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The possibility of insertional mutagenesis in retroviral gene therapy can be reduced by using a vector lacking the enhancer sequence present in the U3 of the long-terminal repeats. However, such vectors suffer from many pitfalls. We attempted to improve a murine leukemia virus-based retroviral vector containing the enhancer-free U3, first by making it easier to construct a producer line and then by introducing the cellular RPL10 promoter as an internal promoter. The reverse orientation of the expression cassette of the transgene was found to give higher transducing titer and higher-level gene expression. The deletion analysis revealed that the 54-bp-long sequence of U3 (34 and 20 bp present at 5' and 3' extreme ends, respectively) was sufficient for the functions of retroviral vectors. The data from the in vitro cell culture assay indicated that the final construct, ROK, containing all these features, had little cis-activation activity, even if it was placed right upstream from the RNA start site of the neighboring gene. Our data suggested that the newly developed vector might provide increased safety, while still producing high viral titer from a stable producer line and high-level gene expression in various target cells including human CD34(+) stem cells.

RNA interference, due to its target specificity, may be highly effective as a novel therapeutic modality, but direct delivery of synthetic small interfering RNA still remains a major obstacle for this approach. To induce long-term expression and specific gene silencing, novel delivery vector system is also required. In this study, we have generated an efficient oncolytic adenovirus (Ad)-based short hairpin (shRNA) expression system (Ad-DeltaB7-U6shIL8) against IL-8, a potent proangiogenic factor. To demonstrate IL-8-specificity of this newly engineered Ad-based shRNA, we also manufactured replication-incompetent Ads (Ad-DeltaE1-CMVshIL8 and Ad-DeltaE1-U6shIL8) under the control of the cytomegalovirus (CMV) and U6 promoters, respectively. Ad-DeltaE1-U6shIL8 was highly effective in reducing IL-8 expression, and was much more effective in driving IL-8-specific shRNA than the CMV promoter-driven vector. The reduced IL-8 expression then translated into decreased angiogenesis in vitro as measured by migration, tube formation and rat aortic ring sprouting assays. In addition to its effect on endothelial cells, Ad-DeltaE1-U6shIL8 also effectively suppressed the migration and invasion of cancer cells. In vivo, intratumoral injection of Ad-DeltaB7-U6shIL8 significantly inhibited the growth of Hep3B and A549 human tumor xenografts. Histopathological analysis of Ad-DeltaB7-U6shIL8-treated tumors revealed an increase in apoptotic cells and a reduction in vessel density. Finally, Ad-DeltaB7-U6shIL8 was also shown to inhibit the growth of disseminated MDA-MB-231 breast cancer metastases. Taken together, these findings demonstrate the utility and antitumor effectiveness of oncolytic Ad expressing shRNA against IL-8.

Radiation therapy, a mainstay for anti-tumor therapeutic regimens for a variety of tumor types, triggers tumor cell apoptotic pathways by either directly eliciting DNA damage or indirectly inducing the formation of oxygen radicals. In an effort to augment radiation therapy, we generated a double E1B 19 kDa- and E1B 55 kDa-deleted oncolytic adenovirus (Ad-DeltaE1B19/55). In combination with radiotherapy, greater cytotoxicity was observed for Ad-DeltaE1B19/55 than for the single E1B 55 kDa-deleted oncolytic Ad (Ad-DeltaE1B55). Consistent with this observation, higher levels of p53, phospho-p53, phospho-Chk1, phospho-Chk2, PI3K (phosphatidylinositol-3-kinase), phospho-AKT, cytochrome c, and cleavage of PARP (poly (ADP-ribose) polymerase) and caspase-3 were observed in cells treated with Ad-DeltaE1B19/55 compared with those treated with Ad-DeltaE1B55, indicating that the E1B 19 kDa present in Ad-DeltaE1B55 may partially block radiation-induced apoptosis. A significant therapeutic benefit was also observed in vivo when oncolytic Ads and radiation were combined. Tumors treated with Ad-DeltaE1B19/55 and radiation showed large areas of necrosis and apoptosis with the corresponding induction of p53. Finally, consistent with in vitro observations, the combination of Ad-DeltaE1B19/55 and radiation was more efficacious than the combination of Ad-DeltaE1B55 and radiation. Taken together, these results present a strong therapeutic rationale for combining radiation therapy with E1B 19 kDa-deleted oncolytic Ad.

