Incidence Of Spontaneous Tumors Research Articles

R-loop functions in Brca1-associated mammary tumorigenesis

Deleterious accumulation of R-loops, a DNA-RNA hybrid structure, contributes to genome instability. They are associated with BRCA1 mutation-related breast cancer, an estrogen receptor α negative (ERα-) tumor type originating from luminal progenitor cells. However, a presumed causality of R-loops in tumorigenesis has not been established in vivo. Here, we overexpress mouse Rnaseh1 (Rh1-OE) in vivo to remove accumulated R-loops in Brca1-deficient mouse mammary epithelium (BKO). R-loop removal exacerbates DNA replication stress in proliferating BKO mammary epithelial cells, with little effect on homology-directed repair of double-strand breaks following ionizing radiation. Compared to their BKO counterparts, BKO-Rh1-OE mammary glands contain fewer luminal progenitor cells but more mature luminal cells. Despite a similar incidence of spontaneous mammary tumors in BKO and BKO-Rh1-OE mice, a significant percentage of BKO-Rh1-OE tumors express ERα and progesterone receptor. Our results suggest that rather than directly elevating the overall tumor incidence, R-loops influence the mammary tumor subtype by shaping the cell of origin for Brca1 tumors.

Spontaneous tumours indogs: Aclinical and pathomorphological study inKyrgyzstan.

The aim ofthis study isto investigate the correlation between the incidence ofspontaneous tumours ofvarious origins and the localisation indogs with sex, breed, and age factors. Atotal of360tumours with various localisation were studied pathomorphologically. Histopathologic data sets from 360dog tissue samples were processed and statistically examined. Achi-square test ofindependence was conducted toexamine the relationships among the various levels ofthe specified variables. Logistic regression models were employed for dichotomous outcomes toascertain the influence ofcertain explanatory variables onthe tumour types. Characteristic pathomorphological changes observed during examination ofdogs with oncologic diseases were determined. The most common neoplasms were mammary tumours, accounting for 43% ofthe cases. The mammary gland tumours were most common inmongrel dogs (25%), with German Shepherds (17.3%), Poodles, Dachshunds, Central Asian Shepherds (6.7% each), and Rottweilers (5.7%) following. The highest frequency ofthese tumours appeared at8years ofage, predominantly originating from the ductal epithelium, which represented 46.4% ofall the malignant cases.

Abstract 2440: Cancer driver mutations as quantitative biomarkers of cancer risk interspecies analyses using CarcSeq

Abstract Unmet needs in cancer risk assessment include the ability to predict rodent life-time tumor responses from short-term exposures and a scientific basis for rodent to human extrapolation. As an approach to address these needs, the use of hotspot cancer driver mutations (CDMs) as biomarkers of cancer risk was integrated with an error-corrected, next generation sequencing (NGS) approach. We have developed and investigated the sensitivity of a high-throughput NGS method capable of detecting a panel of the most prevalent point mutations observed in human oncogenes and tumor suppressor genes. This method, CarcSeq, involves performing multiple, high-fidelity PCR reactions to amplify the most prevalent mutations reported to occur in human tumors, tagging the amplicons with 9 bp unique identifier sequences at each end, constructing libraries using Illumina ChIP Seq kits, sequencing the libraries on an Illumina NextSeq500 platform and generating single-strand consensus sequences (SSCS), bioinformatically, as a means of error-correction. We validated CarcSeq mutant fraction measurements through observations related to known cancer driver tissue-specificities and mutation spectra for normal human breast and lung, ductal carcinoma, and lung adenocarcinoma samples. Performance of a reconstruction experiment established CarcSeq has a sensitivity of 104. The approach has now been adapted to analyze analogous conserved codons in rat and mouse. For each of the three species, the developed panel includes 13-15 amplicons encompassing known cancer driver genes (e.g., KRAS, PIK3CA, and TP53) encompasses the equivalent of 30 known human hotspot codons and has a combined target sequence length of ~1 kb. Amplicons were generated from DNA isolated from 16-week-old, untreated rodent tissue samples with known differences in spontaneous tumor incidence: female Wistar, Sprague Dawley, and F344 rat mammary samples and male and female B6C3F1 and CD-1 mouse lung samples. The rodent panel was optimized to generate ~100,000 SSCS/amplicon. CDMs were observed at conserved codons in young, untreated rodents, and results are consistent with what was expected based on strain differences in spontaneous tumorigenesis. Citation Format: Kelly L. Harris, Binsheng Gong, Barbara Parsons, Jennifer Faske, Joshua Xu. Cancer driver mutations as quantitative biomarkers of cancer risk interspecies analyses using CarcSeq [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2440.

