Stable Synthetic Bacteriochlorins for Photodynamic Therapy: Role of Dicyano Peripheral Groups, Central Metal Substitution (2H, Zn, Pd), and Cremophor EL Delivery

摘要

A series of four stable synthetic bacteriochlorins was tested in vitro in HeLa cells for their potential in photodynamic therapy (PDT). The parent bacteriochlorin (BC), dicyano derivative (NC)2BC and corresponding zinc chelate (NC)2BC-Zn and palladium chelate (NC)2BC-Pd were studied. Direct dilution of a solution of bacteriochlorin in an organic solvent (N,N-dimethyl-acetamide) into serum-containing medium was compared with the dilution of bacteriochlorin in Cremophor EL (CrEL; polyoxy-ethylene glycerol triricinoleate) micelles into the same medium. CrEL generally reduced aggregation (as indicated by absorption and fluorescence) and increased activity up to tenfold (depending on bacteriochlorin), although it decreased cel- lular uptake. The order of PDT activity against HeLa human cancer cells after 24 h incubation and illumination with 10 J cm~(-2) of near infrared (NIR) light is (NC)2BC-Pd (LD_(50)=25 nM) > (NC)2BC > (NC2BC-Zn ≈ BC. Subcellular localization was determined to be in the endoplasmic reticulum, mitochondria and lysosomes, depending on the bacleriochlorin. (NC) BC-Pd showed PDT-mediated damage to mitochondria and lysosomes, and the greatest production of hydroxyl radicals as determined using a hydroxyphenylfluorescein probe. The incorporation of cyano subsliluents provides an excellent motif for the enhancement of the photoactivity and photosta-bility of bacteriochlorins as PDT photosensilizers.