Cai, Wenjing

OBJECTIVE Defects in the apoptotic machinery and augmented survival signals contribute to drug resistance in glioblastoma (GBM). Moreover, another complexity related to GBM treatment is the concept that GBM development and recurrence may arise from the expression of GBM stem cells (GSCs). Therefore, the use of a multifaceted approach or multitargeted agents that affect specific tumor cell characteristics will likely be necessary to successfully eradicate GBM. The objective of this study was to investigate the usefulness of sulforaphane (SFN)—a constituent of cruciferous vegetables with a multitargeted effect—as a therapeutic agent for GBM. METHODS The inhibitory effects of SFN on established cell lines, early primary cultures, CD133-positive GSCs, GSC-derived spheroids, and GBM xenografts were evaluated using various methods, including GSC isolation and the sphere-forming assay, analysis of reactive oxygen species (ROS) and apoptosis, cell growth inhibition assay, comet assays for assessing SFN-triggered DNA damage, confocal microscopy, Western blot analysis, and the determination of in vivo efficacy as assessed in human GBM xenograft models. RESULTS SFN triggered the significant inhibition of cell survival and induced apoptotic cell death, which was associated with caspase 3 and caspase 7 activation. Moreover, SFN triggered the formation of mitochondrial ROS, and SFN-triggered cell death was ROS dependent. Comet assays revealed that SFN increased single- and double-strand DNA breaks in GBM. Compared with the vehicle control cells, a significantly higher amount of γ-H2AX foci correlated with an increase in DNA double-strand breaks in the SFN-treated samples. Furthermore, SFN robustly inhibited the growth of GBM cell–induced cell death in established cell cultures and early-passage primary cultures and, most importantly, was effective in eliminating GSCs, which play a major role in drug resistance and disease recurrence. In vivo studies revealed that SFN administration at 100 mg/kg for 5-day cycles repeated for 3 weeks significantly decreased the growth of ectopic xenografts that were established from the early passage of primary cultures of GBM10. CONCLUSIONS These results suggest that SFN is a potent anti-GBM agent that targets several apoptosis and cell survival pathways and further preclinical and clinical studies may prove that SFN alone or in combination with other therapies may be potentially useful for GBM therapy.

OBJECTIVE Improvement in treatment outcome for patients with glioblastoma multiforme (GBM) requires a multifaceted approach due to dysregulation of numerous signaling pathways. The murine double minute 2 (MDM2) protein may fulfill this requirement because it is involved in the regulation of growth, survival, and invasion. The objective of this study was to investigate the impact of modulating MDM2 function in combination with front-line temozolomide (TMZ) therapy in GBM. METHODS The combination of TMZ with the MDM2 protein–protein interaction inhibitor nutlin3a was evaluated for effects on cell growth, p53 pathway activation, expression of DNA repair proteins, and invasive properties. In vivo efficacy was assessed in xenograft models of human GBM. RESULTS In combination, TMZ/nutlin3a was additive to synergistic in decreasing growth of wild-type p53 GBM cells. Pharmacodynamic studies demonstrated that inhibition of cell growth following exposure to TMZ/nutlin3a correlated with: 1) activation of the p53 pathway, 2) downregulation of DNA repair proteins, 3) persistence of DNA damage, and 4) decreased invasion. Pharmacokinetic studies indicated that nutlin3a was detected in human intracranial tumor xenografts. To assess therapeutic potential, efficacy studies were conducted in a xenograft model of intracranial GBM by using GBM cells derived from a recurrent wild-type p53 GBM that is highly TMZ resistant (GBM10). Three 5-day cycles of TMZ/nutlin3a resulted in a significant increase in the survival of mice with GBM10 intracranial tumors compared with single-agent therapy. CONCLUSIONS Modulation of MDM2/p53-associated signaling pathways is a novel approach for decreasing TMZ resistance in GBM. To the authors' knowledge, this is the first study in a humanized intracranial patient-derived xenograft model to demonstrate the efficacy of combining front-line TMZ therapy and an inhibitor of MDM2 protein–protein interactions.

Abstract Glioblastoma multiforme (GBM) comprises the largest group of brain tumors which are drug resistant and respond very poorly to the current therapies. In this study, we used sulforaphane (SFN), a multi-targeting agent with cancer preventive and anti-cancer activities and showed that it targets GBM established cell lines, early primary cultures, and CD133+ GBM stem cells as well as in GBM stem-like spheroids. SFN at 5-50 μM triggered significant inhibition of cell survival and induced apoptotic cell death in GBM cells and CD133+ stem cells isolated from four GBM cell lines. SFN induced apoptosis in U87MG cells was associated with caspase-7 activation. Moreover, SFN triggered formation of intracellular reactive oxygen species (ROS) and when the cells were pre-treated with 10 mM N-acetyl cysteine (NAC), ROS production and cell survival in cells treated with 5-10 μM were similar to the control untreated U87MG cells, revealing that SFN-triggered cell death is ROS-dependent. Moreover, SFN-generated ROS in U87MG cells were formed at the Mitochondrial Respiratory Chain (MRC) level. SFN also increased expression of the TRAIL receptor DR5 in GBM cells, U87MG and SF767 cells by 24 h post-exposure. Moreover, as revealed by comet assay, SFN increased single- and double-strand DNA breaks in GBM. Compared to untreated control cells, a significantly higher amount of γ-H2AX foci and as consequence higher number of DNA double-strand breaks (DSBs) breaks were observed in the SFN-treated sample. In vivo studies, using NOD/SCID mice revealed that SFN administration via oral gavage at 100 mg/kg for 3 cycles significantly decreases the growth of ectopic xenografts established from the early passage primary cultures of GBM10. Our results show that SFN robustly inhibits growth of GBM cells in vitro and in vivo and induces cell death in established cell cultures, early passage primary cultures, as well as it is effective in eliminating GBM cancer stem cells, which play a major role in drug resistance and disease recurrence. These results suggest that use of SFN alone or in combination with other agents, may potentially improve survival of brain tumor patients. Citation Format: Khadijeh Bijangi-Vishehsaraei, Mohammad R. Saadatzadeh, Haiyan Wang, Malgorzata M. Kamocka, Wenjing Cai, Aaron A. Cohen-Gadol, Stacey L. Halum, Karen E. Pollok, Jann N. Sarkaria, Ahmad R. Safa. Sulforaphane depresses proliferation and induces cell death in glioblastoma multiforme (GBM) cells, GBM stem cell-like spheroids, and tumor xenografts through modulation of multiple cell signaling pathways. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2267. doi:10.1158/1538-7445.AM2014-2267