DNA repair targeting and radiotherapy: a focus on the therapeutic ratio

Hyperthermia and radiotherapy: physiological basis for a synergistic effect

In cancer treatment, mild hyperthermia (HT) represents an old, but recently revived opportunity to increase the efficacy of radiotherapy (RT) without increasing side effects, thereby widening the therapeutic window. HT disrupts cellular homeostasis by acting on multiple targets, and its combination with RT produces synergistic antitumoral effects on specific pathophysiological mechanisms, associated to DNA damage and repair, hypoxia, stemness and immunostimulation. HT is furthermore associated to direct tumor cell kill, particularly in higher temperature levels. A phenomenon of temporary resistance to heat, known as thermotolerance, follows each HT session. Cancer treatment requires innovative concepts and combinations to be tested but, for a meaningful development of clinical trials, the understanding of the underlying mechanisms of the tested modalities is essential. In this mini-review, we aimed to describe the synergistic effects of the combination of HT with RT as well as the phenomena of thermal shock and thermotolerance, in order to stimulate clinicians in new, clinically relevant concepts and combinations, which become particularly relevant in the era of technological advents in both modalities but also cancer immunotherapy.

DNA Double-Strand Break Repair Kinetics after Exposure to Photons and Ions: A Systematic Review

This study offers a review of published data on DNA double strand break (DSB) repair kinetics after exposure to ionizing radiation. By compiling a database, which currently includes 285 DNA DSB repair experiments utilizing both photons and ions, we investigate the impact of distinct experimental parameters on the kinetics of DNA DSB repair. Methodological differences and inconsistencies in reporting make the comparison of data generated by different research groups challenging. Nevertheless, by implementing filtering criteria, we can compare repair kinetics obtained with normal and tumor cells derived from human or animal tissues, as well as cells exposed to photons or ions ranging from hydrogen to iron ions. In addition, several repair curves of repair deficient cell lines were included. The study aims to provide researchers with a comprehensive overview of experimental factors that may confound results and emphasize the importance of precise reporting of experimental parameters. Moreover, we identify gaps in the literature that require attention in future studies, aiming to address clinically relevant questions related to radiotherapy. The database can be freely accessed at: https://github.com/weradstake/DRDNA.

Bone Metastases

ABSTRACT

Bone metastases occur frequently in common malignancies such as breast and prostate cancer. They are responsible for considerable morbidity and skeletal-related events. Fortunately, there are now several systemic, focal, and targeted therapies that can improve quality and length of life, including radionuclide therapies. It is therefore important that bone metastases can be detected as early as possible and that treatment can be accurately and sensitively monitored. Several bone-specific and tumor-specific single-photon emission computed tomography and positron emission tomography molecular imaging agents are available, for detection and monitoring response to systemic therapeutics, as well as theranostic agents to confirm target expression and predict response to radionuclide therapies.

Human Intestinal Organoids and Microphysiological Systems for Modeling Radiotoxicity and Assessing Radioprotective Agents

Radiotherapy is a commonly employed treatment for colorectal cancer, yet its radiotoxicity-related impact on healthy tissues raises significant health concerns. This highlights the need to use radioprotective agents to mitigate these side effects. This review presents the current landscape of human translational radiobiology, outlining the limitations of existing models and proposing engineering solutions. We delve into radiotherapy principles, encompassing mechanisms of radiation-induced cell death and its influence on normal and cancerous colorectal cells. Furthermore, we explore the engineering aspects of microphysiological systems to represent radiotherapy-induced gastrointestinal toxicity and how to include the gut microbiota to study its role in treatment failure and success. This review ultimately highlights the main challenges and future pathways in translational research for pelvic radiotherapy-induced toxicity. This is achieved by developing a humanized in vitro model that mimics radiotherapy treatment conditions. An in vitro model should provide in-depth analyses of host-gut microbiota interactions and a deeper understanding of the underlying biological mechanisms of radioprotective food supplements. Additionally, it would be of great value if these models could produce high-throughput data using patient-derived samples to address the lack of human representability to complete clinical trials and improve patients' quality of life.

The Mechanism of Ubiquitination or Deubiquitination Modifications in Regulating Solid Tumor Radiosensitivity

Radiotherapy, a treatment method employing radiation to eradicate tumor cells and subsequently reduce or eliminate tumor masses, is widely applied in the management of numerous patients with tumors. However, its therapeutic effectiveness is somewhat constrained by various drug-resistant factors. Recent studies have highlighted the ubiquitination/deubiquitination system, a reversible molecular modification pathway, for its dual role in influencing tumor behaviors. It can either promote or inhibit tumor progression, impacting tumor proliferation, migration, invasion, and associated therapeutic resistance. Consequently, delving into the potential mechanisms through which ubiquitination and deubiquitination systems modulate the response to radiotherapy in malignant tumors holds paramount significance in augmenting its efficacy. In this paper, we comprehensively examine the strides made in research and the pertinent mechanisms of ubiquitination and deubiquitination systems in governing radiotherapy resistance in tumors. This underscores the potential for developing diverse radiosensitizers targeting distinct mechanisms, with the aim of enhancing the effectiveness of radiotherapy.

The development of radioresistant oral squamous carcinoma cell lines and identification of radiotherapy-related biomarkers

BACKGROUND

In the treatment of oral squamous cell carcinoma (OSCC), radiation resistance remains an important obstacle to patient outcomes. Progress in understanding the molecular mechanisms of radioresistance has been limited by research models that do not fully recapitulate the biological features of solid tumors. In this study, we aimed to develop novel in vitro models to investigate the underlying basis of radioresistance in OSCC and to identify novel biomarkers.

METHODS

Parental OSCC cells (SCC9 and CAL27) were repeatedly exposed to ionizing radiation to develop isogenic radioresistant cell lines. We characterized the phenotypic differences between the parental and radioresistant cell lines. RNA sequencing was used to identify differentially expressed genes (DEGs), and bioinformatics analysis identified candidate molecules that may be related to OSCC radiotherapy.

RESULTS

Two isogenic radioresistant cell lines for OSCC were successfully established. The radioresistant cells displayed a radioresistant phenotype when compared to the parental cells. Two hundred and sixty DEGs were co-expressed in SCC9-RR and CAL27-RR, and thirty-eight DEGs were upregulated or downregulated in both cell lines. The associations between the overall survival (OS) of OSCC patients and the identified genes were analyzed using data from the Cancer Genome Atlas (TCGA) database. A total of six candidate genes (KCNJ2, CLEC18C, P3H3, PIK3R3, SERPINE1, and TMC8) were closely associated with prognosis.

CONCLUSION

This study demonstrated the utility of constructing isogenic cell models to investigate the molecular changes associated with radioresistance. Six genes were identified based on the data from the radioresistant cells that may be potential targets in the treatment of OSCC.

