The fluorescence biodistribution and kinetics of aminolevulinic acid induced protoporphyrin IX in the bladder of a rat model with orthotopic urothelial carcinoma

Purpose: Photodynamic therapy is an alternative intravesical therapy modality for superficial bladder cancer. Aminolevulinic acid (ALA) induces the production of the endogenous photosensitizer protoporphyrin IX (PpIX). We compared intravenous versus intravesical administration of ALA and established the proper timing and dose of ALA for photodynamic therapy. To characterize the distribution of ALA in rat bladder tumor and normal bladder layers a cooled charge coupled device camera was used. Materials and Methods: A total of 40 female Fisher F344 rats were used as test animals, including 36 inoculated with AY-27 tumor cells intravesically. PpIX accumulation was investigated by fluorescence microscopy comparing 100 and 300 mg./kg. intravenous administration with a 100 mg./ml. intravesical dose of ALA. Three areas of urothelium, submucosa and muscularis of the bladder wall were chosen for analysis. The software used allowed semiquantitative analysis by calculating the mean fluorescence count plus or minus standard error of mean within any chosen area on the fluorescence image. Results: In this study the highest fluorescence difference in PpIX accumulation in tumor and the normal epithelium to the muscularis layer was achieved at 2 hours with intravenous administration (7:1 to 50:1). The highest absolute fluorescence levels were observed at 2 hours with the 100 mg./kg. intravenous dose and at 4 hours with the higher 300 mg./kg. dose. The difference in fluorescence intensity in tumor tissue to normal urothelium, was 2:1 to 3:1 at 2 hours. At 4 hours it was less than 2:1. After intravesical administration no difference in PpIx accumulation in tumor and normal urothelium was observed. However, there was a 7:1 ratio in regard to the muscularis layer at 4 hours. Conclusions: According to the results of this study a difference in PpIX accumulation in urothelial carcinoma or normal urothelium and the muscular layer of the bladder can be achieved by each route of ALA administration. Although intravesical installation provided tumor and normal urothelium labeling comparable to the intravenous route, it lost the selectivity of PpIX accumulation in tumor and normal urothelium. The effect of this finding on clinical therapy results remains to be resolved in the future.