Replication-selective virotherapy for cancer: Biological principles, risk management and future directions

Development of targeted oncolytic virotherapeutics through translational research

BACKGROUND

Oncolytic virotherapeutics is a promising platform for cancer treatment but the product class has yet been successful. The key to success is integration of bidirectional translational research to rapidly address issues encountered in the laboratory and the clinics.

OBJECTIVE

We highlight the hurdles identified for the targeted oncolytic virotherapy approach, specifically those identified in clinical trials with wild-type viruses and first-generation targeted agents. We also analyze the translational research and development that has been applied to overcome these hurdles, including virus engineering and design improvements for next-generation virotherapeutics.

RESULTS/CONCLUSION

The iterative loop between the clinic and the lab can function as a major driving force to optimize products from this platform.

The effects of trichostatin A on the oncolytic ability of herpes simplex virus for oral squamous cell carcinoma cells

Combining the use of a chemotherapeutic agent with oncolytic virotherapy is a useful way to increase the efficiency of the treatment of cancer. The effect of the histone diacetylase (HDAC) inhibitor trichostatin A (TSA) on the antitumor activity of a herpes simplex virus type-1 (HSV-1) mutant was examined in oral squamous cell carcinoma (SCC) cells. Immunoblotting analysis and immunoflourescence staining revealed that a cytoplasmic nuclear factor-kappaB (NF-kappaB) component, p65, translocated into the nucleus after infection with gamma(1)34.5 gene-deficient HSV-1 R849, indicating that R849 activated NF-kappaB. TSA induced acetylation of p65 and increased the amount of p65 in the nucleus of oral SCC cells. Treatment of R849-infected cells with TSA also increased the amount of nuclear p65 and binding of NF-kappaB to its DNA-binding site and an NF-kappaB inhibitor SN50 diminished the increase in nuclear p65. In the presence of TSA, the production of virus and the expression of LacZ integrated into R849 and glycoprotein D, but not ICP0, ICP6 and thymidine kinase, were increased. The viability of cells treated with a combination of R849 and TSA was lower than that of those treated with R849 only. After treatment with TSA, expression of the cell cycle kinase inhibitor p21 was upregulated and the cell cycle was arrested at G1. These results indicate that TSA enhanced the replication of the HSV-1 mutant through the activation of NF-kappaB and induced cell cycle arrest at G1 to inhibit cell growth. TSA can be used as an enhancing agent for oncolytic virotherapy for oral SCC with gamma(1)34.5 gene-deficient HSV-1.

Enhanced oncolytic potency of vesicular stomatitis virus through vector-mediated inhibition of NK and NKT cells

Recombinant oncolytic viruses represent a promising alternative option for the treatment of malignant cancers. We have reported earlier the safety and efficacy of recombinant vesicular stomatitis virus (VSV) vectors in a rat model of hepatocellular carcinoma (HCC). However, the full potential of VSV therapy is limited by a sudden decline in intratumoral virus replication observed early after viral administration, a phenomenon that coincides with an accumulation of inflammatory cells within infected lesions. To overcome the antiviral function of these cells, we present a recombinant virus, rVSV-UL141, which expresses a protein from human cytomegalovirus known to downregulate the natural killer (NK) cell-activating ligand CD155. The modified vector resulted in an inhibition of NK cell recruitment in vitro, as well as decreased intratumoral accumulations of NK and NKT cells in vivo. Administration of rVSV-UL141 through hepatic artery infusion in immune-competent Buffalo rats harboring orthotopic, multi-focal HCC lesions resulted in a one-log elevation of intratumoral virus replication over a control rVSV vector, which translated to enhance tumor necrosis and substantial prolongation of survival. Moreover, these results were achieved in the absence of apparent toxicities. The present study suggests the applicability of this strategy for the development of effective and safe oncolytic agents to treat multi-focal HCC, and potentially a multitude of other cancers, in the future.

Use of biological therapy to enhance both virotherapy and adoptive T-cell therapy for cancer

To protect viral particles from neutralization, sequestration, nonspecific adhesion, and mislocalization following systemic delivery, we have previously exploited the natural tumor-homing properties of antigen-specific CD8+ T cells. Thus, OT-I T cells, preloaded in vitro with the oncolytic vesicular stomatitis virus (VSV), can deliver virus to established B16ova tumors to generate significantly better therapy than that achievable with OT-I T cells, or systemically delivered VSV, alone. Here, we demonstrate that preconditioning immune-competent mice with Treg depletion and interleukin-2 (IL-2), before adoptive T-cell therapy with OT-I T cells loaded with VSV, leads to further highly significant increases in antitumor therapy. Therapy was associated with antitumor immune memory, but with no detectable toxicities associated with IL-2, Treg depletion, or systemic dissemination of the oncolytic virus. Efficacy was contributed by multiple factors, including improved persistence of T cells; enhanced delivery of VSV to tumors; increased persistence of OT-I cells in vivo resulting from tumor oncolysis; and activation of NK cells, which acquire potent antitumor and proviral activities. By controlling the levels of virus loaded onto the OT-I cells, adoptive therapy was still effective in mice preimmune to the virus, indicating that therapy with virus-loaded T cells may be useful even in virus-immune patients. Taken together, our data show that it is possible to combine adoptive T-cell therapy, with biological therapy (Treg depletion+IL-2), and VSV virotherapy, to treat established tumors under conditions where none of the individual modalities alone is successful.

Chemical targeting of the innate antiviral response by histone deacetylase inhibitors renders refractory cancers sensitive to viral oncolysis

Intratumoral innate immunity can play a significant role in blocking the effective therapeutic spread of a number of oncolytic viruses (OVs). Histone deacetylase inhibitors (HDIs) are known to influence epigenetic modifications of chromatin and can blunt the cellular antiviral response. We reasoned that pretreatment of tumors with HDIs could enhance the replication and spread of OVs within malignancies. Here, we show that HDIs markedly enhance the spread of vesicular stomatitis virus (VSV) in a variety of cancer cells in vitro, in primary tumor tissue explants and in multiple animal models. This increased oncolytic activity correlated with a dampening of cellular IFN responses and augmentation of virus-induced apoptosis. These results illustrate the general utility of HDIs as chemical switches to regulate cellular innate antiviral responses and to provide controlled growth of therapeutic viruses within malignancies. HDIs could have a profoundly positive impact on the clinical implementation of OV therapeutics.

Evaluation of E1A double mutant oncolytic adenovectors in anti-glioma gene therapy

Malignant glioma, in particular glioblastoma multiforme (GBM), represents one of the most devastating cancers currently known and existing treatment regimens do little to change patient prognosis. Conditionally replicating adenoviral vectors (CRAds) represent attractive experimental anti-cancer agents with potential for clinical application. However, early protein products of the wild type adenovirus backbone--such as E1A--limit CRAds' replicative specificity. In this study, we evaluated the oncolytic potency and specificity of CRAds in which p300/CPB and/or pRb binding capacities of E1A were ablated to reduce non-specific replicative cytolysis. In vitro cytopathic assays, quantitative PCR analysis, Western blot, and flow cytometry studies demonstrate the superior anti-glioma efficacy of a double-mutated CRAd, Ad2/24CMV, which harbors mutations that reduce E1A binding to p300/CPB and pRb. When compared to its single-mutated and wild type counterparts, Ad2/24CMV demonstrated attenuated replication and cytotoxicity in representative normal human brain while displaying enhanced replicative cytotoxicity in malignant glioma. These results have implications for the development of double-mutated CRAd vectors for enhanced GBM therapy.

