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

Modulation of Reoviral Cytolysis (I): Combination Therapeutics

Patients with stage IV gastric cancer suffer from dismal outcomes, a challenge especially in many Asian populations and for which new therapeutic options are needed. To explore this issue, we used oncolytic reovirus in combination with currently used chemotherapeutic drugs (irinotecan, paclitaxel, and docetaxel) for the treatment of gastric and other gastrointestinal cancer cells in vitro and in a mouse model. Cell viability in vitro was quantified by WST-1 assays in human cancer cell lines treated with reovirus and/or chemotherapeutic agents. The expression of reovirus protein and caspase activity was determined by flow cytometry. For in vivo studies, athymic mice received intratumoral injections of reovirus in combination with irinotecan or paclitaxel, after which tumor size was monitored. In contrast to expectations, we found that reoviral oncolysis was only poorly correlated with Ras pathway activation. Even so, the combination of reovirus with chemotherapeutic agents showed synergistic cytopathic effects in vitro, plus enhanced reovirus replication and apoptosis. In vivo experiments showed that reovirus alone can reduce tumor size and that the combination of reovirus with chemotherapeutic agents enhances this effect. Thus, we find that oncolytic reovirus therapy is effective against gastric cancer. Moreover, the combination of reovirus and chemotherapeutic agents synergistically enhanced cytotoxicity in human gastric cancer cell lines in vitro and in vivo. Our data support the use of reovirus in combination with chemotherapy in further clinical trials, and highlight the need for better biomarkers for reoviral oncolytic responsiveness.

Immunosuppressive cells in oncolytic virotherapy for glioma: challenges and solutions

Glioblastoma is a highly aggressive form of brain cancer characterized by the abundance of myeloid lineage cells in the tumor microenvironment. Tumor-associated macrophages and microglia (TAM) and myeloid-derived suppressor cells (MDSCs), play a pivotal role in promoting immune suppression and tumor progression. Oncolytic viruses (OVs) are self-amplifying cytotoxic agents that can stimulate local anti-tumor immune responses and have the potential to suppress immunosuppressive myeloid cells and recruit tumor-infiltrating T lymphocytes (TILs) to the tumor site, leading to an adaptive immune response against tumors. However, the impact of OV therapy on the tumor-resident myeloid population and the subsequent immune responses are not yet fully understood. This review provides an overview of how TAM and MDSC respond to different types of OVs, and combination therapeutics that target the myeloid population to promote anti-tumor immune responses in the glioma microenvironment.

Expanding the Spectrum of Pancreatic Cancers Responsive to Vesicular Stomatitis Virus-Based Oncolytic Virotherapy: Challenges and Solutions

Pancreatic ductal adenocarcinoma (PDAC) is a devastating malignancy with poor prognosis and a dismal survival rate, expected to become the second leading cause of cancer-related deaths in the United States. Oncolytic virus (OV) is an anticancer approach that utilizes replication-competent viruses to preferentially infect and kill tumor cells. Vesicular stomatitis virus (VSV), one such OV, is already in several phase I clinical trials against different malignancies. VSV-based recombinant viruses are effective OVs against a majority of tested PDAC cell lines. However, some PDAC cell lines are resistant to VSV. Upregulated type I IFN signaling and constitutive expression of a subset of interferon-simulated genes (ISGs) play a major role in such resistance, while other mechanisms, such as inefficient viral attachment and resistance to VSV-mediated apoptosis, also play a role in some PDACs. Several alternative approaches have been shown to break the resistance of PDACs to VSV without compromising VSV oncoselectivity, including (i) combinations of VSV with JAK1/2 inhibitors (such as ruxolitinib); (ii) triple combinations of VSV with ruxolitinib and polycations improving both VSV replication and attachment; (iii) combinations of VSV with chemotherapeutic drugs (such as paclitaxel) arresting cells in the G2/M phase; (iv) arming VSV with p53 transgenes; (v) directed evolution approach producing more effective OVs. The latter study demonstrated impressive long-term genomic stability of complex VSV recombinants encoding large transgenes, supporting further clinical development of VSV as safe therapeutics for PDAC.

Chemovirotherapy for pancreatic cancer: Gemcitabine plus oncolytic measles vaccine virus

Oncolytic virotherapy with vaccine viruses employs replicative vectors, which quite selectively infect tumor cells leading to massive virus replication followed by subsequent profound tumor cell death (oncolysis). Measles vaccine virus (MeV) has already shown great oncolytic activity against different types of cancers, including pancreatic cancer. Gemcitabine is a first line chemotherapeutic drug used for pancreatic cancer in palliative treatment plans. Furthermore, this drug can be used to induce senescence, a permanent cell cycle arrest, in tumor cells. In our preclinical work, three well-characterized immortalized human pancreatic cancer cell lines were used to investigate the combinatorial effect of MeV-based virotherapy together with the chemotherapeutic compound gemcitabine. Viability assays revealed that the combination of only small amounts of MeV together with subtherapeutic concentrations of gemcitabine resulted in a tumor cell mass reduction of >50%. To further investigate the replication of the oncolytic MeV vectors under these distinct combinatorial conditions, viral growth curves were generated. As a result, viral replication was found to be only slightly diminished in the presence of gemcitabine. As gemcitabine induces senescence, the effect of MeV on that phenomenon was explored using a senescence-associated β-galactosidase assay. Notably, gemcitabine-induced tumor cell senescence was not impaired by MeV. Accordingly, the chemovirotherapeutic combination of gemcitabine plus oncolytic MeV constitutes a novel therapeutic option for advanced pancreatic carcinoma that is characterized by the mutual improvement of the effectiveness of each therapeutic component.

Virotherapy: Current Trends and Future Prospects for Treatment of Colon and Rectal Malignancies

Colorectal cancer (CRC) is one of the most common malignancies. In recent decades, early diagnosis and conventional therapies have resulted in a significant reduction in mortality. However, late stage metastatic disease still has very limited effective treatment options. There is a growing interest in using viruses to help target therapies to tumour sites. In recent years the evolution of immunotherapy has emphasised the importance of directing the immune system to eliminate tumour cells; we aim to give a state-of-the-art over-view of the diverse viruses that have been investigated as potential oncolytic agents for the treatment of CRC.

Bibliometric analysis of oncolytic virus research, 2000 to 2018

BACKGROUND

Accumulating evidence in the last decade has pointed to the effectiveness of oncolytic virus in the treatment of a variety of cancer types in preclinical or clinical studies, showing high potency and low toxicity compared to conventional treatments. To track this research trend and highlight future directions, we conducted a bibliometric analysis of oncolytic virus research to date.

METHODS

Relevant studies were obtained from the Web of Science Core Collection between January 2000 and December 2018. Data were collected in terms of the number of publications, country, journal of publication, journal scope, author, and keywords or topics. Analysis and visual representation of the data were performed with CiteSpace V.

RESULTS

The trend in publications related to oncolytic virus showed a dramatic increase, from 10 publications in 2000 to 199 publications in 2018. The United States clearly dominates this field (981 publications, 52.770%), followed by Canada (244, 13.125%) and China (205, 11.027%). The top 15 academic journals account for over one third of the total publications on oncolytic virus research (724, 38.95%). Most of the related papers were published in journals with a focus on biology, medicine, immunology, medicine, molecular biology, and clinical perspectives, as represented by the dual-map overlay. The most highly cited papers were published in journals in the fields of nursing, molecular biology, general biology, genetics, health, and medicine. Over 1300 institutions have focused their attention on oncolytic virus research to date, and cooperation among mainstream institutions is common.

CONCLUSION

The global field of oncolytic virus research has expanded at a rapid pace from 2000 to 2018. There is no doubt that North America currently has the most powerful impact on the field with respect to both productivity and contribution. However, European and some East Asian institutions are also prominent in this field. Overall, this bibliometric study identifies the top 4 hotspots in oncolytic virus research: T-cells, vaccinia virus, dendritic cells, and apoptosis. Thus, further research focuses on these topics may be more helpful to promote the clinical translation of this treatment strategy to bring a benefit to cancer patients in the near future.

