Direct and bystander radiation effects: a biophysical model and clinical perspectives

Preliminary Results of the Effects of Localized High-Dose Radiotherapy Combined with Total Body Low-Dose Irradiation on Tumor Growth and Stimulating the Immune System in Tumor-Bearing Mice

Background

The immune system plays an extensive role in eliminating tumor cells. On the other hand, low-dose irradiation stimulates the immune system.

Objective

The present study aimed to investigate the therapeutic outcomes of localized high-dose radiotherapy (LH) alone and combined with total body low-dose irradiation (TB).

Material and Methods

In this experimental study, B16F0 tumor cells were injected into the right flank of C57JL/6 mice. The mice were treated with LH alone (13 Gy X-rays to the tumor surface) (LH group) or combined with TB (85 mGy X-rays at the skin) (TB+LH group). Then the tumor volume, the mice's lifespan, the number of lymphocytes extracted from the spleen, and interferon gamma (IFN-γ) production were measured.

Results

Reduced number of lymphocytes, compared to non-irradiated mice (control group), was observed in LH and TB+LH groups. However, the identical number of cultured lymphocytes produced a higher level of IFN-γ in irradiated groups. Comparing the irradiated groups, the number of lymphocytes and their IFN-γ production, tumor growth control, and the mice's lifespan were statistically higher in TB+LH group.

Conclusion

Observing a higher level of IFN-γ in TB+LH group compared to LH group indicates that low-dose radiation enhanced the stimulating effects of high-dose radiation on the immune system. It caused the mice in TB+LH group to have a more prolonged lifespan and a lower tumor growth rate. Therefore, it is worth our attention for future studies to investigate whether total body low-dose irradiation can be utilized before radiotherapy to enhance its efficiency.

Novel unconventional radiotherapy techniques: Current status and future perspectives - Report from the 2nd international radiation oncology online seminar

•Improvement of therapeutic ratio by novel unconventional radiotherapy approaches.•Immunomodulation using high-dose spatially fractionated radiotherapy.•Boosting radiation anti-tumor effects by adding an immune-mediated cell killing.

Ionizing Radiation: Effective Physical Agents for Economic Crop Seed Priming and the Underlying Physiological Mechanisms

To overcome various factors that limit crop production and to meet the growing demand for food by the increasing world population. Seed priming technology has been proposed, and it is considered to be a promising strategy for agricultural sciences and food technology. This technology helps to curtail the germination time, increase the seed vigor, improve the seedling establishment, and enhance the stress tolerance, all of which are conducive to improving the crop yield. Meanwhile, it can be used to reduce seed infection for better physiological or phytosanitary quality. Compared to conventional methods, such as the use of water or chemical-based agents, X-rays, gamma rays, electron beams, proton beams, and heavy ion beams have emerged as promising physics strategies for seed priming as they are time-saving, more effective, environmentally friendly, and there is a greater certainty for yield improvement. Ionizing radiation (IR) has certain biological advantages over other seed priming methods since it generates charged ions while penetrating through the target organisms, and it has enough energy to cause biological effects. However, before the wide utilization of ionizing priming methods in agriculture, extensive research is needed to explore their effects on seed priming and to focus on the underlying mechanism of them. Overall, this review aims to highlight the current understanding of ionizing priming methods and their applicability for promoting agroecological resilience and meeting the challenges of food crises nowadays.

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.

Quantifying the influences of radiation therapy on deformability of human red blood cells by dual-beam optical tweezers

Radiation therapy is widely used as a treatment tool for malignancies. However, radiation-related complications are still unavoidable risks for off-target cells. Little is known about radiation therapy's possible effects on mechanical features of the off-target cells such as human red blood cells (RBCs). RBCs are nucleus-free circulating cells that can deform without losing functionality in healthy conditions. Thus, to evaluate in vitro effects of radiation therapy on the healthy plasma membrane of cells, RBCs were selected as a primary test model. RBCs were exposed to clinically prescribed radiotherapy doses of 2 Gy, 12 Gy and, 25 Gy, and each radiotherapy dose group was compared to a non-irradiated group. Cells were characterized by stretching using dual-beam optical tweezers and compared using the resulting deformability index. The group receiving the highest radiation dose was found statistically distinguishable from the control group (DI_0Gy = 0.33 ± 0.08), and revealed the highest deformability index (DI_25Gy = 0.38 ± 0.11, p = 0.0068), while no significant differences were found for 2 Gy (DI_2Gy = 0.33 ± 0.08, p = 0.9) and 12 Gy (DI_12Gy = 0.31 ± 0.09, p = 0.2) dose groups. Based on these findings, we conclude that radiotherapy exposure may alter the deformability of red blood cells depending on the dose amount, and measurement of deformability index by dual-beam optical tweezers can serve as a sensitive biomarker to probe responses of cells to the radiotherapy.

