Effects of photodynamic therapy on the absorption properties of disulphonated aluminum phthalocyanine in tumor-bearing mice

Time-resolved reflectance spectroscopy was performed on tumor-bearing mice, administered with disulphonated aluminum phthalocyanine (AlS2Pc, 5 mg/kg body weight), before, during and after photodynamic therapy. This allowed us to evaluate the absorption spectrum of AlS2Pc in vivo from 610 to 700 nm, and to investigate how the therapeutic irradiation affects it. Two tumor locations (intraderma on the back and intramuscular in the leg), and two uptake times (3 and 12 h) were considered. As already observed previously, the absorption spectrum of AlS2Pc in vivo is centered at 680–685 nm. The irradiation causes a blue-shift of the measured line shape, more or less marked depending on the experimental conditions. A reduction in absorption is also often observed upon illumination with therapeutic light doses.