Oncolytic Herpes Simplex Virus Vectors Research Articles

Oncolytic virus expressing PD-1 inhibitors activates a collaborative intratumoral immune response to control tumor and synergizes with CTLA-4 or TIM-3 blockade

BackgroundOncolytic viruses (OVs) are capable to inflame the tumor microenvironment (TME) and elicit infiltrating tumor-specific T cell responses. However, OV treatment negatively alters the cancer-immune set point in tumors to...

Engineering HSV-1 Vectors for Gene Therapy.

Virus vectors have been employed as gene transfer vehicles for various preclinical and clinical gene therapy applications and with the approval of Glybera (Alipogene tiparvovec) as the first gene therapy product as a standard medical treatment (Yla-Herttuala, Mol Ther 20:1831-1832, 2013), gene therapy has reached the status of being a part of standard patient care. Replication-competent herpes simplex virus (HSV) vectors that replicate specifically in actively dividing tumor cells have been used in Phase I-III human trials in patients with glioblastoma multiforme (GBM), a fatal form of brain cancer, and in malignant melanoma. In fact, Imlygic® (T-VEC, Talimogene laherparepvec, formerly known as OncoVex GM-CSF), displayed efficacy in a recent Phase-III trial when compared to standard GM-CSF treatment alone (Andtbacka et al., J Clin Oncol 31:sLBA9008, 2013), and has since become the first FDA-approved viral gene therapy product used in standard patient care (October 2015) (Pol et al., Oncoimmunology 5:e1115641, 2016). Moreover, increased efficacy was observed when Imlygic® was combined with checkpoint inhibitory antibodies as a frontline therapy for malignant melanoma (Ribas et al., Cell 170:1109-1119.e1110, 2017; Dummer et al., Cancer Immunol Immunother 66:683-695, 2017). In addition to the replication-competent oncolytic HSV vectors like T-VEC, replication-defective HSV vectors have been employed in Phase I-II human trials and have been explored as delivery vehicles for disorders such as pain, neuropathy and other neurodegenerative conditions. Research during the last decade on the development of HSV vectors has resulted in the engineering of recombinant vectors that are completely replication defective, nontoxic, and capable of long-term transgene expression in neurons. This chapter describes methods for the construction of recombinant genomic HSV vectors based on the HSV-1 replication-defective vector backbones, steps in their purification, and their small-scale production for use in cell culture experiments as well as preclinical animal studies.

Oncolytic Herpes Simplex Virus Vectors Fully Retargeted to Tumor- Associated Antigens.

Oncolytic virotherapy is a novel therapeutic modality for malignant diseases that exploits selective viral replication in cancer cells. Herpes simplex virus (HSV) is a promising agent for oncolytic virotherapy due to its broad cell tropism and the identification of mutations that favor its replication in tumor over normal cells. However, these attenuating mutations also tend to limit the potency of current oncolytic HSV vectors that have entered clinical studies. As an alternative, vector retargeting to novel entry receptors has the potential to achieve tumor specificity at the stage of virus entry, eliminating the need for replication-attenuating mutations. Here, we summarize the molecular mechanism of HSV entry and recent advances in the development of fully retargeted HSV vectors for oncolytic virotherapy. Retargeted HSV vectors offer an attractive platform for the creation of a new generation of oncolytic HSV with improved efficacy and specificity.

Syncytial Mutations Do Not Impair the Specificity of Entry and Spread of a Glycoprotein D Receptor-Retargeted Herpes Simplex Virus.

Herpes simplex virus (HSV) is investigated not only as a human pathogen but also as a promising agent for oncolytic virotherapy. We previously showed that both the initial entry and subsequent lateral spread of HSV can be retargeted to cells expressing tumor-associated antigens by single-chain antibodies fused to a receptor-binding-deficient envelope glycoprotein D (gD). Here we introduced syncytial mutations into the gB and/or gK gene of gD-retargeted HSVs to determine whether viral tropism remained dependent on the interaction of gD with the target receptor. Entry and spread profiles of the recombinant viruses indicated that gD retargeting does not abolish the hyperfusogenic activity of syncytial mutations and that these mutations do not eliminate the dependence of HSV entry and spread on a specific gD-receptor interaction. These observations suggest that syncytial mutations may be valuable for increasing the tumor-specific spreading of retargeted oncolytic HSV vectors.

Development of an oncolytic HSV vector fully retargeted specifically to cellular EpCAM for virus entry and cell-to-cell spread.

