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Highly efficient "theranostics" system based on surface-modified gold nanocarriers for imaging and photodynamic therapy of cancer.

Nanoparticle technologies are significantly impacting the development of both therapeutic and diagnostic agents. At the intersection between treatment and diagnosis, interest has grown for combining both paradigms into clinically effective formulations. In this study we describe a highly efficient drug vector for photodynamic therapy (PDT) and cell imaging developed by designing multifunctional and biodegradable block copolymer-gold nanoparticle (AuNP) conjugates. These conjugates act as water-soluble and biocompatible carriers that allow the delivery of a hydrophobic photosensitizer to a tumor site for PDT action. The 17.6 nm citrate-stabilized AuNPs used herein were modified with folic acid (FA)-conjugated biocompatible block copolymers through a bidentate dihydrolipoic acid (DHLA) linker. The FA-PEG-P(Asp-Hyd)-DHLA-modified AuNPs (FA-PEG-P(Asp-Hyd)-DHLA-AuNPs) were sufficiently stable that their optical properties were not changed under very harsh conditions. Then, the hydrophobic photosensitizer, pheophorbide a (Pheo), was conjugated to the stable vectors through a pH-sensitive linkage. The synthesis and composition of all copolymers were confirmed by 1H NMR measurement. The size of Pheo-conjugated FA-PEG-P(Asp-Hyd)-DHLA-AuNPs-Pheo determined by light-scattering measurements was about 54.7 nm. FE-SEM and FE-TEM images showed that these nanoparticles have a spherical shape and adequate dispersivity after modification. Confocal microscopy, flow cytometry assay, and bio-TEM measurements were used for determining the cellular uptake of Pheo and AuNPs in HeLa cells. The FA-PEG-P(Asp-Hyd)-DHLA-AuNPs-Pheo showed 99.16% cellular uptake and exhibited an excellent phototoxicity compared to free Pheo and FA-unconjugated nanoparticles at pH 6.4.