Repair Of Radiation Damage Research Articles

Long non-coding RNA PANDAR promoted radiation and cisplatin-induced DNA damage repair through ATR/CHK1 in NSCLC.

DNA-damaging agents, including radiation and platinum-based chemotherapy, are indispensable treatments for non-small cell lung cancer (NSCLC) patients. However, cancer cells tend to be resistant to both radiation and chemotherapy, thus resulting in treatment failure or recurrence. The purpose of this study was to explore the effect and mechanism of long non-coding RNA (lncRNA) PANDAR (promoter of CDKN1A antisense DNA damage-activated RNA) on NSCLC sensitivity to radiation and chemotherapy. Cell counting kit (CCK-8), colony formation and flow cytometry were respectively performed to determine the cell cycle and apoptosis of NSCLC cells treated with γ-ray radiation and cisplatin. The extent of DNA damage was evaluated using a comet assay and immunofluorescence staining against γH2AX. In addition, we explored the role of PANDAR in DNA damage response pathways through western blot analysis. Finally, a nude mouse subcutaneous xenograft model was established to assess the sensitivity to radiation and chemotherapy in vivo. In cell experiments, PANDAR knockdown can increase the sensitivity of NSCLC cells to radiation and cisplatin. The CCK-8 results showed that cell viability was significantly increased in the overexpression group after radiation and cisplatin treatments. The overexpression group also showed more colonies, less apoptosis and DNA damage, and G2/M phase arrest was aggravated to provide the time necessary for DNA repair. Contrary to PANDAR overexpression, the trends were reversed in the PANDAR knockdown group. Furthermore, PANDAR knockdown inhibited radiation and cisplatin-activated phosphorylation levels of ATR and CHK1 in NSCLC cells. Finally, our in vivo model showed that targeting PANDAR significantly sensitized NSCLC to radiation and cisplatin. Our study showed that PANDAR knockdown promoted sensitivity to radiation and cisplatin in NSCLC by regulating the ATR/CHK1 pathway, thus providing a novel understanding as well as a therapeutic target for NSCLC treatment. In NSCLC cells, lncRNA PANDAR negatively regulates sensitivity to radiation and cisplatin. PANDAR can promote the repair of radiation and cisplatin-induced DNA damage and activation of the G2/M checkpoint through the ATR/CHK1 pathway. PANDAR knockdown results in defects in DNA damage repair accompanied by more cell apoptosis.

The gut microbiome and melanoma: A review.

Disturbances in the microbial ecosystem have been implemented in chronic inflammation, immune evasion and carcinogenesis, with certain microbes associated with the development of specific cancers. In recent times, the gut microbiome has been recognised as a potential novel player in the pathogenesis and treatment of malignant melanoma. It has been shown that the composition of gut microbiota in early-stage melanoma changes from in situ to invasive and then to metastatic disease. The gut bacterial and fungal profile has also been found to be significantly different in melanoma patients compared to controls. Multiple studies of immune checkpoint inhibitor (ICI) therapies have shown that the commensal microbiota may have an impact on anti-tumor immunity and therefore ICI response in cancer patients. When it comes to chemotherapy and radiotherapy treatments, studies demonstrate that gut microbiota are invaluable in the repair of radiation and chemotherapy-induced damage and therapeutic manipulation of gut microbiota can be an effective strategy to deal with side effects. Studies demonstrate the oncogenic and tumor-suppressive properties of the gut microbiome, which may play a role in the pathogenesis of melanoma. Despite this, investigations into specific interactions are still in its infancy, but starting to gain momentum as more significant and clinically relevant effects are emerging.

Low Dose Gamma Irradiation of Trypanosoma evansi Parasites Identifies Molecular Changes That Occur to Repair Radiation Damage and Gene Transcripts That May Be Involved in Establishing Disease in Mice Post-Irradiation.

