Histone deacetylase 6 regulates the immunosuppressive properties of cancer-associated fibroblasts in breast cancer through the STAT3–COX2-dependent pathway

The natural polyphenol curcumin induces apoptosis by suppressing STAT3 signaling in esophageal squamous cell carcinoma

Background

We and others have previously shown that the STAT3 signaling pathway is activated in some esophageal squamous cell carcinoma (ESCC) cells and is required for the survival and growth of these primary ESCC-derived xenografts. It has also been shown that the natural polyphenol curcumin is an effective anti-tumor agent.

Methods

Luciferase assay and immunoblotting were performed to examine whether curcumin suppressed STAT3 signaling. CCK-8 assay and xenografts were utilized for analyzing ESCC cell growth in culture and mice. Soft agar assay was carried out to determine the colony formation ability of ESCC cells in the presence or absence of curcumin. Cell death and cell cycle were assessed by In CELL Analyzer 2000. Immunohistochemistry and TUNEL assay were used for detecting apoptosis in ESCC tisuses. Molecular docking was performed to evaluate the interaction of curcumin with JAK2. JAK2 activity was assessed using an in vitro cell-free system. HE staining was used to evaluate the ESCC tissues.

Results

The natural polyphenol curcumin inhibited STAT3 phosphorylation rapidly and blocked STAT3-mediated signaling in ESCC cells. It also induced growth arrest and apoptosis in cultured ESCC cells, which were attenuated by enforced expression of STAT3. Furthermore, curcumin preferentially blocked the growth of primary ESCC-derived xenografts that harbored activated STAT3.

Conclusions

Curcumin is able to exert anti-tumor action through inhibiting the STAT3 signaling pathway. Giving its wide use in traditional medicines with low toxicity and few adverse reactions, it is conceivable that curcumin might be further explored as a unique STAT3 inhibitor for anti-cancer therapies.

CD8+ cytotoxic T lymphocytes in cancer immunotherapy: A review

CD8⁺ cytotoxic T lymphocytes (CTLs) are preferred immune cells for targeting cancer. During cancer progression, CTLs encounter dysfunction and exhaustion due to immunerelated tolerance and immunosuppression within the tumor microenvironment (TME), with all favor adaptive immune-resistance. Cancer-associated fibroblasts (CAFs), macrophage type 2 (M2) cells, and regulatory T cells (Tregs) could make immunologic barriers against CD8 ⁺ T cell-mediated antitumor immune responses. Thus, CD8 ⁺ T cells are needed to be primed and activated toward effector CTLs in a process called tumor immunity cycle for making durable and efficient antitumor immune responses. The CD8 ⁺ T cell priming is directed essentially as a corroboration work between cells of innate immunity including dendritic cells (DCs) and natural killer (NK) cells with CD4 ⁺ T cells in adoptive immunity. Upon activation, effector CTLs infiltrate to the core or invading site of the tumor (so-called infiltrated-inflamed [I-I] TME) and take essential roles for killing cancer cells. Exogenous reactivation and/or priming of CD8 ⁺ T cells can be possible using rational immunotherapy strategies. The increase of the ratio for costimulatory to coinhibitory mediators using immune checkpoint blockade (ICB) approach. Programmed death-1 receptor (PD-1)-ligand (PD-L1) and CTL-associated antigen 4 (CTLA-4) are checkpoint receptors that can be targeted for relieving exhaustion of CD8 ⁺ T cells and renewing their priming, respectively, and thereby eliminating antigen-expressing cancer cells. Due to a diverse relation between CTLs with Tregs, the Treg activity could be dampened for increasing the number and rescuing the functional potential of CTLs to induce immunosensitivity of cancer cells.

Tumor microenvironment: Interactions and therapy

Tumor microenvironment (TME) is a host for a complex network of heterogeneous stromal cells with overlapping or opposing functions depending on the dominant signals within this milieu. Reciprocal paracrine interactions between cancer cells with cells within the tumor stroma often reshape the TME in favor of the promotion of tumor. These complex interactions require more sophisticated approaches for cancer therapy, and, therefore, advancing knowledge about dominant drivers of cancer within the TME is critical for designing therapeutic schemes. This review will provide knowledge about TME architecture, multiple signaling, and cross communications between cells within this milieu, and its targeting for immunotherapy of cancer.

Extracellular matrix (ECM) stiffness and degradation as cancer drivers

Alteration in the density and composition of extracellular matrix (ECM) occurs in tumors. The alterations toward both stiffness and degradation are contributed to tumor growth and progression. Cancer-associated fibroblasts (CAFs) are the main contributors to ECM stiffness and degradation. The cells interact with almost all cells within the tumor microenvironment (TME) that could enable them to modulate ECM components for tumorigenic purposes. Cross-talks between CAFs with cancer cells and macrophage type 2 (M2) cells are pivotal for ECM stiffness and degradation. CAFs induce hypoxia within the TME, which is one of the key inducers of both stiffness and degradation. Cancer cell modulatory roles in integrin receptors are key for adjusting ECM constituents to either fates. Cancer cell proliferation, migration, and invasion as well as angiogenesis are consequences of ECM stiffness and degradation. ECM stiffness in a transforming growth factor-β (TGF-β) related pathway could make a bridge in the basement membrane, and ECM degradation in a matrix metalloproteinase (MMP)-related pathway could make a path in the TME, both of which contribute to cancer cell invasion. ECM stiffness is also obstructive for drug penetration to the tumor site. Therefore, it would be a promising strategy to make a homeostasis in ECM for easy penetration of chemotherapeutic drugs and increasing the efficacy of antitumor approaches. MMP and TGF-β inhibitors, CAF and M2 reprogramming toward their normal counterparts, reduction of TME hypoxia and hampering integrin signaling are among the promising approaches for the modulation of ECM in favor of tumor regression.

Contribution of regulatory T cells to cancer: A review

Regulatory T cells (Tregs) represent a low number of T-cell population under normal conditions, and they play key roles for maintaining immune system in homeostasis. The number of these cells is extensively increased in nearly all cancers, which is for dampening responses from immune system against cancer cells, metastasis, tumor recurrence, and treatment resistance. The interesting point is that apoptotic Tregs are stronger than their live counterparts for suppressing responses from immune system. Tregs within the tumor microenvironment have extensive positive cross-talks with other immunosuppressive cells including cancer-associated fibroblasts, cancer cells, macrophage type 2 cells, and myeloid-derived suppressor cells, and they have negative interactions with immunostimulatory cells including cytotoxic T lymphocytes (CTL) and natural killer cells. A wide variety of markers are expressed in Tregs, among them forkhead box P3 (FOXP3) is the most specific marker and the master regulator of these cells. Multiple signals are activated by Tregs including transforming growth factor-β, signal transducer and activator of transcription, and mTORC1. Treg reprogramming from an immunosuppressive to immunostimulatory proinflammatory phenotype is critical for increasing the efficacy of immunotherapy. This would be applicable through selective suppression of tumor-bearing receptors in Tregs, including FOXP3, programmed death-1, T-cell immunoglobulin mucin-3, and CTL-associated antigen-4, among others. Intratumoral Tregs can also be targeted by increasing the ratio for CTL/Treg.