TGF-β1 mediates the radiation response of prostate cancer

A new target of radiotherapy combined with immunotherapy: regulatory T cells

Radiotherapy is one important treatment for malignant tumours. It is widely believed today that radiotherapy has not only been used as a local tumour treatment method, but also can induce systemic anti-tumour responses by influencing the tumour microenvironment, but its efficacy is limited by the tumour immunosuppression microenvironment. With the advancement of technology, immunotherapy has entered a golden age of rapid development, gradually occupying a place in clinical tumour treatment. Regulatory T cells (Tregs) widely distributing in the tumour microenvironment play an important role in mediating tumour development. This article analyzes immunotherapy, the interaction between Tregs, tumours and radiotherapy. It briefly introduces immunotherapies targeting Tregs, aiming to provide new strategies for radiotherapy combined with Immunotherapy.

Carbon ion irradiation exerts antitumor activity by inducing cGAS-STING activation and immune response in prostate cancer-bearing mice

BACKGROUND AND PURPOSE

As an advanced radiotherapy technique, carbon ion radiotherapy has demonstrated good efficacy and low toxicity for prostate cancer patients, but the radiobiological mechanism of killing tumor cells has not been fully elucidated. This study aims to explore the antitumor effects of carbon ion irradiation (CIR) through investigating the immune response induced by CIR in prostate cancer-bearing mice and the underlying molecular mechanism.

MATERIALS AND METHODS

We established subcutaneous transplantation tumor models of prostate cancer to evaluate the tumor inhibition effect of CIR. Investigation of immunophenotype alterations were assessed by flow cytometry. Immunofluorescence, western blot, and real-time quantitative PCR was employed to analyze the activation of cGAS-STING pathway.

RESULTS

CIR showed more powerful tumor growth control than photon irradiation in immunocompetent syngeneic C57BL/6 mice. CIR exerts antitumor effect by triggering immune response, characterized by increased CD4+ T cells and macrophages in tumor, enhanced CD8+ T cells and T effector memory cells in spleen, improved IFN-γ production of CD8+ tumor-infiltrating lymphocytes, and reduced exhausted T cells in tumor and spleen. Additionally, production of cytoplasmic double-stranded DNA, protein levels of p-TBK1 and p-IRF3 in the cGAS-STING pathway, and gene expression levels of downstream interferon-stimulated genes were significantly increased after CIR in a dose-dependent manner. Treatment of RM1 tumor-bearing mice with the STING inhibitor C-176 impaired the antitumor effect of CIR.

CONCLUSION

The excellent antitumor activity of CIR in immunocompetent prostate cancer-bearing C57BL/6 mice may be attributed to stronger induction of antitumor immune response and higher activation of cGAS-STING pathway.

Making "cold" tumors "hot"- radiotherapy remodels the tumor immune microenvironment of pancreatic cancer to benefit from immunotherapy: a case report

Immune checkpoint inhibitors have limited efficacy in metastatic pancreatic cancer due to the complex tumor immune microenvironment (TIME). Studies have shown that radiotherapy can cause cell lesions to release tumor antigens and then take part in the remodeling of the tumor environment and the induction of ectopic effects via regional and systemic immunoregulation. Here, we reported a case of advanced metastatic pancreatic cancer treated with immunotherapy combined with chemotherapy and radiotherapy and a sharp shift of the TIME from T3 to T2 was also observed. One hepatic metastasis within the planning target volume (PTV) was evaluated complete response (CR), the other one was evaluated partial response (PR) and 2 hepatic metastases outside the PTV were surprisingly considered PR. In the study, we found that immunotherapy combined with chemotherapy and radiotherapy achieved significant therapeutic benefits, which may provide a new strategy for the treatment of advanced pancreatic cancer.

