Introduction to clinical radiation biology

Comprehensive Insights into Keloid Pathogenesis and Advanced Therapeutic Strategies

Keloid scars, characterized by abnormal fibroproliferation and excessive extracellular matrix (ECM) production that extends beyond the original wound, often cause pruritus, pain, and hyperpigmentation, significantly impacting the quality of life. Keloid pathogenesis is multifactorial, involving genetic predisposition, immune response dysregulation, and aberrant wound-healing processes. Central molecular pathways such as TGF-β/Smad and JAK/STAT are important in keloid formation by sustaining fibroblast activation and ECM deposition. Conventional treatments, including surgical excision, radiation, laser therapies, and intralesional injections, yield variable success but are limited by high recurrence rates and potential adverse effects. Emerging therapies targeting specific immune pathways, small molecule inhibitors, RNA interference, and mesenchymal stem cells show promise in disrupting the underlying mechanisms of keloid pathogenesis, potentially offering more effective and lasting treatment outcomes. Despite advancements, further research is essential to fully elucidate the precise mechanisms of keloid formation and to develop targeted therapies. Ongoing clinical trials and research efforts are vital for translating these scientific insights into practical treatments that can markedly enhance the quality of life for individuals affected by keloid scars.

Disrupting prostate cancer research: Challenge accepted; report from the 2023 Coffey-Holden Prostate Cancer Academy Meeting

INTRODUCTION

The 2023 Coffey-Holden Prostate Cancer Academy (CHPCA) Meeting, themed "Disrupting Prostate Cancer Research: Challenge Accepted," was convened at the University of California, Los Angeles, Luskin Conference Center, in Los Angeles, CA, from June 22 to 25, 2023.

METHODS

The 2023 marked the 10th Annual CHPCA Meeting, a discussion-oriented scientific think-tank conference convened annually by the Prostate Cancer Foundation, which centers on innovative and emerging research topics deemed pivotal for advancing critical unmet needs in prostate cancer research and clinical care. The 2023 CHPCA Meeting was attended by 81 academic investigators and included 40 talks across 8 sessions.

RESULTS

The central topic areas covered at the meeting included: targeting transcription factor neo-enhancesomes in cancer, AR as a pro-differentiation and oncogenic transcription factor, why few are cured with androgen deprivation therapy and how to change dogma to cure metastatic prostate cancer without castration, reducing prostate cancer morbidity and mortality with genetics, opportunities for radiation to enhance therapeutic benefit in oligometastatic prostate cancer, novel immunotherapeutic approaches, and the new era of artificial intelligence-driven precision medicine.

DISCUSSION

This article provides an overview of the scientific presentations delivered at the 2023 CHPCA Meeting, such that this knowledge can help in facilitating the advancement of prostate cancer research worldwide.

Artificial keloid skin models: understanding the pathophysiological mechanisms and application in therapeutic studies

Keloid is a type of scar formed by the overexpression of extracellular matrix substances from fibroblasts following inflammation after trauma. The existing keloid treatment methods include drug injection, surgical intervention, light exposure, cryotherapy, etc. However, these methods have limitations such as recurrence, low treatment efficacy, and side effects. Consequently, studies are being conducted on the treatment of keloids from the perspective of inflammatory mechanisms. In this study, keloid models are created to understand inflammatory mechanisms and explore treatment methods to address them. While previous studies have used animal models with gene mutations, chemical treatments, and keloid tissue transplantation, there are limitations in fully reproducing the characteristics of keloids unique to humans, and ethical issues related to animal welfare pose additional challenges. Consequently, studies are underway to create in vitro artificial skin models to simulate keloid disease and apply them to the development of treatments for skin diseases. In particular, herein, scaffold technologies that implement three-dimensional (3D) full-thickness keloid models are introduced to enhance mechanical properties as well as biological properties of tissues, such as cell proliferation, differentiation, and cellular interactions. It is anticipated that applying these technologies to the production of artificial skin for keloid simulation could contribute to the development of inflammatory keloid treatment techniques in the future.

Post-Excision Soft X-Ray Radiotherapy for Keloids: Experience in a Tertiary Referral Center

INTRODUCTION

Keloid is an abnormal proliferation of scar tissue that grows beyond the original margins of the injury. Even after complete resection, recurrences are common and pose a poorly understood challenge in dermatology. There is lack of large prospective clinical trials; thus, treatment recommendations are based on retrospective analyses and small cohort studies. Superficial radiotherapy is recommended in recurrent keloids; however, the successful treatment rates vary greatly. The aim of this study was to evaluate the keloid recurrence rate after post-excision soft X-ray radiotherapy and the associated factors.

METHODS

We reviewed retrospective data of all patients, treated with adjuvant post-excision soft X-ray radiotherapy with 12 Gy in 6 sessions at the tertiary referral center, Department of Dermatology, University Hospital Zurich, Switzerland, between 2005 and 2018. We analyzed individual keloids as separate cases. Successful treatment was defined as no sign of recurrence within 2 years.

RESULTS

Of the 200 identified patients, 90 met the inclusion criteria and were included in the final analysis. In 90 patients, 104 cases of treated keloids were analyzed. Keloids were mainly located on the trunk (49%) and were mostly caused by previous surgery (52.2%). 50% of the keloids did not relapse within 2 years after therapy. A significant factor leading to recurrence was the presence of previous therapy, with prior topical therapies, such as steroid injections or 5-fluorouracil, leading to most relapses. 69.2% of keloid cases who relapsed were pretreated. Soft X-ray radiotherapy was well tolerated, with posttreatment hyperpigmentation noted in 34% of patients, particularly in patients with non-Caucasian origin (61.3%).

CONCLUSION

Treatment of refractory keloids is difficult. Post-excision radiotherapy is an established adjuvant treatment option; nevertheless, recurrence rates are high, especially in pretreated keloids. Prospective studies determining the exact dosage and fraction of post-excisional radiotherapy are needed to determine the optimal radiation parameters.

