A novel SPARC-driven oncolytic adenovirus therapeutically effective in both cancer and tumor-associated stromal cells

MARIA VERONICA LOPEZ; DIEGO VIALE; EDUARDO G. CAFFERATA; OSVALDO L. PODHAJCER

Valle Hermoso Cordoba Argentina

Workshop; Tango Lessons for Brain cancer Research; 2007

James S McDonnell Foundation

SPARC is a secreted protein that is overexpressed in the malignant and stromal cell components of human cancer types of neuroectodermal origin such as gliomas and melanomas. In adenocarcinomas SPARC is mainly expressed by the stromal components of the tumor. We hypothesized that SPARC promoter could be a good candidate for generating a conditional replicating oncolytic adenovirus. In addition, targeting the tumor´s vessels potentially offers enhanced viral spread via the tumor´s blood supply avoiding resistance to treatment due to somatic mutations occuring in malignant cells. By using luciferase expression as a reporter gene, we selected a promoter sequence (–513 / +35) named F512, which showed the best ratio of activity vs. specificity in human melanoma cells compared to non-melanoma malignant and normal cells. We constructed three adenoviral vectors in which the E1A gene was driven by F512. The lytic capacity of viruses was initially tested in vitro on a panel of malignant cells and normal cells. We found that CRAds based on SPARC promoter seem to replicate specifically in cancer cells or SPARC-expressing cells while preserving normal cells. Finally, nude mice harboring SB2 (melanoma cells) or combinations SB2/fibroblast, SB2/endothelium or SB2/fibroblast/endothelium tumors (mean 120 mm3) were treated intratumoraly with three administrations of 1010 vp/mouse of adenoviruses. The treatment resulted in a potent antitumor effect. These results indicate that CRAds based on SPARC selectively replicate in and eliminate a panel of cancer cells and subcutaneous tumors, suggesting that they might be useful as oncolytic viruses.