Virotherapy with a type 2 herpes simplex virus-derived oncolytic virus induces potent antitumor immunity against neuroblastoma.

PURPOSE: We recently constructed an oncolytic virus from type 2 herpes simplex virus (HSV-2) that selectively targets and kills tumor cells with an activated Ras signaling pathway. Designated FusOn-H2, this virus has shown several discrete killing mechanisms. Here, we evaluated the antitumor immune responses after FusOn-H2-mediated virotherapy in a syngeneic murine neuroblastoma model. EXPERIMENTAL DESIGN: We directly injected FusOn-H2 into established tumors and then measured its antitumor effect and the accompanying tumor-specific immune responses. Several oncolytic HSVs constructed from HSV-1 were included in the same experiments for comparisons. RESULTS: Our data show that tumor destruction by FusOn-H2 in vivo induces potent antitumor immune responses in this syngeneic neuroblastoma model. The elicited cellular immunity not only eradicated neuroblastoma cells in vitro but also inhibited the growth of tumors at sites distant from the virus injection site. Moreover, adoptive transfer of splenocytes from mice receiving virotherapy to na?ve mice resulted in a measurable antitumor effect. CONCLUSION: We conclude that the ability of FusOn-H2 to induce tumor-specific cellular immunity expands the oncolytic repertoire of this virus and increases the likelihood that its use in patients would produce significant therapeutic benefits.     

An armed oncolytic herpes simplex virus expressing thrombospondin‐1 has an enhanced in vivo antitumor effect against human gastric cancer

Advanced gastric cancer is a common disease, but the conventional treatments are unsatisfactory because of the high recurrence rate. One of the promising new therapies is oncolytic virotherapy, using oncolytic herpes simplex viruses (HSVs). Thrombospondin‐1 (TSP‐1) suppresses tumor progression via multiple mechanisms including antiangiogenesis. Our approach to enhance the effects of oncolytic HSVs is to generate an armed oncolytic HSV that combines the direct viral oncolysis with TSP‐1‐mediated function for gastric cancer treatment. Using the bacterial artificial chromosome (BAC) system, a 3rd generation oncolytic HSV (T‐TSP‐1) expressing human TSP‐1 was constructed for human gastric cancer treatment. The enhanced efficacy of T‐TSP‐1 was determined in both human gastric cancer cell lines in vitro and subcutaneous tumor xenografts of human gastric cancer cells in vivo. In addition, we examined the apoptotic effect of T‐TSP‐1 in vitro, and the antiangiogenic effect of T‐TSP‐1 in vivo compared with a non‐armed 3rd generation oncolytic HSV, T‐01. No apparent apoptotic induction by T‐TSP‐1 was observed for human gastric cancer cell lines TMK‐1 cells but for MKN1 cells in vitro. Arming the viruses with TSP‐1 slightly inhibited their replication in some gastric cancer cell lines, but the viral cytotoxicity was not attenuated. In addition, T‐TSP‐1 exhibited enhanced therapeutic efficacy and inhibition of angiogenesis compared with T‐01 in vivo. In this study, we established a novel armed oncolytic HSV, T‐TSP‐1, which enhanced the antitumor efficacy by providing a combination of direct viral oncolysis with antiangiogenesis. Arming oncolytic HSVs may be a useful therapeutic strategy for gastric cancer therapy.     

Effective therapy of metastatic ovarian cancer with an oncolytic herpes simplex virus incorporating two membrane fusion mechanisms.

