Tissue distribution and penetration of 5-ALA induced fluorescence in an amelanotic melanoma after topical application

Background: Photodynamic therapy (PDT) following topical application of 5-a minolevulinic aid (ALA) is increasingly employed for several types of malig nancies. However, data with respect to tissue penetration and distribution of ALA-included porphyrins after topical application nle scarce. Therefore it was our aim to study tissue distribution and the penetration potency of topically applied ALA. Material and Methods: We used Syrian golden hamsters implanted with the amelanotic melanoma A-Mel-3 growing in a transparent do rsal skinfold chamber: ALA was topically applied in aqueous solution at a c oncentration of 3% for 4 hours. The fluorescence pattern was qualified by f luorescence microscopy and digital image analysis from cryosections and giv e as percentage of a reference standard in medians (25%, 75% quartiles). Re sults: Fluorescence intensities in tumors were 90.8% (56.2%, 115.2% of a re ference standard, p<0.01 vs. normal tissue) significantly exceeding normal surroundings host tissue yielding fluorescence intensities of 12.1% (9.1%, 16.1%,). The tumor selectivity, that is the ratio of Fluorescence intensiti es between tumor and normal tissue, was 7.3 (6.1, 9.1). For superficial tum ors with a thickness of approximately 1 mm no fluorescence gradients after topical application of ALA could be observed. Conclusion: In superficial ca ncerous lesions the fluorescence distribution of ALA induced porphyrins is tumor selective without significant fluorescence gradients throughout the t umor. Thus, by optimising the treatment modalities fol topical ALA-PDT an e nhanced efficacy and selectivity will be reached.