E1A, E1B double-restricted replicative adenovirus at low dose greatly augments tumor-specific suicide gene therapy for gallbladder cancer

Exploring the role of oncolytic viruses in hepatobiliary cancers

The standard of care for early hepatobiliary cancers (HBC) includes surgical resection. Liver transplantations or locoregional therapies are beneficial in early hepatocellular carcinoma (HCC) under certain circumstances. Systemic treatments have some benefit in advanced HBC, though long-term prognosis remains poor. We evaluated the role of oncolytic viruses in the treatment of HBCs through a systematic literature review. The recombinant vaccinia virus JX-594 improved median survival in patients with local/metastatic HCC more strongly at high dose than at low dose (14.1 vs 6.7 months; p = 0.08) in a Phase II study. A Phase III study with JX-594 and sorafenib in advanced HCC is ongoing. No survival benefit in HCC was seen with two other recombinant adenoviruses (Ad-TK and DL1520). Several preclinical trials using oncolytic viruses in HBC showed promising results, warranting clinical studies.

A novel approach to glioma therapy using an oncolytic adenovirus with two specific promoters

Gliomas are the most common type of primary brain tumor in adults, where more than half of the cases are malignant, and the prognosis is poor. The early viral 1A (E1A) protein has been widely recognized to be essential for adenoviral replication and production of progeny virions in human cells, a process that is regulated by human telomerase reverse transcriptase. The p53 gene, as a tumor suppressor, regulates diverse cellular processes, including cell cycle arrest, cell autophagy, senescence and apoptosis. Dysfunction of the p53 pathways is common in malignant gliomas. Exogenous expression of p53 during adenovirus replication in human cancer cells may accelerate cell death and improve the release of early virus progeny. In the present study, a conditionally replicative adenovirus (CRAd) Ad-Tp-E1A-Gp-p53, which expressed functional p53 protein when replicating in cancer cells, was constructed. Next, the level of p53 expression in U251 cells was determined by western blot analysis, and the inhibitory effect of Ad-Tp-E1A-Gp-p53 on U251 cells was detected via an MTT assay. The results indicated that p53 expression was upregulated with an increase in the multiplicity of infection (MOI) of Ad-Tp-E1A-Gp-p53. Additionally, the inhibitory effects of Ad-Tp-E1A-Gp-p53 in different groups were significantly different (P<0.05), with the inhibition ratio of the experimental groups being higher, compared with the control group (P<0.05). Furthermore, the inhibition ratio increased with increases in the MOI of Ad-Tp-E1A-Gp-p53. Therefore, the expression of functional p53 and that of E1A may increase the potency of CRAd, and overexpression of p53 through CRAd is a promising approach to more effective treatments in a number of human cancer types.

Adenovirus-Mediated Gene Delivery: Potential Applications for Gene and Cell-Based Therapies in the New Era of Personalized Medicine

With rapid advances in understanding molecular pathogenesis of human diseases in the era of genome sciences and systems biology, it is anticipated that increasing numbers of therapeutic genes or targets will become available for targeted therapies. Despite numerous setbacks, efficacious gene and/or cell-based therapies still hold the great promise to revolutionize the clinical management of human diseases. It is wildly recognized that poor gene delivery is the limiting factor for most in vivo gene therapies. There has been a long-lasting interest in using viral vectors, especially adenoviral vectors, to deliver therapeutic genes for the past two decades. Among all currently available viral vectors, adenovirus is the most efficient gene delivery system in a broad range of cell and tissue types. The applications of adenoviral vectors in gene delivery have greatly increased in number and efficiency since their initial development. In fact, among over 2,000 gene therapy clinical trials approved worldwide since 1989, a significant portion of the trials have utilized adenoviral vectors. This review aims to provide a comprehensive overview on the characteristics of adenoviral vectors, including adenoviral biology, approaches to engineering adenoviral vectors, and their applications in clinical and pre-clinical studies with an emphasis in the areas of cancer treatment, vaccination and regenerative medicine. Current challenges and future directions regarding the use of adenoviral vectors are also discussed. It is expected that the continued improvements in adenoviral vectors should provide great opportunities for cell and gene therapies to live up to its enormous potential in personalized medicine.

Progresses towards safe and efficient gene therapy vectors

The emergence of genetic engineering at the beginning of the 1970′s opened the era of biomedical technologies, which aims to improve human health using genetic manipulation techniques in a clinical context. Gene therapy represents an innovating and appealing strategy for treatment of human diseases, which utilizes vehicles or vectors for delivering therapeutic genes into the patients' body. However, a few past unsuccessful events that negatively marked the beginning of gene therapy resulted in the need for further studies regarding the design and biology of gene therapy vectors, so that this innovating treatment approach can successfully move from bench to bedside. In this paper, we review the major gene delivery vectors and recent improvements made in their design meant to overcome the issues that commonly arise with the use of gene therapy vectors. At the end of the manuscript, we summarized the main advantages and disadvantages of common gene therapy vectors and we discuss possible future directions for potential therapeutic vectors.

