The tumor microenvironment and radiotherapy response; a central role for cancer-associated fibroblasts

Understanding the molecular mechanism responsible for developing therapeutic radiation-induced radioresistance of rectal cancer and improving the clinical outcomes of radiotherapy - A review

Rectal cancer accounts for the second highest cancer-related mortality, which is predominant in Western civilizations. The treatment for rectal cancers includes surgery, radiotherapy, chemotherapy, and immunotherapy. Radiotherapy, specifically external beam radiation therapy, is the most common way to treat rectal cancer because radiation not only limits cancer progression but also significantly reduces the risk of local recurrence. However, therapeutic radiation-induced radioresistance to rectal cancer cells and toxicity to normal tissues are major drawbacks. Therefore, understanding the mechanistic basis of developing radioresistance during and after radiation therapy would provide crucial insight to improve clinical outcomes of radiation therapy for rectal cancer patients. Studies by various groups have shown that radiotherapy-mediated changes in the tumor microenvironment play a crucial role in developing radioresistance. Therapeutic radiation-induced hypoxia and functional alterations in the stromal cells, specifically tumor-associated macrophage (TAM) and cancer-associated fibroblasts (CAF), play a crucial role in developing radioresistance. In addition, signaling pathways, such as - the PI3K/AKT pathway, Wnt/β-catenin signaling, and the hippo pathway, modulate the radiation responsiveness of cancer cells. Different radiosensitizers, such as small molecules, microRNA, nanomaterials, and natural and chemical sensitizers, are being used to increase the effectiveness of radiotherapy. This review highlights the mechanism responsible for developing radioresistance of rectal cancer following radiotherapy and potential strategies to enhance the effectiveness of radiotherapy for better management of rectal cancer.

MHC-I and PD-L1 Expression is Associated with Decreased Tumor Outgrowth and is Radiotherapy-inducible in the Murine Head and Neck Squamous Cell Carcinoma Model MOC1

INTRODUCTION

Combined radiotherapy and immune checkpoint inhibition is a potential treatment option for head and neck squamous cell carcinoma (HNSCC). Immunocompetent mouse models can help to successfully develop radio- immunotherapy combinations and to increase our understanding of the effects of radiotherapy on the tumor microenvironment for future clinical translation. Therefore, the aim of this study was to develop a homogeneous, reproducible HNSCC model originating from the Mouse Oral Cancer 1 (MOC1) HNSCC cell line, and to explore the radiotherapy-induced changes in its tumor microenvironment, using flow cytometry and PD-L1 microSPECT/CT imaging.

MATERIALS AND METHODS

In vivo growing tumors originating from the parental MOC1 line were used to generate single cell derived clones. These clones were screened in vitro for their ability to induce programmed cell death ligand 1 (PD-L1) and major histocompatibility complex class I (MHC-I) following IFNγ exposure. Clones with different IFNγ sensitivity were inoculated in C57BL/6 mice and assessed for tumor outgrowth. The composition of the tumor microenvironment of a stably growing (non)irradiated MOC1-derived clone was assessed by immunohistochemistry, flow cytometry and PD-L1 microSPECT/CT.

RESULTS

Low in vitro inducibility of MHC-I and PD-L1 by IFNγ was associated with increased tumor outgrowth of MOC1 clones in vivo. Flow cytometry analysis of cells derived from a stable in vivo growing MOC1 clone MOC1.3D5low showed expression of MHC-I and PD-L1 on several cell populations within the tumor. Upon irradiation, MHC-I and PD-L1 increased on leukocytes (CD45.2+) and cancer associated fibroblasts (CD45.2-/EpCAM-/CD90.1+). Furthermore, PD-L1 microSPECT/CT showed increased tumor uptake of radiolabeled PD-L1 antibodies with a heterogeneous spatial distribution of the radio signal, which co-localized with PD-L1+ and CD45.2+ areas.

DISCUSSION

PD-L1 and MHC-I inducibility by IFNγ in vitro is associated with tumor outgrowth of MOC1 clones in vivo. In tumors originating from a stably growing MOC1-derived clone, expression of these immune-related markers was induced by irradiation shown by flow cytometry on several cell populations within the tumor microenvironment such as immune cells and cancer associated fibroblasts. PD-L1 microSPECT/CT showed increased tumor uptake following radiotherapy, and autoradiography showed correlation of uptake with areas that are heavily infiltrated by immune cells. Knowledge of radiotherapy-induced effects on the tumor microenvironment in this model can help optimize timing and dosage for radio- immunotherapy combination strategies in future research.

Abscopal effect: from a rare phenomenon to a new frontier in cancer therapy

Radiotherapy (RT) controls local lesions, meantime it has the capability to induce systemic response to inhibit distant, metastatic, non-radiated tumors, which is referred to as the "abscopal effect". It is widely recognized that radiotherapy can stimulate systemic immune response. This provides a compelling theoretical basis for the combination of immune therapy combined with radiotherapy(iRT). Indeed, this phenomenon has also been observed in clinical treatment, bringing significant clinical benefits to patients, and a series of basic studies are underway to amplify this effect. However, the molecular mechanisms of immune response induced by RT, determination of the optimal treatment regimen for iRT, and how to amplify the abscopal effect. In order to amplify and utilize this effect in clinical management, these key issues require to be well addressed; In this review, we comprehensively summarize the growing consensus and emphasize the emerging limitations of enhancing the abscopal effect with radiotherapy or immunotherapy. Finally, we discuss the prospects and barriers to the current clinical translational applications.

miRNAs in radiotherapy resistance of cancer; a comprehensive review

While intensity-modulated radiation therapy-based comprehensive therapy increases outcomes, cancer patients still have a low five-year survival rate and a high recurrence rate. The primary factor contributing to cancer patients' poor prognoses is radiation resistance. A class of endogenous non-coding RNAs, known as microRNAs (miRNAs), controls various biological processes in eukaryotes. These miRNAs influence tumor cell growth, death, migration, invasion, and metastasis, which controls how human carcinoma develops and spreads. The correlation between the unbalanced expression of miRNAs and the prognosis and sensitivity to radiation therapy is well-established. MiRNAs have a significant impact on the regulation of DNA repair, the epithelial-to-mesenchymal transition (EMT), and stemness in the tumor radiation response. But because radio resistance is a complicated phenomena, further research is required to fully comprehend these mechanisms. Radiation response rates vary depending on the modality used, which includes the method of delivery, radiation dosage, tumor stage and grade, confounding medical co-morbidities, and intrinsic tumor microenvironment. Here, we summarize the possible mechanisms through which miRNAs contribute to human tumors' resistance to radiation.

The preclinical gap in pancreatic cancer and radiotherapy

Pancreatic ductal adenocarcinoma is an aggressive malignancy with limited treatment options. Chemotherapy offers little benefit and, although there is some evidence that radiotherapy may improve response, its use in the clinical management of pancreatic cancer remains controversial due to conflicting reports on its survival benefit. There has also been a lack of clinical trials that directly investigate the efficacy of radiotherapy in pancreatic cancer. The limited progress in the development of radiotherapeutic strategies in pancreatic cancer can be attributed, at least in part, to a dearth of preclinical research and our limited understanding of the effects of radiation on the pancreatic tumour microenvironment. In this Perspective, we discuss how insight into the immunosuppressive tumour microenvironment and the complex signalling between tumour and stromal cells following radiation is needed to develop effective radiosensitising strategies for pancreatic cancer. We also highlight that to have the best chance for successful clinical translation, more preclinical research is required in appropriately complex models.

