Intestinal tumorigenesis in Min mice is enhanced by X-irradiation in an age-dependent manner

The effects of antioxidant administration in the early stages of radiation-induced tumorigenesis

ApcMin/+ mouse was a model mouse for human familial adenomatous polyposis, and irradiation at an early age increases tumors in the small and large intestine. To study the effects of antioxidant administration on tumor incidence after continuous whole-body exposure to gamma rays, ApcMin/+ mice were exposed to a medium-dose-rate, 200 mGy/d, from postnatal Day 0 to 21 of age or a high-dose-rate of 0.65 Gy/min (total dose 4.2 Gy) on postnatal Day 7. The dams and pups were supplied with the N-acetylcysteine (NAC) in drinking water (7 g/L), from gestation Day 15 until weaning (21 days-old). A significant increase in the number of intestinal tumors were observed in ApcMin/+ mice irradiated with high dose-rate gamma rays as compared with the non-irradiated controls, but there was no significant difference in tumor counts between the non-irradiated controls and the medium-dose rate irradiation groups. NAC administration did not have any significant effect at least at this dose. These results suggest that the supplementation of anti-oxidant at the early stage of tumorigenesis does not suppress the formation of irradiation-induced small intestinal tumors.

Age-Dependent Differences in Radiation-Induced DNA Damage Responses in Intestinal Stem Cells

Age at exposure is a critical modifier of the risk of radiation-induced cancer. However, the effects of age on radiation-induced carcinogenesis remain poorly understood. In this study, we focused on tissue stem cells using Lgr5-eGFP-ires-CreERT2 mice to compare radiation-induced DNA damage responses between Lgr5+ and Lgr5- intestinal stem cells. Three-dimensional immunostaining analyses demonstrated that radiation induced apoptosis and the mitotic index more efficiently in adult Lgr5- stem cells than in adult Lgr5+ stem cells but not in infants, regardless of Lgr5 expression. Supporting this evidence, rapid and transient p53 activation occurred after irradiation in adult intestinal crypts but not in infants. RNA sequencing revealed greater variability in gene expression in adult Lgr5+ stem cells than in infant Lgr5+ stem cells after irradiation. Notably, the cell cycle and DNA repair pathways were more enriched in adult stem cells than in infant stem cells after irradiation. Our findings suggest that radiation-induced DNA damage responses in mouse intestinal crypts differ between infants and adults, potentially contributing to the age-dependent susceptibility to radiation carcinogenesis.

Combined effects of radiation and simulated microgravity on intestinal tumorigenesis in C3B6F1 ApcMin/+ mice

Explorations of the Moon and Mars are planned as future manned space missions, during which humans will be exposed to both radiation and microgravity. We do not, however, know the health effects for such combined exposures. In a ground-based experiment, we evaluated the combined effects of radiation and simulated microgravity on tumorigenesis by performing X-irradiation and tail suspension in C3B6F1 ApcMin/+ mice, a well-established model for intestinal tumorigenesis. Mice were irradiated at 2 weeks of age and underwent tail suspension for 3 or 11 weeks using a special device that avoids damage to the tail. The tail suspension treatment significantly reduced the thymus weight after 3 weeks but not 11 weeks, suggesting a transient stress response. The combination of irradiation and tail suspension significantly increased the number of small intestinal tumors less than 2 mm in diameter as compared with either treatment alone. The combined treatment also increased the fraction of malignant tumors among all small intestinal tumors as compared with the radiation-only treatment. Thus, the C3B6F1 ApcMin/+ mouse is a useful model for assessing cancer risk in a simulated space environment, in which simulated microgravity accelerates tumor progression when combined with radiation exposure.

A wild-derived inbred mouse strain, MSM/Ms, provides insights into novel skin tumor susceptibility genes

Cancer is one of the most catastrophic human genetic diseases. Experimental animal cancer models are essential for gaining insights into the complex interactions of different cells and genes in tumor initiation, promotion, and progression. Mouse models have been extensively used to analyze the genetic basis of cancer susceptibility. They have led to the identification of multiple loci that confer, either alone or in specific combinations, an increased susceptibility to cancer, some of which have direct translatability to human cancer. Additionally, wild-derived inbred mouse strains are an advantageous reservoir of novel genetic polymorphisms of cancer susceptibility genes, because of the evolutionary divergence between wild and classical inbred strains. Here, we review mapped Stmm (skintumor modifier of MSM) loci using a Japanese wild-derived inbred mouse strain, MSM/Ms, and describe recent advances in our knowledge of the genes responsible for Stmm loci in the 7,12-dimethylbenz(a)anthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA) two-stage skin carcinogenesis model.

