Nicotinamide reduces photodynamic therapy-induced immunosuppression in humans

Background The immune suppressive effects of topical photodynamic therapy (PDT) are potential contributors to treatment failure after PDT for nonmelanoma skin cancer. Nicotinamide (vitamin B-3) prevents immune suppression by ultraviolet radiation, but its effects on PDT-induced immunosuppression are unknown. Objectives To determine the effects of topical and oral nicotinamide on PDT-induced immunosuppression in humans. Methods Twenty healthy Mantoux-positive volunteers received 5% nicotinamide lotion or vehicle to either side of the back daily for 3 days. Another group of 30 volunteers received 500 mg oral nicotinamide or placebo twice daily for 1 week in a randomized, double-blinded, crossover design. In each study, methylaminolaevulinate cream was applied to discrete areas on the back, followed by narrowband red light irradiation (37 J cm(-2)) delivered at high (75 mW cm(-2)) or low (15 mW cm(-2)) irradiance rates. Adjacent, nonirradiated sites served as controls. Delayed-type hypersensitivity (Mantoux) reactions were assessed at treatment and control sites to determine immunosuppression. Results High irradiance rate PDT with vehicle or with placebo caused significant immunosuppression (equivalent to 48% and 50% immunosuppression, respectively; both P < 0.0001); topical and oral nicotinamide reduced this immunosuppression by 59% and 66%, respectively (both P < 0.0001). Low irradiance rate PDT was not significantly immunosuppressive in the topical nicotinamide study (15% immunosuppression, not significant), but caused 22% immunosuppression in the oral study (placebo arm; P = 0.006); nicotinamide reduced this immunosuppression by 69% (P = 0.045). Conclusions While the clinical relevance of these findings is currently unknown, nicotinamide may provide an inexpensive means of preventing PDT-induced immune suppression and enhancing PDT cure rates.