NanoPDT · Efficient Tumor Targeting and Therapy Using Near-Infrared Nanoparticles

Periodic Report Summary 1 - NANOPDT (Efficient Tumor Targeting and Therapy Using Near-Infrared Nanoparticles)

NanoPDT is a project focusing on the rational design and evaluation of biocompatible nanoparticles for fluorescence guided surgery and photodynamic therapy. This work is a collaboration between the Center for Molecular Imaging (Harvard, Boston) and the Institut Albert Bonniot (Université Joseph Fourier, Grenoble). The project aimed at respecting the CHOI criteria for nanoparticles, defined by our partner of the Center for Molecular Imaging: (i) hydrodynamic radius less than 10 nm, (ii) hydrophilic surface and (iii) less than 5-10 ligand per particles. These criteria were defined to produce nanoparticles that can be cleared in less than 4 hours through renal pathway, to ensure minimal side effects and high contrast in clinical imaging. To this end, particles were synthesized with epsilon-polylysine as a backbone grafted with cyclodextrins to enable non-covalent drug loading of either a fluorescent dye or a photodynamic agent. Particles’ charge was modified using either succinic anhydride or acetic acid and. The project focused on using straightforward and water-compatible reactions to ensure simplicity of production and biocompatibility of the final product. Several variations of the particles were produced and equivalent polymers without cyclodextrin were produced to study the influence of both charge and cyclodextrins on the biodistribution in vivo. Interestingly, these particles showed ubiquitous distribution in early times, but only the zwitterionic nanoparticles and acetylated polylysine showed rapid renal-only excretion. Zwitterionic nanoparticles also showed prolonged distribution and terminal half-lives in blood (4,5 and 45 minutes respectively) compared to unmodified cyclodextrin-grafted polylysine (2,0 and 23 minutes). This prolonged circulation could prove advantageous for targeting strategies while still being short enough to ensure rapid clearence. A synthetic route for targeting ligand grafting has also been developed. Again keeping in mind the need for straightforward water-compatible reactions, RGD peptides were grafted onto the polylysine backbone using an activated suberic acid. While these RGD-targeted nanoparticles didn’t show uptake improvement on HEKβ3 cell line (αvβ3 integrin positive cell line), the same synthetic route can be applied to graft cyclic RGD peptides, which are known to have a better affinity constant for αvβ3 integrin than the linear peptide. The main obstacle encountered during the project is the selection of a suitable dye for cyclodextrin encapsulation. Thanks to the collaboration of the CMI with the Department of Chemistry of Georgia State University, various dye structures have been tested for their affinity with the particles: indocyanines, phenoxazines, xanthenes, prophyrins, phthalocyanins, BODIPY and cholesterol mimetics. Although some of these dyes proved to have very high affinity constants for the particles during standard in vitro tests, they failed to form a stable complex with cyclodextrins in serum. To circumvent this problem, adamantane conjugated dyes were synthesized. Their affinity for the particles was assessed in serum using FRET techniques, showing the stability of the complex formation. As a result, a change in the loading and targeting strategy is considered: IRdye700 DX, a commercially available phthalocyanin with phototoxic capability, would be grafted directly on the polymer backbone and cyclodextrins would be used as anchors for adamantane derivatives of targeting ligands. This strategy would enable the production of a photosensitizing block with rapid renal clearance thanks to the modified polylysine backbone, and offer versatile targeting options where one or several targeting ligands could be easily attached to the nanoparticles without need for chemical reaction or purification.

Data: CORDIS, © European Union