High linear energy transfer carbon-ion irradiation increases the release of the immune mediator high mobility group box 1 from human cancer cells

Experimental evidence that carbon-ion radiotherapy utilizes cytotoxic T lymphocyte-mediated anti-tumor immunity for shrinking tumors compared to X-ray therapy

The therapeutic efficacy of radiotherapy (RT) is primarily driven by two factors: biophysical DNA damage in cancer cells and radiation-induced anti-tumor immunity. However, Anti-tumor immune responses between X-ray RT (XRT) and carbon-ion RT (CIRT) remain unclear. In this study, we, employed mouse models to assess the immunological contribution, especially cytotoxic T-lymphocyte (CTL)-mediated immunity, to the therapeutic effectiveness of XRT and CIRT in shrinking tumors. We irradiated mouse intradermal tumors of B16F10-ovalbumin (OVA) mouse melanoma cells and 3LL-OVA mouse lung cancer cells with carbon-ion beams or X-rays in the presence or absence of CTLs. CTL removal was performed by administration of anti-CD8 monoclonal antibody (mAb) in mice. Based on tumor growth delay, we determined the tumor growth and regression curves. The enhancement ratio (ER) of the slope of regression lines in the presence of CTLs, relative to the absence of CTLs, indicates the dependency of RT on CTLs for shrinking mouse tumors, and the biological effectiveness (RBE) of CIRT relative to XRT were calculated. Tumor growth curves revealed that the elimination of CD8+ CTLs by administrating anti-CD8 mAb accelerated tumor growth compared to the presence of CTLs in both RTs. The ERs were larger in CIRT compared to XRT in the B16F10-OVA tumor models, but not in the 3LL-OVA models, suggesting a greater contribution of CTL-mediated anti-tumor immunity to tumor reduction in CIRT compared to XRT in the B16F10-OVA tumor model. In addition, the RBE values for both models were larger in the presence of CTLs compared to models without CTLs, suggesting that CIRT may utilize CTL-mediated anti-tumor immunity more than X-ray. The findings from this study suggest that although immunological contribution to therapeutic efficacy may vary depending on the type of tumor cell, CIRT utilizes CTL-mediated immunity to a greater extent compared to XRT.

Killing two birds with one stone: Abscopal effect mechanism and its application prospect in radiotherapy

Abscopal effects are characterized by the emergence of neoplasms in regions unrelated to the primary radiation therapy site, displaying a gradual attenuation or regression throughout the progression of radiation therapy, which have been of interest to scientists since Mole's proposal in 1953. The incidence of abscopal effects in radiation therapy is intricately linked to the immune system, with both innate and adaptive immune responses playing crucial roles. Biological factors impacting abscopal effects ultimately exert their influence on the intricate workings of the immune system. Although abscopal effects are rarely observed in clinical cases, the underlying mechanism remains uncertain. This article examines the biological and physical factors influencing abscopal effects of radiotherapy. Through a review of preclinical and clinical studies, this article aims to offer a comprehensive understanding of abscopal effects and proposes new avenues for future research in this field. The findings presented in this article serve as a valuable reference for researchers seeking to explore this topic in greater depth.

MHY1485 potentiates immunogenic cell death induction and anti-cancer immunity following irradiation

Recent in vitro experiments showed that combined treatment with MHY1485, a low-molecular-weight compound, and X-ray irradiation significantly increased apoptosis and senescence in tumor cells, which was associated with oxidative stress, endoplasmic reticulum (ER) stress and p21 stabilization, compared to radiation treatment alone. However, evidence for MHY1485 treatment-mediated suppression of tumor growth in animals is still lacking. Furthermore, it has been shown that ER stress enhances immunogenic cell death (ICD) in tumor cells, as it can exert a favorable influence on the anti-cancer immune system. In the present study, we examined whether co-treatment of MHY1485 and X-ray irradiation induces ICD and in vivo tumor growth suppression using the CT26 and Lewis lung carcinoma murine tumor cell lines. We found that MHY1485 + X-ray treatment promotes ICD more effectively than X-ray treatment alone. MHY1485 suppresses tumor growth in vivo under co-treatment with X-rays and increases INF-γ, tumor necrosis factor, interleukin-2 and interleukin-12 levels in the spleen as well as the presence of CD8+ cells in the tumor. The results suggest that MHY1485 treatment leads to the conversion of irradiated tumors into effective vaccines. Thus, MHY1485 is a promising lead compound for use in combination with radiotherapy.

