Radioprotection of normal tissue cells

The effect of photobiomodulation on the radiosensitivity of cancer cells: a literature review

The goal of radiotherapy (RT) in cancer treatment is to destroy tumor tissue while preserving nearby healthy tissue. However, RT often causes adverse effects that significantly impact patients' quality of life. Tumor cells, which have high proliferation rates, are susceptible to radiation, especially during the G2 and mitosis phases of the cell cycle. Numerous studies have explored ways to enhance the Radiosensitivity of tumors to make RT more effective while minimizing harm to healthy cells. This review examines the potential use of photobiomodulation (PBM) as a radiosensitizer for cancer cells to improve the effectiveness and safety of radiotherapy. A literature search was conducted in the MEDLINE/PubMed and Google Scholar databases using keywords like "PBM, low-level light therapy, cancer cells, tumor cells, radiosensitizer, and ionizing radiation." Studies meeting the inclusion criteria were reviewed and analyzed. Several studies investigated PBM as a radiosensitizer for various cancer cell lines, including HeLa, HeLa Kyoto, A431, SCC9, and Cal 27. Most of these studies found that pre-exposure of cancer cells to PBM improved the effectiveness of radiation in destroying tumor cells. PBM is a promising, affordable, and noninvasive technique that could improve cancer treatment outcomes by increasing tumor sensitivity to radiation and reducing side effects. However, more research is needed to thoroughly assess the benefits of combining PBM with RT. Clinical trial number: not applicable. Clinical trial number: not applicable.

Comparative Analysis of Cystamine and Cysteamine as Radioprotectors and Antioxidants: Insights from Monte Carlo Chemical Modeling under High Linear Energy Transfer Radiation and High Dose Rates

This study conducts a comparative analysis of cystamine (RSSR), a disulfide, and cysteamine (RSH), its thiol monomer, to evaluate their efficacy as radioprotectors and antioxidants under high linear energy transfer (LET) and high-dose-rate irradiation conditions. It examines their interactions with reactive primary species produced during the radiolysis of the aqueous ferrous sulfate (Fricke) dosimeter, offering insights into the mechanisms of radioprotection and highlighting their potential to enhance the therapeutic index of radiation therapy, particularly in advanced techniques like FLASH radiotherapy. Using Monte Carlo multi-track chemical modeling to simulate the radiolytic oxidation of ferrous to ferric ions in Fricke-cystamine and Fricke-cysteamine solutions, this study assesses the radioprotective and antioxidant properties of these compounds across a variety of irradiation conditions. Concentrations were varied in both aerated (oxygen-rich) and deaerated (hypoxic) environments, simulating conditions akin to healthy tissue and tumors. Both cystamine and cysteamine demonstrate radioprotective and strong antioxidant properties. However, their effectiveness varies significantly depending on the concentration employed, the conditions of irradiation, and whether or not environmental oxygen is present. Specifically, excluding potential in vivo toxicity, cysteamine substantially reduces the adverse effects of ionizing radiation under aerated, low-LET conditions at concentrations above ~1 mM. However, its efficacy is minimal in hypoxic environments, irrespective of the concentration used. Conversely, cystamine consistently offers robust protective effects in both oxygen-rich and oxygen-poor conditions. The distinct protective capacities of cysteamine and cystamine underscore cysteamine's enhanced potential in radiotherapeutic settings aimed at safeguarding healthy tissues from radiation-induced damage while effectively targeting tumor tissues. This differential effectiveness emphasizes the need for personalized radioprotective strategies, tailored to the specific environmental conditions of the tissue involved. Implementing such approaches is crucial for optimizing therapeutic outcomes and minimizing collateral damage in cancer treatment.

Radioprotective effectiveness of a novel delta-tocotrienol prodrug on mouse hematopoietic system against 60Co gamma-ray irradiation through inducing granulocyte-colony stimulating factor production

Considering the increasing risk of nuclear attacks worldwide, the development of develop potent and safe radioprotective agents for nuclear emergencies is urgently needed. γ-tocotrienol (GT3) and δ-tocotrienol (DT3) have demonstrated a potent radioprotective effect by inducing the production of granulocyte-colony stimulating factor (G-CSF) in vivo. However, their application is limited because of their low bioavailability. The utilization of ester prodrugs can be an effective strategy for modifying the pharmacokinetic properties of drug molecules. In this study, we initially confirmed that DT3 exhibited the most significant potential for inducing G-CSF effects among eight natural vitamin E homologs. Consequently, we designed and synthesized a series of DT3 ester and ether derivatives, leading to improved radioprotective effects. The metabolic study conducted in vitro and in vivo has identified DT3 succinate 5b as a prodrug of DT3 with an approximately seven-fold higher bioavailability compared to DT3 alone. And DT3 ether derivative 8a were relatively stable and approximately 4 times more bioavailable than DT3 prototype. Furthermore, 5b exhibited superior ability to mitigate radiation-induced pancytopenia, enhance the recovery of bone marrow hematopoietic stem and progenitor cells, and promote splenic extramedullary hematopoiesis in sublethal irradiated mice. Similarly, 8a shown potential radiation protection, but its radiation protection is less than DT3. Based on these findings, we identified 5b as a DT3 prodrug, and providing an attractive candidate for further drug development.

Fluacrypyrim Protects Hematopoietic Stem and Progenitor Cells against Irradiation via Apoptosis Prevention

Ionizing radiation (IR)-induced hematopoietic injury has become a global concern in the past decade. The underlying cause of this condition is a compromised hematopoietic reserve, and this kind of hematopoietic injury could result in infection or bleeding, in addition to lethal mishaps. Therefore, developing an effective treatment for this condition is imperative. Fluacrypyrim (FAPM) is a recognized effective inhibitor of STAT3, which exhibits anti-inflammation and anti-tumor effects in hematopoietic disorders. In this context, the present study aimed to determine whether FAPM could serve as a curative agent in hematopoietic-acute radiation syndrome (H-ARS) after total body irradiation (TBI). The results revealed that the peritoneally injection of FAPM could effectively promote mice survival after lethal dose irradiation. In addition, promising recovery of peripheral blood, bone marrow (BM) cell counts, hematopoietic stem cell (HSC) cellularity, BM colony-forming ability, and HSC reconstituting ability upon FAPM treatment after sublethal dose irradiation was noted. Furthermore, FAPM could reduce IR-induced apoptosis in hematopoietic stem and progenitor cells (HSPCs) both in vitro and in vivo. Specifically, FAPM could downregulate the expressions of p53-PUMA pathway target genes, such as Puma, Bax, and Noxa. These results suggested that FAPM played a protective role in IR-induced hematopoietic damage and that the possible underlying mechanism was the modulation of apoptotic activities in HSCs.

