Effects of 2-deoxy-D-glucose on the photosensitisation-induced bioenergetic changes in Saccharomyces cerevisiae as observed by in vivo NMR spectroscopy.

Haematoporphyrin (HP), a photosensitiser used for photodynamic therapy (PDT) of tumours, has been observed to affect the cellular energy metabolism both in the absence and presence of light. The effects of HP alone and in combination with 2-deoxy-D-glucose (2-DG) on photosensitisation-induced bioenergetic changes in yeast (Saccharomyces cerevisiae) were monitored and compared using in vivo NMR spectroscopy. Presence of HP was seen to reduce polyphosphates and inorganic phosphate in the dark. Upon photo-irradiation, polyphosphates and sugar phosphates decrease drastically with concomitant rise in inorganic phosphates. Presence of 2-DG in the medium also induced a decrease in polyphosphates and nucleotide triphosphates and the build-up of 2-deoxy-D-glucose-6-phosphate (2-DG-6-P) was clearly detectable. The combination of 2-DG and HP followed by photo-irradiation, however, induced a significant reduction in intracellular pH and beta phosphate of ATP/inorganic phosphate (beta-ATP/Pi) ratio decreased to a larger extent as compared to similar treatment without 2-DG. These observations confirm that polyphosphates are utilised as phosphogen, as phosphate store to be used during phosphate deprivation and as alternative energy source under conditions of energy deficiency induced by HP-PDT and/or 2-DG. The present results further suggest that photodynamic therapy could be made more effective in conjunction with 2-DG administration.

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.