Little is known about radiation therapy's possible effects on mechanical features of off-target cells such as human red blood cells. Here, irradiated human red blood cells were stretched using dual-beam optical tweezers and compared using the resulting deformability index.

Rationale for the Use of Radiation-Activated Mesenchymal Stromal/Stem Cells in Acute Respiratory Distress Syndrome

We have previously shown that the combination of radiotherapy with human umbilical-cord-derived mesenchymal stromal/stem cells (MSCs) cell therapy significantly reduces the size of the xenotumors in mice, both in the directly irradiated tumor and in the distant nonirradiated tumor or its metastasis. We have also shown that exosomes secreted from MSCs preirradiated with 2 Gy are quantitatively, functionally and qualitatively different from the exosomes secreted from nonirradiated mesenchymal cells, and also that proteins, exosomes and microvesicles secreted by MSCs suffer a significant change when the cells are activated or nonactivated, with the amount of protein present in the exosomes of the preirradiated cells being 1.5 times greater compared to those from nonirradiated cells. This finding correlates with a dramatic increase in the antitumor activity of the radiotherapy when is combined with MSCs or with preirradiated mesenchymal stromal/stem cells (MSCs*). After the proteomic analysis of the load of the exosomes released from both irradiated and nonirradiated cells, we conclude that annexin A1 is the most important and significant difference between the exosomes released by the cells in either status. Knowing the role of annexin A1 in the control of hypoxia and inflammation that is characteristic of acute respiratory-distress syndrome (ARDS), we designed a hypothetical therapeutic strategy, based on the transplantation of mesenchymal stromal/stem cells stimulated with radiation, to alleviate the symptoms of patients who, due to pneumonia caused by SARS-CoV-2, require to be admitted to an intensive care unit for patients with life-threatening conditions. With this hypothesis, we seek to improve the patients' respiratory capacity and increase the expectations of their cure.

Enhancing the Bystander and Abscopal Effects to Improve Radiotherapy Outcomes

In this paper, we summarize published articles and experiences related to the attempt to improve radiotherapy outcomes and, thus, to personalize the radiation treatment according to the individual characteristics of each patient. The evolution of ideas and the study of successively published data have led us to envisage new biophysical models for the interpretation of tumor and healthy normal tissue response to radiation. In the development of the model, we have shown that when mesenchymal stem cells (MSCs) and radiotherapy are administered simultaneously in experimental radiotherapy on xenotumors implanted in a murine model, the results of the treatment show the existence of a synergic mechanism that is able to enhance the local and systemic actions of the radiation both on the treated tumor and on its possible metastasis. We are convinced that, due to the physical hallmarks that characterize the neoplastic tissues, the physical-chemical tropism of MSCs, and the widespread functions of macromolecules, proteins, and exosomes released from activated MSCs, the combination of radiotherapy plus MSCs used intratumorally has the effect of counteracting the pro-tumorigenic and pro-metastatic signals that contribute to the growth, spread, and resistance of the tumor cells. Therefore, we have concluded that MSCs are appropriate for therapeutic use in a clinical trial for rectal cancer combined with radiotherapy, which we are going to start in the near future.