Effect of adenosine treatment on ionizing radiation toxicity in zebrafish early life stages

The danger of ionizing radiation exposure to human health is a concern. Since its wide use in medicine and industry, the development of radioprotectors has been very significant. Adenosine exerts anti-inflammatory actions and promotes tissue protection and repair, by activating the P1 receptors (A1, A2A, A2B, and A3). Zebrafish (Danio rerio) is an appropriate tool in the fields of toxicology and pharmacology, including the evaluation of radiobiological outcomes and in the search for radioprotector agents. This study aims to evaluate the effect of adenosine in the toxicity induced by radiation in zebrafish. Embryos were treated with 1, 10, or 100 µM adenosine, 30 min before the exposure to 15 Gy of gamma radiation. Adenosine potentiated the effects of radiation in heart rate, body length, and pericardial edema. We evaluated oxidative stress, tissue remodeling and inflammatory. It was seen that 100 µM adenosine reversed the inflammation induced by radiation, and that A2A2 and A2B receptors are involved in these anti-inflammatory effects. Our results indicate that P1R activation could be a promising pharmacological strategy for radioprotection.

Radiotherapy in bone sarcoma: the quest for better treatment option

Bone sarcomas are rare tumors representing 0.2% of all cancers. While osteosarcoma and Ewing sarcoma mainly affect children and young adults, chondrosarcoma and chordoma have a preferential incidence in people over the age of 40. Despite this range in populations affected, all bone sarcoma patients require complex transdisciplinary management and share some similarities. The cornerstone of all bone sarcoma treatment is monobloc resection of the tumor with adequate margins in healthy surrounding tissues. Adjuvant chemo- and/or radiotherapy are often included depending on the location of the tumor, quality of resection or presence of metastases. High dose radiotherapy is largely applied to allow better local control in case of incomplete primary tumor resection or for unresectable tumors. With the development of advanced techniques such as proton, carbon ion therapy, radiotherapy is gaining popularity for the treatment of bone sarcomas, enabling the delivery of higher doses of radiation, while sparing surrounding healthy tissues. Nevertheless, bone sarcomas are radioresistant tumors, and some mechanisms involved in this radioresistance have been reported. Hypoxia for instance, can potentially be targeted to improve tumor response to radiotherapy and decrease radiation-induced cellular toxicity. In this review, the benefits and drawbacks of radiotherapy in bone sarcoma will be addressed. Finally, new strategies combining a radiosensitizing agent and radiotherapy and their applicability in bone sarcoma will be presented.

Exploring Natural Products as Radioprotective Agents for Cancer Therapy: Mechanisms, Challenges, and Opportunities

Radiotherapy is an important cancer treatment. However, in addition to killing tumor cells, radiotherapy causes damage to the surrounding cells and is toxic to normal tissues. Therefore, an effective radioprotective agent that prevents the deleterious effects of ionizing radiation is required. Numerous synthetic substances have been shown to have clear radioprotective effects. However, most of these have not been translated for use in clinical applications due to their high toxicity and side effects. Many medicinal plants have been shown to exhibit various biological activities, including antioxidant, anti-inflammatory, and anticancer activities. In recent years, new agents obtained from natural products have been investigated by radioprotection researchers, due to their abundance of sources, high efficiency, and low toxicity. In this review, we summarize the mechanisms underlying the radioprotective effects of natural products, including ROS scavenging, promotion of DNA damage repair, anti-inflammatory effects, and the inhibition of cell death signaling pathways. In addition, we systematically review natural products with radioprotective properties, including polyphenols, polysaccharides, alkaloids, and saponins. Specifically, we discuss the polyphenols apigenin, genistein, epigallocatechin gallate, quercetin, resveratrol, and curcumin; the polysaccharides astragalus, schisandra, and Hohenbuehelia serotina; the saponins ginsenosides and acanthopanax senticosus; and the alkaloids matrine, ligustrazine, and β-carboline. However, further optimization through structural modification, improved extraction and purification methods, and clinical trials are needed before clinical translation. With a deeper understanding of the radioprotective mechanisms involved and the development of high-throughput screening methods, natural products could become promising novel radioprotective agents.

Nanodrugs with intrinsic radioprotective exertion: Turning the double-edged sword into a single-edged knife

Ionizing radiation (IR) poses a growing threat to human health, and thus ideal radioprotectors with high efficacy and low toxicity still receive widespread attention in radiation medicine. Despite significant progress made in conventional radioprotectants, high toxicity, and low bioavailability still discourage their application. Fortunately, the rapidly evolving nanomaterial technology furnishes reliable tools to address these bottlenecks, opening up the cutting-edge nano-radioprotective medicine, among which the intrinsic nano-radioprotectants characterized by high efficacy, low toxicity, and prolonged blood retention duration, represent the most extensively studied class in this area. Herein, we made the systematic review on this topic, and discussed more specific types of radioprotective nanomaterials and more general clusters of the extensive nano-radioprotectants. In this review, we mainly focused on the development, design innovations, applications, challenges, and prospects of the intrinsic antiradiation nanomedicines, and presented a comprehensive overview, in-depth analysis as well as an updated understanding of the latest advances in this topic. We hope that this review will promote the interdisciplinarity across radiation medicine and nanotechnology and stimulate further valuable studies in this promising field.

Effect of low-level light therapy before radiotherapy in oral squamous cell carcinoma: An in vitro study

Radiation therapy for head and neck squamous cell carcinoma (HNSCC) is associated with several complications. Although photobiomodulation (PBM) has radioprotective effects in normal tissue, it could also enhance the growth of neoplastic cells. Thus, the present study aimed to investigate the cellular response of oral squamous cell carcinoma with pre-exposure to low-level phototherapy before radiotherapy. SCC9, Cal-27, A431, and HaCaT cell lines were subjected to low-level light therapy and radiotherapy. The cells were treated with a single energy density (300 J/cm²) of a light-emitting diode (660 nm) prior to ionizing radiation at different doses (0, 2, 4, and 6 Gy). After 24 h, wound scratch, proliferation, clonogenic cell survival, cell death, and reactive oxygen species (ROS) analyses were performed to evaluate cell response. The cell lines pre-exposed to PBM at the analyzed dosage were radiosensitive. The treatment significantly reduced cell proliferation and clonogenic cell survival. Migration and cell death assays also revealed positive results, with the treatment group showing lower rate of migration and higher cell death than did the control group. Moreover, PBM effectively increased the intracellular levels of ROS. PBM at 300 J/cm² is a promising radiosensitizing modality to reduce the radiation dose and avoid the intolerable side effects of radiotherapy for HNSCC, thus increasing the probability of successful treatment. However, further studies are needed to support and confirm the results.