The radiation response measurement of a single and multiple cell ionization of neuroblastoma cells by infrared laser trap

Neuroblastoma (NB) is a common type of cancer found mostly in infants and arising from the immature neural crest cells of the sympathetic nervous system. Using laser trapping (LT) technique, the present work contributes to advancing radiotherapy (RT), a leading treatment method for cancer. A single, 2-cells, 3-cells, 4-cells, and 5-cells were trapped using the high-intensity gradient infrared laser at 1064 nm and allowed to become ionized. In this work, a systematic study of Threshold Ionization Energy (TIE) and Threshold Radiation Dose (TRD) versus mass for both single and multi-cell ionization using laser trapping (LT) techniques on NB is presented. The results show that TIE increased as the mass of cells increased, meanwhile TRD decreased with the increase of cell mass. We observed an inverse correlation between TRD and cell mass. We demonstrate how to compute the maximum radiation dosage for cell death using the LT technique. Results show a possible blueprint for computing the TRD in vivo. The use of multiple cell ionization to determine radiation dosage along with better data accuracy concerning the tumor size and density will have profound implications for radiation dosimetry. The diminution in TRD becomes more significant in multiple cell ionization as we see in TRD vs the number of cells entering the trap. This is due to the chain effect generated by radiation and the absorption by water molecules at 1064 nm. This result provides us with better insight into the optimization of the therapeutic ratio.

Sex dimorphism in the tumor microenvironment - From bench to bedside and back

Cancer represents a significant cause of death and suffering in both the developed and developing countries. Key underlying issues in the mortality of cancer are delayed diagnosis and resistance to treatments. However, improvements in biomarkers represent one important step that can be taken for alleviating the suffering caused by malignancy. Precision-based medicine is promising for revolutionizing diagnostic and treatment strategies for cancer patients worldwide. Contemporary methods, including various omics and systems biology approaches, as well as advanced digital imaging and artificial intelligence, allow more accurate assessment of tumor characteristics at the patient level. As a result, treatment strategies can be specifically tailored and adapted for individual and/or groups of patients that carry certain tumor characteristics. This includes immunotherapy, which is based on characterization of the immunosuppressive tumor microenvironment (TME) and, more specifically, the presence and activity of immune cell subsets. Unfortunately, while it is increasingly clear that gender strongly affects immune regulation and response, there is a knowledge gap concerning differences in sex-specific immune responses and how these contribute to the immunosuppressive TME and the response to immunotherapy. In fact, sex dimorphism is poorly understood in cancer progression and is typically ignored in current clinical practice. In this review, we aim to survey the available literature and highlight the existing knowledge gap in order to encourage further studies that would contribute to understanding both gender-biased immunosuppression in the TME and the driver of tumor progression towards invasive and metastatic disease. The review highlights the need to include sex optimized/genderized medicine as a new concept in future medicine cancer diagnostics and treatments.

The schemes, mechanisms and molecular pathway changes of Tumor Treating Fields (TTFields) alone or in combination with radiotherapy and chemotherapy

Tumor Treating Fields (TTFields) is a physical therapy that uses moderate frequency (100-300 kHz) and low-intensity (1-3 V/cm) alternating electric fields to inhibit tumors. Currently, the Food and Drug Administration approves TTFields for treating recurrent or newly diagnosed glioblastoma (GBM) and malignant pleural mesothelioma (MPM). The classical mechanism of TTFields is mitotic inhibition by hindering the formation of tubulin and spindle. In addition, TTFields inhibits cell proliferation, invasion, migration and induces cell death, such as apoptosis, autophagy, pyroptosis, and cell cycle arrest. Meanwhile, it regulates immune function and changes the permeability of the nuclear membrane, cell membrane, and blood-brain barrier. Based on the current researches on TTFields in various tumors, this review comprehensively summarizes the in-vitro effects, changes in pathways and molecules corresponding to relevant parameters of TTFields (frequency, intensity, and duration). In addition, radiotherapy and chemotherapy are common tumor treatments. Thus, we also pay attention to the sequence and dose when TTFields combined with radiotherapy or chemotherapy. TTFields has inhibitory effects in a variety of tumors. The study of TTFields mechanism is conducive to subsequent research. How to combine common tumor therapy such as radiotherapy and chemotherapy to obtain the maximum benefit is also a problem that's worthy of our attention.

CD9- and CD81-positive extracellular vesicles provide a marker to monitor glioblastoma cell response to photon-based and proton-based radiotherapy

Glioblastoma multiforme (GBM) is the most aggressive tumor of the central nervous system with a poor prognosis. In the treatment of GBM tumors, radiotherapy plays a major role. Typically, GBM tumors cannot be cured by irradiation because of intrinsic resistance machanisms. An escalation of the irradiation dose in the GBM tumor is difficult due to the high risk of severe side effects in the brain. In the last decade, the development of new irradiation techniques, including proton-based irradiation, promised new chances in the treatment of brain tumors. In contrast to conventional radiotherapy, irradiation with protons allows a dosimetrically more confined dose deposition in the tumor while better sparing the normal tissue surrounding the tumor. A systematic comparison of both irradiation techniques on glioblastoma cells has not been performed so far. Despite the improvements in radiotherapy, it remains challenging to predict the therapeutical response of GBM tumors. Recent publications suggest extracellular vesicles (EVs) as promising markers predicting tumor response. Being part of an ancient intercellular communication system, virtually all cells release specifically composed EVs. The assembly of EVs varies between cell types and depends on environmental parameters. Here, we compared the impact of photon-based with proton-based radiotherapy on cell viability and phenotype of four different glioblastoma cell lines. Furthermore, we characterized EVs released by different glioblastoma cells and correlated released EVs with the cellular response to radiotherapy. Our results demonstrated that glioblastoma cells reacted more sensitive to irradiation with protons than photons, while radiation-induced cell death 72 h after single dose irradiation was independent of the irradiation modality. Moreover, we detected CD9 and CD81-positive EVs in the supernatant of all glioblastoma cells, although at different concentrations. The amount of released CD9 and CD81-positive EVs increased after irradiation when cells became apoptotic. Although secreted EVs of non-irradiated cells were not predictive for radiosensitivity, their increased EV release after irradiation correlated with the cytotoxic response to radiotherapy 72 h after irradiation. Thus, our data suggest a novel application of EVs in the surveillance of anti-cancer therapies.

Role of melatonin mediated G-CSF induction in hematopoietic system of gamma-irradiated mice

AIMS

Hematopoietic acute radiation syndrome (H-ARS) can cause lethality, and therefore, the necessity of a safe radioprotector. The present study was focused on investigating the role of melatonin in granulocytes colony-stimulating factor (G-CSF) and related mechanisms underlying the reduction of DNA damage in hematopoietic system of irradiated mice.

MAIN METHODS

C57BL/6 male mice were exposed to 2, 5, and 7.5Gy of whole-body irradiation (WBI), 30 min after intra-peritoneal administration of melatonin with different doses. Mice were sacrificed at different time intervals after WBI, and bone marrow, splenocytes, and peripheral blood lymphocytes were isolated for studying various parameters including micronuclei (MN), cell cycle, comet, γ-H2AX, gene expression, amino acid profiling, and hematology.

KEY FINDINGS

Melatonin100mg/kg ameliorated radiation (7.5Gy and 5Gy) induced MN frequency and cell death in bone marrow without mortality. At 24 h of post-WBI (2Gy), the frequency of micronucleated polychromatic erythrocytes (mnPCE) with different melatonin doses revealed 20 mg/kg as optimal i.p. dose for protecting the hematopoietic system against radiation injury. In comet assay, a significant reduction in radiation-induced % DNA tail (p ≤ 0.05) was observed at this dose. Melatonin reduced γ-H2AX foci/cell and eventually reached to the control level. Melatonin also decreased blood arginine levels in mice after 24 h of WBI. The gene expression of G-CSF, Bcl-2-associated X protein (BAX), and Bcl2 indicated the role of melatonin in G-CSF regulation and downstream pro-survival pathways along with anti-apoptotic activity.

SIGNIFICANCE

The results revealed that melatonin recovers the hematopoietic system of irradiated mice by inducing G-CSF mediated radioprotection.