Incidence of spontaneous tumours in guinea pigs: a retrospective study of 153 cases

The aim of this study was to investigate the incidence of spontaneous tumours in guinea pigs in biopsy and necropsy samples in the monitored period (2016–2022) on a representative number of cases and to determine their occurrence in relation to age and sex of the animals. A total of 204 samples from various pathological lesions were examined, while 153 cases (75.00%) were true tumours and 51 cases (25.00%) were pseudotumorous non-neoplastic lesions. The distribution of the incidence of true neoplasms in relation to sex was uneven. In the examined group, more neoplasms were diagnosed in males (n = 88, 57.52%) compared to females (n = 65, 42.48%). The mean age of guinea pigs with diagnosed tumour in our group was 4.2 years. Thyroid adenocarcinoma was the most frequent tumour. The majority of thyroid tumours (67.86%) were diagnosed in animals aged 4–5 years, as a significant result in terms of incidence in this age range, as well as a predisposition to tumour formation in males (78.57%). Mammary gland tumours occurred in the age range of 2–7 years, with a mean age of incidence of 4.7 years. In all cases, these were malignant variants and showing a significant higher incidence in males, in the age range of 4–5 years. The processing of a representative number of samples and epidemiological data on the incidence of spontaneous tumours in guinea pigs can contribute to the overall expansion of knowledge about this topic in veterinary medicine.

Aberrant expression and localization of the RAP1 shelterin protein contribute to age-related phenotypes.

Short telomeres induce a DNA damage response (DDR) that evokes apoptosis and senescence in human cells. An extant question is the contribution of telomere dysfunction-induced DDR to the phenotypes observed in aging and telomere biology disorders. One candidate is RAP1, a telomere-associated protein that also controls transcription at extratelomeric regions. To distinguish these roles, we generated a knockin mouse carrying a mutated Rap1, which was incapable of binding telomeres and did not result in eroded telomeres or a DDR. Primary Rap1 knockin embryonic fibroblasts showed decreased RAP1 expression and re-localization away from telomeres, with an increased cytosolic distribution akin to that observed in human fibroblasts undergoing telomere erosion. Rap1 knockin mice were viable, but exhibited transcriptomic alterations, proinflammatory cytokine/chemokine signaling, reduced lifespan, and decreased healthspan with increased body weight/fasting blood glucose levels, spontaneous tumor incidence, and behavioral deficits. Taken together, our data present mechanisms distinct from telomere-induced DDR that underlie age-related phenotypes.

Abstract 3141: Toll-like receptor 4 knockout promotes cutaneous tumorigenesis in mice lack of Ikka heterozygous loss in keratinocytes

Abstract Role of recognizing pathogen-associated molecular patterns in skin carcinogenesis has not been extensively studied. Toll-like receptor 4 (TLR4) recognizes gram-negative lipopolysaccharide. To explore the impact of interplay between TLR4-regulated microbiota and host epithelial cells on tumorigenesis, we adopted a mouse model that expresses hemizygous Ikkα gene induced by a keratin 5 Cre (K5.Cre, IkkααKC/+). IkkααKC mice die within 3 weeks after birth. Inducible Ikkα ablation mediated by K15.CrePR1 or K5.CreER results in spontaneous skin tumors. We found an increased incidence of spontaneous skin tumors in Tlr4-/-;IkkααKC/+ mice compared to Tlr4-/- or IkkααKC/+ mice. We detected markedly elevated bacteria numbers on the surface of skin tumors compared to the adjacent skin. Interestingly, the oral cavity of Tlr4-/-;IkkααKC/+ mice showed an elevated proportion of gram-negative bacteria compared to Tlr4-/- or IkkααKC/+ mice. To further determine the effect of bone marrow (BM)-derived hemopoietic cells on tumorigenesis, we performed BM transplant experiments. IkkααKC/+ mice with Tlr4-/- BM developed more cutaneous skin tumors than IkkααKC/+ mice with WT BM. Based on these findings, we hypothesized that Tlr4-/- hemopoietic cells regulate microbiota, which further results in altered skin carcinogenesis. We are revealing the detailed mechanism of how Tlr4-/- hemopoietic cells contribute to microbiota changes and tumorigenic promotion. Citation Format: Amit Kumar Singh. Toll-like receptor 4 knockout promotes cutaneous tumorigenesis in mice lack of Ikka heterozygous loss in keratinocytes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3141.

