Discovered 45 years ago, ribavirin still proves useful as a broad-spectrum anti-viral drug against different RNA and DNA viruses. Although many cellular and molecular mechanisms of ribavirin action have been proposed during several decades of the extensive research, the complete spectrum of its actions is still not fully known. The direct mechanisms of ribavirin anti-viral action involve RNA polymerase inhibition and lethal mutagenesis. The main intracellular target of ribavirin action is inosine 5'-monophosphate dehydrogenase (IMPDH), the rate-limiting enzyme in a de novo synthesis of guanine nucleotides. The inhibition of IMPDH activity leads to depletion of the guanine nucleotide pool and the consequent attenuation of GTPdependent cellular processes, inducing cell cycle arrest, and the interruption of DNA and RNA synthesis. Since these processes are essential for the normal as well as mitogenic functions of all cells, the inhibition of IMPDH probably represents the central mechanism of ribavirin action, including its cytotoxic effect. Recent data suggest that ribavirin may also be effective as an anti-cancer drug. By inhibiting the eukaryotic translation initiation factor e4E (eIF4E), ribavirin impedes eIF4E-mediated oncogenic transformation. Additionally, immunomodulatory and immunosuppressive actions of ribavirin have been shown in different in vivo and in vitro models of neuroinflammation. Accumulating evidence points to important cell type-specific differences in response to ribavirin that may arise from cell specific variations in ribavirin metabolism, as well as the functional status of targeted cells. This chapter reviews the antiviral, anticancer and anti-inflammatory activities of ribavirin and its metabolites, and discusses the possible mechanisms of action.
Keywords: Anaemia, Astrocytes, Cancer, Cap structure, Encephalitis, Guanosine nucleotides, Hepatitis C, Inhibition, Immunomodulation, Immunosuppression, Leukaemia, Microglia, Multiple sclerosis, Mutagenesis, Nucleoside analogue, Nucleoside transporters, Oncogenes, Ribavirin, RNA viruses, T-cells.