Conflicts of interest Both authors declare no conflicts of interest.
Imiquimod: mode of action
Version of Record online: 7 DEC 2007
British Journal of Dermatology
Volume 157, Issue Supplement s2, pages 8–13, December 2007
How to Cite
Schön, M.P. and Schön, M. (2007), Imiquimod: mode of action. British Journal of Dermatology, 157: 8–13. doi: 10.1111/j.1365-2133.2007.08265.x
- Issue online: 7 DEC 2007
- Version of Record online: 7 DEC 2007
- Accepted for publication 4 September 2007
- immune response modifier;
- skin cancer;
- toll-like receptors
Objective Since imiquimod, a nucleoside analogue of the imidazoquinoline family, has shown efficacy against many tumour entities, its mode of action has become a focus of scientific interest.
Results The major biologic effects of imiquimod are mediated through agonistic activity towards toll-like receptors (TLR) 7 and 8, and consecutively, activation of nuclear factor-kappa B (NF-κB). The result of this activity is the induction of pro-inflammatory cytokines, chemokines and other mediators leading to activation of antigen-presenting cells and other components of innate immunity and, eventually, the mounting of a profound T-helper (Th1)-weighted antitumoral cellular immune response. Several secondary effects on the molecular and cellular level may also be explained, at least in part, by the activation of NF-κB. Moreover, independent of TLR-7 and TLR-8, imiquimod appears to interfere with adenosine receptor signalling pathways, and the compound causes receptor-independent reduction of adenylyl cyclase activity. This novel mechanism may augment the pro-inflammatory activity of the compound through suppression of a negative regulatory feedback mechanism which normally limits inflammatory responses.
Finally, imiquimod induces apoptosis of tumour cells at higher concentrations. The pro-apoptotic activity of imiquimod involves caspase activation and appears to depend on B cell lymphoma/leukemia protein (Bcl)-2 proteins.
Conclusions Overall, imiquimod acts on several levels, which appear to synergistically underlie the profound antitumoral activity of the compound.