Oncolytic herpes simplex virus (HSV) vectors have attracted increasing attention as novel anti-cancer agents. HSV entry is triggered by the binding of glycoprotein D (gD) to its receptors, such as herpesvirus entry mediator or nectin-1. We have recently reported the construction of a fully retargeted HSV platform that incorporates single-chain antibodies (scFv) into gD to mediate entry exclusively via tumor-associated antigens. In this study, we created an scFv directed against epithelial cell adhesion molecule (EpCAM), a recognized carcinoma-associated antigen, and inserted it into the retargeted HSV platform that is ablated for gD recognition of its canonical receptors and contains the entry-enhancing mutations in gB we previously identified. We observed that both initial entry and subsequent cell-to-cell spread of the retargeted virus were stringently dependent on cellular EpCAM expression. Interestingly, the retargeted virus developed larger plaques on some of the human tumor lines tested than the control virus bearing wild-type gD. Intratumoral injection of the retargeted virus revealed antitumor activity in a mouse xenograft model. These observations illustrate the versatility of our retargeted HSV platform as it allows expansion of the oncolytic virus toolbox for the treatment of diverse cancers.

The oncolytic herpes simplex virus vector, G47Δ, effectively targets tamoxifen-resistant breast cancer cells.

The aim of the present study was to establish a tamoxifen-resistant cell line (MCF-7/TAM-R) and to investigate the therapeutic effect of G47Δ on this cell line both in vitro and in vivo. In the present study, the MCF-7/TAM-R monoclonal subline was established after exposing MCF-7 cells to tamoxifen for 21 days. Then, it was compared with a wild-type MCF-7 subline (MCF-7W), which was not treated with tamoxifen. Cell proliferation, viability, cell cycle and apoptosis analyses were carried out to examine the characteristics of the MCF-7/TAM-R cells. Both in vitro and in vivo toxicity studies were conducted to investigate the therapeutic effect of G47Δ on the MCF-7/TAM-R cells. Compared to the MCF-7W cells, we found that the MCF-7/TAM-R cells exhibited a higher proliferation ability (P<0.05) and a stronger resistance to the cytotoxic effects induced by 4-hydroxytamoxifen (4-OHT) (P<0.05). G47Δ demonstrated a high cytotoxic effect on both the MCF-7/TAM-R and MCF-7W cell lines. After being infected with G47Δ at an MOI of 0.01, >90% of the MCF-7/TAM-R and MCF-7W cells died on day 5. G47Δ induced cell cycle arrest in the G2/M phase. Furthermore, G47Δ inhibited tumor growth in subcutaneous tumor models of both MCF-7/TAM-R and MCF-7W. Thus, we conclude that G47Δ, a third generation oncolytic herpes simplex virus, is highly sensitive and safe in targeting tamoxifen-resistant breast cancer cells both in vitro and in vivo.

Impact of new oncolytic herpes simplex virus vector armed with interleukine-12 for cervical cancer therapy.

3102 Background: Cervical cancer is the third most common cancer in women, and the seventh overall, the incidence and mortality of cervical cancer in the world was approximately 530,000 and 275,000...

An oncolytic herpes simplex virus vector, G47Δ, synergizes with paclitaxel in the treatment of breast cancer

Paclitaxel-containing treatment regimens are standard chemotherapy schemes for breast cancer patients. The use of oncolytic herpes simplex virus (oHSV) vectors has been shown to be a safe and effective therapeutic approach for different types of cancer. We hypothesized that paclitaxel in combination with an oHSV vector would present an enhanced killing effect when used against breast cancer cells. In the present study, we demonstrated that the combined use of the oHSV vector G47Δ and paclitaxel produced a synergistic effect against breast cancer cells both invitro and invivo. Invitro studies demonstrated that paclitaxel and G47Δ both caused dose-dependent cytotoxicity against the human breast cancer cell lines MCF-7 and MDA-MB-468. G47Δ and paclitaxel also demonstrated synergistic cytotoxicity when applied together, with Chou-Talalay combination indices ranging from 0.44 to 0.77 for MCF-7 cells and 0.68 to 0.83 for MDA-MB‑468 cells. Paclitaxel did not enhance viral replication or viral spread among tumor cells. However, G47Δ increased the antitumor ability of paclitaxel by inducing mitotic arrest and apoptosis. Invivo studies indicated that when combined with G47Δ, the dose of paclitaxel could be reduced at least 5-fold while maintaining levels of tumor reduction similar to those achieved with the administration of paclitaxel alone. Combination therapy resulted in no morbidity invivo. Our data demonstrated that G47Δ and paclitaxel combination therapy had synergistic effects in the treatment of breast cancer. This combination therapy may be promising for breast cancer patients.

