Previous reports showed that the
photosensitizer mono-L-aspartyl chlorin e6 (
NPe6) binds to
serum proteins. However, the influence of this binding on the cellular uptake and
photodynamic therapy (
PDT)
phototoxicity of
NPe6 is still undefined. In this paper, we studied how serum in medium affected the P388 cellular uptake and
PDT phototoxicity of
NPe6 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) detection of intracellular concentration of
NPe6 by HPLC and (3) measurements of the cell survival ratio after
PDT by MTT assay. The 654 nm Q band peak of
NPe6 shifted to 665 nm after binding of
NPe6 and
serum proteins. The
protein-bound
NPe6 cannot be uptaken by cells, thus there was no
PDT phototoxicity. Nevertheless,
phototoxicity recovered when the 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 medium, and that only free
NPe6 is accumulated by P388 cells even during relatively long incubations. The cytotoxicity of
PDT mainly depends on the free
NPe6 level in the medium.