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).

In-Cell Activation of Organo-Osmium(II) Anticancer Complexes

The family of iodido OsII arene phenylazopyridine complexes [Os(η6 -p-cym)(5-R1 -pyridylazo-4-R2 -phenyl))I]+ (where p-cym=para-cymene) exhibit potent sub-micromolar antiproliferative activity towards human cancer cells and are active in vivo. Their chemical behavior is distinct from that of cisplatin: they do not readily hydrolyze, nor bind to DNA bases. We report here a mechanism by which they are activated in cancer cells, involving release of the I- ligand in the presence of glutathione (GSH). The X-ray crystal structures of two active complexes are reported, 1-I (R1 =OEt, R2 =H) and 2-I (R1 =H, R2 =NMe2 ). They were labelled with the radionuclide 131 I (β- /γ emitter, t1/2 8.02 d), and their activity in MCF-7 human breast cancer cells was studied. 1-[131 I] and 2-[131 I] exhibit good stability in both phosphate-buffered saline and blood serum. In contrast, once taken up by MCF-7 cells, the iodide ligand is rapidly pumped out. Intriguingly, GSH catalyzes their hydrolysis. The resulting hydroxido complexes can form thiolato and sulfenato adducts with GSH, and react with H2 O2 generating hydroxyl radicals. These findings shed new light on the mechanism of action of these organo-osmium complexes.

Combatting AMR: photoactivatable ruthenium(ii)-isoniazid complex exhibits rapid selective antimycobacterial activity

The novel photoactive ruthenium(ii) complex cis-[Ru(bpy)2(INH)2][PF6]2 (1·2PF6, INH = isoniazid) was designed to incorporate the anti-tuberculosis drug, isoniazid, that could be released from the Ru(ii) cage by photoactivation with visible light. In aqueous solution, 1 rapidly released two equivalents of isoniazid and formed the photoproduct cis-[Ru(bpy)2(H2O)2]2+ upon irradiation with 465 nm blue light. We screened for activity against bacteria containing the three major classes of cell envelope: Gram-positive Bacillus subtilis, Gram-negative Escherichia coli, and Mycobacterium smegmatis in vitro using blue and multi-colored LED multi-well arrays. Complex 1 is inactive in the dark, but when photoactivated is 5.5× more potent towards M. smegmatis compared to the clinical drug isoniazid alone. Complementary pump-probe spectroscopy measurements along with density functional theory calculations reveal that the mono-aqua product is formed in <500 ps, likely facilitated by a 3MC state. Importantly, complex 1 is highly selective in killing mycobacteria versus normal human cells, towards which it is relatively non-toxic. This work suggests that photoactivatable prodrugs such as 1 are potentially powerful new agents in combatting the global problem of antibiotic resistance.

Os2 -Os4 Switch Controls DNA Knotting and Anticancer Activity

Dinuclear trihydroxido‐bridged osmium–arene complexes are inert and biologically inactive, but we show here that linking dihydroxido‐bridged Os^II–arene fragments by a bridging di‐imine to form a metallacycle framework results in strong antiproliferative activity towards cancer cells and distinctive knotting of DNA. The shortened spacer length reduces biological activity and stability in solution towards decomposition to biologically inactive dimers. Significant differences in behavior toward plasmid DNA condensation are correlated with biological activity.

Upconverting Nanoparticles Prompt Remote Near-Infrared Photoactivation of Ru(II)-Arene Complexes

