DNA mismatch repair and the DNA damage response to ionizing radiation: Making sense of apparently conflicting data

Clinicopathologic features of conjunctival MALT lymphomas refractory to radiation therapy

OBJECTIVE

Clinicopathologic features of patients with limited-stage mucosa-associated lymphoid tissue (MALT) lymphoma refractory to radiotherapy have not been fully elucidated. This study aimed to elucidate clinicopathologic features of localized conjunctival MALT lymphoma concerning radiosensitivity by analyzing cell proliferation and expression of mismatch repair proteins.

METHODS

We enrolled 26 patients with localized conjunctival MALT lymphoma treated with radiotherapy from November 2007 to March 2020. Monoclonal immunoglobulin H gene rearrangement was tested in addition to histopathologic evaluation. Thirty-six specimens were immunostained with antibodies to Ki-67 and MutL protein homologue 1 (MLH1), MutS protein homologue 2 (MSH2), and MutS protein homologue 6 (MSH6). Positive rates under a high-power field at a hot spot were counted manually.

RESULTS

After radiotherapy, 21 patients showed clinical disappearance of the tumour without recurrence (effective group). Three patients showed temporary disappearance of the tumour, which later recurred (relapse group). Two patients did not show disappearance of the tumour (ineffective group). The 2 ineffective patients were young, had bilateral lesions, and received x-ray beam therapy. The mean positive rates of Ki-67, MLH1, MSH2, and MSH6 were higher in tumours with complete remission (CR) than in those without CR (23.4% ± 4.0% and 18.7% ± 4.7%, 14.7% ± 2.3% and 7.1% ± 3.7%, 23.9% ± 4.7% and 14.4% ± 5.2%, and 11.5% ± 3.2% and 5.4% ± 2.2%; p > 0.05 for each, respectively).

CONCLUSIONS

A few patients could not achieve CR following radiotherapy, whereas there were no significant differences in proliferation activity and mismatch repair proteins between tumours with and without CR.

Modelling radiobiology

Radiotherapy has played an essential role in cancer treatment for over a century, and remains one of the best-studied methods of cancer treatment. Because of its close links with the physical sciences, it has been the subject of extensive quantitative mathematical modelling, but a complete understanding of the mechanisms of radiotherapy has remained elusive. In part this is because of the complexity and range of scales involved in radiotherapy-from physical radiation interactions occurring over nanometres to evolution of patient responses over months and years. This review presents the current status and ongoing research in modelling radiotherapy responses across these scales, including basic physical mechanisms of DNA damage, the immediate biological responses this triggers, and genetic- and patient-level determinants of response. Finally, some of the major challenges in this field and potential avenues for future improvements are also discussed.

Genomic Correlates of Prostate-Specific Membrane Antigen Expression and Response to 177Lu-PSMA-617: A Retrospective Multicenter Cohort Study

PURPOSE

While 177Lu-PSMA-617 (LuPSMA) is an effective therapy for many patients with metastatic castration-resistant prostate cancer (mCRPC), biomarkers associated with outcomes are not well defined. We hypothesized that prostate cancer mutational profile may associate with clinical activity of LuPSMA. We devised a study to evaluate associations between mCRPC mutational profile with LuPSMA clinical outcomes.

METHODS

This was a multicenter retrospective analysis of patients with mCRPC with next-generation sequencing (NGS) who received LuPSMA. PSA50 response (ie, ≥50% decline in prostate-specific antigen [PSA]) rate, PSA progression free survival (PSA PFS), and overall survival (OS) were compared between genetically defined subgroups.

RESULTS

One hundred twenty-six patients with NGS results who received at least one cycle of LuPSMA were identified. The median age was 73 (IQR, 68-78) years, 124 (98.4%) received ≥1 prior androgen receptor-signaling inhibitor, and 121 (96%) received ≥1 taxane-based chemotherapy regimen. Fifty-eight (46%) patients with a DNA damage repair gene mutation (DNA damage response group) and 59 (46.8%) with a mutation in TP53, RB1, or PTEN tumor suppressor genes (TSG group) were identified. After adjusting for relevant confounders, the presence of ≥1 TSG mutation was associated with shorter PSA PFS (hazard ratio [HR], 1.93 [95% CI, 1.05 to 3.54]; P = .034) and OS (HR, 2.65 [95% CI, 1.15 to 6.11]; P = .023). There was improved OS favoring the DNA damage response group (HR, 0.37 [95% CI, 0.14 to 0.97]; P = .044) on multivariable analysis. Univariate analysis of patients with ATM mutations had significantly higher rates of PSA50 response, PSA PFS, and OS.

CONCLUSION

Outcomes on LuPSMA varied on the basis of mutational profile. Prospective studies to define the clinical activity of LuPSMA in predefined genomic subgroups are justified.

Integrating evolutionarily conserved mechanism of response to radiation for exploring novel Caenorhabditis elegans radiation-responsive genes for estimation of radiation dose associated with spaceflight

During space exploration, space radiation is widely recognized as an inescapable perilous stressor, owing to its capacity to induce genomic DNA damage and escalate the likelihood of detrimental health outcomes. Rapid and reliable estimation of space radiation dose holds paramount significance in accurately assessing the health risks associated with spaceflight. However, the identification of space radiation-responsive genes, with their potential to serve as early indicators for diagnosing radiation dose associated with spaceflight, continues to pose a significant challenge. In this study, based on the evolutionarily conserved mechanism of radiation response, an in silico analysis method of homologous comparison was performed to identify the Caenorhabditis elegans orthologues of human radiation-responsive genes with possible roles in the major processes of response to radiation, and thereby to explore the potential C. elegans radiation-responsive genes for evaluating the levels of space radiation exposure. The results showed that there were 60 known C. elegans radiation-responsive genes and 211 C. elegans orthologues of human radiation-responsive genes implicated in the major processes of response to radiation. Through an investigation of all available transcriptomic datasets obtained from space-flown C. elegans, it was observed that the expression levels of the majority of these putative C. elegans radiation-responsive genes identified in this study were notably changed across various spaceflight conditions. Furthermore, this study indicated that within the identified genes, 19 known C. elegans radiation-responsive genes and 40 newly identified C. elegans orthologues of human radiation-responsive genes exhibited a remarkable positive correlation with the duration of spaceflight. Moreover, a noteworthy presence of substantial multi-collinearity among the majority of these identified genes was observed. This observation lends support to the possibility of treating each identified gene as an independent indicator of radiation dose in space. Ultimately, a subset of 15 potential radiation-responsive genes was identified, presenting the most promising indicators for estimation of radiation dose associated with spaceflight in C. elegans.

Chronic Ionizing Radiation of Plants: An Evolutionary Factor from Direct Damage to Non-Target Effects

In present times, the levels of ionizing radiation (IR) on the surface of Earth are relatively low, posing no high challenges for the survival of contemporary life forms. IR derives from natural sources and naturally occurring radioactive materials (NORM), the nuclear industry, medical applications, and as a result of radiation disasters or nuclear tests. In the current review, we discuss modern sources of radioactivity, its direct and indirect effects on different plant species, and the scope of the radiation protection of plants. We present an overview of the molecular mechanisms of radiation responses in plants, which leads to a tempting conjecture of the evolutionary role of IR as a limiting factor for land colonization and plant diversification rates. The hypothesis-driven analysis of available plant genomic data suggests an overall DNA repair gene families' depletion in land plants compared to ancestral groups, which overlaps with a decrease in levels of radiation exposure on the surface of Earth millions of years ago. The potential contribution of chronic IR as an evolutionary factor in combination with other environmental factors is discussed.

