Terbium-Based AGuIX-Design Nanoparticle to Mediate X-ray-Induced Photodynamic Therapy

Abstract

X-ray-induced photodynamic therapy is based on the energy transfer from a nanoscintillator to a photosensitizer molecule, whose activation leads to singlet oxygen and radical species generation, triggering cancer cells to cell death. Herein, we synthesized ultra-small nanoparticle chelated with Terbium (Tb) as a nanoscintillator and 5-(4-carboxyphenyl succinimide ester)-10,15,20-triphenyl porphyrin (P1) as a photosensitizer (AGuIX@Tb-P1). The synthesis was based on the AGuIX@ platform design. AGuIX@Tb-P1 was characterised for its photo-physical and physico-chemical properties. The effect of the nanoparticles was studied using human glioblastoma U-251 MG cells and was compared to treatment with AGuIX@ nanoparticles doped with Gadolinium (Gd) and P1 (AGuIX@Gd-P1). We demonstrated that the AGuIX@Tb-P1 design was consistent with X-ray photon energy transfer from Terbium to P1. Both nanoparticles had similar dark cytotoxicity and they were absorbed in a similar rate within the cells. Pre-treated cells exposure to X-rays was related to reactive species production. Using clonogenic assays, establishment of survival curves allowed discrimination of the impact of radiation treatment from X-ray-induced photodynamic effect. We showed that cell growth arrest was increased (35%-increase) when cells were treated with AGuIX@Tb-P1 compared to the nanoparticle doped with Gd.

Added Value of Scintillating Element in Cerenkov-Induced Photodynamic Therapy

“…When we added P1 to the nanoparticle, P1 fluorescence increased twice as Tb peaks decreased, demonstrating the energy transfer between Tb and P1. The same observation was made experimentally in a previous work dealing with the same nanoplatform under X-ray exposure [ 29 ]. Our simulations revealed that scintillation PDT can be dramatically improved when scintillators are added to the PS.…”

“…With Cerenkov radiations also emitting UV light, potential bias would have flawed our results. Nevertheless, when we exposed AGuIX@Tb or AGuIX@Gd to high energy photons, we did not observe any SOSG increase at the activity concentrations used in our previous experiments [ 29 ].…”

“…Pre-treated cells with AGuIX@Tb-P1 and irradiated in the presence of 1 and 3 MBq of 68 Ga, led to a significant decrease in the formation of cell clones compared to non-irradiated cells ( p = 0.004 and p = 0.0006, respectively; Figure 5 b). Furthermore, compared to the radioactive concentration of 3 MBq, similar results for clonogenic capacity were obtained with cells treated in the presence of AGuIX@Tb-P1 and X-ray irradiated at 2.0 Gy [ 29 ]. Moreover, we did not observe any effect on clone formation for activities less than 1 MBq.…”

“…Indeed, single P1 exposed to 68 Ga highlighted its characteristic fluorescence peak at 652 nm. When we modelled the AGuIX@Gd-P1 nanoparticle, we did not observe any P1 fluorescence increase as expected as there is no overlap between Gd luminescence (~350 nm) and P1 absorption spectrum, id est, Soret band at 405 nm [ 29 ]. AGuIX@Tb exposed to 68 Ga solution showed the characteristic Tb scintillation spectrum.…”

“…Moreover, nanoparticles’ pre-treated cell exposure to 68 Ga is associated with the decrease in the capability of cell clone formation ( Figure 5 ). Cell treatment conditions, as 1 µM equivalent Tb, were previously chosen since cell clone formation was mainly inhibited when cells were pre-treated with 2.5 µM AGuIX@Tb-P1 and then irradiated with a low X-ray dose [ 29 ]. Interestingly, when cells were exposed to AGuIX@Gd, AGuIX@Tb or AGuIX@Gd-P1, cell growth was not significantly lowered ( Figure 5 b,c) supporting the concept that both Tb, as NS, and P1, as PS, are needed to obtain an efficient therapeutic effect related to the phototherapeutic performance by positron and Cerenkov radiations.…”