Number Of Small Intestinal Tumors Research Articles

Intraepithelial Lymphocytes Suppress Intestinal Tumor Growth by Cell-to-Cell Contact via CD103/E-Cadherin Signal.

Background & AimsThe reason why small intestinal cancer is rarer than colorectal cancer is not clear. We hypothesized that intraepithelial lymphocytes (IELs), which are enriched in the small intestine, are the closest immune cells to epithelial cells, exclude tumor cells via cell-to-cell contact.MethodsWe developed DPE-green fluorescent protein (DPE-GFP) × adenomatous polyposis coli; multiple intestinal neoplasia (APCmin ) mice, which is a T-cell–reporter mouse with spontaneous intestinal tumors. We visualized the dynamics of IELs in the intestinal tumor microenvironment and the interaction between IELs and epithelial cells, and the roles of cell-to-cell contact in anti-intestinal tumor immunity using a novel in vivo live-imaging system and a novel in vitro co-culture system.ResultsIn the small intestinal tumor microenvironment, T-cell movement was restricted around blood vessels and the frequency of interaction between IELs and epithelial cells was reduced. Genetic deletion of CD103 decreased the frequency of interaction between IELs and epithelial cells, and increased the number of small intestinal tumors. In the co-culture system, wild-type IELs expanded and infiltrated to intestinal tumor organoids from APCmin mice and reduced the viability of them, which was cell-to-cell contact and CD103 dependent.ConclusionsThe abundance of IELs in the small intestine may contribute to a low number of tumors, although this system may not work in the colon because of the sparseness of IELs. Strategies to increase the number of IELs in the colon or enhance cell-to-cell contact between IELs and epithelial cells may be effective for the prevention of intestinal tumors in patients with a high cancer risk.

DNMT3B Oncogenic Activity in Human Intestinal Cancer Is Not Linked to CIMP or BRAFV600E Mutation.

SummaryApproximately 10% of human colorectal cancer (CRC) are associated with activated BRAFV600E mutation, typically in absence of APC mutation and often associated with a CpG island methylator (CIMP) phenotype. To protect from cancer, normal intestinal epithelial cells respond to oncogenic BRAFV600E by activation of intrinsic p53 and p16-dependent tumor suppressor mechanisms, such as cellular senescence. Conversely, CIMP is thought to contribute to bypass of these tumor suppressor mechanisms, e.g. via epigenetic silencing of tumor suppressor genes, such as p16. It has been repeatedly proposed that DNMT3B is responsible for BRAFV600E-induced CIMP in human CRC. Here we set out to test this by in silico, in vitro, and in vivo approaches. We conclude that although both BRAFV600E and DNMT3B harbor oncogenic potential in vitro and in vivo and show some evidence of cooperation in tumor promotion, they do not frequently cooperate to promote CIMP and human intestinal cancer.

HuR Small-Molecule Inhibitor Elicits Differential Effects in Adenomatosis Polyposis and Colorectal Carcinogenesis.

HuR is an RNA-binding protein implicated in immune homeostasis and various cancers, including colorectal cancer. HuR binding to AU-rich elements within the 3' untranslated region of mRNAs encoding oncogenes, growth factors, and various cytokines leads message stability and translation. In this study, we evaluated HuR as a small-molecule target for preventing colorectal cancer in high-risk groups such as those with familial adenomatosis polyposis (FAP) or inflammatory bowel disease (IBD). In human specimens, levels of cytoplasmic HuR were increased in colonic epithelial cells from patients with IBD, IBD-cancer, FAP-adenoma, and colorectal cancer, but not in patients with IBD-dysplasia. Intraperitoneal injection of the HuR small-molecule inhibitor MS-444 in AOM/DSS mice, a model of IBD and inflammatory colon cancer, augmented DSS-induced weight loss and increased tumor multiplicity, size, and invasiveness. MS-444 treatment also abrogated tumor cell apoptosis and depleted tumor-associated eosinophils, accompanied by a decrease in IL18 and eotaxin-1. In contrast, HuR inhibition in APCMin mice, a model of FAP and colon cancer, diminished the number of small intestinal tumors generated. In this setting, fecal microbiota, evaluated by 16S rRNA gene amplicon sequencing, shifted to a state of reduced bacterial diversity, with an increased representation of Prevotella, Akkermansia, and Lachnospiraceae Taken together, our results indicate that HuR activation is an early event in FAP-adenoma but is not present in IBD-dysplasia. Furthermore, our results offer a preclinical proof of concept for HuR inhibition as an effective means of FAP chemoprevention, with caution advised in the setting of IBD. Cancer Res; 77(9); 2424-38. ©2017 AACR.

