Rationale for Combining Radiotherapy and Immune Checkpoint Inhibition for Patients With Hypoxic Tumors

Establishment and Application of Novel Hypoxia-driven Dual-reporter Model to Investigate Hypoxic Impact on Radiation Sensitivity in Human Nasopharyngeal Carcinoma Xenografts

Background: Tumor hypoxia has been frequently detected in nasopharyngeal carcinoma (NPC) and is intently associated with therapeutic resistance. The aim of the study is to establish a clonogenically stable hypoxia-inducible dual reporter model and apply it to investigate the effect of tumor hypoxia on DNA double strand break (DSB) and synergistic effect of irradiation in combination with chemotherapy or targeted therapy. Methods: The plasmid vector consisting of hypoxia response elements to regulate HSV1-TK and GFP genes, was constructed and stably transfected into human NPC cells. The expected clone was identified and validated by in vivo and in vitro assay. DSB repair was measured by γH2AX foci formation. Tumor growth delay assay and spatial biodistribution of various biomarkers was designed to investigate the anti-tumor effect. Results: The system has the propensity of high expression of reporter genes under hypoxia and low to no expression under normoxia. Intratumoral biodistributions of GFP and classic hypoxic biomarkers were identical in poor-perfused region. Upon equilibration with 10% O2, the xenografts showed higher expression of hypoxic biomarkers. Cisplatin radiosensitized SUNE-1/HRE cells under hypoxia by suppressing DSB repair while the addition of PI3K/mTOR inhibitor further enhanced the anti-tumoral therapeutic efficacy. Combination of IR, DDP and NVP-BEZ235 exhibited most effective anti-tumor response in vivo. These observations underline the importance of dual reporter model for imaging tumor hypoxia in therapeutic study. Conclusions: Our preclinical model enables the investigation of heterogeneous tumor hypoxic regions in xenograft tissues and explores the treatment efficacy of combinations of various therapeutic approaches to overcome hypoxia.

Photodynamic Therapy and Adaptive Immunity Induced by Reactive Oxygen Species: Recent Reports

Cancer is one of the most significant causes of death worldwide. Despite the rapid development of modern forms of therapy, results are still unsatisfactory. The prognosis is further worsened by the ability of cancer cells to metastasize. Thus, more effective forms of therapy, such as photodynamic therapy, are constantly being developed. The photodynamic therapeutic regimen involves administering a photosensitizer that selectively accumulates in tumor cells or is present in tumor vasculature prior to irradiation with light at a wavelength corresponding to the photosensitizer absorbance, leading to the generation of reactive oxygen species. Reactive oxygen species are responsible for the direct and indirect destruction of cancer cells. Photodynamically induced local inflammation has been shown to have the ability to activate an adaptive immune system response resulting in the destruction of tumor lesions and the creation of an immune memory. This paper focuses on presenting the latest scientific reports on the specific immune response activated by photodynamic therapy. We present newly discovered mechanisms for the induction of the adaptive response by analyzing its various stages, and the possible difficulties in generating it. We also present the results of research over the past 10 years that have focused on improving the immunological efficacy of photodynamic therapy for improved cancer therapy.

A simulation study on the radiation-induced immune response of tumors after single fraction high-dose irradiation

PURPOSE

We investigated radiation-induced antitumor immunity and its suppression by hypoxia-inducible factor (HIF-1α) for radiosurgery (SRS) using an improved cellular automata (CA) model.

METHOD

A two-dimensional Cellular Automata (CA) model was employed to simulate the impact of radiation on cancer cell death and subsequent immune responses. Cancer cells died from direct cell death from radiation and indirect cell death due to radiation-induced vascular damage. The model also incorporated radiation-induced immunity and immuno-suppression. It was incorporated into the model assuming that the death of cancer cells generates effector cells, forming complexes with cancer cells, and high radiation doses lead to vascular damage, inducing tumor hypoxia and increasing HIF-1α expression. The model was validated and subjected to sensitivity analysis by evaluating tumor volume changes post-irradiation and exploring the effects and sensitivity of radiation-induced immune responses.

RESULTS

The ratios of the tumor volume at 360 days post-irradiation and the SRS day (rTV) decreased with a higher PME, a higher Pcomp, and a lower ThHIF. The rTVs were 4.6 and 2.0 for PME = 0.1 and 0.9, 12.0 and 2.2 for Pcomp = 0.1 and 0.9, and 1.5 and 15.3 for ThHIF = 0.1 and 10.0, respectively.

CONCLUSIONS

By modeling the activation and deactivation of the effectors, the improved CA model showed that the radiation-induced immunogenic cell death in the tumor caused a decrease in the post-irradiation volume by a factor of four for the therapeutic doses relative to non-immune reaction cases. Furthermore, the suppressive effects of HIF-1α induced by hypoxia decreased radiation-induced immune effects by more than 50.

The Anti-hypoxia Potentials of Trans-sodium Crocetinate in Hypoxiarelated Diseases: A Review

Crocetin is a kind of apocarotenoid carboxylic acid extracted from saffron (Crocus sativus L.), which is effective in upregulating tissue oxygenation. However, crocetin is difficult to solubilize. It was shown that the trans isomer of crocetin is effective in improving oxygen diffusivity, while its cis isomer appears not to be. Hence, the isolated trans isomer of crocetin or trans-sodium crocetinate (TSC) can be used instead of crocetin. It is shown that TSC can upregulate hypoxic tissue oxygenation and be effective in treating some hypoxia-related diseases. Moreover, experimental and clinical studies have reported no adverse effects following TSC treatment, even at high doses. The current study will discuss the potential role of TSC in hemorrhagic shock, ischemia, brain tumor radiotherapy, and others.

Therapeutic In Situ Cancer Vaccine Using Pulsed Stereotactic Body Radiotherapy-A Translational Model

Both radiation and cancer therapeutic vaccine research are more than 100 years old, and their potential is likely underexplored. Antiangiogenics, nanoparticle targeting, and immune modulators are some other established anticancer therapies. In the meantime, immunotherapy usage is gaining momentum in clinical applications. This article proposes the concept of a pulsed/intermittent/cyclical endothelial-sparing single-dose in situ vaccination (ISVRT) schedule distinguishable from the standard therapeutic stereotactic body radiotherapy (SBRT) and stereotactic radiosurgery (SRS) plans. This ISVRT schedule can repeatedly generate tumor-specific neoantigens and epitopes for primary and immune modulation effects, augment supplementary immune enhancement techniques, activate long-term memory cells, avoid extracellular matrix fibrosis, and essentially synchronize with the vascular normalized immunity cycle. The core mechanisms of ISVRT impacting in situ vaccination would be optimizing cascading antigenicity and adjuvanticity. The present proposed hypothesis can be validated using the algorithm presented. The indications for the proposed concept are locally progressing/metastatic cancers that have failed standard therapies. Immunotherapy/targeted therapy, chemotherapy, antiangiogenics, and vascular-lymphatic normalization are integral to such an approach.