Backscatter from therapeutic doses of ionizing irradiation does not impair cell migration on titanium implants in vitro

OBJECTIVE

The influence of radiation backscatter from titanium on DNA damage and migration capacity of human osteoblasts (OBs) and mesenchymal stem cells (MSCs) may be critical for the osseointegration of dental implants placed prior to radiotherapy. In order to evaluate effects of radiation backscatter, the immediate DNA damage and migration capacity of OBs and MSCs cultured on titanium or plastic were compared after exposure to ionizing irradiation.

MATERIALS AND METHODS

Human OBs and MSCs were seeded on machined titanium, moderately rough fluoride-modified titanium, or tissue culture polystyrene, and irradiated with nominal doses of 2, 6, 10, or 14 Gy. Comet assay was performed immediately after irradiation, while a scratch wound healing assay was initiated 24 h post-irradiation. Fluorescent live cell imaging documented the migration.

RESULTS

DNA damage increased with higher dose and with backscatter from titanium, and MSCs were significantly more affected than OBs. All doses of radiation accelerated the cell migration on plastic, while only the highest dose of 10 Gy inhibited the migration of both cell types on titanium.

CONCLUSIONS

High doses (10 Gy) of radiation inhibited the migration capacity of both cell types on titanium, whereas lower doses (2 and 6 Gy) did not affect the migration of either OBs or MSCs.

CLINICAL RELEVANCE

Fractionated doses of 2 Gy/day, as distributed in conventional radiotherapy, appear not to cause severe DNA damage or disturb the migration of OBs or MSCs during osseointegration of dental implants.

Radioprotective effects of melatonin and thymoquinone on liver, parotid gland, brain, and testis of rats exposed to total body irradiation

BACKGROUND

This study aimed to investigate thymoquinone (TQ), and melatonin's radioprotective effects on liver, parotid gland, brain, and testis of rats which were exposed to total body irradiation (IR).

METHODS

Thirty adult Wistar rats were randomly divided into four groups that are Group 1 (control group): total body IR only, Group 2: IR-Melatonin (10 mg/kg), Group 3: IR-TQ (10 mg/kg), and Group 4 (sham group): nothing. Total body IR dose was 6 Gy. Tissue samples were taken 90 min after IR. The measurements of malondialdehyde (MDA), glutathione peroxidase (GSH-Px), and superoxide dismutase (SOD) were performed in all groups.

RESULTS

In IR group, GSH-Px and SOD activities significantly decreased whereas MDA levels significantly increased when compared with the sham in all tissues. We recorded a significant decrease in MDA levels in IR-TQ group in liver and parotid gland of rats. Moreover, SOD did not change in IR-TQ group compared with IR only group.

DISCUSSION

Melatonin, a powerful antioxidant, plays role in preventing oxidative stress. We revealed that premedication with TQ significantly inhibited the increase in MDA induced by IR in liver and parotid gland and protected the activities of SOD, an antioxidant enzyme, in all other tissues. It has been revealed that TQ has a potential effect preventing IR-induced damage as much as melatonin.

LncRNA ANRIL promotes HR repair through regulating PARP1 expression by sponging miR-7-5p in lung cancer

BACKGROUND

Radiotherapy is an important treatment for lung cancer, mainly by triggering DNA double-strand breaks to induce cell death. Blocking DNA damage repair can increase the radiosensitivity of tumor cells. Recent studies have identified long noncoding RNAs as key regulators in DNA damage repair. The lncRNA ANRIL was previously shown to be involved in homologous recombination (HR) repair, but its specific mechanism has not been fully elucidated.

METHODS

The downstream interacting miRNAs of ANRIL were predicted according to miRanda software. Fluorescence quantitative PCR was used to detect the expression levels of ANRIL and candidate miRNAs. Clone formation experiment and cell viability assays detect cell viability after ionizing radiation. Apoptosis assay was used to detect the apoptosis of cells after 8 h of ionizing radiation. Western blot analysis and immunofluorescence assays verified the protein expression levels of the downstream target molecule PARP1 of miR-7-5p and key molecules in the HR pathway. Fluorescent reporter gene experiments were used to verify the interaction between ANRIL and miR-7-5p and between miR-7-5p and PARP1.

RESULTS

Bioinformatics analysis and qPCR validation suggested that miR-7-5p might be a downstream molecule of ANRIL. The expression of miR-7-5p was up-regulated after knockdown of ANRIL, and the expression of miR-7-5p was down-regulated after overexpression of ANRIL. Meanwhile, there was a negative correlation between ANRIL and miR-7-5p expression changes before and after ionizing radiation. The luciferase reporter gene assay confirmed the existence of ANRIL binding site with miR-7-5p, and found that transfection of miR-7-5p inhibitor can reduce the radiation sensitivity of ANRIL-KD cells. A downstream target molecule of miR-7-5p related to HR repair, PARP1, was screened through website prediction. Subsequently, it was confirmed by Western blot and luciferase reporter assays that miR-7-5p could down-regulate the expression of PARP1, and there was a miR-7-5p binding site on the 3'UTR of PARP1 mRNA. This suggests that ANRIL may act as a competitive endogenous RNA to bind miR-7-5p and upregulate the expression of PARP1. Western blot and immunofluorescence staining were used to detect the expression changes of HR repair factors in ANRIL-KD cells after ionizing radiation, and it was found that knockdown of ANRIL can inhibit the expression of PARP1, BRCA1 and Rad51, hinder radiation-induced HR repair, and eventually result in resensitizing ANRIL-KD cells to ionizing radiation.

CONCLUSIONS

Our findings provide evidence that ANRIL targets the miR-7-5p/PARP1 axis to exert its regulatory effect on HR repair, suggesting that altering ANRIL expression may be a promising strategy to overcome radiation resistance.

