Triple gene-deleted oncolytic herpes simplex virus vector double-armed with interleukin 18 and soluble B7-1 constructed by bacterial artificial chromosome-mediated system

Conditionally replicating herpes simplex virus type 1 (HSV-1) vectors are promising therapeutic agents for cancer. Certain antitumor functions may be added to oncolytic activities of recombinant HSV-1 vectors by inserting transgenes into the viral genome. Because conventional homologous recombination techniques had required time-consuming processes to create "armed" oncolytic HSV-1 vectors, we established an innovative construction system using bacterial artificial chromosome and two recombinase systems (Cre/loxP and FLPe/FRT). Using G47Delta, a safe and efficacious oncolytic HSV-1 with triple gene mutations, as the backbone, this system allowed a rapid generation of multiple vectors with desired transgenes inserted in the deleted ICP6 locus. Four oncolytic HSV-1 vectors, expressing murine interleukin 18 (mIL-18), soluble murine B7-1 [B7-1-immunoglobulin (B7-1-Ig)], both, or none, were created simultaneously within 3 months. In vitro, all newly created recombinant vectors exhibited virus yields and cytopathic effects similar to the parental G47Delta. In two immunocompetent mouse tumor models, TRAMP-C2 prostate cancer and Neuro2a neuroblastoma, the vector expressing both mIL-18 and B7-1-Ig showed a significant enhancement of antitumor efficacy via T-cell-mediated immune responses. The results show that "arming" with multiple transgenes can improve the efficacy of oncolytic HSV-1 vectors. The use of our system may facilitate the development and testing of various armed oncolytic HSV-1 vectors.     

Enhanced antitumor effect of oncolytic adenovirus expressing interleukin-12 and B7-1 in an immunocompetent murine model.

PURPOSE: We investigated whether an armed viral platform, where lytic property of a viral infection is coupled to viral-mediated delivery of therapeutic genes, could increase the therapeutic potential of a viral-based therapy. EXPERIMENTAL DESIGN: We generated interleukin (IL)-12-expressing oncolytic adenovirus (YKL-IL-12) and IL-12- and B7-1-expressing (YKL-IL12/B7) oncolytic adenovirus. Therapeutic efficacy of these newly engineered adenoviruses was then evaluated in vivo using an immunocompetent mouse bearing murine melanoma B16-F10 tumors. Overall survival was assessed with the Kaplan-Meier method. The induction of immune cell cytotoxicity was assessed by CTL assay, IFN-gamma enzyme-linked immunospot assay, and immunohistochemical studies. RESULTS: YKL-IL12/B7 oncolytic adenovirus, expressing both IL-12 and B7-1, showed a higher incidence of complete tumor regression compared with the analogous oncolytic adenovirus, YKL-1, or IL-12-expressing, YKL-IL12. Significant survival advantage was also seen in response to YKL-IL12/B7. Moreover, IL-12 and IFN-gamma levels produced in tumors treated with YKL-IL12/B7 was significantly greater than those treated with YKL-IL12. The enhanced survival advantage was mediated by the induction of immune cell cytotoxicity. In agreement with these results, massive infiltration of CD4(+) and CD8(+) T cells into tissues surrounding the necrotic area of the tumor was observed following in situ delivery of YKL-IL12/B7. CONCLUSION: Combination of oncolysis and the enhancement of antitumor immune response by oncolytic adenovirus expressing both IL-12 and B7-1 elicits potent antitumor effect and survival advantage.     