Potential risks associated with the use of ionizing radiation for imaging and treatment of colorectal cancer in Lynch syndrome patients

The aim of this review is to investigate the literature pertaining to the potential risks of low-dose ionizing radiation to Lynch syndrome patients by use of computed tomography (CT), either diagnostic CT colonography (CTC), standard staging CT or CT surveillance. Furthermore, this review explores the potential risks of using radiotherapy for treatment of rectal cancer in these patients. No data or longitudinal observational studies of the impact of radiation exposure on humans with Lynch syndrome were identified. Limited experimental studies utilizing cell lines and primary cells exposed to both low and high radiation doses have been carried out to help determine radio-sensitivity associated with DNA mismatch repair gene deficiency, the defining feature of Lynch syndrome. On balance, these studies suggest that mismatch repair deficient cells may be relatively radio-resistant (particularly for low dose rate exposures) with higher mutation rates, albeit no firm conclusions can be drawn. Mouse model studies, though, showed an increased risk of developing colorectal tumors in mismatch repair deficient mice exposed to radiation doses around 2 Gy. With appropriate ethical approval, further studies investigating radiation risks associated with CT imaging and radiotherapy relevant doses using cells/tissues derived from confirmed Lynch patients or genetically modified animal models are urgently required for future clinical guidance.

Comparative genomics reveals putative evidence for high-elevation adaptation in the American pika (Ochotona princeps)

High-elevation environments have lower atmospheric oxygen content, reduced temperatures, and higher levels of UV radiation than found at lower elevations. As such, species living at high elevations must overcome these challenges to survive, grow, and reproduce. American pikas (Ochotona princeps) are alpine lagomorphs that are habitat specialists typically found at elevations >2,000 m. Previous research has shown putative evidence for high-elevation adaptation; however, investigations to date have been limited to a fraction of the genome. Here, we took a comparative genomics approach to identify putative regions under selection using a chromosomal reference genome assembly for the American pika relative to 8 other mammalian species targeted based on phylogenetic relatedness and (dis)similarity in ecology. We first identified orthologous gene groups across species and then extracted groups containing only American pika genes as well as unclustered pika genes to inform functional enrichment analyses; among these, we found 141 enriched terms with many related to hypoxia, metabolism, mitochondrial function/development, and DNA repair. We identified 15 significantly expanded gene families within the American pika across all orthologous gene groups that displayed functionally enriched terms associated with hypoxia adaptation. We further detected 196 positively selected genes, 41 of which have been associated with putative adaptation to hypoxia, cold tolerance, and response to UV following a literature review. In particular, OXNAD1, NRDC, and those genes critical in DNA repair represent important targets for future research to examine their functional implications in the American pika, especially as they may relate to adaptation to rapidly changing environments.

Radiation-response in primary fibroblasts of long-term survivors of childhood cancer with and without second primary neoplasms: the KiKme study

Background

The etiology and most risk factors for a sporadic first primary neoplasm in childhood or subsequent second primary neoplasms are still unknown. One established causal factor for therapy-associated second primary neoplasms is the exposure to ionizing radiation during radiation therapy as a mainstay of cancer treatment. Second primary neoplasms occur in 8% of all cancer survivors within 30 years after the first diagnosis in Germany, but the underlying factors for intrinsic susceptibilities have not yet been clarified. Thus, the purpose of this nested case–control study was the investigation and comparison of gene expression and affected pathways in primary fibroblasts of childhood cancer survivors with a first primary neoplasm only or with at least one subsequent second primary neoplasm, and controls without neoplasms after exposure to a low and a high dose of ionizing radiation.

Methods

Primary fibroblasts were obtained from skin biopsies from 52 adult donors with a first primary neoplasm in childhood (N1), 52 with at least one additional primary neoplasm (N2+), as well as 52 without cancer (N0) from the KiKme study. Cultured fibroblasts were exposed to a high [2 Gray (Gy)] and a low dose (0.05 Gy) of X-rays. Messenger ribonucleic acid was extracted 4 h after exposure and Illumina-sequenced. Differentially expressed genes (DEGs) were computed using limma for R, selected at a false discovery rate level of 0.05, and further analyzed for pathway enrichment (right-tailed Fisher’s Exact Test) and (in-) activation (z ≥|2|) using Ingenuity Pathway Analysis.

Results

After 0.05 Gy, least DEGs were found in N0 (n = 236), compared to N1 (n = 653) and N2+ (n = 694). The top DEGs with regard to the adjusted p-value were upregulated in fibroblasts across all donor groups (SESN1, MDM2, CDKN1A, TIGAR, BTG2, BLOC1S2, PPM1D, PHLDB3, FBXO22, AEN, TRIAP1, and POLH). Here, we observed activation of p53 Signaling in N0 and to a lesser extent in N1, but not in N2+. Only in N0, DNA (excision-) repair (involved genes: CDKN1A, PPM1D, and DDB2) was predicted to be a downstream function, while molecular networks in N2+ were associated with cancer, as well as injury and abnormalities (among others, downregulation of MSH6, CCNE2, and CHUK). After 2 Gy, the number of DEGs was similar in fibroblasts of all donor groups and genes with the highest absolute log₂ fold-change were upregulated throughout (CDKN1A, TIGAR, HSPA4L, MDM2, BLOC1SD2, PPM1D, SESN1, BTG2, FBXO22, PCNA, and TRIAP1). Here, the p53 Signaling-Pathway was activated in fibroblasts of all donor groups. The Mitotic Roles of Polo Like Kinase-Pathway was inactivated in N1 and N2+. Molecular Mechanisms of Cancer were affected in fibroblasts of all donor groups. P53 was predicted to be an upstream regulator in fibroblasts of all donor groups and E2F1 in N1 and N2+. Results of the downstream analysis were senescence in N0 and N2+, transformation of cells in N0, and no significant effects in N1. Seven genes were differentially expressed in reaction to 2 Gy dependent on the donor group (LINC00601, COBLL1, SESN2, BIN3, TNFRSF10A, EEF1AKNMT, and BTG2).

Conclusion

Our results show dose-dependent differences in the radiation response between N1/N2+ and N0. While mechanisms against genotoxic stress were activated to the same extent after a high dose in all groups, the radiation response was impaired after a low dose in N1/N2+, suggesting an increased risk for adverse effects including carcinogenesis, particularly in N2+.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-022-00520-6.

Genomic instability detected from the saliva of Head and Neck Squamous Cell Carcinoma patients: Association with clinical implications

OBJECTIVES

Genomic instability in cancers is often associated with poor disease outcomes. In Head and Neck Squamous Cell Carcinoma (HNSCC), saliva being the contact fluid contains cancers cells shed from the primary tumour. This study detected genomic instability from cancer cells shed in saliva and correlated the same with clinical implications.

