Resistance of human glioblastoma multiforme cells to growth factor inhibitors is overcome by blockade of inhibitor of apoptosis proteins
David S. Ziegler, … , Leigh Zawel, Andrew L. Kung
David S. Ziegler, … , Leigh Zawel, Andrew L. Kung
Published August 1, 2008
Citation Information: J Clin Invest. 2008;118(9):3109-3122. https://doi.org/10.1172/JCI34120.
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Research Article Oncology

Resistance of human glioblastoma multiforme cells to growth factor inhibitors is overcome by blockade of inhibitor of apoptosis proteins

Abstract

Multiple receptor tyrosine kinases (RTKs), including PDGFR, have been validated as therapeutic targets in glioblastoma multiforme (GBM), yet inhibitors of RTKs have had limited clinical success. As various antiapoptotic mechanisms render GBM cells resistant to chemo- and radiotherapy, we hypothesized that these antiapoptotic mechanisms also confer resistance to RTK inhibition. We found that in vitro inhibition of PDGFR in human GBM cells initiated the intrinsic pathway of apoptosis, as evidenced by mitochondrial outer membrane permeabilization, but downstream caspase activation was blocked by inhibitor of apoptosis proteins (IAPs). Consistent with this, inhibition of PDGFR combined with small molecule inactivation of IAPs induced apoptosis in human GBM cells in vitro and had synergistic antitumor effects in orthotopic mouse models of GBM and in primary human GBM neurospheres. These results demonstrate that concomitant inhibition of IAPs can overcome resistance to RTK inhibitors in human malignant GBM cells, and suggest that blockade of IAPs has the potential to improve treatment outcomes in patients with GBM.

Authors

David S. Ziegler, Renee D. Wright, Santosh Kesari, Madeleine E. Lemieux, Mary A. Tran, Monish Jain, Leigh Zawel, Andrew L. Kung

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Figure 2

Synergistic effects of LBW242 and imatinib.

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Synergistic effects of LBW242 and imatinib. (A) U87 and LN827 cells were...
(A) U87 and LN827 cells were treated with the indicated concentrations of imatinib in combination with LBW242 (50 μM) or DMSO control. Cell numbers were determined 72 hours later via MTS. Data are expressed as mean ± SEM of triplicates. Similar results were observed in >3 independent experiments. (B) U87 and LN827 cells were seeded in 96-well plates and treated with LBW242 (50 μM), imatinib (8 μM), LBW242 plus imatinib, or DMSO control. The number of viable cells was measured via MTS assay after 24, 48, 72, and 96 hours. The data are expressed relative to the first day of treatment and are represented as the mean ± SEM of triplicates. (C) Serum-starved LN827 cells were treated for 90 minutes with dosages of imatinib and LBW242 as indicated. Levels of PDGFR and phospho-PDGFR were measured following immunoprecipitation and immunoblotting. (D) U87 and LN827 cells were seeded in 96-well plates and treated with the PDGFR inhibitor AMN107 at the dosages indicated in combination with LBW242 (50 μM) or DMSO control. Cellular proliferation was measured via MTS assay after 72 hours of incubation. Data are represented as the mean ± SEM or triplicates.