"Radio-Protective Effect of Aminocaproic Acid in Human Spermatozoa"

BACKGROUND

The negative effects of ionizing radiation on organs and the reproductive system are well known and documented. Exposure to gamma radiation can lead to oligospermia, azoospermia and DNA damage. Up to date, there is no effective pharmaceutical compound for protecting the male reproductive system and sperm.

OBJECTIVE

This study aimed at investigating the ability of Ɛ-aminocaproic acid (EACA) to prevent the damage of human spermatozoa and DNA induced by ionizing radiation.

MATERIALS AND METHODS

Sperm samples were obtained from healthy volunteers (35 men; 31.50 ± 7.34 years old). There were 4 experimental groups: 1) control group (CG), 2) group exposed to maximal radiation dose 67.88 mGy (RMAX), 3) low-dose radiation (minimal) 22.62 mGy (RMIN), and 4) group treated with radiation (67.88 mGy) and EACA (dose 50 ng/ml). Sperm motility, viability, and DNA damage were assessed.

RESULTS

We observed a significant decrease in total sperm motility of the RMAX group compared to CG (p < 0.05). Sperm viability in the RMAX group was also reduced in comparison to the control (p < 0.05). A significant increase in DNA fragmentation was detected in the RMAX group. The results demonstrated that the treatment of sperm with EACA led to a decrease in the fragmentation of the sperm DNA (compared to the RMAX group) (p < 0.05).

CONCLUSION

The results indicate that EACA effectively protects human spermatozoa from DNA damage induced by ionizing radiation. Treatment of spermatozoa with EACA led to the preservation of cell motility, viability, and DNA integrity upon radiation exposure.

Radioprotective Effects of Plants from the Lamiaceae Family

BACKGROUND

Edible and medicinal plants are still an interesting source of promising biologically active substances for drug discovery and development. At a time of increasing cancer incidence in the world, alleviating the bothersome side effects of radiotherapy in debilitated cancer patients is becoming an important challenge.

OBJECTIVE

The aim of the study was to overview the literature data concerning the radioprotective activity of extracts, essential oils, and some chemical compounds obtained from 12 species belonging to the Lamiaceae family, gathering of numerous spice and medicinal plants rich in valuable phytochemicals.

RESULTS

The analysis of available publications showed radioprotective effectiveness of essential oils and complex extracts containing phenolic acids and flavonoids in various in vitro and in vivo models. Relatively welldocumented preventive properties exhibited the following species: Mentha × piperita, Ocimum tenuiflorum, Origanum vulgare, and Rosmarinus officinalis. However, few plants such as Lavandula angustifolia, Mentha arvensis, M. spicata, Plectranthus amboinicus, Salvia miltiorrhiza, S. officinalis, Scutellaria baicalensis, and Zataria multiflora should be more investigated in the future. Among the mechanisms of radioprotective effects of well-studied extracts and phytochemicals, it can be mentioned mainly the protection against chromosomal damage, scavenging free radicals, decreasing of lipid peroxidation and elevating of glutathione, superoxide dismutase, catalase, and alkaline phosphatase enzyme levels as well as the reduction of the cell death. The plant substances protected the gastrointestinal tract, bone marrow and lung fibroblasts.

CONCLUSION

The studied species of Lamiaceae family and their active chemical compounds are potent in alleviating the side effects of radiotherapy and should be considered as a complementary therapy.

Rational Design of Nanomaterials for Various Radiation-Induced Diseases Prevention and Treatment

Radiation treatments often unfavorably damage neighboring healthy organs and cause a series of radiation sequelae, such as radiation-induced hematopoietic system diseases, radiation-induced gastrointestinal diseases, radiation-induced lung diseases, and radiation-induced skin diseases. Recently, emerging nanomaterials have exhibited good superiority for these radiation-induced disease treatments. Given this background, the rational design principle of nanomaterials, which helps to optimize the therapeutic efficiency, has been an increasing need. Consequently, it is of great significance to perform a systematic summarization of the advances in this field, which can trigger the development of new high-performance nanoradioprotectors with drug efficiency maximization. Herein, this review highlights the advances and perspectives in the rational design of nanomaterials for preventing and treating various common radiation-induced diseases. Furthermore, the sources, clinical symptoms, and pathogenesis/injury mechanisms of these radiation-induced diseases will also be introduced. Furthermore, current challenges and directions for future efforts in this field are also discussed.

Catalytic Nanozyme for Radiation Protection

Radiotherapy has been widely used in clinical cancer treatment. However, the ionizing radiation required to kill the tumor will inevitably cause damage to the surrounding normal tissues. To minimize the radiation damage and side effects, small molecular radioprotective agents have been used as clinical adjuvants for radiation protection of healthy tissues. However, the shortcomings of small molecules such as short circulation time and rapid kidney clearance from the body greatly hinder their biomedical applications. In recent years, nanozymes have attracted much attention because of their potential to treat a variety of diseases. Nanozymes exhibit catalytic properties and antioxidant capabilities to provide a potential solution for the development of high-efficiency radioprotective agents in radiotherapy and nuclear radiation accidents. Therefore, in this review, we systematically summarize the catalytic nanozymes used for radiation protection of healthy tissues and discuss the challenges and future prospects of nanomaterials in the field of radiation protection.

Radioprotectors.org: an open database of known and predicted radioprotectors

The search for radioprotectors is an ambitious goal with many practical applications. Particularly, the improvement of human radioresistance for space is an important task, which comes into view with the recent successes in the space industry. Currently, all radioprotective drugs can be divided into two large groups differing in their effectiveness depending on the type of exposure. The first of these is radioprotectors, highly effective for pulsed, and some types of relatively short exposure to irradiation. The second group consists of long-acting radioprotectors. These drugs are effective for prolonged and fractionated irradiation. They also protect against impulse exposure to ionizing radiation, but to a lesser extent than short-acting radioprotectors. Creating a database on radioprotectors is a necessity dictated by the modern development of science and technology. We have created an open database, Radioprotectors.org, containing an up-to-date list of substances with proven radioprotective properties. All radioprotectors are annotated with relevant chemical and biological information, including transcriptomic data, and can be filtered according to their properties. Additionally, the performed transcriptomics analysis has revealed specific transcriptomic profiles of radioprotectors, which should facilitate the search for potent radioprotectors.

