The radiobiology of TGFβ

Revisiting the TGFβ paradox: insights from HPV-driven cancer and the DNA damage response

The transforming growth factor-β (TGFβ) paradox refers to the well-established role of TGFβ in suppressing cancer in healthy tissues yet promoting malignancy in established cancers. Although this positioned TGFβ inhibitors as a potential therapeutic strategy for malignancy, therapuetic blockade has failed in multiple clinical trials. The general lack of selection principles for defining which patients would most benefit from the addition of a TGFβ inhibitor has probably hindered its deployment. Here, we highlight the therapeutic potential in TGFβ regulation of DNA repair using human papillomavirus (HPV)-driven head and neck squamous cell carcinoma (HNSCC) as an illustrative example. HPV inhibits TGFβ signalling, which in turn reduces DNA damage repair, ultimately conferring sensitivity to cancer treatments and thus contributing to the favourable prognosis of HPV-positive HNSCC. Here, we review the DNA repair deficit caused by a loss of TGFβ signalling and how this could be targeted to induce synthetic lethality. Moreover, we explore its role in predicting response to immune checkpoint inhibitors and the potential of biomarkers to select which patients with cancer could ultimately benefit from TGFβ inhibition.

Identification of a conserved subset of cold tumors responsive to immune checkpoint blockade

BACKGROUND

The efficacy of immune checkpoint blockade (ICB) depends on restoring immune recognition of cancer cells that have evaded immune surveillance. Transforming growth factor-beta (TGFβ) is associated with immune-poor, so-called cold tumors whereas loss of its signaling promotes DNA misrepair that could stimulate immune response.

METHODS

We analyzed transcriptomic data from IMvigor210, The Cancer Genome Atlas, and Tumor Immune Syngeneic MOuse data sets to evaluate the predictive value of high βAlt, a score representing low expression of a signature consisting of TGFβ targets and high expression of genes involved in error-prone DNA repair. The immune context of βAlt was assessed by evaluating tumor-educated immune signatures. An ICB-resistant, high βAlt preclinical tumor model was treated with a TGFβ inhibitor, radiation, and/or ICB and assessed for immune composition and tumor control.

RESULTS

We found that a high βAlt score predicts ICB response yet is paradoxically associated with an immune-poor tumor microenvironmentcancer in both human and mouse tumors. We postulated that high βAlt cancers consist of cancer cells in which loss of TGFβ signaling generates a TGFβ rich, immunosuppressive tumor microenvironment. Accordingly, preclinical modeling showed that TGFβ inhibition followed by radiotherapy could convert an immune-poor, high βAlt tumor to an immune-rich, ICB-responsive tumor. Mechanistically, TGFβ inhibition increased activated natural killer (NK) cells, which were required to recruit lymphocytes to respond to ICB in irradiated tumors. NK cell activation signatures were also increased in high βAlt, cold mouse and human tumors that responded to ICB.

CONCLUSIONS

These studies indicate that loss of TGFβ signaling competency and gain of error-prone DNA repair identifies a subset of cold tumors that are responsive to ICB. Our mechanistic studies show that inhibiting TGFβ activity can convert a high βAlt, cold tumor into ICB-responsive tumors via NK cells. A biomarker consisting of combined TGFβ, DNA repair, and immune context signatures is a means to prospectively identify patients whose cancers may be converted from cold to hot with appropriate therapy.

A conserved subset of cold tumors responsive to immune checkpoint blockade

Background

The efficacy of immune checkpoint blockade (ICB) depends on restoring immune recognition of cancer cells that have evaded immune surveillance. At the time of diagnosis, patients with lymphocyte-infiltrated cancers are the most responsive to ICB, yet a considerable fraction of patients have immune-poor tumors.

Methods

We analyzed transcriptomic data from IMvigor210, TCGA, and TISMO datasets to evaluate the predictive value of βAlt, a score representing the negative correlation of signatures consisting of transforming growth factor beta (TGFβ) targets and genes involved in error-prone DNA repair. The immune context of βAlt was assessed by evaluating tumor-educated immune signatures. An ICB-resistant, high βAlt preclinical tumor model was treated with a TGFβ inhibitor, radiation, and/or ICB and assessed for immune composition and tumor control.

