Impact of time interval and dose rate on cell survival following low-dose fractionated exposures

The impact of dose rate on responses of human lens epithelial cells to ionizing irradiation

The knowledge on responses of human lens epithelial cells (HLECs) to ionizing radiation exposure is important to understand mechanisms of radiation cataracts that are of concern in the field of radiation protection and radiation therapy. However, biological effects in HLECs following protracted exposure have not yet fully been explored. Here, we investigated the temporal kinetics of γ-H2AX foci as a marker for DNA double-strand breaks (DSBs) and cell survival in HLECs after exposure to photon beams at various dose rates (i.e., 150 kVp X-rays at 1.82, 0.1, and 0.033 Gy/min, and 137Cs γ-rays at 0.00461 Gy/min (27.7 cGy/h) and 0.00081 Gy/min (4.9 cGy/h)), compared to those in human lung fibroblasts (WI-38). In parallel, we quantified the recovery for DSBs and cell survival using a biophysical model. The study revealed that HLECs have a lower DSB repair rate than WI-38 cells. There is no significant impact of dose rate on cell survival in both cell lines in the dose-rate range of 0.033-1.82 Gy/min. In contrast, the experimental residual γ-H2AX foci showed inverse dose rate effects (IDREs) compared to the model prediction, highlighting the importance of the IDREs in evaluating radiation effects on the ocular lens.

Intra-fractional dose rate effect in continuous and interrupted irradiation of the MCF-7 cell line: Possible radiobiological implications for breath-hold techniques in breast radiotherapy?

PURPOSE

To investigate the effects of different dose rates (DRs) in continuous and interrupted irradiation on in-vitro survival of the MCF-7 cell line, towards finding possible radiobiological effects of breath-hold techniques in breast radiotherapy (RT), in which intra-fractional beam interruptions and delivery prolongation can occur.

MATERIALS AND METHODS

MCF-7 cells were irradiated continuously or with regular interruptions using 6 MV x-rays at different accelerator DRs (50-400 cGy/min) to deliver a 2 Gy dose. The interrupted irradiation was delivered in a 10 s on, 10 s off manner. Then, cell survival and viability were studied using colony and MTT assays, respectively.

RESULTS

Survival and viability with continuous and interrupted irradiation were similar ( P > 0.5). A significant increase in survival at 50, 100, and 400 cGy/min compared to 200 and 300 cGy/min was observed, also a significant decreasing and then increasing trend from 50 to 200 cGy/min and 200 to 400 cGy/min, respectively ( P < 0.04). Relative to 200 cGy/min, the survival fractions at 50, 100, 300, and 400 cGy/min were 1.24, 1.23, 1.05, and 1.20 times greater, respectively. Cell viability did not show significant differences between the DRs, despite following the same trend as cell survival.

CONCLUSION

Our results suggest that for continuous irradiation of in-vitro MCF-7 cells, with increasing DR within the 50-400 cGy/min range, sensitivity increases and then decreases (inverse effect), also that up to doubling of treatment time in breath-hold techniques does not affect in-vitro radiobiological efficacy with 200-400 cGy/min accelerator DRs. Further confirmatory studies are required.

Persons chronically exposed to low doses of ionizing radiation: A cytogenetic dosimetry study

The dosimetry and control of exposure for individuals chronically exposed to ionizing radiation are important and complex issues. Assessment may be optimized by evaluating individual adaptation and radiosensitivity, but it is not possible for a single model to account for all relevant parameters. Our goal was to develop approaches for the calculation of doses for persons chronically exposed to ionizing radiation, taking their radiosensitivities into consideration. On the basis of ex vivo radiation of blood samples, dose-effect models were constructed for dose ranges 0.01-2.0 and 0.01-0.4 Gy, using different cytogenetic criteria. The frequencies of "dicentric chromosomes and rings" at low doses are too low to have predictive value. The different responses of subjects to radiation made it possible to categorize them according to their radiosensitivities and to generate separate dose-effect curves for radiosensitive, average, and radioresistant individuals, reducing the amount of error in retrospective dosimetry.

Theranostic 64Cu-DOTHA2-PSMA allows low toxicity radioligand therapy in mice prostate cancer model

Introduction

We have previously shown that copper-64 (⁶⁴Cu)-DOTHA₂-PSMA can be used for positron emission tomography (PET) imaging of prostate cancer. Owing to the long-lasting, high tumoral uptake of ⁶⁴Cu-DOTHA₂-PSMA, the objective of the current study was to evaluate the therapeutic potential of ⁶⁴Cu-DOTHA₂-PSMA in vivo.

