Yutaka Tokairin

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)‐βRII mutation, which resulted in the expression of TGF‐βRII 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.

Mild inflammation accelerates colon carcinogenesis in Mlh1-deficient mice

Objective: Inflammatory bowel disease, which frequently accompanies silencing of Mlh1, plays a key role in the pathogenesis of colorectal cancer. The interaction between inflammation and mismatch repair deficiency, however, remains unclear. The aim of this study was to determine the effect of inflammation on colorectal carcinogenesis in Mlh1-deficient mice. Method: Inflammatory colitis was induced by treatment with 1% dextran sodium sulfate (DSS) in drinking water for 1 week in Mlh1 knockout (Mlh1–/–), Mlh1 heterozygous (Mlh1+/–) and wild-type (Mlh1+/+) mice at 10 weeks of age. The development of colon tumors was followed for a subsequent 15 weeks and the tumors were analyzed immunohistochemically for the expression and localization of iNOS, β-catenin and p53. Results: Male and female Mlh1–/– mice with DSS showed a 63 and 44% incidence of tumors, respectively, whereas no tumors were observed in Mlh1+/– and Mlh1+/+ mice. The mice without DSS treatment did not develop any tumors regardless of the genotype. While aberrant expression of β-catenin was not detected in colonic neoplasms, p53 and iNOS expression was increased in 100 and 77%, respectively. These immunohistochemical changes were consistent with those of human colon cancers associated with ulcerative colitis. Conclusion: Our results indicate that Mlh1 deficiency strongly accelerates colon carcinogenesis when combined with inflammation. Thus the cells with Mlh1 deficiency, either inherently or colitis associated, may be at an increased risk of cancer under inflammatory conditions.

Diffusion‐tensor MRI and tractography of the esophageal wall ex vivo

To demonstrate the feasibility of diffusion‐tensor magnetic resonance imaging (MRI) and tractography as a means of evaluating the individual layers of the normal esophageal wall by using esophageal specimens containing carcinoma.

Mammary Tumorigenesis in ApcMin/+ Mice is Enhanced by X Irradiation with a Characteristic Age Dependence

Abstract Imaoka, T., Okamoto, M., Nishimura, M., Nishimura, Y., Ootawara, M., Kakinuma, S., Tokairin, Y. and Shimada, Y. Mammary Tumorigenesis in ApcMin/+ Mice is Enhanced by X Irradiation with a Characteristic Age Dependence. Radiat. Res. 165, 165–173 (2006). The ApcMin/+ (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 β-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 β-catenin signaling.

Esophageal Carcinoma: Ex Vivo Evaluation with Diffusion-Tensor MR Imaging and Tractography at 7 T

PURPOSE To determine the feasibility of diffusion-tensor magnetic resonance (MR) imaging and tractography as a means of evaluating the depth of mural invasion by esophageal carcinomas. MATERIALS AND METHODS This study was approved by the institutional review board, and written informed consent was obtained from each patient. Twenty esophageal specimens, each containing a carcinoma, were studied with a 7.0-T MR imaging system equipped with a four-channel phased-array surface coil. Diffusion-tensor MR images were obtained with a field of view of 50-60 mm × 25-30 mm, matrix of 256 × 128, section thickness of 1 mm, b value of 1000 sec/mm(2), and motion-probing gradient in seven noncollinear directions. The MR images were compared with the histopathologic findings as the reference standard. The differences in diffusion-tensor MR imaging parameters between the carcinoma and the layers of the esophageal wall were statistically analyzed by using the Dunnett test. RESULTS In all 20 carcinomas (100%), the diffusion-weighted images, apparent diffusion coefficient (ADC) maps, fractional anisotropy (FA) maps, λ1 maps, and direction-encoded color FA maps made it possible to determine the depth of tumor invasion of the esophageal wall that was observed during histopathologic examination. The λ1 maps showed the best contrast between the carcinomas and the layers of the esophageal wall. The carcinomas had both lower ADC values and lower FA values than the normal esophageal wall; thus, the carcinomas were clearly demarcated from the normal esophageal wall. Diffusion-tensor tractography images were also useful for determining the depth of tumor invasion of the esophageal wall. CONCLUSION Diffusion-tensor MR imaging and tractography are feasible in esophageal specimens and provide excellent morphologic data for the evaluation of mural invasion by esophageal carcinomas.

Ikaros is a mutational target for lymphomagenesis in Mlh1-deficient mice.

