Ki26894, a novel transforming growth factor-beta type I receptor kinase inhibitor, inhibits in vitro invasion and in vivo bone metastasis of a human breast cancer cell line

Advances and Challenges in Targeting TGF-β Isoforms for Therapeutic Intervention of Cancer: A Mechanism-Based Perspective

The TGF-β family is a group of 25 kDa secretory cytokines, in mammals consisting of three dimeric isoforms (TGF-βs 1, 2, and 3), each encoded on a separate gene with unique regulatory elements. Each isoform plays unique, diverse, and pivotal roles in cell growth, survival, immune response, and differentiation. However, many researchers in the TGF-β field often mistakenly assume a uniform functionality among all three isoforms. Although TGF-βs are essential for normal development and many cellular and physiological processes, their dysregulated expression contributes significantly to various diseases. Notably, they drive conditions like fibrosis and tumor metastasis/progression. To counter these pathologies, extensive efforts have been directed towards targeting TGF-βs, resulting in the development of a range of TGF-β inhibitors. Despite some clinical success, these agents have yet to reach their full potential in the treatment of cancers. A significant challenge rests in effectively targeting TGF-βs' pathological functions while preserving their physiological roles. Many existing approaches collectively target all three isoforms, failing to target just the specific deregulated ones. Additionally, most strategies tackle the entire TGF-β signaling pathway instead of focusing on disease-specific components or preferentially targeting tumors. This review gives a unique historical overview of the TGF-β field often missed in other reviews and provides a current landscape of TGF-β research, emphasizing isoform-specific functions and disease implications. The review then delves into ongoing therapeutic strategies in cancer, stressing the need for more tools that target specific isoforms and disease-related pathway components, advocating mechanism-based and refined approaches to enhance the effectiveness of TGF-β-targeted cancer therapies.

Deciphering the Dual Role of Heligmosomoides polygyrus Antigens in Macrophage Modulation and Breast Cancer Cell Growth

In our study, we explored how parasitic nematodes, specifically Heligmosomoides polygyrus, influence the immune response, focusing on their potential role in tumor growth. The study aimed to understand the mechanisms by which these parasites modify immune cell activation, particularly in macrophages, and how this might create an environment conducive to tumor growth. Our methods involved analyzing the effects of H. polygyrus excretory-secretory antigens on macrophage activation and their subsequent impact on breast cancer cell lines EMT6 and 4T1. We observed that these antigens significantly increased the expression of genes associated with both pro-inflammatory and anti-inflammatory molecules, such as inducible nitric oxide synthase, TNF-α, (Tumor Necrosis Factor) Il-6 (Interleukin), and arginase. Additionally, we observed changes in the expression of macrophage surface receptors like CD11b, F4/80, and TLR4 (Toll-like receptor 4). Our findings indicate that the antigens from H. polygyrus markedly alter macrophage behavior and increase the proliferation of breast cancer cells in a laboratory setting. This study contributes to a deeper understanding of the complex interactions between parasitic infections and cancer development, highlighting the need for further research in this area to develop potential new strategies for cancer treatment.

Multifaceted TGF-β signaling, a master regulator: From bench-to-bedside, intricacies, and complexities

Physiological embryogenesis and adult tissue homeostasis are regulated by transforming growth factor-β (TGF-β), an evolutionarily conserved family of secreted polypeptide factors, acting in an autocrine and paracrine manner. The role of TGF-β in inflammation, fibrosis, and cancer is complex and sometimes even contradictory, exhibiting either inhibitory or promoting effects depending on the stage of the disease. Under pathological conditions, especially fibrosis and cancer, overexpressed TGF-β causes extracellular matrix deposition, epithelial-mesenchymal transition, cancer-associated fibroblast formation, and/or angiogenesis. In this review article, we have tried to dive deep into the mechanism of action of TGF-β in inflammation, fibrosis, and carcinogenesis. As TGF-β and its downstream signaling mechanism are implicated in fibrosis and carcinogenesis blocking this signaling mechanism appears to be a promising avenue. However, targeting TGF-β carries substantial risk as this pathway is implicated in multiple homeostatic processes and is also known to have tumor-suppressor functions. There is a need for careful dosing of TGF-β drugs for therapeutic use and patient selection.

Exploring the dynamic interplay between cancer stem cells and the tumor microenvironment: implications for novel therapeutic strategies

Cancer stem cells (CSCs) have emerged as key contributors to tumor initiation, growth, and metastasis. In addition, CSCs play a significant role in inducing immune evasion, thereby compromising the effectiveness of cancer treatments. The reciprocal communication between CSCs and the tumor microenvironment (TME) is observed, with the TME providing a supportive niche for CSC survival and self-renewal, while CSCs, in turn, influence the polarization and persistence of the TME, promoting an immunosuppressive state. Consequently, these interactions hinder the efficacy of current cancer therapies, necessitating the exploration of novel therapeutic approaches to modulate the TME and target CSCs. In this review, we highlight the intricate strategies employed by CSCs to evade immune surveillance and develop resistance to therapies. Furthermore, we examine the dynamic interplay between CSCs and the TME, shedding light on how this interaction impacts cancer progression. Moreover, we provide an overview of advanced therapeutic strategies that specifically target CSCs and the TME, which hold promise for future clinical and translational studies in cancer treatment.

TGF-β signaling pathway: Therapeutic targeting and potential for anti-cancer immunity

Transforming growth factor-β (TGFβ) is a pleiotropic secretory cytokine exhibiting both cancer-inhibitory and promoting properties. It transmits its signals via Suppressor of Mother against Decapentaplegic (SMAD) and non-SMAD pathways and regulates cell proliferation, differentiation, invasion, migration, and apoptosis. In non-cancer and early-stage cancer cells, TGFβ signaling suppresses cancer progression via inducing apoptosis, cell cycle arrest, or anti-proliferation, and promoting cell differentiation. On the other hand, TGFβ may also act as an oncogene in advanced stages of tumors, wherein it develops immune-suppressive tumor microenvironments and induces the proliferation of cancer cells, invasion, angiogenesis, tumorigenesis, and metastasis. Higher TGFβ expression leads to the instigation and development of cancer. Therefore, suppressing TGFβ signals may present a potential treatment option for inhibiting tumorigenesis and metastasis. Different inhibitory molecules, including ligand traps, anti-sense oligo-nucleotides, small molecule receptor-kinase inhibitors, small molecule inhibitors, and vaccines, have been developed and clinically trialed for blocking the TGFβ signaling pathway. These molecules are not pro-oncogenic response-specific but block all signaling effects induced by TGFβ. Nonetheless, targeting the activation of TGFβ signaling with maximized specificity and minimized toxicity can enhance the efficacy of therapeutic approaches against this signaling pathway. The molecules that are used to target TGFβ are non-cytotoxic to cancer cells but designed to curtail the over-activation of invasion and metastasis driving TGFβ signaling in stromal and cancer cells. Here, we discussed the critical role of TGFβ in tumorigenesis, and metastasis, as well as the outcome and the promising achievement of TGFβ inhibitory molecules in the treatment of cancer.