Regulatory Experience Assessing the Carcinogenic Potential of a Monoclonal Antibody Inhibiting PCSK9, Bococizumab, Including a 2-Year Carcinogenicity Study in Rats.

Bococizumab is an anti-PCSK9 monoclonal antibody that was intended for the treatment of hypercholesterolemia. After reviewing the 6-month rat toxicity study data, in which there was a low spontaneous tumor incidence, unrelated to bococizumab administration, the U.S. FDA granted a carcinogenicity waiver request based on a weight-of-evidence assessment of low carcinogenic risk. Subsequently, after reviewing 6-month rat toxicity study data from another anti-PCSK9 antibody, RN317, with a similar low tumor incidence (unrelated to RN317), the U.S. FDA rescinded the bococizumab carcinogenicity study waiver and requested a full 2-year rat carcinogenicity study be conducted. The resulting 2-year carcinogenicity study demonstrated no bococizumab-related increase in tumors, confirming the weight-of-evidence evaluation and alleviating concerns regarding the carcinogenic potential. Here we report the scientific and regulatory background that led to the request for a rat carcinogenicity study, the feedback on the design of the carcinogenicity study, and the results from this study which affirmed the original weight-of-evidence assessment of low carcinogenic risk.

Tpl2 kinase regulates inflammation but not tumorigenesis in mice

Tumor progression locus 2 (Tpl2, gene name MAP3K8), a mitogen-activated protein kinase, is widely expressed in immune and non-immune cells to integrate tumor necrosis factor (TNF), toll-like receptors (TLRs), and interleukin-1 (IL1) receptor signaling to regulate inflammatory response. Given its central role in inflammatory response, Tpl2 is an attractive small molecule drug target. However, the role of Tpl2 as an oncogene or tumor suppressor gene remains controversial, and its function outside immune cells is not understood. We therefore utilized a Tpl2 kinase dead (Tpl2-KD) mouse model in an 18-month aging study to further elucidate Tpl2 effects on lifespan and chronic disease. Histopathological studies revealed the incidence and severity of spontaneous tumors and non-neoplastic lesions were comparable between wild type and Tpl2-KD mice. The only finding was that male Tpl2-KD mice had higher bodyweight and an increased incidence of liver steatosis, suggesting a sex-specific role for Tpl2 in hepatic lipid metabolism. In conclusion, loss of Tpl2 kinase activity did not lead to increased tumorigenesis over aging in mice but affected likely alterations in lipid metabolism in male animals.

Analysis of β-catenin gene mutations and gene expression in liver tumours of C57BL/10J mice produced by chronic administration of sodium phenobarbital

In this study liver tumours produced in male and female mice of the low spontaneous liver tumour incidence C57BL/10J strain treated for 99 weeks with 1000 ppm in the diet with the model constitutive androstane receptor (CAR) activator sodium phenobarbital (NaPB) were analysed for β-catenin mutations by Western immunoblotting and DNA/RNA analysis. Some gene array analysis was also performed to identify genes involved in CAR activation and in β-catenin and Hras gene mutations. Analysis of 8 male and 2 female NaPB-induced liver tumour samples (comprising 2 adenomas, 6 carcinomas and 2 samples containing separate adenomas and carcinomas) revealed truncated β-catenin forms in just 4 male liver tumour samples, with the presence of the truncated β-catenin forms being confirmed by β-catenin exon 1–3 mutation analysis. Microarray gene expression analysis was performed with three of the NaPB-induced male mouse liver tumour samples where β-catenin mutations had not been identified by Western immunoblotting and DNA/RNA analysis and with three liver samples from both NaPB-induced non-tumour tissue and control animals. Treatment with NaPB resulted in induction of Cyp2b subfamily gene expression in both NaPB-induced mouse liver tumours and in NaPB-treated non-tumour tissue. In addition, the gene expression analysis demonstrated that the β-catenin and Hras pathways were not modified in NaPB-induced mouse liver tumours not exhibiting truncated β-catenin forms. Overall, while chronic administration of the model CAR activator NaPB results in both hepatocellular adenoma and carcinoma in the low spontaneous liver tumour incidence C57BL/10J mouse strain, only 40 % of the liver tumours evaluated in this study had β-catenin mutations. These results are in agreement with previous studies with the CAR activator oxazepam and demonstrate that mouse liver tumours induced by nongenotoxic CAR activators in the absence of initiation with a genotoxic agent are due to a number of mechanisms, including those largely independent of either the Wnt/β-catenin signalling pathway or Hras oncogene mutations.

