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

Oncolyic Virotherapy for Prostate Cancer: Lighting a Fire in Winter

As the most common cancer of the genitourinary system, prostate cancer (PCa) is a global men's health problem whose treatments are an urgent research issue. Treatment options for PCa include active surveillance (AS), surgery, endocrine therapy, chemotherapy, radiation therapy, immunotherapy, etc. However, as the cancer progresses, the effectiveness of treatment options gradually decreases, especially in metastatic castration-resistant prostate cancer (mCRPC), for which there are fewer therapeutic options and which have a shorter survival period and worse prognosis. For this reason, oncolytic viral therapy (PV), with its exceptional properties of selective tumor killing, relatively good safety in humans, and potential for transgenic delivery, has attracted increasing attention as a new form of anti-tumor strategy for PCa. There is growing evidence that OV not only kills tumor cells directly by lysis but can also activate anticancer immunity by acting on the tumor microenvironment (TME), thereby preventing tumor growth. In fact, evidence of the efficacy of this strategy has been observed since the late 19th century. However, subsequently, interest waned. The renewed interest in this therapy was due to advances in biotechnological methods and innovations at the end of the 20th century, which was also the beginning of PCa therapy with OV. Moreover, in combination with chemotherapy, radiotherapy, gene therapy or immunotherapy, OV viruses can have a wide range of applications and can provide an effective therapeutic result in the treatment of PCa.

The phosphatase and tensin homolog gene inserted between NP and P gene of recombinant New castle disease virus oncolytic effect test to glioblastoma cell and xenograft mouse model

Background

Glioblastoma is one of the most serious brain cancer. Previous studies have demonstrated that PTEN function disorder affects the causing and exacerbation of glioblastoma. Newcastle disease virus (NDV) has been studied as a cancer virotherapeutics. In this study, PTEN gene was delivered to glioblastoma by recombinant NDV (rNDV) and translated into protein at the cytoplasm of the glioblastoma.

Methods

We did comparison tests PTEN protein expression efficiency and oncolytic effect depend on the PTEN gene insertion site at the between NP and P genes and the between P and M gene. PTEN protein mRNA transcription, translation in glioblastoma cell, and functional PTEN protein effect of the rNDV in vitro and in vivo test performed using western blotting, RT-qPCR, MTT assay, and Glioblastoma xenograft animal model test.

Results

The result of this study demonstrates that rNDV-PTEN kills glioblastoma cells and reduces cancer tissue better than rNDV without the PTEN gene. In molecular immunological and cytological assays, PTEN expression level was high at located in the between NP and P gene, and PTEN gene was successfully delivered to the glioblastoma cell using rNDV and PTEN gene translated to functional protein and inhibits hTERT and AKT gene.

Conclusions

PTEN gene enhances the oncolytic effect of the rNDV. And our study demonstrated that NP and P gene site is better than P and M gene site which is commonly and conventionally used. PTEN gene containing rNDV is a good candidate virotherapeutics for glioblastoma.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12985-022-01746-w.

In Situ Cancer Vaccination and Immunovirotherapy Using Oncolytic HSV

Herpes simplex virus (HSV) can be genetically altered to acquire oncolytic properties so that oncolytic HSV (oHSV) preferentially replicates in and kills cancer cells, while sparing normal cells, and inducing anti-tumor immune responses. Over the last three decades, a better understanding of HSV genes and functions, and improved genetic-engineering techniques led to the development of oHSV as a novel immunovirotherapy. The concept of in situ cancer vaccination (ISCV) was first introduced when oHSV was found to induce a specific systemic anti-tumor immune response with an abscopal effect on non-injected tumors, in the process of directly killing tumor cells. Thus, the use of oHSV for tumor vaccination in situ is antigen-agnostic. The research and development of oHSVs have moved rapidly, with the field of oncolytic viruses invigorated by the FDA/EMA approval of oHSV talimogene laherparepvec in 2015 for the treatment of advanced melanoma. Immunovirotherapy can be enhanced by arming oHSV with immunomodulatory transgenes and/or using them in combination with other chemotherapeutic and immunotherapeutic agents. This review offers an overview of the development of oHSV as an agent for ISCV against solid tumors, describing the multitude of different oHSVs and their efficacy in immunocompetent mouse models and in clinical trials.

Targeted Delivery of IL-12 Adjuvants Immunotherapy by Oncolytic Viruses

The great hopes raised by the discovery of the immunoregulatory cytokine interleukin 12 (IL-12) as an anticancer agent were marred during early clinical experimentation because of severe adverse effects, which prompted a search for alternative formulations and routes of administration. Onco-immunotherapeutic viruses (OIVs) are wild-type or genetically engineered viruses that exert antitumor activity by causing death of the tumor cells they infect and by overcoming a variety of immunosuppressive mechanisms put in place by the tumors. OIVs have renewed the interest in IL-12, as they offer the opportunity to encode the cytokine transgenically from the viral genome and to produce it at high concentrations in the tumor bed. A large body of evidence indicates that IL-12 serves as a potent adjuvant for the immunotherapeutic response elicited by OIVs in murine tumor models. The list of OIVs includes onco-immunotherapeutic herpes simplex, adeno, measles, Newcastle disease, and Maraba viruses, among others. The large increase in IL-12-mediated adjuvanticity was invariably observed for all the OIVs analyzed. Indirect evidence suggests that locally delivered IL-12 may also increase tumor antigenicity. Importantly, the OIV/IL-12 treatment was not accompanied by adverse effects and elicited a long-lasting immune response capable of halting the growth of distant tumors. Thus, OIVs provide an avenue for reducing the clinical toxicity associated with systemic IL-12 therapy, by concentrating the cytokine at the site of disease. The changes to the tumor microenvironment induced by the IL-12-armed OIVs primed the tumors to an improved response to the checkpoint blockade therapy, suggesting that the triple combination is worth pursuing in the future. The highly encouraging results in preclinical models have prompted translation to the clinic. How well the IL-12-OIV-checkpoint inhibitors' combination will perform in humans remains to be fully investigated.

The discovery and development of oncolytic viruses: are they the future of cancer immunotherapy?

