (DC), dexamethasone (DX), dihydrocortisol (DL), and aldosterone (AL) covalently bound with DNA. However, progesterone (PG), 17 alpha-hydroxyprogesterone (HG), estrone (E1), estradiol (E2), estriol (E3), testosterone (TS), cortol (CR) and the original compound for biosynthesis, CS, did not form adducts. In absence of DNA, the steroids themselves did not give rise to any spot on TLC under the same conditions. The dose-responses of DNA binding by DC, DL, CC, CL and CN were linear. The relative adduct labeling of reactive steroids at a concentration of 2 mM were as follows: 68.8 (CX), 53.2 (PS), 39.6 (CN), 29.9 (CL), 20.9 (TC), 12.9 (CC), 12.3 (DC), 7.5 (DX), 4.7 (DL), 1.2 (AL) adducts per 10(8) nucleotides. Reactive and nonreactive steroids were distinguishable by the presence or absence of the carbonyl group (-CO-CH2OH) at carbon seventeen (C17) of the cholesterol skeleton. This implies that the electrophilic carbonyl or a neighboring group perhaps involved in the formation of covalent bond with DNA. To investigate the nature of target base(s) of these DNA reactive steroids, mononucleotides of all four bases of DNA were reacted with CN, CL, CC and cochromatographed with the obtained spots of DNA reactions. The results of which stated that these steroids and guanine reaction gave the same spots as observed in DNA reaction, indicating guanine is the main target of these DNA reactive steroids. Hep G2 human hepatocellular carcinoma cells were used as an alternative model. Although nine steroids (CL, DL, TC, PS, DX, PG, E2, TX, CR) did not react with intracellular DNA under our experimental conditions, our findings suggested that some hormonal steroids can form covalent DNA adducts in vivo.

Formation of DNA-adducts by selected sex steroids in rat liver

1. We are reporting investigations into the potential of the steroid hormones chlormadinone acetate (CMA), cyproterone acetate (CPA), ethinylestradiol (EE2) gestodene (GEST), megestrol acetate (MGA), norethisterone acetate (NET-Ac), estradiol (E2), and progesterone (P) to form DNA-adducts in rat liver in vivo. 2. Compound-related DNA-adduct spots were detected in male and female rat liver following CMA, CPA, and MGA using the 32P-postlabeling-technique. Substance-specific DNA-adducts were also observed in male rats after administration of E2. The other compounds showed no DNA-adduct formation. After treatment with CMA, CPA or MGA, the relative adduct labeling (RAL) differed sex- and substance-specifically.

Cyproterone acetate: is it hepato- or genotoxic?

The preclinical safety assessment of cyproterone acetate (CPA) with regard to liver tumorigenesis was based on tumorigenicity studies, which revealed no mutagenic potential. Recently, in vitro studies on the formation of adducts and the enhancement of DNA repair synthesis with CPA have been published. These results are not unique to CPA, and the role of adducts and increased DNA synthesis in mutagenesis is still not clear. Dose-related hepatic toxicity has been reported with the prolonged use of CPA. An active surveillance study of patients taking long term CPA treatment has shown no correlation between the duration of CPA treatment and the prevalence of liver enzyme elevations. In a multicentre surveillance study of long term CPA use in 2506 patients included so far, not a single case of hepatocellular carcinoma has been observed. These findings do not support the theory of an elevated risk of hepatocellular carcinoma as a result of CPA treatment. In conclusion, there have been no observations which could point to an increased risk of proliferative liver change as a result of CPA treatment.