The protozoan parasite Trypanosoma evansi is responsible for causing surra in a variety of mammalian hosts and is spread by many vectors over a wide geographical area making it an ideal target for irradiation as a tool to study the initial events that occur during infection. Parasites irradiated at the representative doses 100Gy, 140Gy, and 200Gy were used to inoculate BALB/c mice revealing that parasites irradiated at 200Gy were unable to establish disease in all mice. Cytokine analysis of mice inoculated with 200Gy of irradiated parasites showed significantly lower levels of interleukins when compared to mice inoculated with non-irradiated and 100Gy irradiated parasites. Irradiation also differentially affected the abundance of gene transcripts in a dose-dependent trend measured at 6- and 20-hours post-irradiation with 234, 325, and 484 gene transcripts affected 6 hours post-irradiation for 100Gy-, 140Gy- and 200Gy-irradiated parasites, respectively. At 20 hours post-irradiation, 422, 381, and 457 gene transcripts were affected by irradiation at 100Gy, 140Gy, and 200Gy, respectively. A gene ontology (GO) term analysis was carried out for the three representative doses at 6 hours and 20 hours post-irradiation revealing different processes occurring at 20 hours when compared to 6 hours for 100Gy irradiation. The top ten most significant processes had a negative Z score. These processes fall in significance at 140Gy and even further at 200Gy, revealing that they were least likely to occur at 200Gy, and thus may have been responsible for infection in mice by 100Gy and 140Gy irradiated parasites. When looking at 100Gy irradiated parasites 20 hours post-irradiation processes with a positive Z score, we identified genes that were involved in multiple processes and compared their fold change values at 6 hours and 20 hours. We present these genes as possibly necessary for repair from irradiation damage at 6 hours and suggestive of being involved in the establishment of disease in mice at 20 hours post-irradiation. A potential strategy using this information to develop a whole parasite vaccine is also postulated.

Histone chaperone FACT complex inhibitor CBL0137 interferes with DNA damage repair and enhances sensitivity of medulloblastoma to chemotherapy and radiation.

Medulloblastoma (MB) is a malignant pediatric brain tumor with a poor prognosis. Post-surgical radiation and cisplatin-based chemotherapy have been a mainstay of treatment, which often leads to substantial neurocognitive impairments and morbidity, highlighting the need for a novel therapeutic target to enhance the sensitivity of MB tumors to cytotoxic therapies. We performed a comprehensive study using a cohort of 71MB patients' samples and pediatric MB cell lines and found that MB tumors have elevated levels of nucleosome remodeling FACT (FAcilitates Chromatin Transcription) complex and DNA repair enzyme AP-endonuclease1 (APE1). FACT interacts with APE1 and facilitates recruitment and acetylation of APE1 to promote repair of radiation and cisplatin-induced DNA damage. Further, levels of FACT and acetylated APE1 both are correlate strongly with MB patients' survival. Targeting FACT complex with CBL0137 inhibits DNA repair and alters expression of a subset of genes, and significantly improves the potency of cisplatin and radiation in vitro and in MB xenograft. Notably, combination of CBL0137 and cisplatin significantly suppressed MB tumor growth in an intracranial orthotopic xenograft model. We conclude that FACT complex promotes chemo-radiation resistance in MB, and FACT inhibitor CBL0137 can be used as a chemo-radiation sensitizer to augment treatment efficacy and reduce therapy-related toxicity in high-risk pediatric patients.

Characteristic differences in radiation-induced DNA damage response in human papillomavirus-negative and human papillomavirus-positive head and neck cancers with accumulation of fractional radiation dose.

