The emerging role of exosomes in radiotherapy

Extracellular vesicles as the common denominator among the 7 Rs of radiobiology: From the cellular level to clinical practice

Extracellular vesicles (EVs) are lipid-bound particles released by tumor cells and widely explored in cancer development, progression, and treatment response, being considered as valuable components to be explored as biomarkers or cellular targets to modulate the effect of therapies. The mechanisms underlying the production and profile of EVs during radiotherapy (RT) require addressing radiobiological aspects to determine cellular responses to specific radiation doses and fractionation. In this review, we explore the role of EVs in the 7 Rs of radiobiology, known as the molecular basis of a biological tissue response to radiation, supporting EVs as a shared player in all the seven processes. We also highlight the relevance of EVs in the context of liquid biopsy and resistance to immunotherapy, aiming to establish the connection and utility of EVs as tools in contemporary and precision radiotherapy.

Systemic effects of 177Lu-DOTATATE therapy to patients with metastatic neuroendocrine tumors: mechanistic insights and role of exosome

PURPOSE

The present study aimed to evaluate the systemic redox status in metastatic neuroendocrine tumor (NET) patients following 177Lu-DOTATATE therapy and to explore the role of exosomes in communicating the redox signals in-vitro.

METHODS

Levels of reactive oxygen species (ROS), enzymes associated with oxidative stress and lipid peroxidation, gene expression of oxidative stress markers (COX2, iNOS, NF-κB and SOD) were determined in peripheral blood mononuclear cells (PBMCs) and serum isolated from a total of 30 NET subjects at three time points viz.: before, 4 weeks after first and fourth cycle of 177Lu-DOTATATE therapy. Serum cytokine levels (IL-2, IL-6, IFN-γ, TNF-α, IL-4, IL-10 and TGF-β) were measured by ELISA. DNA damage was assessed by checking the expression of γH2AX and DNA repair genes (ATM: Ataxia-Telangiectasia Mutated and ATR: Ataxia-Telangiectasia and Rad3-related). Plasma-derived exosomes were characterized, their uptake by PBMCs was visualized and consequent ROS generation was assessed in in-vitro co-culture.

RESULTS

The study exhibits a significant increase in ROS level and relatively higher expression of COX2 and iNOS in PBMCs of NET patients post therapy. Serum inflammatory cytokines including IL-2, IL-6 and TNF-α were found elevated. The study did not find any change in the expression of genes associated with DNA damage. In-vitro co-culture of PBMCs (isolated before therapy) with exosomes derived after therapy exhibited significant increase in ROS as compared to control cells.

CONCLUSION

The study concludes that 177Lu-DOTATATE therapy alters redox status, however it does not cause DNA damage, suggestive of its safety. Further, the study demonstrates the role of exosomes in spreading of oxidative stress systemically.

Exosomes-mediated CRISPR/Cas delivery: A cutting-edge frontier in cancer gene therapy

Cancer is considered the second most common disease globally. In the past few decades, many approaches have been proposed for cancer treatment. One among those is targeted therapy using CRISPR/Cas system which plays a significant role in translational research through gene editing. However, due to its inability to cope with specific targeting, off-target effects, and limited tumor penetration, it is very challenging to use this approach in cancer studies. To increase its efficacy, CRISPR components are engineered into the extracellular vesicles (EVs), especially exosomes (a subpopulation of EVs). Exosomes have a significant role in cellular communication. Exosomes-based CRISPR/Cas system transport for gene editing enhances specificity, reduces off-target effects, and improves the therapeutic potential. This review highlights the role of exosomes and the CRISPR/Cas system in cancer research, exosomes-based CRISPR delivery for cancer treatment, and its future orientation.

Evaluation of the influence of radiation-induced cohort effect in cell populations receiving different doses

PURPOSE

A non-targeted effect called radiation-induced cohort effect, which results in interactions among irradiated neighboring cells through cellular communication, has been reported. In high-precision radiotherapy, the dose is localized to the tumor, and rapid spatial changes occur in dose distribution. However, the effect of irradiating a population of cells with non-uniform doses remains unknown. In this study, we evaluated the influence of cohort effect by creating cell populations irradiated with different doses using human oral squamous cell carcinoma (SAS) and human lung (A549) cells.

