Hepatoma Formation Research Articles

Unusual Presentation of Hepatocellular Carcinoma with Peritoneal Carcinomatosis: Importance of Abdominal Distension as a Clinical Indicator

Hepatocellular carcinoma (HCC) is a common malignancy of the liver. It is frequently diagnosed in the male gender with a racial predilection towards Asian and African populations. In addition to distant metastasis, large tumors can result in direct extrahepatic metastasis to the peritoneum and diaphragm through rupture of exophytic tumor hepatocellular carcinoma in peritoneal cavity. We report a case of a 55-year-old male having hepatocellular carcinoma secondary to hepatitis C with peritoneal metastasis. The CT abdomen with contrast triphasic study was suggestive of alarming features of chronic liver disease with multicentric hepatoma formation predominantly in segment VIII with the localized subcapsular collection. Additionally, an extensive omental thickening and nodularity were also seen in subhepatic space. Multiple nodules were seen in right cardiophrenic angle, right lower abdomen, and rectovesical pouch. In contrast to conventional chemotherapy with sorafenib, cytoreduction surgery with hyperthermic intraperitoneal chemotherapy has been shown to dramatically improve survival in patients

Control of Cell Growth and Proliferation by the Tribbles Pseudokinase: Lessons from Drosophila.

Simple SummaryTribbles pseudokinases represent a sub-branch of the CAMK (Ca2+/calmodulin-dependent protein kinase) subfamily and are associated with disease-associated signaling pathways associated with various cancers, including melanoma, lung, liver, and acute leukemia. The ability of this class of molecules to regulate cell proliferation was first recognized in the model organism Drosophila and the fruit fly genetic model and continues to provide insight into the molecular mechanism by which this family of adapter molecules regulates both normal development and disease associated with corruption of their proper regulation and function.The Tribbles (Trib) family of pseudokinase proteins regulate cell growth, proliferation, and differentiation during normal development and in response to environmental stress. Mutations in human Trib isoforms (Trib1, 2, and 3) have been associated with metabolic disease and linked to leukemia and the formation of solid tumors, including melanomas, hepatomas, and lung cancers. Drosophila Tribbles (Trbl) was the first identified member of this sub-family of pseudokinases and shares a conserved structure and similar functions to bind and direct the degradation of key mediators of cell growth and proliferation. Common Trib targets include Akt kinase (also known as protein kinase B), C/EBP (CAAT/enhancer binding protein) transcription factors, and Cdc25 phosphatases, leading to the notion that Trib family members stand athwart multiple pathways modulating their growth-promoting activities. Recent work using the Drosophila model has provided important insights into novel facets of conserved Tribbles functions in stem cell quiescence, tissue regeneration, metabolism connected to insulin signaling, and tumor formation linked to the Hippo signaling pathway. Here we highlight some of these recent studies and discuss their implications for understanding the complex roles Tribs play in cancers and disease pathologies.

Inhibition of diethylnitrosamine-induced liver cancer in rats by Rhizoma paridis saponin.

Rhizoma Paridis saponin (RPS) had been regarded as the main active components responsible for the anti-tumor effects of the herb Paris polyphylla var. yunnanensis (Franch.) Hand.-Mazz. In the present research, we set up a rat model of diethylnitrosamine (DEN) induced hepatoma to evaluate antitumor effect of RPS. After 20 weeks treatment, rats were sacrificed to perform histopathological examinations, liver function tests, oxidative stress assays and so forth. As a result, DEN-induced hepatoma formation. RPS alleviated levels of liver injury through inhibiting liver tissues of malondialdehyde (MDA) and nitric oxide (NO) formation, increasing superoxide dismutases (SOD) production, and up-regulating expression of GST-α/μ/π in DEN-induced rats. All in all, RPS would be a potent agent inhibiting chemically induced liver cancer in the prospective application.