Diverse tumour susceptibility in Collaborative Cross mice: identification of a new mouse model for human gastric tumourigenesis

ObjectiveThe Collaborative Cross (CC) is a mouse population model with diverse and reproducible genetic backgrounds used to identify novel disease models and genes that contribute to human disease. Since spontaneous...

The Incidence of Canine Spontaneous Tumours Diagnosed on the Basis of Cytology and Histology in Malwa Region

The Incidence of Canine Spontaneous Tumours Diagnosed on the Basis of Cytology and Histology in Malwa Region

High Background Incidence of Spontaneous Subcapsular Adrenal Gland Hyperplasia of Tg.rasH2 Mice Used in 26-week Carcinogenicity Studies.

The Tg.rasH2 model was accepted by regulatory agencies worldwide for 26-week carcinogenicity assays as an alternative to the standard 2-year assays in conventional mice in 2003. Several references documenting spontaneous nonneoplastic findings and incidences of spontaneous tumors in the Tg.rasH2 mice have been published. The purpose of this publication is to add adrenal gland subcapsular hyperplasia to the database pertaining to spontaneous lesions noted in Tg.rasH2 mice, review physiology related to this finding, and discuss its significance. The incidence of spontaneous subcapsular adrenal gland hyperplasia was determined in control Tg.rasH2 mice from nine 26-week carcinogenicity studies carried out within the last 5 years at two contract research organizations. Incidence of this finding ranged from 56% to 79% in males and 88% to 100% in females, with an incidence average of 62% in males and 93% in females. Adrenal gland subcapsular hyperplasia is a common finding in male and female Tg.rasH2 mice that did not progress to neoplasia in Tg.rasH2 mice. In general, it tends to be more frequent and severe in females in comparison to males.

Pathologic changes of spontaneous tumors in Sprague-Dawley and Wistar rats

Objective: To investigate the spontaneous neoplastic lesions and their incidences in Sprague-Dawley (SD) and Wistar rats, and to accumulate background data for carcinogenicity studies. Methods: One hundred and eighty SD rats and 240 Wistar rats (4-week old) , half in each sex, were used in this study. The rats were housed routinely under specific pathogen-free environment and euthanized after 104 weeks. Histopathological examination was undertaken for all animals including deaths and scheduled euthanasia. The types and incidences of spontaneous tumors were gathered statistically. Results: Total 411 rats (176 SD rats and 235 Wistar rats) were examined in this study. The total tumor incidence of the 411 rats was 57.7%(237/411). The total tumor incidence in SD rats was 55.7%(98/176), benign tumor incidence was 48.9%(86/176) and malignant tumor incidence was 15.9%(28/176). The total tumor incidence in Wistar rats was 59.1%(139/235), benign tumor incidence was 51.5%(121/235) and malignant tumor incidence was 14.5%(34/235). The main benign tumors were pituitary adenoma (23.3% in SD rats, 12.3% in Wistar rats), breast fibroadenoma (21.3% in SD rats, 12.9% in Wistar rats) and breast adenoma (16.9% in SD rats, 9.5% in Wistar rats) in females; testis Leydig cell tumor (0 in SD rats, 14.3% in Wistar rats) in males. The main malignant tumors were breast carcinoma (10.1% in SD rats, 3.4% in Wistar rats) and uterine leiomyosarcoma (0 in SD rats, 2.6% in Wistar rats) in females; squamous cell carcinoma of skin (2.3% in SD rats, 0.9% in Wistar rats); subcutaneous fibrosarcoma (1.1% in SD rats, 2.1% in Wistar rats); brain malignant glioma (1.1% in SD rats, 1.7% in Wistar rats). Conclusions: In the study, a high incidence of spontaneous tumors is reported in both SD and Wistar rats housed for 2 years. The incidence of benign tumors is higher than that of malignant rumors. The benign tumors mainly are pituitary adenoma, breast fibroadenoma and breast adenoma in females, and testis Leydig cell tumor in males. The malignant tumors mainly are breast carcinoma and some soft tissue sarcomas. The results of the study enrich the data of spontaneous tumor in SD and Wisar rats and provide background data for carcinogenicity studies for new drugs.