MATERIALS AND METHODS

Cell populations irradiated with different doses were created in two ways: direct contact co-culture (DCC) using a cell tracer dye and indirect contact co-culture (ICC) using cell culture inserts to assess the effects of soluble factors. Target cells were irradiated with 4 Gy and co-cultured cells with 0, 0.8, 3.2, and 4 Gy. In DCC, cell proliferation assays were performed using a flow cytometer, and in ICC, modified high-density survival, clonogenic, and apoptosis assays were performed.

RESULTS

In DCC, irradiation of co-cultured cells with X-rays increased the relative proliferation rate of the target cells. Similarly, irradiating co-cultured cells using ICC with X-rays increased the relative survival rate of target cells.

CONCLUSIONS

The results of this study showed that, even if there is a sharp decrease in dose near the tumor, the cytocidal effect on the tumor is not adversely affected. In addition, soluble factors were found to be involved in cohort effect.

Developing anti-TDE vaccine for sensitizing cancer cells to treatment and metastasis control

Tumor-derived exosomes (TDEs) mediate oncogenic communication, which modifies target cells to reinforce a tumor-promoting microenvironment. TDEs support cancer progression by suppressing anti-tumor immune responses, promoting metastasis, and conferring drug resistance. Thus, targeting TDEs could improve the efficacy of anti-cancer treatments and control metastasis. Current strategies to inhibit TDE-mediated oncogenic communication including drug-based and genetic modification-based inhibition of TDE release and/or uptake, have proved to be inefficient. In this work, we propose TDE surface engineering to express foreign antigens that will trigger life-long anti-TDE immune responses. The possibility of combining the anti-TDE vaccines with other treatments such as chemotherapy, radiotherapy, targeted therapy, and surgery is also explored.

The Effect of Ionising Radiation on the Properties of Tumour-Derived Exosomes and Their Ability to Modify the Biology of Non-Irradiated Breast Cancer Cells-An In Vitro Study

The vast majority of breast cancer patients require radiotherapy but some of them will develop local recurrences and potentially metastases in the future. Recent data show that exosomal cargo is essential in these processes. Thus, we investigated the influence of ionising radiation on exosome properties and their ability to modify the sensitivity and biology of non-irradiated cells. Exosomes were isolated from breast cancer cell lines (MDA-MB-231, MCF7, and SKBR3) irradiated with 2 Gy (Exo 2 Gy) or no irradiation (Exo 0 Gy). Despite some differences in their molecular profiles, they did not affect cell viability, proliferation, cell cycle phase distribution, and radioresistance; however, both populations showed the ability to modify cell migration and invasion potential, as confirmed by the downregulation of β-catenin, which is responsible for maintaining the epithelial phenotype. Interestingly, exosomes from irradiated BCa cells were more actively deposited in the endothelial cells (EA.hy926). Furthermore, exosomes tend to lower the expression of CD31, which is responsible for maintaining intact vascularity. This preliminary study demonstrates the vital role of exosomes and their altered profile due to irradiation in the pathobiology of breast cancer.

Known and unknown: Exosome secretion in tumor microenvironment needs more exploration

Exosomes, extracellular vesicles originating from endosomes, were discovered in the late 1980s and their function in intercellular communication has since garnered considerable interest. Exosomes are lipid bilayer-coated vesicles that range in size from 30 to 150 nm and appear as sacs under the electron microscope. Exosome secretion is crucial for cell-to-cell contact in both normal physiology and the development and spread of tumors. Furthermore, cancer cells can secrete more exosomes than normal cells. Scientists believe that intercellular communication in the complex tissue environment of the human body is an important reason for cancer cell invasion and metastasis. For example, some particles containing regulatory molecules are secreted in the tumor microenvironment, including exosomes. Then the contents of exosomes can be released by donor cells into the environment and interact with recipient cells to promote the migration and invasion of tumor cells. Therefore, in this review, we summarized the biogenesis of exosome, as well as exosome cargo and related roles. More importantly, this review introduces and discusses the factors that have been reported to affect exosome secretion in tumors and highlights the important role of exosomes in tumors.

