Local and systemic therapy of human prostate adenocarcinoma with the conditionally replicating herpes simplex virus vector G207

Oncolytic viruses for cancer therapy II. Cell-internal factors for conditional growth in neoplastic cells

Recent advances in our understanding of virus-host interactions have fueled new studies in the field of oncolytic viruses. The first part of this review explained how cell-external factors, such as cellular receptors, influence tumor tropism and specificity of oncolytic virus candidates. In the second part of this review, we focus on cellinternal factors that mediate tumor-specific virus growth. An oncolytic virus must be able to replicate within cancerous cells and kill them without collateral damage to healthy surrounding cells. This desirable property is inherent to some proposed oncolytic viral agents or has been achieved by genetic manipulation in others.

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.

Herpes simplex virus-induced, death receptor-dependent apoptosis and regression of transplanted human cancers

Inoculation of a live attenuated herpes simplex virus (HSV) vector, betaH1, into human U87MG glioblastoma cells transplanted into athymic nude mice induced complete regression of tumors. The infected cells underwent histochemically confirmed apoptosis without lymphocyte infiltration after expressing CD30, CD30 ligand (CD30L), tumor necrosis factor (TNF)-alpha, TNF receptor 1 (TNF-R1), FAS, and FAS ligand (FAS-L) with activation of caspases 3 and 8. Induction of the transcripts of these receptors and ligands in inoculated tumors was confirmed by quantitative RT-PCR. To examine the specificity of apoptosis in the transplanted tumor, we inoculated betaH1 into transplanted human lung, breast, gastric, and colon cancer tumors, and similar tumor regression with apoptosis was observed in all tumors. We analyzed the roles of expression of CD30, CD30L, TNF-alpha, TNF-R1, FAS, and FAS-L in the tumors, and found that HSV-induced apoptosis was suppressed by the respective antibodies. These findings indicate that the CD30/CD30L, TNF-alpha/TNF-R1, and FAS/FAS-L interactions resulted in apoptosis and tumor regression in immunocompromised mice. In addition to the death receptor-dependent apoptosis induced by HSV, the expressed ligands and receptors might enhance the susceptibility of tumor cells to cell-mediated cyto-toxicity and augment the activation of tumor-killing lymphocytes in immunocompetent models.

Transfection of IL-2 and/or IL-12 genes into spleen in treatment of rat liver cancer

AIM: To test the efficacy of gene therapy in rat liver tumor.

METHODS: A retroviral vector GCIL12EIL2PN encoding human IL-2 (hIL-2) and mouse IL-12 (mIL-12) fused gene and its packaging cell were constructed. The packaging cell lines contained of IL-2 and/or IL-12 genes were injected intrasplenically to transfect splenocyte at different time. The therapeutic effect, immune function and toxic effect were evaluated.

RESULTS: The average survival times of the 4 groups using IL genes at days 1, 3, 5 and 7 after tumor implantation were 53.3 ± 3.7, 49.3 ± 4.2, 31.0 ± 2.1 and 24.3 ± 1.4 d respectively in IL-2/IL-12 fused gene group, 25.0 ± 2.5, 23.5 ± 2.0, 18.3 ± 2.4 and 12.0 ± 1.8 d respectively in IL-2 gene treatment group, and 39.0 ± 4.8, 32.0 ± 3.9, 23.0 ± 2.5 and 19.4 ± 2.1 d respectively in IL-12 gene treatment group (P < 0.01, n = 10). In the IL-12/IL-2 fused gene treatment group, 30% of rats treated at days 1 and 3 survived more than 60 d and serum mIL-12 and hIL-2 levels were still high at day 3 after treatment. Compared with IL alone, NK cell activity was strongly stimulated by IL-2/IL-12 gene. Microscopy showed that livers were infiltrated by a number of lymphocytes.

CONCLUSION: IL-2 and/or IL-12 genes injected directly into spleen increase serum IL-2 and IL-12 levels and enhance the NK cell activity, which may inhibit the liver tumor growth. The therapy of fused gene IL-2/IL-12 is of low toxicity and relatively high NK cell activity. Our data suggest that IL-2/IL-12 fused gene may be a safe and efficient gene therapy for liver tumor. The gene therapy should be administrated as early as possible.

Utilizing tumor hypoxia to enhance oncolytic viral therapy in colorectal metastases

OBJECTIVE

To determine the effects of hypoxia-induced ribonucleotide reductase (RR) production on herpes oncolytic viral therapy.

SUMMARY BACKGROUND DATA

Hypoxia is a common tumor condition correlated with therapeutic resistance and metastases. Attenuated viruses offer a unique cancer treatment by specifically infecting and lysing tumor cells. G207 is an oncolytic herpes virus deficient in RR, a rate-limiting enzyme for viral replication.

METHODS

A multimerized hypoxia-responsive enhancer was constructed (10xHRE) and functionally tested by luciferase assay. 10xHRE was cloned upstream of UL39, the gene encoding the large subunit of RR (10xHRE-UL39). CT26 murine colorectal cancer cells were transfected with 10xHRE-UL39, incubated in hypoxia (1% O2) or normoxia (21% O2), and infected with G207 for cytotoxicity assays. CT26 liver metastases, with or without 10xHRE-UL39, were created in syngeneic Balb/C mice (n = 40). Livers were treated with G207 or saline. Tumors were assessed and stained immunohistochemically for G207.

RESULTS

10xHRE increased luciferase expression 33-fold in hypoxia versus controls (P < 0.001). In normoxia, 10xHRE-UL39 transfection did not improve G207 cytotoxicity. In hypoxia, G207 cytotoxicity increased 87% with 10xHRE-UL39 transfection versus nontransfected cells (P < 0.001). CT26 were resistant to G207 alone. Combining 10xHRE-UL39 with G207 resulted in a 66% decrease in tumor weights (P < 0.0001) and a 65% reduction in tumor nodules (P < 0.0001) versus G207 monotherapy. 10xHRE-UL39-transfected tumors demonstrated greater viral staining.

CONCLUSIONS

Hypoxia-driven RR production significantly enhances viral cytotoxicity in vitro and reduces tumor burden in vivo. G207 combined with RR under hypoxic control is a promising treatment for colorectal cancer, which would otherwise be resistant to oncolytic herpes virus alone.