Replication competent Semliki Forest virus prolongs survival in experimental lung cancer

We evaluated the therapeutic potential of the replication competent vector VA7-EGFP, which is based on the avirulent Semliki Forest virus (SFV) strain A7 (74) carrying the EGFP marker gene in an orthotopic lung cancer tumor model in nude mice. We have previously shown that this oncolytic vector destroys tumor cells efficiently in vitro and in vivo (in subcutaneous tumor model). Tumor growth in animals with orthotopically implanted adenocarcinoma cells (A549) were monitored during the study with small animal CT. We show that locally administered virotherapy with VA7-EGFP increased survival rate in experimental lung cancer significantly (p < 0.001) comparable to results obtained with the second generation conditionally replicating adenoviral vector Ad5-Delta24TK-GFP, used for comparison. The limited efficacy in systemically administered oncolytic viruses is the essential problem in oncolytic virotherapy and also in this study we were not able to elicit significant response with systemic administration route. Despite the fact that tumor microenvironment in orthotopic lung cancer is more optimal, viruses failed to home to the tumors and were unable to initiate efficient intratumoral replication. Clearly, the efficacy of virotherapy is influenced by many factors such as the route of virus administration, immunological and physiological barriers and cancer cell-specific features (IFN-responsiveness).

Antiviral activity of cidofovir against telomerase-specific replication-selective oncolytic adenovirus, OBP-301 (Telomelysin)

We constructed a replication-competent oncolytic adenovirus, OBP-301 (Telomelysin), in which human telomerase reverse transcriptase (hTERT) promoter drives E1 genes. OBP-301 is currently being used in a phase-I clinical trial for various types of tumors. Under such conditions, anti-adenoviral agents should be available for safety use against OBP-301 since any adenoviral viremia could cause severe adverse effects. Cidofovir (CDV) is an acyclic nucleoside phosphonate that has a broad antiviral activity against DNA viruses. Here, we examined the antiviral effects of CDV against OBP-301. The in vitro cytopathic effects of OBP-301 were suppressed by CDV. Moreover, CDV decreased the adenoviral E1A gene copy number after OBP-301 infection. These results suggest that CDV is a potentially useful antiviral agent for OBP-301.

Systemic therapy for cervical cancer with potentially regulatable oncolytic adenoviruses

Clinical trials have confirmed the safety of selectively oncolytic adenoviruses for treatment of advanced cancers. However, increasingly effective viruses could result in more toxicity and therefore it would be useful if replication could be abrogated if necessary. We analyzed viruses containing the cyclooxygenase-2 (Cox-2) or vascular endothelial growth factor (VEGF) promoter for controlling replication. Anti-inflammatory agents can lower Cox-2 protein levels and therefore we hypothesized that also the promoter might be affected. As Cox-2 modulates expression of VEGF, also the VEGF promoter might be controllable. First, we evaluated the effect of anti-inflammatory agents on promoter activity or adenovirus infectivity in vitro. Further, we analyzed the oncolytic potency of the viruses in vitro and in vivo with and without the reagents. Moreover, the effect of on virus replication was analyzed. We found that RGD-4C or Ad5/3 modified fibers improved the oncolytic potency of the viruses in vitro and in vivo. We found that both promoters could be downregulated with dexamethasone, sodium salicylate, or salicylic acid. Oncolytic efficacy correlated with the promoter activity and in vitro virus production could be abrogated with the substances. In vivo, we saw good therapeutic efficacy of the viruses in a model of intravenous therapy of metastatic cervical cancer, but the inhibitory effect of dexamethasone was not strong enough to provide significant differences in a complex in vivo environment. Our results suggest that anti-inflammatory drugs may affect the replication of adenovirus, which might be relevant in case of replication associated side effects.

Killing of p53-deficient hepatoma cells by parvovirus H-1 and chemotherapeutics requires promyelocytic leukemia protein

AIM: To evaluate the synergistic targeting and killing of human hepatocellular carcinoma (HCC) cells lacking p53 by the oncolytic autonomous parvovirus (PV) H-1 and chemotherapeutic agents and its dependence on functional promyelocytic leukemia protein (PML).

METHODS: The role of p53 and PML in regulating cytotoxicity and gene transfer mediated by wild-type (wt) PV H-1 were explored in two pairs of isogenic human hepatoma cell lines with different p53 status. Furthermore, H-1 PV infection was combined with cytostatic drug treatment.

RESULTS: While the HCC cells with different p53 status studied were all susceptible to H-1 PV-induced apoptosis, the cytotoxicity of H-1 PV was more pronounced in p53-negative than in p53-positive cells. Apoptosis rates in p53-negative cell lines treated by genotoxic drugs were further enhanced by a treatment with H-1 PV. In flow cytometric analyses, H-1 PV infection resulted in a reduction of the mitochondrial transmembrane potential. In addition, H-1 PV cells showed a significant increase in PML expression. Knocking down PML expression resulted in a striking reduction of the level of H-1 PV infected tumor cell death.

CONCLUSION: H-1 PV is a suitable agent to circumvent the resistance of p53-negative HCC cells to genotoxic agents, and it enhances the apoptotic process which is dependent on functional PML. Thus, H-1 PV and its oncolytic vector derivatives may be considered as therapeutic options for HCC, particularly for p53-negative tumors.

Biodistribution and kinetics of the novel selective oncolytic adenovirus M1 after systemic administration

Oncolytic adenoviruses represent a promising novel therapeutic option for the treatment of cancer. Despite their demonstrated safety in human clinical trials, the fundamental properties of oncolytic adenovirus biodistribution, spread, viral persistence, and replication in vivo have not been well characterized. The aim of this study was to evaluate the kinetics of viral distribution, spread, replication, and antitumoral efficacy after i.v. administration of a novel oncolytic mutant M1. This mutant consists of the E1A CR2-deleted Adv5 with a fragment of antisense polo-like kinase 1 (plk1) cDNA inserted into the deleted 6.7K/gp19K region, which combines oncolytic properties with efficient plk1 silencing, as described in our previous reports. In the present study, we established a new human orthotopic gastric carcinoma with a high frequency metastasis mouse model and showed that M1 spread not only in local primary tumors but also in disseminated metastases. M1 could effectively replicate in tumor cells leading to "oncolysis" and was able to eliminate expression of the targeted gene plk1 in human orthotopic gastric carcinoma model mice. Therefore, i.v. administration of M1 could prolong the survival time of tumor-bearing mice.

A very late viral protein triggers the lytic release of SV40

How nonenveloped viruses such as simian virus 40 (SV40) trigger the lytic release of their progeny is poorly understood. Here, we demonstrate that SV40 expresses a novel later protein termed VP4 that triggers the timely lytic release of its progeny. Like VP3, VP4 synthesis initiates from a downstream AUG start codon within the VP2 transcript and localizes to the nucleus. However, VP4 expression occurs approximately 24 h later at a time that coincides with cell lysis, and it is not incorporated into mature virions. Mutation of the VP4 initiation codon from the SV40 genome delayed lysis by 2 d and reduced infectious particle release. Furthermore, the co-expression of VP4 and VP3, but not their individual expression, recapitulated cell lysis in bacteria. Thus, SV40 regulates its life cycle by the later temporal expression of VP4, which results in cell lysis and enables the 50-nm virus to exit the cell. This study also demonstrates how viruses can generate multiple proteins with diverse functions and localizations from a single reading frame.

Treg depletion-enhanced IL-2 treatment facilitates therapy of established tumors using systemically delivered oncolytic virus

There are several roadblocks that hinder systemic delivery of oncolytic viruses to the sites of metastatic disease. These include the tumor vasculature, which provides a physical barrier to tumor-specific virus extravasation. Although interleukin-2 (IL-2) has been used in antitumor therapy, it is associated with endothelial cell injury, leading to vascular leak syndrome (VLS). Here, we demonstrate that IL-2-mediated VLS, accentuated by depletion of regulatory T cells (Treg), facilitates localization of intravenously (i.v.) delivered oncolytic virus into established tumors in immune-competent mice. IL-2, in association with Treg depletion, generates "hyperactivated" natural killer (NK) cells, possessing antitumor activity and secreting factors that facilitate virus spread/replication throughout the tumor by disrupting the tumor architecture. As a result, the combination of Treg depletion/IL-2 and systemic oncolytic virotherapy was found to be significantly more therapeutic against established disease than either treatment alone. These data demonstrate that it is possible to combine biological therapy with oncolytic virotherapy to generate systemic therapy against established tumors.