Oncolytic herpes simplex virus and immunotherapy

BACKGROUND

Oncolytic viruses have been proposed to be employed as a potential treatment of cancer. Well targeted, they will serve the purpose of cracking tumor cells without causing damage to normal cells. In this category of oncolytic viral drugs human pathogens herpes simplex virus (HSV) is especially suitable for the cause. Although most viral infection causes antiviral reaction in the host, HSV has multiple mechanisms to evade those responses. Powerful anti-tumor effect can thus be achieved via genetic manipulation of the HSV genes involved in this evading mechanism, namely deletions or mutations that adapt its function towards a tumor microenvironment. Currently, oncolytic HSV (oHSV) is widely use in clinical; moreover, there's hope that its curative effect will be further enhanced through the combination of oHSV with both traditional and emerging therapeutics.

RESULTS

In this review, we provide a summary of the HSV host antiviral response evasion mechanism, HSV expresses immune evasion genes such as ICP34.5, ICP0, Us3, which are involved in inducing and activating host responses, so that the virus can evade the immune system and establish effective long-term latent infection; we outlined details of the oHSV strains generated by removing genes critical to viral replication such as ICP34.5, ICP0, and inserting therapeutic genes such as LacZ, granulocyte macrophage colony-stimulating factor (GM-CSF); security and limitation of some oHSV such G207, 1716, OncoVEX, NV1020, HF10, G47 in clinical application; and the achievements of oHSV combined with immunotherapy and chemotherapy.

CONCLUSION

We reviewed the immunotherapy mechanism of the oHSV and provided a series of cases. We also pointed out that an in-depth study of the application of oHSV in cancer treatment will potentially benefits cancer patients more.

Oncolytic Viruses on Drugs: Achieving Higher Therapeutic Efficacy

Over the past 20 years there has been a dramatic expansion in the testing of oncolytic viruses (OVs) for the treatment of cancer. OVs are unique biotherapeutics that induce multimodal responses toward tumors, from direct cytopathic effects on cancer cells, to tumor associated blood vessel disruption, and ultimately potent stimulation of anti-tumor immune activation. These agents are highly targeted and can be efficacious as cancer treatments resulting in some patients experiencing complete tumor regression and even cures from OV monotherapy. However, most patients have limited responses with viral replication in tumors often found to be modest and transient. To augment OV replication, increase bystander killing of cancer cells, and/or stimulate stronger targeted anti-cancer immune responses, drug combination approaches have taken center stage for translation to the clinic. Here we comprehensively review drugs that have been combined with OVs to increase therapeutic efficacy, examining the proposed mechanisms of action, and we discuss trends in pharmaco-viral immunotherapeutic approaches currently being investigated.

A non-controlled, single arm, open label, phase II study of intravenous and intratumoral administration of ParvOryx in patients with metastatic, inoperable pancreatic cancer: ParvOryx02 protocol

BACKGROUND

Metastatic pancreatic cancer has a dismal prognosis, with a mean six-month progression-free survival of approximately 50% and a median survival of about 11 months. Despite intensive research, only slight improvements of clinical outcome could be achieved over the last decades. Hence, new and innovative therapeutic strategies are urgently required. ParvOryx is a drug product containing native parvovirus H-1 (H-1PV). Since H-1PV was shown to exert pronounced anti-neoplastic effects in pre-clinical models of pancreatic cancer, the drug appears to be a promising candidate for treatment of this malignancy.

METHODS

ParvOryx02 is a non-controlled, single arm, open label, dose-escalating, single center trial. In total seven patients with pancreatic cancer showing at least one hepatic metastasis are to be treated with escalating doses of ParvOryx according to the following schedule: i) 40% of the total dose infused intravenously in equal fractions on four consecutive days, ii) 60% of the total dose injected on a single occasion directly into the hepatic metastasis at varying intervals after intravenous infusions. The main eligibility criteria are: age ≥ 18 years, disease progression despite first-line chemotherapy, and at least one hepatic metastasis. Since it is the second trial within the drug development program, the study primarily explores safety and tolerability after further dose escalation of ParvOryx. The secondary objectives are related to the evaluation of certain aspects of anti-tumor activity and clinical efficacy of the drug.

DISCUSSION

This trial strongly contributes to the clinical development program of ParvOryx. The individual hazards for patients included in the current study and the environmental risks are addressed and counteracted adequately. Besides information on safety and tolerability of the treatment after further dose escalation, thorough evaluations of pharmacokinetics and intratumoral spread as well as proof-of-concept (PoC) in pancreatic cancer will be gained in the course of the trial.

TRIAL REGISTRATION

ClinicalTrials.gov-ID: NCT02653313 , Registration date: Dec. 4th, 2015.

Chemovirotherapy of Pancreatic Adenocarcinoma by Combining Oncolytic Vaccinia Virus GLV-1h68 with nab-Paclitaxel Plus Gemcitabine

Oncolytic viruses have proven their therapeutic potential against a variety of different tumor entities both in vitro and in vivo. Their ability to selectively infect and lyse tumor cells, while sparing healthy tissues, makes them favorable agents for tumor-specific treatment approaches. Particularly, the addition of virotherapeutics to already established chemotherapy protocols (so-called chemovirotherapy) is of major interest. Here we investigated the in vitro cytotoxic effect of the oncolytic vaccinia virus GLV-1h68 combined with dual chemotherapy with nab-paclitaxel plus gemcitabine in four human pancreatic adenocarcinoma cell lines (AsPc-1, BxPc-3, MIA-PaCa-2, and Panc-1). This chemovirotherapeutic protocol resulted in enhanced tumor cell killing in two tumor cell lines compared to the respective monotherapies. We were thereby able to show that the combination of oncolytic vaccinia virus GLV-1h68 with nab-paclitaxel and gemcitabine has great potential in the chemovirotherapeutic treatment of advanced pancreatic adenocarcinoma. However, the key to a successful combinatorial chemovirotherapeutic treatment seems to be a profound viral replication, as tumor cell lines that were non-responsive to the combination therapy exhibited a reduced viral replication in the presence of the chemotherapeutics. This finding is of special significance when aiming to achieve a virus-mediated induction of a profound and long-lasting antitumor immunity.

Promising oncolytic agents for metastatic breast cancer treatment

New therapies for metastatic breast cancer patients are urgently needed. The long-term survival rates remain unacceptably low for patients with recurrent disease or disseminated metastases. In addition, existing therapies often cause a variety of debilitating side effects that severely impact quality of life. Oncolytic viruses constitute a developing therapeutic modality in which interest continues to build due to their ability to spare normal tissue while selectively destroying tumor cells. A number of different viruses have been used to develop oncolytic agents for breast cancer, including herpes simplex virus, adenovirus, vaccinia virus, measles virus, reovirus, and others. In general, clinical trials for several cancers have demonstrated excellent safety records and evidence of efficacy. However, the impressive tumor responses often observed in preclinical studies have yet to be realized in the clinic. In order for the promise of oncolytic virotherapy to be fully realized for breast cancer patients, effectiveness must be demonstrated in metastatic disease. This review provides a summary of oncolytic virotherapy strategies being developed to target metastatic breast cancer.

Targeted oncolytic herpes simplex virus type 1 eradicates experimental pancreatic tumors

As many other cancers, pancreatic ductal adenocarcinoma (PDAC) progression is associated with a series of hallmark changes for cancer cells to secure their own growth success. Yet, these very changes render cancer cells highly sensitive to viral infection. A promising strategy may rely on and exploit viral replication for tumor destruction, whereby infection of tumor cells by a replication-conditional virus may lead to cell destruction and simultaneous release of progeny particles that can spread and infect adjacent tumor cells, while sparing healthy tissues. In the present study, we used Myb34.5, a second-generation replication-conditional herpes simplex virus type 1 (HSV-1) mutant in which ICP6 gene expression is defective and expression of the HSV-1 γ134.5 gene is regulated by the cellular B-myb promoter. We found that B-myb is present in experimental PDAC and tumors, and is overexpressed in patients' tumors, as compared with normal adjacent pancreas. Myb34.5 replicates to high level in human PDAC cell lines and is associated with cell death by apoptosis. In experimental models of PDAC, mice receiving intratumoral Myb34.5 injections appeared healthy and tumor progression was inhibited, with evidence of tumor necrosis, hemorrhage, viral replication, and cancer cell death by apoptosis. Combining standard-of-care chemotherapy with Myb34.5 successfully led to a very impressive antitumoral effect that is rarely achieved in this experimental model, and resulted in a greater reduction in tumor growth than chemotherapy alone. These promising results warrant further evaluation in early phase clinical trial for patients diagnosed with PDAC for whom no effective treatment is available.

