Carcinogen-specific gene expression profiles in short-term treated Eker and wild-type rats indicative of pathways involved in renal tumorigenesis

Eker rats heterozygous for a dominant germline mutation in the tuberous sclerosis 2 (Tsc2) tumor suppressor gene were used as a model to study renal carcinogenesis. Eker and corresponding wild-type rats were exposed to genotoxic aristolochic acid (AA) or non-genotoxic ochratoxin A (OTA) to elucidate early carcinogen-specific gene expression changes and to test whether Eker rats are more sensitive to carcinogen-induced changes in gene expression. Male Eker and wild-type rats were gavaged daily with AA (10 mg/kg body weight) or OTA (210 microg/kg body weight). After 1, 3, 7, and 14 days of exposure, renal histopathology, tubular cell proliferation, and Affymetrix gene expression profiles from renal cortex/outer medulla were analyzed. AA-treated Eker and wild-type rats were qualitatively comparable in all variables assessed, suggesting a Tsc2-independent mechanism of action. OTA treatment resulted in slightly increased cortical pathology and significantly elevated cell proliferation in both strains, although Eker rats were more sensitive. Deregulated genes involved in the phosphatidylinositol 3-kinase-AKT-Tsc2-mammalian target of rapamycin signaling, among other important genes prominent in tumorigenesis, in conjunction with the enhanced cell proliferation and presence of preneoplastic lesions suggested involvement of Tsc2 in OTA-mediated toxicity and carcinogenicity, especially as deregulation of genes involved in this pathway was more prominent in the Tsc2 mutant Eker rat.     

Estrogen treatment enhances hereditary renal tumor development in Eker rats

Hormonal influences are known to affect the development of renal cell carcinoma in man and laboratory animal models. We tested the hypothesis that estrogen treatment or ovariectomy of rats modulates renal tumor development using tuberous sclerosis 2 (Tsc2) heterozygous mutant (Eker) rats in which a germline mutation predisposes the animals to renal cell tumor development. Two-month-old female wild-type and Eker rats were ovariectomized or sham-operated and treated with placebo or 5 mg 17beta-estradiol in s.c. pellets for 6 or 10 months. Rats were examined at 8 or 12 months of age, at which time the numbers of renal tumors and preneoplastic foci were quantitated and the severity of nephropathy was assessed. In contrast to what may have been expected, prolonged estrogen treatment enhanced the development of hereditary renal cell tumors, with a 2-fold greater number of preneoplastic and neoplastic renal lesions compared with untreated Eker rats. Ovariectomized Eker rats had 33% fewer renal lesions than the unmanipulated control group. No tumors or preneoplastic lesions were present in wild-type rats at either time point. Estrogen treatment increased the severity of nephropathy in both wild-type and Eker rats, whereas ovariectomy was protective against nephropathic changes. Although estrogen is not a rat renal carcinogen, it enhanced the development of hereditary renal cell tumors when administered to Eker rats. Eker rats heterozygous for a mutation in the Tsc2 locus provide a good model in which to study how genetic and hormonal factors contribute to the development of renal cell tumors and to understand the influence genetic susceptibility has on the development of renal cell carcinoma.      

Niban gene is commonly expressed in the renal tumors: a new candidate marker for renal carcinogenesis

Functional inactivation of tuberous sclerosis 2 gene (Tsc2) leads to renal carcinogenesis in the hereditary renal carcinoma Eker rat models. Recent studies revealed a role of tuberin, a TSC2 product, in suppressing the p70 S6 kinase (p70S6K) activity via inhibition of mammalian target of rapamycin (mTOR). Phosphorylated S6 protein, a substrate of p70S6K, was expressed in the early lesions in Eker rats, and this expression was suppressed by the treatment of rapamycin, an inhibitor of mTOR. We previously isolated the novel gene Niban expressed in renal carcinogenesis of Eker rats. In this study, we demonstrated that the expression of Niban was detected from early preneoplastic lesions in Eker rats. Interestingly, in contrast to the phosphorylated S6 protein, the expression of Niban was unchanged and early lesions still remained even after treatment with rapamycin. These results might suggest the existence of another pathway independent of mTOR-S6K pathway in Tsc2 mutant renal carcinogenesis. In addition, Niban was also expressed in other renal carcinoma models, including Tsc1 and Tsc2 knockout mice, and various types of human renal cell carcinomas. Thus, Niban was commonly expressed in renal carcinomas and might be a new marker for renal carcinogenesis.     

