Yaohe Wang

Rational strain selection and engineering creates a broad-spectrum, systemically effective oncolytic poxvirus, JX-963

Replication-selective oncolytic viruses (virotherapeutics) are being developed as novel cancer therapies with unique mechanisms of action, but limitations in i.v. delivery to tumors and systemic efficacy have highlighted the need for improved agents for this therapeutic class to realize its potential. Here we describe the rational, stepwise design and evaluation of a systemically effective virotherapeutic (JX-963). We first identified a highly potent poxvirus strain that also trafficked efficiently to human tumors after i.v. administration. This strain was then engineered to target cancer cells with activation of the transcription factor E2F and the EGFR pathway by deletion of the thymidine kinase and vaccinia growth factor genes. For induction of tumor-specific cytotoxic T lymphocytes, we further engineered the virus to express human GM-CSF. JX-963 was more potent than the previously used virotherapeutic Onyx-015 adenovirus and as potent as wild-type vaccinia in all cancer cell lines tested. Significant cancer selectivity of JX-963 was demonstrated in vitro in human tumor cell lines, in vivo in tumor-bearing rabbits, and in primary human surgical samples ex vivo. Intravenous administration led to systemic efficacy against both primary carcinomas and widespread organ-based metastases in immunocompetent mice and rabbits. JX-963 therefore holds promise as a rationally designed, targeted virotherapeutic for the systemic treatment of cancer in humans and warrants clinical testing.

Analysis of gene expression in cancer cell lines identifies candidate markers for pancreatic tumorigenesis and metastasis

Pancreatic cancer is a highly aggressive type of malignancy and the prognosis for disease presenting typically at a late stage is extremely poor. A comprehensive understanding of its molecular genetics is required in order to develop new approaches to clinical management. To date, serial analysis of gene expression and more recently oligo/cDNA microarray technologies have been employed in order to identify genes involved in pancreatic neoplasia that can be developed as diagnostic markers and drug targets for this dismal disease. This study describes the expression profile obtained from 20 pancreatic cell lines using cDNA microarrays containing 9,932 human gene elements. Numerous genes were identified as being differentially expressed, some of which have been previously implicated in pancreatic adenocarcinoma (S100P, S100A4, prostate stem cell antigen, lipocalin 2, claudins 3 and 4, trefoil factors 1 and 2) as well as several novel genes. The differentially expressed genes identified are involved in a variety of cellular functions, including control of transcription, regulation of the cell cycle, proteolysis, cell adhesion and signaling. Validation of our array results was performed by exploring the SAGEmap database and by immunohistochemistry for a selection of 4 genes that have not previously been studied in pancreatic cancer: anterior gradient 2 homologue (Xenopus laevis), insulin‐like growth factor binding protein 3 and 4 and Forkhead box J1. Immunostaining was performed using pancreas‐specific tissue microarrays containing core biopsies from 305 clinical specimens. In addition, using statistical group comparison and hierarchical clustering, a selection of genes was identified that may be linked to the site of metastasis from which these cell lines were isolated.

E3 gene manipulations affect oncolytic adenovirus activity in immunocompetent tumor models

Oncolytic replication-selective adenoviruses constitute a rapidly growing therapeutic platform for cancer. However, the role of the host immune response and the E3 immunoregulatory genes of the human adenovirus were unknown until now. We identified four mouse carcinoma lines of variable permissivity for adenoviral gene expression, cytopathic effects and/or burst size. To determine E3 gene effects in immunocompetent tumor-bearing hosts, we injected tumors with one of three adenoviruses: Ad5 (E3 wild type), dl309 (del. E3 10.4/14.5, 14.7 kDa) or dl704 (del. E3 gp19 kDa). Compared with Ad5 and dl704, dl309 was cleared much more rapidly and/or its activity was lower in all four models. Intratumoral injection with dl309 resulted in markedly greater macrophage infiltration and expression of both tumor necrosis factor and interferon-γ. Adenovirus replication, CD8+ lymphocyte infiltration and efficacy were similar upon intratumoral injection with either dl704 or Ad5. E3-dependent differences were not evident in athymic mice. These findings have important implications for the design of oncolytic adenoviruses and may explain the rapid clearance of E3-10.4/14.5,14.7-deleted adenoviruses in patients.