Phenozan, a Synthetic Phenolic Antioxidant, Inhibits the Development of Spontaneous Tumors in Rats and Mice

Synthetic phenolic antioxidant β-(4-hydroxy-3,5-di-tert-butylphenyl) propionic acid, named phenozan, is a potential antiepileptic drug. In pre-clinical trials this substance did not manifest any toxicity, and also inhibited the development of some spontaneous tumors in animals. The purpose of this study was to evaluate inhibiting effect of phenozan on spontaneous carcinogenesis in rats and mice. In experiments with rats LIO and mice SHR of local breeding, with high spontaneous tumor incidence, phenozan was dissolved in sunflower oil and administered by gavage in therapeutic dose 5 mg/kg 3 times per week for 18 months. There were no any signs of toxicity and differences in weight of animals during the phenozan treatment compared with the control (sunflower oil). Phenozan significantly reduced the overall incidence and multiplicity of all tumors but only multiplicity of malignant tumors, compared with the control. Moreover a significant decrease of overall incidence and multiplicity was observed in pituitary and breast tumors in females and only overall multiplicity of tumors of pituitary and lymphoid tissue in males. In mice phenozan reduced overall incidence and multiplicity of lung tumors (in females) and also overall multiplicity of all tumors (in females) and only malignant tumors (in males). These findings allow us to classify phenozan as anticarcinogenic agent. Anticarcinogenic activity of phenozan is important because clinical study of this drug as the possible antiepileptic drug goes along and it is known that such drugs are designed for long-term use.

Quantitative analysis by next generation sequencing of hematopoietic stem and progenitor cells (LSK) and of splenic B cells transcriptomes from wild-type and Usp3-knockout mice.

The data described here provide genome-wide expression profiles of murine primitive hematopoietic stem and progenitor cells (LSK) and of B cell populations, obtained by high throughput sequencing. Cells are derived from wild-type mice and from mice deficient for the ubiquitin-specific protease 3 (USP3; Usp3Δ/Δ). Modification of histone proteins by ubiquitin plays a crucial role in the cellular response to DNA damage (DDR) (Jackson and Durocher, 2013) [1]. USP3 is a histone H2A deubiquitinating enzyme (DUB) that regulates ubiquitin-dependent DDR in response to DNA double-strand breaks (Nicassio et al., 2007; Doil et al., 2008) [2], [3]. Deletion of USP3 in mice increases the incidence of spontaneous tumors and affects hematopoiesis [4]. In particular, Usp3-knockout mice show progressive loss of B and T cells and decreased functional potential of hematopoietic stem cells (HSCs) during aging. USP3-deficient cells, including HSCs, display enhanced histone ubiquitination, accumulate spontaneous DNA damage and are hypersensitive to ionizing radiation (Lancini et al., 2014) [4]. To address whether USP3 loss leads to deregulation of specific molecular pathways relevant to HSC homeostasis and/or B cell development, we have employed the RNA-sequencing technology and investigated transcriptional differences between wild-type and Usp3Δ/Δ LSK, naïve B cells or in vitro activated B cells. The data relate to the research article “Tight regulation of ubiquitin-mediated DNA damage response by USP3 preserves the functional integrity of hematopoietic stem cells” (Lancini et al., 2014) [4]. The RNA-sequencing and analysis data sets have been deposited in NCBI׳s Gene Expression Omnibus (Edgar et al., 2002) [5] and are accessible through GEO Series accession number GSE58495 (http://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE58495). With this article, we present validation of the RNA-seq data set through quantitative real-time PCR and comparative analysis.

Spontaneous tumor development in bone marrow-rescued DNA-PKcs(3A/3A) mice due to dysfunction of telomere leading strand deprotection.