Introduction: Despite diverse treatment modalities and novel therapies, many cancers and patients are not effectively treated. Cancer immunotherapy has recently achieved breakthrough status yet is not effective in all cancer types or patients and can generate serious adverse effects. Oncolytic viruses (OVs) are a promising new therapeutic modality that harnesses virus biology and host interactions to treat cancer. OVs, genetically engineered or natural, preferentially replicate in and kill cancer cells, sparing normal cells/tissues, and mediating anti-tumor immunity.Areas covered: This review focuses on OVs as cancer therapeutic agents from a historical perspective, especially strategies to boost their immunotherapeutic activities. OVs offer a multifaceted platform, whose activities are modulated based on the parental virus and genetic alterations. In addition to direct viral effects, many OVs can be armed with therapeutic transgenes to also act as gene therapy vectors, and/or combined with other drugs or therapies.Expert opinion: OVs are an amazingly versatile and malleable class of cancer therapies. They tend to target cellular and host physiology as opposed to specific genetic alterations, which potentially enables broad responsiveness. The biological complexity of OVs have hindered their translation; however, the recent approval of talimogene laherparepvec (T-Vec) has invigorated the field.

Herpes Simplex Virus Oncolytic Immunovirotherapy: The Blossoming Branch of Multimodal Therapy

Oncolytic viruses are smart therapeutics against cancer due to their potential to replicate and produce the needed therapeutic dose in the tumor, and to their ability to self-exhaust upon tumor clearance. Oncolytic virotherapy strategies based on the herpes simplex virus are reaching their thirties, and a wide variety of approaches has been envisioned and tested in many different models, and on a range of tumor targets. This huge effort has culminated in the primacy of an oncolytic HSV (oHSV) being the first oncolytic virus to be approved by the FDA and EMA for clinical use, for the treatment of advanced melanoma. The path has just been opened; many more cancer types with poor prognosis await effective and innovative therapies, and oHSVs could provide a promising solution, especially as combination therapies and immunovirotherapies. In this review, we analyze the most recent advances in this field, and try to envision the future ahead of oHSVs.

Oncolytic Virus Encoding a Master Pro-Inflammatory Cytokine Interleukin 12 in Cancer Immunotherapy

Oncolytic viruses (OVs) are genetically modified or naturally occurring viruses, which preferentially replicate in and kill cancer cells while sparing healthy cells, and induce anti-tumor immunity. OV-induced tumor immunity can be enhanced through viral expression of anti-tumor cytokines such as interleukin 12 (IL-12). IL-12 is a potent anti-cancer agent that promotes T-helper 1 (Th1) differentiation, facilitates T-cell-mediated killing of cancer cells, and inhibits tumor angiogenesis. Despite success in preclinical models, systemic IL-12 therapy is associated with significant toxicity in humans. Therefore, to utilize the therapeutic potential of IL-12 in OV-based cancer therapy, 25 different IL-12 expressing OVs (OV-IL12s) have been genetically engineered for local IL-12 production and tested preclinically in various cancer models. Among OV-IL12s, oncolytic herpes simplex virus encoding IL-12 (OHSV-IL12) is the furthest along in the clinic. IL-12 expression locally in the tumors avoids systemic toxicity while inducing an efficient anti-tumor immunity and synergizes with anti-angiogenic drugs or immunomodulators without compromising safety. Despite the rapidly rising interest, there are no current reviews on OV-IL12s that exploit their potential efficacy and safety to translate into human subjects. In this article, we will discuss safety, tumor-specificity, and anti-tumor immune/anti-angiogenic effects of OHSV-IL12 as mono- and combination-therapies. In addition to OHSV-IL12 viruses, we will also review other IL-12-expressing OVs and their application in cancer therapy.

Engineered oncolytic virus for the treatment of cholesteatoma: A pilot in vivo study

Objective

Determine if oncolytic herpes simplex virus (oHSV) can eradicate cholesteatoma (CHST) in a gerbil model.

Methods

An in vivo model of CHST was developed in Mongolian gerbils by combining Pseudomonas aeruginosa inoculation with double ligation of the external auditory canal (EAC). CHST size and bone thickness were measured using morphometric and volumetric quantification techniques via micro‐computed tomography (micro‐CT). The CHST induction and quantification techniques were then used in an additional group of 10 gerbils (n = 20 ears) to determine the within‐group treatment efficacy of oHSV against CHST in vivo. Treated animals received either one, two, or three intrabullar injections of oHSV between 2 and 6 weeks postinduction of CHST.

Results

The P. aeruginosa inoculation plus double EAC ligation technique successfully induced a range of CHST growth in 100% of the ears in the model‐development group. Osteolytic effects of CHST were observed in 6% of ears whereas osteoblastic effects were observed in 31% of ears. CHST volume decreased by 50% or more in 12 of the 20 ears in the oHSV‐treatment groups. An apparent reversal of osteoblastic effects was also observed in three out of four ears 6 weeks following the third oHSV injection.

Conclusions

P. aeruginosa inoculation plus double EAC ligation reliably induces CHST formation in gerbil. CT‐based volumetric measures are significantly more accurate than single‐slice morphometric area measures for quantification of CHST size. Treatment with oHSV appears to be efficacious for reducing CHST volume by as much as 77% with as few as one treatment.

Level of Evidence

NA

Immunotherapeutic Challenges for Pediatric Cancers

Solid tumors contain a mixture of malignant cells and non-malignant infiltrating cells that often create a chronic inflammatory and immunosuppressive microenvironment that restricts immunotherapeutic approaches. Although childhood and adult cancers share some similarities related to microenvironmental changes, pediatric cancers are unique, and adult cancer practices may not be wholly applicable to our pediatric patients. This review highlights the differences in tumorigenesis, viral infection, and immunologic response between children and adults that need to be considered when trying to apply experiences from experimental therapies in adult cancer patients to pediatric cancers.

Oncolytic herpes simplex virus tumor targeting and neutralization escape by engineering viral envelope glycoproteins

Oncolytic herpes simplex viruses (oHSVs) have been approved for clinical usage and become more and more popular for tumor virotherapy. However, there are still many issues for the oHSVs used in clinics and clinical trials. The main issues are the limited anti-tumor effects, intratumor injection, and some side effects. To overcome such challenges, here we review the genetic engineering of the envelope glycoproteins for oHSVs to target tumors specifically, and at the same time we summarize the many neutralization antibodies against the envelope glycoproteins and align the neutralization epitopes with functional domains of the respective glycoproteins for future identification of new functions of the glycoproteins and future engineering of the epitopes to escape from host neutralization.

