Ultraviolet A split-dose therapy, a novel approach to improve the aminolevulinate-based photodynamic therapy of skin lesions

Abstract

Topical aminolevulinate-based photodynamic therapy (ALA-PDT) is an effective method for treating skin lesions such as multiple actinic keratoses (AK). The major side effect of ALA-PDT is the pain experienced during the treatment. Management of treatment-related pain still remains a considerable challenge in patients. Further optimization of the treatment protocol including light source, dose and duration therefore seems crucial to try and alleviate pain. Previous data from this laboratory have demonstrated that ALA-treated human skin fibroblasts become highly sensitive to Ultraviolet A (UVA, 320-400nm)-induced cytotoxicity. In the present study, we provide further evidence that ALA-PDT with UVA is also effective in photokilling of human skin keratinocyte HaCaT cells despite their known resistance to UVA. The UVA-mediated damage in ALA-treated skin cells may be due to rapid release of potentially harmful transit labile iron (LI) in cells that in conjunction with increased generation of singlet oxygen (1O2) and other reactive oxygen species (ROS) by endogenously accumulated Protoporphyrin IX (PPIX) further exacerbate the oxidative damage in skin cells leading to cell death. We therefore hypothesized that by using UVA as the light source and by fractionating the dose applied into two short pulses with 1h dark interval, the ALA-treated skin cells could be further sensitized to UVA-induced damage, since the first dose of UVA would trigger the formation of ROS and extensive release of LI which in turn would intensify the damage caused by the second challenge dose of UVA. By using a series of UVA split-dose combinations, we could demonstrate that applying short pulses of UVA radiation to ALA-treated skin cells is a fast and efficient way to promote cell death. Furthermore the results of this project highlighted the importance of the first UVA dose in determining the efficiency of cell killing following the second UVA dose. The critical role of iron in exacerbating the UVA-induced damage of ALA-treated cells was confirmed with experiments showing that iron loading of cells with hemin prior to ALA-treatment could further sensitise the keratinocytes to very low doses of UVA. The damaging effects of short pulses of low UVA doses following ALA-treatment can be exploited to provide a rapid mean to improve the effectiveness of ALA-PDT of skin lesions while reducing considerably the therapy time and the discomfort/pain associated with prolonged high intensity visible light treatments.

Date of Award	1 Sept 2010
Original language	English
Awarding Institution	University of Bath
Supervisor	Charareh Pourzand (Supervisor)