The synthesis and full characterisation (including X-ray diffraction studies and DFT calculations) of two new piano-stool Ru(II) -arene complexes, namely [(η(6) -p-cym)Ru(bpy)(m-CCH-Py)][(PF)6]2 (1) and [(η(6) -p-cym)Ru(bpm)(m-CCH-Py)][(PF)6]2 (2; p-cym=p-cymene, bpy=2,2'-bipyridine, bpm=2,2'-bipyrimidine, and m-CCH-Py=3-ethynylpyridine), is described and discussed. The reaction of the m-CCH-Py ligand of 1 and 2 with diethyl-3-azidopropyl phosphonate by Cu-catalysed click chemistry affords [(η(6) -p-cym)Ru(bpy)(P-Trz-Py)][(PF)6]2 (3) and [(η(6) -p-cym)Ru(bpm)(P-Trz-Py)][(PF)6]2 (4; P-Trz-Py=[3-(1-pyridin-3-yl-[1,2,3]triazol-4-yl)-propyl]phosphonic acid diethyl ester). Upon light excitation at λ=395 nm, complexes 1-4 photodissociate the monodentate pyridyl ligand and form the aqua adduct ions [(η(6) -p-cym)Ru(bpy)(H2O)](2+) and [(η(6) -p-cym)Ru(bpm)(H2O)](2+). Thulium -doped upconverting nanoparticles (UCNPs) are functionalised with 4, thus exploiting their surface affinity for the phosphonate group in the complex. The so-obtained nanosystem UCNP@4 undergoes near-infrared (NIR) photoactivation at λ=980 nm, thus producing the corresponding reactive aqua species that binds the DNA-model base guanosine 5'-monophosphate.

Spin-labelled photo-cytotoxic diazido platinum(iv) anticancer complex

We report the synthesis and characterisation of the nitroxide spin-labelled photoactivatable Pt(iv) prodrugtrans,trans,trans-[Pt(N₃)₂(OH)(OCOCH₂CH₂CONH-TEMPO)(Py)₂] (Pt-TEMPO).

Nanoparticles of chitosan conjugated to organo-ruthenium complexes

The synthesis of nanoparticles of conjugates of caffeic acid-modified chitosan with ruthenium arene complexes is described.

Half-sandwich rhodium(III) transfer hydrogenation catalysts: Reduction of NAD(+) and pyruvate, and antiproliferative activity

Organometallic complexes have the potential to behave as catalytic drugs. We investigate here Rh(III) complexes of general formula [(Cp(x))Rh(N,N')(Cl)], where N,N' is ethylenediamine (en), 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen) or N-(2-aminoethyl)-4-(trifluoromethyl)benzenesulfonamide (TfEn), and Cp(x) is pentamethylcyclopentadienyl (Cp*), 1-phenyl-2,3,4,5-tetramethylcyclopentadienyl (Cp(xPh)) or 1-biphenyl-2,3,4,5-tetramethyl cyclopentadienyl (Cp(xPhPh)). These complexes can reduce NAD(+) to NADH using formate as a hydride source under biologically-relevant conditions. The catalytic activity decreased in the order of N,N-chelated ligand bpy > phen > en with Cp* as the η(5)-donor. The en complexes (1-3) became more active with extension to the Cp(X) ring, whereas the activity of the phen (7-9) and bpy (4-6) compounds decreased. [Cp*Rh(bpy)Cl](+) (4) showed the highest catalytic activity, with a TOF of 37.4±2h(-1). Fast hydrolysis of the chlorido complexes 1-10 was observed by (1)H NMR (<10min at 310K). The pKa* values for the aqua adducts were determined to be ca. 8-10. Complexes 1-9 also catalysed the reduction of pyruvate to lactate using formate as the hydride donor. The efficiency of the transfer hydrogenation reactions was highly dependent on the nature of the chelating ligand and the Cp(x) ring. Competition reactions between NAD(+) and pyruvate for reduction by formate catalysed by 4 showed a preference for reduction of NAD(+). The antiproliferative activity of complex 3 towards A2780 human ovarian cancer cells increased by up to 50% when administered in combination with non-toxic doses of formate, suggesting that transfer hydrogenation can induce reductive stress in cancer cells.

