"Reinforcement" by Tumor Microenvironment: The Seventh "R" of Radiobiology

Extracellular vesicles as the common denominator among the 7 Rs of radiobiology: From the cellular level to clinical practice

Extracellular vesicles (EVs) are lipid-bound particles released by tumor cells and widely explored in cancer development, progression, and treatment response, being considered as valuable components to be explored as biomarkers or cellular targets to modulate the effect of therapies. The mechanisms underlying the production and profile of EVs during radiotherapy (RT) require addressing radiobiological aspects to determine cellular responses to specific radiation doses and fractionation. In this review, we explore the role of EVs in the 7 Rs of radiobiology, known as the molecular basis of a biological tissue response to radiation, supporting EVs as a shared player in all the seven processes. We also highlight the relevance of EVs in the context of liquid biopsy and resistance to immunotherapy, aiming to establish the connection and utility of EVs as tools in contemporary and precision radiotherapy.

Clonal hematopoiesis, cardiovascular disease and cancer treatment-induced cardiotoxicity

Clonal hematopoiesis (CH) arises when a substantial proportion of mature blood cells is derived from a single hematopoietic stem cell lineage. It is considered to be a premalignant state that predisposes individuals to an increased risk of cancers. Recently, emerging evidence has demonstrated a strong association between CH and both the incidence and mortality of cardiovascular diseases (CVD), with the relative risks being comparable to those attributed to traditional cardiovascular risk factors. In addition, CH has been suggested to play a role in CVD and anti-cancer treatment-related cardiotoxicity amongst cancer survivors. Moreover, certain forms of chemotherapy and radiation therapy have been shown to promote the clonal expansion of specific CH-related mutations. Consequently, CH may play a substantial role in the realm of cardio-oncology. In this review, we discuss the association between CH with cancer and CVD, with a special focus on anti-cancer treatment-related cardiotoxicity, discuss possible future research avenues and propose a systematic approach for clinical practice.

Radiobiology and modelling in Brachytherapy: A review inspired by the ESTRO Brachytherapy pre-meeting course

Brachytherapy (BT) plays a key role in cancer treatment by delivering a high dose to a small volume over a short time. The use of BT is currently validated in a wide range of cancers such as cervical, prostate and breast cancers while being a favourable choice for organ preservation, such as in penile or rectal cancer, or in the setting of reirradiation. Consideration of the radiobiology of BT is integral to the choices made around dose and fractionation and combination with other techniques such as external beam radiotherapy (EBRT). Much of the radiobiology of brachytherapy is based on historic data, but fortunately there is a drive to integrate translational research including radiobiologic parameters into modern BT research. In a changing therapeutic landscape moving to a high dose rate (HDR) based on high dose per fraction, it is important to ensure that the incorporation of new radiobiology knowledge helps to drive clinical practice. This manuscript takes the ESTRO Brachytherapy pre-meeting course (May 3, 2024 - Glasgow ESTRO meeting) as a base and develops the concepts to present an overview of radiobiology in brachytherapy. Presented are 3 different considerations: the fundamentals of BT radiobiology (BT radiobiology history, biology and BT, α/β and re-irradiation), the pre-clinical radiobiology approach (pulsed dose radiotherapy (PDR) vs HDR, BT vs best EBRT techniques, high dose regions and integrated boost) and clinical radiobiology approaches (optimal number of BT fractions, radiobiology in BR for cervical, prostate, breast, skin/H&N and gastro-intestinal cancers). Presented is an analysis of radiobiology and modelling in BT aiding the integration of scientific pre-clinical and clinical data to allow a better understanding of the use of radioactive sources for cancer treatment.