Inhibition of pulmonary adenoma in diethylnitrosamine-induced rats by Rhizoma paridis saponins

Nowadays, people pay more and more attention to the natural products based on their multiple targets in the antitumor treatment. In our previous research, Rhizoma paridis saponins (RPS) were regarded as potent anticancer agent that elicits programmed cell death and inhibits metastases in murine lung adenocarcinoma in vivo. In the present study, we set up a rat model of diethylnitrosamine (DEN) induced pulmonary adenoma to evaluate the antitumor effects of RPS again. After 20 weeks treatment, rats were sacrificed in order to perform histopathological examinations, blood biochemistry, immunohistochemistry, western blot, PCR and metabonomics. As a result, DEN induced pulmonary adenoma generation in the lungs and damaged hepatocytes and hepatoma formation in the livers. RPS effectively attenuated hepatotoxic and inhibited pulmonary adenoma through down-regulating expression of MMP-9 and up-regulating level of TIMP-2 in DEN-induced rats. Meanwhile, RPS remarkably decreased energy metabolism, and glycine, serine and threonine metabolism to block the tumor growth. In conclusion, RPS would be a potent anticancer agent used in the prospective application.

Chitosan oligosaccharides in combination with Agaricus blazei Murill extract reduces hepatoma formation in mice with severe combined immunodeficiency.

Chitosan and Agaricus blazei Murill (ABM) extracts possess antitumor activities. The aim of the present study was to investigate whether chitosan, ABM extract or the two in combination were effective against tumors in tumor-bearing mice. The mice were subcutaneously injected with SK-Hep 1 cells and were then were divided into the following six groups: Group 1, control group; group 2, chitosan 5 mg/kg/day; group 3, chitosan 20 mg/kg/day; group 4, ABM (246 mg/kg/day) and chitosan (5 mg/kg/day) combined; group 5, ABM (984 mg/kg/day) and chitosan (20 mg/kg/day) combined; and group 6, ABM (984 mg/kg/day). The mice were treated with the different concentrations of chitosan, ABM or combinations of the two for 6 weeks. The levels of glutamic oxaloacetic transaminase (GOT), glutamic pyruvic transaminase (GPT) and vascular endothelial growth factor (VEGF), and tissue histopathological features were examined in the surviving animals. Based on the results of the investigation, the treatments performed in groups 2, 3 and 4 were identified as being capable of reducing the weights of the tumors, however, group 4, which was treated with chitosan (5 mg/kg/day) in combination with ABM (246 mg/kg/day) was able to reduce the levels of GOT and VEGF. As a result, treatment with chitosan in combination with ABM may offer potential in cancer therapy and requires further investigation.

Primary biliary cirrhosis: Pathophysiology, clinical presentation and therapy.

Primary biliary cirrhosis (PBC) is an autoimmune, slowly progressive, cholestatic, liver disease characterized by a triad of chronic cholestasis, circulating anti-mitochondrial antibodies (AMA), and characteristic liver biopsy findings of nonsuppurative destructive cholangitis and interlobular bile duct destruction. About 10% of PBC patients, however, lack AMA. A variant, called PBC-autoimmune hepatitis (AIH) overlap, is characterized by the above findings of PBC together with findings of elevated serum alanine aminotransferase, elevated serum immunoglobulin G, and circulating anti-smooth muscle antibodies, with liver biopsy demonstrating periportal or periseptal, lymphocytic, piecemeal necrosis. PBC is hypothesized to be related to environmental exposure in genetically vulnerable individuals. It typically occurs in middle-aged females. Prominent clinical features include fatigue, pruritis, jaundice, xanthomas, osteoporosis, and dyslipidemia. The Mayo Risk score is the most widely used and best prognostic system. Ursodeoxycholic acid is the primary therapy. It works partly by reducing the concentration and injury from relatively toxic bile acids. PBC-AIH overlap syndrome is treated with ursodeoxycholic acid and corticosteroids, especially budesonide. Obeticholic acid and fibrate are promising new, but incompletely tested, therapies. Liver transplantation is the definitive therapy for advanced disease, with about 70% 10-year survival after transplantation. Management of pruritis includes local skin care, dermatologist referral, avoiding potential pruritogens, cholestyramine, and possibly opioid antagonists, sertraline, or rifaximin. Management of osteoporosis includes life-style modifications, administration of calcium and vitamin D, and alendronate. Statins are relatively safe to treat the osteopenia associated with PBC. Associated Sjogren's syndrome is treated by artificial tears, cyclosporine ophthalmic emulsion to stimulate tear production; and saliva substitutes, cholinergic agents, and scrupulous oral and dental care. Complications of cirrhosis from advanced PBC include esophageal varices, ascites, spontaneous bacterial peritonitis, hepatorenal syndrome, and hepatoma formation.