The oncolytic herpes simplex virus vector G47Δ effectively targets breast cancer stem cells

Accumulating evidence suggests that breast cancer originates from cancer stem cells (CSCs), which comprise a small percentage of the overall tumor but are highly tumorigenic and pluripotent with unlimited proliferation potential. Furthermore, CSCs are highly resistant to conventional treatment, which may explain certain difficulties in treating cancer with current therapy options. In this study, the third generation oncolytic herpes simplex virus (oHSV) vector G47∆ effectively killed different subtypes of breast cancer cells, with more than 98% of the tumor cells killed by Day5. Moreover, G47∆ targeted equally non-cancer stem cells (NCSCs) and CSCs which showed resistance to paclitaxel. We demonstrated that G47∆ effectively replicated and spread among CSCs. G47∆ also impaired the self-renewal ability of CSCs, as the viable cells were unable to form secondary tumor spheres. We also showed that G47∆ was able to induce the regression of tumor xenografts in BALB/c nude mice and demonstrated the ability of G47∆ to synergize with paclitaxel by killing both NCSCs and CSCs, suggesting that oHSV may be an effective treatment modality for patients with breast cancer.

Combination of vinblastine and oncolytic herpes simplex virus vector expressing IL-12 therapy increases antitumor and antiangiogenic effects in prostate cancer models

Oncolytic herpes simplex virus-1 (oHSV)–based vectors selectively replicate in tumor cells causing direct killing, ie., oncolysis, while sparing normal cells. oHSV’sare promising anticancer agents, but their efficacy, when used as single agents, leaves room for improvement. We hypothesized that combining the direct oncolytic and antiangiogenic activities of the IL-12 secreting NV1042 oHSV with microtubule disrupting agents (MDA’s) would be an effective means to enhance antitumor efficacy. Vinblastine (VB) was identified among several MDA’s screened that displayed consistent and potent cytotoxic killing of both prostate cancer and endothelial cell lines. In matrigel tube forming assays, VB was found to be highly effective at inhibiting tube formation of HUVEC cells. The combination of VB with NV1023 (the parental virus lacking IL-12) or NV1042 showed additive or synergistic activity against prostate cancer cell lines and was not due to increased oHSV replication by VB. In athymic mice bearing CWR22 prostate tumors, VB in combination with NV1042 was superior to the combination of VB plus NV1023 in reducing tumor burden, appeared to be nontoxic and resulted in a statistically significant diminution in the number of CD31+ cells as compared to other treatment groups. In human organotypic cultures using surgical samples from radical prostatectomies, both NV1023 and NV1042 were localized specifically to the epithelial cells of prostatic glands but not to the surrounding stroma. These data highlight the therapeutic advantage of combining the dual-acting anti-tumor and anti-angiogenic activities of oHSV’s and MDA’s.

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.

Abstract P2-18-01: Treatment of Human Breast Tumors by Oncolytic Herpes Simplex Virus