Targeted irradiation in an autochthonous mouse model of pancreatic cancer

The value of radiotherapy in the treatment of pancreatic cancer has been the subject of much debate but limited preclinical research. We hypothesise that the poor translation of radiation research into clinical trials of radiotherapy in pancreatic cancer is due, in part, to inadequate preclinical study models. Here, we developed and refined methods for targeted irradiation in autochthonous mouse models of pancreatic cancer, using a small animal radiotherapy research platform. We tested and optimised strategies for administration of contrast agents, iohexol and the liver imaging agent Fenestra LC, to enable the use of computed tomography imaging in tumour localisation. We demonstrate accurate tumour targeting, negligible off-target effects and therapeutic efficacy, depending on dose, number of fractions and tumour size, and provide a proof of concept that precise radiation can be delivered effectively to mouse pancreatic tumours with a clinically relevant microenvironment. This advance will allow investigation of the radiation response in murine pancreatic cancer, discovery of mechanisms and biomarkers of radiosensitivity or resistance, and development of radiosensitising strategies to inform clinical trials for precision radiotherapy in this disease.

Individualized High Dose Intravenous Anakinra Treatment in Cancer Patients with COVID-19 Associated Cytokine Storm: A Retrospective Controlled Study

Objective

Patients with COVID-19 accompanying cancer have been reported to have higher morbidity and mortality. In this study, we aimed to evaluate the high-dose high intravenous anakinra treatment response and outcome in patients with COVID-19-associated cytokine storm accompanying cancer.

Materials and Methods

This retrospective observational study was carried out at a tertiary referral center between September 01, 2021, and February 01, 2022, in Turkey. The study population consisted of two groups: patients receiving high-dose intravenous anakinra and patients treated with standard care.

Results

Data from 146 patients in the anakinra group and 114 patients in the control group were analyzed. Malignancy frequency was 11% (n=16) in the anakinra group and 7% (n=8) in the control group. In survival analysis, a significantly lower survival rate was observed in patients with malignancy than those without in the control group (log-rank: p=0.002) and patients with malignancy in the control group compared to the anakinra group (log-rank: p=0.013). However, it did not differ between patients with and without malignancy in the anakinra group (log-rank: p=0.9).

Conclusion

In the control group, mortality was higher in patients with malignancy compared to those without malignancy, but not in the anakinra group. Also, mortality was higher in patients receiving SoC compared to anakinra. Intravenous high-dose anakinra treatment is safe and effective in patients with COVID-19 accompanying cancer.

Optimising of axillary therapy in breast cancer: lessons from the past to plan for a better future

In this narrative review, we aim to explore the ability of radiation therapy to eradicate breast cancer regional node metastasis. It is a journey through data of older trials without systemic therapy showing the magnitude of axillary therapy (surgery versus radiation) on cancer control. Considering that both systemic and loco-regional therapies were shown to reduce any recurrence with a complex interaction, our review includes surgical, radiation, and radiobiology consideration for breast cancer, and provide our view of future practise. The aim is to provide information optimise radiation therapy in the era of primary systemic therapy.

Oral Cavity Squamous Cell Carcinoma: Review of Pathology, Diagnosis, and Management

Squamous cell carcinoma of the oral cavity presents a significant global health burden, primarily due to risk factors such as tobacco smoking, smokeless tobacco use, heavy alcohol consumption, and betel quid chewing. Common clinical manifestations of oral cavity cancer include visible lesions and sores, often accompanied by pain in advanced stages. Diagnosis relies on a comprehensive assessment involving detailed history, physical examination, and biopsy. Ancillary imaging studies and functional evaluations aid in accurate staging and facilitate treatment planning. Prognostic information is obtained from histopathological factors, such as tumor grade, depth of invasion, lymphovascular invasion, and perineural invasion. Notably, lymph node metastasis, found in approximately half of the patients, carries significant prognostic implications. Effective management necessitates a multidisciplinary approach to optimize patient outcomes. Surgical resection is the backbone of treatment, aimed at complete tumor removal while preserving functional outcomes. Adjuvant therapies, including radiation and chemotherapy, are tailored according to pathological factors. Further work in risk stratification and treatment is necessary to optimize outcomes in squamous cell carcinoma of the oral cavity.

Shooting the messenger: a systematic review investigating extracellular vesicle isolation and characterisation methods and their influence on understanding extracellular vesicles-radiotherapy interactions in glioblastoma

BACKGROUND

Extracellular vesicles (EVs) hold promise for improving our understanding of radiotherapy response in glioblastoma due to their role in intercellular communication within the tumour microenvironment (TME). However, methodologies to study EVs are evolving with significant variation within the EV research community.

METHODS

We conducted a systematic review to critically appraise EV isolation and characterisation methodologies and how this influences our understanding of the findings from studies investigating radiotherapy and EV interactions in glioblastoma. 246 articles published up to 24/07/2023 from PubMed and Web of Science were identified using search parameters related to radiotherapy, EVs, and glioblastoma. Two reviewers evaluated study eligibility and abstracted data.

RESULTS

In 26 articles eligible for inclusion (16 investigating the effects of radiotherapy on EVs, five investigating the effect of EVs on radiation response, and five clinical studies), significant heterogeneity and frequent omission of key characterisation steps was identified, reducing confidence that the results are related to EVs and their cargo as opposed to co-isolated bioactive molecules. However, the results are able to clearly identify interactions between EVs and radiotherapy bi-directionally within different cell types within the glioblastoma TME. These interactions facilitate transferable radioresistance and oncogenic signalling, highlighting that EVs are an important component in the variability of glioblastoma radiotherapy response.

CONCLUSIONS

Future multi-directional investigations interrogating the whole TME are required to improve subsequent clinical translation, and all studies should incorporate up to date controls and reporting requirements to increase the validity of their findings. This would be facilitated by increased collaboration between less experienced and more experienced EV research groups.

Suppression of the antitumoral activity of natural killer cells under indirect coculture with cancer-associated fibroblasts in a pancreatic TIME-on-chip model

BACKGROUND

Recently, natural killer (NK) cells emerged as a treatment option for various solid tumors. However, the immunosuppressive tumor immune microenvironment (TIME) can reduce the cytotoxic ability of NK cells in pancreatic ductal adenocarcinoma. Cancer-associated fibroblasts within the tumor stroma can suppress immune surveillance by dysregulating factors involved in the cellular activity of NK cells. Herein, the effect of activated pancreatic stellate cells (aPSCs) on NK cell-mediated anticancer efficacy under three-dimensional (3D) coculture conditions was investigated.

METHODS

3D cocultures of PANC-1 tumor spheroids (TSs) with aPSCs and NK-92 cells in a collagen matrix were optimized to identify the occurring cellular interactions and differential cytokine profiles in conditioned media using microchannel chips. PANC-1 TSs and aPSCs were indirectly cocultured, whereas NK-92 cells were allowed to infiltrate the TS channel using convective medium flow.

RESULTS

Coculture with aPSCs promoted PANC-1 TSs growth and suppressed the antitumor cytotoxic effects of NK-92 cells. Mutual inhibition of cellular activity without compromising migration ability was observed between aPSCs and NK-92 cells. Moreover, the reduced killing activity of NK-92 cells was found to be related with reduced granzyme B expression in NK cells.

CONCLUSIONS

Herein, a novel TIME-on-chip model based on the coculture of PANC-1 TSs, aPSCs, and NK-92 cells was described. This model may be useful for studying the detailed mechanisms underlying NK cells dysregulation and for exploring future therapeutic interventions to restore NK cell activity in the tumor microenvironment.

Epigenetics as a determinant of radiation response in cancer

Radiation therapy is a cornerstone of modern cancer treatment. Treatment is based on depositing focal radiation to the tumor to inhibit cell growth, proliferation and metastasis, and to promote the death of cancer cells. In addition, radiation also affects non-tumor cells in the tumor microenvironmental (TME). Radiation resistance of the tumor cells is the most common cause of treatment failure, allowing survival of cancer cell and subsequent tumor growing. Molecular radioresistance comprises genetic and epigenetic characteristics inherent in cancer cells, or characteristics acquired after exposure to radiation. Furthermore, cancer stem cells (CSCs) and non-tumor cells into the TME as stromal and immune cells have a role in promoting and maintaining radioresistant tumor phenotypes. Different regulatory molecules and pathways distinctive of radiation resistance include DNA repair, survival signaling and cell death pathways. Epigenetic mechanisms are one of the most relevant events that occur after radiotherapy to regulate the expression and function of key genes and proteins in the differential radiation-response. This article reviews recent data on the main molecular mechanisms and signaling pathways related to the biological response to radiotherapy in cancer; highlighting the epigenetic control exerted by DNA methylation, histone marks, chromatin remodeling and m6A RNA methylation on gene expression and activation of signaling pathways related to radiation therapy response.