Genetically and dietary induced obesity associate differently with gut microbiota in a murine intestinal tumorigenesis model

Background: Overweight and obesity are risk factors for human colorectal cancer. Growing evidence suggests that the gut microbiome affects both obesity and cancer. In this study, we examined how the murine microbiota composition correlated with obesity, intestinal tumorigenesis, glucose regulation, and inflammation. Materials and Methods: We used 16S ribosomal RNA gene analyses of feces and data obtained from a double-mutant mouse model; multiple intestinal neoplasia (Min), mice, which spontaneously develop intestinal tumors, crossed with obesity (ob), mice, which develop obesity, fed 10% or 45% fat diet. Results: We found that diet and genotypes imposed a major impact on the gut microbiota composition. Likewise, we found strong associations of the microbiota composition with obesity, number of small intestinal tumors, and blood glucose levels. Specifically, bacteria related to Clostridium perfringens and Lactobacillus showed strong positive associations with both dietary induced and genetically induced obesity, while Bacteroidales showed strong negative associations. Representatives of Lachnospiraceae and Peptostreptococcaceae only showed significant negative associations with genetically induced obesity and no associations with dietary induced obesity. Conclusions: We found complex associations between the microbiota and genetic background, diet, obesity, glucose levels, inflammation, and intestinal tumorigenesis. This could contribute to the lack of consensus between the results in previous studies regarding correlations of microbiota with obesity and cancer.

Daikenchuto (TU-100) Suppresses Tumor Development in the Azoxymethane and APCmin/+ Mouse Models of Experimental Colon Cancer.

Chemopreventative properties of traditional medicines and underlying mechanisms of action are incompletely investigated. This study demonstrates that dietary daikenchuto (TU-100), comprised of ginger, ginseng, and Japanese pepper effectively suppresses intestinal tumor development and progression in the azoxymethane (AOM) and APCmin/+ mouse models. For the AOM model, TU-100 was provided after the first of six biweekly AOM injections. Mice were sacrificed at 30 weeks. APCmin/+ mice were fed diet without or with TU-100 starting at 6 weeks, and sacrificed at 24 weeks. In both models, dietary TU-100 decreased tumor size. In APC min/+ mice, the number of small intestinal tumors was significantly decreased. In the AOM model, both TU-100 and Japanese ginseng decreased colon tumor numbers. Decreased Ki-67 and β-catenin immunostaining and activation of numerous transduction pathways involved in tumor initiation and progression were observed. EGF receptor expression and stimulation/phosphorylation in vitro were investigated in C2BBe1 cells. TU-100, ginger, and 6-gingerol suppressed EGF receptor induced Akt activation. TU-100 and ginseng and to a lesser extent ginger or 6-gingerol inhibited EGF ERK1/2 activation. TU-100 and some of its components and metabolites of these components inhibit tumor progression in two mouse models of colon cancer by blocking downstream pathways of EGF receptor activation. Copyright © 2016 John Wiley & Sons, Ltd.