Superior treatment responses by patients with human papillomavirus (HPV) positive head and neck squamous cell carcinoma (HNSCC), compared to patients with HNSCC from other causes, drive biomarker research to optimize treatment. Most HNSCC patients receive radiation therapy delivered as a fractionated course. Changing HPV status in HNSCC from a positive prognostic marker to a predictive one requires biomarkers that capture cellular radiation response to cumulative dose. Nuclear enlargement, γH2AX expression and micronuclei count, were studied in six HNSCC cell lines after 4 Gy fractionated X-irradiation. All HNSCC cell lines displayed altered cellular responses, indicating increasing inability to repair radiation damage with subsequent radiation fractions. Increases in nuclear area were significantly greater among HPV positive cell lines (207% and 67% for the HPV positive and HPV negative groups, respectively). A different character of DNA repair dysfunction in the HPV positive group suggests greater chromosomal translocation with accumulated radiation dose.

Dual Characters of GH-IGF1 Signaling Pathways in Radiotherapy and Post-radiotherapy Repair of Cancers.

Radiotherapy remains one of the most important cancer treatment modalities. In the course of radiotherapy for tumor treatment, the incidental irradiation of adjacent tissues could not be completely avoided. DNA damage is one of the main factors of cell death caused by ionizing radiation, including single-strand (SSBs) and double-strand breaks (DSBs). The growth hormone-Insulin-like growth factor 1 (GH-IGF1) axis plays numerous roles in various systems by promoting cell proliferation and inhibiting apoptosis, supporting its effects in inducing the development of multiple cancers. Meanwhile, the GH-IGF1 signaling involved in DNA damage response (DDR) and DNA damage repair determines the radio-resistance of cancer cells subjected to radiotherapy and repair of adjacent tissues damaged by radiotherapy. In the present review, we firstly summarized the studies on GH-IGF1 signaling in the development of cancers. Then we discussed the adverse effect of GH-IGF1 signaling in radiotherapy to cancer cells and the favorable impact of GH-IGF1 signaling on radiation damage repair to adjacent tissues after irradiation. This review further summarized recent advances on research into the molecular mechanism of GH-IGF1 signaling pathway in these effects, expecting to specify the dual characters of GH-IGF1 signaling pathways in radiotherapy and post-radiotherapy repair of cancers, subsequently providing theoretical basis of their roles in increasing radiation sensitivity during cancer radiotherapy and repairing damage after radiotherapy.

Everything you wanted to know about space radiation but were afraid to ask

The space radiation environment is a complex combination of fast-moving ions derived from all atomic species found in the periodic table. The energy spectrum of each ion species varies widely but is prominently in the range of 400–600 MeV/n. The large dynamic range in ion energy is difficult to simulate in ground-based radiobiology experiments. Most ground-based irradiations with mono-energetic beams of a single one ion species are delivered at comparatively high dose rates. In some cases, sequences of such beams are delivered with various ion species and energies to crudely approximate the complex space radiation environment. This approximation may cause profound experimental bias in processes such as biologic repair of radiation damage, which are known to have strong temporal dependencies. It is possible that this experimental bias leads to an over-prediction of risks of radiation effects that have not been observed in the astronaut cohort. None of the primary health risks presumably attributed to space radiation exposure, such as radiation carcinogenesis, cardiovascular disease, cognitive deficits, etc., have been observed in astronaut or cosmonaut crews. This fundamentally and profoundly limits our understanding of the effects of GCR on humans and limits the development of effective radiation countermeasures.

Mesenchymal Stem Cell-Derived Exosomes: Biological Function and Their Therapeutic Potential in Radiation Damage.

Radiation-induced damage is a common occurrence in cancer patients who undergo radiotherapy. In this setting, radiation-induced damage can be refractory because the regeneration responses of injured tissues or organs are not well stimulated. Mesenchymal stem cells have become ideal candidates for managing radiation-induced damage. Moreover, accumulating evidence suggests that exosomes derived from mesenchymal stem cells have a similar effect on repairing tissue damage mainly because these exosomes carry various bioactive substances, such as miRNAs, proteins and lipids, which can affect immunomodulation, angiogenesis, and cell survival and proliferation. Although the mechanisms by which mesenchymal stem cell-derived exosomes repair radiation damage have not been fully elucidated, we intend to translate their biological features into a radiation damage model and aim to provide new insight into the management of radiation damage.