The Japanese Wild-Derived Inbred Mouse Strain, MSM/Ms in Cancer Research

MSM/Ms is a unique inbred mouse strain derived from the Japanese wild mouse, Mus musculus molossinus, which has been approximately 1 million years genetically distant from standard inbred mouse strains mainly derived from M. m. domesticus. Due to its genetic divergence, MSM/Ms has been broadly used in linkage studies. A bacterial artificial chromosome (BAC) library was constructed for the MSM/Ms genome, and sequence analysis of the MSM/Ms genome showed approximately 1% of nucleotides differed from those in the commonly used inbred mouse strain, C57BL/6J. Therefore, MSM/Ms mice are thought to be useful for functional genome studies. MSM/Ms mice show unique characteristics of phenotypes, including its smaller body size, resistance to high-fat-diet-induced diabetes, high locomotive activity, and resistance to age-onset hearing loss, inflammation, and tumorigenesis, which are distinct from those of common inbred mouse strains. Furthermore, ES (Embryonic Stem) cell lines established from MSM/Ms allow the MSM/Ms genome to be genetically manipulated. Therefore, genomic and phenotypic analyses of MSM/Ms reveal novel insights into gene functions that were previously not obtained from research on common laboratory strains. Tumorigenesis-related MSM/Ms-specific genetic traits have been intensively investigated in Japan. Furthermore, radiation-induced thymic lymphomas and chemically-induced skin tumors have been extensively examined using MSM/Ms.

Strain difference in transgene-induced tumorigenesis and suppressive effect of ionizing radiation

Transgenic expression in medaka of the Xiphophorus oncogene xmrk, under a pigment cell specific mitf promoter, induces hyperpigmentation and pigment cell tumors. In this study, we crossed the Hd-rR and HNI inbred strains because complete genome information is readily available for molecular and genetic analysis. We prepared an Hd-rR (p53+/-, p53-/-) and Hd-rR HNI hybrid (p53+/-) fish-based xmrk model system to study the progression of pigment cells from hyperpigmentation to malignant tumors on different genetic backgrounds. In all strains examined, most of the initial hyperpigmentation occurred in the posterior region. On the Hd-rR background, mitf:xmrk-induced tumorigenesis was less frequent in p53+/- fish than in p53-/- fish. The incidence of hyperpigmentation was more frequent in Hd-rR/HNI hybrids than in Hd-rR homozygotes; however, the frequency of malignant tumors was low, which suggested the presence of a tumor suppressor in HNI genetic background fish. The effects on tumorigenesis in xmrk-transgenic immature medaka of a single 1.3 Gy irradiation was assessed by quantifying tumor progression over 4 consecutive months. The results demonstrate that irradiation has a different level of suppressive effect on the frequency of hyperpigmentation in purebred Hd-rR compared with hybrids.

Individual response of humans to ionising radiation: governing factors and importance for radiological protection

Tissue reactions and stochastic effects after exposure to ionising radiation are variable between individuals but the factors and mechanisms governing individual responses are not well understood. Individual responses can be measured at different levels of biological organization and using different endpoints following varying doses of radiation, including: cancers, non-cancer diseases and mortality in the whole organism; normal tissue reactions after exposures; and, cellular endpoints such as chromosomal damage and molecular alterations. There is no doubt that many factors influence the responses of people to radiation to different degrees. In addition to the obvious general factors of radiation quality, dose, dose rate and the tissue (sub)volume irradiated, recognized and potential determining factors include age, sex, life style (e.g., smoking, diet, possibly body mass index), environmental factors, genetics and epigenetics, stochastic distribution of cellular events, and systemic comorbidities such as diabetes or viral infections. Genetic factors are commonly thought to be a substantial contributor to individual response to radiation. Apart from a small number of rare monogenic diseases such as ataxia telangiectasia, the inheritance of an abnormally responsive phenotype among a population of healthy individuals does not follow a classical Mendelian inheritance pattern. Rather it is considered to be a multi-factorial, complex trait.

Dosimetry in Micro-computed Tomography: a Review of the Measurement Methods, Impacts, and Characterization of the Quantum GX Imaging System

Purpose

X-ray micro-computed tomography (μCT) is a widely used imaging modality in preclinical research with applications in many areas including orthopedics, pulmonology, oncology, cardiology, and infectious disease. X-rays are a form of ionizing radiation and, therefore, can potentially induce damage and cause detrimental effects. Previous reviews have touched on these effects but have not comprehensively covered the possible implications on study results. Furthermore, interpreting data across these studies is difficult because there is no widely accepted dose characterization methodology for preclinical μCT. The purpose of this paper is to ensure in vivo μCT studies can be properly designed and the data can be appropriately interpreted.