Cyclophosphamide facilitates antitumor efficacy against subcutaneous tumors following intravenous delivery of reovirus

PURPOSE

The purpose of the present study was to investigate whether it is possible to achieve truly systemic delivery of oncolytic reovirus, in immunocompetent hosts, using cyclophosphamide to overcome some of the barriers to effective intratumoral delivery and replication of i.v. injected virus.

EXPERIMENTAL DESIGN

I.v. delivery of reovirus was combined with different regimens of i.p. administered cyclophosphamide in C57Bl/6 mice bearing established s.c. B16 tumors. Intratumoral viral replication, tumor size, and survival were measured along with levels of neutralizing antibody (NAb) in the blood. Finally, differential toxicities of the virus/cyclophosphamide regimens were monitored through viral replication in systemic organs, survival, and cardiac damage.

RESULTS

Repeated i.v. injection of reovirus was poorly effective at seeding intratumoral viral replication/oncolysis. However, by combining i.v. virus with cyclophosphamide, viral titers of between 10(7) and 10(8) plaque-forming units per milligram were recovered from regressing tumors. Doses of cyclophosphamide that ablated NAb were associated with severe toxicities, characterized by viral replication in systemic organs--toxicities that are mirrored by repeated reovirus injections into B-cell knockout mice. Next, we restructured the dosing of cyclophosphamide and i.v. virus such that a dose of 3 mg cyclophosphamide was administered 24 h before reovirus injection, and this schedule was repeated every 6 days. Using this protocol, high levels of intratumoral viral access and replication ( approximately 10(7) plaque-forming units per milligram tumor) were maintained along with systemically protective levels of NAb and only very mild, non-life-threatening toxicity.

CONCLUSION

NAb to oncolytic viruses play a dual role in the context of systemic viral delivery; on one hand, they hinder repeated administration of virus but on the other, they provide an important safety mechanism by which virus released from vigorous intratumoral replication is neutralized before it can disseminate and cause toxicity. These data support the use of cyclophosphamide to modulate, but not ablate, patient NAb, in development of carefully controlled clinical trials of the systemic administration of oncolytic viruses.

Oncolytic herpes virus with defective ICP6 specifically replicates in quiescent cells with homozygous genetic mutations in p16

Oncolytic herpes simplex viruses (HSVs), in clinical trials for the treatment of malignant gliomas, are assumed to be selective for tumor cells because their replication is strongly attenuated in quiescent cells, but not in cycling cells. Oncolytic selectivity is thought to occur because mutations in viral ICP6 (encoding a viral ribonucleotide reductase function) and/or γ34.5 function are respectively complemented by mammalian ribonucleotide reductase and GADD34, whose genes are expressed in cycling cells. However, it is estimated that only 5–15% of malignant glioma cells are in mitosis at any one time. Therefore, effective replication of HSV oncolytic viruses might be limited to a subpopulation of tumor cells, since at any one time the majority of tumor cells would not be cycling. However, we report that an HSV with defective ICP6 function replicates in quiescent cultured murine embryonic fibroblasts obtained from mice with homozygous p16 deletions. Furthermore, intracranial inoculation of this virus into the brains of p16−/− mice provides evidence of viral replication that does not occur when the virus is injected into the brains of wild-type mice. These approaches provide in vitro and in vivo evidence that ICP6-negative HSVs are ‘molecularly targeted,’ because they replicate in quiescent tumor cells carrying specific oncogene deletions, independent of cell cycle status.

Loading of oncolytic vesicular stomatitis virus onto antigen-specific T cells enhances the efficacy of adoptive T-cell therapy of tumors

Although adoptive T-cell therapy has shown clinical success, efficacy is limited by low levels of T-cell trafficking to, and survival in, the immunosuppressive environment of an established tumor. Oncolytic virotherapy has recently emerged as a promising approach to induce both direct tumor cell killing and local proinflammatory environments within tumors. However, inefficient systemic delivery of oncolytic viruses remains a barrier to use of these agents against metastatic disease that is not directly accessible to the end of a needle. Here we show that the ability of antigen-specific T cells to circulate freely, and to localize to tumors, can be exploited to achieve the systemic delivery of replication-competent, oncolytic vesicular stomatitis virus (VSV). Thus, VSV loaded onto OT-I T cells, specific for the SIINFEKL epitope of the ovalbumin antigen, was efficiently delivered to established B16ova tumors in the lungs of fully immune-competent C57Bl/6 mice leading to significant increases in therapy compared to the use of virus, or T cells, alone. Although OT-I T-cell-mediated delivery of VSV led to viral replication within tumors and direct viral oncolysis, therapy was also dependent upon an intact host immune system. Moreover, VSV loading onto the T cells increased both T-cell activation in vitro and T-cell trafficking in vivo. The combination of adoptive T-cell transfer of antigen-specific T cells, along with oncolytic virotherapy, can, therefore, increase the therapeutic utility of both approaches through multiple mechanisms and should be of direct translational value.

Treatment of metastatic renal cancer with capsid-modified oncolytic adenoviruses

Renal cancer is a common and deadly disease that lacks curative treatments when metastatic. Here, we have used oncolytic adenoviruses, a promising developmental approach whose safety has recently been validated in clinical trials. Although preliminary clinical efficacy data exist for selected tumor types, potency has generally been less than impressive. One important reason may be that expression of the primary receptor, coxsackie-adenovirus receptor, is often low on many or most advanced tumors, although not evaluated in detail with renal cancer. Here, we tested if fluorescence-assisted cell sorting could be used to predict efficacy of a panel of infectivity-enhanced capsid-modified marker gene expressing adenoviruses in renal cancer cell lines, clinical specimens, and subcutaneous and orthotopic murine models of peritoneally metastatic renal cell cancer. The respective selectively oncolytic adenoviruses were tested for killing of tumor cells in these models, and biodistribution after locoregional delivery was evaluated. In vivo replication was analyzed with noninvasive imaging. Ad5/3-Delta24, Ad5-Delta24RGD, and Ad5.pK7-Delta24 significantly increased survival of mice compared with mock or wild-type virus and 50% of Ad5/3-Delta24 treated mice were alive at 320 days. Because renal tumors are often highly vascularized, we investigated if results could be further improved by adding bevacizumab, a humanized antivascular endothelial growth factor antibody. The combination was well tolerated but did not improve survival, suggesting that the agents may be best used in sequence instead of together. These results set the stage for clinical testing of oncolytic adenoviruses for treatment of metastatic renal cancer currently lacking other treatment options.

Modeling of cancer virotherapy with recombinant measles viruses

The Edmonston vaccine strain of measles virus has potent and selective activity against a wide range of tumors. Tumor cells infected by this virus or genetically modified strains express viral proteins that allow them to fuse with neighboring cells to form syncytia that ultimately die. Moreover, infected cells may produce new virus particles that proceed to infect additional tumor cells. We present a model of tumor and virus interactions based on established biology and with proper accounting of the free virus population. The range of model parameters is estimated by fitting to available experimental data. The stability of equilibrium states corresponding to complete tumor eradication, therapy failure and partial tumor reduction is discussed. We use numerical simulations to explore conditions for which the model predicts successful therapy and tumor eradication. The model exhibits damped, as well as stable oscillations in a range of parameter values. These oscillatory states are organized by a Hopf bifurcation.