PURPOSE AND EXPERIMENTAL DESIGN: Replication-competent herpes simplex virus [HSV (oncolytic HSV)] holds considerable promise for treating malignant solid tumors, although the potency of the virus needs improvement if its full clinical potential is to be realized. Incorporation of membrane fusion capability into an oncolytic HSV, either by screening for a syncytial HSV mutant after random mutagenesis or by inserting a hyperfusogenic glycoprotein from gibbon ape leukemia virus into the viral genome, can significantly enhance the antitumor effects of the virus (X. Fu and X. Zhang, Cancer Res., 62: 2306-2312, 2002; X. Fu et al., Mol. Ther., in press, 2003). We reasoned that both fusogenic strategies, incorporated into a single oncolytic HSV, might significantly improve virotherapy for ovarian cancer. RESULTS: In vitro characterization of a doubly fusogenic oncolytic HSV (Synco-2D) showed that this virus produces a distinctive syncytial phenotype, leading to a significantly increased tumor cell killing ability, compared with that of a nonfusogenic virus. When injected directly into the abdominal cavity of mice bearing human ovarian cancer xenografts, Synco-2D eradicated all tumor masses in 75% of the animals, whereas no animals in the conventional oncolytic HSV-treated group were tumor free. CONCLUSIONS: This newly generated fusogenic oncolytic HSV is a promising candidate for clinical testing against advanced ovarian cancer.     

Effective treatment of pancreatic cancer xenografts with a conditionally replicating virus derived from type 2 herpes simplex virus.

PURPOSE: Pancreatic cancer is a devastating disease that is almost universally fatal because of the lack of effective treatments. We recently constructed a novel oncolytic virus (FusOn-H2) from the type 2 herpes simplex virus. Because the replication potential of FusOn-H2 depends on the activation of the Ras signaling pathway, we evaluated its antitumor effect against pancreatic cancer, which often harbors K-ras gene mutations. EXPERIMENTAL DESIGN: Human pancreatic cancer xenografts were established in nude mice either s.c. or orthotopically (n = 8/group). FusOn-H2 was injected either directly (s.c. tumors) or by the i.v. or i.p. route (orthotopic tumors). Tumor volume, weight, and survival time were recorded for each animal. Statistical analyses were done by Student's t test. RESULTS: A single intratumor injection of FusOn-H2 completely eradicated s.c. pancreatic cancers in all animals. Systemic injection of the oncolytic virus produced clear antitumor effects but did not abolish tumors in any animal. The most striking antitumor effect was seen when the virus was given i.p. Delivery of FusOn-H2 by this route completely eradicated established orthotopic tumors in 75% of the animals and completely prevented local metastases. CONCLUSIONS: FusOn-H2 has potent activity against human pancreatic cancer xenografts and may be a promising candidate for investigative virotherapy of this malignancy.     

Treatment of breast cancer stem cells with oncolytic herpes simplex virus

Cancer stem cells have recently been isolated from several different solid tumors. In breast cancer, the CD44(+)CD24(-/low) population is considered to comprise stem-like cells. The identification of cancer stem cells has provided new targets for the development of therapeutics. Oncolytic herpes simplex viruses (oHSVs) are an effective strategy for killing breast cancer cells and treating breast tumors in preclinical models. Here, we examined the efficacy of the oHSV G47Δ in killing breast cancer stem cells. Human breast cancer cell line SK-BR-3 and human primary breast cancer cells were cultured in suspension under conditions conducive to the growth of stem cells. They generated mammospheres, which had cancer stem cell properties. The proportion of CD44(+)CD24(-/low) cells in these mammospheres exceeded 95%, as determined by flow cytometry. The mammospheres were found to be highly tumorigenic when implanted subcutaneously in nude BALB/c mice. G47Δ contains the LacZ gene, and X-gal staining of infected cells in vitro and in vivo showed the replication and spread of the virus. G47Δ was found to be highly cytotoxic to the CD44(+)CD24(-/low) population in vitro, even when injected at low multiplicities of infection, and G47Δ treatment in vivo significantly inhibited tumor growth compared with mock treatment. This study demonstrates that oHSV is effective against breast cancer stem cells and could be a beneficial strategy for treating breast cancer patients.     