The prognostic value of excision repair cross-complementing Group 1 expression in nasopharyngeal cancer patients.

Background:Overexpression of excision repair cross-complementing Group 1 (ERCC-1) is related to cisplatin resistance and defective repair of radiation damage. The purpose of this study was to evaluate the clinical significance of excision (ERCC-1) expression in nasopharyngeal cancer (NPC).Materials and Methods:We conducted a retrospective review of patients diagnosed with NPC between 2000 and 2013. The archived tissues were analyzed using immunohistochemistry to determine ERCC-1 expression. The ERCC-1 expression level along with other clinical factors and overall survival (OS) were analyzed. Hazard ratio (HR) with a 95% confidence interval was calculated to assess the risk.Results:The analysis of ERCC-1 expression was available in 262 NPC patients who had medical records at our hospital. Among those patients, 221 (84%) were treated with curative radiotherapy (RT)/concurrent chemoradiotherapy, 22 (7%) were treated with palliative RT alone, and 19 (9%) were given best supportive care. There was no correlation between ERCC-1 expression and stage of cancer or OS. No difference in 5-year OS was found between patients with low ERCC-1 expression and high ERCC-1 expression (38% vs. 36%; P = 0.981). The adjusted HR (aHR) of cancer death increased with cancer stage (aHR = 2.93 for advanced Stages III–IV; P = 0.001) and age (aHR = 2.11 for age >55; P ≤ 0.001). ERCC-1 expression exhibited no prognostic significance in our study (aHR = 1).Conclusion:In this study, ERCC-1 expression has no statistical significance to be considered a prognostic factor for OS among NPC patients. On the other hand, cancer stage, age, and types of treatment can be prognostic factors in NPC patients.

Degradation and regeneration of radiation-induced defects in silicon: A study of vacancy-hydrogen interactions

Silicon lattice vacancies exist in all silicon wafers, will increase in concentration due to high temperature processing, can form recombination active defects and have been proposed as a possible candidate for LeTID. Despite this, there have been relatively few studies in the solar field dedicated to investigating vacancies, their recombination properties or their interaction with hydrogen. In this work, we use high energy electron radiation to create large numbers of vacancies in silicon and study the lifetime response to subsequent thermal processes in the presence or absence of bulk hydrogen. The radiation results in the formation of radiation-induced defects which we interpret as being related to the creation of vacancies in the silicon bulk. Modelling of injection dependent minority carrier lifetime finds that the defects formed via this radiation process have different Shockley-Read-Hall properties to LeTID and are as such, unlikely to be related. Furthermore, this defect can be removed during low temperature annealing but only if hydrogen is present in the bulk of the silicon wafers. This is in contrast to samples with no bulk hydrogen which do not recover during low temperature annealing. The study thus finds no evidence for any link between LeTID and vacancies in silicon, but it does demonstrate the ability of hydrogen to repair radiation damage.

Analysis of DNA Damage Response Gene Alterations and Tumor Mutational Burden Across 17,486 Tubular Gastrointestinal Carcinomas: Implications for Therapy.