Strategies and developments of immunotherapies in osteosarcoma

Osteosarcoma (OS) is a frequently observed primary malignant tumor. Current therapy for osteosarcoma consists of comprehensive treatment. The long-term survival rate of patients exhibiting nonmetastatic OS varies between 65-70%. However, a number of OS cases have been observed to be resistant to currently used therapies, leading to disease recurrence and lung metastases, which are the primary reasons leading to patient mortality. In the present review, a number of pieces of evidence provide support for the potential uses of immunotherapy, including immunomodulation and vaccine therapy, for the eradication of tumors via upregulation of the immune response. Adoptive T-cell therapy and oncolytic virotherapy have been used to treat OS and resulted in objective responses. Immunologic checkpoint blockade and targeted therapy are also potentially promising therapeutic tools. Immunotherapy demonstrates significant promise with regard to improving the outcomes for patients exhibiting OS.

Dissecting the roles of E1A and E1B in adenoviral replication and RCAd-enhanced RDAd transduction efficacy on tumor cells

Oncolytic viruses have recently received widespread attention for their potential in innovative cancer therapy. Many telomerase promoter-regulated oncolytic adenoviral vectors retain E1A and E1B. However, the functions of E1A and E1B proteins in the oncolytic role of replication-competent adenovirus (RCAd) and RCAd enhanced transduction of replication defective adenoviruses (RDAd) have not been addressed well. In this study, we constructed viruses expressing E1A alone, E1A plus E1B-19 kDa, and E1A plus E1B-19 kDa/55 kDa. We then tested their roles in oncolysis and replication of RCAd as well as their roles in RCAd enhanced transfection rate and transgene expression of RDAd in various cancer cells in vitro and in xenografted human NCI-H460 tumors in nude mice. We demonstrated that RCAds expressing E1A alone and plus E1B-19 kDa exhibited an obvious ability in replication and oncolytic effects as well as enhanced RDAd replication and transgene expression, with the former showed more effective oncolysis, while the latter exhibited superior viral replication and transgene promotion activity. However, RCAd expressing both E1A and E1B-19 kDa/55 kDa was clearly worst in all these abilities. The effects of E1A and E1B observed through using RCAd were further validated by using plasmids expressing E1A alone, E1A plus E1B-19 kDa, and E1A plus E1B-19 kDa/55 kDa proteins. Our study provided evidence that E1A was essential for inducing replication and oncolytic effects of RCAd as well as RCAd enhanced RDAd transduction, and expression of E1B-19 kDa other than E1B-55 kDa could promote these effects. E1B-55 kDa is not necessary for the oncolytic effects of adenoviruses and somehow inhibits RCAd-mediated RDAd replication and transgene expression.

Cyclophosphamide enhances antitumor efficacy of oncolytic adenovirus expressing uracil phosphoribosyltransferase (UPRT) in immunocompetent Syrian hamsters

Oncolytic viruses (OVs) are novel cancer therapeutics with great promise, but host antiviral immunity represents the hurdle for their efficacy. Immunosuppression by cyclophosphamide (CP) has thus been shown to enhance the oncolytic efficacy of many OVs, but its effects on OVs armed with therapeutic genes remain unknown. We have previously reported on the efficacy of AxE1CAUP, an oncolytic adenovirus (OAd) expressing uracil phosphoribosyltransferase (UPRT), an enzyme that markedly enhanced the toxicity of 5-fluorouracil (5-FU), in immunodeficient, Ad-nonpermissive nude mice. Here we explored the efficacy and safety of intratumoral (i.t.) AxE1CAUP/5-FU therapy and of its combination with CP for syngenic HaP-T1 pancreatic cancers in immunocompetent, Ad-permissive Syrian hamsters. AxE1CAUP infected, replicated, expressed UPRT, and increased the sensitivity to 5-FU in HaP-T1 cells in vitro. I.t. AxE1CAUP/5-FU treatment inhibited the growth of subcutaneous HaP-T1 allografts. The combination with high-dose CP inhibited serum Ad-neutralizing antibody formation, increased intratumoral AxE1CAUP replication and UPRT expression, and resulted in further enhanced therapeutic effects with 5-FU. Neither body weight nor histology of the liver and lung changed during these treatments. A clinically-approved, intermediate-dose CP also enhanced the efficacy of i.t. AxE1CAUP/5-FU treatment in these hamsters, which was not affected by preexisting immunity to the vector. These data demonstrate the excellent antitumor efficacy and safety of an OAd armed with a suicide gene in combination with CP for treating syngenic tumors in immunocompetent, Ad-permissive animals, indicating the efficacy of CP in overcoming the hurdle of antiviral immunity for effective OV-mediated gene therapy.

