STAT3 Activation In Tumor Cells Research Articles

Abstract 2782: Small molecule H182 suppresses Stat3 activation in tumor cells and combines with radiation therapy to block breast tumor growth in mouse syngeneic models

Abstract Signal transducer and activator of transcription 3 (Stat3) is a latent transcription factor that contributes to tumor cell growth and survival in constitutively-active form in several types of human cancers, and hence, serves as a therapeutic target. The azetidine-based compound, H182 irreversibly binds to Stat3. In cell-free DNA-binding assay, H182 selectively inhibited Stat3 DNA-binding activity (IC50 0.38-0.66 μM) over Stat1 or Stat5 (IC50>15.8 μM) in vitro. In treated pancreatic cancer cells, H182 specifically blocked the association of Stat3 with gp130 and JAK2, and inhibited Stat3 tyrosine phosphorylation and DNA-binding activity. Coimmunoprecipitation and colocalization studies of hemagglutinin (HA)-tagged Stat3 and EGFP-tagged Stat3 expressed in prostate cancer cells showed that treatment with H182 blocked the HA-Stat3:EGFP-Stat3 interactions in intact cells. Immunofluorescence staining with laser-scanning confocal microscopy analysis for the intracellular localization of Stat3 showed treatment of H182 disrupted Stat3 nuclear accumulation and promoted the aggregation of Stat3 at the perinuclear region. H182 consequently suppressed Stat3-dependent transcriptional activity and the expression of Stat3 downstream genes, including Cyclin A, Bcl-2, Cyclin B1, and Mcl-1. Moreover, H182 significantly inhibited the colony survival, migration, and invasion in vitro of breast, pancreatic and prostate cancer cells harboring aberrant Stat3 activation. Significantly, in vivo administration of H182 in combination with radiation induced a strong antitumor response against mouse triple-negative breast cancer in syngeneic models and prolonged survival. Thus, our study provides a novel Stat3 inhibitor with significant antitumor activity against human tumors cancer harboring persistently active STAT3. Citation Format: Yue Chen, Peibin Yue, Wenzhen Fu, Weiliang Chen, Kathleen M. Kershaw, Stephen L. Shiao, Marcus A. Tius, Francisco Lopez-Tapia, James Turkson. Small molecule H182 suppresses Stat3 activation in tumor cells and combines with radiation therapy to block breast tumor growth in mouse syngeneic models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2782.

Cyclic sulfur compounds targeting macrophage polarization into M2/protumor phenotype and their anti-tumor effects.

Tumor-associated macrophages (TAMs), especially the M2-like phenotype, promote tumor progression, making them candidate targets for anti-tumor therapy. We previously discovered a cyclic sulfur compound, Onionin A (ONA), which suppresses tumor progression by inhibiting the M2-polarization of TAMs. In the present study, we sought to find new candidate compounds possessing a stronger effect compared to ONA by exploring compounds with structures similar to those of ONA among several cyclic sulfur compounds. A total of 81 cyclic sulfur compounds were screened, and their effects on macrophage polarization toward an M2-like phenotype were tested using human monocyte-derived macrophages (HMDMs). The anti-tumor effects of the identified candidate compounds were examined in a tumor-bearing mouse model. Three candidate compounds inhibited both IL-10- and tumor culture supernatant (TCS)-induced M2-polarization of HMDMs. These compounds also suppressed STAT3 activation in HMDMs stimulated by IL-10 and TCS, whereas these compounds had no effect on STAT3 activation in tumor cells. Furthermore, these compounds inhibited tumor cell proliferation under co-culture conditions with HMDMs, indicating that the three candidate compounds suppress tumor proliferation by regulating cell-cell interactions between tumor cells and macrophages. In addition, two of these candidate compounds had inhibitory effects on tumor growth and lung metastasis in the LM8 tumor-bearing mouse model. Our study identified new candidate cyclic sulfur compounds for anti-tumor therapy targeting the M2-polarization of TAMs.

Targeting TGFβR2-mutant tumors exposes vulnerabilities to stromal TGFβ blockade in pancreatic cancer.

TGFβ is important during pancreatic ductal adenocarcinoma (PDA) progression. Canonical TGFβ signaling suppresses epithelial pancreatic cancer cell proliferation; as a result, inhibiting TGFβ has not been successful in PDA. In contrast, we demonstrate that inhibition of stromal TGFβR2 reduces IL‐6 production from cancer‐associated fibroblasts, resulting in a reduction of STAT3 activation in tumor cells and reversion of the immunosuppressive landscape. Up to 7% of human PDA have tumor cell‐specific deficiency in canonical TGFβ signaling via loss of TGFβR2. We demonstrate that in PDA that harbors epithelial loss of TGFβR2, inhibition of TGFβ signaling is selective for stromal cells and results in a therapeutic benefit. Our study highlights the potential benefit of TGFβ blockade in PDA and the importance of stratifying PDA patients who might benefit from such therapy.

