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

Safety of non-replicative and oncolytic replication-selective HSV vectors

Herpes simplex virus type 1 (HSV-1) is a DNA virus and human pathogen used to construct promising therapeutic vectors. HSV-1 vectors fall into two classes: replication-selective oncolytic vectors for cancer therapy and defective non-replicative vectors for gene therapy. Vectors from each class can accommodate ≥30 kb of inserts, have been approved clinically, and demonstrate a relatively benign safety profile. Despite oncolytic HSV (oHSV) replication in tumors and elicited immune responses, the virus is well tolerated in cancer patients. Current non-replicative vectors elicit only limited immune responses. Seropositivity and immune responses against HSV-1 do not eliminate either the vector or infected cells, and the vectors can therefore be re-administered. In this review we highlight vectors that have been translated to the clinic and host-virus immune interactions that impact on the safety and efficacy of HSVs.

Cancer therapy with the viral and bacterial pathogens: The past enemies can be considered the present allies

Cancer continues to be one of the leading causes of mortality worldwide despite significant advancements in cancer treatment. Many difficulties have arisen as a result of the detrimental consequences of chemotherapy and radiotherapy as a common cancer therapy, such as drug inability to penetrate deep tumor tissue, and also the drug resistance in tumor cells continues to be a major concern. These obstacles have increased the need for the development of new techniques that are more selective and effective against cancer cells. Bacterial-based therapies and the use of oncolytic viruses can suppress cancer in comparison to other cancer medications. The tumor microenvironment is susceptible to bacterial accumulation and proliferation, which can trigger immune responses against the tumor. Oncolytic viruses (OVs) have also gained considerable attention in recent years because of their potential capability to selectively target and induce apoptosis in cancer cells. This review aims to provide a comprehensive summary of the latest literature on the role of bacteria and viruses in cancer treatment, discusses the limitations and challenges, outlines various strategies, summarizes recent preclinical and clinical trials, and emphasizes the importance of optimizing current strategies for better clinical outcomes.

Preclinical safety assessment of toxicity and biodistribution of oncolytic virus HSV-1 expressing human PD-1 antibody in mice

HSV-1/hPD-1 is composed of engineered herpes simplex virus type-1 and two inserted copies of the human PD-1 antibody sequence. It is a novel oncolytic virus product designed to cure malignancies. The objective of this study was to estimate its toxicity in mice. In the single-dose toxicity study, no mortality and abnormal symptoms were observed in animals injected with 4.0 × 10⁷ pfu/mouse dose. In the repeat-dose toxicity study, HSV-1/hPD-1 in animals intramuscularly treated with 1.0 × 10⁷, 2.0 × 10⁷, or 4.0 × 10⁷ pfu/mouse doses was well tolerated in terms of clinical observation, body weight, food consumption, hematology and biochemistry indexes, T lymphocyte counting, immune reaction, and organ weight, except for some histopathological changes, such as the irreversible degeneration of the sciatic nerve, which was considered related to the adopted administration route. Synchronously, a biodistribution study in mice was performed to examine whether HSV-1/hPD-1 could spread to the injection site, gonads, liver, lung, heart, mesenteric and inguinal lymph nodes, skin, dorsal root ganglia, and blood, and then be gradually eliminated. Thus, two safety dose levels-the maximum tolerance dose of 4.0 × 10⁷ pfu/mouse and the no-observed-adverse-effect-level dose of 1.0 × 10⁷ pfu/mouse-were determined to help design patients' dose regimens. Our research data have been successfully accepted for investigational new drug (IND) application in China.

Delivery and Biosafety of Oncolytic Virotherapy

In recent years, oncolytic virotherapy has emerged as a promising anticancer therapy. Oncolytic viruses destroy cancer cells, without damaging normal tissues, through virus self-replication and antitumor immunity responses, showing great potential for cancer treatment. However, the clinical guidelines for administering oncolytic virotherapy remain unclear. Delivery routes for oncolytic virotherapy to patients vary in existing studies, depending on the tumor sites and the objective of studies. Moreover, the biosafety of oncolytic virotherapy, including mainly uncontrolled adverse events and long-term complications, remains a serious concern that needs to be accurately measured. This review provides a comprehensive and detailed overview of the delivery and biosafety of oncolytic virotherapy.

The Characteristics of Herpes Simplex Virus Type 1 Infection in Rhesus Macaques and the Associated Pathological Features

As one of the major pathogens for human herpetic diseases, herpes simplex virus type 1 (HSV1) causes herpes labialis, genital herpes and herpetic encephalitis. Our aim here was to investigate the infectious process of HSV1 in rhesus macaques and the pathological features induced during this infection. Clinical symptoms that manifested in the rhesus macaque during HSV1 infection included vesicular lesions and their pathological features. Viral distribution in the nervous tissues and associated pathologic changes indicated the typical systematic pathological processes associated with viral distribution of HSV1. Interestingly, vesicular lesions recurred in oral skin or in mucosa associated with virus shedding in macaques within four to five months post-infection, and viral latency-associated transcript (LAT) mRNA was found in the trigeminal ganglia (TG) on day 365 post-infection. Neutralization testing and enzyme-linked immunospot (ELISpot) detection of specific T cell responses confirmed the specific immunity induced by HSV1 infection. Thus, rhesus macaques could serve as an infectious model for HSV1 due to their typical clinical symptoms and the pathological recurrence associated with viral latency in nervous tissues.