Methods

LNCaP tumor-bearing NOD-Rag1^nullIL2rg^null (NRG) mice were treated with an intraveinous single-dose of ⁶⁴Cu-DOTHA₂-PSMA at maximal tolerated injected activity, ^natCu-DOTHA₂-PSMA at equimolar amount (control) or lutetium-177 (¹⁷⁷Lu)-PSMA-617 at 120 MBq to assess their impact on survival. Weight, well-being and tumor size were followed until mice reached 62 days post-injection or ethical limits. Toxicity was assessed through weight, red blood cells (RBCs) counts, pathology and dosimetry calculations.

Results

Survival was longer with ⁶⁴Cu-DOTHA₂-PSMA than with ^natCu-DOTHA₂-PSMA (p < 0.001). Likewise, survival was also longer when compared to ¹⁷⁷Lu-PSMA-617, although it did not reach statistical significance (p = 0.09). RBCs counts remained within normal range for the ⁶⁴Cu-DOTHA₂-PSMA group. ⁶⁴Cu-DOTHA₂-PSMA treated mice showed non-pathological fibrosis and no other signs of radiation injury. Human extrapolation of dosimetry yielded an effective dose of 3.14 × 10^-2 mSv/MBq, with highest organs doses to gastrointestinal tract and liver.

Discussion

Collectively, our data showed that ⁶⁴Cu-DOTHA₂-PSMA-directed radioligand therapy was effective for the treatment of LNCaP tumor-bearing NRG mice with acceptable toxicity and dosimetry. The main potential challenge is the hepatic and gastrointestinal irradiation.

Pulsed low dose-rate radiotherapy: radiobiology and dosimetry

Pulsed low dose-rate radiotherapy (PLDR) relies on two radiobiological findings, the hyper-radiosensitivity of tumor cells at small doses and the reduced normal tissue toxicity at low dose rates. This is achieved by delivering the daily radiation dose of 2 Gy in 10 sub-fractions (pulses) with a 3 min time interval, resulting in an effective low dose rate of 0.067 Gy min−1. In vitro cell studies and in vivo animal experiments demonstrated the therapeutic potential of PLDR treatments and provided useful preclinical data. Various treatment optimization strategies and delivery techniques have been developed for PLDR on existing linear accelerators. Preliminary results from early clinical studies have shown favorable outcomes for various treatment sites especially for recurrent cancers. This paper reviews the experimental findings of PLDR and dosimetric requirements for PLDR treatment planning and delivery, and summarizes major clinical studies on PLDR cancer treatments.

The Effect of High-Dose-Rate Pulsed Radiation on the Survival of Clinically Relevant Radioresistant Cells

We demonstrated that low dose pulsed radiation (0.25 Gy) at a high-dose-rate, even for very short intervals (10 s), decreases cell survival to a greater extent than single exposure to a similar total dose and dose rate. The objective of this study was to clarify whether high-dose-rate pulsed radiation is effective against SAS-R, a clinically relevant radioresistant cell line. Cell survival following high-dose-rate pulsed radiation was evaluated via a colony assay. Flow cytometry was utilized to evaluate γH2AX, a molecular marker of DNA double-strand breaks and delayed reactive oxygen species (ROS) associated with radiation-induced apoptosis. Increased cytotoxicity was observed in SAS-R and parent SAS cells in response to high dose rate pulsed radiation compared to single dose, as determined by colony assays. Residual γH2AX in both cells subjected to high-dose-rate pulsed radiation showed a tendency to increase, with a significant increase observed in SAS cells at 72 h. In addition, high-dose-rate pulsed radiation increased delayed ROS more than the single exposure did. These results indicate that high-dose-rate pulsed radiation was associated with residual γH2AX and delayed ROS, and high-dose-rate pulsed radiation may be used as an effective radiotherapy procedure against radioresistant cells.

Variation of 4 MV X-ray dose rate in fractionated irradiation strongly impacts biological endothelial cell response in vitro

PURPOSE

Even though X-ray beams are widely used in medical diagnosis or radiotherapy, the comparisons of their dose rates are scarce. We have recently demonstrated in vitro (clonogenic assay, cell viability, cell cycle, senescence) and in vivo (weight follow-up of animals and bordering epithelium staining of lesion), that for a single dose of irradiation, the relative biological effectiveness (RBE) deviates from 1 (up to twofold greater severe damage at the highest dose rate depending on the assay) when increasing the dose rate of high energy X-ray beams.