Celecoxib suppresses hepatoma stemness and progression by up-regulating PTEN.

Celecoxib, a COX-2 inhibitor and non-steroidal anti-inflammatory drug, can prevent several types of cancer, including hepatocellular carcinoma (HCC). Here we show that celecoxib suppressed the self-renewal and drug-pumping functions in HCC cells. Besides, celecoxib depleted CD44+/CD133+ hepatic cancer stem cells (hCSC). Prostaglandin E2 (PGE2) and CD133 overexpression did not reverse the celecoxib-induced depletion of hCSC. Also, celecoxib inhibited progression of rat Novikoff hepatoma. Moreover, a 60-day celecoxib program increased the survival rate of rats with hepatoma. Histological analysis revealed that celecoxib therapy reduced the abundance of CD44+/CD133+ hCSCs in hepatoma tissues. Besides, the hCSCs depletion was associated with elevated apoptosis and blunted proliferation and angiogenesis in hepatoma. Celecoxib therapy activated peroxisome proliferator-activated receptor γ (PPARγ) and up-regulated PTEN, thereby inhibiting Akt and disrupting hCSC expansion. PTEN gene delivery by adenovirus reduced CD44/CD133 expression in vitro and hepatoma formation in vivo. This study suggests that celecoxib suppresses cancer stemness and progression of HCC via activation of PPARγ/PTEN signaling.

Overexpression of insulin-like growth factor-I receptor as a pertinent biomarker for hepatocytes malignant transformation

To investigate the dynamic features of insulin-like growth factor-I receptor (IGF-IR) expression in rat hepatocarcinogenesis, and the relationship between IGF-IR and hepatocytes malignant transformation at mRNA or protein level. Hepatoma models were made by inducing with 2-fluorenylacetamide (2-FAA) on male Sprague-Dawley rats. Morphological changes of hepatocytes were observed by pathological Hematoxylin and eosin staining, the dynamic expressions of liver and serum IGF-IR were quantitatively analyzed by an enzyme-linked immunosorbent assay. The distribution of hepatic IGF-IR was located by immunohistochemistry. The fragments of IGF-IR gene were amplified by reverse transcription-polymerase chain reaction, and confirmed by sequencing. Rat hepatocytes after induced by 2-FAA were changed dynamically from granule-like degeneration, precancerous to hepatoma formation with the progressing increasing of hepatic mRNA or IGF-IR expression. The incidences of liver IGF-IR, IGF-IR mRNA, specific IGF-IR concentration (ng/mg wet liver), and serum IGF-IR level (ng/mL) were 0.0%, 0.0%, 0.63 ± 0.17, and 1.33 ± 0.47 in the control; 50.0%, 61.1%, 0.65 ± 0.2, and 1.51 ± 0.46 in the degeneration; 88.9%, 100%, 0.66 ± 0.14, and 1.92 ± 0.29 in the precancerosis; and 100%, 100%, 0.96 ± 0.09, and 2.43 ± 0.57 in the cancerous group, respectively. IGF-IR expression in the cancerous group was significantly higher (P < 0.01) than that in any of other groups at mRNA or protein level. The closely positive IGF-IR relationship was found between livers and sera (r = 0.91, t = 14.222, P < 0.01), respectively. IGF-IR expression may participate in rat hepatocarcinogenesis and its abnormality should be an early marker for hepatocytes malignant transformation.

A novel antihepatitis drug, bicyclol, prevents liver carcinogenesis in diethylnitrosamine-initiated and phenobarbital-promoted mice tumor model.

