Radiation-induced Normal Tissue Toxicity Research Articles

Temporally feathered intensity-modulated radiation therapy: A planning technique to reduce normal tissue toxicity.

Intensity-modulated radiation therapy (IMRT) has allowed optimization of three-dimensional spatial radiation dose distributions permitting target coverage while reducing normal tissue toxicity. However, radiation-induced normal tissue toxicity is a major contributor to patients' quality of life and often a dose-limiting factor in the definitive treatment of cancer with radiation therapy. We propose the next logical step in the evolution of IMRT using canonical radiobiological principles, optimizing the temporal dimension through which radiation therapy is delivered to further reduce radiation-induced toxicity by increased time for normal tissue recovery. We term this novel treatment planning strategy "temporally feathered radiation therapy" (TFRT). Temporally feathered radiotherapy plans were generated as a composite of five simulated treatment plans each with altered constraints on particular hypothetical organs at risk (OARs) to be delivered sequentially. For each of these TFRT plans, OARs chosen for feathering receive higher doses while the remaining OARs receive lower doses than the standard fractional dose delivered in a conventional fractionated IMRT plan. Each TFRT plan is delivered a specific weekday, which in effect leads to a higher dose once weekly followed by four lower fractional doses to each temporally feathered OAR. We compared normal tissue toxicity between TFRT and conventional fractionated IMRT plans by using a dynamical mathematical model to describe radiation-induced tissue damage and repair over time. Model-based simulations of TFRT demonstrated potential for reduced normal tissue toxicity compared to conventionally planned IMRT. The sequencing of high and low fractional doses delivered to OARs by TFRT plans suggested increased normal tissue recovery, and hence less overall radiation-induced toxicity, despite higher total doses delivered to OARs compared to conventional fractionated IMRT plans. The magnitude of toxicity reduction by TFRT planning was found to depend on the corresponding standard fractional dose of IMRT and organ-specific recovery rate of sublethal radiation-induced damage. TFRT is a novel technique for treatment planning and optimization of therapeutic radiotherapy that considers the nonlinear aspects of normal tissue repair to optimize toxicity profiles. Model-based simulations of TFRT to carefully conceptualized clinical cases have demonstrated potential for radiation-induced toxicity reduction in a previously described dynamical model of normal tissue complication probability (NTCP).

Inhibition of Radiation-Induced Ccl2 Signaling Protects Lungs from Vascular Dysfunction and Endothelial Cell Loss.

Aims: Radiation-induced normal tissue toxicity often precludes the application of curative radiation doses. Here we investigated the therapeutic potential of chemokine C-C motif ligand 2 (Ccl2) signaling inhibition to protect normal lung tissue from radiotherapy (RT)-induced injury. Results: RT-induced vascular dysfunction and associated adverse effects can be efficiently antagonized by inhibition of Ccl2 signaling using either the selective Ccl2 inhibitor bindarit (BIN) or mice deficient for the main Ccl2 receptor CCR2 (KO). BIN-treatment efficiently counteracted the RT-induced expression of Ccl2, normalized endothelial cell (EC) morphology and vascular function, and limited lung inflammation and metastasis early after irradiation (acute effects). A similar protection of the vascular compartment was detected by loss of Ccl2 signaling in lungs of CCR2-KO mice. Long-term Ccl2 signaling inhibition also significantly limited EC loss and accompanied fibrosis progression as adverse late effect. With respect to the human situation, we further confirmed that Ccl2 secreted by RT-induced senescent epithelial cells resulted in the activation of normally quiescent but DNA-damaged EC finally leading to EC loss in ex vivo cultured human normal lung tissue. Innovation: Abrogation of certain aspects of the secretome of irradiated resident lung cells, in particular signaling inhibition of the senescence-associated secretory phenotype-factor Ccl2 secreted predominantly by RT-induced senescent epithelial cells, resulted in protection of the endothelial compartment. Conclusions: Radioprotection of the normal tissue via Ccl2 signaling inhibition without simultaneous protection or preferable radiosensitization of tumor tissue might improve local tumor control and survival, because higher doses of radiation could be used.