Protection to immune system of mice by N-acetyl tryptophan glucoside (NATG) against gamma radiation induced immune suppression

Immune system is a critical modulator of radiation-induced biological effects. In this study, we have assessed protective potential of N-acetyl tryptophan glucoside (NATG) pre-treatment in bone marrow of gamma radiation challenged mice. Isolated bone marrow cells were analysed for cell cycle progression by flow cytometry, while various pro-/anti-inflammatory cytokine profiles were performed by ELISA method. Overall radioprotective ability of NATG in ensuring protection against gamma radiation-induced damage was assessed by evaluating whole body survival analysis and haematological studies on 9 Gy irradiated mice with/without NATG pre-treatment. Results exhibited pre-treatment with 150 mg/kg b.wt oral administration of NATG as most effective against 9 Gy radiation exposure. Moreover, NATG showed non-interfering effect on cell cycle progression in pre-treated irradiated mice group when compared to radiation alone group. In addition, cytokine expression analysis indicated significant (p > 0.05) elevation in levels of IFN-γ, IL-2, IL-12, IL-13 and IL-17 in NATG pre-treated irradiated mice in comparison to radiation alone group. On the contrary, NATG pre-treatment was observed to alleviate levels of TNF-α and IL-10 significantly (p < 0.05) in radiated group as compared to only irradiated mice group. Furthermore, NATG pre-treatment to 9 Gy radiation exposed mice aided in restoring their haematological parameters in terms of haemoglobin counts, RBC counts, WBC counts, hematocrit levels, platelets and granulocyte levels in comparison to irradiated alone mice, thus enhancing their immune system and contributing towards a better survival against gamma radiation-induced deleterious effects. Conclusively, this study highlights the potential of NATG as a prospective radiation countermeasure agent against ionizing radiation-induced assaults to the immune system.

miR-27a-containing Exosomes Secreted by Irradiated Skin Keratinocytes Delayed the Migration of Unirradiated Skin Fibroblasts

Radiation-induced bystander effect (RIBE), e.g. the biological response occurring in unirradiated cells when their neighboring cells are irradiated, is the consequence of intercellular communication between irradiated and unirradiated cells and intracellular signal transduction of these two cell populations. Although several miRNAs have been found to play an important role in RIBEs, the evidence for the regulatory effects of miRNAs on RIBEs is still limited. In this study, by using a two cell-line co-culture system, we first found that the migration of unirradiated bystander WS1 skin fibroblasts was inhibited after co-culture with irradiated HaCaT skin keratinocytes. Further study revealed that HaCaT cells exposed to α-particles and X-rays quickly showed an elevated miR-27a expression, which was essential for the induction of the bystander effect, resulting in the secretion of miR-27a-containing exosomes as a major RIBE signaling factor. Upon uptake of these exosomes, the recipient unirradiated WS1 cells displayed oxidative stress and increased miR-27a levels. Elevated levels of miR-27a that targets MMP2 in the recipient WS1 cells then led to slowed cell migration, which was dependent upon the redox status of WS1 cells. To summarize, the present study has revealed a critical role of miR-27a in every step of the induction of bystander migration inhibition of unirradiated WS1 fibroblasts co-cultured with irradiated HaCaT keratinocytes, confirming the important regulatory effects of miRNAs in RIBEs. Additionally, we provided direct evidence that RIBEs could affect wound healing.

Enhancing low-dose risk assessment using mechanistic mathematical models of radiation effects

Mechanistic mathematical modeling of ionizing radiation (IR) effects has a long history spanning several decades. Models that mathematically represent current knowledge and hypotheses about how radiation damages cells and organs, leading to deleterious outcomes such as carcinogenesis, are particularly useful for estimating radiation risks at doses that are relevant for radiation protection, but are too low to provide a strong 'signal-to-noise ratio' in epidemiological or experimental studies with realistic sample sizes. Here, I discuss examples of models in several relevant areas, including radionuclide biokinetics, non-targeted IR effects, DNA double-strand break (DSB) rejoining and radiation carcinogenesis. I do not provide a detailed review of the vast modeling literature in these fields, but focus on concepts that we have implemented, such as using continuous probability distributions of exponential rates to model radionuclide biokinetics and DSB rejoining, and combining short and long time scales in carcinogenesis models. Improvements in models, including the ability to generate new hypotheses based on model predictions, may come from the introduction of additional novel concepts and from integrating multiple data types.