MATERIAL AND METHODS

To further investigate the impact of the dose rate on RBE, in this study, we performed in vitro fractionated irradiations by using the same two dose rates (0.63 and 2.5 Gy.min^-1) of high-energy X-rays (both at 4 MV) on normal endothelial cells (HUVECs). We investigated the viability/mortality, characterized radiation-induced senescence by using flow cytometry and measured gene analysis deregulations on custom arrays.

RESULTS

The overall results enlighten that, in fractionated irradiations when varying the dose rate of high-energy X-rays, the RBE of photons deviates from 1 (up to 2.86 for viability/mortality experiments performed 21 days postirradiation).

CONCLUSION

These results strengthen the interest of multiparametric analysis approaches in providing an accurate evaluation of the outcomes of irradiated cells in support of clonogenic assays, especially when such assays are not feasible.

[Comparison of 186Re to 662 keV photon radiation concerning biological radiation effect on the human B-cell line BV-173]

ZIEL: Ziel der Untersuchung ist es, die Strahlenwirkung des β--Emitters 186Re und von 662keV-Photonenstrahlung zu ermitteln, um die biologische Wirkung von Strahlung niedriger Dosisleistung (186Re) mit der hoher Dosisleistung zu vergleichen.

MATERIAL UND METHODEN

Zellen der humanen Leukämie-Zelllinie BV-173 wurden mit 662keV-Photonenstrahlung respektive 186Re bestrahlt. In einem Inkubationszeitraum von 7 Tagen wurden Zahl und Vitalität der Zellen täglich bestimmt und als Dosiseffektkurven basierend auf der Vitalität dargestellt. Hierfür wurde der Zeitpunkt mit minimalem Überleben verwendet (72h 186Re und 24h Photonenstrahlung).

ERGEBNISSE

Beide Strahlenarten zeigen am Auswertezeitpunkt (72h nach Versuchsbeginn für 186Re und 24h nach Versuchsbeginn für Photonenstrahlung) eine Überlebenskurve mit biexponentiellem Verlauf. Für Photonenstrahlung ist dies erklärbar durch eine Hypersensitivität im niedrigen Dosisbereich bis 1Gy, für die sich eine D0 von 3,3Gy ergibt, für Dosen über 1,0Gy liegt die D0 bei 10Gy. Für die 186Re-Inkubation ergibt sich eine D0 von 11,1Gy bei niedrigen Dosen verursacht durch die Reparatur subletaler Schäden, durch welche die biologische Wirkung abgeschwächt wird. Ab einer akkumulierten Dosis von etwa 1,6Gy zeichnet sich für 186Re ein wesentlich steilerer Kurvenverlauf mit einer D0 von 4,0Gy ab, der eine in diesem Bereich 2,5-fach stärkere biologische Wirkung als akute Photonenstrahlung wiedergibt (D0 4Gy für 186Re bzw. 10Gy für Photonen).

SCHLUSSFOLGERUNG

Strahlung niedriger Dosisleistung zeigt eine geringere biologische Wirkung als eine akute Bestrahlung. Es existiert aber ein Grenzwert der akkumulierten Dosis, ab dem die biologische Wirkung von β-Strahlung die der Photonenstrahlung sogar übertrifft.

The Role and Mechanism of ATM-Mediated Autophagy in the Transition From Hyper-Radiosensitivity to Induced Radioresistance in Lung Cancer Under Low-Dose Radiation

Objective: This study aimed to investigate the effect of ataxia telangiectasia mutated (ATM)–mediated autophagy on the radiosensitivity of lung cancer cells under low-dose radiation and to further investigate the role of ATM and its specific mechanism in the transition from hyper-radiosensitivity (HRS) to induced radioresistance (IRR).

Methods: The changes in the HRS/IRR phenomenon in A549 and H460 cells were verified by colony formation assay. Changes to ATM phosphorylation and cell autophagy in A549 and H460 cells under different low doses of radiation were examined by western blot, polymerase chain reaction (PCR), and electron microscopy. ATM expression was knocked down by short interfering RNA (siRNA) transfection, and ATM-regulated molecules related to autophagy pathways were screened by transcriptome sequencing analysis. The detection results were verified by PCR and western blot. The differential metabolites were screened by transcriptome sequencing and verified by colony formation assay and western blot. The nude mouse xenograft model was used to verify the results of the cell experiments.

