Resiquimod, a topical drug for viral skin lesions and skin cancer.

INTRODUCTION: Resiquimod is an immune response modifier which stimulates cells through a toll-like receptors (TLR) 7 and 8 dependent pathway resulting in activation of immune responses that are effective against viral and tumor lesions. AREAS COVERED: Studies on genital herpes, hepatitis C and actinic keratosis (AK) as well as papers of molecular activities of resiquimod were identified by a PubMed search. Although effective against genital HSV-2 in animal models, development of topical resiquimod for the treatment of recurrent genital herpes in humans was stopped due to inconsistent results in clinical trials. Reduction of HCV viral load was achieved by oral application but was associated with unacceptable side effects. Topical treatment of AK was well tolerated and effective with clearance rates higher compared to imiquimod. The molecular mode of action underlying the clinical efficacy primarily depends on cytokine induction in TLR7/8 expressing dendritic cells in the skin. EXPERT OPINION: Topical resiquimod was shown to be a safe and effective treatment option for AK and appears to have potential as a treatment modality for patients with extended skin areas affected with AK (field cancerization). Resiquimod may also have potential for the therapy or prevention of epithelial viral infections.