Deficiencies in DNA mismatch repair (MMR) result in replication errors within key tumor suppressor genes or oncogenes, and cause hereditary nonpolyposis colorectal cancer (HNPCC). Hematological malignancy with microsatellite instability is also associated with defective MMR, but little is known about the target genes for MMR. Here we identified Ikaros, a master transcription factor of lymphoid lineage commitment and differentiation, as a mutational target in spontaneous and radiation-induced T-cell lymphomas in Mlh1-deficient mice. Three quarters of lymphomas lacked Ikaros protein expression, which resulted from a frameshift mutation that created a stop codon. Mononucleotide repeat sequences at 1029–1034(C)6 and 1567–1572(G)6 in Ikaros were mutational hot spots with a one-base deletion occurring with a frequency of 45 and 50%, respectively. Point mutations and splicing alterations were also observed. In total, 85% of the lymphomas showed aberrations in Ikaros. The characteristic of Mlh1-deficient lymphomas is harboring of multiple mutations simultaneously in the same tumor, displaying a combination of two frameshift mutations at different repeats, frameshift and point mutations, and/or deletion mutations. This is the first report of Ikaros mutations coupled with Mlh1 deficiency in lymphomagenesis.

Internal Pressure of the Conduit during Endoscopy on the Day after Esophagectomy

Background: In gastrointestinal surgery, anastomosis can result in various complications. Anastomosis is evaluated using classical examinations. The most reliable one is endoscopy, which provides direct information on the anastomosis and conduit. But the influence of endoscopy on anastomosis is uncertain. Methods: The internal pressure of a graft during endoscopy was measured in 36 patients who received esophagectomy, by utilizing the decompression tube which was inserted into the graft during operation. We filled the tube with water and measured the maximum water level in a centimeter water column. All examinations were routinely performed on the day after operation, and thin endoscopes were selected for reducing the stress. Results: The internal pressure before endoscopy ranged from 6 to 20 cm H2O, and during endoscopy ranged from 9 to 27 cm H2O. The difference in the internal conduit pressure in each patient ranged from 1 to 9 cm H2O. There was no increase in complications caused by endoscopy, including anastomotic leakage. Conclusion: This study is the first to report changes in internal pressure due to the endoscope by direct measurement. The pressure gradient observed was below the physiological pressure during swallowing. These results suggest that endoscopy is a safe examination even after surgery.

Esophageal carcinoma: Evaluation with q-space diffusion-weighted MR imaging ex vivo

To determine the usefulness of q‐space MR imaging as means of evaluating the depth of mural invasion, the histologic grades, and lymph node metastasis in esophageal carcinomas.

Ultra-high-resolution MR imaging of esophageal carcinoma at ultra-high field strength (7.0T) ex vivo: correlation with histopathologic findings.

PURPOSE To determine the usefulness of ultra-high-resolution magnetic resonance (MR) imaging at an ultra-high field strength (7.0T), using a voxel volume of 9.5-14nL, as means of evaluating the depth of mural invasion by esophageal carcinomas. MATERIALS AND METHODS Twenty esophageal specimens containing 20 carcinomas were studied using a 7.0-T MR imaging system with a four-channel surface coil. Ultra-high-resolution MR images were obtained with a field of view of 50-60mm×25-30mm, a matrix of 512×256, and a section thickness of 1.0mm, resulting in a voxel volume of 0.0095-0.014mm(3) (9.5-14nL). Differences between tumor tissue and the esophageal wall layers and between tumor tissue and fibrosis were evaluated using visual signal intensity scoring measurements. MR images were then compared with histopathologic findings as the reference standard. RESULTS Ultra-high-resolution T2-weighted MR images at 7.0T clearly depicted the normal esophageal wall in all 20 specimens (100%) as consisting of eight layers, which clearly corresponded to the tissue layers of the esophageal wall. Ultra-high-resolution T2-weighted MR images made it possible to differentiate between the tumor tissue and fibrosis clearly (P<0.01). In all 20 esophageal carcinomas (100%), ultra-high-resolution T2-weighted MR images made it possible to determine the depth of tumor invasion in the esophageal wall as observed in the histopathologic sections. Regional lymph node involvement was also clearly depicted in four specimens. CONCLUSION Ultra-high-resolution 7.0-T MR imaging, using a voxel volume of 9.5-14nL, provides clear delineation of the esophageal wall layers, clear differentiation of tumor tissue from fibrosis, and excellent diagnostic accuracy for evaluating mural invasion by esophageal carcinomas.

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.