Minimally invasive localization of oncolytic herpes simplex viral therapy of metastatic pleural cancer

Herpes simplex virus-1 (HSV-1) oncolytic therapy and gene therapy are promising treatment modalities against cancer. NV1066, one such HSV-1 virus, carries a marker gene for enhanced green fluorescent protein (EGFP). The purpose of this study was to determine whether NV1066 is cytotoxic to lung cancer and whether EGFP is a detectable marker of viral infection in vitro and in vivo. We further investigated whether EGFP expression in infected cells can be used to localize the virus and to identify small metastatic tumor foci (<1 mm) in vivo by means of minimally invasive endoscopic systems equipped with fluorescent filters. In A549 human lung cancer cells, in vitro viral replication was determined by plaque assay, cell kill by LDH release assay, and EGFP expression by flow cytometry. In vivo, A549 cells were injected into the pleural cavity of athymic mice. Mice were treated with intrapleural injection of NV1066 or saline and examined for EGFP expression in tumor deposits using a stereomicroscope or a fluorescent thoracoscopic system. NV1066 replicated in, expressed EGFP in infected cells and killed tumor cells in vitro. In vivo, treatment with intrapleural NV1066 decreased pleural disease burden, as measured by chest wall nodule counts and organ weights. EGFP was easily visualized in tumor deposits, including microscopic foci, by fluorescent thoracoscopy. NV1066 has significant oncolytic activity against a human NSCLC cell line and is effective in limiting the progression of metastatic disease in an in vivo orthotopic model. By incorporating fluorescent filters into endoscopic systems, a minimally invasive means for diagnosing small metastatic pleural deposits and localization of viral therapy for thoracic malignancies may be developed using the EGFP marker gene inserted in oncolytic herpes simplex viruses.     

Oncolytic herpes simplex virus treatment of metastatic breast cancer

The high prevalence and poor prognosis of breast cancer provides a strong rationale for developing new treatment strategies and preventive and therapeutic agents. Oncolytic replication-competent herpes simplex virus (HSV) can infect tumor cells, replicating and killing the cells by direct cytopathic effect and then spreading within the tumor. Replication of oncolytic HSV leads to the destruction of the infected tumor cell and release of new virions, which are able to infect adjacent cells until potentially all tumor cells are destroyed. In this study, the cytotoxicity of a third-generation oncolytic HSV vector, designated G47Δ, was examined in human breast cancer cell lines, as well as in immortalized and normal breast cells. A pulmonary metastatic model of breast cancer established in Balb/c nude mice was used to evaluate the efficacy of G47Δ treatment. Systemic treatment by intravenous administration of G47Δ for metastatic lung tumors was initiated 14 days after injection of tumor cells. On Day 56, the mice were sacrificed and tumor nodules on the surface of the lung were counted. G47Δ was highly cytotoxic to breast cancer and immortalized breast cells in vitro at low multiplicities of infection (MOI), while normal breast cells remained viable 5 days after infection. In the pulmonary metastatic model, the average number of surface lung tumor nodules in the G47Δ-treated group was approximately 9?fold less than in the control-treated group. X-gal staining illustrated viral replication and spread in the tumor cells in vitro and in vivo. In conclusion, G47Δ effectively killed human breast cancer cells and immortalized breast cells but not normal breast cells. Systemic administration of G47Δ by tail vein injection was effective in inhibiting the growth of established breast cancer lung metastases.     

Anti-tumor effect of oncolytic herpes simplex virus G47delta on human nasopharyngeal carcinoma

