CCL2-CCR2 Axis Inhibition in Osteosarcoma Cell Model: The Impact of Oxygen Level on Cell Phenotype.

Treatment of osteosarcoma is hampered by tumor hypoxia and requires alternative approaches. Although the CCL2-CCR2 axis is indispensable in tumor-induced inflammation and angiogenesis, its blockade has not been effective to date. This study aimed to characterize how CCR2 inhibition affects the crosstalk of osteosarcoma cells with immune cells to better delineate tumor resistance mechanisms that help withstand such treatment. In this study, 143B cells were exposed to healthy donor PBMC supernatants in a transwell assay lacking direct cell-to-cell contact and subjected to different oxygen concentrations. In addition, mice bearing orthotopic 143B tumors were subjected to CCR2 antagonist treatment. Our findings show that hypoxic conditions alter cytokine and cancer- related protein expression on cells and impair CCR2 antagonist effects in the experimental osteosarcoma model. CCL2-CCR2 axis blockade in the 143B xenografts, which are positive for hypoxia marker CAIX, did not slow 143B tumor growth or metastasis but altered tumor microenvironment by VEGFR downregulation and shift in the CD44-positive cell population towards high CD44 expression. This study highlights differential responses of tumor cells to CCR2 antagonists in the presence of different oxygen saturations and expands our knowledge of compensatory mechanisms leading to CCL2-CCR2 treatment resistance.