Developing a clinically relevant radiosensitizer for temozolomide-resistant gliomas

The prognosis for patients with glioblastoma (GB) remains grim. Concurrent temozolomide (TMZ) radiation—the cornerstone of glioma control—extends the overall median survival of GB patients by only a few months over radiotherapy alone. While these survival gains could be partly attributed to radiosensitization, this benefit is greatly minimized in tumors expressing O⁶-methylguanine DNA methyltransferase (MGMT), which specifically reverses O⁶-methylguanine lesions. Theoretically, non-O⁶-methylguanine lesions (i.e., the N-methylpurine adducts), which represent up to 90% of TMZ-generated DNA adducts, could also contribute to radiosensitization. Unfortunately, at concentrations attainable in clinical practice, the alkylation capacity of TMZ cannot overwhelm the repair of N-methylpurine adducts to efficiently exploit these lesions. The current therapeutic application of TMZ therefore faces two main obstacles: (i) the stochastic presence of MGMT and (ii) a blunted radiosensitization potential at physiologic concentrations. To circumvent these limitations, we are developing a novel molecule called NEO212—a derivatization of TMZ generated by coupling TMZ to perillyl alcohol. Based on gas chromatography/mass spectrometry and high-performance liquid chromatography analyses, we determined that NEO212 had greater tumor cell uptake than TMZ. In mouse models, NEO212 was more efficient than TMZ at crossing the blood-brain barrier, preferentially accumulating in tumoral over normal brain tissue. Moreover, in vitro analyses with GB cell lines, including TMZ-resistant isogenic variants, revealed more potent cytotoxic and radiosensitizing activities for NEO212 at physiologic concentrations. Mechanistically, these advantages of NEO212 over TMZ could be attributed to its enhanced tumor uptake presumably leading to more extensive DNA alkylation at equivalent dosages which, ultimately, allows for N-methylpurine lesions to be better exploited for radiosensitization. This effect cannot be achieved with TMZ at clinically relevant concentrations and is independent of MGMT. Our findings establish NEO212 as a superior radiosensitizer and a potentially better alternative to TMZ for newly diagnosed GB patients, irrespective of their MGMT status.

Precision radiotherapy for non-small cell lung cancer

Precision medicine is becoming the standard of care in anti-cancer treatment. The personalized precision management of cancer patients highly relies on the improvement of new technology in next generation sequencing and high-throughput big data processing for biological and radiographic information.

Systemic precision cancer therapy has been developed for years. However, the role of precision medicine in radiotherapy has not yet been fully implemented. Emerging evidence has shown that precision radiotherapy for cancer patients is possible with recent advances in new radiotherapy technologies, panomics, radiomics and dosiomics.

This review focused on the role of precision radiotherapy in non-small cell lung cancer and demonstrated the current landscape.

Multiple Mechanisms Involving in Radioresistance of Nasopharyngeal Carcinoma

Nasopharyngeal carcinoma (NPC) is the malignant tumor with ethnic and geographical distribution preference. Although intensity-modulated radiotherapy (IMRT)-based radiotherapy combined with chemotherapy and targeted therapy has dramatically improved the overall survival of NPC patients, there are still some patients suffering from recurrent tumors and the prognosis is poor. Multiple mechanisms may be responsible for radioresistance of NPC, such as cancer stem cells (CSCs) existence, gene mutation or aberrant expression of genes, epigenetic modification of genes, abnormal activation of certain signaling pathways, alteration of tumor microenvironment, stress granules (SGs) formation, etc. We conduct a comprehensive review of the published literatures focusing on the causes of radioresistance, retrospect the regulation mechanisms following radiation, and discuss future directions of overcoming the resistance to radiation.

High pATM is Associated With Poor Local Control in Supraglottic Cancer Treated With Radiotherapy

Objectives

Most early stage laryngeal squamous cell carcinomas (LSCC) are treated with radiotherapy. Discovery of new biomarkers are needed to improve prediction of outcome after radiotherapy and to identify potential targets for systemic targeted therapy. The ataxia telangiectasia mutated (ATM) gene plays a critical role in DNA damage response induced by ionizing radiation.

Methods

The prognostic value of immunohistochemical expression of pATM, pChk2, and p53 were investigated in 141 patients with T1‐T2 LSCC curatively treated with external beam radiotherapy. Uni‐ and multivariable Cox regression analyses were performed to examine the relation between expression levels of markers and local control.

Results

Local control was significantly worse in cases with high levels of pATM (HR 2.14; 95% CI, 1.08–4.24; P = .03). No significant associations with local control were found for pChk2 and p53 expression. The association of high pATM expression with poor local control was only found for supraglottic LSCC (HR 10.9; 95% CI, 1.40–84.4; P = .02).

Conclusion

Our findings suggest a potential role for ATM in response to radiotherapy in early stage supraglottic LSCC and imply ATM inhibition as a possibility to improve response to radiotherapy.

Level of Evidence

NA Laryngoscope, 130: 1954–1960, 2020

Modulation of Caspase-3 activity using a redox active vitamin K3 analogue, plumbagin, as a novel strategy for radioprotection

Radiation induced damage to normal cells is a major shortcoming of conventional radiotherapy, which necessitates the development of novel radio-protective drugs. An ideal radio-modulator would protect normal cells while having cytotoxic effects on cancer cells. Plumbagin is a potent anti-tumour agent and has been shown to sensitize tumour cells to radiation-induced damage. In the present study, we have evaluated the radio-protective potential of plumbagin and found that it protected normal lymphocytes against radiation-induced apoptosis, but did not protect cancer cells against radiation. Plumbagin offered radioprotection even when it was added to cells after irradiation. The ability of only thiol based antioxidants to abrogate the radio-protective effects of plumbagin suggested a pivotal role of thiol groups in the radio-protective activity of plumbagin. Further, protein interaction network (PIN) analysis was used to predict the molecular targets of plumbagin. Based on the inputs from plumbagin's PIN and in light of its well-documented ability to modulate thiol groups, we proposed that plumbagin may act via modulation of caspase enzyme which harbours a critical catalytic cysteine. Indeed, plumbagin suppressed radiation-induced increase in homogenous caspase and caspase-3 activity in lymphocytes. Plumbagin also inhibited the activity of recombinant caspase-3 and mass spectrometric analysis revealed that plumbagin covalently interacts with caspase-3. Further, the in vivo radioprotective efficacy of plumbagin (single dose of 2mg/kg body weight) was demonstrated by its ability to rescue mice against radiation (7.5 Gy; Whole Body Irradiation) induced mortality. These results indicate that plumbagin prevents radiation induced apoptosis specifically in normal cells by inhibition of caspase-3 activity.

Altering DNA Repair to Improve Radiation Therapy: Specific and Multiple Pathway Targeting

Radiation therapy (RT) is widely used in cancer care strategies. Its effectiveness relies mainly on its ability to cause lethal damage to the DNA of cancer cells. However, some cancers have shown to be particularly radioresistant partly because of efficient and redundant DNA repair capacities. Therefore, RT efficacy might be enhanced by using drugs that can disrupt cancer cells' DNA repair machinery. Here we review the recent advances in the development of novel inhibitors of DNA repair pathways in combination with RT. A large number of these compounds are the subject of preclinical/clinical studies and target key enzymes involved in one or more DNA repair pathways. A totally different strategy consists of mimicking DNA double-strand breaks via small interfering DNA (siDNA) to bait the whole DNA repair machinery, leading to its global inhibition.