Downregulation of Mcl-1 synergizes the apoptotic response to combined treatment with cisplatin and a novel fiber chimeric oncolytic adenovirus

The aim of this study was to examine the effects of SG511, a novel fiber chimeric oncolytic adenovirus with E1B 55-kDa deleted, combined with cisplatin on cancer cells and to identify their underlying mechanisms. The combined effect of SG511 and cisplatin on HeLa and HT-29 cells was assessed by a crystal violet assay and an MTT assay, followed by combination index analysis. Cell apoptosis was evaluated by DAPI staining and visualized by fluorescein-mediated signal detection. Mitochondrial membrane potential was detected by flow cytometric analysis of Rhodamine 123 accumulation. The activation of the caspase pathway and the expression of Bcl-2 family proteins were examined by western blotting. Results show that SG511 vector infected various human cancer cell lines and induced growth inhibition effectively. Of note, SG511 synergistically enhanced the anti-proliferative activity of cisplatin, a DNA-damaging agent, against HeLa and HT-29 cells in vitro, concomitantly with increased apoptosis and activation of the mitochondrial pathway. Furthermore, treatment with SG511 alone or in combination with cisplatin resulted in reduced expression the anti-apoptotic Bcl-2 family member Mcl-1 in HeLa and HT-29 cells. Importantly, this combination did not increase the growth inhibitory effects of cisplatin on human normal liver cells. Collectively, SG511, a novel fiber chimeric oncolytic adenovirus, sensitizes cancer cells to apoptosis by reducing anti-apoptotic Mcl-1 protein levels.

Verapamil results in increased blood levels of oncolytic adenovirus in treatment of patients with advanced cancer

Calcium channel blockers including verapamil have been proposed to enhance release and antitumor efficacy of oncolytic adenoviruses in preclinical studies but this has not been studied in humans before. Here, we studied if verapamil leads to increased replication of oncolytic adenovirus in cancer patients, as measured by release of virions from tumor cells into the systemic circulation. The study was conducted as a matched case-control study of advanced cancer patients treated with oncolytic adenoviruses with or without verapamil. We observed that verapamil increased mean virus titers present in blood after treatment (P < 0.05). The frequency or severity of adverse events was not increased, nor were cytokine responses or neutralizing antibody levels different between groups. Signs of possible treatment-related clinical benefits were observed in both groups, but there was no significant difference in responses or survival. Thus, our data suggests that the combination of verapamil with oncolytic adenoviruses is safe and well tolerated. Moreover, verapamil treatment seems to result in higher virus titers in blood, indicating enhanced overall replication in tumors. A randomized trial is needed to confirm these findings and to study if enhanced replication results in benefits to patients.

EpCAM- and EGFR-targeted selective gene therapy for biliary cancers using Z33-fiber-modified adenovirus

A critical issue in adenovirus (Ad)-based cancer gene therapy is to improve the specificity of gene delivery to cancer cells for better efficacy and safety. We explored methods of retargeting Ad vectors for selective gene therapy of human biliary cancers using the Ad incorporating an IgG Fc-binding motif (Z33) from the Staphylococcus protein A (Ad-FZ33) combined with tumor-specific antibodies. Flow cytometry analysis revealed high-expression levels of epithelial cell adhesion molecule (EpCAM) and epidermal growth factor receptor (EGFR) on human biliary cancer cells. Ad-FZ33 expressing LacZ combined with antibodies against EpCAM or EGFR, followed by β-gal assay, demonstrated highly efficient gene transduction in these biliary cancer cells, compared to the treatment with control antibody or without antibody. Ad-FZ33 expressing uracil phosphoribosyl transferase (UPRT), an enzyme which greatly enhances the toxicity of 5-fluorouracil (FU), combined with antibodies against EpCAM or EGFR, remarkably enhanced the sensitivity of biliary cancer cells to 5-FU. By contrast, the treatment did not affect the 5-FU sensitivity of the cells not expressing EpCAM or EGFR including normal hepatocytes. Finally, treatments with the UPRT-expressing Ad-FZ33 with antibodies against EpCAM or EGFR, followed by 5-FU administration, significantly suppressed the growth of biliary cancer xenografts in nude mice. These results indicate that the gene therapy mediated by the Z33 fiber modified Ad with anti-EpCAM or anti-EGFR antibodies offers a potentially effective therapeutic modality against biliary cancers.

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.

Intelligent design: combination therapy with oncolytic viruses

Metastatic cancer remains an incurable disease in the majority of cases and thus novel treatment strategies such as oncolytic virotherapy are rapidly advancing toward clinical use. In order to be successful, it is likely that some type of combination therapy will be necessary to have a meaningful impact on this disease. Although it may be tempting to simply combine an oncolytic virus with the existing standard radiation or chemotherapeutics, the long-term goal of such treatments must be to have a rational, potentially synergistic combination strategy that can be safely and easily used in the clinical setting. The combination of oncolytic virotherapy with existing radiotherapy and chemotherapy modalities is reviewed along with novel biologic therapies including immunotherapies, in order to help investigators make intelligent decisions during the clinical development of these products.