Contribution of the immune system to bystander and non-targeted effects of ionizing radiation

Quantification of biochemical PSA dynamics after radioligand therapy with [177Lu]Lu-PSMA-I&T using a population pharmacokinetic/pharmacodynamic model

BACKGROUND

There is an unmet need for prediction of treatment outcome or patient selection for [177Lu]Lu-PSMA therapy in patients with metastatic castration-resistant prostate cancer (mCRPC). Quantification of the tumor exposure-response relationship is pivotal for further treatment optimization. Therefore, a population pharmacokinetic (PK) model was developed for [177Lu]Lu-PSMA-I&T using SPECT/CT data and, subsequently, related to prostate-specific antigen (PSA) dynamics after therapy in patients with mCRPC using a pharmacokinetic/pharmacodynamic (PKPD) modelling approach.

METHODS

A population PK model was developed using quantitative SPECT/CT data (406 scans) of 76 patients who received multiple cycles [177Lu]Lu-PSMA-I&T (± 7.4 GBq with either two- or six-week interval). The PK model consisted of five compartments; central, salivary glands, kidneys, tumors and combined remaining tissues. Covariates (tumor volume, renal function and cycle number) were tested to explain inter-individual variability on uptake into organs and tumors. The final PK model was expanded with a PD compartment (sequential fitting approach) representing PSA dynamics during and after treatment. To explore the presence of a exposure-response relationship, individually estimated [177Lu]Lu-PSMA-I&T tumor concentrations were related to PSA changes over time.

RESULTS

The population PK model adequately described observed data in all compartments (based on visual inspection of goodness-of-fit plots) with adequate precision of parameters estimates (< 36.1% relative standard error (RSE)). A significant declining uptake in tumors (k14) during later cycles was identified (uptake decreased to 73%, 50% and 44% in cycle 2, 3 and 4-7, respectively, compared to cycle 1). Tumor growth (defined by PSA increase) was described with an exponential growth rate (0.000408 h-1 (14.2% RSE)). Therapy-induced PSA decrease was related to estimated tumor concentrations (MBq/L) using both a direct and delayed drug effect. The final model adequately captured individual PSA concentrations after treatment (based on goodness-of-fit plots). Simulation based on the final PKPD model showed no evident differences in response for the two different dosing regimens currently used.

CONCLUSIONS

Our population PK model accurately described observed [177Lu]Lu-PSMA-I&T uptake in salivary glands, kidneys and tumors and revealed a clear declining tumor uptake over treatment cycles. The PKPD model adequately captured individual PSA observations and identified population response rates for the two dosing regimens. Hence, a PKPD modelling approach can guide prediction of treatment response and thus identify patients in whom radioligand therapy is likely to fail.

Radiotherapy and radio-sensitization in H3K27M -mutated diffuse midline gliomas

BACKGROUND

H3^K27M mutated diffuse midline gliomas (DMGs) are extremely aggressive and the leading cause of cancer-related deaths in pediatric brain tumors with 5-year survival <1%. Radiotherapy is the only established adjuvant treatment of H3^K27M DMGs; however, the radio-resistance is commonly observed.

METHODS

We summarized current understandings of the molecular responses of H3^K27M DMGs to radiotherapy and provide crucial insights into current advances in radiosensitivity enhancement.

RESULTS

Ionizing radiation (IR) can mainly inhibit tumor cell growth by inducing DNA damage regulated by the cell cycle checkpoints and DNA damage repair (DDR) system. In H3K27M DMGs, the aberrant genetic and epigenetic changes, stemness genotype, and epithelial-mesenchymal transition (EMT) disrupt the cell cycle checkpoints and DDR system by altering the associated regulatory signaling pathways, which leads to the development of radio-resistance.

CONCLUSIONS

The advances in mechanisms of radio-resistance in H3^K27M  DMGs promote the potential targets to enhance the sensitivity to radiotherapy.

Checkpoint Inhibitor Immune-Related Adverse Events: A Multimodality Pictorial Review

Cancer immunotherapies are drugs that modulate the body's own immune system as an anticancer strategy. Checkpoint inhibitor immunotherapies interfere with cell surface binding proteins that function to promote self-recognition and tolerance, ultimately leading to upregulation of the immune response. Given the striking success of these agents in early trials in melanoma and lung cancer, they have now been studied in many types of cancer and have become a pillar of anticancer therapy for many tumor types. However, abundant upregulation results in a new class of side effects, known as immune-related adverse events (IRAEs). It is critical for the practicing radiologist to be able to recognize these events to best contribute to care for patients on checkpoint inhibitor immunotherapy. Here, we provide a comprehensive system-based review of immune-related adverse events and associated imaging findings. Further, we detail the best imaging modalities for each as well as describe problem solving modalities. Given that IRAEs can be subclinical before becoming clinically apparent, radiologists may be the first provider to recognize them, providing an opportunity for early treatment. Awareness of IRAEs and how to best image them will prepare radiologists to make a meaningful contribution to patient care as part of the clinical team.

Implications and Emerging Therapeutic Avenues of Inflammatory Response in HPV+ Head and Neck Squamous Cell Carcinoma

Head and neck squamous cell carcinomas (HNSCC) are a heterogeneous group of malignancies which have shown exponential incidence in the last two decades especially due to human papillomavirus (HPV) infection. The HPV family comprises more than 100 types of viruses with HPV16 and HPV18 being the most prevalent strains in HNSCC. Literature data reveal that the mutation profile as well as the response to chemotherapy and radiotherapy are distinct among HPV+ versus HPV-negative tumors. Furthermore, the presence of the virus induces activation of an immune response, in particular the recruitment of specific antiviral T lymphocytes to tumor sites. These T cells when activated produce soluble factors including cytokines and chemokines capable of modifying the local immune tumor microenvironment and impact on tumor response to the treatment. In this comprehensive review we investigated current knowledge on how the presence of an HPV can modify the inflammatory response systemically and within the tumor microenvironment's immunological responses, thereby impacting on disease prognosis and survival. We highlighted the research gaps and emerging approaches necessary to discover novel immunotherapeutic targets for HPV-associated HNSCC.

ASSESSMENT OF THE STATE OF IMMUNE SYSTEM IN PATIENTS WITH METASTATIC AND GLIAL BRAIN TUMORS AT THE PREPARATORY STAGE OF RADIOTHERAPY

OBJECTIVE

The aim: To assess the state of the immune system in patients before radiation therapy and radiosurgery and compare the features of immunity in metastatic and glial brain tumors.

PATIENTS AND METHODS

Materials and methods: Our study presents the results of immunograms of 41 patients. Of these: 18 patients with primary glial tumors and 23 patients with secondary metastatic tumors to the brain. The results of 20 conditionally healthy patients who did not have cancer are presented as a control group. The age of patients was 24-75 years. All patients have histological confirmation of the tumor diagnosis. Surgery was performed 1.0-3.0 years before the examination.

RESULTS

Results: When comparing the immune parameters of the number of T and B subpopulations of lymphocytes in patients with primary malignant brain tumors and secondary metastatic tumors, no statistically significant difference was found between these indicators. Glioblastomas show higher levels of IgG and IgA than other tumors, while the concentration of IgM is almost at the same level in all three groups of patients. There is a tendency to decrease the level of IgG and IgM in the blood of patients with metastatic tumors. In the study group of patients there is an inhibition of myeloperoxidase activity of neutrophils on the background of maintaining the function of NBT cell activity.

CONCLUSION

Conclusions: Both metastatic and primary malignant glial have partial changes in various parts of the immune system.