The Lymphatic Endothelium in the Context of Radioimmuno-Oncology

The study of lymphatic tumor vasculature has been gaining interest in the context of cancer immunotherapy. These vessels constitute conduits for immune cells' transit toward the lymph nodes, and they endow tumors with routes to metastasize to the lymph nodes and, from them, toward distant sites. In addition, this vasculature participates in the modulation of the immune response directly through the interaction with tumor-infiltrating leukocytes and indirectly through the secretion of cytokines and chemokines that attract leukocytes and tumor cells. Radiotherapy constitutes the therapeutic option for more than 50% of solid tumors. Besides impacting transformed cells, RT affects stromal cells such as endothelial and immune cells. Mature lymphatic endothelial cells are resistant to RT, but we do not know to what extent RT may affect tumor-aberrant lymphatics. RT compromises lymphatic integrity and functionality, and it is a risk factor to the onset of lymphedema, a condition characterized by deficient lymphatic drainage and compromised tissue homeostasis. This review aims to provide evidence of RT's effects on tumor vessels, particularly on lymphatic endothelial cell physiology and immune properties. We will also explore the therapeutic options available so far to modulate signaling through lymphatic endothelial cell receptors and their repercussions on tumor immune cells in the context of cancer. There is a need for careful consideration of the RT dosage to come to terms with the participation of the lymphatic vasculature in anti-tumor response. Here, we provide new approaches to enhance the contribution of the lymphatic endothelium to radioimmuno-oncology.

Molecular and biological rationale of hyperthermia as radio- and chemosensitizer

Mild hyperthermia, local heating of the tumour up to temperatures <43 °C, has been clinically applied for almost four decades and has been proven to substantially enhance the effectiveness of both radiotherapy and chemotherapy in treatment of primary and recurrent tumours. Clinical results and mechanisms of action are discussed in this review, including the molecular and biological rationale of hyperthermia as radio- and chemosensitizer as established in in vitro and in vivo experiments. Proven mechanisms include inhibition of different DNA repair processes, (in)direct reduction of the hypoxic tumour cell fraction, enhanced drug uptake, increased perfusion and oxygen levels. All mechanisms show different dose effect relationships and different optimal scheduling with radiotherapy and chemotherapy. Therefore, obtaining the ideal multi-modality treatment still requires elucidation of more detailed data on dose, sequence, duration, and possible synergisms between modalities. A multidisciplinary approach with different modalities including hyperthermia might further increase anti-tumour effects and diminish normal tissue damage.

Toward a New Framework for Clinical Radiation Biology

Radiation biology has entered the era of precision oncology, and this article reviews time-tested factors that determine the effects of fractionated radiation therapy in a wide variety of tumor types and normal tissues: the association of tumor control with radiation dose, the importance of fractionation and overall treatment time, and the role of tumor hypoxia. Therapeutic gain can only be achieved if the increased tumor toxicity produced by biological treatment modifications is balanced against injury to early-responding and late-responding normal tissues. Developments in precision oncology and immuno-oncology will allow an emphasis on treatment individualization and predictive biomarker development.

Role of radiotherapy in the treatment of metastatic head and neck cancer

In metastatic or locally advanced head and neck tumors that present in frail patients or after chemotherapy progression, radiotherapy is normally used as a palliative treatment, with a high rate of symptom palliation and improvement in quality of life. However, there is controversy about what the optimal regimen is. Moreover, despite the poor prognosis of metastatic head and neck cancer, different retrospective studies have shown that a minority of patients with oligometastatic disease experience prolonged disease-free survival after adding curative radiotherapy treatment to the metastatic disease and/or primary tumor. Different retrospective studies have identified clinical prognostic factors that may be used to select candidate patients with metastatic head and neck cancer for a radical approach with radiotherapy. The purpose of this manuscript is to review the role of radiotherapy in metastatic and locally advanced head and neck tumors.

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.

Immunological Mechanisms Responsible for Radiation-Induced Abscopal Effect

Radiotherapy has been used for more than a hundred years as a local tumor treatment. The occurrence of systemic antitumor effects manifesting as regression of tumors outside of the irradiated field (abscopal effect) was occasionally observed but deemed too rare and unpredictable to be a therapeutic goal. This has changed with the advent of immunotherapy. Remarkable systemic effects have been observed in patients receiving radiotherapy to control tumors that were progressing during immune checkpoint blockade, stimulating interest in using radiation to overcome primary and acquired cancer resistance to immunotherapy. Here, we review the immunological mechanisms that are responsible for the ability of focal radiation to promote antitumor T cell responses that mediate tumor rejection and, in some cases, result in systemic effects.

Precision Oncology and Genomically Guided Radiation Therapy: A Report From the American Society for Radiation Oncology/American Association of Physicists in Medicine/National Cancer Institute Precision Medicine Conference

PURPOSE

To summarize important talking points from a 2016 symposium focusing on real-world challenges to advancing precision medicine in radiation oncology, and to help radiation oncologists navigate the practical challenges of precision, radiation oncology.

METHODS AND MATERIALS

The American Society for Radiation Oncology, American Association of Physicists in Medicine, and National Cancer Institute cosponsored a meeting on precision medicine in radiation oncology. In June 2016 numerous scientists, clinicians, and physicists convened at the National Institutes of Health to discuss challenges and future directions toward personalized radiation therapy. Various breakout sessions were held to discuss particular components and approaches to the implementation of personalized radiation oncology. This article summarizes the genomically guided radiation therapy breakout session.

RESULTS

A summary of existing genomic data enabling personalized radiation therapy, ongoing clinical trials, current challenges, and future directions was collected. The group attempted to provide both a current overview of data that radiation oncologists could use to personalize therapy, along with data that are anticipated in the coming years. It seems apparent from the provided review that a considerable opportunity exists to truly bring genomically guided radiation therapy into clinical reality.

CONCLUSIONS

Genomically guided radiation therapy is a necessity that must be embraced in the coming years. Incorporating these data into treatment recommendations will provide radiation oncologists with a substantial opportunity to improve outcomes for numerous cancer patients. More research focused on this topic is needed to bring genomic signatures into routine standard of care.

