Diethylnitrosamine-induced Liver Tumorigenesis Research Articles

Diethylnitrosamine-Induced Liver Tumorigenesis in Mice Under High-Hat High-Sucrose Diet: Stepwise High-Resolution Ultrasound Imaging and Histopathological Correlations.

The hepatotoxic N-nitroso compound diethylnitrosamine (DEN) administered intraperitoneally (i.p.) induces liver neoplasms in rodents that reproducibly recapitulate some aspects of human hepatocarcinogenesis. In particular, DEN drives the stepwise formation of pre-neoplastic and neoplastic (benign or malignant) hepatocellular lesions reminiscent of the initiation-promotion-progression sequence typical of chemical carcinogenesis. In humans, the development of hepatocellular carcinoma (HCC) is also a multi-step process triggered by continuous hepatocellular injury, chronic inflammation, and compensatory hyperplasia that fuel the emergence of dysplastic liver lesions followed by the formation of early HCC. The DEN-induced liver tumorigenesis model represents a versatile preclinical tool that enables the study of many tumor development modifiers (genetic background, gene knockout or overexpression, diets, pollutants, or drugs) with a thorough follow-up of the multistage process on live animals by means of high-resolution imaging. Here, we provide a comprehensive protocol for the induction of hepatocellular neoplasms in wild-type C57BL/6J male mice following i.p. DEN injection (25mg/kg) at 14days of age and 36weeks feeding of a high-fat high-sucrose (HFHS) diet. We emphasize the use of ultrasound liver imaging to follow tumor development and provide histopathological correlations. We also discuss the extrinsic and intrinsic factors known to modify the course of liver tumorigenesis in this model.

Oncogenic challenge of bromocriptine and L-arginine versus conventional antidiabetics on diethyl nitrosamine-induced liver tumorigenesis in diabetic rats: focus on AMPK activation

Background: Diabetes mellitus (DM) is associated with a spectrum of cancers where the metabolic antecedents, consequences, and therapy might affect cancer risk. The association between hepatocellular carcinoma (HCC) and DM had been confirmed. Approaches to HCC prevention focus on the molecular regulators of the disease process defined as the inflammation-fibrosis-cancer axis. The AMP-activated protein kinase (AMPK) is an interesting metabolic tumor suppressor and a promising target for cancer prevention and therapy. This study aimed to investigate the effects of bromocriptine mesylate and L-arginine on hepatic carcinogenesis on a rat model of hepatic neoplasia induced by diethyl nitrosamine (DENA) and promoted by type-2 DM in contrast to the conventional antidiabetics.Methods: One hundred male Wistar rats were randomly assigned into two sets; control set (normal, HCC, DM, and combined HCC/DM) and treated set where rats received one of the following drugs for another 5 weeks: insulin glargine, glimepiride, metformin, pioglitazone, bromocriptine mesylate, or L-arginine. Bodyweight changes, blood glucose level, liver functions tests, serum C-peptide and alpha-fetoprotein (AFP), and hepatic activated AMPK were assessed beside the hepatic histopathological changes.Results: Equivalent to metformin, bromocriptine and L-arginine treatment significantly reduced AFP, despite their minor glycemic control. L-arginine induced AMPK activation, yet less than metformin. Histopathologic examination revealed a reduction in hepatic intra-lobular chronic inflammatory cell infiltration, steatosis and necrosis by metformin, bromocriptine, and L-arginine. Hepatic necro-inflammatory changes were most prominent in insulin-treated rats.Conclusions: L-arginine and bromocriptine mesylate prevent early neoplastic changes almost equivalent to metformin at least partially via hepatic AMPK activation.

Rhubarb granule promotes diethylnitrosamine-induced liver tumorigenesis by activating the oxidative branch of pentose phosphate pathway via G6PD in rats

