Resistance of human glioblastoma multiforme cells to growth factor inhibitors is overcome by blockade of inhibitor of apoptosis proteins
David S. Ziegler, Renee D. Wright, Santosh Kesari, Madeleine E. Lemieux, Mary A. Tran, Monish Jain, Leigh Zawel, Andrew L. Kung
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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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 6

AMN107 and LBW242 combine to inhibit the growth of intracranial LN827 orthografts and primary human glioblastoma neurospheres in vitro and in vivo.

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AMN107 and LBW242 combine to inhibit the growth of intracranial LN827 or...
(A) Bioluminescent images from control and treated animals at the start and end of a 15-day treatment with the indicated doses of LBW242 and/or AMN107. (B) Tumor burden was assessed by serial bioluminescence imaging and expressed relative to the start of treatment. Data are mean values ± SEM, n = 6 animals per group. (C) Primary human glioma neurospheres were derived from 2 different patients (BT69, white bars; BT79, black bars) and were treated with imatinib and/or LBW242. (D) Total neurosphere numbers were counted and photographed 10 days after plating, with data expressed as relative mean ± SD of triplicates. (E) Tumor neurospheres treated for 72 hours with imatinib, AMN107 (AMN), and/or LBW242 (LBW) were lysed and activated caspase-3 was assessed by immunoblot. (F) Kaplan-Meier survival curves for mice implanted with primary human glioma orthografts. Mice were treated for 12 consecutive days with vehicle, AMN107, LBW242, or a combination of AMN107 and LBW242, with treatments beginning 12 days after implant. *P = 0.01, combination versus all other groups, for experimental day 60 and all time points thereafter.