Bicyclol, an antihepatitis drug developed by Chinese scientists, has been shown to prevent the malignant transformation induced by 3-methylcholanthrene and 12-O-tetradecanoylphorbol-13-acetate in WB-F344 rat liver epithelial cells. This study provides further evidence on its role as a chemopreventive agent in experimental mice with diethylnitrosamine- (DEN-) initiated and phenobarbital- (PB-) promoted liver carcinoma. Liver tissue and serum were collected. In the two-stage model of hepatocarcinogenesis in mice, oral administration of bicyclol (100, 200 mg/kg) before DEN injection showed significant reduction in the incidence of hepatocellular foci, nodules, or carcinoma. Histopathological examination revealed that there was no hepatocellular carcinoma (HCC) and hepatoma formation in the mice pretreated with bicyclol (200 mg/kg) at week 20, while the mice treated with DEN/PB developed 33.3% HCC and 55.6% hepatoma. Furthermore, the serum levels of alanine aminotransferase (ALT), alkaline phosphatase (ALP), and α-fetal protein (AFP) in serum significantly increased in the DEN/PB model group in comparison with the control group. Pretreatment with bicyclol showed a marked reduction in the above condition. Bicyclol also decreased the expression of AFP and proliferating cell nuclear antigen level in the liver tissue and attenuated the decrease in body weight. In this study, we also found that 10 weeks after stopping the administration of PB and drugs, the control and bicyclol-treated (200 mg/kg) animals showed no HCC and hepatoma formation at the time of termination whereas DEN/PB-induced mice developed 100% hepatoma and 50% HCC. These results further indicate that bicyclol has the chemopreventive potential for liver carcinogenesis induced by carcinogens.

Retraction Note: Androgen activates PEG10 to promote carcinogenesis in hepatic cancer cells

The molecular mechanism of striking higher prevalence of hepatocellular carcinoma (HCC) in male subjects has not yet been fully elucidated. Here, we report that androgen receptor (AR) is differentially expressed in different HCC cell lines. AR agonist dihydrotestosterone (DHT) enhances HCC cell growth and apoptotic resistance. Antagonist flutamide (FLU) blocks the effects of DHT on the HCC cell lines. Paternally expressed gene 10 (PEG10) is expressed in HCC cell lines at substantial high level. Using small interfering RNAs against AR and PEG10 in AR- and PEG10-expressing BEL-7404 hepatoma cells and HuH7 hepatoma cells (HuH7) cells, and AR-transfection technique in AR-lacking and PEG10-expressing HepG2 cells, we have confirmed that through upregulation and activation of PEG10, DHT enhances HCC cell growth and apoptotic resistance. We have further demonstrated that DHT upregulates expression of human telomerase reverse transcriptase (hTERT) in HCC cell lines in a PEG10-dependent manner. Moreover, AR directly interacts in vivo with androgen-responsive elements in the regions of promoter and exon 2 of PEG10 gene in HCC cell lines. DHT promotes the hepatoma formation in vivo nude mice through PEG10 activation. AR antagonists (FLU and valproate) inhibit the hepatoma formation. These findings suggest that PEG10 plays an essential role in hepatocarcinogenesis. The PEG10 inhibition can be a novel approach for therapy of HCC.

The Bisecting GlcNAc on N-Glycans Inhibits Growth Factor Signaling and Retards Mammary Tumor Progression

The branching of complex N-glycans attached to growth factor receptors promotes tumor progression by prolonging growth factor signaling. The addition of the bisecting GlcNAc to complex N-glycans by Mgat3 has varying effects on cell adhesion, cell migration, and hepatoma formation. Here, we show that Chinese hamster ovary cells expressing Mgat3 and the polyoma middle T (PyMT) antigen have reduced cell proliferation and growth factor signaling dependent on a galectin lattice. The Mgat3 gene is not expressed in virgin mammary gland but is upregulated during lactation and is expressed in mouse mammary tumor virus (MMTV)/PyMT tumors. Mice lacking Mgat3 that cannot transfer the bisecting GlcNAc to N-glycans acquire PyMT-induced mammary tumors more rapidly and have an increased tumor burden, increased migration of tumor cells, and increased early metastasis to lung. Tumors and tumor-derived cells lacking Mgat3 exhibit enhanced signaling through the Ras pathway and reduced amounts of functionally glycosylated alpha-dystroglycan. Constitutive overexpression of an MMTV/Mgat3 transgene inhibits early mammary tumor development and tumor cell migration. Thus, the addition of the bisecting GlcNAc to complex N-glycans of mammary tumor cell glycoprotein receptors is a cell autonomous mechanism serving to retard tumor progression by reducing growth factor signaling.