Ethnopharmacological relevanceRhubarb is a natural herbal medicine widely used clinically with numerous pharmacological activities including anti-cancer. Specifically, several studies reported that free anthraquinones from Rhubarb suppressed the proliferation of hepatoma cells. Nonetheless, recent studies revealed that Rhubarb caused hepatotoxicity in vivo, confirming its “two-way” effect on the liver. Therefore, the efficacy and safety of Rhubarb in the in vivo treatment of liver cancer should be further elucidated.Aim of the study: This study investigated the presence of hepatoprotection or hepatotoxicity of Rhubarb in diethylnitrosamine (DEN)-induced hepatocarcinogenesis. Material and methodsA total of 112 male Sprague-Dawley rats weighing 190–250 g were enrolled. The rats were induced hepatocarcinogenesis using diethylnitrosamine (0.002 g/rat) until 17 weeks. Starting at week 11, Rhubarb granules (4 g/kg and 8 g/kg) were intragastrically administered daily for 7 weeks. All rats were euthanized at week 20 and the livers were analyzed via non-targeted metabolomics analysis. We established hepatic glucose 6 phosphate (6PG) levels and glucose 6 phosphate dehydrogenase (G6PD) activities to assess the pentose phosphate pathway (PPP). And the liver injuries of rats were analyzed via histological changes, hepatic function, as well as hepatic protein levels of alpha-fetoprotein (AFP), pyruvate kinase isozyme type M2 (PKM2), and proliferating cell nuclear antigen (PCNA). Furthermore, polydatin (0.1 g/kg/d) as a specific inhibitor of G6PD was used to treat rats. Notably, their histological changes, hepatic function, hepatic 6PG levels, hepatic G6PD activities, PCNA levels, and PKM2 levels were recorded. ResultsNon-targeted metabolomics revealed that Rhubarb regulated the PPP in the liver of Rhubarb-DEN-treated rats. Besides, Rhubarb activated the oxidative branch of the PPP by activating G6PD (a rate-limiting enzyme in the oxidative PPP) in the liver of Rhubarb-DEN-treated rats. Meanwhile, Rhubarb promoted DEN-induced hepatocarcinogenesis. Moreover, polydatin attenuated the promoting effect of Rhubarb on DEN-induced hepatocarcinogenesis. ConclusionsRhubarb promoted DEN-induced hepatocarcinogenesis by activating the PPP, indicating that the efficacy and safety of Rhubarb in the treatment of liver cancer deserve to be deliberated.

USP48 Is Upregulated by Mettl14 to Attenuate Hepatocellular Carcinoma via Regulating SIRT6 Stabilization.

Exploiting cancer metabolism for the clinical benefit of patients with hepatocellular carcinoma (HCC) is a topic under active investigation. Ubiquitin-specific peptidase 48 (USP48), a member of the ubiquitin-specific protease family, is involved in tumor growth, inflammation, and genome stability. However, the role of USP48 in HCC tumorigenesis remains unknown. In this study, we report that expression of USP48 is downregulated in diethylnitrosamine-induced liver tumorigenesis in mice as well as in human HCC. USP48 physically bound and stabilized SIRT6 by K48-linked deubiquitination at the K33 and K128 sites of SIRT6, which impeded metabolic reprogramming to hamper HCC tumorigenesis. Moreover, methyltransferase-like 14 (Mettl14)-induced m6A modification participated in the regulation of USP48 in HCC by maintaining USP48 mRNA stability. Our work uncovers the tumor-suppressive function of the Mettl14-USP48-SIRT6 axis via modulation of glycolysis, providing new insights into the critical roles of metabolic activities in HCC and identifying an attractive target for future treatment studies. SIGNIFICANCE: These findings demonstrate that USP48 is regulated by Mettl14-induced m6A modification and stabilizes SIRT6 to attenuate HCC glycolysis and malignancy.

Diethylnitrosamine-induced liver tumorigenesis in mice.

Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide and the third leading cause of cancer related mortality with a 10 year survival rate of merely 22-35%. Tumorigenesis frequently occurs in patients with chronic liver disease where continued liver cell damage, compensatory proliferation and inflammation provide the basis for tumor initiation, promotion and progression. Animal models of HCC are particularly useful to better understand molecular events underlying liver tumorigenesis. To this end, chemical carcinogenesis protocols based on the injection of genotoxic compounds such as diethylnitrosamine (DEN) are widely used to model liver tumorigenesis in rodents. DEN injection into 2 week old mice is sufficient to cause liver tumorigenesis after 8-10 months. When injected into older mice, DEN has to be combined with administration of tumor promoting agents such as phenobarbital or feeding high fat diet. Such protocols allow to dissect the different steps of tumor formation (i.e., tumor initiation and promotion) experimentally and to model liver pathologies in mice which frequently lead to HCC in human patients such as non-alcoholic fatty liver disease. Here, we review several established chemical carcinogenesis protocols based on DEN injection into mice and discuss their advantages as well as potential limitations.