Contrasting Anticancer Activity of Half-Sandwich Iridium(III) Complexes Bearing Functionally Diverse 2-Phenylpyridine Ligands

We report the synthesis, characterization, and antiproliferative activity of 15 iridium(III) half-sandwich complexes of the type [(η5-Cp*)Ir(2-(R'-phenyl)-R-pyridine)Cl] bearing either an electron-donating (-OH, -CH2OH, -CH3) or electron-withdrawing (-F, -CHO, -NO2) group at various positions on the 2-phenylpyridine (2-PhPy) chelating ligand giving rise to six sets of structural isomers. The X-ray crystal structures of [(η5-Cp*)Ir(2-(2'-fluorophenyl)pyridine)Cl] (1) and [(η5-Cp*)Ir(2-(4'-fluorophenyl)pyridine)Cl] (2) exhibit the expected "piano-stool" configuration. DFT calculations showed that substituents caused only localized effects on the electrostatic potential surface of the chelating 2-PhPy ligand of the complexes. Hydrolysis of all complexes is rapid, but readily reversed by addition of NaCl. The complexes show preferential binding to 9-ethylguanine over 9-methyladenine and are active catalysts for the oxidation of NADH to NAD+. Antiproliferative activity experiments in A2780 ovarian, MCF-7 breast, A549 lung, and HCT116 colon cancer cell lines showed IC50 values ranging from 1 to 89 μM, with the most potent complex, [(η5-Cp*)Ir(2-(2'-methylphenyl)pyridine)Cl] (13) (A2780 IC50 = 1.18 μM), being 10× more active than the parent, [(η5-Cp*)Ir(2-phenylpyridine)Cl], and 2× more active than [(η5-CpxPh)Ir(2-phenylpyridine)Cl]. Intriguingly, contrasting biological activities are observed between structural isomers despite exhibiting similar chemical reactivity. For pairs of structural isomers both the nature and position of the functional group can affect the hydrophobicity of the complex. An increase in hydrophobicity resulted in enhanced cellular-iridium accumulation in A2780 ovarian cells, which generally gave rise to an increase in potency. The structural isomers [(η5-Cp*)Ir(2-(4'-fluorophenyl)pyridine)Cl] (2) and [(η5-Cp*)Ir(2-phenyl-5-fluoropyridine)Cl] (4) preferentially localized in the cytosol > membrane and particulate > nucleus > cytoskeleton. This work highlights the strong dependence of biological behavior on the nature and position of the substituent on the chelating ligand and shows how this class of organometallic anticancer complexes can be fine-tuned to increase their potency without using extended cyclopentadienyl systems.

Photorelease of Pyridyl Esters in Organometallic Ru(II) Arene Complexes

New Ru(II) arene complexes of formula [(η6-p-cym)Ru(N-N)(X)]2+ (where p-cym = para-cymene, N-N = 2,2'-bipyrimidine (bpm) or 2,2'-bipyridine (bpy) and X = m/p-COOMe-Py, 1-4) were synthesised and characterized, including the molecular structure of complexes [(η6-p-cym)Ru(bpy)(m-COOMe-Py)]2+ (3) and [(η6-p-cym)Ru(bpy) (p-COOMe-Py)]2+ (4) by single-crystal X-ray diffraction. Complexes 1-4 are stable in the dark in aqueous solution over 48 h and photolysis studies indicate that they can photodissociate the monodentate m/p-COOMe-Py ligands selectively with yields lower than 1%. DFT and TD-DFT calculations (B3LYP/LanL2DZ/6-31G**) performed on singlet and triplet states pinpoint a low-energy triplet state as the reactive state responsible for the selective dissociation of the monodentate pyridyl ligands.

Potent Half-Sandwich Iridium(III) Anticancer Complexes Containing C∧N-Chelated and Pyridine Ligands