Mesenchymal Stem Cell Therapy Protects Lungs from Radiation-Induced Endothelial Cell Loss by Restoring Superoxide Dismutase 1 Expression.

Radiation-induced normal tissue toxicity is closely linked to endothelial cell (EC) damage and dysfunction (acute effects). However, the underlying mechanisms of radiation-induced adverse late effects with respect to the vascular compartment remain elusive, and no causative radioprotective treatment is available to date. The importance of injury to EC for radiation-induced late toxicity in lungs after whole thorax irradiation (WTI) was investigated using a mouse model of radiation-induced pneumopathy. We show that WTI induces EC loss as long-term complication, which is accompanied by the development of fibrosis. Adoptive transfer of mesenchymal stem cells (MSCs) either derived from bone marrow or aorta (vascular wall-resident MSCs) in the early phase after irradiation limited the radiation-induced EC loss and fibrosis progression. Furthermore, MSC-derived culture supernatants rescued the radiation-induced reduction in viability and long-term survival of cultured lung EC. We further identified the antioxidant enzyme superoxide dismutase 1 (SOD1) as a MSC-secreted factor. Importantly, MSC treatment restored the radiation-induced reduction of SOD1 levels after WTI. A similar protective effect was achieved by using the SOD-mimetic EUK134, suggesting that MSC-derived SOD1 is involved in the protective action of MSC, presumably through paracrine signaling. In this study, we explored the therapeutic potential of MSC therapy to prevent radiation-induced EC loss (late effect) and identified the protective mechanisms of MSC action. Adoptive transfer of MSCs early after irradiation counteracts radiation-induced vascular damage and EC loss as late adverse effects. The high activity of vascular wall-derived MSCs for radioprotection may be due to their tissue-specific action. Antioxid. Redox Signal. 26, 563-582.

Individual patient data meta-analysis shows a significant association between the ATM rs1801516 SNP and toxicity after radiotherapy in 5456 breast and prostate cancer patients

PurposeSeveral small studies have indicated that the ATM rs1801516 SNP is associated with risk of normal tissue toxicity after radiotherapy. However, the findings have not been consistent. In order to test this SNP in a well-powered study, an individual patient data meta-analysis was carried out by the International Radiogenomics Consortium. Materials and methodsThe analysis included 5456 patients from 17 different cohorts. 2759 patients were given radiotherapy for breast cancer and 2697 for prostate cancer. Eight toxicity scores (overall toxicity, acute toxicity, late toxicity, acute skin toxicity, acute rectal toxicity, telangiectasia, fibrosis and late rectal toxicity) were analyzed. Adjustments were made for treatment and patient related factors with potential impact on the risk of toxicity. ResultsFor all endpoints except late rectal toxicity, a significantly increased risk of toxicity was found for carriers of the minor (Asn) allele with odds ratios of approximately 1.5 for acute toxicity and 1.2 for late toxicity. The results were consistent with a co-dominant pattern of inheritance. ConclusionThis study convincingly showed a significant association between the ATM rs1801516 Asn allele and increased risk of radiation-induced normal tissue toxicity.

SP-0009: Uncomplicated cures - a paradigm shift in cancer survivorship research

Changes in cancer incidence and mortality have been modest during the past several decades, but the number of cancer survivors has almost tripled during the same period. With the increasing cohort of cancer survivors, efforts to prevent, diagnose and manage adverse effects of cancer therapy, in general, and those of radiation therapy specifically, have intensified. Considerable progress towards reducing toxicity of radiation therapy has been achieved by the introduction of so-called dose-sculpting treatment techniques. Moreover, new insights into the underlying pathophysiology have resulted in an improved understanding of mechanisms of radiation-induced normal tissue toxicity and in development of new diagnostic strategies and management opportunities. However, the risk of normal tissue toxicity still limits the dose of cytotoxic therapy that can be given, thus limiting the curability of cancer. The steadily increasing number of cancer survivors and the demand for uncomplicated cancer cures require a paradigm shift in cancer survivorship research. Research must shift from simply describing and palliating side effects (“doing head-counts”) to adopt a more modern, goal-oriented approach. The new approach encompasses 1) epidemiological, psychosocial, and outcomes research aimed at characterizing and ameliorating the problems that afflict current cancer survivors; 2) applied clinical and preclinical research aimed at developing new treatments or response modifiers to prevent or minimize shortand longterm side effects of cancer therapy; and 3) basic research aimed at improving our understanding of the cellular and molecular mechanisms that are responsible for treatmentrelated toxicities. This three-pronged approach will ensure that progress is made toward our ultimate goal, i.e., to increase the uncomplicated cancer cure rate.