The Role of Regulatory T Cells in Cancer Treatment Resistance

Despite tremendous progress in cancer treatment in recent years, treatment resistance is still a major challenge for a great number of patients. One of the main causes is regulatory T lymphocytes (Tregs), which suppress excessive inflammatory responses via the secretion of immunosuppressive cytokines and upregulate the immune checkpoints. Their abundance causes an immunosuppressive reprogramming of the tumor environment, which is ideal for tumor growth and drug inefficiency. Hence, regiments that can regain tumor immunogenicity are a promising strategy to overcome Tregs-mediated drug resistance. However, to develop effective therapeutic regimens, it is essential to understand the molecular mechanisms of Treg-mediated resistance. In this article, we gathered a comprehensive summary of the current knowledge on molecular mechanisms and the role of Tregs in cancer treatment resistance, including cancer immunotherapy, targeted therapy, chemotherapy, and radiotherapy.

Transforming Growth Factor Beta and Epithelial to Mesenchymal Transition Alter Homologous Recombination Repair Gene Expression and Sensitize BRCA Wild-Type Ovarian Cancer Cells to Olaparib

Epithelial ovarian cancer (EOC) remains the most lethal gynecologic malignancy, largely due to metastasis and drug resistant recurrences. Fifteen percent of ovarian tumors carry mutations in BRCA1 or BRCA2, rendering them vulnerable to treatment with PARP inhibitors such as olaparib. Recent studies have shown that TGFβ can induce "BRCAness" in BRCA wild-type cancer cells. Given that TGFβ is a known driver of epithelial to mesenchymal transition (EMT), and the connection between EMT and metastatic spread in EOC and other cancers, we asked if TGFβ and EMT alter the susceptibility of EOC to PARP inhibition. Epithelial EOC cells were transiently treated with soluble TGFβ, and their clonogenic potential, expression, and function of EMT and DNA repair genes, and response to PARP inhibitors compared with untreated controls. A second epithelial cell line was compared to its mesenchymal derivative for EMT and DNA repair gene expression and drug responses. We found that TGFβ and EMT resulted in the downregulation of genes responsible for homologous recombination (HR) and sensitized cells to olaparib. HR efficiency was reduced in a dose-dependent manner. Furthermore, mesenchymal cells displayed sensitivity to olaparib, cisplatin, and the DNA-PK inhibitor Nu-7441. Therefore, the treatment of disseminated, mesenchymal tumors may represent an opportunity to expand the clinical utility of PARP inhibitors and similar agents.

A human-in-the-loop based Bayesian network approach to improve imbalanced radiation outcomes prediction for hepatocellular cancer patients with stereotactic body radiotherapy

Background

Imbalanced outcome is one of common characteristics of oncology datasets. Current machine learning approaches have limitation in learning from such datasets. Here, we propose to resolve this problem by utilizing a human-in-the-loop (HITL) approach, which we hypothesize will also lead to more accurate and explainable outcome prediction models.

Methods

A total of 119 HCC patients with 163 tumors were used in the study. 81 patients with 104 tumors from the University of Michigan Hospital treated with SBRT were considered as a discovery dataset for radiation outcomes model building. The external testing dataset included 59 tumors from 38 patients with SBRT from Princess Margaret Hospital. In the discovery dataset, 100 tumors from 77 patients had local control (LC) (96% of 104 tumors) and 23 patients had at least one grade increment of ALBI (I-ALBI) during six-month follow up (28% of 81 patients). Each patient had a total of 110 features, where 15 or 20 features were identified by physicians as expert knowledge features (EKFs) for LC or I-ALBI prediction. We proposed a HITL based Bayesian network (HITL-BN) approach to enhance the capability of selecting important features from imbalanced data in terms of accuracy and explainability through humans' participation by integrating feature importance ranking and Markov blanket algorithms. A pure data-driven Bayesian network (PD-BN) method was applied to the same discovery dataset of HCC patients as a benchmark.

Results

In the training and testing phases, the areas under receiver operating characteristic curves of the HITL-BN models for LC or I-ALBI prediction during SBRT are 0.85 (95% confidence interval: 0.75-0.95) or 0.89 (0.81-0.95) and 0.77 or 0.78, respectively. They significantly outperformed the during-treatment PD-BN model in predicting LC or I-ALBI based on the discovery cross-validation and testing datasets from the Delong tests.

