[Non-targeted effects (bystander, abscopal) of external beam radiation therapy: an overview for the clinician]

Immune Priming with Spatially Fractionated Radiation Therapy

PURPOSE OF REVIEW

This review aims to summarize the current preclinical and clinical evidence of nontargeted immune effects of spatially fractionated radiation therapy (SFRT). We then highlight strategies to augment the immunomodulatory potential of SFRT in combination with immunotherapy (IT).

RECENT FINDINGS

The response of cancer to IT is limited by primary and acquired immune resistance, and strategies are needed to prime the immune system to increase the efficacy of IT. Radiation therapy can induce immunologic effects and can potentially be used to synergize the effects of IT, although the optimal combination of radiation and IT is largely unknown. SFRT is a novel radiation technique that limits ablative doses to tumor subvolumes, and this highly heterogeneous dose deposition may increase the immune-rich infiltrate within the targeted tumor with enhanced antigen presentation and activated T cells in nonirradiated tumors. The understanding of nontargeted effects of SFRT can contribute to future translational strategies to combine SFRT and IT. Integration of SFRT and IT is an innovative approach to address immune resistance to IT with the overall goal of improving the therapeutic ratio of radiation therapy and increasing the efficacy of IT.

Therapeutic efficacy of 166Holmium siloxane in microbrachytherapy of induced glioblastoma in minipig tumor model

Glioblastoma is considered the most common malignant primary tumor of central nervous system. In spite of the current standard and multimodal treatment, the prognosis of glioblastoma is poor. For this reason, new therapeutic approaches need to be developed to improve the survival time of the glioblastoma patient. In this study, we performed a preclinical experiment to evaluate therapeutic efficacy of 166Ho microparticle suspension administered by microbrachytherapy on a minipig glioblastoma model. Twelve minipigs were divided in 3 groups. Minipigs had injections into the tumor, containing microparticle suspensions of either 166Ho (group 1; n = 6) or 165Ho (group 2; n = 3) and control group (group 3; n = 3). The survival time from treatment to euthanasia was 66 days with a good state of health of all minipigs in group 1. The median survival time from treatment to tumor related death were 8.6 and 7.3 days in groups 2 and control, respectively. Statistically, the prolonged life of group 1 was significantly different from the two other groups (p < 0.01), and no significant difference was observed between group 2 and control (p=0.09). Our trial on the therapeutic effect of the 166Ho microparticle demonstrated an excellent efficacy in tumor control. The histological and immunohistochemical analysis showed that the efficacy was related to a severe 166Ho induced necrosis combined with an immune response due to the presence of the radioactive microparticles inside the tumors. The absence of reflux following the injections confirms the safety of the injection device.

Application of Advanced Non-Linear Spectral Decomposition and Regression Methods for Spectroscopic Analysis of Targeted and Non-Targeted Irradiation Effects in an In-Vitro Model

Irradiation of the tumour site during treatment for cancer with external-beam ionising radiation results in a complex and dynamic series of effects in both the tumour itself and the normal tissue which surrounds it. The development of a spectral model of the effect of each exposure and interaction mode between these tissues would enable label free assessment of the effect of radiotherapeutic treatment in practice. In this study Fourier transform Infrared microspectroscopic imaging was employed to analyse an in-vitro model of radiotherapeutic treatment for prostate cancer, in which a normal cell line (PNT1A) was exposed to low-dose X-ray radiation from the scattered treatment beam, and also to irradiated cell culture medium (ICCM) from a cancer cell line exposed to a treatment relevant dose (2 Gy). Various exposure modes were studied and reference was made to previously acquired data on cellular survival and DNA double strand break damage. Spectral analysis with manifold methods, linear spectral fitting, non-linear classification and non-linear regression approaches were found to accurately segregate spectra on irradiation type and provide a comprehensive set of spectral markers which differentiate on irradiation mode and cell fate. The study demonstrates that high dose irradiation, low-dose scatter irradiation and radiation-induced bystander exposure (RIBE) signalling each produce differential effects on the cell which are observable through spectroscopic analysis.

Radiation-induced bystander and abscopal effects: important lessons from preclinical models

Radiotherapy is a pivotal component in the curative treatment of patients with localised cancer and isolated metastasis, as well as being used as a palliative strategy for patients with disseminated disease. The clinical efficacy of radiotherapy has traditionally been attributed to the local effects of ionising radiation, which induces cell death by directly and indirectly inducing DNA damage, but substantial work has uncovered an unexpected and dual relationship between tumour irradiation and the host immune system. In clinical practice, it is, therefore, tempting to tailor immunotherapies with radiotherapy in order to synergise innate and adaptive immunity against cancer cells, as well as to bypass immune tolerance and exhaustion, with the aim of facilitating tumour regression. However, our understanding of how radiation impacts on immune system activation is still in its early stages, and concerns and challenges regarding therapeutic applications still need to be overcome. With the increasing use of immunotherapy and its common combination with ionising radiation, this review briefly delineates current knowledge about the non-targeted effects of radiotherapy, and aims to provide insights, at the preclinical level, into the mechanisms that are involved with the potential to yield clinically relevant combinatorial approaches of radiotherapy and immunotherapy.