STAT5 deficiency in hepatocytes reduces diethylnitrosamine-induced liver tumorigenesis in mice

Chronic liver diseases and the development of hepatocellular carcinoma are closely linked and pose a major medical challenge as treatment options are limited. Animal studies have shown that genetic deletion of the signal transducer and activator of transcription (STAT) 5 in liver is associated with higher susceptibility to fatty liver disease, fibrosis and cancer, indicating a protective role of hepatic STAT5 in mouse models of chronic liver disease. To investigate the role of STAT5 in the etiology of liver cancer in more detail, we applied the chemical carcinogen diethylnitrosamine (DEN) to mice harboring a hepatocyte-specific deletion of Stat5 (S5KO). At 8 months after DEN injections, tumor formation in S5KO was significantly reduced. This was associated with diminished tumor frequency and less aggressive liver cancer progression. Apoptosis and inflammation markers were not changed in S5KO livers suggesting that the reduced tumor burden was not due to impaired inflammatory response. Despite reduced mRNA expression of the DEN bio-activator cytochrome P450 2e1 (Cyp2e1) in S5KO livers, protein levels were similar. Yet, delayed tumor formation in S5KO mice coincided with decreased activation of c-Jun N-terminal Kinase (JNK). Taken together, while STAT5 has a protective role in fatty liver-associated liver cancer, it exerts oncogenic functions in DEN-induced liver cancer.

Preventive effects of the sodium glucose cotransporter 2 inhibitor tofogliflozin on diethylnitrosamine-induced liver tumorigenesis in obese and diabetic mice.

Sodium glucose cotransporter 2 inhibitors are expected to ameliorate the abnormalities associated with metabolic syndrome including non-alcoholic fatty liver disease. In this study, we investigated the effects of the sodium glucose cotransporter 2 inhibitor tofogliflozin on the development of non-alcoholic fatty liver disease-related liver tumorigenesis in C57BL/KsJ-+Leprdb/+Leprdb obese and diabetic mice. The direct effects of tofogliflozin on human liver cancer cell proliferation were also evaluated. Mice were administered diethylnitrosamine-containing water for 2 weeks and were treated with tofogliflozin throughout the experiment. In mice treated with tofogliflozin, the development of hepatic preneoplastic lesions was markedly suppressed, and hepatic steatosis and inflammation significantly reduced, as evaluated using the non-alcoholic fatty liver disease activity score, in comparison with the control mice. Serum levels of glucose and free fatty acid and mRNA expression levels of pro-inflammatory markers in the liver were reduced by tofogliflozin treatment. Conversely, the proliferation of sodium glucose cotransporter 2 protein-expressing liver cancer cells was not inhibited by this agent. These findings suggest that tofogliflozin suppressed the early phase of obesity- and non-alcoholic fatty liver disease-related hepatocarcinogenesis by attenuating chronic inflammation and hepatic steatosis. Therefore, sodium glucose cotransporter 2 inhibitors may have a chemopreventive effect on obesity-related hepatocellular carcinoma.

Abstract 4052: The role of the phosphorylated RXRα on diethylnitrosamine-induced liver tumorigenesis in mice

Abstract We have previously reported that a malfunction of RXRα due to aberrant phosphorylation at serine 260 by MAPK is associated with the development of hepatocellular carcinoma (HCC). The phosphorylated RXRα impairs normal receptor functions of either RXR or RAR, which are respective homodimeric or heterodimeric partner of RXRα, in a dominant-negative manner. Besides, these impaired receptor functions result in the downregulation of their target gene expression and inducing hepatocarcinogenesis by stimulating cell proliferation and inhibiting apoptosis, suggesting that phosphorylated RXRα plays a crucial role in the development of HCC. However, these findings were revealed primarily using HCC cell lines that express the phosphorylated-RXRα (p-RXRα) proteins and it still remains unclear whether p-RXRα may impact in the process of hepatocarcinogenesis in vivo. Therefore, in order to investigate the biological functions of p-RXRα on hepatocarcinogenesis in vivo, we generated doxycycline-inducible ES cell line and transgenic mouse, both of which overexpress phosphomimic mutant of RXRα (T82D/S260D). Interestingly, the transcriptional activities of Retinoid X Receptor Response Element (RXRE) were significantly reduced in the Mouse Embryonic Fibroblasts (MEFs) derived from the transgenic mice, suggesting that the retinoid signaling via RXRα were impaired in the mice. Moreover, the development of liver tumors induced by liver carcinogen diethylnitrosamine (DEN) was enhanced in the transgenic mice that overexpress T82D/S260D protein in the liver. Notably, the increased liver tumors in the transgenic mice resulted from the promotion of cell cycle progression, not the inhibition of apoptosis. Interestingly, expression of β-catenin and its target genes, cyclin D1 and c-myc, were increased in transgenic liver tumors, although the expression of retinoid-related genes, such as RARβ, p21 and p27, were not altered compared with control mice. These results suggest that the phospho-modification of RXRα may promote the development of DEN-induced liver tumors through the activation of β-catenin signaling pathways in mice. Citation Format: Hiroyasu Sakai, Yohei Shirakami, Masahito Shimizu. The role of the phosphorylated RXRα on diethylnitrosamine-induced liver tumorigenesis in mice. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4052.

