Synthesis of long-wavelength-absorbing photosensitizer/nanoparticle conjugates and their in vitro PDT evaluation on colorectal cancer cell lines

Starting from purpurin-18, a stable purpurin-18 imide derivative with intensive absorption in the near infrared has been synthesized. The opening of the exocycle anhydride by a primary alkylamine bearing an adamantyl group, allows after cyclization the formation of an imide function. This reaction led to the purpurinimide adamantane derivative (PIA) which enables the inclusion of a photosensitizer in the cavity of cationic cyclodextrin coupled to cellulose nanocrystals (CNCs/β-CD + ). Preliminary in vitro results showed that CNCs/β-CD + complexes improved internalization of photosensitizers into HCT116 and HT-29 colorectal cancer cell lines. Moreover, MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay of CNCs/β-CD + /PIA complexes showed significant dose-dependent phototoxicity after illumination with red light, with IC 50 values of 2.5 and 8.7 nM, for HT 116 and HT-29, respectively, and very low dark toxicity. The current results suggest that these nanoparticle/photosensitizer complexes are promising and useful tools for photodynamic therapy (PDT).