Procedures

Studies from the scientific literature that investigate the biological effects of radiation doses relevant to μCT were reviewed. The different dose measurement methodologies used in the peer-reviewed literature were also reviewed. The CT dose index 100 (CTDI₁₀₀) was then measured on the Quantum GX μCT instrument. A low contrast phantom, a hydroxyapatite phantom, and a mouse were also imaged to provide examples of how the dose can affect image quality.

Results

Data in the scientific literature indicate that scenarios exist where radiation doses used in μCT imaging are high enough to potentially bias experimental results. The significance of this effect may relate to the study outcome and tissue being imaged. CTDI₁₀₀ is a reasonable metric to use for dose characterization in μCT. Dose rates in the Quantum GX vary based on the amount of material in the beam path and are a function of X-ray tube voltage. The CTDI₁₀₀ in air for a Quantum GX can be as low as 5.1 mGy for a 50 kVp scan and 9.9 mGy for a 90 kVp scan. This dose is low enough to visualize bone both in a mouse image and in a hydroxyapatite phantom, but applications requiring higher resolution in a mouse or less noise in a low-contrast phantom benefit from longer scan times with increased dose.

Conclusions

Dose management should be considered when designing μCT studies. Dose rates in the Quantum GX are compatible with longitudinal μCT imaging.

Genotoxic effects of high dose rate X-ray and low dose rate gamma radiation in ApcMin/+ mice

Risk estimates for radiation-induced cancer in humans are based on epidemiological data largely drawn from the Japanese atomic bomb survivor studies, which received an acute high dose rate (HDR) ionising radiation. Limited knowledge exists about the effects of chronic low dose rate (LDR) exposure, particularly with respect to the application of the dose and dose rate effectiveness factor. As part of a study to investigate the development of colon cancer following chronic LDR vs. acute HDR radiation, this study presents the results of genotoxic effects in blood of exposed mice. CBAB6 F1 Apc+/+ (wild type) and ApcMin/+ mice were chronically exposed to estimated whole body absorbed doses of 1.7 or 3.2 Gy 60 Co-γ-rays at a LDR (2.2 mGy h-1 ) or acutely exposed to 2.6 Gy HDR X-rays (1.3 Gy min-1 ). Genotoxic endpoints assessed in blood included chromosomal damage (flow cytometry based micronuclei (MN) assay), mutation analyses (Pig-a gene mutation assay), and levels of DNA lesions (Comet assay, single-strand breaks (ssb), alkali labile sites (als), oxidized DNA bases). Ionising radiation (ca. 3 Gy) induced genotoxic effects dependent on the dose rate. Chromosomal aberrations (MN assay) increased 3- and 10-fold after chronic LDR and acute HDR, respectively. Phenotypic mutation frequencies as well as DNA lesions (ssb/als) were modulated after acute HDR but not after chronic LDR. The ApcMin/+ genotype did not influence the outcome in any of the investigated endpoints. The results herein will add to the scant data available on genotoxic effects following chronic LDR of ionising radiation. Environ. Mol. Mutagen. 58:560-569, 2017. © 2017 The Authors Environmental and Molecular Mutagenesis published by Wiley Periodicals, Inc. on behalf of Environmental Mutagen Society.

Ionizing radiation, inflammation, and their interactions in colon carcinogenesis in Mlh1-deficient mice

Genetic, physiological and environmental factors are implicated in colorectal carcinogenesis. Mutations in the mutL homolog 1 (MLH1) gene, one of the DNA mismatch repair genes, are a main cause of hereditary colon cancer syndromes such as Lynch syndrome. Long-term chronic inflammation is also a key risk factor, responsible for colitis-associated colorectal cancer; radiation exposure is also known to increase colorectal cancer risk. Here, we studied the effects of radiation exposure on inflammation-induced colon carcinogenesis in DNA mismatch repair-proficient and repair-deficient mice. Male and female Mlh1^−/− and Mlh1^+/+ mice were irradiated with 2 Gy X-rays when aged 2 weeks or 7 weeks and/or were treated with 1% dextran sodium sulfate (DSS) in drinking water for 7 days at 10 weeks old to induce mild inflammatory colitis. No colon tumors developed after X-rays and/or DSS treatment in Mlh1^+/+ mice. Colon tumors developed after DSS treatment alone in Mlh1^−/− mice, and exposure to radiation prior to DSS treatment increased the number of tumors. Histologically, colon tumors in the mice resembled the subtype of well-to-moderately differentiated adenocarcinomas with tumor-infiltrating lymphocytes of human Lynch syndrome. Immunohistochemistry revealed that expression of both p53 and β-catenin and loss of p21 and adenomatosis polyposis coli proteins were observed at the later stages of carcinogenesis, suggesting a course of molecular pathogenesis distinct from typical sporadic or colitis-associated colon cancer in humans. In conclusion, radiation exposure could further increase the risk of colorectal carcinogenesis induced by inflammation under the conditions of Mlh1 deficiency.