Potent antitumor activity after systemic delivery of a doubly fusogenic oncolytic herpes simplex virus against metastatic prostate cancer

BACKGROUND

Although conventional radiation therapy and surgery are potentially curative treatments for organ-confined prostate cancer, there are few effective treatments for metastatic disease. Oncolytic viruses have shown considerable promise for the treatment of solid tumors including prostate cancer. We recently demonstrated that incorporation of a cell membrane fusion capability into an oncolytic herpes simplex virus (HSV) can significantly increase the antitumor potency of the virus.

METHODS

We used a mouse model of primary and metastatic human prostate cancer established from PC-3M-Pro4 to evaluate three different types of oncolytic HSVs: non-fusogenic Baco-1, singly fusogenic Synco-2, and doubly fusogenic Synco-2D.

RESULTS

Our results show that Synco-2D has greater oncolytic activity than either Baco-1 or Synco-2 virus. Against lung metastases of human prostate cancer xenografts, intravenous administration of Synco-2D had produced a significant reduction of tumor nodules by day 40 post-inoculation as compared with Synco-2 (P < 0.05), Baco-1 (P < 0.01), and PBS control (P < 0.01).

CONCLUSIONS

We conclude that the doubly fusogenic Synco-2D is an effective therapeutic agent for human metastatic prostate cancer.

Effect of murine liver cell proliferation on herpes viral behavior: implications for oncolytic viral therapy

Replication-competent herpes simplex oncolytic viruses are promising anticancer agents that partly target increased DNA synthesis in tumor cells. Investigators have proposed that these DNA viruses may be combined with liver resection to enhance killing of liver malignancies. Whether or not the cellular alterations associated with hepatic regeneration affect the efficacy and toxicity of these promising anticancer agents is unknown. This study examined the behavior of two oncolytic viruses, NV1020 and G207, during liver regeneration. When delivered during the peak of liver regeneration, replication and appearance of both G207 and NV1020 in hepatic tissue are enhanced as demonstrated by histochemical staining for the marker gene lac Z, immunohistochemical staining, and quantitative polymerase chain reaction. This increased appearance of virus in liver tissue correlates with increases in cellular ribonucleotide reductase activity and DNA synthesis and is also associated with increased viral binding. However, increased viral presence is transient, and viral detection declines to baseline within 7 days. When these viruses were delivered to animals even as early as 7 days after hepatectomy, there proved to be no measurable viral replication in any organ and no increased morbidity or mortality. In conclusion, the early stages of hepatic regeneration after resection provide an environment suitable for viral replication. Administration of replication-competent herpes simplex virus during the peak of hepatocyte regeneration (24-48 hours) permits viral productivity in tissue that otherwise does not support viral growth. The increase in hepatotoxicity after hepatectomy is short-lived and can be predicted by peak hepatocyte DNA synthesis.

Up-regulation of GADD34 mediates the synergistic anticancer activity of mitomycin C and a gamma134.5 deleted oncolytic herpes virus (G207)

Oncolytic viruses used for gene therapy have been genetically modified to selectively target tumor cells while sparing normal host tissue. The multimutant virus G207 has been attenuated by inactivation of viral ribonucleotide reductase and by deletion of both viral gamma134.5 genes. Deletion of gamma134.5 greatly decreases the neurovirulence of this mutant virus but also reduces its antitumor efficacy. The mammalian homologue to the gamma134.5 gene product is the GADD34 protein. This protein can functionally substitute for the gamma134.5 gene and is also up-regulated during DNA damage. We postulated that combining use of the chemotherapy agent mitomycin C (MMC) with G207 will selectively up-regulate GADD34 in tumor that may complement the gamma134.5 gene deletion and augment viral antitumor efficacy. This hypothesis was tested in human gastric cells in vitro and in vivo. Using both the isobologram method and combination-index method of Chou-Talalay, significant synergism was demonstrated between MMC and G207. As a result of such synergism, a dose-reduction for each agent can be accomplished over a wide range of drug-effect levels without sacrificing tumor cell kill. Northern blot analysis confirmed that expression of GADD34 mRNA was increased by MMC treatment. SiRNA directed at GADD34 decreased MMC-associated enhancement of viral proliferation and resulted in decreased viral synergy with MMC. These data indicate that induction of GADD34 selectively restores the virulent phenotype of the deleted gene in G207 and thus provides a cellular basis for the combined use of DNA-damaging agents and gamma134.5 HSV mutants in the treatment of cancer.

Effective Intravenous Therapy of Murine Pulmonary Metastases with an Oncolytic Herpes Virus Expressing Interleukin 12

PURPOSE

There currently is no therapy that enhances the survival of patients with distantly metastatic squamous cell carcinoma (SCC). Engineered herpes oncolytic viruses are effective therapeutic agents when delivered directly to tumors in animal models, but their efficacy in treating disseminated disease is poorly defined.

EXPERIMENTAL DESIGN

We treated disseminated pulmonary SCC in mice with an interleukin (IL)-12-expressing oncolytic herpes virus (NV1042) or with the parent oncolytic virus (NV1023, IL-12 deficient) by i.v. tail vein administration.

RESULTS

Lung IL-12 was 16.1 pg/mg and IFN-gamma was 4.3 pg/mg at day 1 after a single dose of NV1042 (5 x 10(7) plaque-forming units); levels of both were undetectable for NV1023. 5-Bromo-4-chloro-3-indolyl-beta-D-galactopyranoside histochemistry demonstrated viral infection of disseminated pulmonary tumor nodules by both vectors at day 1, with sparing of adjacent alveolar cells. NV1042-treated lungs showed no surface nodules at day 12, in contrast to NV1023-treated (92 +/- 27 surface nodules) and PBS-treated (225 +/- 9 surface nodules) lungs. Significantly enhanced survival was observed in NV1042-treated animals compared with NV1023- and PBS-treated animals (log rank < 0.05). In animals with a low tumor burden, 100% of NV1042-treated, 70% of NV1023-treated, and none of the control animals achieved long-term survival. NV1042 efficacy was similar to NV1023 efficacy in animals depleted of CD4/CD8 T lymphocytes, showing that IL-12 expression enhances oncolytic activity through immune effects. Histology showed no cytopathic effects in non-tumor-bearing lung, brain, spleen, liver, and pancreas after completion of viral therapy. No animals demonstrated any visible side effects attributable to viral therapy.

CONCLUSIONS

The i.v. delivery of an oncolytic herpes virus may achieve effective infection, oncolysis, and transgene expression at distant tumor sites. This approach to systemic therapy combining oncolysis with IL-12 immune stimulation led to significantly improved survival in animals with disseminated SCC.