Radiation-Induced Tumor-Derived Extracellular Vesicles Combined with Tyrosine Kinase Inhibitors: An Effective and Safe Therapeutic Approach for Lung Adenocarcinoma with EGFR19Del

BACKGROUND

Combining radiotherapy with targeted therapy benefits patients with advanced epidermal growth factor receptor-mutated non-small cell lung cancer (EGFRm NSCLC). However, the optimal strategy to combine EGFR tyrosine kinase inhibitors (TKIs) with radiotherapy for maximum efficacy and minimal toxicity is still uncertain. Notably, EVs, which serve as communication mediators among tumor cells, play a crucial role in the anti-tumor immune response. Methods To exploit the role of EVs in the delivery of tumor antigens, we formulated a therapeutic strategy that involves the use of radiation-induced tumor-derived EVs (TEXs) loaded onto dendritic cells (DCs) as a kind of vaccine in conjunction with EGFR TKIs and assessed the efficacy and safety of this approach in the treatment of EGFRm NSCLC. Results In our study, we characterized the release of immunogens as influenced by various modes of cell death, examining the impact of different levels of cell death under diverse irradiation modalities. Our results demonstrated that a radiation mode of 6Gy*3f exhibited the most promising potential to stimulate anti-tumor immune responses. This radiotherapy fraction, combined with TKIs, showed promising results in a tumor-bearing mouse model with an EGFR mutation, although there is a risk of radiation-associated pneumonitis. Furthermore, we found that 6Gy*3f-TEXs in vitro activate DCs and promote T cell proliferation as well as cytotoxic T lymphocyte-mediated tumor cell destruction. The administration of EGFR-TKIs combined DCs loaded with 6Gy*3f-TEXs exhibited the potential to inhibit tumor growth and mitigate the risk of pneumonitis. Together, the research shows that TEXs from high-dose fractionation radiation can mature DCs and boost the killing of cytotoxic T lymphocytes. Combining these DC vaccines with Osimertinib offers a promising and safe treatment for EGFRm NSCLC.

Exosomes: intriguing mediators of intercellular communication in the organism's response to noxious agents

Exosomes are small extracellular vesicles that range from 30 to 150 nm in size and are formed through cellular endocytosis. They consist of proteins, lipids, and nucleic acids at varying ratios and quantities. The composition and spatiotemporal dynamics of exosomes suggest that they play a crucial role in intercellular communication. The information conveyed by exosomes significantly impacts the regulation of health and disease states in the organism. The term "noxious" refers to all harmful environmental agents and conditions that can disrupt the physiological equilibrium and induce pathological states, regardless whether of radiological, biological, or chemical origin. This review comprehensively examines the presence of such noxious agents within the organism in relation to exosome formation and function. Furthermore, it explores the cause-effect relationship between noxious agents and exosomes, aiming to restore physiological homeostasis and prepare the organism for defence against harmful agents. Regardless of the specific bioinformatic content associated with each noxious agent, synthesis of data on the interactions between various types of noxious agents and exosomes reveals that an organized defence against these agents is unachievable without the support of exosomes. Consequently, exosomes are identified as the primary communication and information system within an organism, with their content being pivotal in maintaining the health-disease balance.

Recent Advances of Small Extracellular Vesicles for the Regulation and Function of Cancer-Associated Fibroblasts

Cancer-associated fibroblasts (CAFs) are a heterogeneous cell population in the tumor microenvironment (TME) that critically affect cancer progression. Small extracellular vesicles (sEVs) act as information messengers by transmitting a wide spectrum of biological molecules, including proteins, nucleic acids, and metabolites, from donor cells to recipient cells. Previous studies have demonstrated that CAFs play important roles in tumor progression by regulating tumor cell proliferation, metastasis, therapeutic resistance, and metabolism via sEVs. In turn, tumor-derived sEVs can also regulate the activation and phenotype switch of CAFs. The dynamic crosstalk between CAFs and cancer cells via sEVs could ultimately determine cancer progression. In this review, we summarized the recent advance of the biological roles and underlying mechanisms of sEVs in mediating CAF-tumor cell interaction and its impact on cancer progression. We also reviewed the clinical applications of tumor- and CAF-derived sEVs, which could identify novel potential targets and biomarkers for cancer diagnosis, therapy, and prognosis.

