Nucleoside analogue drugs and human papillomavirus associated neoplasia

The anti-viral acyclic nucleoside monophosphate compound Cidofovir has shown efficacy in treatment of Human Papillomavirus (HPV) associated genital intraepithelial neoplasia; however, the mechanism of action of Cidofovir in this setting has not been determined. This investigation focused on modifying nucleoside analogue compounds to increase their efficacy in HPV positive cell models of disease, in addition to determining the molecular mechanism of action of Cidofovir in premalignant HPV associated intraepithelial neoplasia. ProTide modification increases the efficacy of nucleoside analogue compounds by increasing their cellular permeability. Cidofovir was not amenable to ProTide manipulation; however, ProTide derivatives of its sister compounds, Adefovir and Tenofovir, were synthesized. Parent Adefovir and Tenofovir and a range of their respective ProTide modified daughter compounds were examined for inhibition of cell growth and effect on cell size and morphology in HPV positive and negative transformed cell lines. The most effective compounds were further examined for dose response in normal HPV negative untransformed Human Epidermal Keratinocytes (HEKs) and naturally HPV immortalized short term (NHIST) cell lines cloned from vulval and vaginal intraepithelial neoplasia biopsies. ProTide analogues displayed striking increased efficacy in comparison to their parent compounds; however, they did not show specificity to transformed or HPV positive cell lines. Cidofovir did not show specificity to HPV positive cells when examined for growth inhibitory effect in HPV positive and negative cell models. A variety of molecular processes were examined to determine the mechanism by which Cidofovir inhibits cell growth in validated NHIST cell lines and HEK cells. At the concentrations investigated, Cidofovir did not cause apoptosis in HPV positive or negative cells and its growth inhibitory effect appeared likely to be associated with cell cycle arrest or senescence. The effects of radiation on the molecular response induced by Cidofovir were also evaluated as previous studies suggested Cidofovir can function as a radiosensitizer. Cidofovir combined with gamma radiation did not result in apoptosis but was associated with an augmented molecular response in NHIST cell lines. On the contrary, Cidofovir combined with gamma radiation caused a major apoptotic response in HPV negative HEKs, suggesting such a combination could result in disadvantageous effects on healthy tissue if it were used in vivo