The Intrauterine and Nursing Period Is a Window of Susceptibility for Development of Obesity and Intestinal Tumorigenesis by a High Fat Diet inMin/+Mice as Adults

We studied how obesogenic conditions during various life periods affected obesity and intestinal tumorigenesis in adult C57BL/6J-Min (multiple intestinal neoplasia)/+ mice. The mice were given a 10% fat diet throughout life (negative control) or a 45% fat diet in utero, during nursing, during both in utero and nursing, during adult life, or during their whole life-span, and terminated at 11 weeks for tumorigenesis (Min/+) or 23 weeks for obesogenic effect (wild-type). Body weight at 11 weeks was increased after a 45% fat diet during nursing, during both in utero and nursing, and throughout life, but had normalized at 23 weeks. In the glucose tolerance test, the early exposure to a 45% fat diet in utero, during nursing, or during both in utero and nursing, did not affect blood glucose, whereas a 45% fat diet given to adults or throughout life did. However, a 45% fat diet during nursing or during in utero and nursing increased the number of small intestinal tumors. So did exposures to a 45% fat diet in adult life or throughout life, but without increasing the tumor numbers further. The intrauterine and nursing period is a window of susceptibility for dietary fat-induced obesity and intestinal tumor development.

Cables1 is a tumor suppressor gene that regulates intestinal tumor progression in ApcMin mice

The transformation of colonic mucosal epithelium to adenocarcinoma requires progressive oncogene activation and tumor suppressor gene inactivation. Loss of chromosome 18q is common in colon cancer but not in precancerous adenomas. A few candidate tumor suppressor genes have been identified in this region, including CABLES1 at 18q11.2−12.1. This study investigates the role of CABLES1 in an in vivo mouse model of intestinal adenocarcinoma and in human colon cancer cell culture. ApcMin/+ mice were crossed with mice harboring targeted inactivation of the Cables1 gene (Cables1−/−). The intestinal tumor burden and tumor expression of β-catenin and PCNA was compared in Cables1+/+ApcMin/+ and Cables1−/−ApcMin/+ mice. β-catenin activity in human colon cancer cells with CABLES1 inactivation and intestinal progenitor cell function in Cables1−/− mice were assayed in vitro. The mean number of small intestinal tumors per mouse was 3.1 ± 0.6 in Cables1+/+ ApcMin/+ mice, compared with 32.4 ± 3.5 in the Cables1−/−ApcMin/+ mice (P < 0.0001). Fewer colonic tumors were observed in Cables1+/+ApcMin/+ mice (mean 0.6 ± 0.1) compared with the Cables1−/−ApcMin/+ mice (mean 1.3 ± 0.3, P = 0.01). Tumors from Cables1−/−ApcMin/+ mice demonstrated increased nuclear expression of β-catenin and an increased number of PCNA-positive cells. In vitro studies revealed that CABLES1 deficiency increased β-catenin dependent transcription and increased intestinal progenitor cell activity. Loss of Cables1 enhances tumor progression in the ApcMin/+ mouse model and activates the Wnt/β-catenin signaling pathway. Cables1 is a tumor suppressor gene on chromosome 18q in this in vivo mouse model and likely has a similar role in human colon cancer.

Abstract 4415: Intestinal tumorigenesis increased by obesity caused by leptin deficiency and/or high fat diet in ApcMin x Lepo b mice involves blood glucose dysregulation