Comparison of Reversibility of Rat Forestomach Lesions Induced by Genotoxic and Non-genotoxic Carcinogens

Reversibility of forestomach lesions induced by genotoxic and non-genotoxic carcinogens was compared histopathologically. Groups of 30 to 33 male F344 rats were given dietary 0.1% 8-nitroquinoline, dietary 0.4–0.2% 2-(2-furyl)-3-(5-nitro-2-furyl)acrylamide, an intragastric dose of 20 mg/kg body weight N-methyl-N'-nitro-N-nitrosoguanidine once a week, or 20 ppm N-methylnitrosourethane in the drinking water as a genotoxic carcinogen, or 2% butylated hydroxyanisole, 2% caffeic acid, 2% sesamol or 2% 4-methoxyphenol in the diet as a non-genotoxic carcinogen for 24 weeks. Ten or 11 rats in each group were killed at week 24. Half of the remainder were maintained on basal diet alone for an additional 24 weeks and the other half were given the same chemical for 48 weeks, and then killed. Forestomach lesions induced by genotoxic carcinogens did not regress after removal of carcinogens. In contrast, simple or papillary hyperplasia (SPH), but not basal cell hyperplasia (BCH), induced by non-genotoxic carcinogens clearly regressed after cessation of insult. SFH labeling indices in the non-genotoxic carcinogen-treated cases decreased after removal of the carcinogenic stimulus whereas BCH values were low irrespective of treatment. Atypical hyperplasia (AH), observed at high incidences in rats treated with genotoxic carcinogens, was also evident in animals receiving non-genotoxic agents, even after their withdrawal, albeit at low incidences. AH labeling indices remained high even without continued insult. These results indicate that even with non-genotoxic carcinogens, heritable alterations at the DNA level could occur during strong cell proliferation and result in AH development. This putative preneoplastic lesion might then progress to produce carcinomas.     

A novel "Nihon" rat model of a Mendelian dominantly inherited renal cell carcinoma.

A novel rat model of hereditary renal cell carcinoma (RC) was found in a rat colony of the Sprague-Dawley strain in Japan, and named the rising "Nihon" rat. In this strain, RCs develop from early preneoplastic lesions, which begin to appear at 4 weeks of age, forming adenomas by the age of 16 weeks. The RCs are predominantly of clear cell type. Southern blot, northern blot and SSCP analyses revealed no change in the Tsc1, Tsc2, VHL, and c-Met genes. Thus, the Nihon rat should be a valuable experimental model for understanding renal carcinogenesis, especially clear cell type, which is common among human RCs.     

A Novel "Nihon'Rat Model of a Mendelian Dominantly Inherited Renal Cell Carcinoma

A novel rat model of hereditary renal cell carcinoma (RC) was found in a rat colony of the Sprague-Dawley strain in Japan, and named the "Nihon'rat. In this strain, RCs develop from early preneoplastic lesions, which begin to appear at 4 weeks of age, forming adenomas by the age of 16 weeks. The RCs are predominantly of clear cell type. Southern blot, northern blot and SSCP analyses revealed no change in the Tsc1, Tsc2, VHL , and c-Met genes. Thus, the Nihon rat should be a valuable experimental model for understanding renal carcinogenesis, especially clear cell type, which is common among human RCs.     

Presence of a modifier gene(s) affecting early renal carcinogenesis in the Tsc2 mutant (Eker) rat model

The Eker (Tsc2 mutant) rat model of renal carcinoma is an example of Mendelian dominantly inherited predisposition to a specific cancer. Effects of genetic background on renal carcinogenesis in the Eker rat model (Eker/Eker > Eker/BN strain) indicate the presence in the BN rat genome of a modifier gene(s) that suppresses tumorigenesis. The identification of such a modifier gene(s) might help clarify the diversity of tuberous sclerosis in humans. i) We found that preneoplastic lesions in 8-week-old F1 rats [(Eker x LE) and (Eker x BN)] were more numerous in the LE strain than in the BN strain although the difference was not large. ii) We next administered N-ethyl-N-nitrosourea (ENU; single injection, i.p.) at the age of 4 weeks to amplify the strain difference in tumorigenesis, as we had done in an earlier study to identify the predisposing gene. iii) This experiment was also done in BN congenic Eker rats to confirm the strain difference in tumorigenesis. Preneoplastic lesions were fewer in BN congenic rats than in Eker rats by a factor of 100. We used this ENU system to perform a backcross experiment [F1(Eker x BN) x Eker] and finally succeeded in mapping a new modifier locus on rat chromosome 5 (the LOD score of the D5Rat12 was 3.13).     

