The tumor microenvironment: part 1

Advances in tumor microenvironment: Applications and challenges of 3D bioprinting

The tumor microenvironment (TME) assumes a pivotal role in the treatment of oncological diseases, given its intricate interplay of diverse cellular components and extracellular matrices. This dynamic ecosystem poses a serious challenge to traditional research methods in many ways, such as high research costs, inefficient translation, poor reproducibility, and low modeling success rates. These challenges require the search for more suitable research methods to accurately model the TME, and the emergence of 3D bioprinting technology is transformative and an important complement to these traditional methods to precisely control the distribution of cells, biomolecules, and matrix scaffolds within the TME. Leveraging digital design, the technology enables personalized studies with high precision, providing essential experimental flexibility. Serving as a critical bridge between in vitro and in vivo studies, 3D bioprinting facilitates the realistic 3D culturing of cancer cells. This comprehensive article delves into cutting-edge developments in 3D bioprinting, encompassing diverse methodologies, biomaterial choices, and various 3D tumor models. Exploration of current challenges, including limited biomaterial options, printing accuracy constraints, low reproducibility, and ethical considerations, contributes to a nuanced understanding. Despite these challenges, the technology holds immense potential for simulating tumor tissues, propelling personalized medicine, and constructing high-resolution organ models, marking a transformative trajectory in oncological research.

Tumor promoting effect of spheroids in an orthotopic prostate cancer mouse model

In this study, we aimed to establish a technique for intraprostatic implantation of prostate cancer (PCa) spheroids and to identify the impact of three-dimensional organization of PCa cells on tumor progression and metastasis in a representative in vivo model. 40,000 LNCaP cells were implanted into the prostate of immunodeficient SCID mice either as single cells (n = 8) or as preformed 3D spheroids (n = 8). For a follow up of 20 weeks, tumor growth was monitored by serum PSA and high-resolution 3D ultrasonography. Eventually, animals were sacrificed and autopsied. The organ dissects were analyzed for the presence of metastases by histology (H&E) and immunohistochemistry (AMACR, AR, Ki-67, CK5, CK8, E-Cadherin, Vimentin). Solid intraprostatic tumors developed in 50% of mice after spheroid implantation and in 50% of mice after implantation of a single cells. Primary tumors of LNCaP spheroids evolved earlier, exhibiting a shorter tumor doubling time whilst developing larger tumor volumes, which was reflected by a higher immunohistochemical expression of Ki-67 and AR, too. Spheroid tumors established lung and lymph node metastases in 75% of mice, in contrast to 50% of mice after single cell implantation. Our technique enables a variety of studies regarding the influence of the tumor microenvironment on PCa progression.

Corrigendum: Immunomodulatory function and anti-tumor mechanism of natural polysaccharides: a review

[This corrects the article DOI: 10.3389/fimmu.2023.1147641.].

Interleukin-33: Friend or Foe in Gastrointestinal Tract Cancers?

Accumulating evidence suggests that Interleukin-33 (IL-33), a member of the IL-1 family, has crucial roles in tissue homeostasis and repair, type 2 immunity, inflammation, and viral infection. IL-33 is a novel contributing factor in tumorigenesis and plays a critical role in regulating angiogenesis and cancer progression in a variety of human cancers. The partially unraveled role of IL-33/ST2 signaling in gastrointestinal tract cancers is being investigated through the analysis of patients' samples and by studies in murine and rat models. In this review, we discuss the basic biology and mechanisms of release of the IL-33 protein and its involvement in gastrointestinal cancer onset and progression.

Immunomodulatory function and anti-tumor mechanism of natural polysaccharides: A review

Polysaccharides extracted from natural resources have attracted extensive attention in biomedical research and pharmaceutical fields, due to their medical values in anti-tumor, immunomodulation, drug delivery, and many other aspects. At present, a variety of natural polysaccharides have been developed as adjuvant drugs in clinical application. Benefit from their structural variability, polysaccharides have great potential in regulating cellular signals. Some polysaccharides exert direct anti-tumor effects by inducing cell cycle arrest and apoptosis, while the majority of polysaccharides can regulate the host immune system and indirectly inhibit tumors by activating either non-specific or specific immune responses. As the essential of microenvironment in the process of tumor development has been gradually revealed, some polysaccharides were found to inhibit the proliferation and metastasis of tumor cells via tumoral niche modulation. Here, we focused on natural polysaccharides with biomedical application potential, reviewed the recent advancement in their immunomodulation function and highlighted the importance of their signaling transduction feature for the antitumor drug development.

