Correlation between anti-proliferative effect and incorporation of cidofovir in human papillomavirus positive and negative cells

Human papillomavirus (HPV) can induce benign and malignant lesions. 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 treatment of HPV related hyperplasias. It has been shown that inhibition of cell proliferation contributes to the effects of CDV and has been associated with apoptosis induction, cell cycle arrest and increased levels of tumor suppressor proteins. Evaluation of the effect of CDV by means of microarray suggested that CDV causes DNA damage. Moreover, we found that CDV incorporates in genomic DNA. In this study we evaluated whether a correlation between DNA-incorporation and the anti-proliferative effect caused by CDV exists. This will allow us to determine the potential use of this drug for the treatment of neoplasias other than those related to HPV. These experiments include HPV+ and HPV- cells of both cervix carcinoma and head and neck squamous cell carcinoma (HNSCC). As a control we compared with primary human keratinocytes (PHKs). The anti-proliferative effect is expressed as the concentration needed to inhibit cell growth by 50% (CC50). Cells were counted with a Coulter counter. CDV drug metabolism and drug incorporation of CDV in genomic DNA was studied by use of radiolabeled [5-3H]-CDV. CDV metabolites were separated by HPLC. Our results showed that the levels of intracellular CDV metabolites (CDV-monophosphate, CDV-diphosphate and CDV-phosphocholine) were not strikingly different in PHKs compared to HPV+ (SiHa, Hela) and HPV- (HaCaT) tumor cells. CDV-diphosphate is the active form of CDV and the only metabolite that can be incorporated in genomic DNA. However, the amount of CDV incorporated in tumor cells was higher (4-fold for HaCaT, 6-fold for HeLa and 9-fold for SiHa) compared to normal keratinocytes where 2 pmol of CDV was found to be incorporated per million cells after 72h of incubation. Experiments on the effect of CDV against HNSCC are in progress. The selectivity of CDV for cancer cells could be associated with a higher incorporation in cancer cell lines and a lack of DNA repair in the cancer cells in comparison to primary cells.status: publishe