CANCER BIOLOGY: Dose dependence of phenobarbital promotion of preneoplastic hepatic lesions in F344 rats and B6C3F1 mice: effects on DNA synthesis and apoptosis

Phenobarbital (PB), a non-genotoxic hepatocarcinogen in rodents,has been studied extensively but its mechanism of carcinogenicaction is unclear. PB appears to function as a tumor promoterby selectively inducing the growth of preneoplastic hepatocytes.In the present study, the comparative effects of PB at tumor-promotingand non-promoting doses were examined in male B6C3F1 mice andmale F344 rats. In addition, the mechanism by which PB producedthe selective induction of preneoplastic cell growth (increasedDNA synthesis/cell proliferation and/or decreased apoptosis)was investigated. Preneoplastic focal lesions were producedusing diethylnitrosamine (DEN). After the lesions were histologicallyapparent, mice and rats were fed PB (10, 100, or 500 mg/kg NIH-07diet) or control diet and sampled after 7, 30 and 60 days oftreatment In both mice and rats, 100 and 500 mg PB/kg increasedthe number and the relative volume of focal lesions. In ratsand mice, 10 mg PB/kg did not enhance focal lesion growth. Thepreneoplastic lesions that clonaUy expanded due to phenobarbitaltreatment were predominantly eosinophilic in appearance. Inaddition, DNA synthesis in focal hepatocytes was significantlyincreased in the 100 and 500 mg PB/kg diet In PB-treated miceand rats, there also was a significant decrease in the ratesof apoptosis in focal hepatocytes. Therefore, our data showedthat PB at doses of 100 and 500 mg/kg diet promoted focal hepaticlesion growth both by increasing DNA synthesis and cell proliferationand by decreasing the rate of apoptosis.     

Age dependence of radiation‐induced renal cell carcinomas in an Eker rat model

(Cancer Sci 2010; 101: 616–623) Exposure to carcinogens early in life may contribute to cancer development later in life. The amount of radiation exposure children experience during medical procedures has been increasing, so it is important to evaluate the radiation risk of cancer in developing organs. Toward this goal, we assessed the risk of developing renal cell carcinoma using Eker rats as a kidney tumor model. F1 hybrids of male Eker (Tsc2 mutant) and female F344 rats were irradiated with 0.5 or 2 Gy gamma radiation on gestation days 15 and 19, and on postnatal days 5, 20, and 49. At 27 weeks of age, kidneys were examined for proliferative lesions. Preneoplastic lesions such as phenotypically altered tubules increased after postnatal irradiation as a function of age‐at‐irradiation, and hyperplasia were greatly increased after perinatal and postnatal irradiation. In contrast, development of adenoma and adenocarcinoma were evident in animals irradiated at perinatal ages, being maximal at gestational day 19. The frequency of LOH at the Tsc2 locus was unexpectedly low – 0% (0 of 4) for the unirradiated control, and 17% (6 of 35) for the irradiated group. Irrespective of LOH, the mTOR (mammalian target of rapamycin) pathway, which is negatively regulated by the Tsc1/2 complex, was activated in both benign and malignant lesions, as evidenced by phosphorylation of S6 ribosomal protein and 4E‐BP1. This suggests that the wild‐type Tsc2 allele may be functionally inactivated. In conclusion, actively growing kidneys in perinatal‐aged (F344 × Eker) F1 rats (Tsc2^+/?) are at risk for radiation‐induced malignant transformation of the renal epithelium associated with mTOR activation.     