Upregulation of IL-6 in CUL4B-deficient myeloid-derived suppressive cells increases the aggressiveness of cancer cells.

Cancer progression depends on a tumor-supportive microenvironment. Myeloid-derived suppressor cells (MDSCs) represent key cellular components in tumor microenvironment and have been demonstrated to facilitate tumor progression by restricting host immune responses and by sustaining the malignancy of cancer cells. CUL4B, which assembles the CUL4B-RING E3 ligase complex (CRL4B), possesses a potent oncogenic property in cancer cells by epigenetically inactivating many tumor suppressors. However, CUL4B in hematopoietic cells exerts tumor-suppressive effect by restricting the accumulation and function of MDSCs. How CUL4B regulates the function of MDSCs is not fully characterized. In the present study, we demonstrate that the enhanced growth and metastasis of transplanted tumor cells in hematopoietic or myeloid cell-specific Cul4b knockout recipient mice is mediated by increased production of IL-6 in MDSCs. CUL4B complex epigenetically represses IL-6 transcription in myeloid cells. The IL-6 produced by MDSCs renders cancer cells stem cell-like properties by activating IL-6/STAT3 signaling. This crosstalk was effectively blocked either by blocking IL-6 in MDSCs or by inhibition of STAT3 activation in tumor cells. These findings provide a new mechanistic insight into the cancer-promoting property of MDSCs.

Abstract B68: Targeted inhibition of Tgfβr2 reduces IL-6 production from cancer-associated fibroblasts, suppresses Stat3 activation in pancreatic cancer cells and reverses immunosuppression

Abstract Pancreatic cancer is characterized by dense stroma consisting of myofibroblasts, abundant extracellular matrix (ECM) and inflammatory/immune cells. Elevated levels of transforming growth factor β (TGFβ), a prominent driver of stromal accumulation, is a negative prognostic indicator for pancreatic cancer patients. However, inhibition of TGFβ has been challenging due to the context-dependent tumor suppressor function of TGFβ in pancreatic cancer. We reported previously that neutralizing the activity of murine TGFβ receptor 2 (Tgfβr2) using a monoclonal antibody (2G8), has potent antitumor activity in orthotopic human pancreatic tumor xenografts. The findings in xenografts highlight that TGFβ induction of stromal cell function is critical for its impact on tumor cell behavior and PDA progression and supports that inhibition of TGFβ-dependent effector functions on stromal cells has potential efficacy in PDA. Herein we demonstrate that inhibition of murine Tgfβr2 reduces IL-6 production from cancer-associated fibroblasts (CAFs), resulting in a reduction of Stat3 activation in tumor cells and reversion of the immunosuppressive landscape of murine models of PDA. Moreover, the reduction of stromal IL-6 results in activation of NK cells. In summary, we found TGFβ induced IL-6 secretion from CAFs in PDA contributes to tumorigenesis and immunosuppression and can be abrogated by inhibition of stromal Tgfβr2. Citation Format: Huocong Huang, Moriah Hagopian, Wenting Du, Yuqing Zhang, Kyla E. Driscoll, Rolf A. Brekken. Targeted inhibition of Tgfβr2 reduces IL-6 production from cancer-associated fibroblasts, suppresses Stat3 activation in pancreatic cancer cells and reverses immunosuppression [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2017 Oct 1-4; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2018;6(9 Suppl):Abstract nr B68.

The STAT3 inhibitor pyrimethamine displays anti-cancer and immune stimulatory effects in murine models of breast cancer.

The transcription factor signal activator and transducer or transcription (STAT3), which regulates genes controlling proliferation, survival, and invasion, is activated inappropriately in many human cancers, including breast cancer. Activation of STAT3 can lead to both malignant cellular behavior and suppression of immune cell function in the tumor microenvironment. Through a chemical-biology screen, pyrimethamine (PYR), an FDA approved anti-microbial drug, was identified as an inhibitor of STAT3 function at concentrations known to be achieved safely in humans. We report that PYR shows therapeutic activity in two independent mouse models of breast cancer, with both direct tumor inhibitory and immune stimulatory effects. PYR-inhibited STAT3 activity in TUBO and TM40D-MB metastatic breast cancer cells in vitro and inhibited tumor cell proliferation and invasion into Matrigel basement membrane matrix. In tumor-transplanted mice, PYR had both direct and indirect tumor inhibitory effects. Tumor-bearing mice treated with PYR showed reduced STAT3 activation in tumor cells, attenuated tumor growth, and reduced tumor-associated inflammation. In addition, expression of Lamp1 by tumor infiltrating CD8+ T cells was elevated, indicating enhanced release of cytotoxic granules. These findings suggest that PYR may have beneficial effects in the treatment of breast cancer.