The Future of Radiobiology

Innovation and progress in radiation oncology depend on discovery and insights realized through research in radiation biology. Radiobiology research has led to fundamental scientific insights, from the discovery of stem/progenitor cells to the definition of signal transduction pathways activated by ionizing radiation that are now recognized as integral to the DNA damage response (DDR). Radiobiological discoveries are guiding clinical trials that test radiation therapy combined with inhibitors of the DDR kinases DNA-dependent protein kinase (DNA-PK), ataxia telangiectasia mutated (ATM), ataxia telangiectasia related (ATR), and immune or cell cycle checkpoint inhibitors. To maintain scientific and clinical relevance, the field of radiation biology must overcome challenges in research workforce, training, and funding. The National Cancer Institute convened a workshop to discuss the role of radiobiology research and radiation biologists in the future scientific enterprise. Here, we review the discussions of current radiation oncology research approaches and areas of scientific focus considered important for rapid progress in radiation sciences and the continued contribution of radiobiology to radiation oncology and the broader biomedical research community.

Radiation-Induced Cardiovascular Toxicity: Mechanisms, Prevention, and Treatment

PURPOSE OF REVIEW

Ionizing radiation is a highly effective treatment for a wide range of malignancies, yet the cardiovascular (CV) toxicity that can result from chest radiotherapy impairs the long-term health of cancer survivors and can be a limiting factor for its use. Despite over 100 years of successful clinical use, the mechanisms by which high-energy photons damage critical components within cells of the heart's myocardium, pericardium, vasculature, and valves remain unclear.

RECENT FINDINGS

Recent studies exploring the acute and chronic effects of radiation therapy on cardiac and vascular tissue have provided new insights into the development and progression of heart disease, including the identification and understanding of age- and complication-associated risk factors. However, key questions relating to the connection from upstream signaling to fibrotic changes remain. In addition, advances in the delivery of chest radiotherapy have helped to limit heart exposure and damage, but additional refinements to delivery techniques and cardioprotective therapeutics are absolutely necessary to reduce patient mortality and morbidity. Radiation therapy (RT)-driven CV toxicity remains a major issue for cancer survivors and more research is needed to define the precise mechanisms of toxicity. However, recent findings provide meaningful insights that may help improve patient outcomes.

The Role of the Mammalian Target of Rapamycin (mTOR) in Pulmonary Fibrosis

The phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR)-dependent pathway is one of the most integral pathways linked to cell metabolism, proliferation, differentiation, and survival. This pathway is dysregulated in a variety of diseases, including neoplasia, immune-mediated diseases, and fibroproliferative diseases such as pulmonary fibrosis. The mTOR kinase is frequently referred to as the master regulator of this pathway. Alterations in mTOR signaling are closely associated with dysregulation of autophagy, inflammation, and cell growth and survival, leading to the development of lung fibrosis. Inhibitors of mTOR have been widely studied in cancer therapy, as they may sensitize cancer cells to radiation therapy. Studies also suggest that mTOR inhibitors are promising modulators of fibroproliferative diseases such as idiopathic pulmonary fibrosis (IPF) and radiation-induced pulmonary fibrosis (RIPF). Therefore, mTOR represents an attractive and unique therapeutic target in pulmonary fibrosis. In this review, we discuss the pathological role of mTOR kinase in pulmonary fibrosis and examine how mTOR inhibitors may mitigate fibrotic progression.

Preoperative chemoradiation with capecitabine, irinotecan and cetuximab in rectal cancer: significance of pre-treatment and post-resection RAS mutations

BACKGROUND

The influence of EGFR pathway mutations on cetuximab-containing rectal cancer preoperative chemoradiation (CRT) is uncertain.

METHODS

In a prospective phase II trial (EXCITE), patients with magnetic resonance imaging (MRI)-defined non-metastatic rectal adenocarinoma threatening/involving the surgical resection plane received pelvic radiotherapy with concurrent capecitabine, irinotecan and cetuximab. Resection was recommended 8 weeks later. The primary endpoint was histopathologically clear (R0) resection margin. Pre-planned retrospective DNA pyrosequencing (PS) and next generation sequencing (NGS) of KRAS, NRAS, PIK3CA and BRAF was performed on the pre-treatment biopsy and resected specimen.

RESULTS

Eighty-two patients were recruited and 76 underwent surgery, with R0 resection in 67 (82%, 90%CI: 73-88%) (four patients with clinical complete response declined surgery). Twenty-four patients (30%) had an excellent clinical or pathological response (ECPR). Using NGS 24 (46%) of 52 matched biopsies/resections were discrepant: ten patients (19%) gained 13 new resection mutations compared to biopsy (12 KRAS, one PIK3CA) and 18 (35%) lost 22 mutations (15 KRAS, 7 PIK3CA). Tumours only ever testing RAS wild-type had significantly greater ECPR than tumours with either biopsy or resection RAS mutations (14/29 [48%] vs 10/51 [20%], P=0.008), with a trend towards increased overall survival (HR 0.23, 95% CI 0.05-1.03, P=0.055).

CONCLUSIONS

This regimen was feasible and the primary study endpoint was met. For the first time using pre-operative rectal CRT, emergence of clinically important new resection mutations is described, likely reflecting intratumoural heterogeneity manifesting either as treatment-driven selective clonal expansion or a geographical biopsy sampling miss.

Expression of cross-tolerance to a wide range of conditions in a human lung cancer cell line after adaptation to nitric oxide

Previously, we have shown that A549, a human lung adenocarcinoma, can be adapted to nitric oxide (NO^●). NO^● is a nitrogen-based free radical that is synthesized by a family of enzymes known as nitric oxide synthases. NO^● has been shown to be overexpressed in patient populations of different cancers. In addition, it has been observed that patients who express high levels of nitric oxide synthases tend to have poorer clinical outcomes than those with low levels of expression. The original cell line A549 (parent) and the adapted A549-HNO (high nitric oxide) cell line serve as a useful model system to investigate the role of NO^● in tumor progression and prognosis. We have previously shown that the A549-HNO-adapted cells grow aggressively when compared to A549-parent cells. Furthermore, we have shown that the A549-HNO-adapted cells exhibit a higher percentage of cell viability when exposed to ultraviolet and X-ray radiation than the A549-parent cells. Cancer patients who develop resistance to one treatment often become resistant to other previously unencountered forms of treatment. This phenomenon is known as cross-tolerance. To determine whether NO^● is a potential cross-tolerance causing agent, we have expanded our research by conducting parallel studies to a variety of other agents and conditions beyond radiation and ultraviolet exposure. We exposed both cell lines to varying levels of chemotherapeutic drugs (taxol and doxorubicin), temperature, pH, calcium chloride, cadmium chloride, copper chloride, sodium chloride, ferrous chloride, and sodium-R-lipoic acid. Our results show that the A549-HNO cells exhibit greater viability than the A549-parent cells when exposed to each of the various conditions. Therefore, NO^● is one potential driving force that can make tumor cells exhibit cross-tolerance.

