Lysosome-escaping and nucleus-targeting nanomedicine for enhanced cancer catalytic internal radiotherapy

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.