Potential drugs against cervical cancer: Zinc-ejecting inhibitors of the human papillomavirus type 16 E6 oncoprotein

Background: The principal agent in the etiology of cervical cancer, i.e., h uman papillomavirus (HPV) type 16, encodes three oncoproteins, E5, E6, and E7, Structural and mutational studies have identified two potential zinc-fi nger domains as critical for E6 protein function. We investigated several a ssays to identify and characterize compounds that interfere with the bindin g of zinc to E6, Methods: Thirty-six compounds were selected on the basis o f their structure, which would facilitate their participation in sulfhydryl residue-specific redox reactions, and were tested for their ability to rel ease zinc from E6 protein. The zinc-ejecting compounds were then tested for their ability to inhibit E6 binding to E6-associated protein (E6AP) and E6 -binding protein (E6BP), two coactivators of E6-mediated cellular transform ation, The binding of E6 to E6BP and E6AP was measured by use of surface pl asmon resonance (a technique that monitors molecular interactions by measur ing changes in refractive index) and by use of in vitro translation assays. The compounds were also tested for their effects on the viability of HPV-c ontaining cell lines. Results: Nine of the 36 tested compounds ejected zinc from E6, Two of the nine compounds inhibited the interaction of E6 with E6 AP and E6BP, and one of these two, 4,4'-dithiodimorpholine, selectively inh ibited cell viability and induced higher levels of p53 protein (associated with the induction of apoptosis [programmed cell death]) in tumorigenic HPV -containing cells. Conclusion: We have described assay systems to identify compounds, such as 4,4'-dithiodimorpholine, that can potentially interfere with the biology and pathology of HPV, These assay systems may be useful in the development of drugs against cervical cancer, genital warts, and asymp tomatic infections by genital HPVs.