Vascular effects of photodynamic therapy in an intraocular retinoblastoma-like tumour.

Results from experimental tumours suggest that the mechanism of action of photodynamic therapy (PDT) involves both a direct killing of tumour cells, and a secondary effect resulting from vascular damage. We have investigated the possible vascular changes induced by PDT in an intraocular retinoblastoma-like rat tumour model using the 86RbCl extraction procedure. Light irradiation (90 J/cm2; 633 nm; 30 min) of intraocular tumours 24 h after an intraperitoneal injection of 5 mg/kg Photofrin II produced an increase in the tumour uptake of 86RbCl during the treatment period. However, 24 h later these values had decreased to 25% of that normally found in control animals. These effects were observed in both the tumour material and associated normal eye tissue, but not in PDT treated normal eyes without tumours. The results confirm that the vasculature of this eye tumour model is a target for some of the PDT effects.