Cytokine-secreting herpes viral mutants effectively treat tumor in a murine metastatic colorectal liver model by oncolytic and T-cell-dependent mechanisms

In this model of hepatic micrometastases, the antitumor efficacy and role of the T-cell and natural killer (NK) cell populations were studied for oncolytic herpes simplex virus type-1 (HSV-1) viral mutants containing the granulocyte-monocyte colony stimulating factor (GM-CSF (NV1034)) or interluken-12 (IL-12 (NV1042)) cytokine genes. These were compared to saline and control virus (NV1023) in vitro and in vivo. HSV-1 mutants were assessed for cytotoxicity, replication and cytokine expression in CT-26 cells. A syngeneic micrometastatic liver model was then established in naive and immune cell-depleted animals to assess the antitumor efficacy of these viruses. In vitro cytotoxicity and viral replication were similar for each virus, resulting in greater than 80 and 98% cytotoxicity at multiplicity of infection of 1 and 10, respectively. Peak viral titers were 25- to 50-fold higher than initial titer and were not significantly different between viruses. In vivo, all three viruses reduced metastases relative to control, but cytokine-secreting viruses did so with greater efficacy compared to NV1023. This effect was abrogated by T-cell depletion, but not NK-cell depletion. Single-agent therapy with oncolytic viral agents containing GM-CSF or IL-12 is effective in a murine model of liver metastases and likely involves direct viral oncolysis and actions of specific immune effector cells.     

Oncolytic herpes simplex virus expressing yeast cytosine deaminase: relationship between viral replication, transgene expression, prodrug bioactivation

Yeast cytosine deaminase (yCD) is a well-characterized prodrug/enzyme system that converts 5-fluorocytosine (5-FC) to 5-fluorouracil (5-FU), and has been combined with oncolytic viruses. However, in vivo studies of the interactions between 5-FC bioactivation and viral replication have not been previously reported, nor have the kinetics of transgene expression and the pharmacokinetics of 5-FC and 5-FU. We constructed a replication-conditional Herpes simplex virus 1 (HSV-1) expressing yCD and examined cytotoxicity when 5-FC was initiated at different times after viral infection, and observed that earlier 5-FC administration led to greater cytotoxicity than later 5-FC administration in vitro and in vivo. In animal models, 12 days of 5-FC administration was superior to 6 days, but dosing beyond 12 days did not further enhance efficacy. Consistent with the dosing-schedule results, both viral genomic DNA copy number and viral titers were observed to peak on Day 3 after viral injection and gradually decrease thereafter. The virus is replication-conditional and was detected in tumors for as long as 2 weeks after viral injection. The maximum relative extent of yCD conversion of 5-FC to 5-FU in tumors was observed on Day 6 after viral injection and it decreased progressively thereafter. The observation that 5-FU generation within tumors did not lead to appreciable levels of systemic 5-FU (<10?ng?ml?1) is important and has not been previously reported. The approaches used in these studies of the relationship between the viral replication kinetics, transgene expression, prodrug administration and anti-tumor efficacy are useful in the design of clinical trials of armed, oncolytic viruses.     

Phase I study of the intratumoral administration of recombinant canarypox viruses expressing B7.1 and interleukin 12 in patients with metastatic melanoma.

The objective of this study was to evaluate the safety and activity of the intratumoral administration of the immune costimulatory molecule, B7.1, encoded by a vector derived from the canarypox virus, ALVAC (ALVAC-B7.1), alone and with the intratumoral injection of ALVAC encoding the immune-stimulatory cytokine, interleukin 12 (ALVAC-IL-12). Fourteen patients with metastatic melanoma who had s.c. nodules received intratumoral injections on days 1, 4, 8, and 11. Nine patients were given escalating doses of up to 25 x 10(8) plaque-forming units of ALVAC-B7.1. Five patients were given 25 x 10(8) plaque-forming units of ALVAC-B7.1 combined with ALVAC-IL-12 50% tissue culture infective dose of 2 x 10(6). Toxicity was mild to moderate and consisted of inflammatory reactions at the injection site and fever, chills, myalgia, and fatigue. Higher levels of B7.1 mRNA were observed in ALVAC-B7.1-injected tumors compared with saline-injected control tumors. Higher levels of intratumoral vascular endothelial growth factor and IL-10, cytokines with immune suppressive activities, were also observed in ALVAC-B7.1- and ALVAC-IL-12-injected tumors compared with saline-injected controls. Serum levels of vascular endothelial growth factor increased at day 18 and returned to baseline at day 43. All patients developed antibody to ALVAC. Intratumoral IL-12 and IFN-gamma mRNA decreased. Changes in serum IL-12 and IFN-gamma levels were not observed. Tumor regressions were not observed. The intratumoral injections of ALVAC-B7.1 and ALVAC-IL-12 were well tolerated at these dose levels and at this schedule and resulted in measurable biological response. This response included the production of factors that may suppress the antitumor immunologic activity of these vectors.     