Local ablative stereotactic body radiotherapy for oligometastatic prostate cancer

PURPOSE OF REVIEW

The oligometastases is considered an intermediate state of the disease between localized and wide spread metastases. Local ablative therapy to oligometastatic prostate cancer is gaining significant traction and stereotactic body radiotherapy (SBRT) is an emerging treatment modality for this patient population. In this review, we report our literature review of SBRT to prostate oligometastases. Current evidence on the role of SBRT in oligometastatic prostate cancer reported in the last 10 years was summarized. Criteria for inclusion included studies with prostate cancer only as the primary site.

RECENT FINDINGS

The unique properties of the oligometastatic prostate cancer appear to carry a better prognosis than wide spread metastatic disease, especially if these metastases are amenable to local ablative therapies. Our literature review revealed that local ablative therapy, using SBRT to prostate oligometastases, is associated with significant 2-years local control and acceptable toxicity profile.

SUMMARY

SBRT to oligometastatic prostate cancer patients is feasible and carries an acceptable toxicity profile. The randomized phase II and III trials, currently underway, should clearly define the real benefit of this approach on progression-free and overall survival outcomes.

Stereotactic Ablative Radiotherapy Combined with Immune Checkpoint Inhibitors Reboots the Immune Response Assisted by Immunotherapy in Metastatic Lung Cancer: A Systematic Review

Background: Immune checkpoint inhibitors (ICI) have represented a revolution in the treatment of non-small-cell lung cancer (NSCLC). To improve these results, combined approaches are being tested. The addition of stereotactic ablative radiotherapy (SABR) to ICI seems promising. A systematic review was performed in order to assess the safety and efficacy of SABR-ICI combination. Material and Methods: MEDLINE databases from 2009 to March 3, 2019 were reviewed to obtain English language studies reporting clinical outcomes of the combination of ICI-SABR in NSCLC. 18 out of the 429 initial results fulfilled the inclusion criteria and were selected for review. Results: Eighteen articles, including six prospective studies, describing 1736 patients treated with an ICI-SABR combination fulfilled the selection criteria. The reported mean rates for local control and distant/abscopal response rates were 71% and 41%, respectively. Eleven studies reported progression-free survival and overall survival, with a mean of 4.6 and 12.4 months, respectively. Toxicity rates were consistent with the ones attributable to ICI treatment alone. Conclusions: The ICI-SABR combination has a good safety profile and achieves high rates of local control and greater chances of obtaining abscopal responses than SABR alone, with a relevant impact on PFS. More studies are needed to improve patient selection for an optimal benefit from this approach.

Intraoperative Radiotherapy of Breast Cancer and Its Biological Effects

Conservative breast cancer surgery followed by radiation therapy is the standard treatment for this type of cancer. Numerous studies demonstrate that 90% of local recurrences after traditional surgery occur in the same quadrant as the primary cancer. The published data suggest that the wound healing process after surgery alters the area surrounding the original tumor and the modified microenvironment is more favorable for the tumor to recur. The majority of metastases within scar initiated much research, and the consequences of these studies led to clinical trials aimed at assessing whether localized radiotherapy, such as intraoperative radiotherapy (IORT), would be more effective in inhibiting formation of local recurrence than the standard postoperative whole breast radiotherapy. IORT involves irradiation of diseased tissue directly during surgery. The rationale for this approach is the fact that the increase in the radiation dose increases local tumor control, which is the primary goal of radiation therapy. The biological basis of this process are still not thoroughly understood. Gaining new knowledge about the recurrence formation at the molecular level could serve as a starting point for further analysis and to create an opportunity to identify new targets of therapy, and possibly new therapeutic agents.

A reaction-diffusion model for radiation-induced bystander effects

We develop and analyze a reaction-diffusion model to investigate the dynamics of the lifespan of a bystander signal emitted when cells are exposed to radiation. Experimental studies by Mothersill and Seymour 1997, using malignant epithelial cell lines, found that an emitted bystander signal can still cause bystander effects in cells even 60 h after its emission. Several other experiments have also shown that the signal can persist for months and even years. Also, bystander effects have been hypothesized as one of the factors responsible for the phenomenon of low-dose hyper-radiosensitivity and increased radioresistance (HRS/IRR). Here, we confirm this hypothesis with a mathematical model, which we fit to Joiner's data on HRS/IRR in a T98G glioma cell line. Furthermore, we use phase plane analysis to understand the full dynamics of the signal's lifespan. We find that both single and multiple radiation exposure can lead to bystander signals that either persist temporarily or permanently. We also found that, in an heterogeneous environment, the size of the domain exposed to radiation and the number of radiation exposures can determine whether a signal will persist temporarily or permanently. Finally, we use sensitivity analysis to identify those cell parameters that affect the signal's lifespan and the signal-induced cell death the most.