Radioresistance and brain metastases: a review of the literature and applied perspective

Intracranial metastatic disease is a serious complication of cancer, treated through surgery, radiation, and targeted therapies. The central role of radiation therapy makes understanding the radioresistance of metastases a priori a key interest for prognostication and therapeutic development. Although historically defined clinic-radiographically according to tumour response, developments in new techniques for delivering radiation treatment and understanding of radioprotective mechanisms led to a need to revisit the definition of radioresistance in the modern era. Factors influencing radioresistance include tumour-related factors (hypoxia, cancer stem cells, tumour kinetics, tumour microenvironment, metabolic alterations, tumour heterogeneity DNA damage repair, non-coding RNA, exosomes, methylomes, and autophagy), host-related factors (volume effect & dose-limiting non-cancerous tissue, pathophysiology, and exosomes), technical factors, and probabilistic factors (cell cycle and random gravity of DNA damage). Influences on radioresistance are introduced and discussed in the context of brain metastases.

Exosomes as Vehicles for Noncoding RNA in Modulating Inflammation: A Promising Regulatory Approach for Ischemic Stroke and Myocardial Infarction

Exosomes have grown as promising carriers for noncoding RNAs (ncRNAs) in the treatment of inflammation, particularly in conditions like ischemic stroke and myocardial infarction. These ncRNAs, which include microRNAs (miRNAs) and long noncoding RNAs (lncRNAs), play a crucial role in regulating inflammatory pathways, presenting new therapeutic opportunities. In both ischemic stroke and myocardial infarction, inflammation significantly influences disease progression and severity. Exosomes can deliver ncRNAs directly to specific cells and tissues, providing a targeted approach to modulate gene expression and reduce inflammation. Their biocompatibility and low risk of inducing immune responses make exosomes ideal therapeutic vehicles. Ongoing research is focused on optimizing the loading of ncRNAs into exosomes, ensuring efficient delivery, and understanding the mechanisms by which these ncRNAs mitigate inflammation. In ischemic stroke, exosome-derived ncRNAs originate from various cell types, including neurons, M2 microglia, patient serum, genetically engineered HEK293T cells, and mesenchymal stromal cells. In the case of myocardial infarction, these ncRNAs are sourced from mesenchymal stem cells, endothelial cells, and patient plasma. These exosome-loaded ncRNAs play a significant role in modulating inflammation in both ischemic stroke and myocardial infarction. As this research advances, therapies based on exosomes may completely change how diseases linked to inflammation are treated, offering new avenues for patient care and recovery. This review explores the latest advancements in understanding how exosomes impact specific inflammatory components, with a particular emphasis on the role of ncRNAs contained in exosomes. The review concludes by highlighting the clinical potential of exosome-derived ncRNAs as innovative therapeutic and diagnostic tools.

Particle Beam Radiobiology Status and Challenges: A PTCOG Radiobiology Subcommittee Report

Particle therapy (PT) represents a significant advancement in cancer treatment, precisely targeting tumor cells while sparing surrounding healthy tissues thanks to the unique depth-dose profiles of the charged particles. Furthermore, their linear energy transfer and relative biological effectiveness enhance their capability to treat radioresistant tumors, including hypoxic ones. Over the years, extensive research has paved the way for PT's clinical application, and current efforts aim to refine its efficacy and precision, minimizing the toxicities. In this regard, radiobiology research is evolving toward integrating biotechnology to advance drug discovery and radiation therapy optimization. This shift from basic radiobiology to understanding the molecular mechanisms of PT aims to expand the therapeutic window through innovative dose delivery regimens and combined therapy approaches. This review, written by over 30 contributors from various countries, provides a comprehensive look at key research areas and new developments in PT radiobiology, emphasizing the innovations and techniques transforming the field, ranging from the radiobiology of new irradiation modalities to multimodal radiation therapy and modeling efforts. We highlight both advancements and knowledge gaps, with the aim of improving the understanding and application of PT in oncology.

