Gold Nanoparticle Radiosensitization for High-Dose-Rate Brachytherapy: Differential Efficacy of PEG- and RGD-Functionalized Gold Nanoparticles Across 2-Dimensional, 3-Dimensional, and in vivo Prostate Cancer Models.

Purpose: Gold nanoparticles (GNPs) are promising radiosensitizing agents for radiation therapy; however, their implementation into high dose rate brachytherapy (HDR-BT) remains underexplored. Surface functionalization with polyethylene glycol (PEG) or integrin-binding domain RGD impacts their biodistribution and intracellular uptake, but whether active cellular targeting via RGD improves radiosensitization for HDR-BT has not been established in vivo. Methods: Here, we systematically compare the radiosensitization efficacy of non-targeted PEGylated GNPs versus actively targeted PEG-RGD GNPs on PC3 prostate cancer cells in vitro and in vivo, using clinically plausible concentrations, dosing procedures, and purpose-built irradiation platforms. 2-dimensional (2-D) and 3-dimensional (3-D) cell cultures, and male NRG mice were irradiated via a 192-Ir source delivered from a clinical HDR-BT afterloader. In vitro samples were dosed at 10 μg [Au]/mL and mice were intratumourally injected with 50 μL at 2 mg [Au]/kg bodyweight. Results: PEGylated GNPs did not elicit any radiosensitization either in 2-D, 3-D, or in vivo. RGD-functionalized GNPs elicited a 17% ( Conclusion: This research represents the first systematic in vitro and in vivo demonstration of GNP-induced radiosensitization using an HDR-BT source with clinically informed intratumoural delivery. Active cellular targeting with RGD functionalization was found to be a critical determinant of radiosensitization efficacy both in vitro and in vivo. Both GNP formulations demonstrated tolerability at the delivered dosing concentrations, and further research into the clinical deliverability of GNPs for HDR-BT is necessitated.