Oncolytic herpes viruses as a potential mechanism for cancer therapy

Oncolytic viruses have been considered as a potential form of cancer treatment throughout the last century because of their ability to lyse and destroy tumor cells both in tissue culture and in animal models of cancer. However, it is only during the past decade that new molecular technologies have become available and understanding of genetic and molecular components of these viruses has increased to the point that they can be manipulated and made safe for use in treatment in humans. Thus there has been a revival of the concepts of conditionally replication-competent viruses and suicide gene therapy to supplement currently existing cancer therapies. While a wide variety of viruses have been closely studied for this purpose, herpes simplex virus type-1 (HSV-1) has received particularly close attention. The inherent cytotoxicity of this virus, if harnessed and made to be selective in the context of a tumor microenvironment, makes this an ideal candidate for further development. Furthermore, its large genome size, ability to infect cells with a high degree of efficiency, and the presence of an inherent viral-specific thymidine kinase gene add to its potential capabilities. This review explores work performed in this field and its potential for application in the treatment of cancers in humans.

Treatment of aggressive thyroid cancer with an oncolytic herpes virus

Although many thyroid cancers carry a favorable prognosis, there is a subgroup of patients with more aggressive histologies. Current therapies offer no significant survival benefit to patients with anaplastic thyroid carcinomas, which are considered fatal. Oncolytic herpes simplex viruses (HSVs) have potent antitumor effects against a variety of human malignancies. We assessed the activity of a replication-competent, attenuated, oncolytic HSV (NV1023) against 7 different thyroid cancers, including one papillary (NPA-187), one follicular (WRO82-1), one medullary (DRO81-1) and 4 anaplastic (DRO90-1, ARO, KAT-4C and KAT-18) cell lines. Only the follicular WRO82-1 line was resistant to NV1023 infection and cell lysis at a concentration of 5 viral pfu per cell (MOI 5). All other cell lines at MOI 5 demonstrated >95% infection in vitro at day 2 by X-gal staining and >88% cell death at day 4 by cytotoxicity assays. Even at MOI 0.1, 4 of these lines displayed complete cell death by day 7. Viral proliferation assays revealed that all of the nonfollicular cell lines supported logarithmic viral replication. Flank tumors of NPA-187, DRO81-1, DRO90-1 and ARO in athymic nude mice were treated with NV1023 (2 x 10(7) pfu). All NPA-187 tumors completely regressed following a single dose. DRO81-1 tumors demonstrated partial response with a single dose and significant improvement with 3 serial doses. ARO and DRO90-1 tumors showed a significant response following either single injection (54 +/- 22 and 292 +/- 138 mm3, respectively) or 3 serial injections (33 +/- 14 and 241 +/- 68 mm3, respectively) compared to saline injections (472 +/- 193 and 1,257 +/- 204 mm3, respectively) at day 20. These data suggest that herpes oncolytic therapy may be effective for the treatment of aggressive thyroid carcinomas and merits further investigation.

Optical imaging: bacteria, viruses, and mammalian cells encoding light-emitting proteins reveal the locations of primary tumors and metastases in animals

Early detection of tumors and their metastases is crucial for the prognosis of cancer treatment. Traditionally, tumor detection is achieved by various methods, including magnetic resonance imaging and computerized tomography. With the recent cloning, cellular expression, and real-time imaging of light-emitting proteins, such as Renilla luciferase (Ruc), bacterial luciferase (Lux), firefly luciferase (Luc), green fluorescent protein (GFP), or Ruc-GFP fusion protein, significant efforts have been focused on using these marker proteins for tumor detection. It has also been demonstrated that certain bacteria, viruses, and mammalian cells (BVMC), when administered systemically, are able to gain entry and replicate selectively in tumors. In addition, many tissue/tumor specific promoters have been cloned which allow transgene expression specifically in tumor tissues. Therefore, when light-emitting protein encoded BVMC are injected systemically into rodents, tumor-specific marker gene expression is achieved and is detected in real time based on light emission. Consequently, the locations of primary tumors and previously unknown metastases in animals are revealed in vivo. In the future it will likely be feasible to use engineered light-emitting BVMC as probes for tumor detection and as gene-delivery vehicles in vivo for cancer therapy.

Lymphomas and Oncolytic Virus Therapy

There are several well-documented cases in medical literature of the remission of leukemias and malignant lymphomas following natural human viral infections. In the hope of being able to reproduce these spontaneous tumor regressions, investigators have studied various viruses with distinct oncolytic properties. The first attempts to treat patients with oncolytic viruses took place > 80 years ago; however, it achieved little success. With modern technologies and current knowledge of viruses and cancer, there is an expectation for the discovery of efficient oncolytic viral therapies. This article will review the current knowledge of oncolytic viruses in relation to the treatment of lymphoma.

Expression of a fusogenic membrane glycoprotein by an oncolytic herpes simplex virus potentiates the viral antitumor effect

Oncolytic viruses have shown considerable promise in the treatment of solid tumors, but their potency must be improved if their full clinical potential is to be realized. We inserted the gene encoding a truncated form of the gibbon ape leukemia virus envelope fusogenic membrane glycoprotein (GALV.fus) into an oncolytic herpes simplex virus, using an enforced ligation procedure. Subsequent in vitro and in vivo studies showed that expression of GALV.fus in the context of an oncolytic virus significantly enhances the antitumor effect of the virus. Furthermore, by controlling GALV.fus expression through a strict late viral promoter, whose activity depends on the initiation of viral DNA replication, we were able to express this glycoprotein in tumor cells but not in normal nondividing cells. It will be of interest to confirm whether functional expression of a strong fusogenic gene by an oncolytic herpes simplex virus enhances viral antitumor activity without increasing its toxicity.

Immunotherapy and prostate cancer

Prostate cancer is the second leading cause of cancer death in the US, largely because of the limitations of our current therapeutic options, especially once the cancer has metastasized. Investigators have long sought new therapeutic modalities such as angiogenesis inhibitors, vaccines, and gene therapy, among others. It appears that a combination approach will be required to cure the majority of malignancies. Immunotherapy for prostate cancer appears feasible and a likely therapeutic modality in the armamentarium. Unfortunately, further research in basic immunology and the interaction of the immune system with other forms of therapy is needed. Many obstacles exist in immunotherapy, including vector design, tumouricidal specificity, and tumor evasion, which will have to be overcome in order to realize the maximum therapeutic benefit from this treatment modality.