Mechanisms and applications of radiation-induced oxidative stress in regulating cancer immunotherapy

Radiotherapy (RT) is an effective treatment option for cancer patients, which induces the production of reactive oxygen species (ROS) and causes oxidative stress (OS), leading to the death of tumor cells. OS not only causes apoptosis, autophagy and ferroptosis, but also affects tumor immune response. The combination of RT and immunotherapy has revolutionized the management of various cancers. In this process, OS caused by ROS plays a critical role. Specifically, RT-induced ROS can promote the release of tumor-associated antigens (TAAs), regulate the infiltration and differentiation of immune cells, manipulate the expression of immune checkpoints, and change the tumor immune microenvironment (TME). In this review, we briefly summarize several ways in which IR induces tumor cell death and discuss the interrelationship between RT-induced OS and antitumor immunity, with a focus on the interaction of ferroptosis with immunogenic death. We also summarize the potential mechanisms by which ROS regulates immune checkpoint expression, immune cells activity, and differentiation. In addition, we conclude the therapeutic opportunity improving radiotherapy in combination with immunotherapy by regulating OS, which may be beneficial for clinical treatment.

PD-1/PD-L1 checkpoint inhibitors in advanced hepatocellular carcinoma immunotherapy

Hepatocellular carcinoma (HCC) has a high prevalence and mortality rate worldwide. Sorafenib monotherapy has been the standard of first-line treatment for advanced HCC for a long time, but there are still many shortcomings. In recent years, with the deepening of research on tumor immune microenvironment, researchers have begun to explore new approaches in immunotherapy, and the introduction of immune checkpoint inhibitors has brought fundamental changes to the treatment of HCC. Programmed cell death protein 1 (PD-1) is an immune checkpoint molecule that plays an important role in down-regulating immune system function and promoting tolerance. Programmed cell death ligand 1 (PDL-1) is involved in tumor immune evasion by binding to PD-1, resulting in failure of treatment. Currently, immunotherapy targeting the PD-1/PD-L1 axis has achieved unprecedented success in HCC, but it also faces great challenges, with its low remission rate still to be solved. For most patients with HCC, the PD-1/PD-L1 pathway is not the only rate limiting factor of antitumor immunity, and blocking only the PD-1/PD-L1 axis is not enough to stimulate an effective antitumor immune response; thus, combination therapy may be a better option. In this study, changes in the immune microenvironment of HCC patients were reviewed to clarify the feasibility of anti-PD-1/PD-L1 therapy, and a series of monotherapy and combination therapy clinical trials were summarized to verify the safety and efficacy of this newly developed treatment in patients with advanced HCC. Furthermore, we focused on hyperprogressive disease and drug resistance to gain a better understanding of PD-1/PD-L1 blockade as a promising treatment.

Natural Radiosensitizers in Radiotherapy: Cancer Treatment by Combining Ionizing Radiation with Resveratrol

Conventional cancer treatment is mainly based on the surgical removal of the tumor followed by radiotherapy and/or chemotherapy. When surgical removal is not possible, radiotherapy and, less often, chemotherapy is the only way to treat patients. However, despite significant progress in understanding the molecular mechanisms of carcinogenesis and developments in modern radiotherapy techniques, radiotherapy (alone or in combination) does not always guarantee treatment success. One of the main causes is the radioresistance of cancer cells. Increasing the radiosensitivity of cancer cells improves the processes leading to their elimination during radiotherapy and prolonging the survival of cancer patients. In order to enhance the effect of radiotherapy in the treatment of radioresistant neoplasms, radiosensitizers are used. In clinical practice, synthetic radiosensitizers are commonly applied, but scientists have recently focused on using natural products (phytocompounds) as adjuvants in radiotherapy. In this review article, we only discuss naturally occurring radiosensitizers currently in clinical trials (paclitaxel, curcumin, genistein, and papaverine) and those whose radiation sensitizing effects, such as resveratrol, have been repeatedly confirmed by many independent studies.

Efficacy and safety of endostar combined with chemoradiotherapy versus chemoradiotherapy alone in locally advanced cervical cancer: A PRISMA-compliant systematic review and meta-analysis

BACKGROUND

To evaluate the role and safety of endostar in cervical cancer by comparing the efficacy and adverse reactions of endostar combined with concurrent chemoradiotherapy in patients with locally advanced cervical carcinoma.

METHODS

The quality of the included literature was evaluated by searching the database for the comparison of endostar combined with concurrent radiotherapy and chemotherapy in cervical cancer patients; objective response rate (ORR) and disease control rate (DCR) were used as the main outcome indicators, and statistical analysis was performed using RevMan5.3 and State15.3 software.

RESULTS

A total of 13 studies were included in this study, including 1057 patients with locally advanced cervical cancer, suggesting that endostar combined with chemoradiotherapy can significantly improve the objective response rate (ORR: odds ratio 3.88, 95% confidence interval 2.77-5.45, P < .00001) and disease control rate (DCR: odds ratio 4.43, 95% confidence interval 2.78-7.04; P < .00001), and there was no significant increase in treatment-related adverse reactions.

CONCLUSIONS

In this meta-analysis, endostar combined with concurrent chemoradiotherapy significantly improved ORR and DCR in patients with locally advanced cervical cancer without increasing toxicity. However, this study only analyzed the short-term efficacy of endostar, and its influence on overall survival and progression-free survival needs to be further verified in large randomized controlled trials with long-term follow-up.

HIF-1α Inhibition Improves Anti-Tumor Immunity and Promotes the Efficacy of Stereotactic Ablative Radiotherapy (SABR)

Simple Summary

Stereotactic ablative radiotherapy (SABR), which irradiates tumors with high-dose radiation per fraction, promotes anti-tumor immunity by stimulating various immune processes. SABR also induces vascular damage and obstructs blood flow, thereby increasing tumor hypoxia and upregulation of hypoxia-inducible factors HIF-1α and HIF-2α, master transcription factors for the cellular response to hypoxia. HIF-1α and HIF-2α are key players in the upregulation of immune suppression in hypoxia. Therefore, the radiation-induced increase in anti-tumor immunity is masked by the HIF-mediated immune suppression. Pre-clinical experiments show that inhibition of HIF-1α effectively prevents immune suppression and improves anti-tumor immunity. A combination of HIF-1α inhibitors with immunotherapy with checkpoint blocking antibodies may represent a novel approach to boost anti-tumor immunity and enhance the efficacy of SABR.

Abstract

High-dose hypofractionated radiation such as SABR (stereotactic ablative radiotherapy) evokes an anti-tumor immune response by promoting a series of immune-stimulating processes, including the release of tumor-specific antigens from damaged tumor cells and the final effector phase of immune-mediated lysis of target tumor cells. High-dose hypofractionated radiation also causes vascular damage in tumors, thereby increasing tumor hypoxia and upregulation of hypoxia-inducible factors HIF-1α and HIF-2α, the master transcription factors for the cellular response to hypoxia. HIF-1α and HIF-2α are critical factors in the upregulation of immune suppression and are the master regulators of immune evasion of tumors. Consequently, SABR-induced increase in anti-tumor immunity is counterbalanced by the increase in immune suppression mediated by HIFα. Inhibition of HIF-1α with small molecules such as metformin downregulates immunosuppressive pathways, including the expression of immune checkpoints, and it improves or restores the anti-tumor immunity stimulated by irradiation. Combinations of HIFα inhibitors, particularly HIF-1α inhibitors, with immune checkpoint blocking antibodies may represent a novel approach to boost the overall anti-tumor immune profile in patients and thus enhance outcomes after SABR.