We report the synthesis and characterization of eight half-sandwich cyclopentadienyl IrIII pyridine complexes of the type [(η5-Cpxph)Ir(phpy)Z]PF6, in which Cpxph = C5Me4C6H5 (tetramethyl(phenyl)cyclopentadienyl), phpy = 2-phenylpyridine as C∧N-chelating ligand, and Z = pyridine (py) or a pyridine derivative. Three X-ray crystal structures have been determined. The monodentate py ligands blocked hydrolysis; however, antiproliferative studies showed that all the Ir compounds are highly active toward A2780, A549, and MCF-7 human cancer cells. In general the introduction of an electron-donating group (e.g., Me, NMe2) at specific positions on the pyridine ring resulted in increased antiproliferative activity, whereas electron-withdrawing groups (e.g., COMe, COOMe, CONEt2) decreased anticancer activity. Complex 5 displayed the highest anticancer activity, exhibiting submicromolar potency toward a range of cancer cell lines in the National Cancer Institute NCI-60 screen, ca. 5 times more potent than the clinical platinum(II) drug cisplatin. DNA binding appears not to be the major mechanism of action. Although complexes [(η5-Cpxph)Ir(phpy)(py)]+ (1) and [(η5-Cpxph)Ir(phpy)(4-NMe2-py)]+ (5) did not cause cell apoptosis or cell cycle arrest after 24 h drug exposure in A2780 human ovarian cancer cells at IC50 concentrations, they increased the level of reactive oxygen species (ROS) dramatically and led to a loss of mitochondrial membrane potential (ΔΨm), which appears to contribute to the anticancer activity. This class of organometallic Ir complexes has unusual features worthy of further exploration in the design of novel anticancer drugs.

Insights into the binding sites of organometallic ruthenium anticancer compounds on peptides using ultra-high resolution mass spectrometry

The binding sites of two ruthenium(II) organometallic complexes of the form [(η(6)-arene)Ru(N,N)Cl](+), where arene/N,N = biphenyl (bip)/bipyridine (bipy) for complex AH076, and biphenyl (bip)/o-phenylenediamine (o-pda) for complex AH078, on the peptides angiotensin and bombesin have been investigated using Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. Fragmentation was performed using collisionally activated dissociation (CAD), with, in some cases, additional data being provided by electron capture dissociation (ECD). The primary binding sites were identified as methionine and histidine, with further coordination to phenylalanine, potentially through a π-stacking interaction, which has been observed here for the first time. This initial peptide study was expanded to investigate protein binding through reaction with insulin, on which the binding sites proposed are histidine, glutamic acid, and tyrosine. Further reaction of the ruthenium complexes with the oxidized B chain of insulin, in which two cysteine residues are oxidized to cysteine sulfonic acid (Cys-SO3H), and glutathione, which had been oxidized with hydrogen peroxide to convert the cysteine to cysteine sulfonic acid, provided further support for histidine and glutamic acid binding, respectively.

The potent oxidant anticancer activity of organoiridium catalysts

Platinum complexes are the most widely used anticancer drugs; however, new generations of agents are needed. The organoiridium(III) complex [(η⁵-Cp^xbiph)Ir(phpy)(Cl)] (1-Cl), which contains π-bonded biphenyltetramethylcyclopentadienyl (Cp^xbiph) and C∧N-chelated phenylpyridine (phpy) ligands, undergoes rapid hydrolysis of the chlorido ligand. In contrast, the pyridine complex [(η⁵-Cp^xbiph)Ir(phpy)(py)]⁺ (1-py) aquates slowly, and is more potent (in nanomolar amounts) than both 1-Cl and cisplatin towards a wide range of cancer cells. The pyridine ligand protects 1-py from rapid reaction with intracellular glutathione. The high potency of 1-py correlates with its ability to increase substantially the level of reactive oxygen species (ROS) in cancer cells. The unprecedented ability of these iridium complexes to generate H₂O₂ by catalytic hydride transfer from the coenzyme NADH to oxygen is demonstrated. Such organoiridium complexes are promising as a new generation of anticancer drugs for effective oxidant therapy.

De novo generation of singlet oxygen and ammine ligands by photoactivation of a platinum anticancer complex

Worth the excitement: Highly reactive oxygen and nitrogen species are generated by photoactivation of the anticancer platinum(IV) complex trans,trans,trans-[Pt(N3 )2 (OH)2 (MA)(Py)] (MA=methylamine, Py=pyridine). Singlet oxygen is formed from the hydroxido ligands and not from dissolved oxygen, and ammine ligands are products from the conversion of azido ligands to nitrenes. Both processes can induce oxidation of guanine.