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 1,* , Rachel C. Botham 2,* , Lisa J. Schlein 3 , Howard S. Roth 2 , Antonella Mangraviti 1 , Alexandra Borodovsky 1 , Betty Tyler 1 , Steve Joslyn 4 , Jayme S. Looper 5 , Michael Podell 6 , Timothy M. Fan 7 , Paul J. Hergenrother 2 and Gregory J. Riggins 1 1 Department of Neurosurgery, School of Medicine, Johns Hopkins University, Baltimore, MD, USA 2 Department of Chemistry, University of Illinois Urbana-Champaign, Urbana, IL, USA 3 Department of Pathobiology, University of Illinois Urbana-Champaign, Urbana, IL, USA 4 VetCT Australia, Fremantle WA, Australia 5 Department of Veterinary Clinical Sciences, Louisiana State University, Baton Rouge, LA, USA 6 Department of Neurology, MedVet Chicago, Chicago, IL, USA 7 Department of Veterinary Clinical Medicine, University of Illinois Urbana-Champaign, Urbana, IL, USA * These authors have contributed equally to this work Correspondence to: Gregory J. Riggins, email: // Paul J. Hergenrother, email: // Timothy M. Fan, email: // Keywords : PAC-1, procaspase-3 activator, glioblastoma, small molecule therapy Received : March 29, 2017 Accepted : June 09, 2017 Published : July 07, 2017 Abstract Purpose: Glioblastoma 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 Design: Using 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. Results: Procaspase-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. Conclusions: Procaspase-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.