Systemic therapy of spontaneous prostate cancer in transgenic mice with oncolytic herpes simplex viruses

Oncolytic viruses are an innovative therapeutic strategy for cancer, wherein viral replication and cytotoxicity are selective for tumor cells. Here we show the efficacy of systemically administered oncolytic viruses for the treatment of spontaneously arising tumors, specifically the use of oncolytic herpes simplex viruses (HSV) administered i.v. to treat spontaneously developing primary and metastatic prostate cancer in the transgenic TRAMP mouse, which recapitulates human prostate cancer progression. Four administrations of systemically delivered NV1023 virus, an HSV-1/HSV-2 oncolytic recombinant, to TRAMP mice at 12 or 18 weeks of age (presence of prostate adenocarcinoma or metastatic disease, respectively) inhibited primary tumor growth and metastases to lymph nodes. Expression of interleukin 12 (IL-12) from NV1042 virus, a derivative of NV1023, was additionally effective, significantly reducing the frequency of development of prostate cancer and lung metastases, even when the mice were treated after the onset of metastasis at 18 weeks of age. NV1042-infected cells, as detected by 5-bromo-4-chloro-3-indolyl-beta-d-galactopyranoside staining for Lac Z expressed by the virus, were present in prostate tumors 1 week after the final virus injection and viral DNA was detected at 2 weeks after final virus injection by real-time PCR in primary and metastatic tumors but not in liver or blood. No toxicity was observed in any of the treated mice. The efficacy of the IL-12-expressing NV1042 virus in this aggressive prostate cancer model using a clinically relevant treatment paradigm merits its consideration for clinical studies.     

Evaluation of ganciclovir-mediated enhancement of the antitumoral effect in oncolytic, multimutated herpes simplex virus type 1 (G207) therapy of brain tumors

G207 is a multimutated, conditionally replicating herpes simplex virus type 1 (HSV-1) that retains an intact viral thymidine kinase (HSV-tk) gene. The virus exhibits oncolytic activity in various tumors and is being evaluated in patients with recurrent malignant glioma. In view of the potential for ganciclovir (GCV) to either enhance or inhibit the antitumoral activity of HSV-tk-retaining HSV-1 vectors, we evaluated the effect of GCV administration on the antitumoral activity of G207. In culture, addition of GCV either had no effect or inhibited the cytocidal action of G207 at replication-permissive temperatures, while it significantly increased the cell killing in three of the four cell lines studied when virus replication was inhibited at nonpermissive temperatures. Using a G207-permissive immunocompetent mouse tumor model, subcutaneous N18 neuroblastoma in syngeneic A/J mice, we found that GCV treatment did not affect G207-mediated tumor growth inhibition at a variety of viral doses (10(5), 10(7), and 10(7) x 2 plaque-forming units). In A/J mice harboring intracerebral N18 tumors, GCV administration had no significant effect on the prolongation of survival by G207 inoculation. These findings suggest that GCV administration may not be beneficial to the efficacy of G207 tumor therapy under conditions that favor active viral replication, because the potential HSV-tk/GCV-mediated enhancement of G207 oncolytic activity may be balanced out by the inhibitory action of GCV on viral replication.     

Angiogenesis inhibition by an oncolytic herpes virus expressing interleukin 12.