Cancer-associated fibroblasts: Mediators of head and neck tumor microenvironment remodeling

Cancer-associated fibroblasts (CAFs) are involved in critical aspects of head and neck squamous cell carcinoma (HNSCC) pathogenesis, such as the formation of a tumor-permissive extracellular matrix structure, angiogenesis, or immune and metabolic reprogramming of the tumor microenvironment (TME), with implications for metastasis and resistance to radiotherapy and chemotherapy. The pleiotropic effect of CAFs in TME is likely to reflect the heterogeneity and plasticity of their population, with context-dependent effects on carcinogenesis. The specific properties of CAFs provide many targetable molecules that could play an important role in the future therapy of HNSCC. In this review article, we will focus on the role of CAFs in the TME of HNSCC tumors. We will also discuss clinically relevant agents targeting CAFs, their signals, and signaling pathways, which are activated by CAFs in cancer cells, with the potential for repurposing for HNSCC therapy.

The Effect of Radiotherapy on Cell Survival and Inflammatory Cytokine and Chemokine Secretion in a Co-Culture Model of Head and Neck Squamous Cell Carcinoma and Normal Cells

Radiotherapy (RT) is one of the main treatments for head and neck squamous cell carcinomas (HNSCCs). Unfortunately, radioresistance is observed in many cases of HNSCCs. The effectiveness of RT depends on both the direct effect inducing cell death and the indirect effect of changing the tumor microenvironment (TME). Knowledge of interactions between TME components after RT may help to design a new combined treatment with RT. In the study, we investigated the effect of RT on cell survival and cell secretion in a co-culture model of HNSCCs in vitro. We examined changes in cell proliferation, colony formation, cell cycle phases, type of cell death, cell migration and secretion after irradiation. The obtained results suggest that the presence of fibroblasts and endothelial cells in co-culture with HNSCCs inhibits the function of cell cycle checkpoints G₁/S and G₂/M and allows cells to enter the next phase of the cell cycle. We showed an anti-apoptotic effect in co-culture of HNSCCs with fibroblasts or endothelial cells in relation to the execution phase of apoptosis, although we initially observed increased activation of the early phase of apoptosis in the co-cultures after irradiation. We hypothesize that the anti-apoptotic effect depends on increased secretion of IL-6 and MCP-1.

Tumor Microenvironment and Glioblastoma Cell Interplay as Promoters of Therapeutic Resistance

The invasive nature of glioblastoma is problematic in a radical surgery approach and can be responsible for tumor recurrence. In order to create new therapeutic strategies, it is imperative to have a better understanding of the mechanisms behind tumor growth and invasion. The continuous cross-talk between glioma stem cells (GSCs) and the tumor microenvironment (TME) contributes to disease progression, which renders research in this field difficult and challenging. The main aim of the review was to assess the different possible mechanisms that could explain resistance to treatment promoted by TME and GSCs in glioblastoma, including the role of M2 macrophages, micro RNAs (miRNAs), and long non-coding RNAs (lncRNAs) from exosomes from the TME. A systematic review of the literature on the role of the TME in developing and promoting radioresistance and chemoresistance of GBM was performed according to PRISMA-P (Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols) guidelines. A dedicated literature review search was also performed on the immunotherapeutic agents against the immune TME. We identified 367 papers using the reported keywords. The final qualitative analysis was conducted on 25 studies. A growing amount of evidence in the current literature supports the role of M2 macrophages and non-coding RNAs in promoting the mechanisms of chemo and radioresistance. A better insight into how GBM cells interact with TME is an essential step towards comprehending the mechanisms that give rise to resistance to standard treatment, which can help to pave the way for the development of novel therapeutic strategies for GBM patients.

Harnessing the Immunological Effects of Radiation to Improve Immunotherapies in Cancer

Ionizing radiation (IR) is used to treat 50% of cancers. While the cytotoxic effects related to DNA damage with IR have been known since the early 20th century, the role of the immune system in the treatment response is still yet to be fully determined. IR can induce immunogenic cell death (ICD), which activates innate and adaptive immunity against the cancer. It has also been widely reported that an intact immune system is essential to IR efficacy. However, this response is typically transient, and wound healing processes also become upregulated, dampening early immunological efforts to overcome the disease. This immune suppression involves many complex cellular and molecular mechanisms that ultimately result in the generation of radioresistance in many cases. Understanding the mechanisms behind these responses is challenging as the effects are extensive and often occur simultaneously within the tumor. Here, we describe the effects of IR on the immune landscape of tumors. ICD, along with myeloid and lymphoid responses to IR, are discussed, with the hope of shedding light on the complex immune stimulatory and immunosuppressive responses involved with this cornerstone cancer treatment. Leveraging these immunological effects can provide a platform for improving immunotherapy efficacy in the future.

Novel Generation of FAP Inhibitor-Based Homodimers for Improved Application in Radiotheranostics

Radiopharmaceuticals based on the highly potent FAP inhibitor (FAPi) UAMC-1110 have shown great potential in molecular imaging, but the short tumor retention time of the monomers do not match the physical half-lives of the important therapeutic radionuclides ¹⁷⁷Lu and ²²⁵Ac. This was improved with the dimer DOTAGA.(SA.FAPi)₂, but pharmacological and radiolabeling properties still need optimization. Therefore, the novel FAPi homodimers DO3A.Glu.(FAPi)₂ and DOTAGA.Glu.(FAPi)₂. were synthesized and quantitatively radiolabeled with ⁶⁸Ga, ⁹⁰Y, ¹⁷⁷Lu and ²²⁵Ac. The radiolabeled complexes showed high hydrophilicity and were generally stable in human serum (HS) and phosphate-buffered saline (PBS) at 37 °C over two half-lives, except for [²²⁵Ac]Ac-DOTAGA.Glu.(FAPi)₂ in PBS. In vitro affinity studies resulted in subnanomolar IC₅₀ values for FAP and high selectivity for FAP over the related proteases PREP and DPP4 for both compounds as well as for [^natLu]Lu-DOTAGA.Glu.(FAPi)₂. In a first proof-of-principle patient study (medullary thyroid cancer), [¹⁷⁷Lu]Lu-DOTAGA.Glu.(FAPi)₂ was compared to [¹⁷⁷Lu]Lu-DOTAGA.(SA.FAPi)₂. High uptake and long tumor retention was observed in both cases, but [¹⁷⁷Lu]Lu-DOTAGA.Glu.(FAPi)₂ significantly reduces uptake in non-target and critical organs (liver, colon). Overall, the novel FAPi homodimer DOTAGA.Glu.(FAPi)₂ showed improved radiolabeling in vitro and pharmacological properties in vivo compared to DOTAGA.(SA.FAPi)₂. [¹⁷⁷Lu]Lu-DOTAGA.Glu.(FAPi)₂ and [²²⁵Ac]Ac-DOTAGA.Glu.(FAPi)₂ appear promising for translational application in patients.

Fibroblast Activation Protein Inhibitor Theranostics

Fibroblast activation protein (FAP)-radioligand therapy might be effective in some patients without being curative. FAP-radioligands deliver ionizing radiation directly to FAP⁺ cancer-associated fibroblasts and, in some cancers, to FAP⁺ tumor cells; in addition, they indirectly irradiate FAP^- cells in tumor tissue via cross-fire and bystander effects. Here, we discuss the potential to improve FAP-radioligand therapy through interfering with DNA damage repair, immunotherapy, and co-targeting cancer-associated fibroblasts. As the molecular and cellular effects of FAP-radioligands on the tumor and its microenvironment have not been investigated yet, we call for future research to close this gap in knowledge, which prevents the development of more effective FAP-radioligand therapies.

