Nucleoside analogue

Both types of compounds can deviate from what they mimick in a number of ways, as changes can be made to any of the constituent parts (nucleobase, sugar, phosphate).

Nucleoside and nucleotide analogues can be used in therapeutic drugs, including a range of antiviral products used to prevent viral replication in infected cells.

There is a large family of nucleoside analogue reverse transcriptase inhibitors, because DNA production by reverse transcriptase is very different from normal human DNA replication, so it is possible to design nucleoside analogues that are preferentially incorporated by the former.

Less selective nucleoside analogues are used as chemotherapy agents to treat cancer, e.g. gemcitabine.

Since nucleoside analogues require two phosphorylations to be activated, one carried out by a viral enzyme and the other by enzymes in the host cell, mutations in viral thymidine kinase interfere with the first of these phosphorylations; in such cases the drug remains ineffective.