Results

Here, we show that high βAlt is associated with an immune-poor context yet is predictive of ICB response in both humans and mice. A high βAlt cancer in which TGFβ signaling is compromised generates a TGFβ rich, immunosuppressive tumor microenvironment. Accordingly, preclinical modeling showed that TGFβ inhibition followed by radiotherapy could convert an immune-poor, ICB-resistant tumor to an immune-rich, ICB-responsive tumor. Mechanistically, TGFβ blockade in irradiated tumors activated natural killer cells that were required to recruit lymphocytes to respond to ICB. In support of this, natural killer cell activation signatures were also increased in immune-poor mouse and human tumors that responded to ICB.

Conclusions

These studies suggest that loss of TGFβ competency identifies a subset of cold tumors that are candidates for ICB. Our mechanistic studies show that inhibiting TGFβ activity converts high βAlt, cold tumors into ICB-responsive tumors via NK cells. Thus, a biomarker consisting of combined TGFβ, DNA repair, and immune context signatures provides a means to prospectively identify patients whose cancers may be converted from 'cold' to 'hot,' which could be exploited for therapeutic treatment.

WFDC3 sensitizes colorectal cancer to chemotherapy by regulating ATM/ATR kinase signaling pathway

Chemoresistance is an ongoing challenge for colorectal cancer (CRC) that significantly compromises the anti-tumor efficacy of current drugs. Identifying effective targets or drugs for overcoming chemoresistance is urgently needed. Our previous study showed that WFDC3 served as a tumor suppressor that hindered CRC metastasis. However, the function of WFDC3 in chemotherapy remains unknown. Here, we found that high WFDC3 expression in CRC patients treated with oxaliplatin was associated with a better prognosis. Concordantly, overexpression of WFDC3 significantly increased sensitivity to oxaliplatin in CRC cells, whereas knocking down WFDC3 led to oxaliplatin resistance. In addition, WFDC3 promoted oxaliplatin-mediated suppression of tumor growth in vivo. Subsequently, we found that WFDC3 could enhance oxaliplatin-induced DNA damage through inhibiting ATM/ATR signaling. WFDC3 knockdown showed the opposite effects. Moreover, a combination treatment of oxaliplatin and inhibitors for ATM or ATR partially reversed chemoresistance to oxaliplatin in CRC cells with low WFDC3 expression. Our results demonstrate that WFDC3 is possibly a biomarker for increasing oxaliplatin sensitivity in CRC by modulating ATM/ATR kinase signaling. Thus, a combination of oxaliplatin with an ATM or ATR inhibitor is a potential treatment option for improving CRC outcome.

Neoadjuvant lutetium PSMA, the TIME and immune response in high-risk localized prostate cancer

High-risk localized prostate cancer remains a lethal disease with high rates of recurrence, metastases and death, despite attempts at curative local treatment including surgery. Disease recurrence is thought to be a result of failure of local control and occult micrometastases. Neoadjuvant strategies before surgery have been effective in many cancers, but, to date, none has worked in this setting for prostate cancer. Prostate-specific membrane antigen (PSMA)-based theranostics is an exciting and rapidly evolving field in prostate cancer. The novel intravenous radionuclide therapy, [177Lu]Lu-PSMA-617 (lutetium PSMA) has been shown to be effective in treating men with metastatic castration-resistant prostate cancer, targeting cells expressing PSMA throughout the body. When given in a neoadjuvant setting, lutetium PSMA might also improve long-term oncological outcomes in men with high-risk localized disease. A component of radiotherapy is potentially an immunogenic form of cancer cell death. Lutetium PSMA could cause cancer cell death, resulting in release of tumour antigens and induction of a tumour-specific systemic immune response. This targeted radioligand treatment has the potential to treat local and systemic tumour sites by directly targeting cells that express PSMA, but might also act indirectly via this systemic immune response. In selected patients, lutetium PSMA could potentially be combined with systemic immunotherapies to augment the antitumour T cell response, and this might produce long-lasting immunity in prostate cancer.

The development and the genetic diseases of the ciliary body

The ciliary body, located at the junction of the choroid and iris, is crucial in the development of the embryonic eye. Notch2 signalling, Wnt signalling, transforming growth factor β (TGF-β) signalling, and Pax6 signalling are critical for coordinating the ciliary body formation. These signalling pathways are coordinated with each other and participate in the ciliary body development, ensuring the precise formation and optimal functioning of the eye structure. Although rare, ciliary body hypoplasia, ciliary tumours, and genetic-related iritis indicate the intricate nature of ciliary body development. Given the ciliary body's important biological significance and potential medical relevance, we aim to provide a comprehensive overview of the developmental molecular mechanisms governing ciliary body formation and function. Here, we focus on the intricate signalling pathways governing ciliary body development and corresponding genetic ciliary diseases.