Results: (1) A549 cells with high expression of ATM showed positive HRS/IRR, whereas H460 cells with low expression of ATM showed negative HRS/IRR. After the expression of ATM decreased, the HRS phenomenon in A549 cells increased, and the radiosensitivity of H460 cells also increased. This phenomenon was associated with the increase in the autophagy-related molecules phosphorylated c-Jun N-terminal kinase (p-JNK) and autophagy/Beclin 1 regulator 1 (AMBRA1). (2) DL-Norvaline, a product of carbon metabolism in cells, inhibited autophagy in A549 cells under low-dose radiation. DL-Norvaline increased the expression levels of ATM, JNK, and AMBRA1 in A549 cells. (3) Mouse experiments confirmed the regulatory role of ATM in autophagy and metabolism and its function in HRS/IRR.

Conclusion: ATM may influence autophagy through p-JNK and AMBRA1 to participate in the regulation of the HRS/IRR phenomenon. Autophagy interacts with the cellular carbon metabolite DL-Norvaline to participate in regulating the low-dose radiosensitivity of cells.

4-Methylumbelliferone administration enhances radiosensitivity of human fibrosarcoma by intercellular communication

Hyaluronan synthesis inhibitor 4-methylumbelliferone (4-MU) is a candidate of radiosensitizers which enables both anti-tumour and anti-metastasis effects in X-ray therapy. The curative effects under such 4-MU administration have been investigated in vitro; however, the radiosensitizing mechanisms remain unclear. Here, we investigated the radiosensitizing effects under 4-MU treatment from cell experiments and model estimations. We generated experimental surviving fractions of human fibrosarcoma cells (HT1080) after 4-MU treatment combined with X-ray irradiation. Meanwhilst, we also modelled the pharmacological effects of 4-MU treatment and theoretically analyzed the synergetic effects between 4-MU treatment and X-ray irradiation. The results show that the enhancement of cell killing by 4-MU treatment is the greatest in the intermediate dose range of around 4 Gy, which can be reproduced by considering intercellular communication (so called non-targeted effects) through the model analysis. As supposed to be the involvement of intercellular communication in radiosensitization, the oxidative stress level associated with reactive oxygen species (ROS), which leads to DNA damage induction, is significantly higher by the combination of 4-MU treatment and irradiation than only by X-ray irradiation, and the radiosensitization by 4-MU can be suppressed by the ROS inhibitors. These findings suggest that the synergetic effects between 4-MU treatment and irradiation are predominantly attributed to intercellular communication and provide more efficient tumour control than conventional X-ray therapy.

Radioprotective effect of melatonin against radiotherapy-induced cerebral cortex and cerebellum damage in rat

PURPOSE

The present study aims to investigate the radioprotective effect of melatonin (MEL) against early period brain damage caused by different dose rate beams in the experimental rat model.

MATERIALS AND METHODS

Forty-eight Sprague Dawley rats were randomly divided into six groups; the control, only melatonin, low dose rate-radiotherapy (LDR-RT), high dose rate-radiotherapy (HDR-RT) groups and (LDR-RT) + MEL and (HDR-RT) + MEL radiotherapy plus melatonin groups. Each rat administered melatonin was given a dose of 10 mg/kg through intraperitoneal injection, 15 minutes before radiation exposure. The head and neck region of each rat in only radiotherapy and radiotherapy plus melatonin groups was irradiated with a single dose of 16 Gy in LDR-RT and HDR-RT beams. Rats in all groups were examined for histopathology and biochemistry analysis 10 days after radiotherapy.

RESULTS

Comparing the findings for LDR-RT and HDR-RT only radiotherapy groups and the control group, there was a statistically significant difference in histopathological and biochemical parameters, however, melatonin administered in radiotherapy plus melatonin groups contributed improving these parameters (p < .05). There was no statistically significant difference between LDR-RT and HDR-RT beams (p > .05).

CONCLUSIONS

It was concluded that melatonin applied before LDR-RT and HDR-RT radiotherapy protected early period radiotherapy-induced brain damage. The effects of clinically low and high dose beams on the cerebral cortex and cerebellum were investigated histopathologically for the first time. HDR beams can be safely applied in brain radiotherapy. However, more experimental rat and clinical studies are needed to explain the radiobiological uncertainties about the clinic dose rate on different cancerous and healthy tissues.