High efficiency of alphaviral gene transfer in combination with 5-fluorouracil in a mouse mammary tumor model

Background

The combination of virotherapy and chemotherapy may enable efficient tumor regression that would be unachievable using either therapy alone. In this study, we investigated the efficiency of transgene delivery and the cytotoxic effects of alphaviral vector in combination with 5-fluorouracil (5-FU) in a mouse mammary tumor model (4 T1).

Methods

Replication-deficient Semliki Forest virus (SFV) vectors carrying genes encoding fluorescent proteins were used to infect 4 T1 cell cultures treated with different doses of 5-FU. The efficiency of infection was monitored via fluorescence microscopy and quantified by fluorometry. The cytotoxicity of the combined treatment with 5-FU and alphaviral vector was measured using an MTT-based cell viability assay. In vivo experiments were performed in a subcutaneous 4 T1 mouse mammary tumor model with different 5-FU doses and an SFV vector encoding firefly luciferase.

Results

Infection of 4 T1 cells with SFV prior to 5-FU treatment did not produce a synergistic anti-proliferative effect. An alternative treatment strategy, in which 5-FU was used prior to virus infection, strongly inhibited SFV expression. Nevertheless, in vivo experiments showed a significant enhancement in SFV-driven transgene (luciferase) expression upon intratumoral and intraperitoneal vector administration in 4 T1 tumor-bearing mice pretreated with 5-FU: here, we observed a positive correlation between 5-FU dose and the level of luciferase expression.

Conclusions

Although 5-FU inhibited SFV-mediated transgene expression in 4 T1 cells in vitro, application of the drug in a mouse model revealed a significant enhancement of intratumoral transgene synthesis compared with 5-FU untreated mice. These results may have implications for efficient transgene delivery and the development of potent cancer treatment strategies using alphaviral vectors and 5-FU.

Chemotherapy and Oncolytic Virotherapy: Advanced Tactics in the War against Cancer

Cancer is a traitorous archenemy that threatens our survival. Its ability to evade detection and adapt to various cancer therapies means that it is a moving target that becomes increasingly difficult to attack. Through technological advancements, we have developed sophisticated weapons to fight off tumor growth and invasion. However, if we are to stand a chance in this war against cancer, advanced tactics will be required to maximize the use of our available resources. Oncolytic viruses (OVs) are multi-functional cancer-fighters that can be engineered to suit many different strategies; in particular, their retooling can facilitate increased capacity for direct tumor killing (oncolytic virotherapy) and elicit adaptive antitumor immune responses (oncolytic immunotherapy). However, administration of these modified OVs alone, rarely induces successful regression of established tumors. This may be attributed to host antiviral immunity that acts to eliminate viral particles, as well as the capacity for tumors to adapt to therapeutic selective pressure. It has been shown that various chemotherapeutic drugs with distinct functional properties can potentiate the antitumor efficacy of OVs. In this review, we summarize the chemotherapeutic combinatorial strategies used to optimize virally induced destruction of tumors. With a particular focus on pharmaceutical immunomodulators, we discuss how specific therapeutic contexts may alter the effects of these synergistic combinations and their implications for future clinical use.

Epithelial-mesenchymal transition enhances response to oncolytic herpesviral therapy through nectin-1

Cancers exhibiting epithelial-mesenchymal transition (EMT) are associated with aggressive behavior and increased metastatic potential. Therapies that are able to target EMT would have significant clinical value. Nectin-1 is a cell surface herpes simplex virus type 1 (HSV-1) receptor that also forms a component of intercellular adherens junctions, which are typically disrupted in EMT. To explore relationships between HSV-1 sensitivity and EMT, we generated cell lines with a stable EMT phenotype from human follicular thyroid cancer (WRO82-1) through E-cadherin silencing with short hairpin RNA (shEcadWRO). HSV-1 viral attachment and gene expression were both enhanced in shEcadWRO as compared with shControl. Immunoblotting and immunostaining revealed enhanced nectin-1 expression by shEcadWRO. Receptor-blocking assays demonstrated that increased herpesviral entry into shEcadWRO as compared with shControl was mediated predominantly through nectin-1. Colocalization of green fluorescent protein-tagged HSV-1 and tdTomato-tagged nectin-1 confirmed an increase in viral attachment to nectin-1 in shEcadWRO. Cell viability assays demonstrated increased susceptibility of shEcadWRO to HSV-1 oncolysis, and a murine flank tumor model showed significantly enhanced regression of shEcadWRO tumors in response to oncolytic HSV-1 as compared with control tumors. A separate model of EMT induction through transforming growth factor-β stimulation confirmed enhanced HSV-1 susceptibility in Panc1 cells. These results demonstrate that the process of EMT leads to increased herpesviral susceptibility through enhanced cell surface nectin-1 expression, suggesting that cancers exhibiting EMT may be naturally sensitive targets for herpesviral therapy.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Oncolytic vaccinia virus in combination with radiation shows synergistic antitumor efficacy in pancreatic cancer

Combining oncolytic viruses with conventional therapy such as radiation is an innovative option for pancreatic cancer. We demonstrated that combination of GLV-1h151 and radiation yielded a synergistic cytotoxic effect, with the greatest effect achieved in the AsPC-1cell line. Combination treatment significantly increased apoptosis compared with either single treatment or the control group. In mice bearing human pancreatic tumor xenografts, combination treatment resulted in significantly enhanced inhibition of tumor growth. No evidence of toxicity was observed in mice. These results indicate that the combination of GLV-1h151 and radiation has great potential for translation into clinic practice.

Oncolytic herpes viruses, chemotherapeutics, and other cancer drugs

Oncolytic viruses are emerging as a potential new way of treating cancers. They are selectively replication-competent viruses that propagate only in actively dividing tumor cells but not in normal cells and, as a result, destroy the tumor cells by consequence of lytic infection. At least six different oncolytic herpes simplex viruses (oHSVs) have undergone clinical trials worldwide to date, and they have demonstrated an excellent safety profile and intimations of efficacy. The first pivotal Phase III trial with an oHSV, talimogene laherparepvec (T-Vec [OncoVex(GM-CSF)]), is almost complete, with extremely positive early results reported. Intuitively, therapeutically beneficial interactions between oHSV and chemotherapeutic and targeted therapeutic drugs would be limited as the virus requires actively dividing cells for maximum replication efficiency and most anticancer agents are cytotoxic or cytostatic. However, combinations of such agents display a range of responses, with antagonistic, additive, or, perhaps most surprisingly, synergistic enhancement of antitumor activity. When synergistic interactions in cancer cell killing are observed, chemotherapy dose reductions that achieve the same overall efficacy may be possible, resulting in a valuable reduction of adverse side effects. Therefore, the combination of an oHSV with "standard-of-care" drugs makes a logical and reasonable approach to improved therapy, and the addition of a targeted oncolytic therapy with "standard-of-care" drugs merits further investigation, both preclinically and in the clinic. Numerous publications report such studies of oncolytic HSV in combination with other drugs, and we review their findings here. Viral interactions with cellular hosts are complex and frequently involve intracellular signaling networks, thus creating diverse opportunities for synergistic or additive combinations with many anticancer drugs. We discuss potential mechanisms that may lead to synergistic interactions.

Advance in herpes simplex viruses for cancer therapy

Oncolytic virotherapy is an attractive approach that uses live viruses to selectively kill cancer cells. Oncolytic viruses can be genetically engineered to induce cell lyses through virus replication and cytotoxic protein expression. Herpes simplex virus (HSV) has become one of the most widely clinically used oncolytic agent. Various types of HSV have been studied in basic or clinical research. Combining oncolytic virotherapy with chemotherapy or radiotherapy generally produces synergic action with unclear molecular mechanisms. Arming HSV with therapeutic transgenes is a promising strategy and can be used to complement conventional therapies. As an efficient gene delivery system, HSV has been successfully used to deliver various immunomodulatory molecules. Arming HSV with therapeutic genes merits further investigation for potential clinical application.