Oncolytic adenoviral vectors are currently being developed as biologic anticancer agents. Coupling the lytic function of an oncolytic adenovirus (Ad) with its ability as a transgene delivery system represents a powerful extension of this methodology. A clear advantage is the amplification of a therapeutic gene, as replicating vectors would be able to infect and deliver the gene of interest to neighboring cells. Granulocyte-macrophage colony-stimulating factor (GM-CSF) is one of the most potent stimulators of a specific and long-lasting antitumor immunity and its important role in the maturation of antigen-presenting cells to induce T-cell activation has been well documented. Similarly, the B7 family has also been shown to play an integral role in mediating an antitumor response. Most tumor cells, however, lack the expression of these costimulatory molecules on their surface, thus escaping immune system recognition. To increase the antitumor effect of an oncolytic Ad, we have generated an E1B 55 kDa-deleted oncolytic adenoviral vector, YKL-GB, that expresses both GM-CSF and B7-1. The therapeutic efficacy of YKL-GB Ad was evaluated in immunocompetent mice bearing murine melanoma B16-F10 tumors. Significant inhibition of tumor growth was seen in mice treated with YKL-GB compared to those treated with the analogous vector, YKL-1. Moreover, YKL-GB oncolytic Ad demonstrated enhanced antitumor activity and higher incidences of tumor regression compared to a replication-incompetent Ad, dl-GB, which coexpresses GM-CSF and B7-1. Localized GM-CSF and B7-1 gene transfer also conferred long-lasting immunity against a tumor re-challenge. To establish that the observed antitumor effect is associated with the generation of a tumor-specific immune response, we carried out interferon-gamma enzyme-linked immune spot assay. We observed that YKL-GB induced significantly higher immune cell activation than YKL-1. Furthermore, immunohistochemical studies demonstrated robust dendritic cells and CD4(+)/CD8(+) T-cell infiltration in these mice compared to the YKL-1-treated groups. In agreement with these results, splenocytes from tumor-bearing mice treated with YKL-GB expressed high levels of the costimulatory and activation molecules. These findings demonstrate the effectiveness of enhancing the immune response against tumors with an oncolytic Ad expressing both GM-CSF and B7-1 and provide a potential therapeutic strategy for the management of neoplasia.

A retroviral vector constructed from the murine leukemia virus (MLV) can only express transgenes in cells undergoing mitosis, indicating its suitability as a delivery vehicle for cancer gene therapy. However, the transduction efficiency (TE) of retroviruses embedding endogenous envelope proteins in human cancer cells was found to be unsatisfactory. Recently, several research groups have demonstrated the feasibility of a retroviral vector pseudotyped with a vesicular stomatitis virus G (VSV-G) protein. In this study, the potential of VSV-G pseudotyped MLV-based retrovirus was examined as a delivery vehicle in a variety of human cancer cells including brain tumor cells in vitro and in vivo. The transduction efficiency of the 293T/G/GP/LacZ retrovirus in cell culture was superior in most cancer cells, particularly in brain tumor cells, compared with that of other retroviruses, such as PA317- or PG13-derived. The relative growth rate and phosphatidylserine expression level on the plasma membrane of target cells mainly influenced the transduction efficiency of VSV-G pseudotyped retrovirus, which suggested that both the relative growth rate and phosphatidylserine expression level were major determinants of TE. Furthermore, 293T/G/GP/LacZ could efficiently transduce human cancer cells regardless of the presence of chemical additives, whereas in other retroviruses, cationic chemical additives such as polybrene or liposomes were essential during virus infection. Finally, an average of 10% gene expression was routinely obtained exclusively in the tumor mass when 293T/G/GP/LacZ concentrated by simple ultracentrifugation was directly administrated to pre-established brain tumors in animal models (U251-N nu/nu mice or C6 Wistar rats). All told, the present study suggests that the VSV-G pseudotyped retrovirus is a suitable vector for brain tumor gene therapy.