B591 Infectious RNA: A Novel Therapeutic Modality for Myeloma

Abstract

Introduction and Aims: Coxsackievirus A21 (CVA21) selectively propagates in myeloma cells leading to eradication of myeloma x enografts in SCID mice. However, repeat intravenous administration of this agent in a clinical setting will be problematic since CVA21 viral particles are neutralized by antiviral antibodies whose circulating titers will increase between treatments. Also, because of the high mutation rates of picornaviral polymerases (3 r 10-3), picornavirus preparations are heavily contaminated with ‘quasispecies’ whose genome sequences do not match the product specification. On average, each picornavirus has one or two randomly mutated bases in its genome. Picornaviruses therefore present substantial manufacturing challenges. To address these problems, we sought to determine whether infectious RNA could be used in place of virus particles to initiate an oncolytic CVA21 infection in vivo. Materials and Methods: Infectious RNA encoding CVA21 was transcribed from plasmid DNA using T7 polymerase (err or rate 3 r 10-6) and purified by gel-extraction. Varying doses of RNA (1, 2, 4, 8, 16 or 32 micrograms) or CVA21 virus particles were injected directly into subcutaneous KAS6/1 myeloma xenografts (0.5 cm average diameter) in tumor-bearing SCID mice. Animals were monitored for tumor regression, signs of CVA21-induced myositis (a known toxicity of the virus in this model), and CVA21 viremia. In ongoing studies, RNA corresponding to a retargeted CVA21 that is nontoxic to muscle is also being administered to KAS6/1 tumorbearing animals. Results and Conclusions: Within 48 hours of injecting the RNA into subcutaneous KAS6/1 xenografts, high titers of infectious CVA21 virions wer e detected in the bloodstream. Tumors regressed rapidly thereafter and mice developed signs of myositis. At euthanasia, CVA21 was recovered from regressing tumors and from skeletal muscles. Treatment outcomes did not differ between animals treated by intratumoral injection of RNA or fully infectious CVA21 virus particles. Dose-response studies showed that an effective oncolytic infection could be established by intratumoral injection of as little as 1 mg of infectious RNA. The oncolytic infection could also be initiated by intravenous injection of infectious RNA. Our study demonstrates that INA is a highly promising alternative drug formulation for oncolytic CVA21 virotherapy of multiple myeloma.