Adenovirus E1B55K region is required to enhance cyclin E expression for efficient viral DNA replication

Adenoviruses (Ads) with E1B55K mutations can selectively replicate in and destroy cancer cells. However, the mechanism of Ad-selective replication in tumor cells is not well characterized. We have shown previously that expression of several cell cycle-regulating genes is markedly affected by the Ad E1b gene in WI-38 human lung fibroblast cells (X. Rao, et al., Virology 350:418-428, 2006). In the current study, we show that the Ad E1B55K region is required to enhance cyclin E expression and that the failure to induce cyclin E overexpression due to E1B55K mutations prevents viral DNA from undergoing efficient replication in WI-38 cells, especially when the cells are arrested in the G(0) phase of the cell cycle by serum starvation. In contrast, cyclin E induction is less dependent on the function encoded in the E1B55K region in A549 and other cancer cells that are permissive for replication of E1B55K-mutated viruses, whether the cells are in the S phase or G(0) phase. The small interfering RNA that specifically inhibits cyclin E expression partially decreased viral replication. Our study provides evidence suggesting that E1B55K may be involved in cell cycle regulation that is important for efficient viral DNA replication and that cyclin E overexpression in cancer cells may be associated with the oncolytic replication of E1B55K-mutated viruses.

A phase I trial of Ad.hIFN-beta gene therapy for glioma

Interferon-beta (IFN-beta) is a pleiotropic cytokine with antitumoral activity. In an effort to improve the therapeutic index of IFN-beta by providing local, sustained delivery of IFN-beta to gliomas, the safety and biological activity of a human IFN-beta (hIFN-beta)-expressing adenovirus vector (Ad.hIFN-beta) was evaluated in patients with malignant glioma by stereotactic injection, followed 4-8 days later by surgical removal of tumor with additional injections of Ad.hIFN-beta into the tumor bed. Eleven patients received Ad.hIFN-beta in cohorts of 2 x 10(10), 6 x 10(10), or 2 x 10(11) vector particles (vp). The most common adverse events were considered by the investigator as being unrelated to treatment. One patient, who was enrolled in the cohort with the highest dose levels, experienced dose-limiting, treatment-related Grade 4 confusion following the post-operative injection. Ad.hIFN-beta DNA was detected within the tumor, blood, and nasal swabs in a dose-dependent fashion and hIFN-beta protein was detectable within the tumor. At the highest doses tested, a reproducible increase in tumor cell apoptosis in post-treatment versus pre-treatment biopsies with associated tumor necrosis was observed. Direct Ad.hIFN-beta injection into the tumor and the surrounding normal brain areas after surgical removal was feasible and associated with apoptosis induction.

Exponential enhancement of oncolytic vesicular stomatitis virus potency by vector-mediated suppression of inflammatory responses in vivo

Oncolytic virotherapy is a promising strategy for treatment of malignancy, although its effectiveness is hampered by host antiviral inflammatory responses. The efficacy of treatment of oncolytic vesicular stomatitis virus (VSV) in rats bearing multifocal hepatocellular carcinoma (HCC) can be substantially elevated by antibody-mediated depletion of natural killer (NK) cells. In order to test the hypothesis that the oncotyic potency of VSV can be exponentially elevated by evasion of inflammatory responses in vivo, we constructed a recombinant VSV vector expressing equine herpes virus-1 glycoprotein G, which is a broad-spectrum viral chemokine binding protein (rVSV-gG). Infusion of rVSV-gG via the hepatic artery into immune-competent rats bearing syngeneic and multifocal HCC in their livers, resulted in a reduction of NK and NKT cells in the tumors and a 1-log enhancement in intratumoral virus titer in comparison with a reference rVSV vector. The treatment led to increased tumor necrosis and substantially prolonged animal survival without toxicities. These results indicate that rVSV-gG has the potential to be developed as an effective and safe oncolytic agent to treat patients with advanced HCC. Furthermore, the novel concept that oncolytic potency can be substantially enhanced by vector-mediated suppression of host antiviral inflammatory responses could have general applicability in the field of oncolytic virotherapy for cancer.

Targeting of interferon-beta to produce a specific, multi-mechanistic oncolytic vaccinia virus

BACKGROUND

Oncolytic viruses hold much promise for clinical treatment of many cancers, but a lack of systemic delivery and insufficient tumor cell killing have limited their usefulness. We have previously demonstrated that vaccinia virus strains are capable of systemic delivery to tumors in mouse models, but infection of normal tissues remains an issue. We hypothesized that interferon-beta (IFN-beta) expression from an oncolytic vaccinia strain incapable of responding to this cytokine would have dual benefits as a cancer therapeutic: increased anticancer effects and enhanced virus inactivation in normal tissues. We report the construction and preclinical testing of this virus.

METHODS AND FINDINGS

In vitro screening of viral strains by cytotoxicity and replication assay was coupled to cellular characterization by phospho-flow cytometry in order to select a novel oncolytic vaccinia virus. This virus was then examined in vivo in mouse models by non-invasive imaging techniques. A vaccinia B18R deletion mutant was selected as the backbone for IFN-beta expression, because the B18R gene product neutralizes secreted type-I IFNs. The oncolytic B18R deletion mutant demonstrated IFN-dependent cancer selectivity and efficacy in vitro, and tumor targeting and efficacy in mouse models in vivo. Both tumor cells and tumor-associated vascular endothelial cells were targeted. Complete tumor responses in preclinical models were accompanied by immune-mediated protection against tumor rechallenge. Cancer selectivity was also demonstrated in primary human tumor explant tissues and adjacent normal tissues. The IFN-beta gene was then cloned into the thymidine kinase (TK) region of this virus to create JX-795 (TK-/B18R-/IFN-beta+). JX-795 had superior tumor selectivity and systemic intravenous efficacy when compared with the TK-/B18R- control or wild-type vaccinia in preclinical models.

CONCLUSIONS

By combining IFN-dependent cancer selectivity with IFN-beta expression to optimize both anticancer effects and normal tissue antiviral effects, we were able to achieve, to our knowledge for the first time, tumor-specific replication, IFN-beta gene expression, and efficacy following systemic delivery in preclinical models.

Depletion of peripheral macrophages and brain microglia increases brain tumor titers of oncolytic viruses

Clinical trials have proven oncolytic virotherapy to be safe but not effective. We have shown that oncolytic viruses (OV) injected into intracranial gliomas established in rodents are rapidly cleared, and this is associated with up-regulation of markers (CD68 and CD163) of cells of monocytic lineage (monocytes/microglia/macrophages). However, it is unclear whether these cells directly impede intratumoral persistence of OV through phagocytosis and whether they infiltrate the tumor from the blood or the brain parenchyma. To investigate this, we depleted phagocytes with clodronate liposomes (CL) in vivo through systemic delivery and ex vivo in brain slice models with gliomas. Interestingly, systemic CL depleted over 80% of peripheral CD163+ macrophages in animal spleen and peripheral blood, thereby decreasing intratumoral infiltration of these cells, but CD68+ cells were unchanged. Intratumoral viral titers increased 5-fold. In contrast, ex vivo CL depleted only CD68+ cells from brain slices, and intratumoral viral titers increased 10-fold. These data indicate that phagocytosis by both peripheral CD163+ and brain-resident CD68+ cells infiltrating tumor directly affects viral clearance from tumor. Thus, improved therapeutic efficacy may require modulation of these innate immune cells. In support of this new therapeutic paradigm, we observed intratumoral up-regulation of CD68+ and CD163+ cells following treatment with OV in a patient with glioblastoma.

Oncolytic adenovirus Ad5/3-delta24 and chemotherapy for treatment of orthotopic ovarian cancer

OBJECTIVE

Oncolytic adenoviruses capable of replication selectively in tumor cells are an appealing approach for the treatment of neoplastic diseases refractory to conventional therapies. The aim of this study was to evaluate the effect of dose and scheduling of a tropism-modified, adenovirus serotype 3 receptor-targeted, Rb/p16 pathway-selective replication-competent adenovirus, Ad5/3-delta24, against human ovarian adenocarcinoma. As oncolytic viruses and chemotherapy can have synergistic interactions, the antitumor efficacy of Ad5/3-delta24 was also studied in combination with epirubicin and gemcitabine, common second-line treatment options for platinum-resistant ovarian cancer.