Divide and conquer: spatially fractionated radiation therapy

Spatially fractionated radiation therapy (SFRT) challenges some of the classical dogmas in conventional radiotherapy. The highly modulated spatial dose distributions in SFRT have been shown to lead, both in early clinical trials and in small animal experiments, to a significant increase in normal tissue dose tolerances. Tumour control effectiveness is maintained or even enhanced in some configurations as compared with conventional radiotherapy. SFRT seems to activate distinct radiobiological mechanisms, which have been postulated to involve bystander effects, microvascular alterations and/or immunomodulation. Currently, it is unclear which is the dosimetric parameter which correlates the most with both tumour control and normal tissue sparing in SFRT. Additional biological experiments aiming at parametrizing the relationship between the irradiation parameters (beam width, spacing, peak-to-valley dose ratio, peak and valley doses) and the radiobiology are needed. A sound knowledge of the interrelation between the physical parameters in SFRT and the biological response would expand its clinical use, with a higher level of homogenisation in the realisation of clinical trials. This manuscript reviews the state of the art of this promising therapeutic modality, the current radiobiological knowledge and elaborates on future perspectives.

Commonalities in the Features of Cancer and Chronic Fatigue Syndrome (CFS): Evidence for Stress-Induced Phenotype Instability?

Chronic Fatigue Syndrome/Myalgic Encephalomyelitis (CFS/ME) and Cancer-Related Fatigue (CRF) are syndromes with considerable overlap with respect to symptoms. There have been many studies that have compared the two conditions, and some of this research suggests that the etiologies of the conditions are linked in some cases. In this narrative review, CFS/ME and cancer are introduced, along with their known and putative mechanistic connections to multiple stressors including ionizing radiation. Next, we summarize findings from the literature that suggest the involvement of HPA-axis dysfunction, the serotonergic system, cytokines and inflammation, metabolic insufficiency and mitochondrial dysfunction, and genetic changes in CRF and CFS/ME. We further suspect that the manifestation of fatigue in both diseases and its causes could indicate that CRF and CFS/ME lie on a continuum of potential biological effects which occur in response to stress. The response to this stress likely varies depending on predisposing factors such as genetic background. Finally, future research ideas are suggested with a focus on determining if common biomarkers exist in CFS/ME patients and those afflicted with CRF. Both CFS/ME and CRF are relatively heterogenous syndromes, however, it is our hope that this review assists in future research attempting to elucidate the commonalities between CRF and CFS/ME.

The Treatment for a Patient with Cancer of Unknown Primary: A Case Report

Background

Cancer of unknown primary (CUP) is metastatic at diagnosis with an unknown primary site, indicating a high degree of malignancy with a poor prognosis. The development and application of targeted therapy and immunotherapy are current research hotspots, which provide additional treatment options for CUP.

Case Presentation

A 36-year-old male presented with pain on the right hip in April 2018. After various examinations, he was diagnosed with CUP. This patient received chemotherapy, immunotherapy, and local radiotherapy in our department. However, the use of radiotherapy after immunotherapy resulted in severe pneumonia.

Conclusion

Compared with traditional treatments, immunotherapy is an effective treatment with fewer side effects and better patient tolerance. However, treating physicians should be still pay special attention to the occurrence of side effects when radiotherapy is combined with immunotherapy.

Changes in Blood Biomarkers of Angiogenesis and Immune Modulation after Radiation Therapy and Their Association with Outcomes in Thoracic Malignancies

The effects of radiotherapy on systemic immunity remain to be fully characterized in a disease-specific manner. The aim of the study was to examine potential biomarkers of systemic immunomodulation when using radiotherapy for thoracic malignancies. Serial blood samples were collected from 56 patients with thoracic malignancies prior (RTbaseline), during (RTduring) and at the end of radiotherapy (RTend), as well as at the first (FU1) and second follow-up (FU2). The changes in serum levels of IL-10, IFN-γ, IL-12p70, IL-13, IL-1β, IL-4, IL-6, IL-8, TNF-α, bFGF, sFlt-1, PlGF, VEGF, VEGF-C, VEGF-D and HGF were measured by multiplexed array and tested for associations with clinical outcomes. We observed an increase in the levels of IL-10, IFN-γ, PlGF and VEGF-D and a decrease in those of IL-8, VEGF, VEGF-C and sFlt-1 during and at the end of radiotherapy. Furthermore, baseline concentration of TNF-α significantly correlated with OS. IL-6 level at RTend and FU1,2 correlated with OS (RTend: p = 0.039, HR: 1.041, 95% CI: 1.002-1.082, FU1: p = 0.001, HR: 1.139, 95% CI: 1.056-1.228, FU2: p = 0.017, HR: 1.101 95% CI: 1.018-1.192), while IL-8 level correlated with OS at RTduring and RTend (RTduring: p = 0.017, HR: 1.014, 95% CI: 1.002-1.026, RTend: p = 0.004, HR: 1.007, 95% CI: 1.061-1.686). In conclusion, serum levels of TNF-α, IL-6 and IL-8 are potential biomarkers of response to radiotherapy. Given the recent implementation of immunotherapy in lung and esophageal cancer, these putative blood biomarkers should be further validated and evaluated in the combination or sequential therapy setting.

The Evidence of the Bystander Effect after Bleomycin Electrotransfer and Irreversible Electroporation

One of current applications of electroporation is electrochemotherapy and electroablation for local cancer treatment. Both of these electroporation modalities share some similarities with radiation therapy, one of which could be the bystander effect. In this study, we aimed to investigate the role of the bystander effect following these electroporation-based treatments. During direct CHO-K1 cell treatment, cells were electroporated using one 100 µs duration square wave electric pulse at 1400 V/cm (for bleomycin electrotransfer) or 2800 V/cm (for irreversible electroporation). To evaluate the bystander effect, the medium was taken from directly treated cells after 24 h incubation and applied on unaffected cells. Six days after the treatment, cell viability and colony sizes were evaluated using the cell colony formation assay. The results showed that the bystander effect after bleomycin electrotransfer had a strong negative impact on cell viability and cell colony size, which decreased to 2.8% and 23.1%, respectively. On the contrary, irreversible electroporation induced a strong positive bystander effect on cell viability, which increased to 149.3%. In conclusion, the results presented may serve as a platform for further analysis of the bystander effect after electroporation-based therapies and may ultimately lead to refined application of these therapies in clinics.

Biological consequences of cancer radiotherapy in the context of oral squamous cell carcinoma

Approximately 50% of subjects with cancer have been treated with ionizing radiation (IR) either as a curative, adjuvant, neoadjuvant or as a palliative agent, at some point during the clinical course of their disease. IR kills cancer cells directly by injuring their DNA, and indirectly by inducing immunogenic cell killing mediated by cytotoxic T cells; but it can also induce harmful biological responses to non-irradiated neighbouring cells (bystander effect) and to more distant cells (abscopal effect) outside the primary tumour field of irradiation.Although IR can upregulate anti-tumour immune reactions, it can also promote an immunosuppressive tumour microenvironment. Consequently, radiotherapy by itself is seldom sufficient to generate an effective long lasting immune response that is capable to control growth of metastasis, recurrence of primary tumours and development of second primary cancers. Therefore, combining radiotherapy with the use of immunoadjuvants such as immune checkpoint inhibitors, can potentiate IR-mediated anti-tumour immune reactions, bringing about a synergic immunogenic cell killing effect.The purpose of this narrative review is to discuss some aspects of IR-induced biological responses, including factors that contributes to tumour radiosensitivity/radioresistance, immunogenic cell killing, and the abscopal effect.

