Radio-nanomedicine, such as 125I-labelled TiO2 nanoparticles (125I-TiO2 NPs), presents a promising tumour treatment approach. By leveraging 125I as an electron donor to activate TiO2 NPs and promote γ-ray–induced H2O radiolysis, 125I-TiO2 generates reactive oxygen species (ROS) and induces DNA damage, thus enabling catalytic internal radiotherapy (CIR). Since DNA is a key target of radiation and ROS-induced damage, enhancing nuclear delivery is critical. However, lysosomal entrapment of 125I-TiO2 NPs greatly restricts the efficacy of CIR. To overcome this limitation, we conjugated 125I-TiO2 with transactivator of transcription/hemagglutinin-2 (125I-TiO2-TAT/HA2), hypothesising that TAT/HA2-mediated lysosomal escape and nuclear accumulation could improve the anti-tumour effects of 125I-TiO2.

TiO2 NPs and TiO2-TAT/HA2 were synthesised and labelled with 125I. Subcellular localisation was observed by confocal microscopy and biological transmission electron microscopy (bio-TEM). The effects of 125I-TiO2-TAT/HA2 on PANC-1 cells were assessed by the CCK-8 assay (cell viability), flow cytometry (apoptosis and ROS generation), proliferating cell nuclear antigen (PCNA) staining (proliferation), γ-H2AX immunofluorescence (DNA damage), and western blotting (DNA repair protein expression). In a subcutaneous pancreatic cancer mouse model, the intratumoural intra-tumoural retention of cyanine 5-labelled NPs (Cy5-NPs) was tracked via fluorescence imaging, whereas 125I-TiO2-TAT/HA2 was monitored by single-photon emission computed tomography (SPECT). Mice received intra-tumoural injections of DMEM, 125I, 125I-TiO2, or 125I-TiO2-TAT/HA2, and tumour volume and mouse weight and survival were recorded. Tumour glycometabolism was evaluated using 18F-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) before and after treatment. Haematoxylin and eosin (H&E), TdT-mediated dUTP nick end labelling (TUNEL), and immunohistochemical staining (Ki-67, DNA repair proteins) were performed.

The labelling rates of 125I-TiO2 and 125I-TiO2-TAT/HA2 averaged 89.0% and 90.1%, respectively. Confocal microscopy and bio-TEM confirmed the nucleus-targeting ability of TiO2-TAT/HA2. In vitro, 125I-TiO2-TAT/HA2 significantly increased apoptosis and DNA damage and reduced DNA repair protein expression (RAD51and 53BP1) versus 125I-TiO2 (all p < 0.05). 125I-TiO2-TAT/HA2 additionally reduced PCNA expression and increased ROS production (both p > 0.05). In vivo, Cy5-NPs, 125I-TiO2, and 125I-TiO2-TAT/HA2 exhibited prolonged intra-tumoural retention. Tumours treated with 125I-TiO2-TAT/HA2 displayed a significantly smaller volume, enhanced necrosis and apoptosis (H&E, TUNEL), and downregulated DNA repair protein expression (all p < 0.05) and reduced Ki-67 expression (p > 0.05) compared with the effects of 125I-TiO2.

125I-TiO2-TAT/HA2 exhibited markedly enhanced efficacy, likely through the precise nuclear delivery of ROS rather than increased ROS production. This strategy presents a promising method to improve tumour therapy, and it could be adapted for other macromolecular therapeutics.