Abstract Background: Breast cancer is the most common cancer for women in the world, although current therapies have improve the outcome, the breast cancer deaths are still the second highest among cancers in women. Metastasis to the lung frequently results in severe complications, and currently, there are no curative treatment options available for patients with metastetic breast cancer. Oncolytic viral therapy is a new strategy for treating cancers. Replication-competent herpes simplex virus (HSV) can infect, replicate and kill tumor cells by a direct cytopathic effect and then spread within the tumor cells. In this study, the cytotoxicity of HSV vectors, G47Δ were examined on different human breast cancer cell lines, immortalized human breast cell lines, and primary culture normal human breast cells. Pulmonary metastasis model of breast cancer was constructed and the treatment effect of G47D was evaluated. Methods: Human BC cell lines SK-BR-3, MDA-MB-453, and MCF-7, immortalized breast cells MCF-10A and 76N-tert, and cultured primary normal breast cells HMEC1 and HMEC2 were cultured in vitro and infected with G47Δ at different multiplicities of infection (MOIs). The viability of infected cells was measured. G47Δ-infected cells were identified using X-gal histochemistry for LacZ expression. A pulmonary metastatic BC model was established with Balb-c nude mice by tail vein injection of MDA-MB-435 cells. Treatment was initiated 21 days after injection of tumor cells, with the virus group treated twice weekly with four total i.v. administrations of G47Δ (2*107pfu/100ul) and on day 60 mice were sacrificed and tumor nodules on the surface of the lung counted after Indian ink staining. Results: G47Δ was highly cytotoxic to BC cells and 76N-tert in vitro at very low MOI (0.01). For all of these cell lines, more than 85% and 95% cells were killed at MOI=0.01 and MOI=0.1 respectively on the fifth day after infection. However, both HMEC1 and HMEC2 cells were viable even 5 days after infection. A slight effect was found with MCF-10A, of which only 7% and 24.5% were killed at MOI=0.01 and MOI=0.1 respectively on day 5. In the pulmonary metastatic model, the average number of surface lung tumor nodules in the G47Δ group was one, but ten in the control group. X-gal staining illustrated viral replication and spread in the tumor cells in vitro and in vivo. Conclusions: Recently constructed oncolytic HSV vector G47Δ was effective at killing human breast cancer cells and immortalized breast cells, but didn't infect the normal breast cells. The i.v. administrations of G47Δ could effectively cure metastatic breast cancer. Our studies demonstrated that as a novel therapeutic agents, G47Δ was safe and exhibited superior antitumor effects, thereby making it appropriate for human clinical trials. It is worth noting that G47Δ was effective for lung metastatic breast cancer, which could assure the long survival rate of patients with advance breast cancer. The efficiency of G47Δ warrants consideration of clinical application. (Key words) breast cancer; cancer therapy; herpes simplex virus; oncolytic virus; gene therapy; Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P2-18-01.

Cytotoxicity of oncolytic herpes simplex virus vector on breast cancer stem cells.

e13637 Background: CD44+CD24−/low is an important marker of breast cancer stem cells, which underlies the incurable and relapse characteristics of breast cancer in clinic. A third-generation oncolytic herpes simplex virus (HSV) vector G47D is a novel agent for the treatment of many cancers. In this study, we investigate the cytotoxity of G47Δ on CD44+CD24−/low cells that were purified from the human SK-BR-3 cell line. Methods: Breast cancer cell line SK-BR-3 was cultured in suspension to generate primary mammospheres. After 10 days of culture, the proportion of CD44+CD24-/low cells from mammospheres was measured by flow cytometry. Then, the CD44+CD24-/low population were adherent cultured and infected with G47Δ of different multiplicities of infection (MOI). G47Δ-infected cells were detected with X-gal staining. Results: The proportion of CD44+CD24-/low cells in SK-BR-3 mammospheres was 95.3% +2.1% after 10 days of suspension culture. At day 9 of adherent culture, the proportion of CD44+CD24-/low cells was 90.2%+1.9%. G47Δ was highly cytotoxic for CD44+CD24-/low cells in vitro at both low MOIs (Table). X-gal staining showed the G47Δ infected cells. Conclusions: Recently constructed oncolytic HSV vector G47Δ was effective at killing breast cancer CD44+CD24-/low cells in vitro. The efficiency and specificity of this novel cancer therapy deserve further investigation and consideration of animal models and clinical studies. Percentage of CD44+CD24−/low SK-BR-3 cells killed by G47Δ MOI D1 D2 D3 D4 D5 D6 0.01 2 10 38 55 72 91 0.1 8 21 63 85 92 97 No significant financial relationships to disclose.

Oncolytic Herpes Simplex Virus Vectors and Chemotherapy: Are Combinatorial Strategies More Effective for Cancer?

Despite aggressive treatments, including chemotherapy and radiotherapy, cancers often recur owing to resistance to conventional therapies. Oncolytic viruses such as oncolytic herpes simplex virus (oHSV) represent an exciting biological approach to cancer therapy. A range of viral mutations has been engineered into HSV to engender oncolytic activity. While oHSV as a single agent has been tested in a number of cancer clinical trials, preclinical studies have demonstrated enhanced efficacy when it is combined with cytotoxic anticancer drugs. Among the strategies that will be discussed in this article are combinations with standard-of-care chemotherapeutics, expression of prodrug-activating enzymes to enhance chemotherapy and small-molecule inhibitors. The combination of oHSV and chemotherapy can achieve much more efficient cancer cell killing than either single agent alone, often through synergistic interactions. This can be clinically important not just for improving efficacy but also for permitting lower and less toxic chemotherapeutic doses. The viral mutations in an oHSV vector often determine the favorability of its interactions with chemotherapy, just as different cancer cells, due to genetic alterations, vary in their response to chemotherapy. As chemotherapeutics are often the standard of care, combining them with an investigational new drug, such as oHSV, is clinically easier than combining multiple novel agents. As has become clear for most cancer therapies, multimodal treatments are usually more effective. In this article, we will discuss the recent progress of these combinatorial strategies between virotherapy and chemotherapy and future directions.