Oncolytic Herpes Simplex Virus and PI3K Inhibitor BKM120 Synergize to Promote Killing of Prostate Cancer Stem-like Cells

Novel therapies to override chemo-radiation resistance in prostate cancer (PCa) are needed. Prostate cancer sphere-forming cells (PCSCs) (also termed prostate cancer stem-like cells) likely participate in tumor progression and recurrence, and they are important therapeutic targets. We established PCSC-enriched spheres by culturing human (DU145) and murine (TRAMP-C2) PCa cells in growth factor-defined serum-free medium, and we characterized stem-like properties of clonogenicity and tumorigenicity. The efficacy of two different oncolytic herpes simplex viruses (oHSVs) (G47Δ and MG18L) in PCSCs was tested alone and in combination with radiation; chemotherapy; and inhibitors of phosphoinositide 3-kinase (PI3K), Wnt, and NOTCH in vitro; and, G47Δ was tested with the PI3K inhibitor BKM120 in a PCSC-derived tumor model in vivo. PCSCs were more tumorigenic than serum-cultured parental cells. Human and murine PCSCs were sensitive to oHSV and BKM120 killing in vitro, while the combination was synergistic. oHSV combined with radiation, docetaxel, Wnt, or NOTCH inhibitors was not. In athymic mice bearing DU145 PCSC-derived tumors, the combination of intra-tumoral G47Δ and systemic BKM120 induced complete regression of tumors in 2 of 7 animals, and it exhibited superior anti-tumor activity compared to either monotherapy alone, with no detectable toxicity. oHSV synergizes with BKM120 in killing PCSCs in vitro, and the combination markedly inhibits tumor growth, even inducing regression in vivo.

Recombinant adenovirus expressing a dendritic cell-targeted melanoma surface antigen for tumor-specific immunotherapy in melanoma mice model

Viral vectors represent a potential strategy for the treatment of human malignant tumors. Currently, recombinant adenovirus vectors are commonly used as gene therapy vehicles, as it possesses a proven safety profile in normal human cells. The recombinant adenovirus system has an ability to highly express exogenous genes and increase the stability of the carrier, which is only transiently expressed in the host cell genome, without integrating. Malignant melanoma cells are produced by the skin, and melanocyte tumors that exhibit higher malignant degrees lead to earlier transfer and higher mortality. In the present study, a recombinant adenovirus (rAd) was generated to express Anti-programmed death-1 (rAd-Anti-PD-1) and used to investigate the efficacy in melanoma cells and tumors. The results demonstrated that B16-F10 cell growth was significantly inhibited and the apoptosis incidence rate was markedly promoted following rAd-PD-1 treatment. The present study demonstrated that the production of α and β interferon was increased, which led to the induction of dendritic cell (DCs) maturation in rAd-anti-PD-1-treated mice. The present study indicated that rAd-anti-PD-1 exhibited the ability to generate more cluster of differentiation (CD)4⁺CD8⁺ T cells and induce a PD-1-specific cytotoxic T lymphocyte through DC-targeted surface antigens in mice. This resulted in a further enhanced recognition of melanoma cells due to DCs being targeted by the rAd-anti-PD-1-encoded PD-1. Notably, mice treated with the rAd-anti-PD-1-targeted PD-1 demonstrated an improved protection compared with tumor-bearing mice from the challenge group treated with a recombinant gutless adenovirus and Anti-PD-1. In conclusion, the present study demonstrated that targeting the melanoma surface antigens via the rAd-anti-PD-1-infected tumor cells enhanced the ability of recombinant adenovirus to induce a potent tumor-inhibitory effect and antigen-specific immune response.

Overexpression of p53 delivered using recombinant NDV induces apoptosis in glioma cells by regulating the apoptotic signaling pathway

Malignant glioma is the most common primary brain carcinoma in the world and has a poor survival rate. Previous studies have demonstrated that p53 dysfunction contributes to the development and severity of malignant glioma. It has also been demonstrated that Newcastle disease virus (NDV) may be a viable candidate for the treatment of various types of cancer. In the present study, a p53 oncolytic agent delivered using recombinant NDV (rNDV-p53) was constructed and its anti-tumor effects in vitro and in vivo were assessed. Glioma cell lines and a xenograft mouse model were utilized to assess the ability of p53 and rNDV to promote apoptosis and induce immunotherapy, respectively. The mechanism of rNDV-p53 in glioma therapy was investigated using quantitative polymerase chain reaction and immunohistochemistry. Tumor-specific cytotoxic T-lymphocyte (CTL) responses and lymphocyte infiltration were also analyzed in glioma-bearing models. The results of the present study demonstrate that rNDV-p53 may be a potential therapeutic agent that improves the prognosis of mice with glioma. It was revealed that rNDV-p53 inhibits glioma cell growth and aggressiveness in vitro and in vivo compared with rNDV and p53 alone. The results also demonstrated that rNDV-p53 induced glioma cell apoptosis by upregulating apoptosis-related genes. In addition, the present study demonstrated that rNDV-p53 significantly stimulated CTL responses and lymphocyte infiltration whilst increasing the number of apoptotic bodies in vivo. Furthermore, rNDV-p53 therapy inhibited tumor regression and prolonged the survival of glioma-bearing mice. In conclusion, rNDV-p53 invoked an immune response against glioma cells, which may serve as a comprehensive immunotherapeutic schedule for glioma.

The effects of interleukin 2 and rAd-p53 as a treatment for glioblastoma

Interleukin 2 (IL-2) is an anti-cancer cytokine that stimulates T cell propagation, triggering innate and adaptive immunity. IL-2 has been used for cancer therapy and has achieved curative effects. Recombinant adenovirus p53 injection (rAd‑p53) is a gene therapeutic agent that may improve the prognosis of patients with glioblastoma (GBM). In the present study, the effect of combined IL‑2 and rAd‑p53 treatment was studied. The ability of IL‑2 to stimulate immunoregulation and the ability of p53 to induce apoptosis for GBM was researched in the GBM tumor model. In addition, the activity of IL‑2 was analyzed. The antitumor potential of IL‑2 and rAd‑p53 was studied using xenograph mice carrying GBM cells. Tumor‑specific CD4+ and CD8+ T cells were also analyzed in the GBM‑bearing models. The results demonstrated that IL‑2 and rAd‑p53 not only stimulated tumor‑specific cytotoxic T‑lymphocyte responses and increased regulatory CD4+ and cytotoxic CD8+ T cell proliferation, however additionally increased expression of apoptosis‑associated genes. The treatment with IL‑2 and rAd‑p53 resulted in tumor regression and prolonged the survival of glioma‑bearing mice. Taken together, a combination of IL‑2 and rAd‑p53 treatment combines the effects of immunotherapy and oncolytic therapy and may be a comprehensive therapeutic schedule for clinical application in future cancer therapies.