DESIGN

Genomic instability in HNSCC patients (n = 81) was analysed and compared with control subjects (n = 30). Alu sequences were amplified from the DNA of the cells shed in saliva and from the blood (Germline DNA) using Alu-PCR. Band variations between amplified products of salivary cells' DNA and germline DNA were compared. 'Instability Score' was calculated by counting the band variation(s). The 'Instability Score' was further used as a measure of genomic instability.

RESULTS

Higher instability was detected in patients as compared to the controls (p < 0.0001). After treatment, there was a significant decrease (p < 0.0001) in the Instability score and patients with higher instability scores responded better to radiotherapy. The patient group consuming both tobacco and alcohol had a higher instability score in comparison to the tobacco group (p = 0.0056). Also, Instability scores are inversely correlated with nodal metastasis (p = 0.0075). A high Instability score before treatment resulted in a better prognosis in HNSCC patients (HR: 1.8, 95%CI: 1.024-3.164, p = 0.0306).

CONCLUSION

Our data suggest that genomic instability estimated from the tumour cells shed in the saliva of HNSCC patients by amplifying Alu sequence (Alu-PCR) is associated with radiotherapy response.

Prostate radiotherapy and the risk of secondary rectal cancer-a meta-analysis

PURPOSE

Radiotherapy is being used increasingly in the treatment of prostate cancer. However, ionising radiation may confer a small risk of a radiation-induced secondary malignancy. We aim to assess the risk of rectal cancer following pelvic radiotherapy for prostate cancer.

METHODS

A search was conducted of the PubMed/MEDLINE, EMBASE and Web of Science databases identifying studies reporting on the risk of rectal cancer following prostatic radiotherapy. Studies must have included an appropriate control group of non-irradiated prostate cancer patients. A meta-analysis was performed to assess the risk of prostatic radiotherapy on subsequent rectal cancer diagnosis.

RESULTS

In total, 4757 articles were screened with eight studies meeting the predetermined criteria. A total of 796,386 patients were included in this meta-analysis which showed an increased odds ratio (OR) for subsequent rectal cancer in prostate cancer patients treated with radiotherapy compared to those treated by non-radiotherapy means (OR 1.45, 1.07-1.97, p = 0.02).

CONCLUSION

These findings confirm that prostate radiotherapy significantly increases the risk of subsequent rectal cancer. This risk has implications for treatment selection, surveillance and patient counselling. However, it is crucial that this information is presented in a rational and comprehensible manner that does not disproportionately frighten or deter patients from what might be their most suitable treatment modality.

Expressing MLH1 in HCT116 cells increases cellular resistance to radiation by activating the PRKAC

Mut L homolog-1 (MLH1) is a key DNA mismatch repair protein which participates in the sensitivity to DNA damaging agents. However, its role in the radiosensitivity of tumor cells is less well characterized. In this study, we investigated the role of MLH1 in cellular responses to ionizing radiation (IR) and explored the signaling molecules involved. The isogenic pair of MLH1 proficient (MLH1⁺) and deficient (MLH1^-) human colorectal cancer HCT116 cells was exposed to IR for 24 h at the dose of 3 cGy. The clonogenic survival was examined by the colony formation assay. Cell cycle distribution was analyzed with flow cytometry. Changes in the protein level of MLH1, DNA damage marker γH2AX, and protein kinase A catalytic subunit (PRKAC), a common target for anti-tumor drugs, were examined with Western blotting. The results showed that the HCT116 (MLH1⁺) cells demonstrated increased radio-resistance with increased S population, decreased G2 population, a low level of γH2AX, a reduced ratio of phosphorylated PRKACαβ to total PRKAC, and an elevated level of total PRKAC and phosphorylated PRKACβII following IR compared with the HCT116 (MLH1^-) cells. Importantly, silencing PRKAC in HCT116 (MLH1⁺) cells increased the cellular radiosensitivity. In conclusion, MLH1 may increase cellular resistance to IR by activating PRKAC. Our finding is the first to demonstrate the important role of PRKAC in MLH1-mediated radiosensitivity, suggesting that PRKAC has potential as a biomarker and a therapeutic target for increasing radio-sensitization.

Mutational burden and immune recognition of gliomas

PURPOSE OF REVIEW

Recent evidence suggests high tumor mutational burden (TMB-H) as a predictor of response to immune checkpoint blockade (ICB) in cancer. However, results in TMB-H gliomas have been inconsistent. In this article, we discuss the main pathways leading to TMB-H in glioma and how these might affect immunotherapy response.

RECENT FINDINGS

Recent characterization of TMB-H gliomas showed that 'post-treatment' related to mismatch repair (MMR) deficiency is the most common mechanism leading to TMB-H in gliomas. Unexpectedly, preliminary evidence suggested that benefit with ICB is rare in this population. Contrary to expectations, ICB response was reported in a subset of TMB-H gliomas associated with constitutional MMR or polymerase epsilon (POLE) defects (e.g., constitutional biallelic MMRd deficiency). In other cancers, several trials suggest increased ICB efficacy is critically associated with increased lymphocyte infiltration at baseline which is missing in most gliomas. Further characterization of the immune microenvironment of gliomas is needed to identify biomarkers to select the patients who will benefit from ICB.

SUMMARY

Intrinsic molecular and immunological differences between gliomas and other cancers might explain the lack of efficacy of ICB in a subset of TMB-H gliomas. Novel combinations and biomarkers are awaited to improve immunotherapy response in these cancers.

Non-Lethal Concentration of MeHg Causes Marked Responses in the DNA Repair, Integrity, and Replication Pathways in the Exposed Human Salivary Gland Cell Line

In Brazilian northern Amazon, communities are potentially exposed and vulnerable to methylmercury (MeHg) toxicity through the vast ingestion of fish. In vivo and in vitro studies demonstrated that the salivary glands as a susceptible organ to this potent environmental pollutant, reporting alterations on physiological, biochemical, and proteomic parameters. However, the alterations caused by MeHg on the gene expression of the exposed human salivary gland cells are still unknown. Therefore, the goal was to perform the transcriptome profile of the human salivary gland cell line after exposure to MeHg, using the microarray technique and posterior bioinformatics analysis. The cell exposure was performed using 2.5 µM MeHg. A previously published study demonstrated that this concentration belongs to a range of concentrations that caused biochemical and metabolic alterations in this linage. As a result, the MeHg exposure did not cause lethality in the human salivary gland cells line but was able to alter the expression of 155 genes. Downregulated genes (15) are entirety relating to the cell metabolism impairment, and according to KEGG analysis, they belong to the glycosphingolipid (GSL) biosynthesis pathway. On the other hand, most of the 140 upregulated genes were related to cell-cycle progression, DNA repair, and replication pathway, or cellular defenses through the GSH basal metabolism. These genomic changes revealed the effort to the cell to maintain physiological and genomic stability to avoid cell death, being in accordance with the nonlethality in the toxicity test. Last, the results support in-depth studies on nonlethal MeHg concentrations for biomarkers identification that interpret transcriptomics data in toxicological tests serving as an early alert of physiological changes in vitro biological models.

