Pullulan conjugates (i.e. PFP1, PFP4) formed via DCC/DMAP coupling of porphyrin derivatives possessing one (P1) or four (P4) carboxylic acid moieties with folate-appended pullulans (PF) were prepared for application as photosensitizers (PS) for photodynamic therapy. To maximize the desired PS characteristics, the assembly size of PS should be less than 200 nm in water medium. In a PBS buffer solution, PFP4 forms smaller assemblies (~100 nm) than PFP1 (~320 nm) due to its enhanced intramolecular hydrophilicity.

Photosensitizers can produce highly reactive singlet oxygen with exposure to visible light and are used in photodynamic therapy to treat a variety of tumors. We report on the synthesis of triethylene glycol dendron-conjugated pheophorbide-a 5, a novel photosensitizer. The characteristic absorption bands (Soret and Q-bands, l max = 405 and 670 nm, respectively) of 5 were appeared clearly in aqueous solution, due to the improved water-solubility of the dendron moiety. The value of singlet oxygen quantum yield of 5 (F D = 0.22) was higher than free pheophorbide-a (F D = 0.17) as reference in aqueous solution. Compound 5 also exhibited an enhanced in vitro phototoxicity than pheophorbide-a (PhA) in the concentration range of 1.0-5.0 mg/mL: cell viability in cells treated with 5 was reduced by ~20%, indicating a cell death rate of ~80%, while PhA treatment resulted in a cell death rate of only about 10%. These results indicate that 5 will likely be more efficient in PDT applications. Compared with free PhA, compound 5 showed highly enhanced singlet oxygen generation ability and in vitro photocytotoxicity.