Integrative and comparative genomics analysis of early hepatocellular carcinoma differentiated from liver regeneration in young and old

BackgroundHepatocellular carcinoma (HCC) is the third-leading cause of cancer-related deaths worldwide. It is often diagnosed at an advanced stage, and hence typically has a poor prognosis. To identify distinct molecular mechanisms for early HCC we developed a rat model of liver regeneration post-hepatectomy, as well as liver cells undergoing malignant transformation and compared them to normal liver using a microarray approach. Subsequently, we performed cross-species comparative analysis coupled with copy number alterations (CNA) of independent early human HCC microarray studies to facilitate the identification of critical regulatory modules conserved across species.ResultsWe identified 35 signature genes conserved across species, and shared among different types of early human HCCs. Over 70% of signature genes were cancer-related, and more than 50% of the conserved genes were mapped to human genomic CNA regions. Functional annotation revealed genes already implicated in HCC, as well as novel genes which were not previously reported in liver tumors. A subset of differentially expressed genes was validated using quantitative RT-PCR. Concordance was also confirmed for a significant number of genes and pathways in five independent validation microarray datasets. Our results indicated alterations in a number of cancer related pathways, including p53, p38 MAPK, ERK/MAPK, PI3K/AKT, and TGF-β signaling pathways, and potential critical regulatory role of MYC, ERBB2, HNF4A, and SMAD3 for early HCC transformation.ConclusionsThe integrative analysis of transcriptional deregulation, genomic CNA and comparative cross species analysis brings new insights into the molecular profile of early hepatoma formation. This approach may lead to robust biomarkers for the detection of early human HCC.

Epigenetic Inhibition of Nuclear Receptor Small Heterodimer Partner Is Associated With and Regulates Hepatocellular Carcinoma Growth

Aberrant hypermethylation of promoter regions in cytosine-guanine dinucleotides (CpG) islands has been shown to be associated with transcriptional silencing of tumor-suppressor genes in many cancers. This study evaluated the methylation profile and the tumor-suppressive function of the small heterodimer partner (SHP, NR0B2) in the development of human hepatocellular carcinoma (HCC). Human HCC pathologic specimens and cell lines were used as model systems in this study. The expression of SHP is diminished in HCC pathologic specimens and cell lines by epigenetic silencing owing to SHP promoter hypermethylation. In vitro methylation decreased SHP promoter transactivation and nuclear receptor LRH-1 binding, an event that was reversed by demethylation. Overexpression of SHP inhibited HCC foci formation, arrested HCC tumor growth in xenografted nude mice, and increased the sensitivity of HCC cells to apoptotic stimuli. Further analysis of a total of 19 normal liver and 57 HCC specimens showed that down-regulation of SHP gene expression may be a common denominator of HCC. We propose that SHP functions as a novel tumor suppressor in the development of HCC. These findings provide new insight into the molecular mechanisms leading to this common cancer and may have both diagnostic and therapeutic applications.