Durable response after immune checkpoint inhibitor-related diabetes in mismatch repair deficient pancreatic cancer

Mismatch repair protein deficiency occurs in 0.8-2% of pancreatic ductal adenocarcinomas and confers susceptibility to immunotherapy. Herein, we report the case of a patient with Lynch syndrome-associated, locally advanced mismatch repair protein deficiency pancreatic ductal adenocarcinomas who demonstrated a sustained response to second-line treatment with pembrolizumab, but eventually developed immune-related diabetic ketoacidosis requiring discontinuation of treatment. He has since remained in remission, off treatment, over the following 3 years, with regular surveillance showing no clinical or radiographic evidence of disease progression. The patient's unusual disease course raises the question of whether this serious immune-related adverse event affecting the organ of malignant involvement may have predicted his remarkable and durable response.

Metabolic profile of irradiated whole blood by chemical isotope-labeling liquid chromatography-mass spectrometry

Irradiated blood is a new type of blood product used to prevent transfusion-associated graft-versus-host disease. However, the effects of irradiation on the metabolism of plasma, red blood cells (RBCs), and peripheral blood mononuclear cells (PBMCs) are largely unknown. We developed a workflow for testing metabolic changes in whole blood to determine the impact of irradiation by chemical isotope labeling liquid chromatography-mass spectrometry (CIL LC-MS). Blood parameters, PBMC proliferation and apoptosis were examined before and after irradiation. Next, the amine/phenol metabolites in the blood components were assayed by ¹²C- and¹³C-dansylation labeling LC-MS. We identified 1654, 1730, and 1666 peak pairs in plasma, RBCs, and PBMCs, respectively. We screened out 367, 177, and 219 significant metabolites in plasma, RBCs, and PBMCs, respectively, by principle component analyses, volcano plots, and Venn plots. Metabolic pathway analyses showed that irradiation modulated taurine and hypotaurine metabolism in plasma and purine metabolism in RBCs and PBMCs. Changes in potential biomarkers, including an increase in hypoxanthine level and a decrease in adenine level, may be related to the dysfunction of DNA synthesis in PBMCs. The decreased AMP level in RBCs may interfere with RBC storage lesions. Our research provides a more comprehensive perspective on blood metabolism associated with irradiation.

Head and neck cancer: Current challenges and future perspectives

Head and neck cancers are a heterogeneous, aggressive and genetically complex collection of malignancies of the oral cavity, nasopharynx, oropharynx, hypopharynx, larynx, paranasal sinuses and salivary glands, which are difficult to treat. About 90% of all head and neck cancers are squamous cell carcinomas (HNSCC). Larynx and Oral cavity carcinomas are generally related with tobacco consumption, alcohol abuse (or both), but pharynx carcinomas are generally associated with infection of human papillomavirus (HPV), especially HPV-16 subtype. Thus, usually HNSCC can be separated into HPV-negative and HPV-positive categories. Despite substantial efforts invested into therapeutic development of HNSCC, the 5-year survival rate of patients with HNSCC still remains dismal. The primary reason being late diagnosis, recurrent metastasis, relapse and resistance to therapies. Currently surgery and radiotherapy represent the baseline treatment options for most initial stage HNSCC patients, but these treatments are associated with significant morbidity and poor prognosis. Moreover, the issue of resistance to both radiotherapy/chemotherapy and recurrent relapse are common in HNSCC. Elucidation of the genetic landscape, tumor microenvironment and aberrant signaling pathways have generated new insights into the molecular pathogenesis of this disease. Thus, the scientific research has therefore been focused on the understanding of HNSCC biology and immunobiology to identification of predictive/prognostic biomarkers, which will be key to develop more effective targeted therapies with less toxicity and high specificity.

Micronuclei Formation upon Radioiodine Therapy for Well-Differentiated Thyroid Cancer: The Influence of DNA Repair Genes Variants

Radioiodine therapy with ¹³¹I remains the mainstay of standard treatment for well-differentiated thyroid cancer (DTC). Prognosis is good but concern exists that ¹³¹I-emitted ionizing radiation may induce double-strand breaks in extra-thyroidal tissues, increasing the risk of secondary malignancies. We, therefore, sought to evaluate the induction and 2-year persistence of micronuclei (MN) in lymphocytes from 26 ¹³¹I-treated DTC patients and the potential impact of nine homologous recombination (HR), non-homologous end-joining (NHEJ), and mismatch repair (MMR) polymorphisms on MN levels. MN frequency was determined by the cytokinesis-blocked micronucleus assay while genotyping was performed through pre-designed TaqMan^® Assays or conventional PCR-restriction fragment length polymorphism (RFLP). MN levels increased significantly one month after therapy and remained persistently higher than baseline for 2 years. A marked reduction in lymphocyte proliferation capacity was also apparent 2 years after therapy. MLH1 rs1799977 was associated with MN frequency (absolute or net variation) one month after therapy, in two independent groups. Significant associations were also observed for MSH3 rs26279, MSH4 rs5745325, NBN rs1805794, and tumor histotype. Overall, our results suggest that ¹³¹I therapy may pose a long-term challenge to cells other than thyrocytes and that the individual genetic profile may influence ¹³¹I sensitivity, hence its risk-benefit ratio. Further studies are warranted to confirm the potential utility of these single nucleotide polymorphisms (SNPs) as radiogenomic biomarkers in the personalization of radioiodine therapy.

Ionizing Radiation Alters the Transition/Transversion Ratio in the Exome of Human Gingiva Fibroblasts

Little is known about the mutational impact of ionizing radiation (IR) exposure on a genome-wide level in mammalian tissues. Recent advancements in sequencing technology have provided powerful tools to perform exome-wide analyses of genetic variation. This also opened up new avenues for studying and characterizing global genomic IR-induced effects. However, genotypes generated by next generation sequencing (NGS) studies can contain errors, which may significantly impact the power to detect signals in common and rare variant analyses. These genotyping errors are not explicitly detected by the standard Genotype Analysis ToolKit (GATK) and Variant Quality Score Recalibration (VQSR) tool and thus remain a potential source of false-positive variants in whole exome sequencing (WES) datasets. In this context, the transition-transversion ratio (Ti/Tv) is commonly used as an additional quality check. In case of IR experiments, this is problematic when Ti/Tv itself might be influenced by IR treatment. It was the aim of this study to determine a suitable threshold for variant filters for NGS datasets from irradiated cells in order to achieve high data quality using Ti/Tv, while at the same time being able to investigate radiation-specific effects on the Ti/Tv ratio for different radiation doses. By testing a variety of filter settings and comparing the obtained results with publicly available datasets, we observe that a coverage filter setting of depth (DP) 3 and genotype quality (GQ) 20 is sufficient for high quality single nucleotide variants (SNVs) calling in an analysis combining GATK and VSQR and that Ti/Tv values are a consistent and useful indicator for data quality assessment for all tested NGS platforms. Furthermore, we report a reduction in Ti/Tv in IR-induced mutations in primary human gingiva fibroblasts (HGFs), which points to an elevated proportion of transversions among IR-induced SNVs and thus might imply that mismatch repair (MMR) plays a role in the cellular damage response to IR-induced DNA lesions.

