Written by Dai Zhifei
Updated: 2012-4-9
Porphyrin was successfully conjugated to nanohybrid cerasomes for photodynamic therapy of cancer, which was reported in Angew Chem Int Ed (2011，50，11622-11627) as a VIP paper and highlighted in frontispiece (Figure 1).
Fig. 1 Porphyrin cerasome was reported in Angew Chem Int Ed as a VIP paper and highlighted in frontispiece
Photodynamic therapy (PDT), combining light, photosensitizers (PSs) and tissue oxygen, is an emerging treatment used to eradicate premalignant and early-stage cancer and reduce the tumor size in end-stage cancers. However, most photosensitizers that are in use clinically or in preclinical development are hydrophobic and strongly aggregate in aqueous media. This aggregation significantly reduces their photosensitizing efficacy since only monomeric species are appreciably photoactive. With the aim of improving the efficacy and safety of PDT, liposomes with their flexibility to accommodate PSs with variable physicochemical properties, came into focus as a valuable carrier and delivery system. However, the insufficient morphological stability of the conventional liposomes may lead to rapid clearance of the vesicles from circulation often before reaching their target. In addition, in liposomes, the drug contents are generally less than 10%. Therefore, the highly stable liposomes with a high PS loading efficiency stand a better chance in becoming carriers of photosensitizers.
Fig. 2 Schematic illustration for the formation of porphyrin cerasome.
Porphyrins are the most popular PSs for PDT. Attacking the above problems head on, we fabricated a porphyrin bilayer cerasome (PBC) for the first time by sol–gel reaction and self-assembly process from a conjugate of porphyrin-organoalkoxysilylated lipid (PORSIL) with dual triethoxysilyl heads, a hydrophobic double-chain segment, a porphyrin moiety and a connector unit among them (Figure 2). Compared with the reported cerasomes and liposomes, the PBCs take more advantages: ①Their drug loading efficiency (33.46%) is significantly higher than the physically entrapping cerasomes or liposomes (generally less than 10%). ②The covalent incorporation of porphyrins into cerasomes is expected to avoid the premature release of PSs during systemic circulation and thus enhance the outcome of PDT. ③The orderly arranging mode of porphyrins in the lipid bilayer ensures the efficacy of singlet oxygen production even at an extremely high number of porphyrins, effectively prevent fluorescence loss of porphyrins, permitting a powerful tool for in vivo imaging and photodynamic diagnostics. The capability to load chemotherapy drugs into the internal aqueous core of PBCs makes it possible to develop a drug-carrier system for the synergistic combination of chemotherapy and PDT for the treatment of cancer.
Nanomedicine & Biosensor Laboratory website http://nanobio.hit.edu.cn/a/en/news/2012/0324/142.html