Genetically engineered recombinant adenovirus expressing interleukin‑2 for hepatocellular carcinoma therapy

Regulatory and effector T cells possess immunological cytotoxicity for tumor cells in the tumor microenvironment during tumor progression and are the primary suppressors inhuman cancer therapy. Interleukin‑2 (IL‑2) is an anticancer cytokine, which triggers human innate and adaptive immunity by stimulating T cell propagation and lymphocyte infiltration into tumor sites. IL‑2 has been used successfully for cancer therapy. Recombinant adenovirus expressing IL‑2 (rAd‑IL‑2) injection is a gene therapy agent that may improve prognosis of hepatocellular carcinoma (HCC) patients. In the present study, the ability of IL‑2 to stimulate an immune response and the ability of recombinant adenovirus to inhibit tumor cell growth in HCC was investigated in a HCC tumor model. It was demonstrated that the regulatory and effector cell‑mediated tumor suppression by antitumor cluster of differentiation (CD)4+ and CD8+ T cells stimulated by rAd‑IL‑2 is tumor‑specific. Furthermore, rAd‑IL‑2 significantly stimulated tumor‑specific cytotoxic T lymphocyte responses, increased interferon‑γ release and enhanced antitumor immunity by inducing CD4+ and CD8+ T cell recruitment into the tumor, and additionally induced memory to protect tumor‑bearing mice against tumor challenge. Treatment with rAd‑IL‑2 led to tumor regression and long‑term survival of mice in the 120‑day treatment period. Tumor challenge experiments demonstrated that rAd‑IL‑2 induced memory, protecting against reinfection. In conclusion, rAd‑IL‑2 may promote tumor‑associated effector and regulatory T cell expansion and may be a potential therapeutic agent for clinical immunotherapy application in the treatment of cancer.

Stem cell-released oncolytic herpes simplex virus has therapeutic efficacy in brain metastatic melanomas

The recent Food and Drug Administration approval of immunogenic oncolytic virus (OV) has opened a new era in the treatment of advanced melanoma; however, approximately 50% of patients with melanoma develop brain metastasis, and currently there are no beneficial treatment options for such patients. To model the progression of metastases seen in patients and to overcome the hurdles of systemic delivery of OV, we developed melanoma brain metastasis models in immunocompromised and immunocompetent mice, and tested the fate and efficacy of oncolytic herpes simplex virus (oHSV)-armed mesenchymal stem cells (MSCs). Using brain-seeking patient-derived melanoma cells and real-time in vivo imaging, we show a widespread distribution of micrometastases and macrometastases in the brain, recapitulating the progression of multifoci metastases seen in patients. We armed MSCs with different oHSV variants (MSC-oHSV) and found that intracarotid administration of MSC-oHSV, but not of purified oHSV alone, effectively tracks metastatic tumor lesions and significantly prolongs the survival of brain tumor-bearing mice. In a syngeneic model of melanoma brain metastasis, a combination of MSC-oHSV and PD-L1 blockade increases IFNγ-producing CD8⁺ tumor-infiltrating T lymphocytes and results in a profound extension of the median survival of treated animals. This study thus demonstrates the utility of MSCs as OV carriers to disseminated brain lesions, and provides a clinically applicable therapeutic platform to target melanoma brain metastasis.

Systemic delivery of HER2-retargeted oncolytic-HSV by mesenchymal stromal cells protects from lung and brain metastases

Fully retargeted oncolytic herpes simplex viruses (o-HSVs) gain cancer-specificity from redirection of tropism to cancer-specific receptors, and are non-attenuated. To overcome the hurdles of systemic delivery, and enable oncolytic viruses (o-viruses) to reach metastatic sites, carrier cells are being exploited. Mesenchymal stromal cells (MSCs) were never tested as carriers of retargeted o-viruses, given their scarse-null expression of the cancer-specific receptors. We report that MSCs from different sources can be forcedly infected with a HER2-retargeted oncolytic HSV. Progeny virus spread from MSCs to cancer cells in vitro and in vivo. We evaluated the organ distribution and therapeutic efficacy in two murine models of metastatic cancers, following a single i.v. injection of infected MSCs. As expected, the highest concentration of carrier-cells and of viral genomes was in the lungs. Viral genomes persisted throughout the body for at least two days. The growth of ovarian cancer lung metastases in nude mice was strongly inhibited, and the majority of treated mice appeared metastasis-free. The treatment significantly inhibited also breast cancer metastases to the brain in NSG mice, and reduced by more than one-half the metastatic burden in the brain.

Retargeting Strategies for Oncolytic Herpes Simplex Viruses

Most of the oncolytic herpes simplex viruses (HSVs) exhibit a high safety profile achieved through attenuation. They carry defects in virulence proteins that antagonize host cell response to the virus, including innate response, apoptosis, authophagy, and depend on tumor cell proliferation. They grow robustly in cancer cells, provided that these are deficient in host cell responses, which is often the case. To overcome the attenuation limits, a strategy is to render the virus highly cancer-specific, e.g., by retargeting their tropism to cancer-specific receptors, and detargeting from natural receptors. The target we selected is HER-2, overexpressed in breast, ovarian and other cancers. Entry of wt-HSV requires the essential glycoproteins gD, gH/gL and gB. Here, we reviewed that oncolytic HSV retargeting was achieved through modifications in gD: the addition of a single-chain antibody (scFv) to HER-2 coupled with appropriate deletions to remove part of the natural receptors' binding sites. Recently, we showed that also gH/gL can be a retargeting tool. The insertion of an scFv to HER-2 at the gH N-terminus, coupled with deletions in gD, led to a recombinant capable to use HER-2 as the sole receptor. The retargeted oncolytic HSVs can be administered systemically by means of carrier cells-forcedly-infected mesenchymal stem cells. Altogether, the retargeted oncolytic HSVs are highly cancer-specific and their replication is not dependent on intrinsic defects of the tumor cells. They might be further modified to express immunomodulatory molecules.