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

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

Bugs and drugs: oncolytic virotherapy in combination with chemotherapy

Single agent therapies are rarely successful in treating cancer, particularly at metastatic or end stages, and survival rates with monotherapies alone are generally poor. The combination of multiple therapies to treat cancer has already driven significant improvements in the standard of care treatments for many types of cancers. The first combination treatments exploited for cancer therapy involved the use of several cytotoxic chemotherapy agents. Later, with the development of more targeted agents, the use of novel, less toxic drugs, in combination with the more classic cytotoxic drugs has proven advantageous for certain cancer types. Recently, the combination of oncolytic virotherapy with chemotherapy has shown that the use of these two therapies with very distinct anti-tumor mechanisms may also lead to synergistic interactions that ultimately result in increased therapeutic effects not achievable by either therapy alone. The mechanisms of synergy between oncolytic viruses (OVs) and chemotherapeutic agents are just starting to be elucidated. It is evident, however, that the success of these OV-drug combinations depends greatly on the particular OV, the drug(s) selected, and the cancer type targeted. This review summarizes the different OV-drug combinations investigated to date, including the use of second generation armed OVs, which have been studied with the specific purpose of generating synergistic interactions with particular chemotherapy agents. The known mechanisms of synergy between these OV-drug combinations are also summarized. The importance of further investigating these mechanisms of synergy will be critical in order to maximize the therapeutic efficacy of OV-drug combination therapies in the future.

Concurrent chemotherapy inhibits herpes simplex virus-1 replication and oncolysis

Herpes simplex virus-1 (HSV-1) replication in cancer cells leads to their destruction (viral oncolysis) and has been under investigation as an experimental cancer therapy in clinical trials as single agents, and as combinations with chemotherapy. Cellular responses to chemotherapy modulate viral replication, but these interactions are poorly understood. To investigate the effect of chemotherapy on HSV-1 oncolysis, viral replication in cells exposed to 5-fluorouracil (5-FU), irinotecan (CPT-11), methotrexate (MTX) or a cytokine (tumor necrosis factor-α (TNF-α)) was examined. Exposure of colon and pancreatic cancer cells to 5-FU, CPT-11 or MTX in vitro significantly antagonizes both HSV-1 replication and lytic oncolysis. Nuclear factor-κB (NF-κB) activation is required for efficient viral replication, and experimental inhibition of this response with an IκBα dominant-negative repressor significantly antagonizes HSV-1 replication. Nonetheless, cells exposed to 5-FU, CPT-11, TNF-α or HSV-1 activate NF-κB. Cells exposed to MTX do not activate NF-κB, suggesting a possible role for NF-κB inhibition in the decreased viral replication observed following exposure to MTX. The role of eukaryotic initiation factor 2α (eIF-2α) dephosphorylation was examined; HSV-1-mediated eIF-2α dephosphorylation proceeds normally in HT29 cells exposed to 5-FU, CPT-11 or MTX. This report demonstrates that cellular responses to chemotherapeutic agents provide an unfavorable environment for HSV-1-mediated oncolysis, and these observations are relevant to the design of both preclinical and clinical studies of HSV-1 oncolysis.

Local control of experimental malignant pancreatic tumors by treatment with a combination of chemotherapy and intratumoral 224radium-loaded wires releasing alpha-emitting atoms

We developed (224)Ra-loaded wires that when inserted into solid tumors, release radioactive atoms that spread in the tumor and irradiate it effectively with alpha particles (diffusing alpha-emitters radiation therapy [DaRT]). In this study, we tested the ability of intratumoral (224)Ra-loaded wires to control the local growth of pancreatic tumors and the enhancement of this effect by chemotherapy. Pancreatic mouse tumors (Panc02) were treated with (224)Ra-loaded wire(s) with or without gemcitabine. The tumor size and survival were monitored, and autoradiography was performed to evaluate the spread of radioactive atoms inside the tumor. Mouse and human pancreatic cancer cells, irradiated in vitro by alpha particles with or without chemotherapy, were evaluated for cell growth inhibition. The insertion of (224)Ra-loaded wires into pancreatic tumors in combination with gemcitabine achieved significant local control and was superior to each treatment alone. A dosimetric analysis showed the spread of radioactive atoms in the tumor around the wires. Alpha particles combined with gemcitabine or 5-FU killed mouse and human cells in vitro better than each treatment alone. DaRT in combination with gemcitabine was proven effective against pancreatic tumors in vivo and in vitro, and the process may be applicable as a palliative treatment for patients with pancreatic cancer.

Oncolytic herpes simplex virus expressing yeast cytosine deaminase: relationship between viral replication, transgene expression, prodrug bioactivation

Yeast cytosine deaminase (yCD) is a well-characterized prodrug/enzyme system that converts 5-fluorocytosine (5-FC) to 5-fluorouracil (5-FU), and has been combined with oncolytic viruses. However, in vivo studies of the interactions between 5-FC bioactivation and viral replication have not been previously reported, nor have the kinetics of transgene expression and the pharmacokinetics of 5-FC and 5-FU. We constructed a replication-conditional HSV-1 expressing yCD and examined cytotoxicity when 5-FC was initiated at different times after viral infection, and observed that earlier 5-FC administration led to greater cytotoxicity than later 5-FC administration in vitro and in vivo. Twelve days of 5-FC administration was superior to 6 days in animal models, but dosing beyond 12 days did not further enhance efficacy. Consistent with the dosing schedule results, both viral genomic DNA copy number and viral titers were observed to peak on Day 3 after viral injection and gradually decrease thereafter. The virus is replication-conditional and was detected in tumors for as long as 2 weeks after viral injection. The maximum relative extent of yCD conversion of 5-FC to 5-FU in tumors was observed on Day 6 after viral injection and it decreased progressively thereafter. The observation that 5-FU generation within tumors did not lead to appreciable levels of systemic 5-FU (<10 ng/ml) is important and has not been previously reported. The approaches used in these studies of the relationship between the viral replication kinetics, transgene expression, prodrug administration and anti-tumor efficacy are useful in the design of clinical trials of armed, oncolytic viruses.

Synergistic effects of oncolytic reovirus and docetaxel chemotherapy in prostate cancer

Background

Reovirus type 3 Dearing (T3D) has demonstrated oncolytic activity in vitro, in in vivo murine models and in early clinical trials. However the true potential of oncolytic viruses may only be realized fully in combination with other modalities such as chemotherapy, targeted therapy and radiotherapy. In this study, we examine the oncolytic activity of reovirus T3D and chemotherapeutic agents against human prostate cancer cell lines, with particular focus on the highly metastatic cell line PC3 and the chemotherapeutic agent docetaxel. Docetaxel is the standard of care for metastatic prostate cancer and acts by disrupting the normal process of microtubule assembly and disassembly. Reoviruses have been shown to associate with microtubules and may require this association for efficient viral replication.

Methods

The effects of reovirus and chemotherapy on in vitro cytotoxicity were investigated in PC3 and Du 145 cells and the interactions between agents were assessed by combination index analysis. An Annexin V/propidium iodide fluorescence-activated cell sorting-based assay was used to determine mode of cell death. The effects of reovirus and docetaxel administered as single agent or combination therapy were tested in vivo in a murine model. The effects of docetaxel and reovirus, alone and together, on microtubule stabilisation were investigated by Western blot analysis.

Results

Variable degrees of synergistic cytotoxicity were observed in PC3 and Du 145 cells exposed to live reovirus and several chemotherapy agents. Combination of reovirus infection with docetaxel exposure led to increased late apoptotic/necrotic cell populations. Reovirus/docetaxel combined therapy led to reduced tumour growth and increased survival in a PC3 tumour bearing mouse model. Microtubule stabilization was enhanced in PC3 cells treated with reovirus/docetaxel combined therapy compared to other reovirus/chemotherapy combinations.

Conclusions

The co-administration of a variety of chemotherapeutic agents with live reovirus was able to enhance cytotoxicity synergistically in vitro. The combination of docetaxel with reovirus also delayed tumour growth and improved survival in vivo. Enhanced microtubule stabilisation following this combination treatment may, in part, explain the mechanism of synergy. These results provide evidence to support the ongoing clinical trials using these agents.

Engineered herpes simplex virus vectors for antitumor therapy and vaccine delivery

Genetically modified herpes simplex viruses (HSVs) have been exploited for both antitumor therapy and vaccine delivery. These mutant viruses retain their ability to replicate and lyse permissive cells, including many tumor types, and are referred to as oncolytic HSVs. In addition, deletion of nonessential genes permits the introduction of foreign genes to augment the antitumor effect by either immune stimulation, targeting for select tumors, or expression of tumor or vaccine antigens. This article reviews the development of oncolytic HSVs as an anticancer therapy, as well as the application of HSV-1 vectors for delivery of targeted antigens or as vaccine adjuvants. The impact of these novel vectors with respect to enhanced antitumor activity and development of antitumor vaccination strategies is discussed.