Abstract 3950: Integrative analysis of acute and late radiotherapy effects using genome-wide transcriptomics and quantitative proteomics

Abstract Pulmonary microvascular endothelial cells are critically involved in development of radiation-induced acute inflammation and late fibrosis often limiting the delivery of sufficient dose to optimally treat lung cancer. Moreover, tumor-endothelium communication has emerged as a key target to augment radiotherapy by resensitizing endothelial-specific survival signals. Therefore, we aimed to employ high-throughput genome-wide gene expression and whole proteome analysis to uncover the molecular mechanisms governing tumor-vessel communication and radiation-induced normal tissue toxicity. Human primary isolated pulmonary microvascular endothelial cells (HPMEC) were irradiated with 0 or 6Gy. Cells were harvested two hours (acute) and six days (late) after irradiation and proteins as well as RNA were extracted. Gene expression analysis was performed using 47k Illumina microarray (HumanHT-12 v4) platform. Mass spectrometry on an LTQ-Orbitrap instrument was employed for protein identification and relative quantification using label-free quantification techniques. An IMAC/TiO2 enrichment step to obtain phosphorylated peptides was carried out and analyzed by mass spectrometry as well. The regulation of candidate radiation-regulated genes and proteins were confirmed in-vitro and in irradiated lung specimen (C57BL/6 mouse) by real-time qRT-PCR, western blot and ELISA. At the early timepoint a strong induction of genes involved in apoptosis and DNA-damage response such as GADD45A, PARP3 and DDB2 was identified. In contrast to the acute radiation response, cell adhesion (Integrins), pro-inflammatory (Interleukines), pro-angiogenic and matrix-remodeling related genes (MMPs, PDGFs, VEGFs) were induced late after irradiation. Integrative analysis of protein quantification, phosphorylation and gene-expression further revealed novel insights to an intricate gene/protein regulatory network underlying late radiation response in microvascular endothelium. The here identified genes and proteins involved in late radiation response constitute attractive targets for modulation of radiotherapy effects in tumor-endothelium or prevention of undesired radiotherapy-induced late side effects. Citation Format: Tilmann Rackwitz, Philipp Seidel, Martin Winter, Cheng Zhou, Ramona Mayer, Uwe Warnken, Peter Hofner, Jürgen Debus, Martina Schnölzer, Amir Abdollahi. Integrative analysis of acute and late radiotherapy effects using genome-wide transcriptomics and quantitative proteomics. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3950. doi:10.1158/1538-7445.AM2014-3950

Radioprotection of normal tissue cells

Improvements of radiotherapy in combination with surgery and systemic therapy have resulted in increased survival rates of tumor patients. However, radiation-induced normal tissue toxicity is still dose limiting. Several strategies have been pursued with the goal to develop substances which may prevent or reduce damage to normal tissue. Drugs applied before radiotherapy are called radioprotectors; those given after radiotherapy to reduce long-term effects are radiomitigators. Despite more than 50 years of research, until now only two substances, amifostine and palifermin, have overcome all obstacles of clinical approval and are applied during radiotherapy of head and neck cancer or total body irradiation, respectively. However, better understanding of the cellular pathways involved in radiation response has allowed the development of several highly promising drugs functioning as scavengers of reactive oxygen species or targeting specific molecules involved in regulation of cell death pathways or cell cycle arrest. The present review describes the major targets for radioprotectors or radiomitigators currently tested in clinical trials.

Mechanisms of radiation-induced normal tissue toxicity and implications for future clinical trials.