Abstract Our objective was to study how obesity affects intestinal cancer in a double mutant mouse model obtained by intercrossing of C57BL/6J-ApcMin (multiple intestinal neoplasia)/+ and C57BL/6J-Lepob (obese)/+ mice. The Min mouse has a mutated tumor suppressor gene adenomatous polyposis coli (Apc), involved in both inherited and sporadic colorectal cancer. The obesity (ob) gene is coding for leptin, a hormone that regulates food intake and energy expenditure, leading to obesity if mutated. The offspring were given one s.c. injection of 25 mg/kg body weight (bw) of the food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) or the vehicle 0.9% NaCl on day 3-6 after birth, and were given a 10 or 45 % fat diet from weaning to termination at 11 weeks. To test the hypothesis that obesity affects intestinal cancer via dysregulation of glucose, we measured blood glucose levels at weeks 6 and 11 and did a glucose tolerance test (GTT) at week 6. Colon and small intestine were fixed in formalin and stained with methylene blue. The number, diameter and localization of spontaneous (0.9% NaCl group) and PhIP-induced tumors were scored by transillumination in an inverse light microscope. Terminal bw was significantly higher in ob/ob mice compared with both ob/wt and wt/wt mice, and in mice on 45 vs on 10% fat diet. The incidence of small intestinal tumors was 100% in all mice of Min/+ background independent of treatment, diet or ob background. PhIP significantly increased the number of colonic and small intestinal tumors. The number of small intestinal tumors was significantly higher in ob/ob mice compared with ob/wt and wt/wt mice of both genders, and increased even further in mice on 45 vs 10% fat diet. The majority of the tumors were located in the distal half of the small intestine, but in ob/ob mice additional tumors were observed in the proximal part, again increased on 45 vs 10% fat diet. The incidence, number, size or localization of the few colonic tumors present was not affected by either ob genotype or diet. The blood sugar levels at both week 6 and 11 were significantly higher in ob/ob mice compared with ob/wt and wt/wt mice of both genders, and increased even further in mice on 45 vs 10% fat diet. The GTT test showed that ob/ob mice had a much slower decrease in blood glucose seen as higher area under the curve (AUC) after challenge than ob/wt and wt/wt mice. AUC was increased further in all ob genotypes by 45% fat. For all end points, ob/wt and wt/wt mice were essentially similar. Conclusions: Obesity induced by lack of leptin hormone significantly increased small intestinal tumorigenesis in Min/+ mice, which was increased further with a high fat diet. These obese mice also had significantly increased blood sugar levels and showed slower decrease after challenge in GTT, indicating a dysregulation of glucose as a possible cause of the increased intestinal tumorigenesis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4415. doi:1538-7445.AM2012-4415

Inhibitory effects of calcium against intestinal cancer in human colon cancer cells andApcMin/+mice

The aim of the study was to investigate the inhibitory effects of calcium against intestinal cancer in vitro and in vivo. We first investigated the effects of calcium treatment in HCT116 and HT29 human colon cancer cells. At the concentration range of 0.8-2.4 mM, calcium significantly inhibited cell growth (by 9-29%), attachment (by 12-26%), invasion (by 15-31%), and migration (by 19-61%). An immunofluorescence microscope analysis showed that the treatment with calcium (1.6 mM) for 24 h increased plasma membrane β-catenin but decreased nuclear β-catenin levels in HT29 cells. We then investigated the effect of dietary calcium on intestinal tumorigenesis in ApcMin/+ mice. Mice received dietary treatment starting at 6 weeks of age for the consecutive 8 weeks. The basal control diet contained high-fat (20% mixed lipids by weight) and low-calcium (1.4 mg/g diet) to mimic the average Western diet, while the treatment diet contained an enriched level of calcium (5.2 mg calcium/g diet). The dietary calcium treatment decreased the total number of small intestinal tumors (by 31.4%; P < 0.05). The largest decrease was in tumors which were ≥ 2 mm in diameter, showing a 75.6% inhibition in the small intestinal tumor multiplicity (P < 0.001). Immunohistochemical analysis showed significantly reduced nuclear staining of β-catenin (expressed as nuclear positivity), but increased plasma membrane staining of β-catenin, in the adenomas from the calcium-treated groups in comparison to those from the control group (P < 0.001). These results demonstrate intestinal cancer inhibitory effects of calcium both in human colon cancer cells and ApcMin/+ mice. The decreased β-catenin nuclear localization caused by the calcium treatment may contribute to the inhibitory action.