Activatable Dual Cancer-Related RNA Imaging and Combined Gene-Chemotherapy through the Target-Induced Intracellular Disassembly of Functionalized DNA Tetrahedron

The desire for a cancer theranostic system with simultaneously accurate diagnosis and efficient therapy is undeniably interminable. Heretofore, theranostic systems with simple components were designed for cancer theranostics but with confined accuracy of diagnosis and side effects of administered drugs. Here, we report an activatable theranostic system for simultaneously imaging dual cancer-related RNAs, mRNA Bcl-2 and piRNA-36026, and combined gene-chemotherapy through the target-induced intracellular disassembly of DNA tetrahedron. Briefly, five customized oligonucleotides are used to assemble the functionalized DNA tetrahedron. The relevant functional nucleic acids, including the antisequence of mRNA Bcl-2, the antisequence of piRNA-36026, and aptamer AS1411, are designed in the customized oligonucleotides with the signal reporters Cy3 and Cy5. Doxorubicin (DOX) is loaded in the functionalized DNA tetrahedron by inlaying between cytosine and guanine to form the activatable cancer theranostic system. The activatable cancer theranostic system is able to recognize MCF-7 cells by aptamer AS1411 and then enter the cells. In the presence of targets, the antisequences in the activatable cancer theranostic system hybridize with intracellular mRNA Bcl-2 and piRNA-36026, leading to the fluorescence signal recovery of Cy3 and Cy5 and the downregulation of two targets in the cytoplasm as well as the consequent apoptosis of MCF-7 cells in the form of gene therapy. Interestingly, as the antisequences are designed in the assembly strands, the hybridization between targets and the antisequences results in the disassembly of the activatable cancer theranostic system and the release of DOX as well as sequential chemotherapy. Advantageously, the activatable cancer theranostic system can achieve imaging of dual cancer-related RNAs with an imaging time window as long as 15 h and exhibit an obvious therapeutic effect in vivo. Therefore, this work is in furtherance of exploration for activatable cancer theranostic systems with high accuracy and efficiency and sheds new light on the development of precision medicine.

Paradoxical role of interleukin-33/suppressor of tumorigenicity 2 in colorectal carcinogenesis: Progress and therapeutic potential

Colorectal cancer (CRC) is presently the second most prevalent global mortality-inducing cancer. CRC carcinogenesis is a multifactorial process involving internal genetic mutations and the external environment. In addition, non-neoplastic cell activities within tumor microenvironments for CRC development have been established. However, interleukin (IL)-33, secreted by such cell types, plays a pivotal role in cancer progression due to interaction with cellular constituents within the tumor-inflammation microenvironment. IL-33 belongs to the IL-1 cytokine family and acts as binding attachments for the suppressor of tumorigenicity (ST)2 receptor. Therefore, how to coordinate tumor microenvironment, design and optimize treatment strategies suitable for CRC, based on IL-33/ST2 signal is a challenge. Even though it has established influences upon immunity-linked conditions, IL-33 effects on CRC progression and prevention and related mechanisms are still controversial. Our review depicts controversial activities for IL-33/ST2 within carcinogenesis and cancer prevention. Moreover, IL-33/ST2 signaling is a potential therapeutic target for CRC.

Signal transducer and activator of transcription 3 signaling in tumor immune evasion

The underlying mechanism of tumor immune evasion is a highly concerning subject for researchers. Increasing evidences reveal that the over-activated signal transducer and activator of transcription 3 (STAT3) is a crucial molecular hub in malignant tumors. STAT3 controls autophagy molecules that impair CTL-mediated tumor cell lysis, inhibiting natural killer cells and inducing apoptosis in T lymphocytes to create an immunosuppressive environment. STAT3 signaling regulates the expression of immune factors and recruits immunosuppressive cells to establish a tolerant tumor microenvironment (TME). STAT3 signaling regulates the expression of immune factors and recruits immunosuppressive cells to create an immunosuppressive environment. All this aid tumor cells in escaping from immune surveillance. In this review, we outlined the STAT3-mediated mechanisms involved in tumor immune evasion and their potential regulatory functions in the TME. We discussed the impact of STAT3 signaling on PD-L1, HIF-1α, exosome, lncRNA, and autophagy in the promotion of tumor immune evasion and highlighted the recent research on STAT3 signaling and tumor immune evasion that may assist in developing effective STAT3-targeted drugs for advancing immunotherapy.

