Improved photodynamic activity of porphyrin loaded into nanoparticles: an in vivo evaluation using chick embryos

Hydrophobic porphyrins are potentially interesting molecules for the photodynamic therapy (PDT) of solid cancers or ocular vascularization diseases. Their pharmaceutical development is, however, hampered by their lipophilicity, which renders formulation difficult especially when intravenous administration is needed. Encapsulation of a lipophilic derivative of porphyrin, the meso-tetra(p-hydroxyphenyl)porphyrin (p-THPP), into polymeric biodegradable poly(D,L-lactide-co-glycolide) (PLGA) nanoparticles proved to enhance its photodynamic activity against mammary tumour cells when compared to free drug. In order to further investigate these carriers, the efficacy of the encapsulated drug was assessed on the chick embryo chorioallantoic membrane (CAM) model. First, we identified a suitable solvent for the drug in terms of p-THPP solubility and tolerability by chick embryos. This solution was used as a reference. Then, the fluorescence pharmacokinetics and the photodynamic effects of the porphyrin on CAM vessels were evaluated after intravenous administration of either a p-THPP solution (free drug) or the drug loaded into nanoparticles. The results showed that: (i) the drug remained longer in the vascular compartment when incorporated into nanoparticles and (ii) vascular effects of p-THPP after light irradiation were enhanced with nanoparticle carriers. These results are discussed taking into account the extravasation of intravascular circulating photosensitizers and its influence on PDT performance.