IL6 Receptor Blockade Enhances Chemotherapy Efficacy in Pancreatic Ductal Adenocarcinoma.

Inflammation mediated by activation of JAK/STAT signaling is a major cause of chemotherapy resistance in cancer. We studied the impact of selectively blocking the IL6 receptor (IL6R) as a strategy to inhibit IL6-induced STAT activation and to overcome chemoresistance in pancreatic ductal adenocarcinoma (PDAC). To do this, STAT activation was investigated in tumors arising spontaneously in LSL-KrasG12D/+;LSL-Trp53R172H/+;Pdx-1Cre (KPC) mice. Plasma from patients with PDAC was assessed for its ability to activate STAT3/SOCS3 in human monocytes using immunofluorescence microscopy and quantitative gene expression assays. KPC mice and syngeneic mice (wild type and IL6-/-) implanted with KPC-derived cell lines were treated with an IL6R-blocking antibody (anti-IL6R). The impact of treatment on tumor growth in KPC mice and mice with KPC-derived tumor implants was monitored using ultrasonography and calipers, respectively. Tumors were analyzed by IHC to detect changes in STAT activation, tumor viability, and proliferation. We found that STAT3 was the most activated STAT protein in PDAC tumors from KPC mice. Plasma from patients with advanced PDAC stimulated STAT3/SOCS3 activation in human monocytes. In mice, anti-IL6R antibodies targeted Ly6Chi monocytes, inhibited STAT3 activation in tumor cells, and decreased tumor cell proliferation in vivo IL6R blockade in combination with chemotherapy induced tumor cell apoptosis, tumor regressions, and improved overall survival. Overall, we show that IL6 signaling drives STAT3 activation in tumor cells and mediates chemoresistance in PDAC. Thus, disrupting IL6 signaling using anti-IL6R antibodies holds promise for improving chemotherapy efficacy in PDAC. Mol Cancer Ther; 16(9); 1898-908. ©2017 AACR.

Onionin A inhibits epithelial ovarian cancer proliferation by the suppression of STAT3 activation in tumor cells and macrophages

Onionin A inhibits epithelial ovarian cancer proliferation by the suppression of STAT3 activation in tumor cells and macrophages

Abstract SY06-02: Revisiting the STATs of cancer: Emergence of stem-like cancer cells

Abstract Activation of the STAT3 signaling pathway is now well established as an important factor in cancer progression and as a promising molecular target for cancer therapy. Persistent STAT3 activation in tumor cells prevents apoptosis and promotes cell proliferation. In the tumor microenvironment, STAT3 activation enhances angiogenesis and suppresses anti-tumor immune responses. Communication between tumor cells and stromal cells in the tumor microenvironment, by inflammatory cytokines like interleukin (IL)-6, results in a feed-forward loop that enhances cancer progression and confers resistance to therapy. Recently, we have uncovered another critical role for STAT3 in cancer progression and resistance to therapy. We now show that activation of STAT3 signaling promotes a stem-like cell phenotype in prostate cancer, concomitant with loss of androgen receptor (AR) expression. AR is important for prostate cancer progression, and androgen deprivation often leads to drug resistance and eventual cancer recurrence. We demonstrate that loss of AR expression as a consequence of androgen ablation results in STAT3 activation in prostate cancer cells. This STAT3 activation in turn leads to development of prostate cancer stem-like cells. AR downregulation-induced STAT3 activation is mediated through increased IL-6 expression in the tumor microenvironment. Elevated stem-like cell markers in human prostate tumor specimens coincides with high STAT3 activity and low AR expression. Treatment of mice with soluble IL-6 receptor or silencing STAT3 in tumor cells suppresses prostate tumor growth and inhibits development of stem-like cancer cells. In sum, our results demonstrate that blockade of AR mediates activation of STAT3 signaling through up-regulation of IL-6, which is associated with development of a stem-like cancer cell phenotype. Conversely, inhibition of the IL-6/STAT3 pathway diminishes the stem-like cancer cell population, and results in reduced tumor growth. Our findings provide new mechanistic insights into the role of STAT3 activation upon AR blockade on prostate cancer relapse and drug resistance. We further propose inhibition of STAT3 signaling in combination with anti-androgens as a potential strategy to prevent emergence of drug-resistant recurrent prostate cancer. Citation Format: Richard Jove. Revisiting the STATs of cancer: Emergence of stem-like cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr SY06-02. doi:10.1158/1538-7445.AM2014-SY06-02

