Psoralen photobiology and photochemotherapy: 50 years of science and medicine.

In 1998 it is appropriate to commemorate the 50th anniversary of el Mofty's use of purified 8-methoxypsoralen (8-MOP) in the treatment of vitiligo (el Mofty AM. A preliminary clinical report on the treatment of leukoderma with Ammi majus linn. J R Egypt Med Assn 1948,31:651 65. el Mofty AM, el Sawalhy H, el Mofty M. Clinical study of a new preparation of 8-methoxypsoralen in photochemotherapy. Int J Dermatol 1994;8:588 92). Two young American dermatologists (Aaron Lerner and Thomas Fitzpatrick) were intrigued by the potency of this material. After Lerner determined that artificial long wavelength ultraviolet (320-400 nm, UVA) radiation was the most efficient for activating 8-MOP. the development of artificial sources enabled the efficient delivery of these photons to skin containing 8-MOP. Their initial studies for vitiligo led to further development of this therapy for the treatment of psoriasis (Parrish JA, Fitzpatrick TB, Tannenbaum L, et al. Photochemotherapy of psoriasis with oral methoxsalen and long-wave ultraviolet light. New Engl J Med 1974;291:1207-11. Honigsmann H, Fitzpatrick TB, Pathak MA, et al. Oral photochemotherapy with psoralen and UVA (PUVA): principles and practice. In: Fitzpatrick TB, Eisen AZ, Wolf K, editors. Dermatology in General Medicine. New York: McGraw-Hill, 1987:1728-54). This photochemotherapy came to be called 'PUVA' (psoralen + UVA). The position PUVA holds today as one of the most common procedures performed in dermatology can be traced to their initial curiosity and their subsequent ingenuity. Further developments in more recent years capitalized on their seminal work. The therapy met with unprecedented success from the outset, leaving little perceived need to understand underlying science. However, in recent years there has been a new found interest in the basic aspects of psoralen photobiology and molecular mechanistic events contributing to therapeutic responses as well as to the development of skin cancers in PUVA patients. These will be surveyed in this review commemorating the 50 years of modern psoralen photobiology and photomedicine.