Survival Impact of Cardiac Dose Following Lung Stereotactic Body Radiotherapy

INTRODUCTION

The purpose of this study was to determine the impact of radiation dose to substructures of the heart in lung stereotactic body radiotherapy (SBRT) patients on non-cancer-related deaths.

METHODS

Patients treated with lung SBRT at a single institution from 2005 to 2013 were included. The heart and its substructures were contoured, and dose was calculated including mean, max, and max 10 cc dose. Clinical variables including stage, histology, age, gender, Charlson comorbidity index (CCI), preexisting cardiac disease, pulmonary function (forced expiratory volume in 1 second, diffusion capacity), and smoking status were explored for association with non-cancer-related deaths in univariable (UVA) and multivariable (MVA) analyses. Heart dosimetric parameters were correlated with the risk of radiation pneumonitis (RP) using UVA and MVA.

RESULTS

A total of 189 patients were included with median age of 76 years (range, 48-93 years). Of these patients, 45.5% were female, 27.5% were T2, 16.9% were current smokers, 64% had preexisting cardiac risk factors, and 34.5% had CCI score of ≥ 3. Mean lung dose ± SD was 456 ± 231 cGy. Heart max, mean, and 10 cc doses were 1867 ± 1712 cGy, 265 ± 269 cGy, and 1150 ± 1075 cGy, respectively. There were 14 (7.4%) ≥ Grade 2 RP and 3 (1.6%) were ≥ Grade 3. The median overall survival was 37.3 months (95% confidence interval, 29.8-45.3 months). On UVA, female gender (P < .01), higher Eastern Cooperative Oncology Group (P = .01), cardiac risk (P < .01), CCI (P < .01), and bilateral ventricles max dose (P = .02) were associated with non-cancer-related deaths; on MVA, bilateral ventricles max dose was significant (P = .05). No heart parameters were associated with RP.

CONCLUSIONS

Higher bilateral ventricles max dose is associated with poorer survival. Heart dose parameters should be considered when planning patients for SBRT.

Microarray Studies on 211At Administration in BALB/c Nude Mice Indicate Systemic Effects on Transcriptional Regulation in Nonthyroid Tissues

Targeted α-therapy is a promising treatment option for various types of malignant tumors. Radiolabeled cancer-seeking agents, however, undergo degradation, resulting in a certain percentage of free radionuclide in the body. The radiohalogen ²¹¹At accumulates in various tissues, with specifically high uptake in the thyroid. When normal thyroid function is disturbed because of ionizing radiation (IR) exposure, deleterious effects can occur in tissues that depend on thyroid hormone (TH) regulation for normal physiologic function. However, knowledge of systemic effects is still rudimentary. We previously reported similarities in transcriptomic regulation between the thyroid and other tissues despite large differences in absorbed dose from ²¹¹At. Here, we present supportive evidence on systemic effects after ²¹¹At administration.

METHODS

Expression microarray data from the kidney cortex and medulla, liver, lungs, and spleen were used from previous studies in which mice were intravenously injected with 0.064-42 kBq of ²¹¹At and killed after 24 h or injected with 1.7 kBq of ²¹¹At and killed after 1, 6, or 168 h. Controls were mock-treated and killed after 24 h. Literature-based gene signatures were used to evaluate the relative impact from IR- or TH-induced regulation. Thyroid- and TH-associated upstream regulators as well as thyroid-related diseases and functions were generated using functional analysis software.

RESULTS

Responses in IR- or TH-associated gene signatures were tissue-specific and varied over time, and the relative impact of each gene signature differed between the investigated tissues. The liver showed a clear dominance of TH-responding genes. In the kidney cortex, kidney medulla, and lungs, the TH-associated signature was detected to at least an extent similar to the IR-associated signature. The spleen was the single tissue showing regulation of only IR-associated signature genes. Various thyroid-associated diseases and functions were inferred from the data: L-triiodothyronine, TH, TH receptor, and triiodothyronine (reverse) were inferred as upstream regulators with differences in incidence and strength of regulation depending on tissue type.

CONCLUSION

These findings indicate that transcriptional regulation in various nonthyroid tissues was-in part-induced by thyroid (hormone)-dependent signaling. Consideration of the systemic context between tissues could contribute to normal tissue risk assessment and planning of remedial measures.

Stereotactic Body Radiation Therapy Boost After Concurrent Chemoradiation for Locally Advanced Non-Small Cell Lung Cancer: A Phase 1 Dose Escalation Study

PURPOSE

Stereotactic body radiation therapy (SBRT) boost to primary and nodal disease after chemoradiation has potential to improve outcomes for advanced non-small cell lung cancer (NSCLC). A dose escalation study was initiated to evaluate the maximum tolerated dose (MTD).

METHODS AND MATERIALS

Eligible patients received chemoradiation to a dose of 50.4 Gy in 28 fractions and had primary and nodal volumes appropriate for SBRT boost (<120 cc and <60 cc, respectively). SBRT was delivered in 2 fractions after chemoradiation. Dose was escalated from 16 to 28 Gy in 2 Gy/fraction increments, resulting in 4 dose cohorts. MTD was defined when ≥2 of 6 patients per cohort experienced any treatment-related grade 3 to 5 toxicity within 4 weeks of treatment or the maximum dose was reached. Late toxicity, disease control, and survival were also evaluated.

