Cell division cycle 25 homolog c effects on low-dose hyper-radiosensitivity and induced radioresistance at elevated dosage in A549 cells

Datasets of in vitro clonogenic assays showing low dose hyper-radiosensitivity and induced radioresistance

Low dose hyper-radiosensitivity and induced radioresistance are primarily observed in surviving fractions of cell populations exposed to ionizing radiation, plotted as the function of absorbed dose. Several biophysical models have been developed to quantitatively describe these phenomena. However, there is a lack of raw, openly available experimental data to support the development and validation of quantitative models. The aim of this study was to set up a database of experimental data from the public literature. Using Google Scholar search, 46 publications with 101 datasets on the dose-dependence of surviving fractions, with clear evidence of low dose hyper-radiosensitivity, were identified. Surviving fractions, their uncertainties, and the corresponding absorbed doses were digitized from graphs of the publications. The characteristics of the cell line and the irradiation were also recorded, along with the parameters of the linear-quadratic model and/or the induced repair model if they were provided. The database is available in STORE^DB, and can be used for meta-analysis, for comparison with new experiments, and for development and validation of biophysical models.

Measurement(s)	surviving fraction of cells
Technology Type(s)	optical microscopy
Factor Type(s)	absorbed dose
Sample Characteristic - Organism	Homo sapiens • Chinese hamster • Rattus sp.
Sample Characteristic - Environment	cell culture

Radiation-induced G2/M arrest rarely occurred in glioblastoma stem-like cells

PURPOSE

The purpose of this study is to systematically study the cell-cycle alterations of glioblastoma stem-like cells (GSLCs) after irradiation, possibly enriching the mechanisms of radioresistance of GSLCs.

MATERIALS AND METHODS

GSLCs were enriched and identified, and then the radioresistance of GSLCs was validated by analyzing cell survival, cell proliferation, and radiation-induced apoptosis. The discrepancy of the cell-cycle distribution and expression of cell-cycle-related proteins between GSLCs and glioblastoma differentiated cells (GDCs) after irradiation was completely analyzed.

RESULTS

The survival fractions and the cell viabilities of GSLCs were significantly higher than those of GDCs after irradiation. Radiation-induced apoptosis was less prominent in GSLCs than in GDCs. After irradiation with high-dose X-rays, the percentages of GDCs in G2/M phase was evidently increased. However, radiation-induced G2/M arrest occurred less frequently in GSLCs, but S-phase arrest occurred in GSLCs after irradiation with 8 Gy. Further mechanistic studies showed that the expressions levels of Cdc25c, Cdc2, and CyclinB1 in GSLCs were not apparently changed after irradiation, while those of p-ATM and p-Chk1 were sharply increased after irradiation in GSLCs. The basal level of Cdc25c expression in GSLCs was much higher than that in GDCs.

CONCLUSIONS

We explored the cell-cycle alterations and cell-cycle-related proteins expression levels in GSLCs after irradiation, providing a novel mechanism of radioresistance of GSLCs.

The emerging roles of the ubiquitination/deubiquitination system in tumor radioresistance regarding DNA damage responses, cell cycle regulation, hypoxic responses, and antioxidant properties: Insight into the development of novel radiosensitizing strategies

Radiation therapy is one of the first-line treatments for many cancers, with no less than half of cancer patients receiving it in the US. Despite the development of innovative and high-precision radiation therapy strategies, many patients still experience local tumor recurrence after the treatment, at least in part, due to the existence of radioresistant cells in malignant tumor tissues. Among the various biological processes known to induce radioresistance, a post-translational protein modification, ubiquitination, has received marked attention in recent years. Ubiquitination, in which highly conserved ubiquitin polypeptides are covalently attached to their target proteins, has long been recognized as a system to tag unnecessary proteins for 26S proteasome-dependent proteolysis. However, accumulating lines of evidence recently revealed that it acts as a signal molecule in diverse biological processes as well, and its functional disorder was found to cause not only tumor development and various diseases but also tumor radioresistance. The present review summarizes the latest knowledge about how the cancer-related disorder of the ubiquitination systems induces the radioresistance of cancer cells by influencing intrinsic pathways, each of which potentially affects the radioresistance/radiosensitivity of cells, such as DNA damage responses, cell cycle regulation, hypoxic responses, and antioxidant properties. In addition, this review aims to provide insights into how we can exploit the disorders in order to develop novel radiosensitizing strategies.

Downregulation of cell division cycle 25 homolog C reduces the radiosensitivity and proliferation activity of esophageal squamous cell carcinoma

Radiation therapy is one of the most important methods of contemporary cancer treatment. Cells in the G2 and M phases are more sensitive to radiation therapy, and cell division cycle 25 homolog C (CDC25C) is essential in shifting the cell cycle between these two phases. In this study, the knockdown of CDC25C in human esophageal squamous carcinoma EC9706 cells was mediated by transfecting shRNA against human CDC25C-subcloning into pGV248. The levels of CDC25C mRNA and protein expression were assessed by reverse transcription-polymerase chain reaction (RT-PCR) and western blotting, respectively. Moreover, cell proliferation and radiosensitivity were measured. Stable CDC25C-knockdown EC9706 cell lines were successfully established. Furthermore, the proliferation of both control and CDC25C-shRNA-EC9706 cells was inhibited after the cells were treated with increasing X-ray doses, and the proliferation of the control cells was affected more significantly (p<0.05). Moreover, cell colony formation assays allowed us to reach the same conclusion. Taken together, our experiments demonstrated that the knockdown of CDC25C can reduce both the radiotherapy sensitivity and the proliferation activity of EC9706 cells. Thus, CDC25C might be a potential biomarker for radiotherapy treatment.

