Background Treatment for malignant glioma generally consists of cytoreductive surgery followed by radiotherapy and chemotherapy. In this study, we intended to investigate the effects of 2-propylpentanoic acid （VPA）, a histone deacetylase inhibitor, on chemosensitivity and radiosensitivity in human glioma cell lines. Methods Human glioma cell lines, T98-G, and SF295, were treated with temozolomide （TMZ） or irradiation （IR）, with or without VPA （1.0 mmol/L）. Then, cytotoxicity and clonogenic survival assay was performed. Cell cycle stage, apoptosis, and autophagy were also detected using flow cytometry and dansyl monocadaverin （MDC） incorporation assay. One-way analysis of variance （ANOVA） and t-test were used to analyze the differences among variant groups. Results Mild cytotoxicity of VPA was revealed in both cell lines, T98-G and SF295, with the 50% inhibiting concentration （IC50） value of （3.85±0.58） mmol/L and （2.15±0.38） mmol/L, respectively; while the IC50 value of TMZ was （0.20±0.09） mmol/L for T98-G and （0.08＋0.02） mmol/L for SF295. Moreover, if combined with VPA （1.0 mmol/L） for 96 hours, the sensitivity of glioma cells to TMZ was significant increased （P 〈0.05）. The surviving fractions at 2 Gy （SF2） of T98-G and SF295 cells exposed to IR alone were 0.52 and 0.58. However, when VPA was combined with IR, the SF2 of T98-G and SF295 dropped to 0.39 （P=0.047） and 0.49 （P=0.049）, respectively. Treatment with VPA plus TMZ or IR also resulted in a significant decrease in the proportion of cells in the G2 phase and increased apoptotic rates as well as autophagy in T98-G and SF295 cell lines （P 〈0.01）. Conclusion VPA may enhance the activities of TMZ and IR on glioma cells possibly through cell cycle block and promote autophagy, and thus could be a potential sensitizer of glioma treatment.
O6-methylguanine DNA methyltransferase(MGMT) can remove DNA alkylation adducts, thereby repairing damaged DNA and contributing to the drug resistance of gliomas to alkylating agents. In addition, glioma stem-like cells(GSCs) have been demonstrated to be involved in the recurrence and treatment resistance of gliomas. In this study, we aimed to investigate MGMT expression and regulatory mechanisms in GSCs and the association of MGMT with temozolomide(TMZ) sensitivity. GSCs were enriched from one MGMT-positive cell line(SF-767) and 7 MGMT-negative cell lines(U251, SKMG-4, SKMG-1, SF295, U87, MGR1, and MGR2) through serum-free clone culture. GSCs from the U251G, SKMG-4G, SF295G, and SKMG-1G cell lines became MGMT-positive, but those from the U87G, MGR1G, and MGR2G cell lines remained MGMT-negative. However, all the GSCs and their parental glioma cell lines were positive for nuclear factor-κB(NF-κB). In addition, GSCs were more resistant to TMZ than their parental glioma cell lines(P < 0.05). However, there was no significant difference in the 50% inhibition concentration(IC50) of TMZ between MGMT-positive and MGMT-negative GSCs(P > 0.05). When we treated the MGMT-positive GSCs with TMZ plus MG-132(an NF-κB inhibitor), the antitumor activity was significantly enhanced compared to that of GSCs treated with TMZ alone(P < 0.05). Furthermore, we found that MGMT expression decreased through the down-regulation of NF-κB expression by MG-132. Our results show that MG-132 may inhibit NF-κB expression and further decrease MGMT expression, resulting in a synergistic effect on MGMT-positive GSCs. These results indicate that enhanced MGMT expression contributes to TMZ resistance in MGMT-positive GSCs.