Inflammation enhanced X-irradiation-induced colonic tumorigenesis in the Min mouse

Inflammation is potential risk factor of various human malignancies. Inflammatory bowel syndromes such as ulcerative colitis are well known as risk factors for colon cancer. Here, we examined enhancing effects of dextran sulfate sodium (DSS)-associated inflammation on X-irradiation induced colonic tumorigenesis in Min and wild-type (WT) mice. Animals were X-irradiated at 1.5 Gy at 5 weeks of age (at 0 experimental week) and 2% DSS in drinking water was administered at 5 or 11 experimental weeks. Mice were sacrificed at 16 weeks and incidence and multiplicity of colonic tumors were assessed. Incidence of colonic tumors in Min mouse was increased from 33.3% to 100% (p<0.05) with X-irradiation alone, whereas no tumors were developed in WT mice. In DSS-treated Min mice, X-irradiation increased the number of colonic tumors. Total number of colonic tumors was increased 1.57 times to 30.7±3.83 tumors/mouse with X-irradiation+DSS at 5 weeks comapared to 19.6±2.9 in corresponding DSS alone group (p<0.05). When the duration of inflammation was compared, longer period of DSS effect promoted more colonic tumorigenesis. Collectively, we conclude that X-irradiation and DSS-induced inflammation act synergistically for colonic tumorigenesis.

High-incidence spontaneous tumors in JF1/Ms mice: relevance of hypomorphic germline mutation and subsequent promoter methylation of Ednrb

PURPOSE

JF1/Ms mice, an inbred strain derived from Japanese wild mice, carry a germline hypomorphic mutation in the endothelin receptor type B gene (Ednrb). We observed that the JF1/Ms mice develop various spontaneous tumors at a high incidence late in life. The aim of this study was to elucidate the mechanism responsible for spontaneous tumors in these mice. Possible relevance of milk-borne mammary tumor virus and gene alterations in Ednrb to tumorigenesis was explored.

METHODS

Expression and methylation status of Ednrb were quantitatively analyzed in normal and cancer tissues of mammary gland, liver, submandibular gland as well as in a cultured cell line, MW1, established from a submandibular gland adenocarcinoma. The biological effects of EDNRB were examined in the MW1 cells transfected with wild-type Ednrb.

RESULTS

Transcripts of Ednrb were barely detectable, and the promoter region of Ednrb was hypermethylated in tumor tissues and the MW1 cells. In contrast, normal counterpart tissues showed positive expression of Ednrb transcripts and had unmethylated promoter regions. Treatment of the MW1 cells with 5-Aza-dC restored transcription of Ednrb to normal levels. Transfection of the MW1 cells with Ednrb1 (MW1-Ednrb1) resulted in lower growth rates and morphological changes compared with the mock-transfected MW1 cells (MW1-mock1). Furthermore, the MW1-Ednrb1 cells transplanted in syngeneic mice showed a lower proliferation rate than the MW1-mock1 cells.

CONCLUSIONS

Germline mutation and subsequent promoter methylation of Ednrb may be relevant to cancer susceptibility in the JF1/Ms mice. These data indicate that Ednrb acts as a tumor suppressor, as reported in human prostate, bladder, and clear cell renal carcinomas.

Independent genetic control of early and late stages of chemically induced skin tumors in a cross of a Japanese wild-derived inbred mouse strain, MSM/Ms