Androgen activates PEG10 to promote carcinogenesis in hepatic cancer cells

The molecular mechanism of striking higher prevalence of hepatocellular carcinoma (HCC) in male subjects has not yet been fully elucidated. Here, we report that androgen receptor (AR) is differentially expressed in different HCC cell lines. AR agonist dihydrotestosterone (DHT) enhances HCC cell growth and apoptotic resistance. Antagonist flutamide (FLU) blocks the effects of DHT on the HCC cell lines. Paternally expressed gene 10 (PEG10) is expressed in HCC cell lines at substantial high level. Using small interfering RNAs against AR and PEG10 in AR- and PEG10-expressing BEL-7404 hepatoma cells and HuH7 hepatoma cells (HuH7) cells, and AR-transfection technique in AR-lacking and PEG10-expressing HepG2 cells, we have confirmed that through upregulation and activation of PEG10, DHT enhances HCC cell growth and apoptotic resistance. We have further demonstrated that DHT upregulates expression of human telomerase reverse transcriptase (hTERT) in HCC cell lines in a PEG10-dependent manner. Moreover, AR directly interacts in vivo with androgen-responsive elements in the regions of promoter and exon 2 of PEG10 gene in HCC cell lines. DHT promotes the hepatoma formation in vivo nude mice through PEG10 activation. AR antagonists (FLU and valproate) inhibit the hepatoma formation. These findings suggest that PEG10 plays an essential role in hepatocarcinogenesis. The PEG10 inhibition can be a novel approach for therapy of HCC.

Differential Sensitivity of Mouse Epithelial Tissues to the Polyomavirus Middle T Oncogene

To determine how different epithelial cell types respond to the same oncogenic stimulation, we have used a modified human keratin 18 gene to conditionally express the polyomavirus middle T antigen (PyMT) oncogene in simple epithelial tissues of transgenic mice. Activation of PyMT expression by transgenic Cre recombinase in mammary epithelial cells resulted in carcinomas in all bitransgenic females. PyMT expression induced by K18-driven Cre in internal epithelial organs resulted in pancreatic acinar metaplasia and ductal dysplasia with remarkable desmoplastic stromal responses in all 25 bitransgenic mice. Hepatoma formation with altered lipid metabolism and gastric adenocarcinoma occurred in 96 and 54% of these mice, respectively. Elevated PyMT RNA expression also correlated with intraepithelial neoplasia in the prostate. Activated Erk2 was found in mammary tumors, pancreatic tissues, and affected livers. Hes1 RNA, a target of Notch signaling that has been implicated downstream of Ras pathway activation, was elevated in pancreatic and liver lesions. The variety of responses of different epithelia to PyMT demonstrates the importance of the differentiated state in interpreting oncogenic signals.

Distinctive gene expression of receptor-type tyrosine kinase families during rat hepatocarcinogenesis

Growth factor receptor tyrosine kinase signaling plays key roles in regulating growth of normal hepatocytes, however, which receptor-type tyrosine kinase (RTK) is involved in hepatocarcinogenesis remains undetermined. The aim of this study was to characterize the expression of these receptors in different stages of rat liver carcinogenesis. We compared the expression profile of RTK genes in rat normal liver and diethylnitrosamine-induced hepatoma tissues using a homology cloning method with degenerated primers. In situ hybridization, immunohistochemical staining, and RT-PCR were performed to analyze the cell type-specific expression of target RTKs during the chemically-induced hepatocarcinogenesis. Sequence analysis of 459 clones identified 23 different RTK genes. The Tie-2, c-Met, and Flk-1 genes were the most abundant RTK genes cloned in rat hepatoma compared to normal liver. In situ hybridization and immunohistochemical studies showed overexpression of c-Met and Flk-1 in GST-P positive preneoplastic lesions as well as neoplastic lesions. Tie-2 was expressed not only in endothelial cells but also in so-called oval cells, which are thought to be liver stem cells. Tie-2 ligand, angiopointin-1, mRNA was detected in both normal livers and hepatoma cells/tissues. In contrast, angiopoietin-2 mRNA was detected only in hepatoma tissues. These results indicate that c-Met, Tie-2 and Flk-1 signals play important roles in different stages of chemically-induced hepatocarcinogenesis. Distinctive gene expression of RTK may contribute to epigenic implication of hepatoma formation.