Carbon ion irradiation combined with PD-1 inhibitor trigger abscopal effect in Lewis lung cancer via a threshold dose

Background and goal: Carbon ion beam is radio-biologically more efficient than photons and is beneficial for treating radio-resistant tumors. Several animal experiments with tumor-bearing suggest that carbon ion beam irradiation in combination with immunotherapy yields better results, especially in controlling distant metastases. This implies that carbon ion induces a different anti-tumor immune response than photon beam. More complex molecular mechanisms need to be uncovered. This in vivo and in vitro experiment was carried out in order to examine the radio-immune effects and the mechanism of action of carbon ion beam versus X-ray in combination with PD-1 inhibitors. Methods and Materials: Lewis lung adenocarcinoma cells and C57BL/6 mice were used to create a tumor-bearing mouse model, with the non-irradiated tumor growing on the right hind leg and the irradiated tumor on the left rear. 10Gy carbon ion beam or X-ray radiation, either alone or in combination with PD-1 inhibitor, were used to treat the left back tumor. The expression of molecules linked to immunogenicity and the infiltration of CD8+ T lymphocytes into tumor tissues were both identified using immunohistochemistry. IFN-β in mouse serum was measured using an ELISA, while CD8+ T cells in mouse peripheral blood were measured using flow cytometry. Lewis cells were exposed to different dose of X-ray and carbon ion. TREX1, PD-L1, and IFN-β alterations in mRNA and protein levels were identified using Western blot or RT-PCR, respectively. TREX1 knockdown was created by siRNA transfection and exposed to various radiations. Using the CCK8 test, EdU assay, and flow cytometry, changes in cell viability, proliferation, and apoptosis rate were discovered. Results: Bilateral tumors were significantly inhibited by the use of carbon ion or X-ray in combination with PD-1, particularly to non-irradiated tumor(p<0.05). The percentage of infiltrating CD8+ T cells and the level of IFN-β expression were both raised by 10Gy carbon ion irradiation in the irradiated side tumor, although PD-L1 and TREX1 expression levels were also elevated. Lewis cell in vitro experiment further demonstrated that both X-ray and carbon ion irradiation can up-regulate the expression levels of PD-L1 and TREX1 with dose-dependent in tumors, particularly the trend of up-regulation TREX1 is more apparent at a higher dose in carbon ion, i.e. 8 or 10Gy, while the level of IFN-β is decreased. IFN-β levels were considerably raised under hypofractionated doses of carbon ion radiation by gene silencing TREX1. Conclusions: By enhancing tumor immunogenicity and increasing CD8+T infiltration in TME through a threshold dosage, X-ray or carbon ion radiation and PD-1 inhibitors improve anti-tumor activity and cause abscopal effect in Lewis lung adenocarcinoma-bearing mice. TREX1 is a possible therapeutic target and prognostic marker.

High-LET charged particles: radiobiology and application for new approaches in radiotherapy

The number of patients treated with charged-particle radiotherapy as well as the number of treatment centers is increasing worldwide, particularly regarding protons. However, high-linear energy transfer (LET) particles, mainly carbon ions, are of special interest for application in radiotherapy, as their special physical features result in high precision and hence lower toxicity, and at the same time in increased efficiency in cell inactivation in the target region, i.e., the tumor. The radiobiology of high-LET particles differs with respect to DNA damage repair, cytogenetic damage, and cell death type, and their increased LET can tackle cells' resistance to hypoxia. Recent developments and perspectives, e.g., the return of high-LET particle therapy to the US with a center planned at Mayo clinics, the application of carbon ion radiotherapy using cost-reducing cyclotrons and the application of helium is foreseen to increase the interest in this type of radiotherapy. However, further preclinical research is needed to better understand the differential radiobiological mechanisms as opposed to photon radiotherapy, which will help to guide future clinical studies for optimal exploitation of high-LET particle therapy, in particular related to new concepts and innovative approaches. Herein, we summarize the basics and recent progress in high-LET particle radiobiology with a focus on carbon ions and discuss the implications of current knowledge for charged-particle radiotherapy. We emphasize the potential of high-LET particles with respect to immunogenicity and especially their combination with immunotherapy.

Particle radiotherapy in the era of radioimmunotherapy

Radiotherapy (RT) is one of the key modalities for cancer treatment, and more than 70% of tumor patients will receive RT during the course of their disease. Particle radiotherapy, such as proton radiotherapy, carbon-ion radiotherapy (CIRT) and boron neutron capture therapy (BNCT), is currently available for the treatment of patients Immunotherapy combined with photon RT has been successfully used in the clinic. The effect of immunotherapy combined with particle RT is an area of interest. However, the molecular mechanisms underlying the effects of combined immunotherapy and particle RT remain largely unknown. In this review, we summarize the properties of different types of particle RT and the mechanisms underlying their radiobiological effects. Additionally, we compared the main molecular players in photon RT and particle RT and the mechanisms involved the RT-mediated immune response.

Emerging evidence for adapting radiotherapy to immunotherapy

Immunotherapy has revolutionized the clinical management of many malignancies but is infrequently associated with durable objective responses when used as a standalone treatment approach, calling for the development of combinatorial regimens with superior efficacy and acceptable toxicity. Radiotherapy, the most commonly used oncological treatment, has attracted considerable attention as a combination partner for immunotherapy owing to its well-known and predictable safety profile, widespread clinical availability, and potential for immunostimulatory effects. However, numerous randomized clinical trials investigating radiotherapy-immunotherapy combinations have failed to demonstrate a therapeutic benefit compared with either modality alone. Such a lack of interaction might reflect suboptimal study design, choice of end points and/or administration of radiotherapy according to standard schedules and target volumes. Indeed, radiotherapy has empirically evolved towards radiation doses and fields that enable maximal cancer cell killing with manageable toxicity to healthy tissues, without much consideration of potential radiation-induced immunostimulatory effects. Herein, we propose the concept that successful radiotherapy-immunotherapy combinations might require modifications of standard radiotherapy regimens and target volumes to optimally sustain immune fitness and enhance the antitumour immune response in support of meaningful clinical benefits.