MSM/Ms is an inbred mouse strain derived from a Japanese wild mouse, Mus musculus molossinus. In this study, we showed that MSM/Ms mice exhibit dominant resistance when crossed with susceptible FVB/N mice and subjected to the two-stage skin carcinogenesis protocol using 7,12-dimethylbenz(a)anthracene (DMBA)/ 12-O-tetradecanoylphorbol-13-acetate (TPA). A series of F1 backcross mice were generated by crossing p53(+/+) or p53(+/-) F1 (FVB/N × MSM/Ms) males with FVB/N female mice. These generated 228 backcross animals, approximately half of which were p53(+/-), enabling us to search for p53-dependent skin tumor modifier genes. Highly significant linkage for papilloma multiplicity was found on chromosomes 6 and 7 and suggestive linkage was found on chromosomes 3, 5 and 12. Furthermore, in order to identify stage-dependent linkage loci we classified tumors into three categories (<2mm, 2-6mm and >6mm), and did linkage analysis. The same locus on chromosome 7 showed strong linkage in groups with <2mm or 2-6mm papillomas. No linkage was detected on chromosome 7 to papillomas >6mm, but a different locus on chromosome 4 showed strong linkage both to papillomas >6mm and to carcinomas. This locus, which maps near the Cdkn2a/p19(Arf) gene, was entirely p53-dependent, and was not seen in p53 (+/-) backcross animals. Suggestive linkage conferring susceptibility to carcinoma was also found on chromosome 5. These results clearly suggest distinct loci regulate each stage of tumorigenesis, some of which are p53-dependent.

Induction and persistence of radiation-induced DNA damage is more pronounced in young animals than in old animals

Younger individuals are more prone to develop cancer upon ionizing radiation (IR) exposure. Radiation-induced tumors are associated with inefficient repair of IR-induced DNA damage and genome instability. Phosphorylation of histone H2AX (γ-H2AX) is the initial event in repair of IR-induced DNA damage on the chromatin flanking the DNA strand breaks. This step is crucially important for the repair of DNA strand breaks and for the maintenance of genome stability. We studied the molecular underpinnings of the age-related IR effects using an animal model. By assaying for IR-induced γ-H2AX foci we analyzed the induction and repair of the DNA strand breaks in spleen, thymus, liver, lung, kidney, cerebellum, hippocampus, frontal cortex and olfactory bulb of 7, 14, 24, 30 and 45 days old male and female mice as a function of age. We demonstrate that tissues of younger animals are much more susceptible to IR-induced DNA damage. Younger animals exhibited higher levels of γ-H2AX formation which partially correlated with cellular proliferation and expression of DNA repair proteins. Induction and persistence of γ-H2AX foci was the highest in lymphoid organs (thymus and spleen) of 7 and 14 day old mice. The lowest focal induction was seen in lung and brain of young animals. The mechanisms of cell and tissue-specificity of in vivo IR responses need to be further dissected. This study provides a roadmap for the future analyses of DNA damage and repair induction in young individuals.

Intestinal tumours induced in Apc(Min/+) mice by X-rays and neutrons

PURPOSE

To compare the development of intestinal adenomas following neutron and X-ray exposure of Apc(Min/+) mice (Apc - adenomatous polyposis coli; Min - multiple intestinal neoplasia).

MATERIALS AND METHODS

Adult mice were exposed to acute doses of X-rays or fission neutrons. Tumour counting was undertaken 200 days later and samples were taken for Loss of Heterozygosity (LOH) analysis.

RESULTS

Tumour numbers (adenomas and microadenomas) increased by 1.4-fold, 1.7-fold, 2.7-fold and 9-fold, after 0.5, 1, 2 and 5 Gy X-rays, respectively, and by 2.4-fold and 5.7-fold, after 0.5 and 1 Gy fission neutrons, respectively. LOH analysis of tumours from neutron-exposed mice showed that 63% had lost Apc and 90% (cf. 53% in controls) had lost D18mit84, a marker for Epb4.1l4a/NBL4 (erythrocyte protein band 4.1-like 4a/novel band 4.1-like 4), known to be involved in the Wnt (wingless-related mouse mammary tumour virus integration site) pathway. Some tumours from neutron-exposed mice appeared to have homozygous loss of some chromosomal markers.

CONCLUSIONS

X-ray or fission neutron irradiation results in strongly enhanced tumour multiplicities. Comparison of tumour yields indicated a low Relative Biological Effectiveness of around 2-8 for fission neutrons compared with X-rays. LOH in intestinal tumours from neutron-exposed mice appeared to be more complex than previously reported for tumours from X-irradiated mice.