Alterations in the DNA damage response (DDR) pathway confer sensitivity to certain chemotherapies, radiation, and other DNA damage repair targeted therapies. BRCA1/2 are the most well-studied DDR genes, but recurrent alterations are described in other DDR pathway members across cancers. Deleterious DDR alterations may sensitize tumor cells to poly (ADP-ribose) polymerase inhibition, but there are also increasing data suggesting that there may also be synergy with immune checkpoint inhibitors. The relevance of DDR defects in gastrointestinal (GI) cancers is understudied. We sought to characterize DDR-defective GI malignancies and to explore genomic context and tumor mutational burden (TMB) to provide a platform for future rational investigations. Tumor samples from 17,486 unique patients with advanced colorectal, gastroesophageal, or small bowel carcinomas were assayed using hybrid-capture-based comprehensive genomic profiling including sequencing of 10 predefined DDR genes: ARID1A, ATM, ATR, BRCA1, BRCA2, CDK12, CHEK1, CHEK2, PALB2, and RAD51. TMB (mutations per megabase [mut/Mb]) was calculated from up to 1.14 Mb of sequenced DNA. Clinicopathologic features were extracted and descriptive statistics were used to explore genomic relationships among identified subgroups. DDR alterations were found in 17% of cases: gastric adenocarcinoma 475/1,750 (27%), small bowel adenocarcinoma 148/666 (22%), esophageal adenocarcinoma 467/2,501 (19%), and colorectal cancer 1,824/12,569 (15%). ARID1A (9.2%) and ATM (4.7%) were the most commonly altered DDR genes in this series, followed by BRCA2 (2.3%), BRCA1 (1.1%), CHEK2 (1.0%), ATR (0.8%), CDK12 (0.7%), PALB2 (0.6%), CHEK1 (0.1%) and RAD51 (0.1%). More than one DDR gene alteration was found in 24% of cases. High microsatellite instability (MSI-H) and high TMB (TMB-H, ≥20 mut/Mb) were found in 19% and 21% of DDR-altered cases, respectively. Of DDR-altered/TMB-H cases, 87% were also MSI-H. However, even in the microsatellite stable (MSS)/DDR-wild-type (WT) versus MSS/DDR-altered, TMB-high was seen more frequently (0.4% vs. 3.3%, P < .00001.) Median TMB was 5.4 mut/Mb in the MSS/DDR-altered subset versus 3.8 mut/Mb in the MSS/DDR-WT subset (P ≤ .00001), and ATR alterations were enriched in the MSS/TMB-high cases. This is the largest study to examine selected DDR defects in tubular GI cancers and confirms that DDR defects are relatively common and that there is an association between the selected DDR defects and a high TMB in more than 20% of cases. Microsatellite stable DDR-defective tumors with elevated TMB warrant further exploration. Deleterious DNA damage response (DDR) alterations may sensitize tumor cells to poly (ADP-ribose) polymerase inhibition, but also potentially to immune checkpoint inhibitors, owing to accumulation of mutations in DDR-defective tumors. The relevance of DDR defects in gastrointestinal (GI) cancers is understudied. This article characterizes DDR-defective GI malignancies and explores genomic context and tumor mutational burden to provide a platform for future rational investigations.

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.

Phase III Multi-Center, Prospective Randomized Trial Comparing High Dose Single Fraction Radiation Therapy to a 3-Fraction SBRT Regimen in the Treatment of Oligometastatic Human Cancer

Pre-clinical and clinical evidence have shown that high single dose radiation therapy (SDRT) is associated with superior tumor control compared to multi-fraction (MF) regimens, due to SDRT’s ability to engage a microvascular response interfering with the ability to repair radiation damage to tumor cell DNA. The primary objective of this study was to compare local control rates with either a single dose of 24Gy versus 27Gy in three 9Gy fractions in patients with oligometastatic disease. A secondary objective was to compare toxicity outcomes between the two cohorts. A total of 174 patients were enrolled at three institutions. 155 patients (75 randomized to the SDRT and 80 to the MF regimen) were assessable for treatment-related toxicities having met protocol criteria. A total of 117 patients with 154 treated lesions, were evaluable for the local disease control end point. Eligibility criteria for enrollment included ≤5 metastatic lesions documented on imaging studies, and no prior radiation therapy to the treated site. Eligible lesions were limited to non-mobile targets (osseous or lymph node metastases). Potential candidates whose target lesions were adjacent to critical organs, precluding treatment with SDRT due to the risk of treatment-induced complications, were excluded. Patients were followed every 6 months for a minimum of 2 years, and imaging evaluation of the treated site at 12 and 24 months post-treatment was mandatory. Responses were measured using standard RECIST criteria. For the assessment of toxicity, a minimum follow-up of 6 months was required. Median follow up was 39 months (range, 11-85). Lesions treated with SDRT demonstrated a significantly lower incidence of local disease progression (LR) compared to those treated with MF (p<0.0005). The 3-year incidence of LR was 6.1% of the lesions compared to 23% for the SDRT and MF regimens, respectively. A reduction in distant metastatic (DM) progression was noted among those treated with SDRT compared to the MF regimen The 3-year incidence of DM progression was 4.1% compared to 17.5% for the SDRT and MF regimens, respectively(p<0.02). There was no significant difference in grade 3+ toxicity between the two arms (SDRT: 10.7%; MF: 5%; p=0.24). The specific incidence of grade 3+ pain, peripheral neuropathy and bone fractures for the SDRT regimen was 5.3%, 2.7% and 1.3%. The corresponding incidence for these toxicities for the MF regimen was 1.3%, 0% and 2.5%. No overall survival differences were observed between the arms. The study provides Level 1 evidence that SDRT was associated with superior tumor control outcomes compared to a standard 3-fraction regimen in a cohort of patients with oligometastatic osseous/nodal disease. SDRT was well tolerated, rendering comparable toxicity outcomes to a current standard-of-care hypofractionated SBRT treatment regimen.

