Mesenchymal Stem Cells: Their Role in the Tumor Microenvironment.

Mesenchymal stem cells (MSCs) have been seen for years as great candidates for treating different diseases and an alternative to embryonic stem cells due to their differentiation capacity in vitro. More recent research has focused on their ability to modulate the immune response and regeneration at sites associated with inflammation, activities attributable to the release of trophic factors into the extracellular medium, a set of components known as the secretome. It has been possible to demonstrate the presence of these cells within the tumor microenvironment, which is associated with their tropism for sites of inflammation; however, their role here needs to be clarified. In different investigations, the feasibility of using MSCs or their secretome to treat cancer has been sought, with these results being ambiguous. It has been described that MSCs can be activated and present various phenotypes, which could explain the divergence in their action; however, these activation mechanisms and the different phenotypes still need to be well known. This review explores MSCs and their use in regenerative medicine with a targeted approach to cancer. Impact Statement This text addresses the diverging findings on the role of mesenchymal stem cells in the tumor microenvironment and discrepancies on the use of these cells as cancer treatment, separating the direct use of the cells from the use of the secretome. Multiple authors refer equally to the cells and their secretome to conclude on the positive or negative outcome, without taking into consideration how the cells are affected by their surroundings.

Inorganic Phosphate (Pi) in the Breast Cancer Microenvironment: Production, Transport and Signal Transduction as Potential Targets for Anticancer Strategies.

Tumor cells develop a high demand for inorganic phosphate (Pi) due to their high growth rates and energy requirements. Serum Pi concentrations in cancer patients have been found to be two to four times higher than baseline levels in healthy individuals. Twofold Pi accumulation was observed in breast cancer cells in the mouse tumor microenvironment. In the breast tumoral microenvironment, ectonucleotidases and ectophosphatases-presenting catalytic sites facing the extracellular environment-could be involved in the extracellular release of Pi to be internalized by Pi transporters to fuel the high energy requirement typical of cancer cells. Two Pi transporters were characterized in breast cancer cells (Na+-dependent and H+-dependent) with strong associations with tumor processes such as proliferation, migration, adhesion, and epithelium-mesenchymal transition (EMT). Moreover, a high extracellular Pi concentration stimulates ROS production in triple-negative breast cancer cells by Pi transport stimulation. Several compounds show a potent ability to inhibit ectonucleotidases, ectophosphatases, Pi transporters, and Pi-modulated signal pathways in breast cancer cells and regulate proliferation, migration, adhesion, and EMT. This review article aimed to gather the relevant experimental records regarding Pi's effects on the breast cancer microenvironment and points to possible inhibitors for ectonucleotidases, ectophosphatases, Pi transporters, and Pi-modulated signal pathways as potential chemotherapeutic agents or Pi acting as a potent enhancer of classical chemical-induced cytotoxicity in triple-negative breast cancer cells.

Cytokines as an important player in the context of CAR-T cell therapy for cancer: Their role in tumor immunomodulation, manufacture, and clinical implications.

CAR-T cell therapies have been recognized as one of the most advanced and efficient strategies to treat patients with hematologic malignancies. However, similar results have not been observed for the treatment of solid tumors. One of the explanations is the fact that tumors have extremely hostile microenvironments for the infiltration and effector activity of T-cells, mainly due to the presence of highly suppressive cytokines, hypoxia, and reactive oxygen species. Taking advantage of cytokines functionally, new fourth-generation CAR constructs have been developed to target tumor cells and additionally release cytokines that can contribute to the cytotoxicity of T-cells. The manufacturing process, including the use of cytokines in the expansion and differentiation of T cells, is also discussed. Finally, the clinical aspects and the influence of cytokines on the clinical condition of patients, such as cytokine release syndrome, who receive treatment with CAR-T cells are addressed. Therefore, this review aims to highlight how important cytokines are as one of the major players of cell therapy.