Oncolytic viruses: From bench to bedside with a focus on safety

Oncolytic viruses are a relatively new class of anti-cancer immunotherapy agents. Several viruses have undergone evaluation in clinical trials in the last decades, and the first agent is about to be approved to be used as a novel cancer therapy modality. In the current review, an overview is presented on recent (pre)clinical developments in the field of oncolytic viruses that have previously been or currently are being evaluated in clinical trials. Special attention is given to possible safety issues like toxicity, environmental shedding, mutation and reversion to wildtype virus.

Evaluation of the safety and biodistribution of M032, an attenuated herpes simplex virus type 1 expressing hIL-12, after intracerebral administration to aotus nonhuman primates

Herpes simplex virus type 1 (HSV-1) mutants lacking the γ(1)34.5 neurovirulence loci are promising agents for treating malignant glioma. Arming oncolytic HSV-1 to express immunostimulatory genes may potentiate therapeutic efficacy. We have previously demonstrated improved preclinical efficacy, biodistribution, and safety of M002, a γ(1)34.5-deleted HSV-1 engineered to express murine IL-12. Herein, we describe the safety and biodistribution of M032, a γ(1)34.5-deleted HSV-1 virus that expresses human IL-12 after intracerebral administration to nonhuman primates, Aotus nancymae. Cohorts were administered vehicle, 10(6), or 10(8) pfu of M032 on day 1 and subjected to detailed clinical observations performed serially over a 92-day trial. Animals were sacrificed on days 3, 31, and 91 for detailed histopathologic assessments of all organs and to isolate and quantify virus in all organs. With the possible exception of one animal euthanized on day 16, neither adverse clinical signs nor sex- or dose-related differences were attributed to M032. Elevated white blood cell and neutrophil counts were observed in virus-injected groups on day 3, but no other significant changes were noted in clinical chemistry or coagulation parameters. Minimal to mild inflammation and fibrosis detected, primarily in meningeal tissues, in M032-injected animals on days 3 and 31 had mostly resolved by day 91. The highest viral DNA levels were detected at the injection site and motor cortex on day 3 but decreased in central nervous system tissues over time. These data demonstrate the requisite safety of intracerebral M032 administration for consideration as a therapeutic for treating malignant brain tumors.

Progress of oncolytic viruses in sarcomas

Oncolytic virotherapy has shown exciting promise for the treatment of many types of solid tumors. Pediatric sarcomas are an aggressive type of pediatric malignancy known to show limited responsiveness to current therapies, leading to unacceptably high morbidity and mortality. Oncolytic viruses have only recently been used for the treatment of this challenging cancer, and results have been encouraging. Five clinical trials are currently open evaluating the use of oncolytic viruses in pediatric malignancies. Advances in genetic engineering of the viruses include improving the ability of the virus to infect tumor cells, engineering the virus with transgenes which improve the virus' ability to kill tumor cells and manipulating the virus to enhance concomitantly administered therapies. Further understanding of the antiviral immune response and a viral induced anti-tumor immune response will permit a maximization of oncolytic virotherapy.

HSV Recombinant Vectors for Gene Therapy

The very deep knowledge acquired on the genetics and molecular biology of herpes simplex virus (HSV), has allowed the development of potential replication-competent and replication-defective vectors for several applications in human healthcare. These include delivery and expression of human genes to cells of the nervous systems, selective destruction of cancer cells, prophylaxis against infection with HSV or other infectious diseases, and targeted infection to specific tissues or organs. Replication-defective recombinant vectors are non-toxic gene transfer tools that preserve most of the neurotropic features of wild type HSV-1, particularly the ability to express genes after having established latent infections, and are thus proficient candidates for therapeutic gene transfer settings in neurons. A replication-defective HSV vector for the treatment of pain has recently entered in phase 1 clinical trial. Replication-competent (oncolytic) vectors are becoming a suitable and powerful tool to eradicate brain tumours due to their ability to replicate and spread only within the tumour mass, and have reached phase II/III clinical trials in some cases. The progress in understanding the host immune response induced by the vector is also improving the use of HSV as a vaccine vector against both HSV infection and other pathogens. This review briefly summarizes the obstacle encountered in the delivery of HSV vectors and examines the various strategies developed or proposed to overcome such challenges.

HSV Recombinant Vectors for Gene Therapy

The very deep knowledge acquired on the genetics and molecular biology of herpes simplex virus (HSV), has allowed the development of potential replication-competent and replication-defective vectors for several applications in human healthcare. These include delivery and expression of human genes to cells of the nervous systems, selective destruction of cancer cells, prophylaxis against infection with HSV or other infectious diseases, and targeted infection to specific tissues or organs. Replication-defective recombinant vectors are non-toxic gene transfer tools that preserve most of the neurotropic features of wild type HSV-1, particularly the ability to express genes after having established latent infections, and are thus proficient candidates for therapeutic gene transfer settings in neurons. A replication-defective HSV vector for the treatment of pain has recently entered in phase 1 clinical trial. Replication-competent (oncolytic) vectors are becoming a suitable and powerful tool to eradicate brain tumours due to their ability to replicate and spread only within the tumour mass, and have reached phase II/III clinical trials in some cases. The progress in understanding the host immune response induced by the vector is also improving the use of HSV as a vaccine vector against both HSV infection and other pathogens. This review briefly summarizes the obstacle encountered in the delivery of HSV vectors and examines the various strategies developed or proposed to overcome such challenges.