Is Chronic Ice Water Ingestion a Risk Factor for Gastric Cancer Development? An Evidence-Based Hypothesis Focusing on East Asian Populations

This article introduces a novel risk factor for gastric cancer (GC) by analyzing available epidemiological data from East Asian populations. A significantly higher age-standardized GC rate was observed in Japanese and Korean populations than in Chinese populations, despite nearly identical ethnicity, food habits, obesity rates, and alcohol consumption. Given the pivotal role of environmental factors in GC development, particularly for the intestinal type, a thorough evaluation of the lifestyles of these three populations was conducted to identify commonalities and disparities. It was observed that Japanese and Korean individuals prefer consuming ice water, while Chinese individuals tend to drink warm water, potentially influenced by traditional Chinese medicine disciplines. Considering the key features of GC development, a literature review was conducted to investigate the mechanisms through which the consumption of ice water might contribute to GC initiation and progression. Mechanistically, exposing gastric cells to hypothermia can increase the risk of carcinogenesis through multiple pathways. This includes the promotion of Helicobacter pylori colonization, prolonged gastric inflammation, and mitochondrial dysfunction in gastric cells. Furthermore, drinking ice water can enhance the survival, proliferation, and invasion of GC cells by releasing cold shock proteins, increasing gastric acid secretion, and delaying gastric emptying. Additionally, hypothermia can boost the immune evasion of cancer cells by weakening the antitumor immune system and activating different components of the tumor microenvironment. This paper also explores the association between exposure of GC cells to hypothermia and current insights into cancer hallmarks. These findings may partially elucidate the higher incidence of GC in Japanese and Korean populations and provide a clue for future experimental studies.Graphical abstract available for this article.

Intra-Parotid Recurrent Nasopharyngeal Carcinoma Following Intensity-Modulated Radiation Therapy: A Case Report

Introduction

Intra-parotid metastasis refers to the spread of cancerous cells from a primary tumor to the lymph nodes within the parotid gland. To our best knowledge, we report the first described case in the literature of a patient who received IMRT for nasopharyngeal carcinoma (UCNT) without sparing the parotid gland and still experienced a recurrence.

Case presentation

A 57-year-old male patient of north African origin presented with a left parotid mass that had been evolving for 6 months. He was previously diagnosed with and treated for nasopharyngeal carcinoma 2 years prior to admission, with Intensity-Modulated Radiotherapy (IMRT) without sparing the parotid gland, as well as chemotherapy. Medical imaging was suggestive of recurrence of nasopharyngeal carcinoma and metastasis due to the patient's medical history. The patient benefited from a total parotidectomy; The histopathological analysis of the surgical specimen confirmed the presence of a poorly differentiated carcinoma (UCNT) with nodal metastasis.

Conclusion

Intensity-Modulated Radiation Therapy (IMRT) holds great promise as an alternative treatment option. However, it should be reserved for specific cases with minimal lymph node involvement, and always preceded by a thorough clinical and radiological examination.

Best practices and novel approaches for the preclinical development of drug-radiotherapy combinations for cancer treatment

Drug-radiation combination therapy is a practical approach to improving clinical outcomes for many tumours. Unfortunately, most clinical combination studies combine drugs with radiotherapy empirically and do not exploit mechanistic synergy in cell death and the interconnectivity of molecular pathways of tumours or rationale for selecting the dose, fractionation, and schedule, which can result in suboptimal efficacy and exacerbation of toxic effects. However, opportunities exist to generate compelling preclinical evidence for combination therapies from fit-for-purpose translational studies for simulating the intended clinical study use scenarios with standardised preclinical assays and algorithms to evaluate complex molecular interactions and analysis of synergy before clinical research. Here, we analyse and discuss the core issues in the translation of preclinical data to enhance the relevance of preclinical assays, in vitro clonogenic survival along with apoptosis, in vivo tumour regression and growth delay assays, and toxicology of organs at risk without creating barriers to innovation and provide a synopsis of emerging areas in preclinical radiobiology.

The mitochondrial stress signaling tunes immunity from a view of systemic tumor microenvironment and ecosystem

Mitochondria play important roles in cell fate, calcium signaling, mitophagy, and the signaling through reactive oxygen species (ROS). Recently, mitochondria are considered as a signaling organelle in the cell and communicate with other organelles to constitute the mitochondrial information processing system (MIPS) that transduce input-to-output biological information. The success in immunotherapy, a concept of systemic therapy, has been proved to be dependent on paracrine interactions within the tumor microenvironment (TME) and distant organs including microbiota and immune components. We will adopt a broader view from the concept of TME to tumor micro- and macroenvironment (TM 2 E) or tumor-organ ecosystem (TOE). In this review, we will discuss the role of mitochondrial signaling by mitochondrial ROS, calcium flux, metabolites, mtDNA, vesicle transportation, and mitochondria-derived peptide in the TME and TOE, in particular immune regulation and effective cancer immunotherapy.