Immunomodulatory Macrophages Enable E-MNC Therapy for Radiation-Induced Salivary Gland Hypofunction

A newly developed therapy using effective-mononuclear cells (E-MNCs) is reportedly effective against radiation-damaged salivary glands (SGs) due to anti-inflammatory and revascularization effects. However, the cellular working mechanism of E-MNC therapy in SGs remains to be elucidated. In this study, E-MNCs were induced from peripheral blood mononuclear cells (PBMNCs) by culture for 5-7 days in medium supplemented with five specific recombinant proteins (5G-culture). We analyzed the anti-inflammatory characteristics of macrophage fraction of E-MNCs using a co-culture model with CD3/CD28-stimulated PBMNCs. To test therapeutic efficacy in vivo, either E-MNCs or E-MNCs depleted of CD11b-positive cells were transplanted intraglandularly into mice with radiation-damaged SGs. Following transplantation, SG function recovery and immunohistochemical analyses of harvested SGs were assessed to determine if CD11b-positive macrophages contributed to tissue regeneration. The results indicated that CD11b/CD206-positive (M2-like) macrophages were specifically induced in E-MNCs during 5G-culture, and Msr1- and galectin3-positive cells (immunomodulatory macrophages) were predominant. CD11b-positive fraction of E-MNCs significantly inhibited the expression of inflammation-related genes in CD3/CD28-stimulated PBMNCs. Transplanted E-MNCs exhibited a therapeutic effect on saliva secretion and reduced tissue fibrosis in radiation-damaged SGs, whereas E-MNCs depleted of CD11b-positive cells and radiated controls did not. Immunohistochemical analyses revealed HMGB1 phagocytosis and IGF1 secretion by CD11b/Msr1-positive macrophages from both transplanted E-MNCs and host M2-macrophages. Thus, the anti-inflammatory and tissue-regenerative effects observed in E-MNC therapy against radiation-damaged SGs can be partly explained by the immunomodulatory effect of M2-dominant macrophage fraction.

Efficacy of immune checkpoint inhibitor treatment for head and neck mucosal melanoma recurrence in patients treated with carbon-ion radiotherapy

BACKGROUND

Carbon-ion radiotherapy (C-ion RT) is effective for head and neck mucosal melanoma (HN-MM), including radioresistant mucosal melanoma. Melanoma also responds effectively to immune checkpoint inhibitors (ICIs). Data on the efficacy and safety of ICIs for HN-MM are insufficient.

AIMS

To analyze the efficacy and safety of ICI salvage therapy in patients with HN-MM recurrence after C-ion RT.

METHODS AND RESULTS

This retrospective study analyzed the medical records of 52 patients with HN-MM treated with C-ion RT between 2012 and 2020. A dose of 57.6 or 64.0 Gy (relative biological effectiveness) was provided in 16 fractions. The primary endpoint was 3-year overall survival (OS) rate. The median follow-up time was 26.8 months for all patients. A total of 29 patients had local recurrence or distant metastasis, and 16 patients who received ICI therapy. The 3-year OS rate in the ICI group (n = 16) and best supportive care group (n = 13) were 53.8% and 0.0%, respectively (p = 0.837); the difference was not statistically significant. There were no deaths after 1 year among patients who underwent ICI therapy. No adverse events associated with C-ion RT were related to or exacerbated by ICI.

CONCLUSION

ICI salvage therapy is effective and safe for patients with HN-MM recurrence after C-ion RT.

Immunotherapy progress and clinical strategy of unresectable locally advanced non-small cell lung cancer

Non-small cell lung cancer negative for actionable molecular markers entered the splendid era of immunotherapy. This review aims to provide an evidence-based summary for immunotherapy for unresectable locally advanced non-small cell lung cancer, and references for clinical strategies of immunotherapy. Through literature review, the standard treatment for unresectable locally advanced non-small cell lung cancer should be radical concurrent radiotherapy and chemotherapy followed by consolidation immunotherapy. However, the efficacy of concurrent radiotherapy, chemotherapy combined with immunotherapy has not been improved, and its safety should be further validated. It is believed that induction immunotherapy plus concurrent radiotherapy and chemotherapy plus consolidation immunotherapy is promising. In clinical practice, the delineation of radiotherapy target should be relatively small. Pemetrexed combined with PD-1 inhibitor induces the strongest immunogenicity in chemotherapy, which is suggested by preclinical pathway study. Although there is no significant difference between PD1 and PD1 for effect, PD-L1 inhibitor is better in the combination treatment of radiotherapy which presents significantly less adverse events.

