Anti-tumor effect of cidofovir against human papillomavirus positive and negative cells is not exclusively due to DNA damage

Introduction: Human papillomavirus (HPV) can induce both benign and malignant hyper proliferations. It is involved in almost all cervix carcinoma and in an increasing amount of head and neck cancers. Cidofovir (CDV) was found to be efficacious in the treatment of HPV related lesions. In this study, we evaluated whether a correlation exists between DNA incorporation, DNA damage and the anti-proliferative effects caused by CDV. We will provide a better insight on how CDV kills specifically tumor cells, without harming normal cells. Methods: In the present work, HPV+ and HPV- cells of both cervix carcinoma and head and neck squamous cell carcinoma were included. As a control, we compared with primary human keratinocytes (PHKs), human embryonic lung (HEL) fibroblasts and primary epithelial tonsil (PET) cells. The anti-proliferative effect is expressed as the concentration needed to inhibit cell growth by 50% (CC50). CDV drug metabolism and incorporation into genomic DNA was studied by use of radiolabeled [5-3H]-CDV and metabolites were separated by HPLC. DNA damage was evaluated by a flow cytometry assay using a double staining with propidium iodide and a monoclonal antibody against γ-H2AX, a selective marker for double stranded DNA breaks. Results: Our results showed that the levels of intracellular CDV metabolites were higher in PHKs and PET cells compared to HPV+ and HPV- tumor cells and HEL cells. However, the amount of CDV incorporated in tumor cells was higher compared to normal cells. We demonstrated that CDV causes double stranded DNA breaks in each phase of the cell cycle. The percentage of cells that are γ-H2AX positive was higher in the tumor cells compared to the normal cells. CC50 values, CDV incorporation and DNA damage were compared to investigate whether a correlation exists between them. We observed a significant correlation between DNA incorporation and DNA damage and between CDV incorporation and CC50 . No correlation was observed between CC50 and DNA damage. Conclusions: Taking together, these results indicate that the CC50 value results from incorporation of CDV into genomic DNA which causes DNA damage. However the anti-tumor effect of CDV cannot be explained exclusively by DNA damage.status: publishe