Circulating α-Klotho Counteracts Transforming Growth Factor-β-Induced Sarcopenia

α-Klotho is a longevity-related protein. Its deficiency shortens lifespan with prominent senescent phenotypes, including muscle atrophy and weakness in mice. α-Klotho has two forms: membrane α-Klotho and circulating α-Klotho (c-α-Klotho). Loss of membrane α-Klotho impairs a phosphaturic effect, thereby accelerating phosphate-induced aging. However, the mechanisms of senescence on c-α-Klotho loss remain largely unknown. Here, we show that, with the aging of wild-type mice, c-α-Klotho declined, whereas Smad2, an intracellular transforming growth factor (TGF)-β effector, became activated in skeletal muscle. Moreover, c-α-Klotho suppressed muscle-wasting TGF-β molecules, including myostatin, growth and differentiation factor 11, activin, and TGF-β1, through binding to ligands as well as type I and type II serine/threonine kinase receptors. Indeed, c-α-Klotho reversed impaired in vitro myogenesis caused by these TGF-βs. Oral administration of Ki26894, a small-molecule inhibitor of type I receptors for these TGF-βs, restored muscle atrophy and weakness in α-Klotho (-/-) mice and in elderly wild-type mice by suppression of activated Smad2 and up-regulated Cdkn1a (p21) transcript, a target of phosphorylated Smad2. Ki26894 also induced the slow to fast myofiber switch. These findings show c-α-Klotho's potential as a circulating inhibitor counteracting TGF-β-induced sarcopenia. A novel therapy involving TGF-β blockade could thus be developed to prevent sarcopenia.

Tumour-derived exosomal piR-25783 promotes omental metastasis of ovarian carcinoma by inducing the fibroblast to myofibroblast transition

Ovarian carcinoma inherently possesses a distinct metastatic organotropism for the adipose-rich omentum, contributing to disease progression. Although the premetastatic microenvironment (PMM) has been known to often play a prometastatic role during the process, incomplete mechanistic insight into PMM formation has prevented its therapeutic targeting. Omental fibroblasts can be activated by tumour cells to differentiate into myofibroblasts, termed the fibroblast-to-myofibroblast transition (FMT), which, in turn, enhances cancer aggressiveness. Here, we report crosstalk between cancer cells and omental fibroblasts through exosomal piR-25783, which fuels tumour metastasis. Tumour cell-secreted exosomal piR-25783 activates the TGF-β/SMAD2/SMAD3 pathway in fibroblasts and promotes the FMT in the omentum along with the secretion of various cytokines and elevation of proliferative, migratory, and invasive properties, contributing to the formation of PMMs. Furthermore, piR-25783-induced myofibroblasts promote tumour implantation and growth in the omentum. In addition, the overexpression of piR-25783 in ovarian carcinoma is associated with unfavourable clinicopathological characteristics and shorter survival. In this study, we provide molecular, functional, and translational evidence suggesting that exosomal piR-25783 plays an important role in the formation of PMMs and the development of metastatic diseases in vitro and in vivo and may serve as a potential therapeutic target for ovarian carcinoma with metastasis.

xcore: an R package for inference of gene expression regulators

BACKGROUND

Elucidating the Transcription Factors (TFs) that drive the gene expression changes in a given experiment is a common question asked by researchers. The existing methods rely on the predicted Transcription Factor Binding Site (TFBS) to model the changes in the motif activity. Such methods only work for TFs that have a motif and assume the TF binding profile is the same in all cell types.

RESULTS

Given the wealth of the ChIP-seq data available for a wide range of the TFs in various cell types, we propose that gene expression modeling can be done using ChIP-seq "signatures" directly, effectively skipping the motif finding and TFBS prediction steps. We present xcore, an R package that allows TF activity modeling based on ChIP-seq signatures and the user's gene expression data. We also provide xcoredata a companion data package that provides a collection of preprocessed ChIP-seq signatures. We demonstrate that xcore leads to biologically relevant predictions using transforming growth factor beta induced epithelial-mesenchymal transition time-courses, rinderpest infection time-courses, and embryonic stem cells differentiated to cardiomyocytes time-course profiled with Cap Analysis Gene Expression.

CONCLUSIONS

xcore provides a simple analytical framework for gene expression modeling using linear models that can be easily incorporated into differential expression analysis pipelines. Taking advantage of public ChIP-seq databases, xcore can identify meaningful molecular signatures and relevant ChIP-seq experiments.

TGF-β at the crossroads of multiple prognosis in breast cancer, and beyond

Transforming growth factor β (TGF-β), a pluripotent cytokine and a multifunctional growth factor has a crucial role in varied biological mechanisms like invasion, migration, epithelial-mesenchymal transition, apoptosis, wound healing, and immunosuppression. Moreover, it also has an imperative role both in normal mammary gland development as well as breast carcinogenesis. TGF-β has shown to have a paradoxical role in breast carcinogenesis, by transitioning from a growth inhibitor to a growth promoter with the disease advancement. The inter-communication and crosstalk of TGF-β with different signaling pathways has strengthened the likelihood to explore it as a comprehensive biomarker. In the last two decades, TGF-β has been studied extensively and has been found to be a promising biomarker for early detection, disease monitoring, treatment selection, and tumor progression making it beneficial for disease management. In this review, we focus on the signaling pathways and biological activities of the TGF-β family in breast cancer pathogenesis and its role as a circulatory and independent biomarker for breast cancer progression and metastasis. Moreover, this review highlights TGF-β as a drug target, and the underlying mechanisms through which it is involved in tumorigenesis that will aid in the development of varied therapies targeting the different stages of breast cancer.

Synthesis and preclinical evaluation of [11C]LR111 and [18F]EW-7197 as PET tracers of the activin-receptor like kinase-5

The transforming growth factor β (TGFβ) pathway plays a complex role in cancer biology, being involved in both tumour suppression as well as promotion. Overactive TGFβ signalling has been linked to multiple diseases, including cancer, pulmonary arterial hypertension, and fibrosis. One of the key meditators within this pathway is the TGFβ type I receptor, also termed activin receptor-like kinase 5 (ALK5). ALK5 expression level is a key determinant of TGFβ signalling intensity and duration, and perturbation has been linked to diseases. A validated ALK5 positron emission tomography (PET) tracer creates an opportunity, therefore, to study its role in human diseases. To develop ALK5 PET tracers, two small molecule ALK5 kinase inhibitors were selected as lead compounds, which were labelled with carbon-11 and fluorine-18, respectively. [¹¹C]LR111 was synthesized with a yield of 17 ± 6%, a molar activity of 126 ± 79 GBq·μmol^-1 and a purity of >95% (n = 44). [¹⁸F]EW-7197 was synthesized with a yield of 10 ± 5%, a molar activity of 183 ± 126 GBq·μmol^-1 and a purity of >95% (n = 11). Metabolic stability was evaluated in vivo in mice, showing 39 ± 2% of intact [¹¹C]LR111 and 21 ± 2% of intact [¹⁸F]EW-7197 in blood plasma at 45 min p.i. In vitro binding experiments were conducted in breast cancer MDA-MB-231 and lung cancer A431 cell lines. In addition, both tracers were used for PET imaging in MDA-MB-231 xenograft models. Selective uptake of [¹⁸F]EW-7197 and [¹¹C]LR111 was observed in MDA-MB-231 cells, in the MDA-MB-231 tumour xenografts in vivo and in the autoradiograms. As [¹¹C]LR111 and [¹⁸F]EW-7197 showed selectivity of binding to ALK5 in vivo and in vitro. Both tracers are thereby valuable tools for the detection of ALK5 activity.