Radiation-primed TGF-β trapping by engineered extracellular vesicles for targeted glioblastoma therapy

The poor outcome of glioblastoma multiforme (GBM) treated with immunotherapy is attributed to the profound immunosuppressive tumor microenvironment (TME) and the lack of effective delivery across the blood-brain barrier. Radiation therapy (RT) induces an immunogenic antitumor response that is counteracted by evasive mechanisms, among which transforming growth factor-β (TGF-β) activation is the most prominent factor. We report an extracellular vesicle (EV)-based nanotherapeutic that traps TGF-β by expressing the extracellular domain of the TGF-β type II receptor and targets GBM by decorating the EV surface with RGD peptide. We show that short-burst radiation dramatically enhanced the targeting efficiency of RGD peptide-conjugated EVs to GBM, while the displayed TGF-β trap reversed radiation-stimulated TGF-β activation in the TME, offering a synergistic effect in the murine GBM model. The combined therapy significantly increased CD8+ cytotoxic T cells infiltration and M1/M2 macrophage ratio, resulting in the regression of tumor growth and prolongation of overall survival. These results provide an EV-based therapeutic strategy for immune remodeling of the GBM TME and eradication of therapy-resistant tumors, further supporting its clinical translation.

PALB2-mutated human mammary cells display a broad spectrum of morphological and functional abnormalities induced by increased TGFβ signaling

Heterozygous mutations in any of three major genes, BRCA1, BRCA2 and PALB2, are associated with high-risk hereditary breast cancer susceptibility frequently seen as familial disease clustering. PALB2 is a key interaction partner and regulator of several vital cellular activities of BRCA1 and BRCA2, and is thus required for DNA damage repair and alleviation of replicative and oxidative stress. Little is however known about how PALB2-deficiency affects cell function beyond that, especially in the three-dimensional setting, and also about its role during early steps of malignancy development. To answer these questions, we have generated biologically relevant MCF10A mammary epithelial cell lines with mutations that are comparable to certain clinically important PALB2 defects. We show in a non-cancerous background how both mono- and biallelically PALB2-mutated cells exhibit gross spontaneous DNA damage and mitotic aberrations. Furthermore, PALB2-deficiency disturbs three-dimensional spheroid morphology, increases the migrational capacity and invasiveness of the cells, and broadly alters their transcriptome profiles. TGFβ signaling and KRT14 expression are enhanced in PALB2-mutated cells and their inhibition and knock down, respectively, lead to partial restoration of cell functions. KRT14-positive cells are also more abundant with DNA damage than KRT14-negative cells. The obtained results indicate comprehensive cellular changes upon PALB2 mutations, even in the presence of half dosage of wild type PALB2 and demonstrate how PALB2 mutations may predispose their carriers to malignancy.

TGF-β3 increases the severity of radiation-induced oral mucositis and salivary gland fibrosis in a mouse model

PURPOSE

Toxicities from head and neck (H&N) radiotherapy (RT) may affect patient quality of life and can be dose-limiting. Proteins from the transforming growth factor beta (TGF-β) family are key players in the fibrotic response. While TGF-β1 is known to be pro-fibrotic, TGF-β3 has mainly been considered anti-fibrotic. Moreover, TGF-β3 has been shown to act protective against acute toxicities after radio- and chemotherapy. In the present study, we investigated the effect of TGF-β3 treatment during fractionated H&N RT in a mouse model.

MATERIALS AND METHODS

30 C57BL/6J mice were assigned to three treatment groups. The RT + TGF-β3 group received local fractionated H&N RT with 66 Gy over five days, combined with TGF-β3-injections at 24-hour intervals. Animals in the RT reference group received identical RT without TGF-β3 treatment. The non-irradiated control group was sham-irradiated according to the same RT schedule. In the follow-up period, body weight and symptoms of oral mucositis and lip dermatitis were monitored. Saliva was sampled at five time points. The experiment was terminated 105 d after the first RT fraction. Submandibular and sublingual glands were preserved, sectioned, and stained with Masson's trichrome to visualize collagen.