Oncolytic Viruses for Cancer Therapy: Overcoming the Obstacles

Targeted therapy of cancer using oncolytic viruses has generated much interest over the past few years in the light of the limited efficacy and side effects of standard cancer therapeutics for advanced disease. In 2006, the world witnessed the first government-approved oncolytic virus for the treatment of head and neck cancer. It has been known for many years that viruses have the ability to replicate in and lyse cancer cells. Although encouraging results have been demonstrated in vitro and in animal models, most oncolytic viruses have failed to impress in the clinical setting. The explanation is multifactorial, determined by the complex interactions between the tumor and its microenvironment, the virus, and the host immune response. This review focuses on discussion of the obstacles that oncolytic virotherapy faces and recent advances made to overcome them, with particular reference to adenoviruses.

Expression of the IAP protein family is dysregulated in pancreatic cancer cells and is important for resistance to chemotherapy

Pancreatic cancer is one of the most aggressive human tumors with a 5‐year survival rate of only 3% and a striking resistance to chemotherapy and radiotherapy. The search for new therapeutic approaches includes strategies exploiting the deregulation of apoptotic pathways commonly found in cancer cells. The IAP proteins are inhibitors of apoptosis that have altered activity in numerous cancer types and are implicated in resistance to chemotherapy, and therefore are potentially interesting as therapeutic targets. We investigated alterations in the expression of IAPs and their inhibitors in pancreatic adenocarcinoma by using real‐time PCR, in situ hybridization and immunohistochemistry. We found differential expression of various IAPs in this malignancy, and particularly we observed overexpression of cIAP‐2, survivin, livin and XIAP. We also looked for correlations between the expression of IAPs and resistance to paclitaxel, doxorubicin, CDDP and 5‐fluorouracil, and found that resistance to these drugs correlates most significantly with expression of cIAP‐2. Using RNAi to downregulate these proteins we further confirmed that the levels of cIAP‐2 and XIAP influence the response to the anti‐cancer drugs, although only marginally for 5‐FU. We conclude that anti‐tumor strategies based on the inhibition of particular IAPs can be useful in targeting pancreatic adenocarcinoma.

Novel Immunocompetent Murine Tumor Models for the Assessment of Replication-Competent Oncolytic Adenovirus Efficacy

Oncolytic replication-selective adenoviruses constitute a rapidly expanding experimental approach to the treatment of cancer. However, due to the lack of an immunocompetent and replication-competent efficacy model, the role of the host immune response and viral E3 immunoregulatory genes remained unknown. We screened nine murine carcinoma lines for adenovirus (Ad5) uptake, gene expression, replication, and cytopathic effects. In seven of these murine cell lines the infectability and cytopathic effects were similar to those seen with human carcinoma lines. Surprisingly, productive viral replication was demonstrated in several lines; replication varied from levels similar to those for some human carcinoma lines (e.g., CMT-64) to very low levels. Seven of these lines were grown as subcutaneous xenografts in immunocompetent mice and were subsequently injected directly with Ad5, saline, or a replication-deficient control adenovirus particle to assess intratumoral viral gene expression, replication, and antitumoral effects. E1A, coat protein expression, and cytopathic effects were documented in five xenografts; Ad5 replication was demonstrated in CMT-64 and JC xenografts. Ad5 demonstrated significant efficacy compared to saline and nonreplicating control Ad particles in both replication-permissive xenografts (CMT-64, JC) and poorly permissive tumors (CMT-93); efficacy against CMT-93 tumors was significantly greater in immunocompetent mice compared to athymic mice. These murine tumor xenograft models have potential for elucidating viral and host immune mechanisms involved in oncolytic adenovirus antitumoral effects.