Analysis of genetically engineered oncolytic herpes simplex viruses in human prostate cancer organotypic cultures

Oncolytic herpes simplex viruses type 1 (oHSVs) such as G47Delta and G207 are genetically engineered for selective replication competence in cancer cells. Several factors can influence the overall effectiveness of oHSV tropism, including HSV-1 receptor expression, extracellular matrix milieu and cellular permissiveness. We have taken advantage of human prostate organ cultures derived from radical prostatectomies to investigate oHSV tropism. In this study, we show that both G47Delta and G207 specifically replicate in epithelial cells of the prostatic glands but not in the surrounding stroma. In contrast, both the epithelial and stromal cell compartments were readily infected by wild-type HSV-1. Analysis of oHSV replication in prostate surgical specimens 3 days post infection showed that G47Delta generated approximately 30-fold more viral progeny than did G207. This correlated with the enhanced expression of G47Delta-derived glycoprotein gB protein levels as compared with G207. In benign prostate tissues, G207 and G47Delta titers were notably reduced, whereas strain F titers were maintained at similar levels compared with prostate cancer specimens. Overall, our results show that these oncolytic herpes vectors show both target specificity and replication competence in human prostate cancer specimens and point to the utility of using human prostate organ cultures in assessing oHSV tropism and cellular specificity.

Molecular and traditional chemotherapy: a united front against prostate cancer

Castrate resistant prostate cancer (CRPC) is essentially incurable. Recently though, chemotherapy demonstrated a survival benefit ( approximately 2months) in the treatment of CRPC. While this was a landmark finding, suboptimal efficacy and systemic toxicities at the therapeutic doses warranted further development. Smart combination therapies, acting through multiple mechanisms to target the heterogeneous cell populations of PC and with potential for reduction in individual dosing, need to be developed. In that, targeted molecular chemotherapy has generated significant interest with the potential for localized treatment to generate systemic efficacy. This can be further enhanced through the use of oncolytic conditionally replicative adenoviruses (CRAds) to deliver molecular chemotherapy. The prospects of chemotherapy and molecular-chemotherapy as single and as components of combination therapies are discussed.

Oncolytic virus therapy for prostate cancer

The use of replication-competent viruses that can selectively replicate in and destroy neoplastic cells is an attractive strategy for treating cancer. Various oncolytic viruses have been taken to clinical trials since a recombinant virus was first applied to cancer patients a decade ago. The concept of the therapy is simple: infectious virus kills the host cancer cells in the course of viral replication. It is important, however, that the virus does not harm the surrounding normal tissue. Oncolytic viruses can be classified largely into two groups: DNA viruses genetically engineered to achieve cancer specificity (e.g. adenovirus, herpes simplex virus and vaccinia) and RNA viruses of which human is not the natural host (e.g. Newcastle disease virus and reovirus). Prostate cancer has always been one of the major targets of oncolytic virus therapy development. The result of six clinical trials for prostate cancer has been published and several trials are now going on. Forty-eight of 83 (58%) patients evaluated in the phase I studies demonstrated a >25% decrease in serum prostate-specific antigen level without evidence of severe toxicities. The result shows the oncolytic virus therapy is promising toward clinical application. Here, we review the recent advances in the field and summarize the results from clinical trials.

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.

Ras signaling influences permissiveness of malignant peripheral nerve sheath tumor cells to oncolytic herpes

Lack of expression of neurofibromin in neurofibromatosis 1 and its lethal derivative, malignant peripheral nerve sheath tumors (MPNSTs), is thought to result in the overactivation of the Ras signaling pathway. Our previous studies have shown that cells with overactivation in the Ras pathway are more permissive to infection with herpes simplex virus 1 and its mutant version R3616. In this study, we show that among five different mouse MPNST cell lines, only the ones with elevated levels of Ras signaling are highly permissive to infection with oncolytic herpes G207. Specific inhibitors of the Ras, ERK, and JNK pathways all reduced the synthesis of viral proteins in MPNST cells. The cell lines that contained lower levels of Ras and decreased activation of downstream signaling components underwent an enhancement in apoptosis upon exposure to G207. Additionally, mouse SW10 Schwann cells were able to become infected by parental herpes but were found to be resistant to G207. The immortalization of these cell lines with the expression of SV40 large T antigen increased the levels of Ras activation and permissiveness to oncolytic herpes. A Ras/Raf kinase inhibitor reduced the synthesis of both herpes simplex virus-1 and G207 proteins in SW10 cells. The results of this study, therefore, introduce Ras signaling as a divergent turning point for the response of MPNST cells to an assault by oncolytic herpes.