Brain Damage and Patterns of Neurovascular Disorder after Ionizing Irradiation. Complications in Radiotherapy and Radiation Combined Injury

Exposure to ionizing radiation, mechanical trauma, toxic chemicals or infections, or combinations thereof (i.e., combined injury) can induce organic injury to brain tissues, the structural disarrangement of interactive networks of neurovascular and glial cells, as well as on arrays of the paracrine and systemic destruction. This leads to subsequent decline in cognitive capacity and decompensation of mental health. There is an ongoing need for improvement in mitigating and treating radiation- or combined injury-induced brain injury. Cranial irradiation per se can cause a multifactorial encephalopathy that occurs in a radiation dose- and time-dependent manner due to differences in radiosensitivity among the various constituents of brain parenchyma and vasculature. Of particular concern are the radiosensitivity and inflammation susceptibility of: 1. the neurogenic and oligodendrogenic niches in the subependymal and hippocampal domains; and 2. the microvascular endothelium. Thus, cranial or total-body irradiation can cause a plethora of biochemical and cellular disorders in brain tissues, including: 1. decline in neurogenesis and oligodendrogenesis; 2. impairment of the blood-brain barrier; and 3. ablation of vascular capillary. These changes, along with cerebrovascular inflammation, underlie different stages of encephalopathy, from the early protracted stage to the late delayed stage. It is evident that ionizing radiation combined with other traumatic insults such as penetrating wound, burn, blast, systemic infection and chemotherapy, among others, can exacerbate the radiation sequelae (and vice versa) with increasing severity of neurogenic and microvascular patterns of radiation brain damage.

Low dose ionizing radiation effects on the immune system

Ionizing radiation interacts with the immune system in many ways with a multiplicity that mirrors the complexity of the immune system itself: namely the need to maintain a delicate balance between different compartments, cells and soluble factors that work collectively to protect, maintain, and restore tissue function in the face of severe challenges including radiation damage. The cytotoxic effects of high dose radiation are less relevant after low dose exposure, where subtle quantitative and functional effects predominate that may go unnoticed until late after exposure or after a second challenge reveals or exacerbates the effects. For example, low doses may permanently alter immune fitness and therefore accelerate immune senescence and pave the way for a wide spectrum of possible pathophysiological events, including early-onset of age-related degenerative disorders and cancer. By contrast, the so called low dose radiation therapy displays beneficial, anti-inflammatory and pain relieving properties in chronic inflammatory and degenerative diseases. In this review, epidemiological, clinical and experimental data regarding the effects of low-dose radiation on the homeostasis and functional integrity of immune cells will be discussed, as will be the role of immune-mediated mechanisms in the systemic manifestation of localized exposures such as inflammatory reactions. The central conclusion is that ionizing radiation fundamentally and durably reshapes the immune system. Further, the importance of discovery of immunological pathways for modifying radiation resilience amongst other research directions in this field is implied.

Efficacy of Stereotactic Body Radiotherapy in Patients With Hepatocellular Carcinoma Not Suitable for Transarterial Chemoembolization (HERACLES: HEpatocellular Carcinoma Stereotactic RAdiotherapy CLinical Efficacy Study)

The aim of this prospective observational trial was to evaluate the efficacy, toxicity and quality of life after stereotactic body radiation therapy (SBRT) in patients with hepatocellular carcinoma (HCC) and to assess the results of this treatment in comparison to trans-arterial chemoembolization (TACE). Patients with HCC, treated with TACE or SBRT, over a period of 12 months, enrolled in the study. The primary endpoint was feasibility; secondary endpoints were toxicity, quality of life (QOL), local progression (LP) and overall survival (OS). Between 06/2016 and 06/2017, 19 patients received TACE and 20 SBRT, 2 of whom were excluded due to progression. The median follow-up was 31 months. The QOL remained stable before and after treatment and was comparable in both treatment groups. Five patients developed grade ≥ 3 toxicities in the TACE group and 3 in the SBRT group. The cumulative incidence of LP after 1-, 2- and 3-years was 6, 6, 6% in the SBRT group and 28, 39, and 65% in the TACE group (p = 0.02). The 1- and 2- years OS rates were 84% and 47% in the TACE group and 44% and 39% in the SBRT group (p = 0.20). In conclusion, SBRT is a well-tolerated local treatment with a high local control rates and can be safely delivered, while preserving the QOL of HCC patients.

Spatially Modulated Proton Minibeams Results in the Same Increase of Lifespan as a Uniform Target Dose Coverage in F98-Glioma-Bearing Rats

Proton minibeam radiation therapy (pMBRT) is a new approach in proton radiotherapy, by which a significant increase in the therapeutic index has already been demonstrated in RG2 glioma-bearing rats. In the current study we investigated the response of other types of glioma (F98) and performed a comparative evaluation of tumor control effectiveness by pMBRT (with different levels of dose heterogeneity) versus conventional proton therapy. The results of our study showed an equivalent increase in the lifespan for all evaluated groups (conventional proton irradiation and pMBRT) and no significant differences in the histopathological analysis of the tumors or remaining brain tissue. The reduced long-term toxicity observed with pMBRT in previous evaluations at the same dose suggests a possible use of pMBRT to treat glioma with less side effects while ensuring the same tumor control achieved with standard proton therapy.

The Evolving Role of Radiation Therapy in the Treatment of Biliary Tract Cancer

Biliary tract cancers (BTC) are a disease entity comprising diverse epithelial tumors, which are categorized according to their anatomical location as intrahepatic (iCCA), perihilar (pCCA), distal (dCCA) cholangiocarcinomas, and gallbladder carcinomas (GBC), with distinct epidemiology, biology, and prognosis. Complete surgical resection is the mainstay in operable BTC as it is the only potentially curative treatment option. Nevertheless, even after curative (R0) resection, the 5-year survival rate ranges between 20 and 40% and the disease free survival rates (DFS) is approximately 48–65% after one year and 23–35% after three years without adjuvant treatment. Improvements in adjuvant chemotherapy have improved the DFS, but the role of adjuvant radiotherapy is unclear. On the other hand, more than 50% of the patients present with unresectable disease at the time of diagnosis, which limits the prognosis to a few months without treatment. Herein, we review the role of radiotherapy in the treatment of cholangiocarcinoma in the curative and palliative setting.

Proteomic analysis of radio-resistant breast cancer xenografts: Increased TGF-β signaling and metabolism

Our previous studies have shown that MCF-7 breast cancer cell line exposed to 6 Gy and allowed to recover for 7 days (D7-6G) developed radio-resistance. In this study, we have tested the ability of these cells to form tumors in severe combined immunodeficiency (SCID) mice and characterized these tumors by proteomic analyses. Untreated (MCF-C) and D7-6G cells (MCF-R) were injected s.c. in SCID mice and tumor growth monitored. On Day 18, the mice were killed and tumor tissues were fixed in formalin or RNA later. Expression of genes was assessed by reverse transcription-polymerase chain reaction and proteins by enzyme-linked immunosorbent assay/antibody labeling and flow cytometry. Label free proteomic analyses was carried out by liquid chromatography-mass spectrometry. Metabolic analysis was carried out using Seahorse analyzer. MCF-R cells had a shorter latency and formed larger tumors. These tumors were characterized by an increased expression of transforming growth factor β (TGF-β) isoforms; its downstream genes pSMAD3, Snail-1, Zeb-1, HMGA2; hybrid epithelial/mesenchymal phenotype; migration, enrichment of cancer stem cells and radioresistance following challenge dose of radiation. Proteomic analysis of MCF-7R tumors resulted in identification of a total of 649 differentially expressed proteins and pathway analyses using protein annotation through evolutionary relationship indicated enrichment of genes involved in metabolism. Data are available via ProteomeXchange with identifier PXD022506. Seahorse analyzer confirmed increased metabolism in these cells with increased oxidative phosphorylation as well as glycolysis. Increased uptake of 2-NBDG further confirmed increased glycolysis. In summary, we demonstrate that radioresistant breast cancer cells had an enrichment of TGF-β signaling and increased metabolism.