Hot and Cold Tumors: Is Endoglin (CD105) a Potential Target for Vessel Normalization?

Tumors are complex masses formed by malignant but also by normal cells. The interaction between these cells via cytokines, chemokines, growth factors, and enzymes that remodel the extracellular matrix (ECM) constitutes the tumor microenvironment (TME). This TME can be determinant in the prognosis and the response to some treatments such as immunotherapy. Depending on their TME, two types of tumors can be defined: hot tumors, characterized by an immunosupportive TME and a good response to immunotherapy; and cold tumors, which respond poorly to this therapy and are characterized by an immunosuppressive TME. A therapeutic strategy that has been shown to be useful for the conversion of cold tumors into hot tumors is vascular normalization. In this review we propose that endoglin (CD105) may be a useful target of this strategy since it is involved in the three main processes involved in the generation of the TME: angiogenesis, inflammation, and cancer-associated fibroblast (CAF) accumulation. Moreover, the analysis of endoglin expression in tumors, which is already used in the clinic to study the microvascular density and that is associated with worse prognosis, could be used to predict a patient's response to immunotherapy.

The Pro-tumorigenic IL-33 Involved in Antitumor Immunity: A Yin and Yang Cytokine

Interleukin-33 (IL-33), considered as an alarmin released upon tissue stress or damage, is a member of the IL-1 family and binds the ST2 receptor. First described as a potent initiator of type 2 immune responses through the activation of T helper 2 (T_H2) cells and mast cells, IL-33 is now also known as an effective stimulator of T_H1 immune cells, natural killer (NK) cells, iNKT cells, and CD8 T lymphocytes. Moreover, IL-33 was shown to play an important role in several cancers due to its pro and anti-tumorigenic functions. Currently, IL-33 is a possible inducer and prognostic marker of cancer development with a direct effect on tumor cells promoting tumorigenesis, proliferation, survival, and metastasis. IL-33 also promotes tumor growth and metastasis by remodeling the tumor microenvironment (TME) and inducing angiogenesis. IL-33 favors tumor progression through the immune system by inducing M2 macrophage polarization and tumor infiltration, and upon activation of immunosuppressive cells such as myeloid-derived suppressor cells (MDSC) or regulatory T cells. The anti-tumor functions of IL-33 also depend on infiltrated immune cells displaying T_H1 responses. This review therefore summarizes the dual role of this cytokine in cancer and suggests that new proposals for IL-33-based cancer immunotherapies should be considered with caution.

Metastatic Lung Lesions as a Preferred Resection Site for Immunotherapy With Tumor Infiltrating Lymphocytes

Adoptive cell therapy with tumor infiltrating lymphocytes (TIL) yields 50% response rates in metastatic melanoma and shows promising clinical results in other solid tumors. Autologous TIL cultures are isolated from resected tumor tissue, expanded ex vivo to large numbers and reinfused to the preconditioned patient. In this prospective study, we validate the origin of the tumor biopsy and its effect on T-cell function and clinical response. One hundred forty-four patients underwent surgery and 79 patients were treated with TIL adoptive cell therapy. Cultures from lung tissue were compared with other origins. The success rate of establishing TIL culture from lung tissue was significantly higher compared with nonlung tissue (94% vs. 72%, respectively, P≤0.003). Lung-derived TIL cultures gave rise to higher cell numbers (P≤0.011) and exhibited increased in vitro antitumor reactivity. The average fold expansion for lung-derived TIL during a rapid expansion procedure was 1349±557 compared with 1061±473 for nonlung TIL (P≤0.038). Patients treated with TIL cultures of lung origin (compared with nonlung) had prolonged median overall survival (29 vs. 9.5 mo; P≤0.065). Given the remarkable advancement in minimally invasive thoracic surgery and the results of this study, we suggest efforts should be taken to resect lung metastasis rather than other sites to generate TIL cultures for clinical use.

