Gold Nanoparticles Functionalised with 197mHg/197Hgfor Receptor-IndependentNanobrachytherapy of Triple-Negative Breast Cancer and Glioblastoma

Introduction: This study aimed to develop a novel therapeutic strategy for treatment- -resistant cancers based on nano-brachytherapy, using gold nanoparticles as carriers for the Auger-electron–emitting radionuclides 197mHg and 197Hg. Methods: Five-nanometre PEGylated gold nanoparticles were functionalised with 197mHg/197Hg via surface amalgamation and evaluated in vitro in triple-negative breast cancer (MDA-MB-231) and glioblastoma (T98G) cell lines. Cellular internalisation and subcellular distribution were assessed by uptake studies and fractionation. Cytotoxicity was evaluated using MTS assays, while therapeutic efficacy in three-dimensional models was investigated in tumour spheroids. Flow cytometry was employed to analyse apoptosis and cell-cycle distribution. DNA double-strand breaks were quantified by γ-H2AX phosphorylation. Ex vivo biodistribution studies compared intratumoural and intravenous administration routes. Results: The radio-conjugate underwent straightforward synthesis, exhibited very high radio-labelling efficiency at low mercury loading, and maintained excellent colloidal stability. Efficient cellular uptake and pronounced nuclear accumulation were observed in both cell lines. In vitro studies demonstrated strong, time- and dose-dependent cytotoxicity predominantly mediated by apoptosis, with minimal necrosis, accompanied by significant induction of DNA double-strand breaks. In three-dimensional cultures, MDA-MB-231 spheroids underwent rapid, dose-dependent disintegration, whereas T98G spheroids displayed increased resistance. Ex vivo biodistribution revealed high tumour retention following intratumoural administration, minimal systemic exposure and predominantly renal clearance. Conclusions: 197mHg/197Hg-functionalised gold nanoparticles represent a promising receptor-independent platform for localised nano-brachytherapy and warrant further preclinical evaluation in aggressive and therapy-resistant tumours.