PURPOSE: Oncolytic herpes simplex viruses (HSVs) may have significant antitumor effects resulting from the direct lysis of cancer cells. HSVs may also be used to express inserted transgenes to exploit additional therapeutic strategies. The ability of an interleukin (IL)-12-expressing HSV to treat squamous cell carcinoma (SCC) by inhibition of tumor angiogenesis is investigated in this study. EXPERIMENTAL DESIGN: A replication-competent, attenuated, oncolytic HSV carrying the murine IL-12 gene (NV1042), its non-cytokine-carrying analog (NV1023), or saline was used to treat established murine SCC flank tumors by intratumoral injection. The expression of secondary antiangiogenic mediators was measured. Angiogenesis inhibition was assessed by in vivo Matrigel plug assays, flank tumor subdermal vascularity, and in vitro endothelial cell tubule formation assay. RESULTS: Intratumoral injections of NV1042 (2 x 10(7) plaque-forming units) into murine SCC VII flank tumors resulted in smaller tumor volumes as compared with NV1023 or saline. IL-12 and IFN-gamma expression in tumors was 440 and 2.2 pg/mg, respectively, at 24 h after NV1042 injection, but both IL-12 and IFN-gamma were undetectable (<0.2 pg/mg) after NV1023 or saline injections. Expression of two antiangiogenesis mediators, monokine induced by IFN-gamma and IFN-inducible protein 10, was elevated after NV1042 treatment. Matrigel plug assays of NV1042-transfected SCC VII tumor cells demonstrated significantly decreased hemoglobin content and microvessel density as compared with NV1023 and PBS. Excised murine flank tumors treated with NV1042 had decreased subdermal vascularity as compared with NV1023 and PBS. Both splenocytes and IL-12 expression by NV1042 were required for in vitro inhibition of endothelial tubule formation. CONCLUSIONS: IL-12 expression by an oncolytic herpes virus enhances therapy of SCC through antiangiogenic mechanisms. Strategies combining HSV oncolysis with angiogenesis inhibition merit further investigation for potential clinical application.     

Enhanced therapeutic efficacy of IL-12, but not GM-CSF, expressing oncolytic herpes simplex virus for transgenic mouse derived prostate cancers

Replication competent oncolytic herpes simplex viruses (HSV) with broad-spectrum activity against various cancers, including prostate cancer, exert a dual effect by their direct cytocidal action and by eliciting tumor-specific immunity. These viruses can deliver immunoregulatory molecules to tumors so as to enhance the cumulative antitumor response. This is particularly desirable for prostate cancers, which are usually poorly immunogenic. Initial studies described herein comparing the efficacy of three different oncolytic HSVs (G207, G47Delta, and NV1023) to inhibit the growth of the poorly immunogenic TRAMP-C2 mouse prostate tumors demonstrated that NV1023 was most effective in treating established tumors. The expression of IL-12 on an NV1023 background (NV1042), but not the expression of GM-CSF (NV1034), further enhanced the efficacy of NV1023 in two murine prostate cancer models with highly variable MHC class I levels, Pr14-2 with 91% and TRAMP-C2 with 2% of cells staining. NV1042 also inhibited the growth of distant noninoculated tumors in both prostate cancer models. NV1042 treated tumors exhibited increased immune cell infiltration and decreased levels of angiogenesis. Thus, an IL-12 expressing oncolytic herpes virus, which is capable of direct cytotoxicity and can modulate the otherwise suboptimal immune response through concomitant expression of the cytokine at the site of tumor destruction, could serve as a valuable clinical agent to seek out both overt and occult prostate cancers.     

