https://www.cell.com/cell/pdf/0092-8674(82)90400-7.pdf

The catalog of human cytokeratins: Patterns of expression in normal epithelia, tumors and cultured cells

The exact role of hepatitis B virus in the development of liver cancer is not known The recent identification of a viral regulatory gene HBx suggests a possible direct involvement of the virus whereby the HBx protein, acting as a transcriptional transactivator of viral genes, may alter host gene expression and lead to the development of hepatocellular carcinoma We have tested this possibility of placing the entire HBx gene under its own regulatory elements directly into the germline of mice Transgenic animals harbouring this viral gene succumbed to progressive histopathological changes specifically in the liver, beginning with multifocal areas of altered hepatocytes, followed by the appearance of benign adenomas, and proceeding to the development of malignant carcinomas Male mice developed disease and died much earlier than females This transgenic animal model appears ideal for defining the molecular events that follow the expression of the viral HBx gene and are responsible for the development of liver cancer

HBx gene of hepatitis B virus induces liver cancer in transgenic mice

Pyruvate kinase type M2 and its role in tumor growth and spreading

A key hallmark of many cancers, particularly the most aggressive, is the capacity to metabolize glucose at an elevated rate, a phenotype detected clinically using positron emission tomography (PET). This phenotype provides cancer cells, including those that participate in metastasis, a distinct competitive edge over normal cells. Specifically, after rapid entry of glucose into cancer cells on the glucose transporter, the highly glycolytic phenotype is supported by hexokinase (primarily HK II) that is overexpressed and bound to the outer mitochondrial membrane via the porin-like protein voltage-dependent anion channel (VDAC). This protein and the adenine nucleotide transporter move ATP, newly synthesized by the inner membrane located ATP synthase, to active sites on HK II. The abundant amounts of HK II bind both the ATP and the incoming glucose producing the product glucose-6-phosphate, also at an elevated rate. This critical metabolite then serves both as a biosynthetic precursor to support cell proliferation and as a precursor for lactic acid, the latter exiting cancer cells causing an unfavorable environment for normal cells. Although helping facilitate this chemical warfare, HK II via its mitochondrial location also suppresses the death of cancer cells, thus increasing their possibility for metastasis and the ultimate death of the human host. For these reasons, targeting this key enzyme is currently being investigated in several laboratories in a strategy to develop novel therapies that may turn the tide on the continuing struggle to find effective cures for cancer. One such candidate is 3-bromopyruvate that has been shown recently to eradicate advanced stage, PET positive hepatocellular carcinomas in an animal model without apparent harm to the animals.

Hexokinase II: Cancer's double-edged sword acting as both facilitator and gatekeeper of malignancy when bound to mitochondria

The performance of a battery of three of the most commonly used in vitro genotoxicity tests--Ames+mouse lymphoma assay (MLA)+in vitro micronucleus (MN) or chromosomal aberrations (CA) test--has been evaluated for its ability to discriminate rodent carcinogens and non-carcinogens, from a large database of over 700 chemicals compiled from the CPDB ("Gold"), NTP, IARC and other publications. We re-evaluated many (113 MLA and 30 CA) previously published genotoxicity results in order to categorise the performance of these assays using the response categories we established. The sensitivity of the three-test battery was high. Of the 553 carcinogens for which there were valid genotoxicity data, 93% of the rodent carcinogens evaluated in at least one assay gave positive results in at least one of the three tests. Combinations of two and three test systems had greater sensitivity than individual tests resulting in sensitivities of around 90% or more, depending on test combination. Only 19 carcinogens (out of 206 tested in all three tests, considering CA and MN as alternatives) gave consistently negative results in a full three-test battery. Most were either carcinogenic via a non-genotoxic mechanism (liver enzyme inducers, peroxisome proliferators, hormonal carcinogens) considered not necessarily relevant for humans, or were extremely weak (presumed) genotoxic carcinogens (e.g. N-nitrosodiphenylamine). Two carcinogens (5-chloro-o-toluidine, 1,1,2,2-tetrachloroethane) may have a genotoxic element to their carcinogenicity and may have been expected to produce positive results somewhere in the battery. We identified 183 chemicals that were non-carcinogenic after testing in both male and female rats and mice. There were genotoxicity data on 177 of these. The specificity of the Ames test was reasonable (73.9%), but all mammalian cell tests had very low specificity (i.e. below 45%), and this declined to extremely low levels in combinations of two and three test systems. When all three tests were performed, 75-95% of non-carcinogens gave positive (i.e. false positive) results in at least one test in the battery. The extremely low specificity highlights the importance of understanding the mechanism by which genotoxicity may be induced (whether it is relevant for the whole animal or human) and using weight of evidence approaches to assess the carcinogenic risk from a positive genotoxicity signal. It also highlights deficiencies in the current prediction from and understanding of such in vitro results for the in vivo situation. It may even signal the need for either a reassessment of the conditions and criteria for positive results (cytotoxicity, solubility, etc.) or the development and use of a completely new set of in vitro tests (e.g. mutation in transgenic cell lines, systems with inherent metabolic activity avoiding the use of S9, measurement of genetic changes in more cancer-relevant genes or hotspots of genes, etc.). It was very difficult to assess the performance of the in vitro MN test, particularly in combination with other assays, because the published database for this assay is relatively small at this time. The specificity values for the in vitro MN assay may improve if data from a larger proportion of the known non-carcinogens becomes available, and a larger published database of results with the MN assay is urgently needed if this test is to be appreciated for regulatory use. However, specificity levels of <50% will still be unacceptable. Despite these issues, by adopting a relative predictivity (RP) measure (ratio of real:false results), it was possible to establish that positive results in all three tests indicate the chemical is greater than three times more likely to be a rodent carcinogen than a non-carcinogen. Likewise, negative results in all three tests indicate the chemical is greater than two times more likely to be a rodent non-carcinogen than a carcinogen. This RP measure is considered a useful tool for industry to assess the likelihood of a chemical possessing carcinogenic potential from batteries of positive or negative results.