Enhanced intestinal tumor multiplicity and grade in vivo after HZE exposure: mouse models for space radiation risk estimates

Carcinogenesis induced by space radiation is considered a major risk factor in manned interplanetary and other extended missions. The models presently used to estimate the risk for cancer induction following deep space radiation exposure are based on data from A-bomb survivor cohorts and do not account for important biological differences existing between high-linear energy transfer (LET) and low-LET-induced DNA damage. High-energy and charge (HZE) radiation, the main component of galactic cosmic rays (GCR), causes highly complex DNA damage compared to low-LET radiation, which may lead to increased frequency of chromosomal rearrangements, and contribute to carcinogenic risk in astronauts. Gastrointestinal (GI) tumors are frequent in the United States, and colorectal cancer (CRC) is the third most common cancer accounting for 10% of all cancer deaths. On the basis of the aforementioned epidemiological observations and the frequency of spontaneous precancerous GI lesions in the general population, even a modest increase in incidence by space radiation exposure could have a significant effect on health risk estimates for future manned space flights. Ground-based research is necessary to reduce the uncertainties associated with projected cancer risk estimates and to gain insights into molecular mechanisms involved in space-induced carcinogenesis. We investigated in vivo differential effects of gamma-rays and HZE ions on intestinal tumorigenesis using two different murine models, ApcMin/+ and Apc1638N/+. We showed that gamma- and/or HZE exposure significantly enhances development and progression of intestinal tumors in a mutant-line-specific manner, and identified suitable models for in vivo studies of space radiation-induced intestinal tumorigenesis.

X radiation up-regulates the occurrence and the multiplicity of invasive carcinomas in the intestinal tract of Apc(min/+) mice

X rays are well known to cause genetic damage and to induce many types of carcinomas in humans. The Apc(min/+) mouse, an animal model for human familial adenomatous polyposis (FAP), contains a truncating mutation in the APC gene and spontaneously develops intestinal adenomas. To elucidate the role of X rays in the development of intestinal tumors, we examined the promotion of carcinogenesis in X-irradiated Apc(min/+) mice. Forty out of 77 (52%) X-irradiated Apc(min/+) mice developed adenocarcinomas that invaded the proprial muscle layer of the small intestine; 24 of 44 (55%) were in males, and 16 of 33 (49%) were in females. In contrast, invasive carcinomas were detected in the small intestines of only 13 of 64 (20%) nonirradiated Apc(min/+) mice; nine of 32 (28%) were in males and four of 32 (13%) were in females. These differences between X-irradiated and nonirradiated Apc(min/+) mice in the occurrence of invasive intestinal carcinomas were statistically significant (P < 0.05 for males, P < 0.005 for females). In wild-type mice, invasive carcinomas were not detected in either X-irradiated or nonirradiated mice. Apc(min/+) mice had many polyps in the large intestine with or without X irradiation; there was no difference in the number of polyps between the two groups. Also, invasive carcinomas were not detected in the large intestine with or without irradiation. The occurrence of mammary tumors, which was observed in Apc(min/+) mice, was found to be increased in irradiated Apc(min/+) mice (P < 0.01). Apc(min/+) mice had many polyps in the small and large intestines with or without X irradiation. X-irradiated Apc(min/+) mice had highly invasive carcinomas in the small intestine with multiplicities associated with invasiveness. Our results suggest that X radiation may promote the invasive activity of intestinal tumors in Apc(min/+) mice.

Breast cancer metastasis to bone: evaluation of bioluminescent imaging and microSPECT/CT for detecting bone metastasis in immunodeficient mice

This study sought to determine if weekly X-ray exposure affected breast cancer cell metastasis to bone and to also evaluate the use of bioluminescent imaging (BLI) and microSPECT for detection of metastatic bone lesions. Five week old nude mice were randomly assigned to the CT exposed (n = 7) and no CT exposure (n = 6) treatment groups. Mice received an intracardiac injection of MDA-MB-435 human breast cancer cells transduced with luciferase, or a sham injection (saline). The CT exposed group of mice received CT irradiation once a week for 5 weeks. All mice underwent weekly BLI and select mice received Tc-99m-MDP followed by microSPECT imaging after 5 weeks. Pathological evaluation and histomorphometry were used to assess the affect of CT X-rays on bone metastasis and to evaluate BLI. BLI results found no significant difference in metastasis between animals that received CT and those that did not (P > 0.05); however, histomorphometry of the knee joints revealed a significant increase (P = 0.029) in tumor area of the leg bones in mice that received CT exposure (60% +/- 7%) compared to animals that did not receive CT scans (33% +/- 8%). Compared to histological analysis, BLI of the leg and spine was determined to have excellent sensitivity (100%), good specificity (80-90%) and accuracy (90-96%), a positive predictive value of 81-93% and a 100% negative predictive value. Thus, multi-modality imaging techniques can be very useful for monitoring bone metastasis, however microCT X-rays should be used judiciously in order to limit irradiation that may stimulate increased metastasis to specific regions of the skeleton. MicroSPECT imaging did not detect metastatic lesions in the legs of these young nude mice.