Regional treatment of hepatic micrometastasis by adenovirus vector-mediated delivery of interleukin-2 and interleukin-12 cDNAs to the hepatic parenchyma

We hypothesize that adenovirus (Ad) vector-mediated delivery of the human interleukin-2 (IL-2) cDNA (AdIL2) or the murine IL-12 cDNA heterodimer (AdIL12) would produce high concentrations of cytokines in the local hepatic milieu to induce host responses sufficient to inhibit the growth of experimental colon carcinoma-derived hepatic metastases. Ad vectors administered intravenously, which is a route known to deliver >90% of the vector to the hepatic parenchyma, achieved significant levels of each cytokine locally, with minimal levels in the sera. To examine the therapeutic effect, the AdIL2 and AdIL12 vectors were evaluated in a hepatic metastasis model that was established by injecting 3 x 10(4) cells from the poorly immunogenic syngeneic C26 colon carcinoma cell line into the right lobe of the livers of BALB/c mice. Animals received AdIL2, AdIL12, or control virus (10(8) plaque-forming units each) intravenously for 2 days after tumor implantation, and tumor growth was compared with naive controls. The AdNull control tumors measured 116 +/- 25 mm2 at 2 weeks. The control virus showed no significant antitumor effect. In marked contrast, both AdIL2 and AdIL12 vectors that were delivered regionally had significant antitumor effects, with AdIL2-treated animals having an average tumor size of 16 +/- 8 mm2; AdIL12-treated tumors measured 6 +/- 6 mm2 (P < .01, both compared with control). Both the AdIL2 and AdIL12 vectors provided a significant survival advantage by log-rank analysis (P < .01), but only AdIL12 translated into an increase in mean survival from 27 (naive control) to 37 days. To evaluate whether these antitumor effects were T-cell-mediated, splenocytes from AdIL2-treated, AdIL12-treated, and naive control groups were stimulated in vitro with gamma-irradiated C26 tumor cells for 5 days and tested for C26 tumor cell cytolysis by an in vitro cytotoxicity assay. Splenocytes from both AdIL2- and AdIL12-treated animals showed a dose-dependent, T-cell-mediated, specific cytolysis of CT26 cells. AdIL12 and to a lesser extent AdIL2 induced natural killer cell activity, as determined by a dose-dependent increase in lysis of the natural killer-specific target cell YAC-1. Overall, these data suggest that regional Ad-mediated delivery of IL-2 and IL-12 cDNAs may be useful for local tumor control and may warrant further investigation as a potentially useful adjuvant for the treatment of hepatic micrometastasis.     

An oncolytic virus derived from type 2 herpes simplex virus has potent therapeutic effect against metastatic ovarian cancer

Oncolytic viruses derived from herpes simplex virus (HSV) have shown considerable promise as antitumor agents against solid tumors including ovarian cancer. The current group of oncolytic HSVs was constructed exclusively from type 1 HSV. To exploit further the therapeutic potential of replication-selective viruses, we constructed an oncolytic virus from type 2 HSV by deleting the protein kinase domain of the viral ICP10 gene, which targets the activated Ras signaling pathway in tumor cells. In the study reported here, we administered this HSV-2-derived virus intraperitoneally (i.p.) to nude mice bearing metastatic human ovarian tumor xenografts, evaluated its oncolytic activity, and compared with to that of a virus constructed from HSV-1. Two injections of the HSV-2-derived virus (3 x 10(6) pfu per dose) led to complete eradication of disseminated tumors in the peritoneal cavity in more than 87% of the mice, whereas the HSV-1-based oncolytic virus, administered at the same dose and on the same schedule, eradicated tumor nodules in only 12% of mice (P<0.01). We conclude that i.p. administration of this HSV-2-based oncolytic virus may provide effective treatment for metastatic human ovarian cancer.     