Molecular analysis of human cancer cells infected by an oncolytic HSV-1 reveals multiple upregulated cellular genes and a role for SOCS1 in virus replication

Oncolytic herpes simplex viruses (oHSVs) are promising anticancer therapeutics. We sought to characterize the functional genomic response of human cancer cells to oHSV infection using G207, an oHSV previously evaluated in a phase I trial. Five human malignant peripheral nerve sheath tumor cell lines, with differing sensitivity to oHSV, were infected with G207 for 6 h. Functional genomic analysis of virus-infected cells demonstrated large clusters of downregulated cellular mRNAs and smaller clusters of those upregulated, including 21 genes commonly upregulated in all five lines. Of these, 7 are known to be HSV-1 induced and 14 represent novel virus-regulated genes. Gene ontology analysis revealed that a majority of G207-upregulated genes are involved in Janus kinase/signal transducer and activator of transcription signaling, transcriptional regulation, nucleic acid metabolism, protein synthesis and apoptosis. Ingenuity networks highlighted nodes for AP-1 subunits and interferon signaling via STAT1, suppressor of cytokine signaling-1 (SOCS1), SOCS3 and RANTES. As biological confirmation, we found that virus-mediated upregulation of SOCS1 correlated with sensitivity to G207 and that depletion of SOCS1 impaired virus replication by >10-fold. Further characterization of roles provided by oHSV-induced cellular genes during virus replication may be utilized to predict oncolytic efficacy and to provide rational strategies for designing next-generation oncolytic viruses.

Efficacy and safety of the oncolytic herpes simplex virus rRp450 alone and combined with cyclophosphamide

Oncolytic herpes simplex virus (oHSV) mutants are under development as anticancer therapeutics. One such vector, rRp450, is ICP6-deleted and expresses a prodrug enzyme for cyclophosphamide (CPA) (rat CYP2B1). Little is known about rRp450's toxicity profile, especially in combination with CPA. We tested rRp450/CPA for antitumor efficacy in an aggressive human xenograft sarcoma model, measured virus production in primary cells, and tested rRp450/CPA for safety in immunocompetent mice. CPA enhanced the antitumor efficacy of rRp450. Relative to wild-type HSV-1, rRp450 replication was attenuated approximately 10,000-fold in human primary hepatocytes, differentiated primary foreskin keratinocytes, and primary Schwann cells. In vivo, intravenous and intracranial (IC) rRp450 injection at the strength of 10(8) plaque-forming units (pfu) alone or followed 24 hours later by intraperitoneal (IP) CPA was well tolerated and had no significant effect clinically on blood counts or chemistries. By contrast, intravenous KOS was found to be uniformly neurotoxic at 10(5) and fatal at 10(6) pfu, and IC virus was fatal in most mice at 10(4) pfu. Low levels of virus DNA were detected in some organs following intravenous and IC virus injection, but were not significantly altered by CPA. HSV replication was not detected in reactivation studies of isolated organs. Our findings suggest rRp450/CPA is safe and warrants further study as a potential combination in anticancer therapeutics.

Feasibility of herpes simplex virus type 1 mutants labeled with radionuclides for tumor treatment

For over one hundred years, viruses have been recognized as capable of killing tumor cells. At present, people are still researching and constructing more suitable oncolytic viruses for treating different malignant tumors. Although extensive studies have demonstrated that herpes simplex virus type 1 (HSV-1) is the most potential oncolytic virus, therapies based on herpes simplex virus type 1 vectors still arouse bio-safety and risk management issues. Researchers have therefore introduced the new idea of treating cancer with HSV-1 mutants labeled with radionuclides, combining radionuclide and oncolytic virus therapies. This overview briefly summarizes the status and mechanisms by which oncolytic viruses kill tumor cells, discusses the application of HSV-1 and HSV-1 derived vectors for tumor therapy, and demonstrates the feasibility and prospect of HSV-1 mutants labeled with radionuclides for treating tumors.

[Oncolytic virotherapy: new strategies in oncology]

The introduction of new therapeutical approaches to the medical practice has never been an easy task. On the one hand, modern therapies have to fulfil the strict requirements of the industry, on the other, patients and therapists have usually high expectations towards them. Thus, the public's initial euphoric emotions can quickly turn into pessimism following the experience of the first complications and difficulties of the new therapeutic method. Regarding oncolytic virotherapy, the emerging troubles and the lack of complete success upon the first clinical trials also led to the rejection of this promising new approach to the treatment of cancer. In the last few decades, however, due to the advances in molecular and cell biology, oncolytic virotherapy has been put in the lime-light again, and some of the newly developed virotherapeutic agents have been tested in various clinical trials all around the world. This review focuses on the current situation of the field and summarizes the available results.

Systemic Therapy of Spontaneous Prostate Cancer in Transgenic Mice with Oncolytic Herpes Simplex Viruses

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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.

Imaging and therapy of malignant pleural mesothelioma using replication-competent herpes simplex viruses

BACKGROUND

Malignant pleural mesothelioma (MPM) is an aggressive cancer that is refractory to current treatment modalities. Oncolytic herpes simplex viruses (HSV) used for gene therapy are genetically engineered, replication-competent viruses that selectively target tumor cells while sparing normal host tissue. The localized nature, the potential accessibility and the relative lack of distant metastasis make MPM a particularly suitable disease for oncolytic viral therapy.

METHODS

The infectivity, selective replication, vector spread and cytotoxic ability of three oncolytic HSV: G207, NV1020 and NV1066, were tested against eleven pathological types of MPM cell lines including those that are resistant to radiation therapy, gemcitabine or cisplatin. The therapeutic efficacy and the effect on survival of NV1066 were confirmed in a murine MPM model.

RESULTS

All three oncolytic HSV were highly effective against all the MPM cell lines tested. Even at very low concentrations of MOI 0.01 (MOI: multiplicity of viral infection, ratio of viral particles per cancer cell), HSV were highly effective against MPM cells that are resistant to radiation, gemcitabine and cisplatin. NV1066, an oncolytic HSV that expresses green fluorescent protein (GFP), was able to delineate the extent of the disease in a murine model of MPM due to selective infection and expression of GFP in tumor cells. Furthermore, NV1066 was able to reduce the tumor burden and prolong survival even when treatment was at an advanced stage of the disease.