RESULTS

A subset of mice in the RT + TGF-β3 group displayed increased severity of oral mucositis and increased weight loss, resulting in a significant increase in mortality. Collagen content was significantly increased in the submandibular and sublingual glands for the surviving RT + TGF-β3 mice, compared with non-irradiated controls. In the RT reference group, collagen content was significantly increased in the submandibular gland only. Both RT groups displayed lower saliva production after treatment compared to controls. TGF-β3 treatment did not impact saliva production.

CONCLUSIONS

When repeatedly administered during fractionated RT at the current dose, TGF-β3 treatment increased acute H&N radiation toxicities and increased mortality. Furthermore, TGF-β3 treatment may increase the severity of radiation-induced salivary gland fibrosis.

Radiation-induced effects on TGF-β and PDGF receptor signaling in cancer-associated fibroblasts

BACKGROUND

Cancer-associated fibroblasts (CAFs) consist of heterogeneous connective tissue cells and are often constituting the most abundant cell type in the tumor stroma. Radiation effects on tumor stromal components like CAFs in the context of radiation treatment is not well-described.

AIM

This study explores potential changes induced by ionizing radiation (IR) on platelet-derived growth factor (PDGF)/PDGFRs and transforming growth factor-beta (TGF-β)/TGFβRs signaling systems in CAFs.

METHODS AND RESULTS

Experiments were carried out by employing primary cultures of human CAFs isolated from freshly resected non-small cell lung carcinoma tumor tissues. CAF cultures from nine donors were treated with one high (1 × 18 Gy) or three fractionated (3 × 6 Gy) radiation doses. Alterations in expression levels of TGFβRII and PDGFRα/β induced by IR were analyzed by western blots and flow cytometry. In the presence or absence of cognate ligands, receptor activation was studied in nonirradiated and irradiated CAFs. Radiation exposure did not exert changes in expression of PDGF or TGF-β receptors in CAFs. Additionally, IR alone was unable to trigger activation of either receptor. The radiation regimens tested did not affect PDGFRβ signaling in the presence of PDGF-BB. In contrast, signaling via pSmad2/3 and pSmad1/5/8 appeared to be down-regulated in irradiated CAFs after stimulation with TGF-β, as compared with controls.

CONCLUSION

Our data demonstrate that IR by itself is insufficient to induce measurable changes in PDGF or TGF-β receptor expression levels or to induce receptor activation in CAFs. However, in the presence of their respective ligands, exposure to radiation at certain doses appear to interfere with TGF-β receptor signaling.

Dual effects of radiotherapy on tumor microenvironment and its contribution towards the development of resistance to immunotherapy in gastrointestinal and thoracic cancers

Successful clinical methods for tumor elimination include a combination of surgical resection, radiotherapy, and chemotherapy. Radiotherapy is one of the crucial components of the cancer treatment regimens which allow to extend patient life expectancy. Current cutting-edge radiotherapy research is focused on the identification of methods that should increase cancer cell sensitivity to radiation and activate anti-cancer immunity mechanisms. Radiation treatment activates various cells of the tumor microenvironment (TME) and impacts tumor growth, angiogenesis, and anti-cancer immunity. Radiotherapy was shown to regulate signaling and anti-cancer functions of various TME immune and vasculature cell components, including tumor-associated macrophages, dendritic cells, endothelial cells, cancer-associated fibroblasts (CAFs), natural killers, and other T cell subsets. Dual effects of radiation, including metastasis-promoting effects and activation of oxidative stress, have been detected, suggesting that radiotherapy triggers heterogeneous targets. In this review, we critically discuss the activation of TME and angiogenesis during radiotherapy which is used to strengthen the effects of novel immunotherapy. Intracellular, genetic, and epigenetic mechanisms of signaling and clinical manipulations of immune responses and oxidative stress by radiotherapy are accented. Current findings indicate that radiotherapy should be considered as a supporting instrument for immunotherapy to limit the cancer-promoting effects of TME. To increase cancer-free survival rates, it is recommended to combine personalized radiation therapy methods with TME-targeting drugs, including immune checkpoint inhibitors.