Synergistic action of oncolytic herpes simplex virus and radiotherapy in pancreatic cancer cell lines

BACKGROUND

Despite much research in chemotherapy and radiotherapy, pancreatic adenocarcinoma remains a fatal disease, highly resistant to all treatment modalities. Recent developments in the field of herpes simplex virus (HSV) engineering have allowed the generation of a number of promising virus vectors for treatment of many cancers, including pancreatic tumours. This study examined the use of one such virus, NV1023, in combination with radiation therapy in pancreatic cancer cell lines.

METHODS

HSV therapy in combination with radiotherapy was investigated in pancreatic cancer cell lines Hs766T, Panc-1 and MIA PaCa-2. Multiple therapy effect analysis was performed by computerized simulation. Mechanisms underlying synergy, such as virus replication and apoptosis, were investigated.

RESULTS

The combination of NV1023 and radiation yielded a synergistic oncolytic effect in all tested pancreatic cancer cell lines, with the greatest effect achieved in MIA PaCa-2. This effect was not mediated by an increase in rapid viral replication, but by a substantial increase in apoptosis.

CONCLUSION

The synergistic oncolytic actions of HSV and radiotherapy observed in pancreatic cancer cell lines encourage further testing of this multimodality treatment.

Oncolytic herpes simplex virus vectors and chemotherapy: are combinatorial strategies more effective for cancer?

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

Hyperthermia potentiates oncolytic herpes viral killing of pancreatic cancer through a heat shock protein pathway

BACKGROUND

Oncolytic herpes simplex virus-1 (HSV-1) is designed to specifically infect, replicate in, and lyse cancer cells. This study investigates a novel therapeutic regimen, combining the effects of NV1066 (a recombinant HSV-1) and hyperthermia in the treatment of pancreatic cancer.

METHODS

NV1066 is an attenuated HSV-1 that replicates in cells resistant to apoptosis. Heat shock protein 72 (Hsp72) is a member of a family of proteins that is upregulated after hyperthermic insult, lending cellular protection by inhibiting apoptosis. In these experiments, we test the hypothesis that increased Hsp72 expression in response to hyperthermia enhances anti-apoptotic mechanisms, thereby increasing viral replication and tumor cell kill. Hs 700T pancreatic cancer cells were treated with hyperthermia alone (42 degrees C), NV1066 alone, and combination therapy. Cell survival and viral growth were measured. The effect of siRNA-directed Hsp72 knockdown was also measured.

RESULTS

Combining hyperthermia and viral treatment produced a synergistic effect on cell kill. Viral growth increased greater than 6-fold in the presence of hyperthermia (P < .05). Hyperthermia alone showed minimal cytotoxic activity against Hs 700T cells, while NV1066 infection resulted in approximately 50% cell kill. The combination of hyperthermia and viral infection significantly increased cell kill to approximately 80% (P < .01). Hsp72 knockdown attenuated this synergistic effect.

CONCLUSION

Hyperthermia enhances NV1066 replication, thereby potentiating the viral oncolytic response against pancreatic cancer cells. This finding has potential clinical application in the use of heated perfusion or permissive hyperthermia for delivery of oncolytic viral therapies.

Synergistic effects of oncolytic reovirus and cisplatin chemotherapy in murine malignant melanoma

PURPOSE

To test combination treatment schedules of reovirus and cisplatin chemotherapy in human and murine melanoma cell lines and murine models of melanoma and to investigate the possible mechanisms of synergistic antitumor effects.

EXPERIMENTAL DESIGN

The effects of reovirus +/- chemotherapy on in vitro cytotoxicity and viral replication were assessed using 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assay and plaque assay. Interactions between agents were assessed by combination index analysis. Mode of cell death was assessed by Annexin V/propidium iodide fluorescence-activated cell sorting-based assays; gene expression profiling of single versus combination treatments was completed using the Agilent microarray system. Single agent and combination therapy effects were tested in vivo in two immunocompetent models of murine melanoma.

RESULTS

Variable degrees of synergistic cytotoxicity between live reovirus and several chemotherapy agents were observed in B16.F10 mouse melanoma cells, most significantly with cisplatin (combination index of 0.42 +/- 0.03 at ED(50)). Combination of cisplatin and reovirus exposure led to increased late apoptotic/necrotic cell populations. Cisplatin almost completely abrogated the inflammatory cytokine gene up-regulation induced by reovirus. Combination therapy led to significantly delayed tumor growth and improved survival in vivo (P < 0.0001 and P = 0.0003, respectively). Cisplatin had no effect on the humoral response to reovirus in mice. However, cisplatin treatment suppressed the cytokine and chemokine response to reovirus in vitro and in vivo.

CONCLUSION

The combination of reovirus and several chemotherapeutic agents synergistically enhanced cytotoxicity in human and murine melanoma cell lines in vitro and murine tumors in vivo. The data support the current reovirus/chemotherapy combination phase I clinical studies currently ongoing in the clinic.

Combination of conditionally replicative adenovirus and standard chemotherapies shows synergistic antitumor effect in pancreatic cancer

Due to devastating prognosis, novel therapies are needed for pancreatic cancer. We are in preparation for a human clinical trial of a conditionally replicative adenovirus (CRAd) we developed. While most patients in the target population are receiving either gemcitabine or 5-fluorouracil chemotherapy, the combination with CRAd has not yet been studied. This study was designed to evaluate combination therapies with CRAd and current standard chemotherapies in pancreatic cancer. When the combination therapy was tested in vitro, gemcitabine pretreatment showed a synergistic effect in two out of four cell lines whereas CRAd followed by gemcitabine exhibited a synergistic effect in one cell line. With 5-fluorouracil, pretreatment with 5-fluorouracil produced a synergistic effect in three cell lines whereas post-treatment was synergistic in only one cell line. These effects were not fully explained by either induction of cyclooxygenase (Cox) 2 activity or adenoviral receptors with chemotherapeutics. In in vivo analyses with Hs766T xenograft, 5-fluorouracil slightly improved the CRAd antitumor effect but it was not significant. Pretreatment with gemcitabine embodied a significant tumor reduction compared with single therapy with gemcitabine. The most significant antitumor effect occurred when tumors were treated with 5/3COX2CRAdF and subsequent gemcitabine (P = 0.001 vs gemcitabine alone, P = 0.012 vs 5/3COX2CRAdF alone) at day 12. In MIA Paca-2, pretreatments with either 5-fluorouracil or gemcitabine improved the CRAd therapeutic effect when administered before CRAd injection (P = 0.03 and P = 0.01, respectively). These experiments indicate the possible benefit of combination therapies, and thus it is not necessary to interrupt chemotherapeutics when receiving CRAd therapy.

Synergistic antitumor activity of oncolytic reovirus and chemotherapeutic agents in non-small cell lung cancer cells

Background

Reovirus type 3 Dearing strain (ReoT3D) has an inherent propensity to preferentially infect and destroy cancer cells. The oncolytic activity of ReoT3D as a single agent has been demonstrated in vitro and in vivo against various cancers, including colon, pancreatic, ovarian and breast cancers. Its human safety and potential efficacy are currently being investigated in early clinical trials. In this study, we investigated the in vitro combination effects of ReoT3D and chemotherapeutic agents against human non-small cell lung cancer (NSCLC).

Results

ReoT3D alone exerted significant cytolytic activity in 7 of 9 NSCLC cell lines examined, with the 50% effective dose, defined as the initial virus dose to achieve 50% cell killing after 48 hours of infection, ranging from 1.46 ± 0.12 ~2.68 ± 0.25 (mean ± SD) log₁₀ pfu/cell. Chou-Talalay analysis of the combination of ReoT3D with cisplatin, gemcitabine, or vinblastine demonstrated strong synergistic effects on cell killing, but only in cell lines that were sensitive to these compounds. In contrast, the combination of ReoT3D and paclitaxel was invariably synergistic in all cell lines tested, regardless of their levels of sensitivity to either agent. Treatment of NSCLC cell lines with the ReoT3D-paclitaxel combination resulted in increased poly (ADP-ribose) polymerase cleavage and caspase activity compared to single therapy, indicating enhanced apoptosis induction in dually treated NSCLC cells. NSCLC cells treated with the ReoT3D-paclitaxel combination showed increased proportions of mitotic and apoptotic cells, and a more pronounced level of caspase-3 activation was demonstrated in mitotically arrested cells.

Conclusion

These data suggest that the oncolytic activity of ReoT3D can be potentiated by taxanes and other chemotherapeutic agents, and that the ReoT3D-taxane combination most effectively achieves synergy through accelerated apoptosis triggered by prolonged mitotic arrest.