Importance of direct macrophage ‐ Tumor cell interaction on progression of human glioma

We previously showed tumor-associated macrophages/microglia (TAMs) polarized to the M2 phenotype were significantly involved in tumor cell proliferation and poor clinical prognosis in patients with high grade gliomas. However, the detailed molecular mechanisms involved in the interaction between TAMs and tumor cells have been unclear. Current results reveal that, in coculture with human macrophages, BrdU incorporation was significantly elevated in glioma cells, and signal transducer and activator of transcription-3 (Stat3) activation was found in both cell types. Direct mixed coculture led to stronger Stat3 activation in tumor cells than did indirect separate coculture in Transwell chamber dishes. Screening with an array kit for phospho-receptor tyrosine kinases revealed that phosphorylation of macrophage-colony stimulating factor receptor (M-CSFR, CD115, or c-fms) is possibly involved in this cell-cell interaction; M-CSFR activation was detected in both cell types. Coculture-induced tumor cell activation was suppressed by siRNA-mediated downregulation of the M-CSFR in macrophages and by an inhibitor of M-CSFR (GW2580). Immunohistochemical analysis of phosphorylated (p)M-CSFR, pStat3, M-CSF, M2 ratio, and MIB-1(%) in high grade gliomas revealed that higher staining of pM-CSFR in tumor cells was significantly associated with higher M-CSF expression and higher MIB-1(%). Higher staining of pStat3 was associated with higher MIB-1(%). High M2 ratios were closely correlated with high MIB-1(%) and poor clinical prognosis. Targeting these molecules or deactivating M2 macrophages might be useful therapeutic strategies for high grade glioma patients.

M2 Macrophage/Microglial Cells Induce Activation of Stat3 in Primary Central Nervous System Lymphoma

Primary central nervous system lymphoma (PCNSL) is one of the most aggressive malignant lymphomas with a median survival of less than 20~40 months. Interest in signal transducer and activator of transcription 3 (Stat3) has increased during the past decade because Stat3 activation was found to contribute to tumor progression by inducing angiogenesis, immunosuppression, and metastasis. We previously demonstrated a significant correlation between Stat3 activation in tumor cells and infiltrating anti-inflammatory (M2) macrophages. Here, we focused on the phenotypes of infiltrating macrophages/microglial cells and Stat3 activation in PCNSL cells. The correlation of Stat3 activation or density of M2 macrophage infiltration with patient prognosis was also evaluated. We performed immunostaining for CD68, CD163, CD204, and pStat3 using paraffin-embedded PCNSL specimens obtained from 43 patients. CD163 and CD204 served as markers of the M2 phenotype. Dense infiltration of CD68(+) macrophages was found in all samples. High numbers of CD163(+) and CD204(+) M2 macrophages/microglial cells were observed in 29 and 25 cases, respectively. Stat3 activation in lymphoma cells was enhanced in the patients who showed denser infiltration of CD163(+) macrophages/microglial cells in tumor tissues. In vitro co-culture experiment to investigate cell-cell interactions between macrophages and lymphoma cells found that Stat3 in lymphoma cells was strongly activated by co-culture with macrophages. Numbers of CD68(+), CD163(+), and CD204(+) tumor-associated macrophages/microglial cells (TAMs) and Stat3 activation in lymphoma cells were not correlated with prognosis. However, because Stat3 involvement in tumor development was demonstrated in several malignant tumors, our present finding that cell-cell interactions of M2 macrophage/microglial cells with lymphoma cells induced Stat3 activation may provide novel insights into PCNSL pathogenesis.

TGF-β Suppresses Tumor Progression in Colon Cancer by Inhibition of IL-6 trans-Signaling

Alterations of TGF-β signaling have been described in colorectal cancer, although the molecular consequences are largely unknown. By using transgenic mice overexpressing TGF-β or a dominant-negative TGF-βRII, we demonstrate that TGF-β signaling in tumor infiltrating T lymphocytes controls the growth of dysplastic epithelial cells in experimental colorectal cancer, as determined by histology and a novel system for high-resolution chromoendoscopy. At the molecular level, TGF-β signaling in T cells regulated STAT-3 activation in tumor cells via IL-6. IL-6 signaling required tumor cell-derived soluble IL-6R rather than membrane bound IL-6R and suppression of such TGF-β-dependent IL-6 trans-signaling prevented tumor progression in vivo. Taken together, our data provide novel insights into TGF-β signaling in colorectal cancer and suggest novel therapeutic approaches for colorectal cancer based on inhibition of TGF-β-dependent IL-6 trans-signaling.