Radiation Modifiers

Radiation therapy is one of the most commonly used treatments for cancer. Radiation modifiers are agents that alter tumor or normal tissue response to radiation, such as radiation sensitizers and radiation protectors. Radiation sensitizers target aspects of tumor molecular biology or physiology to enhance tumor cell killing after irradiation. Radioprotectors prevent damage of normal tissues selectively. Radiation modifiers remain largely investigational at present, with the promise that molecular characterization of tumors may enhance the capacity for successful clinical development moving forward. A variety of radiation modifiers are described.

Radiation therapy-induced reactive oxygen species specifically eliminates CD19+IgA+ B cells in nasopharyngeal carcinoma

Purpose

Nasopharyngeal carcinoma (NPC) is one of the most common head and neck cancers and is thought to be related to the mucosal immune system. Radiation therapy (RT) is the primary treatment for NPC due to the high radiosensitivity of cancer cells. However, little is known about the impact of RT on the mucosal immune system.

Patients and methods

In this study, the expression of immune markers CD19, CD24, CD27, CD8, and IgA before and after RT, were analyzed using flow cytometry. Cytokines were assessed using the enzyme-linked immunosorbent assay. Reactive oxygen species (ROS) was assayed by flow cytometry and fluorescence staining using 2ʹ,7ʹ -dichlorofluorescein diacetate.

Results

We found that primary NPC patients had a significant increase in CD19⁺CD138⁻IgA⁺ B cells, which was then decreased after RT. Interestingly, the changes in CD19⁺CD138⁻IgA⁺ B cell frequency was accompanied by corresponding frequency changes in cytotoxic T cells (CTL), which are powerful anti-tumor lymphocytes. Mechanistically, we found that ROS release during RT specifically eliminated CD19⁺CD138⁻IgA⁺ B cells.

Conclusion

These findings suggest that RT may regulate the immune system and opens up new avenues for the utilization of immune-radiotherapy in NPC.

Self-assembled angiopep-2 modified lipid-poly (hypoxic radiosensitized polyprodrug) nanoparticles delivery TMZ for glioma synergistic TMZ and RT therapy

The addition of temozolomide (TMZ) to radiotherapy (RT) improves survival of patients with glioblastoma (GBM). However, TMZ + RT causes excess toxicity in patients. In this study, we prepared angiopep-2 (A2) modified lipid-poly (hypoxic radiosensitized polyprodrug) nanoparticles for TMZ delivery (A2-P(MIs)25/TMZ) to achieve synergistic effects against glioma. This A2-P(MIs)25/TMZ display highly promising advantages: (1) a hydrophobic P-(MIs)25 core where poorly water-soluble TMZ can be encapsulated; (2) nitro groups of the hydrophobic P-(MIs)25 core that are converted into hydrophilic amino groups (P(NH₂s)25) under low oxygen conditions to mimic the oxygen-increased sensitization to RT; (3) a lipid monolayer at the interface of the core and the shell to modify the A2 (a specific ligand for low-density lipoprotein receptor-related protein-1 (LRP-1), which are expressed in the blood-brain barrier (BBB) and human glioma cells), thereby enhancing the drug encapsulation efficiency in glioma. These nanoparticles appear as a promising and robust nanoplatforms for TMZ and hypoxic cell radiosensitization delivery.

Targeting DNA Double-Strand Break Repair Pathways to Improve Radiotherapy Response

More than half of cancer patients receive radiotherapy as a part of their cancer treatment. DNA double-strand breaks (DSBs) are considered as the most lethal form of DNA damage and a primary cause of cell death and are induced by ionizing radiation (IR) during radiotherapy. Many malignant cells carry multiple genetic and epigenetic aberrations that may interfere with essential DSB repair pathways. Additionally, exposure to IR induces the activation of a multicomponent signal transduction network known as DNA damage response (DDR). DDR initiates cell cycle checkpoints and induces DSB repair in the nucleus by non-homologous end joining (NHEJ) or homologous recombination (HR). The canonical DSB repair pathways function in both normal and tumor cells. Thus, normal-tissue toxicity may limit the targeting of the components of these two pathways as a therapeutic approach in combination with radiotherapy. The DSB repair pathways are also stimulated through cytoplasmic signaling pathways. These signaling cascades are often upregulated in tumor cells harboring mutations or the overexpression of certain cellular oncogenes, e.g., receptor tyrosine kinases, PIK3CA and RAS. Targeting such cytoplasmic signaling pathways seems to be a more specific approach to blocking DSB repair in tumor cells. In this review, a brief overview of cytoplasmic signaling pathways that have been reported to stimulate DSB repair is provided. The state of the art of targeting these pathways will be discussed. A greater understanding of the underlying signaling pathways involved in DSB repair may provide valuable insights that will help to design new strategies to improve treatment outcomes in combination with radiotherapy.

The Radiosensitization of Sodium Glycididazole on Nasopharyngeal Carcinoma Cells via Enhancing DNA Damage and Promoting Apoptosis

Background: The radioresistance of nasopharyngeal carcinoma (NPC) was the main cause of radiotherapy failure and it was still a challenge in the treatment of advanced NPC patients. Previous clinical studies demonstrated that sodium glycididazole(CMNA) can enhance the radiosensitivity of NPC, but the corresponding cellular mechanisms or processes remains largely unclear. Methods: To clarify the radiosensitizing effects of CMNA on NPC cells and reveal its cellular mechanisms, its effect on cell survival of NPC cells was assessed by MTT and clonogenic assay, with or without radiation. The potential cellular mechanisms such as cell cycle distribution, apoptosis and DNA damage were assessed. A retrospective analysis of the outcome of patients with III-IV stage NPC who undergo same radiochemotherapy with or without concurrent CMNA treatment was performed to elucidate the role of CMNA in the improvement of the curative effects. Results: The treatment with CMNA at the concentration lower or close to the clinical dosage had little effect on cell survival, cell cycle distribution and a weak effect on DNA damage and cell apoptosis of NPC cells. The combination of CMNA and radiation significantly increased the DNA damage and enhanced the apoptosis of NPC cells, but did not significantly alter the cell cycle distribution as compared with the irradiation (IR) alone. A total of 99 patients who underwent radiochemotherapy were categorized into those with (treatment group, n=52) and without (control group, n=47) the treatment with CMNA. The complete response rates of patients in treatment group were significantly higher than in control group. Conclusions: Our results suggested that CMNA enhance the sensitivity of the NPC cells to radiation via enhancing DNA damage and promoting cell apoptosis. It provides clues for further investigation of the molecular mechanism of the radiosensitization of CMNA on NPC cells.

Potential of serum microRNAs as biomarkers of radiation injury and tools for individualization of radiotherapy

Due to tremendous technological advances, radiation oncologists are now capable of personalized treatment plans and deliver the dose in a highly precise manner. However, a crucial challenge is how to escalate radiation doses to cancer cells while reducing damage to surrounding healthy tissues. This determines the probability of achieving therapeutic success whilst safeguarding patients from complications. The current dose constraints rely on observational data. Therefore, incidental toxicity observed in a minority of patients limits the admissible dose thresholds for the whole population, theoretically narrowing down the curative potential of radiotherapy. Future tools for measurements of individual's radiosensitivity before and during treatment would allow proper treatment personalization. Variation in tissue tolerance is at least partially genetically-determined and recent progress in the field of molecular biology raises the possibility that novel assays will allow to predict the response to ionizing radiation. Recently, microRNAs have garnered interest as stable biomarkers of tumor radiation response and normal-tissue toxicity. Preclinical studies in mice and nonhuman primates have shown that serum circulating microRNAs can be used to accurately distinguish pre- and postirradiation states and predict the biological impact of high-dose irradiation. First reports from human studies are also encouraging, however biology-driven precision radiation oncology, which tailors treatment to individual patient's needs, still remains to be translated into clinical studies. In this review, we summarize current knowledge about the potential of serum microRNAs as biodosimeters and biomarkers for radiation injury to lung and hematopoietic cells.

