Nanoparticles (NPs) possess unique physical and chemical properties due to their high surface area and nanoscale size (typically 1-100 nm). Over the last decade, the development of nanoparticles for medical applications has become increasingly popular as they have shown the ability to overcome limitations of conventional chemotherapy. One of the main advantages of NPs is that they can be chemically tailored in such way to specifically target cancer cells and tissues and can be used in a variety of imaging modalities: fluorescent imaging (FI), magnetic imaging resonance (MRI). When coated with a matrix to target cancer cells, these NPs can be used to visualize cancer lesions using FI and/or MRI.
Tb-161 has gathered increasing interest in recent years due to its favorable properties for targeted radionuclide therapy (TRNT). Tb-161 decays (t1/2 = 6.9 d) by the emission of low-energy β- particles (Eβ−average = 154 keV). These β- particles have a maximal tissue range of 0.29 mm and a linear energy transfer (LET) of around 0.32 keV/μm, which is suitable for the treatment of metastasized malignancies. In addition to this, the decay process of Tb-161 releases Auger/conversion electrons (energy ≤ 50 keV). These Auger/conversion electrons release much higher local dose density due to their shorter range in tissue (0.5 – 30 µm), thereby contributing to the therapeutic anti-tumor effects of Tb-161 (Muller et al. 2014) without causing additional renal side effects.
Up to now, only few studies have evaluated the therapeutic potential of Tb-161, which makes it an innovative radionuclide. These preliminary therapy studies revealed that the therapeutic effect of Tb-161-labelled compounds was superior to the effect of their Lu-177-, Cu-67- or Sc-47 -labelled counterparts when applied at the same dose. Tb-161 is typically bound to vector molecules (peptides, nanobodies, proteins, …) through coordination of the Tb-161 atom to a chelating ligand such as DOTA. A potential issue with using such a Tb-161-construct is that these metal complexes can suffer from instability under physiological conditions. Therefore, chelator bound Tb-161 has to risk to be released from the chelator which would result in off target accumulation of the free Tb-161. Therefore, we try to circumvent this issue by to consolidating the Tb-161 into a NP. By incorporating a therapeutic radionuclide such as Tb-161 inside nanoparticles could drastically increase the application potential of Tb-161.
The project is a SCK•CEN-KU Leuven collaboration and the overall objective of this PhD proposal is to develop and pre-clinically evaluate Tb-161-doped-NPs modified to induce biological affinity for the treatment of cancers. To achieve this overall objective the project has been divided in 3 different work packages:
WP1 - Synthesis and characterization of the Tb-161-doped-NPs: Monodispersed terbium-doped lanthanide NPs will be synthesized by the thermal decomposition of Ln3+ precursors following procedures described in literature. Initial steps will be taken in non-radioactive conditions to optimize the production process. After optimization of the production process, we will introduce Tb-161 to the thermal decomposition reaction mixture in order to spike the NPs. Tb-161 will be produced in the Belgian Reactor 2 (BR2) at SCK•CEN by neutron irradiation of highly enriched Gd-160 and can thereafter be isolated from the target material chemically. The pure Tb-161 will be provided by the radiochemistry group from SCK•CEN using a known in-house separation method (Burgoyne et al. 2019). After purification by filtration, the doping efficiency will be monitored by instant thin-layer chromatography (iTLC). Production of NPs will be followed by post-synthetic modification of the surface of the NPs with a biological matrix.
WP2 - In vitro evaluation of Tb-161-doped-NPs: Following synthesis optimization, the stability of the NPs needs to be investigated, in storage and physiological conditions. The in vitro stability will be evaluated in storage conditions as well as in physiologically relevant conditions such as human serum, solutions with increasing concentrations of metals etc. Furthermore, in this WP we will focus on the targeting properties of the Tb-161-doped-NPs. Saturation binding assays will be used to determine binding affinity of the Tb-161-doped-NPs. Finally, internalization and cytotoxicity of the Tb-161-doped-NPs will be evaluated in the same cancer cell lines.
WP3 - In vivo evaluation of biodistribution and therapeutic potential of Tb-161-doped-NPs: In vivo targeting of Tb-161-doped-NPs will be evaluated in a preclinical setting to monitor the biodistribution, the stability, tissue penetration, tumor targeting and toxicity. A maximum tolerated dose assay will be performed to estimate the toxicity of Tb-161-doped-NPs in healthy mice. Following this dose estimation, the therapeutic effect of the Tb-161-doped-NPs will be evaluated in a gynecological cancer model.