Conclusion

By allowing the human expert to be part of the model building process, the HITL-BN approach yielded significantly improved accuracy as well as better explainability when dealing with imbalanced outcomes in the prediction of post-SBRT treatment response of HCC patients when compared to the PD-BN method.

Immunomodulatory effects of carbon ion radiotherapy in patients with localized prostate cancer

PURPOSE

Radiotherapy is one of the main local treatment modalities for prostate cancer, while immunosuppressive effect induced by radiotherapy is an important factor of radiation resistance and treatment failure. Carbon ion radiotherapy (CIRT) is a novel radiotherapy technique and the immunomodulatory effect of CIRT provides the possibility of overcoming radioresistance and improving efficacy. The aim of this study was to assess the immune response evoked by CIRT in localized prostate cancer patients.

METHODS

Thirty-two patients were treated by CIRT combined with or without hormone therapy and peripheral blood samples were collected before and after CIRT. Investigation of peripheral immune cell frequency, proliferation, and cytokine expression was conducted by flow cytometry, real-time quantitative PCR and ELISA.

RESULTS

There were no significant differences in the frequencies of CD3 + , CD4 + , CD8 + T cells and NK cells after CIRT. CD4/CD8 ratio increased whereas B cells decreased. All lymphocyte subsets except regulatory T cells (Tregs) displayed increased proliferation and T cells exhibited increased functionality after CIRT, characterized by modestly increased cytokine secretion of TNF. Moreover, higher frequencies of Tregs were shown. Neither monocytic myeloid-derived suppressor cells (MDSCs) nor early MDSCs changed after CIRT. TGF-β1 gene expression decreased while IL-6 showed a non-significant trend towards a decrease. Both IL-10 gene expression and plasma TGF-β1 level were unchanged.

CONCLUSION

CIRT demonstrates the potential to elicit immune activation in localized prostate cancer patients, based on sparing lymphocytes, increased lymphocyte proliferation, enhanced T-cell functionality, together with limited induction of immunosuppressive cells and reduced expression of immunosuppressive cytokines.

Radiotherapy combined with immunotherapy: the dawn of cancer treatment

Radiotherapy (RT) is delivered for purposes of local control, but can also exert systemic effect on remote and non-irradiated tumor deposits, which is called abscopal effect. The view of RT as a simple local treatment has dramatically changed in recent years, and it is now widely accepted that RT can provoke a systemic immune response which gives a strong rationale for the combination of RT and immunotherapy (iRT). Nevertheless, several points remain to be addressed such as the interaction of RT and immune system, the identification of the best schedules for combination with immunotherapy (IO), the expansion of abscopal effect and the mechanism to amplify iRT. To answer these crucial questions, we roundly summarize underlying rationale showing the whole immune landscape in RT and clinical trials to attempt to identify the best schedules of iRT. In consideration of the rarity of abscopal effect, we propose that the occurrence of abscopal effect induced by radiation can be promoted to 100% in view of molecular and genetic level. Furthermore, the “radscopal effect” which refers to using low-dose radiation to reprogram the tumor microenvironment may amplify the occurrence of abscopal effect and overcome the resistance of iRT. Taken together, RT could be regarded as a trigger of systemic antitumor immune response, and with the help of IO can be used as a radical and systemic treatment and be added into current standard regimen of patients with metastatic cancer.

Transforming growth factor-beta (TGF-β) in prostate cancer: A dual function mediator?

