Base-modified thymidine and thymine analogs with low cytotoxicity effectively obstruct DNA replication in papovaviridae

Abstract

Background: Current chemotherapeutic antimetabolites often exhibit severe side effects that limit their use as drugs; therefore, we designed nucleoside compounds with mechanisms of action focusing on inhibiting DNA replication rather than targeting multiple pathways. We previously discovered cytotoxic basemodified thymidine and thymine analogs that show higher selectivity against cancerous versus normal cells compared to the current antimetabolites used in cancer chemotherapy. We anticipated these antimetabolites have the potential to effectively inhibit viral DNA replication while showing low cytotoxicity. Methods: Base-modified thymidine and thymine analogs were synthesized and their anti-viral activity was evaluated in human cells infected with human pappiloma, John Cunningham, and BK viruses using quantitative DNA polymerase chain reaction assay. In addition, their toxicity toward host cells was determined using CellTiter-Glo assay, and compared to cytotoxicity toward human breast cancer cells. Results: Novel lead compounds with high activity against human papilloma (HPV) and John Cunningham (JCV) viruses have been identified. Their EC50 values lie in low micromolar range (1-2 µM), which is significantly less than that of cidofovir (9-10 µM), a current drug used against DNA viruses. Cytotoxicity of the leads toward the host cells was found to be in 200-300 µM range, which is generally higher than that observed toward MCF-7 human breast cancer cells. None of the tested compounds significantly inhibited BK viral DNA replication. Conclusion: The lead compounds affect the viruses substantially more selectively than the host cells, which makes them a novel class of bioactive compounds with the potential to become effective anti-viral drugs.