METHODS

Orthotopic murine models of peritoneally disseminated ovarian cancer were utilized to compare survival of mice treated with either a single viral dose or weekly delivery. The lowest effective dose of intraperitoneal Ad5/3-delta24 was determined. Combinations of Ad5/3-delta24 and gemcitabine or epirubicin were studied in vitro as well as in vivo.

RESULTS

Treatment outcome after administration of a single dose of Ad5/3-delta24 was as effective as delivery of several weekly doses. Our results also demonstrate that a single intraperitoneal injection of 100 viral particles significantly increased the survival of mice compared to untreated animals. Further, combining Ad5/3-delta24 with either gemcitabine or epirubicin resulted in greater therapeutic benefit than either agent alone.

CONCLUSION

These preclinical data suggest that Ad5/3-delta24 represents a promising treatment strategy for advanced ovarian cancer as a single agent or in combination with chemotherapy.

Herpes Simplex Virus Us3(−) Mutant as Oncolytic Strategy and Synergizes with Phosphatidylinositol 3-Kinase-Akt–Targeting Molecular Therapeutics

PURPOSE

Oncolytic herpes simplex virus (HSV) vectors have shown safety in clinical trials, but efficacy remains unsatisfactory. Novel HSV vectors that possess tumor selectivity with enhanced potency are therefore needed. The gene product of HSV Us3 protects virus-infected cells from apoptosis, a cellular pathway frequently dysfunctional in tumors. We hypothesized that Us3 mutants, whose replication would be inhibited by apoptosis in normal cells, would be selective for tumor cells.

EXPERIMENTAL DESIGN

HSV mutants G207 (ribonucleotide reductase-/gamma34.5-), R7041 (Us3-), and R7306 (Us3 revertant) were tested in normal and tumor cells for viral replication, antitumoral potency, apoptosis induction, and Akt activation. Safety and biodistribution after systemic administration and antitumoral efficacy after intratumoral (i.t.) or i.v. administration were examined.

RESULTS

Us3 deletion results in up to 3-log replication inhibition in normal cells, which correlates with enhanced apoptosis induction. In contrast, R7041 replicates very well in tumor cells, showing 1 to 2 log greater yield than G207. In vivo, R7041 shows no signs of toxicity after systemic delivery in both immunocompetent and immunodeficient mice and shows preferential and prolonged replication in tumors compared with normal tissues. R7041 displays significant antitumoral efficacy after i.t. or i.v. administration. An additional feature of Us3 mutants is enhanced Akt activation compared with wild-type infection, which sensitizes cells to phosphatidylinositol 3-kinase-Akt inhibitors (LY294002, Akt inhibitor IV), shown by synergistic antitumoral activity in vitro and enhanced efficacy in vivo.

CONCLUSIONS

Us3 deletion confers enhanced tumor selectivity and antitumoral potency on herpes simplex virus-1 and provides for a novel mechanism of combination therapy with phosphatidylinositol 3-kinase-Akt-targeting molecular therapeutics.

E1A, E1B double-restricted adenovirus with RGD-fiber modification exhibits enhanced oncolysis for CAR-deficient biliary cancers

PURPOSE

Cancers of biliary system represent highly malignant diseases of dismal prognosis. We have previously introduced AxdAdB3, an E1A, E1B double-restricted oncolytic adenovirus, which showed excellent oncolytic efficacy for approximately half of the biliary cancer lines with an enhanced safety to normal cells. The purpose of this study was to evaluate whether RGD-fiber modification (AxdAdB3-F/RGD), which enables integrin-dependent infection, can improve the infectivity and efficacy of AxdAdB3 for biliary cancers.

EXPERIMENTAL DESIGN

Expressions of adenoviral receptors, coxsackievirus adenovirus receptor (CAR) and integrins (alpha(v)beta(3) and alpha(v)beta(5)), were compared with the level of infectivity of LacZ-expressing replication-defective adenoviruses with wild-type fibers or RGD-modified fibers in a panel of biliary cancer cell lines in vitro. Viral replication and cytotoxicity in vitro of AxdAdB3-F/RGD, a novel E1A, E1B double-restricted replication-selective adenovirus with RGD-modified fibers, were compared with those of its parent virus, AxdAdB3, in various biliary cancer cells and in normal cells. In vivo antitumor effects of these oncolytic viruses were compared in a xenograft tumor model.

RESULTS

Expression of CAR significantly correlated with the adenovirus infectivity, whereas integrin alpha(v)beta(5) was abundantly expressed in almost all biliary cancer cells. Whereas AxdAdB3 effectively replicated and lysed only the biliary cancer cells with a preserved expression of CAR, AxdAdB3-F/RGD exhibited efficient replication and potent oncolysis in both CAR-positive and CAR-negative biliary cancer cells. AxdAdB3-F/RGD showed attenuated replication and little cytopathy in human normal cells (i.e., hepatocytes, WI-38 cells) as well as AxdAdB3. Furthermore, in nude mice with s.c. xenografts of CAR-deficient human biliary cancer, i.t. AxdAdB3-F/RGD therapy caused a marked inhibition of tumor growth.

CONCLUSIONS

The RGD-fiber modification strategy enhanced the infectivity, replication, and oncolytic effects of the E1A, E1B double-restricted oncolytic adenovirus for CAR-deficient biliary cancers. In addition, it preserved the merit of excellent safety of the double-restricted virus for normal cells. These results suggest a potential use of this agent for the treatment of biliary cancers.

The status of gene therapy for brain tumors

The advent of gene therapy in the early 1990's raised expectations for brain tumor therapies; however, whereas clinical trials in patients with malignant gliomas provided evidence of safety, therapeutic benefit was not convincing. These early forays resembled the historical introductions of other therapies that seemed promising, only to fail in human trials. Nevertheless, re-study in the laboratory and retesting in iterative laboratory-clinic processes enabled therapies with strong biological rationales to ultimately show evidence of success in humans and become accepted. Examples, such as organ transplantation, monoclonal antibody therapy and antiangiogenic therapy, provide solace that a strategy's initial lack of success in humans provides an opportunity for its further refinement in the laboratory and development of solutions that will translate into patient success stories. The authors herein summarize results from clinical trials of gene therapy for malignant gliomas, and discuss the influence of these results on present thought in preclinical research.

Systemic efficacy of oncolytic adenoviruses in imagable orthotopic models of hormone refractory metastatic breast cancer

Conditionally replicating oncolytic adenoviruses represent a promising developmental strategy for the treatment of cancer refractory to current treatments, such as hormone refractory metastatic breast cancer. In clinical cancer trials, adenoviral agents have been well tolerated, but gene transfer has been insufficient for clinical benefit. One of the main reasons may be the deficiency of the primary adenovirus receptor, and therefore viral capsid modifications have been employed. Another obstacle to systemic delivery is rapid clearance of virus by hepatic Kupffer cells and subsequent inadequate bioavailability. In this study, we compared several capsid-modified oncolytic adenoviruses for the treatment of breast cancer with and without Kupffer cell inactivation. Replication deficient capsid-modified viruses were analyzed for their gene transfer efficacy in vitro in breast cancer cell lines and clinical samples and in vivo in orthotopic models of breast cancer. The effect of Kupffer cell depleting agents on gene transfer efficacy in vivo was evaluated. An aggressive lung metastatic model was developed to study the effect of capsid-modified oncolytic adenoviruses on survival. Capsid-modified viruses displayed increased gene transfer and cancer cell killing in vitro and resulted in increased survival in an orthotopic model of lung metastatic breast cancer in mice. Biodistribution of viruses was favorable, tumor burden and treatment response could be monitored repeatedly. Kuppfer cell inactivation led to enhanced systemic gene delivery, but did not increase the survival of mice. These results facilitate clinical translation of oncolytic adenoviruses for the treatment of hormone refractory metastatic breast cancer.