Taking Gene Therapy into the Clinic

Gene therapy represents a promising novel treatment strategy for colorectal cancer. Preclinical data has been encouraging and several clinical trials are underway. Many phase 1 trials have proven the safety of the reagents but have yet to demonstrate significant therapeutic benefit. Ongoing efforts are being made to improve the efficiency of gene delivery and accuracy of gene targeting with the aim of enhancing antitumor potency. It is envisaged that gene therapy will be used in combination with other therapies including surgery, chemotherapy, and radiotherapy to facilitate the improvements in cancer treatments in the future.

Emerging cancer-targeted therapies

There is reason to believe that the unfolding revolution in molecular biology and translational research will allow selective targeting of tumor cells, and radically change the way general practitioners and pediatric oncologists treat and follow children with cancer. This article highlights some of the most promising approaches being tested in the field. By learning about the underlying biology, the remaining hurdles, the projected timeline, and the possible impact of new therapies on the practice of pediatric oncology, health care professionals and patients should be better prepared for the future of pediatric oncology.

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.

Comparison of safety, delivery, and efficacy of two oncolytic herpes viruses (G207 and NV1020) for peritoneal cancer

G207 and NV1020 are two replication-competent, multimutant oncolytic herpes simplex viruses evaluated in the current studies for their anticancer effects in the treatment of gastric cancer. Deletion of both gamma(1)34.5 genes and inactivation of ICP6 (ribonucleotide reductase) allows G207 to selectively replicate within tumor cells. NV1020 is another attenuated recombinant herpes virus with deletions of the HSV joint region, with deletion of only one copy of the gamma(1)34.5 gene, and with the ICP6 gene intact. In vitro, both G207 and NV1020 effectively infected, replicated, and killed human gastric cancer cells, with NV1020 being more effective at lower concentrations of virus. In a murine xenograft model of peritoneally disseminated gastric cancer, both NV1020 and G207 reduced tumor burden when given intraperitoneally (i.p.) at higher doses. When viral doses were lowered or when advanced tumor was treated, i.p. NV1020 was superior to i.p. G207. In vitro viral replication and cytotoxicity predicted the in vivo antitumor response. Intravenous delivery of either G207 or NV1020 failed to reduce tumor burden, demonstrating the importance of regional therapy as treatment for compartmentalized malignancy. Both agents were safe for use in animals, and immunohistochemistry performed on mouse tissue revealed selective viral targeting of tumor. Oncolytic therapy using genetically engineered HSVs represents a promising strategy for peritoneal malignancies.

Oncolytic viral gene therapy for prostate cancer using two attenuated, replication-competent, genetically engineered herpes simplex viruses

BACKGROUND

Attenuated, replication-competent herpes simplex virus mutants offer an exciting new modality in cancer therapy through their ability to selectively replicate within and kill malignant cells with minimal harm to normal tissues.

METHODS

This study investigates the efficacy of two such viruses, G207 and NV1020, in human prostatic carcinoma. In vitro studies were performed on four human prostatic carcinoma cell lines, and in vivo single/multiple dose studies were undertaken on mice by using two human cell types. Tumor volume, histopathology at necropsy, and serum prostate specific antigen (PSA) were used as measures of antiproliferative effect in the in vivo experiments.

RESULTS

Both viruses were effective in producing cytolytic effects in vitro at various multiplicities of infection in all cell lines tested. Both viruses demonstrated antitumor effects in vivo with a statistically significant decrease in serum PSA and inhibition of growth of both PC-3 and C4-2 subcutaneous xenografts. Tumor-free animals at necropsy were observed in the treated groups but not in control animals.

CONCLUSION

These results display impressive activity against human prostate cancer and offer promise for the use of this modality in the future.

Differential susceptibility of pediatric sarcoma cells to oncolysis by conditionally replication-competent herpes simplex viruses

PURPOSE

Attenuated viruses derived from herpes simplex virus (HSV) type 1 that kill tumor cells (oncolysis) are currently in clinical trials for selected cancers, primarily carcinomas and gliomas. The authors sought to determine if pediatric sarcoma cells are also sensitive to HSV-mediated oncolysis.

MATERIALS AND METHODS

The authors tested a panel of ten cell lines derived from rhabdomyosarcoma, osteosarcoma, Ewing sarcoma, and a secondary malignant fibrous histiocytoma for survival after exposure to attenuated HSV vectors. The viruses used included NV1020, haploid for the neurovirulence gene, and G207, deleted for both and ribonucleotide reductase but expressing the beta-galactosidase reporter gene. G207 transduction was determined by measuring beta-galactosidase expression.

RESULTS

Sarcoma cells differed in their sensitivity to viral oncolysis but were relatively consistent by histologic type. Rhabdomyosarcoma and malignant fibrous histiocytoma cells were most sensitive while osteosarcoma cells were intermediately sensitive to oncolysis by both HSV recombinants. Although Ewing sarcoma cells showed efficient viral entry and gene transfer, these cells were the least susceptible to oncolysis by HSV.

CONCLUSIONS

Conditionally replication-competent HSV-derived vectors may be useful for the treatment of rhabdomyosarcoma and osteosarcoma, but may not be as efficacious for treating Ewing sarcoma until the mechanism of resistance is defined and circumvented.

Replication-competent herpes virus NV1020 as direct treatment of pleural cancer in a rat model

OBJECTIVE

Innovative treatments are needed for metastatic disease involving the pleura. NV1020 is a novel, multimutated, replication-restricted herpes simplex virus under investigation for its ability to selectively kill tumors by means of direct cell lysis. This study examines NV1020 in a rat model of pleura-based lung cancer.

METHODS

Cytotoxicity and viral proliferation were evaluated in vitro by exposure of the human non-small cell lung cancer cell line A549 to virus. NV1020 was also tested in an in vivo pleura-based cancer model established by injecting 1 x 10(7) A549 cells into the thoracic cavity of nude rats. Intrapleural treatments (1 x 10(7) viral particles) were given 3 hours or 3 days after tumor injection to model treatment of microscopic or macroscopic disease (n = 8-9/group). Tumor burden was assessed at 5 weeks. NV1020 infection and dissemination within the thoracic cavity was determined by means of immunohistochemistry.

RESULTS

In vitro, at multiplicities of infection (viral particles per tumor cell) of 0.01, 0.1, and 1.0, cell killing of A549 by NV1020 was 66%, 90%, and 97%, respectively, at 7 days after infection. Viral burst occurred by day 2. Intrapleural treatment was effective for both the microscopic (P <.001) and macroscopic (P <.05) in vivo tumor models. Virus was detectable by means of immunohistochemistry in tumors but not in adjacent normal intrathoracic tissues.

