Ex-Vivo Quantification and Localization of PSMA-Targeted GNPs via X-ray Fluorescence Imaging

Gold nanoparticles (GNPs) are widely studied in medical research due to their favorable biocompatibility, variety in shape and size, and simple surface modification. Nanoparticles are particularly valuable in cancer research due to their enhanced permeation and retention effect property whereby nanoparticles accumulate in tumors. However, imaging GNPs are a challenge for most imaging modalities. Therefore, recent studies using x-ray fluorescence (XRF) imaging offer a potential for precise quantification and localization of GNPs without single endpoint studies such as immunohistochemistry and mass spectrometry. This study aims to accurately quantify and localize GNPs in ex-vivo tissue from GNP injected mice. 15-nm PEGylated GNPs were conjugated to anti-PSMA antibodies using 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxy sulfosuccinimide. 3 SCID mice per group bearing subcutaneous LNCaP xenografts were intravenously injected with either anti-PSMA antibody conjugated GNPs (15mg/mL, 200 mu L) or Mouse IgG GNPs 24hrs prior to dissection. 11 organs along with the tumor were collected from the mice. Each organs' GNP content was measured for quantification and localization via XRF on an in-house-developed dual-modality computed tomography and XRF system. Following imaging, organs were dehydrated and dissolved for quantification with inductively coupled plasma mass spectrometry analysis. XRF imaging quantified GNPs in tissue down to 25ng/g. Quantification with XRF imaging showed similar to 2x times greater accumulation of GNPs in the tumor with anti-PSMA targeted GNPs compared to Mouse IgG control GNPs. Additionally, XRF imaging of anti-PSMA targeted GNPs in all organs showed accurate quantification when compared to ICPMS analysis. XRF computed tomography further confirmed quantification of GNPs in tumors and spleen. This study confirmed the viability of XRF imaging for accurate quantification of anti-PSMA targeted GNPs in ex-vivo tissues.