Multitargeted Flavonoids in Glioblastoma Therapy

Glioblastoma (GB) is the most aggressive primary central nervous system tumor in adults and the most common malignant primary brain tumor, representing approximately 50.9% of all malignant CNS tumors, with a median overall survival of approximately 14.6 months despite standard multimodal treatment, consisting of surgical resection, concurrent radiotherapy, and temozolomide (TMZ), followed by adjuvant TMZ (Stupp protocol). Tumor recurrence is inevitable and attributed to diffuse infiltration of neoplastic cells into the brain parenchyma, marked intratumoral heterogeneity, the presence of glioma stem cells, and the protection conferred by the BBB. Flavonoids are plant-derived polyphenolic compounds with more than 8000 identified. They have attracted growing interest as potential therapeutic agents because of their capacity to modulate multiple oncogenic signaling pathways and their favorable toxicity profile. Here we synthesize the preclinical evidence on the main flavonoids with documented activity in GB models, with emphasis on quercetin, apigenin, luteolin, and EGCG, while distinguishing glioblastoma-specific evidence from indirect findings derived from other experimental systems. We analyze their underlying molecular mechanisms, including induction of apoptosis through the intrinsic and extrinsic pathways, inhibition of cell proliferation and angiogenesis, suppression of migration and invasion, epigenetic modulation, and, particularly, the capacity to target the glioma stem cell population. We also examine the limited oral bioavailability and restricted penetration across the BBB, as these factors remain major barriers to translational development. We conclude with an analysis of emerging nanotechnological strategies, targeted delivery systems, and synergistic combinations with conventional chemotherapeutic agents, together with a cautious assessment of the current clinical evidence, which remains insufficient to support the use of flavonoids outside controlled clinical trials.