Tumor immunotherapies by immune checkpoint inhibitors (ICIs); the pros and cons

The main breakthrough in tumor immunotherapy was the discovery of immune checkpoint (IC) proteins, which act as a potent suppressor of the immune system by a myriad of mechanisms. After that, scientists focused on the immune checkpoint molecules mainly. Thereby, much effort was spent to progress novel strategies for suppressing these inhibitory axes, resulting in the evolution of immune checkpoint inhibitors (ICIs). Then, ICIs have become a promising approach and shaped a paradigm shift in tumor immunotherapies. CTLA-4 plays an influential role in attenuation of the induction of naïve and memory T cells by engagement with its responding ligands like B7-1 (CD80) and B7-2 (CD86). Besides, PD-1 is predominantly implicated in adjusting T cell function in peripheral tissues through its interaction with programmed death-ligand 1 (PD-L1) and PD-L2. Given their suppressive effects on anti-tumor immunity, it has firmly been documented that ICIs based therapies can be practical and rational therapeutic approaches to treat cancer patients. Nonetheless, tumor inherent or acquired resistance to ICI and some treatment-related toxicities restrict their application in the clinic. The current review will deliver a comprehensive overview of the ICI application to treat human tumors alone or in combination with other modalities to support more desired outcomes and lower toxicities in cancer patients. Video Abstract.

Integration of immune and hypoxia gene signatures improves the prediction of radiosensitivity in breast cancer

Immunity and hypoxia are two important factors that affect the response of cancer patients to radiotherapy. At the same time, considering the limited predictive value of a single predictive model and the uncertainty of grouping patients near the cutoff value, we developed and validated a combined model based on immune- and hypoxia-related gene expression profiles to predict the radiosensitivity of breast cancer patients. This study was based on breast cancer data from The Cancer Genome Atlas (TCGA). Spike-and-slab Lasso regression analysis was performed to select three immune-related genes and develop a radiosensitivity model. Lasso Cox regression modeling selected 11 hypoxia-related genes for development of radiosensitivity model. Three independent datasets (Molecular Taxonomy of Breast Cancer International Consortium [METABRIC], E-TABM-158, GSE103746) were used to validate the predictive value of radiosensitivity signatures. In the TCGA dataset, the 10-year survival probabilities of the immune radioresistant (IRR) and hypoxia radioresistant (HRR) groups were 0.189 (0.037, 0.973) and 0.477 (0.293, 0.776), respectively. The 10-year survival probabilities of the immune radiosensitive (IRS) and hypoxia radiosensitive (HRS) groups were 0.778 (0.676, 0.895) and 0.824 (0.723, 0.939), respectively. Based on these two gene signatures, we further constructed a combined model and divided all patients into three groups (IRS/HRS, mixed, IRR/HRR). We identified the IRS/HRS patients most likely to benefit from radiotherapy; the 10-year survival probability was 0.886 (0.806, 0.976). The 10-year survival probability of the IRR/HRR group was 0. In conclusion, a combined model integrating immune- and hypoxia-related gene signatures could effectively predict the radiosensitivity of breast cancer and more accurately identify radiosensitive and radioresistant patients than a single model.

The importance of hypoxia in radiotherapy for the immune response, metastatic potential and FLASH-RT

PURPOSE

Hypoxia (low oxygen) is a common feature of solid tumors that has been intensely studied for more than six decades. Here we review the importance of hypoxia to radiotherapy with a particular focus on the contribution of hypoxia to immune responses, metastatic potential and FLASH radiotherapy, active areas of research by leading women in the field.

CONCLUSION

Although hypoxia-driven metastasis and immunosuppression can negatively impact clinical outcome, understanding these processes can also provide tumor-specific vulnerabilities that may be therapeutically exploited. The different oxygen tensions present in tumors and normal tissues may underpin the beneficial FLASH sparing effect seen in normal tissue and represents a perfect example of advances in the field that can leverage tumor hypoxia to improve future radiotherapy treatments.

The impact of hypoxia on immune state in cancer

Hypoxia is a known feature of solid tumors and a critical promoter of tumor hallmarks. Hypoxia influences tumor immunity in a way favoring immune evasion and resistance. Extreme hypoxia and aberrant hypoxia-inducible factor-1 (HIF-1) activity in tumor microenvironment (TME) is a drawback for effective immunotherapy. Infiltration and activity of CD8⁺ T cells is reduced in such condition, whereas regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs) show high activities. Highly hypoxic TME also impairs maturation and activity of dendritic cell (DCs) and natural killer (NK) cells. In addition, the hypoxic TME positively is linked positively with metabolic changes in cells of immune system. These alterations are indicative of a need for hypoxia modulation as a complementary targeting strategy to go with immune checkpoint inhibitor (ICI) therapy.

Targeting hypoxia and hypoxia-inducible factor-1 in the tumor microenvironment for optimal cancer immunotherapy

The development of new strategies of anticancer immunotherapies has provided promising approaches in the treatment of solid tumors. However, despite the improved survival in responders, most of the patients show incomplete responses with a lack of remarkable clinical improvement. Hypoxia has been identified as a common characteristic of solid tumors contributing to different aspects of tumor progression, including invasion, metastasis, and the creation of the immunosuppressive tumor microenvironment. Hypoxia, through its main mediator, hypoxia-inducible factor-1 (HIF-1) is also associated with the limited efficacy of immunotherapies. Therefore, designing new strategies for immunotherapy implicating therapeutic targeting of HIF-1 molecules may enhance the clinical effectiveness of immunotherapy. Here, we discuss the contribution of hypoxia to the development of the immunosuppressive tumor microenvironment. We will also outline different strategies for targeting hypoxia to provide insight into the therapeutic potential of the application of such strategies to improve the clinical benefit of cancer immunotherapy.

Repurposing Disulfiram for Targeting of Glioblastoma Stem Cells: An In Vitro Study

Mesenchymal glioblastoma stem cells (GSCs), a subpopulation in glioblastoma that are responsible for therapy resistance and tumor spreading in the brain, reportedly upregulate aldehyde dehydrogenase isoform-1A3 (ALDH1A3) which can be inhibited by disulfiram (DSF), an FDA-approved drug formerly prescribed in alcohol use disorder. Reportedly, DSF in combination with Cu²⁺ ions exerts multiple tumoricidal, chemo- and radio-therapy-sensitizing effects in several tumor entities. The present study aimed to quantify these DSF effects in glioblastoma stem cells in vitro, regarding dependence on ALDH1A3 expression. To this end, two patient-derived GSC cultures with differing ALDH1A3 expression were pretreated (in the presence of CuSO₄, 100 nM) with DSF (0 or 100 nM) and the DNA-alkylating agent temozolomide (0 or 30 µM) and then cells were irradiated with a single dose of 0–8 Gy. As read-outs, cell cycle distribution and clonogenic survival were determined by flow cytometry and limited dilution assay, respectively. As a result, DSF modulated cell cycle distribution in both GSC cultures and dramatically decreased clonogenic survival independently of ALDH1A3 expression. This effect was additive to the impairment of clonogenic survival by radiation, but not associated with radiosensitization. Of note, cotreatment with temozolomide blunted the DSF inhibition of clonogenic survival. In conclusion, DSF targets GSCs independent of ALDH1A3 expression, suggesting a therapeutic efficacy also in glioblastomas with low mesenchymal GSC populations. As temozolomide somehow antagonized the DSF effects, strategies for future combination of DSF with the adjuvant standard therapy (fractionated radiotherapy and concomitant temozolomide chemotherapy followed by temozolomide maintenance therapy) are not supported by the present study.