Cancer-associated fibroblasts in breast cancer: Challenges and opportunities

The tumor microenvironment is proposed to contribute substantially to the progression of cancers, including breast cancer. Cancer-associated fibroblasts (CAFs) are the most abundant components of the tumor microenvironment. Studies have revealed that CAFs in breast cancer originate from several types of cells and promote breast cancer malignancy by secreting factors, generating exosomes, releasing nutrients, reshaping the extracellular matrix, and suppressing the function of immune cells. CAFs are also becoming therapeutic targets for breast cancer due to their specific distribution in tumors and their unique biomarkers. Agents interrupting the effect of CAFs on surrounding cells have been developed and applied in clinical trials. Here, we reviewed studies examining the heterogeneity of CAFs in breast cancer and expression patterns of CAF markers in different subtypes of breast cancer. We hope that summarizing CAF-related studies from a historical perspective will help to accelerate the development of CAF-targeted therapeutic strategies for breast cancer.

The Role of TGF-β in Bone Metastases

Complications associated with advanced cancer are a major clinical challenge and, if associated with bone metastases, worsen the prognosis and compromise the survival of the patients. Breast and prostate cancer cells exhibit a high propensity to metastasize to bone. The bone microenvironment is unique, providing fertile soil for cancer cell propagation, while mineralized bone matrices store potent growth factors and cytokines. Biologically active transforming growth factor β (TGF-β), one of the most abundant growth factors, is released following tumor-induced osteoclastic bone resorption. TGF-β promotes tumor cell secretion of factors that accelerate bone loss and fuel tumor cells to colonize. Thus, TGF-β is critical for driving the feed-forward vicious cycle of tumor growth in bone. Further, TGF-β promotes epithelial-mesenchymal transition (EMT), increasing cell invasiveness, angiogenesis, and metastatic progression. Emerging evidence shows TGF-β suppresses immune responses, enabling opportunistic cancer cells to escape immune checkpoints and promote bone metastases. Blocking TGF-β signaling pathways could disrupt the vicious cycle, revert EMT, and enhance immune response. However, TGF-β’s dual role as both tumor suppressor and enhancer presents a significant challenge in developing therapeutics that target TGF-β signaling. This review presents TGF-β’s role in cancer progression and bone metastases, while highlighting current perspectives on the therapeutic potential of targeting TGF-β pathways.

Visualization of the cancer cell cycle by tissue-clearing technology using the Fucci reporter system

Tissue-clearing technology is an emerging imaging technique currently utilized not only in neuroscience research but also in cancer research. In our previous reports, tissue-clearing methods were used for the detection of metastatic tumors. Here, we showed that the cell cycles of primary and metastatic tumors were visualized by tissue-clearing methods using a reporter system. First, we established cancer cell lines stably expressing fluorescent ubiquitination-based cell cycle indicator (Fucci) reporter with widely used cancer cell lines A549 and 4T1. Fluorescence patterns of the Fucci reporter were investigated in various tumor inoculation models in mice. Interestingly, fluorescence patterns of the Fucci reporter of tumor colonies were different between various organs, and even among colonies in the same organs. The effects of antitumor drugs were also evaluated using these Fucci reporter cells. Of the three antitumor drugs studied, 5-fluorouracil treatment on 4T1-Fucci cells resulted in characteristic fluorescent patterns by the induction of G2 /M arrest both in vitro and in vivo. Thus, the combination of a tissue-clearing method with the Fucci reporter is useful for analyzing the mechanisms of cancer metastasis and drug resistance.

The Anticancer Properties of Silibinin: Its Molecular Mechanism and Therapeutic Effect in Breast Cancer

BACKGROUND

Silibinin (SB), the main component of Silymarin (SM), is a natural substance obtained from the seeds of the milk thistle. SM contains up to 70% of SB as two isoforms: A and B. It has an antioxidant and anti-inflammatory effect on hepatocytes and is known to inhibit cell proliferation, induce apoptosis, and curb angiogenesis. SB has demonstrated activity against many cancers, such as skin, liver, lung, bladder, and breast carcinomas.

METHODS

This review presents current knowledge of the use of SM in breast cancer, this being one of the most common types of cancer in women. It describes selected molecular mechanisms of the action of SM; for example, although SB influences both Estrogen Receptors (ER), α and β, it has opposite effects on the two. Its action on ERα influences the PI3K/AKT/mTOR and RAS/ERK signaling pathways, while by up-regulating ERβ, it increases the numbers of apoptotic cells. In addition, ERα is involved in SB-induced autophagy, while ERβ is not. Interestingly, SB also inhibits metastasis by suppressing TGF-β2 expression, thus suppressing Epithelial to Mesenchymal Transition (EMT). It also influences migration and invasive potential via the Jak2/STAT3 pathway.

RESULTS

SB may be a promising enhancement of BC treatment: when combined with chemotherapeutic drugs such as carboplatin, cisplatin, and doxorubicin, the combination exerts a synergistic effect against cancer cells. This may be of value when treating aggressive types of mammary carcinoma.

CONCLUSION

Summarizing, SB inhibits proliferation, induces apoptosis, and restrains metastasis via several mechanisms. It is possible to combine SB with different anticancer drugs, an approach that represents a promising therapeutic strategy for patients suffering from BC.

Extracellular matrix and its therapeutic potential for cancer treatment

The extracellular matrix (ECM) is one of the major components of tumors that plays multiple crucial roles, including mechanical support, modulation of the microenvironment, and a source of signaling molecules. The quantity and cross-linking status of ECM components are major factors determining tissue stiffness. During tumorigenesis, the interplay between cancer cells and the tumor microenvironment (TME) often results in the stiffness of the ECM, leading to aberrant mechanotransduction and further malignant transformation. Therefore, a comprehensive understanding of ECM dysregulation in the TME would contribute to the discovery of promising therapeutic targets for cancer treatment. Herein, we summarized the knowledge concerning the following: (1) major ECM constituents and their functions in both normal and malignant conditions; (2) the interplay between cancer cells and the ECM in the TME; (3) key receptors for mechanotransduction and their alteration during carcinogenesis; and (4) the current therapeutic strategies targeting aberrant ECM for cancer treatment.

Novel therapies emerging in oncology to target the TGF-β pathway

The TGF-β signaling pathway governs key cellular processes under physiologic conditions and is deregulated in many pathologies, including cancer. TGF-β is a multifunctional cytokine that acts in a cell- and context-dependent manner as a tumor promoter or tumor suppressor. As a tumor promoter, the TGF-β pathway enhances cell proliferation, migratory invasion, metastatic spread within the tumor microenvironment and suppresses immunosurveillance. Collectively, the pleiotropic nature of TGF-β signaling contributes to drug resistance, tumor escape and undermines clinical response to therapy. Based upon a wealth of preclinical studies, the TGF-β pathway has been pharmacologically targeted using small molecule inhibitors, TGF-β-directed chimeric monoclonal antibodies, ligand traps, antisense oligonucleotides and vaccines that have been now evaluated in clinical trials. Here, we have assessed the safety and efficacy of TGF-β pathway antagonists from multiple drug classes that have been evaluated in completed and ongoing trials. We highlight Vactosertib, a highly potent small molecule TGF-β type 1 receptor kinase inhibitor that is well-tolerated with an acceptable safety profile that has shown efficacy against multiple types of cancer. The TGF-β ligand traps Bintrafusp alfa (a bifunctional conjugate that binds TGF-β and PD-L1), AVID200 (a computationally designed trap of TGF-β receptor ectodomains fused to an Fc domain) and Luspatercept (a recombinant fusion that links the activin receptor IIb to IgG) offer new ways to fight difficult-to-treat cancers. While TGF-β pathway antagonists are rapidly emerging as highly promising, safe and effective anticancer agents, significant challenges remain. Minimizing the unintentional inhibition of tumor-suppressing activity and inflammatory effects with the desired restraint on tumor-promoting activities has impeded the clinical development of TGF-β pathway antagonists. A better understanding of the mechanistic details of the TGF-β pathway should lead to more effective TGF-β antagonists and uncover biomarkers that better stratify patient selection, improve patient responses and further the clinical development of TGF-β antagonists.