Are charged particles a good match for combination with immunotherapy? Current knowledge and perspectives

Charged particle radiotherapy, mainly using protons and carbon ions, provides physical characteristics allowing for a volume conformal irradiation and a reduction of the integral dose to normal tissue. Carbon ion therapy additionally features an increased biological effectiveness resulting in peculiar molecular effects. Immunotherapy, mostly performed with immune checkpoint inhibitors, is nowadays considered a pillar in cancer therapy. Based on the advantageous features of charged particle radiotherapy, we review pre-clinical evidence revealing a strong potential of its combination with immunotherapy. We argue that the combination therapy deserves further investigation with the aim of translation in clinics, where a few studies have been set up already.

A Consistent Protocol Reveals a Large Heterogeneity in the Biological Effectiveness of Proton and Carbon-Ion Beams for Various Sarcoma and Normal-Tissue-Derived Cell Lines

Simple Summary

Using a consistent experimental protocol, we found a large heterogeneity in the relative biological effectiveness (RBE) values of both proton and carbon-ion beams in various sarcomas and normal-tissue-derived cell lines. Our data suggest that proton beam therapy may be more beneficial for some types of tumors. In carbon-ion therapy, for some types of tumors, large heterogeneity in RBE should prompt consideration of dose reduction or an increased dose per fraction. In particular, a higher RBE value in normal tissues requires caution. Specific dose evaluations for tumor and normal tissues are needed for both proton and carbon-ion therapies.

Abstract

This study investigated variations in the relative biological effectiveness (RBE) values among various sarcoma and normal-tissue-derived cell lines (normal cell line) in proton beam and carbon-ion irradiations. We used a consistent protocol that specified the timing of irradiation after plating cells and detailed the colony formation assay. We examined the cell type dependence of RBE for proton beam and carbon-ion irradiations using four human sarcoma cell lines (MG63 osteosarcoma, HT1080 fibrosarcoma, SW872 liposarcoma, and SW1353 chondrosarcoma) and three normal cell lines (HDF human dermal fibroblast, hTERT-HME1 mammary gland, and NuLi-1 bronchus epithelium). The cells were irradiated with gamma rays, proton beams at the center of the spread-out Bragg peak, or carbon-ion beams at 54.4 keV/μm linear energy transfer. In all sarcoma and normal cell lines, the average RBE values in proton beam and carbon-ion irradiations were 1.08 ± 0.11 and 2.08 ± 0.36, which were consistent with the values of 1.1 and 2.13 used in current treatment planning systems, respectively. Up to 34% difference in the RBE of the proton beam was observed between MG63 and HT1080. Similarly, a 32% difference in the RBE of the carbon-ion beam was observed between SW872 and the other sarcoma cell lines. In proton beam irradiation, normal cell lines had less variation in RBE values (within 10%), whereas in carbon-ion irradiation, RBE values differed by up to 48% between hTERT-HME1 and NuLi-1. Our results suggest that specific dose evaluations for tumor and normal tissues are necessary for treatment planning in both proton and carbon-ion therapies.

Particle radiotherapy and molecular therapies: mechanisms and strategies towards clinical applications

Immunotherapy and targeted therapy are now commonly used in clinical trials in combination with radiotherapy for several cancers. While results are promising and encouraging, the molecular mechanisms of the interaction between the drugs and radiation remain largely unknown. This is especially important when switching from conventional photon therapy to particle therapy using protons or heavier ions. Different dose deposition patterns and molecular radiobiology can in fact modify the interaction with drugs and their effectiveness. We will show here that whilst the main molecular players are the same after low and high linear energy transfer radiation exposure, significant differences are observed in post-exposure signalling pathways that may lead to different effects of the drugs. We will also emphasise that the problem of the timing between drug administration and radiation and the fractionation regime are critical issues that need to be addressed urgently to achieve optimal results in combined treatments with particle therapy.

A Promising Treatment Strategy for Lung Cancer: A Combination of Radiotherapy and Immunotherapy

Lung cancer is a leading cause of cancer-related deaths worldwide despite advances in treatment. In the past few decades, radiotherapy has achieved outstanding technical advances and is being widely used as a definitive, prophylactic, or palliative treatment of patients with lung cancer. The anti-tumor effects of radiotherapy are considered to result in DNA damage in cancer cells. Moreover, recent evidence has demonstrated another advantage of radiotherapy: the induction of anti-tumor immune responses, which play an essential role in cancer control. In contrast, radiotherapy induces an immunosuppressive response. These conflicting reactions after radiotherapy suggest that maximizing immune response to radiotherapy by combining immunotherapy has potential to achieve more effective anti-tumor response than using each alone. Immune checkpoint molecules, such as cytotoxic T-lymphocyte-associated protein 4, programmed cell death-1/programmed death-ligand 1, and their inhibitors, have attracted significant attention for overcoming the immunosuppressive conditions in patients with cancer. Therefore, the combination of immune checkpoint inhibitors and radiotherapy is promising. Emerging preclinical and clinical studies have demonstrated the rationale for these combination strategies. In this review, we outlined evidence suggesting that combination of radiotherapy, including particle therapy using protons and carbon ions, with immunotherapy in lung cancer treatment could be a promising treatment strategy.