Pentoxifylline prevents nonalcoholic steatohepatitis-related liver pre-neoplasms by inhibiting hepatic inflammation and lipogenesis.

Nonalcoholic steatohepatitis (NASH) has gained attention as a hepatic manifestation associated with metabolic syndrome and one of the causes for chronic liver damage leading to hepatocellular carcinoma. Although no standard medicinal treatment for NASH has been established, pentoxifylline (PTX), a medicine used to improve circulation, has recently been reported to ameliorate the histopathological appearance of NASH. In the present study, we investigated the effects of PTX on the development of NASH and diethylnitrosamine-induced liver tumorigenesis in C57BLKS/J- +Lepr/+Lepr obese and diabetic mice, which are considered a rodent model for NASH-related hepatocarcinogenesis. Mice were administered diethylnitrosamine, and then they received water with or without PTX. At the time of sacrifice, the development of hepatic pre-neoplastic lesions was significantly suppressed in the PTX groups. Hepatic triglyceride contents were decreased by PTX administration. The serum levels of triglyceride, free fatty acid, and alanine aminotransferase were all decreased by PTX treatment, as was the mRNA expression of proinflammatory cytokines, macrophage-inducing chemokines, and several lipogenic genes in the liver. In-vitro studies also showed that PTX treatment decreased the expression of several lipogenic genes and chemokines in cell lines. These findings suggest that PTX prevents NASH-related liver tumorigenesis by attenuating chronic hepatic inflammation and decreasing lipogenic gene expression in the liver.

Resveratrol Down-Regulates Myosin Light Chain Kinase, Induces Apoptosis and Inhibits Diethylnitrosamine-Induced Liver Tumorigenesis in Rats

Hepatocellular carcinoma (HCC) is a serious healthcare problem worldwide because of its increasing morbidity and high mortality rates. However, our understanding of the mechanism of liver tumorigenesis remains incomplete. We report the expression of myosin light chain kinase (MLCK) in the livers of rats with diethylnitrosamine (DENA)-induced HCC and investigated the correlation between MLCK and liver tumorigenesis by observing the expression of MLCK in a rat model of HCC. HCC was induced in rats by an intraperitoneal injection of DENA, and resveratrol-treated rats were orally administered resveratrol with 50 mg/kg body weight/day. The livers of rats were excised after 20 weeks and immersed in 10% formaldehyde prior to immunohistochemical and Western blot analyses for determining the level of MLCK expression. These analyses indicated that the MLCK expression was higher in the livers of HCC rats than in normal and resveratrol-treated rats. High level of MLCK expression was responsible for proliferation and anti-apoptotic effects. However, resveratrol down-regulated the expression of MLCK, which induced cell apoptosis and inhibited liver tumorigenesis in rats with DENA-induced HCC. Our results suggest that the over expression of MLCK may be related to the development of liver tumorigenesis.