ATR signaling cooperates with ATM in the mechanism of low dose hypersensitivity induced by carbon ion beam

Little work has been done on the mechanism of low dose hyper-radiosensitivity (HRS) and later appeared radioresistance (termed induced radioresistance (IRR)) after irradiation with medium and high linear energy transfer (LET) particles. The aim of this study was to find out whether ATR pathway is involved in the mechanism of HRS induced by high LET radiation. GM0639 cells and two ATM deficient/mutant cells, AT5BIVA and AT2KY were irradiated by carbon ion beam. Thymidine block technique was developed to enrich the G2-phase population. Radiation induced early G2/M checkpoint was quantitatively assess with dual-parameter flow cytometry by detecting the cells positive for phospho-histone H3. The involvement of ATR pathway in HRS/IRR response was detected with pretreatment of specific inhibitors prior to carbon ion beam. The link between the early G2/M checkpoint and HRS/IRR under carbon ion beam was first confirmed in GM0639 cells, through the enrichment of cell population in G2-phase or with Aurora kinase inhibitor that attenuates the transition from G2 to M phase. Interestingly, the early G2/M arrest could still be observed in ATM deficient/mutant cells with an effect of ATR signaling, which was discovered to function in an LET-dependent manner, even as low as 0.2Gy for carbon ion radiation. The involvement of ATR pathway in heavy particles induced HRS/IRR was determined with the specific ATR inhibitor in GM0639 cells, which affected the HRS/IRR occurrence similarly as ATM inhibitor. These data demonstrate that ATR pathway may cooperate with ATM in the mechanism of low dose hypersensitivity induced by carbon ion beam.

Local Tumor Control and Normal Tissue Toxicity of Pulsed Low-Dose Rate Radiotherapy for Recurrent Lung Cancer: An In Vivo Animal Study

OBJECTIVES

This study investigates (1) local tumor control and (2) normal tissue toxicity of pulsed low-dose rate radiotherapy (PLDR) for recurrent lung cancer.

METHODS

For study 1, nude mice were implanted with A549 tumors and divided into the following 3 groups: (1) control (n = 10), (2) conventional radiotherapy (RT; n = 10), and (3) PLDR (n = 10). Tumor-bearing mice received 2 Gy daily dose for 2 consecutive days. Weekly magnetic resonance imaging was used for tumor growth monitoring. For study 2, 20 mice received 8 Gy total body irradiation either continuously (n = 10) or 40 × 0.2 Gy pulses with 3-minute intervals (n = 10).

RESULTS

For study 1, both conventional RT and PLDR significantly inhibited the growth of A549 xenografts compared with the control group (>35% difference in the mean tumor volume; P < .05). The PLDR results were slightly better than conventional RT (8% difference in the mean tumor volume; P > .05). For study 2, the average weight was 20.94 ± 1.68 g and 25.69 ± 1.27 g and the survival time was 8 days and 12 days for mice treated with conventional RT and PLDR (P < .05), respectively.

CONCLUSION

This study showed that PLDR could control A549 tumors as effectively as conventional RT, and PLDR induced much less normal tissue toxicity than conventional RT. Thus, PLDR would be a good modality for recurrent lung cancers.

ADVANCES IN KNOWLEDGE

This article reports our results of an in vivo animal investigation of PLDR for the treatment of recurrent cancers, which may not be eligible for treatment because of the dose limitations on nearby healthy organs that have been irradiated in previous treatments. This was the first in vivo study to quantify the tumor control and normal tissue toxicities of PLDR using mice with implanted tumors, and our findings provided evidence to support the clinical trials that employ PLDR treatment techniques.

Functional genomics screening utilizing mutant mouse embryonic stem cells identifies novel radiation-response genes

Elucidating the genetic determinants of radiation response is crucial to optimizing and individualizing radiotherapy for cancer patients. In order to identify genes that are involved in enhanced sensitivity or resistance to radiation, a library of stable mutant murine embryonic stem cells (ESCs), each with a defined mutation, was screened for cell viability and gene expression in response to radiation exposure. We focused on a cancer-relevant subset of over 500 mutant ESC lines. We identified 13 genes; 7 genes that have been previously implicated in radiation response and 6 other genes that have never been implicated in radiation response. After screening, proteomic analysis showed enrichment for genes involved in cellular component disassembly (e.g. Dstn and Pex14) and regulation of growth (e.g. Adnp2, Epc1, and Ing4). Overall, the best targets with the highest potential for sensitizing cancer cells to radiation were Dstn and Map2k6, and the best targets for enhancing resistance to radiation were Iqgap and Vcan. Hence, we provide compelling evidence that screening mutant ESCs is a powerful approach to identify genes that alter radiation response. Ultimately, this knowledge can be used to define genetic variants or therapeutic targets that will enhance clinical therapy.