Overview of Methods for Overcoming Hindrance to Drug Delivery to Tumors, with Special Attention to Tumor Interstitial Fluid

Every drug used to treat cancer (chemotherapeutics, immunological, monoclonal antibodies, nanoparticles, radionuclides) must reach the targeted cells through the tumor environment at adequate concentrations, in order to exert their cell-killing effects. For any of these agents to reach the goal cells, they must overcome a number of impediments created by the tumor microenvironment (TME), beginning with tumor interstitial fluid pressure (TIFP), and a multifactorial increase in composition of the extracellular matrix (ECM). A primary modifier of TME is hypoxia, which increases the production of growth factors, such as vascular endothelial growth factor and platelet-derived growth factor. These growth factors released by both tumor cells and bone marrow recruited myeloid cells form abnormal vasculature characterized by vessels that are tortuous and more permeable. Increased leakiness combined with increased inflammatory byproducts accumulates fluid within the tumor mass (tumor interstitial fluid), ultimately creating an increased pressure (TIFP). Fibroblasts are also up-regulated by the TME, and deposit fibers that further augment the density of the ECM, thus, further worsening the TIFP. Increased TIFP with the ECM are the major obstacles to adequate drug delivery. By decreasing TIFP and ECM density, we can expect an associated rise in drug concentration within the tumor itself. In this overview, we will describe all the methods (drugs, nutraceuticals, and physical methods of treatment) able to lower TIFP and to modify ECM used for increasing drug concentration within the tumor tissue.

Netrin-1 as a potential target for metastatic cancer: focus on colorectal cancer

Despite advanced screening technology and cancer treatments available today, metastasis remains an ongoing major cause of cancer-related deaths worldwide. Typically, colorectal cancer is one of the cancers treatable by surgery in conjunction with chemotherapy when it is detected at an early stage. However, it still ranks as the second highest modality and mortality of cancer types in western countries, and this is mostly due to a recurrence of metastatic colorectal cancer post-resection of the primary malignancy. Colorectal cancer metastases predominantly occur in the liver and lung, and yet the molecular mechanisms that regulate these organ-specific colorectal cancer metastases are largely unknown. Therefore, the identification of any critical molecule, which triggers malignancy in colorectal cancer, would be an excellent target for treatment. Netrin-1 was initially discovered as a chemotropic neuronal guidance molecule, and has been marked as a regulator for many cancers including colorectal cancer. Here, we summarise key findings of the role of netrin-1 intrinsic to colorectal cancer cells, extrinsic to the tumour microenvironment and angiogenesis, and consequently, we evaluate netrin-1 as a potential target molecule for metastasis.

AZD1480 delays tumor growth in a melanoma model while enhancing the suppressive activity of myeloid-derived suppressor cells

AZD1480 is a potent, competitive small-molecule inhibitor of JAK1/2 kinase which inhibits STAT3 phosphorylation and tumor growth. Here we investigated the effects of AZD1480 on the function of different immune cell populations in a melanoma model. When MO4 tumor-bearing mice were treated with AZD1480 we observed a strong inhibition of tumor growth as well as a prolonged survival. Moreover, a significant decrease in the percentage of myeloid-derived suppressor cells (MDSCs) was observed after treatment with AZD1480. However, AZD1480 enhanced the suppressive capacity of murine MDSCs while at the same time impairing the proliferative as well as the IFN-γ secretion capacity of murine T cells. The addition of AZD1480 to co-cultures of human MDSCs and T cells does not affect the suppressive activity of MDSCs but it does reduce the IFN-γ secretion and the proliferative capacity of T cells. We showed that although AZD1480 has the ability to delay the tumor growth of MO4 tumor-bearing mice, this drug has detrimental effects on several aspects of the immune system. These data indicate that systemic targeting of the JAK/STAT pathway by JAK1/2 inhibition can have divergent effects on tumor growth and anti-tumor immune responses.