Mediation of radiation-induced bystander effect and epigenetic modification: The role of exosomes in cancer radioresistance

Exosomes are nano-sized extracellular vesicles produced by almost all mammalian cells. They play an important role in cell-to-cell communication by transferring biologically active molecules from the cell of origin to the recipient cells. Ionizing radiation influences exosome production and molecular cargo loading. In cancer management, ionizing radiation is a form of treatment that exerts its cancer cytotoxicity by induction of DNA damage and other alterations to the targeted tissue cells. However, normal bystander non-targeted cells may exhibit the effects of ionizing radiation, a phenomenon called radiation-induced bystander effect (RIBE). The mutual communication between the two groups of cells (targeted and non-targeted) via radiation-influenced exosomes enables the exchange of radiosensitive molecules. This facilitates indirect radiation exposure, leading, among other effects, to epigenetic remodeling and subsequent adaptation to radiation. This review discusses the role exosomes play in epigenetically induced radiotherapy resistance through the mediation of RIBE.

Role of Exosomes in Cancer and Aptamer-Modified Exosomes as a Promising Platform for Cancer Targeted Therapy

Exosomes are increasingly recognized as important mediators of intercellular communication in cancer biology. Exosomes can be derived from cancer cells as well as cellular components in tumor microenvironment. After secretion, the exosomes carrying a wide range of bioactive cargos can be ingested by local or distant recipient cells. The released cargos act through a variety of mechanisms to elicit multiple biological effects and impact most if not all hallmarks of cancer. Moreover, owing to their excellent biocompatibility and capability of being easily engineered or modified, exosomes are currently exploited as a promising platform for cancer targeted therapy. In this review, we first summarize the current knowledge of roles of exosomes in risk and etiology, initiation and progression of cancer, as well as their underlying molecular mechanisms. The aptamer-modified exosome as a promising platform for cancer targeted therapy is then briefly introduced. We also discuss the future directions for emerging roles of exosome in tumor biology and perspective of aptamer-modified exosomes in cancer therapy.

Novel Blood Biomarkers for Response Prediction and Monitoring of Stereotactic Ablative Radiotherapy and Immunotherapy in Metastatic Oligoprogressive Lung Cancer

Up to 80% of patients under immune checkpoint inhibitors (ICI) face resistance. In this context, stereotactic ablative radiotherapy (SABR) can induce an immune or abscopal response. However, its molecular determinants remain unknown. We present early results of a translational study assessing biomarkers of response to combined ICI and SABR (I-SABR) in liquid biopsy from oligoprogressive patients in a prospective observational multicenter study. Cohort A includes metastatic patients in oligoprogression to ICI maintaining the same ICI due to clinical benefit and who receive concomitant SABR. B is a comparative group of oligometastatic patients receiving only SABR. Blood samples are extracted at baseline (T1), after the first (T2) and last (T3) fraction, two months post-SABR (T4) and at further progression (TP). Response is evaluated by iRECIST and defined by the objective response rate (ORR)-complete and partial responses. We assess peripheral blood mononuclear cells (PBMCs), circulating cell-free DNA (cfDNA) and small RNA from extracellular vesicles. Twenty-seven patients could be analyzed (cohort A: n = 19; B: n = 8). Most were males with non-small cell lung cancer and one progressing lesion. With a median follow-up of 6 months, the last ORR was 63% (26% complete and 37% partial response). A decrease in cfDNA from T2 to T3 correlated with a good response. At T2, CD8+PD1+ and CD8+PDL1+ cells were increased in non-responders and responders, respectively. At T2, 27 microRNAs were differentially expressed. These are potential biomarkers of response to I-SABR in oligoprogressive disease.

Shooting the messenger: a systematic review investigating extracellular vesicle isolation and characterisation methods and their influence on understanding extracellular vesicles-radiotherapy interactions in glioblastoma

BACKGROUND

Extracellular vesicles (EVs) hold promise for improving our understanding of radiotherapy response in glioblastoma due to their role in intercellular communication within the tumour microenvironment (TME). However, methodologies to study EVs are evolving with significant variation within the EV research community.

METHODS

We conducted a systematic review to critically appraise EV isolation and characterisation methodologies and how this influences our understanding of the findings from studies investigating radiotherapy and EV interactions in glioblastoma. 246 articles published up to 24/07/2023 from PubMed and Web of Science were identified using search parameters related to radiotherapy, EVs, and glioblastoma. Two reviewers evaluated study eligibility and abstracted data.