Patient-derived organoids as individual patient models for chemoradiation response prediction in gastrointestinal malignancies

Chemoradiotherapy (CRT) is an important treatment modality for specific gastrointestinal (GI) cancers, as it has been shown to improve clinical outcomes. Recent developments in the neoadjuvant setting such as wait-and-see strategies for rectal as well as for esophageal cancers have even proven that CRT might be an effective organ-sparing treatment. However, due to molecular heterogeneity, only a subset of patients will show a complete response to CRT, which addresses the need for an individualized treatment approach. In recent years, the demand for more physiologically relevant predictive in vitro models has fostered the development of patient-derived tumor organoids. In this review, we describe the current treatment options for patients with GI cancers who are treated with (neo)adjuvant CRT. Furthermore, we provide an in-depth discussion of the organoid technology in the context of predicting CRT response for GI cancers as well as possible challenges for clinical implementation.

Evaluation of STAT3 decoy oligodeoxynucleotides' synergistic effects on radiation and/or chemotherapy in metastatic breast cancer cell line

Resistance to radiotherapy and chemotherapy has been a major problem of conventional cancer therapies, which consequently leads to cancer relapse and cancer-related death. It is known that cancer stem cells (CSCs) play a key role in therapy resistance and CSC-based targeted therapies have been considered as a powerful tool for cancer treatment. In the current study, we investigated the synergistic effects of suppressing signal transducer and activator of transcription (STAT3) function by decoy ODNs on X-irradiation (XI) and methotrexate (MTX) exposure as a combinational therapy in triple-negative breast cancer (TNBC) MDA-MB-231 cells. Lipofectamine 2000® was used as a transfecting agent and the cells treated with Scramble ODNs (SCR) and decoy ODNs were subjected to irradiation with 2 Gy at single/fractionated (XI group) doses, different concentration of MTX group, and X-irradiation-methotrexate (XI/MTX group). Synergistic effects of STAT3 SCR and decoy ODNs on cells were investigated by cell viability (MTT), cell cycle profile, apoptosis rate, migration, and invasion assays. Statistical analysis of obtained data showed that STAT3 decoy ODNs significantly decreased the cell viability, arrested the growth at G0/G1 phase, increased apoptosis rate, and reduced migrated and invaded cells through transwell membrane, in XI, MTX, and XI/MTX exposed groups. Since STAT3 is a master transcription factor in breast cancer cells stemness, aggressiveness, TNBC's heterogeneity, and therapy resistance; therefore, inhibition of this transcription factor by decoy ODNs could increase antitumor efficiencies of XI and MTX exposure strategies. Accordingly, this method could have the potential to increase the efficiency of combination therapies.

Increasing the colon cancer cells sensitivity toward radiation therapy via application of Oct4-Sox2 complex decoy oligodeoxynucleotides

Low sensitivity of cancer stem cells toward regular cancer therapy strategies is an important issue in the field of cancer remedy. The concept of cancer stem cell elimination has been a topic of interest in the field of molecular medicine for a long time. At the current study, it was aimed to elevate the sensitivity of cancer stem-like cells toward radiotherapy by treating with Oct4-Sox2 complex decoy oligodeoxynucleotides (ODNs). After treating HT29 and HT29-ShE cells with Oct4-Sox2 complex decoy ODNs, and analyzing the cellular uptake and localization of decoys, treated cells and control groups were subjected to irradiation by fractionated 6MV X-ray with a final dose of 2 Gy. Thereafter, the influence of radiotherapy on ODNs treated groups and control group was investigated on cell viability, cell cycle, apoptosis, colonosphere formation and scratch assay. Cellular uptake and localization assays demonstrated that decoy ODNs can efficiently be transfected to the cells and reside in subcellular compartment, where they pose their action on gene regulation. Post radiotherapy analysis indicated statistical significance in decoy ODNs treated cells by means of lower cell viability, cell cycle arrest in G2/M phase, increased cellular apoptosis, and reduced cell motility. Also, formed colonospheres were smaller in size and fewer in numbers. Considering the role of Oct4, and Sox2 transcription factors in signaling pathways of preserving stemness and inducing reverse EMT, application of decoy strategy could increase the sensitivity of cancer cells toward irradiation, which has a potential to eliminate the cancerous cells from tumors and support cancer treatment.