RESULTS

Twelve patients (3 per dose level) underwent treatment. All treatment plans met predetermined dose-volume constraints. The mean age was 64 years. Most patients had stage III disease (92%) and were medically inoperable (92%). The maximum dose level was reached with no grade 3 to 5 acute toxicities. At a median follow-up time of 16 months, 1-year local-regional control (LRC) was 78%. LRC was 50% at <24 Gy and 100% at ≥24 Gy (P=.02). Overall survival at 1 year was 67%. Late toxicity (grade 3-5) was seen in only 1 patient who experienced fatal bronchopulmonary hemorrhage (grade 5). There were no predetermined dose constraints for the proximal bronchial-vascular tree (PBV) in this study. This patient's 4-cc PBV dose was substantially higher than that received by other patients in all 4 cohorts and was associated with the toxicity observed: 20.3 Gy (P<.05) and 73.5 Gy (P=.07) for SBRT boost and total treatment, respectively.

CONCLUSIONS

SBRT boost to both primary and nodal disease after chemoradiation is feasible and well tolerated. Local control rates are encouraging, especially at doses ≥24 Gy in 2 fractions. Toxicity at the PBV is a concern but potentially can be avoided with strict dose-volume constraints.

Integration of Stereotactic Body Radiation Therapy With Tyrosine Kinase Inhibitors in Stage IV Oncogene-Driven Lung Cancer

: Genotype-based selection of patients for targeted therapies has had a substantial impact on the treatment of non-small cell lung cancers (NSCLCs). Tyrosine kinase inhibitors (TKIs) directed at cancers driven by oncogenes, such as epidermal growth factor receptor mutations or anaplastic lymphoma kinase rearrangements, often achieve dramatic responses and result in prolonged survival compared with chemotherapy. However, TKI resistance invariably develops. Disease progression can be limited to only one or a few sites and might not be symptomatic, raising the important question of whether this type of oligoprogression warrants a change in systemic therapy or consideration of local treatment. Recent clinical observations suggest a growing role for stereotactic body radiation therapy (SBRT) in the treatment of oligoprogressive and perhaps even oligopersistent disease (primary and/or metastases) in oncogene-driven NSCLC. SBRT might allow patients to continue with existing TKI treatments longer and delay the need to switch to other systemic options. We review the current data with regard to the use of SBRT for metastatic NSCLC and particularly oncogene-driven disease. Although there is great promise in the marriage of targeted therapies with SBRT, prospective data are urgently needed. In the meantime, such strategies are being used in carefully selected patients, with risk-adapted SBRT dose-fractionation regimens used to optimize the therapeutic index.

IMPLICATIONS FOR PRACTICE

Stereotactic body radiation therapy (SBRT) or SBRT-like treatments are increasingly being used for oligoprogression in patients with oncogene-driven non-small cell lung cancer. This approach allows patients to extend the duration of tyrosine kinase inhibitor therapy and has the potential to prolong survival times. Careful patient selection and risk-adapted radiation dosing is of critical importance to minimize toxicity and preserve patient quality of life.

Targeting DNA Damage Response in the Radio(Chemo)therapy of Non-Small Cell Lung Cancer

Lung cancer is the leading cause of cancer death worldwide due to its high incidence and mortality. As the most common lung cancer, non-small cell lung cancer (NSCLC) is a terrible threat to human health. Despite improvements in diagnosis and combined treatments including surgical resection, radiotherapy and chemotherapy, the overall survival for NSCLC patients still remains poor. DNA damage is considered to be the primary cause of lung cancer development and is normally recognized and repaired by the intrinsic DNA damage response machinery. The role of DNA repair pathways in radio(chemo)therapy-resistant cancers has become an area of significant interest in the clinical setting. Meanwhile, some studies have proved that genetic and epigenetic factors can alter the DNA damage response and repair, which results in changes of the radiation and chemotherapy curative effect in NSCLC. In this review, we focus on the effect of genetic polymorphisms and epigenetic factors such as miRNA regulation and lncRNA regulation participating in DNA damage repair in response to radio(chemo)therapy in NSCLC. These may provide novel information on the radio(chemo)therapy of NSCLC based on the individual DNA damage response.

Torin2 Suppresses Ionizing Radiation-Induced DNA Damage Repair

Several classes of inhibitors of the mammalian target of rapamycin (mTOR) have been developed based on its central role in sensing growth factor and nutrient levels to regulate cellular metabolism. However, its ATP-binding site closely resembles other phosphatidylinositol 3-kinase-related kinase (PIKK) family members, resulting in reactivity with these targets that may also be therapeutically useful. The ATP-competitive mTOR inhibitor, Torin2, shows biochemical activity against the DNA repair-associated proteins ATM, ATR and DNA-PK, which raises the possibility that Torin2 and related compounds might radiosensitize cancerous tumors. In this study Torin2 was also found to enhance ionizing radiation-induced cell killing in conditions where ATM was dispensable, confirming the requirement for multiple PIKK targets. Moreover, Torin2 did not influence the initial appearance of γ-H2AX foci after irradiation but significantly delayed the disappearance of radiation-induced γ-H2AX foci, indicating a DNA repair defect. Torin2 increased the number of radiation-induced S-phase specific chromosome aberrations and reduced the frequency of radiation-induced CtIP and Rad51 foci formation, suggesting that Torin2 works by blocking homologous recombination (HR)-mediated DNA repair resulting in an S-phase specific DNA repair defect. Accordingly, Torin2 reduced HR-mediated repair of I-Sce1-induced DNA damage and contributed to replication fork stalling. We conclude that radiosensitization of tumor cells by Torin2 is associated with disrupting ATR- and ATM-dependent DNA damage responses. Our findings support the concept of developing combination cancer therapies that incorporate ionizing radiation therapy and Torin2 or compounds with similar properties.

Polymorphisms in double strand break repair related genes influence radiosensitivity phenotype in lymphocytes from healthy individuals

BACKGROUND

A range of individual radiosensitivity observed in humans can influence individual's susceptibility toward cancer risk and radiotherapy outcome. Therefore, it is important to measure the variation in radiosensitivity and to identify the genetic factors influencing it.