Low-Dose Non-Targeted Effects and Mitochondrial Control

Non-targeted effects (NTE) have been generally regarded as a low-dose ionizing radiation (IR) phenomenon. Recently, regarding long distant abscopal effects have also been observed at high doses of IR) relevant to antitumor radiation therapy. IR is inducing NTE involving intracellular and extracellular signaling, which may lead to short-ranging bystander effects and distant long-ranging extracellular signaling abscopal effects. Internal and "spontaneous" cellular stress is mostly due to metabolic oxidative stress involving mitochondrial energy production (ATP) through oxidative phosphorylation and/or anaerobic pathways accompanied by the leakage of O₂^- and other radicals from mitochondria during normal or increased cellular energy requirements or to mitochondrial dysfunction. Among external stressors, ionizing radiation (IR) has been shown to very rapidly perturb mitochondrial functions, leading to increased energy supply demands and to ROS/NOS production. Depending on the dose, this affects all types of cell constituents, including DNA, RNA, amino acids, proteins, and membranes, perturbing normal inner cell organization and function, and forcing cells to reorganize the intracellular metabolism and the network of organelles. The reorganization implies intracellular cytoplasmic-nuclear shuttling of important proteins, activation of autophagy, and mitophagy, as well as induction of cell cycle arrest, DNA repair, apoptosis, and senescence. It also includes reprogramming of mitochondrial metabolism as well as genetic and epigenetic control of the expression of genes and proteins in order to ensure cell and tissue survival. At low doses of IR, directly irradiated cells may already exert non-targeted effects (NTE) involving the release of molecular mediators, such as radicals, cytokines, DNA fragments, small RNAs, and proteins (sometimes in the form of extracellular vehicles or exosomes), which can induce damage of unirradiated neighboring bystander or distant (abscopal) cells as well as immune responses. Such non-targeted effects (NTE) are contributing to low-dose phenomena, such as hormesis, adaptive responses, low-dose hypersensitivity, and genomic instability, and they are also promoting suppression and/or activation of immune cells. All of these are parts of the main defense systems of cells and tissues, including IR-induced innate and adaptive immune responses. The present review is focused on the prominent role of mitochondria in these processes, which are determinants of cell survival and anti-tumor RT.

Monitoring TGFβ signaling in irradiated tumors

Transforming growth factor β (TGFβ) is exquisitely regulated under physiological conditions but its activity is highly dysregulated in cancer. All cells make TGFβ and have receptors for the ligand, which is sequestered in the extracellular matrix in a latent form. Ionizing radiation elicits rapid release of TGFβ from these stores, so-called activation, over a wide range of doses and exposures, including low dose (<1Gy) whole-body irradiation, creating an extraordinarily potent signal in the irradiated tissue or tumor. Hence, accurate evaluation of TGFβ activity is complicated because of its ubiquitous distribution as a latent complex. Here we describe conditions for assays that reveal TGFβ activity in situ using either tissue preparations or functional imaging.

Molecular Pathways and Mechanisms of TGFβ in Cancer Therapy

Even though the number of agents that inhibit TGFβ being tested in patients with cancer has grown substantially, clinical benefit from TGFβ inhibition has not yet been achieved. The myriad mechanisms in which TGFβ is protumorigenic may be a key obstacle to its effective deployment; cancer cells frequently employ TGFβ-regulated programs that engender plasticity, enable a permissive tumor microenvironment, and profoundly suppress immune recognition, which is the target of most current early-phase trials of TGFβ inhibitors. Here we discuss the implications of a less well-recognized aspect of TGFβ biology regulating DNA repair that mediates responses to radiation and chemotherapy. In cancers that are TGFβ signaling competent, TGFβ promotes effective DNA repair and suppresses error-prone repair, thus conferring resistance to genotoxic therapies and limiting tumor control. Cancers in which TGFβ signaling is intrinsically compromised are more responsive to standard genotoxic therapy. Recognition that TGFβ is a key moderator of both DNA repair and immunosuppression might be used to synergize combinations of genotoxic therapy and immunotherapy to benefit patients with cancer.

Cancer-associated fibroblasts in radiotherapy: Bystanders or protagonists?

BACKGROUND

The primary goal of radiotherapy (RT) is to induce cellular damage on malignant cells; however, it is becoming increasingly recognized the important role played by the tumor microenvironment (TME) in therapy outcomes. Therapeutic irradiation of tumor lesions provokes profound cellular and biological reconfigurations within the TME that ultimately may influence the fate of the therapy.

