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

Spectroscopic studies on photoinduced reactions of the anticancer prodrug, trans,trans,trans-[Pt(N3)2(OH)2(py)2]

The photodecomposition mechanism of trans,trans,trans-[Pt(N3)2(OH)2(py)2] (1, py = pyridine), an anticancer prodrug candidate, was probed using complementary Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR), transient electronic absorption and UV-Vis spectroscopy. Data fitting using Principal Component Analysis (PCA) and multi-curve resolution alternating least squares, suggests the formation of a trans-[Pt(N3)(py)2(OH/H2O)] intermediate and trans [Pt(py)2(OH/H2O)2] as the final product upon 420 nm irradiation of 1 in water. Rapid disappearance of the hydroxido ligand stretching vibration upon irradiation is correlated with a -10 cm-1 shift to the anti-symmetric azido vibration, suggesting a possible second intermediate. Experimental proof of subsequent dissociation of azido ligands from platinum is presented, where at least one hydroxyl radical is formed in the reduction of Pt(IV) to Pt(II). Additionally, the photoinduced reaction of 1 with 5'-guanosine monophosphate was studied, and the identity of key photoproducts was assigned with the help of ATR FTIR spectroscopy, mass spectrometry and DFT calculations. The identification of marker bands for photoproducts, e.g. trans-[Pt(N3)(py)2(5'-GMP)] and trans-[Pt(py)2(5'-GMP)2], will aid elucidation of the chemical and biological mechanism of anticancer action of 1. In general, these studies demonstrate the potential of vibrational spectroscopic techniques as promising tools for studying such metal complexes

Comprehensive vibrational spectroscopic investigation of trans,trans,trans-[Pt(N3)2(OH)2(py)2], a Pt(IV) diazido anticancer prodrug candidate

We report a detailed study of a promising photoactivatable metal-based anticancer prodrug candidate, trans,trans,trans-[Pt(N3)2(OH)2(py)2] (C1; py = pyridine), using vibrational spectroscopic techniques. Attenuated total reflection Fourier transform infrared (ATR-FTIR), Raman, and synchrotron radiation far-IR (SR-FIR) spectroscopies were applied to obtain highly resolved ligand and Pt-ligand vibrations for C1 and its precursors (trans-[Pt(N3)2(py)2] (C2) and trans-[PtCl2(py)2] (C3)). Distinct IR- and Raman-active vibrational modes were assigned with the aid of density functional theory calculations, and trends in the frequency shifts as a function of changing Pt coordination environment were determined and detailed for the first time. The data provide the ligand and Pt-ligand (azide, hydroxide, pyridine) vibrational signatures for C1 in the mid- and far-IR region, which will provide a basis for the better understanding of the interaction of C1 with biomolecules

New materials for cancer imaging and therapy

The increasing burden of cancer on society drives the development of more effective chemotherapeutic agents. The work in this thesis is therefore centred on the examination of a new series of metal-based anticancer prodrug candidates. These metal-based compounds do not exhibit toxicity in the dark, but can be activated with light in cancerous areas, avoiding unwanted side-effects in healthy tissues. A range of state-of-the- art spectroscopic techniques, including vibrational spectroscopy and synchrotron radiation, are applied to study the chemical and biological properties of these compounds, revealing new insights into their mechanism of action

Supramolecular photoactivatable anticancer hydrogels

A photoactivatable dopamine-conjugated platinum(IV) anticancer complex (Pt-DA) has been incorporated into G-quadruplex G4K+ borate hydrogels by using borate ester linkages (Pt-G4K+B hydrogel). These were characterized by 11B NMR, attenuated total reflection Fourier transform infrared spectroscopy, circular dichroism, scanning electron microscopy and transmission electron microscopy. Microscopy investigations revealed the transformation of an extended fiber assembly into discrete flakes after incorporation of Pt-DA. Pt-DA showed photocytotoxicity against cisplatin-resistant A2780Cis human ovarian cancer cells (IC50 74 μM, blue light) with a photocytotoxic index 5. Most notably, Pt-DA and Pt-G4K+B hydrogels show selective phototoxicity for cancer cells versus normal fibroblast cells (MRC5)