A Logarithmic Formula to Describe the Relationship between the Increased Radiosensitivity at Low Doses and the Survival at 2 Gray

OBJECTIVES

Intrinsic radiosensitivity at doses used in radiotherapy is linked to hypersensitivity (HRS) and increased radio resistance (IRR) at low doses. The aim of this study was to explore this relationship.

METHODS

Survival curves for 18 human tumour cell lines were analysed, using two models to fit the data points in order to extract the necessary parameters relevant for this study.

RESULTS

The IRR ratio αs/αr versus the survival at 2 gray (Gy) can be described by a logarithmic relation which leads to a series of straight lines.

CONCLUSION

The relationship obtained implies that there is a direct link between HRS/IRR and survival at clinically relevant doses of 2 Gy.

Suppression of low-dose hyper-radiosensitivity in human lung cancer cell line A549 by radiation-induced autophagy

This study explored the role of radiation-induced autophagy in low-dose hyperradiosensitivity (HRS) in the human lung cancer cell line A549. A549 cells, either treated with an autophagic inhibitor 3-methyladenine (3-MA), or with a vehicle control, were irradiated at different low doses (≤0.5 Gy). The generation of autophagy was examined by laser scanning confocal microscopy. Western blotting was used to detect the expression of microtubule-associated protein l light chain 3B II (LC3B-II). Flow cytometry (FCM) and clonogenic assays were used to measure the fraction of surviving cells at the low irradiation doses. Our results showed that there was a greater inhibition of autophagic activity, but a higher degree of low-dose HRS in A549 cells treated with 3-MA than in control group. Our data demonstrated that radiation-induced autophagy is correlated with HRS in A549 cells, and is probably one of the mechanisms underlying HRS.

Honokiol as a Radiosensitizing Agent for Colorectal cancers

Radioresistance is a frustrating obstacle for patients with colorectal cancers (CRCs) undergoing radiotherapy. There is an urgent need to find an effective agent to increase the sensitivity of CRCs to radiation. Honokiol, an active compound purified from Magnolia, was found to radiosensitize colorectal cancer cells both in vitro and in vivo. However, the mechanisms control important signaling that enhances radiosensitivity is currently unknown. In this study, we have reviewed important signaling pathways that are closely related to radiosensitization, such as cell cycle arrest, tumor angiogenesis, JAK/STAT3 signaling pathway and Mismatch repair. Studies show that honokiol can interfere with these pathways at different levels. With overall analysis, it may bring light on finding the possible mechanism by which honokiol acts as a radiosensitizing agent for CRCs.

Determining if low dose hyper-radiosensitivity (HRS) can be exploited to provide a therapeutic advantage: a cell line study in four glioblastoma multiforme (GBM) cell lines

PURPOSE

To determine if ultra-fractionation using repeated pulses of radiation (10 × 0.2 Gray [Gy]) would be more cytotoxic than continuously-delivered radiation to the same total dose (2 Gy) in four glioma cell lines.

MATERIALS AND METHODS

Human T98G, U373, U87MG and U138MG cells were conventionally X-irradiated with 0.1-8 Gy and clonogenic survival assessed. Next, cells were treated with either a single dose of 2 Gy or 10 pulses of 0.2 Gy using a 3-min inter-pulse interval and DNA (Deoxyribonucleic acid) repair (pHistone H2A.X), G2-phase cell cycle checkpoint arrest (pHistone H3) and apoptosis (caspase-3) compared between the two regimens. A dose of 0.2 Gy was selected as this reflects the hyper- radiosensitivity (HRS)/increased radioresistance (IRR) transition point of the low-dose cell survival curve.

RESULTS

T98G, U87MG and U138MG exhibited distinct HRS responses and survival curves were well-described by the Induced Repair model. Despite the prolonged delivery time, ultra-fractionation (10 × 0.2 Gy) was equally effective as a single continuously-delivered 2 Gy dose. However, ultra-fractionation was more effective when given for five consecutive days to a total dose of 10 Gy. The increased effectiveness of ultra-fractionation could not be attributed directly to differences in DNA damage, repair processes or radiation-induced apoptosis.

CONCLUSIONS

Ultra-fractionation (10 × 0.2 Gy) is an effective modality for killing glioma cell lines compared with standard 2 Gy dosing when multiple days of treatment are given.

Exposure to low dose ionising radiation: molecular and clinical consequences

This review article provides a comprehensive overview of the experimental data detailing the incidence, mechanism and significance of low dose hyper-radiosensitivity (HRS). Important discoveries gained from past and present studies are mapped and highlighted to illustrate the pathway to our current understanding of HRS and the impact of HRS on the cellular response to radiation in mammalian cells. Particular attention is paid to the balance of evidence suggesting a role for DNA repair processes in the response, evidence suggesting a role for the cell cycle checkpoint processes, and evidence investigating the clinical implications/relevance of the effect.