Voluntary exercise inhibits intestinal tumorigenesis in Apc Min/+mice and azoxymethane/dextran sulfate sodium-treated mice

BackgroundEpidemiological studies suggest that physical activity reduces the risk of colon cancer in humans. Results from animal studies, however, are inconclusive. The present study investigated the effects of voluntary exercise on intestinal tumor formation in two different animal models, ApcMin/+ mice and azoxymethane (AOM)/dextran sulfate sodium (DSS)-treated mice.MethodsIn Experiments 1 and 2, five-week old female ApcMin/+ mice were either housed in regular cages or cages equipped with a running wheel for 6 weeks (for mice maintained on the AIN93G diet; Experiment 1) or 9 weeks (for mice on a high-fat diet; Experiment 2). In Experiment 3, male CF-1 mice at 6 weeks of age were given a dose of AOM (10 mg/kg body weight, i.p.) and, 12 days later, 1.5% DSS in drinking fluid for 1 week. The mice were then maintained on a high-fat diet and housed in regular cages or cages equipped with a running wheel for 16 weeks.ResultsIn the ApcMin/+ mice maintained on either the AIN93G or the high-fat diet, voluntary exercise decreased the number of small intestinal tumors. In the AOM/DSS-treated mice maintained on a high-fat diet, voluntary exercise also decreased the number of colon tumors. In ApcMin/+ mice, voluntary exercise decreased the ratio of serum insulin like growth factor (IGF)-1 to IGF binding protein (BP)-3 levels. It also decreased prostaglandin E2 and nuclear β-catenin levels, but increased E-cadherin levels in the tumors.ConclusionThese results indicate hat voluntary exercise inhibited intestinal tumorigenesis in ApcMin/+ mice and AOM/DSS-treated mice, and the inhibitory effect is associated with decreased IGF-1/IGFBP-3 ratio, aberrant β-catenin signaling, and arachidonic acid metabolism.

Role of nucleotide excision repair deficiency in intestinal tumorigenesis in multiple intestinal neoplasia ( Min) mice

Mice deficient in the Xeroderma pigmentosum group A ( Xpa) gene are defective in nucleotide excision repair (NER) and highly susceptible to skin carcinogenesis after dermal exposure to UV light or chemicals. Min (multiple intestinal neoplasia) mice, heterozygous for a germline nonsense mutation in the tumor suppressor gene adenomatous polyposis coli ( Apc), develop intestinal tumors spontaneously and show additional intestinal tumors after exposure to the food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5- b]pyridine (PhIP). In this study, we investigated the impact of loss of XPA function on PhIP-induced intestinal tumorigenesis in F1 offspring of Min/+ ( Apc +/−) mice crossed with Xpa gene-deficient mice. Apc +/− mice lacking both alleles of Xpa had higher susceptibility towards toxicity of PhIP, higher levels of PhIP–DNA adducts in the middle and distal small intestines, as well as in liver, and a higher number of small intestinal tumors at 11 weeks, compared with Apc +/− mice with one or two intact Xpa alleles. Localization of tumors was not affected, being highest in middle and distal small intestines in all genotypes. At 11 weeks of age, the number of spontaneous intestinal tumors was not significantly increased by homozygous loss of Xpa, but untreated Apc +/−/ Xpa −/− mice had significantly shorter life-spans than their XPA-proficient littermates. Heterozygous loss of Xpa did not affect any of the measured end points. In conclusion, the Xpa gene and the NER pathway are involved in repair of bulky PhIP–DNA adducts in the intestines and the liver, and most probably of DNA lesions leading to spontaneous intestinal tumors. These results confirm a role of the NER pathway also in protection against cancer in internal organs, additional to its well-known importance in protection against skin cancer. An effect of Apc +/− on adduct levels, additional to that of Xpa −/−, indicates that the truncated APC protein may affect a repair pathway other than NER.

