SERINE CONJUGATES OF CHLOROPHYLL AND BACTERIOCHLOROPHYLL - PHOTOCYTOTOXICITY IN-VITRO AND TISSUE DISTRIBUTION IN MICE BEARING MELANOMA TUMORS

Chlorophyll (Chl) and bacteriochlorophyll (Bchl) have been made water soluble by transesterfication with serine (Ser) at the propionyl resid ue and tested as potential reagents for photodynamic therapy (PDT). Ph otocytotoxicity of the conjugates Chl-Ser and Bchl-Ser in M2R mouse me lanoma was tested in cell cultures, Tissue uptake and clearance of the photosensitizers in CD1 nude and C57B1 mice implanted with M2R tumors are described, Photocytotoxicity in cell cultures was determined micr oscopically and by [H-3]thymidine incorporation, The LD, values in vit ro were 0.05-0.1 mu M for both sensitizers while that of the commercia lly available hematoporphyrin derivative (HPD, Photosan) was over 100 times higher for the same light intensity (45 mW/cm(2)). Pigment conce ntrations were determined fluorometrically in acetone extracts of the tissues of interest at different times after intraperitoneal injection of 20 mg pigment/kg body weight, The distribution pattern of Chl-Ser in the different tissues resembled that reported for Photofrin, chlori n and bacteriochlorin derivatives, Clearance from normal tissues was e ssentially completed within 16 h for Bchl-Ser and 72 h for Chl-Ser wit h mean half-lives (t(1/2)) of about 2 and 7 h, respectively, In contra st, the clearance rates of these pigments and their metabolites from m elanoma tumor tissue were significantly longer: t(1/2) = 20 h for Chl- Ser and 15 h for Bchl-Ser and metabolites, The clearance rates showed biphasic or single exponential decay patterns in normal tissues and in tumors, respectively, Cumulatively the high phototoxicity, simple mod e of delivery and fast tissue clearance rates reported here suggest th at polar conjugates of Chi and Bchl promise to be highly effective PDT reagents.