Variation of 4 MV X-ray dose rate strongly impacts biological response both in vitro and in vivo

Whereas an RBE > 1 is described for very low-energy X-ray beams (in the range of 25–50 kV), there is a consensus that the RBE of X-rays (from 0.1 to 3 MeV) is equal to 1, whatever the energy or dose rate of the beam. Comparisons of X-ray beam dose rates are scarce even though these beams are widely used in medical diagnosis or radiotherapy. By using two dose rates (0.63 and 2.5 Gy.min⁻¹) of high-energy X-rays on normal endothelial cells (HUVECs), we have studied the clonogenic assay, but also viability/mortality, cell cycle analysis and measured cellular senescence by flow cytometry, and have performed gene analysis on custom arrays. In order to consolidate these data, we performed localized irradiation of exteriorized small intestine at 0.63 and 2.5 Gy.min⁻¹. Interestingly, in vivo validation has shown a significantly higher loss of weight at the higher dose when irradiating to 19 Gy a small fragment of exteriorized small intestine of C57Bl6J mice. Nevertheless, no significant differences were observed in lesioned scores between the two dose rates, while bordering epithelium staining indicated twofold greater severe damage at 2.5 Gy.min⁻¹ compared to 0.63 Gy.min⁻¹ at one week post-irradiation. Taken together, these experiments systematically show that the relative biological effectiveness of photons is different from 1 when varying the dose rate of high-energy X-rays. Moreover, these results strongly suggest that, in support of clonogenic assay, multiparametric analysis should be considered to provide an accurate evaluation of the outcome of irradiated cells.

Pulsed low dose-rate irradiation response in isogenic HNSCC cell lines with different radiosensitivity

Background

Management of locoregionally recurrent head and neck squamous cell carcinomas (HNSCC) is challenging due to potential radioresistance. Pulsed low-dose rate (PLDR) irradiation exploits phenomena of increased radiosensitivity, low-dose hyperradiosensitivity (LDHRS), and inverse dose-rate effect. The purpose of this study was to evaluate LDHRS and the effect of PLDR irradiation in isogenic HNSCC cells with different radiosensitivity.

Materials and methods

Cell survival after different irradiation regimens in isogenic parental FaDu and radioresistant FaDu-RR cells was determined by clonogenic assay; post irradiation cell cycle distribution was studied by flow cytometry; the expression of DNA damage signalling genes was assesed by reverse transcription-quantitative PCR.

Results

Radioresistant Fadu-RR cells displayed LDHRS and were more sensitive to PLDR irradiation than parental FaDu cells. In both cell lines, cell cycle was arrested in G₂/M phase 5 hours after irradiation. It was restored 24 hours after irradiation in parental, but not in the radioresistant cells, which were arrested in G₁-phase. DNA damage signalling genes were under-expressed in radioresistant compared to parental cells. Irradiation increased DNA damage signalling gene expression in radioresistant cells, while in parental cells only few genes were under-expressed.

Conclusions

We demonstrated LDHRS in isogenic radioresistant cells, but not in the parental cells. Survival of LDHRS-positive radioresistant cells after PLDR was significantly reduced. This reduction in cell survival is associated with variations in DNA damage signalling gene expression observed in response to PLDR most likely through different regulation of cell cycle checkpoints.

Modulating the dose-rate differently affects the responsiveness of human epithelial prostate- and mesenchymal rhabdomyosarcoma-cancer cell line to radiation

Purpose: Radiation therapy (RT), by using ionizing radiation (IR), destroys cancer cells inducing DNA damage. Despite several studies are continuously performed to identify the best curative dose of IR, the role of dose-rate, IR delivered per unit of time, on tumor control is still largely unknown.Materials and methods: Rhabdomyosarcoma (RMS) and prostate cancer (PCa) cell lines were irradiated with 2 or 10 Gy delivered at dose-rates of 1.5, 2.5, 5.5 and 10.1 Gy/min. Cell-survival rate and cell cycle distribution were evaluated by clonogenic assays and flow cytometry, respectively. The production of reactive oxygen species (ROS) was detected by cytometry. Quantitative polymerase chain reaction assessed the expression of anti-oxidant-related factors including NRF2, SODs, CAT and GPx4 and miRNAs (miR-22, -126, -210, -375, -146a, -34a). Annexin V and caspase-8, -9 and -3 activity were assessed to characterize cell death. Senescence was determined by assessing β-galactosidase (SA-β-gal) activity. Immunoblotting was performed to assess the expression/activation of: i) phosphorylated H2AX (γ-H2AX), markers of DNA double strand breaks (DSBs); ii) p19^Kip1/Cip1, p21^Waf1/Cip1 and p27^Kip1/Cip1, senescence-related-markers; iii) p62, LC3-I and LC3-II, regulators of autophagy; iv) ATM, RAD51, DNA-PKcs, Ku70 and Ku80, mediators of DSBs repair.Results: Low dose-rate (LDR) more efficiently induced apoptosis and senescence in RMS while high dose-rate (HDR) necrosis in PCa. This paralleled with a lower ability of LDR-RMS and HDR-PCa irradiated cells to activate DSBs repair. Modulating the dose rate did not differently affect the anti-oxidant ability of cancer cells.Conclusion: The present results indicate that a stronger cytotoxic effect was induced by modulating the dose-rate in a cancer cell-dependent manner, this suggesting that choose the dose-rate based on the individual patient's tumor characteristics could be strategic for effective RT exposures.

