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/H2 O)] intermediate and trans-[Pt(py)2 (OH/H2 O)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 antisymmetric azido vibration, suggesting a possible second intermediate. Experimental proof of subsequent dissociation of azido ligands from platinum is presented, in which at least one hydroxyl radical is formed in the reduction of PtIV to PtII . Additionally, the photoinduced reaction of 1 with the nucleotide 5'-guanosine monophosphate (5'-GMP) was comprehensively studied, and the identity of key photoproducts was assigned with the help of ATR-FTIR spectroscopy, mass spectrometry, and density functional theory calculations. The identification of marker bands for some of these 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.

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 <2, whereas Pt-G4K+B hydrogels exhibited more potent photocytotoxicity (IC50 3 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 trans-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 (k1 ≫ 3 min-1), while release of the second CO molecule proceeds at a much more modest rate (k2 = 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 (k1 = 0.46-1.3 min-1 and k2 = 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.

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.

Probing the action of a novel anti-leukaemic drug therapy at the single cell level using modern vibrational spectroscopy techniques.

Acute myeloid leukaemia (AML) is a life threatening cancer for which there is an urgent clinical need for novel therapeutic approaches. A redeployed drug combination of bezafibrate and medroxyprogesterone acetate (BaP) has shown anti-leukaemic activity in vitro and in vivo. Elucidation of the BaP mechanism of action is required in order to understand how to maximise the clinical benefit. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, Synchrotron radiation FTIR (S-FTIR) and Raman microspectroscopy are powerful complementary techniques which were employed to probe the biochemical composition of two AML cell lines in the presence and absence of BaP. Analysis was performed on single living cells along with dehydrated and fixed cells to provide a large and detailed data set. A consideration of the main spectral differences in conjunction with multivariate statistical analysis reveals a significant change to the cellular lipid composition with drug treatment; furthermore, this response is not caused by cell apoptosis. No change to the DNA of either cell line was observed suggesting this combination therapy primarily targets lipid biosynthesis or effects bioactive lipids that activate specific signalling pathways.