CONCLUSIONS

NV1020 is not only highly cytotoxic to the human lung cancer line A549 in vitro but can be delivered in a clinically relevant fashion to safely and effectively treat pleura-based tumor in vivo in a rat model.

Oncolytic herpesvirus effectively treats murine squamous cell carcinoma and spreads by natural lymphatics to treat sites of lymphatic metastases

Oncolytic herpesviruses have significant antitumoral effects in animal models when delivered directly to established tumors. Lymphatic metastases are a common occurrence for many tumor types. This study investigates the potential of an attenuated, replication-competent, oncolytic herpes simplex virus (NV1023) both to treat a primary tumor by direct injection and to travel through the lymphatic system to treat metastatic tumor within the lymph nodes draining lymph from the site of primary cancer. Isosulfan blue dye was injected into murine auricles to determine normal lymphatic drainage patterns and demonstrated consistent blue staining of a group of ipsilateral cervical lymph nodes. Auricular injections of NV1023 resulted in viral transit to these lymph nodes as measured by 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside histochemistry and viral plaque assay. An oncolytic herpesvirus (NV1066) expressing green fluorescent protein also demonstrated viral transit from the auricle to the cervical lymph nodes on fluorescence microscopy. Using the SCC VII cell line, a novel murine model of auricular squamous cell carcinoma was developed with an approximately 20% incidence of cervical lymph node metastases. Delivery of NV1023 or NV1066 to the surgical beds after excision of auricular SCC VII tumors resulted in successful viral infection of metastatic SCC VII cells within the cervical lymph nodes. After a 7-week follow-up, significantly enhanced locoregional control (p < 0.05, Fisher exact test) and disease-free survival (p < 0.05, log rank test) were evident with NV1023 treatment. This study demonstrates that the delivery of an oncolytic herpesvirus to a primary tumor site after surgical excision may have a significant impact on reducing both primary site recurrence and regional nodal metastases.

Viral oncolysis

The concept of using replicating viruses as anticancer agents is not a new one, but the ability to genetically modify these viruses into increasingly potent and tumor-specific vectors is a recent phenomenon. As more is learned about the functions of viral gene products in controlling the mammalian cell cycle and in disabling cellular defense mechanisms, specific viral functions can be augmented or eliminated to enhance antineoplastic efficacy. In this article, general mechanisms by which oncolytic viruses achieve their antitumor efficacy and specificity are reviewed. The paradoxical roles of the immune response are addressed with respect to oncolytic viral therapy, as it, on one hand, impedes the spread of viral infection, and on the other, augments tumor cell destruction through the recruitment of T cells "vaccinated" against tumor antigens. The most commonly used oncolytic viruses are each reviewed in turn, including adenoviruses, herpes simplex viruses, vaccinia viruses, reoviruses, and Newcastle disease viruses. Special attention is focused on the unique biology of each of these viruses as well as the status of several of these mutants in clinical trials.

In situ cancer vaccination with a replication-conditional HSV for the treatment of liver metastasis of colon cancer

In this study, we investigated the therapeutic efficacy of a replication-conditional mutant HSV, G207, for the treatment of liver metastasis of colon carcinoma. Three liver metastasis models in syngeneic BALB/c mice were developed: (i) splenic injection, (ii) splenic and subcutaneous (s.c.) injection, and (iii) orthotopic implantation of CT26 colon carcinoma. In the splenic injection model, G207 was injected into the established splenic tumor on day 7. In the splenic and s.c. injection model, G207 were injected into the established s.c. tumor on days 5 and 8. In the orthotopic implantation model, a piece of CT26 tumor tissue was transplanted onto the wall of the cecum and G207 was injected in the established cecum tumor on day 7. On day 21 or 28, animals were sacrificed and liver metastases were evaluated. In all three models in immunocompetent mice, liver metastases were significantly reduced by intratumoral inoculation with G207 compared to the control. In athymic mice, however, there was no significant therapeutic effect of intratumoral inoculation with G207 on liver metastases. Tumor-specific cytotoxic T-lymphocyte responses were induced in mice treated with G207 in the orthotopic implantation model. These results suggest that intratumoral inoculation of G207, as an in situ cancer vaccine, can be an effective approach against liver metastasis of colon cancer and the efficacy involves tumor-specific T-cell responses.

Prostate cancer gene therapy and the role of radiation

Even though prostate cancer is detected earlier than in the pre-PSA era, prostate cancer is the second leading cause of cancer mortality in the American male. Prostate cancer therapy is not ideal, especially for high-risk localized and metastatic cancer; therefore, investigators have sought new therapeutic modalities such as angiogenesis inhibitors, inhibitors of the cell signaling pathway, vaccines, and gene therapy. Gene therapy has emerged as potential therapy for both localized and systemic prostate cancer. Gene therapy has been shown to work supra-additively with radiation in controlling prostate cancer in vivo. With further technological advances in radiation therapy, gene therapy, and the understanding of prostate cancer biology, gene therapy will potentially have an important role in prostate cancer therapy.

The use of a genetically engineered herpes simplex virus (R7020) with ionizing radiation for experimental hepatoma

The herpes simplex virus (HSV) recombinant virus R7020 is an attenuated virus designed as a candidate for immunization against both HSV-1 and HSV-2 infections. It was extensively tested in an experimental animal system and in a healthy human adult population without significant untoward effects. We report on the use of R7020 with ionizing radiation as an oncolytic agent for hepatomas. Two hepatoma cell lines were studied, Hep3B and Huh7. R7020 replicated to higher titers in Hep3B cells than in Huh7 cells. Tissue culture studies correlated with hepatoma xenograft responses to R7020. R7020 was more effective in mediating Hep3B tumor xenograft regression compared with Huh7. Ionizing radiation combined with R7020 also showed differential results in antitumor efficacy between the two cell lines in tumor xenografts. Ionizing radiation enhanced the replication of R7020 in Hep3B xenografts. Moreover, the combination of ionizing radiation and virus caused a greater regression of xenograft volume than either R7020 or radiation alone. Ionizing radiation had no effect on the replication of R7020 virus in Huh7 xenografts. These results indicate that a regimen involving infection with an appropriate herpesvirus such as R7020 in combination with ionizing radiation can be highly effective in eradicating certain tumor xenografts.

Gene therapy for colorectal cancer

Gene therapy has been developed as a potential novel treatment modality for colorectal cancer. The preclinical data have been promising and several clinical trials are under way for colorectal cancer. Data from many phase 1 trials have proven the safety of the reagents, but have not yet demonstrated significant therapeutic benefit. In order to refine this approach, continuing efforts should be made to improve the antitumour potency, efficiency of gene delivery, and accuracy of gene targeting. It is likely that gene therapy will be integrated into pre-existing therapies including surgery, chemotherapy and radiotherapy to establish its niche in tomorrow's medicine.

