Sulfanyl porphyrazines: Molecular barrel-like self-assembly in crystals, optical properties and in vitro photodynamic activity towards cancer cells

Novel sulfanyl porphyrazines with peripheral 4-bromobenzyl and 4-biphenylylmethyl substituents were synthesized, characterized by photochemical methods and evaluated as sensitizers for photodynamic therapy (PDT). The X-ray crystallography study performed for sulfanyl porphyrazine with 4-biphenylylmethyl substituents revealed that the biphenylyl residues from two consecutive molecules form barrel-like cages with a macrocyclic core constituting a bottom and a top of the barrel and pyridine molecules enclosed inside. The optical properties of both porphyrazines were evaluated in various protic and aprotic solvents. To complement the conventional fluorescence measurements excitation-emission maps were recorded. The potential photosensitizing efficiency of the novel sulfanyl porphyrazines was evaluated by assessing the quantum yields of photosensitized singlet oxygen production. For this purpose the emission of light specific for the transition of singlet oxygen to ground state oxygen was measured. Photodynamic activities of porphyrazines and their liposomal formulations with different surface charge toward two oral squamous cell carcinoma cells (CAL 27, HSC-3) and human cervical epithelial adenocarcinoma cells (HeLa) were determined. Sulfanyl porphyrazines incorporated in cationic liposomes showed high activity, in contrast to the lack of activity of the free form porphyrazines in solution. Thus, cationic liposomes composed of 1,2-dioleoyl-3-trimethylammonium-propane and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine can be considered as a promising drug delivery system for the sulfanyl porphyrazines for the photodynamic therapy of cancers