Irradiation-Induced Changes in the Immunogenicity of Lung Cancer Cell Lines: Based on Comparison of X-rays and Carbon Ions

Increasing the immunogenicity of tumors is considered to be an effective means to improve the synergistic immune effect of radiotherapy. Carbon ions have become ideal radiation for combined immunotherapy due to their particular radiobiological advantages. However, the difference in time and dose of immunogenic changes induced by Carbon ions and X-rays has not yet been fully clarified. To further explore the immunogenicity differences between carbon ions and X-rays induced by radiation in different "time windows" and "dose windows." In this study, we used principal component analysis (PCA) to screen out the marker genes from the single-cell RNA-sequencing (scRNA-seq) of CD8⁺ T cells and constructed a protein-protein interaction (PPI) network. Also, ELISA was used to test the exposure levels of HMGB1, IL-10, and TGF-β under different "time windows" and "dose windows" of irradiation with X-rays and carbon ions for A549, H520, and Lewis Lung Carcinoma (LLC) cell lines. The results demonstrated that different marker genes were involved in different processes of immune effect. HMGB1 was significantly enriched in the activated state, while the immunosuppressive factors TGF-β and IL-10 were mainly enriched in the non-functional state. Both X-rays and Carbon ions promoted the exposure of HMGB1, IL-10, and TGF-β in a time-dependent manner. X-rays but not Carbon ions increased the HMGB1 exposure level in a dose-dependent manner. Besides, compared with X-rays, carbon ions increased the exposure of HMGB1 while relatively reduced the exposure levels of immunosuppressive factors IL-10 and TGF-β. Therefore, we speculate that Carbon ions may be more advantageous than conventional X-rays in inducing immune effects.

Charged Particle and Conventional Radiotherapy: Current Implications as Partner for Immunotherapy

Radiotherapy (RT) has been shown to interfere with inflammatory signals and to enhance tumor immunogenicity via, e.g., immunogenic cell death, thereby potentially augmenting the therapeutic efficacy of immunotherapy. Conventional RT consists predominantly of high energy photon beams. Hypofractionated RT regimens administered, e.g., by stereotactic body radiation therapy (SBRT), are increasingly investigated in combination with cancer immunotherapy within clinical trials. Despite intensive preclinical studies, the optimal dose per fraction and dose schemes for elaboration of RT induced immunogenic potential remain inconclusive. Compared to the scenario of combined immune checkpoint inhibition (ICI) and RT, multimodal therapies utilizing other immunotherapy principles such as adoptive transfer of immune cells, vaccination strategies, targeted immune-cytokines and agonists are underrepresented in both preclinical and clinical settings. Despite the clinical success of ICI and RT combination, e.g., prolonging overall survival in locally advanced lung cancer, curative outcomes are still not achieved for most cancer entities studied. Charged particle RT (PRT) has gained interest as it may enhance tumor immunogenicity compared to conventional RT due to its unique biological and physical properties. However, whether PRT in combination with immune therapy will elicit superior antitumor effects both locally and systemically needs to be further investigated. In this review, the immunological effects of RT in the tumor microenvironment are summarized to understand their implications for immunotherapy combinations. Attention will be given to the various immunotherapeutic interventions that have been co-administered with RT so far. Furthermore, the theoretical basis and first evidences supporting a favorable immunogenicity profile of PRT will be examined.

Effect of radiotherapy on T cell and PD-1 / PD-L1 blocking therapy in tumor microenvironment

Cancer is a worldwide problem that threatens human health. Radiotherapy plays an important role in a variety of cancer treatment methods. The administration of radiotherapy can alter the differentiation pathways and functions of T cells, which in turn improves the immune response of T cells. Radiotherapy can also induce up-regulation of PD-L1 expression, which means that it has great potential for enhancing the therapeutic effect of anti-PD-1/PD-L1 inhibitors and reducing the risk of drug resistance toward them. At present, the combination of radiotherapy and anti-PD-1/PD-L1 inhibitors has shown significant therapeutic effects in clinical tumor research. This review focuses on the mechanism of radiotherapy on T cells reported in recent years, as well as related research progress in the application of PD-1/PD-L1 blockers. It will provide a theoretical basis for the rational clinical application of radiotherapy combined with PD-1/PD-L1 inhibitors.

