Introduction While it is accepted that inflammation is a key component of cancer development, the intricate mechanism linking the two are not fully defined. Unparalleled progress has been underway to provide better understanding of this mechanism. We investigate the role of bacterial microbiota in promoting an inflammatory environment through the induction of the pro-inflammatory molecule, S100A7, and its activation of STAT-3 signaling pathways to promote tumor growth and metastasis in breast cancer (BC). Methods Immune-competent mouse models of orthotopic breast cancer was used to identify and characterize populations of bacterial microbiota in the cancerous breast tissue at tumor onset. Isolated tissues were homogenized and cultured, then processed for DNA extraction. Bacterial species were identified by aligning the sequences on NCBI BLAST. Mouse mammary tissue and tumors were analyzed for S100a7 after intraperitoneal exposure to LPS after cancer cell injections. Isolated tissues were analyzed by IHC, Western Blot analysis and real time RT-PCR. mRNA and Protein expression using real time PCR, western blot and flow cytometry, and binding assays analyzed expression and affinity of LPS/S100A7/TLR4 in BC cell lines in vitro under varying conditions. Protein expression and In vitro functional assays including matrigel invasion and wound closure assays determined the effect of LPS/S100A7 on TLR4 and STAT-3 expression and signaling pathways in promoting tumor invasiveness. Results We observed microbiota in cancerous breast tissue, which is predominantly composed of Gram-negative bacteria at tumor onset. The population of mainly gram negative bacteria at tumor initiation is unique from those populations from feces and skin. This suggests that breast tissue microbiota may be a potential source of LPS in breast tumors. Stimulation with LPS induces secretion/expression of S100A7 in mouse mammary tissue and tumors, as well as BC cell lines. Furthermore, inhibition of LPS by polymixin B decreases S100A7 to basal levels in BC cell lines. LPS/S100A7 combinational treatment has an additive effect on the invasive potential induced by LPS in BC cell lines as shown by invasion assays and wound closure assays. S100A7 over expression increases TLR4 expression as observed by TLR4 mRNA by real time PCR and protein by flow cytometry. Furthermore, secreted S100A7 protein promotes interaction between S100A7 protein and TLR4 receptor in cell lines with endogenous TLR4 expression. In addition, both S100A7 and LPS stimulation of TLR4 can activate STAT3 signaling pathway, and inhibition of either S100A7 and or TLR4 impairs the invasiveness of BC cell lines. Conclusion A unique population of gram negative bacteria characterizes breast cancer tissues. LPS of bacterial cells walls, representative of gram negative bacteria induces S100A7, which interacts with TLR4 to activate the STAT-3 pathway in tumors. This LPS-S100A7-TLR4-STAT3 axis in turn increases the invasiveness of tumor cells to promote tumor metastasis. This suggests that microbiota plays an important role in the initiation and progression of breast cancer through regulation of the pro-inflammatory molecule S100A7. Citation Format: Wilkie T, Zhao H, Nasser M, Ahirwar D, Mishra S, Satoskar A, Pancholi V, Ganju R. The role of S100A7 in microbiota mediated inflammation and breast cancer progression [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P1-01-19.
This abstract was not presented at the symposium.
Metabolism of immune cells plays an important role in regulating tumor growth by modulating the anti-tumor M1 phenotype or pro-tumor M2 phenotype in macrophages. However, the role of bone marrow derived macrophages (BMDM) and their metabolic profile in promoting tumor growth is unknown. Slit2 is an anti-tumor molecule that is suppressed in breast cancer; however, the mechanism by which Slit2 mediates its function is not fully elucidated. We hypothesize that Slit2 mediated metabolic reprogramming of BMDMs favors anti-tumor M1 phenotype in these macrophages, which in turn reduces tumor growth. Here we assessed cellular metabolism in BMDMs from the MMTV-PyMT mouse, a model showing spontaneous tumor development. Shortly, age matched female mice with palpable tumors and control mice without tumors were treated with recombinant Slit2 (Slit2) or PBS intraperitoneally every third for 2 weeks (n=4 mice per group). Tumor volume was measured in each mouse before and at the end of treatment. Next, mice were euthanized and bone marrow was flushed from both the tibia and femor for culturing in vitro in the presence of macrophage chemotactic factor rich conditioned media. Rate of glycolysis was described based on extracellular acidification rate (ECAR) as measured by the Seahorse Bioanalyzer® under glycostress conditions. Lactate dehydrogenase (LDH) activity, which is linked with breast cancer progression and pro-tumor macrophage phenotype in experimental models, was also assayed using a commercially available kit. Finally, to elucidate potential pathways involved in Slit2 induced metabolic change, we assessed the expression of several proteins and factors involved in cellular metabolism. Firstly, we observed that PyMT mice treated with Slit2 showed lower tumor volume compared to mice treated with PBS confirming Slit2 anti-tumor activity. Hematoxylin & Eosin staining of tumor sections from these mice also showed better tissue structure, with a higher cytoplasm to nuclear ratio in Slit2 treated PyMT mice compared to PBS treated mice. Furthermore, BMDMs from PyMT mice show lower aerobic glycolysis with higher lactate dehydrogenase activity (LDH) compared to control mice. Moreover, treatment with Slit2 appeared to lower LDH activity and trended to increase glycolysis in the BMDMs isolated from Slit2 treated PyMT compared to PBS treated PyMT. Expression analyses using quantitative PCR showed a 2-4 fold decrease in PGC-1α and CPT-2 in Slit2 treated BMDMs, indicating a reduction in fatty acid oxidation in these cells. This coupled with a 3 fold increase in IL-6 expression, and 2-3 fold decrease in arginase and IL-10 expression in tumor tissue suggest a potential shift from pro-tumor M2 to anti-tumor M1 phenotype. In spite of these preliminary trends, changes in metabolism and associated signals may be clearer in isolated, enriched populations of macrophages alone. Nevertheless, our findings suggest that Slit2 reduces tumor growth by affecting immune cell metabolism. Furthermore, these studies provide novel evidence of the potential immunomodulatory effects of Slit2 on macrophages. This may lead to development of Slit2 as a novel non-invasive therapeutic strategy against highly aggressive and metastatic cancers associated with high mortality and low quality of life. Citation Format: Kaul K, Ahirwar DK, Benej M, Denko N, Ganju R. Slit2 induced anti-tumor activity may be mediated through metabolism driven immunomodulation [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-02-08.
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