Synergistic and targeted therapy with a procaspase-3 activator and temozolomide extends survival in glioma rodent models and is feasible for the treatment of canine malignant glioma patients.

Avadhut D Joshi,Paul J Hergenrother,Betty Tyler,Jayme S Looper,Timothy M Fan,Gregory J Riggins,Alexandra Borodovsky,Rachel C Botham,Howard S Roth,Antonella Mangraviti,Lisa J Schlein,Michael Podell,Steve Joslyn

doi:10.18632/oncotarget.19085

Abstract

PurposeGlioblastoma is a deadly brain cancer with a median survival time of ∼15 months. Ionizing radiation plus the DNA alkylator temozolomide (TMZ) is the current standard therapy. PAC-1, a procaspase-3 activating small molecule, is blood-brain barrier penetrant and has previously demonstrated ability to synergize with diverse pro-apoptotic chemotherapeutics. We studied if PAC-1 could enhance the activity of TMZ, and whether addition of PAC-1 to standard treatment would be feasible in spontaneous canine malignant gliomas.Experimental DesignUsing cell lines and online gene expression data, we identified procaspase-3 as a potential molecular target for most glioblastomas. We investigated PAC-1 as a single agent and in combination with TMZ against glioma cells in culture and in orthotopic rodent models of glioma. Three dogs with spontaneous gliomas were treated with an analogous human glioblastoma treatment protocol, with concurrent PAC-1.ResultsProcaspase-3 is expressed in gliomas, with higher gene expression correlating with increased tumor grade and decreased prognosis. PAC-1 is cytotoxic to glioma cells in culture and active in orthotopic rodent glioma models. PAC-1 added to TMZ treatments in cell culture increases apoptotic death, and the combination significantly increases survival in orthotopic glioma models. Addition of PAC-1 to TMZ and radiation was well-tolerated in 3 out of 3 pet dogs with spontaneous glioma, and partial to complete tumor reductions were observed.ConclusionsProcaspase-3 is a clinically relevant target for treatment of glioblastoma. Synergistic activity of PAC-1/TMZ in rodent models and the demonstration of feasibility of the combined regime in canine patients suggest potential for PAC-1 in the treatment of glioblastoma.

Highlights

Gliomas are the most common type of malignant primary brain tumor, with ~17,000 newly diagnosed cases each year in the United States [1]
PAC-1 is cytotoxic to glioma cells in culture and active in orthotopic rodent glioma models
Synergistic activity of PAC-1/TMZ in rodent models and the demonstration of feasibility of the combined regime in canine patients suggest potential for PAC-1 in the treatment of glioblastoma

Summary

Introduction

Gliomas are the most common type of malignant primary brain tumor, with ~17,000 newly diagnosed cases each year in the United States [1]. Analysis of primary tumor samples and cancer cell lines have shown procaspase-3 levels to be elevated in numerous cancer types [9]. Common hallmarks of cancers are malignant alterations that inhibit apoptotic signaling [10], these cells paradoxically express elevated levels of the executioner caspase responsible for carrying out the cellular proteolysis. While there appears to be little or no expression of procaspase-3 in most types of normal brain cells [11], limited analysis of glioblastoma cell lines and patient samples suggests robust expression of procaspase-3 in glioblastoma [7, 12,13,14]. Because procaspase-3 is downstream in the apoptotic cascade from the typical anti-apoptotic alterations (such as Bcl-2 overexpression), this procaspase-3 elevation offers an opportunity for the selective induction of apoptotic cell death in glioblastoma

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Results

Conclusion