Characteristics of PSA Bounce after Radiotherapy for Prostate Cancer: A Meta-Analysis

The rate and characteristics of prostate-specific antigen (PSA) bounce post-radiotherapy remain unclear. To address this issue, we performed a meta-analysis. Reports of PSA bounce post-radiotherapy with a cutoff of 0.2 ng/mL were searched by using Medline and Web of Science. The primary endpoint was the occurrence rate, and the secondary endpoints were bounce characteristics such as amplitude, time to occurrence, nadir value, and time to nadir. Radiotherapy modality, age, risk classification, androgen deprivation therapy, and the follow-up period were extracted as clinical variables. Meta-analysis and univariate meta-regression were performed with random-effect modeling. Among 290 search-positive studies, 50 reports including 26,258 patients were identified. The rate of bounce was 31%; amplitude was 1.3 ng/mL; time to occurrence was 18 months; nadir value was 0.5 ng/mL; time to nadir was 33 months. Univariate meta-regression analysis showed that radiotherapy modality (29.7%), age (20.2%), and risk classification (12.2%) were the major causes of heterogeneity in the rate of bounce. This is the first meta-analysis of PSA bounce post-radiotherapy. The results are useful for post-radiotherapy surveillance of prostate cancer patients.

Carbon Ion Radiotherapy in the Treatment of Pancreatic Cancer: A Review

Pancreatic cancer is the fourth most common cause of cancer-related morality worldwide, and the prognosis remains poor despite aggressive therapy. Carbon ion radiotherapy has favorable radiobiological and physical characteristics in the treatment, including a higher linear energy transfer and higher relative biological effectiveness, which increase the cell kill while potentially reducing toxicities to nearby normal tissues. Although small, early clinical studies have shown promise in both the resectable and unresectable settings to improve local control and overall survival while minimizing toxicities. Currently, there are several trials, including 2 sponsored by institutions in the United States, investigating the role of carbon ion radiotherapy for the treatment of locally advanced pancreatic cancer.

Mitigating Coronavirus-Induced Acute Respiratory Distress Syndrome by Radiotherapy

The acute respiratory distress syndrome (ARDS) induced by SARS-CoV-2-mediated cytokine storm (CS) in lungs leads to the high mortality in COVID-19 patients. To reduce ARDS, an ideal approach is to diminish virus loading by activating immune cells for CS prevention or to suppress the overactive cytokine-releasing immune cells for CS inhibition. Here, a potential radiation-mediated CS regulation is raised by reevaluating the radiation-mediated pneumonia control in the 1920s, with the following latent advantages of lung radiotherapy (LR) in treatment of COVID-19: (1) radiation accesses poorly circulated tissue more efficiently than blood-delivered medications; (2) low-dose radiation (LDR)-mediated metabolic rewiring and immune cell activation inhibit virus loading; (3) pre-consumption of immune reserves by LDR decreases CS severity; (4) higherdose radiation (HDR) within lung-tolerable doses relieves CS by eliminating in situ overactive cytokine-releasing cells. Thus, LDR and HDR or combined with antiviral and life-supporting modalities may mitigate SARS-CoV-2 and other virus-mediated ARDS.

Preliminary study on radiosensitivity to carbon ions in human breast cancer

The aim of the study was to investigate the various effects of high linear energy transfer (LET) carbon ion (12C6+) and low LET X-ray radiation on MDA-MB-231 and MCF-7 human breast cancer cells and to explore the underlying mechanisms of radiation sensitivity. Cell proliferation, cell colony formation, cell cycle distribution, cell apoptosis and protein expression levels [double-strand break marker γ-H2AX, cell cycle-related protein cyclin B1, apoptosis-related proteins Bax and Bcl-2, and the Akt/mammalian target of rapamycin (mTOR)/ribosomal protein S6 kinase B1 (p70S6K) pathway] were detected after irradiation with carbon ions or X-rays at doses of 0, 2, 4 and 8 Gy. Our results showed that the inhibition of cell proliferation and cell colony formation and the induction of G2/M phase arrest, DNA lesions and cell apoptosis/necrosis elicited by carbon ion irradiation were more potent than the effects elicited by X-ray radiation at the same dose. Simultaneously, compared with X-ray radiation, carbon ion radiation induced a marked increase in Bax and prominent decreases in cyclin B1 and Bcl-2 in a dose-dependent manner. Furthermore, the Akt/mTOR/p70S6K pathway was significantly inhibited by carbon ion radiation in both breast cancer cell lines. These results indicate that carbon ion radiation kills MDA-MB-231 and MCF-7 breast cancer cells more effectively than X-ray radiation, which might result from the inhibition of the Akt/mTOR/p70S6K pathway.

Individual response of humans to ionising radiation: governing factors and importance for radiological protection

Tissue reactions and stochastic effects after exposure to ionising radiation are variable between individuals but the factors and mechanisms governing individual responses are not well understood. Individual responses can be measured at different levels of biological organization and using different endpoints following varying doses of radiation, including: cancers, non-cancer diseases and mortality in the whole organism; normal tissue reactions after exposures; and, cellular endpoints such as chromosomal damage and molecular alterations. There is no doubt that many factors influence the responses of people to radiation to different degrees. In addition to the obvious general factors of radiation quality, dose, dose rate and the tissue (sub)volume irradiated, recognized and potential determining factors include age, sex, life style (e.g., smoking, diet, possibly body mass index), environmental factors, genetics and epigenetics, stochastic distribution of cellular events, and systemic comorbidities such as diabetes or viral infections. Genetic factors are commonly thought to be a substantial contributor to individual response to radiation. Apart from a small number of rare monogenic diseases such as ataxia telangiectasia, the inheritance of an abnormally responsive phenotype among a population of healthy individuals does not follow a classical Mendelian inheritance pattern. Rather it is considered to be a multi-factorial, complex trait.