Widespread Non-Canonical Epigenetic Modifications in MMTV-NeuT Breast Cancer

Breast tumors in (FVB × BALB-NeuT) F1 mice have characteristic loss of chromosome 4 and sporadic loss or gain of other chromosomes. We employed the Illumina GoldenGate genotyping platform to quantitate loss of heterozygosity (LOH) across the genome of primary tumors, revealing strong biases favoring chromosome 4 alleles from the FVB parent. While allelic bias was not observed on other chromosomes, many tumors showed concerted LOH (C-LOH) of all alleles of one or the other parent on sporadic chromosomes, a pattern consistent with cytogenetic observations. Surprisingly, comparison of LOH in tumor samples relative to normal unaffected tissues from these animals revealed significant variegated (stochastic) deviations from heterozygosity (V-LOH) in every tumor genome. Sequence analysis showed expected changes in the allelic frequency of single nucleotide polymorphisms (SNPs) in cases of C-LOH. However, no evidence of LOH due to mutations, small deletions, or gene conversion at the affected SNPs or surrounding DNA was found at loci with V-LOH. Postulating an epigenetic mechanism contributing to V-LOH, we tested whether methylation of template DNA impacts allele detection efficiency using synthetic oligonucleotide templates in an assay mimicking the GoldenGate genotyping format. Methylated templates were systematically over-scored, suggesting that the observed patterns of V-LOH may represent extensive epigenetic DNA modifications across the tumor genomes. As most of the SNPs queried do not contain standard (CpG) methylation targets, we propose that widespread, non-canonical DNA modifications occur during Her2/neuT-driven tumorigenesis.

Paradoxical role of DNA methylation in activation of FoxA2 gene expression during endoderm development

The transcription factor FoxA2 is a master regulator of endoderm development and pancreatic beta cell gene expression. To elucidate the mechanisms underlying the activation of the FoxA2 gene during differentiation, we have compared the epigenetic status of undifferentiated human embryonic stem cells (hESCs), hESC-derived early endoderm stage cells (CXCR4+ cells), and pancreatic islet cells. Unexpectedly, a CpG island in the promoter region of the FoxA2 gene displayed paradoxically high levels of DNA methylation in expressing tissues (CXCR4+, islets) and low levels in nonexpressing tissues. This CpG island region was found to repress reporter gene expression and bind the Polycomb group protein SUZ12 and the DNA methyltransferase (DNMT)3b preferentially in undifferentiated hESCs as compared with CXCR4+ or islets cells. Consistent with this, activation of FoxA2 gene expression, but not CXCR4 or SOX17, was strongly inhibited by 5-aza-2'-deoxycytidine and by knockdown of DNMT3b. We hypothesize that in nonexpressing tissues, the lack of DNA methylation allows the binding of DNA methyltransferases and repressing proteins, such as Polycomb group proteins; upon differentiation, DNMT activation leads to CpG island methylation, causing loss of repressor protein binding. These results suggest a novel and unexpected role for DNA methylation in the activation of FoxA2 gene expression during differentiation.

Oncolytic viral therapy for pancreatic cancer: current research and future directions

The development of targeted agents and chemotherapies for pancreatic cancer has only modestly affected clinical outcome and not changed 5-year survival. Fortunately the genetic and molecular mechanisms underlying pancreatic cancer are being rapidly uncovered and are providing opportunities for novel targeted therapies. Oncolytic viral therapy is one of the most promising targeted agents for pancreatic cancer. This review will look at the current state of the development of these self-replicating nanoparticles in the treatment of pancreatic cancer.

CIB1 synergizes with EphrinA2 to regulate Kaposi's sarcoma-associated herpesvirus macropinocytic entry in human microvascular dermal endothelial cells

KSHV envelope glycoproteins interact with cell surface heparan sulfate and integrins, and activate FAK, Src, PI3-K, c-Cbl, and Rho-GTPase signal molecules in human microvascular dermal endothelial (HMVEC-d) cells. c-Cbl mediates the translocation of virus bound α3β1 and αVβ3 integrins into lipid rafts (LRs), where KSHV interacts and activates EphrinA2 (EphA2). EphA2 associates with c-Cbl-myosin IIA and augmented KSHV-induced Src and PI3-K signals in LRs, leading to bleb formation and macropinocytosis of KSHV. To identify the factor(s) coordinating the EphA2-signal complex, the role of CIB1 (calcium and integrin binding protein-1) associated with integrin signaling was analyzed. CIB1 knockdown did not affect KSHV binding to HMVEC-d cells but significantly reduced its entry and gene expression. In contrast, CIB1 overexpression increased KSHV entry in 293 cells. Single virus particle infection and trafficking during HMVEC-d cell entry was examined by utilizing DiI (envelope) and BrdU (viral DNA) labeled virus. CIB1 was associated with KSHV in membrane blebs and in Rab5 positive macropinocytic vesicles. CIB1 knockdown abrogated virus induced blebs, macropinocytosis and virus association with the Rab5 macropinosome. Infection increased the association of CIB1 with LRs, and CIB1 was associated with EphA2 and KSHV entry associated signal molecules such as Src, PI3-K, and c-Cbl. CIB1 knockdown significantly reduced the infection induced EphA2, Src and Erk1/2 activation. Mass spectrometry revealed the simultaneous association of CIB1 and EphA2 with the actin cytoskeleton modulating myosin IIA and alpha-actinin 4 molecules, and CIB1 knockdown reduced EphA2's association with myosin IIA and alpha-actinin 4. Collectively, these studies revealed for the first time that CIB1 plays a role in virus entry and macropinocytosis, and suggested that KSHV utilizes CIB1 as one of the key molecule(s) to coordinate and sustain the EphA2 mediated signaling involved in its entry, and CIB1 is an attractive therapeutic target to block KSHV infection.

Arming viruses in multi-mechanistic oncolytic viral therapy: current research and future developments, with emphasis on poxviruses

The field of oncolytic virology has made great strides in recent years. However, one key finding has been that the use of viral agents that replicate selectively in tumors is usually insufficient to achieve anything beyond small and transient responses. Instead, like most cancer therapies, oncolytic viruses are most effective in combination with other therapies, which is where they have proven therapeutic effects in clinical and preclinical studies. In cases of some of the smaller RNA viruses, effects can only be achieved through combination regimens with chemotherapy, radiotherapy, or targeted conventional therapies. However, larger DNA viruses are able to express one or more transgenes; thus, therapeutic mechanisms can be built into the viral vector itself. The incorporated approaches into arming oncolytic viruses through transgene expression will be the main focus of this review, including use of immune activators, prodrug converting enzymes, anti-angiogenic factors, and targeting of the stroma. This will focus on poxviruses as model systems with large cloning capacities, which have routinely been used as transgene expression vectors in different settings, including vaccine and oncolytic viral therapy.