Quantitative Longitudinal Imaging Reveals that Inhibiting Hedgehog Activity Alleviates the Hypoxic Tumor Landscape

Metastases account for the majority of mortalities related to breast cancer. The onset and sustained presence of hypoxia strongly correlates with increased incidence of metastasis and unfavorable prognosis in patients with breast cancer. The Hedgehog (Hh) signaling pathway is dysregulated in breast cancer, and its abnormal activity enables tumor progression and metastasis. In addition to programming tumor cell behavior, Hh activity enables tumor cells to craft a metastasis-conducive microenvironment. Hypoxia is a prominent feature of growing tumors that impacts multiple signaling circuits that converge upon malignant progression. We investigated the role of Hh activity in crafting a hypoxic environment of breast cancer. We used radioactive tracer [¹⁸F]-fluoromisonidazole (FMISO) positron emission tomography (PET) to image tumor hypoxia. We show that tumors competent for Hh activity are able to establish a hypoxic milieu; pharmacologic inhibition of Hh signaling in a syngeneic mammary tumor model mitigates tumor hypoxia. Furthermore, in hypoxia, Hh activity is robustly activated in tumor cells and institutes increased HIF signaling in a VHL-dependent manner. The findings establish a novel perspective on Hh activity in crafting a hypoxic tumor landscape and molecularly navigating the tumor cells to adapt to hypoxic conditions. IMPLICATIONS: Importantly, we present a translational strategy of utilizing longitudinal hypoxia imaging to measure the efficacy of vismodegib in a preclinical model of triple-negative breast cancer.

Repurposing Proton Beam Therapy through Novel Insights into Tumour Radioresistance

Despite improvements in radiotherapy, radioresistance remains an important clinical challenge. Radioresistance can be mediated through enhanced DNA damage response mechanisms within the tumour or through selective pressures exerted by the tumour microenvironment (TME). The effects of the TME have in recent times gained increased attention, in part due to the success of immune modulating strategies, but also through improved understanding of the downstream effects of hypoxia and dysregulated wound healing processes on mediating radioresistance. Although we have a better appreciation of these molecular mechanisms, efforts to address them through novel combination approaches have been scarce, owing to limitations of photon therapy and concerns over toxicity. At the same time, proton beam therapy (PBT) represents an advancement in radiotherapy technologies. However, early clinical results have been mixed and the clinical strategies around optimal use and patient selection for PBT remain unclear. Here we highlight the role that PBT can play in addressing radioresistance, through better patient selection, and by providing an improved toxicity profile for integration with novel agents. We will also describe the developments around FLASH PBT. Through close examination of its normal tissue-sparing effects, we will highlight how FLASH PBT can facilitate combination strategies to tackle radioresistance by further improving toxicity profiles and by directly mediating the mechanisms of radioresistance.

Therapeutic potentials of resveratrol in combination with radiotherapy and chemotherapy during glioblastoma treatment: a mechanistic review

Glioblastoma, WHO grade IV astrocytoma, is the most aggressive type of brain tumors. These cancerous cells have a rapid growth rate, tendency to penetrate vital brain structures, molecular heterogeneity, etc. and this cancer is associated with a poor prognosis and low survival rate. Due to the resistance of glioblastoma cells to conventional therapeutic modalities (such as radiation therapy and chemotherapy) as well as the adverse effects of these modalities, the researchers have attempted to discover an appropriate alternative or adjuvant treatment for glioblastoma. Resveratrol, as an herbal and natural polyphenolic compound, has anti-tumoral property and has shown to be effective in GBM treatment. Resveratrol exerts its anti-tumoral effect through various mechanisms such as regulation of cell cycle progression and cell proliferation, autophagy, oxidant system, apoptosis pathways, and so on. Resveratrol in combination with radiation therapy and chemotherapy has also been used. In the present study, we summarized the current findings on therapeutic potentials of resveratrol in glioblastoma radiotherapy and chemotherapy.

Radiotherapy planning parameters correlate with changes in the peripheral immune status of patients undergoing curative radiotherapy for localized prostate cancer

Purpose

The influence of radiotherapy on patient immune cell subsets has been established by several groups. Following a previously published analysis of immune changes during and after curative radiotherapy for prostate cancer, this analysis focused on describing correlations of changes of immune cell subsets with radiation treatment parameters.

Patients and methods

For 13 patients treated in a prospective trial with radiotherapy to the prostate region (primary analysis) and five patients treated with radiotherapy to prostate and pelvic nodal regions (exploratory analysis), already published immune monitoring data were correlated with clinical data as well as radiation planning parameters such as clinical target volume (CTV) and volumes receiving 20 Gy (V20) for newly contoured volumes of pelvic blood vessels and bone marrow.

Results

Most significant changes among immune cell subsets were observed at the end of radiotherapy. In contrast, correlations of age and CD8⁺ subsets (effector and memory cells) were observed early during and 3 months after radiotherapy. Ratios of T cells and T cell proliferation compared to baseline correlated with CTV. Early changes in regulatory T cells (Treg cells) and CD8⁺ effector T cells correlated with V20 of blood vessels and bone volumes.

Conclusions

Patient age as well as radiotherapy planning parameters correlated with immune changes during radiotherapy. Larger irradiated volumes seem to correlate with early suppression of anti-cancer immunity. For immune cell analysis during normofractionated radiotherapy and correlations with treatment planning parameters, different time points should be looked at in future projects.

Trial registration number:

NCT01376674, 20.06.2011

Supplementary Information

The online version contains supplementary material available at 10.1007/s00262-021-03002-6.

Hypoxia in Lung Cancer Management: A Translational Approach

Simple Summary

Hypoxia is a common feature of lung cancers. Nonetheless, no guidelines have been established to integrate hypoxia-associated biomarkers in patient management. Here, we discuss the current knowledge and provide translational novel considerations regarding its clinical detection and targeting to improve the outcome of patients with non-small-cell lung carcinoma of all stages.

Abstract

Lung cancer represents the first cause of death by cancer worldwide and remains a challenging public health issue. Hypoxia, as a relevant biomarker, has raised high expectations for clinical practice. Here, we review clinical and pathological features related to hypoxic lung tumours. Secondly, we expound on the main current techniques to evaluate hypoxic status in NSCLC focusing on positive emission tomography. We present existing alternative experimental approaches such as the examination of circulating markers and highlight the interest in non-invasive markers. Finally, we evaluate the relevance of investigating hypoxia in lung cancer management as a companion biomarker at various lung cancer stages. Hypoxia could support the identification of patients with higher risks of NSCLC. Moreover, the presence of hypoxia in treated tumours could help clinicians predict a worse prognosis for patients with resected NSCLC and may help identify patients who would benefit potentially from adjuvant therapies. Globally, the large quantity of translational data incites experimental and clinical studies to implement the characterisation of hypoxia in clinical NSCLC management.

EVA1C Is a Potential Prognostic Biomarker and Correlated With Immune Infiltration Levels in WHO Grade II/III Glioma

Background

Immunotherapy is an effective therapeutic approach for multiple human cancer types. However, the correlations between EVA1C and patients’ prognosis as well as immune infiltration remain obscure. Herein, we employed transcriptomic and clinical data extracted from two independent databases to systematically investigate the role of EVA1C in the oncological context.