Drug discovery strategies for acute radiation syndrome

Introduction: There are at the minimum two major, quite different approaches to advance drug discovery. The first being the target-based drug discovery (TBDD) approach that is commonly referred to as the molecular approach. The second approach is the phenotype-based drug discovery (PBDD), also known as physiology-based drug discovery or empirical approach. Area covered: The authors discuss, herein, the need for developing radiation countermeasure agents for various sub-syndromes of acute radiation syndromes (ARS) following TBDD and PBDD approaches. With time and continuous advances in radiation countermeasure drug development research, the expectation is to have multiple radiation countermeasure agents for each sub-syndrome made available to radiation exposed victims. Expert opinion: The majority of the countermeasures currently being developed for ARS employ the PBDD approach, while the TBDD approach is clearly under-utilized. In the future, an improved drug development strategy might be a 'hybrid' strategy that is more reliant on TBDD for the initial drug discovery via large-scale screening of potential candidate agents, while utilizing PBDD for secondary screening of those candidates, followed by tertiary analytics phase in order to pinpoint efficacious candidates that target the specific sub-syndromes of ARS.

Radioprotective effects of mistletoe extract in zebrafish embryos in vivo

Introduction: Radioprotectors can enhance the efficacy of cancer radiotherapy, but their clinical use remains uncommon. The present study aimed to assess the radioprotective potential of mistletoe extract (commercial name: Abnoba Viscum), a well-known complementary cancer medicine, in zebrafish larvae. Materials and methods: Wild-type AB zebrafish embryos at 4 h-post-fertilization were exposed to 5 Gy 9-MeV electron beam irradiation after being treated for 1 h with 4 mMl/L amifostine or 0.2 mg/ml Abnoba Viscum A, F, M, or Q. Primary endpoints were abnormality-free survival and abnormality-free rates among survivors at 5 days-post-fertilization. Results: The crude abnormality-free survival rates were 33.7%, 49.0%, 38.8%, 43.9%, 38.1%, and 52.6%, whereas abnormality-free rates among survivors were 36.4%, 49.6%, 37.8%, 45.6%, 52.0%, and 62.8% for the control (with no pharmacologic treatment), amifostine, Abnoba Viscum A, F, M, and Q groups, respectively. Abnormality-free survival rates in the amifostine and Abnoba Viscum Q groups were significantly different from those in the control (p = .040 and .012, respectively), with an odds ratio (OR) of 1.90 [95% confidence interval (CI): 1.03-3.51] and 2.20 (95% CI: 1.19-4.08), respectively. Abnormality-free rates among survivors in the amifostine and Abnoba Viscum M and Q groups were significantly different from those in the control group (p = .048, .042, and <.001, respectively), with an OR of 1.79 (95% CI: 1.00-3.20), 1.82 (95% CI: 1.02-3.26), and 2.98 (1.67-5.33), respectively. Conclusion: Abnoba Viscum Q has at least a similar radioprotective effect to that of amifostine. Mistletoe extracts have been clinically applied for a long time and their effectiveness and feasibility have been verified. Abnoba Viscum Q might be a new candidate radioprotectant to enhance cancer radiotherapy efficacy.

Radioprotective properties of food colorant sodium copper chlorophyllin on human peripheral blood cells in vitro

Sodium copper chlorophyllin (CHL) is a food colorant that exhibits many beneficial properties, including potential for use in radiotherapy. Nevertheless, genotoxicity studies investigating radioprotective properties against γ-radiation on human cells are rather scarce. The aim of this study was to assess the cytotoxicity, genotoxicity and induction of malondialdehyde formation on CHL pre-treated whole blood cells after an absorbed dose of 5 Gy γ-radiation. Irradiated whole blood cells pre-treated with 100, 500, and 1000 μg/mL CHL showed less DNA-strand breaks (10.92 ± 0.74%, 10.69 ± 0.68%, and 8.81 ± 0.69%, respectively) than untreated irradiated cells (12.58 ± 0.88%). At the same time, the level of malondialdehyde was lower in CHL pre-treated samples with 100, 500, and 1000 μg/mL CHL (14.11 ± 0.43, 16.35 ± 2.82, and 13.08 ± 1.03 μmol/L, respectively) compared to untreated irradiated samples (24.11 ± 0.25 μmol/L). Regarding cytotoxicity, no changes were observed in the samples tested. Another important finding is that CHL had no cyto/genotoxic properties toward human blood cells. Taken together, since CHL had no cyto/genotoxic effects and showed good radioprotective properties in human blood cells, further studies should be conducted in order to find its possible application in radiotherapy.

Progressive breast fibrosis caused by extreme radiosensitivity: Oncocytogenetic diagnosis and treatment by reconstructive flap surgery

BACKGROUND

Fibrosis, a proliferative response of fibrocytes after tissue injury, is a common sequela of external radiotherapy and can vary greatly among patients even in the absence of DNA repair syndromes, due to their different intrinsic radiosensitivity. Fibrosis is also a serious cosmetic problem for patients, and in some cases it can also imply pain.

CASE

Here, we report a case of a severe fibrosis 2 years after breast conserving surgery and postoperative 3D conformal breast irradiation. Furthermore, our patient had the suspicion of tumour recurrence. Our examinations were aimed at diagnosing recurrence or the lack of recurrence and investigating whether the symptoms occurred due to overdosing or extreme intrinsic radiosensitivity. Therefore, examining the patients' radiosensitivity, a cytogenetic test was performed, which revealed the patient's increased susceptibility to ionizing radiation, and therefore we rejected the prospect of overdosage. As a solution for the fibrosis, mastectomy was effectuated, and a latissimus dorsi musculocutaneous flap was used for reconstruction.

CONCLUSIONS

We suggest a multi-disciplinary approach to manage fibrosis and propose cytogenetic markers to be used as predictors to identify patients who most likely benefit from a certain therapeutic regimen in terms of reduction of therapy-related side effects.

