KINETICS, BIODISTRIBUTION AND THERAPEUTIC EFFICACY OF HEXYLESTER 5-AMINOLEVULINATE INDUCED PHOTODYNAMIC THERAPY IN AN ORTHOTOPIC RAT BLADDER TUMOR MODEL

Abstract

To optimize photodynamic therapy (PDT) we investigated the kinetics and biodistribution of hexylester 5-aminolevulinate (hALA) induced protoporphyrin IX (PpIX) and the therapeutic efficacy of PDT at different drug and light doses in an orthotopic rat bladder tumor model. Healthy and tumor bearing rats were instilled intravesically with hALA (4, 8 and 16 mM) for 1 hour. Fluorescence was recorded spectroscopically in situ. PpIX fluorescence distribution and quantification across the bladders was visualized with fluorescence microscopy. PDT efficacy at different fluences (15 to 80 J/cm2) was histologically assessed 48 hours and 1 week after treatment. Spectroscopic analysis in normal or tumor bearing rats showed the highest tumor-to-normal ratios 2 or 3 hours after the end of the 8 or 16 mM hALA instillation (5.4 and 5.7, respectively). Within the same tumor bearing animal the same fluorescence levels were observed in normal epithelium and transitional cell carcinoma, whereas the tumor-to-muscle ratio was 3. Tumor necrosis with an intact normal bladder wall was observed with a fluence of 20 J/cm2 for 8 mM hALA, while 15 J/cm2 was ineffective and 25 J/cm2 induced total wall necrosis. Although it induced comparable PpIX fluorescence, 16 mM hALA did not result in tumor eradication at any fluence. An optimal PDT effect was obtained with 8 mM hALA and a fluence of 20 J/cm2. While different hALA concentrations ind uce identical PpIX fluorescence intensities, the PDT outcome was considerably different. Thus, fluorescence does not necessarily predict the therapeutic efficacy of PDT.