SYNERGY OF CONCURRENT PI3K-MAPK INHIBITION IN GLIOBLASTOMA STEM CELLS: VIABILITY, MORPHOLOGICAL CHANGES AND <EM >IN VIVO</EM> HISTOPATHOLOGY

Glioblastoma is the most aggressive primary brain tumor with a median survival of only 15 months. A key challenge it is the persistence of glioblastoma stem cells (GSCs), which display overactivation of PI3K-mTOR and MAPK pathways. These pathways are the target of novel kinase-directed therapies. However, they converge in downstream functions, compensate for each other and promote treatment resistance. To overcome this, PI3K and MAPK co-treatments are being investigated. Our aim is to shed light on their mechanisms of action using in vitro and in vivo models. GSCs were concurrent and sequential co-treated for 48 h and 72 h at 100 and 500 nM for PI3K inhibitors (alpelisib or copanlisib), and 50 nM for MAPK inhibitor (trametinib). Cell morphology was assessed by optical microscopy and viability was measured by MTT assay. Long-concurrent co-treatment enhanced a differentiation-like morphology, and concurrent co-treatment for 48 h reduced cell viability more effectively than the sequential approach. To evaluate the concurrent co-treatment in vivo, a preliminary experiment was performed. GSCs and drugs were intracranially injected using stereotaxy into C57BL/6 mice. After 24 days, brains were dissected and histopathology was analyzed by hematoxylin and eosin staining. Control group showed marked haemorrhage, whereas co-treated group exhibited a higher immune cell infiltrate. In summary, concurrent co-treatment in vitro displays greater synergy, and histopathology reveals marked differences between groups. Therefore, concurrent co-treatment may represent a potential therapy by simultaneously blocking compensatory mechanisms.