Imiquimod and resiquimod as novel immunomodulators

Augmenting the host's natural immune response to viruses by the administration of exogenous cytokines such as interferon-alpha (IFN-alpha) is a strategy increasingly employed in antiviral therapeutics. Enhancing the release of endogenous cytokines is, however, an alternative approach. The imidazoquinolinamines imiquimod and resiquimod have demonstrated potency as inducers of IFN-alpha and other cytokines both in vitro and in vivo. Cytokine gene activation is mediated via the signal transducer and activator of transcription 1 (STAT-1) and involves the transcription factors NFkappaB and alpha4F1. Antiviral activity has been demonstrated against a variety of viruses, and clinical efficacy has been demonstrated against genital warts, herpes genitalis and molluscum contagiosum. Imiquimod is administered as a 5% cream (Aldara) and has been licensed for the treatment of anogenital warts in immunocompetent patients. Complete clearance of warts has been observed in up to half of treated patients with only local side effects reported. Resiquimod can be administered topically but also exists as an oral formulation. The range of potential infections for which these agents may have clinical utility includes chronic hepatitis C virus infection and Kaposi's sarcoma. In addition, the imidazoquinolinamines may find roles in the therapy of cancers and as vaccine adjuvants.