Amelioration of sodium barbital-induced nephropathy and regenerative tubular hyperplasia after a single injection of streptozotocin does not abolish the renal tumor promoting effect of barbital sodium in male F344/NC4 rats

The renal tumor promoting activity of barbital sodium (BBNa) and the role of renal tubular cell hyperplasia in tumor promotion following initiation with streptozotocin (STZ) was investigated. Six week old male F344/NCr rats were given STZ as a single i.p. injection of 50 mg/kg body wt and beginning 2 weeks later were fed diets containing 0 or 4000 p.p.m. of BBNa until they were killed at 33, 52 or 72 experimental weeks for histological evaluation and determination of levels of renal DNA synthesis by bromodeoxyuridine (Brdu) immunohistochemistry. A promoting effect on renal carcinogenesis was found by 72 weeks, but not at 33 or 52 weeks, confirming that prolonged administration of BBNa is necessary to promote renal tubular cell neoplasms. The promoting effect was evident as a higher incidence of large renal tubular tumors after 52 weeks, rather than an increase in number of dysplastic tubules, putative preneoplastic lesions. These findings suggest that the targets for the promoting activity of BBNa may be dysplastic lesions which may progress to tumors. Detailed examination by the step section technique through the entire kidneys revealed that STZ or BBNa administration induced a high incidence of putative preneoplastic renal tubular lesions (dysplasias) which seemed to be derived from the P1 or P2 segment of the nephron, also a site of high Brdu labeling index (LI) associated with BBNa toxicity. STZ administration was also associated with attenuation of BBNa-induced nephropathy and with diabetes from pancreatic islet degeneration and atrophy. The reduction in severity of nephropathy was correlated with a reduction in the LI of the renal cortical and medullary tubules, but not with the renal tumor incidence. These results indicate that decreased DNA synthesis in target cells does not eliminate tumor promoting activity in renal tubular epithelium. In addition, BBNa alone induced papillomas of the transitional epithelium of the renal pelvis and renal tubular cell adenomas.     

DNA damage triggers imbalance of proliferation and apoptosis during development of preneoplastic foci in the liver of Long-Evans Cinnamon rats

The mutant strain Long-Evans Cinnamon (LEC) rat accumulates copper, resulting in spontaneous hepatitis and subsequent development of hepatocellular carcinomas (HCCs) in the liver, providing a promising model for investigation of the relationship between hepatitis induced by oxidative stress and hepatocarcinogenesis. We examined DNA strand breaks in peripheral blood cells and p53 expression in livers during acute and chronic hepatitis in LEC rats, along with preneoplastic lesions, and cell proliferation and apoptosis in non-cancerous portions of livers from LEC rats aged 7-115 weeks. Immunohistochemistry using antibodies against glutathione S-transferase placental-form (GST-P), proliferating cell nuclear antigen (PCNA), and in situ DNA nick labeling (TUNEL) were used. Long-Evans Agouti (LEA) rats, a sibling line of the LEC strain, were used as controls. In the LEC rats, DNA strand breaks and expression of p53 were significantly higher than that of LEA rats at 24 weeks of age. The number of GST-P-positive (GST-P+) foci/cm2 increased and peaked at 48 weeks old, and the areas rapidly expanded thereafter. The level of cell proliferation increased with the development of hepatitis and was highest at about 48 weeks old. The induction of apoptosis in LEC rats was transiently higher than that in LEA rats during the period from 24 to 34 weeks of age. However, the ratio of PCNA-positive cells to the apoptotic index showed a growth imbalance in favor of cell proliferation, supporting sustained net growth in LEC rats. These findings suggest that DNA damage, reflected in DNA strand breaks, plays a critical role in the development of hepatocellular preneoplastic foci, with an imbalance between high proliferation and relatively low apoptosis.     

Carcinogenic Risk Assessment: are there Dose Thresholds for Carcinogens?

While it has been generally accepted that genotoxic carcinogens have no dose threshold for their carcinogenic potential, there is increasing evidence that very low doses in fact are incapable of inducing tumours or preneoplastic lesions. Thus not only so-called epigenetic ‘non-genotoxic’ compounds like phenobarbital and benzene hexachloride, but also unequivocally genotoxic carcinogens like the heterocyclic amines, 2-amino-3,8-dimethyl-imidazo[4,5-f]quinoxaline and amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, and the nitrosamines diethylnitrosamine, and dimethylnitrosamine, may exhibit a practical dose threshold below which they do not induce histopathologically assessable lesions. Some form of physiological adaptation may thus be expected to occur in response to low doses of all types of DNA-damaging agents. With ‘non-genotoxic’ agents there may even be hormesis or paradoxical protection at very low dose.     

