Topical PDT in the Treatment of Benign Skin Diseases: Principles and New Applications

Abstract

Photodynamic therapy (PDT) uses a photosensitizer, light energy, and molecular oxygen to cause cell damage. Cells exposed to the photosensitizer are susceptible to destruction upon light absorption because excitation of the photosensitizing agents leads to the production of reactive oxygen species and, subsequently, direct cytotoxicity. Using the intrinsic cellular heme biosynthetic pathway, topical PDT selectively targets abnormal cells, while preserving normal surrounding tissues. This selective cytotoxic effect is the basis for the use of PDT in antitumor treatment. Clinically, PDT is a widely used therapeutic regimen for oncologic skin conditions such as actinic keratosis, squamous cell carcinoma in situ, and basal cell carcinoma. PDT has been shown, under certain circumstances, to stimulate the immune system and produce antibacterial, and/or regenerative effects while protecting cell viability. Thus, it may be useful for treating benign skin conditions. An increasing number of studies support the idea that PDT may be effective for treating acne vulgaris and several other inflammatory/infective skin diseases, including psoriasis, rosacea, viral warts, and aging-related changes. This review provides an overview of the clinical investigations of PDT and discusses each of the essential aspects of the sequence: its mechanism of action, common photosensitizers, light sources, and clinical applications in dermatology. Of the numerous clinical trials of PDT in dermatology, this review focuses on those studies that have reported remarkable therapeutic benefits following topical PDT for benign skin conditions such as acne vulgaris, viral warts, and photorejuvenation without causing severe side effects.

Keywords: acne vulgaris; benign skin disease; photodynamic therapy; photorejuvenation; topical photosensitizer; wart.

Figure 1

Side effects of PDT treatments. (A) Ulceration on the great toe after treatment of a wart with ILI-PDT; and (B) Diffuse mild erythema on the forehead after first treatment session of actinic keratosis with chlorophyll-PDT. ILI: intralesional injection; PDT: photodynamic therapy.

Figure 2

Representative photographs before (A,B) and after chlorophyll-PDT treatment (C,D). After three treatment sessions of chlorophyll-PDT, there was a significant decrease in the number of papules and pustules in moderate inflammatory acne patient [34].

Figure 3

Representative photographs before and after ILI-PDT. Wart lesions on the foot at baseline (A,C) and 1 month after three sessions of ILI-PDT (B,D). Marked reduction of warts was shown on the great toe and little toe [67].