Biogenic ZnO Nanoparticles Synthesized by B. licheniformis: A Selective Cytotoxicity Against NG-108 Glioblastoma Cells

Abstract

Glioblastoma multiforme (GBM) remains the most aggressive primary brain tumor with median survival of 14.6 months, necessitating novel therapeutic approaches. Here, we report the biogenic synthesis of zinc oxide nanoparticles (ZnO NPs) using Bacillus licheniformis strain TT14s isolated from mining environments and demonstrate their selective anti-glioma efficacy. ZnO NPs exhibited hexagonal wurtzite structure (crystallite size: 15.48 nm) with spherical morphology (19.37 ± 5.28 nm diameter) as confirmed by XRD, HRTEM, and comprehensive physicochemical characterization. Colloidal stability analysis revealed an isoelectric point at pH 7.46, ensuring optimal dispersion in biological media. Cytotoxicity evaluation revealed remarkable selectivity: at 100 μg/mL, ZnO NPs reduced NG-108 glioblastoma cell viability to 36.07 ± 1.89% within 1 h while maintaining 78.9 ± 0.94% viability in primary retinal cells. The selective cytotoxicity was attributed to the interplay of convergent mechanisms acting under dark conditions, including defect-mediated ROS generation supported by photoluminescence analysis revealing a characteristic oxygen vacancy emission at 550 nm, pH-dependent dissolution enhanced in the acidic tumor microenvironment, and preferential cellular uptake by rapidly proliferating cancer cells with compromised antioxidant defenses. Time-course analysis demonstrated concentration-dependent effects with therapeutic windows favoring normal cell preservation. The intrinsic cytotoxic activity under dark laboratory conditions eliminates the need for external activation, providing practical advantages for therapeutic applications. These findings establish ZnO NPs as promising candidates for targeted glioblastoma therapy, warranting further in vivo validation and mechanistic elucidation for clinical translation.