Human Glioblastoma–Derived Cancer Stem Cells: Establishment of Invasive Glioma Models and Treatment with Oncolytic Herpes Simplex Virus Vectors

Glioblastoma, the most malignant type of primary brain tumor, is one of the solid cancers where cancer stem cells have been isolated, and studies have suggested resistance of those cells to chemotherapy and radiotherapy. Here, we report the establishment of CSC-enriched cultures derived from human glioblastoma specimens. They grew as neurospheres in serum-free medium with epidermal growth factor and fibroblast growth factor 2, varied in the level of CD133 expression and very efficiently formed highly invasive and/or vascular tumors upon intracerebral implantation into immunodeficient mice. As a novel therapeutic strategy for glioblastoma-derived cancer stem-like cells (GBM-SC), we have tested oncolytic herpes simplex virus (oHSV) vectors. We show that although ICP6 (UL39)-deleted mutants kill GBM-SCs as efficiently as wild-type HSV, the deletion of gamma34.5 significantly attenuated the vectors due to poor replication. However, this was significantly reversed by the additional deletion of alpha47. Infection with oHSV G47Delta (ICP6(-), gamma34.5(-), alpha47(-)) not only killed GBM-SCs but also inhibited their self-renewal as evidenced by the inability of viable cells to form secondary tumor spheres. Importantly, despite the highly invasive nature of the intracerebral tumors generated by GBM-SCs, intratumoral injection of G47Delta significantly prolonged survival. These results for the first time show the efficacy of oHSV against human GBM-SCs, and correlate this cytotoxic property with specific oHSV mutations. This is important for designing new oHSV vectors and clinical trials. Moreover, the new glioma models described in this study provide powerful tools for testing experimental therapeutics and studying invasion and angiogenesis.

Design and application of oncolytic HSV vectors for glioblastoma therapy

Glioblastoma multiforme is one of the most common human brain tumors. The tumor is generally highly infiltrative, making it extremely difficult to treat by surgical resection or radiotherapy. This feature contributes to recurrence and a very poor prognosis. Few anticancer drugs have been shown to alter rapid tumor growth and none are ultimately effective. Oncolytic vectors have been employed as a treatment alternative based on the ability to tailor virus replication to tumor cells. The human neurotropic herpes simplex virus (HSV) is especially attractive for development of oncolytic vectors (oHSV) because this virus is highly infectious, replicates rapidly and can be readily modified to achieve vector attenuation in normal brain tissue. Tumor specificity can be achieved by deleting viral genes that are only required for virus replication in normal cells and permit mutant virus replication selectively in tumor cells. The anti-tumor activity of oHSV can be enhanced by arming the vector with genes that either activate chemotherapeutic drugs within the tumor tissue or promote anti-tumor immunity. In this review, we describe current designs of oHSV and the experience thus far with their potential utility for glioblastoma therapy. In addition, we discuss the impediments to vector effectiveness and describe our view of future developments in vector improvement.

Oncolytic herpes simplex virus vectors and taxanes synergize to promote killing of prostate cancer cells

Genetically engineered oncolytic herpes simplex virus-1 (HSV-1) vectors selectively replicate in tumor cells causing direct killing whereas sparing normal cells. One clinical limitation of using oncolytic HSV vectors is their attenuated growth. We hypothesized that the appropriately chosen chemotherapeutic agent combined with an oncolytic HSV could be an effective means to promote augmented prostate cancer cell killing both in vitro and in vivo. Here we have identified that G47Delta synergizes with the microtubule-stabilizing taxane agents docetaxel and paclitaxel to enhance the in vitro killing of prostate cancer cells. In vivo efficacy studies show that when combined with docetaxel, G47Delta could be reduced at least 10-fold. Immunoblot analysis revealed that docetaxel-induced accumulation of the phospho-specific mitotic markers op18/stathmin or histone-H3 was markedly reduced by G47Delta, which correlated with enhanced apoptosis and required active viral replication. Furthermore, cell-cycle analysis demonstrated that in the presence of G47Delta, the majority of 4N cells arrested in mitosis were MPM-2-negative, indicative of cells exiting mitosis prematurely. These findings suggest that G47Delta may act in part, on mitotically blocked cells to enhance cell death, which may account for the enhanced antitumor efficacy observed in vivo.