The Effects of Gynecological Tumor Irradiation on the Immune System

Radiobiology has evolved from a mechanistic model based on DNA damage and response factors into a more complex model that includes effects on the immune system and the tumor microenvironment (TME). Irradiation has an immunomodulatory effect that can manifest as increased anti-tumor immunity or immunosuppression. Irradiation promotes an inflammatory microenvironment through the release of pro-inflammatory cytokines and endothelial damage, which recruit immune system cells to the irradiated area. Radiation-induced immunogenic cell death (ICD), characterized by the release of damage-associated molecular patterns (DAMPs) and tumor antigens, triggers an anti-tumor immune response of both innate and adaptive immunity. Anti-tumor immunity can manifest at a distance from the irradiated area, a phenomenon known as the abscopal effect (AE), which involves dendritic cells and CD8+ T cells. Irradiation also produces an immunosuppressive effect mediated by tumor-associated macrophages (TAMs) and regulatory T lymphocytes (Tregs), which counterbalances the immunostimulatory effect. In this work, we review the mechanisms involved in the radiation-induced immune response, which support the combined treatment of RT and immunotherapy, focusing, where possible, on gynecologic cancer.

Advances in personalized radiotherapy

Radiotherapy is a mainstay of cancer treatment. The clinical response to radiotherapy is heterogeneous, from a complete response to early progression. Recent studies have explored the importance of patient characteristics in response to radiotherapy. In this editorial, we invite contributions for a BMC Cancer collection of articles titled 'Advances in personalized radiotherapy' towards the improvement of treatment response.

Salvage Ablative Radiotherapy for Isolated Local Recurrence of Pancreatic Adenocarcinoma following Definitive Surgery

Introduction: The rate of isolated locoregional recurrence after surgery for pancreatic adenocarcinoma (PDAC) approaches 25%. Ablative radiation therapy (A-RT) has improved outcomes for locally advanced disease in the primary setting. We sought to evaluate the outcomes of salvage A-RT for isolated locoregional recurrence and examine the relationship between subsequent patterns of failure, radiation dose, and treatment volume. Methods: We conducted a retrospective analysis of all consecutive participants who underwent A-RT for an isolated locoregional recurrence of PDAC after prior surgery at our institution between 2016 and 2021. Treatment consisted of ablative dose (BED10 98-100 Gy) to the gross disease with an additional prophylactic low dose (BED10 < 50 Gy), with the elective volume covering a 1.5 cm isotropic expansion around the gross disease and the circumference of the involved vessels. Local and locoregional failure (LF and LRF, respectively) estimated by the cumulative incidence function with competing risks, distant metastasis-free and overall survival (DMFS and OS, respectively) estimated by the Kaplan-Meier method, and toxicities scored by CTCAE v5.0 are reported. Location of recurrence was mapped to the dose region on the initial radiation plan. Results: Among 65 participants (of whom two had two A-RT courses), the median age was 67 (range 37-87) years, 36 (55%) were male, and 53 (82%) had undergone pancreaticoduodenectomy with a median disease-free interval to locoregional recurrence of 16 (range, 6-71) months. Twenty-seven participants (42%) received chemotherapy prior to A-RT. With a median follow-up of 35 months (95%CI, 26-56 months) from diagnosis of recurrence, 24-month OS and DMFS were 57% (95%CI, 46-72%) and 22% (95%CI, 14-37%), respectively, while 24-month cumulative incidence of in-field LF and total LRF were 28% (95%CI, 17-40%) and 36% (95%CI 24-48%), respectively. First failure after A-RT was distant in 35 patients (53.8%), locoregional in 12 patients (18.5%), and synchronous distant and locoregional in 10 patients (15.4%). Most locoregional failures occurred in elective low-dose volumes. Acute and chronic grade 3-4 toxicities were noted in 1 (1.5%) and 5 patients (7.5%), respectively. Conclusions: Salvage A-RT achieves favorable OS and local control outcomes in participants with an isolated locoregional recurrence of PDAC after surgical resection. Consideration should be given to extending high-dose fields to include adjacent segments of at-risk vessels beyond direct contact with the gross disease.