CONCLUSION

These findings support the continued investigation of oncolytic HSV as potential therapy for patients with therapy-resistant MPM.

Real-time intraoperative detection of breast cancer axillary lymph node metastases using a green fluorescent protein-expressing herpes virus

OBJECTIVE

To investigate the use of a green fluorescent protein (GFP)-expressing oncolytic herpes virus to enable real-time intraoperative detection of breast cancer lymph node metastases.

SUMMARY BACKGROUND DATA

Axillary lymph node status is the most important factor determining treatment, recurrence, and overall survival for women with breast cancer. The current methods of determining nodal status, however, have limitations. NV1066 is a novel oncolytic herpes viral strain that specifically infects cancer cells and expresses GFP.

METHODS

Seven human breast cancer cell lines were infected in vitro with NV1066 and assessed for GFP expression, viral replication, and cytotoxicity. An in vivo model of breast cancer lymphatic metastasis was established in mice. Tumor-bearing mice were treated with NV1066 via injection into the primary tumor. Axillary lymph nodes were analyzed using an in vivo fluorescent imaging system. Histologic and molecular assessment of lymph nodes were performed using immunohistochemistry and reverse transcriptase PCR and operating characteristics were determined.

RESULTS

NV1066 infected, expressed GFP, replicated within, and killed all human breast cancer cell lines in vitro. Injection of NV1066 into primary breast tumors resulted in viral transit to axillary lymph nodes, infection of lymphatic metastases, and GFP expression that was visualized with in vivo fluorescent imaging. Histologic and molecular confirmation demonstrated favorable operating characteristics of this method (sensitivity 80%; specificity 96%).

CONCLUSIONS

We introduce a novel, sensitive, and specific method of lymphatic mapping that utilizes NV1066-guided cancer cell-specific viral production of GFP to enable real-time intraoperative detection of lymphatic metastases.

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.

Herpes simplex virus 1 (HSV-1) for cancer treatment

Cancer remains a serious threat to human health, causing over 500 000 deaths each year in US alone, exceeded only by heart diseases. Many new technologies are being developed to fight cancer, among which are gene therapies and oncolytic virotherapies. Herpes simplex virus type 1 (HSV-1) is a neurotropic DNA virus with many favorable properties both as a delivery vector for cancer therapeutic genes and as a backbone for oncolytic viruses. Herpes simplex virus type 1 is highly infectious, so HSV-1 vectors are efficient vehicles for the delivery of exogenous genetic materials to cells. The inherent cytotoxicity of this virus, if harnessed and made to be selective by genetic manipulations, makes this virus a good candidate for developing viral oncolytic approach. Furthermore, its large genome size, ability to infect cells with a high degree of efficiency, and the presence of an inherent replication controlling mechanism, the thymidine kinase gene, add to its potential capabilities. This review briefly summarizes the biology of HSV-1, examines various strategies that have been used to genetically modify the virus, and discusses preclinical as well as clinical results of the HSV-1-derived vectors in cancer treatment.

Oncolytic herpes simplex virus vector g47delta in combination with androgen ablation for the treatment of human prostate adenocarcinoma

PURPOSE

The use of oncolytic herpes simplex virus type 1 is a promising stategy for cancer treatment. We constructed herpes simplex virus type 1 vector G47Delta by deleting the alpha47 gene and the promoter region of US11 from G207. We now report studies demonstrating the potential of G47Delta as a therapeutic modality for prostate cancer in combination with androgen ablation.

EXPERIMENTAL DESIGN

The cytopathic activities of G47Delta at low multiplicities of infection was tested in human prostate cancer cell lines LNCaP, PC-3, and DU145 in vitro. Two androgen-dependent mouse s.c. tumor models, murine TRAMP and human HONDA, were used to investigate the in vivo efficacy of G47Delta in combination with androgen ablation.

RESULTS

G47Delta at low multiplicities of infection showed more rapid tumor cell killing than G207 in LNCaP and DU145 in vitro and showed a 22-fold higher virus yield in a single-step growth experiment. In vivo, G47Delta treatment resulted in reduced tumor growth of established s.c. TRAMP and HONDA tumors and inhibited the growth of recurrent HONDA tumors that once regressed by androgen ablation therapy. In both TRAMP and HONDA tumor xenografts, the combination therapy of G47Delta with androgen ablation led to significantly enhanced inhibition of the tumor growth and prolonged survival.

CONCLUSIONS

These results suggest that oncolytic virus therapy with G47Delta can be usefully combined with androgen ablation therapy for the treatment of prostate cancer.

Oncolytic viruses derived from the gamma34.5-deleted herpes simplex virus recombinant R3616 encode a truncated UL3 protein

Replication-competent herpes simplex virus (HSV-1) mutants are used in clinical trials in the experimental treatment of cancer. Mutants G207, HSV1716, NV1020, and Oncovex GM-CSF share in common a defect in one or both copies of the gene encoding the neurovirulence factor, ICP34.5, and are thus neuroattenuated. These viruses are acknowledged to differ from one another (a) in the specific types of mutations intentionally introduced during their derivation and (b) in the inherent genetic differences retained from the different parent strains used in their construction. Unintended mutations are expected to emerge at some low frequency during the selection for and passage of mutant viruses. Here we demonstrate that during the construction of the oncolytic virus R3616, a nonsense mutation arose in an untargeted region of the HSV-1 genome that resulted in a substantial truncation of the viral protein known as UL3. This report is the first published documentation that oncolytic herpesviruses developed and used in clinical trials contain adventitious mutations. The implications of these findings for the characterization and development of vectors proposed for use in clinical trials are discussed.

