Abstract BACKGROUND Zotiraciclib, an orally administered multi-kinase inhibitor, has shown anti-glioma effect via suppression of transcriptional process and mitochondrial function. Here, we investigate the impact of zotiraciclib on the glioma immune microenvironment. METHODS Mouse glioma was generated by intracranial injection of mouse syngeneic cells (IDH1-wildtype NPA cells or IDH1R132H-mutant NPAI cells) in C57BL/6 mice. Zotiraciclib was administered (30 mg/kg, intraperitoneal injection, twice per week) starting seven days after tumor implantation. NPA and NPAI tumors were dissected after 10 and 22 days’ treatment, respectively. Immune cells in the tumor tissue were isolated and examined using flow cytometry. Primary human CD8+ cells and CD14+ monocytes isolated from the blood of a healthy donor were used to further investigate the effect of zotiraciclib (15 nM and 50 nM) on human cytotoxic T cell activation and immunosuppressive M2 macrophage polarization, respectively, using flow cytometry. RESULTS No significant difference in the abundance of T cells, myeloid cells, NK cells, NKT cells, DCs, and B cells between zotiraciclib-treated and vehicle-treated groups was detected in neither NPA nor NPAI tumors. The treatment-induced change in the abundance of cytotoxic T cells, helper T cells, macrophages, monocytes, neutrophils, M-MDSCs, PMN-MDSCs, Tregs, and M2 macrophages wasn’t observed. Zotiraciclib reduced the expansion of human CD8+ cytotoxic T cells, but did not affect the expression of CD25, HLA-DR, TNFα and IFNγ after activation in vitro. The viability of human M2 macrophages during differentiation and polarization was not affected, while the expression of CD163 and CD206 was reduced by zotiraciclib. CONCLUSIONS The immunophenotyping performed for this study demonstrates that zotiraciclib does not alter the mouse glioma immune microenvironment. Complementary studies using human immune cells shows that zotiraciclib does not suppress the activation of cytotoxic T cells but reduces the polarization of immunosuppressive M2 macrophages, supporting combining zotiraciclib and immune stimulatory approach in glioma treatment.

TMIC-50. IMPACT OF ZOTIRACICLIB ON GLIOMA TUMOR MICROENVIRONMENT