Experimental studies of photodynamic therapy in a retinoblastoma-like tumour.

Combination therapy with a purified hematoporphyrin derivative, Photofrin II, and red light (photodynamic therapy) was investigated in a retinoblastoma-like tumour growing in the eyes of rats in vivo and in cell cultures. There was a marked dose-response relationship between Photofrin II and the light energy both in vitro and in vivo. Up to 33% of the tumours could be controlled in vivo. In vivo/in vitro assays indicated Photofrin II uptake in the tumour cells in vivo in relation to the administered doses. Studies of cell death kinetics suggested that the mechanisms of photodynamic therapy were both a primary cell kill effect and a secondary tissue destruction, probably as a consequence of vascular damage.