Whole-organ analysis of TGF-β-mediated remodelling of the tumour microenvironment by tissue clearing

Tissue clearing is one of the most powerful strategies for a comprehensive analysis of disease progression. Here, we established an integrated pipeline that combines tissue clearing, 3D imaging, and machine learning and applied to a mouse tumour model of experimental lung metastasis using human lung adenocarcinoma A549 cells. This pipeline provided the spatial information of the tumour microenvironment. We further explored the role of transforming growth factor-β (TGF-β) in cancer metastasis. TGF-β-stimulated cancer cells enhanced metastatic colonization of unstimulated-cancer cells in vivo when both cells were mixed. RNA-sequencing analysis showed that expression of the genes related to coagulation and inflammation were up-regulated in TGF-β-stimulated cancer cells. Further, whole-organ analysis revealed accumulation of platelets or macrophages with TGF-β-stimulated cancer cells, suggesting that TGF-β might promote remodelling of the tumour microenvironment, enhancing the colonization of cancer cells. Hence, our integrated pipeline for 3D profiling will help the understanding of the tumour microenvironment.

Role and clinical significance of TGF‑β1 and TGF‑βR1 in malignant tumors (Review)

The appearance and growth of malignant tumors is a complicated process that is regulated by a number of genes. In recent years, studies have revealed that the transforming growth factor-β (TGF-β) signaling pathway serves an important role in cell cycle regulation, growth and development, differentiation, extracellular matrix synthesis and immune response. Notably, two members of the TGF-β signaling pathway, TGF-β1 and TGF-β receptor 1 (TGF-βR1), are highly expressed in a variety of tumors, such as breast cancer, colon cancer, gastric cancer and hepatocellular carcinoma. Moreover, an increasing number of studies have demonstrated that TGF-β1 and TGF-βR1 promote proliferation, migration and epithelial-mesenchymal transition of tumor cells by activating other signaling pathways, signaling molecules or microRNAs (miRs), such as the NF-κB signaling pathway and miR-133b. In addition, some inhibitors targeting TGF-β1 and TGF-βR1 have exhibited positive effects in in vitro experiments. The present review discusses the association between TGF-β1 or TGF-βR1 and tumors, and the development of some inhibitors, hoping to provide more approaches to help identify novel tumor markers to restrain and cure tumors.

Recent progress in TGF-β inhibitors for cancer therapy

Transforming growth factor-β (TGF-β) is a multifunctional cytokine that is involved in proliferation, metastasis, and many other important processes in malignancy. Inhibitors targeting TGF-β have been considered by pharmaceutical companies for cancer therapy, and some of them are in clinical trial now. Unfortunately, several of these programs have recently been relinquished, and most companies that remain in the contest are progressing slowly and cautiously. This review summarizes the TGF-β signal transduction pathway, its roles in oncogenesis and fibrotic diseases, and advancements in antibodies and small-molecule inhibitors of TGF-β.

Role of the bone microenvironment in bone metastasis of malignant tumors - therapeutic implications

BACKGROUND

Bone is one of the most common sites for solid tumor metastasis. Bone metastasis of a malignant tumor seriously affects the quality of life and the overall survival of patients. Evidence has suggested that bone provides a favorable microenvironment that enables disseminated tumor cells to home, proliferate and colonize, leading to the formation of metastases. In the process of bone metastasis the bone microenvironment may be considered as an orchestra that plays a dissonant melody through blending (e.g. cross-talk between osteoclasts, osteoblasts and/or other cells), adding (e.g. a variety of biological factors) or taking away (e.g. blocking a specific pathway) players.

CONCLUSIONS

Here, we review the normal bone microenvironment, bone microenvironment-related factors that promote bone metastasis, as well as mechanisms underlying bone metastasis. In addition, we elude on directions for clinical bone metastasis management, focusing on potential therapeutic approaches to target bone microenvironment-related factors, including bisphosphonate, denosumab, CXCR4/CXCL12 antagonists and cathepsin K inhibitors.

Transforming growth factor β signaling pathway: A promising therapeutic target for cancer

Transforming growth factor β (TGF-β) is part of the transforming growth factor β superfamily which is involved in many physiological processes and closely related to the carcinogenesis. Here, we discuss the TGF-β structure, function, and its canonical Smads signaling pathway. Importantly, TGF-β has been proved that it plays both tumor suppressor as well as an activator role in tumor progression. In an early stage, TGF-β inhibits cell proliferation and is involved in cell apoptosis. In an advanced tumor, TGF-β signaling pathway induces tumor invasion and metastasis through promoting angiogenesis, epithelial-mesenchymal transition, and immune escape. Furthermore, we are centered on updated research results into the inhibitors as drugs which have been studied in preclinical or clinical trials in tumor carcinogenesis to prevent the TGF-β synthesis and block its signaling pathways such as antibodies, antisense molecules, and small-molecule tyrosine kinase inhibitors. Thus, it is highlighting the crucial role of TGF-β in tumor therapy and may provide opportunities for the new antitumor strategies in patients with cancer.

Current status and future prospects of transforming growth factor-β as a potential prognostic and therapeutic target in the treatment of breast cancer

The transforming growth factor-β (TGF-β) signaling pathway is one of the important pathways involved in the cancer cell proliferation, invasion, migration, angiogenesis, apoptosis, as well as in metastasis by agitation or invasion of metastasis-related factors, including matrix metalloproteinase (MMP), epithelial-to-mesenchymal transition (EMT), tumor microenvironment (TME), cancer stem cells (CSCs), and cell adhesion molecules (CAMs). These data suggest its potential value as a therapeutic object in the treatment of malignancies including breast cancer. Several pharmacological approaches have been established to suppress TGF-β pathway; such as vaccines, small molecular inhibitors, antisense oligonucleotides, and monoclonal antibodies. Some of these are now approved by the US Food and Drug Administration for targeting the TGF-β signaling pathway. This study attempts to summarize the current data about the functions of TGF-β in cancer cells, and their probable application in the cancer therapy with a specific emphasis on recent preclinical and clinical research in the treatment of breast cancer and its prognostic value.

Cancer-associated fibroblasts as key regulators of the breast cancer tumor microenvironment

Tumor cells exist in close proximity with non-malignant cells. Extensive and multilayered crosstalk between tumor cells and stromal cells tailors the tumor microenvironment (TME) to support survival, growth, and metastasis. Fibroblasts are one of the largest populations of non-malignant host cells that can be found within the TME of breast, pancreatic, and prostate tumors. Substantial scientific evidence has shown that these cancer-associated fibroblasts (CAFs) are not only associated with tumors by proximity but are also actively recruited to developing tumors where they can influence other cells of the TME as well as influencing tumor cell survival and metastasis. This review discusses the impact of CAFs on breast cancer biology and highlights their heterogeneity, origin and their role in tumor progression, ECM remodeling, therapy resistance, metastasis, and the challenges ahead of targeting CAFs to improve therapy response.