MAIN CONTENT

Cancer-associated fibroblasts (CAFs) are known to participate in all stages of cancer progression and are increasingly acknowledged to contribute to therapy resistance. Accumulated evidence suggests that, upon radiation, fibroblasts/CAFs avoid cell death but instead enter a permanent senescent state, which in turn may influence the behavior of tumor cells and other components of the TME. Despite the proposed participation of senescent fibroblasts on tumor radioprotection, it is still incompletely understood the impact that RT has on CAFs and the ultimate role that irradiated CAFs have on therapy outcomes. Some of the current controversies may emerge from generalizing observations obtained using normal fibroblasts and CAFs, which are different cell entities that may respond differently to radiation exposure.

CONCLUSION

In this review we present current knowledge on the field of CAFs role in radiotherapy; we discuss the potential tumorigenic functions of radiation-induced senescent fibroblasts and CAFs and we make an effort to integrate the knowledge emerging from preclinical experimentation with observations from the clinics. Video Abstract.

The Role of TGF-β3 in Radiation Response

Transforming growth factor-beta 3 (TGF-β3) is a ubiquitously expressed multifunctional cytokine involved in a range of physiological and pathological conditions, including embryogenesis, cell cycle regulation, immunoregulation, and fibrogenesis. The cytotoxic effects of ionizing radiation are employed in cancer radiotherapy, but its actions also influence cellular signaling pathways, including that of TGF-β3. Furthermore, the cell cycle regulating and anti-fibrotic effects of TGF-β3 have identified it as a potential mitigator of radiation- and chemotherapy-induced toxicity in healthy tissue. This review discusses the radiobiology of TGF-β3, its induction in tissue by ionizing radiation, and its potential radioprotective and anti-fibrotic effects.

Radiation-induced pulmonary fibrosis: roles of therapy-induced senescence and microRNAs

PURPOSE

Progressive, irreversible radiation-induced pulmonary fibrosis (RIPF) is a clinically significant intermediate- to a late-occurring side effect of radiotherapy. Known mechanisms of RIPF include oxidative stress-induced activation of TGF-β with activation of SMAD signaling, TNF-α elaboration, and activation of the Angiotensin Converting Enzyme (ACE) mediated production of angiotensin II with resulting activation of profibrotic cytokine signaling and vasoconstriction. The pioneering work of John Moulder, to whom this paper is dedicated, and several of his colleagues demonstrated that inhibiting the conversion of ACE with drugs such as Captopril, Enalapril, and Losartan can ameliorate radiation fibrosis in various tissues. While this work led several groups to probe mechanism-based pharmacological mitigation of RIPF, in this article, we explore and discuss the roles of microRNAs (miRNA) and therapy-induced senescence (TIS) in the pathogenesis of and potential biomarkers for RIPF.

CONCLUSION

Our analysis of the published literature in the last decade on RIPF, miRNA, and TIS identifies TIS as a mechanism in the onset and progression of RIPF, which is regulated through several miRNAs. This work may lead to the discovery and development of the next generation of miRNA therapeutics and/or the repurposing of approved pharmaceutical agents and the development of early biomarker panels to predict RIPF.

A review of the biology and therapeutic implications of cancer-associated fibroblasts (CAFs) in muscle-invasive bladder cancer

Cancer-associated fibroblasts (CAFs) play a fundamental role in the development of cancers and their response to therapy. In recent years, CAFs have returned to the spotlight as researchers work to unpick the mechanisms by which they impact tumour evolution and therapy responses. However, study of CAFs has largely been restricted to a select number of common cancers, whereas research into CAF biology in bladder cancer has been relatively neglected. In this review, we explore the basics of CAF biology including the numerous potential cellular origins of CAFs, alongside mechanisms of CAF activation and their diverse functionality. We find CAFs play an important role in the progression of bladder cancer with significant implications on tumour cell signaling, epithelial to mesenchymal transition and the capacity to modify components of the immune system. In addition, we highlight some of the landmark papers describing CAF heterogeneity and find trends in the literature to suggest that the iCAF and myCAF subtypes defined in bladder cancer share common characteristics with CAF subtypes described in other settings such as breast and pancreatic cancer. Moreover, based on findings in other common cancers we identify key therapeutic challenges associated with CAFs, such as the lack of specific CAF markers, the paucity of research into bladder-specific CAFs and their relationship with therapies such as radiotherapy. Of relevance, we describe a variety of strategies used to target CAFs in several common cancers, paying particular attention to TGFβ signaling as a prominent regulator of CAF activation. In doing so, we find parallels with bladder cancer that suggest CAF targeting may advance therapeutic options in this setting and improve the current poor survival outcomes in bladder cancer which sadly remain largely unchanged over recent decades.

