1. ¹Division of Hematology/Oncology, Cincinnati Children's Hospital Medical Center, University of Cincinnati College of Medicine, Cincinnati, Ohio, USA
2. ²Division of Infectious Diseases, Cincinnati Children's Hospital Medical Center, University of Cincinnati College of Medicine, Cincinnati, Ohio, USA
3. ³Division of Pathology, Cincinnati Children's Hospital Medical Center, University of Cincinnati College of Medicine, Cincinnati, Ohio, USA
4. ⁴Dardinger Center for Neuro-Oncology and Neurosciences, Department of Neurological Surgery, The Ohio State University Medical Center and James Hospital Comprehensive Cancer Center, Columbus, Ohio, USA

Correspondence: Timothy P. Cripe, Division of Hematology/Oncology, Cincinnati Children's Hospital Medical Center, University of Cincinnati College of Medicine, MLC R7015, 3333 Burnet Avenue, Cincinnati, Ohio 45229, USA. E-mail: timothy.cripe@cchmc.org

Received 14 August 2007; Accepted 21 February 2008; Published online 25 March 2008.

Abstract

Oncolytic herpes simplex virus (oHSV) mutants are under development as anticancer therapeutics. One such vector, rRp450, is ICP6-deleted and expresses a prodrug enzyme for cyclophosphamide (CPA) (rat CYP2B1). Little is known about rRp450's toxicity profile, especially in combination with CPA. We tested rRp450/CPA for antitumor efficacy in an aggressive human xenograft sarcoma model, measured virus production in primary cells, and tested rRp450/CPA for safety in immunocompetent mice. CPA enhanced the antitumor efficacy of rRp450. Relative to wild-type HSV-1, rRp450 replication was attenuated 10,000-fold in human primary hepatocytes, differentiated primary foreskin keratinocytes, and primary Schwann cells. In vivo, intravenous and intracranial (IC) rRp450 injection at the strength of 10⁸ plaque-forming units (pfu) alone or followed 24 hours later by intraperitoneal (IP) CPA was well tolerated and had no significant effect clinically on blood counts or chemistries. By contrast, intravenous KOS was found to be uniformly neurotoxic at 10⁵ and fatal at 10⁶ pfu, and IC virus was fatal in most mice at 10⁴ pfu. Low levels of virus DNA were detected in some organs following intravenous and IC virus injection, but were not significantly altered by CPA. HSV replication was not detected in reactivation studies of isolated organs. Our findings suggest rRp450/CPA is safe and warrants further study as a potential combination in anticancer therapeutics.