Modeling cancer immunoediting in tumor microenvironment with system characterization through the ising-model Hamiltonian.

BACKGROUND AND OBJECTIVE: Cancer Immunoediting (CI) describes the cellular-level interaction between tumor cells and the Immune System (IS) that takes place in the Tumor Micro-Environment (TME). CI is a highly dynamic and complex process comprising three distinct phases (Elimination, Equilibrium and Escape) wherein the IS can both protect against cancer development as well as, over time, promote the appearance of tumors with reduced immunogenicity. Herein we present an agent-based model for the simulation of CI in the TME, with the objective of promoting the understanding of this process. METHODS: Our model includes agents for tumor cells and for elements of the IS. The actions of these agents are governed by probabilistic rules, and agent recruitment (including cancer growth) is modeled via logistic functions. The system is formalized as an analogue of the Ising model from statistical mechanics to facilitate its analysis. The model was implemented in the Netlogo modeling environment and simulations were performed to verify, illustrate and characterize its operation. RESULTS: A main result from our simulations is the generation of emergent behavior in silico that is very difficult to observe directly in vivo or even in vitro. Our model is capable of generating the three phases of CI; it requires only a couple of control parameters and is robust to these. We demonstrate how our simulated system can be characterized through the Ising-model energy function, or Hamiltonian, which captures the "energy" involved in the interaction between agents and presents it in clear and distinct patterns for the different phases of CI. CONCLUSIONS: The presented model is very flexible and robust, captures well the behaviors of the target system and can be easily extended to incorporate more variables such as those pertaining to different anti-cancer therapies. System characterization via the Ising-model Hamiltonian is a novel and powerful tool for a better understanding of CI and the development of more effective treatments. Since data of CI at the cellular level is very hard to procure, our hope is that tools such as this may be adopted to shed light on CI and related developing theories.

Differences in glucose concentration shows new perspectives in gastric cancer metabolism.

Gastric cancer (GC) is among the deadliest cancers worldwide despite available therapies, highlighting the need for novel therapies and pharmacological agents. Metabolic deregulation is a potential study area for new anticancer targets, but the in vitro metabolic studies are controversial, as different ranges of glucose used in the culture media can influence results. In this study, we evaluated cellular viability, glucose uptake, and LDH activity in gastric cancer cell lines when exposed to different glucose concentrations: high (HG, 25mM), low (LG, 5.5mM), and free (FG, 0mM) glucose media. Moreover, we evaluated how glucose variations may influence cellular phenotype and the expression of genes related to epithelial-mesenchymal transition (EMT), metabolism, and cancer development in metastatic GC cells (AGP-01). Results showed that metastatic cells exposed to FG medium evidenced higher alterations when compared to other cell lines. Most phenotypic assays did not show difference when exposed to either HG or LG media. However, gene expression profile of cells exposed to LG revealed differences in mRNA levels of metabolism-related genes when compared to HG medium. According to our results, we recommend using LG medium for metabolic studies since the glucose concentration is closer to physiological levels. These findings point out new relevant targets in metabolic reprogramming that can be alternatives to current chemotherapies in patients with metastatic GC.

The cross talk between gastric cancer stem cells and the immune microenvironment: a tumor-promoting factor.