Radiotherapy-induced oxidative stress and fibrosis in breast cancer are suppressed by vactosertib, a novel, orally bioavailable TGF-β/ALK5 inhibitor

Radio-resistance resulting from radiotherapy-induced fibrosis is a major clinical obstacle in breast cancer treatment because it typically leads to cancer recurrence, treatment failure, and patient death. Transforming growth factor-β (TGF-β) is a key signal messenger in fibrosis, which plays an important role in radiation-induced fibrosis and cancer stem cell (CSC) development, may be mediated through the generation of oxidative stress. This study was conducted to confirm the efficacy of vactosertib, a TGF-β/ALK5 inhibitor, as a potent inhibitor in radiation-induced oxidative stress generation, fibrosis and CSC development. We used a 4T1-Luc allograft BALB/c syngeneic mouse model and 4T1-Luc and MDA-MB-231 cells for histological analysis, qRT-PCR, western blotting, ROS analysis, mammosphere formation analysis, monolayer fluorescence imaging analysis. Radiotherapy induces TGF-β signaling, oxidative stress markers (4-HNE, NOX2, NOX4, PRDX1, NRF2, HO-1, NQO-1), fibrosis markers (PAI-1, α-SMA, FIBRONECTIN, COL1A1), and CSC properties. However, combination therapy with vactosertib not only inhibits these radiation-induced markers and properties by blocking TGF-β signaling, but also enhances the anticancer effect of radiation by reducing the volume of breast cancer. Therefore, these data suggest that vactosertib can effectively reduce radiation fibrosis and resistance in breast cancer treatment by inhibiting radiation-induced TGF-β signaling and oxidative stress, fibrosis, and CSC.

A ‘Hybrid’ Radiotherapy Regimen Designed for Immunomodulation: Combining High-Dose Radiotherapy with Low-Dose Radiotherapy

Simple Summary

Radiotherapy is an important cancer treatment. Aside from its direct killing effect, it also affects anti-tumor immunity. However, radiotherapy’s immune effect is not clear; it depends on the dose and fraction, cancer type, combined immunotherapy, and many other factors. Studies have focused on the optimal radiotherapy regimen to stimulate anti-tumor immunity, but conflicts exist, especially regarding the best radiation dose and fractions. Interestingly, high-dose radiotherapy and low-dose radiotherapy have complementary effects on stimulating anti-tumor immunity. Preclinical studies supporting this finding have accumulated, but gaps between theory and clinical practice still exist. This review summarizes the evidence supporting the use of this ‘hybrid’ radiotherapy approach to effectively stimulate anti-tumor immunity, explains the immune mechanisms of this combination, raises questions that must be addressed in clinical practice, and provides ideas for designing individualized treatment to increase efficiency in stimulating anti-tumor immunity using high-dose plus low-dose radiotherapy.

Abstract

Radiotherapy (RT) affects anti-tumor immunity. However, the exact impact of RT on anti-tumor immune response differs among cancer types, RT dose and fractions, patients’ innate immunity, and many other factors. There are conflicting findings on the optimal radiation dose and fractions to stimulate effective anti-tumor immunity. High-dose radiotherapy (HDRT) acts in the same way as a double-edged sword in stimulating anti-tumor immunity, while low-dose radiotherapy (LDRT) seems to play a vital role in modulating the tumor immune microenvironment. Recent preclinical data suggest that a ‘hybrid’ radiotherapy regimen, which refers to combining HDRT with LDRT, can reap the advantages of both. Clinical data have also indicated a promising potential. However, there are still questions to be addressed in order to put this novel combination therapy into clinical practice. For example, the selection of treatment site, treatment volume, the sequencing of high-dose radiotherapy and low-dose radiotherapy, combined immunotherapy, and so on. This review summarizes the current evidence supporting the use of HDRT + LDRT, explains possible immune biology mechanisms of this ‘hybrid’ radiotherapy, raises questions to be considered when working out individualized treatment plans, and lists possible avenues to increase efficiency in stimulating anti-tumor immunity using high-dose plus low-dose radiotherapy.