Experimental therapeutic approaches to peripheral nerve tumors

✓Discovery that the Schwann cell is the primary cell type responsible for both the neurofibroma as well as the schwannoma has proven to represent a crucial milestone in understanding the pathogenesis of peripheral nerve tumor development. This information and related findings have served as a nidus for research aimed at more fully characterizing this family of conditions. Recent discoveries in the laboratory have clarified an understanding of the molecular mechanisms underlying the pathogenesis of benign peripheral nerve tumors. Similarly, the mechanisms whereby idiopathic and syndromic (NF1- andNF2-associated) nerve sheath tumors progress to malignancy are being elucidated. This detailed understanding of the molecular pathogenesis of peripheral nerve tumors provides the information necessary to create a new generation of therapies tailored specifically to the prevention, cessation, or reversal of pathological conditions at the fundamental level of dysfunction. The authors review the data that have helped to elucidate the molecular pathogenesis of this category of conditions, explore the current progress toward exploitation of these findings, and discuss potential therapeutic avenues for future research.

Oncolytic immunovirotherapy for melanoma using vesicular stomatitis virus

Relatively little attention has been paid to the role of virotherapy in promoting antitumor immune responses. Here, we show that CD8+ T cells are critical for the efficacy of intratumoral vesicular stomatitis virus virotherapy and are induced against both virally encoded and tumor-associated immunodominant epitopes. We tested three separate immune interventions to increase the frequency/activity of activated antitumoral T cells. Depletion of Treg had a negative therapeutic effect because it relieved suppression of the antiviral immune response, leading to early viral clearance. In contrast, increasing the circulating levels of tumor antigen-specific T cells using adoptive T cell transfer therapy, in combination with intratumoral virotherapy, generated significantly improved therapy over either adoptive therapy or virotherapy alone. Moreover, the incorporation of a tumor-associated antigen within the oncolytic vesicular stomatitis virus increased the levels of activation of naïve T cells against the antigen, which translated into increased antitumor therapy. Therefore, our results show that strategies which enhance immune activation against tumor-associated antigens can also be used to enhance the efficacy of virotherapy.

Oncolytic viruses in cancer therapy

Oncolytic virotherapy is a promising form of gene therapy for cancer, employing nature’s own agents to find and destroy malignant cells. The purpose of this review is to provide an introduction to this very topical field of research and to point out some of the current observations, insights and ideas circulating in the literature. We have strived to acknowledge as many different oncolytic viruses as possible to give a broader picture of targeting cancer using viruses. Some of the newest additions to the panel of oncolytic viruses include the avian adenovirus, foamy virus, myxoma virus, yaba-like disease virus, echovirus type 1, bovine herpesvirus 4, Saimiri virus, feline panleukopenia virus, Sendai virus and the non-human coronaviruses. Although promising, virotherapy still faces many obstacles that need to be addressed, including the emergence of virus-resistant tumor cells.

Luciferase imaging for evaluation of oncolytic adenovirus replication in vivo

Oncolytic viruses kill cancer cells by tumor-selective replication. Clinical data have established the safety of the approach but also the need of improvements in potency. Efficacy of oncolysis is linked to effective infection of target cells and subsequent productive replication. Other variables include intratumoral barriers, access to target cells, uptake by non-target organs and immune response. Each of these aspects relates to the location and degree of virus replication. Unfortunately, detection of in vivo replication has been difficult, labor intensive and costly and therefore not much studied. We hypothesized that by coinfection of a luciferase expressing E1-deleted virus with an oncolytic virus, both viruses would replicate when present in the same cell. Photon emission due to conversion of D-Luciferin is sensitive and penetrates tissues well. Importantly, killing of animals is not required and each animal can be imaged repeatedly. Two different murine xenograft models were used and intratumoral coinjections of luciferase encoding virus were performed with eight different oncolytic adenoviruses. In both models, we found significant correlation between photon emission and infectious virus production. This suggests that the system can be used for non-invasive quantitation of the amplitude, persistence and dynamics of oncolytic virus replication in vivo, which could be helpful for the development of more effective and safe agents.

Chlorpromazine and apigenin reduce adenovirus replication and decrease replication associated toxicity

BACKGROUND

Adenoviruses can cause severe toxicity in immunocompromised individuals. Although clinical trials have confirmed the potency and safety of selectively oncolytic adenoviruses for treatment of advanced cancers, increasingly effective agents could result in more toxicity and therefore it would be useful if replication could be abrogated if necessary.

METHODS

We analyzed the effect of chlorpromazine, an inhibitor of clathrin-dependent endocytosis and apigenin, a cell cycle regulator, on adenovirus replication and toxicity. First, we evaluated the in vitro replication of a tumor targeted Rb-p16 pathway selective oncolytic adenovirus (Ad5/3-Delta24) and a wild-type adenovirus in normal cells, fresh liver samples and in ovarian cancer cell lines. Further, we analyzed the in vitro cell killing efficacy of adenoviruses in the presence and absence of the substances. Moreover, the effect on in vivo efficacy, replication and liver toxicity of the adenoviruses was evaluated.

RESULTS

We demonstrate in vitro and in vivo reduction of adenovirus replication and associated toxicity with chlorpromazine and apigenin. Effective doses were well within what would be predicted safe in humans.

CONCLUSIONS

Chlorpromazine and apigenin might reduce the replication of adenovirus, which could provide a safety switch in case replication-associated side effects are encountered in patients. In addition, these substances could be useful for the treatment of systemic adenoviral infections in immunosuppressed patients.

Oncolytic Treatment and Cure of Neuroblastoma by a Novel Attenuated Poliovirus in a Novel Poliovirus-Susceptible Animal Model

Neuroblastoma is one of the most common solid tumors in children. Treatment is of limited utility for high-risk neuroblastoma and prognosis is poor. Resistance of neuroblastoma to conventional therapies has prompted us to search for a novel therapeutic approach based on genetically modified polioviruses. Poliovirus targets motor neurons leading to irreversible paralysis. Neurovirulence can be attenuated by point mutations or by exchange of genetic elements between different picornaviruses. We have developed a novel and stable attenuated poliovirus, replicating in neuroblastoma cells, by engineering an indigenous replication element (cre), copied from a genome-internal site, into the 5'-nontranslated genomic region (mono-crePV). An additional host range mutation (A(133)G) conferred replication in mouse neuroblastoma cells (Neuro-2a(CD155)) expressing CD155, the poliovirus receptor. Crossing immunocompetent transgenic mice susceptible to poliovirus (CD155 tg mice) with A/J mice generated CD155 tgA/J mice, which we immunized against poliovirus. Neuro-2a(CD155) cells were then transplanted into these animals, leading to lethal tumors. Despite preexisting high titers of anti-poliovirus antibodies, established lethal s.c. Neuro-2a(CD155) tumors in CD155 tgA/J mice were eliminated by intratumoral administrations of A(133)Gmono-crePV. No signs of paralysis were observed. Interestingly, no tumor growth was observed in mice cured of neuroblastoma that were reinoculated s.c. with Neuro-2a(CD155). This result indicates that the destruction of neuroblastoma cells by A(133)Gmono-crePV may lead to a robust antitumor immune response. We suggest that our novel attenuated oncolytic poliovirus is a promising candidate for effective oncolytic treatment of human neuroblastoma or other cancer even in the presence of present or induced antipolio immunity.

Clinical trial results with oncolytic virotherapy: a century of promise, a decade of progress

Therapeutic oncolytic viruses (virotherapeutics) constitute a novel class of targeted anticancer agents that have unique mechanisms of action compared with other cancer therapeutics. The development of virotherapeutics has evolved from the use of in vitro-passaged strains (first generation), to genetically engineered selectivity-enhanced viruses (second generation) and finally to genetically engineered transgene-expressing 'armed' oncolytic viruses (third generation). Descriptions of cancer remissions following virus infections date back to a century ago. Initial patient treatment publications, written up to 50 years ago, consisted of case reports or case series of treatment with first-generation, non-engineered viruses. Over the past decade, hundreds of patients with cancer have been treated on prospectively designed clinical trials (including phase III), evaluating over 10 different agents, inlcluding engineered second-generation and third-generation viruses. This Review summarizes and interprets the data from clinical reports over the last century, including safety, efficacy and biological end points (viral and immunologic). Systemic safety and efficiacy has been clearly demonstrated with some virotherapeutics. The implications of these data for future virotherapy development are discussed.