Hypoxia-responsive lipid-poly-(hypoxic radiosensitized polyprodrug) nanoparticles for glioma chemo- and radiotherapy

Treatment of malignant glioma is a challenge facing cancer therapy. In addition to surgery, and chemotherapy, radiotherapy (RT) is one of the most effective modalities of glioma treatment. However, there are two crucial challenges for RT facing malignant glioma therapy: first, gliomas are known to be resistant to radiation due to their intratumoral hypoxia; second, radiosensitizers may exhibit a lack of target specificity, which may cause a lower concentration of radiosensitizers in tumors and toxic side effects in normal tissues. Thus, novel angiopep-2-lipid-poly-(metronidazoles)n (ALP-(MIs)n) hypoxic radiosensitizer-polyprodrug nanoparticles (NPs) were designed to enhance the radiosensitizing effect on gliomas. Methods: In this study, different degrees and biodegradabilites of hypoxic radiosensitizer MIs-based polyprodrug (P-(MIs)n) were synthesized as a hydrophobic core. P-(MIs)n were mixed with DSPE-PEG2000, angiopep-2-DSPE-PEG2000 and lecithin to self-assemble ALP-(MIs)n through a single-step nanoprecipitation method. The ALP-(MIs)n encapsulate doxorubicin (DOX) (ALP-(MIs)n/DOX) and provoke the release of DOX under hypoxic conditions for glioma chemo- and radiotherapy. In vivo glioma targeting was tested in an orthotopic glioma using live animal fluorescence/bioluminescence imaging. The effect on sensitization to RT of ALP-(MIs)n and the combination of chemotherapy and RT of ALP-(MIs)n/DOX for glioma treatment were also investigated both in vitro and in vivo. Results: ALP-(MIs)n/DOX effectively accumulated in gliomas and could reach the hypoxic glioma site after systemic in vivo administration. These ALP-(MIs)n showed a significant radiosensitizing effect on gliomas and realized combination chemotherapy and RT for glioma treatment both in vitro and in vivo. Conclusions: In summary, we constructed a lipid-poly-(hypoxic radiosensitized polyprodrug) nanoparticles for enhancing the RT sensitivity of gliomas and achieving the combination of radiation and chemotherapy for gliomas.

Sinomenine hydrochloride sensitizes cervical cancer cells to ionizing radiation by impairing DNA damage response

The use of plant-based compounds derived from traditional medicine to improve human diseases has been gaining momentum, due to their high bioavailability and moderate adverse effects. Sinomenine is one such biomonomer alkali compound derived from Sinomenium acutum and is known for its anti-inflammatory and antitumor effects. However, the molecular mechanism(s) of its antitumor properties are not fully characterized. In the present study, we evaluated the radiosensitizing effects of the water-soluble sinomenine, sinomenine hydrochloride (SH) in human cervical cancer cell line (HeLa). SH sensitized HeLa cells to ionizing radiation (IR) by promoting accumulation of IR-induced DNA double-strand breaks (DSBs) and also by interfering with DNA damage checkpoint activation. We then investigated the molecular mechanisms underlying the SH-mediated cellular sensitization to IR and found that SH inhibited the expression of DNA damage response (DDR) factors Ku80 and Rad51 at the transcription level. Finally, the radiosensitizing activity of SH was confirmed in a cervical cancer mouse xenograft model. The combinatorial treatment of SH and IR significantly slowed the tumor growth rate compared with IR alone. Collectively, our study not only provides molecular insights into the novel role of SH in cellular response to IR, but also suggests a therapeutic potential of SH as a radiosensitizer in cervical cancer therapy.

AZD9291 Increases Sensitivity to Radiation in PC-9-IR Cells by Delaying DNA Damage Repair after Irradiation and Inducing Apoptosis

AZD9291 is a novel, irreversible epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI), which is administered orally. It has been proven effective in non-small cell lung cancer (NSCLC) patients, with both EGFR-sensitizing and EGFR T790M mutations in preclinical models. However, the potential therapeutic effects of AZD9291 combined with other modalities, including ionizing radiation, are not well understood. The presence of AZD9291 significantly increases the cell-killing effects of radiation in PC-9-IR cells with a secondary EGFR mutation (T790M), which was developed from NSCLC PC-9 cells (human lung adenocarcinoma cell with EGFR 19 exon 15 bp deletion) after chronic exposure to increasing doses of gefitinib, and in H1975 cells (human lung adenocarcinoma cell with EGFR exon 20 T790M mutation de novo), but not in PC-9 cells or in H460 cells (human lung adenocarcinoma cell with wild-type EGFR). In PC-9-IR cells, AZD9291 remarkably decreases phosphorylation levels of EGFR, extracellular regulated protein kinase (ERK), and protein kinase B (AKT). AZD9291 increases sensitivity to radiation in PC-9-IR cells by delaying deoxyribonucleic acid (DNA) damage repair after irradiation and inducing apoptosis, and enhances tumor growth inhibition when combined with radiation in PC-9-IR xenografts. Our findings suggest a potential therapeutic effect of AZD9291 as a radiation sensitizer in lung cancer cells with an acquired EGFR T790M mutation, providing a rationale for a clinical trial using the combination of AZD9291 and radiation in NSCLCs harboring acquired T790M mutation.

Changes in skin microcirculation during radiation therapy for breast cancer

BACKGROUND

The majority of breast cancer patients who receive radiation treatment are affected by acute radiation-induced skin changes. The assessment of these changes is usually done by subjective methods, which complicates the comparison between different treatments or patient groups. This study investigates the feasibility of new robust methods for monitoring skin microcirculation to objectively assess and quantify acute skin reactions during radiation treatment.

MATERIAL AND METHODS

Laser Doppler flowmetry, laser speckle contrast imaging, and polarized light spectroscopy imaging were used to measure radiation-induced changes in microvascular perfusion and red blood cell concentration (RBC) in the skin of 15 patients undergoing adjuvant radiation therapy for breast cancer. Measurements were made before treatment, once a week during treatment, and directly after the last fraction.

RESULTS

In the treated breast, perfusion and RBC concentration were increased after 1-5 fractions (2.66-13.3 Gy) compared to baseline. The largest effects were seen in the areola and the medial area. No changes in perfusion and RBC concentration were seen in the untreated breast. In contrast, Radiation Therapy Oncology Group (RTOG) scores were increased only after 2 weeks of treatment, which demonstrates the potential of the proposed methods for early assessment of skin changes. Also, there was a moderate to good correlation between the perfusion (r = 0.52) and RBC concentration (r = 0.59) and the RTOG score given a week later.

CONCLUSION

We conclude that radiation-induced microvascular changes in the skin can be objectively measured using novel camera-based techniques before visual changes in the skin are apparent. Objective measurement of microvascular changes in the skin may be valuable in the comparison of skin reactions between different radiation treatments and possibly in predicting acute skin effects at an earlier stage.

