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Simple Summary: Oncolytic herpes simplex viruses (oHSVs) employ as natural entry receptors nectin1 or HVEM. In contrast, retargeted oHSVs (ReHVs) employ as an entry receptor a tumor-associated antigen that no longer interacts with nectin1/HVEM and, thus, spares normal cells. Prior to entry, both oHSVs and ReHVs attach to cells by interaction of gC and gB glycoproteins with heparan sulphates and chondroitin sulphates (glycosaminoglycans–GAGs). The systemic delivery of oncolytic viruses would be the ideal route for hard-to-reach or metastatic cancers that constitute unmet clinical needs. In an accompanying paper, we reported that the blood complement and the antiviral neutralizing antibodies represent the major blood factors that inactivate systemically administered ReHVs. Here, we asked whether ReHV adsorption to GAGs acts as a sink and subtracts the virus from circulation. We report that a genetic modification in gC, which reduced its interaction with GAGs, resulted in a longer half-life of circulating ReHV and a higher anticancer efficacy of systemically (but not intratumorally) administered ReHV. The role of the interaction with cell-surface glycosaminoglycans (GAGs) during in vivo HSV infection is currently unknown. The rationale of the current investigation was to improve the anticancer efficacy of systemically administered retargeted oHSVs (ReHVs) by decreasing their binding to GAGs, including those of endothelial cells, blood cells, and off-tumor tissues. As a proof-of-principle approach, we deleted seven amino acids critical for interacting with GAGs from the glycoprotein C (gC) of R-337 ReHV. The modification in the resulting R-399 recombinant prolonged the half-life in the blood of systemically administered R-399 and enhanced its biodistribution to tumor-positive lungs and to the tumor-negative liver. Ultimately, it greatly increased the R-399 efficacy against metastatic-like lung tumors upon IV administration but not against subcutaneous tumors upon IT administration. These results provide evidence that the increased efficacy seen upon R-399 systemic administration correlated with the slower clearance from the circulation. To our knowledge, this is the first in vivo evidence that the partial impairment of the gC interaction with GAGs resulted in a prolonged half-life of circulating ReHV, an increase in the amount of ReHV taken up by tissues and tumors, and, ultimately, an enhanced anticancer efficacy of systemically administered ReHV. [ABSTRACT FROM AUTHOR]

Simple Summary: Oncolytic viruses were introduced as innovative anticancer agents in preclinical and clinical settings. Upon intralesional administration, they directly kill the cancer cells and also stimulate the anticancer immunity, i.e., function as immunotherapeutics. Thus, owing oncolytic and immunostimulatory activities, they inhibit the growth not only of the injected tumors but also, in part, of distant untreated lesions. Although systemic administration of oncolytic viruses would be the ideal treatment for hard-to-reach and metastatic cancers, blood antiviral factors—especially prior immunity to the virus -, tissue absorption, and off-tumor infections hinder this route of administration. The tropism-retargeted oncolytic herpes viruses (ReHVs) were designed to avoid the off-tumor infections consequent to the widespread occurrence of the viral natural receptors. ReHVs specifically infect those cancer cells that express a tumor-specific receptor of choice and spare cells harboring the natural viral receptors. Given their ability to not cause off-tumor and off-target infections, ReHVs are more suitable for systemic delivery. We investigated the anticancer efficacy, blood clearance, and tissue biodistribution of systemically administered retargeted oncolytic herpes simplex viruses (ReHVs) in HSV-naïve and HSV-preimmunized (HSV-IMM) mice. Efficacy was tested against lung tumors formed upon intravenous administration of cancer cells, a model of metastatic disease, and against subcutaneous distant tumors. In naïve mice, HER2- and hPSMA-retargeted viruses, both armed with mIL-12, were highly effective, even when administered to mice with well-developed tumors. Efficacy was higher for combination regimens with immune checkpoint inhibitors. A significant amount of infectious virus persisted in the blood for at least 1 h. Viral genomes, or fragments thereof, persisted in the blood and tissues for days. Remarkably, the only sites of viral replication were the lungs of tumor-positive mice and the subcutaneous tumors. No replication was detected in other tissues, strengthening the evidence of the high cancer specificity of ReHVs, a property that renders ReHVs suitable for systemic administration. In HSV-IMM mice, ReHVs administered at late times failed to exert anticancer efficacy, and the circulating virus was rapidly inactivated. Serum stability and in vivo whole blood stability assays highlighted neutralizing antibodies as the main factor in virus inactivation. Efforts to deplete mice of the neutralizing antibodies are ongoing. [ABSTRACT FROM AUTHOR]