Protection Against Ionizing Radiation-Induced Normal Tissue Damage by Resveratrol: A Systematic Review

The use of some agents as radioprotectors has been evaluated for protection against normal tissue toxicity following exposure to ionizing radiation. Resveratrol, a natural flavonoid, with antioxidant and anti-inflammatory properties has attracted research interests for its radioprotective potential. This study systematically evaluates existing studies to examine the radioprotective effectiveness of resveratrol. A literature search of the electronic databases, including PubMed, Scopus, and Embase was conducted to retrieve articles investigating the protective effect of resveratrol against ionizing radiation-induced damage to normal tissues. The search timeframe ranged from the inception of each database to January 2020. From an initial search of 231 articles, and after the removal of duplicates as well as applying the predetermined inclusion and exclusion criteria, 33 articles were finally included for this systematic review. Results showed promising protective effect of resveratrol against ionizing radiation-induced damage to normal tissues. Furthermore, no adverse effect was observed after administering resveratrol. Resveratrol showed the potential to protect against ionizing radiation-induced damage to normal tissue cells via notable mechanisms, including anti-apoptotic and anti-inflammatory effects. However, further studies on the efficacy of clinical translation of resveratrol would open up more insights, while other gray areas such as the optimal radioprotective dosage of resveratrol requires further investigation. Overall, resveratrol is a potential double-edged sword in cancer therapy while protecting healthy tissues.

Immunomodulatory Effects of Radiotherapy

Radiation therapy (RT), an integral component of curative treatment for many malignancies, can be administered via an increasing array of techniques. In this review, we summarize the properties and application of different types of RT, specifically, conventional therapy with x-rays, stereotactic body RT, and proton and carbon particle therapies. We highlight how low-linear energy transfer (LET) radiation induces simple DNA lesions that are efficiently repaired by cells, whereas high-LET radiation causes complex DNA lesions that are difficult to repair and that ultimately enhance cancer cell killing. Additionally, we discuss the immunogenicity of radiation-induced tumor death, elucidate the molecular mechanisms by which radiation mounts innate and adaptive immune responses and explore strategies by which we can increase the efficacy of these mechanisms. Understanding the mechanisms by which RT modulates immune signaling and the key players involved in modulating the RT-mediated immune response will help to improve therapeutic efficacy and to identify novel immunomodulatory drugs that will benefit cancer patients undergoing targeted RT.

A review of radiation induced abscopal effect: combining radiotherapy and immunotherapy to treat the untreated distant metastatic tumours

Background:

Radiotherapy is an effective and significant mode of definitive cancer treatment with well-established local tumour control success, especially in the treatment of localised tumours. Although, for metastatic disease, the role of radiotherapy has generally been limited to palliation of symptoms. In the treatment of metastatic diseases settings, the radiation therapy technique has always been confronted with the challenge of the simultaneous treatment of all of the various distant metastatic tumour sites, however, some recent evidence suggests that radiotherapy can potentially induce anticancer immune responses whose effectors potentially migrate to distant metastatic tumours to provoke their regression in cancer patients. Thus, unirradiated distant metastatic tumour sites can exhibit a delayed therapeutic response termed the abscopal effect.

Materials and methods:

This paper reports on a review of the abscopal effect, including its biological mechanism, the effect of radiation dose and fractionation regime and the timing of immunotherapy administration on radiotherapy-induced abscopal effect, the enhancement of radiotherapy-induced abscopal effects with immunotherapy, the effect of the location of the irradiated tumour and the radiotherapy of multiple tumour sites on the likelihood and effectiveness of inducing abscopal responses in the preclinical and clinical settings and also reports on some evidence of clinical observations in patients.

Conclusions:

Although abscopal effects of radiotherapy are still relatively rare in patients, it has gained a lot of interest due to recent development and use of immunotherapy strategies incorporating combinations of targeted immunomodulators and immune checkpoint blockade with radiation therapy. The enhancement of cancer immunotherapy could potentially enable the translation of the concept of abscopal effect into the clinics as a new strategy to induce therapeutically effective anti-tumour immune responses in cancer patients. The combination of radiotherapy and immunotherapy has the potential to expand the role of radiotherapy from a purely local tumour control treatment to play a significant role in advanced and metastatic tumour control and this could likely lead to a paradigm shift in the treatment of patients with metastatic cancer.

Radiation protection by Ex-RAD: a systematic review

Protection of normal tissues against ionizing radiation-induced damages is a critical issue in clinical and environmental radiobiology. One of the ways of accomplishing radiation protection is through the use of radioprotectors. In the search for the most effective radioprotective agent, factors such as toxicity, effect on tumors, number of tissues protected, ease of administration, long-term stability, and compatibility with other drugs need to be assessed. Thus, in the present study, we systematically review existing studies on a chemical radioprotector, Ex-RAD, with the aim of examining its efficacy of radiation protection as well as underlying mechanisms. To this end, a systematic search of the electronic databases including Pubmed, Scopus, Embase, and Google Scholar was conducted to retrieve articles investigating the radioprotective effect of Ex-RAD. From an initial search of 268 articles, and after removal of duplicates as well as applying the predetermined inclusion and exclusion criteria, 10 articles were finally included for this systematic review. Findings from the reviewed studies indicated that Ex-RAD showed potentials for effective radioprotection of the studied organs with no side effect. Furthermore, the inhibition of apoptosis through p53 signaling pathway was the main mechanism of radioprotection by Ex-RAD. However, its radioprotective effect would need to be investigated for more organs in future studies.

Intra-hepatic Abscopal Effect Following Radioembolization of Hepatic Metastases

Purpose

To search for abscopal effects (AE) distant to the site of radiation after sequential Yittrium-90 (Y-90) radioembolization (RE) of liver malignancies.

Methods and Materials

In this retrospective analysis, all patients treated by RE between 2007 and 2018 (n = 907) were screened for the following setting/conditions: sequential RE of left and right liver lobe in two sessions, liver-specific MRI (MRI1) acquired max. 10 days before or after first RE (RE1), liver-specific MRI (MRI2) acquired with a minimum time interval of 20 days after MRI1, but before second RE (RE2). No systemic tumor therapies between MRI1 and MRI2. No patients with liver cirrhosis. Metastases > 5 mm in untreated liver lobes were compared in MRI1 and MRI2 and rated as follows: same size or larger in MRI2 = no abscopal effect (NAE); > 30% shrinkage without Y-90 contamination in SPECT/CT = abscopal effect (AE).

Results

Ninety six of 907 patients met aforementioned criteria. Median time-frame between RE1 and MRI2 was 34 (20–64) days. These 96 cases had 765 metastases which were evaluable (median 5(1–40) metastases per patient). Four patients could be identified with at least one shrinking metastasis of the untreated site: one patient with breast cancer (3 metastases: 0 NAE; 3 AE), one patient with prostate cancer (6 metastases: 3 NAE; 3 metastases > 30% shrinkage but possible Y-90 contamination) and two patients with shrinkage of one metastasis each but less than 30%.

Conclusion

Our retrospective study documents AE after RE of liver tumors in 1 out of 96 cases, 3 other cases remain unclear.

Research Progress and Existing Problems for Abscopal Effect

Radiation therapy plays a vital role in the treatment of tumours. In particular, the occurrence of the “abscopal effect” brings about a favourable turn for the treatment of patients with advanced metastatic malignant tumours. Because of the abscopal effect, non-irradiated areas are also treated. However, the abscopal effect occurs by chance, not through seeking. Although the abscopal effect has been studied enthusiastically, the desired result does not appear to be achieved. Moreover, its combination with immunotherapy appears to be overwhelming. There is an opinion that abscopal effect is difficult to achieve by irradiation of a single tumour, and irradiation of multiple or total lesions is advocated to increase the possibility of obtaining clinically meaningful outcomes. Obviously, there are still questions about the mechanism, condition and possibility underlying the occurrence of the abscopal effect. Can the abscopal effect truly change the future treatment strategy as the researchers expect? What are the current problems? This article reviewed the research in recent years to explore the progress and controversy surrounding the abscopal effect of radiation therapy.