Anticancer and Apoptogenic Effect of Graviola and Low-Dose Radiation in Tumor Xenograft in Mice

Background: Annona muricata (graviola) has been claimed for its potential against various diseases including cancer. Objective: The present study aimed to investigate the anticancer effect of graviola extract on Ehrlich solid tumor (EST) mice along with or without a low dose of γ radiation (LDR). Methods: Mice were treated with graviola 50 mg/kg body weight orally for 30 days after EST induction and exposed to γ-ray (2 Gy/week for 3 weeks). Cell cycle, CD44, TGF-β, Bcl-2, and annexin V were determined in tumor tissue. Results: The result obtained showed a significant decrease (P < .05) of tumor size in 28 graviola-treated EST-bearing mice group (EG) or graviola-treated and irradiated EST-30-bearing mice (EGR) groups versus the EST group. The large number of cells in the sub-G0/G1 population and low cell number at S and M phases signify tumor cell apoptosis and inhibition of cell division in EG or EGR groups. Additionally, significant increases in the expression of CD44 and TGF-β were recorded in EST mice as compared with EG or EGR mice. Furthermore, EST mice exhibited a decrease in the apoptotic marker annexin v and increase in antiapoptotic Bcl-2 compared with EG and EGR mice. Conclusion: It could be suggested that graviola exerts its antitumor effect throughout the regulation of the tumor cell cycle as well as inducing apoptotic signals. The combined treatment of graviola and LDR augments their effect on tumor proliferation.

RISK EVALUATION IN THE LOW-DOSE RANGE CT FOR RADIATION-EXPOSED CHILDREN, BASED ON DNA DAMAGE

One of the most common usages of radiation in current medical diagnosis is computed tomography (CT) using X-rays. The potential health risk of CT scans has been discussed in various studies to determine whether low-dose radiation from CT could enhance the chromosome aberration yields in pediatric patients and increase their risk of carcinogenesis. For this reason, it is of great interest to study the effects of low-dose radiation. The induction of DNA damage by a CT scan examination has been demonstrated in several reports by the γ-H2AX assay, the micronuclei assay and dicentrics measurements. However, the results of most studies showed limitations. On the other hand, epidemiological studies give contradictory results for post-natal radiation exposure in the low-dose range, so it is still difficult to draw conclusions about the effects of CT examinations and risk of carcinogenesis. This article provides an overview of previously published data and summarizes the current state of knowledge.

Increased risk for second primary rectal cancer after pelvic radiation therapy

BACKGROUND

The aim of this study was to analyse the association between pelvic radiation therapy (RT) and the development of rectal cancer as a second primary cancer.

METHODS

Data on patients treated for a primary pelvic cancer between 1989 and 2007 were retrieved from the population-based Netherlands Cancer Registry. Patients treated for more than one pelvic cancer were excluded. To estimate the cumulative incidence of rectal cancer, Fine and Gray's competing risk model was used with death as a competing event. Survival was calculated using multivariable Cox regression.

RESULTS

A total of 192,658 patients were included, of which 62,630 patients were treated with RT for their pelvic cancer. Primary tumours were located in the prostate (50.1%), bladder (19.2%), endometrium (13.9%), ovaries (10.0%), cervix (6.4%) and vagina (0.4%). At a median interval of 6 years (range 0-24), 1369 patients developed a rectal cancer. Overall, the risk for rectal cancer was increased in patients who underwent RT for the previous pelvic cancer (subhazard ratio [SHR]: 1.72, 95% confidence interval [CI]: 1.55-1.91). Analysis for each tumour location specifically showed an increased risk in patients who received RT for prostate (SHR: 1.89, 95% CI: 1.66-2.16) or endometrial cancer (SHR: 1.50, 95% CI: 1.13-2.00). A protective effect of RT was observed for patients with bladder cancer (SHR 0.67, 95% CI: 0.47-0.94). There was no survival difference between patients with rectal cancer with or without previous RT (hazard ratio: 0.94, 95% CI: 0.79-1.11).

CONCLUSIONS

Patients who received RT for a previous pelvic cancer were at increased risk for rectal cancer. The risk was modest and pronounced in patients receiving RT for prostate and endometrial cancer.

The expression of MLH1 and MSH2 genes among inhabitants of high background radiation area of Ramsar, Iran

Previous studies evidenced the critical role of the mismatch repair system in DNA damage recognition, cell cycle arrest, apoptosis and DNA repair. MLH1 and MSH2 genes belong to repairing complexes of mismatch repair system. The side effects of ionizing radiation on the human health were proved, but researches on the inhabitants of high background radiation areas, with extra-ordinary radiation exposure, showed that the prevalence of cancer or radiation-related diseases is not significantly higher than normal background areas. The city of Ramsar, in northern Iran, has the highest level of natural background radiation in the world and in this study, we aimed to evaluate the expression of MLH1 and MSH2 genes among the inhabitants of high background radiation areas of Ramsar compared to normal background radiation areas. In the present study, 60 blood sample from high and normal background inhabitants were collected and we MLH1, and MSH2 genes expressions in residents of high background radiation area compared with normal background radiation area were evaluated by Quantitative Real-Time PCR. Our results showed a significant upregulation of MLH1 in residents of high background radiation area. Also, there is a significant association between MLH1 and MSH2 gene expression in both sexes. Also, the increased expression of MLH1 in HBRA is notable. There is an increased expression of MLH1 in age above 50 and a decreased expression of MSH2 in ages under 50 years (P < 0.0001). These findings are suggesting the triggering of Mismatch Repair system in response to high-level of natural background radiation.

Temozolomide-associated hypermutation in gliomas

Low-grade gliomas cause considerable morbidity and most will recur after initial therapy. At recurrence, low-grade gliomas can undergo transformation to high-grade gliomas (grade III or grade IV), which are associated with worse prognosis. Temozolomide (TMZ) provides survival benefit in patients with glioblastomas, but its value in patients with low-grade gliomas is less clear. A subset of TMZ-treated, isocitrate dehydrogenase‒mutant, low-grade astrocytomas recur as more malignant tumors with thousands of de novo, coding mutations bearing a signature of TMZ-induced hypermutation. Preliminary studies raise the hypothesis that TMZ-induced hypermutation may contribute to malignant transformation, although with highly variable latency. On the other hand, hypermutated gliomas have radically altered genomes that present new opportunities for therapeutic intervention. In light of these findings and the immunotherapy clinical trials they inspired, how do patients and providers approach the risks and benefits of TMZ therapy? This review discusses what is known about the mechanisms and consequences of TMZ-induced hypermutation and outstanding questions regarding its clinical significance.

Clinical update on head and neck cancer: molecular biology and ongoing challenges

Head and neck squamous cell carcinomas (HNSCCs) are an aggressive, genetically complex and difficult to treat group of cancers. In lieu of truly effective targeted therapies, surgery and radiotherapy represent the primary treatment options for most patients. But these treatments are associated with significant morbidity and a reduction in quality of life. Resistance to both radiotherapy and the only available targeted therapy, and subsequent relapse are common. Research has therefore focussed on identifying biomarkers to stratify patients into clinically meaningful groups and to develop more effective targeted therapies. However, as we are now discovering, the poor response to therapy and aggressive nature of HNSCCs is not only affected by the complex alterations in intracellular signalling pathways but is also heavily influenced by the behaviour of the extracellular microenvironment. The HNSCC tumour landscape is an environment permissive of these tumours' aggressive nature, fostered by the actions of the immune system, the response to tumour hypoxia and the influence of the microbiome. Solving these challenges now rests on expanding our knowledge of these areas, in parallel with a greater understanding of the molecular biology of HNSCC subtypes. This update aims to build on our earlier 2014 review by bringing up to date our understanding of the molecular biology of HNSCCs and provide insights into areas of ongoing research and perspectives for the future.