Radiation-assisted strategies provide new perspectives to improve the nanoparticle delivery to tumor

Nanoparticles (NPs), with advantages in tumor targeting, have been extensively developed for anticancer treatment. However, the delivery efficacy of NPs tends to be heterogeneous in clinical research. Surprisingly, a traditional cancer treatment, radiotherapy (radiation), has been observed with the potential to improve the delivery of NPs by influencing the features of the tumor microenvironment, which provides new perspectives to overcome the barriers in the NPs delivery. Since the effect of radiation can also be enhanced by versatile NPs, these findings of radiation-assisted NPs delivery suggest innovative strategies combining radiotherapy with nanotherapeutics. This review summarizes the research on the delivery and therapeutic efficacy of NPs that are improved by radiation, focusing on relative mechanisms and existing challenges and opportunities.

ALKBH5-mediated m6 A demethylation of TIRAP mRNA promotes radiation-induced liver fibrosis and decreases radiosensitivity of hepatocellular carcinoma

BACKGROUND

Radiation-induced hepatic stellate cell (HSC) activation promotes radiation-induced liver fibrosis (RILF), a complication for hepatocellular carcinoma (HCC) radiotherapy. The demethylase alpha-ketoglutarate-dependent dioxygenase alkB homolog 5 (ALKBH5) decreases N6-methyladenylate methylation (m6 A) modification of RNA, while its role in regulating RILF pathogenesis and HCC radiosensitivity remains unknown.

METHODS

Methylated RNA immunoprecipitation sequencing (MeRIP-seq) and RNA-sequencing (RNA-seq) were used to screen target genes regulated by ALKBH5. HSC with altered ALKBH5 expression was used to assess irradiation-induced HSC activation and the effect of HSC on recruitment and polarisation of monocytes. Key cytokines in medium from irradiated HSC-educated monocytes were identified by cytokine array detection. The effects of blocking ALKBH5 and key cytokines on RILF and HCC radiosensitivity were also evaluated.

RESULTS

Radiation-induced ALKBH5 expression in HSC mediated m6 A demethylation of toll-interleukin 1 receptor domain containing adaptor protein (TIRAP) mRNA and activated its downstream NF-κB and JNK/Smad2 pathways to promote HSC activation. Additionally, ALKBH5 regulated CCL5 secretion by irradiated HSC to promote monocyte recruitment and M2 macrophage polarisation. Notably, polarised monocytes secreted CCL20 to up-regulate ALKBH5 expression in HSC, and reduce HCC radiosensitivity by activating ALKBH5/TIRAP axis in HCC cells. ALKBH5 knockdown-combined CCR6 (CCL20 receptor) inhibitor significantly alleviated RILF and improved HCC radiosensitivity in mice. HCC patients with high ALKBH5 and TIRAP expression were prone to radiation-induced liver injury and poor tumour response to radiotherapy.

CONCLUSIONS

Collectively, irradiation up-regulates ALKBH5 in HSC to mediate monocyte recruitment and M2 polarisation and form positive feedback to promote RILF and reduce HCC radiosensitivity. The dual roles of ALKBH5 as a microenvironmental regulator and radiosensitisation target provide new ideas for RILF prevention and radiosensitisation of HCC.

Immunotherapy combined with radiotherapy to reverse immunosuppression in microsatellite stable colorectal cancer

In recent years, the exploration of immune checkpoint inhibitors (ICIs) has resulted in substantial progress and has changed the pattern of cancer treatment. ICIs have revolutionized the treatment landscape of microsatellite instable colorectal cancer while the efficacy is very limited in patients with microsatellite stable colorectal cancer. Therefore, sensitizing MSS CRC to immunotherapy is a major challenge in the field of CRC immunotherapy. Immunotherapy-based combination therapy is an effective strategy. This review of radiotherapy (RT) as a local treatment has dramatically changed in recent years, and it is now widely accepted that RT can deeply reshape the tumor environment by modulating the immune response. Such evidence gives a strong rationale for the synergism of radiotherapy and immunotherapy, introducing the era of 'immunoradiotherapy'. How to give full play to the synergistic effect of radiotherapy and immunotherapy to improve the therapeutic effect of MSS CRC and bring good prognosis is a hot problem to be solved in the field of cancer treatment.This article reviews the development of CRC immunotherapy, the immune resistance mechanism of MSS CRC, and the impact and potential value of immunotherapy combined with radiotherapy on the immune environment of CRC.

Cancer-associated fibroblasts: The chief architect in the tumor microenvironment

Stromal heterogeneity of tumor microenvironment (TME) plays a crucial role in malignancy and therapeutic resistance. Cancer-associated fibroblasts (CAFs) are one of the major players in tumor stroma. The heterogeneous sources of origin and subsequent impacts of crosstalk with breast cancer cells flaunt serious challenges before current therapies to cure triple-negative breast cancer (TNBC) and other cancers. The positive and reciprocal feedback of CAFs to induce cancer cells dictates their mutual synergy in establishing malignancy. Their substantial role in creating a tumor-promoting niche has reduced the efficacy of several anti-cancer treatments, including radiation, chemotherapy, immunotherapy, and endocrine therapy. Over the years, there has been an emphasis on understanding CAF-induced therapeutic resistance in order to enhance cancer therapy results. CAFs, in the majority of cases, employ crosstalk, stromal management, and other strategies to generate resilience in surrounding tumor cells. This emphasizes the significance of developing novel strategies that target particular tumor-promoting CAF subpopulations, which will improve treatment sensitivity and impede tumor growth. In this review, we discuss the current understanding of the origin and heterogeneity of CAFs, their role in tumor progression, and altering the tumor response to therapeutic agents in breast cancer. In addition, we also discuss the potential and possible approaches for CAF-mediated therapies.

Combination, Modulation and Interplay of Modern Radiotherapy with the Tumor Microenvironment and Targeted Therapies in Pancreatic Cancer: Which Candidates to Boost Radiotherapy?

Pancreatic ductal adenocarcinoma cancer (PDAC) is a highly diverse disease with low tumor immunogenicity. PDAC is also one of the deadliest solid tumor and will remain a common cause of cancer death in the future. Treatment options are limited, and tumors frequently develop resistance to current treatment modalities. Since PDAC patients do not respond well to immune checkpoint inhibitors (ICIs), novel methods for overcoming resistance are being explored. Compared to other solid tumors, the PDAC's tumor microenvironment (TME) is unique and complex and prevents systemic agents from effectively penetrating and killing tumor cells. Radiotherapy (RT) has the potential to modulate the TME (e.g., by exposing tumor-specific antigens, recruiting, and infiltrating immune cells) and, therefore, enhance the effectiveness of targeted systemic therapies. Interestingly, combining ICI with RT and/or chemotherapy has yielded promising preclinical results which were not successful when translated into clinical trials. In this context, current standards of care need to be challenged and transformed with modern treatment techniques and novel therapeutic combinations. One way to reconcile these findings is to abandon the concept that the TME is a well-compartmented population with spatial, temporal, physical, and chemical elements acting independently. This review will focus on the most interesting advancements of RT and describe the main components of the TME and their known modulation after RT in PDAC. Furthermore, we will provide a summary of current clinical data for combinations of RT/targeted therapy (tRT) and give an overview of the most promising future directions.

The Stockholm Syndrome of Cancer: Fibroblasts as a Powerful Shield against Colorectal Cancer Therapy

Fibroblasts are incredible cells [...].