Cross talk between cancer cells and the immune system is determinant for cancer progression. Emerging evidence demonstrates that GC characteristics such as metastasis, treatment resistance, and disease recurrence are associated with a tumor subpopulation called gastric cancer stem cells (GCSCs). However, the specific interaction between GCSCs and the immune microenvironment is still under investigation. Although immune evasion has been well described for cancer stem cells (CSCs), recent studies show that GCSCs can also regulate the immune system and even benefit from it. This review will provide an overview of bidirectional interactions between CSCs and immune cells in GC, compiling relevant data about how CSCs can induce leukocyte reprogramming, resulting in pro-tumoral immune cells that orchestrate promotion of metastasis, chemoresistance, tumorigenicity, and even increase in number of cancer cells with stem properties. Some immune cells studied are tumor-associated macrophages (TAMs), neutrophils, Th17 and T regulatory (Treg) cells, mesenchymal stem cells (MSCs), and cancer-associated fibroblasts (CAFs), as well as the signaling pathways involved in these pro-tumoral activities. Conversely, although there are cytotoxic leukocytes that can potentially eliminate GCSCs, we describe mechanisms for immune evasion in GCSCs and their clinical implications. Furthermore, we describe current available immunotherapy targeting GCSC-related markers as possible treatment for GC, discussing how the CSC-modified immune microenvironment can mitigate or inactivate these immunotherapies, limiting their effectiveness. Finally, we summarize key concepts and relevant evidence to understand the cross talk between GCSCs and the immune microenvironment as an important process for effective design of therapies against GCSCs that improve the outcome of patients with GC.

ATR mediates cisplatin resistance in 3D-cultured breast cancer cells via translesion DNA synthesis modulation

Tissue architecture and cell–extracellular matrix (cell–ECM) interaction determine the organ specificity; however, the influences of these factors on anticancer drugs preclinical studies are highly neglected. For considering such aspects, three-dimensional (3D) cell culture models are relevant tools for accurate analysis of cellular responses to chemotherapy. Here we compared the MCF-7 breast cancer cells responses to cisplatin in traditional two-dimensional (2D) and in 3D-reconstituted basement membrane (3D-rBM) cell culture models. The results showed a substantial increase of cisplatin resistance mediated by 3D microenvironment. This phenotype was independent of p53 status and autophagy activity and was also observed for other cellular models, including lung cancer cells. Such strong decrease on cellular sensitivity was not due to differences on drug-induced DNA damage, since similar levels of ?-H2AX and cisplatin–DNA adducts were detected under both conditions. However, the processing of these cisplatin-induced DNA lesions was very different in 2D and 3D cultures. Unlike cells in monolayer, cisplatin-induced DNA damage is persistent in 3D-cultured cells, which, consequently, led to high senescence induction. Moreover, only 3D-cultured cells were able to progress through S cell cycle phase, with unaffected replication fork progression, due to the upregulation of translesion (TLS) DNA polymerase expression and activation of the ATR-Chk1 pathway. Co-treatment with VE-821, a pharmacological inhibitor of ATR, blocked the 3D-mediated changes on cisplatin response, including low sensitivity and high TLS capacity. In addition, ATR inhibition also reverted induction of REV3L by cisplatin treatment. By using REV3L-deficient cells, we showed that this TLS DNA polymerase is essential for the cisplatin sensitization effect mediated by VE-821. Altogether, our results demonstrate that 3D-cell architecture-associated resistance to cisplatin is due to an efficient induction of REV3L and TLS, dependent of ATR. Thus co-treatment with ATR inhibitors might be a promising strategy for enhancement of cisplatin treatment efficiency in breast cancer patients.

The emerging role of Snail1 in the tumor stroma.

The transcription factor Snail1 leads to the epithelial-mesenchymal transition by repressing the adherent and tight junctions in epithelial cells. This process is related to an increase of cell migratory and mesenchymal properties during both embryonic development and tumor progression. Although Snail1 expression is very limited in adult animals, emerging evidence has placed Snail at the forefront of medical science. As a transcriptional repressor, Snail1 confers cancer stem cell-like traits on tumor cells and promotes drug resistance, tumor recurrence and metastasis. In this review, we summarize recent reports that suggest the pro-tumorigenic roles of Snail1 expression in tumor stroma. The crosstalk between tumor and stromal cells mediated by Snail1 regulates paracrine communication, pro-tumorigenic abilities of cancer cells, extracellular matrix characteristics and mesenchymal differentiation in cancer stem cells and cancer-associated fibroblasts. Therefore, understanding the regulation and functional roles of Snail1 in the tumor microenvironment will provide us with new therapies for treating metastatic disease.