Preparation, characterization, and in vitro phototoxic effect of zinc phthalocyanine cucurbit[7]uril complex encapsulated into liposomes

• An inclusion complex between cucurbit[7]uril and zinc phthalocyanine was prepared.
• The inclusion complex increased aqueous solubility of lipophilic zinc phthalocyanine.
• Liposomes containing the inclusion complex showed an excellent photocytotoxic effect.

Inclusion complexes improve the solubility, dissolution, and bioavailability of hydrophobic drugs. In this study, we used the cucurbit[7]uril (CB[7]) to improve the solubility of zinc phthalocyanine (ZnPc) in water. The CB[7]:ZnPc complex was prepared by co-evaporation, characterized it by 1H NMR spectroscopy, differential scanning calorimetry, X-ray diffraction, UV–vis spectroscopy, and molecular simulation. Next, the CB[7]:ZnPc inclusion complex was incorporated into liposomes (CB[7]:ZnPc-Lp) to obtain a drug delivery system and assess the in vitro phototoxicity of both free and liposomal CB[7]:ZnPc on B16-F10 melanoma cells. 1H NMR confirmed that the CB[7]/ZnPc proportion in the inclusion complex was 1:1, as corroborated by X-ray diffraction, differential scanning calorimetry, and UV–vis spectroscopy. Molecular simulation evidenced that the structures of ZnPc and CB[7] interact in the inclusion complex. The thin lipid film method with subsequent extrusion furnished liposomes containing CB[7]:ZnPc compared with the free inclusion complex, CB[7]:ZnPc-Lp exerted excellent phototoxic effect on melanoma cells. In conclusion, inclusion complexes effectively solubilize hydrophobic compounds, such as zinc phthalocyanine and allow for their incorporation into liposomes, generating excellent drug delivery systems.

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