Clinical Radiobiology for Radiation Oncology

This chapter is focused on radiobiological aspects at the molecular, cellular, and tissue level which are relevant for the clinical use of ionizing radiation (IR) in cancer therapy. For radiation oncology, it is critical to find a balance, i.e., the therapeutic window, between the probability of tumor control and the probability of side effects caused by radiation injury to the healthy tissues and organs. An overview is given about modern precision radiotherapy (RT) techniques, which allow optimal sparing of healthy tissues. Biological factors determining the width of the therapeutic window are explained. The role of the six typical radiobiological phenomena determining the response of both malignant and normal tissues in the clinic, the 6R’s, which are Reoxygenation, Redistribution, Repopulation, Repair, Radiosensitivity, and Reactivation of the immune system, is discussed. Information is provided on tumor characteristics, for example, tumor type, growth kinetics, hypoxia, aberrant molecular signaling pathways, cancer stem cells and their impact on the response to RT. The role of the tumor microenvironment and microbiota is described and the effects of radiation on the immune system including the abscopal effect phenomenon are outlined. A summary is given on tumor diagnosis, response prediction via biomarkers, genetics, and radiomics, and ways to selectively enhance the RT response in tumors. Furthermore, we describe acute and late normal tissue reactions following exposure to radiation: cellular aspects, tissue kinetics, latency periods, permanent or transient injury, and histopathology. Details are also given on the differential effect on tumor and late responding healthy tissues following fractionated and low dose rate irradiation as well as the effect of whole-body exposure.

Bioinspired nanovehicle of furoxans-oxaliplatin improves tumoral distribution for chemo-radiotherapy

The spatiotemporal distribution of therapeutic agents in tumors remains an essential challenge of radiation-mediated therapy. Herein, we rationally designed a macrophage microvesicle-inspired nanovehicle of nitric oxide donor-oxaliplatin (FO) conjugate (M-PFO), aiming to promote intratumor permeation and distribution profiles for chemo-radiotherapy. FO was responsively released from M-PFO in intracellular acidic environments, and then be activated by glutathione (GSH) into active oxaliplatin and NO molecules in a programmed manner. M-PFO exhibited notable accumulation, permeation and cancer cell accessibility in tumor tissues. Upon radiation, the reactive peroxynitrite species (ONOO^-) were largely produced, which could diffuse into regions over 400 μm away from the tumor vessels and be detectable after 24 h of radiation, thereby exhibiting superior efficacy in improving the spatiotemporal distribution in tumors versus common reactive oxygen species (ROS). Moreover, M-PFO mediated chemo-radiotherapy caused notable inhibition of tumor growth, with an 89.45% inhibition in HT-29 tumor models and a 92.69% suppression in CT-26 tumor models. Therefore, this bioinspired design provides an encouraging platform to improve intratumor spatiotemporal distribution to synergize chemo-radiotherapy.

The Lymphatic Endothelium in the Context of Radioimmuno-Oncology

The study of lymphatic tumor vasculature has been gaining interest in the context of cancer immunotherapy. These vessels constitute conduits for immune cells' transit toward the lymph nodes, and they endow tumors with routes to metastasize to the lymph nodes and, from them, toward distant sites. In addition, this vasculature participates in the modulation of the immune response directly through the interaction with tumor-infiltrating leukocytes and indirectly through the secretion of cytokines and chemokines that attract leukocytes and tumor cells. Radiotherapy constitutes the therapeutic option for more than 50% of solid tumors. Besides impacting transformed cells, RT affects stromal cells such as endothelial and immune cells. Mature lymphatic endothelial cells are resistant to RT, but we do not know to what extent RT may affect tumor-aberrant lymphatics. RT compromises lymphatic integrity and functionality, and it is a risk factor to the onset of lymphedema, a condition characterized by deficient lymphatic drainage and compromised tissue homeostasis. This review aims to provide evidence of RT's effects on tumor vessels, particularly on lymphatic endothelial cell physiology and immune properties. We will also explore the therapeutic options available so far to modulate signaling through lymphatic endothelial cell receptors and their repercussions on tumor immune cells in the context of cancer. There is a need for careful consideration of the RT dosage to come to terms with the participation of the lymphatic vasculature in anti-tumor response. Here, we provide new approaches to enhance the contribution of the lymphatic endothelium to radioimmuno-oncology.

The poorly immunogenic tumor microenvironment of pancreatic cancer: the impact of radiation therapy, and strategies targeting resistance

Pancreatic cancer is one of the most lethal cancers, due to its uniquely aggressive behavior and resistance to therapy. The tumor microenvironment of pancreatic cancer is immunosuppressive, and attempts at utilizing immunotherapies have been unsuccessful. Radiation therapy (RT) results in immune activation and antigen presentation in other cancers, but in pancreatic cancer has had limited success in stimulating immune responses. RT activates common pathways of fibrosis and chronic inflammation seen in pancreatic cancer, resulting in immune suppression. Here we describe the pancreatic tumor microenvironment with regard to fibrosis, myeloid and lymphoid cells, and the impact of RT. We also describe strategies of targeting these pathways that have promise to improve outcomes by harnessing the cytotoxic and immune-activating aspects of RT.

A multi-omics signature to predict the prognosis of invasive ductal carcinoma of the breast

BACKGROUND

Precisely evaluating the prognosis of invasive ductal carcinoma (IDC) of the breast is challenging as most prognostic signatures use single-omics data based on gene or clinical information.

METHODS

Whole-slide images (WSIs), transcriptome, and clinical data of breast IDC were collected from the Cancer Genome Atlas Database. The cancer-associated fibroblast (CAF) gene sets were downloaded from the Molecular Signatures Database. The WSI feature was extracted by artificial feature engineering. The CAF prognostic genes were determined by the Gene Set Enrichment Analysis, the Wilcoxon test, and univariate Cox regression. The IDC patients were divided into the training and test sets. The prognostic signatures based on WSIs, IDC-CAFs, bi-omics, and tri-omics were constructed using multivariate Cox regression. The samples were divided into low- and high-risk groups according to the median risk score. The Kaplan-Meier survival and receiver operating characteristic curves were applied to validate the prediction performance of the four signatures.

RESULTS

In total, 508 IDC patients with complete data were included. The area under the curve (AUC) of single-omics signature based on WSI characteristics and CAFs was 0.765 and 0.775, whereas the AUC of bi-omics was 0.823. The tri-omics signature based on WSIs, CAFs, and lymph node status demonstrated the best predictive value with an AUC of 0.897.

CONCLUSION

The multi-omics signature based on WSIs, CAFs, and clinical characteristics showed excellent prediction ability in breast IDC patients, whose risk factors can also provide a valuable diagnostic reference for the clinical course.

Single-cell transcriptome analysis of tumor immune microenvironment characteristics in colorectal cancer liver metastasis

BACKGROUND

Liver metastasis is the leading cause of death in colorectal cancer (CRC) patients, and the precise mechanisms remain unclear. In this study, single-cell RNA sequencing (scRNA-seq) was used to analyze the cellular and molecular heterogeneity between CRC primary lesion and corresponding liver metastasis, and to clarify the characteristics of the tumor microenvironment (TME) in synchronous liver metastasis of CRC.

METHODS

A case of microsatellite stable (MSS) sigmoid carcinoma with synchronous liver metastasis was selected, and tissues from the primary tumor and the liver metastasis were collected for scRNA-seq. The EdgeR package software was used to identify the differentially expressed genes between cells. Gene Set Enrichment Analysis (GSEA) was performed and the clusterProfiler R package was used for Gene Ontology (GO) enrichment analysis. The SCENIC and CellphoneDB packages were used to reconstruct the transcriptional regulatory networks and to analyze the intercellular interaction network, respectively.