RESULTS

In 26 articles eligible for inclusion (16 investigating the effects of radiotherapy on EVs, five investigating the effect of EVs on radiation response, and five clinical studies), significant heterogeneity and frequent omission of key characterisation steps was identified, reducing confidence that the results are related to EVs and their cargo as opposed to co-isolated bioactive molecules. However, the results are able to clearly identify interactions between EVs and radiotherapy bi-directionally within different cell types within the glioblastoma TME. These interactions facilitate transferable radioresistance and oncogenic signalling, highlighting that EVs are an important component in the variability of glioblastoma radiotherapy response.

CONCLUSIONS

Future multi-directional investigations interrogating the whole TME are required to improve subsequent clinical translation, and all studies should incorporate up to date controls and reporting requirements to increase the validity of their findings. This would be facilitated by increased collaboration between less experienced and more experienced EV research groups.

Dual effects of radiotherapy on tumor microenvironment and its contribution towards the development of resistance to immunotherapy in gastrointestinal and thoracic cancers

Successful clinical methods for tumor elimination include a combination of surgical resection, radiotherapy, and chemotherapy. Radiotherapy is one of the crucial components of the cancer treatment regimens which allow to extend patient life expectancy. Current cutting-edge radiotherapy research is focused on the identification of methods that should increase cancer cell sensitivity to radiation and activate anti-cancer immunity mechanisms. Radiation treatment activates various cells of the tumor microenvironment (TME) and impacts tumor growth, angiogenesis, and anti-cancer immunity. Radiotherapy was shown to regulate signaling and anti-cancer functions of various TME immune and vasculature cell components, including tumor-associated macrophages, dendritic cells, endothelial cells, cancer-associated fibroblasts (CAFs), natural killers, and other T cell subsets. Dual effects of radiation, including metastasis-promoting effects and activation of oxidative stress, have been detected, suggesting that radiotherapy triggers heterogeneous targets. In this review, we critically discuss the activation of TME and angiogenesis during radiotherapy which is used to strengthen the effects of novel immunotherapy. Intracellular, genetic, and epigenetic mechanisms of signaling and clinical manipulations of immune responses and oxidative stress by radiotherapy are accented. Current findings indicate that radiotherapy should be considered as a supporting instrument for immunotherapy to limit the cancer-promoting effects of TME. To increase cancer-free survival rates, it is recommended to combine personalized radiation therapy methods with TME-targeting drugs, including immune checkpoint inhibitors.

Cancer Stem Cells and Glioblastoma: Time for Innovative Biomarkers of Radio-Resistance?

Despite countless papers in the field of radioresistance, researchers are still far from clearly understanding the mechanisms triggered in glioblastoma. Cancer stem cells (CSC) are important to the growth and spread of cancer, according to many studies. In addition, more recently, it has been suggested that CSCs have an impact on glioblastoma patients' prognosis, tumor aggressiveness, and treatment outcomes. In reviewing this new area of biology, we will provide a summary of the most recent research on CSCs and their role in the response to radio-chemotherapy in GB. In this review, we will examine the radiosensitivity of stem cells. Moreover, we summarize the current knowledge of the biomarkers of stemness and evaluate their potential function in the study of radiosensitivity.

Connection between Radiation-Regulating Functions of Natural Products and miRNAs Targeting Radiomodulation and Exosome Biogenesis