Human mesenchymal stem cells enhance the systemic effects of radiotherapy

The outcome of radiotherapy treatment might be further improved by a better understanding of individual variations in tumor radiosensitivity and normal tissue reactions, including the bystander effect. For many tumors, however, a definitive cure cannot be achieved, despite the availablity of more and more effective cancer treatments. Therefore, any improvement in the efficacy of radiotherapy will undoubtedly benefit a significant number of patients. Many experimental studies measure a bystander component of tumor cell death after radiotherapy, which highlights the importance of confirming these observations in a preclinical situation. Mesenchymal stem cells (MSCs) have been investigated for use in the treatment of cancers as they are able to both preferentially home onto tumors and become incorporated into their stroma. This process increases after radiation therapy. In our study we show that in vitro MSCs, when activated with a low dose of radiation, are a source of anti-tumor cytokines that decrease the proliferative activity of tumor cells, producing a potent cytotoxic synergistic effect on tumor cells. In vivo administration of unirradiated mesenchymal cells together with radiation leads to an increased efficacy of radiotherapy, thus leading to an enhancement of short and long range bystander effects on primary-irradiated tumors and distant-non-irradiated tumors. Our experiments indicate an increased cell loss rate and the decrease in the tumor cell proliferation activity as the major mechanisms underlying the delayed tumor growth and are a strong indicator of the synergistic effect between RT and MSC when they are applied together for tumor treatment in this model.

Bystander effects and compartmental stress response to X-ray irradiation in L929 cells

Bystander effects are indirect consequences of radiation and many other stress factors. They occur in cells that are not directly exposed to these factors, but receive signals from affected cells either by gap junctions or by molecules released in the medium. Characterizing these effects and deciphering the underlying mechanisms involved in radiation-induced bystander effects are relevant for cancer radiotherapy and radioprotection. At doses of X-ray radiation 0.5 and 1 Gy, we detected bystander effects as increased numbers of micronuclei shortly after the treatment, through medium transfer and by co-cultures. Interestingly, bystander cells did not exhibit long-term adverse changes in viability. Evaluation of several compartmental stress markers (CHOP, BiP, mtHsp60, cytHsp70) by qRT-PCR did not reveal expression changes at transcriptional level. We investigated the involvement of ROS and NO in this process by addition of specific scavengers of these molecules, DMSO or c-PTIO in the transferred medium. This approach proved that ROS but not NO is involved in the induction of lesions in the acceptor cells. These results indicate that L929 cells are susceptible to stress effects of radiation-induced bystander signaling.

Oligometastases in prostate cancer: restaging stage IV cancers and new radiotherapy options

There are various subgroups of patients with metastatic prostate cancer: polymetastatic, oligometastatic, or oligo-recurrent cancers whose progression follows different courses and for whom there are different treatment options. Knowledge of tumor dissemination pathways and different genetic and epigenetic tumor profiles, as well as their evolution during disease progression, along with new diagnostic and therapeutic advances has allowed us to address these situations with local ablative treatments such as stereotactic body radiation therapy or stereotactic radiosurgery. These treatments provide high rates of local control with low toxicity in metastatic spread for primary cancers including those of pulmonary, digestive, and renal origin, while these types of treatments are still emerging for cancers of prostatic origin. There are several retrospective studies showing the effectiveness of such treatments in prostate cancer metastases, which has led to the emergence of prospective studies on the issue and even some phase II studies intended to prevent or delay systemic treatments such as chemotherapy. Here we collect together and review these past experiences and the studies currently underway. These types of radiotherapy treatments redefine how we approach extracranial metastatic disease and open up new possibilities for combination therapy with new systemic treatment agents.