Auger electron-emitting EGFR-targeted and non-targeted [197Hg]Hg-gold nanoparticles for treatment of glioblastoma multiforme (GBM).

Abstract

Background: We describe here radiation nanomedicines for glioblastoma multiforme (GBM) composed of gold nanoparticles (AuNPs) that integrate the Auger electron-emitter, ¹⁹⁷Hg. [¹⁹⁷Hg]Hg-AuNPs were conjugated to anti-epidermal growth factor receptor (EGFR) panitumumab or were non-targeted. Our aim was to compare the cytotoxicity and DNA-damaging properties in vitro of panitumumab-[¹⁹⁷Hg]Hg-AuNPs and non-targeted [¹⁹⁷Hg]Hg-AuNPs on U251-Luc human GBM cells and estimate their cellular dosimetry. We further aimed to compare the biodistribution in vivo of panitumumab-[¹⁹⁷Hg]Hg-AuNPs and [¹⁹⁷Hg]Hg-AuNPs after convection-enhanced delivery (CED) in NRG mice with U251-Luc tumours in the brain and estimate the absorbed doses in the tumour and surrounding margins of healthy brain.

Results: [¹⁹⁷Hg]Hg-AuNPs (26.8 ± 6.4 nm) were produced with a radiochemical yield of 98 ± 1% by incorporating ¹⁹⁷Hg into the Turkevich synthesis method, forming a mercury-gold amalgam. Panitumumab-[¹⁹⁷Hg]Hg-AuNPs exhibited high affinity (K_D = 1.8 × 10^-9 mol/L) binding to EGFR-positive U251-Luc cells. The binding of panitumumab-[¹⁹⁷Hg]Hg-AuNPs to U251-Luc cells was 15-fold higher than [¹⁹⁷Hg]Hg-AuNPs, and internalization and nuclear uptake were 12-fold and 18-fold greater, respectively. Panitumumab-[¹⁹⁷Hg]Hg-AuNPs caused 84-fold more DNA double-strand breaks (DSBs) in U251-Luc cells than [¹⁹⁷Hg]Hg-AuNPs. Panitumumab-[¹⁹⁷Hg]Hg-AuNPs were ninefold more effective at reducing the clonogenic survival of U251-Luc cells than [¹⁹⁷Hg]Hg-AuNPs. Panitumumab-[¹⁹⁷Hg]Hg-AuNPs were twofold more cytotoxic than non-radioactive panitumumab-AuNPs (P = 0.04) and fivefold more cytotoxic than panitumumab (P = 0.01). The absorbed doses in the nucleus of U251-Luc cells treated in vitro with panitumumab-[¹⁹⁷Hg]Hg-AuNPs or [¹⁹⁷Hg]Hg-AuNPs were 8.8 ± 2.9 Gy and 0.6 ± 0.1 Gy, respectively. SPECT/CT imaging showed that panitumumab-[¹⁹⁷Hg]Hg-AuNPs and [¹⁹⁷Hg]Hg-AuNPs were strongly retained at the infusion site in the brain after CED up to 7 d in NRG mice with orthotopic U251-Luc tumours. Uptake of panitumumab-[¹⁹⁷Hg]Hg-AuNPs in the tumour-bearing right hemisphere [484.5% injected dose/g (%ID/g)] was 172-fold and 579-fold greater than in the healthy left hemisphere and cerebellum, respectively. The uptake of [¹⁹⁷Hg]Hg-AuNPs (423.9% ID/g) in the tumour-bearing right hemisphere was 85-fold and 64-fold higher than the left hemisphere and cerebellum, respectively. Most normal tissue uptake was < 1% ID/g, except for kidneys (9-20% ID/g), spleen (3.5-6.6% ID/g) and liver (0.6-3.3% ID/g). Dosimetry showed that 58% of the tumour received > 190 Gy for CED of 1.0 MBq of panitumumab-[¹⁹⁷Hg]Hg-AuNPs vs. 0.6% of the tumour for non-targeted [¹⁹⁷Hg]Hg-AuNPs, but both agents deposited > 50 Gy in 95% of the tumour. Doses decreased dramatically to 1.7 and 3.3 Gy at 1-3 mm from the tumour edge for panitumumab-[¹⁹⁷Hg]Hg-AuNPs and [¹⁹⁷Hg]Hg-AuNPs, respectively.

Conclusion: Radiation nanomedicines incorporating the AE-emitter, ¹⁹⁷Hg administered by CED are a promising approach to treatment of GBM. Panitumumab-[¹⁹⁷Hg]Hg-AuNPs are particularly attractive due to their EGFR-mediated binding, internalization and nuclear importation in GBM cells, which amplifies their in vitro cytotoxicity.