HSV-NIS, an oncolytic herpes simplex virus type 1 encoding human sodium iodide symporter for preclinical prostate cancer radiovirotherapy

Several clinical trials have shown that oncolytic herpes simplex virus type 1 (oHSV-1) can be safely administered to patients. However, virus replication in tumor tissue has generally not been monitored in these oHSV clinical trials, and the data suggest that its oncolytic potency needs to be improved. To facilitate noninvasive monitoring of the in vivo spread of an oHSV and to increase its antitumor efficacy, the gene coding for human sodium iodide symporter (NIS) was incorporated into a recombinant oHSV genome and the corresponding virus (oHSV-NIS) rescued in our laboratory. Our data demonstrate that a human prostate cancer cell line, LNCap, efficiently concentrates radioactive iodine after the cells have been infected in vitro or in vivo. In vivo replication of oHSV-NIS in tumors was noninvasively monitored by computed tomography/single-photon emission computed tomography imaging of the biodistribution of pertechnetate and was confirmed. LNCap xenografts in nude mice were eradicated by intratumoral administration of oHSV-NIS. Systemic administration of oHSV-NIS prolonged the survival of tumor-bearing mice, and the therapeutic effect was further enhanced by administration of ¹³¹I after the intratumoral spread of the virus had peaked. oHSV-NIS has the potential to substantially enhance the outcomes of standard therapy for patients with prostate cancer.

Preclinical therapy of disseminated HER-2⁺ ovarian and breast carcinomas with a HER-2-retargeted oncolytic herpesvirus

Oncolytic viruses aim to specifically kill tumor cells. A major challenge is the effective targeting of disseminated tumors in vivo. We retargeted herpes simplex virus (HSV) tropism to HER-2 oncoprotein p185, overexpressed in ovary and breast cancers. The HER-2-retargeted R-LM249 exclusively infects and kills tumor cells expressing high levels of human HER-2. Here, we assessed the efficacy of systemically i.p. delivered R-LM249 against disseminated tumors in mouse models that recapitulate tumor spread to the peritoneum in women. The human ovarian carcinoma SK-OV-3 cells implanted intraperitoneally (i.p.) in immunodeficient Rag2⁻/⁻;Il2rg⁻/⁻ mice gave rise to a progressive peritoneal carcinomatosis which mimics the fatal condition in advanced human patients. I.p. administration of R-LM249 strongly inhibited carcinomatosis, resulting in 60% of mice free from peritoneal diffusion, and 95% reduction in the total weight of neoplastic nodules. Intraperitoneal metastases are a common outcome in breast cancer: i.p. administration of R-LM249 strongly inhibited the growth of ovarian metastases of HER-2+ MDA-MB-453 breast cells. Brain metastases were also reduced. Cumulatively, upon i.p. administration the HER-2-redirected oncolytic HSV effectively reduced the growth of ovarian and breast carcinoma disseminated to the peritoneal cavity.

Viral therapy for pancreatic cancer: tackle the bad guys with poison

Pancreatic cancer is one of the most devastating diseases with very poor prognosis. Only a small proportion is curable by surgical resection, whilst standard chemotherapy for patients with advanced disease has only modest effect with substantial toxicity. Therefore, there is an urgent need for the development of novel therapeutic approaches to improve the patient outcome. Recently the viral therapy is emerging as a novel effective therapeutic approach for cancer with the potential to selectively treat both primary tumor and metastatic lesions. This review provides an overview of the current status of viral treatment for pancreatic cancer, both in the laboratories and in clinical settings.

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 (oHSV)-1-based vectors selectively replicate in tumor cells causing direct killing, that is, oncolysis, while sparing normal cells. The oHSVs are 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 interleukin (IL)-12-secreting NV1042 oHSV with microtubule disrupting agents (MDAs) would be an effective means to enhance antitumor efficacy. Vinblastine (VB) was identified among several MDAs screened, which 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 human umbilical vein endothelial 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 with 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 antitumor and antiangiogenic activities of oHSVs and MDAs.

Combination of pet imaging with viral vectors for identification of cancer metastases

There are three main ways for dissemination of solid tumors: direct invasion, lymphatic spread and hematogenic spread. The presence of metastases is the most significant factor in predicting prognosis and therefore evidence of metastases will influence decision-making regarding treatment. Conventional imaging techniques are limited in the evaluation and localization of metastases due to their restricted ability to identify subcentimeter neoplastic disease. Hence, there is a need for an effective noninvasive modality that can accurately identify occult metastases in cancer patients. One such method is the combination of positron emission tomography (PET) with vectors designed for delivery of reporter genes into target cells. Vectors expressing the herpes simplex virus-1 thymidine kinase (HSV1-tk) reporter system have recently been shown to allow localization of micrometastases in animal models of cancer using non invasive imaging. Combination of HSV1-tk and PET imaging is based on the virtues of vectors which can carry and selectively express the HSV1-tk reporter gene in a variety of cancer cells but not in normal tissue. A radioactive tracer which is applied systemically is phosphorylated by the HSV1-tk enzyme, and as a consequence, the tracer accumulates in proportion to the level of HSV1-tk expression which can be imaged by PET. In this paper we review the recent developments in molecular imaging of micrometastases using replication-competent viral or nonviral vectors carrying the HSV1-tk gene using PET imaging. These diagnostic paradigms introduce an advantageous new concept in noninvasive molecular imaging with the potential benefits for improving patient care by providing guidance for therapy to patients with risk for metastases.

Combinational therapy: new hope for pancreatic cancer?

Pancreatic cancer is a devastating disease with a low overall survival rate. Chemotherapy is the most common treatment for patients presenting with advanced pancreatic cancer. Gemcitabine achieves a modest improvement in overall survival and is the gold standard for advanced pancreatic cancer treatment. Capecitabine and S-1, derivatives of 5-fluorouracil (5-FU), offers minimal clinical benefits. Folfirinox represents a new and aggressive regimen that might benefit patients of metastatic pancreatic cancer with good performance status. Other chemotherapy drugs such as platinums and irinotecan do not provide significant improvement in overall survival, but have been used as part of combinational therapies. Comparing to systemically delivered chemotherapy, regional intra-arterial chemotherapy achieves higher local drug concentration in tumors with lower systemic drug toxicity, and may serve as a better treatment regimen. Although there have been progress made in chemotherapeutic strategies against pancreatic cancer, the overall survival is not significantly improved in the last decade. Recently, development of chemotherapy in combination with molecular targeted therapies holds great promise in pancreatic cancer treatment, especially in patients with metastatic disease. Growing bodies of preclinical and clinical evidences indicate that the combination of conventional modalities with specific molecular targeted therapy increase the efficacy of the monotherapy without an increase in toxicity. In this review, we summarized the current regimens of chemotherapy and molecular targeted therapy for advanced pancreatic cancer and highlighted the novel combinational treatments tested in recent clinical trials.