A Sleeping Beauty mutagenesis screen reveals a tumor suppressor role for Ncoa2/Src-2 in liver cancer

The Sleeping Beauty (SB) transposon mutagenesis system is a powerful tool that facilitates the discovery of mutations that accelerate tumorigenesis. In this study, we sought to identify mutations that cooperate with MYC, one of the most commonly dysregulated genes in human malignancy. We performed a forward genetic screen with a mouse model of MYC-induced liver cancer using SB-mediated mutagenesis. We sequenced insertions in 63 liver tumor nodules and identified at least 16 genes/loci that contribute to accelerated tumor development. RNAi-mediated knockdown in a liver progenitor cell line further validate three of these genes, Ncoa2/Src-2, Zfx, and Dtnb, as tumor suppressors in liver cancer. Moreover, deletion of Ncoa2/Src-2 in mice predisposes to diethylnitrosamine-induced liver tumorigenesis. These findings reveal genes and pathways that functionally restrain MYC-mediated liver tumorigenesis and therefore may provide targets for cancer therapy.

Abstract 1616: Preventive effects of EGCG on diethylnitrosamine-induced liver tumorigenesis in obese and diabetic C57BL/KsJ-db/db mice

Abstract Background and aims: Obesity and related metabolic abnormalities, including insulin resistance and a state of chronic inflammation, increase the risk of hepatocellular carcinoma (HCC). Abnormal activation of the IGF/IGF-1R axis is also involved in obesity-related liver tumorigenesis. In the present study, we examined the effects of (-)-epigallocatechin gallate (EGCG), a major biologically active component of green tea, on the development of diethylnitrosamine (DEN)-induced liver tumorigenesis in C57BL/KsJ-db/db (db/db) obese mice. Methods: Male db/db mice were given tap water containing 40 ppm DEN for 2 weeks and then they received drinking water containing 0.1% EGCG for 34 weeks. Results: At sacrifice, drinking water with EGCG significantly inhibited the development of liver cell adenomas in comparison to the control EGCG-untreated group. EGCG inhibited the phosphorylation of the IGF-1R, ERK, Akt, GSK-3β, Stat3, and JNK proteins in the livers of experimental mice. The serum levels of insulin, IGF-1, IGF-2, free fatty acid, and TNF-α were all decreased by drinking EGCG. EGCG also decreased the expression of TNF-α, IL-6, IL-1α, and IL-18 mRNAs in the livers. In addition, EGCG improved liver steatosis and activated the AMPK protein in the liver. Conclusion: EGCG prevents obesity-related liver tumorigenesis by inhibiting the IGF/IGF-1R axis, improving hyperinsulinemia, and attenuating chronic inflammation. EGCG, therefore, may be useful in the chemoprevention of liver tumorigenesis in obese individuals. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1616. doi:1538-7445.AM2012-1616

Abstract 844: Acyclic retinoid inhibits diethylnitrosamine-induced liver tumorigenesis in obese and diabetic C57BL/KsJ-db/db mice

Abstract Background and aims: Obesity and the related metabolic abnormalities are associated with increased risk of hepatocellular carcinoma (HCC). Malfunctioning of retinoid X receptor (RXR)-α due to phosphorylation by Ras/MAPK also plays a critical role in liver carcinogenesis. In the present study, we examined the effects of acyclic retinoid (ACR), which targets RXRα, on the development of diethylnitrosamine (DEN)-induced liver tumorigenesis in C57BL/KsJ-db/db (db/db) obese and diabetic mice. Methods: Male db/db mice were given tap water containing 40 ppm DEN for 2 weeks, after which they were fed a diet containing 0.03% or 0.06% of ACR throughout the experiment. Results: In mice treated with either dose of ACR for 34 weeks, the development of liver cell adenomas was significantly inhibited as compared to basal diet-fed mice. ACR markedly inhibited the activation of Ras and phosphorylation of the ERK, RXRα, and Stat3 proteins in the livers of experimental mice. It also increased the expression of RARβ and p21CIP1 mRNA, while decreasing the expression of cyclin D1, c-Fos, and c-Jun mRNA in the liver, thereby restoring RXRα function. Administration of ACR improved liver steatosis and activated the AMPK protein. The serum levels of insulin were decreased by ACR treatment, whereas the QUICKI values were increased, indicating improved insulin sensitivity. The serum levels of TNF-α and the expression levels of TNF-α, IL-6, and IL-1β mRNA in the livers of DEN-treated db/db mice were decreased by ACR treatment, suggesting attenuation of the chronic inflammation induced by excessive fatty deposits. Conclusion: ACR may be, therefore, useful in the chemoprevention of obesity-related HCC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 844. doi:10.1158/1538-7445.AM2011-844