Controls on lithium concentration and diffusion in zircon

Thermal annealing of zircons prior to uranium-lead dating by laser ablation inductively coupled plasma mass spectrometry is a commonly-implemented procedure which improves data accuracy and precision by partially repairing radiation damage from the decay of uranium and thorium. However, it also leads to significantly higher concentrations of lithium in the zircon lattice, which become positively correlated with trivalent yttrium and rare earth elements. Prior to such treatments, zircons typically contain lithium below detection limits (typically <0.55 μg g−1), unless correlated with lanthanum and aluminum (i.e., melt/mineral inclusion tracer elements). This suggests that lithium in zircon is primarily sequestered within inclusions, and is able to permeate the crystal lattice to couple with yttrium and rare earth elements during the thermal annealing procedure. This process occurs 2–3 orders of magnitude faster than diffusion experiments have previously determined, indicating that another diffusion mechanism may apply. A model is proposed, whereby: (i) charge compensation of stoichiometrically over-abundant trivalent cations under water-rich magmatic conditions is likely accomplished by hydrogen, given the incompatibility of lithium in zircon and the abundance of hydrogen. However, (ii) conditions that are high temperature and low pressure (characteristic of both thermal annealing and the syn-eruptive environment), drive silicate melt inclusions to exsolve water, generating a motive force for both hydrogen and lithium from inclusions to permeate the lattice in order to reestablish electrochemical equilibrium between the interior and exterior of the zircon. To test the pressure dependency of lithium migration in the zircon lattice, thermal annealing experiments were performed at 850 °C and 1 bar, 2 kbar and 6 kbar using zircons from the Fish Canyon Tuff. The experiments demonstrate that thermal annealing at 2 and 6 kbar inhibits lithium mobility, with zircons registering lithium concentrations below detection limits similar to controls. The experimental results suggest that lithium concentrations in zircon are vulnerable to rapid perturbation by decompression (concurrent with high temperatures), which further indicate that lithium-in-zircon diffusion data should be interpreted with caution.

Abstract A111: The alkyl phosphocholine analog CLR1404 delays radiation-induced dsDNA damage repair in pediatric and adult solid tumors

