Replication-competent retrovirus vector-mediated prodrug activator gene therapy in experimental models of human malignant mesothelioma

Replication-competent retrovirus (RCR) vectors have been shown to achieve significantly enhanced tumor transduction efficiency and therapeutic efficacy in various cancer models. In the present study, we investigated RCR vector-mediated prodrug activator gene therapy for the treatment of malignant mesothelioma, a highly aggressive tumor with poor prognosis. RCR vector expressing the green fluorescent protein marker gene (RCR-GFP) successfully infected and efficiently replicated in human malignant mesothelioma cell lines, as compared to non-malignant mesothelial cells in vitro . In mice with pre-established subcutaneous tumor xenografts, RCR-GFP vector showed robust spread throughout entire tumor masses after intratumoral administration. Next, RCR-CD, expressing the yeast cytosine deaminase (CD) prodrug activator gene, showed efficient transmission of the prodrug activator gene associated with replicative spread of the virus, resulting in efficient killing of malignant mesothelioma cells in a prodrug 5-fluorocytosine (5FC)-dose dependent manner in vitro . After a single intratumoral injection of RCR-CD followed by intraperitoneal administration of 5FC, RCR vector-mediated prodrug activator gene therapy achieved significant inhibition of subcutaneous tumor growth, and significantly prolonged survival in the disseminated peritoneal model of malignant mesothelioma. These data indicate the potential utility of RCR vector-mediated prodrug activator gene therapy in the treatment of malignant mesothelioma

Enhanced antitumor efficacy of fiber-modified, midkine promoter-regulated oncolytic adenovirus in human malignant mesothelioma

Oncolytic virotherapy using adenoviruses has potential for therapeutic benefits in malignant mesothelioma. However, the downregulation of coxsackie virus/adenovirus receptor (CAR) expression is frequently a critical rate-limiting factor that impedes the effectiveness of adenovirus serotype 5 (Ad5)-based vectors in many cancer types. We evaluated CAR (Ad5 receptor) and CD46 (adenovirus serotype 35 [Ad35] receptor) expression in six human malignant mesothelioma cell lines. Very low CAR expression was observed in MSTO-211H and NCI-H2052 cells, whereas the other cell lines showed strong expression. In contrast, CD46 was highly expressed in all mesothelioma cell lines. On this basis, we replaced the CAR binding sequence of Ad5 with the CD46 binding sequence of Ad35 in the replication-defective adenoviruses and the tumor-specific midkine promoter-regulated oncolytic adenoviruses. By this fiber modification, the infectivity, virus progeny production, and in vitro cytocidal effects of the adenoviruses were significantly enhanced in low CAR-expressing MSTO-211H and NCI-H2052 cells, also resulting in similar or even higher levels in high CAR-expressing mesothelioma cell lines. In MSTO-211H xenograft models, the fiber-modified oncolytic adenovirus significantly enhanced antitumor effect compared to its equivalent Ad5-based vector. Our data demonstrate that Ad35 fiber modification of binding tropism in a midkine promoter-regulated oncolytic Ad5 vector confers transductional targeting to oncolytic adenoviruses, thereby facilitating more effective treatment of malignant mesothelioma

Enhanced antitumor efficacy of fiber‐modified, midkine promoter‐regulated oncolytic adenovirus in human malignant mesothelioma

Oncolytic virotherapy using adenoviruses has potential for therapeutic benefits in malignant mesothelioma. However, the downregulation of coxsackie virus/adenovirus receptor (CAR) expression is frequently a critical rate-limiting factor that impedes the effectiveness of adenovirus serotype 5 (Ad5)-based vectors in many cancer types. We evaluated CAR (Ad5 receptor) and CD46 (adenovirus serotype 35 [Ad35] receptor) expression in six human malignant mesothelioma cell lines. Very low CAR expression was observed in MSTO-211H and NCI-H2052 cells, whereas the other cell lines showed strong expression. In contrast, CD46 was highly expressed in all mesothelioma cell lines. On this basis, we replaced the CAR binding sequence of Ad5 with the CD46 binding sequence of Ad35 in the replication-defective adenoviruses and the tumor-specific midkine promoter-regulated oncolytic adenoviruses. By this fiber modification, the infectivity, virus progeny production, and in vitro cytocidal effects of the adenoviruses were significantly enhanced in low CAR-expressing MSTO-211H and NCI-H2052 cells, also resulting in similar or even higher levels in high CAR-expressing mesothelioma cell lines. In MSTO-211H xenograft models, the fiber-modified oncolytic adenovirus significantly enhanced antitumor effect compared to its equivalent Ad5-based vector. Our data demonstrate that Ad35 fiber modification of binding tropism in a midkine promoter-regulated oncolytic Ad5 vector confers transductional targeting to oncolytic adenoviruses, thereby facilitating more effective treatment of malignant mesothelioma

Adenovirus–Retrovirus Hybrid Vectors Achieve Highly Enhanced Tumor Transduction and Antitumor Efficacy In Vivo

Murine leukemia virus (MLV)–based replication-competent retrovirus (RCR) vectors have been shown to mediate efficient, selective, and persistent tumor transduction, thereby achieving significant therapeutic benefit in a wide variety of cancer models. To further augment the efficiency of this strategy, we have developed a delivery method employing a gutted adenovirus encoding an RCR vector (AdRCR); thus, tumor cells transduced with the adenoviral vector transiently become RCR vector producer cells in situ. As expected, high-titer AdRCR achieved significantly higher initial transduction levels in human cancer cells both in vitro and in vivo, as compared to the original RCR vector itself. Notably, even at equivalent initial transduction levels, more secondary RCR progeny were produced from AdRCR-transduced cells as compared to RCR-transduced cells, resulting in further acceleration of subsequent RCR replication kinetics. In pre-established tumor models in vivo, prodrug activator gene therapy with high-titer AdRCR could achieve enhanced efficacy compared to RCR alone, in a dose-dependent manner. Thus, AdRCR hybrid vectors offer the advantages of high production titers characteristic of adenovirus and secondary production of RCR in situ, which not only accelerates subsequent vector spread and progressive tumor transduction, but can also significantly enhance the therapeutic efficacy of RCR-mediated prodrug activator gene therapy