Interdependence of drug dose, incubation time & light dose on hematoporphyrin derivative induced photoinactivation of brain tumour cells.

The relationship between photosensitizer concentration, light dose, incubation time and cellular damage in human cerebral glioma cells in culture, was studied. Cells were incubated with hematoporphyrin derivative (Hpd) for different durations at 37 degrees C. Immediately after specified period of incubation, cells were irradiated with white light. Cellular damage was assessed by colony forming ability of cells. A progressive reduction in the surviving fraction was observed as a function of drug and light dose. The survival curves were of exponential nature with an initial shoulder. The cell survival was found to be dependent on the time of incubation with Hpd. These results suggest that photodynamic cellular damage can be enhanced at low drug and light dose by increasing the incubation time.