METHODS

By adopting a pathway specific genotype-phenotype design, we established the variability in cellular radiosensitivity by performing γ-H2AX foci assay in healthy individuals. Further, we genotyped ten selected SNPs in candidate genes XRCC3 (rs861539), XRCC4 (rs1805377), XRCC5 (rs3835), XRCC6 (rs2267437), ATM (rs3218698, rs1800057), LIG4 (rs1805388), NBN (rs1805794), RAD51 (rs1801320) and PRKDC (rs7003908), and analysed their influence on observed variation in radiosensitivity.

RESULTS

The rs2267437 polymorphisms in XRCC6 was associated (P=0.0326) with increased DSB induction while rs1805388 in LIG4 (P=0.0240) was associated with increased radioresistance. Further, multiple risk alleles decreased the DSB repair capacity in an additive manner. Polymorphisms in candidate DSB repair genes can act individually or in combination to the efficacy of DSB repair process, resulting in variation of cellular radiosensitivity.

CONCLUSIONS

Current study suggests that γ-H2AX assay may fulfil the role of a rapid and sensitive biomarker that can be used for epidemiological studies to measure variations in radiosensitivity. DSB repair gene polymorphisms can impact the formation and repair of DSBs.

IMPACT

γ-H2AX foci analysis as well as DSBs repair gene polymorphisms can be used to assess cellular radiosensitivity, which will be useful in population risk assessment, disease prediction, individualization of radiotherapy and also in setting the radiation protection standards.

Principles of radiation therapy

Although resection remains the mainstay in the treatment of gliomas, microscopically complete resection of most central nervous system tumors remains challenging, and is, in fact, rarely accomplished. Considering their invasive nature, gross total resections to clearly negative margins often do or would require removal or transection of functional brain, with likely serious neurologic deficits. Consequently, radiotherapy has emerged as an indispensable component of therapy. It is delivered primarily by external-beam radiotherapy or brachytherapy techniques. Herein, we present the biologic principles, techniques, and applications of radiotherapy in glioma treatment today.

Adapting a drug screening platform to discover associations of molecular targeted radiosensitizers with genomic biomarkers

Large collections of annotated cancer cell lines are powerful tools for precisely matching targeted drugs with genomic alterations that can be tested as biomarkers in the clinic. Whether these screening platforms, which utilize short-term cell survival to assess drug responses, can be applied to precision radiation medicine is not established. To this end, 32 cancer cell lines were screened using 18 targeted therapeutic agents with known or putative radiosensitizing properties (227 combinations). The cell number remaining after drug exposure with or without radiation was assessed by nonclonogenic assays. We derived short-term radiosensitization factors (SRF2Gy) and calculated clonogenic survival assay-based dose enhancement factors (DEFSF0.1). Radiosensitization was characterized by SRF2Gy values of mostly ∼1.05 to 1.2 and significantly correlated with drug-induced changes in apoptosis and senescence frequencies. SRF2Gy was significantly correlated with DEFSF0.1, with a respective sensitivity and specificity of 91.7% and 81.5% for a 3-day endpoint, and 82.8% and 84.2% for a robotic 5-day assay. KRAS mutations (codons 12/13) were found to be a biomarker of radiosensitization by midostaurin in lung cancer, which was pronounced under conditions that enriched for stem cell-like cells. In conclusion, although short-term proliferation/survival assays cannot replace the gold-standard clonogenic survival assay for measuring cellular radiosensitivity, they capture with high accuracy the relative change in radiosensitivity that is caused by a radiosensitzing targeted agent.

IMPLICATIONS

This study supports a paradigm shift regarding the utility of short-term assays for precision radiation medicine, which should facilitate the identification of genomic biomarkers to guide the testing of novel drug/radiation combinations.

Accelerated repopulation as a cause of radiation treatment failure in non-small cell lung cancer: review of current data and future clinical strategies

Despite convincing evidence that the principles of accelerated repopulation would open up additional therapeutic opportunities in the treatment of advanced-stage non-small cell lung cancer, this strategy has been generally underexplored. The implementation of accelerated radiotherapy schedules has been hampered by logistical barriers, concerns about acute toxicity, and the prioritization of integrating concurrent chemotherapy into the standard treatment platform. At present, it is unclear to what extent accelerated fractionation will influence future treatment paradigms in non-small cell lung cancer, although technical advances in radiotherapy, allowing higher dose delivery with reduced toxicity, could permit the development of more convenient and tolerable forms of accelerated schedules.

EGFR-mediated chromatin condensation protects KRAS-mutant cancer cells against ionizing radiation

Therapeutics that target the epidermal growth factor receptor (EGFR) can enhance the cytotoxic effects of ionizing radiation (IR). However, predictive genomic biomarkers of this radiosensitization have remained elusive. By screening 40 non-small cell lung cancer cell (NSCLC) lines, we established a surprising positive correlation between the presence of a KRAS mutation and radiosensitization by the EGFR inhibitors erlotinib and cetuximab. EGFR signaling in KRAS-mutant NSCLC cells promotes chromatin condensation in vitro and in vivo, thereby restricting the number of DNA double-strand breaks (DSB) produced by a given dose of IR. Chromatin condensation in interphase cells is characterized by an unexpected mitosis-like colocalization of serine 10 phosphorylation and lysine 9 trimethylation on histone H3. Aurora B promotes this process in a manner that is codependent upon EGFR and protein kinase C α (PKCα). PKCα, in addition to MEK/ERK signaling, is required for the suppression of DSB-inducible premature senescence by EGFR. Blockade of autophagy results in a mutant KRAS-dependent senescence-to-apoptosis switch in cancer cells treated with IR and erlotinib. In conclusion, we identify EGFR as a molecular target to overcome a novel mechanism of radioresistance in KRAS-mutant tumor cells, which stands in contrast to the unresponsiveness of KRAS-mutant cancers to EGFR-directed agents in monotherapy. Our findings may reposition EGFR-targeted agents for combination with DSB-inducing therapies in KRAS-mutant NSCLC.