Therapeutic potential of pharmacological TGF-β signaling pathway inhibitors in the pathogenesis of breast cancer

The TGF-β signaling pathway plays an important role in cancer cell proliferation, growth, inflammation, angiogenesis, and metastasis. The role of TGF-β signaling in the pathogenesis of breast cancer is complex. TGF-β acts as a tumor suppressor in the early stages of disease, and as a tumor promoter in its later stages. Over-activation of the TGF-β signaling pathway and over-expression of the TGF-β receptors are frequently found in breast tumors. Suppression of TGF-β pathway using biological or pharmacological inhibitors is a potentially novel therapeutic approach for breast cancer treatment. This review summarizes the regulatory role of TGF-β signaling in the pathogenesis of breast cancer for a better understanding and hence a better management of this disease.

Bone metastasis: Interaction between cancer cells and bone microenvironment

BACKGROUND

Bone is one of the most common target organs for cancer metastasis, especially in patients with advanced breast and prostate cancers. Despite recent advances in therapeutic approaches, bone metastases remain incurable and produce multiple complications called skeletal-related events, including hypercalcemia, pathological fractures, spinal compression, and bone pain, which are associated with poor prognosis.

HIGHLIGHT

Although the precise mechanisms are yet to be fully elucidated, accumulating evidence suggests that bone provides a favorable microenvironment that enables circulating cancer cells to home, proliferate, and colonize, resulting in the formation of metastasis. Cancer cells that metastasize to bone also possess unique features, enabling them to utilize the bone microenvironment. Thus, communication between cancer cells and bone is believed to be critical for the development and progression of bone metastases.

CONCLUSION

Continued studies are warranted to understand the molecular mechanisms underlying bone metastases and to develop mechanism-based and effective therapeutic interventions.

Efficacy of an orally active small-molecule inhibitor of RANKL in bone metastasis

Bone is one of the preferred sites for the metastasis of malignant tumours, such as breast cancer, lung cancer and malignant melanoma. Tumour cells colonizing bone have the capacity to induce the expression of receptor activator of nuclear factor-κB ligand (RANKL), which promotes osteoclast differentiation and activation. Tumour-induced osteoclastic bone resorption leads to a vicious cycle between tumours and bone cells that fuels osteolytic tumour growth, causing bone pain and hypercalcaemia. Furthermore, RANKL contributes to bone metastasis by acting as a chemoattractant to bone for tumour cells that express its receptor, RANK. Thus inhibition of the RANKL-RANK pathway is a promising treatment for bone metastasis, and a human monoclonal anti-RANKL antibody, denosumab, has been used in the clinic. However, orally available drugs targeting RANKL must be developed to increase the therapeutic benefits to patients. Here we report the efficacy of the small-molecule RANKL inhibitor AS2676293 in treating bone metastasis using mouse models. Oral administration of AS2676293 markedly inhibited bone metastasis of human breast cancer cells MDA-MB-231-5a-D-Luc2 as well as tumour-induced osteolysis. AS2676293 suppressed RANKL-mediated tumour migration in the transwell assay and inhibited bone metastasis of the murine cell line B16F10, which is known not to trigger osteoclast activation. Based on the results from this study, RANKL inhibition with a small-molecule compound constitutes a promising therapeutic strategy for treating bone metastasis by inhibiting both osteoclastic bone resorption and tumour migration to bone.

Reciprocal expression of Slug and Snail in human oral cancer cells

Snail, also called Snai1, is a key regulator of EMT. Snail plays crucial roles in cancer progression, including resistance to anti-tumor drugs and invasion by various cancer cells. Slug, also known as Snai2, is also involved in the aggravation of certain tumors. In this study, we examined the roles of Slug in human oral squamous cell carcinoma (OSCC) cells. Slug is highly expressed in these cells, and Slug siRNA effectively represses anti-tumor drug resistance and invasive properties. In addition, transforming growth factor (TGF)-β upregulates the expression of Snail and Slug and promotes resistance to anti-tumor drugs in OSCC cells. Surprisingly, Slug siRNA appears to upregulate Snail expression considerably in OSCC cells. Snail siRNA also appears to upregulate Slug expression. Thus, either Slug or Snail siRNA alone partially mitigates malignant phenotypes in the presence of TGF-β, whereas both Slug and Snail siRNAs together dramatically suppress them. Therefore, Slug and Snail in tandem, but not alone, are potential therapeutic targets for nucleic acid medicines to treat oral cancer.

Long noncoding RNA NORAD regulates transforming growth factor-β signaling and epithelial-to-mesenchymal transition-like phenotype

Long noncoding RNAs are involved in a variety of cellular functions. In particular, an increasing number of studies have revealed the functions of long noncoding RNA in various cancers; however, their precise roles and mechanisms of action remain to be elucidated. NORAD, a cytoplasmic long noncoding RNA, is upregulated by irradiation and functions as a potential oncogenic factor by binding and inhibiting Pumilio proteins (PUM1/PUM2). Here, we show that NORAD upregulates transforming growth factor-β (TGF-β) signaling and regulates TGF-β-induced epithelial-to-mesenchymal transition (EMT)-like phenotype, which is a critical step in the progression of lung adenocarcinoma, A549 cells. However, PUM1 does not appear to be involved in this process. We thus focused on importin β1 as a binding partner of NORAD and found that knockdown of NORAD partially inhibits the physical interaction of importin β1 with Smad3, inhibiting the nuclear accumulation of Smad complexes in response to TGF-β. Our findings may provide a new mechanism underlying the function of NORAD in cancer cells.

Transforming growth factor-β in stem cells and tissue homeostasis

TGF-β 1-3 are unique multi-functional growth factors that are only expressed in mammals, and mainly secreted and stored as a latent complex in the extracellular matrix (ECM). The biological functions of TGF-β in adults can only be delivered after ligand activation, mostly in response to environmental perturbations. Although involved in multiple biological and pathological processes of the human body, the exact roles of TGF-β in maintaining stem cells and tissue homeostasis have not been well-documented until recent advances, which delineate their functions in a given context. Our recent findings, along with data reported by others, have clearly shown that temporal and spatial activation of TGF-β is involved in the recruitment of stem/progenitor cell participation in tissue regeneration/remodeling process, whereas sustained abnormalities in TGF-β ligand activation, regardless of genetic or environmental origin, will inevitably disrupt the normal physiology and lead to pathobiology of major diseases. Modulation of TGF-β signaling with different approaches has proven effective pre-clinically in the treatment of multiple pathologies such as sclerosis/fibrosis, tumor metastasis, osteoarthritis, and immune disorders. Thus, further elucidation of the mechanisms by which TGF-β is activated in different tissues/organs and how targeted cells respond in a context-dependent way can likely be translated with clinical benefits in the management of a broad range of diseases with the involvement of TGF-β.