Low-Level Radiofrequency Exposure Does Not Induce Changes in MSC Biology: An in vitro Study for the Prevention of NIR-Related Damage

Background

The ubiquitous diffusion of radiofrequency (RF) radiation across human living environments has attracted the attention of scientists. Though the adverse health effects of RF exposure remain debatable, it has been reported that the interaction of such radiation with biological macromolecular structures can be deleterious for stem cells, inducing impairment of their main functions involving self-renewal and differentiation.

Purpose

The purpose of this study was to determine whether exposure to RF of 169 megahertz (MHz) that is part of very high radiofrequency (VHF) range 30–300 MHz, could cause damage to stem cells by inducing senescence and loss of regenerative and DNA repair capacity.

Methods

The study was conducted on mesenchymal stromal cells (MSCs) containing a subpopulation of stem cells. The MSCs were exposed to RFs of 169 MHz administered via an open meter 2G “Smart Meter” for different durations of time.

Result

We did not observe modifications in MSC biology as a result of the RF exposure conducted in our experiments.

Conclusion

We concluded that MSCs are insensitive to RF radiation exposure at 169 MHz for various time intervals, including longer durations.

Impact of dimethyl sulfoxide on irradiation-related DNA double-strand-break induction, -repair and cell survival

Dimethyl sulfoxide (DMSO) is an effective radical scavenger and, when added to cells, reduces the initial number of radiation-induced DNA double-strand breaks (DSB). The aim of this study was to investigate modification by DMSO of both DSB induction and DSB repair by means of pulsed-field gel electrophoresis (PFGE) as well as gamma-H2AX immunofluorescence staining. WiDr cells (human colon carcinoma provided by DKFZ) were incubated with 2% DMSO for 2 h (or mock-treated) prior to irradiation with varying X-ray doses and subsequent incubation for repair. Sample processing for PFGE analysis or counting of γ-H2AX foci was performed according to standard protocols. Effects on apoptosis induction and cell survival were investigated additionally by standard protocols. DMSO reduced DSB yield after 20-80 Gy measured by PFGE. A qualitatively similar result was found after low-dose irradiation (1 Gy) using γ-H2AX immunofluorescence staining. During incubation for repair, both DNA fragment rejoining (PFGE) as well as γ-H2AX foci removal occurred at a reduced rate when cells had been pre-treated with DMSO. But this effect was clearly more pronounced for the PFGE-analyzed double-strand breakage, particularly at early repair times. WiDr cells treated with DMSO (2%) showed a significantly increased clonogenic survival after irradiation doses above 8 Gy. Apoptosis rates were not changed by DMSO. The radio-protective effect of DMSO, well known from other PFGE studies, could be confirmed for the formation of γ-H2AX foci. DSB generated in the presence of DMSO were less rapidly repaired. DMSO showed radio-protective effects on clonogenic survival but not on apoptosis.

Differential miRNA expression profiling reveals miR-205-3p to be a potential radiosensitizer for low- dose ionizing radiation in DLD-1 cells