Oncolytic herpes simplex virus (HSV) can replicate in and kill cancer cells without harming normal tissue. G47delta is a third-generation HSV vector. In this study, the therapeutic effects of G47delta on human nasopharyngeal carcinoma (NPC) were determined in vitro and in vivo. The human NPC cell lines CNE-2 and SUNE-1, primary normal nasopharyngeal epithelial cells (NPECs), and immortalized nasopharyngeal cells NP-69 and NPEC2/Bmi1 were infected with G47delta at different multiplicities of infection (MOIs). The survival of infected cells was observed daily. Two subcutaneous models of NPC were established with CNE-2 and SUNE-1 in Balb/c nude mice. G47delta or virus buffer as control was injected into the subcutaneous tumors. Tumor size was measured twice a week, and animals were euthanized when the diameter of their tumors exceeded 18 mm or when the animals appeared moribund. For the NPC cell lines CNE-2 and SUNE-1, more than 85% and 95% of cells were killed on day 5 after G47delta infection at MOI = 0.01 and MOI = 0.1, respectively. Similar results were observed for an immortalized cell line NPEC2/Bmi-1. A moderate effect of G47delta was also found on another immortalized cell line NP-69, of which only 27.7% and 75.9% of cells were killed at MOI = 0.01 and MOI = 0.1, respectively. On the contrary, there was almost no effect observed on NPECs. The in vivo experiments showed that tumors in mice in the G47delta-treated group regressed completely, and the mice exhibited much longer survival time than those in the control groups. Our results suggest that the potential therapeutic effects of G47delta would be applicable for treatment of NPC patients in the future.     

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.     

Potent systemic antitumor activity from an oncolytic herpes simplex virus of syncytial phenotype

Conditionally replicating (oncolytic) viruses, which selectively replicate in tumor cells but not in normal cells, show great promise as antitumor agents for cancer therapy. The principal antitumor activity of these viruses derives from their replication within tumor cells, which results in cell destruction and the production of progeny virions that can spread to adjacent tumor cells. However, one potential limitation of this approach is that viral gene deletions conferring tumor selectivity also result frequently in reduced potency of the virus in tumors. Therefore, strategies designed to enhance the potency of current oncolytic viruses will likely increase their chance of clinical success. Here we report the construction of an oncolytic herpes simplex virus (HSV) of which the infection also causes strong cell membrane fusion (syncytial formation). In vitro characterization on a variety of human tumor cells of different tissue origins showed that the plaques from this virus (Fu-10) are phenotypically unique and are significantly larger than those from the parental G207 virus, a well-characterized oncolytic HSV lacking fusogenic function. Furthermore, the syncytial formation caused by this virus depended on HSV replication, indicating that cell membrane fusion will only occur in dividing cells (such as tumor cells) where the virus can undergo a full infection cycle but not in normal cells where the viral replication is restricted. Systemic administration of Fu-10 into mice with established lung metastatic breast cancer resulted in a dramatic therapeutic effect. These studies demonstrate that incorporation of fusogenic function into an oncolytic virus can significantly increase the potency of viral oncolysis; this may lead to an enhanced clinical performance, especially in late-stage cancer patients.     

Systemic oncolytic herpes virus therapy of poorly immunogenic prostate cancer metastatic to lung.

PURPOSE: Our goal was to evaluate whether systemic administration of NV1042, an interleukin-12 (IL-12)-expressing oncolytic herpes simplex virus, and its noncytokine parental vector NV1023 are effective against preexisting metastatic prostate cancer in an immunocompetent mice model. EXPERIMENTAL DESIGN: Metastatic TRAMP-C2 lung tumors established in C57Bl/6 or nude mice were treated on day 21 with four i.v. administrations of NV1042 or NV1023 and sacrificed on day 42 to assess virus efficacy and the potential mechanism of efficacy. RESULTS: NV1042 or NV1023 treatment was similarly effective in eliminating extrapleural and hemorrhagic tumors present in mock-treated mice. However, NV1042 was further effective compared with NV1023 in controlling the growth of lung tumors (as determined by mean surface tumor nodule number, lung weights, and surface tumor burden) and in extending survival. NV1042-treated mice exhibited a transient increase of serum IL-12 1 day posttreatment, whereas IL-12 levels in tumor bearing lungs persisted a further 2 days at least. Only splenocytes from NV1042-treated mice secreted IFN-gamma in response to TRAMP-C2 stimulation and displayed natural killer activity. The IL-12-mediated enhancement observed with NV1042 in the syngeneic model was abrogated in athymic mice treated in a similar manner, thus indicating a role for T cells in the augmented efficacy of NV1042 virus. CONCLUSIONS: Systemic administration of the IL-12-expressing NV1042 virus is more effective than its noncytokine parent, NV1023, against preestablished metastatic lung tumors. Given the clinical safety profile of NV1020, the parental vector of NV1023, and NV1042's enhanced efficacy and ability to activate the host immune system, NV1042 merits clinical consideration for treating metastatic prostate cancers.     