Enhanced cytotoxicity with a novel system combining the paclitaxel-2'-ethylcarbonate prodrug and an HSV amplicon with an attenuated replication-competent virus, HF10 as a helper virus

We previously demonstrated that HF10, which is a natural, non-engineered HSV-1, has potent oncolytic activity in the treatment of solid malignant tumors in vitro and in vivo [H. Takakuwa, F. Goshima, N. Nozawa, T. Yoshikawa, H. Kimata, A. Nakao, et al., Oncolytic viral therapy using a spontaneously generated herpes simplex virus type 1 variant for disseminated peritoneal tumor in immunocompetent mice, Arch. Virol. 148 (2003) 813-825; S. Kohno, C. Lou, F. Goshima, Y. Nishiyama, T. Sata, Y. Ono, Herpes simplex virus type 1 mutant HF10 oncolytic viral therapy for bladder cancer, Urology 66 (2005) 1116-1121; D. Watanabe, F. Goshima, I. Mori, Y. Tamada, Y. Matsumoto, Y. Nishiyama, Oncolytic virotherapy for malignant melanoma with herpes simplex virus type 1 mutant HF10, J. Dermatol. Sci. 50 (2008) 185-196; A. Nawa, C. Luo, L. Zhang, Y. Ushijima, D. Ishida, M. Kamakura, et al., Non-engineered, naturally oncolytic herpes simplex virus HSV1 HF10: applications for cancer gene therapy, Curr. Gene. Ther. 8 (2008) 208-221]. Previous reports have also shown that a combination of HF10 and paclitaxel (TAX) was more efficacious than either regimen alone for some types of malignant tumors [S. Shimoyama, F. Goshima, O. Teshigahara, H. Kasuya, Y. Kodera, A. Nakao, et al., Enhanced efficacy of herpes simplex virus mutant HF10 combined with paclitaxel in peritoneal cancer dissemination models, Hepatogastroenterology 54 (2007) 1038-1042]. In this study, we investigated the efficacy of gene-directed enzyme prodrug therapy (GDEPT) using a novel system that combines the paclitaxel-2'-ethylcarbonate prodrug (TAX-2'-Et) and an HSV amplicon expressing rabbit-carboxylesterase (CES) with HF10 as a helper virus. This GDEPT system aims to produce high level of CES at the tumor site, resulting in efficient local conversion of the TAX-2'-Et prodrug into the active drug TAX [A. Nawa, T. Tanino, C. Lou, M. Iwaki, H. Kajiyama, K. Shibata, et al., Gene directed enzyme prodrug therapy for ovarian cancer: could GDEPT become a promising treatment against ovarian cancer?, Anti-Cancer Agents Med Chem 8 (2008) 232-239]. We demonstrated that the green fluorescent protein (GFP) gene, as a trace maker, was more efficiently introduced by the HSV amplicon compared to the expression vector, pHGCX, and that the HSV amplicon system expressed an active CES enzyme that could convert TAX-2'-Et to TAX in Cos7 cells. Furthermore, although the cytotoxicity of this amplicon system was not enhanced in virus-sensitive tumor cells, it was significantly enhanced in low virus-sensitive tumor cells in the presence of the prodrug in a concentration-dependent manner, compared to the control virus alone (p<0.05). These results indicate that the addition of a prodrug converting enzyme may be a feasible approach to further enhance the efficacy of HF10 as a cancer therapeutics in low HF10-sensitive malignancies.

Imaging a Genetically Engineered Oncolytic Vaccinia Virus (GLV-1h99) Using a Human Norepinephrine Transporter Reporter Gene

PURPOSE

Oncolytic viral therapy continues to be investigated for the treatment of cancer, and future studies in patients would benefit greatly from a noninvasive modality for assessing virus dissemination, targeting, and persistence. The purpose of this study was to determine if a genetically modified vaccinia virus, GLV-1h99, containing a human norepinephrine transporter (hNET) reporter gene, could be sequentially monitored by [(123)I]metaiodobenzylguanidine (MIBG) gamma-camera and [(124)I]MIBG positron emission tomography (PET) imaging.

EXPERIMENTAL DESIGN

GLV-1h99 was tested in human malignant mesothelioma and pancreatic cancer cell lines for cytotoxicity, expression of the hNET protein using immunoblot analysis, and [(123)I]MIBG uptake in cell culture assays. In vivo [(123)I]MIBG gamma-camera and serial [(124)I]MIBG PET imaging was done in MSTO-211H orthotopic pleural mesothelioma tumors.

RESULTS

GLV-1h99 successfully infected and provided dose-dependent levels of transgene hNET expression in human malignant mesothelioma and pancreatic cancer cells. The time course of [(123)I]MIBG accumulation showed a peak of radiotracer uptake at 48 hours after virus infection in vitro. In vivo hNET expression in MSTO-211H pleural tumors could be imaged by [(123)I]MIBG scintigraphy and [(124)I]MIBG PET 48 and 72 hours after GLV-1h99 virus administration. Histologic analysis confirmed the presence of GLV-1h99 in tumors.

CONCLUSION

GLV-1h99 shows high mesothelioma tumor cell infectivity and cytotoxic efficacy. The feasibility of imaging virus-targeted tumor using the hNET reporter system with [(123)I]MIBG gamma-camera and [(124)I]MIBG PET was shown in an orthotopic pleural mesothelioma tumor model. The inclusion of human reporter genes into recombinant oncolytic viruses enhances the potential for translation to clinical monitoring of oncolytic viral therapy.

Gene therapy: the end of the rainbow?

The increased understanding of the molecular basis of oral cancer has led to expectations that correction of the genetic defects will lead to improved treatments. Nevertheless, the first clinical trials for gene therapy of oral cancer occurred 20 years ago, and routine treatment is still not available. The major difficulty is that genes are usually delivered by virus vectors whose effects are weak and temporary. Viruses that replicate would be better, and the field includes many approaches in that direction. If any of these are effective in patients, then gene therapy will become available in the next few years. Without significant advances, however, the treatment of oral cancer by gene therapy will remain as remote as the legendary pot of gold at the end of the rainbow.

Oncolytic adenoviral mutants with E1B19K gene deletions enhance gemcitabine-induced apoptosis in pancreatic carcinoma cells and anti-tumor efficacy in vivo

PURPOSE

Pancreatic adenocarcinoma is a rapidly progressive malignancy that is highly resistant to current chemotherapeutic modalities and almost uniformly fatal. We show that a novel targeting strategy combining oncolytic adenoviral mutants with the standard cytotoxic treatment, gemcitabine, can markedly improve the anticancer potency.

EXPERIMENTAL DESIGN

Adenoviral mutants with the E1B19K gene deleted with and without E3B gene expression (AdDeltaE1B19K and dl337 mutants, respectively) were assessed for synergistic interactions in combination with gemcitabine. Cell viability, mechanism of cell death, and antitumor efficacy in vivo were determined in the pancreatic carcinoma cells PT45 and Suit2, normal human bronchial epithelial cells, and in PT45 xenografts.

RESULTS

The DeltaE1B19K-deleted mutants synergized with gemcitabine to selectively kill cultured pancreatic cancer cells and xenografts in vivo with no effect in normal cells. The corresponding wild-type virus (Ad5) stimulated drug-induced cell killing to a lesser degree. Gemcitabine blocked replication of all viruses despite the enhanced cell killing activity due to gemcitabine-induced delay in G1/S-cell cycle progression, with repression of cyclin E and cdc25A, which was not abrogated by viral E1A-expression. Synergistic cell death occurred through enhancement of gemcitabine-induced apoptosis in the presence of both AdDeltaE1B19K and dl337 mutants, shown by increased cell membrane fragmentation, caspase-3 activation, and mitochondrial dysfunction.

CONCLUSIONS

Our data suggest that oncolytic mutants lacking the antiapoptotic E1B19K gene can improve efficacy of DNA-damaging drugs such as gemcitabine through convergence on cellular apoptosis pathways. These findings imply that less toxic doses than currently practiced in the clinic could efficiently target pancreatic adenocarcinomas when combined with adenoviral mutants.

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.