Expanding the therapeutic index of radiation therapy by normal tissue protection

Normal tissue damages induced by radiation therapy remain dose-limiting factors in radiation oncology and this is still true despite recent advances in treatment planning and delivery of image-guided radiation therapy. Additionally, as the number of long-term cancer survivors increases, unacceptable complications emerge and dramatically reduce the patients' quality of life. This means that patients and clinicians expect discovery of new options for the therapeutic management of radiation-induced complications. Over the past four decades, research has enhanced our understanding of the pathophysiological, cellular and molecular processes governing normal tissue toxicity. Those processes are complex and involve the cross-talk between the various cells of a tissue, including fibroblasts, endothelial, immune and epithelial cells as well as soluble paracrine factors including growth factors and proteases. We will review the translatable pharmacological approaches that have been developed to prevent, mitigate, or reverse radiation injuries based upon the targeting of cellular and signalling pathways. We will summarize the different steps of the research strategy, from the definition of initial biological hypotheses to preclinical studies and clinical translation. We will also see how novel research and therapeutic hypotheses emerge along the way as well as briefly highlight innovative approaches based upon novel radiotherapy delivery procedures.

Dark tea extract mitigates hematopoietic radiation injury with antioxidative activity

The hematopoietic system is widely studied in radiation research. Tea has been proved to have antioxidative activity. In the present study, we describe the protective effects of dark tea extract (DTE) on radiation-induced hematopoietic injury. DTE administration significantly enhanced the survival rate of mice after 7.0 and 7.5 Gy total body irradiation (TBI). The results showed that DTE not only markedly increased the numbers and cloning potential of hematopoietic cells, but also decreased DNA damages after mice were exposed to 6.0 Gy total body irradiation (TBI). In addition, DTE also decreased the levels of reactive oxygen species (ROS) in hematopoietic cells by inhibiting NOX4 expression and increasing the dismutase, catalase and glutathione peroxidase in livers. These data demonstrate that DTE can prevent radiation-induced hematopoietic syndromes, which is beneficial for protection from radiation injuries.

The Addition of Manganese Porphyrins during Radiation Inhibits Prostate Cancer Growth and Simultaneously Protects Normal Prostate Tissue from Radiation Damage

Radiation therapy is commonly used for prostate cancer treatment; however, normal tissues can be damaged from the reactive oxygen species (ROS) produced by radiation. In separate reports, we and others have shown that manganese porphyrins (MnPs), ROS scavengers, protect normal cells from radiation-induced damage but inhibit prostate cancer cell growth. However, there have been no studies demonstrating that MnPs protect normal tissues, while inhibiting tumor growth in the same model. LNCaP or PC3 cells were orthotopically implanted into athymic mice and treated with radiation (2 Gy, for 5 consecutive days) in the presence or absence of MnPs. With radiation, MnPs enhanced overall life expectancy and significantly decreased the average tumor volume, as compared to the radiated alone group. MnPs enhanced lipid oxidation in tumor cells but reduced oxidative damage to normal prostate tissue adjacent to the prostate tumor in combination with radiation. Mechanistically, MnPs behave as pro-oxidants or antioxidants depending on the level of oxidative stress inside the treated cell. We found that MnPs act as pro-oxidants in prostate cancer cells, while in normal cells and tissues the MnPs act as antioxidants. For the first time, in the same in vivo model, this study reveals that MnPs enhance the tumoricidal effect of radiation and reduce oxidative damage to normal prostate tissue adjacent to the prostate tumor in the presence of radiation. This study suggests that MnPs are effective radio-protectors for radiation-mediated prostate cancer treatment.

Radioprotective agents to prevent cellular damage due to ionizing radiation

Medical imaging has become a central component of patient care to ensure early and accurate diagnosis. Unfortunately, many imaging modalities use ionizing radiation to generate images. Ionizing radiation even in low doses can cause direct DNA damage and generate reactive oxygen species and free radicals, leading to DNA, protein, and lipid membrane damage. This cell damage can lead to apoptosis, necrosis, teratogenesis, or carcinogenesis. As many as 2% of cancers (and an associated 15,000 deaths annually) can be linked to computed tomography exposure alone. Radioprotective agents have been investigated using various models including cells, animals, and recently humans. The data suggest that radioprotective agents working through a variety of mechanisms have the potential to decrease free radical damage produced by ionizing radiation. Radioprotective agents may be useful as an adjunct to medical imaging to reduced patient morbidity and mortality due to ionizing radiation exposure. Some radioprotective agents can be found in high quantities in antioxidant rich foods, suggesting that a specific diet recommendation could be beneficial in radioprotection.

Modifiers of radiation effects in the eye

World events, including the threat of radiological terrorism and the fear of nuclear accidents, have highlighted an urgent need to develop medical countermeasures to prevent or reduce radiation injury. Similarly, plans for manned spaceflight to a near-Earth asteroid or journey to Mars raise serious concerns about long-term effects of space radiation on human health and the availability of suitable therapeutic interventions. At the same time, the need to protect normal tissue from the deleterious effects of radiotherapy has driven considerable research into the design of effective radioprotectors. For more than 70 years, animal models of radiation cataract have been utilized to test the short and long-term efficacy of various radiation countermeasures. While some compounds, most notably the Walter Reed (WR) class of radioprotectors, have reported limited effectiveness when given before exposure to low-LET radiation, the human toxicity of these molecules at effective doses limits their usefulness. Furthermore, while there has been considerable testing of eye responses to X- and gamma irradiation, there is limited information about using such models to limit the injurious effects of heavy ions and neutrons on eye tissue. A new class of radioprotector molecules, including the sulfhydryl compound PrC-210, are reported to be effective at much lower doses and with far less side effects. Their ability to modify ocular radiation damage has not yet been examined. The ability to non-invasively measure sensitive, radiation-induced ocular changes over long periods of time makes eye models an attractive option to test the radioprotective and radiation mitigating abilities of new novel compounds.

Experimental Study of Yeast RNA Preparation as a Possible Radioprotective Agent for Radiotherapy of Malignant Tumors

We studied radioprotective effects of a preparation based on yeast RNA and its influence on therapeutic efficiency of ionizing radiation against transplanted tumors. Parenteral administration of yeast RNA preparation to mice in a dose of 10 mg 1 h prior to exposure to ionizing γ-radiation (¹³⁷Cs) in a lethal dose (LD_80/30) increased 30-day survival by 66%; by day 80, 80% of animals survived (vs. 2.5% in the control). Whole-body exposure to ionizing γ-radiation in a dose of 7 Gy significantly increased the mean lifespan of mice with experimental lung metastases or intraperitoneally transplanted leukemia L-1210 by 42 and 20.8%, respectively. RNA preparation injected to the mice with tumors 1 h before irradiation did not affect the therapeutic efficiency of ionizing radiation or significantly potentiated it (in mice with transplanted leukemia L-1210). These results suggest that yeast RNA preparation protects healthy tissues during radiotherapy of malignant tumors.

