Preclinical study on gene therapy of cervical carcinoma using adeno-associated virus vectors

Approximately 90% of cervical carcinomas are causally linked to infections with high-risk human papillomaviruses (HPVs), whose oncogenicity has been assigned to the continued expression of two early genes, E6 and E7. Reversal of the transformed phenotype by inhibiting E6/E7 gene expression therefore provides a suitable goal for future tumor therapy. Using recombinant adeno-associated virus type 2 (AAV-2) vectors, two types of therapeutic genes were expressed in cervical carcinoma cells with the aim of suppressing the E6/E7 oncogenes: (a) antisense E6/E7 and ribozyme genes and (b) the monocyte chemoattractant protein-1 (MCP-1) gene encoding MCP-1. Previous studies have shown that the MCP-1 protein is able to indirectly repress E6/E7 gene expression and is consistently absent in tumorigenic HPV-positive cervical carcinoma cell lines. Here, the effect of these therapeutic genes on tumor formation is analyzed in nude mice after ex vivo gene transfer into a HPV16- or HPV18-positive cervical carcinoma cell line (HeLa or SiHa, respectively). Whereas AAV-2 vector-mediated transfer of antisense or even ribozyme genes did not significantly influence tumor formation from implanted SiHa cells, the transfer and expression of human MCP-1 strongly inhibited the development of tumors derived from either HeLa or SiHa cells. Similar results were also obtained after in vivo delivery of these genes into SiHa-derived tumors. This suggests that transfer of therapeutic genes mediating a systemic effect via recombinant AAV-2 vectors offers a promising approach for the development of gene therapies directed against papillomavirus-induced human cancers.