Treatment of Schwannomas with an Oncolytic Recombinant Herpes Simplex Virus in Murine Models of Neurofibromatosis Type 2

Gene therapy for schwannomas was evaluated in two mouse models of neurofibromatosis type 2 (NF2): (1) a transgenic model in which mice express a dominant mutant form of merlin and spontaneously develop schwannomas, and (2) a xenograft model in which human schwannoma tissue is implanted subcutaneously into immune- compromised mice. In both models, schwannoma volumes were monitored by magnetic resonance imaging (MRI) and showed strong gadolinium enhancement typical of these tumors in humans. Both types of tumor were positive for the Schwann cell marker S100, and highly infectable with herpes simplex virus (HSV) vectors. Schwannomas were injected with an oncolytic HSV-1 recombinant virus vector, G47Delta, which has deletions in genes for ribonucleotide reductase (ICP6), gamma34.5, and ICP47. In the NF2 transgenic model, schwannomas were reduced by more than half their original size by 10 days after infection. In the case of subcutaneous schwannoma xenografts, reduction in size after infection occurred more slowly, with a mean reduction of onethird by 42 days after treatment. Schwannomas injected with control vehicles continued to grow slowly over time in both schwannoma models. These studies demonstrate the ability of an oncolytic recombinant HSV vector to reduce the volume of schwannoma tumors in NF2 tumor models in mice and extend the possible therapeutic applications of oncolytic vectors for benign tumors to reduce mass while minimizing nerve damage.

5-fluorouracil and gemcitabine potentiate the efficacy of oncolytic herpes viral gene therapy in the treatment of pancreatic cancer

Oncolytic herpes viruses are attenuated, replication-competent viruses that selectively infect, replicate within, and lyse cancer cells and are highly efficacious in the treatment of a wide variety of experimental cancers. The current study seeks to define the pharmacologic interactions between chemotherapeutic drugs and the oncolytic herpes viral strain NV1066 in the treatment of pancreatic cancer cell lines. The human pancreatic cancer cell lines Hs 700T, PANC-1, and MIA PaCa-2 were treated in vitro with NV1066 at multiplicities of infection (MOI; ratio of the number of viral particles per tumor cell) ranging from 0.01 to 1.0 with or without 5-fluorouracil (5-FU) or gemcitabine. Synergistic efficacy was determined by the isobologram and combination-index methods of Chou and Talalay. Viral replication was measured using a standard plaque assay. Six days after combination therapy, 76% of Hs 700T cells were killed compared with 43% with NV1066 infection alone (MOI = 0.1) or 0% with 5-FU alone (2 micromol/L) (P < .01). Isobologram and combination-index analyses confirmed a strongly synergistic pharmacologic interaction between the agents at all viral and drug combinations tested (LD5 to LD95) in the three cell lines. Dose reductions up to 6- and 78-fold may be achieved with combination therapy for NV1066 and 5-FU, respectively, without compromising cell kill. 5-FU increased viral replication up to 19-fold compared with cells treated with virus alone. Similar results were observed by combining gemcitabine and NV1066. We have demonstrated that 5-FU and gemcitabine potentiate oncolytic herpes viral replication and cytotoxicity across a range of clinically achievable doses in the treatment of human pancreatic cancer cell lines. The potential clinical implications of this synergistic interaction include improvements in efficacy, treatment-associated toxicity, tolerability of therapeutic regimens, and quality of life. These data provide the cellular basis for the clinical investigation of combined oncolytic herpes virus therapy and chemotherapy in the treatment of pancreatic cancer.

The potential of oncolytic virus therapy for pancreatic cancer

The objective of this paper was to review a new category of gene therapy using oncolytic viruses for the treatment of pancreatic cancer. The eligibility and feasibility of oncolytic virus therapy as a novel therapeutic agent against pancreatic cancer are discussed as well as basic research for clinical trials, including a historical perspective and the current status of these novel agents. Even combination therapy, such as surgery with radiation and chemotherapy, has not significantly improved the survival rate of pancreatic cancer. Recently, a clinical trial (phase I and II) using an oncolytic adenovirus, ONYX-015, was completed in patients with pancreatic cancer. The phase II trial yielded beneficial results (tumor reduction or stabilization) in about 50% of the patients. A phase I study of the efficacy of oncolytic herpes viruses, G207, OncoVEX GM-CSF, and 1716 against a variety of tumors has been completed, and G207 is in phase II trials for use against brain tumors. In addition, a phase I trial using the herpesvirus showed good tolerance at all dosages. We discuss the basic scientific principles and current results of the above clinical trials with respect to these oncolytic viruses, and then compare the relative advantages and disadvantages of adenoviruses and herpesviruses as oncolytic agents. We also review the published literature on newly developed oncolytic viruses. The concept of oncolytic therapy has been studied for a century. Recent technological developments have made these oncolytic viruses more tumor-specific by exploiting the tumor cell environments. In addition, these viruses have been reported to increase the immunosusceptibility of the tumor cells, and have been designed to express other genes to increase the susceptibility of tumor cells to other therapeutic agents. Oncolytic virus therapy certainly appears to be a feasible treatment for pancreatic cancer.