Preventive Effects of (−)-Epigallocatechin Gallate on Diethylnitrosamine-Induced Liver Tumorigenesis in Obese and Diabetic C57BL/KsJ-db/db Mice

Obesity and related metabolic abnormalities, including insulin resistance and a state of chronic inflammation, increase the risk of hepatocellular carcinoma. Abnormal activation of the insulin-like growth factor (IGF)/ IGF-1 receptor (IGF-1R) axis is also involved in obesity-related liver tumorigenesis. In the present study, we examined the effects of (-)-epigallocatechin gallate (EGCG), a major biologically active component of green tea, on the development of diethylnitrosamine (DEN)-induced liver tumorigenesis in C57BL/KsJ-db/db (db/db) obese mice. Male db/db mice were given tap water containing 40 ppm DEN for 2 weeks and then they received drinking water containing 0.1% EGCG for 34 weeks. At sacrifice, drinking water with EGCG significantly inhibited the development of liver cell adenomas in comparison with the control EGCG-untreated group. EGCG inhibited the phosphorylation of the IGF-1R, ERK (extracellular signal-regulated kinase), Akt, GSK-3β (glycogen synthase kinase-3β), Stat3, and JNK (c-Jun NH(2)-terminal kinase) proteins in the livers of experimental mice. The serum levels of insulin, IGF-1, IGF-2, free fatty acid, and TNF-α were all decreased by drinking EGCG, which also decreased the expression of TNF-α, interleukin (IL)-6, IL-1β, and IL-18 mRNAs in the livers. In addition, EGCG improved liver steatosis and activated the AMP-activated kinase protein in the liver. These findings suggest that EGCG prevents obesity-related liver tumorigenesis by inhibiting the IGF/IGF-1R axis, improving hyperinsulinemia, and attenuating chronic inflammation. EGCG, therefore, may be useful in the chemoprevention of liver tumorigenesis in obese individuals. Cancer Prev Res; 4(3); 396-403. ©2011 AACR.

INHIBITORY EFFECT OF TRANSIENT ADMINISTRATION OF FLUTAMIDE (SCH-13521, 4'-NITRO-3'-TRIFLUOROMETHYLISOBUTYRANILIDE) ON DIETHYL-NITROSAMINE (DEN) INDUCED LIVER-TUMORS IN MALE B6C3F1 MICE

In order to understand the role of androgen in DEN induced liver tumorigenesis in mice, we studied the influence of anti-androgenic compound, flutamide (SCH 13521, 4'-Nitro-3'-trifluoromethylisobutyranilide) on liver tumors, in B6C3F1 male mice. At 6 weeks of age mice were treated with DEN, (0.2 muM/g body weight). Transient administration of flutamide (0.5 mg/g food) in diet to male mice for (i) three weeks immediately after diethylnitrosamine (DEN) treatment, for (ii) three weeks starting at the age of 25 weeks and (iii) starting at 25 weeks of age until end of experiment inhibited liver tumors incidence to 63%, 50% and 53%, respectively, compared to that of DEN alone, 81.3% (significantly different). However, continuous administration of this drug throughout the experimental period (58 weeks) produced 96.9% liver tumor incidence. The time-dependent sacrifice of DEN alone treated mice at 25, 30, 38, 44 and 58 weeks of age produced liver tumor incidence of 0, 12.5, 31.5, 43.8 and 81.3%, respectively (r = 0.99). Mean tumor number and size were also correlatively increased with the prolongation of latency and highest value was noted at 58 weeks of age. Implantation of testosterone pellet after castration significantly increased cytosolic androgen receptor levels but decreased in mice treated with flutamide. Three weeks administration of flutamide to male B6C3F1 mice enhanced nuclear BrdU incorporated cells in the liver. Our results suggested that flutamide reduces cytosolic androgen receptor levels and increases DNA synthesis. These factors may in part be responsible for the liver tumor inhibitory effect of flutamide in male mice.

Changes in the Labeling Index and DNA Content of Liver Cells During Diethylnitrosamine-Induced Liver Tumorigenesis in <italic>Oryzias latipes</italic><xref ref-type="fn" rid="fn2">2</xref>

Changes in the Labeling Index and DNA Content of Liver Cells During Diethylnitrosamine-Induced Liver Tumorigenesis in <italic>Oryzias latipes</italic><xref ref-type="fn" rid="fn2">2</xref>