Enhanced radiosensitivity at low doses of ionizing radiation (IR) (0.2 to 0.6 Gy) has been reported in several cell lines. This phenomenon, known as low doses hyper-radiosensitivity (LDHRS), appears as an opportunity to decrease toxicity of radiotherapy and to enhance the effects of chemotherapy. However, the effect of low single doses IR on cell death is subtle and the mechanism underlying LDHRS has not been clearly explained, limiting the utility of LDHRS for clinical applications. To understand the mechanisms responsible for cell death induced by low-dose IR, LDHRS was evaluated in DLD-1 human colorectal cancer cells and the expression of 80 microRNAs (miRNAs) was assessed by qPCR array. Our results show that DLD-1 cells display an early DNA damage response and apoptotic cell death when exposed to 0.6 Gy. miRNA expression profiling identified 3 over-expressed (miR-205-3p, miR-1 and miR-133b) and 2 down-regulated miRNAs (miR-122-5p, and miR-134-5p) upon exposure to 0.6 Gy. This miRNA profile differed from the one in cells exposed to high-dose IR (12 Gy), supporting a distinct low-dose radiation-induced cell death mechanism. Expression of a mimetic miR-205-3p, the most overexpressed miRNA in cells exposed to 0.6 Gy, induced apoptotic cell death and, more importantly, increased LDHRS in DLD-1 cells. Thus, we propose miR-205-3p as a potential radiosensitizer to low-dose IR.

Investigation of dose-rate effects and cell-cycle distribution under protracted exposure to ionizing radiation for various dose-rates

During exposure to ionizing radiation, sub-lethal damage repair (SLDR) competes with DNA damage induction in cultured cells. By virtue of SLDR, cell survival increases with decrease of dose-rate, so-called dose-rate effects (DREs). Here, we focused on a wide dose-rate range and investigated the change of cell-cycle distribution during X-ray protracted exposure and dose-response curves via hybrid analysis with a combination of in vitro experiments and mathematical modelling. In the course of flow-cytometric cell-cycle analysis and clonogenic assays, we found the following responses in CHO-K1 cells: (1) The fraction of cells in S phase gradually increases during 6 h exposure at 3.0 Gy/h, which leads to radio-resistance. (2) Slight cell accumulation in S and G2/M phases is observed after exposure at 6.0 Gy/h for more than 10 hours. This suggests that an increase of SLDR rate for cells in S phase during irradiation may be a reproducible factor to describe changes in the dose-response curve at dose-rates of 3.0 and 6.0 Gy/h. By re-evaluating cell survival for various dose-rates of 0.186-60.0 Gy/h considering experimental-based DNA content and SLDR, it is suggested that the change of S phase fraction during irradiation modulates the dose-response curve and is possibly responsible for some inverse DREs.

Investigation of dose-rate effects and cell-cycle distribution under protracted exposure to ionizing radiation for various dose-rates

During exposure to ionizing radiation, sub-lethal damage repair (SLDR) competes with DNA damage induction in cultured cells. By virtue of SLDR, cell survival increases with decrease of dose-rate, so-called dose-rate effects (DREs). Here, we focused on a wide dose-rate range and investigated the change of cell-cycle distribution during X-ray protracted exposure and dose-response curves via hybrid analysis with a combination of in vitro experiments and mathematical modelling. In the course of flow-cytometric cell-cycle analysis and clonogenic assays, we found the following responses in CHO-K1 cells: (1) The fraction of cells in S phase gradually increases during 6 h exposure at 3.0 Gy/h, which leads to radio-resistance. (2) Slight cell accumulation in S and G₂/M phases is observed after exposure at 6.0 Gy/h for more than 10 hours. This suggests that an increase of SLDR rate for cells in S phase during irradiation may be a reproducible factor to describe changes in the dose-response curve at dose-rates of 3.0 and 6.0 Gy/h. By re-evaluating cell survival for various dose-rates of 0.186-60.0 Gy/h considering experimental-based DNA content and SLDR, it is suggested that the change of S phase fraction during irradiation modulates the dose-response curve and is possibly responsible for some inverse DREs.

Response of rats to dose rates of ionizing radiation evaluated by dielectric properties of bone marrow

The response of adult Wistar albino female rats toward two dose rates of gamma radiation delivered as acute dose of 7 Gy is investigated using classical methodologies as chemical, hematological and histological parameters in comparison with newly introduced dielectric parameters. Two groups of rats were exposed to γ ray with dose rates 533.35 mGy/min and 325.89 mGy/min. Then the irradiated groups were followed up for two weeks after irradiation. In case of higher dose rate, high percentage of animals was lost and there were substantial alterations in the dielectric parameters in addition to massive damage in liver and bone marrow cells. On the other hand, a reduction of death rate of rats, different behavior in the dielectric parameters of bone marrow and lesser injury of liver tissue were well noticeable in case of lower dose rate. Moreover, the sensitivity of dielectric parameters toward the two different dose rates was well pronounced during the 1st and 2nd weeks after irradiation more than other parameters.