The future of radiation-induced abscopal response: beyond conventional radiotherapy approaches

Advances in the immunological pharmaceuticals, such as checkpoint inhibitors and agonists, have positive implications for the future of the radiotherapy abscopal response. A once rare phenomenon, whereby distant nonirradiated tumor sites regressed after radiotherapy alone, may become more common when combined with the immune modulating agents. Radiotherapy can increase neoantigen expression, increased tumor PD-L1 expression, increase MHC class I expression, reverse exhausted CD8 T cells and increase tumor-infiltrating tumors within the tumor microenvironment. These changes in the tumor and the tumor microenvironment after radiotherapy could potentiate responses to anti-CTL-4, anti-PD-L1/PD-1 and other immunotherapy agents. Thus, advances in checkpoint inhibitors have increased interest in re-evaluation of the role of conventional radiotherapy approaches on the immune system. We reviewed newer nonconventional approaches such as SBRT-PATHY, GRID, FLASH, carbon ion and proton therapy and their role in eliciting immune responses. We believe that combining these novel radiation methods may enhance the outcome with the newly US FDA approved immune modulating agents.

Rationale of combination of anti-PD-1/PD-L1 antibody therapy and radiotherapy for cancer treatment

Significant technological advances in radiotherapy have been made in the past few decades. High-precision radiotherapy has recently become popular and is contributing to improvements in the local control of the irradiated target lesions and the reduction of adverse effects. Accordingly, for long-term survival, the importance of systemic cancer control, including at non-irradiated sites, is growing. Toward this challenge, the treatment methods in which anti-PD-1/PD-L1 antibodies that exert systemic effects by restoring anti-tumour immunity are combined with radiotherapy has attracted attention in recent years. Previous studies have reported the activation of anti-tumour immunity by radiotherapy, which simultaneously elevates PD-L1 expression, suggesting a potential for combination therapy. Radiotherapy induces so-called ‘immunogenic cell death’, which involves cell surface translocation of calreticulin and extracellular release of high-mobility group protein box 1 (HMGB-1) and adenosine-5′-triphosphate (ATP). Furthermore, radiotherapy causes immune activation via MHC class I upregulation and cGAS–STING pathway. In contrast, induction of immunosuppressive lymphocytes and the release of immunosuppressive cytokines and chemokines by radiotherapy contribute to immunosuppressive reactions. In this article, we review immune responses induced by radiotherapy as well as previous reports to support the rationale of combination of radiotherapy and anti-PD-1/PD-L1 antibodies. A number of preclinical and clinical studies have shown the efficacy of radiotherapy combined with immune checkpoint inhibition, hence combination therapy is considered to be an important future strategy for cancer treatment.

Glycyrrhizin mitigates radiation-induced acute lung injury by inhibiting the HMGB1/TLR4 signalling pathway

Radiation‐induced lung injury (RILI) is the major complication of thoracic radiation therapy, and no effective treatment is available. This study explored the role of high‐mobility group box 1 (HMGB1) in acute RILI and the therapeutic effect of glycyrrhizin, an inhibitor of HMGB1, on RILI. C57BL/6 mice received a 20 Gy dose of X‐ray radiation to the whole thorax with or without administration of glycyrrhizin. Severe lung inflammation was present 12 weeks after irradiation, although only a mild change was noted at 2 weeks and could be alleviated by administration of glycyrrhizin. Glycyrrhizin decreased the plasma concentrations of HMGB1 and sRAGE as well as TNF‐α, IL‐1β and IL‐6 levels in the bronchoalveolar lavage fluid (BALF). The expression of RAGE was decreased while that of TLR4 was significantly increased at 12 weeks, but not 2 weeks, after irradiation in mouse lung tissue. In vitro, the expression of TLR4 increased in RAW 264.7 cells after conditioning with the supernatant from the irradiated MLE‐12 cells containing HMGB1 but showed no change when conditioned medium without HMGB1 was used. However, conditioned culture had no effect on RAGE expression in RAW 264.7 cells. Glycyrrhizin also inhibited the related downstream transcription factors of HMGB/TLR4, such as NF‐κB, JNK and ERK1/2, in lung tissue and RAW 264.7 cells when TLR4 was activated. In conclusion, the HMGB1/TLR4 pathway mediates RILI and can be mitigated by glycyrrhizin.

Harnessing radiation to improve immunotherapy: better with particles?