Loss of Msh2 and a single-radiation hit induce common, genome-wide, and persistent epigenetic changes in the intestine

Background

Mismatch repair (MMR)-deficiency increases the risk of colorectal tumorigenesis. To determine whether the tumors develop on a normal or disturbed epigenetic background and how radiation affects this, we quantified genome-wide histone H3 methylation profiles in macroscopic normal intestinal tissue of young radiated and untreated MMR-deficient VCMsh2^LoxP/LoxP (Msh2^−/−) mice months before tumor onset.

Results

Histone H3 methylation increases in Msh2^−/− compared to control Msh2^+/+ mice. Activating H3K4me3 and H3K36me3 histone marks frequently accumulate at genes that are H3K27me3 or H3K4me3 modified in Msh2^+/+ mice, respectively. The genes recruiting H3K36me3 enrich in gene sets associated with DNA repair, RNA processing, and ribosome biogenesis that become transcriptionally upregulated in the developing tumors. A similar epigenetic effect is present in Msh2^+/+ mice 4 weeks after a single-radiation hit, whereas radiation of Msh2^−/− mice left their histone methylation profiles almost unchanged.

Conclusions

MMR deficiency results in genome-wide changes in histone H3 methylation profiles preceding tumor development. Similar changes constitute a persistent epigenetic signature of radiation-induced DNA damage.

Electronic supplementary material

The online version of this article (10.1186/s13148-019-0639-8) contains supplementary material, which is available to authorized users.

The mismatch repair-dependent DNA damage response: Mechanisms and implications

An important role for the DNA mismatch repair (MMR) pathway in maintaining genomic stability is embodied in its conservation through evolution and the link between loss of MMR function and tumorigenesis. The latter is evident as inheritance of mutations within the major MMR genes give rise to the cancer predisposition condition, Lynch syndrome. Nonetheless, how MMR loss contributes to tumorigenesis is not completely understood. In addition to preventing the accumulation of mutations, MMR also directs cellular responses, such as cell cycle checkpoint or apoptosis activation, to different forms of DNA damage. Understanding this MMR-dependent DNA damage response may provide insight into the full tumor suppressing capabilities of the MMR pathway. Here, we delve into the proposed mechanisms for the MMR-dependent response to DNA damaging agents. We discuss how these pre-clinical findings extend to the clinical treatment of cancers, emphasizing MMR status as a crucial variable in selection of chemotherapeutic regimens. Also, we discuss how loss of the MMR-dependent damage response could promote tumorigenesis via the establishment of a survival advantage to endogenous levels of stress in MMR-deficient cells.

In vitro expansion affects the response of human bone marrow stromal cells to irradiation

BACKGROUND

Bone marrow stromal cells (BMSCs) are extensively used in regeneration therapy and cytology experiments simulate how BMSCs respond to radiation. Due to the small number and the heterogeneity of primary isolated BMSCs, extensive in vitro expansion is usually required before application, which affects the cellular characteristics and gene expression of BMSCs. However, whether the radiation response of BMSCs changes during in vitro expansion is unclear.

METHODS

In this study, BMSCs were passaged in vitro and irradiated at passage 6 (P6) and passage 10 (P10). Then, apoptosis, the cell cycle, senescence, the cytokine secretion and the gene expression profile were analysed for the P6, P10, and non-irradiated (control) BMSCs at different post-irradiation time points.

RESULTS

The P6 BMSCs had a lower percentage of apoptotic cells than the P10 BMSCs at 24 and 48 h post-irradiation but not compared to that of the controls at 2 and 8 h post-irradiation. The P6 BMSCs had a lower percentage of cells in S phase and a higher percentage in G1 phase than the P10 BMSCs at 2 and 8 h post-irradiation. The radiation had similar effects on the senescent cell level and impaired immunomodulation capacity of the P6 and P10 BMSCs. Regardless of whether they were irradiated, the P6 and P10 BMSCs always expressed a distinctive set of genes. The upregulated genes were enriched in pathways including the cell cycle, DNA replication and oocyte meiosis. Then, a subset of conserved irradiation response genes across the BMSCs was identified, comprising 12 differentially upregulated genes and 5 differentially downregulated genes. These genes were especially associated with the p53 signaling pathway, DNA damage and DNA repair. Furthermore, validation experiments revealed that the mRNA and protein levels of these conserved genes were different between the P6 and P10 BMSCs after irradiation. Weighted gene co-expression network analysis supported these findings and further revealed the effects of cell passage on the irradiation response in BMSCs.

CONCLUSION

The results indicated that cell passage in vitro affected the irradiation response of BMSCs via molecular mechanisms that mediated differences in apoptosis, the cell cycle, senescence and the cytokine secretion. Thus, accurate cell passage information is not only important for transplantation therapy but also for future studies on the radiation response in BMSCs.

Role of N-acetyl cysteine and acetyl-l-carnitine combination treatment on DNA-damage-related genes induced by radiation in HEI-OC1 cells

PURPOSE

The aim of the present study was to evaluate the effect of acetyl-l-carnitine (ALC) and N-acetyl cysteine (NAC) on ionizing radiation (IR)-induced cytotoxicity and change in DNA damage-related genes in House Ear Institute-Organ of Corti 1 (HEI-OC1) cells.

METHODS

HEI-OC1 cells were irradiated with 5 Gy radiation and treated by eight combinations of NAC and/or ALC: control, NAC, ALC, IR, NAC + IR, ALC + NAC, ALC + IR, and ALC + NAC + IR. Cell viability, apoptotic cell death, and DNA damage were measured at the 72nd hour. Eighty-four IR-induced DNA-damage-related genes were determined by RT-PCR gene array and >10-fold changes were considered significant.

RESULTS

IR decreased cell viability by about 50% at 72 hours of incubation. In particular, the ALC and/or NAC combination before IR protected the HEI-OC1 cells (p < .05). Single and combination treatment prior to IR led to lower apoptotic cell death (p < .05). There was a significant lower DNA damage in ALC + NAC + IR group compared to IR group (p < .05). Expressions of Brca2, Xpc, Mlh3, Rad51, Xrcc2, Hus1, Rad9a, Cdkn1a, Gadd45a which are the DNA-repair genes were found to be significantly higher in NAC + ALC + IR group than those in individual treatment of ALC or NAC.

CONCLUSIONS

ALC and/or NAC treatment prior to IR led to higher cell viability and lower apoptotic cell damage compared to the IR group. The results of the study show that the ALC + NAC combination treatment inhibits DNA damage and induces DNA-repair genes to repair radiation damage, and this combination treatment is more effective against radiation-induced DNA damage than NAC or ALC therapy individually.