Applications of magnetotactic bacteria and magnetosome for cancer treatment: A review emphasizing on practical and mechanistic aspects

Magnetotactic bacteria (MTB) synthesize iron oxide (Fe₃O₄) nanoparticles (NPs), called magnetosomes, with large sizes leading to a ferrimagnetic behavior and a stable magnetic moment at physiological temperature, a chain structure that prevents NP aggregation and promotes uniform NP distribution, and a mineral core of magnetite/maghemite composition, which can be stabilized by an organic coating. Such properties can favor magnetosome administration to humans under certain optimized non-toxic conditions of fabrication. In this review, I describe the fabrication methods, physico-chemical properties, and the anti-tumor activity of different types of MTB/magnetosome preparations, highlighting the bio-compatibility and excellent anti-tumor activity of purified non-pyrogenic magnetosome minerals stabilized by a synthetic chemical compound.

Pure abscopal effect of radiotherapy in a salivary gland carcinoma: Case report, literature review, and a search for new approaches

We report the case of an 84-year-old woman with poorly differentiated non-small cell carcinoma of the right parotid who presented with headache, was found to have a primary right parotid gland cancer as well as metastatic disease, and underwent palliative radiotherapy to the primary site. The patient received no chemotherapy or immunotherapy, but both the primary site and several non-irradiated foci in the lungs regressed or completely resolved. The patient remained free of disease for about one year before progression. The case is a rare instance of abscopal regression of metastatic disease in the absence of pharmacologic immunomodulation. A literature review surveys the history of the abscopal effect of radiation therapy, attempts to understand the mechanisms of its successes and failures, and points to new approaches that can inform and improve the outcomes of radioimmunotherapy.

Combination of Gas Plasma and Radiotherapy Has Immunostimulatory Potential and Additive Toxicity in Murine Melanoma Cells in Vitro

Despite continuous advances in therapy, malignant melanoma is still among the deadliest types of cancer. At the same time, owing to its high plasticity and immunogenicity, melanoma is regarded as a model tumor entity when testing new treatment approaches. Cold physical plasma is a novel anticancer tool that utilizes a plethora of reactive oxygen species (ROS) being deposited on the target cells and tissues. To test whether plasma treatment would enhance the toxicity of an established antitumor therapy, ionizing radiation, we combined both physical treatment modalities targeting B16F10 murine melanoma cell in vitro. Repeated rather than single radiotherapy, in combination with gas plasma-introduced ROS, induced apoptosis and cell cycle arrest in an additive fashion. In tendency, gas plasma treatment sensitized the cells to subsequent radiotherapy rather than the other way around. This was concomitant with increased levels of TNFα, IL6, and GM-CSF in supernatants. Murine JAWS dendritic cells cultured in these supernatants showed an increased expression of cell surface activation markers, such as MHCII and CD83. For PD-L1 and PD-L2, increased expression was observed. Our results are the first to suggest an additive therapeutic effect of gas plasma and radiotherapy, and translational tumor models are needed to develop this concept further.

FLASH and minibeams in radiation therapy: the effect of microstructures on time and space and their potential application to protontherapy

After years of lethargy, studies on two non-conventional microstructures in time and space of the beams used in radiation therapy are enjoying a huge revival. The first effect called “FLASH” is based on very high dose-rate irradiation (pulse amplitude ≥10⁶ Gy/s), short beam-on times (≤100 ms) and large single doses (≥10 Gy) as experimental parameters established so far to give biological and potential clinical effects. The second effect relies on the use of arrays of minibeams (e.g., 0.5–1 mm, spaced 1–3.5 mm). Both approaches have been shown to protect healthy tissues as an endpoint that must be clearly specified and could be combined with each other (e.g., minibeams under FLASH conditions). FLASH depends on the presence of oxygen and could proceed from the chemistry of peroxyradicals and a reduced incidence on DNA and membrane damage. Minibeams action could be based on abscopal effects, cell signalling and/or migration of cells between “valleys and hills” present in the non-uniform irradiation field as well as faster repair of vascular damage. Both effects are expected to maintain intact the tumour control probability and might even preserve antitumoural immunological reactions. FLASH in vivo experiments involving Zebrafish, mice, pig and cats have been done with electron beams, while minibeams are an intermediate approach between X-GRID and synchrotron X-ray microbeams radiation. Both have an excellent rationale to converge and be applied with proton beams, combining focusing properties and high dose rates in the beam path of pencil beams, and the inherent advantage of a controlled limited range. A first treatment with electron FLASH (cutaneous lymphoma) has recently been achieved, but clinical trials have neither been presented for FLASH with protons, nor under the minibeam conditions. Better understanding of physical, chemical and biological mechanisms of both effects is essential to optimize the technical developments and devise clinical trials.

Relevance of Non-Targeted Effects for Radiotherapy and Diagnostic Radiology; A Historical and Conceptual Analysis of Key Players

Non-targeted effects (NTE) such as bystander effects or genomic instability have been known for many years but their significance for radiotherapy or medical diagnostic radiology are far from clear. Central to the issue are reported differences in the response of normal and tumour tissues to signals from directly irradiated cells. This review will discuss possible mechanisms and implications of these different responses and will then discuss possible new therapeutic avenues suggested by the analysis. Finally, the importance of NTE for diagnostic radiology and nuclear medicine which stems from the dominance of NTE in the low-dose region of the dose–response curve will be presented. Areas such as second cancer induction and microenvironment plasticity will be discussed.

Absence of mutations in the human interferon alpha-2b gene in workers chronically exposed to ionising radiation

Individuals chronically exposed to low-level ionising radiation (IR) run the risk of harmful and long-term adverse health effects, including gene mutations and cancer development. The search for reliable biomarkers of IR exposure in human population is still of great interest, as they may have a great implementation potential for the surveillance of occupationally exposed individuals. In this context, and considering previous literature, this study aimed to identify mutations in the human interferon alpha-2b (hIFNα-2b) as a potential biomarker of occupational chronic low-dose IR exposure linking low-IR exposure to the effects on haematopoiesis and reduced immunity. The analysis was performed in the genomic DNA of 51 uranium miners and 38 controls from Kazakhstan, and in 21 medical radiology workers and 21 controls from Italy. hIFNα-2b gene mutations were analysed with the real-time polymerase chain reaction (PCR) or Sanger sequencing. However, none of the investigated workers had the hIFNα-2b mutation. This finding highlights the need for further research to identify biomarkers for early detection of health effects associated with chronic low-dose IR exposure.

Piperlongumine increases sensitivity of colorectal cancer cells to radiation: Involvement of ROS production via dual inhibition of glutathione and thioredoxin systems

Piperlongumine (PL), naturally synthesized in long pepper, is known to selectively kill tumor cells via perturbation of reactive oxygen species (ROS) homeostasis. ROS are the primary effector molecules of radiation, and increase of ROS production by pharmacological modulation is known to enhance radioresponse. We therefore investigated the radiosensitizing effect of PL in colorectal cancer cells (CT26 and DLD-1) and CT26 tumor-bearing mice. Firstly, we found that PL induced excessive production of ROS due to depletion of glutathione and inhibition of thioredoxin reductase. Secondly, PL enhanced both the intrinsic and hypoxic radiosensitivity of tumor cells, linked to ROS-mediated increase of DNA damage, G2/M cell cycle arrest, and inhibition of cellular respiration. Finally, the radiosensitizing effect of PL was verified in vivo. PL improved the tumor response to both single and fractionated radiation, resulting in a significant increase of survival rate of tumor-bearing mice, while it was ineffective on its own. In line with in vitro findings, enhanced radioresponse is associated with inhibition of antioxidant systems. In conclusion, our results suggest that PL could be a potential radiosensitizer in colorectal cancer.

