Purine and pyrimidine nucleosides have been widely studied for the development of a range of antiviral drugs to prevent viral replication in infected cells. They have been particularly exploited to develop drugs against HBV, HCV, herpes simplex virus, and HIV. Once they are phosphorylated, they work as antimetabolites by being similar enough to be incorporated into growing DNA strands. They can act as chain terminators and inhibit viral DNA polymerase.
Purine nucleotides and nucleosides act as extracellular messengers, according to the concept of purinergic signaling first proposed over 30 years ago by Burnstock. Since then, receptor subtypes for adenosine-selective (P1 receptors) and purine and pyrimidine selective (P2 receptors) have been cloned and characterized. Almost every tissue in the body expresses P1 and/or P2 receptors.