Nanoparticle-Mediated Radiation-Triggered Release Of Nitrate, Precursor Of Reactive Nitrogen Species, Improves Local Tumor Control

Abstract

The efficacy of gold nanoparticles (AuNP) as dose-enhancing agents are adversely affected by low tumor uptake, low membrane penetration, and the locality of the AuNP dose enhancement away from relevant targets. To address these limitations, we propose a novel AuNP system for radiation-triggered release of nitrate, a precursor of reactive nitrogen species, and investigate the AuNP efficacy in-vivo. AuNPs were functionalized through PEGylation for increased in vivo circulation time, addition of cell-penetrating peptides (CPP) ([email protected]) for increased membrane penetration, and addition of nitroimidazole (nIm) ([email protected]) to transform local dose enhancement in nitrite release and subsequent generation of reactive nitrogen species that contribute to cell death. NU/NU mice with subcutaneous tumors of the radioresistant breast tumor model 4T1 were injected with either [email protected] or [email protected] via intra-peritoneal injection. Uptake in tumor and normal tissue uptake was assessed at 6 and 24 h after injection. Another cohort of mice was injected and irradiated to a dose of 18 Gy 24h after injection and followed for 2 weeks post irradiation to evaluate tumor response. The mean physical and hydrodynamic size of the nanoparticle systems was 5 and 15 nm, respectively. The addition of nIm on the surface of the nanoparticles did not significantly affect size distribution. A nIm loading of 1 wt% was determined. The tumor accumulation (percent of injected dose per gram (%ID/g)) of [email protected] was significantly lower than the [email protected] accumulation (0.2%ID/g vs 1.2%ID/g). The reverse was seen for normal tissue where [email protected] showed higher accumulation in liver and spleen compared to [email protected] Concerning tumor response, no differential effect was found in un-irradiated mice injected with either saline or [email protected] alone. Furthermore, the combination of [email protected] and radiation had no differential effect from radiation alone. A significant delay in tumor regrowth was observed in the irradiated [email protected] group compared to irradiated controls. The successful synthesis of AuNP functionalized with CPP and nIm showed a significantly increased therapeutic response compared to the same nanoparticle system without nIm. This was observed despite an order of magnitude lower accumulation in tumor tissue. With improved biokinetics, this nanoparticle system would be a promising novel sensitizer of radioresistant and hypoxic tumors.