Methods

The differential expression of EVA1C was analyzed via TCGA and Oncomine databases. We evaluated the influence of EVA1C on clinical prognosis using Kaplan-Meier plotter. We then used the expression profiler to calculate stromal score, immune score, and ESTIMATE score based on the ESTIMATE algorithm. The abundance of infiltrating immune cells was calculated via TIMER. The correlations between EVA1C expression and immune infiltration levels were analyzed in two independent cohorts.

Results

In patients with World Health Organization (WHO) grade II/III glioma, high EVA1C expression was associated with malignant clinicopathological features and poor overall survival in both cohorts. EVA1C expression was positively associated with immune infiltration levels of B cell, CD4+ T cell, neutrophil, macrophage, and dendritic cells (DCs). Besides, EVA1C expression strongly correlated with diverse immune marker sets. And the predictive power of EVA1C was better than that of other indicators in predicting high immune infiltration levels in glioma.

Conclusions

For the first time, we identified the overexpression of EVA1C in glioma, which was tightly correlated with the high infiltration levels of multiple immune cells as well as poor prognosis. Meanwhile, EVA1C might be a potential biomarker for predicting high immune infiltration in WHO grade II/III gliomas.

Combined Radiochemotherapy: Metalloproteinases Revisited

Besides cytotoxic DNA damage irradiation of tumor cells triggers multiple intra- and intercellular signaling processes, that are part of a multilayered, treatment-induced stress response at the unicellular and tumor pathophysiological level. These processes are intertwined with intrinsic and acquired resistance mechanisms to the toxic effects of ionizing radiation and thereby co-determine the tumor response to radiotherapy. Proteolysis of structural elements and bioactive signaling moieties represents a major class of posttranslational modifications regulating intra- and intercellular communication. Plasma membrane-located and secreted metalloproteinases comprise a family of metal-, usually zinc-, dependent endopeptidases and sheddases with a broad variety of substrates including components of the extracellular matrix, cyto- and chemokines, growth and pro-angiogenic factors. Thereby, metalloproteinases play an important role in matrix remodeling and auto- and paracrine intercellular communication regulating tumor growth, angiogenesis, immune cell infiltration, tumor cell dissemination, and subsequently the response to cancer treatment. While metalloproteinases have long been identified as promising target structures for anti-cancer agents, previous pharmaceutical approaches mostly failed due to unwanted side effects related to the structural similarities among the multiple family members. Nevertheless, targeting of metalloproteinases still represents an interesting rationale alone and in combination with other treatment modalities. Here, we will give an overview on the role of metalloproteinases in the irradiated tumor microenvironment and discuss the therapeutic potential of using more specific metalloproteinase inhibitors in combination with radiotherapy.

The regulation of immune checkpoints by the hypoxic tumor microenvironment

The tumor microenvironment (TME) influences the occurrence and progression of tumors, and hypoxia is an important characteristic of the TME. The expression of programmed death 1 (PD1)/programmed death-ligand 1 (PDL1), cytotoxic T-lymphocyte-associated antigen 4 (CTLA4), and other immune checkpoints in hypoxic malignant tumors is often significantly increased, and is associated with poor prognosis. The application of immune checkpoint inhibitors (ICIs) for treating lung cancer, urothelial carcinoma, and gynecological tumors has achieved encouraging efficacy; however, the rate of efficacy of ICI single-drug treatment is only about 20%. In the present review, we discuss the possible mechanisms by which the hypoxic TME regulates immune checkpoints. By activating hypoxia-inducible factor-1α (HIF-1α), regulating the adenosine (Ado)-A2aR pathway, regulating the glycolytic pathway, and driving epithelial-mesenchymal transition (EMT) and other biological pathways, hypoxia regulates the expression levels of CTLA4, PD1, PDL1, CD47, lymphocyte activation gene 3 (LAG3), T-cell immunoglobulin and mucin domain 3 (TIM3), and other immune checkpoints, which interfere with the immune effector cell anti-tumor response and provide convenient conditions for tumors to escape immune surveillance. The combination of HIF-1α inhibitors, Ado-inhibiting tumor immune microenvironment regulatory drugs, and other drugs with ICIs has good efficacy in both preclinical studies and phase I-II clinical studies. Exploring the effects of TME hypoxia on the expression of immune checkpoints and the function of infiltrating immune cells has greatly clarified the relationship between the hypoxic TME and immune escape, which is of great significance for the development of new drugs and the search for predictive markers of the efficacy of immunotherapy for treating malignant tumors. In the future, combination therapy with hypoxia pathway inhibitors and ICIs may be an effective anti-tumor treatment strategy.

Enamine N-Oxides: Synthesis and Application to Hypoxia-Responsive Prodrugs and Imaging Agents

Tumor hypoxia induces the large-scale adaptive reprogramming of cancer cells, promoting their transformation into highly invasive and metastatic species that lead to highly negative prognoses for cancer patients. We describe the synthesis and application of a hypoxia-responsive trigger derived from previously inaccessible enamine N-oxide structures. Hypoxia-dependent reduction of this motif by hemeproteins results in the concomitant activation of a caged molecule and a latent electrophile. We exploit the former in a hypoxia-activated prodrug application using a caged staurosporine molecule as a proof-of-principle. We demonstrate the latter in in vivo tumor labeling applications with enamine-N-oxide-modified near-infrared probes. Hypoxia-activated prodrug development has long been complicated by the heterogeneity of tumor hypoxia in patients. The dual drug release and imaging modalities of the highly versatile enamine N-oxide motif present an attractive opportunity for theranostic development that can address the need not only for new therapeutics but paired methods for patient stratification.

Potassium Channels in Cancer

Neoplastic transformation is reportedly associated with alterations of the potassium transport across plasma and intracellular membranes. These alterations have been identified as crucial elements of the tumourigenic reprogramming of cells. Potassium channels may contribute to cancer initiation, malignant progression and therapy resistance of tumour cells. The book chapter focusses on (oncogenic) potassium channels frequently upregulated in different tumour entities, upstream and downstream signalling of these channels, their contribution to the maintenance of cancer stemness and the formation of an immunosuppressive tumour microenvironment. In addition, their role in adaptation to tumour hypoxia, metabolic reprogramming, as well as tumour spreading and metastasis is discussed. Finally, we discuss how (oncogenic) potassium channels may confer treatment resistance of tumours against radiation and chemotherapy and thus might be harnessed for new therapy strategies, for instance, by repurposing approved drugs known to target potassium channels.

MR-Guided Radiotherapy for Head and Neck Cancer: Current Developments, Perspectives, and Challenges

Based on the development of new hybrid machines consisting of an MRI and a linear accelerator, magnetic resonance image guided radiotherapy (MRgRT) has revolutionized the field of adaptive treatment in recent years. Although an increasing number of studies have been published, investigating technical and clinical aspects of this technique for various indications, utilizations of MRgRT for adaptive treatment of head and neck cancer (HNC) remains in its infancy. Yet, the possible benefits of this novel technology for HNC patients, allowing for better soft-tissue delineation, intra- and interfractional treatment monitoring and more frequent plan adaptations appear more than obvious. At the same time, new technical, clinical, and logistic challenges emerge. The purpose of this article is to summarize and discuss the rationale, recent developments, and future perspectives of this promising radiotherapy modality for treating HNC.

