Figure 2. Example highlighting the distinct mechanisms of antiviral actions by pharmacological inhibitors of cellular cyclin-dependent kinases (CDKs) compared to conventional antiviral drugs.

The illustration depicts the viral functions that are directly repressed by CDK inhibitors or by two typical antiviral drugs, acyclovir and foscarnet. Because CDKs are required for transcription of HSV immediate-early (IE), early (E) and perhaps late (L) genes, and for viral DNA replication, CDK inhibitors can target several stages of the viral replication cycle as opposed to blocking a specific viral target(s), such as the viral thymidine kinase (TK) or DNA polymerase (DNA pol). Thus, a single drug targeting a single cellular protein that is required for several viral functions is akin to combination antiviral therapy, in which each drug targets a different viral enzymes. Hel./prim, helicase-primase. Reproduced with permission from Luis Schang.