Distinct pattern of allelic loss and inactivation of cadherin 1 and 5 genes in mammary carcinomas arising in p53(+/-) mice

p53 is one of the most frequently mutated genes in mammary carcinomas (MCs). To detect tumor suppressor genes cooperating with a hetero-deficient p53 gene in mammary carcinogenesis, we first examined allelotypes in MCs from (BALB/cHeA x MSM/Ms) F(1)- p53(+/-) and (BALB/cHeA x 129/SvEv) F(1)- p53(+/-) female mice, and then surveyed down-regulated genes in the allelic loss regions. Genome-wide screening at 42 loci identified frequent (more than 30%) loss of heterozygosity (LOH) on chromosomes 5, 8, 11, 12, 14 and 18 in the MCs from either of the F(1) mice. The MCs in the p53(+/- )mice indicated highly frequent LOH, especially on chromosomes 8, 11 and 12, distinct from other mouse tumors. More than 60% of the 38 MCs from (BALB/cHeA x MSM/Ms) F(1)- p53 (+/-) mice showed LOH in a region ranging from D8Mit85 (105.0 Mb from centromere) to D8Mit113 (111.8 Mb) on chromosome 8, a region syntenic to human chromosome 16q22.1, on which LOH has been found in breast cancers. RT-PCR analyses revealed that the LOH of chromosome 8 was associated with the reduced and/or complete loss of expression of Cdh1 and Cdh5 genes in 15 (58%) and 8 (31%) of 26 MCs derived from the F(1) mice, respectively. Thus, inactivation of Cdh1 and Cdh5 is likely to cooperate with the loss of p53, suggesting a possible tumor suppressive function of these genes in mammary carcinogenesis.

Hair cycle-dependent basal cell carcinoma tumorigenesis in Ptc1neo67/+ mice exposed to radiation

We examined the effects of hair cycle phase on basal cell carcinoma (BCC) tumorigenesis induced by radiation in mice lacking one Patched allele (Ptc1(neo67/+)). Our results show that Ptc1(neo67/+) mouse skin irradiated in early anagen is highly susceptible to tumor induction, as a 3.2-fold incidence of visible BCC-like tumors was observed in anagen-irradiated compared with telogen-irradiated mice. Microscopic nodular BCC-like tumors were also enhanced by irradiation during active hair-follicle growth phases. Interestingly, histologic examination of the tumors revealed a qualitative difference in BCC tumorigenesis depending on hair growth phase at the time of exposure. In fact, in addition to typical BCC-like tumors, we observed development of a distinct basal cell tumor subtype characterized by anti-cytokeratin 14 and anti-smooth muscle actin reactivity. These tumors showed relatively short latency and rapid growth and were strictly dependent on age at irradiation, as they occurred only in mice irradiated in early anagen phase. Examination of anatomic and immunohistochemical relationships revealed a close relation of these tumors with the follicular outer root sheath of anagen skin. In contrast, there are strong indications for the derivation of typical, smooth muscle actin-negative BCC-like tumors from cell progenitors of interfollicular epidermis. These results underscore the role of follicular bulge stem cells and their progeny with high self-renewal capacity in the formation of basal cell tumors and contribute to clarify the relationship between target cell and tumor phenotype in BCC tumorigenesis induced by radiation.

Accelerated growth of intestinal tumours after radiation exposure in Mlh1-knockout mice: evaluation of the late effect of radiation on a mouse model of HNPCC

Mlh1-knockout mice have been developed as a useful model of hereditary non-polyposis colorectal cancer (HNPCC). In this study, we analyzed the pathology of gastrointestinal tumours (GIT) in these mice in detail and examined the possible effects of ionizing radiation on the induction of intestinal tumours to evaluate the late response to radiotherapy in HNPCC. Mlh1-/- mice spontaneously developed GIT and thymic lymphomas by 48 weeks. GIT included not only well differentiated adenocarcinomas but also poorly differentiated and mucinous adenocarcinomas, suggesting that this mouse is a good model for HNPCC. In contrast to colon cancers from HNPCC patients, however, carcinomas of Mlh1-/- mice expressed p53 and showed a lack of transforming growth factor (TGF)-betaRII mutation, which resulted in the expression of TGF-betaRII protein. Irradiation of 10-week-old Mlh1-/- mice accelerated GIT development but had little effect at 2 weeks. Mlh1+/- and Mlh1+/+ mice were not susceptible to spontaneous or radiation-induced thymic lymphomas and GIT until 72 weeks after birth. The development and pathology of GIT in Mlh1-/- mice suggest that this mouse is a good model for HNPCC, although tumour-related responsible genes might be different from HNPCC. As X-ray exposure promoted carcinogenesis of GIT in adult Mlh1-/- mice, an increased risk of secondary cancers after radiotherapy for HNPCC patients should be taken into consideration.