Delivery of herpes simplex virus vectors through liposome formulation

Viral vectors have been widely used as gene delivery vehicles for both experimental and clinical investigations. Although these vectors are capable of achieving high gene transduction efficiency in vitro, one of the major limitations facing the therapeutic viral vectors is that the preexisting host anti-vector immunity can substantially reduce their transduction efficiency in vivo. This is especially of concern when the therapeutic remedy requires repeated systemic administration. Here we report the delivery of herpes simplex virus (HSV) derived vectors through liposome formulation. In these studies, we have prepared HSV vectors in three different forms for liposome formulation: purified viral DNA (obtained from a bacterial artificial chromosome containing an infectious HSV genome), HSV capsids, and intact viral particles. All three forms of HSV were readily transfected into cultured cells and infectious virus was efficiently generated. Furthermore, introduction of HSV vectors as DNA/liposome complexes improved in vivo transduction efficiency, by effectively evading the host anti-HSV immunity during systemic administration. We conclude that viral vectors such as HSV can be systemically delivered through liposome formulation for safe and repeated administration for gene transduction or oncolytic purposes.

Yaba-like disease virus: an alternative replicating poxvirus vector for cancer gene therapy

Vaccinia virus is being investigated as a replicating vector for tumor-directed gene therapy. However, the majority of cancer patients have preformed immunologic reactivity against vaccinia virus, as a result of smallpox vaccination, which may limit its use as a vector. The Yaba-like disease (YLD) virus was investigated here as an alternative, replicating poxvirus for cancer gene therapy. We have demonstrated that the YLD virus does not cross-react with vaccinia virus antibodies, and it replicates efficiently in human tumor cells. YLD virus can be expanded and purified to high titer in CV-1 cells under conditions utilized for vaccinia virus. The YLD virus RNA polymerase was able to express genes regulated by a synthetic promoter designed for use in orthopoxviruses. We sequenced the YLD virus TK gene and created a shuttle plasmid, which allowed the recombination of the green fluorescent protein (GFP) gene into the YLD virus. In a murine model of ovarian cancer, up to 38% of cells in the tumor expressed the GFP transgene 12 days after intraperitoneal virus delivery. YLD virus has favorable characteristics as a vector for cancer gene therapy, and this potential should be explored further.

Gene therapy for prostate cancer: current status and future prospects

PURPOSE

Locally advanced, relapsed and metastatic prostate cancer has a dismal prognosis with conventional therapies offering no more than palliation. In recent years advances achieved in understanding the molecular biology of cancer have afforded clinicians and scientists the opportunity to develop a range of novel genetic therapies for this disease.

MATERIALS AND METHODS

We performed a detailed review of published reports of gene therapy for prostate cancer. Particular emphasis was placed on recent developments in the arena of nonviral (plasmid DNA, DNA coated gold particles, liposomes and polymer DNA complexes) and viral (adenovirus, retrovirus, adeno-associated virus, herpes virus and pox virus) vectors. Therapeutic strategies were categorized as corrective, cytoreductive and immunomodulatory gene therapy for the purpose of data analysis and comparison.

RESULTS

Locoregional administration of nonviral and viral vectors can yield impressive local gene expression and therapeutic effects but to our knowledge no efficient systemically delivered vector is available to date. Corrective gene therapy to restore normal patterns of tumor suppressor gene (p53, Rb, p21 and p16) expression or negate the effect of mutated tumor promoting oncogenes (ras, myc, erbB2 and bcl-2) have efficacy in animal models but this approach suffers from the fact that each cancer cell must be targeted. A wide variety of cytoreductive strategies are under development, including suicide, anti-angiogenic, radioisotopic and pro-apoptotic gene therapies. Each approach has strengths and weaknesses, and may best be suited for use in combination. Immunomodulatory gene therapy seeks to generate an effective local immune response that translates to systemic antitumor activity. Currently most studies involve immunostimulatory cytokine genes, such as granulocyte-macrophage colony-stimulating factor, or interleukin-2 or 12.

CONCLUSIONS

Various therapeutic genes have proved activity against prostate cancer in vitro and in vivo. However, the chief challenge facing clinical gene therapy strategies is the lack of efficient gene delivery by local and systemic routes. For the foreseeable future vector development may remain a major focus of ongoing research. Despite this caveat it is anticipated that gene therapy approaches may significantly contribute to the management of prostate cancer in the future.

Ionizing radiation does not alter the antitumor activity of herpes simplex virus vector G207 in subcutaneous tumor models of human and murine prostate cancer

Viral gene therapy against malignant tumors holds great promise for tumors that are susceptible to the oncolytic activity of viruses. One advantage of oncolytic viral therapy is that it can potentially be combined with other therapies, such as radiotherapy, to obtain an enhanced tumor response. In the case of prostate cancer, herpes simplex virus-mediated therapies have been shown to be highly effective in animal models; however, studies of the efficacy of combined viral and radiation therapy have not yet been reported. In this study, we have combined G207, a multimutated HSV type 1 vector, with external beam radiation therapy of prostate tumors grown subcutaneously in mice. We examined both the human LNCaP tumor in athymic mice and the mouse transgenic TRAMP tumor in either athymic mice or its syngeneic host, C57BL/6 mice. Virus was delivered either intravenously, in the case of LNCaP, or intratumorally, in the case of TRAMP. We found that individually, either G207 or radiation was effective in delaying tumor growth in these models. However, delivering the treatments simultaneously did not produce an enhanced effect.

Oncolytic viruses as therapeutic agents

The concept of using viruses as oncolytic agents has a long history. However, relatively new developments are the use of these viruses as gene delivery vehicles and the restriction of viral replication and lysis to tumour cells. The latter is attempted by the use of tumour-specific promoters, which transcriptionally target viral genes involved in replication, or by deletion of viral functions dispensable for replication in tumour cells but essential for productive infection of normal cells. In addition, retargeting of the viral tropism towards tumours by capsid modifications has been examined. Although much progress has been made in developing oncolytic vectors for clinical use, there is still a long way to go to determine which combinations of virus, gene therapy, surgery, radiation, and/or chemotherapy will provide improved therapy for the control and eradication of a variety of human cancers. First controlled clinical trials with an oncolytic adenovirus in combination with chemotherapy have shown encouraging antineoplastic activity. For future vector developments it will be crucial to achieve maximum vector distribution and transgene expression within tumours, to trigger a specific systemic immune effector response against treated and untreated lesions, and to modulate the immune system to avoid immune-mediated inactivation or destruction of the virus. In the context of replication-competent vectors, suicide genes might be used as fail-safe mechanism in the case of a runaway infection.

