Proteasome inhibition with bortezomib induces cell death in GBM stem-like cells and temozolomide-resistant glioma cell lines, but stimulates GBM stem-like cells' VEGF production and angiogenesis

Abstract

Object. Recurrent malignant gliomas have inherent resistance to traditional chemotherapy. Novel therapies target specific molecular mechanisms involved in abnormal signaling and resistance to apoptosis. The proteasome is a key regulator of multiple cellular functions, and its inhibition in malignant astrocytic lines causes cell growth arrest and apoptotic cell death. The proteasome inhibitor bortezomib was reported to have very good in vitro activity against malignant glioma cell lines, with modest activity in animal models as well as in clinical trials as a single agent. In this paper, the authors describe the multiple effects of bortezomib in both in vitro and in vivo glioma models and offer a novel explanation for its seeming lack of activity.Methods. Glioma stem-like cells (GSCs) were obtained from resected glioblastomas (GBMs) at surgery and expanded in culture. Stable glioma cell lines (U21 and D54) as well as temozolomide (TMZ)-resistant glioma cells derived from U251 and D54-MG were also cultured. GSCs from 2 different tumors, as well as D54 and U251 cells, were treated with bortezomib, and the effect of the drug was measured using an XTT cell viability assay. The activity of bortezomib was then determined in D54-MG and/or U251 cells using apoptosis analysis as well as caspase-3 activity and proteasome activity measurements. Human glioma xenograft models were created in nude mice by subcutaneous injection. Bevacizumab was administered via intraperitoneal injection at a dose of 5 mg/kg daily. Bortezomib was administered by intraperitoneal injection 1 hour after bevacizumab administration in doses of at a dose of 0.35 mg/kg on days 1, 4, 8, and 11 every 21 days. Tumors were measured twice weekly.Results. Bortezomib induced caspase-3 activation and apoptotic cell death in stable glioma cell lines and in glioma stem-like cells (GSCs) derived from malignant tumor specimens Furthermore, TMZ-resistant glioma cell lines retained susceptibility to the proteasome inhibition. The bortezomib activity was directly proportional with the cells' baseline proteasome activity. The proteasome inhibition stimulated both hypoxia-inducible factor (HIF)-1a and vascular endothelial growth factor (VEGF) production in malignant GSCs. As such, the VEGF produced by GSCs stimulated endothelial cell growth, an effect that could be prevented by the addition of bevacizumab (VEGF antibody) to the media. Similarly, administration of bortezomib and bevacizumab to athymic mice carrying subcutaneous malignant glioma xenografts resulted in greater tumor inhibition and greater improvement in survival than administration of either drug alone. These data indicate that simultaneous proteasome inhibition and VEGF blockade offer increased benefit as a strategy for malignant glioma therapy.Conclusions. The results of this study indicate that combination therapies based on bortezomib and bevacizumab might offer an increased benefit when the two agents are used in combination. These drugs have a complementary mechanism of action and therefore can be ...

Phase 2 Study of Bortezomib Combined With Temozolomide and Regional Radiation Therapy for Upfront Treatment of Patients With Newly Diagnosed Glioblastoma Multiforme: Safety and Efficacy Assessment

“…Consequently, finding new agents to integrate into standard treatment for newly-diagnosed GBM is required to improve patient survival. Bortezomib is an FDA approved proteasome inhibitor for hematologic malignances that has shown efficacy towards GBM cell lines in vitro and in vivo (7–8, 14–15). Therefore, we sought to gain a greater insight into the use of bortezomib as a treatment for newly-diagnosed GBM patients, by combining it into current standard of care and examined its efficacy as well as safety.…”

PDGF Engages an E2F-USP1 Signaling Pathway to Support ID2-Mediated Survival of Proneural Glioma Cells

“…Among the cellular processes that are critical for glioblastoma pathology, protein degradation is emerging as an important regulator of tumorigenesis and a target for cancer treatment (13)(14)(15). Ubiquitination and its reverse, deubiquitination, are major regulatory pathways that control protein degradation and contribute to cell-cycle regulation, stem cell maintenance, and cellular survival, as well as other biologic activities of importance for tumorigenesis (16,17).…”

Glioma‐derived cancer stem cells are hypersensitive to proteasomal inhibition

“…Recent studies suggest that PIs can also induce apoptosis in human glioma cell lines and primary glioblastoma multiforme (GBM) explants . PIs were also shown to induce apoptosis in glioma‐derived stem‐like cells . In a recent siRNA screening to identify genes important for GBM cell survival, 22% (12/55) of the hits were components of the 20S and 26S proteasome subunits .…”