Delta-24-RGD combined with radiotherapy exerts a potent antitumor effect in diffuse intrinsic pontine glioma and pediatric high grade glioma models

Pediatric high grade gliomas (pHGG), including diffuse intrinsic pontine gliomas (DIPGs), are aggressive tumors with a dismal outcome. Radiotherapy (RT) is part of the standard of care of these tumors; however, radiotherapy only leads to a transient clinical improvement. Delta-24-RGD is a genetically engineered tumor-selective adenovirus that has shown safety and clinical efficacy in adults with recurrent gliomas. In this work, we evaluated the feasibility, safety and therapeutic efficacy of Delta-24-RGD in combination with radiotherapy in pHGGs and DIPGs models. Our results showed that the combination of Delta-24-RGD with radiotherapy was feasible and resulted in a synergistic anti-glioma effect in vitro and in vivo in pHGG and DIPG models. Interestingly, Delta-24-RGD treatment led to the downregulation of relevant DNA damage repair proteins, further sensitizing tumors cells to the effect of radiotherapy. Additionally, Delta-24-RGD/radiotherapy treatment significantly increased the trafficking of immune cells (CD3, CD4+ and CD8+) to the tumor niche compared with single treatments. In summary, administration of the Delta-24-RGD/radiotherapy combination to pHGG and DIPG models is safe and significantly increases the overall survival of mice bearing these tumors. Our data offer a rationale for the combination Delta-24-RGD/radiotherapy as a therapeutic option for children with these tumors. SIGNIFICANCE: Delta-24-RGD/radiotherapy administration is safe and significantly increases the survival of treated mice. These positive data underscore the urge to translate this approach to the clinical treatment of children with pHGG and DIPGs.

Reduced Number of Lymphocytes by X-ray Irradiation: A Problem in a Combination Therapy Trial that Elicits the Abscopal Effect in Preclinical Studies Using Electron Beam Irradiation

In preclinical studies with model animals, intravenous administration of a derivative of chemokine CCL3, named eMIP, after local electron-beam irradiation, not only enhanced tumor growth inhibition at a target site but also induced tumor killing beyond the treated site (a phenomenon known as the abscopal effect). eMIP works with alarmins such as high mobility group box 1 (HMGB1) and heat shock protein 70 (HSP70) released from overexpressed tumor cells by irradiation. These alarmins at the irradiated tumor bed trap injected eMIP and, by forming complexes with eMIP, play a key role to recruit and activate tumor inhibitory natural killer (NK) cells and CD4⁺ and CD8⁺ T cells. Tumor type-specific secretion of gamma interferon from splenocytes was also demonstrated, which may also activate NK cells. During Phase 1 clinical studies using X-rays, however, no apparent abscopal effect was observed. Instead, we saw frequent reduction in numbers of lymphocytes in the peripheral blood of irradiated patients. The reduced number of lymphocytes recovered poorly once depleted, in contrast to neutrophils, and persisted for months after the treatment. This might have affected outcome after combination treatment of irradiation and eMIP. To enhance host defense mechanisms during and after photon-beam (X-ray) radiotherapy of a deep-seated tumor, it seems essential to keep lymphocytes undamaged by eliminating reactive oxygen species that are formed in the peripheral blood during irradiation.

Exploring the Potential Utility of Pet Dogs With Cancer for Studying Radiation-Induced Immunogenic Cell Death Strategies

Radiotherapy serves as a foundational pillar for the therapeutic management of diverse solid tumors through the generation of lethal DNA damage and induction of cell death. While the direct cytotoxic effects of radiation therapy remain a cornerstone for cancer management, in the era of immunooncology there is renewed and focused interest in exploiting the indirect bystander activities of radiation, termed abscopal effects. In radioimmunobiologic terms, abscopal effects describe the radiotherapy-induced regression of cancerous lesions distant from the primary site of radiation delivery and rely upon the induction of immunogenic cell death and consequent systemic anticancer immune activation. Despite the promise of radiation therapy for awaking potent anticancer immune responses, the purposeful harnessing of abscopal effects with radiotherapy remain clinically elusive. In part, failure to fully leverage and clinically implement the promise of radiation-induced abscopal effects stems from limitations associated with existing conventional tumor models which inadequately recapitulate the complexity of malignant transformation and the dynamic nature of tumor immune surveillance. To supplement this existing gap in modeling systems, pet dogs diagnosed with solid tumors including melanoma and osteosarcoma, which are both metastatic and immunogenic in nature, could potentially serve as unique resources for exploring the fundamental underpinnings required for maximizing radiation-induced abscopal effects. Given the spontaneous course of cancer development in the context of operative immune mechanisms, pet dogs treated with radiotherapy for metastatic solid tumors might be leveraged as valuable model systems for realizing the science and best clinical practices necessary to generate potent abscopal effects with anti-metastatic immune activities.

Abscopal Effect, From Myth to Reality: From Radiation Oncologists' Perspective

The abscopal effect is mediated by a systemic anti-tumor immune response and reflects the regression of non-irradiated metastatic lesions at a distance from the primary site of irradiation. This review will focus on understanding the biological rationale behind the abscopal effect of radiotherapy (RT), which has a recently renewed interest as a result of the successes achieved with immunotherapy and RT in combination. Both RT and immunotherapy are standard components of modern treatment regimens. Combination of these two modalities results in an increased response in the irradiated lesions themselves and the metastatic regions distant from the site of irradiation. We will summarize the abscopal effect of radiotherapy, in particular, the synergistic effect of RT and immunotherapy.

A comparison of mechanism-inspired models for particle relative biological effectiveness (RBE)

BACKGROUND AND SIGNIFICANCE

The application of heavy ion beams in cancer therapy must account for the increasing relative biological effectiveness (RBE) with increasing penetration depth when determining dose prescriptions and organ at risk (OAR) constraints in treatment planning. Because RBE depends in a complex manner on factors such as the ion type, energy, cell and tissue radiosensitivity, physical dose, biological endpoint, and position within and outside treatment fields, biophysical models reflecting these dependencies are required for the personalization and optimization of treatment plans.

AIM

To review and compare three mechanism-inspired models which predict the complexities of particle RBE for various ion types, energies, linear energy transfer (LET) values and tissue radiation sensitivities.

METHODS

The review of models and mechanisms focuses on the Local Effect Model (LEM), the Microdosimetric-Kinetic (MK) model, and the Repair-Misrepair-Fixation (RMF) model in combination with the Monte Carlo Damage Simulation (MCDS). These models relate the induction of potentially lethal double strand breaks (DSBs) to the subsequent interactions and biological processing of DSB into more lethal forms of damage. A key element to explain the increased biological effectiveness of high LET ions compared to MV x rays is the characterization of the number and local complexity (clustering) of the initial DSB produced within a cell. For high LET ions, the spatial density of DSB induction along an ion's trajectory is much greater than along the path of a low LET electron, such as the secondary electrons produced by the megavoltage (MV) x rays used in conventional radiation therapy. The main aspects of the three models are introduced and the conceptual similarities and differences are critiqued and highlighted. Model predictions are compared in terms of the RBE for DSB induction and for reproductive cell survival.