Prostate cancer gene therapy

Cancer-specific gene therapy is still in its infancy. Although the first gene therapy trials were initiated in the late 1980s, it was only more recently that the first successful treatment of a genetic disease was reported.3 The current problems with low efficiency of gene transfer coupled with the immunologic difficulties with certain vectors indicate that more effort needs to be directed at the basic science of gene transfer. Ultimately, successful cancer-specific gene therapy will require combinations of the lessons learned from the ex vivo and in vivo paradigms. The next generation of gene therapy trials likely will focus on combination therapy with conventional chemotherapeutic agents, differentiating agents, or radiation therapy. The obstacles to the development of gene-based human therapeutics (i.e., molecular medicine) are formidable, but the benefits are so great that eventually the technical issues of gene transfer methodology will be worked out, and ultimately this will become the standard of care, not only for inborn errors of metabolism, but also for cancer.

A uniquely stable replication-competent retrovirus vector achieves efficient gene delivery in vitro and in solid tumors

A major obstacle in cancer gene therapy is the limited efficiency of in vivo gene transfer by replication-defective retrovirus vectors in current use. One strategy for circumventing this difficulty would be to use vectors capable of replication within tumor tissues. We have developed a replication-competent retrovirus (RCR) vector derived from murine leukemia virus (MuLV). This vector utilizes a unique design strategy in which an internal ribosome entry site-transgene cassette is positioned between the env gene and the 3' long terminal repeat (LTR). The ability of this vector to replicate and transmit a transgene was examined in culture and in a solid tumor model in vivo. The RCR vector exhibited replication kinetics similar to those of wildtype MuLV and mediated efficient delivery of the transgene throughout an entire population of cells in culture after an initial inoculation with 1 plaque-forming unit (PFU) of vector per 2000 cells. After injection of 6 x 10(3) PFU of vector into established subcutaneous tumors, highly efficient spread of the transgene was observed over a period of 7 weeks, in some cases resulting in spread of the transgene throughout the entire tumor. MuLV-based RCR vectors show significant advantages over standard replication-defective vectors in efficiency of gene delivery both in culture and in vivo. This represents the first example of the use of an RCR vector in an adult mammalian host, and their first application to transduction of solid tumors.

Preclinical safety evaluation of G207, a replication-competent herpes simplex virus type 1, inoculated intraprostatically in mice and nonhuman primates

G207, a replication-competent herpes simplex virus type 1 (HSV-1) virus, has been previously shown to be effective against human prostate cancer xenografts in mice. This study assesses its safety in the prostate of two animal models known for their sensitivity to HSV-1. BALB/c mice were injected intraprostatically with either HSV-1 G207 or strain F and observed for 5 months. None of the G207-injected animals exhibited any clinical signs of disease or died. However, 50% of strain F-injected mice displayed sluggish, hunched behavior and died by day 13. Histopathologically, the G207-injected prostates were normal whereas strain F-injected prostates showed epithelial flattening, sloughing, and stromal edema. Four Aotus nancymae monkeys were also injected with G207 intraprostatically and observed short term (up to 21 days) and long term (56 days). Safety was assessed on the basis of clinical observations, viral biodistribution, virus shedding, and histopathology. None of the injected monkeys displayed evidence of clinical disease, shedding of infectious virus, or spread of the virus into other organs. Except for minor histological changes unrelated to the study, no significant abnormalities were observed. These results demonstrate that G207 can be safely inoculated into the prostate and should be considered for human trials for the treatment of prostate cancer.

In situ gene therapy for prostate cancer: immunomodulatory approaches

The development of effective treatments for prostate cancer is thwarted by the natural history of the disease. The biological and clinical potential of most individual cancers is uncertain. In many cases the disease will not progress to clinical significance but experimental and clinical studies indicate that prostate cancer can and may metastasis early in the course of the disease from relatively small foci (i.e., not necessarily the largest or index cancer). Localised prostate cancer is potentially curable with localised therapies (radical prostatectomy or irradiation therapy). However, there are no curative therapies for metastatic prostate cancer. Gene therapy, especially those approaches with an immunomodulatory component, may provide additional therapeutic options with the potential to affect both localised and systemic disease. We have pioneered the development and application of in situ gene therapy protocols using adenoviral vectors to transduce specific genes that generate cytotoxic activity and/or a systemic antitumour immune response. In addition we have completed initial studies that demonstrate the therapeutic potential of adenoviral vector-mediated gene modified cell-based vaccines. Our review discusses preclinical studies focused on the development of immunostimulatory in situ gene therapy approaches that hopefully will provide novel and effective treatments for localised and metastatic prostate cancer.

Therapeutic efficacy of G207 in a novel peripheral nerve sheath tumor model

Nerve involvement poses a significant obstacle for the management of peripheral nervous system tumors, and nerve injury provides a frequent source of postoperative morbidity. The lack of suitable animal models for peripheral nerve tumors has impeded the development of alternative nerve-sparing therapies. To evaluate the effect of a multimutated replication-competent herpes simplex virus (G207) on the growth of peripheral nerve tumors and on nerve function, we developed a novel peripheral nerve sheath tumor model. Human neuroblastoma-derived cells injected into murine sciatic nerve consistently caused tumor development within the nerve sheath after 2 weeks followed by increasingly severe impairment of nerve function. Tumor treatment by a single intratumoral injection of G207 resulted in significant reduction of functional impairment, inhibition of tumor growth and prolonged survival. Direct injection of G207 viral particles into the healthy nerve sheath caused no obvious neurologic sequelae, whereas injections of wild-type virus resulted in uniform lethality. The results indicate that viral therapy might be considered as a safe alternative to surgical removal of tumors with peripheral nerve involvement.

