Efficacy and Safety of the Oncolytic Herpes Simplex Virus rRp450 Alone and Combined With Cyclophosphamide

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 approximately 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 10(8) 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 10(5) and fatal at 10(6) pfu, and IC virus was fatal in most mice at 10(4) 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.

Myxoma Virus Virotherapy for Glioma in Immunocompetent Animal Models: Optimizing Administration Routes and Synergy with Rapamycin

“…Our study was not designed to test which of these drugs was superior because of several limitations. The dose of cyclophosphamide we used (60 mg/kg) was lower than other studies [(>100 mg/kg for rats (50) or even 300 mg/kg for mice (29)] because these higher doses were not tolerated in the animals used in this study. Hence, the degree of immunosuppression with cyclophosphamide in our hands may have been less than in other studies.…”

Oncolytic HSV-1 Virotherapy: Clinical Experience and Opportunities for Progress

“…Inserted into the ICP6 locus is the rat cytochrome P450 2B1 ( CYP2B1) gene, which encodes for the enzyme that activates oxazophosphorine prodrugs (e.g., cyclophosphamide and ifosfamide) into their anticancer metabolites (e.g., phosphoramide mustard) [16]. Treatment of rats bearing intracranial gliomas and mice with hepatic and sarcoma xenografts resulted in significant anti-tumor efficacy [17, 18]. The replication of rRp450 has been shown to be attenuated in human and mouse hepatocytes by >4 logs compared with wild type KOS [19], and indeed the vector appears to be safe when given by intracranial, intraperitoneal, and intravenous routes alone and in combination with cyclophosphamide [18].…”

“…Treatment of rats bearing intracranial gliomas and mice with hepatic and sarcoma xenografts resulted in significant anti-tumor efficacy [17, 18]. The replication of rRp450 has been shown to be attenuated in human and mouse hepatocytes by >4 logs compared with wild type KOS [19], and indeed the vector appears to be safe when given by intracranial, intraperitoneal, and intravenous routes alone and in combination with cyclophosphamide [18]. rRp450 has also now even been shown to exhibit an antitumor effect when given intravenously, which can be enhanced by combination with anti-VEGF antibodies [20].…”

“…Unlike the preclinical studies that suggested this cancer type is susceptible to HSV1716 oncolysis [32], no antitumor activity was apparent, suggesting in vivo barriers to virus spread must be identified and overcome for this disease such as virus receptor expression [33, 34]. HSV1716 is currently being studied in patients 13 to 30 years of age with non-CNS solid tumors at Cincinnati Children’s Hospital Medical Center (www.clinicaltrial.gov NCT00931931) based on preclinical efficacy of oncolytic HSV in models of sarcomas and neuroblastoma [18, 35–40]. …”

Oncolytic herpes simplex virus 1 (HSV-1) vectors: Increasing treatment efficacy and range through strategic virus design

“…Several vectors have since been engineered to express prodrugs that convert systemically administered prodrugs allowing for ultralocalized concentrations of (activated) drugs at levels previously unattainable without unacceptable systemic toxicity. Most commonly, vectors are armed with enzymes that convert prodrugs into activated forms of classic chemotherapeutic agents, such as cyclophosphamide, taxanes or alkylating agents (102,(113)(114)(115)(116)(117)(118).…”