Oncolytic herpes simplex virus therapy for peripheral nerve tumors

Oncolytic viruses are one of many emerging cancer therapies. The surgical management of peripheral nerve tumors carries an inherent risk of damaging the nerves involved and so the search for novel therapies with reduced risk of morbidity continues. In this review the authors discuss the use of oncolytic herpes simplex virus (HSV) in the treatment of peripheral nerve tumors. Herpes simplex virus has a number of characteristics that make it a useful oncolytic vector, including its large, sequenced genome that can accommodate multiple transgenes, its lack of insertional mutagenesis, its ability to infect a wide array of cell types in various species, and the availability of well-established antiviral therapies to treat it. The efficacy of oncolytic HSV therapy against schwannomas and malignant peripheral nerve sheath tumors has been studied in multiple experimental models both in vitro and in vivo. The virus utilizes cell pathways unique to tumors to enhance its oncolytic efficacy, preferentially and effectively targeting and destroying peripheral nerve tumor cells without harming normal cells. This effect is augmented by transgenes expressing antiangiogenic factors, such as dominant-negative fibroblast growth factor receptor and platelet factor 4, and displays synergy with chemotherapy. Different oncolytic HSV vectors have been tested, including hrR3, G207, and G47D. In addition, new animal models have been developed to test the efficacy of oncolytic HSV therapy in peripheral nerve tumors. The safety of oncolytic HSV is well established and has been tested in nonhuman primates and in human clinical trials.

Treatment of Implantable NF2 Schwannoma Tumor Models with Oncolytic Herpes Simplex Virus G47Δ

Schwannomas are benign tumors composed of dedifferentiated Schwann cells that form along peripheral nerves causing nerve compression often associated with pain and loss of function. Current surgical therapy involves total or subtotal surgical removal of the tumor, which may cause permanent nerve damage. In the present study, we explore an alternate means of therapy in which schwannomas are injected with a replication-conditional herpes simplex virus (HSV) vector to shrink the tumor through cell lysis during virus propagation. The oncolytic vector used, G47Delta, has deletions in HSV genes, which allow it to replicate selectively in dividing cells, sparing neurons. Two schwannoma cell lines were used to generate subcutaneous tumors in nude mice: HEI193, an immortalized human line previously established from an NF2 patient and NF2S-1, a newly generated spontaneous mouse line. Subcutaneous HEI193 tumors grew about ten times as fast as NF2S-1 tumors, and both regressed substantially following injection of G47Delta. Complete regression of HEI193 tumors was achieved in most animals, whereas all NF2S-1 tumors resumed growth within 2 weeks after vector injection. These studies provide a new schwannoma model for testing therapeutic strategies and demonstrate that oncolytic HSV vectors can be successfully used to shrink growing schwannomas.

Effective Treatment of Tumors with Strong β-Catenin/T-Cell Factor Activity by Transcriptionally Targeted Oncolytic Herpes Simplex Virus Vector

The Wnt/beta-catenin/T-cell factor (Tcf) pathway is aberrantly up-regulated in the majority of colorectal cancers (CRC) and hepatoblastomas due to either an APC or beta-catenin gene mutation. We constructed synthetic promoters, T and TE, which contain tandem repeats of a Tcf responsive element without and with the human 4F2 gene intronic enhancer, respectively. Although the T and TE promoters showed higher transcriptional activity than a control promoter in all CRC and hepatoblastoma cell lines tested, with low activities in most other tumor cell lines, the level of transcription varied considerably among the CRC and hepatoblastoma cell lines. In some CRC cell lines, the TE promoter displayed higher levels of transcription than even the human CMV(IE) promoter. In those CRC cells, the APC gene mutations were located within a small segment between the first and second 20-amino-acid repeats in the mutation cluster region of the APC protein. We created a transcriptionally targeted oncolytic herpes simplex virus vector (bM24-TE) in which replication is driven by the TE promoter. This vector efficiently and specifically replicated in and killed tumor cells with strong beta-catenin/Tcf signaling. Intratumoral injection of bM24-TE significantly reduced the growth of highly beta-catenin active SW480 CRC tumors and induced a complete response in half of them, whereas it had no effect on the growth of beta-catenin-inactive A549 tumors. Our results suggest that a transcriptionally regulated oncolytic herpes vector targeting beta-catenin/Tcf signal is very efficacious against CRC tumors carrying an APC gene mutation between the first and second 20-amino-acid repeats.