The role of the interaction with cell-surface glycosaminoglycans (GAGs) during in vivo HSV infection is currently unknown. The rationale of the current investigation was to improve the anticancer efficacy of systemically administered retargeted oHSVs (ReHVs) by decreasing their binding to GAGs, including those of endothelial cells, blood cells, and off-tumor tissues. As a proof-of-principle approach, we deleted seven amino acids critical for interacting with GAGs from the glycoprotein C (gC) of R-337 ReHV. The modification in the resulting R-399 recombinant prolonged the half-life in the blood of systemically administered R-399 and enhanced its biodistribution to tumor-positive lungs and to the tumor-negative liver. Ultimately, it greatly increased the R-399 efficacy against metastatic-like lung tumors upon IV administration but not against subcutaneous tumors upon IT administration. These results provide evidence that the increased efficacy seen upon R-399 systemic administration correlated with the slower clearance from the circulation. To our knowledge, this is the first in vivo evidence that the partial impairment of the gC interaction with GAGs resulted in a prolonged half-life of circulating ReHV, an increase in the amount of ReHV taken up by tissues and tumors, and, ultimately, an enhanced anticancer efficacy of systemically administered ReHV.

We investigated the anticancer efficacy, blood clearance, and tissue biodistribution of systemically administered retargeted oncolytic herpes simplex viruses (ReHVs) in HSV-naïve and HSV-preimmunized (HSV-IMM) mice. Efficacy was tested against lung tumors formed upon intravenous administration of cancer cells, a model of metastatic disease, and against subcutaneous distant tumors. In naïve mice, HER2- and hPSMA-retargeted viruses, both armed with mIL-12, were highly effective, even when administered to mice with well-developed tumors. Efficacy was higher for combination regimens with immune checkpoint inhibitors. A significant amount of infectious virus persisted in the blood for at least 1 h. Viral genomes, or fragments thereof, persisted in the blood and tissues for days. Remarkably, the only sites of viral replication were the lungs of tumor-positive mice and the subcutaneous tumors. No replication was detected in other tissues, strengthening the evidence of the high cancer specificity of ReHVs, a property that renders ReHVs suitable for systemic administration. In HSV-IMM mice, ReHVs administered at late times failed to exert anticancer efficacy, and the circulating virus was rapidly inactivated. Serum stability and in vivo whole blood stability assays highlighted neutralizing antibodies as the main factor in virus inactivation. Efforts to deplete mice of the neutralizing antibodies are ongoing.

We report on the efficacy of the non-attenuated HER2-retargeted oHSV named R-337 against the immunologically hot CT26-HER2 tumor, and an insight into the basis of the immune protection. Preliminarily, we conducted an RNA immune profiling and immune cell content characterization of CT26-HER2 tumor in comparison to the immunologically cold LLC1-HER2 tumor. CT26-HER2 tumor was implanted into HER2-transgenic BALB/c mice. Hallmarks of R-337 effects were the protection from primary tumor, long-term adaptive vaccination directed to both HER2 and CT26-wt cell neoantigens. The latter effect differentiated R-337 from OncoVEXGM-CSF. As to the basis of the immune protection, R-337 orchestrated several changes to the tumor immune profile, which cumulatively reversed the immunosuppression typical of this tumor (graphical abstract). Thus, Ido1 (inhibitor of T cell anticancer immunity) levels and T regulatory cell infiltration were decreased; Cd40 and Cd27 co-immunostimulatory markers were increased; the IFNγ cascade was activated. Of note was the dampening of IFN-I response, which we attribute to the fact that R-337 is fully equipped with genes that contrast the host innate response. The IFN-I shut-down likely favored viral replication and the expression of the mIL-12 payload, which, in turn, boosted the antitumor response. The results call for a characterization of tumor immune markers to employ oncolytic herpesviruses more precisely.

We report on the efficacy of the non-attenuated HER2-retargeted oHSV named R-337 against the immunologically hot CT26-HER2 tumor, and an insight into the basis of the immune protection. Preliminarily, we conducted an RNA immune profiling and immune cell content characterization of CT26-HER2 tumor in comparison to the immunologically cold LLC1-HER2 tumor. CT26-HER2 tumor was implanted into HER2-transgenic BALB/c mice. Hallmarks of R-337 effects were the protection from primary tumor, long-term adaptive vaccination directed to both HER2 and CT26-wt cell neoantigens. The latter effect differentiated R-337 from OncoVEXGM-CSF. As to the basis of the immune protection, R-337 orchestrated several changes to the tumor immune profile, which cumulatively reversed the immunosuppression typical of this tumor (graphical abstract). Thus, Ido1 (inhibitor of T cell anticancer immunity) levels and T regulatory cell infiltration were decreased; Cd40 and Cd27 co-immunostimulatory markers were increased; the IFNγ cascade was activated. Of note was the dampening of IFN-I response, which we attribute to the fact that R-337 is fully equipped with genes that contrast the host innate response. The IFN-I shut-down likely favored viral replication and the expression of the mIL-12 payload, which, in turn, boosted the antitumor response. The results call for a characterization of tumor immune markers to employ oncolytic herpesviruses more precisely. [ABSTRACT FROM AUTHOR]