Kinetics of cellular uptake and retention of the benzoporphyrin derivative (BPD): relevance to photodynamic therapy

Uptake and release/retention of the photosensitizer, benzoporphyrin derivative, monoacid ring A (BPD; 1 - 20 (mu) g/mL) was studied using cell lines (K562, L1210) and normal, non- activated and Concanavalin A-activated murine splenocytes. Concentrations of BPD in cell lysates were determined by fluorescence (440 nm excitation, 694 nm emission). The results showed that BPD was taken up and released rapidly by all types of cells within the same time frame. Maximum of BPD depended on the type of cells and was greatest in tumor cells, lowest in normal, non-activated cells and intermediate in activated cells. In addition, the maximum uptake depended on BPD concentration in the medium, length of incubation and presence of serum. All cells, regardless of type, retained a constant proportion (20 - 30%) of the amount of BPD taken up. This proportion was independent of length of incubation, BPD concentration in the medium and presence of serum. However, due to differences in maximum amounts of BPD taken up under the same conditions, tumor cells retained more BPD than normal cells and activated cells more than non-activated. The retained BPD was able to photosensitize the cells. The results were found to be relevant to the in vivo studies.