Transforming growth factor-beta (TGF-β) is a member of a family of secreted cytokines with vital biological functions in cells. The abnormal expression of TGF-β signaling is a common finding in pathological conditions, particularly cancer. Prostate cancer (PCa) is one of the leading causes of death among men. Several genetic and epigenetic alterations can result in PCa development, and govern its progression. The present review attempts to shed some light on the role of TGF-β signaling in PCa. TGF-β signaling can either stimulate or inhibit proliferation and viability of PCa cells, depending on the context. The metastasis of PCa cells is increased by TGF-β signaling via induction of EMT and MMPs. Furthermore, TGF-β signaling can induce drug resistance of PCa cells, and can lead to immune evasion via reducing the anti-tumor activity of cytotoxic T cells and stimulating regulatory T cells. Upstream mediators such as microRNAs and lncRNAs, can regulate TGF-β signaling in PCa. Furthermore, some pharmacological compounds such as thymoquinone and valproic acid can suppress TGF-β signaling for PCa therapy. TGF-β over-expression is associated with poor prognosis in PCa patients. Furthermore, TGF-β up-regulation before prostatectomy is associated with recurrence of PCa. Overall, current review discusses role of TGF-β signaling in proliferation, metastasis and therapy response of PCa cells and in order to improve knowledge towards its regulation, upstream mediators of TGF-β such as non-coding RNAs are described. Finally, TGF-β regulation and its clinical application are discussed.

Exploiting Canonical TGFβ Signaling in Cancer Treatment

Transforming growth factor β (TGFβ) is a pleiotropic cytokine that plays critical roles to define cancer cell phenotypes, construct the tumor microenvironment, and suppress anti-tumor immune responses. As such, TGFβ is a lynchpin for integrating cancer cell intrinsic pathways and communication among host cells in the tumor and beyond that together affect responses to genotoxic, targeted, and immune therapy. Despite decades of preclinical and clinical studies, evidence of clinical benefit from targeting TGFβ in cancer remains elusive. Here, we review the mechanisms by which TGFβ acts to oppose successful cancer therapy, the reported prognostic and predictive value of TGFβ biomarkers, and the potential impact of inhibiting TGFβ in precision oncology. Paradoxically, the diverse mechanisms by which TGFβ impedes therapeutic response are a principal barrier to implementing TGFβ inhibitors because it is unclear which TGFβ mechanism is functional in which patient. Companion diagnostic tools and specific biomarkers of TGFβ targeted biology will be the key to exploiting TGFβ biology for patient benefit.

Effect of 1α,25-Dihydroxyvitamin D3 on the Radiation Response in Prostate Cancer: Association With IL-6 Signaling

Radiotherapy (RT) is the main treatment modality for prostate cancer (PCa). This study investigated the role of IL-6 in biological sequelae following irradiation and highlighted the effects of 1α,25-dihydroxyvitamin D3 (calcitriol) on the radiation response of PCa and its relationship with IL-6 signaling. Human and murine PCa cell lines were used to examine the response to irradiation in vitro and in vivo. The relationship of IL-6 expression with clinicopathologic characteristics in 104 PCa patients treated with definite RT was also examined. We also investigated the changes in radiation response after calcitriol supplementation and the relationship between calcitriol and IL-6 signaling by conducting cellular and animal experiments. Based on clinical samples, the positivity of IL-6 staining is a significant predictor of biochemical failure-free survival for PCa patients treated with definite RT. Data from preclinical models showed that inhibition of IL-6 increased the response of PCa to radiation, which was associated with increased oxidative DNA damage, attenuated EMT and MDSC recruitment, and decreased tumor regrowth. Moreover, increased vitamin D₃ levels by calcitriol supplementation or induction by UVB-radiation was associated with inhibited IL-6 signaling and increased the response to irradiation observed in animal models. These data demonstrate that IL-6 play a critical role in the radiation response of PCa, which involved tumor cell killing and altering the tumor microenvironment. Directly targeting IL-6 signaling or vitamin D₃ supplement with oral or light treatment could be a promising strategy to increase the response of PCa to radiation.