Cancer Cell Death-Inducing Radiotherapy: Impact on Local Tumour Control, Tumour Cell Proliferation and Induction of Systemic Anti-tumour Immunity

Radiotherapy (RT) predominantly is aimed to induce DNA damage in tumour cells that results in reduction of their clonogenicity and finally in tumour cell death. Adaptation of RT with higher single doses has become necessary and led to a more detailed view on what kind of tumour cell death is induced and which immunological consequences result from it. RT is capable of rendering tumour cells immunogenic by modifying the tumour cell phenotype and the microenvironment. Danger signals are released as well as the senescence-associated secretory phenotype. This results in maturation of dendritic cells and priming of cytotoxic T cells as well as in activation of natural killer cells. However, RT on the other hand can also result in immune suppressive events including apoptosis induction and foster tumour cell proliferation. That's why RT is nowadays increasingly combined with selected immunotherapies.

Mitigation of Radiation-Induced Epithelial Damage by the TLR5 Agonist Entolimod in a Mouse Model of Fractionated Head and Neck Irradiation

Radiation treatment of head and neck cancer frequently causes severe collateral damage to normal tissues including mouth mucosa, salivary glands and skin. This toxicity limits the radiation dose that can be delivered and affects the patient's quality of life. Previous studies in mice and nonhuman primates showed that entolimod, a toll-like receptor 5 (TLR5) agonist derived from bacterial flagellin, effectively reduced radiation damage to hematopoietic and gastrointestinal tissues in both total-body and local irradiation scenarios, with no protection of tumors. Here, using a mouse model, we analyzed the efficacy of entolimod administered before or after irradiation in reducing damage to normal tissues. Animals received local fractionated radiation to the head and neck area, thus modeling radiotherapy of head and neck cancer. Tissue damage was evaluated through histomorphological examination of samples collected at different time points up to four weeks, mice were exposed locally to five daily fractions of 5, 6 or 7 Gy. A semiquantitative scoring system was used to assess the severity of observed pathomorphological changes. In this model, radiation damage was most severe in the lips, tongue and skin, moderate in the upper esophagus and minor in salivary glands. The kinetics of injury appearance and recovery of normal morphology varied among tissues, with maximal damage to the tongue, esophagus and salivary glands developing at earlier times (days 8-11 postirradiation) relative to that of lip and skin mucosa (days 11-15 postirradiation). While both tested regimens of entolimod significantly reduced the extent of radiation damage and accelerated restoration of normal structure in all tissues analyzed, administration of entolimod 1 h after each irradiation was more effective than treatment 30 min before irradiation. These results support the potential clinical use of entolimod as an adjuvant for improving the therapeutic index of head and neck cancer radiotherapy by reducing the radiation toxicity in normal tissues.

Loss of LZAP inactivates p53 and regulates sensitivity of cells to DNA damage in a p53-dependent manner

Chemotherapy and radiation, the two most common cancer therapies, exert their anticancer effects by causing damage to cellular DNA. However, systemic treatment damages DNA not only in cancer, but also in healthy cells, resulting in the progression of serious side effects and limiting efficacy of the treatment. Interestingly, in response to DNA damage, p53 seems to play an opposite role in normal and in the majority of cancer cells-wild-type p53 mediates apoptosis in healthy tissues, attributing to the side effects, whereas mutant p53 often is responsible for acquired cancer resistance to the treatment. Here, we show that leucine zipper-containing ARF-binding protein (LZAP) binds and stabilizes p53. LZAP depletion eliminates p53 protein independently of its mutation status, subsequently protecting wild-type p53 cells from DNA damage-induced cell death, while rendering cells expressing mutant p53 more sensitive to the treatment. In human non-small-cell lung cancer, LZAP levels correlated with p53 levels, suggesting that loss of LZAP may represent a novel mechanism of p53 inactivation in human cancer. Our studies establish LZAP as a p53 regulator and p53-dependent determinative of cell fate in response to DNA damaging treatment.

Hydrogen-Rich Water Ameliorates Total Body Irradiation-Induced Hematopoietic Stem Cell Injury by Reducing Hydroxyl Radical

We examined whether consumption of hydrogen-rich water (HW) could ameliorate hematopoietic stem cell (HSC) injury in mice with total body irradiation (TBI). The results indicated that HW alleviated TBI-induced HSC injury with respect to cell number alteration and to the self-renewal and differentiation of HSCs. HW specifically decreased hydroxyl radical (^∙OH) levels in the c-kit⁺ cells of 4 Gy irradiated mice. Proliferative bone marrow cells (BMCs) increased and apoptotic c-kit⁺ cells decreased in irradiated mice uptaken with HW. In addition, the mean fluorescence intensity (MFI) of γ-H2AX and percentage of 8-oxoguanine positive cells significantly decreased in HW-treated c-kit⁺ cells, indicating that HW can alleviate TBI-induced DNA damage and oxidative DNA damage in c-kit⁺ cells. Finally, the cell cycle (P21), cell apoptosis (BCL-XL and BAK), and oxidative stress (NRF2, HO-1, NQO1, SOD, and GPX1) proteins were significantly altered by HW in irradiated mouse c-kit⁺ cells. Collectively, the present results suggest that HW protects against TBI-induced HSC injury.

Analysis of Radiomodulatory Effect of Low-Level Laser Irradiation by Clonogenic Survival Assay

OBJECTIVE

The aim of this study was to investigate the radiomoulatory effects of low-level laser irradiation (LLLI) in normal and cancer cells exposed to ionizing X-ray radiation on clonogenic survival assay.

BACKGROUND DATA

LLLI does have radioprotective effects on normal tissue. LLLI can reduce the incidence of mucocutaneous complications of ionizing radiation. Few in vitro studies reported adaptive responses for LLLI to ionizing radiation in normal and cancer cells, particularly with respect to clonogenic cell survival assay.

METHODS

Normal NIH 3T3 cells and cancer HeLa cells were irradiated with 685 and 830 nm LLLI at different energy densities prior to ionizing X-ray radiation. The survival fraction was determined after ionizing radiation (0, 2, 4, and 6 Gy). The values of the linear (α) and quadratic (β) parameters were calculated based on the clonogenic survival curves.

RESULTS

Clonogenic radiation survival assay showed that the application of LLLI at 685 nm prior to ionizing radiation could significantly inhibit clonogenic growth of HeLa cells compared with unirradiated HeLa cells. LLLI could also significantly increase the α parameter of the linear quadratic (LQ) model. In contrast, application of LLLI at 830 nm could significantly protect NIH 3T3 cells against radiation and decreased α parameter.