Treatment of hepatocellular carcinoma by AdAFPep/rep, AdAFPep/p53, and 5-fluorouracil in mice

Although conditionally replicable adenovirus (CRAd) has been used in the clinical treatment of hepatocellular carcinoma (HCC), it suffers from the inherent drawback of having relatively low antitumor activity. Here, we have sought to overcome this drawback. First, we combined CRAd (AdAFPep/Rep) driven by alpha-fetoprotein enhancer/promoter (AFPep) with a replication-incompetent adenovirus carrying a p53 transgene that is also driven by AFPep. The synergism of this combination produced a significantly improved tumoricidal effect on the human HCC cell line Hep3B, which has a relatively short doubling time in comparison with other human HCC cell lines, through the transactivation of p53 by early region 1A transcribed by AdAFPep/Rep. This synergistic interaction was augmented by the addition of a subtumoricidal dose (0.5 microg/mL) of 5-fluorouracil (5-FU), which enhanced p53 expression and facilitated the release of virions from tumor cells. When relatively large (10-mm-diameter) Hep3B tumors grown in nude mice were injected with the two viruses in combination, they showed significantly impaired growth in comparison with those treated with each virus separately. The growth suppression effect of the virus combination was enhanced by a low dose (600 microg) of 5-FU. Survival of the tumor-bearing mice treated with these three agents was significantly longer than that of control mice. Moreover, the tumor completely disappeared with the repeated injection of these agents.

CONCLUSION

This combination strategy holds promise for the treatment of relatively large and rapidly growing HCCs that may be encountered clinically.

Killing of p53-deficient hepatoma cells by parvovirus H-1 and chemotherapeutics requires promyelocytic leukemia protein

AIM: To evaluate the synergistic targeting and killing of human hepatocellular carcinoma (HCC) cells lacking p53 by the oncolytic autonomous parvovirus (PV) H-1 and chemotherapeutic agents and its dependence on functional promyelocytic leukemia protein (PML).

METHODS: The role of p53 and PML in regulating cytotoxicity and gene transfer mediated by wild-type (wt) PV H-1 were explored in two pairs of isogenic human hepatoma cell lines with different p53 status. Furthermore, H-1 PV infection was combined with cytostatic drug treatment.

RESULTS: While the HCC cells with different p53 status studied were all susceptible to H-1 PV-induced apoptosis, the cytotoxicity of H-1 PV was more pronounced in p53-negative than in p53-positive cells. Apoptosis rates in p53-negative cell lines treated by genotoxic drugs were further enhanced by a treatment with H-1 PV. In flow cytometric analyses, H-1 PV infection resulted in a reduction of the mitochondrial transmembrane potential. In addition, H-1 PV cells showed a significant increase in PML expression. Knocking down PML expression resulted in a striking reduction of the level of H-1 PV infected tumor cell death.

CONCLUSION: H-1 PV is a suitable agent to circumvent the resistance of p53-negative HCC cells to genotoxic agents, and it enhances the apoptotic process which is dependent on functional PML. Thus, H-1 PV and its oncolytic vector derivatives may be considered as therapeutic options for HCC, particularly for p53-negative tumors.

Targeted delivery of a suicide gene to human colorectal tumors by a conditionally replicating vaccinia virus

We have generated a thymidine kinase gene-deleted vaccinia virus (VV) (Copenhagen strain) that expressed the fusion suicide gene FCU1 derived from the yeast cytosine deaminase and uracil phosphoribosyltransferase genes. Intratumoral inoculation of this thymidine kinase gene-deleted VV encoding FCU1 (VV-FCU1) in the presence of systemically administered prodrug 5-fluorocytosine (5-FC) produced statistically significant reductions in the growth of subcutaneous human colon cancer in nude mice compared with thymidine kinase gene-deleted VV treatments or with control 5-fluorouracil alone. A limitation of prodrug therapies has often been the requirement for the direct injection of the virus into relatively large, accessible tumors. Here we demonstrate vector targeting of tumors growing subcutaneously following systemic administration of VV-FCU1. More importantly we also demonstrate that the systemic injection of VV-FCU1 in nude mice bearing orthotopic liver metastasis of a human colon cancer, with concomitant administration of 5-FC, leads to substantial tumor growth retardation. In conclusion, the insertion of the fusion FCU1 suicide gene potentiates the oncolytic efficiency of the thymidine kinase gene-deleted VV and represents a potentially efficient means for gene therapy of distant metastasis from colon and other cancers.

Myxoma virus is oncolytic for human pancreatic adenocarcinoma cells

BACKGROUND

Viral oncolytic therapy, which seeks to exploit the use of live viruses to treat cancer, has shown promise in the treatment of cancers resistant to conventional anticancer therapies. Among the most difficult to treat cancers is advanced pancreatic adenocarcinoma. Our study investigates the ability of a novel oncolytic agent, myxoma virus, to infect, productively replicate in, and kill human pancreatic cancer cells in vitro.

METHODS

The myxoma virus vMyxgfp was tested against a panel of human pancreatic adenocarcinoma cell lines. Infectivity, viral proliferation, and tumor cell kill were assessed.

RESULTS

Infection of tumor cells was assessed by expression of the marker gene enhanced green fluorescent protein (e-GFP). vMyxgfp had the ability to infect all pancreatic cancer cell lines tested. Killing of tumor cells varied among the 6 cell lines tested, ranging from >90% cell kill at 7 days for the most sensitive Panc-1 cells, to 39% in the most resistant cell line Capan-2. Sensitivity correlated to replication of virus, and was found to maximally exhibit a four-log increase in foci-forming units for the most sensitive Panc-1 cells within 72 h.

CONCLUSION

Our study demonstrates for the first time the ability of the myxoma virus to productively infect, replicate in, and lyse human pancreatic adenocarcinoma cells in vitro. These data encourage further investigation of this virus, which is pathogenic only in rabbits, for treatment of this nearly uniformly fatal cancer.

Oncolytic virotherapy for ovarian carcinomatosis using a replication-selective vaccinia virus armed with a yeast cytosine deaminase gene

In this study, we assessed the ability of a highly tumor-selective oncolytic vaccinia virus armed with a yeast cytosine deaminase gene to infect and lyse human and murine ovarian tumors both in vitro and in vivo. The virus vvDD-CD could infect, replicate in and effectively lyse both human and mouse ovarian cancer cells in vitro. In two different treatment schedules involving either murine MOSEC or human A2780 ovarian carcinomatosis models, regional delivery of vvDD-CD selectively targeted tumor cells and ovarian tissue, effectively delaying the development of either tumor or ascites and leading to significant survival advantages. Oncolytic virotherapy using vvDD-CD in combination with the prodrug 5-fluorocytosine conferred an additional long-term survival advantage upon tumor-bearing immunocompetent mice. These findings demonstrate that a tumor-selective oncolytic vaccinia combined with gene-directed enzyme prodrug therapy is a highly effective strategy for treating advanced ovarian cancers in both syngeneic mouse and human xenograft models. Given the biological safety, tumor selectivity and oncolytic potency of this armed oncolytic virus, this dual therapy merits further investigation as a promising new treatment for metastatic ovarian cancer.

Everolimus and mycophenolate mofetil sensitize human pancreatic cancer cells to gemcitabine in vitro: a novel adjunct to standard chemotherapy?

BACKGROUND/AIMS

Gemcitabine improves survival in pancreatic adenocarcinoma. A variety of drugs have been tested to potentiate gemcitabine treatment for pancreatic cancer cells. Two major immunosuppressive drugs, mycophenolate mofetil (MMF) and everolimus (RAD001) have been shown to exert an anti-tumoral effect, but their ability to sensitize human pancreatic cell lines during gemcitabine treatment remains unclear. We examined the effects of everolimus and MMF on gemcitabine-treated MiaPaCa and Panc-1 cell lines.

METHODS

MiaPaCa and Panc-1 human pancreatic tumor cell lines were subjected to everolimus (0.001-1 microg/ml) or MMF (0.1-100 microg/ml) treatment in combination with gemcitabine (1-10(6) nM). Western blot analysis was performed for Panc-1 cells in the presence or absence of TGF-beta1 and different treatments: 0.1-100 muicro/ml MMF and 0.1-100 microg/ml everolimus. The antiproliferative effect of the treatment was assessed by BrdU test. The results were evaluated by two-way analysis of variance followed by post-hoc tests, and nonlinear regression analysis for dose-response rates.