Hypoxia-Induced Cancer Cell Responses Driving Radioresistance of Hypoxic Tumors: Approaches to Targeting and Radiosensitizing

Simple Summary

Some regions of aggressive malignancies experience hypoxia due to inadequate blood supply. Cancer cells adapting to hypoxic conditions somehow become more resistant to radiation exposure and this decreases the efficacy of radiotherapy toward hypoxic tumors. The present review article helps clarify two intriguing points: why hypoxia-adapted cancer cells turn out radioresistant and how they can be rendered more radiosensitive. The critical molecular targets associated with intratumoral hypoxia and various approaches are here discussed which may be used for sensitizing hypoxic tumors to radiotherapy.

Abstract

Within aggressive malignancies, there usually are the “hypoxic zones”—poorly vascularized regions where tumor cells undergo oxygen deficiency through inadequate blood supply. Besides, hypoxia may arise in tumors as a result of antiangiogenic therapy or transarterial embolization. Adapting to hypoxia, tumor cells acquire a hypoxia-resistant phenotype with the characteristic alterations in signaling, gene expression and metabolism. Both the lack of oxygen by itself and the hypoxia-responsive phenotypic modulations render tumor cells more radioresistant, so that hypoxic tumors are a serious challenge for radiotherapy. An understanding of causes of the radioresistance of hypoxic tumors would help to develop novel ways for overcoming this challenge. Molecular targets for and various approaches to radiosensitizing hypoxic tumors are considered in the present review. It is here analyzed how the hypoxia-induced cellular responses involving hypoxia-inducible factor-1, heat shock transcription factor 1, heat shock proteins, glucose-regulated proteins, epigenetic regulators, autophagy, energy metabolism reprogramming, epithelial–mesenchymal transition and exosome generation contribute to the radioresistance of hypoxic tumors or may be inhibited for attenuating this radioresistance. The pretreatments with a multitarget inhibition of the cancer cell adaptation to hypoxia seem to be a promising approach to sensitizing hypoxic carcinomas, gliomas, lymphomas, sarcomas to radiotherapy and, also, liver tumors to radioembolization.

Hypoxia in Solid Tumors: How Low Oxygenation Impacts the "Six Rs" of Radiotherapy

Radiotherapy is an important component of cancer treatment, with approximately 50% of all cancer patients receiving radiation therapy during their course of illness. Nevertheless, solid tumors frequently exhibit hypoxic areas, which can hinder therapies efficacy, especially radiotherapy one. Indeed, hypoxia impacts the six parameters governing the radiotherapy response, called the « six Rs of radiation biology » (for Radiosensitivity, Repair, Repopulation, Redistribution, Reoxygenation, and Reactivation of anti-tumor immune response), by inducing pleiotropic cellular adaptions, such as cell metabolism rewiring, epigenetic landscape remodeling, and cell death weakening, with significant clinical repercussions. In this review, according to the six Rs, we detail how hypoxia, and associated mechanisms and pathways, impact the radiotherapy response of solid tumors and the resulting clinical implications. We finally illustrate it in hypoxic endocrine cancers through a focus on anaplastic thyroid carcinomas.

Targeting CTLA-4 in cancer: Is it the ideal companion for PD-1 blockade immunotherapy combinations?

Immunotherapy approaches boosting spontaneous and durable antitumor immune responses through immune checkpoint blockade are revolutionizing treatment and patient outcomes in solid tumors and hematological malignancies. Among the various inhibitory molecules employed by the immune system to regulate the adaptive immune responses, cytotoxic T lymphocyte antigen-4 (CTLA-4) is the first successfully targeted immune checkpoint molecule in the clinic, giving rise to significant but selective benefit either when targeted alone or in combination with anti-programmed cell death protein-1 (PD-1) antibodies (Abs). However, the use of anti-CTLA-4 Abs was associated with the incidence of autoimmune-like adverse events (AEs), which were particularly frequent and severe with the use of combinational strategies. Nevertheless, the higher incidence of AEs is associated with an improved clinical benefit indicating treatment response. A prompt recognition of AEs followed by early and adequate treatment with immunosuppressive agents allows the management of these potentially serious AEs. This narrative review aims to summarize CTLA-4 biology, the rationale for the use as a companion for anti-PD-1 Abs in humans with results from the most relevant Phase III clinical trials including anti-CTLA-4 Abs in combination with anti-PD-1 Abs in solid tumors.

Polymorphonuclear-MDSCs Facilitate Tumor Regrowth After Radiation by Suppressing CD8+ T Cells

PURPOSE

Radiation therapy (RT) is widely used in the treatment of cancer. Unfortunately, RT alone is insufficient to control the disease in most cases, as regrowth after irradiation still occur. Thus, it would be meaningful to explore the underlying mechanism of tumor regrowth after irradiation. Myeloid-derived suppressor cells (MDSCs) contribute to the immunosuppressive tumor microenvironment and hinder the therapeutic efficacy of RT. However, it is unclear whether MDSCs-mediated immune suppression contributes to local relapse after irradiation. In this article, we tried to figure out how MDSCs sabotage the therapeutic effect of RT, and tried to determine the potential synergistic effect of combination between targeting MDSCs and RT.

METHODS AND MATERIALS

A syngeneic murine model of Lewis lung cancer was used. The abundance of tumor infiltrating MDSCs and tumor growth after irradiation was assessed. The percentage and functional state of CD8⁺ T cells were measured by flow cytometry, with or without polymorphonuclear (PMN)-MDSCs depletion. Arginase 1 (ARG1) expression and activity of MDSCs were examined by hematoxylin and eosin staining and flow cytometry. ARG1 inhibitor and phosphodiesterase 5 inhibitor sildenafil were administered after RT to figure out the underlying mechanism of MDSCs-mediated immunosuppression.

RESULTS

We demonstrated that irradiation recruited MDSCs, especially the polymorphonuclear subset, into the tumor microenvironment. PMN-MDSCs inhibited the CD8⁺ T cell response by elevating ARG1 expression. Selective depletion of PMN-MDSCs or inhibition on ARG1 promoted the infiltration and activation of intratumoral CD8⁺ T cells, and delayed tumor regrowth after irradiation. We showed that sildenafil reduced the accumulation and ARG1 expression of PMN-MDSCs after irradiation, thus abrogating the MDSCs-mediated immunosuppression.

CONCLUSIONS

Our results have suggested that PMN-MDSCs participate in the irradiation-induced immune suppression through ARG1 activation. We have also found that sildenafil has the potential to facilitate antitumor immunity, which provides a new alternative to delay tumor recurrence after RT.