RESULTS AND CONCLUSIONS

Comparisons of the RBE for DSB induction and for cell survival are presented for proton (¹ H), helium (⁴ He), and carbon (¹² C) ions for the therapeutically most relevant range of ion beam energies. The reviewed models embody mechanisms of action acting over the spatial scales underlying the biological processing of potentially lethal DSB into more lethal forms of damage. Differences among the number and types of input parameters, relevant biological targets, and the computational approaches among the LEM, MK and RMF models are summarized and critiqued. Potential experiments to test some of the seemingly contradictory aspects of the models are discussed.

Radiotherapy and immune response: the systemic effects of a local treatment

Technological developments have allowed improvements in radiotherapy delivery, with higher precision and better sparing of normal tissue. For many years, it has been well known that ionizing radiation has not only local action but also systemic effects by triggering many molecular signaling pathways. There is still a lack of knowledge of this issue. This review focuses on the current literature about the effects of ionizing radiation on the immune system, either suppressing or stimulating the host reactions against the tumor, and the factors that interact with these responses, such as the radiation dose and dose / fraction effects in the tumor microenvironment and vasculature. In addition, some implications of these effects in cancer treatment, mainly in combined strategies, are addressed from the perspective of their interactions with the more advanced technology currently available, such as heavy ion therapy and nanotechnology.

Clinically Relevant Radiation Exposure Differentially Impacts Forms of Cell Death in Human Cells of the Innate and Adaptive Immune System

In cancer treatments, especially high-dose radiotherapy (HDRT) is applied. Patients suffering from chronic inflammatory diseases benefit from low-dose radiation therapy (LDRT), but exposure to very low radiation doses can still steadily increase for diagnostic purposes. Yet, little is known about how radiation impacts on forms of cell death in human immune cells. In this study, the radiosensitivity of human immune cells of the peripheral blood was examined in a dose range from 0.01 to 60 Gy with regard to induction of apoptosis, primary necrosis, and secondary necrosis. Results showed that immune cells differed in their radiosensitivity, with monocytes being the most radioresistant. T cells mainly died by necrosis and were moderately radiosensitive. This was followed by B and natural killer (NK) cells, which died mainly by apoptosis. X-radiation had no impact on cell death in immune cells at very low doses (≤0.1 Gy). Radiation doses of LDRT (0.3–0.7 Gy) impacted on the more radiosensitive NK and B cells, which might contribute to attenuation of inflammation. Even single doses applied during RT of tumors did not erase the immune cells completely. These in vitro studies can be considered as the basis to optimize individual radiation therapy schemes in multimodal settings and to define suited time points for further inclusion of immunotherapies.

Proton minibeam radiation therapy widens the therapeutic index for high-grade gliomas

Proton minibeam radiation therapy (pMBRT) is a novel strategy which has already shown a remarkable reduction in neurotoxicity as to compared with standard proton therapy. Here we report on the first evaluation of tumor control effectiveness in glioma bearing rats with highly spatially modulated proton beams. Whole brains (excluding the olfactory bulb) of Fischer 344 rats were irradiated. Four groups of animals were considered: a control group (RG2 tumor bearing rats), a second group of RG2 tumor-bearing rats and a third group of normal rats that received pMBRT (70 Gy peak dose in one fraction) with very heterogeneous dose distributions, and a control group of normal rats. The tumor-bearing and normal animals were followed-up for 6 months and one year, respectively. pMBRT leads to a significant tumor control and tumor eradication in 22% of the cases. No substantial brain damage which confirms the widening of the therapeutic window for high-grade gliomas offered by pMBRT. Additionally, the fact that large areas of the brain can be irradiated with pMBRT without significant side effects, would allow facing the infiltrative nature of gliomas.

Proton radiation-induced cancer progression

There are considerable health risks related to ionizing and proton radiation exposure. While there is a long history of health risks associated with ionizing (photon) radiation exposure, there is a limited understanding of the long-term health risks associated with proton radiation exposure. Since proton radiation is becoming more common in cancer therapy, the long-term biological effects of proton radiation remain less well characterized in terms of radiotherapy and well as for astronauts during deep space explorations. In this study, we compared the long-term side effects of proton radiation to equivalent doses of X-rays in the initiation and progression of premalignant lesions in a lung cancer susceptible mouse model (K-ras^LA1). We show proton irradiation causes more complex DNA damage that is not completely repaired resulting in increased oxidative stress in the lungs both acutely and persistently. We further observed K-ras^LA1 mice irradiated with protons had an increased number and size of initiated and premalignant lesions and adenomas that were often infiltrated with inflammatory cells. Proton irradiated mice had a lower median survival and increased carcinoma incidence as compared to unirradiated controls and X-rays exposed mice. Our conclusion is that exposure to proton irradiation enhances the progression of premalignant lesions to invasive carcinomas through persistent DNA damage, chronic oxidative stress, and immunosuppression.

Implementation of planar proton minibeam radiation therapy using a pencil beam scanning system: A proof of concept study

PURPOSE

Proton minibeam radiation therapy (pMBRT) is an innovative approach that combines the advantages of minibeam radiation therapy with the more precise ballistics of protons to further reduce the side effects of radiation. One of the main challenges of this approach is the generation of very narrow proton pencil beams with an adequate dose-rate to treat patients within a reasonable treatment time (several minutes) in existing clinical facilities. The aim of this study was to demonstrate the feasibility of implementing pMBRT by combining the pencil beam scanning (PBS) technique with the use of multislit collimators. This proof of concept study of pMBRT with a clinical system is intended to guide upcoming biological experiments.

METHODS

Monte Carlo simulations (TOPAS v3.1.p2) were used to design a suitable multislit collimator to implement planar pMBRT for conventional pencil beam scanning settings. Dose distributions (depth-dose curves, lateral profiles, Peak-to-Valley Dose Ratio (PVDR) and dose-rates) for different proton beam energies were assessed by means of Monte Carlo simulations and experimental measurements in a water tank using commercial ionization chambers and a new p-type silicon diode, the IBA RAZOR. An analytical intensity-modulated dose calculation algorithm designed to optimize the weight of individual Bragg peaks composing the field was also developed and validated.

RESULTS

Proton minibeams were then obtained using a brass multislit collimator with five slits measuring 2 cm × 400 μm in width with a center-to-center distance of 4 mm. The measured and calculated dose distributions (depth-dose curves and lateral profiles) showed a good agreement. Spread-out Bragg peaks (SOBP) and homogeneous dose distributions around the target were obtained by means of intensity modulation of Bragg peaks, while maintaining spatial fractionation at shallow depths. Mean dose-rates of 0.12 and 0.09 Gy/s were obtained for one iso-energy layer and a SOBP conditions in the presence of multislit collimator.

CONCLUSIONS

This study demonstrates the feasibility of implementing pMBRT on a PBS system. It also confirms the reliability of RAZOR detector for pMBRT dosimetry. This newly developed experimental methodology will support the design of future preclinical research with pMBRT.