RESULTS

As expected, standard treatment doses of gemcitabine decreased proliferation dose-dependently. Everolimus increased the actual EC(50) response to gemcitabine treatment (1-10(3) nM) to as much as 83.1 and 82.1% in MiaPaCa and Panc-1 cell lines, respectively. Likewise, concomitant administration with MMF altered the EC(50) of gemcitabine treatment in MiaPaCa cell lines to values between 76.8 and 85.2% for doses of >or=1 microg/ml. Even the minor dose of MMF (0.1 microg/ml) increased the antiproliferative effect of gemcitabine by 43.5% for MiaPaCa and 42.4% for Panc-1 cells. In addition, treatment of Panc-1 cells with MMF (0.1-100 microg/ml) dose-dependently inhibited TGF-beta1-induced collagen expression.

CONCLUSION

We found an overadditive antiproliferative effect of both MMF and everolimus in gemcitabine-treated MiaPaCa and Panc-1 cells in vitro, and an additional inhibitory effect of MMF on TGF-beta1-induced collagen type I expression. Interestingly, both the sensitizing effect of pancreatic cancer cells to gemcitabine treatment and the inhibition of collagen type I expression could be achieved by clinically feasible doses of everolimus and MMF. The use of these drugs is promising as a novel adjunct to standard chemotherapy.

Synergistic activity of troxacitabine (Troxatyl) and gemcitabine in pancreatic cancer

Background

Gemcitabine, a deoxycytidine nucleoside analog, is the current standard chemotherapy used as first-line treatment for patients with locally advanced or metastatic cancer of the pancreas, and extends life survival by 5.7 months. Advanced pancreatic cancer thus remains a highly unmet medical need and new therapeutic agents are required for this patient population. Troxacitabine (Troxatyl™) is the first unnatural L-nucleoside analog to show potent preclinical antitumor activity and is currently under clinical investigation. Troxacitabine was recently evaluated as a first-line therapy in 54 patients with advanced adenocarcinoma of the pancreas and gave comparable overall results to those reported with gemcitabine in recently published randomized trials.

Methods

The human pancreatic adenocarcinoma cell lines, AsPC-1, Capan-2, MIA PaCa-2 and Panc-1, were exposed to troxacitabine or gemcitabine alone or in combination, for 72 h, and the effects on cell growth were determined by electronic particle counting. Synergistic efficacy was determined by the isobologram and combination-index methods of Chou and Talalay. Mechanistic studies addressed incorporation of troxacitabine into DNA and intracellular levels of troxacitabine and gemcitabine metabolites. For in vivo studies, we evaluated the effect of both drugs, alone and in combination, on the growth of established human pancreatic (AsPC-1) tumors implanted subcutaneously in nude mice. Statistical analysis was calculated by a one-way ANOVA with Dunnett as a post-test and the two-tailed unpaired t test using GraphPad prism software.

Results

Synergy, evaluated using the CalcuSyn Software, was observed in all four cell-lines at multiple drug concentrations resulting in combination indices under 0.7 at Fa of 0.5 (50% reduction of cell growth). The effects of drug exposures on troxacitabine and gemcitabine nucleotide pools were analyzed, and although gemcitabine reduced phosphorylation of troxacitabine when cells were exposed at equal drug concentrations, there was no effect on phosphorylated pools at drug combinations that were synergistic. The amount of troxacitabine incorporated into DNA was also not affected by the presence of gemcitabine. In vivo testing against a human pancreatic (AsPC-1) xenograft mouse tumor model indicated that both drugs were more than additive at well-tolerated doses and schedule. The biological basis for this synergy is unclear as we did not observe changes in apoptosis, DNA repair, troxacitabine incorporation into DNA or troxacitabine metabolism in the presence of gemcitabine.

Conclusion

These data, together with phase I clinical data showing tolerability of both agents when combined, suggest combination therapy with troxacitabine and gemcitabine warrants further evaluation in advanced pancreatic cancer patients.

Efficacy of oncolytic herpesvirus NV1020 can be enhanced by combination with chemotherapeutics in colon carcinoma cells

NV1020, an oncolytic herpes simplex virus type 1, can destroy colon cancer cells by selectively replicating within these cells, while sparing normal cells. NV1020 is currently under investigation in a clinical phase I/II trial as an agent for the treatment of colon cancer liver metastases, in combination with conventional chemotherapeutic agents such as 5-fluorouracil (5-FU), SN38 (the active metabolite of irinotecan), and oxaliplatin. To study the synergy of NV1020 and chemotherapy, cytotoxicity and viral replication were evaluated in vitro by treating various human and murine colon carcinoma cell lines, using a colorimetric viability assay, a clonogenic assay, and a plaque-forming assay. In vivo experiments, using a subcutaneous syngeneic CT-26 tumor model in BALB/c mice, were performed to determine the efficacy of combination therapy. In vitro studies showed that the efficacy of NV1020 on human colon carcinoma cell lines HT-29, WiDr, and HCT-116 was additively or synergistically enhanced in combination with 5-FU, SN38, or oxaliplatin. The sequence of application was not important and effects were still apparent after a 21-day incubation period. Three intra-tumoral treatments with NV1020 (1 x 10(7) plaque-forming units), followed by three subcutaneous treatments with 5-FU (50 mg/kg), resulted in substantially higher inhibition of tumor growth and prolongation of survival compared with monotherapies (NV1020/5-FU vs. NV1020, p = 0.027). On WiDr cells, reduced replication of NV1020, in combination with 5-FU, indicated that additive and synergistic effects of combination therapy must be independent from viral replication. These results suggest that NV1020, in combination with chemotherapy, is a promising therapy for treating patients with metastatic colorectal cancer of the liver. We hypothesize that infection of cells with NV1020 sensitizes the infected cells for the cytotoxic effect of the chemotherapeutics.

Complementary effects of HDAC inhibitor 4-PB on gap junction communication and cellular export mechanisms support restoration of chemosensitivity of PDAC cells

Pancreatic ductal adenocarcinoma (PDAC) is a fatal disease and one of the cancer entities with the lowest life expectancy. Beside surgical therapy, no effective therapeutic options are available yet. Here, we show that 4-phenylbutyrate (4-PB), a known and well-tolerable inhibitor of histone deacetylases (HDAC), induces up to 70% apoptosis in all cell lines tested (Panc 1, T4M-4, COLO 357, BxPc3). In contrast, it leads to cell cycle arrest in only half of the cell lines tested. This drug increases gap junction communication between adjacent T3M-4 cells in a concentration-dependent manner and efficiently inhibits cellular export mechanisms in Panc 1, T4M-4, COLO 357 and BxPc3 cells. Consequently, in combination with gemcitabine 4-PB shows an overadditive effect on induction of apoptosis in BxPc3 and T3M-4 cells (up to 4.5-fold compared to single drug treatment) with accompanied activation of Caspase 8, BH3 interacting domain death agonist (Bid) and poly (ADP-ribose) polymerase family, member 1 (PARP) cleavage. Although the inhibition of the mitogen-activated protein kinase-pathway has no influence on fulminant induction of apoptosis, the inhibition of the JNK-pathway by SP600125 completely abolishes the overadditive effect induced by the combined application of both drugs, firstly reported by this study.

Radiation-induced cellular DNA damage repair response enhances viral gene therapy efficacy in the treatment of malignant pleural mesothelioma

BACKGROUND

Malignant pleural mesothelioma (MPM) treated with radiotherapy (RT) has incomplete responses as a result of radiation-induced tumoral stress response that repairs DNA damage. Such stress response is beneficial for oncolytic viral therapy. We hypothesized that a combination of RT and NV1066, an oncolytic herpes virus, might exert an additive or synergistic effect in the treatment of MPM.

METHODS

JMN, a MPM cell line, was infected with NV1066 at multiplicities of infection of .05 to .25 in vitro with and without radiation (1 to 5 Gy). Virus replication was determined by plaque assay, cell kill by lactate dehydrogenase assay, and GADD34 (growth arrest and DNA damage repair 34, a DNA damage-repair protein) by real-time reverse transcriptase-polymerase chain reaction and Western blot test. Synergistic cytotoxicity dependence on GADD34 upregulation was confirmed by GADD34 small inhibitory RNA (siRNA).

RESULTS

Synergism was demonstrated between RT and NV1066 across a wide range of doses. As a result of such synergism, a dose-reduction for each agent (up to 5500-fold) can be accomplished over a wide range of therapeutic-effect levels without sacrificing tumor cell kill. This effect is correlated with increased GADD34 expression and inhibited by transfection of siRNA directed against GADD34.

CONCLUSIONS

RT can be combined with oncolytic herpes simplex virus therapy in the treatment of malignant pleural mesothelioma to achieve synergistic efficacy while minimizing dosage and toxicity.

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