Chlorin e₆Na (Chl), a hydrophilic chlorophyll derivative structurally similar to pheophorbide a (Pheo), had less cell-killing effect on FM3A cells than Pheo. Its cell-killing effect was suggested to be based on the damage of the cell membrane through the same mechanism as that of Pheo, because Chl was distributed mainly in the plasma membrane fraction.
The time required for the maximum build-up of Chl in FM3A tumor tissue after injection was 2-8h. The photodynamic therapy (PDT) at 6 or 24h following administration of Chl caused shorter survival of FM3A tumor-bearing mice in comparison with that obtained when Pheo was used. However, the tumor-to-organ ratios of Chl at 24h after injection were higher than those of Pheo, and Chl was excreted more rapidly from normal tissues than from tumor tissue and had little phototoxicity on normal organs. From these characteristics, Chl may be more suitable as a photosensitizing agent in PDT than Pheo.