Regulation of Single-Strand Annealing and its Role in Genome Maintenance

Single-strand annealing (SSA) is a DNA double-strand break (DSB) repair pathway that uses homologous repeats to bridge DSB ends. SSA involving repeats that flank a single DSB causes a deletion rearrangement between the repeats, and hence is relatively mutagenic. Nevertheless, this pathway is conserved, in that SSA events have been found in several organisms. In this review, we describe the mechanism of SSA and its regulation, including the cellular conditions that may favor SSA versus other DSB repair events. We will also evaluate the potential contribution of SSA to cancer-associated genome rearrangements, and to DSB-induced gene targeting.

What is the best way to radiate the prostate in 2016?

Prostate cancer treatment with definitive radiation therapy (RT) has evolved dramatically in the past 2 decades. From the initial 2-dimensional planning using X-rays, advances in technology led to 3-dimensional conformal RT, which used computerized tomography-based planning. This has allowed delivery of higher doses of radiation to the prostate while reducing dose to the surrounding organs, resulting in improved cancer control. Today, intensity-modulated RT (IMRT) is considered standard, where radiation beams of different shapes and intensities can be delivered from a wide range of angles, thus further decreasing doses to normal organs and likely reducing treatment-related toxicity. In addition, image guidance ascertains the location of the prostate before daily treatment delivery. Brachytherapy is the placement of radioactive seeds directly in the prostate, and has a long track record as a monotherapy for low-risk prostate cancer patients with excellent long-term cancer control and quality of life outcomes. Recent studies including several randomized trials support the use of brachytherapy in combination with external beam RT for higher-risk patients. RT for prostate cancer continues to evolve. Proton therapy has a theoretical advantage over photons as it deposits most of the dose at a prescribed depth with a rapid dose fall-off thereafter; therefore it reduces some doses delivered to the bladder and rectum. Prospective studies have shown the safety and efficacy of proton therapy for prostate cancer, but whether it leads to improved patient outcomes compared to IMRT is unknown. Hypofractionated RT delivers a larger dose of daily radiation compared to conventional IMRT, and thus reduces the overall treatment time and possibly cost. An extreme form of hypofractionation is stereotactic body radiation therapy where highly precise radiation is used and treatment is completed in a total of 4 to 5 sessions. These techniques take advantage of the biological characteristic of prostate cancer, which is more sensitive to larger radiation doses per fraction, and therefore could be more effective than conventional IMRT. Multiple randomized trials have demonstrated noninferiority of moderately hypofractionated RT compared to conventional fractionation. There is also a growing body of data demonstrating the safety and efficacy of stereotactic body radiation therapy for low- and intermediate-risk prostate cancer.

miRNA-148b regulates radioresistance in non-small lung cancer cells via regulation of MutL homologue 1

miR-148b regulates radioresistance of lung cancer cells by modulating MLH1 expression level.

Radioresistance represents a major obstacle in cancer treatment, the underlying mechanism of which is complex and not well understood. miR-148b has been reported to be implicated regulating radioresistance in lymphoma cells. However, this function has not been investigated in lung cancer cells. Microarray analysis was performed in A549 cells 48 h after exposure to 8 Gy of γ-irradiation or sham irradiation to identify differentially expressed miRNAs. miR-148b mimic and inhibitor were transfected, followed by clonogenic survival assay to examine response to irradiation in A549 cells. Western Blot and luciferase assay were performed to investigate the direct target of miR-148b. Xenograft mouse models were used to examine in vivo function of miR-148b. Our data showed that expression of miR-148b was significantly down-regulated in both serum and cancerous tissues of radioresistant lung cancer patients compared with radiosensitive patients. Overexpression of miR-148b reversed radioresistance in A549 cells. MutL homologue 1 (MLH1) is the direct target of miR-148b which is required for the regulatory role of miR-148b in radioresistance. miR-148b mimic sensitized A549 xenografts to irradiation in vivo. Our study demonstrated that miR-148b regulates radioresistance of lung cancer cells by modulating MLH1 expression level. miR-148b may represent a new therapeutic target for the intervention of lung cancer.

Mechanistic Insights into Molecular Targeting and Combined Modality Therapy for Aggressive, Localized Prostate Cancer

Radiation therapy (RT) is one of the mainstay treatments for prostate cancer (PCa). The potentially curative approaches can provide satisfactory results for many patients with non-metastatic PCa; however, a considerable number of individuals may present disease recurrence and die from the disease. Exploiting the rich molecular biology of PCa will provide insights into how the most resistant tumor cells can be eradicated to improve treatment outcomes. Important for this biology-driven individualized treatment is a robust selection procedure. The development of predictive biomarkers for RT efficacy is therefore of utmost importance for a clinically exploitable strategy to achieve tumor-specific radiosensitization. This review highlights the current status and possible opportunities in the modulation of four key processes to enhance radiation response in PCa by targeting the: (1) androgen signaling pathway; (2) hypoxic tumor cells and regions; (3) DNA damage response (DDR) pathway; and (4) abnormal extra-/intracell signaling pathways. In addition, we discuss how and which patients should be selected for biomarker-based clinical trials exploiting and validating these targeted treatment strategies with precision RT to improve cure rates in non-indolent, localized PCa.

The in vitro immunogenic potential of caspase-3 proficient breast cancer cells with basal low immunogenicity is increased by hypofractionated irradiation

BACKGROUND

Radiotherapy is an integral part of breast cancer treatment. Immune activating properties of especially hypofractionated irradiation are in the spotlight of clinicians, besides the well-known effects of radiotherapy on cell cycle and the reduction of the clonogenic potential of tumor cells. Especially combination of radiotherapy with further immune stimulation induces immune-mediated anti-tumor responses. We therefore examined whether hypofractionated irradiation alone or in combination with hyperthermia as immune stimulants is capable of inducing breast cancer cells with immunogenic potential.

METHODS

Clonogenic assay, AnnexinA5-FITC/Propidium iodide assay and ELISA analyses of heat shock protein 70 and high mobility group box 1 protein were applied to characterize colony forming capability, cell death induction, cell death forms and release of danger signals by breast cancer cells in response to hypofractionated radiation (4x4Gy, 6x3Gy) alone and in combination with hyperthermia (41.5 °C for 1 h). Caspase-3 deficient, hormone receptor positive, p53 wild type MCF-7 and caspase-3 intact, hormone receptor negative, p53 mutated MDA-MB231 breast cancer cells, the latter in absence or presence of the pan-caspase inhibitor zVAD-fmk, were used. Supernatants of the treated tumor cells were analyzed for their potential to alter the surface expression of activation markers on human-monocyte-derived dendritic cells.

RESULTS

Irradiation reduced the clonogenicity of caspase deficient MCF-7 cells more than of MDA-B231 cells. In contrast, higher amounts of apoptotic and necrotic cells were induced in MDA-B231 cells after single irradiation with 4Gy, 10Gy, or 20Gy or after hypofractionated irradiation with 4x4Gy or 6x3Gy. MDA-B231 cells consecutively released higher amounts of Hsp70 and HMGB1 after hypofractionated irradiation. However, only the release of Hsp70 was further increased by hyperthermia. Both, apoptosis induction and release of the danger signals, was dependent on caspase-3. Only supernatants of MDA-B231 cells after hypofractionated irradiation resulted in slight changes of activation markers on dendritic cells; especially that of CD86 was upregulated and HT did not further impact on it.