Rapamycin enhances the activity of oncolytic herpes simplex virus against tumor cells that are resistant to virus replication

Oncolytic herpes simplex virus (HSV) is currently in phase III clinical trials for development as a novel therapeutic agent against a broad range of human tumors. Although results have been promising, clinical outcome is likely to be compromised by intrinsic and acquired resistance to HSV replication, leading us to test agents that may overcome this obstacle. We found that, despite showing no effect on HSV replication in tumor cells fully permissive to the virus growth, the mTOR inhibitor rapamycin markedly increased the yield and dissemination of oncolytic HSVs in semipermissive tumor cells. Similar results were obtained in tumor-bearing mice. Co-administration of rapamycin with an HSV-derived oncolytic virus either blocked or reversed the growth of tumor xenografts established from semipermissive human tumor cells, while use of either agent alone produced only transient inhibitory effect. Together, our results suggest that rapamycin could be used to potentiate the activity of oncolytic HSVs against difficult-to-treat human tumors or perhaps to prevent the emergence of resistant tumor cells during virotherapy.     

The potential application of a transcriptionally regulated oncolytic herpes simplex virus for human cancer therapy

Background:

Emerging studies have shown the potential benefit of arming oncolytic viruses with therapeutic genes. However, most of these therapeutic genes are placed under the regulation of ubiquitous viral promoters. Our goal is to generate a safer yet potent oncolytic herpes simplex virus type-1 (HSV-1) for cancer therapy.

Methods:

Using bacterial artificial chromosome (BAC) recombineering, a cell cycle-regulatable luciferase transgene cassette was replaced with the infected cell protein 6 (ICP6) coding region (encoded for UL39 or large subunit of ribonucleotide reductase) of the HSV-1 genome. These recombinant viruses, YE-PC8, were further tested for its proliferation-dependent luciferase gene expression.

Results:

The ability of YE-PC8 to confer proliferation-dependent transgene expression was demonstrated by injecting similar amount of viruses into the tumour-bearing region of the brain and the contralateral normal brain parenchyma of the same mouse. The results showed enhanced levels of luciferase activities in the tumour region but not in the normal brain parenchyma. Similar findings were observed in YE-PC8-infected short-term human brain patient-derived glioma cells compared with normal human astrocytes. intratumoural injection of YE-PC8 viruses resulted in 77% and 80% of tumour regression in human glioma and human hepatocellular carcinoma xenografts, respectively.

Conclusion:

YE-PC8 viruses confer tumour selectivity in proliferating cells and may be developed further as a feasible approach to treat human cancers.     

Multiple strategies to improve the therapeutic efficacy of oncolytic herpes simplex virus in the treatment of glioblastoma

Oncolytic viruses have attracted widespread attention as biological anticancer agents that can selectively kill tumor cells without affecting normal cells. Although progress has been made in therapeutic strategies, the prognosis of patients with glioblastoma (GBM) remains poor and no ideal treatment approach has been developed. Recently, oncolytic herpes simplex virus (oHSV) has been considered a promising novel treatment approach for GBM. However, the therapeutic efficacy of oHSV in GBM, with its intricate pathophysiology, remains unsatisfactory due to several obstacles, such as limited replication and attenuated potency of oHSV owing to deletions or mutations in virulence genes, and ineffective delivery of the therapeutic virus. Multiple strategies have attempted to identify the optimal strategy for the successful clinical application of oHSV. Several preclinical trials have demonstrated that engineering novel oHSVs, developing combination therapies and improving methods for delivering oHSV to tumor cells seem to hold promise for improving the efficacy of this virotherapy.     