Systemic Delivery of Oncolytic Viruses: Hopes and Hurdles

Despite recent advances in both surgery and chemoradiotherapy, mortality rates for advanced cancer remain high. There is a pressing need for novel therapeutic strategies; one option is systemic oncolytic viral therapy. Intravenous administration affords the opportunity to treat both the primary tumour and any metastatic deposits simultaneously. Data from clinical trials have shown that oncolytic viruses can be systemically delivered safely with limited toxicity but the results are equivocal in terms of efficacy, particularly when delivered with adjuvant chemotherapy. A key reason for this is the rapid clearance of the viruses from the circulation before they reach their targets. This phenomenon is mainly mediated through neutralising antibodies, complement activation, antiviral cytokines, and tissue-resident macrophages, as well as nonspecific uptake by other tissues such as the lung, liver and spleen, and suboptimal viral escape from the vascular compartment. A range of methods have been reported in the literature, which are designed to overcome these hurdles in preclinical models. In this paper, the potential advantages of, and obstacles to, successful systemic delivery of oncolytic viruses are discussed. The next stage of development will be the commencement of clinical trials combining these novel approaches for overcoming the barriers with systemically delivered oncolytic viruses.

Enhancing Poxvirus Oncolytic Effects through Increased Spread and Immune Evasion

The antitumoral effects of oncolytic viruses have generally been limited by inefficient spread of the viruses within infected tumors and by inefficient systemic delivery, particularly in preimmunized hosts. Tumor-selective poxviruses have biological characteristics that may overcome these limitations. Nevertheless, physical barriers within the tumor microenvironment, including the extracellular matrix, can still limit intratumoral spread, and neutralizing antibodies can impede systemic delivery. To counter these limitations, we sought to take advantage of a naturally occurring poxvirus form known as extracellular enveloped virus (EEV). The EEV is shrouded by a host cell-derived lipid bilayer containing anticomplement proteins and is typically released from infected cells early during the infection cycle. Therefore, the EEV form evolved for rapid systemic spread within the host and for evasion of immune-mediated clearance. We compared the oncolytic potential of low versus high EEV-producing strains of vaccinia. EEV-enhanced vaccinia strains displayed improved spread within tumors after systemic delivery, resulting in significantly improved antitumor effects. The EEV-enhanced strains also displayed a greater ability to spread between injected and noninjected distant tumors through the blood and, importantly, displayed reduced clearance by neutralizing antibody. Safety was unaffected. The incorporation of EEV-enhancing mutations into next generation oncolytic vaccinia strains may improve the potency of these viruses without sacrificing safety.

Noninvasive Imaging of the Transcriptional Activities of Human Telomerase Promoter Fragments in Mice

We have assessed the feasibility of positron emission tomography (PET) and ex vivo γ-counting to measure the pattern of expression of telomerase promoter fragments in vivo. Promoter fragments from either the RNA [human telomerase RNA (hTR)] or the catalytic components [human telomerase reverse transcriptase (hTERT)] of the telomerase genes were used to drive the expression of the sodium iodide symporter PET reporter gene in recombinant adenoviruses. Both promoter fragments provided cancer-selective expression that could be visualized and quantitated by PET. The transcriptional activity of the hTR promoter was found to be consistently stronger than that of the hTERT promoter. Both promoters appear therefore to be good candidates for safe use in gene therapy, and PET imaging can be used to assess the selectivity of promoters in vivo. Given that this methodology is directly scalable to humans, imaging gene expression using the sodium iodide symporter PET reporter gene could be applied to measure telomerase promoter activity in humans.

Lister strain of vaccinia virus armed with endostatin–angiostatin fusion gene as a novel therapeutic agent for human pancreatic cancer

Survival after pancreatic cancer remains poor despite incremental advances in surgical and adjuvant therapy, and new strategies for treatment are needed. Oncolytic virotherapy is an attractive approach for cancer treatment. In this study, we have evaluated the effectiveness of the Lister vaccine strain of vaccinia virus armed with the endostatin–angiostatin fusion gene (VVhEA) as a novel therapeutic approach for pancreatic cancer. The Lister vaccine strain of vaccinia virus was effective against all human pancreatic carcinoma cells tested in vitro, especially those insensitive to oncolytic adenovirus. The virus displayed inherently high selectivity for cancer cells, sparing normal cells both in vitro and in vivo, with effective infection of tumors after both intravenous (i.v.) and intratumoral (i.t.) administrations. The expression of the endostatin–angiostatin fusion protein was confirmed in a pancreatic cancer model both in vitro and in vivo, with evidence of inhibition of angiogenesis. This novel vaccinia virus showed significant antitumor potency in vivo against the Suit-2 model by i.t. administration. This study suggests that the novel Lister strain of vaccinia virus armed with the endostatin–angiostatin fusion gene is a potential therapeutic agent for pancreatic cancer.