CRISPR/Cas9 library screening uncovered methylated PKP2 as a critical driver of lung cancer radioresistance by stabilizing β-catenin

Radiation resistance is a major cause of lung cancer treatment failure. Armadillo (ARM) superfamily proteins participate in various fundamental cellular processes; however, whether ARM proteins regulate radiation resistance is not fully understood. Here, we used an unbiased CRISPR/Cas9 library screen and identified plakophilin 2 (PKP2), a member of the ARM superfamily of proteins, as a critical driver of radiation resistance in lung cancer. The PKP2 level was significantly higher after radiotherapy than before radiotherapy, and high PKP2 expression after radiotherapy predicted poor overall survival (OS) and postprogression survival (PPS). Mechanistically, mass spectrometry analysis identified that PKP2 was methylated at the arginine site and interacted with protein arginine methyltransferase 1 (PRMT1). Methylation of PKP2 by PRMT1 stabilized β-catenin by recruiting USP7, further inducing LIG4, a key DNA ligase in nonhomologous end-joining (NHEJ) repair. Concomitantly, PKP2-induced radioresistance depended on facilitating LIG4-mediated NHEJ repair in lung cancer. More strikingly, after exposure to irradiation, treatment with the PRMT1 inhibitor C-7280948 abolished PKP2-induced radioresistance, and C-7280948 is a potential radiosensitizer in lung cancer. In summary, our results demonstrate that targeting the PRMT1/PKP2/β-catenin/LIG4 pathway is an effective approach to overcome radiation resistance in lung cancer.

Evaluation of cytokine expression and circulating immune cell subsets as potential parameters of acute radiation toxicity in prostate cancer patients

One of the challenges of radiation oncology in the era of personalized medicine is identification of biomarkers associated with individual radiosensitivity. The aim of research was to evaluate the possible clinical value of the associations between clinical, physical, and biological factors, and risk for development of acute radiotoxicity in patients with prostate cancer. The study involved forty four patients treated with three-dimensional conformal radiotherapy. The concentrations of IL-1β, IL-2, IL-6, IFN-γ and TGF-β1 were assessed before radiotherapy, after 5th, 15th and 25th radiotherapy fractions, at the end, and 1 month after the end of radiotherapy. Cytokine gene expression was determined in peripheral blood mononuclear cells. The univariate analysis of circulating cytokine levels during radiotherapy showed that increased serum concentrations of IL-6 were significantly associated with higher grade of acute genitourinary toxicity. The multivariate analysis demonstrated that increased level of IL-6 during the radiotherapy was significantly associated with higher grade of acute genitourinary toxicity across treatment. TGF-β expression levels significantly decreased during course of radiotherapy. Research indicates that changes in circulating cytokine levels might be important parameter of radiotoxicity in patients with prostate cancer. These findings suggest that future studies based on multi-parameter examination are necessary for prediction of individual radiosensitivity.

The interplay between cancer associated fibroblasts and immune cells in the context of radiation therapy

Fibroblasts are a key component of the tumor microenvironment (TME) that can serve as a scaffold for tumor cell migration and augment the tumor's ability to withstand harsh conditions. When activated by external or endogenous stimuli, normal fibroblasts become cancer associated fibroblasts (CAFs), a heterogeneous group of stromal cells in the tumor that are phenotypically and epigenetically different from normal fibroblasts. Dynamic crosstalk between cancer cells, immune cells, and CAFs through chemokines and surface signaling makes the TME conducive to tumor growth. When activated, CAFs promote tumorigenesis and metastasis through several phenomena including regulation of tumor immunity, metabolic reprogramming of the TME, extracellular matrix remodeling and contraction, and induction of therapeutic resistance. Ionizing radiation (radiation theraphy [RT]) is a potent immunological stimulant that has been shown to increase cytotoxic Teff infiltration and IFN-I stimulated genes. RT, however, is unable to overcome the infiltration and activation of immunosuppressive cells which can contribute to tumor progression. Another paradox of RT is that, while very effective at killing cancer cells, it can contribute to the formation of CAFs. This review examines how the interplay between CAFs and immune cells during RT contributes to organ fibrosis, immunosuppression, and tumor growth. We focus on targeting mechanistic pathways of CAF formation as a potentially effective strategy not only for preventing organ fibrosis, but also in hampering tumor progression in response to RT.

