Rutin increases the cytotoxicity of temozolomide in glioblastoma via autophagy inhibition.

The chemotherapeutic agent temozolomide (TMZ) is widely used in the treatment of glioblastoma multiforme (GBM). Rutin, a citrus flavonoid ecglycoside found in edible plants, has neuroprotective and anticancer activities. This study aimed to investigate the efficacy and the underlying mechanisms of rutin used in combination with TMZ in GBM. In vitro cell viability assay demonstrated that rutin alone had generally low cytotoxic effect, but it enhanced the efficacy of TMZ in a dose-dependent manner. Subcutaneous and orthotopic xenograft studies also showed that tumor volumes were significantly lower in mice receiving combined TMZ/Rutin treatment as compared to TMZ or rutin alone treatment. Moreover, immunoblotting analysis showed that TMZ activated JNK activity to induce protective response autophagy, which was blocked by rutin, resulting in decreased autophagy and increased apoptosis, suggesting that rutin enhances TMZ efficacy both in vitro and in vivo via inhibiting JNK-mediated autophagy in GBM. The combination rutin with TMZ may be a potentially useful therapeutic approach for GBM patient.

Caffeine Sensitizes U87-MG Human Glioblastoma Cells to Temozolomide through Mitotic Catastrophe by Impeding G2 Arrest.

Temozolomide (TMZ) is the first-line chemotherapeutic agent in the treatment of glioblastoma multiforme (GBM). Despite its cytotoxic effect, TMZ also induces cell cycle arrest that may lead to the development of chemoresistance and eventual tumor recurrence. Caffeine, a widely consumed neurostimulant, shows anticancer activities and is reported to work synergistically with cisplatin and camptothecin. The present study aimed to investigate the effects and the mechanisms of action of caffeine used in combination with TMZ in U87-MG GBM cells. As anticipated, TMZ caused DNA damage mediated by the ATM/p53/p21 signaling pathway and induced significant G2 delay. Concurrent treatment with caffeine repressed proliferation and lowered clonogenic capacity on MTT and colony formation assays, respectively. Mechanistic study showed that coadministration of caffeine and TMZ suppressed the phosphorylation of ATM and p53 and downregulated p21 expression, thus releasing DNA-damaged cells from G2 arrest into premature mitosis. Cell cycle analysis demonstrated that the proportion of cells arrested in G2 phase decreased when caffeine was administered together with TMZ; at the same time, the amount of cells with micronucleation and multipolar spindle poles increased, indicative of enhanced mitotic cell death. Pretreatment of cells with caffeine further enhanced mitotic catastrophe development in combined treatment and sensitized cells to apoptosis when followed by TMZ alone. In conclusion, our study demonstrated that caffeine enhanced the efficacy of TMZ through mitotic cell death by impeding ATM/p53/p21-mediated G2 arrest.