Activin B promotes endometrial cancer cell migration by down-regulating E-cadherin via SMAD-independent MEK-ERK1/2-SNAIL signaling

High-risk type II endometrial cancers account for ~30% of cases but ~75% of deaths due, in part, to their tendency to metastasize. Histopathological studies of type II endometrial cancers (non-endometrioid, mostly serous) suggest overproduction of activin B and down-regulation of E-cadherin, both of which are associated with reduced survival. Our previous studies have shown that activin B increases the migration of type II endometrial cancer cell lines. However, little is known about the relationship between activin B signaling and E-cadherin in endometrial cancer. We now demonstrate that activin B treatment significantly decreases E-cadherin expression in both a time- and concentration-dependent manner in KLE and HEC-50 cell lines. Interestingly, these effects were not inhibited by knockdown of SMAD2, SMAD3 or SMAD4. Rather, the suppressive effects of activin B on E-cadherin were mediated by MEK-ERK1/2-induced production of the transcription factor SNAIL. Importantly, activin B-induced cell migration was inhibited by forced-expression of E-cadherin or pre-treatment with the activin/TGF-β type I receptor inhibitor SB431542 or the MEK inhibitor U0126. We have identified a novel SMAD-independent pathway linking enhanced activin B signaling to reduced E-cadherin expression and increased migration in type II endometrial cancer.

Loss of TGF-β signaling in osteoblasts increases basic-FGF and promotes prostate cancer bone metastasis

TGF-β plays a central role in prostate cancer (PCa) bone metastasis, and it is crucial to understand the bone cell-specific role of TGF-β signaling in this process. Thus, we used knockout (KO) mouse models having deletion of the Tgfbr2 gene specifically in osteoblasts (Tgfbr2^Col1CreERT KO) or in osteoclasts (Tgfbr2^LysMCre KO). We found that PCa-induced bone lesion development was promoted in the Tgfbr2^Col1CreERT KO mice, but was inhibited in the Tgfbr2^LysMCre KO mice, relative to their respective control Tgfbr2^FloxE2 littermates. Since metastatic PCa cells attach to osteoblasts when colonized in the bone microenvironment, we focused on the mechanistic studies using the Tgfbr2^Col1CreERT KO mouse model. We found that bFGF was upregulated in osteoblasts from PC3-injected tibiae of Tgfbr2^Col1CreERT KO mice and correlated with increased tumor cell proliferation, angiogenesis, amounts of cancer-associated fibroblasts and osteoclasts. In vitro studies showed that osteoblastogenesis was inhibited, osteoclastogenesis was stimulated, but PC3 viability was not affected, by bFGF treatments. Lastly, the increased PC3-induced bone lesions in Tgfbr2^Col1CreERT KO mice were significantly attenuated by blocking bFGF using neutralizing antibody, suggesting bFGF is a promising target inhibiting bone metastasis.

TUFT1 interacts with RABGAP1 and regulates mTORC1 signaling

The mammalian target of rapamycin (mTOR) pathway is commonly activated in human cancers. The activity of mTOR complex 1 (mTORC1) signaling is supported by the intracellular positioning of cellular compartments and vesicle trafficking, regulated by Rab GTPases. Here we showed that tuftelin 1 (TUFT1) was involved in the activation of mTORC1 through modulating the Rab GTPase-regulated process. TUFT1 promoted tumor growth and metastasis. Consistently, the expression of TUFT1 correlated with poor prognosis in lung, breast and gastric cancers. Mechanistically, TUFT1 physically interacted with RABGAP1, thereby modulating intracellular lysosomal positioning and vesicular trafficking, and promoted mTORC1 signaling. In addition, expression of TUFT1 predicted sensitivity to perifosine, an alkylphospholipid that alters the composition of lipid rafts. Perifosine treatment altered the positioning and trafficking of cellular compartments to inhibit mTORC1. Our observations indicate that TUFT1 is a key regulator of the mTORC1 pathway and suggest that it is a promising therapeutic target or a biomarker for tumor progression.

TGF-β signaling in cancer metastasis

The transforming growth factor (TGF)-β signaling events are well known to control diverse processes and numerous responses, such as cell proliferation, differentiation, apoptosis, and migration. TGF-β signaling plays context-dependent roles in cancer: in pre-malignant cells TGF-β primarily functions as a tumor suppressor, while in the later stages of cancer TGF-β signaling promotes invasion and metastasis. Recent studies have also suggested that the cross-talk between TGF-β signaling and other signaling pathways, such as Hippo, Wnt, EGFR/RAS, and PI3K/AKT pathways, may substantially contribute to our current understanding of TGF-β signaling and cancer. As a result of the wide-ranging effects of TGF-β, blockade of TGF-β and its downstream signaling components provides multiple therapeutic opportunities. Therefore, the outlook for anti-TGF-β signaling therapy for numerous diseases appears bright and will provide valuable information and thinking on the drug molecular design. In this review, we focus on recent insights into the regulation of TGF-β signaling in cancer metastasis which may contribute to the development of novel cancer-targeting therapies.

The molecular signature of breast cancer metastasis to bone

Distant metastasis during the advanced stage of malignant tumor progression can cause considerable morbidity in cancer patients. Bone is known to be one of the most common sites of distant metastasis in patients with breast cancer (BC). BC metastases in bone are associated with excessive skeletal complications. These complications can be fatal and reduce quality of life of patients. It is important to understand the metastatic process of BC to bone to improve quality of life and design new therapeutic methods. At present, the molecular mechanisms leading to the BC metastasis to bone are not fully understood. Studying the molecular basis of BC metastasis to bone might improve our insight into this complex process. In addition, it can provide novel approaches for designing advanced and effective targeted therapies. The present article aimed to review the published papers on the molecular basis of the metastatic process of BC to bone, focusing on involved genes and signaling networks. Furthermore, we propose potential therapeutic targets that may be more effective for the inhibition and treatment of BC metastasis to bone.

Halofuginone inhibits TGF-β/BMP signaling and in combination with zoledronic acid enhances inhibition of breast cancer bone metastasis

More efficient therapies that target multiple molecular mechanisms are needed for the treatment of incurable bone metastases. Halofuginone is a plant alkaloid-derivative with antiangiogenic and antiproliferative effects. Here we demonstrate that halofuginone is an effective therapy for the treatment of bone metastases, through multiple actions that include inhibition of TGFβ and BMP-signaling.

Halofuginone blocked TGF-β-signaling in MDA-MB-231 and PC3 cells showed by inhibition of TGF-β–induced Smad-reporter, phosphorylation of Smad-proteins, and expression of TGF-β-regulated metastatic genes. Halofuginone increased inhibitory Smad7-mRNA and reduced TGF-β-receptor II protein. Proline supplementation but not Smad7-knockdown reversed halofuginone-inhibition of TGF-β-signaling. Halofuginone also decreased BMP-signaling. Treatment of MDA-MB-231 and PC3 cells with halofuginone reduced the BMP-Smad-reporter (BRE)₄, Smad1/5/8-phosphorylation and mRNA of the BMP-regulated gene Id-1. Halofuginone decreased immunostaining of phospho-Smad2/3 and phospho-Smad1/5/8 in cancer cells in vivo.

Furthermore, halofuginone decreased tumor-take and growth of orthotopic-tumors. Mice with breast or prostate bone metastases treated with halofuginone had significantly less osteolysis than control mice. Combined treatment with halofuginone and zoledronic-acid significantly reduced osteolytic area more than either treatment alone. Thus, halofuginone reduces breast and prostate cancer bone metastases in mice and combined with treatment currently approved by the FDA is an effective treatment for this devastating complication of breast and prostate-cancer.

