Photoinactivation of viruses

Although the photodynamic effect was demonstrated against viral targets more than seventy years ago, the use of photosensitisers as antivirals in vivo has been slow in gaining acceptance. From a clinical viewpoint, this may be due to the pronounced side effects produced in several cases of the phototreatment of herpes genitalis in the early 1970s, the unfortunate patients presenting with post-treatment Bowen's disease. Currently, the clinical use of photosensitisers in this field is limited to the treatment of laryngeal papillomata. However, considerable progress has been made in the photodynamic disinfection of blood products. Photoantivirals have traditionally been targeted at viral nucleic acid, in many cases via an intercalative mechanism. However, given the potential for deleterious sequelae associated with this route, the design of new photosensitisers should encourage alternative targets, such as viral enzymes or the cell envelope (where this exists). Targeting is obviously determined by the chemistry of the photosensitiser employed and there are many different structural types available. The chemistry, photochemistry and cellular effects of the various agents are discussed, along with future prospects for this exciting area of medicine.