Low-Dose Radiotherapy Ameliorates Advanced Arthritis in hTNF-α tg Mice by Particularly Positively Impacting on Bone Metabolism

Inflammation and bone erosion are central in rheumatoid arthritis (RA). Even though effective medications for control and treatment of RA are available, remission is only seen in a subset of patients. Treatment with low-dose radiotherapy (LD-RT) which has been already successfully used for amelioration of symptoms in benign diseases should be a promising approach to reduce pain, inflammation, and particularly bone erosion in patients with RA. Even though anti-inflammatory effects of LD-RT are already described with non-linear dose response relationships, and pain-reducing effects have been clinically observed, the underlying mechanisms are widely unknown. Besides immune cells many other cell types, such as fibroblast-like synoviocytes (FLS), osteoclasts, and osteoblast are present in the affected joint and might be modulated by LD-RT. For this study, these cell types were obtained from human tumor necrosis factor-α transgenic (hTNF-α tg) mice and were consecutively exposed to different doses of ionizing radiation (0.1, 0.5, 1.0, and 2.0 Gy, respectively) in vitro. In order to study the in vivo effects of LD-RT within the arthritic joint, hind paws of arthritic hTNF-α tg mice were locally irradiated with 0.5 Gy, a single dose per fraction that is known for good clinical responses. Starting at a dose of 0.5 Gy, proliferation of FLS was reduced and apoptosis significantly enhanced with no changes in necrosis. Further, expression of RANK-L was slightly reduced following irradiation with particularly 0.5 Gy. Starting from 0.5 Gy, the numbers of differentiated osteoclasts were significantly reduced, and a lower bone resorbing activity of treated osteoclasts was also observed, as monitored via pit formation and Cross Laps presence. LD-RT had further a positive effect on osteoblast-induced mineralization in a discontinuous dose response relationship with 0.5 Gy being most efficient. An increase of the gene expression ratio of OPG/RANK-L at 0.1 and 0.5 Gy and of production of OPG at 0.5 and 1.0 Gy was observed. In vivo, LD-RT resulted in less severe arthritis in arthritic hTNF-α tg mice and in significant reduction of inflammatory and erosive area with reduced osteoclasts and neutrophils. Locally applied LD-RT can, therefore, induce a beneficial micro-environment within arthritic joints by predominantly positively impacting on bone metabolism.

Use of a Small Animal Radiation Research Platform (SARRP) facilitates analysis of systemic versus targeted radiation effects in the mouse ovary

BACKGROUND

Radiation exposure is known to cause accelerated aging and damage to the ovary, but the contribution of indirect versus direct effects is not well understood. We used the Small Animal Radiation Research Platform (SARRP) (Xstrahl) to deliver radiation to precise fields equivalent to clinical practice, allowing us to investigate systemic versus targeted damage in a structure as small as the mouse ovary. The X-ray dose was kept constant at 1 Gy, but the field varied. Mice either received total body irradiation (TBI), radiation targeted to both ovaries (T2), or radiation targeted to one ovary (left) while the contralateral ovary (right) was spared (T1). Sham mice, handled similarly to the other cohorts but not exposed to radiation, served as controls. Two weeks post-exposure, ovaries were harvested and analyzed histologically to identify and count follicles within each ovary.

RESULTS

Radiation significantly reduced primordial follicles in the TBI and T2 cohorts compared to the Sham cohort. There were no significant differences between these two irradiated groups. These findings suggest that at 1 Gy, the extent of damage to the ovary caused by radiation is similar despite the different delivery methods. When investigating the T1 cohort, targeted ovaries showed a significant decrease in primordial and growing follicles compared to non-targeted contralateral ovaries.

CONCLUSIONS

These findings demonstrate that the SARRP is an effective strategy for delivering precise ionizing radiation to small organs such as mouse ovaries. Such tools will facilitate identifying the relative risks to ovarian function associated with different radiation fields as well as screening the efficacy of emerging fertoprotective agents.

Melatonin as an adjuvant in radiotherapy for radioprotection and radiosensitization

It is estimated that more than half of cancer patients undergo radiotherapy during the course of their treatment. Despite its beneficial therapeutic effects on tumor cells, exposure to high doses of ionizing radiation (IR) is associated with several side effects. Although improvements in radiotherapy techniques and instruments could reduce these side effects, there are still important concerns for cancer patients. For several years, scientists have been trying to modulate tumor and normal tissue responses to IR, leading to an increase in therapeutic ratio. So far, several types of radioprotectors and radiosensitizers have been investigated in experimental studies. However, high toxicity of chemical sensitizers or possible tumor protection by radioprotectors creates a doubt for their clinical applications. On the other hand, the protective effects of these radioprotectors or sensitizer effects of radiosensitizers may limit some type of cancers. Hence, the development of some radioprotectors without any protective effect on tumor cells or low toxic radiosensitizers can help improve therapeutic ratio with less side effects. Melatonin as a natural body hormone is a potent antioxidant and anti-inflammatory agent that shows some anti-cancer properties. It is able to neutralize different types of free radicals produced by IR or pro-oxidant enzymes which are activated following exposure to IR and plays a key role in the protection of normal tissues. In addition, melatonin has shown the ability to inhibit long-term changes in inflammatory responses at different levels, thereby ameliorating late side effects of radiotherapy. Fortunately, in contrast to classic antioxidants, some in vitro studies have revealed that melatonin has a potent anti-tumor activity when used alongside irradiation. However, the mechanisms of its radiosensitive effect remain to be elucidated. Studies suggested that the activation of pro-apoptosis gene, such as p53, changes in the metabolism of tumor cells, suppression of DNA repair responses as well as changes in biosynthesis of estrogen in breast cancer cells are involved in this process. In this review, we describe the molecular mechanisms for radioprotection and radiosensitizer effects of melatonin. Furthermore, some other proposed mechanisms that may be involved are presented.

Ionizing Radiation Induces Morphological Changes and Immunological Modulation of Jurkat Cells

Impairment or stimulation of the immune system by ionizing radiation (IR) impacts on immune surveillance of tumor cells and non-malignant cells and can either foster therapy response or side effects/toxicities of radiation therapy. For a better understanding of the mechanisms by which IR modulates T-cell activation and alters functional properties of these immune cells, we exposed human immortalized Jurkat cells and peripheral blood lymphocytes (PBL) to X-ray doses between 0.1 and 5 Gy. This resulted in cellular responses, which are typically observed also in naïve T-lymphocytes in response of T-cell receptor immune stimulation or mitogens. These responses include oscillations of cytosolic Ca²⁺, an upregulation of CD25 surface expression, interleukin-2 and interferon-γ synthesis, elevated expression of Ca²⁺ sensitive K⁺ channels and an increase in cell diameter. The latter was sensitive to inhibition by the immunosuppressant cyclosporine A, Ca²⁺ buffer BAPTA-AM, and the CDK1-inhibitor RO3306, indicating the involvement of Ca²⁺-dependent immune activation and radiation-induced cell cycle arrest. Furthermore, on a functional level, Jurkat and PBL cell adhesion to endothelial cells was increased upon radiation exposure and was highly dependent on an upregulation of integrin beta-1 expression and clustering. In conclusion, we here report that IR impacts on immune activation and functional properties of T-lymphocytes that may have implications in both toxic effects and treatment response to combined radiation and immune therapy in cancer patients.

Molecular mechanism of bystander effects and related abscopal/cohort effects in cancer therapy

Cancer cells subjected to ionizing radiation may release signals which can influence nearby non-irradiated cells, termed bystander effects. The transmission of bystander effects among cancer cells involves the activation of inflammatory cytokines, death ligands, and reactive oxygen/nitrogen species. In addition to bystander effects, two other forms of non-target effects (NTEs) have been identified in radiotherapy, as one is called cohort effects and the other is called abscopal effects. Cohort effects represent the phenomenon where irradiated cells can produce signals that reduce the survival of neighboring cells within an irradiated volume. The effects suggest the importance of cellular communication under irradiation with non-uniform dose distribution. In contrast, abscopal effects describe the NTEs that typically occur in non-irradiated cells distant from an irradiated target. These effects can be mediated primarily by immune cells such as T cells. Clinical trials have shown that application of radiation along with immunotherapy may enhance abscopal effects and improve therapeutic efficacy on non-target lesions outside an irradiated field. According to NTEs, cell viability is reduced not only by direct irradiation effects, but also due to signals emitted from nearby irradiated cells. A clinical consideration of NTEs could have a revolutionary impact on current radiotherapy via the establishment of more efficient and less toxic radiobiological models for treatment planning compared to conventional models. Thus, we will review the most updated findings about these effects and outline their mechanisms and potential applications in cancer treatment with a special focus on the brain, lung, and breast cancers.