CONCLUSIONS

This study suggests that various physical parameters of LLLI can be diverse adaptive responses to ionizing radiation on normal and cancer cells.

The Yiqi and Yangyin Formula ameliorates injury to the hematopoietic system induced by total body irradiation

In this study, we examined whether the Yiqi and Yangyin Formula (YYF), used in traditional Chinese medicine, could ameliorate damage to the hematopoietic system induced by total body irradiation (TBI). Treatment with 15 g/kg of YYF increased the survival rate of Institute of Cancer Research (ICR) mice exposed to 7.5 Gy TBI. Furthermore, YYF treatment increased the white blood cell (WBC), red blood cell (RBC), hemoglobin (HGB) and hematocrit (HCT) counts in ICR mice exposed to 2 Gy or 4 Gy TBI. Treatment with YYF also increased the number of bone marrow cells, hematopoietic progenitor cells (HPCs), hematopoietic stem cells (HSCs) and the colony-forming ability of granulocyte-macrophage cells. YYF alleviated TBI-induced suppression of the differentiation ability of HPCs and HSCs and decreased the reactive oxygen species (ROS) levels in bone marrow mononuclear cells (BMMNCs), HPCs and HSCs from mice exposed to 2 Gy or 4 Gy TBI. Overall, our data suggest that YYF can ameliorate myelosuppression by reducing the intracellular ROS levels in hematopoietic cells after TBI at doses of 2 Gy and 4 Gy.

Clinical development of new drug-radiotherapy combinations

In countries with the best cancer outcomes, approximately 60% of patients receive radiotherapy as part of their treatment, which is one of the most cost-effective cancer treatments. Notably, around 40% of cancer cures include the use of radiotherapy, either as a single modality or combined with other treatments. Radiotherapy can provide enormous benefit to patients with cancer. In the past decade, significant technical advances, such as image-guided radiotherapy, intensity-modulated radiotherapy, stereotactic radiotherapy, and proton therapy enable higher doses of radiotherapy to be delivered to the tumour with significantly lower doses to normal surrounding tissues. However, apart from the combination of traditional cytotoxic chemotherapy with radiotherapy, little progress has been made in identifying and defining optimal targeted therapy and radiotherapy combinations to improve the efficacy of cancer treatment. The National Cancer Research Institute Clinical and Translational Radiotherapy Research Working Group (CTRad) formed a Joint Working Group with representatives from academia, industry, patient groups and regulatory bodies to address this lack of progress and to publish recommendations for future clinical research. Herein, we highlight the Working Group's consensus recommendations to increase the number of novel drugs being successfully registered in combination with radiotherapy to improve clinical outcomes for patients with cancer.

Protective effects of rosmarinic acid against radiation-induced damage to the hematopoietic system in mice

Rosmarinic acid (RA) is an ester of caffeic acid and 3, 4-dihydroxyphenyl lactic acid. It is a potent antioxidant that functions by scavenging free radicals. Here, we used a 30-day survival assay to investigate the radioprotective effects of RA. Mice were treated with RA once per day for 10 consecutive days starting at 3 days before gamma irradiation at 7.5 Gy until 7 days post irradiation. Mice treated with 100 and 200 mg/kg body weight (bw) of RA had 30-day survival rates of 89% and 72%, respectively, compared with 32% in the control group, and the differences were statistically significant (P = 0.0008 and 0.0421, respectively). Spleen colony-forming units (CFU-S), the number of nucleated cells in the bone marrow (BMNC), bone marrow DNA content, and hematological parameters of the peripheral blood were measured to investigate the radioprotective effect of RA on the hematopoietic system. The treatment groups that received RA at 50, 100 and 150 mg/kg bw and whole-body exposure to 5.5 Gy of (137)Cs γ- radiation had significantly higher CFU-S, BMNC and DNA content than the irradiation-only group. Assessment of hematological parameters in the peripheral blood showed that the treatment groups receiving RA at doses of 50, 100 and 150 mg/kg bw had higher white blood cell counts, hemoglobin and platelets than the radiation-only group. These results suggested that the administration of RA promoted the recovery of peripheral blood cells in irradiated mice.

Disruption of Notch signaling aggravates irradiation-induced bone marrow injury, which is ameliorated by a soluble Dll1 ligand through Csf2rb2 upregulation

Physical and chemical insult-induced bone marrow (BM) damage often leads to lethality resulting from the depletion of hematopoietic stem and progenitor cells (HSPCs) and/or a deteriorated BM stroma. Notch signaling plays an important role in hematopoiesis, but whether it is involved in BM damage remains unclear. In this study, we found that conditional disruption of RBP-J, the transcription factor of canonical Notch signaling, increased irradiation sensitivity in mice. Activation of Notch signaling with the endothelial cell (EC)-targeted soluble Dll1 Notch ligand mD1R promoted BM recovery after irradiation. mD1R treatment resulted in a significant increase in myeloid progenitors and monocytes in the BM, spleen and peripheral blood after irradiation. mD1R also enhanced hematopoiesis in mice treated with cyclophosphamide, a chemotherapeutic drug that induces BM suppression. Mechanistically, mD1R increased the proliferation and reduced the apoptosis of myeloid cells in the BM after irradiation. The β chain cytokine receptor Csf2rb2 was identified as a downstream molecule of Notch signaling in hematopoietic cells. mD1R improved hematopoietic recovery through up-regulation of the hematopoietic expression of Csf2rb2. Our findings reveal the role of Notch signaling in irradiation- and drug-induced BM suppression and establish a new potential therapy of BM- and myelo-suppression induced by radiotherapy and chemotherapy.

Cellular Pathways in Response to Ionizing Radiation and Their Targetability for Tumor Radiosensitization

During the last few decades, improvements in the planning and application of radiotherapy in combination with surgery and chemotherapy resulted in increased survival rates of tumor patients. However, the success of radiotherapy is impaired by two reasons: firstly, the radioresistance of tumor cells and, secondly, the radiation-induced damage of normal tissue cells located in the field of ionizing radiation. These limitations demand the development of drugs for either radiosensitization of tumor cells or radioprotection of normal tissue cells. In order to identify potential targets, a detailed understanding of the cellular pathways involved in radiation response is an absolute requirement. This review describes the most important pathways of radioresponse and several key target proteins for radiosensitization.