Initiation by nickel acetate and promotion by sodium barbital of renal cortical epithelial tumors in male F344 rats

Soluble nickel(II) ion, given to male F344/NCr rats as a singlei.p. injection of nickel(II) acetate tetrahydrate at a doseof 90 µmol/kg body weight at 5 weeks of age, proved aneffective initiator of renal cortical epithelial tumors. Thetumors were revealed by subsequent dosing with the known renaltumor promoter, sodium barbital (5,5-diethylbarbituric acid,sodium salt) dissolved in drinking water at a concentrationof 500 p.p.m. Only one rat given the nickel injection withoutsubsequent promotion developed a single renal cortical adenoma,while multiple tumors were common in nickel(II) initiated/sodiumbarbital promoted rats. Renal cortical adenocarcinomas, someof them metastatic to lung, liver, and spleen, occurred onlyin initiated/promoted rats. No excess incidence of nickel-initiatedtumors was found in any other tissues in which sodium barbitalis known to promote carcinogenesis, such as liver or thyroid.A single i.p. injection of the Ni (II) salt, 95 µmol/kg,appeared to be associated with an increased concentration of8-hydroxy-2'-deoxyguanosine in DNA extracted from kidneys ofrats 16–48 h after injection.     

Different genetic alterations in rat forestomach tumors induced by genotoxic and non-genotoxic carcinogens

Human beings are exposed to a multitude of carcinogens in their environment, and most cancers are considered to be chemically induced. Here we examined differences in genetic alterations in rat forestomach tumors induced by repeated exposure to a genotoxic carcinogen, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) or N-methylnitrosourethane (MNUR), and chronic treatment with a non-genotoxic carcinogen, butylated hydroxyanisole (BHA) or caffeic acid (CA). A total of 132, 6-week-old male F344 rats were employed. Forty rats were treated with MNNG by intragastric administration at a dose of 20 mg/kg body wt once a week for 32 weeks, and 20 rats received 20 p.p.m. MNUR in their drinking water for 48 weeks. Further groups of 20 animals were administered 2% BHA or 2% CA in the diet for 104 weeks. The remaining rats were maintained without any supplement as controls. Multiple forestomach tumors were observed in all rats of the MNNG-, MNUR-, BHA- and CA-treated groups. Histopathologically, MNUR- and CA-treated groups showed almost the same pattern. On polymerase chain reaction-single strand conformation polymorphism analysis, H-ras and p53 gene mutations were observed at high and relatively low frequencies, respectively, in forestomach tumors induced by MNNG and MNUR. Most H-ras gene mutations were G-->A transitions in codons 7 and 12 of exon 1. On the other hand, forestomach tumors due to the non-genotoxic carcinogens, BHA and CA, had almost no mutations of the H-ras and p53 genes. Moreover, relative overexpression of cyclin D1 and p53 was detected in forestomach tumors induced by the genotoxic carcinogens, while their non-genotoxic counterparts had a tendency to show low expression of those molecules. Mutations of the beta-catenin gene were not detected in any group. The present study demonstrates that rat forestomach tumors induced by genotoxic and non-genotoxic carcinogens have different underlying genetic alterations, even if their pathological features are similar.     

Epigenetic events during the process of cell transformation induced by carcinogens (review).

