Tumor Radiosensitization Using Nuclear-Targeted Gold Nanoparticles

Tumor targeted gold nanoparticles have been shown to enhance radiosensitization. Herein, we evaluate the radiosensitization potential of nuclear-targeted gold nanoparticles in pancreatic cancer cells. Gold nanospheres (AuNSs) were conjugated with a nuclear localization sequence (NLS) peptide to enhance the accumulation of the particles inside the nucleus. Particles were characterized by their zeta potential and size measurements. Internalization of the particles into the cells was achieved using a cell penetrating peptide (CPP). Cellular and nuclear internalization, and in vitro radiosensitization were assessed in human pancreatic adenocarcinoma cancer cells (Panc 1) using transmission electron microscopy, dark field microscopy and clonogenic cell survival with doses between 0 to 6 Gy, respectively. In vitro radiosensitization experiments were carried out using 250-kVp X-rays for 3 groups: radiation only, non-targeted (pAuNSs) and nuclear-targeted spheres (nAuNSs). Zeta potential measurements confirmed the change in surface charge from negative for pAuNSs to neutral or slightly positive for nAuNSs, and size measurements revealed uniformly dispersed particles (around 5nm in diameter by TEM and 20-26nm by dynamic light scattering). Qualitative assessment of cellular internalization showed similar uptake levels of the non-targeted (pegylated) and nuclear-targeted particles. Dark field microscopy revealed an enhanced signal localized to the nucleus for the nAuNSs compared to a non-specific signal present in the cell for the pAuNSs. Clonogenic cell survival indicated a radiosensitization enhancement factor (REF), calculated at the 10% survival fraction, of 1.17 vs. 0.969 (P<0.05) for the nAuNPS vs. pAuNPs, respectively. Our data demonstrates the possibility of achieving enhanced radiosensitization by employing nuclear- targeted gold nanoparticles. These results warrant further investigation in an in vivo setting, which is currently underway.