New materials for cancer imaging and therapy

Metal-based photoactivated chemotherapy (PACT) involves a class of metal- based prodrugs, which may overcome the limitations and side effects of current metal-based chemotherapeutic agents on account of their novel mechanism(s) of action. In this thesis, a number of vibrational spectroscopic methods were developed and applied to study the mechanisms of metal-based PACT agents upon activation with light. A particularly promising PACT agent is the diazido Pt(IV) anticancer prodrug, trans,trans,trans-[Pt(N3)2(OH)2(py)2] (1, py = pyrdine), in which photoinduced cleavage of ligands from platinum yields reactive species, which are likely implicated with the observed biological activity. However, monitoring the azido and hydroxido ligands, and the metal centre simultaneously remains challenging. Vibrational spectroscopy is a potentially powerful tool to study both metal and ligand vibrations without the requirement of labelling and is non- destructive at the same time. The essential first step was the screening of 1 by a range of vibrational spectroscopic methods, including Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR), Raman and synchrotron radiation far-infrared (SR-FIR), aided by Density Functional Theory (DFT). This yielded an extensive vibrational fingerprint of 1 containing individual ligand (pyridine, hydroxide and azide) and platinum to ligand vibrations. The established methodologies provided the necessary basis for elucidating further photodecomposition and photoreaction pathways. Successive ATR-FTIR studies allowed for examinations of the photodecomposition of 1 complemented by transient electronic absorption and UV-Vis spectroscopy under 420 nm or 310 nm irradiation. Chemometric data evaluation using Principal Component Analysis (PCA) and Multi Curve Resolution Alternating Least Squares (MCR-ALS) on the steady state UV-Vis and ATR-FTIR spectra captured the formation of a Pt(II) intermediate, trans-[Pt(N3)(py)2(OH/H2O)] and a final product, trans-[Pt(py)2(OH/H2O)2], in which the trans pyridine scaffolds were retained. Upon irradiation, the rapid removal of the hydroxido stretching vibration was found to correlate to a shift in the anti-symmetric azido vibration, indicative of a possible second intermediate. Experimental evidence of subsequent azido dissociation from platinum suggests that at least one hydroxyl radical is formed in the reduction of Pt(IV) to Pt(II) under such conditions. Additionally, photoproducts formed upon irradiation of 1 in the presence of the DNA nucleotide 5’-guanosine monophosphate (5’- GMP) could be systematically studied using ATR-FTIR, mass spectrometry and DFT calculations. Underpinning methodologies were subsequently applied to study a series of photoactivatable ruthenium-based CO releasing complexes of the formula [RuLCl2(CO)2] (L = 2,2’-bipyridine with 4’ methyl and/or carboxyl substituents). A three-step mechanism involving the sequential formation of [RuL(CO)(CH3CN)Cl2], [RuL(CH3CN)2Cl2] and [RuL(CH3CN)3Cl]+ was deduced upon 350 nm irradiation in acetonitrile. Rapid removal of the first CO ligand (k1 ≫ 3 min−1 ) and a modest rate for the second CO ligand (k2 = 0.099 – 0.17 min−1 ) was observed, with slowest rates found for the electron-withdrawing carboxyl substituents. Aqueous media considerably slowed down the photodecarbonylation (k1 = 0.46 – 1.3 min−1 and k2 = 0.026 – 0.035 min−1 ) and the carboxyl groups were shown to have a less pronounced effect on the rate constants, revealing the possible implications for the design of such candidates intended for clinical application. State-of-the-art synchrotron based infrared spectroscopy was utilised with continued focus on the mechanism of action of 1. ATR-FTIR and synchrotron radiation far-infrared were combined (SR-ATR-FIR) to enable the rapid screening of samples, exposing changes to the metal to ligand vibrations of 1. Additionally, in situ irradiation using liquid transmission SR-FIR revealed the removal of in the platinum to oxygen (hydroxide) and platinum to nitrogen (azide) vibrations simultaneously. Moreover, a mid-infrared live single cell study of 1 on acute myeloid leukaemia cells (K562) by Synchrotron Radiation Infrared Microspectroscopy revealed significant changes to DNA base stacking and lipid vibrations after only four hours of low dose irradiation at 350 nm (2.58 J cm- 2 ). Lastly, the low wavelength excitation of the earlier described photoactivatable metal-based anticancer prodrug candidates was considered, which commonly hamper their clinical feasibility. A range of lanthanide-doped upconverting nanoparticles (UCNPs) were synthesised, allowing for near-infrared light excitation and visible light emission as a potential platform for wavelength activation of PACT agents in a clinically-relevant window