Mesenchymal Stem Cells Isolated From Malignant Pleural Effusion/Ascites Promote Proliferation Of Tumor Cells

INTRODUCTION:Malignant pleural effusion/ascites is a common physical sign seen in cancer patients, especially those in advanced stage. In clinical settings, more often than not, fluid draining and intra-cavity perfusing chemotherapy are used to relieve, and even eliminate, the discomforts caused by pleural effusion/ascites. Malignant pleural effusion/ascites contains many constituents, not limited to tumor cells, such as immune cells, endothelial cells, red blood cell and mesenchymal stem cells. Apart from these cells, large amount of proteins, amino acids, lipids, glucose as well as electrolytes are present in malignant pleural effusion/ascites. Compared with malignant pleural effusion/ascites, tumor microenvironment has many similarities, at least for elements in malignant pleural effusion/ascites. As a result, malignant pleural effusion/ascites is a good model for the research of tumor microenvironment. In this study, we aim to confirm that there are mesenchymal stem cells(MSCs) in malignant pleural effusion/ascites. Additionally, we plan to address the impact of MSCs on tumor cells and uncover the underlying mechanism. Based on these findings, we may develop more effective and more innocent therapy for malignant pleural effusion/ascites based on MSCs.METHODS:CD45-CD90+cells are isolated by micro-beads from malignant pleural effusion/ascites and characterized from morphology, phenotype and differentiation potentials. CD45-cells are gathered and then analyzed in situ under atomic force microscopy or observed in primary culture. Taking advantage of Transwell chambers, the chemo-attraction of MSCs by tumor cells is delineated and blocked by chemokine neutralizing antibody or receptor blocking peptide. The effects of MSCs-conditioned culture medium on tumor cells or tumor cells-conditioned culture medium on MSCs is described in density and quantified by Ki-67and average fluorescence intensity. mRNA is qualified by RT-PCR and sometimes quantified via real-time PCR. RESULTS:CD45-CD90+cells in malignant pleural effusion/ascites were adherent to plastic plates and expressed a series of molecules defining MSCs such as CD73, CD90, CD44, CD29as well as CD105, lacking CD45and CD34. More importantly, this group of cells can successfully differentiate into adipocytes, osteocytes and chondrocytes. For CD45-cells, they could form cassette-like structure, MSCs in the periphery and tumor cells in the center, both in situ and in vitro. In Transwell system, tumor cells were able to recruit MSCs, which could be interrupted by CCL2-neutralizing antibody or CCR2-blocking peptide. In vitro, MSCs-conditioned medium promoted the growth of tumor cells; similarly, tumor cells-conditioned culture medium advanced the proliferation of MSCs, as demonstrated by elevated Ki-67ratio or decreased average fluorescence intensity. And MSCs induced the transcription of IL-1b in tumor cells while tumor cells facilitated the expression of epithelial growth factor(EGF) and epithelial growth factor receptor(EGFR).CONCLUSION:Malignant pleural effusion/ascites has some MSCs with the phenotype of CD90high CD73high CD105low. And tumor cells could attract the migration of MSCs, at least via CCL2-CCR2pathway. In turn, MSCs contribute to the proliferation of tumor cells and vice versa. The growth factor pathways, including hepatocyte growth factor(HGF)/insulin growth factor(IGF)/vascular growth factor(VEGF)-EGFR, may be the underlying mechanisms for the interaction between MSCs and tumor cells.