Evaluation of the ability of a battery of three in vitro genotoxicity tests to discriminate rodent carcinogens and non-carcinogens: I. Sensitivity, specificity and relative predictivity

Hepatocellular glycogenosis and hepatocarcinogenesis

Expression of hepatitis B virus X protein in HBV-infected human livers and hepatocellular carcinomas.

The evaluation of the carcinogenic risk deriving from chemical compounds depends mainly on conventional histopathology up to the present. The accepted end point in carcinogenicity testing is the tumor as defined histologically. A great disadvantage of this approach is the long lag period in the development of tumors induced by chemicals. In order to overcome this drawback, many efforts have been made to detect early biological or morphological lesions which might be specific for carcinogens. A great number of short-term tests carried out in vitro provided valuable information about the reactions of cellular constituents and biological macromolecules to the chemicals tested, but they did not allow an unequivocal prediction of the carcinogenic potential of the respective compounds in whole animals, not to mention man. The introduction of modern micromorphological methods such as electron microscopy and cytochemistry in the evaluation of whole-animal studies also revealed many new aspects on carcinogen-induced cellular and subcellular alterations which appeared to be unreliable as indicators of the carcinogenic risk of chemicals. However, during the past two decades a number of characteristic cellular changes has been detected in various tissues, especially in the liver. These changes regularly precede the development of certain tumor types, and are regarded as preneoplastic lesions (1,2). The altered cell populations usually form well-defined foci. They appear prior to the development of tumors in the target tissue of the carcinogen, and should be duly considered in the evaluation of the carcinogenic risk from chemicals in bioassays.

Preneoplastic lesions as end points in carcinogenicity testing. I. Hepatic preneoplasia.

The livers from a total of 51 Sprague-Dawley rats treated with different doses of N-nitrosomorpholine (80-120 mg/l in the drinking water) for up to 14 weeks together with the livers of 28 control animals were histochemically investigated at the cessation of carcinogenic insult and at varying periods thereafter for their glycogen content, basophilia and activities of various enzymes of carbohydrate metabolism: glycogen synthetase, glycogen phosphorylase, glucose-6-phosphatase, glyceraldehyde-3-phosphate dehydrogenase and glucose-6-phosphate dehydrogenase The enzymatic patterns of normal tissue, preneoplastic and neoplastic lesions were characterized and compared with reference to the morphologically defined stages of tumor development in the liver The early appearing glycogen storing areas, localized in the peripheral and intermediate lobular regions, did not show significant changes in the histochemically demonstrable activities of the enzymes tested After cessation of the carcinogen treatment the more pronounced glycogen storage foci which developed within the aforementioned regions of the liver acinus usually showed a reduction in the activities of phosphorylase and glucose-6-phosphatase while the activity of glucose-6-phosphate dehydrogenase, a key enzyme for the pentose phosphate pathway, was increased The mixed cell foci, neoplastic nodules and tumors which emerged at later stages were characterized by a progressive shift away from glycogen metabolism towards glycolysis and the pentose phosphate pathway, as indicated by an increase in glyceraldehyde-3-phosphate dehydrogenase and glucose-6-phosphate dehydrogenase activities These changes in enzyme pattern are supportive of a developmental sequence leading from glycogen storage foci through mixed cell foci and neoplastic nodules to hepatocellular carcinomas

Peter Bannasch

Papers

Hepatocellular glycogenosis and hepatocarcinogenesis

Expression of hepatitis B virus X protein in HBV-infected human livers and hepatocellular carcinomas.

Preneoplastic lesions as end points in carcinogenicity testing. I. Hepatic preneoplasia.

Correlative histochemistry of some enzymes of carbohydrate metabolism in preneoplastic and neoplastic lesions in the rat liver

Hepatocellular glycogenosis and related pattern of enzymatic changes during hepatocarcinogenesis