ZEB1-regulated inflammatory phenotype in breast cancer cells

Zinc finger E‐box binding protein 1 (ZEB1) and ZEB2 induce epithelial‐mesenchymal transition (EMT) and enhance cancer progression. However, the global view of transcriptional regulation by ZEB1 and ZEB2 is yet to be elucidated. Here, we identified a ZEB1‐regulated inflammatory phenotype in breast cancer cells using chromatin immunoprecipitation sequencing and RNA sequencing, followed by gene set enrichment analysis (GSEA) of ZEB1‐bound genes. Knockdown of ZEB1 and/or ZEB2 resulted in the downregulation of genes encoding inflammatory cytokines related to poor prognosis in patients with cancer, including IL6 and IL8, therefore suggesting that ZEB1 and ZEB2 have similar functions in terms of the regulation of production of inflammatory cytokines. Antibody array and ELISA experiments confirmed that ZEB1 controlled the production of the IL‐6 and IL‐8 proteins. The secretory proteins regulated by ZEB1 enhanced breast cancer cell proliferation and tumor growth. ZEB1 expression in breast cancer cells also affected the growth of fibroblasts in cell culture, and the accumulation of myeloid‐derived suppressor cells in tumors in vivo. These findings provide insight into the role of ZEB1 in the progression of cancer, mediated by inflammatory cytokines, along with the initiation of EMT.

The EMT spectrum and therapeutic opportunities

Carcinomas are phenotypically arrayed along an epithelial–mesenchymal transition (EMT) spectrum, a developmental program currently exploited to understand the acquisition of drug resistance through a re‐routing of growth factor signaling. This review collates the current approaches employed in developing therapeutics against cancer‐associated EMT, and provides an assessment of their respective strengths and drawbacks. We reflect on the close relationship between EMT and chemoresistance against current targeted therapeutics, with a special focus on the epigenetic mechanisms that link these processes. This prompts the hypothesis that carcinoma‐associated EMT shares a common epigenetic pathway to cellular plasticity as somatic cell reprogramming during tissue repair and regeneration. Indeed, their striking resemblance suggests that EMT in carcinoma is a pathological adaptation of an intrinsic program of cellular plasticity that is crucial to tissue homeostasis. We thus propose a revised approach that targets the epigenetic mechanisms underlying pathogenic EMT to arrest cellular plasticity regardless of upstream cancer‐driving mutations.

Transforming growth factor-β: A therapeutic target for cancer

Transforming growth factor-β (TGF-β) regulates cell growth and differentiation, apoptosis, cell motility, extracellular matrix production, angiogenesis, and cellular immunity. It has a paradoxical role in cancer. In the early stages it inhibits cellular transformation and prevents cancer progression. In later stages TGF-β plays a key role in promoting tumor progression through mainly 3 mechanisms: facilitating epithelial to mesenchymal transition, stimulating angiogenesis and inducing immunosuppression. As a result of its opposing tumor promoting and tumor suppressive abilities, TGF-β and its pathway has represented potential opportunities for drug development and several therapies targeting the TGF-β pathway have been identified. This review focuses on identifying the mechanisms through which TGF-β is involved in tumorigenesis and current therapeutics that are under development.

Bone morphogenetic protein signaling mediated by ALK-2 and DLX2 regulates apoptosis in glioma-initiating cells

Bone morphogenetic protein (BMP) signaling exerts antitumor activities in glioblastoma; however, its precise mechanisms remain to be elucidated. Here, we demonstrated that the BMP type I receptor ALK-2 (encoded by the ACVR1 gene) has crucial roles in apoptosis induction of patient-derived glioma-initiating cells (GICs), TGS-01 and TGS-04. We also characterized a BMP target gene, Distal-less homeobox 2 (DLX2), and found that DLX2 promoted apoptosis and neural differentiation of GICs. The tumor-suppressive effects of ALK-2 and DLX2 were further confirmed in a mouse orthotopic transplantation model. Interestingly, valproic acid (VPA), an anti-epileptic compound, induced BMP2, BMP4, ACVR1 and DLX2 mRNA expression with a concomitant increase in phosphorylation of Smad1/5. Consistently, we showed that treatment with VPA induced apoptosis of GICs, whereas silencing of ALK-2 or DLX2 expression partially suppressed it. Our study thus reveals BMP-mediated inhibitory mechanisms for glioblastoma, which explains, at least in part, the therapeutic effects of VPA.

Dynamics of chromatin accessibility during TGF-β-induced EMT of Ras-transformed mammary gland epithelial cells

Epithelial-mesenchymal transition (EMT) is induced by transforming growth factor (TGF)-β and facilitates tumor progression. We here performed global mapping of accessible chromatin in the mouse mammary gland epithelial EpH4 cell line and its Ras-transformed derivative (EpRas) using formaldehyde-assisted isolation of regulatory element (FAIRE)-sequencing. TGF-β and Ras altered chromatin accessibility either cooperatively or independently, and AP1, ETS, and RUNX binding motifs were enriched in the accessible chromatin regions of EpH4 and EpRas cells. Etv4, an ETS family oncogenic transcription factor, was strongly expressed and bound to more than one-third of the accessible chromatin regions in EpRas cells treated with TGF-β. While knockdown of Etv4 and another ETS family member Etv5 showed limited effects on the decrease in the E-cadherin abundance and stress fiber formation by TGF-β, gene ontology analysis showed that genes encoding extracellular proteins were most strongly down-regulated by Etv4 and Etv5 siRNAs. Accordingly, TGF-β-induced expression of Mmp13 and cell invasiveness were suppressed by Etv4 and Etv5 siRNAs, which were accompanied by the reduced chromatin accessibility at an enhancer region of Mmp13 gene. These findings suggest a mechanism of transcriptional regulation during Ras- and TGF-β-induced EMT that involves alterations of accessible chromatin, which are partly regulated by Etv4 and Etv5.

CCT6A suppresses SMAD2 and promotes prometastatic TGF-β signaling

Paradoxically, during early tumor development in many cancer types, TGF-β acts as a tumor suppressor, whereas in the advanced stages of these cancers, increased TGF-β expression is linked to high metastasis and poor prognosis. These findings suggest that unidentified mechanisms may function to rewire TGF-β signaling toward its prometastatic role in cancer cells. Our current study using non-small-cell lung carcinoma (NSCLC) cell lines, animal models, and clinical specimens demonstrates that suppression of SMAD2, with SMAD3 function intact, switches TGF-β-induced transcriptional responses to a prometastatic state. Importantly, we identified chaperonin containing TCP1 subunit 6A (CCT6A) as an inhibitor and direct binding protein of SMAD2 and found that CCT6A suppresses SMAD2 function in NSCLC cells and promotes metastasis. Furthermore, selective inhibition of SMAD3 or CCT6A efficiently suppresses TGF-β-mediated metastasis. Our findings provide a mechanism that directs TGF-β signaling toward its prometastatic arm and may contribute to the development of therapeutic strategies targeting TGF-β for NSCLC.

TGFβR1 Blockade with Galunisertib (LY2157299) Enhances Anti-Neuroblastoma Activity of the Anti-GD2 Antibody Dinutuximab (ch14.18) with Natural Killer Cells

PURPOSE

Immunotherapy of high-risk neuroblastoma using the anti-GD2 antibody dinutuximab induces antibody-dependent cell-mediated cytotoxicity (ADCC). Galunisertib, an inhibitor of TGFβR1, was examined for its ability to enhance the efficacy of dinutuximab in combination with human ex vivo activated NK (aNK) cells against neuroblastoma.

