Abstract
Auger-electron emitting radionuclides have potential in targeted treatment of small tumours and micrometastases due to their high-LET (linear energy transfer) but short-range emissions. Thallium-201 (201Tl, t1/2 = 73 h), known for its previous use in myocardial perfusion scintigraphy, decays by electron capture releasing around 37 Auger and secondary electrons. However, its radiotoxic and cancer therapeutic effects remain unexplored. In addition, targeted therapy with 201Tl is currently hindered by the lack of efficient chelators to incorporate 201Tl into bioconjugates.The main focus of this PhD thesis was to evaluate 201Tl radiotoxicity to cancer cells, assess its subcellular localisation, as well as developing chemistry for incorporating this radionuclide into a radiopharmaceutical for cancer therapy. To achieve the main objectives, a variety of different methods were used, such as biological assays with radioactive 201Tl, (e.g. cellular uptake and efflux, DNA damage and clonogenic survival assays), chemical synthesis and physicochemical analysis (e.g. thin layer chromatography, dynamic light scattering, infrared spectroscopy, X-ray diffraction analysis, thermogravimetric analysis, UV-Vis spectroscopy), confocal and electron microscopy, energy dispersive X-ray spectroscopy, ion beam analysis and inductively coupled plasma - mass spectrometry.
Firstly, the radiotoxicity of 201Tl was evaluated by exploring its native cellular uptake via potassium channels in different cancer cell lines. It was demonstrated that 201Tl has a significant radiotoxic effect in breast and prostate cancer cells but only when internalised. Secondly, the ion beam analysis appeared to be the most adequate technique for assessing 201Tl subcellular localisation and revealed not only that thallium is present in the cell nucleus, but in an amount higher than in the cytoplasm. Lastly, three different types of nanoparticles were synthesised as a proposed delivery method for 201Tl: nanotexaphyrins and Prussian blue nanoparticles coated either with citric acid or chitosan. Those nanoparticles were characterised, radiolabelled with [201Tl]TlCl and their pharmacokinetics and radiotoxicity assessed by biological assays. Among them, Prussian blue nanoparticles coated with chitosan were the most promising, showing high radiolabelling efficiency with 201Tl, very good stability in physiological conditions, as well as a high uptake and slow efflux when tested in lung cancer cells. More importantly, they showed significant radiotoxicity, increasing the number of DNA damage foci and reducing the clonogenic survival with estimated activity of 0.43 Bq/cell needed to achieve 90% reduction. Subsequently, these nanoparticles were tested in vivo, where they showcased significantly higher retention of 201Tl in tumours compared to unbound 201Tl 48 h after intratumoral injection.
In conclusion, this PhD thesis presents a radiobiological evaluation of unbound and nanoparticle-bound 201Tl with an emphasis on the subcellular localisation of this potent Auger electron–emitter. Prussian blue nanoparticles coated with chitosan and radiolabelled with 201Tl offer a solution for future 201Tl targeted delivery and its potential use in cancer therapy.
| Date of Award | 1 May 2024 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Vincenzo Abbate (Supervisor) & Philip Blower (Supervisor) |