Radiotherapy for unresectable locally advanced non-small cell lung cancer: a narrative review of the current landscape and future prospects in the era of immunotherapy

Significant recent advances have occurred in the use of radiation therapy for locally advanced non-small cell lung cancer (LA-NSCLC). In fact, the past few decades have seen both therapeutic gains and setbacks in the evolution of radiotherapy for LA-NSCLC. The PACIFIC trial has heralded a new era of immunotherapy and has raised important questions for future study, such as the future directions of radiation therapy for LA-NSCLC in the era of immunotherapy. Modern radiotherapy techniques such as three-dimensional (3D) conformal radiotherapy and intensity-modulated radiotherapy (IMRT) provide opportunities for improved target conformity and reduced normal-tissue exposure. However, the low-dose radiation volume brought by IMRT and its effects on the immune system deserve particular attention when combing radiotherapy and immunotherapy. Particle radiotherapy offers dosimetric advantages and exhibits great immunoregulatory potential. With the ongoing improvement in particle radiotherapy techniques and knowledge, the combination of immunotherapy and particle radiotherapy has tremendous potential to improve treatment outcomes. Of particular importance are questions on the optimal radiation schedule in the settings of radio-immunotherapy. Strategies for the reduction of the irradiated field such as involved-field irradiation (IFI) and omission of clinical target volume (CTV) hold promise for better preservation of immune function while not compromising locoregional and distant control. In addition, different dose-fractionation regimens can have diverse effects on the immune system. Thus, prospective trials are urgently needed to establish the optimal dose fractionation regimen. Moreover, personalized radiotherapy which allows the tailoring of radiation dose to each individual's genetic background and immune state is of critical importance in maximizing the benefit of radiation to patients with LA-NSCLC.

Reprogramming the tumour microenvironment by radiotherapy: implications for radiotherapy and immunotherapy combinations

Radiotherapy (RT) is a highly effective anti-cancer therapy delivered to around 50-60% of patients. It is part of therapy for around 40% of cancer patients who are cured of their disease. Until recently, the focus of this anti-tumour efficacy has been on the direct tumour cytotoxicity and RT-induced DNA damage. Recently, the immunomodulatory effects of RT on the tumour microenvironment have increasingly been recognized. There is now intense interest in potentially using RT to induce an anti-tumour immune response, which has led to rethinking into how the efficacy of RT could be further enhanced. Following the breakthrough of immune check point inhibitors (ICIs), a new era of immuno-oncology (IO) agents has emerged and established immunotherapy as a routine part of cancer treatment. Despite ICI improving outcomes in many cancer types, overall durable responses occur in only a minority of patients. The immunostimulatory effects of RT make combinations with ICI attractive to potentially amplify anti-tumour immunity resulting in increased tumour responses and improved outcomes. In contrast, tumours with profoundly immunosuppressive tumour microenvironments, dominated by myeloid-derived cell populations, remain a greater clinical challenge and RT may potentially further enhance the immunosuppression. To harness the full potential of RT and IO agent combinations, further insights are required to enhance our understanding of the role these immunosuppressive myeloid populations play, how RT influences these populations and how they may be therapeutically manipulated in combination with RT to improve outcomes further. These are exciting times with increasing numbers of IO targets being discovered and IO agents undergoing clinical evaluation. Multidisciplinary research collaborations will be required to establish the optimal parameters for delivering RT (target volume, dose and fractionation) in combination with IO agents, including scheduling to achieve maximal therapeutic efficacy.

Interaction between Immunotherapy and Antiangiogenic Therapy for Cancer

Although immunotherapy has led to durable responses in diverse cancers, unfortunately, there has been limited efficacy and clinical response rates due to primary or acquired resistance to immunotherapy. To maximize the potential of immunotherapy, combination therapy with antiangiogenic drugs seems to be promising. Some phase III trials showed superiority for survival with the combination of immunotherapy and antiangiogenic therapy. In this study, we describe a synergistic mechanism of immunotherapy and antiangiogenic therapy and summarize current clinical trials of these combinations.

Hypoxia dynamics on FMISO-PET in combination with PD-1/PD-L1 expression has an impact on the clinical outcome of patients with Head-and-neck Squamous Cell Carcinoma undergoing Chemoradiation

Tumor-associated hypoxia influences the radiation response of head-and-neck cancer (HNSCC) patients, and a lack of early hypoxia resolution during treatment considerably deteriorates outcomes. As the detrimental effects of hypoxia are partly related to the induction of an immunosuppressive microenvironment, we investigated the interaction between tumor hypoxia dynamics and the PD-1/PD-L1 axis in HNSCC patients undergoing chemoradiation and its relevance for patient outcomes in a prospective trial.

Methods: 49 patients treated with definitive chemoradiation for locally advanced HNSCC were enrolled in this trial and received longitudinal hypoxia PET imaging using fluorine-18 misonidazole ([¹⁸F]FMISO) at weeks 0, 2 and 5 during treatment. Pre-therapeutic tumor biopsies were immunohistochemically analyzed regarding the PD-1/PD-L1 expression both on immune cells and on tumor cells, and potential correlations between the PD-1/PD-L1 axis and tumor hypoxia dynamics during chemoradiation were assessed using Spearman's rank correlations. Hypoxia dynamics during treatment were quantified by subtracting the standardized uptake value (SUV) index at baseline from the SUV values at weeks 2 or 5, whereby SUV index was defined as ratio of maximum tumor [¹⁸F]FMISO SUV to mean SUV in the contralateral sternocleidomastoid muscle (i.e. tumor-to-muscle ratio). The impact of the PD-1/PD-L1 expression alone and in combination with persistent tumor hypoxia on locoregional control (LRC), progression-free survival (PFS) and overall survival (OS) was examined using log-rank tests and Cox proportional hazards models.

Results: Neither PD-L1 nor PD-1 expression levels on tumor-infiltrating immune cells influenced LRC (HR = 0.734; p = 0.480 for PD-L1, HR = 0.991; p = 0.989 for PD-1), PFS (HR = 0.813; p = 0.597 for PD-L1, HR = 0.796; p = 0.713 for PD-1) or OS (HR = 0.698; p = 0.405 for PD-L1, HR = 0.315; p = 0.265 for PD-1). However, patients with no hypoxia resolution between weeks 0 and 2 and PD-L1 expression on tumor cells, quantified by a tumor proportional score (TPS) of at least 1%, showed significantly worse LRC (HR = 3.374, p = 0.022) and a trend towards reduced PFS (HR = 2.752, p = 0.052). In the multivariate Cox regression analysis, the combination of absent tumor hypoxia resolution and high tumoral PD-L1 expression remained a significant prognosticator for impaired LRC (HR = 3.374, p = 0.022). On the other side, tumoral PD-L1 expression did not compromise the outcomes of patients whose tumor-associated hypoxia declined between week 0 and 2 during chemoradiation (LRC: HR = 1.186, p = 0.772, PFS: HR = 0.846, p = 0.766).

Conclusion: In this exploratory analysis, we showed for the first time that patients with both persistent tumor-associated hypoxia during treatment and PD-L1 expression on tumor cells exhibited a worse outcome, while the tumor cells' PD-L1 expression did not influence the outcomes of patients with early tumor hypoxia resolution. While the results have to be validated in an independent cohort, these findings form a foundation to investigate the combination of hypoxic modification and immune checkpoint inhibitors for the unfavorable subgroup, moving forward towards personalized radiation oncology treatment.