Abstract Exposure of normal tissues to radiation is a major limitation in cancer radiotherapy, with significant consequences particularly in the pediatric setting. Increasing the selective anticancer effect of radiation on malignant cells utilizing cancer-targeted drugs could provide an option to lessen adverse radiation effects on healthy tissue. We investigated the radiosensitizing properties of 18-(p-iodophenyl) octadecyl phosphocholine (CLR1404), a clinical-grade phospholipid ether analog with selective sequestration in cancer cells, in pediatric and adult human solid tumor cell lines. Preliminary data in our laboratory using a fluorescently-labeled analog indicated that human cancer cells uptake and retain 6- to 10-fold more CLR1404 when compared with normal primary cells. In vitro, the clonogenic survival of tumor cells after irradiation was significantly decreased when cells were pretreated with CLR1404. This radiosensitizing effect was detected also in vivo, in xenograft-bearing mice treated with CLR1404 during fractionated radiation, resulting in decreased tumor volumes and markedly delayed tumor regrowth in CLR1404-treated mice compared to controls. We investigated mechanisms responsible for the radiosensitizing properties of CLR1404. Western blotting of tumor cell lysates indicated increased accumulation and prolonged persistence of γ-H2AX in irradiated tumor cells pretreated with CLR1404 compared to nontreated controls. Expression of select markers of homologous and non-homologous end-joining dsDNA radiation damage repair pathways were markedly decreased and significantly delayed in CLR1404-treated tumor cells after exposure to irradiation compared to non-CLR1404-treated cells. CLR1404 treatment also markedly decreased the activation of p53 after irradiation in p53-functional rhabdomyosarcoma cells compared to cells treated with radiation alone. In conclusion, our data show that, in both pediatric and adult human solid tumor cell lines, the alkyl phosphocholine analog CLR1404 interferes with sensing of dsDNA damage, delays DNA damage repair, and potentially interferes with other cell survival mechanisms, for example involving p53. These mechanisms might be responsible for the observed in vitro and in vivo radiosensitizing properties of CLR1404. Tumor-targeted radiosensitization with CLR1404 could improve the selective antitumor effect of radiation, and provide a distinct therapeutic benefit to cancer patients. Citation Format: Ankita Shahi, Mohamed Y. Elsaid, Dana C. Baiu, Eric A. Armstrong, Jamey P. Weichert, Paul M. Harari, Mario Otto. The alkyl phosphocholine analog CLR1404 delays radiation-induced dsDNA damage repair in pediatric and adult solid tumors [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A111.

Genomic footprints of dryland stress adaptation in Egyptian fat-tail sheep and their divergence from East African and western Asia cohorts

African indigenous sheep are classified as fat-tail, thin-tail and fat-rump hair sheep. The fat-tail are well adapted to dryland environments, but little is known on their genome profiles. We analyzed patterns of genomic variation by genotyping, with the Ovine SNP50K microarray, 394 individuals from five populations of fat-tail sheep from a desert environment in Egypt. Comparative inferences with other East African and western Asia fat-tail and European sheep, reveal at least two phylogeographically distinct genepools of fat-tail sheep in Africa that differ from the European genepool, suggesting separate evolutionary and breeding history. We identified 24 candidate selection sweep regions, spanning 172 potentially novel and known genes, which are enriched with genes underpinning dryland adaptation physiology. In particular, we found selection sweeps spanning genes and/or pathways associated with metabolism; response to stress, ultraviolet radiation, oxidative stress and DNA damage repair; activation of immune response; regulation of reproduction, organ function and development, body size and morphology, skin and hair pigmentation, and keratinization. Our findings provide insights on the complexity of genome architecture regarding dryland stress adaptation in the fat-tail sheep and showcase the indigenous stocks as appropriate genotypes for adaptation planning to sustain livestock production and human livelihoods, under future climates.

The Relative Biological Effect of Spread-Out Bragg Peak Protons in Sensitive and Resistant Tumor Cells

