RGD peptide-conjugated multimodal NaGdF4:Yb3+/Er 3+ nanophosphors for upconversion luminescence, MR, and PET imaging of tumor angiogenesis

Abstract

Multimodal nanoparticles have been extensively studied for target-specific imaging and therapy of various diseases, including cancer. In this study, radiolabeled arginine-glycine-aspartic acid (RGD)-functionalized Er 3+/Yb3+ co-doped NaGdF4 upconversion nanophosphors (UCNPs) were synthesized and evaluated as a multimodal PET/MR/optical probe with tumor angiogenesis-specific targeting properties. Methods: A dimeric cyclic RGDyk ((cRGDyk)2) peptide was conjugated to polyacrylic acid-coated NaGdF4:Yb3+/Er3+ UCNPs along with polyethylene glycol molecules and was consecutively radiolabeled with 124I. In vitro cytotoxicity testing was performed for 3 d. Upconversion luminescence imaging of (cRGDyk)2-UCNP was performed on U87MG cells with a laboratory-made confocal microscope. In vivo small-animal PET and clinical 3-T T1-weighted MR imaging of 124I-labeled RGD-functionalized UCNPs was acquired with or without blocking of cyclic RGD peptide in a U87MG tumor model. Inductively coupled plasma mass spectrometry and biologic transmission electron microscopy were done to evaluate gadolinium concentration and UCNP localization, respectively. Results: Polymer-coated UCNPs and dimeric RGD-conjugated UCNPs were monodispersely synthesized, and those of hydrodynamic size were 30 ± 8 nm and 32 ± 9 nm, respectively. (cRGDyk)2-UCNPs have a low cytotoxic effect on cells. Upconversion luminescence signals of (cRGDyk)2-UCNP were specifically localized on the surface of U87MG cells. 124I- c(RGDyk)2 - UCNPs specifically accumulated in U87MG tumors (2.8 ± 0.8 vs. 1.3 ± 0.4 percentage injected dose per gram in the blocking experiment), and T1-weighted MR images showed significant positive contrast enhancement in U87MG tumors. Tumor localization of 124I- c(RGDyk)2- UCNPs was confirmed by inductively coupled plasma mass spectrometry and biologic transmission electron microscopy analysis. Conclusion: These results suggest that 124I-labeled RGD-functionalized UCNPs have high specificity for αvβ3integrin-expressing U87MG tumor cells and xenografted tumor models. Multimodal UCNPs can be used as a platform nanoparticle with multimodal imaging for cancer-specific diagnoses. COPYRIGHT © 2013 by the Society of Nuclear Medicine and Molecular Imaging, Inc.