Potentiation of cancerous progression by LISCH7 via direct stimulation of TGFB1 transcription in triple-negative breast cancer

As an aggressive breast cancer (BCa) subtype, triple-negative breast cancer (TNBC) responses poorly to chemotherapy and endocrine therapy, and usually has a worse prognosis. This is largely due to the lack of specific therapeutic targets, laying claim to an imperious demand to clarify the key signaling pathways potentiating TNBC progression. Herein, we report that expression levels of the liver-specific bHLH-Zip transcription factor (LISCH7), a recently identified key player in cancerous progression, preferentially enriched in TNBC in comparison with other BCa subtypes, and this upregulation was observed to be correlated to a poor survival outcome in patients with TNBC. Ablation of LISCH7 in TNBC cells impaired cell proliferation, reduced cell invasiveness, and enhanced sensitivity to the first-line chemotherapeutic drug docetaxel at both in vitro and in vivo levels. Importantly, concurrent induction of TGFB1, the gene encoding transforming growth factor-β1 (TGF-β1), an essential multipluripotent regulator of TNBC, was accompanied with these alterations in cancerous properties. We further showed that LISCH7 could directly bind to the TGFB1 promoter and stimulate TGFB1 transcription in TNBC cells. The recruitment of LISCH7 onto the TGFB1 chromatin and transactivation of TGFB1 were substantially augmented by treatment with the exogenous TGF-β1 in a time- and dose-dependent manner. Collectively, these findings suggest that LISCH7 and TGF-β1 form a reciprocal positive regulatory loop and cooperatively regulate cancerous progression in TNBC cells. Thus, simultaneous inhibition of both LISCH7 and TGF-β1 signaling may represent a more effective approach to counteract advanced TNBC.

The Yin and Yang of Cytoreductive SBRT in Oligometastases and Beyond

Background: Oligometastatic disease has emerged as a possibly distinct metastatic phenotype in numerous cancer histologies. With the advancement in treatment modalities including stereotactic body radiation therapy (SBRT), certain patients may derive benefits from local ablative therapy. SBRT alone has already shown to have potential benefits in certain oligometastatic disease types. However, more understanding of the immunologic modulation and microenvironment is needed to guide which patients may benefit from SBRT alone or with combination therapy, if at all. Purpose: The purpose of this review is to offer an update on the emerging data testing SBRT combined with immunotherapy, review the pro-inflammatory and immunosuppressive effects of the tumor microenvironment, discuss novel molecular targets used to augment the immune response, and review potential methods used to decrease toxicity in order to improve the therapeutic ratio.

Loss of GTPase of immunity-associated protein 5 (Gimap5) promotes pathogenic CD4+ T-cell development and allergic airway disease

BACKGROUND

GTPase of immunity-associated protein 5 (GIMAP5) is essential for lymphocyte homeostasis and survival. Recently, human GIMAP5 single nucleotide polymorphisms have been linked to an increased risk for asthma, whereas loss of Gimap5 in mice has been associated with severe CD4+ T cell-driven immune pathology.

OBJECTIVE

We sought to identify the molecular and cellular mechanisms by which Gimap5 deficiency predisposes to allergic airway disease.

METHODS

CD4+ T-cell polarization and development of pathogenic CD4+ T cells were assessed in Gimap5-deficient mice and a human patient with a GIMAP5 loss-of-function (LOF) mutation. House dust mite-induced airway inflammation was assessed by using a complete Gimap5 LOF (Gimap5sph/sph) and conditional Gimap5fl/flCd4Cre/ert2 mice.

RESULTS

GIMAP5 LOF mutations in both mice and human subjects are associated with spontaneous polarization toward pathogenic TH17 and TH2 cells in vivo. Mechanistic studies in vitro reveal that impairment of Gimap5-deficient TH cell differentiation is associated with increased DNA damage, particularly during TH1-polarizing conditions. DNA damage in Gimap5-deficient CD4+ T cells could be controlled by TGF-β, thereby promoting TH17 polarization. When challenged with house dust mite in vivo, Gimap5-deficient mice displayed an exacerbated asthma phenotype (inflammation and airway hyperresponsiveness), with increased development of TH2, TH17, and pathogenic TH17/TH2 cells.

