BACKGROUND The prognosis of patients with recurrent World Health Organization (WHO) grade IV malignant glioma is dismal, and there is currently no effective therapy. We conducted a dose-finding and toxicity study in this population of patients, evaluating convection-enhanced, intratumoral delivery of the recombinant nonpathogenic polio–rhinovirus chimera (PVSRIPO). PVSRIPO recognizes the poliovirus receptor CD155, which is widely expressed in neoplastic cells of solid tumors and in major components of the tumor microenvironment. METHODS We enrolled consecutive adult patients who had recurrent supratentorial WHO grade IV malignant glioma, confirmed on histopathological testing, with measurable disease (contrast-enhancing tumor of ≥1 cm and ≤5.5 cm in the greatest dimension). The study evaluated seven doses, ranging between 107 and 1010 50% tissue-culture infectious doses (TCID50), first in a dose-escalation phase and then in a dose-expansion phase. RESULTS From May 2012 through May 2017, a total of 61 patients were enrolled and received a dose of PVSRIPO. Dose level −1 (5.0×107 TCID50) was identified as the phase 2 dose. One dose-limiting toxic effect was observed; a patient in whom dose level 5 (1010 TCID50) was administered had a grade 4 intracranial hemorrhage immediately after the catheter was removed. To mitigate locoregional inflammation of the infused tumor with prolonged glucocorticoid use, dose level 5 was deescalated to reach the phase 2 dose. In the dose-expansion phase, 19% of the patients had a PVSRIPO-related adverse event of grade 3 or higher. Overall survival among the patients who received PVSRIPO reached a plateau of 21% (95% confidence interval, 11 to 33) at 24 months that was sustained at 36 months. CONCLUSIONS Intratumoral infusion of PVSRIPO in patients with recurrent WHO grade IV malignant glioma confirmed the absence of neurovirulent potential. The survival rate among patients who received PVSRIPO immunotherapy was higher at 24 and 36 months than the rate among historical controls.

Neuropathogenicity of poliovirus can be attenuated by mutations in the internal ribosomal entry site (IRES) within the 5' nontranslated region of its genome. The Sabin vaccine strains used in prevention of poliomyelitis carry such mutations in their IRES elements. In addition, mutations within the structural and nonstructural proteins of Sabin strains may equally contribute to the attenuation phenotype. Despite their effectiveness as vaccines, the Sabin strains retain a neuropathogenic potential in animal models for poliomyelitis and, at a very low rate, they can cause poliomyelitis in vaccine recipients. The elimination of the neurocytopathic phenotype was achieved through the exchange of the entire poliovirus IRES with its counterpart from human rhinovirus type 2 without affecting growth properties in nonneuronal cells. The attenuating effect of the human rhinovirus type 2 IRES within the context of a poliovirus genome has been mapped to the 3' portion of this genetic element.Models for the mechanism of eukaryotic translation demand ribosomal binding at a 5' terminal cap and ribosome scanning until the proper site of initiation is recognized (1). However, efficient translation of picornavirus RNAs that lack a 5' m7GpppG cap structure (2) occurs via internal ribosomal entry within the 5' nontranslated region (5' NTR) (3-6). The presence of numerous clustered initiation codons with proper context for translational initiation within picornavirus 5' NTRs makes a scanning mechanism implausible. It was found that disproportionally long picornavirus 5' NTRs contain a cis-acting genetic element, the internal ribosomal entry site (IRES), that mediates internal ribosomal entry and capindependent translational initiation (3-8). Trans-acting cellular and viral factors interacting with the IRES, which ensure proper initiation and stimulation of translation, have been identified (9-13). Although a large number of studies on IRES function (mostly in cell-free systems) have shed some light on the mechanism of translational initiation in IRES elements (reviewed in ref.2), their function in determination of viral pathogenesis in vivo remains obscure.We have constructed picornavirus genomic hybrids in which the IRES element of poliovirus (PV) was replaced with that of either encephalomyocarditis virus (EMCV) or human rhinovirus type 2 (HRV2). Exchange of its generic IRES element affected the most distinctive pathogenic property of PV. Neuropathogenicity in a mouse model for poliomyelitis was eliminated in viruses containing the HRV2 IRES while still present in attenuated PV vaccine strains currently in use. Recombinant PV strains featuring the HRV2 IRES regained neurovirulence upon transfer of two distinctive domains derived from the PV IRES. IRES-mediated cell specificity represents a new determinant of picornaviral pathogenesis at the level of viral gene expression.

Poliovirus neuropathogenicity depends on sequences within the 5 nontranslated region of the virus. Exchange of the poliovirus internal ribosomal entry site with its counterpart from human rhinovirus type 2 resulted in attenuation of neurovirulence in primates. Despite deficient virus propagation in cells of neuronal origin, nonpathogenic polio recombinants retain excellent growth characteristics in cell lines derived from glial neoplasms. Susceptibility of malignant glioma cells to poliovirus may be mediated by expression of a poliovirus receptor, CD155, in glial neoplasms. Intergeneric polio recombinants with heterologous internal ribosomal entry site elements unfolded strong oncolytic potential against experimentally induced gliomas in athymic mice. Our observations suggest that highly attenuated poliovirus recombinants may have applicability as biotherapeutic antineoplastic agents.M alignant gliomas are the most common primary tumors of the central nervous system (1). Available treatment is of limited utility for these tumors, and prognosis is therefore poor (1). The resistance of malignant gliomas to conventional therapies has inspired the search for novel strategies, and recently, these strategies have involved animal viruses, either as attenuated variants of pathogenic species with direct oncolytic properties (2, 3) or as delivery vehicles for foreign genetic material (4 -6).Poliovirus is a nonenveloped plus-stranded RNA virus belonging to Picornaviridae and is the causative agent of paralytic poliomyelitis. The vast majority of poliovirus infections remain asymptomatic, but 1-2% of cases result in neurologic complications (7). Restriction of poliovirus cell tropism to lower motor neurons resident within the spinal cord and brainstem gives rise to a highly characteristic clinical syndrome dominated by flaccid paralysis. Selective targeting of motor neurons by poliovirus is most likely determined by the distribution of its cellular receptor, the Ig superfamily molecule CD155. This assumption is supported by the observation that mice transgenic for CD155 develop a polio-like syndrome after poliovirus infection (8-10). In addition, cell-internal conditions favoring viral replication may contribute to poliovirus cell-type specificity.The neuropathogenicity of poliovirus depends on the celltype-specific function of its internal ribosomal entry site (IRES) element in cells of neuronal origin (10). The IRES is part of the 5Ј nontranslated region not only of picornaviruses (11) but also of hepatitis C virus (12, 13). IRES elements assure initiation of translation in a 5Ј end-independent, cap-independent manner (14-16). We have demonstrated that IRES elements encode strong cell-type-specific restrictions toward virus propagation.This restriction is illustrated by the highly attenuated phenotype of intergeneric recombinant polioviruses carrying IRES elements derived from human rhinovirus type 2 (10, 17). We have demonstrated that a prototype intergeneric poliovirus chimera [called PV1(RIPO)] is characterized by exce...