Phosphorylation of the DNA-dependent protein kinase catalytic subunit (DNA-PKcs) at the Thr2609 cluster is essential for its complete function in DNA repair and tissue stem cell homeostasis. This phenomenon is demonstrated by congenital bone marrow failure occurring in DNA-PKcs3A/3A mutant mice, which require bone marrow transplantation (BMT) to prevent early mortality. Surprisingly, an increased incidence of spontaneous tumors, especially skin cancer, was observed in adult BMT-rescued DNA-PKcs3A/3A mice. Upon further investigation we found that spontaneous γH2AX foci occurred in DNA-PKcs3A/3A skin biopsies and primary keratinocytes and that these foci overlapped with telomeres during mitosis, indicating impairment of telomere replication and maturation. Consistently, we observed significantly elevated frequencies of telomere fusion events in DNA-PKcs3A/3A cells as compared to wild type and DNA-PKcs knockout cells. In addition, a previously identified DNA-PKcs Thr2609Pro mutation, found in breast cancer, also induces a similar impairment of telomere leading end maturation. Taken together, our current analyses indicate that the functional DNA-PKcs T2609 cluster is required to facilitate telomere leading strand maturation and prevention of genomic instability and cancer development.

Impairment of the non-homologous end joining and homologous recombination pathways of DNA double strand break repair: Impact on spontaneous and radiation-induced mammary and intestinal tumour risk in Apcmin/+ mice

Female Apcmin/+ mice carrying the BALB/c variant of Prkdc or heterozygous knockout for Xrcc2, were sham- or 2Gy X-irradiated as adults to compare the effect of mild impairments of double–strand break (DSB) repair pathways, non-homologous end joining (NHEJ) and homologous recombination (HR) respectively on spontaneous and radiation–induced mammary and intestinal tumorigenesis. Mice with impaired NHEJ showed no difference in incidence of spontaneous mammary tumours, compared with matched controls, (2.46 fold, P=0.121) and significantly less following irradiation (radiation–induced excess; 0.35 fold, P=0.008). In contrast mice with impaired HR presented with significantly less spontaneous mammary tumours than matched controls (0.33 fold, P=0.027) and significantly more following irradiation (radiation-induced excess; 3.3 fold, P=0.016). Spontaneous and radiation-induced intestinal adenoma multiplicity in the same groups were significantly greater than matched controls for mice with impaired NHEJ (sham; 1.29 fold, P<0.001, radiation–induced excess; 2.55 fold, P<0.001) and mice with impaired HR showed no significant differences (sham; 0.92 fold, P=0.166, radiation-induced excess; 1.16, P=0.274). Genetic insertion events were common in spontaneous tumours from NHEJ impaired mice compared with matched controls. γH2AX foci analysis suggests a significantly faster rate of DSB repair (MANOVA P<0.001) in intestinal than mammary tissue; apoptosis was also higher in irradiated intestine.To conclude, results suggest that pathway of choice for repair of spontaneous and radiation-induced DSBs is influenced by tissue type. NHEJ appears to play a greater role in DSB repair in intestinal tissue since impairment by functional change of Prkdc significantly increases the rate of mis-repair in intestinal but not mammary tissue. HR appears to play a greater role in DSB repair in adult mammary tissue since impaired HR results in significant changes in mammary but not in the intestinal tumorigenesis. This indicates that early DNA damage response and repair is important for cancer susceptibility and plays a role in determining tissue specificity of cancer risk.

Biological relevance of decamethylcyclopentasiloxane (D5) induced rat uterine endometrial adenocarcinoma tumorigenesis: Mode of action and relevance to humans

Decamethylcyclopentasiloxane (D5) is a cyclic siloxane used in the production and formulation of consumer products with potential exposure to manufacturing workers, consumer, and the general public. Following a combined 2-year inhalation chronic bioassay performed in Fischer 344 (F344) rats, an increase in uterine endometrial adenocarcinomas was noted at the highest concentration to which animals were exposed. No other neoplasms were detected. In this study, a dose of 160 ppm produced an incidence of 8% endometrial adenocarcinomas. Based on a number of experimental studies with D5, the current manuscript examines the biological relevance and possible modes of action for the uterine endometrial adenocarcinomas observed in the rat following chronic exposure to D5. Variable rates of spontaneous uterine endometrial adenocarcinomas have been reported for untreated F344 CrlBr rats. As such, we concluded that the slight increase in uterine endometrial adenocarcinomas observed in the D5 chronic bioassay might not be the result of D5 exposure but may be related to variability of the spontaneous tumor incidence in this strain of rat. However, if the uterine endometrial adenocarcinomas are related to D5-exposure, alteration in the estrous cycle in the aging F344 rat is the most likely mode of action. D5 is not genotoxic or estrogenic. The alteration in the estrous cycle is caused by a decrease in progesterone with an increase in the estrogen:progesterone ratio most likely induced by a decrease in prolactin concentration. Available data support that exposure to D5 influences prolactin concentration. Although the effects on prolactin concentrations in a number of experiments were not always consistent, the available data support the conclusion that D5 is acting via a dopamine receptor agonist-like mechanism to alter the pituitary control of the estrous cycle. In further support of this mode of action, studies in F344 aged animals showed that the effects of D5 on estrous cyclicity produced a response consistent with a dopamine-like effect and further suggest that D5 is accelerating the aging of the reproductive endocrine system in the F344 rat utilized in this study. This mode of action for uterine endometrial adenocarcinoma tumorigenesis is not relevant for humans.