Regulatory Aspects in the Development of Gene Therapies

Preclinical therapeutics development research is directed toward fulfilling two overlapping sets of goals. A set of scientific goals includes defining the best molecule or biologic construct for the task at hand, and proving the case for its development. The second set of goals addresses regulatory requirements necessary to introduce the agent into human subjects. In the case of “small molecule” drugs, in most cases the identity of the molecule and appropriate safety studies are straightforward. In contrast, the development of biologic agents, including gene therapies discussed here, presents distinct challenges. The nature of the “drug” may be an organism subject to mutation or selection of variants through recombination. Its properties may vary depending on the scale and method of its preparation, purification, and storage. How to test adequately for its safety prior to first introduction in humans may not be straightforward owing to intrinsic differences in response to the agent expected in humans as compared to animals.

Gene transfer vector biodistribution: pivotal safety studies in clinical gene therapy development

Techniques allowing for gene transfer vectors biodistribution investigation, in the frame of preclinical gene therapy development, are exposed. Emphasis is given on validation and test performance assessment. In the second part, specific gene vector distribution properties are reviewed (adenovirus, AAV, plasmid, retroviruses, herpes-derived vectors, germline transmission risks). The rationale for biodistribution by quantitative PCR, animal study and result interpretation is discussed. The importance and pivotal role of biodistribution study in gene transfer medicine development is shown through the determination of target organs for toxicity, germline transmission assessment and determination of risks of shedding and spreading of vectors in the gene transfer recipient and the environment.

Endocrine aspects of cancer gene therapy

The field of cancer gene therapy is in continuous expansion, and technology is quickly moving ahead as far as gene targeting and regulation of gene expression are concerned. This review focuses on the endocrine aspects of gene therapy, including the possibility to exploit hormone and hormone receptor functions for regulating therapeutic gene expression, the use of endocrine-specific genes as new therapeutic tools, the effects of viral vector delivery and transgene expression on the endocrine system, and the endocrine response to viral vector delivery. Present ethical concerns of gene therapy and the risk of germ cell transduction are also discussed, along with potential lines of innovation to improve cell and gene targeting.

Evolution of a gene therapy clinical trial. From bench to bedside and back

Developing and conducting gene therapy clinical trials poses unique challenges which must be addressed to satisfy regulatory requirements and, most importantly, to protect human subjects. Experimental products used for gene transfer studies, such as viral vectors, are often complex and cannot be sterilized or completely characterized to the extent of a typical pharmaceutical. Thus, quality and characterization must be built into the production process. Extensive preclinical studies must be performed to determine the feasibility of the approach, the safety of the product, and the appropriate dose range to evaluate in humans. Once a clinical trial is initiated, subjects must be followed carefully for short- and long-term toxicity especially since preclinical studies may not adequately predict the toxicity profile of these novel, complicated products. Results of early phase studies in gene therapy have often sent the investigators back to the laboratory to improve the delivery vector or identify a more potent or less toxic gene. This circular developmental process is expected for the early stages of a new technology such as gene therapy. Although these hurdles appear extensive, they can be overcome, as evidenced by the initiation of more than 500 clinical gene therapy trials in the United States to date, and are imperative for the maintenance of high-quality studies and public trust. This article describes the step-by-step process for developing a gene therapy trial incorporating specific examples relevant to neuro-oncology.

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.

Herpes simplex virus type-1 infection upregulates cellular promoters and telomerase activity in both tumor and nontumor human cells

Targeted gene expression through viral vectors has been a promising approach for gene therapy. However, the effects of viral gene products expressed from virus vectors on the expression of the host gene are not well known. In the present study, we examined the activities of cellular promoters, including the promoter for genes of human telomerase reverse transcriptase (hTERT), tyrosinase and probasin, in both tumor and normal cells after infection with herpes simplex virus type 1 (HSV-1) vectors. Our results showed that infection with replication-defective HSV-1 vectors significantly upregulated the activity of all three cellular promoters in a nonsequence specific fashion in all cell types tested. Furthermore, viral infection upregulated activities of the hTERT promoter and endogenous telomerase in nontumoral cells. Additional experiments suggested that the viral immediate-early gene product, infected cell protein 0, might be responsible for the deregulation of cellular promoter activity and activation of telomerase. Our study alerts to the potential risk of oncogenesis through deregulation of host gene expression, such as the telomerase by viral vectors in normal cells.

Gene therapy for mice sarcoma with oncolytic herpes simplex virus-1 lacking the apoptosis-inhibiting gene, icp34.5

A mutant herpes simplex virus 1, mtHSV, was constructed by inserting the E. coli beta-galactosidase gene into the loci of icp34.5, the apoptosis-inhibiting gene of HSV. The mtHSV replicated in and lysed U251 (human glioma cells), EJ (human bladder cells), and S-180 (mice sarcoma cells), but not Wish (human amnion cells) cells. With its intact tk (thymidine kinase) gene, mtHSV exhibited susceptibility to acyclovir (ACV), which provided an approach to control viral replication. An in vivo test with mtHSV was conducted in immune-competent mice bearing sarcoma S-180 tumors, which were treated with a single intratumoral injection of mtHSV or PBS. Tumor dimensions then were measured at serial time points, and the tumor volumes were calculated. Sarcoma growth was significantly inhibited with prolonged time and reduced tumor volume. There was microscopic evidence of necrosis of tumors in treated mice, whereas no damage was found in other organs. Immunohistochemical staining revealed that virus replication was exclusively confined to the treated tumor cells. HSV-1 DNA was detected in tumors, but not in the other organs by a polymerase chain reaction analysis. From these experiments, we concluded that mtHSV should be a safe and promising oncolytic agent for cancer treatment.