Studies of Carbon Monoxide Release from Ruthenium(II) Bipyridine Carbonyl Complexes upon UV-Light Exposure

The UV-light-induced CO release characteristics of a series of ruthenium­(II) carbonyl complexes of the form <i>trans</i>-Cl­[RuLCl₂(CO)₂] (L = 4,4′-dimethyl-2,2′-bipyridine, 4′-methyl-2,2′-bipyridine-4-carboxylic acid, or 2,2′-bipyridine-4,4′-dicarboxylic acid) have been elucidated using a combination of UV–vis absorbance and Fourier transform infrared spectroscopies, multivariate curve resolution alternating least-squares analysis, and density functional theory calculations. In acetonitrile, photolysis appears to proceed via a serial three-step mechanism involving the sequential formation of [RuL­(CO)­(CH₃CN)­Cl₂], [RuL­(CH₃CN)₂Cl₂], and [RuL­(CH₃CN)₃Cl]⁺. Release of the first CO molecule occurs quickly (<i>k</i>₁ ≫ 3 min^–1), while release of the second CO molecule proceeds at a much more modest rate (<i>k</i>₂ = 0.099–0.17 min^–1) and is slowed by the presence of electron-withdrawing carboxyl substituents on the bipyridine ligand. In aqueous media (1% dimethyl sulfoxide in H₂O), the two photodecarbonylation steps proceed much more slowly (<i>k</i>₁ = 0.46–1.3 min^–1 and <i>k</i>₂ = 0.026–0.035 min^–1, respectively) and the influence of the carboxyl groups is less pronounced. These results have implications for the design of new light-responsive CO-releasing molecules (“photoCORMs”) intended for future medical use

Data for Comprehensive vibrational spectroscopic investigation of trans,trans,trans-[Pt(N3)2(OH)2(py)2], a Pt(IV) diazido anticancer prodrug candidate

We report a detailed study of a promising photoactivatable metal-based anticancer prodrug candidate, trans,trans,trans-[Pt(N3)2(OH)2(py)2] (C1; py = pyridine), using vibrational spectroscopic techniques. Attenuated total reflection Fourier transform infrared (ATR-FTIR), Raman, and synchrotron radiation far-IR (SR-FIR) spectroscopies were applied to obtain highly resolved ligand and Pt-ligand vibrations for C1 and its precursors (trans-[Pt(N3)2(py)2] (C2) and trans-[PtCl2(py)2] (C3)). Distinct IR- and Raman-active vibrational modes were assigned with the aid of density functional theory calculations, and trends in the frequency shifts as a function of changing Pt coordination environment were determined and detailed for the first time. The data provide the ligand and Pt-ligand (azide, hydroxide, pyridine) vibrational signatures for C1 in the mid- and far-IR region, which will provide a basis for the better understanding of the interaction of C1 with biomolecules

Comprehensive Vibrational Spectroscopic Investigation of <i>trans,trans,trans</i>-[Pt(N₃)₂(OH)₂(py)₂], a Pt(IV) Diazido Anticancer Prodrug Candidate

We report a detailed study of a promising photoactivatable metal-based anticancer prodrug candidate, <i>trans</i>,<i>trans</i>,<i>trans</i>-[Pt­(N₃)₂(OH)₂(py)₂] (<b>C1</b>; py = pyridine), using vibrational spectroscopic techniques. Attenuated total reflection Fourier transform infrared (ATR-FTIR), Raman, and synchrotron radiation far-IR (SR-FIR) spectroscopies were applied to obtain highly resolved ligand and Pt-ligand vibrations for <b>C1</b> and its precursors (<i>trans</i>-[Pt­(N₃)₂(py)₂] (<b>C2</b>) and <i>trans</i>-[PtCl₂(py)₂] (<b>C3</b>)). Distinct IR- and Raman-active vibrational modes were assigned with the aid of density functional theory calculations, and trends in the frequency shifts as a function of changing Pt coordination environment were determined and detailed for the first time. The data provide the ligand and Pt-ligand (azide, hydroxide, pyridine) vibrational signatures for <b>C1</b> in the mid- and far-IR region, which will provide a basis for the better understanding of the interaction of <b>C1</b> with biomolecules