YM-155 Potentiates the Effect of ABT-737 in Malignant Human Glioma Cells via Survivin and Mcl-1 Downregulation in an EGFR-Dependent Context

Abstract

Antiapoptotic proteins are commonly overexpressed in gliomas, contributing to therapeutic resistance. We recently reported that clinically achievable concentrations of the Bcl-2/Bcl-xL inhibitor ABT-737 failed to induce apoptosis in glioma cells, with persistent expression of survivin and Mcl-1. To address the role of these mediators in glioma apoptosis resistance, we analyzed the effects of YM-155, a survivin suppressant, on survival on a panel of glioma cell lines. YM-155 inhibited growth, and downregulated survivin and Mcl-1 in a dose- and cell line-dependent manner. Whereas U373, LN18, LNZ428, T98G, LN229, and LNZ308 cells exhibited an IC50 of 10–75 nM, A172 cells were resistant (IC50 ~ 250 nM). No correlation was found between sensitivity to YM-155 and baseline expression of survivin or cIAP-1/cIAP-2/XIAP. However, strong correlation was observed between EGFR activation levels and YM-155 response, which was confirmed using EGFR-transduced versus wild-type cells. Because we postulated that decreasing Mcl-1 expression may enhance glioma sensitivity to ABT-737, we examined whether cotreatment with YM-155 promoted ABT-737 efficacy. YM-155 synergistically enhanced ABT-737-induced cytotoxicity and caspase-dependent apoptosis. Down-regulation of Mcl-1 using shRNA also enhanced ABT-737-inducing killing, confirming an important role for Mcl-1 in mediating synergism between ABT-737 and YM-155. As with YM-155 alone, sensitivity to YM-155 and ABT-737 inversely correlated with EGFR activation status. However, sensitivity could be restored in highly resistant U87-EGFRvIII cells by inhibition of EGFR or its downstream pathways, highlighting the impact of EGFR signaling on Mcl-1 expression and the relevance of combined targeted therapies to overcome the multiple resistance mechanisms of these aggressive tumors.

Cucurbitacin-I inhibits Aurora kinase A, Aurora kinase B and survivin, induces defects in cell cycle progression and promotes ABT-737-induced cell death in a caspase-independent manner in malignant human glioma cells

“…30 In summary, our data reveal that the treatment of glioma cells with cucurbitacin potentiated ABT-737-induced cytotoxicity by down-regulating Aurora kinase A, Aurora kinase B and survivin regardless of EGFR/PTEN/ p53 status, suggesting the utilization of these agents for GBM.…”

“…3A) and a histogram obtained from multiple FACS analyses are shown in Figure 3B. Compared to the control (DMSO treated cells), cells accumulated in the G2/M phase with cucurbitacin treatment in a dose-dependent manner irrespective of EGFR or TP53 or PTEN status (see Table 1 for genetic features Cotreatment with cucurbitacin and ABT-737 potentiates glioma cell death in a caspase-independent manner Because survivin 30 signaling inhibited the clinical efficacy of ABT-737 and cucurbitacin affected survivin both at mRNA and protein levels ( Fig. 2C and 2D), we hypothesized that .…”

“…Cell culture conditions of these cell lines were as previously described. 7,30,31,79 Reagents and antibodies ABT-737 and cucurbitacin-I (referred as cucurbitacin in this manuscript) were purchased from Chemie Tek (Indianapolis, IN) and Sigma (St. Louis, MO) respectively. All antibodies were purchased from Cell Signaling Technology (Beverly, MA).…”

“…As a single agent ABT-737, a novel Bcl -2/ Bcl -xL inhibitor triggers apoptosis in various types of human cancers including multiple myeloma, leukemia, lymphoma and small cell lung cancer. [25][26][27][28][29] However, we [30][31][32] and others 33 have demonstrated that ABT-737 minimally inhibits cell growth in glioma when used as a single agent. The complexity of the interactions between cell surface receptors and downstream signaling targets has called into question the clinical utility of blocking any target in isolation, and the results of single agent-based strategies have to date been disappointing in patients with glioma.…”

“…The complexity of the interactions between cell surface receptors and downstream signaling targets has called into question the clinical utility of blocking any target in isolation, and the results of single agent-based strategies have to date been disappointing in patients with glioma. 2,4 Combination approaches can enhance ABT-737-induced glioma cell death, including use with the proteasomal inhibitor bortezomib, 34 the survivin inhibitor YM-155, 30 the PI3K/Akt inhibitor NVP-BKM120, 31 the histone deacetylase inhibitor vorinostat, 35 the alkylating agent temozolomide, 36 or the death receptor ligand TRAIL. 37 We performed a screen of ABT-737 in combination with other signaling inhibitors used at clinically achievable doses; combination of ABT-737 and cucurbitacin-I promoted apoptosis in malignant human glioma cell lines.…”