Recent studies clearly demonstrate that several environmental carcinogens lack the ability to initially induce genetic damage. In that view, multistage chemical carcinogenesis may be processed under the control of a variety of epigenetic events in addition to genotoxic impacts. The understanding of this mechanism as reviewed in this report requires knowledge of early changes induced by carcinogens in target cells, biochemical, biological and molecular reactions closely related to both sides of the growth equation: cell proliferation and programmed death. Among several cell transformation models, the most suitable for carcinogen detection and mechanistic study is the Syrian hamster embryo (SHE) cell transformation assay. This closely mimics the multistage carcinogenesis and we can examine, in a relatively short time (8 days), the mechanisms by which genotoxic and non-genotoxic agents may increase the frequency of cell transformation as a preneoplastic end-point. The mode of action of hundred of compounds, carcinogens and non-carcinogens, has been explored so far using one-stage and two-stage treatment protocols. In general, with the two-stage protocol, all carcinogens, irrespective of their genotoxic or non-genotoxic potential, give unambiguous positive results. Since perturbations of cell proliferation and death are considered essential events in the process of carcinogenesis, studies have been conducted on the dysregulation of two specific parameters, the induction of ornithine decarboxylase (ODC) an enzyme related to cell proliferation, and the apoptosis rate, when SHE cells are exposed to carcinogens. In one-stage treatment (5 h-24 h), only the promoter TPA induces ODC activity, while other carcinogens do not increase this activity. Using the two-stage exposure protocol (1 h xenobiotic/5 h TPA), all carcinogens both genotoxic and non-genotoxic, are able to stimulate ODC activity above the level obtained with TPA alone. Based on the two-stage treatment with carcinogens a close relationship can be obtained between the ODC superinduction and the increase of morphological cell transformation frequency. In cancer development, it is postulated that the inhibition of apoptosis may help altered cells to escape cell death and acquire a tumorigenic phenotype. Two-stage treatment carcinogen/TPA, effectively decreases the apoptotic rate. This is accompanied by an upregulation of the Bcl-2 oncoprotein, a well-known apoptotic inhibitor. However, treatment with a non-carcinogen phthalic anhydride, also inhibits apoptosis while it does not superinduce ODC activity. Although inhibition of apoptosis is not specific to the carcinogenic compound, both superinduction of ODC activity and inhibition of apoptosis via Bcl-2 upregulation may cooperate during the early stages of the carcinogenic process. In a long-term stage transformation assay, the rate of transformed colonies is relatively low (2-8%) bringing about the slow evolution of tumoral disease in humans and tumoral induction in rodents. This could be the consequence of the activation of various cellular repair mechanisms during the exposure time. Experimental data reported so far point out that genotoxic and non-genotoxic carcinogens, thought to be more active in the initiation or in the promotion stage, must share the same stage pathway leading to cancer development.     

In vivo mutagenicity and initiation following oxidative DNA lesion in the kidneys of rats given potassium bromate

To clarify the role of 8-OHdG formation as a starting point for carcinogenesis, we examined the dose-dependence and time-course of changes of OGG1 mRNA expression, 8-OHdG levels and in vivo mutations in the kidneys of gpt delta rats given KBrO3 in their drinking water for 13 weeks. There were no remarkable changes in OGG1 mRNA in spite of some increments being statistically significant. Increases of 8-OHdG occurred after 1 week at 500 p.p.m. and after 13 weeks at 250 p.p.m. Elevation of Spi- mutant frequency, suggestive of deletion mutations, occurred after 9 weeks at 500 p.p.m. In a two-stage experiment, F344 rats were given KBrO3 for 13 weeks then, after a 2-week recovery, treated with 1% NTA in the diet for 39 weeks. The incidence and multiplicity of renal preneoplastic lesions in rats given KBrO3 at 500 p.p.m. followed by NTA treatment were significantly higher than in rats treated with NTA alone. Results suggest that a certain period of time might be required for 8-OHdG to cause permanent mutations. The two-step experiment shows that cells exposed to the alteration of the intranuclear status by oxidative stress including 8-OHdG formation might be able to form tumors with appropriate promotion.     

Modulation of neoplastic development: concepts and examples

Chemical carcinogenesis is classically considered as a multiphasic process within which one identifies an initiation phase followed by a phase of promotion and finally progression and/or conversion. The concept of modulation of neoplastic development will be proposed. That concept characterizes any treatment able to modify the evolution of a carcinogenic process. Such a modification is either an acceleration or a slowing down of carcinogenesis. It is not fully equivalent to promotion since it is not an obligatory phase of carcinogenesis. After an initiating treatment, the evolution of carcinogenesis can thus be modulated either positively or negatively. Modulating agents of liver carcinogenesis can be chemical carcinogens, non-genotoxic xenobiotics, endogenous factors, food ingredients, surgery, infectious agents. Their effect on the development of preneoplastic lesions can be both quantitatively and qualitatively different from their effect on the appearance of liver cancers. They could act through cellular or systemic metabolic perturbations linked with cell proliferation.     