In situ expression of soluble B7-1 in the context of oncolytic herpes simplex virus induces potent antitumor immunity

In vivo delivery of immunomodulatory genes is a promising strategy for solid tumor vaccination. A drawback is that it necessitates induction of a large effect from transgene expression in a small percentage of tumor cells. Although the B7 family is known to be the most potent of the costimulatory molecules, gene transduction of B7 alone has not been effective in inducing antitumor immunity in nonimmunogenic tumors by ex vivo methods, much less in vivo. We have developed a novel approach where a gene encoding soluble B7-1, a fusion protein of the extracellular domain of murine B7-1 and the Fc portion of human IgG1, is delivered to tumor cells in vivo in the context of an oncolytic replication-competent herpes simplex virus, and the gene product is secreted by tumor cells rather than expressed on the cell surface. Defective herpes simplex virus vectors containing the B7-1-immunoglobulin (B7-1-Ig) fusion transgene (dvB7Ig) were generated using G207 as a helper virus and tested in the poorly immunogenic murine neuroblastoma, Neuro2a, in syngeneic A/J mice. Intraneoplastic inoculation of dvB7Ig/G207 at a low titer successfully inhibited the growth of established s.c. tumors, despite the expression of B7-1-Ig being detected in only 1% or fewer of tumor cells at the inoculation site, and prolonged the survival of mice bearing intracerebral tumors. Immunohistochemistry of dvB7Ig/G207-inoculated tumors revealed a significant increase in CD4+ and CD8+ T-cell infiltration compared with control tumors inoculated with defective vector expressing alkaline phosphatase (dvAP/G207). The antitumor effect of dvB7Ig/G207 was not manifested in athymic mice. In vivo depletion of immune cell subsets in A/J mice further revealed that CD8+ T cells, but not CD4+ T cells, were required. Animals cured of their tumors by dvB7Ig/G207 treatment were protected against rechallenge with a lethal dose of Neuro2a cells but not SaI/N cells. The results demonstrate that the use of soluble B7-1 for immune gene therapy is a potent and clinically applicable means of in situ cancer vaccination.     

T-independent response mediated by oncolytic tanapoxvirus recombinants expressing interleukin-2 and monocyte chemoattractant protein-1 suppresses human triple negative breast tumors

Human triple negative breast cancer (TNBC) is an aggressive disease, associated with a high rate of recurrence and metastasis. Current therapeutics for TNBC are limited, highly toxic and show inconsistent efficacy due to a high degree of intra-tumoral and inter-tumoral heterogeneity. Oncolytic viruses (OVs) are an emerging treatment option for cancers. Several OVs are currently under investigation in preclinical and clinical settings. Here, we examine the oncolytic potential of two tanapoxvirus (TPV) recombinants expressing mouse monocyte chemoattractant protein (mMCP)-1 [also known as mCCL2] and mouse interleukin (mIL)-2, in human TNBC, in vitro and in vivo. Both wild-type (wt) TPV and TPV recombinants demonstrated efficient replicability in human TNBC cells and killed cancer cell efficiently in a dose-dependent manner in vitro. TPV/?66R/mCCL2 and TPV/?66R/mIL-2 expressing mCCL2 and mIL-2, respectively, suppressed the growth of MDA-MB-231 tumor xenografts in nude mice significantly, as compared to the mock-injected tumors. Histological analysis of tumors showed areas of viable tumor cells, necrotic foci and immune cell accumulation in virus-treated tumors. Moreover, TPV/?66R/mIL-2-treated tumors showed a deep infiltration of mononuclear immune cells into the tumor capsule and focal cell death in tumors. In conclusion, TPV recombinants expressing mCCL2 and mIL-2 showed a significant therapeutic effect in MDA-MB-231 tumor xenografts, in nude mice through induction of potent antitumor immune responses. Considering the oncolytic potency of armed oncolytic TPV recombinants expressing mCCL2 and mIL-2 in an experimental nude mouse model, these viruses merit further investigation as alternative treatment options for human breast cancer.     

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.     

