New insights into photodynamic therapy using porphyrin precursors

Non- melanoma skin cancer (NMSC) is the most common cancer in Caucasians. The incidence of skin cancer continues to rise faster than that of any other cancer. More than out of 6 Dutch inhabitants develops skin cancer (mainly NMSC) before his 85th year of life.1 The majority of NMSCs are basal cell carcinomas (BCCs) and squamous cell carcinomas (SCCs). Non-melanoma skin pre-malignancies are Bowen’s disease (SCC in situ) and actinic keratosis. In the last 25 years, the absolute numbers of patients in the Netherlands with first, histologically confirmed BCCs increased by about 7-fold in both men and women. In 2015, an incidence of more than 44,000 newly-diagnosed BCC cases is expected, increasing to more than 57,000 in 2020. Subsequent BCCs in patients who have already been diagnosed with the first BCC are not included in these incidences, although the cumulative risk of developing one or more subsequent BCCs 5 years after diagnosis is 29%. The burden of skin cancer is mainly disease burden, functional- and cosmetic problems and care consumption because of the good prognosis (quod vitam). General practitioners and medical specialists will be increasingly burdened with the inspection, the diagnosis and/or the treatment of suspect lesions in the future

Topical photodynamic therapy using different porphyrin precursors leads to differences in vascular photosensitization and vascular damage in normal mouse skin

Different distributions of hexyl aminolevulinate (HAL), aminolevulinic acid (ALA) and methyl aminolevulinate (MAL) in the superficial vasculature are not well studied but they are hypothesized to play an important role in topical photodynamic therapy (PDT). The colocalization of fluorescent CD31 and protoporphyrin IX (PpIX) was calculated using confocal microscopy of mouse skin sections to investigate the vascular distribution after topical application. Vascular damage leads to disruption of the normal endothelial adherens junction complex, of which CD144 is an integral component. Therefore, normal CD31 combined with loss of normal fluorescent CD144 staining was visually scored to assess vascular damage. Both the vascular PpIX concentration and the vascular damage were highest for HAL, then ALA and then MAL. Vascular damage in MAL was not different from normal contralateral control skin. This pattern is consistent with literature data on vasoconstriction after PDT, and with the hypothesis that the vasculature plays a role in light fractionation that increases efficacy for HAL and ALA-PDT but not for MAL. These findings indicate that endothelial cells of superficial blood vessels synthesize biologically relevant PpIX concentrations, leading to vascular damage. Such vascular effects are expected to influence the oxygenation of tissue after PDT which can be important for treatment efficacy. The ability of the vasculature to synthesize PpIX and be damaged by PDT was compared between HAL, ALA and MAL in mouse skin using confocal microscopy and fluorescent CD31 and CD144 antibodies. Colocalization of CD31 and PpIX (left images) was calculated to measure endothelial PpIX synthesis. Vascular damage was scored as loss of normal CD144 staining (right images). Both PpIX synthesis and vascular damage were highest for HAL, then ALA, then MAL. This illustrates that superficial blood vessels synthesize biologically relevant amounts of PpIX. Vascular responses can limit oxygen supply during or after PDT and are expected to influence outcome