Efficient inhibition of intraperitoneal human ovarian cancer growth and prolonged survival by gene transfer of vesicular stomatitis virus matrix protein in nude mice

OBJECTIVE

Vesicular stomatitis virus (VSV) matrix protein (MP) has been reported to be capable of inducing apoptosis in vitro in the absence of other viral components. In the present study, the antitumor effect of a recombinant plasmid encoding VSVMP on human ovarian cancer and its apoptosis-inducing efficacy in vivo were further investigated.

METHODS

The recombinant plasmid DNA carrying VSVMP-cDNA (VSVMP-p) was constructed. SKOV3 ovarian cancer cells were transfected with VSVMP-p and examined for apoptosis by Hoechst 33258 staining and flow cytometric analysis. For in vivo study, intraperitoneal ovarian carcinomatosis models in nude mice were established and randomly assigned into four groups to receive six twice-weekly i.p. administrations of VSVMP-p/liposome complexes, empty plasmid/liposome complexes, liposome alone or 0.9% NaCl solution, respectively. The weight of intraperitoneal carcinomatosis and the survival were monitored. Tumor tissues were inspected for apoptosis by TUNEL and Hoechst-33258 assay.

RESULTS

Plentiful apoptosis were observed in SKOV3 cells transfected with VSVMP-p. VSVMP-p reduced intraperitoneal tumor weight by about approximately 90% compared with control agents (p<0.01) and significantly prolonged the survival of tumor-bearing mice (p<0.05), with in vivo apoptosis index of 12.6+/-2.7% which was much higher than that of control groups (<4%) (p<0.05). Interestingly, this antitumor effect was accompanied by a noticeable NK cell accumulation. The treatment with VSVMP-p was devoid of any conspicuous toxicity.

CONCLUSIONS

These observations suggest that VSVMP-p have strong antitumor effects by inducing apoptosis and possibly NK cell-mediated tumor resistance mechanisms, and it may be a potentially effective novel therapy against human ovarian cancer.

Augmented therapeutic efficacy of an oncolytic herpes simplex virus type 1 mutant expressing ICP34.5 under the transcriptional control of musashi1 promoter in the treatment of malignant glioma

Although second-generation replication-conditional herpes simplex virus type 1 (HSV-1) vectors defective for both ribonucleotide reductase (RR) and the virulence factor gamma(1)34.5 have been proven safe through a number of animal experiments and clinical trials, their therapeutic efficacy was also markedly reduced. To overcome this situation, we concentrated on the use of a tumor-specific promoter in this study, to express ICP34.5 selectively in malignant glioma cells. As a molecular marker for malignant glioma, we focused on the neural RNA-binding protein, Musashi1. On the basis of the results of defective vector dvM345, as reported previously, we created, via homologous recombination, a novel HSV-1 vector termed KeM34.5, which expresses ICP34.5 under the transcriptional control of the musashi1 gene promoter (P/musashi1). Cytotoxicity mediated by KeM34.5 was significantly enhanced in human glioma cell lines (U87MG, U87MG-E6, U251, and T98G), resulting in an approximately 2-log increase in viral yield, compared with its parental vector G207. This virus also showed much higher therapeutic efficacy in the in vivo glioma model, while maintaining the desirable neuroattenuated phenotype. These results suggest that oncolytic HSV-1 expressing ICP34.5 under the transcriptional control of the musashi1 gene promoter could be a promising therapeutic agent for the treatment of malignant glioma.

Isolated limb perfusion: a novel delivery system for wild-type p53 and fiber-modified oncolytic adenoviruses to extremity sarcoma

Isolated limb perfusion (ILP) is a limb salvage surgical modality used to deliver chemotherapy and biologic agents to locally advanced and recurrent extremity soft tissue sarcoma (STS), and may be readily tailored for delivery of gene therapy. We set out to test the feasibility of delivering AdFLAGp53 (replication incompetent adenovirus bearing FLAG-tagged wild-type p53) and Ad.hTC.GFP/E1a.RGD (a fiber-modified, replication selective oncolytic adenovirus) into human leiomyosarcoma xenografts by ILP. Nude rats bearing SKLMS-1 tumors in their hind limbs underwent ILP with escalating doses of AdLacZ or AdFLAGp53 (study 1), or with Ad.CMV.GFP.RGD or Ad.hTC.GFP/E1a.RGD (study 2) following in vitro confirmation of therapeutic potential in STS cell lines and strains. Seventy-two hours after delivery, reverse transcription-polymerase chain reaction confirmed FLAGp53 expression, and immunohistochemistry confirmed diffuse upregulation of p21CIP1/WAF1 in ILP-treated tumors. Ad.hTC.GFP/E1a.RGD perfused tumors demonstrated robust macroscopic transgene expression throughout their substance, but not in perfused normal tissues, 21 days after delivery. Intra-tumoral viral replication was confirmed by immunohistochemical staining for early (E1a) and late (hexon) viral protein expression. Terminal deoxynucleotidyl transferase-mediated-digoxigenin nick end-labeling staining identified foci of cell death within regions of viral replication. In conclusion, therapeutic adenoviral gene therapy against limb borne human STS can be successfully delivered by ILP and warrants further investigation.

Dominant-negative fibroblast growth factor receptor expression enhances antitumoral potency of oncolytic herpes simplex virus in neural tumors

PURPOSE

Oncolytic herpes simplex viruses (HSV) appear to be a promising platform for cancer therapy. However, efficacy as single agents has thus far been unsatisfactory. Fibroblast growth factor (FGF) signaling is important for the growth and migration of endothelial and tumor cells. Here, we examine the strategy of arming oncolytic HSV with a dominant-negative FGF receptor (dnFGFR) that targets the FGF signaling pathway.

EXPERIMENTAL DESIGN

A mouse Nf1:p53 malignant peripheral nerve sheath tumor (MPNST) cell line expressing dnFGFR was generated by transfection. The effects of dnFGFR expression on cell growth and migration in vitro and tumor formation in vivo were determined. The dnFGFR transgene was then inserted into oncolytic HSV G47Delta using a bacterial artificial chromosome construction system. Antitumoral and antiangiogenic activities of bG47Delta-dnFGFR were examined.

RESULTS

MPNST 61E4 cells expressing dnFGFR grew less well than parental control cells. bG47Delta-dnFGFR showed enhanced killing of both tumor (human U87 glioma and F5 malignant meningioma cells and murine MPNST 61E4 and 37-3-18-4 cells) and proliferating endothelial cells (human umbilical vascular endothelial cell and Py-4-1) in vitro compared with the control vector bG47Delta-empty without inhibiting viral replication. In vivo, bG47Delta-dnFGFR was more efficacious than its nonexpressing parent bG47Delta-empty at inhibiting tumor growth and angiogenesis in both human U87 glioma and mouse 37-3-18-4 MPNST tumors in nude mice.

CONCLUSIONS

By using multiple therapeutic mechanisms, including destruction of both tumor cells and tumor endothelial cells, an oncolytic HSV encoding dnFGFR enhances antitumor efficacy. This strategy can be applied to other oncolytic viruses and for clinical translation.

A survivin-mediated oncolytic adenovirus induces non-apoptotic cell death in lung cancer cells and shows antitumoral potential in vivo

BACKGROUND

Conditionally replicating adenoviruses or oncolytic adenoviruses, which can replicate selectively in tumor cells and kill them, represent an innovative class of promising cancer therapeutics. Survivin is the smallest member of the inhibitor of apoptosis (IAP) family, which is transcriptionally upregulated exclusively in most malignant tissues but not in normal tissues. It has been reported that activity of the survivin promoter is tumor-specific, which makes the survivin promoter a good candidate to construct oncolytic viral vectors.