Multiple Mechanisms Involving in Radioresistance of Nasopharyngeal Carcinoma

Nasopharyngeal carcinoma (NPC) is the malignant tumor with ethnic and geographical distribution preference. Although intensity-modulated radiotherapy (IMRT)-based radiotherapy combined with chemotherapy and targeted therapy has dramatically improved the overall survival of NPC patients, there are still some patients suffering from recurrent tumors and the prognosis is poor. Multiple mechanisms may be responsible for radioresistance of NPC, such as cancer stem cells (CSCs) existence, gene mutation or aberrant expression of genes, epigenetic modification of genes, abnormal activation of certain signaling pathways, alteration of tumor microenvironment, stress granules (SGs) formation, etc. We conduct a comprehensive review of the published literatures focusing on the causes of radioresistance, retrospect the regulation mechanisms following radiation, and discuss future directions of overcoming the resistance to radiation.

hERG K+ Channels Promote Survival of Irradiated Leukemia Cells

Many tumor cells express highly elevated activities of voltage-gated K⁺ channels in the plasma membrane which are indispensable for tumor growth. To test for K⁺ channel function during DNA damage response, we subjected human chronic myeloid leukemia (CML) cells to sub-lethal doses of ionizing radiation (0-8 Gy, 6 MV photons) and determined K⁺ channel activity, K⁺ channel-dependent Ca²⁺ signaling, cell cycle progression, DNA repair, and clonogenic survival by whole-cell patch clamp recording, fura-2 Ca²⁺ imaging, Western blotting, flow cytometry, immunofluorescence microscopy, and pre-plating colony formation assay, respectively. As a result, the human erythroid CML cell line K562 and primary human CML cells functionally expressed hERG1. Irradiation stimulated in both cell types an increase in the activity of hERG1 K⁺ channels which became apparent 1-2 h post-irradiation. This increase in K⁺ channel activity was paralleled by an accumulation in S phase of cell cycle followed by a G₂/M cell cycle arrest as analyzed between 8 and 72 h post-irradiation. Attenuating the K⁺ channel function by applying the hERG1 channel inhibitor E4031 modulated Ca²⁺ signaling, impaired inhibition of the mitosis promoting subunit cdc2, overrode cell cycle arrest, and decreased clonogenic survival of the irradiated cells but did not affect repair of DNA double strand breaks suggesting a critical role of the hERG1 K⁺ channels for the Ca²⁺ signaling and the cell cycle control during DNA damage response.

A2AR Antagonism with DZD2269 Augments Antitumor Efficacy of Irradiation in Murine Model

Accumulated extracellular adenosine suppresses antitumor immunity via adenosine 2A receptor (A_2AR). Blockade of A_2AR with DZD2269 can inhibit phosphorylation of cAMP response element-binding protein mediated by adenosine analogue in vitro and in vivo. Irradiation can cause the release of adenosine and lead to a rapid increase in free extracellular adenosine in the tumour area. DZD2269, a novel A_2AR Antagonism, induces incomplete antitumor responses in multiple syngeneic mouse tumour models. Combining DZD2269 with IR can induce a synergistic anticancer effect. IR increases the infiltration of various subtypes of T cells, including CD4+, CD8+ and Foxp3+ T cells, into the tumour area. Combining IR and DZD2269 improves the tumour immune microenvironment, leading to suppressed infiltration of regulatory T (Treg) cells and enhanced IFN-γ expression by tumour-infiltrating lymphocytes. The results support the use of A_2AR antagonism with DZD2269 as a therapeutic strategy for monotherapy or combination therapy with IR.

Combined cytotoxic chemotherapy and immunotherapy of cancer: modern times

Monoclonal antibodies targeting programmed cell death 1/programmed cell death ligand 1 (PD-1/PD-L1) immune checkpoints have improved the treatments of cancers. However, not all patients equally benefit from immunotherapy. The use of cytotoxic drugs is practically inevitable to treat advanced cancers and metastases. The repertoire of cytotoxics includes 80 products that principally target nucleic acids or the microtubule network in rapidly proliferating tumor cells. Paradoxically, many of these compounds tend to become essential to promote the activity of immunotherapy and to offer a sustained therapeutic effect. We have analyzed each cytotoxic drug with respect to effect on expression and function of PD-(L)1. The major cytotoxic drugs—carboplatin, cisplatin, cytarabine, dacarbazine, docetaxel, doxorubicin, ecteinascidin, etoposide, fluorouracil, gemcitabine, irinotecan, oxaliplatin, paclitaxel and pemetrexed—all have the capacity to upregulate PD-L1 expression on cancer cells (via the generation of danger signals) and to promote antitumor immunogenicity, via activation of cytotoxic T lymphocytes, maturation of antigen-presenting cells, depletion of immunosuppressive regulatory T cells and/or expansion of myeloid-derived suppressor cells. The use of ‘immunocompatible’ cytotoxic drugs combined with anti-PD-(L)1 antibodies is a modern approach, not only for increasing the direct killing of cancer cells, but also as a strategy to minimize the activation of immunosuppressive and cancer cell prosurvival program responses.

Integrating tumor hypoxic stress in novel and more adaptable strategies for cancer immunotherapy

Immunotherapy is poised to become an increasingly utilized therapy in the treatment of cancer. However, several abnormalities in the tumor microenvironment (TME) that can thwart the efficacy of immunotherapies have been established. Microenvironmental hypoxia is a determining factor in shaping aggressiveness, metastatic potential and treatment resistance of solid tumors. The characterization of this phenomenon could prove beneficial for determining a patient's treatment path and for the introduction of novel targetable factors that can enhance therapeutic outcome. Indeed, the ablation of hypoxia has the potential to sensitize tumors to immunotherapy by metabolically remodeling their microenvironment. In this review, we discuss the intrinsic contributions of hypoxia to cellular plasticity, heterogeneity, stemness and genetic instability in the context of immune escape. In addition, we will shed light on how managing hypoxia can ameliorate response to immunotherapy and how integrating hypoxia gene signatures could play a role in this pursuit.

Hypoxia in solid tumors: a key promoter of cancer stem cell (CSC) resistance

PURPOSE

Cancer stem cells (CSCs) are highly tumorigenic cell types that reside within specific areas of tumor microenvironment (TME), and are endowed with self-renewal and resistance properties. Here, we aimed to discuss mechanisms involved in hypoxia-derived CSC resistance and targeting for effective cancer therapy.

RESULTS

Preferential localization within hypoxic niches would help CSCs develop adaptive mechanisms, mediated through the modification of responses to various stressors and, as a result, show a more aggressive behavior.

CONCLUSION

Hypoxia, in fact, serves as a multi-tasking strategy to nurture CSCs with this adaptive capacity, complexing targeted therapies.

Cancer stem cell (CSC) resistance drivers

Cancer stem cells (CSCs) are a population of self-renewal cells with high tumorigenic potency. CSCs can adopt easily with changes in the nearby milieu, and are more resistant to conventional therapies than other cells within a tumor. CSC resistance can be induced secondary to radio- and chemotherapy, or even after chemotherapy secession. A combination of both intrinsic and extrinsic factors is contributed to CSC-mediated therapy resistance. CSCs represent protective autophagy and efficient cell cycling, along with highly qualified epithelial-mesenchymal transition (EMT) regulators, reactive oxygen species (ROS) scavengers, drug transporters, and anti-apoptotic and DNA repairing systems. In addition, CSCs develop cross-talking and share some characteristics with other cells within the tumor microenvironment (TME) being more intense in higher stage tumors, and thereby sophisticating tumor-targeted therapies. TME, in fact, is a nest for aggravating resistance mechanisms in CSCs. TME is exposed constantly to the nutritional, metabolic and oxygen deprivation; these conditions promote CSC adaptation. This review is aimed to discuss main (intrinsic and extrinsic) mechanisms of CSC resistance and suggest some strategies to revoke this important promoter of therapy failure.