RESULTS

Compared to the primary tumor, the proportion of myeloid cells in the metastatic tumor was significantly increased, while B cells and plasma cells were decreased. In the metastatic tumor, the myeloid-derived suppressor cell (MDSC) characteristic gene, mannose receptor C-type 1 (MRC1) and tumor associated macrophage 2 (TAM2)-related gene, were highly expressed. Furthermore, angiogenesis, oxidative phosphorylation, and endothelial mesenchymal transition (EMT) of myeloid cells were also significantly enhanced. There were less myeloid cells in primary tumors, and these were mainly monocytes and TAM1; while the number of TAM2 was significantly upregulated in the metastatic samples. In liver metastasis, the T cell population was exhausted, and this was accompanied by a significant increase in the number of CD4+ T cells and a decrease in the number of CD8+ T cells. Furthermore, some immune checkpoint molecules were highly expressed. Interactions between myeloid cells and other cell populations appeared to be strong.

CONCLUSIONS

The TME of CRC liver metastasis is significantly immunosuppressed. Interactions between myeloid cells and other cell populations in the TME contribute to the establishment of a pro-metastatic niche that promotes colonization and growth of CRC cells in the liver. TAMs may be a potential immunotherapeutic target for MSS CRC.

Targeting Tumor Physical Microenvironment for Improved Radiotherapy

Radiotherapy has led to important clinical advances; existing cancer radiotherapy resistance is one remaining major challenge. Recently, biophysical cues in the tumor microenvironment (TME) have been regarded as the new hallmarks of cancer, playing pivotal roles in various cancer behaviors and treatment responses, including radiotherapy resistance. With recent advances in micro/nanotechnologies and functional biomaterials, radiotherapy exerts great influence on biophysical cues in TME, which, in turn, significantly affect the response to radiotherapy. Besides, various strategies have emerged that target biophysical cues in TME, to potentially enhance radiotherapy efficacy. Therefore, this paper reviews the four biophysical cues (i.e., extracellular matrix (ECM) microarchitecture, ECM stiffness, interstitial fluid pressure, and solid stress) that may play important roles in radiotherapy resistance, their possible mechanisms for inducing it, and their change after radiotherapy. The emerging therapeutic strategies targeting the biophysical microenvironment, to explore the mechanism of radiotherapy resistance and develop effective strategies to revert it for improved treatment efficacy are further summarized.

Cancer-associated fibroblast-derived gene signatures predict radiotherapeutic survival in prostate cancer patients

BACKGROUND

Cancer-associated fibroblasts (CAFs) play multiple roles in regulating tumor metastasis and treatment response. Current clinical indicators are insufficient to accurately assess disease risk and radiotherapy response, emphasizing the urgent need for additional molecular prognostic markers.

METHODS

In order to investigate CAF-related genes associated with radiotherapy and construct prognostic CAF-related gene signatures for prostate cancer, we firstly established a radio-resistant prostate CAF cell subline (referred to as CAFR) from Mus-CAF (referred to as CAF) through fractionated irradiation using X-rays. Transcriptome sequencing for CAF and CAFR was conducted, and 2626 CAF-related differentially expressed genes (DEGs) associated with radiotherapy were identified. Human homologous genes of mouse CAF-related DEGs were then obtained.

RESULTS

Functional enrichment analysis revealed that these CAF-related DEGs were significantly enriched ECM- and immune-related functions and pathways. Based on GSE116918 dataset, 186 CAF-related DEGs were correlated with biochemical recurrence-free survival (BCRFS) of prostate cancer patients, 16 of which were selected to construct a BCRFS-related CAF signature, such as ACPP, THBS2, and KCTD14; 142 CAF-related DEGs were correlated with metastasis-free survival (MFS), 16 of which were used to construct a MFS-related CAF signature, such as HOPX, TMEM132A, and ZNF467. Both Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA) datasets confirmed that the two CAF signatures accurately predicted BCRFS and MFS of prostate cancer patients. The risk scores were higher in patients with higher gleason grades and higher clinical T stages. Moreover, the BCRFS-related CAF signature was an independent prognostic factor and a nomogram consisting of BCRFS-related CAF signature and various clinical factors accurately predicted 2-, 3-, and 5-year survival time of prostate cancer patients. Furthermore, the risk score was positively correlated with multiple immune checkpoints.

CONCLUSIONS

Our established CAF signatures could accurately predict BCRFS and MFS in prostate cancer patients undergoing radiotherapy.

Cancer-Associated Fibroblasts: The Origin, Biological Characteristics and Role in Cancer-A Glance on Colorectal Cancer

Simple Summary

Tumor microenvironment is a major contributor to tumor growth, metastasis and resistance to therapy. It consists of many cancer-associated fibroblasts (CAFs), which derive from different types of cells. CAFs detected in different tumor types are linked to poor prognosis, as in the case of colorectal cancer. Although their functions differ according to their subtype, their detection is not easy, and there are no established markers for such detection. They are possible targets for therapeutic treatment. Many trials are ongoing for their use as a prognostic factor and as a treatment target. More research remains to be carried out to establish their role in prognosis and treatment.

Abstract

The therapeutic approaches to cancer remain a considerable target for all scientists around the world. Although new cancer treatments are an everyday phenomenon, cancer still remains one of the leading mortality causes. Colorectal cancer (CRC) remains in this category, although patients with CRC may have better survival compared with other malignancies. Not only the tumor but also its environment, what we call the tumor microenvironment (TME), seem to contribute to cancer progression and resistance to therapy. TME consists of different molecules and cells. Cancer-associated fibroblasts are a major component. They arise from normal fibroblasts and other normal cells through various pathways. Their role seems to contribute to cancer promotion, participating in tumorigenesis, proliferation, growth, invasion, metastasis and resistance to treatment. Different markers, such as a-SMA, FAP, PDGFR-β, periostin, have been used for the detection of cancer-associated fibroblasts (CAFs). Their detection is important for two main reasons; research has shown that their existence is correlated with prognosis, and they are already under evaluation as a possible target for treatment. However, extensive research is warranted.

Biological Mechanisms to Reduce Radioresistance and Increase the Efficacy of Radiotherapy: State of the Art

Cancer treatment with ionizing radiation (IR) is a well-established and effective clinical method to fight different types of tumors and is a palliative treatment to cure metastatic stages. Approximately half of all cancer patients undergo radiotherapy (RT) according to clinical protocols that employ two types of ionizing radiation: sparsely IR (i.e., X-rays) and densely IR (i.e., protons). Most cancer cells irradiated with therapeutic doses exhibit radio-induced cytotoxicity in terms of cell proliferation arrest and cell death by apoptosis. Nevertheless, despite the more tailored advances in RT protocols in the last few years, several tumors show a relatively high percentage of RT failure and tumor relapse due to their radioresistance. To counteract this extremely complex phenomenon and improve clinical protocols, several factors associated with radioresistance, of both a molecular and cellular nature, must be considered. Tumor genetics/epigenetics, tumor microenvironment, tumor metabolism, and the presence of non-malignant cells (i.e., fibroblast-associated cancer cells, macrophage-associated cancer cells, tumor-infiltrating lymphocytes, endothelial cells, cancer stem cells) are the main factors important in determining the tumor response to IR. Here, we attempt to provide an overview of how such factors can be taken advantage of in clinical strategies targeting radioresistant tumors.

Cellular senescence and the tumour microenvironment

The senescence-associated secretory phenotype (SASP), where senescent cells produce a variety of secreted proteins including inflammatory cytokines, chemokines, matrix remodelling factors, growth factors and so on, plays pivotal but varying roles in the tumour microenvironment. The effects of SASP on the surrounding microenvironment depend on the cell type and process of cellular senescence induction, which is often associated with innate immunity. Via SASP-mediated paracrine effects, senescent cells can remodel the surrounding tissues by modulating the character of adjacent cells, such as stromal, immune cells, as well as cancer cells. The SASP is associated with both tumour-suppressive and tumour-promoting effects, as observed in senescence surveillance effects (tumour-suppressive) and suppression of anti-tumour immunity in most senescent cancer-associated fibroblasts and senescent T cells (tumour-promoting). In this review, we discuss the features and roles of senescent cells in tumour microenvironment with emphasis on their context-dependency that determines whether they promote or suppress cancer development. Potential usage of recently developed drugs that suppress the SASP (senomorphics) or selectively kill senescence cells (senolytics) in cancer therapy are also discussed.

