AIMS: Malignant gliomas constitute one of the deadly brain tumors with high degeneration rate. Though temozolomide (TMZ) is the first-line drug for glioma, its efficacy has decreased due to chemo-resistance. Repurposing synthetic and natural compounds have gained increasing interest in glioma. Hence, we combined chloroquine (CHL) a synthetic drug, naringenin (NAR) and phloroglucinol (PGL) (natural derivatives), to investigate whether the apoptotic effect of these drugs both alone and in combination, enhances the anti-tumor effects of TMZ in an in vitro and in vivo orthotopic xenograft glioma model.

MAIN METHODS: The cytotoxic effect of the drugs was assessed in C6 (murine) glioma cells, U-87 MG and LN229 (human) glioblastoma cells, primary astrocytes (isolated from rat brain tissues) and HEK-293 T cells. Mitochondrial depolarization and alterations in the cell cycle was determined by confocal imaging and flow cytometry. The expression of angiogenic and apoptotic markers was evaluated using qRT-PCR and ELISA. The efficacy of the combinatorial treatment was assessed in an orthotopic xenograft model using U-87 MG cells.

KEY FINDINGS: The combinatorial treatment inhibited cell proliferation, induced apoptosis and contributed to cell cycle arrest in glioma cells. The quadruple combinatorial cocktail down-regulated BCL-2 with a concomitant decrease in VEGF. As observed in vitro, the quadruple combinatorial treatment enhanced the median survival of glioma-induced rats with lower cellularity rate.

SIGNIFICANCE: The combination of CHL, NAR and PGL synergistically potentiated the efficacy of TMZ on glioma in vitro and in vivo. Hence, this combination may characterize an advanced strategy for glioma treatment, thereby providing a possible translation to clinical trial.