Lignan Precursors From Flaxseed or Rye Bran Do Not Protect Against the Development of Intestinal Neoplasia in ApcMin Mice

Phytoestrogens, like isoflavonoids and lignans, have been postulated as possible colorectal cancer protective constituents. To investigate this hypothesis, two high-fiber sources rich in lignan precursors, i.e., rye bran and flaxseed, were tested for their ability to modulate intestinal tumor development in ApcMin mice. Test diets consisted of a control diet (a Western-style diet, adjusted for fiber and/or phytate content) supplemented with 5% flaxseed or 30% rye bran. Chemical analysis of diets and blood samples confirmed the enhanced systemic exposure of mice fed the test diets to the major lignan precursors, i.e., secoisolariciresinol and matairesinol. No statistically significant difference was observed in the incidence and multiplicity of small intestinal and colon tumors at terminal sacrifice between mice fed the control diet or the diet supplemented with 5% flaxseed. With the rye bran diet a statistically significant enhancement of the number of small intestinal tumors in female mice was observed. The number of colon tumors, however, was comparable between the control and rye bran-fed mice of either sex. Furthermore, no activating point mutations in the K-ras oncogene nor positive immunohistochemical staining for the p53 gene were observed in a set of 48 colon tumors. In conclusion, our results demonstrate that increased intake of lignan precursors from flaxseed or rye bran, administered in a Western-style diet, does not protect against intestinal tumor development in an appropriate animal model for intestinal neoplasia such as the ApcMin mice.

Neonatal exposure to the food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine via breast milk or directly induces intestinal tumors in multiple intestinal neoplasia mice.

We examined whether the food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) could increase intestinal tumorigenesis in neonatal C57BL/6J-Min/+ mice, a murine model for familial adenomatous polyposis. Min/+ mice are heterozygous for a nonsense mutation in the adenomatous polyposis coli gene and spontaneously develop multiple intestinal adenomas, primarily in the small intestine. Neonatal Min/+ mice (3-6 days old) were exposed to PhIP via breast milk from lactating dams given 8 s.c. injections of 50 mg/kg PhIP three times a week or to 8 s.c. injections of 25 or 50 mg/kg PhIP directly, over the same period. At the age of 11 weeks, the number, diameter and location of the intestinal tumors were scored. Remarkably, a 2- to 4-fold increase in the number of small intestinal tumors was seen in Min/+ mice exposed to PhIP via breast milk (P < 0.001). To our knowledge, this is the first time PhIP has been reported to induce tumors following exposure via breast milk from PhIP-exposed dams. Upon direct exposure to 50 mg/kg PhIP, a 6- to 9-fold increase in the number of small intestinal tumors was observed (P < 0.001). The diameter of the PhIP-induced small intestinal tumors was slightly increased (P < 0.001). In the colon, a 3- to 4-fold increase in the number of tumors was seen in Min/+ mice exposed to PhIP via breast milk (P = 0. 004). Direct exposure to 50 mg/kg PhIP caused a 2- to 6-fold increase in the number of colonic tumors (P = 0.014). The PhIP-induced colonic tumors were located more distally and displayed a smaller diameter than the tumors from the controls (P < 0.05). In contrast to a previous study, where PhIP showed only a moderate tumorigenic effect in adult Min/+ mice, the present study demonstrates a strong tumorigenic effect of PhIP in neonatally exposed Min/+ mice, even after exposure via breast milk from PhIP-exposed dams.

A fish oil derived concentrate enriched in eicosapentaenoic and docosahexaenoic acid as ethyl ester suppresses the formation and growth of intestinal polyps in the Min mouse.