In utero and neonatal sensitivity of ApcMin/+ mice to radiation-induced intestinal neoplasia

PURPOSE

To assess the sensitivity of ApcMin/+ mice (adenomatous polyposis coli Apc, multiple intestinal neoplasia, Min) to the development of intestinal adenomas after x-irradiation in utero, as neonates, or as young adults.

MATERIALS AND METHODS

CHB6 ApcMin/+ mice were exposed to an acute dose of 2 Gy x-rays either in utero on day 7 or 14 post-conception, as 2-day or 10-day neonates or as 35-day young adults. Tumour identification and counting was performed 200-214 days later.

RESULTS

Irradiation as 10-day-old neonates resulted in a significantly greater overall tumour incidence (average of about 130 tumours per animal) than irradiation as 35-day-old young adults (about 70 tumours). Irradiation as 2-day-old neonates resulted in an intermediate incidence (about 85 tumours). In contrast, the greatest tumour incidence observed after in utero irradiation of ApcMin/+ mice, of about 44 tumours per animal after 2 Gy irradiation at 14 days post-conception, was significantly lower than the incidence in irradiated adults. Tumour incidences after irradiation as 7-day embryos was not significantly raised above numbers in unirradiated controls (about 30 tumours). These tumour numbers include cystic crypts, largely radiation-induced, which were classed as early stage microadenomas on the basis of loss of wild-type Apc+ and expression of beta-catenin.

CONCLUSIONS

The sensitivity of ApcMin/+ mice to the induction of intestinal tumours by radiation was shown to be in the order: 10 d neonates>2 d neonates>35 d young adults>14 d fetus>7 d embryo.

Dose-response relationship for life-shortening and carcinogenesis in mice irradiated at day 7 postnatal age with dose range below 1 Gy of gamma rays

This study was designed to elucidate the dose-response relationships for life-shortening and tumorigenic effect in the dose range below 1 Gy of gamma rays delivered during the infant period. Female B6C3F1 mice were irradiated with 0.10, 0.48 or 0.95 Gy at 7 days of age. All irradiated mice were allowed to live out their entire life span together with a simultaneously ongoing control group under a specific pathogen-free condition. Shortening of the mean life span was 1.58% in mice irradiated with 0.10 Gy, which was statistically significant . The coefficient of the linear dose-response relationship for life-shortening was 11.21% Gy(-1). The attributable death fraction for all causes of death in 0.10 Gy group reached 0.092. The excess relative risk for death rate from all causes was 0.102 in the group irradiated with 0.10 Gy. The coefficient of the linear dose-response relationship of the excess relative risk for death rate from all causes was 1.30 Gy(-1). The mean number of types of solid tumors at the time of death in mice irradiated with 0.10 Gy was distinctly larger than that in the control group. The excess relative risk for death rate from solid tumors was 0.45 in mice irradiated with 0.10 Gy. The coefficient of the linear dose-response relationship of excess relative risk for death rate from solid tumors was 4.52 Gy(-1). Increase in incidences of the pituitary, ovarian and adrenal tumors was observed in mice irradiated with 0.10 Gy. The results of the present study showed that infant mice are susceptible to solid tumor induction, especially of the endocrine organs.

Mammary tumorigenesis in ApcMin/+ mice is enhanced by X irradiation with a characteristic age dependence

The Apc(Min/+) (Min) mouse is genetically predisposed to both intestinal and mammary tumorigenesis. We investigated age-related changes in the susceptibility of mice (before, during and after puberty) to radiation-induced mammary tumorigenesis using this model. Female Min and wild-type mice having the C57BL/6J background were irradiated with 2 Gy of X rays at 2, 5, 7 and 10 weeks and killed humanely at 18 weeks of age. Min mice irradiated at 7-10 weeks of age (after puberty) developed mammary tumors with squamous metaplasia, whereas their wild-type littermates did not. Interestingly, irradiation of Min mice at 2-5 weeks (before and during puberty, respectively) did not induce mammary tumors but rather cystic nodules with metaplasia. The mammary tumors exhibited increased nuclear beta-catenin protein and loss of the wild-type Apc allele. Our results show that susceptibility to radiation-induced mammary tumorigenesis increases after puberty in Min mice, suggesting that the tumorigenic effect of ionizing radiation targets the lobular-alveolar progenitor cells, which increase in number with age and are controlled by beta-catenin signaling.