EXPERIMENTAL DESIGN

TGFB1 and TGFBR1 mRNA expression was determined for 249 primary neuroblastoma tumors by microarray analysis. The ability of galunisertib to inhibit SMAD activity induced by neuroblastoma patient blood and bone marrow plasmas in neuroblastoma cells was tested. The impact of galunisertib on TGFβ1-induced inhibition of aNK cytotoxicity and ADCC in vitro and on anti-neuroblastoma activity in NOD-scid gamma (NSG) mice was determined.

RESULTS

Neuroblastomas express TGFB1 and TGFBR1 mRNA. Galunisertib suppressed SMAD activation in neuroblastoma cells induced by exogenous TGFβ1 or by patient blood and bone marrow plasma, and suppressed SMAD2 phosphorylation in human neuroblastoma cells growing in NSG mice. In NK cells treated in vitro with exogenous TGFβ1, galunisertib suppressed SMAD2 phosphorylation and restored the expression of DNAM-1, NKp30, and NKG2D cytotoxicity receptors and the TRAIL death ligand, the release of perforin and granzyme A, and the direct cytotoxicity and ADCC of aNK cells against neuroblastoma cells. Addition of galunisertib to adoptive cell therapy with aNK cells plus dinutuximab reduced tumor growth and increased survival of mice injected with two neuroblastoma cell lines or a patient-derived xenograft.

CONCLUSIONS

Galunisertib suppresses activation of SMAD2 in neuroblastomas and aNK cells, restores NK cytotoxic mechanisms, and increases the efficacy of dinutuximab with aNK cells against neuroblastoma tumors. Clin Cancer Res; 23(3); 804-13. ©2016 AACRSee related commentary by Zenarruzabeitia et al., p. 615.

Ras and TGF-β signaling enhance cancer progression by promoting the ΔNp63 transcriptional program

The p53 family of transcription factors includes p63, which is a master regulator of gene expression in epithelial cells. Determining whether p63 is tumor-suppressive or tumorigenic is complicated by isoform-specific and cellular context-dependent protein associations, as well as antagonism from mutant p53. ΔNp63 is an amino-terminal-truncated isoform, that is, the predominant isoform expressed in cancer cells of epithelial origin. In HaCaT keratinocytes, which have mutant p53 and ΔNp63, we found that mutant p53 antagonized ΔNp63 transcriptional activity but that activation of Ras or transforming growth factor-β (TGF-β) signaling pathways reduced the abundance of mutant p53 and strengthened target gene binding and activity of ΔNp63. Among the products of ΔNp63-induced genes was dual-specificity phosphatase 6 (DUSP6), which promoted the degradation of mutant p53, likely by dephosphorylating p53. Knocking down all forms of p63 or DUSP6 and DUSP7 (DUSP6/7) inhibited the basal or TGF-β-induced or epidermal growth factor (which activates Ras)-induced migration and invasion in cultures of p53-mutant breast cancer and squamous skin cancer cells. Alternatively, overexpressing ΔNp63 in the breast cancer cells increased their capacity to colonize various tissues upon intracardiac injection in mice, and this was inhibited by knocking down DUSP6/7 in these ΔNp63-overexpressing cells. High abundance of ΔNp63 in various tumors correlated with poor prognosis in patients, and this correlation was stronger in patients whose tumors also had a mutation in the gene encoding p53. Thus, oncogenic Ras and TGF-β signaling stimulate cancer progression through activation of the ΔNp63 transcriptional program.

Signaling Receptors for TGF-β Family Members

Transforming growth factor β (TGF-β) family members signal via heterotetrameric complexes of type I and type II dual specificity kinase receptors. The activation and stability of the receptors are controlled by posttranslational modifications, such as phosphorylation, ubiquitylation, sumoylation, and neddylation, as well as by interaction with other proteins at the cell surface and in the cytoplasm. Activation of TGF-β receptors induces signaling via formation of Smad complexes that are translocated to the nucleus where they act as transcription factors, as well as via non-Smad pathways, including the Erk1/2, JNK and p38 MAP kinase pathways, and the Src tyrosine kinase, phosphatidylinositol 3'-kinase, and Rho GTPases.

Silibinin inhibits triple negative breast cancer cell motility by suppressing TGF-β2 expression

Transforming growth factor-beta (TGF-β) is a multifunctional cytokine that regulates many biological events including cell motility and angiogenesis. Here, we investigated the role of elevated TGF-β2 level in triple negative breast cancer (TNBC) cells and the inhibitory effect of silibinin on TGF-β2 action in TNBC cells. Breast cancer patients with high TGF-β2 expression have a poor prognosis. The levels of TGF-β2 expression increased significantly in TNBC cells compared with those in non-TNBC cells. In addition, cell motility-related genes such as fibronectin (FN) and matrix metalloproteinase-2 (MMP-2) expression also increased in TNBC cells. Basal FN, MMP-2, and MMP-9 expression levels decreased in response to LY2109761, a dual TGF-β receptor I/II inhibitor, in TNBC cells. TNBC cell migration also decreased in response to LY2109761. Furthermore, we observed that TGF-β2 augmented the FN, MMP-2, and MMP-9 expression levels in a time- and dose-dependent manner. In contrast, TGF-β2-induced FN, MMP-2, and MMP-9 expression levels decreased significantly in response to LY2109761. Interestingly, we found that silibinin decreased TGF-β2 mRNA expression level but not that of TGF-β1 in TNBC cells. Cell migration as well as basal FN and MMP-2 expression levels decreased in response to silibinin. Furthermore, silibinin significantly decreased TGF-β2-induced FN, MMP-2, and MMP-9 expression levels and suppressed the lung metastasis of TNBC cells. Taken together, these results suggest that silibinin suppresses metastatic potential of TNBC cells by inhibiting TGF-β2 expression in TNBC cells. Thus, silibinin may be a promising therapeutic drug to treat TNBC.

TGF-β Signaling in Cancer

The transforming growth factor-β (TGF-β) is a family of structurally related proteins that comprises of TGF-β, activins/inhibins, and bone morphogenic proteins (BMPs). Members of the TGF-β family control numerous cellular functions including proliferation, apoptosis, differentiation, epithelial-mesenchymal transition (EMT), and migration. The first identified member, TGF-β is implicated in several human diseases, such as vascular diseases, autoimmune disorders, and carcinogenesis. Activation of the TGF-β receptor by its ligands induces the phosphorylation of serine/threonine residues and triggers phosphorylation of the intracellular effectors, SMADs. Upon activation, SMAD proteins translocate to the nucleus and induce transcription of their target genes, regulating several cellular functions. TGF-β dysregulation has been implicated in carcinogenesis. In early stages of cancer, TGF-β exhibits tumor suppressive effects by inhibiting cell cycle progression and promoting apoptosis. However, in late stages TGF-β exerts tumor promoting effects, increasing tumor invasiveness, and metastasis. Furthermore, the TGF-β signaling pathway communicates with other signaling pathways in a synergistic or antagonistic manner and regulates cellular functions. Elevated TGF-β activity has been associated with poor clinical outcome. Given the pivotal role of TGF-β in tumor progression, this pathway is an attractive target for cancer therapy. Several therapeutic tools such as TGF-β antibodies, antisense oligonucleotides, and small molecules inhibitors of TGF-β receptor-1 (TGF-βR1) have shown immense potential to inhibit TGF-β signaling. Finally, in the interest of developing future therapies, further studies are warranted to identify novel points of convergence of TGF-β with other signaling pathways and oncogenic factors in the tumor microenvironment.