METASTATIC AND NON METASTATIC OS CELLS HAVE DISTINCT DIFFERENTIATION CAPACITY AND FUNCTIONAL EFFECTS UPON MESENCHYMAL STEM CELLS, ASSOCIATED TO PROTEOMICS SIGNATURES

LUCIANA M GUTIERREZ; EUGENIE S KLEINERMAN; MARCELA F BOLONTRADE; MATIAS VALENZUELA ALVAREZ; LAURA ALANIZ; ALEJANDRO CORREA; JUAN BAYO; MARIANA GARCIA

Congreso; Isscr 2019; 2019

Osteosarcoma (OS) is the most common bone malignant tumor, affecting mainlychildren and young adults. Lung metastasis is a therapeutic challenge during OSprogression (15?30% survival rate with pulmonary metastasis at diagnosis).Through proteomic run and raw data analysis we identified differential proteomicsignatures between metastatic OS (LM7) and non-metastatic (SAOS2) OS celllines. These differences were associated with variations in both the differentiation capacity and the capacity to induce it. We demonstrated that SAOS2 had higher differentiation towards osteoblastic lineage, suggesting that LM7 cells suffered a loss of differentiation potential in the process of gaining metastatic traits. We used OS cells conditioned medium (CM) to evaluate their capacity to induce differentiation. SAOS2 CM increased osteoblastic differentiation of both metastatic and non-metastatic cells, with a significant effect on SAOS2 cells, suggesting that their paracrine effect may account for calcification observed in lung metastasis. However, LM7 CM did induce differentiation of stromal cell components such as microendothelium, present in the tumor environment. Mesenchymal Stem Cells (MSCs) are critical for tumor niche formation and this step is determinant for metastasis. We evaluated the functional effect of OS cells CM over MSCs stemness capacity. LM7 CM increased the number of cells per colony (CFU-F assay), and the cells adopted a stem-like morphology. By analyzing in MSCs the expression of genes related to an undifferentiated state, LM7 CM induced a higher expression of Nanog, Sox2 and OCT4, while SAOS2 CM diminished their expression, with a notorious decrease in Sox2. All these point out that SAOS2 and LM7 did not only differ in their metastatic capacity, with this being one of the multiple phenotypic-functional differences among both cells types adapted to different microenvironmental selection pressures. Thus, OS metastatic cells would lose characteristics associated to a bonemicroenvironment, gaining traits that could favour the establishment of a suitable metastatic niche, and acquiring a stem cell-like state. Further, the identification of markers associated to this gain in metastatic traits would help in designing best prognostic and early diagnostic tools for OS lung metastatic disease.