Rethinking herpes simplex virus: the way to oncolytic agents

Oncolytic viruses infect, replicate in and kill cancer cells. HSV has emerged as a most promising candidate because it exerts a generally moderate pathogenicity in humans; it is amenable to attenuation and tropism retargeting; the ample genome provides space for heterologous genes; specific antiviral therapy is available in a worst case scenario. The first strategy to convert HSV into an oncolytic agent consisted in deletion of the γ(1) 34.5 gene which counteracts the protein kinase R (PKR) response, and of the UL39 gene which encodes the large ribonucleotide reductase subunit. Tumor specificity resided in low PKR activity, and high deoxyribonucleotides content of cancer cells. These highly attenuated viruses have been and presently are in clinical trials with encouraging results. The preferred route of administration has been intratumor or in tissues adjacent to resected tumors. Although the general population has a high seroprevalence of antibodies to HSV, studies in animals and humans demonstrate that prior immunity is not an obstacle to systemic routes of administration, and that oncolytic HSV (o-HSVs) do populate tumors. As the attenuated viruses undergo clinical experimentation, the research pipeline is developing novel, more potent and highly tumor-specific o-HSVs. These include viruses which overcome tumor heterogeneity in PKR level by insertion of anti-PKR genes, viruses which reinforce the host tumor clearance capacity by encoding immune cytokines (IL-12 or granulocyte-macrophage colony-stimulating factor), and non-attenuated viruses fully retargeted to tumor specific receptors. A strategy to generate o-HSVs fully retargeted to human epidermal growth factor receptor-2 (HER-2) or other cancer-specific surface receptors is detailed.

Adaptive antiviral immunity is a determinant of the therapeutic success of oncolytic virotherapy

Oncolytic virotherapy, the selective killing of tumor cells by oncolytic viruses (OVs), has emerged as a promising avenue of anticancer research. We have previously shown that KM100, a Herpes simplex virus type-1 (HSV) deficient for infected cell protein 0 (ICP0), possesses substantial oncolytic properties in vitro and has antitumor efficacy in vivo, in part by inducing antitumor immunity. Here, we illustrate through T-cell immunodepletion studies in nontolerized tumor-associated antigen models of breast cancer that KM100 treatment promotes antiviral and antitumor CD8(+) cytotoxic T-cell responses necessary for complete tumor regression. In tolerized tumor-associated antigen models of breast cancer, antiviral CD8(+) cytotoxic T-cell responses against infected tumor cells correlated with the induction of significant tumoristasis in the absence of tumor-associated antigen-specific CD8(+) cytotoxic T-cells. To enhance oncolysis, we tested a more cytopathic ICP0-null HSV and a vesicular stomatitis virus M protein mutant and found that despite improved in vitro replication, oncolysis in vivo did not improve. These studies illustrate that the in vitro cytolytic properties of OVs are poor prognostic indicators of in vivo antitumor activity, and underscore the importance of adaptive antiviral CD8(+) cytotoxic T-cells in effective cancer virotherapy.

Susceptibility of breast cancer cells to an oncolytic matrix (M) protein mutant of vesicular stomatitis virus

Matrix (M) protein mutants of vesicular stomatitis virus (VSV), such as rM51R-M virus, are attractive candidates as oncolytic viruses for tumor therapies because of their capacity to selectively target cancer cells. The effectiveness of rM51R-M virus as an antitumor agent for the treatment of breast cancer was assessed by determining the ability of rM51R-M virus to infect and kill breast cancer cells in vitro and in vivo. Several human- and mouse-derived breast cancer cell lines were susceptible to infection and killing by rM51R-M virus. Importantly, non-tumorigenic cell lines from normal mammary tissues were also sensitive to VSV infection suggesting that oncogenic transformation does not alter the susceptibility of breast cancer cells to oncolytic VSV. In contrast to results obtained in vitro, rM51R-M virus was only partially effective at inducing regression of primary breast tumors in vivo. Furthermore, we were unable to induce complete regression of the primary and metastatic tumors when tumor-bearing mice were treated with a vector expressing interleukin (IL)-12 or a combination of rM51R-M virus and IL-12. Our results indicate that although breast cancer cells may be susceptible to VSV in vitro, more aggressive treatment combinations are required to effectively treat both local and metastatic breast cancers in vivo.

VEGF blockade decreases the tumor uptake of systemic oncolytic herpes virus but enhances therapeutic efficacy when given after virotherapy

Effective therapies for metastatic sarcomas remain elusive. Oncolytic viruses have shown promise as anticancer agents, but their access to metastatic sites following systemic delivery is low. As systemic delivery of small-molecule chemotherapy is enhanced by previous treatment with antiangiogenic agents because of changes in intravascular-to-tumor interstitial pressure, we sought to determine whether antiangiogenic pretreatment increases the antitumor efficacy of systemic virotherapy by increasing virus uptake into tumor. Virus biodistribution and antitumor effects were monitored in tumor-bearing mice given antihuman vascular endothelial growth factor (VEGF) or antimouse VEGFR2 before or after an intravenous (i.v.) injection of virus. Without pretreatment, the average virus titers in the tumor samples amplified 1700-fold over 48 h but were undetectable in other organs. After antiangiogenic treatment, average virus titers in the tumor samples were unchanged or in some cases decreased up to 100-fold. Thus, antiangiogenic pretreatment failed to improve the tumor uptake of systemic oncolytic herpes simplex virus (oHSV), in contrast to previously reported enhanced uptake of small molecules. Superior tumor control because of the combined effects of virus and anti-VEGF was seen most dramatically when anti-VEGF was given after virus. Our data suggest that i.v. oHSV can treat distant sites of disease and can be enhanced by antiangiogenic therapy, but only when given in the proper sequence.