Low-fidelity compensatory backup alternative DNA repair pathways may unify current carcinogenesis theories

The somatic mutation carcinogenesis theory has dominated for decades. The alternative theory, tissue organization field theory, argues that the development of cancer is determined by the surrounding microenvironment. However, neither theory can explain all features of cancer. As cancers share the features of uncontrolled proliferation and genomic instability, they are likely to have the same pathogenesis. It has been found that various DNA repair pathways within a cell crosstalk with one another, forming a DNA repair network. When one DNA repair pathways is defective, the others may work as compensatory backups. The latter pathways are explored for synthetic lethal anticancer therapy. In this article, we extend the concept of compensatory alternative DNA repair to unify the theories. We propose that the microenvironmental stress can activate low-fidelity compensatory alternative DNA repair, causing mutations. If the mutation occurs to a DNA repair gene, this secondarily mutated gene can lead to even more mutated genes, including those related to other DNA repair pathways, eventually destabilizing the genome. Therefore, the low-fidelity compensatory alternative DNA repair may mediate microenvironment-dependent carcinogenesis. The proposal seems consistent with the view of evolution: the environmental stress causes mutations to adapt to the changing environment.

Exosome proteomics reveals transcriptional regulator proteins with potential to mediate downstream pathways

Exosomes are virus-sized, membrane-enclosed vesicles with origins in the cellular endosomal system, but are released extracellularly. As a population, these tiny vesicles carry relatively enormous amounts of information in their protein, lipid and nucleic acid content, and the vesicles can have profound impacts on recipient cells. This review employs publically-available data combined with gene ontology applications to propose a novel concept, that exosomes transport transcriptional and translational machinery that may have direct impacts on gene expression in recipient cells. Here, we examine the previously published proteomic contents of medulloblastoma-derived exosomes, focusing on transcriptional regulators; we found that there are numerous proteins that may have potential roles in transcriptional and translational regulation with putative influence on downstream, cancer-related pathways. We expanded this search to all of the proteins in the Vesiclepedia database; using gene ontology approaches, we see that these regulatory factors are implicated in many of the processes involved in cancer initiation and progression. This information suggests that some of the effects of exosomes on recipient cells may be due to the delivery of protein factors that can directly and fundamentally change the transcriptional landscape of the cells. Within a tumor environment, this has potential to tilt the advantage towards the cancer.

Update on the challenges and recent advances in cancer immunotherapy

This overview provides an analysis of some of the immunotherapies currently in use and under investigation, with a special focus on the tumor microenvironment, which we believe is a major factor responsible for the general failure of immunotherapy to date. It is our expectation that combining immunotherapy with methods of altering the tumor microenvironment and targeting regulatory T cells and myeloid cells will yield favorable results.

Targeting tetraspanins in cancer

INTRODUCTION

Tetraspanins are a family of small proteins that cross the membrane four times and form complexes by interacting between themselves and with a variety of transmembrane and cytosolic proteins, building a network of interactions referred to as tetraspanin web or tetraspanin enriched microdomains (TEMs). These domains provide a signaling platform involved in many important cellular functions and malignant processes.

AREAS COVERED

The authors describe the methods and the rationale for targeting tetraspanins in the therapy of cancer in this review.

EXPERT OPINION

Targeting tetraspanins in cancer may be a promising therapy due to the importance of tetraspanins in several steps of tumor formation, communication with the environment, dissemination, and metastasis.

Exosomes in Cancer Microenvironment and Beyond: have we Overlooked these Extracellular Messengers?

Cancer is a complex organ whose behavior is not only influenced by genetic and epigenetic changes in cancer cells but also by stromal cells, local extracellular matrix and specific tissue architecture. Intercellular communications within the cancer microenvironment are critical to coordinate the assembly of multiple cell types for an amalgamated form and function of a cancer. Exosomes are small membrane vesicles with an endosome origin that are released by cells into the extracellular environment. They carry a cargo of proteins, lipids, and nucleic acids and transfer their cargo to recipient cells and altering the recipient cells' biochemical composition, signaling pathways, and gene regulation. Exosomes can thus serve as extracellular messengers mediating cell-cell communication. Both cancer cells and stromal cells release exosomes not only into the cancer microenvironment but also into the circulation. In this review, we summarize the research done so far on cancer-derived exosomes and assess their roles as extracellular messengers facilitating cancer progression and metastasis.