Exosomes are cell-derived membranous structures primarily involved in the delivery of the payload to the recipient cells, and they play central roles in carcinogenesis and metastasis. Radiotherapy is a common cancer treatment that occasionally generates exosomal miRNA-associated modulation to regulate the therapeutic anticancer function and side effects. Combining radiotherapy and natural products may modulate the radioprotective and radiosensitizing responses of non-cancer and cancer cells, but there is a knowledge gap regarding the connection of this combined treatment with exosomal miRNAs and their downstream targets for radiation and exosome biogenesis. This review focuses on radioprotective natural products in terms of their impacts on exosomal miRNAs to target radiation-modulating and exosome biogenesis (secretion and assembly) genes. Several natural products have individually demonstrated radioprotective and miRNA-modulating effects. However, the impact of natural-product-modulated miRNAs on radiation response and exosome biogenesis remains unclear. In this review, by searching through PubMed/Google Scholar, available reports on potential functions that show radioprotection for non-cancer tissues and radiosensitization for cancer among these natural-product-modulated miRNAs were assessed. Next, by accessing the miRNA database (miRDB), the predicted targets of the radiation- and exosome biogenesis-modulating genes from the Gene Ontology database (MGI) were retrieved bioinformatically based on these miRNAs. Moreover, the target-centric analysis showed that several natural products share the same miRNAs and targets to regulate radiation response and exosome biogenesis. As a result, the miRNA-radiomodulation (radioprotection and radiosensitization)-exosome biogenesis axis in regard to natural-product-mediated radiotherapeutic effects is well organized. This review focuses on natural products and their regulating effects on miRNAs to assess the potential impacts of radiomodulation and exosome biogenesis for both the radiosensitization of cancer cells and the radioprotection of non-cancer cells.

Low-Dose Non-Targeted Effects and Mitochondrial Control

Non-targeted effects (NTE) have been generally regarded as a low-dose ionizing radiation (IR) phenomenon. Recently, regarding long distant abscopal effects have also been observed at high doses of IR) relevant to antitumor radiation therapy. IR is inducing NTE involving intracellular and extracellular signaling, which may lead to short-ranging bystander effects and distant long-ranging extracellular signaling abscopal effects. Internal and "spontaneous" cellular stress is mostly due to metabolic oxidative stress involving mitochondrial energy production (ATP) through oxidative phosphorylation and/or anaerobic pathways accompanied by the leakage of O₂^- and other radicals from mitochondria during normal or increased cellular energy requirements or to mitochondrial dysfunction. Among external stressors, ionizing radiation (IR) has been shown to very rapidly perturb mitochondrial functions, leading to increased energy supply demands and to ROS/NOS production. Depending on the dose, this affects all types of cell constituents, including DNA, RNA, amino acids, proteins, and membranes, perturbing normal inner cell organization and function, and forcing cells to reorganize the intracellular metabolism and the network of organelles. The reorganization implies intracellular cytoplasmic-nuclear shuttling of important proteins, activation of autophagy, and mitophagy, as well as induction of cell cycle arrest, DNA repair, apoptosis, and senescence. It also includes reprogramming of mitochondrial metabolism as well as genetic and epigenetic control of the expression of genes and proteins in order to ensure cell and tissue survival. At low doses of IR, directly irradiated cells may already exert non-targeted effects (NTE) involving the release of molecular mediators, such as radicals, cytokines, DNA fragments, small RNAs, and proteins (sometimes in the form of extracellular vehicles or exosomes), which can induce damage of unirradiated neighboring bystander or distant (abscopal) cells as well as immune responses. Such non-targeted effects (NTE) are contributing to low-dose phenomena, such as hormesis, adaptive responses, low-dose hypersensitivity, and genomic instability, and they are also promoting suppression and/or activation of immune cells. All of these are parts of the main defense systems of cells and tissues, including IR-induced innate and adaptive immune responses. The present review is focused on the prominent role of mitochondria in these processes, which are determinants of cell survival and anti-tumor RT.

Radiotherapy-induced tumor physical microenvironment remodeling to overcome immunotherapy resistance

The clinical benefits of immunotherapy are proven in many cancers, but a significant number of patients do not respond well to immunotherapy. The tumor physical microenvironment (TpME) has recently been shown to affect the growth, metastasis and treatment of solid tumors. The tumor microenvironment (TME) has unique physical hallmarks: 1) unique tissue microarchitecture, 2) increased stiffness, 3) elevated solid stress, and 4) elevated interstitial fluid pressure (IFP), which contribute to tumor progression and immunotherapy resistance in a variety of ways. Radiotherapy, a traditional and powerful treatment, can remodel the matrix and blood flow associated with the tumor to improve the response rate of immune checkpoint inhibitors (ICIs) to a certain extent. Herein, we first review the recent research advances on the physical properties of the TME and then explain how TpME is involved in immunotherapy resistance. Finally, we discuss how radiotherapy can remodel TpME to overcome immunotherapy resistance.