Assessment of a combined, adenovirus-mediated oncolytic and immunostimulatory tumor therapy

In this study, we identified murine breast cancer cell lines that support DNA replication of E1-deleted adenovirus vectors and which can be killed by an oncolytic adenovirus expressing adenovirus E1A and tumor necrosis factor (TNF)-related apoptosis inducing ligand (TRAIL) in a replication-dependent manner (Ad.IR-E1A/TRAIL). We showed that systemic or intratumoral (i.t.) injection of adenovirus vectors into mice increases plasma levels of proinflammatory cytokines and chemokines, including TNF-alpha, INF-gamma, and MCP-1, which are potent inducers of dendritic cell maturation. Furthermore, we showed that in vivo expression of Flt3L from an adenovirus vector increases the number of CD11b+ and CD11c+ cells (populations that include dendritic cells) in the blood circulation. Based on these findings, we tested whether Ad.IR-E1A/TRAIL induced killing of tumor cells in combination with dendritic cell mobilization by Ad.Flt3L or, for comparison, Ad.GM-CSF would have an additive antitumor effect. As a model, we used immunocompetent C3H mice with syngeneic s.c. tumors derived from C3L5 cells. We found that vaccination of mice with C3L5 cells that underwent viral oncolysis in combination with Flt3L or granulocyte-macrophage colony-stimulating factor (GM-CSF) expression induces a systemic antitumor immune response. I.t. injection of the oncolytic and Flt3L expressing vectors into established tumors delayed tumor growth but did not cause efficient tumor elimination. This study shows the effectiveness of a combined oncolytic/immunostimulatory tumor therapy approach.     

Oncolytic herpes simplex virus vectors for cancer virotherapy

Oncolytic herpes simplex virus type 1 (HSV-1) vectors are emerging as an effective and powerful therapeutic approach for cancer. Replication-competent HSV-1 vectors with mutations in genes that affect viral replication, neuropathogenicity, and immune evasiveness have been developed and tested for their safety and efficacy in a variety of mouse models. Evidence to-date following administration into the brain attests to their safety, an important observation in light of the neuropathogenicity of the virus. Phase I clinical traits of three vectors, G207, 1716, and NV1020, are either ongoing or completed, with no adverse events attributed to the virus. These and other HSV-1 vectors are effective against a myriad of solid tumors in mice, including glioma, melanoma, breast, prostate, colon, ovarian, and pancreatic cancer. Enhancement of activity was observed when HSV-1 vectors were used in combination with traditional therapies such as radiotherapy and chemotherapy, providing an attractive strategy to pursue in the clinic. Oncolytic HSV-1 vectors expressing "suicide" genes (thymidine kinase, cytosine deaminase, rat cytochrome P450) or immunostimulatory genes (IL-12, GM-CSF, etc.) have been constructed to maximize tumor destruction through multimodal therapeutic mechanisms. Further advances in virus delivery and tumor specificity should improve the likelihood for successful translation to the clinic.     

Triple-mutated oncolytic herpes virus for treating both fast- and slow-growing tumors

Oncolytic virus therapy has emerged as a promising treatment option against cancer. To date, oncolytic viruses have been developed for malignant tumors, but the need for this new therapeutic modality also exists for benign and slow-growing tumors. G47∆ is an oncolytic herpes simplex virus type 1 (HSV-1) with an enhanced replication capability highly selective to tumor cells due to genetically engineered, triple mutations in the γ34.5, ICP6 and α47 genes. To create a powerful, but safe oncolytic HSV-1 that replicates efficiently in tumors regardless of growth speed, we used a bacterial artificial chromosome system that allows a desired promoter to regulate the expression of the ICP6 gene in the G47∆ backbone. Restoration of the ICP6 function in a tumor-specific manner using the hTERT promoter led to a highly capable oncolytic HSV-1. T-hTERT was more efficacious in the slow-growing OS-RC-2 and DU145 tumors than the control viruses, while retaining a high efficacy in the fast-growing U87MG tumors. The safety features are also retained, as T-hTERT proved safe when inoculated into the brain of HSV-1 sensitive A/J mice. This new technology should facilitate the use of oncolytic HSV-1 for all tumors irrespective of growth speed.