CONCLUSION

Activation of Gimap5-deficient CD4+ T cells is associated with increased DNA damage and reduced survival that can be overcome by TGF-β. This leads to selective survival of pathogenic TH17 cells but also TH2 cells in human subjects and mice, ultimately promoting allergic airway disease.

The Response of Prostate Cancer to Androgen Deprivation and Irradiation Due to Immune Modulation

This study investigated changes in the immune system and the biological consequences of androgen deprivation therapy (ADT) and radiotherapy (RT) for augmenting the treatment response in prostate cancer, particularly for castration-resistant prostate cancer (CRPC). Human and murine prostate cancer cell lines were used to examine the response to ADT and RT in vitro and in vivo. Biological changes following treatment and related immune modulation in the tumor microenvironment were examined. Our results showed that CRPC cells were demonstrated to be more resistant to the RT and ADT treatments. ADT increased tumor inhibition following irradiation. The underlying changes included increased cell death, attenuated myeloid-derived suppressor cell recruitment, and an increase in the number of tumor-infiltrating T cells (TILs). Furthermore, when high-dose fractionated RT was given to the primary CRPC tumor, a smaller size of secondary non-irradiated tumor associated with increased TILs was noted in ADT-treated mice. In conclusion, treatment resistance in CRPC was associated with a more immunosuppressive microenvironment. Enhanced antitumor immunity was responsible for the augmented RT-induced tumoricidal effect induced by ADT. Immune modulation could be a promising strategy for prostate cancer, especially for metastatic CRPC.

Anti-glucocorticoid-induced Tumor Necrosis Factor-Related Protein (GITR) Therapy Overcomes Radiation-Induced Treg Immunosuppression and Drives Abscopal Effects

Despite the potential to cure metastatic disease, immunotherapy on its own often fails outright or early on due to tumor immune evasion. To address this obstacle, we investigated combinations of anti-GITR, anti-PD1 and radiation therapy (XRT) in our previously developed anti-PD1 resistant 344SQ non-small cell lung adenocarcinoma preclinical tumor model. We hypothesized that targeting multiple mechanisms of immune evasion with this triple therapy would lead to an enhanced tumor-specific immune response and improve survival more so than any mono- or dual therapy. In a two tumor 344SQR murine model, treatment with anti-GITR, anti-PD1, and XRT led to significantly improved survival and an abscopal response, with half of the mice becoming tumor free. These mice showed durable response and increased CD4+ and CD8+ effector memory on tumor rechallenge. Regulatory T cells (Tregs) expressed the highest level of GITR at the tumor site and anti-GITR therapy drastically diminished Tregs at the tumor site. Anti-tumor effects were largely dependent on CD4+ T cells and partially dependent on CD8+ T cells. Anti-GITR IgG2a demonstrated superior efficacy to anti-GITR IgG1 in driving antitumor effects. Collectively, these results suggest that combinatorial strategies targeting multiple points of tumor immune evasion may lead to a robust and lasting antitumor response.

Stereotactic Radiotherapy Increases Functionally Suppressive Regulatory T Cells in the Tumor Microenvironment

Radiotherapy (RT) enhances innate and adaptive antitumor immunity; however, the effects of radiation on suppressive immune cells, such as regulatory T cells (Treg), in the tumor microenvironment (TME) are not fully elucidated. Although previous reports suggest an increased Treg infiltration after radiation, whether these Tregs are functionally suppressive remains undetermined. To test the hypothesis that RT enhances the suppressive function of Treg in the TME, we selectively irradiated implanted tumors using the small animal radiation research platform (SARRP), which models stereotactic radiotherapy in human patients. We then analyzed tumor-infiltrating lymphocytes (TIL) with flow-cytometry and functional assays. Our data showed that RT significantly increased tumor-infiltrating Tregs (TIL-Treg), which had higher expression of CTLA-4, 4-1BB, and Helios compared with Tregs in nonirradiated tumors. This observation held true across several tumor models (B16/F10, RENCA, and MC38). We found that TIL-Tregs from irradiated tumors had equal or improved suppressive capacity compared with nonirradiated tumors. Our data also indicated that after RT, Tregs proliferated more robustly than other T-cell subsets in the TME. In addition, after RT, expansion of Tregs occurred when T-cell migration was inhibited using Fingolimod, suggesting that the increased Treg frequency was likely due to preferential proliferation of intratumoral Treg after radiation. Our data also suggested that Treg expansion after irradiation was independent of TGFβ and IL33 signaling. These data demonstrate that RT increased phenotypically and functionally suppressive Tregs in the TME. Our results suggest that RT might be combined effectively with Treg-targeting agents to maximize antitumor efficacy. Cancer Immunol Res; 5(11); 992-1004. ©2017 AACR.