Variations in the radiosensitivity of tumor cells within and between tumors impact tumor response to radiation, including the dose required to achieve permanent local tumor control. The increased expression of DNA-PKcs, a key component of a major DNA damage repair pathway in tumors treated by radiation, suggests that DNA-PKcs-dependent repair is likely a cause of tumor cell radioresistance. This study evaluates the relative biological effect of spread-out Bragg-peak protons in DNA-PKcs-deficient cells and the same cells transfected with a functional DNA-PKcs gene. A cloned radiation-sensitive DNA-PKcs-deficient tumor line and its DNA-PKcs-transfected resistant counterpart were used in this study. The presence of functional DNA-PKcs was evaluated by DNA-PKcs autophosphorylation. Cells to be proton irradiated or x-irradiated were obtained from the same single cell suspension and dilution series to maximize precision. Cells were concurrently exposed to 6-MV x-rays or mid 137-MeV spread-out Bragg peak protons and cultured for colony formation. The surviving fraction data were well fit by the linear-quadratic model for each of 8 survival curves. The results suggest that the relative biological effectiveness of mid spread-out Bragg peak protons is approximately 6% higher in DNA-PKcs-mediated resistant tumor cells than in their DNA-PKcs-deficient and radiation-sensitive counterpart. DNA-PKcs-dependent repair of radiation damage is less capable of repairing mid spread-out Bragg peak proton lesions than photon-induced lesions, suggesting protons may be more efficient at sterilizing DNA-PKcs-expressing cells that are enriched in tumors treated by conventional fractionated dose x-irradiation.

Computational methods using genome-wide association studies to predict radiotherapy complications and to identify correlative molecular processes

The biological cause of clinically observed variability of normal tissue damage following radiotherapy is poorly understood. We hypothesized that machine/statistical learning methods using single nucleotide polymorphism (SNP)-based genome-wide association studies (GWAS) would identify groups of patients of differing complication risk, and furthermore could be used to identify key biological sources of variability. We developed a novel learning algorithm, called pre-conditioned random forest regression (PRFR), to construct polygenic risk models using hundreds of SNPs, thereby capturing genomic features that confer small differential risk. Predictive models were trained and validated on a cohort of 368 prostate cancer patients for two post-radiotherapy clinical endpoints: late rectal bleeding and erectile dysfunction. The proposed method results in better predictive performance compared with existing computational methods. Gene ontology enrichment analysis and protein-protein interaction network analysis are used to identify key biological processes and proteins that were plausible based on other published studies. In conclusion, we confirm that novel machine learning methods can produce large predictive models (hundreds of SNPs), yielding clinically useful risk stratification models, as well as identifying important underlying biological processes in the radiation damage and tissue repair process. The methods are generally applicable to GWAS data and are not specific to radiotherapy endpoints.

Escherichia coli RadD Protein Functionally Interacts with the Single-stranded DNA-binding Protein

The bacterial single-stranded DNA binding protein (SSB) acts as an organizer of DNA repair complexes. The radD gene was recently identified as having an unspecified role in repair of radiation damage and, more specifically, DNA double-strand breaks. Purified RadD protein displays a DNA-independent ATPase activity. However, ATP hydrolytic rates are stimulated by SSB through its C terminus. The RadD and SSB proteins also directly interact in vivo in a yeast two-hybrid assay and in vitro through ammonium sulfate co-precipitation. Therefore, it is likely that the repair function of RadD is mediated through interaction with SSB at the site of damage.

Computational analysis of androgen receptor dependent radiosensitivity in prostate cancer.

In this study, we quantitatively analyze the mechanism by which androgen deprivation therapy (ADT) is enhancing radiosensitivity in prostate cancer (PCa) patients. It has been shown in laboratory experiments, as well as in patient data in the literature, that the androgen receptor (AR) reduces the effectiveness of ionizing radiation treatment by enhancing the non-homologous end joining (NHEJ) repair of radiation damage. The suppression of AR by ADT suppresses the activity of NHEJ that leads to radiosensitivity in PCa patients. In this paper, we have studied this positive interaction between AR and NHEJ using mathematical models of the NHEJ that we have developed using both the experimental and clinical data for PCa. Our results show that the biological observation of suppression of AR by ADT leading to down-regulation of the first NHEJ protein Ku and NHEJ is a plausible biological mechanism that explains both the experimental and clinical observations in the literature. The presented analysis is the first step in quantitatively analyzing possible treatment scenarios to find the optimal treatment strategies for PCa using the combination treatment with ADT, NHEJ inhibitors, and IR.