Dactolisib outperforms Rapamycin in potentiating apoptosis induced by XPO1, Bcl-2 and Mcl-1 blockade in preclinical glioblastoma models.

Glioblastoma resists therapy through interconnected survival programs. Combined XPO1, Bcl-2, and Mcl-1 inhibition (Eltanexor, Venetoclax, A1210477; EVA) enhances the efficacy of chemotherapy, yet resistance persists. We hypothesized that PI3K/AKT/mTOR (PAM) signaling drives adaptive escape. TCGA/GTEx analyses and immunohistochemistry indicated PAM pathway activation in glioblastoma, with AKT significantly overexpressed, whereas PIK3CA showed a clear trend towards higher expression, although it did not reach statistical significance. qPCR analysis showed that PAM-component expression was highest in patient-derived glioblastoma stem-like cells (GSCs). In U87, U251, and GSCs, the dual PI3K/mTOR inhibitor Dactolisib combined with EVA and 5-Azacytidine reduced viability and induced apoptosis more effectively than any of the Rapamycin combinations, and the difference in apoptosis was most pronounced in U87 and GSCs. Dactolisib monotherapy shifted the cell cycle towards G1 with a reduced S-phase fraction. In CAM xenografts, [18F]FDG-PET/CT showed decreased tracer uptake, and Caspase-3 activation with PARP cleavage was detected only under EVA + Dactolisib treatment. Taken together, our results suggest that dual PI3K/mTOR inhibition with Dactolisib disables a critical adaptive survival axis, warranting further preclinical evaluation.