Increased Radiosensitivity of Solid Tumors Harboring ATM and BRCA1/2 Mutations.

PURPOSE: Preclinical data indicate that response to radiotherapy (RT) depends on DNA damage repair. In this study, we investigated the role of mutations in genes related to DNA damage repair in treatment outcome after RT. MATERIALS AND METHODS: Patients with solid tumor who participated in next generation sequencing panel screening using biopsied tumor tissue between October 2013 and February 2019 were reviewed and 97 patients that received RT were included in this study. Best response to RT and the cumulative local recurrence rate (LRR) were compared according to absence or presence of missense, nonsense, and frameshift mutations in ATM and/or BRCA1/2. RESULTS: Of the 97 patients, five patients harbored mutation only in ATM, 22 in only BRCA1/2, and six in both ATM and BRCA1/2 (ATMmtBRCAmt). Propensity score matching was performed to select the control group without mutations (ATMwtBRCAwt, n=33). In total, 90 RT-treated target lesions were evaluated in 66 patients. Highest objective response rate of 80% was observed in ATMmtBRCAmt lesions (p=0.007), which was mostly durable. Furthermore, the cumulative 1-year LRR was the lowest in ATMmtBRCAmt lesions and the highest in ATMwtBRCAwt lesions (0% vs. 47.9%, p=0.008). RT-associated toxicities were observed in 10 treatments with no significant difference among the subgroups (p=0.680). CONCLUSION: Tumors with ATM and BRCA1/2 mutations exhibited superior tumor response and local control after RT compared to tumors without these mutations. The results are hypothesis generating and suggest the need for integrating the tumor mutation profile of DNA repair genes during treatment planning.

DNA Double-Strand Breaks Induced in Human Cells by Twelve Metallic Species: Quantitative Inter-Comparisons and Influence of the ATM Protein.

Despite a considerable amount of data, the molecular and cellular bases of the toxicity due to metal exposure remain unknown. Recent mechanistic models from radiobiology have emerged, pointing out that the radiation-induced nucleo-shuttling of the ATM protein (RIANS) initiates the recognition and the repair of DNA double-strand breaks (DSB) and the final response to genotoxic stress. In order to document the role of ATM-dependent DSB repair and signalling after metal exposure, we applied twelve different metal species representing nine elements (Al, Cu, Zn Ni, Pd, Cd, Pb, Cr, and Fe) to human skin, mammary, and brain cells. Our findings suggest that metals may directly or indirectly induce DSB at a rate that depends on the metal properties and concentration, and tissue type. At specific metal concentration ranges, the nucleo-shuttling of ATM can be delayed which impairs DSB recognition and repair and contributes to toxicity and carcinogenicity. Interestingly, as observed after low doses of ionizing radiation, some phenomena equivalent to the biological response observed at high metal concentrations may occur at lower concentrations. A general mechanistic model of the biological response to metal exposure based on the nucleo-shuttling of ATM is proposed to describe the metal-induced stress response and to define quantitative endpoints for toxicity and carcinogenicity.

Mathematical Model of ATM Activation and Chromatin Relaxation by Ionizing Radiation.

We propose a comprehensive mathematical model to study the dynamics of ionizing radiation induced Ataxia-telangiectasia mutated (ATM) activation that consists of ATM activation through dual mechanisms: the initiative activation pathway triggered by the DNA damage-induced local chromatin relaxation and the primary activation pathway consisting of a self-activation loop by interplay with chromatin relaxation. The model is expressed as a series of biochemical reactions, governed by a system of differential equations and analyzed by dynamical systems techniques. Radiation induced double strand breaks (DSBs) cause rapid local chromatin relaxation, which is independent of ATM but initiates ATM activation at damage sites. Key to the model description is how chromatin relaxation follows when active ATM phosphorylates KAP-1, which subsequently spreads throughout the chromatin and induces global chromatin relaxation. Additionally, the model describes how oxidative stress activation of ATM triggers a self-activation loop in which PP2A and ATF2 are released so that ATM can undergo autophosphorylation and acetylation for full activation in relaxed chromatin. In contrast, oxidative stress alone can partially activate ATM because phosphorylated ATM remains as a dimer. The model leads to predictions on ATM mediated responses to DSBs, oxidative stress, or both that can be tested by experiments.

Sensitization of prostate cancer to radiation therapy: Molecules and pathways to target.

Radiation therapy is used to treat cancer by radiation-induced DNA damage. Despite the best efforts to eliminate cancer, some cancer cells survive irradiation, resulting in cancer progression or recurrence. Alteration in DNA damage repair pathways is common in cancers, resulting in modulation of their response to radiation. This article focuses on the recent findings about molecules and pathways that potentially can be targeted to sensitize prostate cancer cells to ionizing radiation, thereby achieving an improved therapeutic outcome.

The PDRG1 is an oncogene in lung cancer cells, promoting radioresistance via the ATM-P53 signaling pathway.

PDRG1, is short for P53 and DNA damage-regulated gene, which have been found over 10 years. Although severe studies have described the roles of PDRG1 separately in many kinds of tumors, how to act as an oncogene are unclear. To better verify the function of PDRG1 in lung cancer, both loss-function and gain-function of PDRG1 studies based on two human lung cancer lines were performed. Following the transfection of PDRG1, both A549 and 95-D cells showed significant changes in cell viability, the expression of some protein and apoptosis, which were all implied the PDRG1 is an oncogene. Another interesting finding is PDRG1 could promote radioresistance involved the ATM-p53 signaling pathway in lung cancer. If we combine radiotherapy with gene-targeted therapy together effectively, predominant effect may be acquired, which is a huge milestone in clinical cure about lung cancer.

