Polyomavirus-related infections are ubiqutious in immunocompromised individuals and in some cases are intractable and fatal. Due to lack of approved drugs to treat polyomavirus infections, cidofovir, a phosphonate nucleotide analog approved to treat cytomegalovirus infections has been repurposed as anti-polyomavirus agent. Cidofovir has been modified in various ways to improve its efficacies as broad-spectrum antiviral agent. However, the actual mechanisms and targets of cidofovir and its modified derivatives as anti-poly omavirus agents are still under research. Here, polyomavirus large tumor antigens (Tag) activities were identified as the viral target of cidofovir derivatives. The alkoxyalkyl-ester derivatives of cidofovir efficiently inhibit polyomavirus DNA replication in cell-free human extracts and a viral in vitro replication system only utilizing purified proteins. We present evidence that DNA helicase, and DNA binding activities of polyomavirus Tags are diminished in the presence of low concentrations of alkoxyalkyl-ester derivatives of cidofovir suggesting that the inhibition of viral DNA replication is at least in part mediated by inhibiting ssDNA and dsDNA binding activities of Tags. These findings show that the alkoxyalkyl-ester derivatives of cidofovir are effective in vitro without undergoing further conversions and conclude that the inhibitory mechanisms of nucleotide analog-based drugs are more complex than previously believed.
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