Dynamics of Heat Shock Protein 70 Serum Levels As a Predictor of Clinical Response in Non-Small-Cell Lung Cancer and Correlation with the Hypoxia-Related Marker Osteopontin

Hypoxia mediates resistance to radio(chemo)therapy (RT) by stimulating the synthesis of hypoxia-related genes, such as osteopontin (OPN) and stress proteins, including the major stress-inducible heat shock protein 70 (Hsp70). Apart from its intracellular localization, Hsp70 is also present on the plasma membrane of viable tumor cells that actively release it in lipid vesicles with biophysical characteristics of exosomes. Exosomal Hsp70 contributes to radioresistance while Hsp70 derived from dying tumor cells can serve as a stimulator of immune cells. Given these opposing traits of extracellular Hsp70 and the unsatisfactory outcome of locally advanced lung tumors, we investigated the role of Hsp70 in the plasma of patients with advanced, non-metastasized non-small-cell lung cancer (NSCLC) before (T1) and 4–6 weeks after RT (T2) in relation to OPN as potential biomarkers for clinical response. Plasma levels of Hsp70 correlate with those of OPN at T1, and high OPN levels are significantly associated with a decreased overall survival (OS). Due to a therapy-induced reduction in viable tumor mass after RT Hsp70 plasma levels dropped significantly at T2 (p = 0.016). However, with respect to the immunostimulatory capacity of Hsp70 derived from dying tumor cells, patients with higher post-therapeutic Hsp70 levels showed a significantly better response to RT (p = 0.034) than those with lower levels at T2. In summary, high OPN plasma levels at T1 are indicative for poor OS, whereas elevated post-therapeutic Hsp70 plasma levels together with a drop of Hsp70 between T1 and T2, successfully predict favorable responses to RT. Monitoring the dynamics of Hsp70 in NSCLC patients before and after RT can provide additional predictive information for clinical outcome and therefore might allow a more rapid therapy adaptation.

Skeletal Tumor Burden on Baseline 18F-Fluoride PET/CT Predicts Bone Marrow Failure After 223Ra Therapy

PURPOSE

Determine if skeletal tumor burden on 18F-fluoride PET/CT (fluoride PET/CT) predicts the risk of bone marrow failure (BMF) after 223Ra dichloride therapy (223Ra).

METHODS

Forty-one metastatic prostate cancer patients (43-89 years old; mean, 71 ± 9 years.) underwent fluoride PET/CT prior to 223Ra. Bone marrow failure was the primary end point and was defined as (1) development of hematologic toxicity (World Health Organization grade 3 or 4) associated with no recovery after 6 weeks or (2) death due to BMF after the last 223Ra dose. Bone marrow failure was correlated to fluoride PET/CT skeletal tumor burden (TLF10 [total lesion on fluoride PET/CT with SUVmax of 10 or greater]), use of chemotherapy, serum hemoglobin concentration, serum ALP, and serum prostate-specific antigen.

RESULTS

The number of 223Ra cycles ranged from 2 to 6 (mean, 5). Of the 41 patients, 16 developed BMF (G3 = 12; G4 = 4). A significantly increased risk of developing BMF was observed in patients with TLF10 of 12,000 or greater (hazard ratio [HR], 11.09; P < 0.0001), hemoglobin of less than 10 g/dL (HR, 7.35; P = 0.0002), and AP > 146 UI/L (HR, 4.52; P = 0.0100). Neither concomitant (HR, 0.91; P = 0.88) nor subsequent use of chemotherapy (HR, 0.14; P = 0.84) increased the risk of BMF, nor was prostate-specific antigen greater than 10 μg/L (HR, 0.90; P = 0.86). Moreover, in a multivariable analysis, TLF10 was the only independent predictor of BMF (HR, 6.66; P = 0.0237).

CONCLUSIONS

223Ra was beneficial and reduced the risk of death even in patients with a high skeletal tumor burden. Fluoride PET/CT is able to determine which patients will benefit from 223Ra and which will develop BMF.

[Radiotherapy and targeted therapy/immunotherapy]

Thanks to recent advances achieved in oncologic systemic and local ablative treatment, the treatments become more and more efficient in term of local control and overall survival. Thus, the targeted therapies, immunotherapy or stereotactic radiotherapy have modified the management of patients, especially in case of oligometastatic disease. Many questions are raised by these innovations, particularly the diagnosis and management of new side effects or that of the combination of these different treatments, depending on the type of primary tumor. Fundamental data are available, while clinical data are still limited. Ongoing trials should help to clarify the clinical management protocols. This manuscript is a review of the combination of radiotherapy and targeted therapy/immunotherapy.