Time, dose and ataxia telangiectasia mutated (ATM) status dependency of coding and noncoding RNA expression after ionizing radiation exposure.

Studies of gene expression have proved important in defining the molecular mechanisms of radiation action and identifying biomarkers of ionizing radiation exposure and susceptibility. The full transcriptional response to radiation is very complex since it also involves epigenetic mechanisms triggered by radiation exposure such as modifications of expression of noncoding RNA such as microRNAs (miRNAs) and long noncoding RNAs (lncRNAs) that have not been fully characterized. To improve our understanding of the transcriptional response to radiation, we simultaneously monitored the expression of ten protein-coding genes, as well as 19 miRNAs and 3 lncRNAs in a time- and dose-dependent manner in stimulated human T lymphocytes obtained from two healthy donors (C1 and C2) and one patient with ataxia telangiectasia (AT), which is a well characterized radiosensitivity disorder. After 2 Gy X irradiation, expression levels were monitored at time points ranging from 15 min up to 24 h postirradiation. The majority of genes investigated responded rapidly to radiation exposure, with the peak up-regulation (CDKN1A, SESN1, ATF3, MDM2, PUMA and GADD45A) or down-regulation (CCNB1) occurring 2-3 h postirradiation, while DDB2, FDXR and CCNG1 responded with slower kinetics reaching a peak of expression between 5 and 24 h. A significant modification of expression after radiation exposure was observed for miR-34a-5p and miR-182-5p, with an up-regulation occurring at late time points reaching two to threefold at 24 h. Differences between two donors in miR-182-5p response to radiation were detected: for C2, up-regulation reached a plateau-phase around 5 Gy, while for C1, up-regulation was at its maximum around 3 Gy and then decreased at higher doses. Among the three lncRNAs studied, TP53TG1 demonstrated a weak up-regulation, reaching a maximum of 1.5-fold at 24 h after radiation exposure. Conversely, FAS-AS1 was up-regulated up to fivefold by 5 Gy irradiation. Our results indicate that expression of the majority of protein-coding genes allows discrimination of the AT from healthy donors when analyzed at 2 h. However, differences in expression between AT and healthy donors are no longer detectable 24 h postirradiation although, interestingly, linear dose responses for some of the genes studied are obtained at this time point. Furthermore, our study shows that miRNAs miR-34a-5p and miR-182-5p are responsive to radiation exposure in a dose- and time-dependent manner. Additionally, to the best of our knowledge, this is the first study to report that FAS-AS1 lncRNA is up-regulated by radiation exposure in an ATM-dependent fashion in human T lymphocytes.

Brd4 shields chromatin from ATM kinase signaling storms.

Upon activation, ataxia telangiectasia mutated (ATM) kinase rapidly phosphorylates hundreds of proteins, setting off chaotic signaling storms from areas of damaged chromatin. Recent work by Kaidi and Jackson and Floyd et al. advance our knowledge of the mechanisms that initiate or limit ATM kinase signaling storms at chromatin.

Activation of the phosphorylation of ATM contributes to radioresistance of glioma stem cells.

Ionizing radiation (IR) is currently the most efficient therapy available for malignant glioma. Unfortunately, this strategy is palliative due to the characteristics of radioresistance of malignant glioma. The aim of our study was to compare glioma stem cells (GSCs) with glioma cells (GCs) to determine whether GSCs are responsible for the radioresistance phenotype and to elucidate whether cell cycle checkpoint proteins are responsible for the radioresistance of GSCs. In this study, CD133 (a marker of brain cancer stem cells) and nestin were co-expressed in GSCs isolated from GCs. The percent of CD133+ cells in GSCs and GCs were >80 and <2%, respectively. Significantly more GSCs survived following 2, 4, 6 and 8 Gy IR than GCs. IR kills cancer cells primarily through DNA double-strand breaks (DSBs). The neutral comet assay is often used to intuitively show the level of DSBs. Significantly fewer GSCs showed DNA damage than GCs following 2 Gy IR. This demonstrated that GSCs are more resistant to in vitro radiation than GCs. Furthermore, activated ataxia telangiectasia mutated (ATM) is essential for the activation of downstream effector kinases, such as checkpoint kinase 2 (Chk2) and p53 which mainly contribute to the proper regulation of IR-induced arrest in the G1 phase. DNA damage induced by IR potently initiated activation of phosphorylation of the ATM, p53 and Chk2 checkpoint proteins. Activation of the phosphorylation of these checkpoint proteins was significantly higher in the GSCs compared to GCs. We found that inhibition of ATM activation induced cell cycle checkpoint defects and increased the rate of apoptosis of GSCs following IR. Our results suggest that GSCs were more resistant to radiation compared to GCs due to high expression of phosphorylated cell cycle checkpoint proteins, and inhibition of ATM could significantly reduce the radioresistance of GSCs and GCs. ATM may represent a source of radioresistance in GSCs and a target of improved radiosensitivity of GSCs.