Gene therapy for mesothelioma : studies of conditionally replicative adenoviruses and measles virus.

Abstract

Malignant mesothelioma (MM) is an aggressive malignancy of the pleural and peritoneal surfaces. Australia has the highest reported national incidence of mesothelioma in the world, and rates are increasing (Leigh et al., 2002). The clinical outcome for patients with this disease is extremely poor, with median survival of 9 to 12 months (Rizzo et al., 2001; Carbone et al., 2002). The latest developments in chemotherapy, radiotherapy and radical surgery have done little to improve the overall survival rate (Kindler 2000; Zellos et al., 2002). New approaches to therapy are thus required (Nowak et al., 2002). Cancer therapy using conditionally replicative adenoviruses (CRAds) and attenuated measles virus (vaccine strain MV-Edm) are novel and promising approaches to cancer treatment. CRAds strategy relies on selective viral replication in tumour cells but not normal cells. Major efforts have been directed toward achieving selective replication by the deletion of viral functions dispensable in tumour cells or by the regulation of viral genes with tumour-specific promoters (Alemany et al., 2000). However, the major clinical limitation of viral therapy has been lack of efficacy rather than safety concerns. In this study, I constructed CRAds in which tumour-specific promoter for Flt-1 (vascular endothelial growth factor receptor) control the essential E1 gene expression, and evaluated the cell-killing efficacy and specificity of CRAds driven by VEGF and Flt-1 promoters in the number of established mesothelioma cell lines and actual primary tumour cells from patients. CRAds with either VEGF or flt-1 promoters showed a strong killeg effect on mesothelioma cells. Co-delivery of CRAds with MMP-9 (matrix metalloproteinase-9) was assessed to determine whether therapeutic efficacy could be improved by reducing tumourassociated fibrosis thereby enhancing viral spread through a tumour mass. Combined therapy did result in greater suppression of tumour growth in vivo. I also identified an immuno-competent murine model of mesothelioma that was permissive for adenoviral replication. Combined viral therapy with immunotherapy (FGK45, an anti-CD40 antibody) in this model resulted in greater effect than Adwt or FGK45 alone and in greatest survival. I evaluated the capacity of MV-Edm to infect human mesothelioma cells to form syncytia, and lead to apoptosis and cell death. I also assessed the mode of death by analysis of markers of apoptosis including caspase-3. In vivo study showed that MVEdm- GFP transduction could be detected in human xenografts in immune deficient mice. Further studies to evaluate the mechanisms and efficacy of anti-tumour immune stimulation induced by tumour cell killing with CRAds and MV-Edm will be discussed in this study. MV-Edm has good killing effect on mesothelioma cells in vitro. In summary the work presented herein provide new insights into stratgies to improve viral therapies for mesothelioma.