Divergent evolution of temozolomide resistance in glioblastoma stem cells is reflected in extracellular vesicles and coupled with radiosensitization

Background

Glioblastoma (GBM) is almost invariably fatal due to failure of standard therapy. The relapse of GBM following surgery, radiation, and systemic temozolomide (TMZ) is attributed to the ability of glioma stem cells (GSCs) to survive, evolve, and repopulate the tumor mass, events on which therapy exerts a poorly understood influence.

Methods

Here we explore the molecular and cellular evolution of TMZ resistance as it emerges in vivo (xenograft models) in a series of human GSCs with either proneural (PN) or mesenchymal (MES) molecular characteristics.

Results

We observed that the initial response of GSC-initiated intracranial xenografts to TMZ is eventually replaced by refractory growth pattern. Individual tumors derived from the same isogenic GSC line expressed divergent and complex profiles of TMZ resistance markers, with a minor representation of O6-methylguanine DNA methyltransferase (MGMT) upregulation. In several independent TMZ-resistant tumors originating from MES GSCs we observed a consistent diminution of mesenchymal features, which persisted in cell culture and correlated with increased expression of Nestin, decline in transglutaminase 2 and sensitivity to radiation. The corresponding mRNA expression profiles reflective of TMZ resistance and stem cell phenotype were recapitulated in the transcriptome of exosome-like extracellular vesicles (EVs) released by GSCs into the culture medium.

Conclusions

Intrinsic changes in the tumor-initiating cell compartment may include loss of subtype characteristics and reciprocal alterations in sensitivity to chemo- and radiation therapy. These observations suggest that exploiting therapy-induced changes in the GSC phenotype and alternating cycles of therapy may be explored to improve GBM outcomes.

CRIF1-CDK2 Interface Inhibitors: An Unprecedented Strategy for Modulation of Cell Radiosensitivity

Cyclin-dependent kinases (CDKs) are historic therapeutic targets implicated in tumorigenic events due to their critical involvement in the cell cycle phase. However, selectivity has proven to be a bottleneck, causing repeated failures. Previously, we reported CR6-interacting factor 1 (CRIF1), acting as a cell cycle negative regulator through interaction with CDK2. In the current report, we identified the CRIF1-CDK2 interaction interface by in silico studies and shortlisted interface inhibitors through virtual screening on CRIF1 using 40 678 drug-like compounds. These compounds were tested by cell proliferation assay, and four of these molecules were found to selectively inhibit the proliferation of osteosarcoma (OS) cell lines, but do not affect normal bone mesenchymal stem cells (BMSC). A binding study reveals significant affinities of the inhibitors on CRIF1. More importantly, treatment of the OS cells with a combination of ionizing radiation (IR) and the best-performing inhibitors remarkably increased IR inhibition potential from 19.9% to 59.6%. This occurred by selectively promoting G2/M arrest and apoptosis related to CDK2 overactivation in OS cells but not in BMSC and was supported by significant CDK2 phosphorylation modifications. Knocking down of CRIF1 by siRNA treatment showed similar effects to the interface inhibitors. Together we substantiate the identification of novel lead molecules, which may provide a new treatment to overcome selectivity issues and enhance the radiosensitivity of tumor cells, opening a conceptually novel strategy of CDK-targeting for different cancer types.

Targeting DNA Double-Strand Break Repair Pathways to Improve Radiotherapy Response

More than half of cancer patients receive radiotherapy as a part of their cancer treatment. DNA double-strand breaks (DSBs) are considered as the most lethal form of DNA damage and a primary cause of cell death and are induced by ionizing radiation (IR) during radiotherapy. Many malignant cells carry multiple genetic and epigenetic aberrations that may interfere with essential DSB repair pathways. Additionally, exposure to IR induces the activation of a multicomponent signal transduction network known as DNA damage response (DDR). DDR initiates cell cycle checkpoints and induces DSB repair in the nucleus by non-homologous end joining (NHEJ) or homologous recombination (HR). The canonical DSB repair pathways function in both normal and tumor cells. Thus, normal-tissue toxicity may limit the targeting of the components of these two pathways as a therapeutic approach in combination with radiotherapy. The DSB repair pathways are also stimulated through cytoplasmic signaling pathways. These signaling cascades are often upregulated in tumor cells harboring mutations or the overexpression of certain cellular oncogenes, e.g., receptor tyrosine kinases, PIK3CA and RAS. Targeting such cytoplasmic signaling pathways seems to be a more specific approach to blocking DSB repair in tumor cells. In this review, a brief overview of cytoplasmic signaling pathways that have been reported to stimulate DSB repair is provided. The state of the art of targeting these pathways will be discussed. A greater understanding of the underlying signaling pathways involved in DSB repair may provide valuable insights that will help to design new strategies to improve treatment outcomes in combination with radiotherapy.

Assessment of DNA Damage After Ionizing Radiation Exposure in Patients Undergoing Cardiac Resynchronization Therapy Device Implantation or Atrial Fibrillation Ablation (The RADAR Study)

Background

There is limited data regarding effect of prolonged radiation exposure during electrophysiological (EP) procedures on direct DNA damage. Comet test has shown to assess DNA damage following radiation exposure.

Methods

We performed a single-center prospective observational study assessing direct DNA damage using the quantitative comet assay in patients undergoing cardiac resynchronization (CRT) and atrial fibrillation (AF) catheter ablation procedures. Venous comet assay was performed pre, immediately post procedure and at 3-month duration in twenty-two (N=22) patients who underwent catheter ablation for symptomatic AF and fourteen (N=14) patients who underwent CRT implantation.

Results

The median [interquartile range (IQR)] fluoroscopy time, radiation dose and dose area product (DAP) were 34.3 (27.97 - 45.48) minutes, 853.07 (611.36 - 1334.76) mGy and 16,994.10 (9,023.65 - 58,845.00) UGym2 in the ablation group and 30.05 (18.75 - 37.33) minutes, 345.00 (165.09 - 924.79) mGy and 11,837.20 [7182.67 - 35567.75] UGym2 in the CRT group. When compared with pre-procedure, there was a statistically significant increase in median (IQR) DNA migration on comet assay in the ablation group immediately post procedure [+6.55 µm (0.78, 10.25, p=0.02)] that subsequently decreased at 3 months [-1.00 µm (-2.20, 0.78), p=0.03] but not in the CRT group.

Conclusion

There was a significant increase in DNA damage as detected by comet assay immediately post procedure that normalized at 3 months in patients undergoing AF ablation. Further large prospective studies are warranted to evaluate the impact of this prolonged radiation exposure and DNA damage on long-term follow up.