Concomitant tumor and minor histocompatibility antigen-specific immunity initiate rejection and maintain remission from established spontaneous solid tumors

Nonmyeloablative hematopoietic cell transplantation can cure patients with hematologic malignancies but has reported limited success against solid tumors. This is possibly because of profound peripheral tolerance mechanisms and/or suboptimal tumor recognition by effector T lymphocytes. We report that in mice developing spontaneous prostate cancer, nonmyeloablative minor histocompatibility mismatched hematopoietic stem cell transplantation, and donor lymphocyte infusion of unmanipulated lymphocytes combined with posttransplant tumor-specific vaccination circumvents tumor-specific tolerance, allowing acute tumor rejection and the establishment of protective immunosurveillance. Although donor-derived tumor-specific T cells readily differentiated into effector cells and infiltrated the tumor soon after infusion, they were alone insufficient for tumor eradication, which instead required the concomitance of minor histocompatibiltiy antigen-specific CD8(+) T-cell responses. The establishment of protective immunosurveillance was best induced by posttransplant tumor-specific vaccination. Hence, these results provide the proof of principle that tumor-specific T-cell responses have to be harnessed together with minor histocompatibility responses and sustained by posttransplant tumor-specific vaccination to improve the efficacy of allotransplantion for the cure of solid tumors.

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.

Inhibition of human tumor growth in mice by an oncolytic herpes simplex virus designed to target solely HER-2-positive cells

Oncolytic virotherapy exploits the ability of viruses to infect, replicate into, and kill tumor cells. Among the viruses that entered clinical trials are HSVs. HSVs can be engineered to become tumor-specific by deletion of selected genes or retargeting to tumor-specific receptors. A clinically relevant surface molecule is HER-2, hyperexpressed in one fourth of mammary and ovary carcinomas, and associated with high metastatic ability. As a previously undescribed strategy to generate HSV recombinants retargeted to HER-2 and detargeted from natural receptors, we replaced the Ig-folded core in the receptor-binding virion glycoprotein gD with anti-HER-2 single-chain antibody. The recombinant entered cells solely via HER-2 and lysed HER-2-positive cancer cells. Because of the high specificity, its safety profile in i.p. injected mice was very high, with a LD(50) >5 x 10(8) pfu, a figure at least 10,000-fold higher than that of corresponding WT-gD carrying virus (LD(50) approximately 5 x 10(4) pfu). When administered intratumorally to nude mice bearing HER-2-hyperexpressing human tumors, it strongly inhibited progressive tumor growth. The results provide a generally applicable strategy to engineer HSV recombinants retargeted to a wide range of receptors for which a single-chain antibody is available, and show the potential for retargeted HSV to exert target-specific inhibition of human tumor growth. Therapy with HER-2-retargeted oncolytic HSV could be effective in combined or sequential protocols with monoclonal antibodies and small inhibitors, particularly in patients resistant to HER-2-targeted therapy because of alterations in HER-2 signaling pathway, or against brain metastases inaccessible to anti-HER-2 antibodies.

Herpes simplex virus oncolytic therapy for pediatric malignancies

Despite improving survival rates for children with cancer, a subset of patients exist with disease resistant to traditional therapies such as surgery, chemotherapy, and radiation. These patients require newer, targeted treatments used alone or in combination with more traditional approaches. Oncolytic herpes simplex virus (HSV) is one of these newer therapies that offer promise for several difficult to treat pediatric malignancies. The potential benefit of HSV therapy in pediatric solid tumors including brain tumors, neuroblastomas, and sarcomas is reviewed along with the many challenges that need to be addressed prior to moving oncolytic HSV therapy from the laboratory to the beside in the pediatric population.

Imaging of lymph node micrometastases using an oncolytic herpes virus and [F]FEAU PET

Background

In patients with melanoma, knowledge of regional lymph node status provides important information on outlook. Since lymph node status can influence treatment, surgery for sentinel lymph node (SLN) biopsy became a standard staging procedure for these patients. Current imaging modalities have a limited sensitivity for detection of micrometastases in lymph nodes and, therefore, there is a need for a better technique that can accurately identify occult SLN metastases.

Methodology/Principal Findings

B16-F10 murine melanoma cells were infected with replication-competent herpes simplex virus (HSV) NV1023. The presence of tumor-targeting and reporter-expressing virus was assessed by [¹⁸F]-2′-fluoro-2′-deoxy-1-β-D-β-arabinofuranosyl-5-ethyluracil ([¹⁸F]FEAU) positron emission tomography (PET) and confirmed by histochemical assays. An animal foot pad model of melanoma lymph node metastasis was established. Mice received intratumoral injections of NV1023, and 48 hours later were imaged after i.v. injection of [¹⁸F]FEAU. NV1023 successfully infected and provided high levels of lacZ transgene expression in melanoma cells. Intratumoral injection of NV1023 resulted in viral trafficking to melanoma cells that had metastasized to popliteal and inguinal lymph nodes. Presence of virus-infected tumor cells was successfully imaged with [¹⁸F]FEAU-PET, that identified 8 out of 8 tumor-positive nodes. There was no overlap between radioactivity levels (lymph node to surrounding tissue ratio) of tumor-positive and tumor-negative lymph nodes.

Conclusion/Significance

A new approach for imaging SLN metastases using NV1023 and [¹⁸F]FEAU-PET was successful in a murine model. Similar studies could be translated to the clinic and improve the staging and management of patients with melanoma.

Analysis of HSV oncolytic virotherapy in organotypic cultures

Tumor-selective replication-competent viral vectors, such as oncolytic herpes simplex virus (HSV) type I (HSV-1), represent an attractive strategy for tumor-based therapies because these viruses can replicate and spread in situ exhibiting cytopathic effects through direct oncolytic activity. These lytic viruses offer a distinct advantage over other forms of cancer therapies in that they are self-perpetuating and can spread not only in the tumor itself, but also to distant micrometastases. Translational studies aimed at identifying novel virotherapies for human cancers are incumbent upon the appropriate experimental models. While animal models are the preferred choice for efficacy studies of HSV virotherapy, we have developed a novel complementary approach toward assessing the effectiveness of oncolytic HSV therapy in both brain and prostate cancers. This experimental model takes advantage of previously published work in which human prostate cancer biopsies and rodent brain slices can be easily maintained ex vivo. The advantage of these systems is that the three-dimensional structure remains intact. Thus, all of the factors that may affect viral entry and replication, such as cell-cell and cell-matrix interactions, and interstitial fluid within this three-dimensional milieu remain preserved. Moreover, with respect to the brain, this system offers the advantage of direct access to brain cells, such as microglia and astrocytes, and circumvents the problems associated with the presence of the blood-brain barrier.