The Spectrum of Diffuse and Focal Liver Lesions in Workers Exposed to Vinylchloridemonomer

The Spectrum of Diffuse and Focal Liver Lesions in Workers Exposed to Vinylchloridemonomer

The electrophilic, mutagenic and tumorigenic activities of phenyl and 4- nitrophenyl vinyl ethers and their epoxide metabolites

The metabolism and mutagenicity of phenyl and 4-nitrophenyl vinyl ethers (PVE and NPVE) and their epoxide metabolites, phenoxyoxirane (PO) and 2'-(4-nitro-phenoxy)oxirane (NPO), were studied including reactions with DNA and tests for carcinogenicity. PVE and NPVE were epoxidized in dry acetone by dimethyldioxirane to give high yields (95%) of the pure epoxides. The epoxides are unstable in aqueous media and in 0.1 N phosphate buffer, pH 7.4, at 37 degrees C; they had half-lives of 2.7 min (PO) and 4.4 min (NPO). These times were reduced to 1.9 min (PO) and 2.5 min (NPO) in the presence of isotonic (154 mM) chloride ion. In neutral phosphate buffer these epoxides hydrolyze to form glycolaldehyde and the corresponding phenols; in the presence of chloride ion, chloroacetaldehyde and several unknown compounds are also formed. Glycolaldehyde was also found as a hydrolysis product of the presumed epoxides generated in the hepatic microsomal oxidation of PVE and NPVE. PO and NPO reacted with DNA to form adducts that depurinated in weak acid to form 7-(2'-oxoethyl)guanine and N(2),3-ethenoguanine. PO was weakly mutagenic in Salmonella typhimurium TA1535 while NPO was much more mutagenic under the same conditions. PO and NPO were found to have mutagenic half-lives that matched their chemical half-lives. PO and NPO were found to be tumorigenic in the skin of mice after single or five initiating doses followed by multiple doses of phorbol ester (TPA). NPO was a stronger tumor initiator than PO. NPO had appreciable activity as an initiator of hepatoma formation in infant male B6C3F1 mice. Thus PO and NPO are electrophilic, mutagenic and tumorigenic metabolites of their corresponding phenyl vinyl ethers.

Pathological mechanisms of hepatic tumour formation in rats exposed chronically to dietary hexachlorobenzene.

The chronic dietary administration of hexachlorobenzene (HCB) to rats for a year or more results in the formation of liver tumours described as hepatocellular carcinomas, hepatomas or haemangiomas. The hepatotoxicity of HCB, which is greatest in hamsters and rats, gives rise to peliosis and necrosis with haemosiderosis. This pattern of hepatotoxicity indicates vascular damage, which through haemosiderosis could increase not only the toxic effect of HCB to hepatocytes but also its tumourogenic potential. The present study confirmed vascular damage by the identification of widespread fibrin deposits in the livers of rats chronically exposed to HCB, using an antibody to rat fibrin. Based on our study we suggest that the formation of hepatomas and haemangiomas with elements of peliosis (cystic blood-filled cavities) could be explained by the compensatory hyperplastic responses to hepatocellular necrosis and by the simultaneous loss of hepatocellular cords. The accumulation of iron in the liver would strongly potentiate the development of hepatic tumours, as has been found in HCB and polychlorinated biphenyl-treated mice with iron overload. The implications of this non-genotoxic mechanism of hepatoma formation for the assessment of human health risk are discussed.

Prevalence of the Mercurial-Sensitive EctoATPase in Human Small Cell Lung Carcinoma: Characterization and Partial Purification

Cell surface ATPase (ectoATPase) activity is detected on many mammalian cells. Previous documentation in the rat hepatocyte-hepatoma system indicated that ectoATPase activity increased during tumorigenesis with accompanying changes in enzymatic properties and localization. These results, combined with the recently established characteristics of two distinct ectoATPases, a mercurial-sensitive ectoATPase, and a mercurial-insensitive ectoATPase, suggest that the former is increased, whereas the latter is decreased, during hepatoma formation. We found that the mercurial-sensitive ectoATPase was also expressed at high levels in three lines of human small cell lung carcinoma (SCLC) cells. During purification of this enzyme from an SCLC xenograft, four isoforms of this enzyme, with similar biochemical properties but different ionic charges were detected. The elution of two proteins of 170 and 150 kDa from a DEAE-cellulose column appeared to correlate with elution of ATPase activity. These characterizations should be useful in the further investigation of the molecular structure and function of the SCLC mercurial-sensitive ectoATPase which may be an important cell surface marker of SCLC cells.