STEM-13EXPRESSION OF STEM CELL, PROLIFERATION AND CHEMORESISTANCE MARKERS IN GLIOMA CELLS IN THE TUMOR PERIPHERY

Gliomas are highly infiltrative tumors incurable with surgery. Although surgery removes the bulk tumor, tumor cells in the periphery are left behind resulting in tumor relapses. The aim of the present study was to characterize the phenotype of tumor cells in the periphery focusing on tumor stemness, proliferation and chemoresistance. This was investigated in situ in patient glioma tissue as well as in orthotopic glioblastoma xenografts. We identified 26 gliomas having the R132 mutation in Isocitrate DeHydrogenase 1 (mIDH1). A double immunofluorescence approach identifying mIDH1 positive tumor cells and a panel of markers was used. The panel comprised of five different stem cell markers (CD133, Musashi-1, Bmi-1, Sox-2 and Nestin), the proliferationmarker Ki-67 as well as MGMT. Computer-based automated classifiers were designed to measure the mIDH1 positive nucleus area-fraction of the chosen markers. Moreover orthotopic glioblastoma xenografts from five different patient-derived spheroid cultures were obtained. A double immunofluorescence approach identifying vimentin positive tumor cells and the same panel of markers were used, except MGMT since most tumors were MGMT methylated. The results showed that tumor cells in the periphery of patient gliomas expressed stem cell markers, however at a significantly lower level than in the tumor core. The Ki-67 level was significantly reduced, whereas the reduction in the MGMT level did not reach significance. In orthotopic glioblastoma xenografts same results were obtained for Sox-2, Nestin and Ki-67, where as the other markers were expressed at the same level in core and periphery. In conclusion tumor cells in the periphery of patient gliomas displayed reduced but to a large degree preserved stemness and proliferation. Novel therapies aiming at preventing recurrence should therefore take tumor stemness into account. Orthotopic glioblastoma xenografts to a large degree mimic patient tumors and therefore have a promising translational potential.