Impact of DNA repair gene polymorphisms on the risk of biochemical recurrence after radiotherapy and overall survival in prostate cancer

The identification of biomarkers of biochemical recurrence (BCR) in prostate cancer (PCa) patients undergoing radiotherapy (RT) represents an unanswered clinical issue. The primary aim of this study was the definition of new genetic prognostic biomarkers in DNA repair genes (DRGs), considering both BCR and overall survival (OS) as clinical end-points. The secondary aim was to explore the potential clinical impact of these genetic variants with the decision curve analysis (DCA) and the sensitivity analysis.We analyzed 22 germline polymorphisms in 14 DRGs on 542 Caucasian PCa patients treated with RT as primary therapy. Significant associations were further tested with a bootstrapping technique. According to our analyses, ERCC2-rs1799793 and EXO1-rs4149963 were significantly associated with BCR (p = 0.01 and p = 0.01, respectively). Moreover, MSH6-rs3136228 was associated with a worse OS (p = 0.04). Nonetheless, the DCA and the sensitivity analyses gave no ultimate response about the clinical impact of such variants.This study highlights the potential prognostic role of polymorphisms in DRGs for PCa, paving the way to the introduction of not invasive tools for the personalization of patients management. Nonetheless, other prospective studies are necessary to ultimately clarify the clinical impact of pharmacogenetics in PCa.

Low-dose irradiation promotes Rad51 expression by down-regulating miR-193b-3p in hepatocytes

Current evidence indicates that there is a relationship between microRNA (miRNA)-mediated gene silencing and low-dose irradiation (LDIR) responses. Here, alterations of miRNA expression in response to LDIR exposure in male BALB/c mice and three different types of hepatocytes were investigated. The miRNome of the LDIR-exposed mouse spleens (0.01 Gy, 6.5 mGy/h) was analyzed, and the expression of miRNA and mRNA was validated by qRT-PCR. Western blotting, chromatin immunoprecipitation (ChIP), and luciferase assays were also performed to evaluate the interaction between miRNAs and their target genes and to gain insight into the regulation of miRNA expression. The expression of miRNA-193b-3p was down-regulated in the mouse spleen and liver and in various hepatocytes (NCTC, Hepa, and HepG2 cell lines) in response to LDIR. The down-regulation of miR-193b-3p expression was caused by histone deacetylation on the miR-193b-3p promoter in the HepG2 cells irradiated with 0.01 Gy. However, the alteration of histone deacetylation and miR-193b-3p and Rad51 expression in response to LDIR was restored by pretreatment with N-acetyl-cyctein. In conclusion, we provide evidence that miRNA responses to LDIR include the modulation of cellular stress responses and repair mechanisms.

Non-canonical actions of mismatch repair

At the heart of the mismatch repair (MMR) system are proteins that recognize mismatches in DNA. Such mismatches can be mispairs involving normal or damaged bases or insertion/deletion loops due to strand misalignment. When such mispairs are generated during replication or recombination, MMR will direct removal of an incorrectly paired base or block recombination between nonidentical sequences. However, when mispairs are recognized outside the context of replication, proper strand discrimination between old and new DNA is lost, and MMR can act randomly and mutagenically on mispaired DNA. Such non-canonical actions of MMR are important in somatic hypermutation and class switch recombination, expansion of triplet repeats, and potentially in mutations arising in nondividing cells. MMR involvement in damage recognition and signaling is complex, with the end result likely dependent on the amount of DNA damage in a cell.

TRIM29 regulates the assembly of DNA repair proteins into damaged chromatin

Although DNA double-strand break (DSB) repair is mediated by numerous proteins accumulated at DSB sites, how DNA repair proteins are assembled into damaged chromatin has not been fully elucidated. Here we show that a member of the tripartite motif protein family, TRIM29, is a histone-binding protein responsible for DNA damage response (DDR). We found that TRIM29 interacts with BRCA1-associated surveillance complex, cohesion, DNA-PKcs and components of TIP60 complex. The dynamics of the TRIM29-containing complex on H2AX nucleosomes is coordinated by a cross-talk between histone modifications. TRIM29 binds to modified histone H3 and H4 tails in the context of nucleosomes. Furthermore, chromatin binding of TRIM29 is required for the phosphorylation of H2AX and cell viability in response to ionizing radiation. Our results suggest that TRIM29 functions as a scaffold protein to assemble DNA repair proteins into chromatin followed by efficient activation of DDR.

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.

Aberrant methylation of the MSH3 promoter and distal enhancer in esophageal cancer patients exposed to first-hand tobacco smoke

PURPOSE

Polymorphisms in MSH3 gene confer risk of esophageal cancer when in combination with tobacco smoke exposure. The purpose of this study was to investigate the methylation status of MSH3 gene in esophageal cancer patients in order to further elucidate possible role of MSH3 in esophageal tumorigenesis.

METHODS

We applied nested methylation-specific polymerase chain reaction to investigate the methylation status of the MSH3 promoter in tumors and matching adjacent normal-looking tissues of 84 esophageal cancer patients from a high-risk South African population. The Cancer Genome Atlas data were used to examine DNA methylation profiles at 17 CpG sites located in the MSH3 locus.

RESULTS

Overall, promoter methylation was detected in 91.9 % of tumors, which was significantly higher compared to 76.0 % in adjacent normal-looking esophageal tissues (P = 0.008). When samples were grouped according to different demographics (including age, gender and ethnicity) and smoking status of patients, methylation frequencies were found to be significantly higher in tumor tissues of Black subjects (P = 0.024), patients of 55-65 years of age (P = 0.032), males (P = 0.037) and tobacco smokers (P = 0.015). Furthermore, methylation of the MSH3 promoter was significantly more frequent in tumor samples from smokers compared to tumor samples from non-smokers [odds ratio (OR) = 31.9, P = 0.031]. The TCGA data confirmed significantly higher DNA methylation level at the MSH3 promoter region in tumors (P = 0.0024). In addition, we found evidence of an aberrantly methylated putative MSH3-associated distal enhancer element.

CONCLUSION

Our results suggest that methylation of MSH3 together with exposure to tobacco smoke is involved in esophageal carcinogenesis. Due to the active role of the MSH3 protein in modulating chemosensitivity of cells, methylation of MSH3 should further be examined in association with the outcome of esophageal cancer treatment using anticancer drugs.

Watermelon (Citrullus lanatus (Thunb.) Matsum. and Nakai) juice modulates oxidative damage induced by low dose X-ray in mice

Watermelon is a natural product that contains high level of antioxidants and may prevent oxidative damage in tissues due to free radical generation following an exposure to ionizing radiation. The present study aimed to investigate the radioprotective effects of watermelon (Citrullus lanatus (Thunb.) Matsum. and Nakai) juice against oxidative damage induced by low dose X-ray exposure in mice. Twelve adult male ICR mice were randomly divided into two groups consisting of radiation (Rx) and supplementation (Tx) groups. Rx received filtered tap water, while Tx was supplemented with 50% (v/v) watermelon juice for 28 days ad libitum prior to total body irradiation by 100 μGy X-ray on day 29. Brain, lung, and liver tissues were assessed for the levels of malondialdehyde (MDA), apurinic/apyrimidinic (AP) sites, glutathione (GSH), and superoxide dismutase (SOD) inhibition activities. Results showed significant reduction of MDA levels and AP sites formation of Tx compared to Rx (P < 0.05). Mice supplemented with 50% watermelon juice restore the intracellular antioxidant activities by significantly increased SOD inhibition activities and GSH levels compared to Rx. These findings may postulate that supplementation of 50% watermelon (Citrullus lanatus (Thunb.) Matsum. and Nakai) juice could modulate oxidative damage induced by low dose X-ray exposure.