The role of TGFBI (βig-H3) in gastrointestinal tract tumorigenesis.

BackgroundTGFβ-induced (TGFBI/βig-H3) is a protein inducible by TGFβ1 and secreted by many types of cells. It binds to collagen, forms part of the extracellular matrix (ECM), and interacts with integrins on cell surfaces. In this study, we investigated the role of TGFBI in tumorigenesis and the underlying mechanisms.MethodsPatient serum TGFBI levels were determined by ELISA. TGFBI transgenic and gene knockout mice and TGFBI-overexpressing liver cells were used for mechanistic studies.ResultsWe demonstrated that patients with cholangiocarcinomas, hepatic carcinomas or gastric carcinomas presented significantly elevated serum TGFBI levels, and the excess TGFBI was derived from the tumor masses. TGFBI overexpression in mice resulted in increased incidence of spontaneous tumors and N,N-diethylnitrosamine (DEN)-induced liver tumor nodules, compared to that in wild type (WT) mice, while TGFBI knockout mice were comparable to WT controls in these 2 aspects. TGFBI promoted the survival of Aml-12 liver cells with DNA damage after irradiation, and augmented their post-irradiation proliferation. It activated the FAK/AKT/AKT1S1/PRS6/EIF4EBP pathway, which is known to modulate cell survival and proliferation.ConclusionsOur data suggest that TGFBI functions as a promoter of certain gastrointestinal tract cancers. It provides a survival advantage to cells with DNA damage. Over a long time span, this advantage could translate into increased tumor risks.

Background data of spontaneous tumors in F344/DuCrlCrlj rats

We investigated the 2-year survival rate and incidence of spontaneous tumors in F344/DuCrlCrlj rats used in carcinogenicity studies of chemical substances. Records for animals used in the control groups of carcinogenicity studies which were conducted during the last 10 years were obtained from the database of the Japan Bioassay Research Center (JBRC). Six hundred ninety-nine males and 550 females were used in 14 and 11 inhalation studies, respectively, and 500 animals of each sex were used in 10 male and 10 female oral studies. In each study, SPF (specific pathogen free) animals were housed for 2 years (104 weeks) as control groups in the carcinogenicity studies. All animals underwent necropsy and histopathological examination. Each study was conducted in accordance with the Good Laboratory Practice. The incidence of interstitial cell tumors was highest in both inhalation studies and oral studies (inhalation studies 86.1%, oral studies 68.6%). Tumors which had an incidence of 6% or higher were adenoma of the pituitary, C-cell adenoma of the thyroid, and mononuclear cell leukemia (LGL leukemia) of the spleen in male and female rats; fibroma of the subcutaneous tissue, adrenal pheochromocytoma, and islet cell adenoma of the pancreas in male rats; and endometrial stromal polyps and fibroadenoma of the mammary gland in female rats. Tumors other than the above had rare incidence rates. A clear difference in the incidence of spontaneous tumors was not observed between the inhalation and oral studies. The incidences of spontaneous tumors in control groups of previous oral studies are similar to our findings. There are no other reports of the spontaneous tumor incidence in the control groups of inhalation studies using F344/DuCrlCrlj rats. The 2-year survival rate was about 77% in both the inhalation and oral studies, and a gender difference was not observed. The F344/DuCrlCrlj rats used at JBRC had a higher 2-year survival rate than F344/N rats. This difference is possibly due to the low incidence of LGL leukemia in the F344/DuCrlCrlj rat. The incidences of spontaneous tumors in F344/DuCrlCrlj rats used in control groups of both inhalation and oral studies during the last 10 years at JBRC are similar to each other and similar to those reported in other studies. This is the first report on the incidence of spontaneous tumors in inhalation studies and contributes to the toxicological evaluation of studies using F344/DuCrlCrlj rats.