CONCLUSIONS

Hypofractionated irradiation is the main stimulus for cell death induction and consecutive dendritic cell activation in caspase proficient breast cancer cells. For the assessment of radiosensitivity and immunological effects of radio- and immunotherapies the readout system is crucial.

In vivo studies of the PARP inhibitor, AZD-2281, in combination with fractionated radiotherapy: An exploration of the therapeutic ratio

BACKGROUND AND PURPOSE

Pre-clinical data have shown that PARP inhibitors (PARPi) may increase the efficacy of radiotherapy in prostate cancer. However, it is uncertain as to whether PARPi lead to clonogenic kill when combined with radiotherapy (RT).

MATERIAL AND METHODS

We tested the PARP inhibitor AZD-2281 as a radiosensitizing agent under oxic and hypoxic conditions for clonogenic survival in vitro and in vivo using the human prostate cancer cell line, 22Rv1. In addition, the effects of PARPi+RT on normal tissue were investigated using a crypt clonogenic assay.

RESULTS

AZD-2281 inhibited cellular PARP activity under both oxic and hypoxic conditions. The addition of AZD-2281 radiosensitized 22Rv1 cells under oxia, acute hypoxia and chronic hypoxia in vitro. The combination of AZD-2281 with fractionated radiotherapy resulted in a significant growth delay and clonogenic kill in vivo. No increased gut toxicity was observed using this combined PARPi+radiotherapy regimen.

CONCLUSIONS

This is the first preclinical study to demonstrate direct clonogenic kill in vivo by the addition of AZD-2281 to radiotherapy. As we did not observe gut toxicity, the use of PARPi in the context of prostate cancer radiotherapy warrants further investigation in clinical trials.

Curcumin-Mediated HDAC Inhibition Suppresses the DNA Damage Response and Contributes to Increased DNA Damage Sensitivity

Chemo- and radiotherapy cause multiple forms of DNA damage and lead to the death of cancer cells. Inhibitors of the DNA damage response are candidate drugs for use in combination therapies to increase the efficacy of such treatments. In this study, we show that curcumin, a plant polyphenol, sensitizes budding yeast to DNA damage by counteracting the DNA damage response. Following DNA damage, the Mec1-dependent DNA damage checkpoint is inactivated and Rad52 recombinase is degraded by curcumin, which results in deficiencies in double-stand break repair. Additive effects on damage-induced apoptosis and the inhibition of damage-induced autophagy by curcumin were observed. Moreover, rpd3 mutants were found to mimic the curcumin-induced suppression of the DNA damage response. In contrast, hat1 mutants were resistant to DNA damage, and Rad52 degradation was impaired following curcumin treatment. These results indicate that the histone deacetylase inhibitor activity of curcumin is critical to DSB repair and DNA damage sensitivity.

DNA repair mechanisms in cancer development and therapy

DNA damage has been long recognized as causal factor for cancer development. When erroneous DNA repair leads to mutations or chromosomal aberrations affecting oncogenes and tumor suppressor genes, cells undergo malignant transformation resulting in cancerous growth. Genetic defects can predispose to cancer: mutations in distinct DNA repair systems elevate the susceptibility to various cancer types. However, DNA damage not only comprises a root cause for cancer development but also continues to provide an important avenue for chemo- and radiotherapy. Since the beginning of cancer therapy, genotoxic agents that trigger DNA damage checkpoints have been applied to halt the growth and trigger the apoptotic demise of cancer cells. We provide an overview about the involvement of DNA repair systems in cancer prevention and the classes of genotoxins that are commonly used for the treatment of cancer. A better understanding of the roles and interactions of the highly complex DNA repair machineries will lead to important improvements in cancer therapy.

Identification of novel radiosensitizers in a high-throughput, cell-based screen for DSB repair inhibitors

Most cancer therapies involve a component of treatment that inflicts DNA damage in tumor cells, such as double-strand breaks (DSBs), which are considered the most serious threat to genomic integrity. Complex systems have evolved to repair these lesions, and successful DSB repair is essential for tumor cell survival after exposure to ionizing radiation (IR) and other DNA-damaging agents. As such, inhibition of DNA repair is a potentially efficacious strategy for chemo- and radiosensitization. Homologous recombination (HR) and nonhomologous end-joining (NHEJ) represent the two major pathways by which DSBs are repaired in mammalian cells. Here, we report the design and execution of a high-throughput, cell-based small molecule screen for novel DSB repair inhibitors. We miniaturized our recently developed dual NHEJ and HR reporter system into a 384-well plate-based format and interrogated a diverse library of 20,000 compounds for molecules that selectively modulate NHEJ and HR repair in tumor cells. We identified a collection of novel hits that potently inhibit DSB repair, and we have validated their functional activity in a comprehensive panel of orthogonal secondary assays. A selection of these inhibitors was found to radiosensitize cancer cell lines in vitro, which suggests that they may be useful as novel chemo- and radio sensitizers. Surprisingly, we identified several FDA-approved drugs, including the calcium channel blocker mibefradil dihydrochloride, that demonstrated activity as DSB repair inhibitors and radiosensitizers. These findings suggest the possibility for repurposing them as tumor cell radiosensitizers in the future. Accordingly, we recently initiated a phase I clinical trial testing mibefradil as a glioma radiosensitizer.

Altering the response to radiation: sensitizers and protectors

A number of agents are used clinically to enhance the efficacy of radiotherapy today, many of which are cytotoxic chemotherapies. Agents that enhance radiation induced tumor cell killing or protect normal tissues from the deleterious effects of ionizing radiation are collectively termed radiation modifiers. A significant effort in radiobiological research is geared towards describing and testing radiation modifiers with the intent of enhancing the therapeutic effects of radiation while minimizing normal tissue toxicity. In this review, we discuss the characteristics of these agents, the testing required to translate these agents into clinical trials, and highlight some challenges in these efforts.

Linking the history of radiation biology to the hallmarks of cancer

Hanahan and Weinberg recently updated their conceptual framework of the "Hallmarks of Cancer". The original article, published in 2000, is among the most highly cited reviews in the field of oncology. The goal of this review is to highlight important discoveries in radiation biology that pertain to the Hallmarks. We identified early studies that exemplified how ionizing radiation affects the hallmarks or how radiation was used experimentally to advance the understanding of key hallmarks. A literature search was performed to obtain relevant primary research, and topics were assigned to a particular hallmark to allow an organized, chronological account of the radiobiological advancements. The hallmarks are reviewed in an order that flows from cellular to microenvironmental effects.

Enhancing radiation therapy for patients with glioblastoma

Radiation therapy has been the foundation of therapy following maximal surgical resection in patients with newly diagnosed glioblastoma for decades and the primary therapy for unresected tumors. Using the standard approach with radiation and temozolomide, however, outcomes are poor, and glioblastoma remains an incurable disease with the majority of recurrences and progression within the radiation treatment field. As such, there is much interest in elucidating the mechanisms of resistance to radiation therapy and in developing novel approaches to overcoming this treatment resistance.

Current and future directions for Phase II trials in high-grade glioma

Despite surgery, radiation and chemotherapy, the prognosis for high-grade glioma (HGG) is poor. Our understanding of the molecular pathways involved in gliomagenesis and progression has increased in recent years, leading to the development of novel agents that specifically target these pathways. Results from most single-agent trials have been modest at best, however. Despite the initial success of antiangiogenesis agents in HGG, the clinical benefit is short-lived and most patients eventually progress. Several novel agents, multi-targeted agents and combination therapies are now in clinical trials for HGG and several more strategies are being pursued.