To summarize current knowledge regarding mechanisms of radiation-induced normal tissue injury and medical countermeasures available to reduce its severity. Advances in radiation delivery using megavoltage and intensity-modulated radiation therapy have permitted delivery of higher doses of radiation to well-defined tumor target tissues. Injury to critical normal tissues and organs, however, poses substantial risks in the curative treatment of cancers, especially when radiation is administered in combination with chemotherapy. The principal pathogenesis is initiated by depletion of tissue stem cells and progenitor cells and damage to vascular endothelial microvessels. Emerging concepts of radiation-induced normal tissue toxicity suggest that the recovery and repopulation of stromal stem cells remain chronically impaired by long-lived free radicals, reactive oxygen species, and pro-inflammatory cytokines/chemokines resulting in progressive damage after radiation exposure. Better understanding the mechanisms mediating interactions among excessive generation of reactive oxygen species, production of pro-inflammatory cytokines and activated macrophages, and role of bone marrow-derived progenitor and stem cells may provide novel insight on the pathogenesis of radiation-induced injury of tissues. Further understanding the molecular signaling pathways of cytokines and chemokines would reveal novel targets for protecting or mitigating radiation injury of tissues and organs.

Hyperbaric Oxygen Treatment, Alpha-Tocopherol, and Ascorbic Acid are Effective for Reducing Late Radiation-induced Side Effects of Pelvic Radiation Therapy

Pelvic radiotherapy (RT) is a key aspect in the management of genitourinary (GU) and gynecologic (GYN) malignancies. Pelvic irradiation may result in urinary and intestinal toxicities. Late radiation-induced normal tissue toxicity can be difficult to manage and significantly impact quality of life. To better appreciate radiation-induced late effects and their potential management, we undertook an analysis of a prospective treatment protocol designed to investigate the efficacy of hyperbaric oxygen therapy (HBOT), oral alphatocopherol (AT) and ascorbic acid (AA) in patients with pelvic radiation disease. An REB approved retrospective review of a prospective adult radiation late effects (LE) treatment protocol was conducted. Twenty patients referred to a multidisciplinary late effects clinic at a tertiary care cancer center were screened to identify those with GU and GYN malignancies who had received pelvic RT. Patient, tumor and treatment factors were abstracted and analyzed. The median time to LE onset, LE symptoms, maximal initial Common Terminology Criteria for Adverse Events Version 4.0 (CTCAE) grade, LE treatment and duration and maximal post CTCAE grade were analyzed.

Development and Dosimetry of a Small Animal Lung Irradiation Platform

Advances in large scale screening of medical countermeasures for radiation-induced normal tissue toxicity are currently hampered by animal irradiation paradigms that are both inefficient and highly variable among institutions. Here, a novel high-throughput small animal irradiation platform is introduced for use in orthovoltage small animal irradiators. Radiochromic film and metal oxide semiconductor field effect transistor detectors were used to examine several parameters, including 2D field uniformity, dose rate consistency, and shielding transmission. The authors posit that this setup will improve efficiency of drug screens by allowing for simultaneous targeted irradiation of multiple animals to improve efficiency within a single institution. Additionally, they suggest that measurement of the described parameters in all centers conducting countermeasure studies will improve the translatability of findings among institutions. The use of tissue equivalent phantoms in performing dosimetry measurements for small animal irradiation experiments was also investigated. Though these phantoms are commonly used in dosimetry, the authors recorded a significant difference in both the entrance and target tissue dose rates between euthanized rats and mice with implanted detectors and the corresponding phantom measurement. This suggests that measurements using these phantoms may not provide accurate dosimetry for in vivo experiments. Based on these measurements, the authors propose that this small animal irradiation platform can increase the capacity of animal studies by allowing for more efficient animal irradiation. They also suggest that researchers fully characterize the parameters of whatever radiation setup is in use in order to facilitate better comparison among institutions.