Role of microRNA in response to ionizing radiations: evidences and potential impact on clinical practice for radiotherapy

MicroRNAs (miRNA) are small, non-coding, RNAs with gene expression regulator roles. As an important class of regulators of many cellular pathways, miRNAs are involved in many signaling pathways and DNA damage repair processes, affecting cellular radiosensitivity. Their role has led to interest in oncological implications to improve treatment results. MiRNAs represent a great opportunity to enhance the efficacy of radiotherapy treatments-they can be used to profile the radioresistance of tumors before radiotherapy, monitor their response throughout the treatment, thus helping to select intensification strategies, and also to define the final response to therapy along with risks of recurrence or metastatization. Even though many interesting studies support such potential, nowadays most studies on patient data are limited to experiments profiling tumor aggressiveness and response to radiotherapy. Moreover many studies report different although not conflicting results on the miRNAs evaluated for each tumor type. Without doubt, the clinical potential of such molecules for radiotherapy is striking and of high interest.

Basic mechanisms of therapeutic resistance to radiation and chemotherapy in lung cancer

In recent years, there have been multiple breakthroughs in our understanding of lung cancer biology. Despite significant advances in molecular targeted therapies, DNA-damaging cytotoxic therapies will remain the mainstay of lung cancer management for the near future. Similar to the concept of personalized targeted therapies, there is mounting evidence that perturbations in DNA repair pathways are common in lung cancers, altering the resistance of the affected tumors to many chemotherapeutics as well as radiation. Defects in DNA repair may be due to a multitude of mechanisms including gene mutations, epigenetic events, and alterations in signal transduction pathways such as epidermal growth factor receptor and phosphoinositide 3-kinase/AKT. Functional biomarkers that assess the subcellular localization of central repair proteins in response to DNA damage may prove useful for individualization of cytotoxic therapies including poly(adenosine diphosphate-ribose) polymerase inhibitors. A better mechanistic understanding of cellular sensitivity and resistance to DNA damaging agents should facilitate the development of novel, individualized treatment approaches. Absolute resistance to radiation therapy, however, does not exist. To some extent, radiation therapy will always have to remain unselective and indiscriminant to eradicate persistent, drug-resistant tumor stem cell pools.

MicroRNAs in the ionizing radiation response and in radiotherapy

Radiotherapy is a form of cancer treatment that utilizes the ability of ionizing radiation to induce cell inactivation and cell death, generally via inflicting DNA double-strand breaks. However, different tumors and their normal surrounding tissues are not equally sensitive to radiation, posing a major challenge in the field: to seek out factors that influence radiosensitivity. In this review, we summarize the evidence for microRNA (miRNA) involvement in the radioresponse and discuss their potential as radiosensitizers. MicroRNAs are endogenous small, noncoding RNAs that regulate gene expression posttranscriptionally, influencing many processes including, as highlighted here, cellular sensitivity to radiation. Profiling studies demonstrate that miRNA expression levels change in response to radiation, while certain miRNAs, when overexpressed or knocked down, alter radiosensitivity. Finally, we discuss specific miRNA-target pairs that affect response to radiation and DNA damage as good potential targets for modulating radioresponsitivity.

Radiation-induced brain tumours after central nervous system irradiation in childhood: a review

OBJECTS

Radiation-induced cerebral tumours constitute a significant risk for subjects undergoing radiotherapy for the management of cerebral neoplasms. Age-related cerebral vulnerability could be a specific factor in the genesis of these complications.

METHODS

The pertinent literature of both paediatric and adult series has been reviewed. Three personal cases were added.

RESULTS

One hundred forty-two paediatric second brain tumours were evaluated. Out of them, 69 were malignant gliomas, 33 meningiomas, 8 sarcomatous lesions and 13 low-grade astrocytomas. The average latency period for the appearance of the second tumour was 8 years. Among the second tumours occurring in adults, meningioma is the most common. In this subgroup, the latency period ranged between 16 and 30 years.

CONCLUSION

Paediatric radiation-induced brain tumours differ from the adult counterpart for both the histological subtypes. These figures indicate a specific vulnerability of the infantile brain demonstrated by the most frequent occurrence of highly malignant lesions.

Radiation-induced cell signaling: inside-out and outside-in

Exposure of tumor cells to clinically relevant doses of ionizing radiation causes DNA damage as well as mitochondria-dependent generation of reactive oxygen species. DNA damage causes activation of ataxia telangiectasia mutated and ataxia telangiectasia mutated and Rad3-related protein, which induce cell cycle checkpoints and also modulate the activation of prosurvival and proapoptotic signaling pathways, such as extracellular signal-regulated kinase 1/2 (ERK1/2) and c-Jun NH(2)-terminal kinase 1/2, respectively. Radiation causes a rapid reactive oxygen species-dependent activation of ERBB family and other tyrosine kinases, leading to activation of RAS proteins and multiple protective downstream signaling pathways (e.g., AKT and ERK1/2), which alter transcription factor function and the apoptotic threshold of cells. The initial radiation-induced activation of ERK1/2 can promote the cleavage and release of paracrine ligands, which cause a temporally delayed reactivation of receptors and intracellular signaling pathways in irradiated and unirradiated bystander cells. Hence, signals from within the cell can promote activation of membrane-associated receptors, which signal back into the cytosol: signaling from inside the cell outward to receptors and then inward again via kinase pathways. However, cytosolic signaling can also cause release of membrane-associated paracrine factors, and thus, paracrine signals from outside of the cell can promote activation of growth factor receptors: signaling from the outside inward. The ultimate consequence of these signaling events after multiple exposures may be to reprogram the irradiated and affected bystander cells in terms of their expression levels of growth-regulatory and cell survival proteins, resulting in altered mitogenic rates and thresholds at which genotoxic stresses cause cell death. Inhibition of signaling in one and/or multiple survival pathways enhances radiosensitivity. Prolonged inhibition of any one of these pathways, however, gives rise to lineages of cells, which have become resistant to the inhibitor drug, by evolutionary selection for the clonal outgrowth of cells with point mutations in the specific targeted protein that make the target protein drug resistant or by the reprogramming of multiple signaling processes within all cells, to maintain viability. Thus, tumor cells are dynamic with respect to their reliance on specific cell signaling pathways to exist and rapidly adapt to repeated toxic challenges in an attempt to maintain tumor cell survival.