Repair of chromosomal double-strand breaks by precise ligation in human cells

Double-strand breaks (DSBs), a common type of DNA lesion, occur daily in human cells as a result of both endogenous and exogenous damaging agents. DSBs are repaired in two general ways: by the homology-dependent, error-free pathways of homologous recombination (HR) and by the homology-independent, error-prone pathways of nonhomologous end-joining (NHEJ), with NHEJ predominating in most cells. DSBs with compatible ends can be re-joined in vitro with DNA ligase alone, which raises the question of whether such DSBs require the more elaborate machinery of NHEJ to be repaired in cells. Here we report that chromosomal DSBs with compatible ends introduced by the rare-cutting endonuclease, ISceI, are repaired by precise ligation nearly 100% of the time in human cells. Precise ligation depends on the classical NHEJ components Ku70, XRCC4, and DNA ligase IV, since siRNA knockdowns of these factors significantly reduced the efficiency of precise ligation. Interestingly, knockdown of the tumor suppressors p53 or BRCA1 showed similar effects as the knockdowns of NHEJ factors. In contrast, knockdown of components involved in alternative NHEJ, mismatch repair, nucleotide excision repair, and single-strand break repair did not reduce precise ligation. In summary, our results demonstrate that DSBs in human cells are efficiently repaired by precise ligation, which requires classical NHEJ components and is enhanced by p53 and BRCA1.

Imatinib radiosensitizes bladder cancer by targeting homologous recombination

Radiotherapy is a major treatment modality used to treat muscle-invasive bladder cancer, with patient outcomes similar to surgery. However, radioresistance is a significant factor in treatment failure. Cell-free extracts of muscle-invasive bladder tumors are defective in nonhomologous end-joining (NHEJ), and this phenotype may be used clinically by combining radiotherapy with a radiosensitizing drug that targets homologous recombination, thereby sparing normal tissues with intact NHEJ. The response of the homologous recombination protein RAD51 to radiation is inhibited by the small-molecule tyrosine kinase inhibitor imatinib. Stable RT112 bladder cancer Ku knockdown (Ku80KD) cells were generated using short hairpin RNA technology to mimic the invasive tumor phenotype and also RAD51 knockdown (RAD51KD) cells to show imatinib's pathway selectivity. Ku80KD, RAD51KD, nonsilencing vector control, and parental RT112 cells were treated with radiation in combination with either imatinib or lapatinib, which inhibits NHEJ and cell survival assessed by clonogenic assay. Drug doses were chosen at approximately IC40 and IC10 (nontoxic) levels. Imatinib radiosensitized Ku80KD cells to a greater extent than RAD51KD or RT112 cells. In contrast, lapatinib radiosensitized RAD51KD and RT112 cells but not Ku80KD cells. Taken together, our findings suggest a new application for imatinib in concurrent use with radiotherapy to treat muscle-invasive bladder cancer. Cancer Res; 73(5); 1611-20. ©2012 AACR.

Interferon-Beta combined with interleukin-2 restores human natural cytotoxicity impaired in vitro by ionizing radiations

It is well known that ionizing radiations induce a marked downregulation of antigen-dependent and natural immunity for a prolonged period of time. This is due, at least in part, to radiation-induced apoptosis of different lymphocyte subpopulations, including natural killer (NK) cells. Aim of this study was to investigate the capability of Beta Interferon (β-IFN) and Interleukin-2 (IL2), alone or in combination, to restore the functional activity of the natural immune system. Mononuclear cells (MNCs) obtained from intact or in vitro irradiated human peripheral blood were treated in vitro with β-IFN immediately before or at the end of the 4-day treatment with IL2. Time-course analysis was performed on the NK activity, the total number and the apoptotic fraction of CD16+ and CD56+ cells, the 2 main NK effector cell subpopulations. The results indicate that radiation-induced impairment of natural cytotoxicity of MNC could be successfully antagonized by the β-IFN+IL2 combination, mainly when exposure to β-IFN preceded IL2 treatment. This radioprotective effect is paralleled by lower levels of radiation-induced apoptosis and increased expression of the antiapoptotic Bcl-2 protein. Since natural immunity can play a significant role in antitumor host's resistance, these results could provide the rational basis for a cytokine-based pharmacological strategy able to restore immune responsiveness and to afford possible therapeutic benefits in cancer patients undergoing radiotherapy.

Radiosensitization of prostate cancer cells by the dual PI3K/mTOR inhibitor BEZ235 under normoxic and hypoxic conditions

BACKGROUND AND PURPOSE

Despite appropriate radiotherapy, high-risk prostate cancer patients often experience local relapse and progression to metastatic disease. Radioresistance may be due to tumor-hypoxia but also due to the PTEN mutation/deletion present in 70% prostate cancers. We investigated whether the novel PI3K/mTOR inhibitor BEZ235 might sensitize prostate cancer cells to radiation and reduce hypoxia-induced radioresistance.

MATERIALS AND METHODS

The potential radiosensitizing properties of BEZ235 were investigated in vitro and in vivo using two prostate cancer cell lines, PC3 (PTEN(-/-)) and DU145 (PTEN(+/+)), under normoxic (21% O(2)) and hypoxic (0.5% O(2)) conditions.

RESULTS

BEZ235 rapidly inhibited PI3K and mTOR signaling in a dose dependent manner and limited tumor cell proliferation and clonogenic survival in both cell lines independently of PTEN status. In vivo, BEZ235 pretreatment enhanced the efficacy of radiation therapy on PC3 xenograft tumors in mice without inducing intestinal radiotoxicity. In culture, BEZ235 radiosensitized both cell lines in a comparable manner. Moreover, BEZ235 inhibited PI3K/mTOR activation and radiosensitized both cell lines under normoxia and hypoxia. BEZ235 radiosensitizing effects correlated with a decrease in γH2AX foci repair and increased G2/M cell cycle arrest.

CONCLUSIONS

BEZ235 is a potent radiosensitizer of normoxic and hypoxic prostate cancer cells.

Inhibition of both EGFR and IGF1R sensitized prostate cancer cells to radiation by synergistic suppression of DNA homologous recombination repair

Reduced sensitivity of prostate cancer (PC) cells to radiation therapy poses a significant challenge in the clinic. Activation of epidermal growth factor receptor (EGFR), type 1 insulin-like growth factor receptor (IGF1R), and crosstalk between these two signaling pathways have been implicated in the development of radiation resistance in PC. This study assessed the effects of targeting both receptors on the regulation of radio-sensitivity in PC cells. Specific inhibitors of EGFR and IGF1R, Erlotinib and AG1024, as well as siRNA targeting EGFR and IGF1R, were used to radio-sensitize PC cells. Our results showed that co-inhibiting both receptors significantly dampened cellular growth and DNA damage repair, and increased radio-sensitivity in PC cells. These effects were carried out through synergistic inhibition of homologous recombination-directed DNA repair (HRR), but not via inhibition of non-homologous end joining (NHEJ). Furthermore, the compromised HRR capacity was caused by reduced phosphorylation of insulin receptor substrate 1 (IRS1) and its subsequent interaction with Rad51. The synergistic effect of the EGFR and IGF1R inhibitors was also confirmed in nude mouse xenograft assay. This is the first study testing co-inhibiting EGFR and IGF1R signaling in the context of radio-sensitivity in PC and it may provide a promising adjuvant therapeutic approach to improve the outcome of PC patients to radiation treatment.