Reliability of Quantitative Ultrasonic Assessment of Normal-Tissue Toxicity in Breast Cancer Radiotherapy

We have recently reported that ultrasound imaging, together with ultrasound tissue characterization (UTC), can provide quantitative assessment of radiation-induced normal-tissue toxicity. This study's purpose is to evaluate the reliability of our quantitative ultrasound technology in assessing acute and late normal-tissue toxicity in breast cancer radiotherapy. Our ultrasound technique analyzes radiofrequency echo signals and provides quantitative measures of dermal, hypodermal, and glandular tissue toxicities. To facilitate easy clinical implementation, we further refined this technique by developing a semiautomatic ultrasound-based toxicity assessment tool (UBTAT). Seventy-two ultrasound studies of 26 patients (720 images) were analyzed. Images of 8 patients were evaluated for acute toxicity (<6 months postradiotherapy) and those of 18 patients were evaluated for late toxicity (≥ 6 months postradiotherapy). All patients were treated according to a standard radiotherapy protocol. To assess intraobserver reliability, one observer analyzed 720 images in UBTAT and then repeated the analysis 3 months later. To assess interobserver reliability, three observers (two radiation oncologists and one ultrasound expert) each analyzed 720 images in UBTAT. An intraclass correlation coefficient (ICC) was used to evaluate intra- and interobserver reliability. Ultrasound assessment and clinical evaluation were also compared. Intraobserver ICC was 0.89 for dermal toxicity, 0.74 for hypodermal toxicity, and 0.96 for glandular tissue toxicity. Interobserver ICC was 0.78 for dermal toxicity, 0.74 for hypodermal toxicity, and 0.94 for glandular tissue toxicity. Statistical analysis found significant changes in dermal (p < 0.0001), hypodermal (p = 0.0027), and glandular tissue (p < 0.0001) assessments in the acute toxicity group. Ultrasound measurements correlated with clinical Radiation Therapy Oncology Group (RTOG) toxicity scores of patients in the late toxicity group. Patients with RTOG Grade 1 or 2 had greater ultrasound-assessed toxicity percentage changes than patients with RTOG Grade 0. Early and late radiation-induced effects on normal tissue can be reliably assessed using quantitative ultrasound.

Molecular markers for prediction of risk of radiation-related injury to normal tissue

Radiotherapy is one of the most effective methods for the treatment of cancer, but occurrence of adverse reactions developing in the co-irradiated normal tissue can be a threat for patients. Identification of individuals at risk of severe reaction is very difficult and considerable efforts have been made to correlate normal tissue toxicity with cellular responses to ionizing radiation. Genetic markers enabling to identify hyper-sensitive patients prior to treatment would considerably improve its outcome. Gene association studies should help to identify such markers. Expression levels of specific transcripts could be putative markers; in fact different studies found associations between gene expression profiles in normal cells and the reaction of normal tissues to radiation therapy. The finding that ionizing radiation induces the deregulation of a high number of genes suggests that also microRNAs that affect the expression of a large number of target genes may be involved. This review briefly introduces the mechanisms of radiation-induced normal tissue toxicity and summarizes clinical research focused on the evaluation of molecular biomarkers for predicting risk of injury to normal tissue, mainly describing gene transcripts alterations.

Molecular markers for prediction of risk of radiation-related injury to normal tissue

Radiotherapy is one of the most effective methods for the treatment of cancer, but occurrence of adverse reactions developing in the co-irradiated normal tissue can be a threat for patients. Identification of individuals at risk of severe reaction is very difficult and considerable efforts have been made to correlate normal tissue toxicity with cellular responses to ionizing radiation. Genetic markers enabling to identify hyper-sensitive patients prior to treatment would considerably improve its outcome. Gene association studies should help to identify such markers. Expression levels of specific transcripts could be putative markers; in fact different studies found associations between gene expression profiles in normal cells and the reaction of normal tissues to radiation therapy. The finding that ionizing radiation induces the deregulation of a high number of genes suggests that also microRNAs that affect the expression of a large number of target genes may be involved. This review briefly introduces the mechanisms of radiation-induced normal tissue toxicity and summarizes clinical research focused on the evaluation of molecular biomarkers for predicting risk of injury to normal tissue, mainly describing gene transcripts alterations.

