THE EFFECTS OF SERUM ON CELLULAR UPTAKE AND PHOTOTOXICITY OF MONO-L-ASPARTYL CHLORIN E6 (NPE6) IN-VITRO

Previous reports showed that the photosensitizer mono-L-aspartyl chlor in e6 (NPe6) binds to serum proteins. However, the influence of this b inding on the cellular uptake and photodynamic therapy (PDT) phototoxi city of NPe6 is still undefined. In this paper, we studied how serum i n medium affected the P388 cellular uptake and PDT phototoxicity of NP e6 in vitro. This was assessed by (1) detection of the red shift (654 nm Q band peak of absorption) induced by protein binding NPe6; (2) det ection of intracellular concentration of NPe6 by HPLC and (3) measurem ents of the cell survival ratio after PDT by MTT assay. The 654 nm Q b and peak of NPe6 shifted to 665 nm after binding of NPe6 and serum pro teins. The protein-bound NPe6 cannot be uptaken by cells, thus there w as no PDT phototoxicity. Nevertheless, phototoxicity recovered when th e concentration of NPe6 excessed the serum protein binding ability or there was free serum protein in the medium. These data suggested that the cellular uptake of NPe6 is inhibited by serum components in the me dium, and that only free NPe6 is accumulated by P388 cells even during relatively long incubations, The cytotoxicity of PDT mainly depends o n the free NPe6 level in the medium.