Potent oncolytic activity of multimutated herpes simplex virus G207 in combination with vincristine against human rhabdomyosarcoma

Replication restricted oncolytic viruses such as multimutated herpes simplex virus type 1 (HSV-1) G207 represent a novel and attractive approach for cancer therapy, including pediatric solid tumors. Rhabdomyosarcoma is the most common soft-tissue sarcoma of childhood and is often diagnosed already as an advanced disseminated disease. Despite aggressive therapeutic approaches, the prognosis for patients with metastatic rhabdomyosarcoma remains grim. Therefore, there is a need for novel effective drugs with superior safety and efficacy profile. In this study, we showed marked in vitro activity of HSV-1 G207 against embryonal and alveolar rhabdomyosarcoma cells. All human embryonal (KF-RMS-1, RD, and CCA) and alveolar RMS (KFR, Rh28, Rh30, and Rh41) cell lines were highly sensitive to cytotoxic and replicative effects of G207 even at a multiplicity of infection of 0.01, except embryonal Rh1 rhabdomyosarcoma cells, which were efficiently killed only upon multiplicity of infection of 1.0. i.v. G207 treatment of xenotransplanted KFR and KF-RMS-1 tumors in mice led to significant tumor growth inhibition of both tumor entities, whereas intraneoplastic G207 treatment additionally resulted in complete tumor disappearance in 25% of animals. No difference has been found between alveolar and embryonal types of rhabdomyosarcoma. Combination treatment of both cell lines with G207 and vincristine led to strongly enhanced in vitro cytotoxicity without affecting infection efficiency and replication of G207 in KFR as well as in KF-RMS-1 cells. In vivo combination treatment using i.v. G207 and vincristine resulted in complete regression of alveolar rhabdomyosarcoma in five of eight animals and significant growth inhibition of embryonal rhabdomyosarcoma. Taking into consideration the proven safety of G207 in humans, we suggest that G207 alone and in combination with vincristine should be additionally evaluated as a potential agent against human rhabdomyosarcoma.     

Angiogenesis inhibition using an oncolytic herpes simplex virus expressing endostatin in a murine lung cancer model

Herpes-mediated viral oncolysis alone is not sufficient to completely eradicate tumors. In this study we used a replication conditional, endostatin-expressing herpes simplex virus-1 mutant (HSV-Endo) in a murine lung cancer model. We hypothesized that the anti-angiogenic action of endostatin would improve upon the oncolytic effect of HSV-1. HSV-Endo was evaluated in a pulmonary metastases and orthotopic flank model, where there was significantly less tumor burden and reduced microvessel density compared to a control virus. Endostatin expression appears to improve the anti-tumor effect of HSV-1 in a lung cancer model.     

In vitro transformation of hamster cells by herpes simplex virus type 2 from human prostatic cancer cells.

A cell-associated herpes simplex virus type 2 found in a human prostatic carcinoma induced in vitro transformation of hamster embryo cells. The transformed cells (YW-74) have been shown to be hamster cells by karyotype analysis. Their epithelial morphology and growth pattern, which are different from the parental cell, have remained stable through cell passages. The presence of herpesvirus antigens in the transformed cells was determined by specific immunofluorescence and colony inhibition tests. Immunofluorescence staining with specific anti-herpes simplex virus type 2 serum showed an intense and distinctive nuclear and perinuclear fluorescence in about 95% of the transformed cells. In addition, exposure of these transformed cells to herpes simplex virus type 2-sensitized lymphocytes resulted in inhibition of growth and colony formation, while no effect was seen with nonsensitized lymphocytes. Both observations are consistent with the involvement of herpesvirus type 2 in the transformation event. This virus, which does not produce a lytic infection and is not found either in extracellular spaces or supernatant fluid of the transformed cell cultures, is unique in the fact that it is cell associated, noncytopathogenic, and capable of transforming cells in vitro, and its antigens are clearly demonstrated in the transformed cells.