Therapeutic efficacy of G207, a conditionally replicating herpes simplex virus type 1 mutant, for gallbladder carcinoma in immunocompetent hamsters

Gallbladder cancer is an extremely difficult disease to cure once metastases occur. In this paper, we explored the potential of G207, an oncolytic, replication-competent herpes simplex virus type 1 mutant, as a new therapeutic means for gallbladder cancer. Gallbladder carcinoma cell lines (four human and one hamster) showed nearly total cell killing within 72 h of G207 infection at a m.o.i. of 0.25 to 2.5 in vitro. The susceptibility to G207 cytopathic activity correlated with the infection efficiency demonstrated by lacZ expression. Intraneoplastic inoculation of G207 (1 x 10(7) pfu) in immunocompetent hamsters bearing established subcutaneous KIGB-5 tumors caused a significant inhibition of tumor growth and prolongation of survival. Repeated inoculations (three times with 4-day intervals) were significantly more efficacious than a single inoculation. In hamsters with bilateral subcutaneous KIGB-5 tumors, inoculation of one tumor alone with G207 caused regression or growth reduction of uninoculated tumors as well as inoculated tumors. In athymic mice, however, the anti-tumor effect was largely reduced in inoculated tumors and completely abolished in remote tumors, suggesting large contribution of T-cell-mediated immune responses to both local and systemic anti-tumor effect of G207. These results indicate that G207 may be useful as a new strategy for gallbladder cancer treatment.

Cytokine gene transfer enhances herpes oncolytic therapy in murine squamous cell carcinoma

Replication-competent, attenuated herpes simplex viruses (HSV) have been demonstrated to be effective oncolytic agents in a variety of malignant tumors. Cytokine gene transfer has also been used as immunomodulatory therapy for cancer. To test the utility of combining these two approaches, two oncolytic HSV vectors (NV1034 and NV1042) were designed to express the murine GM-CSF and murine IL-12 genes, respectively. These cytokine-carrying variants were compared with the analogous non-cytokine-carrying control virus (NV1023) in the treatment of murine SCC VII squamous cell carcinoma. All three viruses demonstrated similar infection efficiency, viral replication, and cytotoxicity in vitro. SCC VII cells infected by NV1034 and NV1042 effectively produced GM-CSF and IL-12, respectively. In an SCC VII subcutaneous flank tumor model in immunocompetent C3H/HeJ mice, intratumoral injection with each virus caused a significant reduction in tumor volume compared with saline injections. The NV1042-treated tumors showed a striking reduction in tumor volume compared with the NV1023- and NV1034-treated tumors. On subsequent rechallenge in the contralateral flank with SCC VII cells, 57% of animals treated with NV1042 failed to develop tumors, in comparison with 14% of animals treated with NV1023 or NV1034, and 0% of naive animals. The increased antitumor efficacy seen with NV1042 in comparison with NV1023 and NV1034 was abrogated by CD4(+) and CD8(+) lymphocyte depletion. NV1042 is a novel, attenuated, oncolytic herpesvirus that effectively expresses IL-12 and elicits a T lymphocyte-mediated antitumor immune response against murine squamous cell carcinoma. Such combined oncolytic and immunomodulatory strategies hold promise in the treatment of cancer.

Effects of preexisting immunity on the response to herpes simplex-based oncolytic viral therapy

Herpes simplex viruses (HSV) type 1 are the basis of a number of anticancer strategies that have proven efficacious in animal models. They are natural human pathogens and the majority of adults have anti-HSV immunity. The current study examined the effect of preexisting immunity on the response to herpes-based oncolytic viral treatment of hepatic metastatic cancer in a murine model designed to simulate a clinical approach likely to be utilized for nonneurological tumors. Specifically, the anticancer effects of NV1020 or G207, two multimutated HSV-1 oncolytic viruses, were tested in immunocompetent mice previously immunized with a wild-type herpes simplex type 1 virus. Mice were documented to have humoral as well as cell-mediated immunity to HSV-1. Tumor response to oncolytic therapy was not measurably abrogated by immunity to HSV at the doses tested. The influence of route of viral administration was also tested in models of regional hepatic arterial and intravenous therapy. Route of viral administration influenced efficacy, as virus delivered intravenously produced some detectable attenuation while hepatic arterial therapy remained unaffected. These results demonstrate that when given at appropriate doses and in reasonable proximity to tumor targets, HSV-based oncolytic therapy can still be expected to be effective treatment for patients with hepatic malignancies.

Oncolytic viral therapy for human prostate cancer by conditionally replicating herpes simplex virus 1 vector G207

Over the last few years, a conditionally replicating herpes simplex virus 1 (HSV-1) vector, G207 has been used for the treatment of several malignant tumors. In this article we evaluate the anti-tumoral effect of G207 against prostate cancer in vitro and in vivo. The susceptibility of the human prostate cancer cell lines, DU145 and PC3 to G207 at a multiplicity of infection (MOI) of 0.1 was examined. In addition, the growth characteristics of G207 were assessed. Athymic mice with s.c. tumors were inoculated in vivo intraneoplastically with 1 x 10(7) plaque-forming units (PFU) of G207. For the pathological analyses, s.c. tumors were stained with X-gal. DU145 and PC3 were efficiently destroyed by G207 within 7 days. The viral yields of G207 increased time-dependently. In vivo, the intraneoplastic inoculation of G207 induced a significant inhibition of the tumor growth. The mean tumor growth ratio was significantly inhibited in the G207-treated tumors (DU145, P < 0.0001; PC3, P < 0.001 versus controls). In a pathological study, many lacZ-positive cells were diffusely present in the G207-treated tumors. G207 showed a significant antitumoral effect against human prostate cancer cell lines, and thus may be considered a useful agent for the treatment of prostate cancer.

Viral shedding and biodistribution of G207, a multimutated, conditionally replicating herpes simplex virus type 1, after intracerebral inoculation in aotus

G207 is a multimutated, conditionally replicating herpes simplex virus type 1 (HSV-1) that is currently in clinical trial for patients with malignant glioma. G207 exhibits an efficient oncolytic activity in tumor cells, yet minimal toxicity in normal tissue when injected into the brains of HSV-susceptible mice or nonhuman primates. In this study, we evaluated the shedding and biodistribution of clinical-grade G207 after intracerebral inoculation (3 x 10(7) pfu) in four New World owl monkeys (Aotus nancymae). Using PCR analyses and viral cultures, neither infectious virus nor viral DNA was detected from tear, saliva, or vaginal secretion samples at any time point up to 1 month postinoculation. Analyses of tissues obtained at necropsy at 1 month from two of the four monkeys, plus one monkey inoculated with laboratory-grade G207 (10(9) pfu) 2 years earlier, showed the distribution of G207 DNA restricted to the brain, although infectious virus was not isolated. Histopathology revealed normal brain tissues including the sites of inoculation. A measurable increase of serum anti-HSV antibody titer was observed in all monkeys, as early as 21 days postinoculation. The results ascertain the safety of G207 in the brain and indicate that strict biohazard management may not be required for G207-treated patients.