Assessment of the Electrolyte Heterogeneity of Tissues in Mandibular Bone-Infiltrating Head and Neck Cancer Using Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) was recently introduced as a rapid bone analysis technique in bone-infiltrating head and neck cancers. Research efforts on laser surgery systems with controlled tissue feedback are currently limited to animal specimens and the use of nontumorous tissues. Accordingly, this study aimed to characterize the electrolyte composition of tissues in human mandibular bone-infiltrating head and neck cancer. Mandible cross-sections from 12 patients with bone-invasive head and neck cancers were natively investigated with LIBS. Representative LIBS spectra (n = 3049) of the inferior alveolar nerve, fibrosis, tumor stroma, and cell-rich tumor areas were acquired and histologically validated. Tissue-specific differences in the LIBS spectra were determined by receiver operating characteristics analysis and visualized by principal component analysis. The electrolyte emission values of calcium (Ca) and potassium (K) significantly (p < 0.0001) differed in fibrosis, nerve tissue, tumor stroma, and cell-rich tumor areas. Based on the intracellular detection of Ca and K, LIBS ensures the discrimination between the inferior alveolar nerve and cell-rich tumor tissue with a sensitivity of ≥95.2% and a specificity of ≥87.2%. The heterogeneity of electrolyte emission values within tumorous and nontumorous tissue areas enables LIBS-based tissue recognition in mandibular bone-infiltrating head and neck cancer.

Tumour response to hypoxia: understanding the hypoxic tumour microenvironment to improve treatment outcome in solid tumours

Hypoxia is a common feature of solid tumours affecting their biology and response to therapy. One of the main transcription factors activated by hypoxia is hypoxia-inducible factor (HIF), which regulates the expression of genes involved in various aspects of tumourigenesis including proliferative capacity, angiogenesis, immune evasion, metabolic reprogramming, extracellular matrix (ECM) remodelling, and cell migration. This can negatively impact patient outcomes by inducing therapeutic resistance. The importance of hypoxia is clearly demonstrated by continued research into finding clinically relevant hypoxia biomarkers, and hypoxia-targeting therapies. One of the problems is the lack of clinically applicable methods of hypoxia detection, and lack of standardisation. Additionally, a lot of the methods of detecting hypoxia do not take into consideration the complexity of the hypoxic tumour microenvironment (TME). Therefore, this needs further elucidation as approximately 50% of solid tumours are hypoxic. The ECM is important component of the hypoxic TME, and is developed by both cancer associated fibroblasts (CAFs) and tumour cells. However, it is important to distinguish the different roles to develop both biomarkers and novel compounds. Fibronectin (FN), collagen (COL) and hyaluronic acid (HA) are important components of the ECM that create ECM fibres. These fibres are crosslinked by specific enzymes including lysyl oxidase (LOX) which regulates the stiffness of tumours and induces fibrosis. This is partially regulated by HIFs. The review highlights the importance of understanding the role of matrix stiffness in different solid tumours as current data shows contradictory results on the impact on therapeutic resistance. The review also indicates that further research is needed into identifying different CAF subtypes and their exact roles; with some showing pro-tumorigenic capacity and others having anti-tumorigenic roles. This has made it difficult to fully elucidate the role of CAFs within the TME. However, it is clear that this is an important area of research that requires unravelling as current strategies to target CAFs have resulted in worsened prognosis. The role of immune cells within the tumour microenvironment is also discussed as hypoxia has been associated with modulating immune cells to create an anti-tumorigenic environment. Which has led to the development of immunotherapies including PD-L1. These hypoxia-induced changes can confer resistance to conventional therapies, such as chemotherapy, radiotherapy, and immunotherapy. This review summarizes the current knowledge on the impact of hypoxia on the TME and its implications for therapy resistance. It also discusses the potential of hypoxia biomarkers as prognostic and predictive indictors of treatment response, as well as the challenges and opportunities of targeting hypoxia in clinical trials.