METHODS

A luciferase reporter assay was used to determine the activity of the survivin promoter in tumor and normal cells. An oncolytic adenovirus (Ad.SP/E1A) was generated by homologous recombination. The oncolytic efficacy of Ad.SP/E1A was evaluated in cell lines and in a human lung xenograft tumor mouse model.

RESULTS

Survivin expression was highly upregulated in tumor cells both at the protein and mRNA level. The luciferase reporter assay showed that survivin promoter activity is tumor-specific. Ad.SP/E1A expressed E1A selectively in tumor cells and induced cytotoxicity, but not in normal cells. Moreover, in animal experiments, intratumoral administration of Ad.SP/E1A significantly suppressed the growth of xenograft tumors. Further investigation showed that Ad.SP/E1A induced cell death by an apoptosis-independent pathway.

CONCLUSIONS

Ad.SP/E1A could be a potent therapeutic agent for cancer gene therapy. The investigation of the mechanisms of oncolytic virus-induced cell death in this work will shed light on the construction of more powerful vectors for cancer therapy.

A three-dimensional assay for measurement of viral-induced oncolysis

Oncolytic viruses represent a novel cancer treatment strategy. Despite their promising preclinical data, however, corresponding clinical trials have disappointed. To aid preclinical analyses, we hypothesized that three-dimensional tumor cell clusters or spheroids might provide an assay system superior to conventional monolayer cell cultures. Spheroids show viral infection, replication and oncolytic patterns distinct from conventional monolayer assays. Therefore, viral tumor penetration and oncolysis measurements may be improved with such three-dimensional models. Also, preclinical analyses of oncolytic viruses frequently measure mitochondrial activity, but more accurate measures of oncolysis might involve quantitation of intracellular protein release. Therefore, we measured luciferase released from luciferase-expressing spheroids and found unique patterns that maintained consistency with various viruses and doses. The relative variations between viruses and doses may represent temporal differences in oncolysis dynamics. Analysis of five recombinant replicative adenoviruses with promise for clinical application showed that Ad5/3-Delta24 produced the most luciferase release 1 week after infection and achieved the earliest and highest peak luciferase release level. Ad5/3-Delta24 also effected the earliest subtotal spheroid cell death. These findings closely parallel monolayer oncolysis assays with these agents. Therefore, the luciferase-expressing tumor spheroid assay represents a promising three-dimensional model for preclinical analysis of replicative oncolytic agents.

Enhanced therapeutic efficacy of oncolytic herpes vector G207 against human non-small cell lung cancer--expression of an RNA-binding protein, Musashi1, as a marker for the tailored gene therapy

BACKGROUND

Oncolytic herpes vectors like G207 have shown considerable promise in the treatment of solid tumors, but their potency must be enhanced for the full achievement of therapeutic efficacy. Deletion of the innate gamma34.5 gene made these vectors extremely safe, but their efficacy was also severely attenuated. Use of tumor-specific promoters is one method to direct toxicity and enhance efficacy against tumors. Recently, Musashi1 has been shown expressed in some tumor tissues.

METHODS

Eleven human cancer cell lines including five non-small cell lung cancers (NSCLCs) were investigated. Musashi1 mRNA expression was examined by RT-PCR analysis. Western blotting was also performed. Transcriptional activity of P/musashi1 in NSCLCs was assayed by GFP reporter plasmids. Then we constructed a defective amplicon vector containing musashi1 promoter/ICP34.5 with G207 as helper virus (dvM345). In vitro cytotoxicity against NSCLCs and growth characteristics of helper virus were examined. A Lu-99 subcutaneous tumor model was used in an animal study. The tumor volume treated with G207 alone or dvM345 was measured.

RESULTS

Musashi1 mRNA was detected in four cell lines. Two in five NSCLCs were positive, and P/musashi1 was proved functional within them. Against these cell lines, dvM345 showed enhanced cytotoxicity, and helper viral growth was augmented. A subcutaneous tumor study confirmed the enhanced therapeutic efficacy of G207 by dvM345 without compromising safety.

CONCLUSIONS

These results suggest that Musashi1 might be involved in the development of several carcinomas including NSCLC. In the context of oncolytic herpes vector strategy, the P/musashi1-ICP34.5 method could be used for the treatment of cancers expressing Musashi1.

Increased safety with preserved antitumoral efficacy on hepatocellular carcinoma with dual-regulated oncolytic adenovirus

PURPOSE

A dual-regulated adenovirus variant CNHK500, in which human telomerase reverse transcriptase promoter drove the adenovirus 5 (Ad5) E1a gene and hypoxia-response promoter controlled the E1b gene, was engineered. This virus has broad anticancer spectrum and higher specificity compared with mono-regulated adenovirus CNHK300. The objective of the current study is to show its antitumor selectivity and therapeutic potential.

EXPERIMENTAL DESIGN

The antitumor specificity of human telomerase reverse transcriptase and hypoxia response promoters was evaluated in a panel of tumor and normal cells. Under the control of these promoters, the tumor-selective expression of E1a and E1b genes was evaluated. Further in vitro antitumor specificity and potency of this virus were characterized by viral replication and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Subsequently, hepatocellular carcinoma xenografts were established to evaluate CNHK500 antitumor efficacy in vivo by different routes of virus administration and different dosages.

RESULTS

Human telomerase reverse transcriptase and hypoxia response promoters were activated in a tumor-selective manner or under hypoxia treatment in a broad panel of cells. Selective adenoviral early gene expression, efficient viral replication, and oncolysis were observed in all tested cancer cells with more attenuated replication capacity in normal cells. Significant regression of hepatocellular carcinoma xenografts and prolonged survival were observed by either i.t. or i.v. administration.

CONCLUSIONS

CNHK500 greatly reduced side effects in normal cells via dual control of adenoviral essential genes while still preserving potent antitumor efficacy on broad-spectrum cancer cells in vitro and in vivo. It can be used as a powerful therapeutic agent not only for liver cancers but also for other solid tumors.

Targeting gene-virotherapy of cancer and its prosperity

Gene and viral therapies for cancer have shown some therapeutic effects, but there has been a lack of real breakthrough. To achieve the goal of complete elimination of tumor xenograft in animal models, we have developed a new strategy called Targeting Gene-Virotherapy of Cancer, which aims to combine the advantages of both gene therapy and virotherapy. This new strategy has produced stronger anti-tumor effects than either gene or viral therapy alone. A tumor-specific replicative adenovirus vector, designated as ZD55, was constructed by deletion of the 55kDa E1B region of adenovirus. The resulting viral construct not only retains a similar function to ONYX-015 by specifically targeting p53 negative tumors, but also allows for the insertion of various therapeutic genes to form appropriate ZD55 derivatives due to the newly introduced cloning site, a task not feasible with the original ONYX-015 virus. We showed that the anti-tumor effect of one such derivative, ZD55-IL-24, is at least 100 times more potent than that of either ZD55 virotherapy or Ad-IL-24 gene therapy. Nevertheless, complete elimination of tumor mass by the use of ZD55-IL-24 was only observed in some but not all mice, indicating that one therapeutic gene was not sufficient to "cure" these mice. When genes with complementary or synergetic effects were separately cloned into the ZD55 vector and used in combination (designated as the Dual Gene Therapy strategy), much better results were obtained; and it was possible to achieve complete elimination of all the xenograft tumor masses in all mice if two suitable genes were chosen. More comprehensive studies based on this new strategy will likely lead to a protocol for clinical trial. Finally, the concept of Double Controlled Targeting Virus-Dual Gene Therapy for cancer treatment, and the implication of the recent progress in cancer stem cells are also discussed.