DNA Repair and Cytokines: TGF-β, IL-6, and Thrombopoietin as Different Biomarkers of Radioresistance

Double strand breaks (DSBs) induced by radiotherapy are highly cytotoxic lesions, leading to chromosomal aberrations and cell death. Ataxia-telangiectasia-mutated (ATM)-dependent DNA-damage response, non-homologous end joining, and homologous recombination pathways coordinately contribute to repairing DSBs in higher eukaryotes. It is known that the expression of DSB repair genes is increased in tumors, which is one of the main reasons for radioresistance. The inhibition of DSB repair pathways may be useful to increase tumor cell radiosensitivity and may target stem cell-like cancer cells, known to be the most radioresistant tumor components. Commonly overexpressed in neoplastic cells, cytokines confer radioresistance by promoting proliferation, survival, invasion, and angiogenesis. Unfortunately, tumor irradiation increases the expression of various cytokines displaying these effects, including transforming growth factor-beta and interleukin-6. Recently, the capabilities of these cytokines to support DNA repair pathways and the ATM-dependent DNA response have been demonstrated. Thrombopoietin, essential for megakaryopoiesis and very important for hematopoietic stem cell (HSC) homeostasis, has also been found to promote DNA repair in a highly selective manner. These findings reveal a novel mechanism underlying cytokine-related radioresistance, which may be clinically relevant. Therapies targeting specific cytokines may be used to improve radiosensitivity. Specific inhibitors may be chosen in consideration of different tumor microenvironments. Thrombopoietin may be useful in fending off irradiation-induced loss of HSCs.

Immunomodulatory effects of radiation: what is next for cancer therapy?

Despite its former reputation as being immunosuppressive, it has become evident that radiation therapy can enhance antitumor immune responses. This quality can be harnessed by utilizing radiation as an adjuvant to cancer immunotherapies. Most studies combine the standard radiation dose and regimens indicated for the given disease state, with novel cancer immunotherapies. It has become apparent that low-dose radiation, as well as doses within the hypofractionated range, can modulate tumor cells making them better targets for immune cell reactivity. Herein, we describe the range of phenotypic changes induced in tumor cells by radiation, and explore the diverse mechanisms of immunogenic modulation reported at these doses. We also review the impact of these doses on the immune cell function of cytotoxic cells in vivo and in vitro.

The effect of ionizing radiation on regulatory T cells in health and disease

Treg cells are key elements of the immune system which are responsible for the immune suppressive phenotype of cancer patients. Interaction of Treg cells with conventional anticancer therapies might fundamentally influence cancer therapy response rates. Radiotherapy, apart from its direct tumor cell killing potential, has a contradictory effect on the antitumor immune response: it augments certain immune parameters, while it depresses others. Treg cells are intrinsically radioresistant due to reduced apoptosis and increased proliferation, which leads to their systemic and/or intratumoral enrichment. While physiologically Treg suppression is not enhanced by irradiation, this is not the case in a tumorous environment, where Tregs acquire a highly suppressive phenotype, which is further increased by radiotherapy. This is the reason why the interest for combined radiotherapy and immunotherapy approaches focusing on the abrogation of Treg suppression has increased in cancer therapy in the last few years. Here we summarize the basic mechanisms of Treg radiation response both in healthy and cancerous environments and discuss Treg-targeted pre-clinical and clinical immunotherapy approaches used in combination with radiotherapy. Finally, the discrepant findings regarding the predictive value of Tregs in therapy response are also reviewed.