We examined whether the n-3 polyunsaturated fatty acid ethyl ester enriched fish oil K85 (54.4% of eicosapentaenoic acid and 30.3% of docosahexaenoic acid as ethyl esters) could inhibit the intestinal tumorigenesis in Min mice, a murine model of familial adenomatous polyposis (FAP). Min mice that are heterozygous for a nonsense mutation in the Apc gene, develop spontaneously multiple intestinal neoplasms, primarily in the small intestine. K85 was dissolved in corn oil (vehicle) and mixed into the AIN-76A diet. The total oil content (K85 + corn oil) was 12% in all diets. The various experimental diets contained 0 (vehicle control), 0.4, 1.25 or 2.5% of K85. In the small intestine, the mean number of tumors/mouse was 105 +/- 18 (SEM) in control males and 70 +/- 11 in control females. Dietary K85 treatment reduced the number of small intestinal tumors: in males, the maximum reduction was 66% (P = 0.002) with 0.4% of K85; and in females, the maximum reduction was 48% (P = 0.043) with 2.5% of K85, but the inhibition was only slightly increased from 0.4% to 2.5% of K85. The mean tumor diameter was 1.33 +/- 0.08 mm in control males and 1.06 +/- 0.08 in control females, and the diameter ranged from <0.1 mm (monocryptal adenomas) to 4 mm. The small intestinal tumor diameter was reduced by K85 in a dose-dependent manner: in males, with a maximum reduction of 26% (r = -0.64, P = 0.004); and in females, with a maximum reduction of 38% (r = -0.61, P < 0.004). In the large intestine, the mean number of tumors/mouse was 1.0 +/- 0.5 in males and 0.8 +/- 0.2 in females. Although K85 treatment tended to reduce the number and diameter of the large intestinal tumors, these effects did not reach statistical significance. Aberrant crypt foci not elevated from the flat mucosa (ACF(Min)) occurring in the colon of Min mice were also scored. The mean number of ACF(Min)/colon (3.8 +/- 0.9) and the crypt multiplicity (1.49 +/- 0.28) in females were reduced by 73% (P = 0.03) and 60% (P = 0.048) with 2.5% of K85, respectively, whereas no significant effect could be observed in the males.

Short-term carcinogenicity testing of a potent murine intestinal mutagen, 2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP), in Apc1638N transgenic mice.

Transgenic Apc1638N mice, heterozygous for a targeted frameshift mutation at codon 1638 of the endogenous adenomatous polyposis coli (APC) gene, are predisposed to develop multiple adenomas and adenocarcinomas along the intestinal tract and to a number of extra-intestinal lesions including, among others, mammary tumors. We have studied these mice in a short-term carcinogenicity test with 2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP), a potent murine small intestinal mutagen and lymphomagen. Upon dietary administration of 0.03% PhIP in a short-term (6 months) study, a significantly increased number of small intestinal tumors as well as an increased number of aberrant crypt foci (ACF) were observed in male Apc+/Apc1638N mice compared with untreated transgenic mice. No differences in intestinal and mammary tumor multiplicity were observed between treated and control Apc+/Apc1638N females.

Development and characterization of an in vivo somatic mutation assay

Mice deficient in the Xeroderma pigmentosum group A (Xpa) gene are defective in nucleotide excision repair (NER) and highly susceptible to skin carcinogenesis after dermal exposure to UV light or chemicals. Min (multiple intestinal neoplasia) mice, heterozygous for a germline nonsense mutation in the tumor suppressor gene adenomatous polyposis coli (Apc), develop intestinal tumors spontaneously and show additional intestinal tumors after exposure to the food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). In this study, we investigated the impact of loss of XPA function on PhIP-induced intestinal tumorigenesis in F1 offspring of Min/+ (Apc+/−) mice crossed with Xpa gene-deficient mice. Apc+/− mice lacking both alleles of Xpa had higher susceptibility towards toxicity of PhIP, higher levels of PhIP–DNA adducts in the middle and distal small intestines, as well as in liver, and a higher number of small intestinal tumors at 11 weeks, compared with Apc+/− mice with one or two intact Xpa alleles. Localization of tumors was not affected, being highest in middle and distal small intestines in all genotypes. At 11 weeks of age, the number of spontaneous intestinal tumors was not significantly increased by homozygous loss of Xpa, but untreated Apc+/−/Xpa−/− mice had significantly shorter life-spans than their XPA-proficient littermates. Heterozygous loss of Xpa did not affect any of the measured end points. In conclusion, the Xpa gene and the NER pathway are involved in repair of bulky PhIP–DNA adducts in the intestines and the liver, and most probably of DNA lesions leading to spontaneous intestinal tumors. These results confirm a role of the NER pathway also in protection against cancer in internal organs, additional to its well-known importance in protection against skin cancer. An effect of Apc+/− on adduct levels, additional to that of Xpa−/−, indicates that the truncated APC protein may affect a repair pathway other than NER.