The combination of radiotherapy and immunotherapy is one of the most promising strategies for cancer treatment. Recent clinical results support the pre-clinical experiments pointing to a benefit for the combined treatment in metastatic patients. Charged particle therapy (using protons or heavier ions) is considered one of the most advanced radiotherapy techniques, but its cost remains higher than conventional X-ray therapy. The most important question to be addressed to justify a more widespread use of particle therapy is whether they can be more effective than X-rays in combination with immunotherapy. Protons and heavy ions have physical advantages compared to X-rays that lead to a reduced damage to the immune cells, that are required for an effective immune response. Moreover, densely ionizing radiation may have biological advantages, due to different cell death pathways and release of cytokine mediators of inflammation. We will discuss results in esophageal cancer patients showing that charged particles can reduce the damage to blood lymphocytes compared to X-rays, and preliminary in vitro studies pointing to an increased release of immune-stimulating cytokines after heavy ion exposure. Pre-clinical and clinical studies are ongoing to test these hypotheses.

The Reciprocity between Radiotherapy and Cancer Immunotherapy

The clinical success of immune checkpoint inhibitors in treating metastatic and refractory cancers has generated significant interest in investigating their role in treating locally advanced diseases, thus requiring them to be combined with standard treatments in the hope of producing synergistic antitumor responses. Radiotherapy, in particular, has long been hypothesized to have actions complementary to those of immune checkpoint blockade, and a growing body of evidence indicates that cancer immunotherapy may also have radiosensitizing effects, which would provide unique benefit for locoregional treatments. Recent studies have demonstrated that when immune cells are activated by immunotherapeutics, they can reprogram the tumor microenvironment in ways that may potentially increase the radiosensitivity of the tumor. In this review, we highlight the evidence that supports reciprocal interactions between cancer immunotherapy and radiotherapy, where in addition to the traditional notion that radiation serves to enhance the activation of antitumor immunity, an alternative scenario also exists in which T-cell activation by cancer immunotherapy may sensitize tumors to radiation treatment through mechanisms that include normalization of the tumor vasculature and tissue hypoxia. We describe the empirical observations from preclinical models that support such effects and discuss their implications for future research and trial design.

Immune targets in the tumor microenvironment treated by radiotherapy

Radiotherapy (RT), the major anti-cancer modality for more than half of cancer patients after diagnosis, has the advantage of local tumor control with relatively less systematic side effects comparing to chemotherapy. However, the efficacy of RT is limited by acquired tumor resistance leading to the risks of relapse and metastasis. To further enhance the efficacy of RT, with the renaissances of targeted immunotherapy (TIT), increasing interests are raised on RT combined with TIT including cancer vaccines, T-cell therapy, and antibody-based immune checkpoint blockers (ICB) such as anti-CTLA-4 and anti-PD1/PD-L1. In achieving a significant synergy between RT and TIT, the dynamics of radiation-induced response in tumor cells and stromal cells, especially the cross-talk between tumor cells and immune cells in the irradiated tumor microenvironment (ITME) as highlighted in recent literature are to be elucidated. The abscopal effect refereeing the RT-induced priming function outside of ITME could be compromised by the immune-suppressive factors such as CD47 and PD-L1 on tumor cells and Treg induced or enhanced in the ITME. Cell surface receptors temporally or permanently induced and bioactive elements released from dead cells could serve antigenic source (radiation-associated antigenic proteins, RAAPs) to the host and have functions in immune regulation on the tumor. This review is attempted to summarize a cluster of factors that are inducible by radiation and targetable by antibodies, or have potential to be immune regulators to synergize tumor control with RT. Further characterization of immune regulators in ITME will deepen our understanding of the interplay among immune regulators in ITME and discover new effective targets for the combined modality with RT and TIT.

Carbon ion irradiation enhances the antitumor efficacy of dual immune checkpoint blockade therapy both for local and distant sites in murine osteosarcoma

Carbon ion radiotherapy has been utilized even for X-ray resistant tumors. However, control of distant metastasis remains a major challenge in carbon ion irradiation. We investigated whether carbon ion irradiation combined with dual immune checkpoint blockade therapy (anti-PD-L1 and anti-CTLA-4 antibodies [P1C4]) provides anti-tumor efficacy for both local and distant sites. A mouse osteosarcoma cell line (LM8) was inoculated into both hind legs of C3H mice assigned to four groups: no treatment (NoTX), P1C4, 5.3 Gy of carbon ion irradiation to one leg (Cion), and combination (Comb) groups. In the Comb group, tumor growth delay was observed not only in the irradiated tumors but also in the unirradiated tumors. Notably, a complete response of unirradiated tumors was observed in 64% of mice in the Comb group, while only 20% of mice in the P1C4 group showed a complete response. Significant activation of immune cells was observed in the Comb group, with an increase in CD8+/GzmB+ tumor-infiltrating lymphocytes (TILs) in the irradiated tumor, and of CD8+/GzmB+ and CD4+ TILs in the unirradiated tumor, respectively. Depletion of CD8 abolished the tumor growth delay in unirradiated tumors in mice treated by Cion and P1C4. Overall survival was significantly prolonged in the Comb group. HMGB-1 release from irradiated tumors was significantly increased after Cion both in vitro and in vivo. These data suggest that carbon ion therapy enhances P1C4 efficacy against osteosarcoma in both the primary tumor and distant metastases mediated by immune activation.