Renal carcinogenic and nephrotoxic effects of the flame retardant tris(2,3-dibromopropyl) phosphate in F344 rats and (C57BL/6N X C3H/HeN)F1 mice.

Tris(2,3-dibromopropyl) phosphate (TBP) was administered in the feed at one of two concentrations to groups of 55 male and 55 female inbred F344 rats and to 50 male and 50 female (C57BL/6N X C3H/HeN)F1 mice. The high and low dietary concentrations of TBP administered orally were 100 and 50 ppm for the rats, respectively, and 1,000 and 500 ppm for the mice, respectively. For each rodent type, 55 animals of each sex were used as contols. In both rodent types, renal epithelial tumors developed at incidences that were significant for male and female rats and mice that received the doses. These tumors included renal tubular cell adenomas and carcinomas that developed from the proximal convoluted tubular epithelium. Among female mice and rats, hyperplasia and/or dysplasia of the proximal convoluted tubular epithelium with or without cystic dilatation of the tubules and increase in the size of cell nuclei were dose dependent and recognized as preneoplastic and/or toxic lesions. The comparative histogenesis of renal tubular neoplasms was discussed.     

Tuberous sclerosis complex 1: an epithelial tumor suppressor essential to prevent spontaneous prostate cancer in aged mice

The phosphoinositide 3-kinase (PI3K) pathway regulates mammalian cell growth, survival, and motility and plays a major pathogenetic role in human prostate cancer (PCa). However, the oncogenic contributions downstream of the PI3K pathway made by mammalian target of rapamycin complex 1 (mTORC1)-mediated cell growth signal transduction in PCa have yet to be elucidated in detail. Here, we engineered constitutive mTORC1 activation in prostate epithelium by a conditional genetic deletion of tuberous sclerosis complex 1 (Tsc1), a potent negative regulator of mTORC1 signaling. Epithelial inactivation was not immediately tumorigenic, but Tsc1-deficient mice developed prostatic intraepithelial neoplasia (mPIN) in lateral and anterior prostates by 6 months of age, with increasing disease penetrance over time. Lateral prostate lesions in 16- to 22-month-old mutant mice progressed to two types of more advanced lesions, adenomatous gland forming lesion (Type 1) and atypical glands embedded in massively expanded reactive stroma (Type 2). Both Type 1 and Type 2 lesions contained multiple foci of microinvasive carcinoma. Epithelial neoplastic and atypical stromal lesions persisted despite 4 weeks of RAD001 chemotherapy. Rapalogue resistance was not due to AKT or extracellular signal-regulated kinase 1/2 activation. Expression of the homeobox gene Nkx3.1 was lost in Tsc1-deficient mPIN, and it cooperated with TSC1 loss in mPIN initiation in doubly mutant Tsc1:Nkx3.1 prostatic epithelial knockout mice. Thus, TSC1 inactivation distal to PI3K and AKT activation is sufficient to activate a molecular signaling cascade producing prostatic neoplasia and focal carcinogenesis.     

Effect of tumour promoters and non-genotoxic carcinogens on terminal differentiation and proliferation in mouse teratoma XB2 cells cultured in low calcium medium.

XB2 cells, a teratocarcinoma derived cell line of keratinocyte lineage, have been shown to proliferate and differentiate in low calcium medium (0.03 mM Ca2+) at a density of 500 cells/9.6 cm2 without the need for fibroblast feeder layers or conditioned medium. The degree of differentiation can be assessed by measurements of keratin production and stratification of colonies of cells. Both of these parameters, as well as the proliferative capacity of the cells, can be altered by treatment of the cultures with various promoting agents and non-genotoxic carcinogens. Treatment with teleocidin and 12-O-tetradecanoyl phorbol-13-acetate induced large increases in proliferation, stratification and keratinization; mezerein-treated cells showed increased stratification at higher doses; butylated hydroxyanisole treatment resulted in hyperkeratinization and hyperstratification to lower levels than that seen with the phorbol-ester-like promoters; butylated hydroxytoluene had purely hyperproliferative effects. We suggest that this culture system may provide a useful model for studies of the mechanism of promotion and non-genotoxic carcinogenesis in epithelial tissues.