Radiation-induced FAP + fibroblasts are involved in keloid recurrence after radiotherapy

Background: Keloid scars (KSs), which are composed of abnormal hyperplastic scar tissue, form during skin wound healing due to excessive fibroblast activation and collagen secretion. Although surgical resection and radiation therapy are used to prevent recurrence, KS recurrence rates range from 15 to 23%, and the underlying mechanism is unclear.

Methods: To elucidate the mechanism of keloid recurrence, we established a PDX model and the grafts remained for over 20 weeks after transplantation on the bilateral backs of the NCG mice.

Results: RNA-seq revealed that KS tissue gene expression was highly consistent before and after transplantation. Then, one side of the KS graft was irradiated with electron beam therapy (10 Gy), significant increases in vimentin and fibroblast activation protein alpha (FAP) expression were observed after irradiation and were accompanied by severe microvascular destruction. Surprisingly, 4 weeks after irradiation, significantly increased recurrence was observed with increased FAP + tissue and cell cycle regulator expression, resulting in a remarkable altered graft volume. Moreover, irradiation-induced FAP upregulation markedly facilitated radiation resistance and increased cell cycle progression, decreased senescence, and increased energy production.

Conclusion: Our findings revealed that irradiation causes increased abundance of FAP + cells, which was associated with cell proliferation and delayed cellular senescence, accompanied by ATP production.

Cancer-Associated Fibroblasts: Tumorigenicity and Targeting for Cancer Therapy

Simple Summary

Cancer-associated fibroblasts (CAFs) are found in the tumor microenvironment and exhibit several protumorigenic functions. Preclinical studies suggest that CAFs can be reduced, eliminated, or reprogrammed; however, clinical translation has not yet occurred. A better understanding of these cells and their functions will undoubtedly improve cancer treatments. In this review, we summarize current research, highlight major challenges, and discuss future opportunities for improving our knowledge of CAF biology and targeting.

Abstract

Cancer-associated fibroblasts (CAFs) are a heterogenous group of activated fibroblasts and a major component of the tumor stroma. CAFs may be derived from fibroblasts, epithelial cells, endothelial cells, cancer stem cells, adipocytes, pericytes, or stellate cells. These complex origins may underlie their functional diversity, which includes pro-tumorigenic roles in extracellular matrix remodeling, the suppression of anti-tumor immunity, and resistance to cancer therapy. Several methods for targeting CAFs to inhibit tumor progression and enhance anti-tumor immunity have recently been reported. While preclinical studies have shown promise, to date they have been unsuccessful in human clinical trials against melanoma, breast cancer, pancreas cancer, and colorectal cancers. This review summarizes recent and major advances in CAF-targeting therapies, including DNA-based vaccines, anti-CAF CAR-T cells, and modifying and reprogramming CAF functions. The challenges in developing effective anti-CAF treatment are highlighted, which include CAF heterogeneity and plasticity, the lack of specific target markers for CAFs, the limitations in animal models recapitulating the human cancer microenvironment, and the undesirable off-target and systemic side effects. Overcoming these challenges and expanding our understanding of the basic biology of CAFs is necessary for making progress towards safe and effective therapeutic strategies against cancers in human patients.

Synergistic effects of radiotherapy and targeted immunotherapy in improving tumor treatment efficacy: a review

Radiotherapy (RT), unlike chemotherapy, is one of the most routinely used and effective genotoxic and immune response inducing cancer therapies with an advantage of reduced side effects. However, cancer can relapse after RT owing to multiple factors, including acquired tumor resistance, immune suppressive microenvironment buildup, increased DNA repair, thus favoring tumor metastasis. Efforts to mitigate these undesirable effects have drawn interest in combining RT with immunotherapy, particularly the use of immune checkpoint inhibitors, to tilt the pre-existing tumor stromal microenvironment into long-lasting therapy-induced antitumor immunity at multiple metastatic sites (abscopal effects). This multimodal therapeutic strategy can alleviate the increased T cell priming and decrease tumor growth and metastasis, thus emerging as a significant approach to sustain as long-term antitumor immunity. To understand more about this synergism, a detailed cellular mechanism underlying the dynamic interaction between tumor and immune cells within the irradiated tumor microenvironment needs to be explored. Hence, in the present review, we have attempted to evaluate various RT-inducible immune factors, which can be targeted by immunotherapy and provide detailed explanation to optimally maximize their synergy with immunotherapy for long-lasting antitumor immunity. Moreover, we have critically assessed various combinatorial approaches along with their challenges and described strategies to modify them in addition to providing approaches for optimal synergistic effects of the combination.

Potential of Gold Nanoparticle in Current Radiotherapy Using a Co-Culture Model of Cancer Cells and Cancer Associated Fibroblast Cells

Simple Summary

Many cancer therapeutics do not account for the complexity of the tumor microenvironment (TME), which may result in failure when applied clinically. In this paper we utilized a simple tumor model made of two types of pancreatic cancer cells that contribute to the tumor environment, i.e., cancer cells and cancer associated fibroblasts. Herein, radiotherapy along with radiosensitizing gold nanoparticles were used to test the efficacy of a co-culture vs. monoculture model. The results show that the co-culture model exhibited heightened resistance to radiation. Furthermore, we found that the combination of gold radiosensitizers with radiotherapy reduced the radioresistance of the co-culture model compared to radiotherapy alone. This study demonstrates the potential of using nanotherapeutics in targeting the complex tumor microenvironment.

Abstract

Many cancer therapeutics are tested in vitro using only tumour cells. However, the tumour promoting effect of cancer associated fibroblasts (CAFs) within the tumour microenvironment (TME) is thought to reduce cancer therapeutics’ efficacy. We have chosen pancreatic ductal adenocarcinoma (PDAC) as our tumor model. Our goal is to create a co-culture of CAFs and tumour cells to model the interaction between cancer and stromal cells in the TME and allow for better testing of therapeutic combinations. To test the proposed co-culture model, a gold nanoparticle (GNP) mediated-radiation response was used. Cells were grown in co-culture with different ratios of CAFs to cancer cells. MIA PaCa-2 was used as our PDAC cancer cell line. Co-cultured cells were treated with 2 Gy of radiation following GNP incubation. DNA damage and cell proliferation were examined to assess the combined effect of radiation and GNPs. Cancer cells in co-culture exhibited up to a 23% decrease in DNA double strand breaks (DSB) and up to a 35% increase in proliferation compared to monocultures. GNP/Radiotherapy (RT) induced up to a 25% increase in DNA DSBs and up to a 15% decrease in proliferation compared to RT alone in both monocultured and co-cultured cells. The observed resistance in the co-culture system may be attributed to the role of CAFs in supporting cancer cells. Moreover, we were able to reduce the activity of CAFs using GNPs during radiation treatment. Indeed, CAFs internalize a significantly higher number of GNPs, which may have led to the reduction in their activity. One reason experimental therapeutics fail in clinical trials relates to limitations in the pre-clinical models that lack a true representation of the TME. We have demonstrated a co-culture platform to test GNP/RT in a clinically relevant environment.

mRNA Subtype of Cancer-Associated Fibroblasts Significantly Affects Key Characteristics of Head and Neck Cancer Cells

Head and neck squamous cell carcinomas (HNSCC) belong among severe and highly complex malignant diseases showing a high level of heterogeneity and consequently also a variance in therapeutic response, regardless of clinical stage. Our study implies that the progression of HNSCC may be supported by cancer-associated fibroblasts (CAFs) in the tumour microenvironment (TME) and the heterogeneity of this disease may lie in the level of cooperation between CAFs and epithelial cancer cells, as communication between CAFs and epithelial cancer cells seems to be a key factor for the sustained growth of the tumour mass. In this study, we investigated how CAFs derived from tumours of different mRNA subtypes influence the proliferation of cancer cells and their metabolic and biomechanical reprogramming. We also investigated the clinicopathological significance of the expression of these metabolism-related genes in tissue samples of HNSCC patients to identify a possible gene signature typical for HNSCC progression. We found that the right kind of cooperation between cancer cells and CAFs is needed for tumour growth and progression, and only specific mRNA subtypes can support the growth of primary cancer cells or metastases. Specifically, during coculture, cancer cell colony supporting effect and effect of CAFs on cell stiffness of cancer cells are driven by the mRNA subtype of the tumour from which the CAFs are derived. The degree of colony-forming support is reflected in cancer cell glycolysis levels and lactate shuttle-related transporters.