Lovastatin attenuates ionizing radiation-induced normal tissue damage in vivo

Background and purpose HMG-CoA-reductase inhibitors (statins) are widely used lipid-lowering drugs. Moreover, they have pleiotropic effects on cellular stress responses, proliferation and apoptosis in vitro. Here, we investigated whether lovastatin attenuates acute and subchronic ionizing radiation-induced normal tissue toxicity in vivo. Materials and methods Four hours to 24 h after total body irradiation (6 Gy) of Balb/c mice, acute pro-inflammatory and pro-fibrotic responses were analyzed. To comprise subchronic radiation toxicity, mice were irradiated twice with 2.5 Gy and analyses were performed 3 weeks after the first radiation treatment. Molecular markers of inflammation and fibrosis as well as organ toxicities were measured. Results Lovastatin attenuated IR-induced activation of NF-κB, mRNA expression of cell adhesion molecules and mRNA expression of pro-inflammatory and pro-fibrotic marker genes (i.e. TNFα, IL-6, TGFβ, CTGF, and type I and type III collagen) in a tissue- and time-dependent manner. γH2AX phosphorylation stimulated by IR was not affected by lovastatin, indicating that the statin has no major impact on the induction of DNA damage in vivo. Radiation-induced thrombopenia was significantly alleviated by lovastatin. Conclusions Lovastatin inhibits both acute and subchronic IR-induced pro-inflammatory and pro-fibrotic responses and cell death in normal tissue in vivo. Therefore, lovastatin might be useful for selectively attenuating acute and subchronic normal tissue damage caused by radiotherapy.

Modulation of the sensitivity in Chinese hamster cells to photons and fast neutrons by cisplatin, vinblastine, and bleomycin

Normal tissue toxicity resulting from chemoradiotherapy is of significant clinical concern. This study used normal Chinese hamster fibroblasts from lung (V79) and ovary (CHO-K1) to assess the modulation of cellular response to photons and neutrons by cisplatin, vinblastine, and bleomycin. Based on the colony formation assay, the drug concentration corresponding to 50% cell survival (EC50) of V79 cells was 1.50 +/- 0.21 micromol/L for cisplatin, 0.97 +/- 0.06 nmol/L for vinblastine, and 1.68 +/- 0.11 micromol/L for bleomycin. The corresponding values for CHO-K1 cells were significantly lower for vinblastine (0.54 +/- 0.02 nmol/L) and bleomycin (0.49 +/- 0.13 micromol/L), but not for cisplatin (1.57 +/- 0.20 micromol/L). No radiosensitivity enhancement was apparent when cells were exposed to p(66)/Be neutrons or photons (60Co gamma-rays) in the presence of these drugs at EC50 concentrations. These data suggest that concurrent use of these drugs with radiation for the treatment of lung and ovarian diseases radiation does not exacerbate radiation-induced normal tissue toxicity, regardless of the quality of radiation. The relatively higher sensitivity of the ovarian cells to vinblastine and bleomycin might constitute a limitation in the use of these drugs for the treatment of lung lesions.

Orazipone, a locally acting immunomodulator, ameliorates intestinal radiation injury: A preclinical study in a novel rat model

Intestinal radiation injury (radiation enteropathy) is relevant to cancer treatment, as well as to radiation accidents and radiation terrorism scenarios. This study assessed the protective efficacy of orazipone, a locally-acting small molecule immunomodulator. Male rats were orchiectomized, a 4-cm segment of small bowel was sutured to the inside of the scrotum, a proximal anteperistaltic ileostomy was created for intraluminal drug administration, and intestinal continuity was re-established by end-to-side anastomosis. After three weeks postoperative recovery, the intestine in the "scrotal hernia" was exposed locally to single-dose or fractionated X-radiation. Orazipone (30 mg/kg/day) or vehicle was administered daily through the ileostomy, either during and after irradiation, or only after irradiation. Structural, cellular, and molecular aspects of intestinal radiation toxicity were assessed two weeks after irradiation. Orazipone significantly ameliorated histologic injury and transforming growth factor-beta immunoreactivity levels, both after single-dose and fractionated irradiation. Intestinal wall thickness was significantly reduced after single-dose and nonsignificantly after fractionated irradiation. Mucosal surface area and numbers of mast cells were partially restored by orazipone after single-dose irradiation. This work (1) demonstrates the utility of the ileostomy rat model for intraluminal administration of response modifiers in single-dose and fractionated radiation studies; (2) shows that mucosal immunomodulation during and/or after irradiation ameliorates intestinal toxicity; and (3) highlights important differences between single-dose and fractionated radiation regimens.