Gold Nanoparticle Targeting with Linear and Cyclic RGD Peptides for Radiotherapy Enhancement
Abstract
Purpose
Gold nanoparticles (GNPs) are candidate cancer cell radiosensitizers, they can be targeted with peptides containing the αvβ3 integrin binding domain RGD (arginine, glycine, aspartic acid). This integrin is overexpressed in many cancer cells. Peptide shape-based uptake has not been extensively tested in-vitro, where linear peptides are commonly used; cyclic are more common in-vivo due to better stability and binding kinetics. GNPs functionalized with linear or cyclic RGD peptides were tested for uptake in model macrophages (Raw 264.7) to determine immune interaction and tumour cells (Mia PaCa-2).
Methods
Cells were dosed at 10 ug/mL with 12.2 nm diameter spherical GNPs. GNPs were functionalized with polyethylene glycol (PEG) and an RGD containing linear or cyclic peptide of the same sequence (GNP+PEG/lRGD and GNP+PEG/cRGD respectively). Uptake was measured with microscopy and Inductively Coupled Plasma Mass Spectrometry. Samples were irradiated at 6X (600MU/min) with a Varian TrueBeam Linear Accelerator (LINAC). Clonogenic and DNA double strand break confocal microscope imaging assays quantified radiation damage.
Results
Uptake of GNP+PEG/cRGD was significantly higher than GNP+PEG/lRGD in Raw 264.7 (2190%, p<10e5 after 4 hours) and Mia PaCa-2 (96.7%, p=0.005 after 24 hours). Mia PaCa-2 cells with 2 Gy irradiation showed no significant difference in DNA double strand breaks with either peptide. There was a non-significant decrease in clonogenic survival with GNP+PEG/cRGD compared to control at 10 Gy (26%, p=0.22) and GNP+PEG/lRGD (21%, p=0.24) and all lower doses.
Conclusion
We saw significantly higher GNP uptake with GNP+PEG/cRGD compared to GNP+PEG/lRGD in Raw 264.7 and Mia PaCa-2. There was no significant change in damage to radioresistant Mia PaCa-2 cells. Higher GNP uptake with GNP+PEG/cRGD in Raw 264.7 macrophages shows a potential issue with cyclic peptides in immunocompetent models. Macrophage uptake should be considered in GNP complex synthesis; modified peptides or macrophage inhibitor functionalization may reduce uptake.