Therapeutic efficacy of an oncolytic adenovirus monitored by in vivo imaging of an ovarian cancer model

Abstract

10061 Background: Although a number of advances in ovarian cancer treatment have occurred in the last decade, most patients will experience a recurrence after standard therapies. Recently, virotherapy has been proposed as a new therapeutic approach for ovarian cancer. Conditionally replicative adenovirus (CRAd) contains tumor-specific promoters that restrict virus replication to cancer cells and has shown particular promise as oncolytic viral agents. However, the lack of a tumor-volume monitoring system hinders the evaluation of CRAd impact on cancer treatment. Therefore, methods for analyzing CRAd efficacy and tumor response are required. Mesothelin, a cell surface glycoprotein, is overexpressed in ovarian cancer but not in normal ovarian tissues. The purpose of this study was to explore the therapeutic utility of a mesothelin promoter-based CRAd in a murine model of ovarian cancer, using a non-invasive biological imaging system. Methods: We constructed a mesothelin promoter based CRAd which also contains a modified fiber (Ad5/3 fiber) previously shown to improve infectivity of many ovarian cancer cells (Ad5/3MSLN). Viral replication and oncolysis were assessed in a panel of ovarian cancer cell lines. To test the oncolytic efficacy of Ad5/3MSLN in murine model, firefly luciferase-expressing SK-OV-3-luc cells were injected intraperitoneally (i.p.), followed by an i.p. injection of viruses. Then, bioluminescence imaging of tumor luciferase activity was carried out. Results: Ad5/3MSLN achieved up to 10,000-fold higher cell killing effect and up to 120-fold higher levels of viral replication in all ovarian cancer cell lines tested, compared to wild type Ad5. In vivo tumor imaging confirmed that Ad5/3MSLN significantly inhibited tumor growth, while the untreated mice had rapid tumor growth (p<0.05). Survival with Ad5/3MSLN was significantly enhanced when compared with no virus, or wild type Ad5-treated group (p<0.05). Conclusions: The robust replication, oncolysis, and in vivo therapeutic efficacy of Ad5/3MSLN demonstrated that this CRAd is a promising candidate for treating ovarian cancer. Importantly, we have established an in vivo non-invasive imaging system, which has allowed repeated and longitudinal measurements of tumor growth after CRAd treatment. No significant financial relationships to disclose.