Inhibition of MGMT is involved in the anti-glioma effects of Si-Jun-Zi-Tang in combination with temozolomide

Glioma is one of the deadliest cancers. Temozolomide (TMZ) is the first-line chemotherapeutic drug for treating glioma. However, the clinical efficacy of TMZ is disappointing (1). Si-Jun-Zi-Tang is a traditional Chinese medicine formula which tonifies “Qi” in human body. In clinical practice, SJZT can enhance the efficacy of chemotherapeutics (2). Whether Si-Jun-Zi-Tang enhances TMZ’s anti-glioma effects is a question to be answered. In this study, we investigated the anti-glioma effects and mechanisms of Si-Jun-Zi-Tang extract (SJZT) in combination with TMZ (SJZT-plus-TMZ). SJZT was prepared by reflux-extraction using 95% ethanol. CCK8 assay results showed that SJZT synergized the cytotoxic effects of TMZ in U-251, T98G, U87 and SF188 glioma cells. In subcutaneous T98G glioma-bearing BALB/c-nu/nu mice, SJZT synergized TMZ in inhibiting tumor growth. Additionally, we found that SJZT reduced hepatic, renal and hematologic toxicities of TMZ. Network pharmacology predicted that MGMT was the key protein responsible for the synergistic anti-glioma effects of SJZT-plus-TMZ. It was reported that inhibition of MGMT sensitizes glioma cells to TMZ (3). RT-qPCR results revealed that SJZT and SJZT-plus-TMZ did not alter MGMT mRNA level. Immunoblotting results demonstrated that SJZT and SJZT-plus-TMZ lowered protein levels of MGMT in T98G cells. SJZT and SJZT-plus-TMZ also inhibited MGMT activity. In summary, our results indicate that SJZT synergizes the anti-glioma effects and reduces the hepatic, renal and hematologic toxicities of TMZ, and inhibition of MGMT is involved in the synergistic effects of the combination. Findings of this study suggest that SJZT-plus-TMZ can be developed into a highly effective anti-glioma medication with low toxicity.