Investigation of Abscopal and Bystander Effects in Immunocompromised Mice After Exposure to Pencilbeam and Microbeam Synchrotron Radiation

Out-of-field effects are of considerable interest in radiotherapy. The mechanisms are poorly understood but are thought to involve signaling processes, which induce responses in non-targeted cells and tissues. The immune response is thought to play a role. The goal of this research was to study the induction of abscopal effects in the bladders of NU-Foxn1 mice after irradiating their brains using Pencil Beam (PB) or microbeam (MRT) irradiation at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. Athymic nude mice injected with F98 glioma cells into their right cerebral hemisphere 7 d earlier were treated with either MRT or PB. After recovery times of 2, 12, and 48 h, the urinary bladders were extracted and cultured as tissue explants for 24 h. The growth medium containing the potential signaling factors was harvested, filtered, and transferred to HaCaT reporter cells to assess their clonogenic survival and calcium signaling potential. The results show that in the tumor-free mice, both treatment modalities produce strong bystander/abscopal signals using the clonogenic reporter assay; however, the calcium data do not support a calcium channel mediated mechanism. The presence of a tumor reduces or reverses the effect. PB produced significantly stronger effects in the bladders of tumor-bearing animals. The authors conclude that immunocompromised mice produce signals, which can alter the response of unirradiated reporter cells; however, a novel mechanism appears to be involved.

[What's next in glioblastoma treatment: Tumor-targeted or immune-targeted therapies?]

INTRODUCTION

Glioblastoma (GBM) is associated with a poor prognosis. This review will discuss different directions of treatment, mostly regarding immunotherapies and combinatorial approaches.

DEVELOPMENT

Standard treatment for newly diagnosed GBM is maximal and safe surgical resection followed by concurrent radiochemotherapy (RCT) based on temozolomide, allowing 14.6 months median survival. Nowadays, no combination with molecular-targeted therapy had significantly improved prognosis. Phases I and II data are emerging, highlighting the potential efficacy of associations with other therapies. Studies have suggested the potential of targeting tumor stem cells, at less partially responsible for resistance to RCT. There is now some evidence that immunotherapy is also relevant for brain tumors. Treatment strategies have mainly explored vaccines strategies, such as the dendritic cell, heat shock protein or EGFRvIII vaccines. Of the work initiated in melanoma, immune checkpoints inhibitors have exhibited stimulating results. Others trials have demonstrated potential of autologous stimulated lymphocytes. Moreover, strong data indicates that radiation therapy has the potential to promote immunogenicity and create a sort of in situ personalized vaccine.

CONCLUSION

These data provide strong evidence to support the potential of associating combinatorial targeted and/or immunotherapeutic regimens in patients with GBM that may change patient outcome.

[Radiation therapy and immunomodulation: Focus on experimental data]

The immunosuppressive effects of radiation therapy have long been the only ones considered. It has been demonstrated that exposure to ionizing radiation induces the release of tumour antigens which activates both the innate immune system and the adaptive immune response of the host. The purpose of tumour immunotherapy is based on the principle that reversal of tolerance to immunogenic tumours would be able to activate an immune response against tumour cells. Preclinical data and clinical studies early phase suggest a potential therapeutic benefit of immunotherapy combined with radiation therapy. The objective of this article is to review how tumour cells interact with the immune system and how ionizing radiation modulate this interaction and finally the combination of perspectives of immunotherapy and ionizing radiation by focusing on existing clinical data.

Radionuclide Therapy of Unresectable Tumors with AvidinOX and (90)Y-biotinDOTA: Tongue Cancer Paradigm

Local treatment of unresectable tumors is challenging, particularly with radioactivity. Current practice relies on external beam irradiation or on a variety of medical devices for brachytherapy. Both approaches proved useful in controlling tumor growth, but are characterized by poor compliance of the patient, significant side-effects, high costs, and technological complexity, which hamper widespread use. The authors recently described a novel form of radionuclide therapy based on the oxidized form of avidin that, chemically reacting with tissue proteins, can secure radioactive biotin within the injected tissue, either when precomplexed or when taken from the blood stream after intravenous administration. AvidinOX-pretargeted ¹⁷⁷Lu-biotinDOTA (¹⁷⁷Lu-ST2210) is currently under clinical investigation for the treatment of liver oligometastases from colorectal cancer (clinicaltrials.gov/NCT02053324). In the present work, the authors show that injected AvidinOX can link tissues of various natures such as prostate, kidney, breast, or brain and can react by contact with scraped tissues such as skin or urinary bladder. AvidinOX injected into human OSC19 tongue cancer masses orthotopically transplanted in nude mice takes up intravenously administered ⁹⁰Y-ST2210, which exerts significant antitumor activity, while preserving the integrity and functionality of the tongue. Present data confirm that AvidinOX-based radionuclide therapy is an innovative and promising approach for the local treatment of inoperable tumors.

[The low doses of radiation: Towards a new reading of the risk assessment]

From Hiroshima bomb explosion data, the risk of radiation-induced cancer is significant from 100 mSv for a population considered as uniform and radioresistant. However, the recent radiobiological data bring some new elements that highlight some features that were not taken into account: the individual factor, the dose rate and the repeated dose effect. The objective evaluation of the cancer risk due to doses lower than 100 mSv is conditioned by high levels of measurability and statistical significance. However, it appears that methodological rigor is not systematically applied in all the papers. Furthermore, unclear communication in press often leads to some announcement effects, which does not improve the readability of the issue. This papers aims to better understand the complexity of the low-dose-specific phenomena as a whole, by confronting the recent biological data with epidemiological data.