Irradiation immunity interactions

The immune system can influence cancer development by both impeding and/or facilitating tumour growth and spread. A better understanding of this complex relationship is fundamental to optimise current and future cancer therapeutic strategies. Although typically regarded as a localised and immunosuppressive anti‐cancer treatment modality, radiation therapy has been associated with generating profound systemic effects beyond the intended target volume. These systemic effects are immune‐driven suggesting radiation therapy can enhance anti‐tumour immunosurveillance in some instances. In this review, we summarise how radiation therapy can positively and negatively affect local and systemic anti‐tumour immune responses, how co‐administration of immunotherapy with radiation therapy may help promote anti‐tumour immunity, and how the use of immune biomarkers may help steer radiation therapy‐immunotherapy personalisation to optimise clinical outcomes.

Radiotherapy resistance: identifying universal biomarkers for various human cancers

Radiotherapy (RT) is considered as a standard in the treatment of most solid cancers, including glioblastoma, lung, breast, rectal, prostate, colorectal, cervical, esophageal, and head and neck cancers. The main challenge in RT is tumor cell radioresistance associated with a high risk of locoregional relapse and distant metastasis. Despite significant progress in understanding mechanisms of radioresistance, its prediction and overcoming remain unresolved. This review presents the state-of-the-art for the potential universal biomarkers correlated to the radioresistance and poor outcome in different cancers. We describe radioresistance biomarkers functionally attributed to DNA repair, signal transduction, hypoxia, and angiogenesis. We also focus on high throughput genetic and proteomic studies, which revealed a set of molecular biomarkers related to radioresistance. In conclusion, we discuss biomarkers which are overlapped in most several cancers.

Pancreatic Cancer and Cellular Senescence: Tumor Microenvironment under the Spotlight

Pancreatic ductal adenocarcinoma (PDAC) has one of the most dismal prognoses of all cancers due to its late manifestation and resistance to current therapies. Accumulating evidence has suggested that the malignant behavior of this cancer is mainly influenced by the associated strongly immunosuppressive, desmoplastic microenvironment and by the relatively low mutational burden. PDAC develops and progresses through a multi-step process. Early in tumorigenesis, cancer cells must evade the effects of cellular senescence, which slows proliferation and promotes the immune-mediated elimination of pre-malignant cells. The role of senescence as a tumor suppressor has been well-established; however, recent evidence has revealed novel pro-tumorigenic paracrine functions of senescent cells towards their microenvironment. Understanding the interactions between tumors and their microenvironment is a growing research field, with evidence having been provided that non-tumoral cells composing the tumor microenvironment (TME) influence tumor proliferation, metabolism, cell death, and therapeutic resistance. Simultaneously, cancer cells shape a tumor-supportive and immunosuppressive environment, influencing both non-tumoral neighboring and distant cells. The overall intention of this review is to provide an overview of the interplay that occurs between senescent and non-senescent cell types and to describe how such interplay may have an impact on PDAC progression. Specifically, the effects and the molecular changes occurring in non-cancerous cells during senescence, and how these may contribute to a tumor-permissive microenvironment, will be discussed. Finally, senescence targeting strategies will be briefly introduced, highlighting their potential in the treatment of PDAC.

The cancer-inhibitory effects of proliferating tumor-residing fibroblasts

Initiation, local progression, and metastasis of cancer are associated with specific morphological, molecular, and functional changes in the extracellular matrix and the fibroblasts within the tumor microenvironment (TME). In the early stages of tumor development, fibroblasts are an obstacle that cancer cells must surpass or nullify to progress. Thus, in early tumor progression, specific signaling from cancer cells activates bio-pathways, which abolish the innate anticancer properties of fibroblasts and convert a high proportion of them to tumor-promoting cancer-associated fibroblasts (CAFs). Following this initial event, a wide spectrum of gene expression changes gradually leads to the development of a stromal fibroblast population with complex heterogeneity, creating fibroblast subtypes with characteristic profiles, which may alternate between being tumor-promotive and tumor-suppressive, topologically and chronologically in the TME. These fibroblast subtypes form the tumor's histological landscape including areas of cancer growth, inflammation, angiogenesis, invasion fronts, proliferating and non-proliferating fibroblasts, cancer-cell apoptosis, fibroblast apoptosis, and necrosis. These features reflect general deregulation of tissue homeostasis within the TME. This review discusses fundamental and current knowledge that has established the existence of anticancer fibroblasts within the various interacting elements of the TME. It is proposed that the maintenance of fibroblast proliferation is an essential parameter for the activation of their anticancer capacity, similar to that by which normal fibroblasts would be activated in wound repair, thus maintaining tissue homeostasis. Encouragement of research in this direction may render new means of cancer therapy and a greater understanding of tumor progression.

Dual inhibition of TGF-β and PD-L1: a novel approach to cancer treatment

Transforming growth factor β (TGF-β) and programmed death ligand 1 (PD-L1) initiate signaling pathways with complementary, nonredundant immunosuppressive functions in the tumor microenvironment (TME). In the TME, dysregulated TGF-β signaling suppresses antitumor immunity and promotes cancer fibrosis, epithelial-to-mesenchymal transition and angiogenesis. Meanwhile, PD-L1 expression inactivates cytotoxic T cells and restricts immunosurveillance in the TME. Anti-PD-L1 therapies have been approved for the treatment of various cancers, but TGF-β signaling in the TME is associated with resistance to these therapies. In this Review, we discuss the importance of the TGF-β and PD-L1 pathways in cancer, as well as clinical strategies using combination therapies that block these pathways separately or approaches with dual-targeting agents (bispecific and bifunctional immunotherapies) that may block them simultaneously. Currently, the furthest developed dual-targeting agent is bintrafusp alfa. This drug is a first-in-class bifunctional fusion protein that consists of the extracellular domain of the TGF-βRII receptor (a TGF-β "trap") fused to a human immunoglobulin G1 (IgG1) monoclonal antibody blocking PD-L1. Given the immunosuppressive effects of the TGF-β and PD-L1 pathways within the TME, colocalized and simultaneous inhibition of these pathways may potentially improve clinical activity and reduce toxicity.

Translation of DNA Damage Response Inhibitors as Chemoradiation Sensitizers From the Laboratory to the Clinic

Combination therapies with agents targeting the DNA damage response (DDR) offer an opportunity to selectively enhance the therapeutic index of chemoradiation or eliminate use of chemotherapy altogether. The successful translation of DDR inhibitors to clinical use requires investigating both their direct actions as (chemo)radiosensitizers and their potential to stimulate tumor immunogenicity. Beginning with high-throughput screening using both viability and DNA damage-reporter assays, followed by validation in gold-standard radiation colony-forming assays and in vitro assessment of mechanistic effects on the DDR, we describe proven strategies and methods leading to the clinical development of DDR inhibitors both with radiation alone and in combination with chemoradiation. Beyond these in vitro studies, we discuss the impact of key features of human xenograft and syngeneic mouse models on the relevance of in vivo tumor efficacy studies, particularly with regard to the immunogenic effects of combined therapy with radiation and DDR inhibitors. Finally, we describe recent technological advances in radiation delivery (using the small animal radiation research platform) that allow for conformal, clinically relevant radiation therapy in mouse models. This overall approach is critical to the successful clinical development and ultimate Food and Drug Administration approval of DDR inhibitors as (chemo)radiation sensitizers.