The Flaxseed-Derived Lignan Phenolic Secoisolariciresinol Diglucoside (SDG) Protects Non-Malignant Lung Cells from Radiation Damage

Plant phenolic compounds are common dietary antioxidants that possess antioxidant and anti-inflammatory properties. Flaxseed (FS) has been reported to be radioprotective in murine models of oxidative lung damage. Flaxseed’s protective properties are attributed to its main biphenolic lignan, secoisolariciresinol diglucoside (SDG). SDG is a free radical scavenger, shown in cell free systems to protect DNA from radiation-induced damage. The objective of this study was to investigate the in vitro radioprotective efficacy of SDG in murine lung cells. Protection against irradiation (IR)-induced DNA double and single strand breaks was assessed by γ-H2AX labeling and alkaline comet assay, respectively. The role of SDG in modulating the levels of cytoprotective enzymes was evaluated by qPCR and confirmed by Western blotting. Additionally, effects of SDG on clonogenic survival of irradiated cells were evaluated. SDG protected cells from IR-induced death and ameliorated DNA damage by reducing mean comet tail length and percentage of γ-H2AX positive cells. Importantly, SDG significantly increased gene and protein levels of antioxidant HO-1, GSTM1 and NQO1. Our results identify the potent radioprotective properties of the synthetic biphenolic SDG, preventing DNA damage and enhancing the antioxidant capacity of normal lung cells; thus, rendering SDG a potential radioprotector against radiation exposure.

Radioprotective agents for radiation therapy: future trends

Only two radioprotective compounds, amifostine and palifermin, currently have the US FDA approval for use in radiation therapy. However, several agents have been reported that show therapeutic promise. Many of these agents are free radical scavengers/antioxidants. Superoxide dismutase and superoxide dismutase mimetics, nitroxides and dietary antioxidants are all being investigated. Recently, alternative strategies of drug development have been evolving, which focus on targeting the series of cellular insult recognition/repair responses initiated following radiation. These agents, which include cytokines/growth factors, angiotensin-converting enzyme inhibitors and apoptotic modulators, show promise of having significant impact on the mitigation of radiation injury. Herein, we review current literature on the development of radioprotectors with emphasis on compounds with proven or potential usefulness in radiation therapy.

Drug radiotherapy combinations: review of previous failures and reasons for future optimism

Combining chemotherapy with radiotherapy has resulted in significant clinical improvements in many different tumour types. However, the non-specific mechanisms by which these drugs exert their effects mean that this is often at the expense of increased side effects. Previous attempts at using targeted drugs to induce more tumour specific radiosensitisation have been generally disappointing. Although cetuximab, an EGFR monoclonal antibody, resulted in improved overall survival in HNSCC when combined with radiotherapy, it has failed to show benefit when added to chemo-radiotherapy. In addition, our inability to successfully use drug treatments to reverse tumour hypoxia is underlined by the fact that no such treatment is currently in widespread clinical use. The reasons for these failures include the lack of robust biomarkers, and the previous use of drugs with unacceptable side-effect profiles. Despite these disappointments, there is reason for optimism. Our improved understanding of key signal transduction pathways and of tumour specific DNA repair deficiencies has produced new opportunities to specifically radiosensitise tumours. Novel strategies to reduce tumour hypoxia include the use of drugs that cause vascular normalisation and drugs that reduce tumour oxygen consumption. These new strategies, combined with better compounds at our disposal, and an ability to learn from our previous mistakes, mean that there is great promise for future drug-radiotherapy combinations to result in significant clinical benefits.

Radioprotection of targeted and bystander cells by methylproamine

Introduction

Radioprotective agents are of interest for application in radiotherapy for cancer and in public health medicine in the context of accidental radiation exposure. Methylproamine is the lead compound of a class of radioprotectors which act as DNA binding anti-oxidants, enabling the repair of transient radiation-induced oxidative DNA lesions. This study tested methylproamine for the radioprotection of both directly targeted and bystander cells.

Methods

T98G glioma cells were treated with 15 μM methylproamine and exposed to ¹³⁷Cs γ-ray/X-ray irradiation and He²⁺ microbeam irradiation. Radioprotection of directly targeted cells and bystander cells was measured by clonogenic survival or γH2AX assay.

Results

Radioprotection of directly targeted T98G cells by methylproamine was observed for ¹³⁷Cs γ-rays and X-rays but not for He²⁺ charged particle irradiation. The effect of methylproamine on the bystander cell population was tested for both X-ray irradiation and He²⁺ ion microbeam irradiation. The X-ray bystander experiments were carried out by medium transfer from irradiated to non-irradiated cultures and three experimental designs were tested. Radioprotection was only observed when recipient cells were pretreated with the drug prior to exposure to the conditioned medium. In microbeam bystander experiments targeted and nontargeted cells were co-cultured with continuous methylproamine treatment during irradiation and postradiation incubation; radioprotection of bystander cells was observed.

Discussion and conclusion

Methylproamine protected targeted cells from DNA damage caused by γ-ray or X-ray radiation but not He²⁺ ion radiation. Protection of bystander cells was independent of the type of radiation which the donor population received.

Platelet factor 4 protects bone marrow mesenchymal stem cells from acute radiation injury

OBJECTIVE

The aim of this study was to find a new radiation protector, platelet factor 4 (PF4) and to identify its effect on haemopoietic microenvironment in vitro and in vivo.

METHODS

Radiation damage on bone marrow mesenchymal stem cells ex and in vitro was set up as models. Growth curve analysis, clonogenic survival assay, FACSCalibur™ (BD Immunocytometry Systems, San Jose, CA), 5-ethynyl-2'-deoxyuridine immunofluorescence staining and quantitative reverse transcription-polymerase chain reaction were employed to assess the characterization of bone marrow mesenchymal stem cells (BMSCs), proliferation, apoptosis, cell cycle and gene expression.

RESULTS

A dose- and time-dependent enhancement of cell viability and survival was observed for PF4 treatment along with 500 cGy γ-radiation in vitro. The same phenomena were noted in vivo, including enhancement of adherence and proliferation ability while inhibition of cell apoptosis, which were associated with a short-term decrease in the G0/G1 ratio owing to S phase arrest. These were accompanied with enhanced Bcl-2 expression and p53/p21 loss.

CONCLUSION

These results uncover that PF4 might be a novel therapeutic approach, which could reduce DNA damage and increase survival of BMSCs, in part, by inhibiting p53/p21 axis and facilitating DNA damage repair.

ADVANCES IN KNOWLEDGE

This study explores the feasibility of a new radioprotector and hence may be clinically important.