Highly efficient and tumor-restricted gene transfer to malignant gliomas by replication-competent retroviral vectors

The first large randomized phase III trial in gene therapy demonstrated no improvement in the survival of patients injected with packaging cells that produced conventional replication-defective retroviral vectors carrying the herpes simplex virus thymidine kinase gene, a disappointing result that was attributed to extremely poor levels of transduction efficiency. To circumvent this problem, we have developed a modified replication-competent retrovirus (RCR) that is capable of transducing human glioma cell lines A-172, U-87, T-98G, U-373, and U-138 and rat glioma cell lines C6 and 9L, over multiple infection cycles in vitro, resulting in a tremendous enhancement in transduction efficiency over conventional replication-defective retroviral vectors at the same dose. Whereas the transduction efficiency of conventional retroviral vectors injected into preestablished subcutaneous U-87 tumors at a dose of 1.0 x 10(5) transducing units (TU) was only 0.2% at 6 weeks postinjection, the same dose of RCR vector resulted in up to 97.2% transduction. When RCR vectors at a dose of 1.0 x 10(4) TU were injected into preestablished intracranial U-87 tumors, transduction efficiency at 2 and 3 weeks was 74 and 98.1%, respectively. Notably, however, intracranial injection of RCR vectors did not result in detectable infection of normal brain cells. Furthermore, using a sensitive polymerase chain reaction assay, no detectable RCR signal could be observed in any extracerebral tissues, including lung, liver, kidney, upper gastrointestinal tract (esophagus and stomach), lower gastrointestinal tract (colon and small intestine), skin, spleen, and bone marrow. Treatment of U-87 intracranial gliomas with RCR vectors carrying the yeast cytosine deaminase suicide gene followed by 5-fluorocytosine prodrug administration resulted in 100% survival over a 60-day follow-up period, compared with 0% survival of control groups receiving vector alone or prodrug alone. Our results demonstrate that RCR vectors can achieve therapeutically significant levels of transduction in malignant human gliomas, and that RCR vector spread after intratumoral injection is restricted to the tumor itself.

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.

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.

Oncolytic virus therapy using genetically engineered herpes simplex viruses

An increasing number of oncolytic virus vectors has been developed lately for cancer therapy. Herpes simplex virus type 1 (HSV-1) vectors are particularly useful, because they can be genetically engineered to replicate and spread highly selectively in tumor cells and can also express multiple foreign transgenes. These vectors can manifest cytopathic effect in a wide variety of tumor types without damaging normal tissues, provide amplified gene delivery within the tumor, and induce specific antitumor immunity. Multiple recombinant HSV-1 vectors have been tested in patients with brain tumors and other cancers, which showed the feasibility of administering replication-competent HSV-1 vectors safely in human organs including the brain. Different approaches are currently undertaken to improve the efficacy of oncolytic HSV-1 therapy which include development of new generation vectors via further genetic engineering of existing safe vectors, combination with immune gene therapy, and combination with conventional therapies. Oncolytic virus therapy is a promising therapeutic modality that awaits establishing as an important treatment option for cancer patients in the near future.

A herpes simplex virus type 1 mutant with gamma 34.5 and LAT deletions effectively oncolyses human U87 glioblastomas in nude mice

OBJECTIVE

We previously constructed a novel recombinant herpes simplex virus with deletions in the gamma 34.5 and LAT genes. LAT was replaced by the gene for green fluorescent protein, to allow monitoring of viral transduction in vitro and in vivo. We previously confirmed that this virus, designated DM33, retains its oncolytic properties in vitro and is inhibited with respect to spontaneous reactivation. The objective of this study was to demonstrate the therapeutic efficiency of this virus in the treatment of human gliomas in nude mice.

METHODS

Thirty BALB/c nude mice underwent stereotactic implantation of U-87 MG gliomas in the right corpus striatum. Subsequently, mice received intratumoral inoculations of either DM33 (n = 20) or virus-free medium (n = 10). Ten mice given injections of DM33 were also treated intraperitoneally with ganciclovir.

RESULTS

Intratumoral administration of DM33 to nude mice bearing intracranial U-87 MG human gliomas prolonged survival times, compared with saline-treated control animals (P < 0.05). Histological analyses of treated tumors demonstrated decreased tumor size and tumor cell lysis. Control tumors averaged 7.05 +/- 0.83 mm(2) (mean +/- standard error), whereas the average for the DM33 group was 4.61 +/- 1.57 mm(2) and that for the DM33 plus ganciclovir group was 2.49 +/- 1.32 mm(2). The difference in tumor sizes between the control group and the DM33 plus ganciclovir group was statistically significant (P = 0.044). Viral infection was limited to the tumors, and replication was not observed in normal neurons or glia.

CONCLUSION

The efficacy of this virus in the treatment of experimental gliomas, its safety (as confirmed by its inability to reactivate), and its attenuated neurovirulence make DM33 a promising oncolytic agent for glioma therapy.