Cyclophilin inhibitors for the treatment of HCV infection.

Cyclophilins (Cyps) constitute one of the three families of peptidyl prolyl isomerase enzymes. CypA is the prototypical member of the Cyp family and is the predominant Cyp expressed in human cells. Recent studies indicate that CypA has an essential role in supporting HCV-specific RNA replication and protein expression. CypA interacts with several virally expressed proteins, including the non-structural (NS) proteins NS2, NS5A and NS5B, and may regulate diverse activities ranging from polypeptide processing to viral assembly. The introduction of non-immunosuppressive Cyp inhibitors into clinical trials confirms that Cyp inhibition is a valid strategy for developing novel therapeutics for the treatment of chronic HCV infection. This review describes the cyclophilin protein family and the potential roles played by cyclophilins in supporting HCV RNA replication and protein expression, as well as the initial clinical results obtained with a novel series of non-immunosuppressive cyclophilin inhibitors that established the clinical proof of concept for this emerging class of therapeutic agents.