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The purine derivative fludarabine is part of frontline therapy for chronic lymphocytic leukaemia (CLL). It has shown positive effects on solid tumours such as melanoma, breast, and colon carcinoma in clinical phase I studies. As the treatment of CLL cells with combinations of fludarabine and metal complexes of antitumoural natural products, e.g., illudin M ferrocene, has led to synergistically enhanced apoptosis, in this research study different complexes of fludarabine itself. Four complexes bearing a trans-[Br(PPh3)2]Pt/Pd fragment attached to atom C-8 via formal η1-sigma or η2-carbene bonds were synthesised in two or three steps without protecting polar groups on the arabinose or adenine. The platinum complexes were more cytotoxic than their palladium analogues, with low single-digit micromolar IC50 values against cells of various solid tumour entities, including cisplatin-resistant ones and certain B-cell lymphoma and CLL, presumably due to the ten-fold higher cellular uptake of the platinum complexes. However, the palladium complexes interacted more readily with isolated Calf thymus DNA. Interestingly, the platinum complexes showed vastly greater selectivity for cancer over non-malignant cells when compared with fludarabine.

Here, we investigated the mechanism of antiproliferative action in cancer cells of new compounds structurally derived from oxaliplatin, namely a pair of enantiomers [Pt(OXA)(1R,2R-DACHEX)] (1) and [Pt(OXA)(1S,2S-DACHEX)] (2) (OXA = oxalate, DACHEX = trans-1,2-diamino-4-cyclohexene). While oxaliplatin is used almost exclusively to treat colorectal and other gastrointestinal cancers, new complex 1 shows instead high potency in malignant pancreatic adenocarcinoma PSN1 cells including superior selectivity for pancreatic cancer over noncancerous cells. Utilizing a multi-platform biochemical approach to study the unique features of the mechanism of action of this new platinum-based drug, we show that 1 has a much greater ability to penetrate pancreatic tumors than its S,S enantiomer 2 and oxaliplatin, and to be transported into cells as bound to plasma proteins. Additionally, the mechanism of action of 1 and, to a lesser extent, oxaliplatin in pancreatic cancer cells involves alterations of the lipogenesis pathway, namely inhibition of de novo lipid synthesis, acting by a new mechanism not yet considered for anticancer action of clinically used antitumor platinum drugs. These data highlight the functional diversity of platinum anticancer compounds and the potential benefits of finding new anticancer drugs applying a mechanism-based rationale.

Photoactivatable agents offer the prospect of highly selective cancer therapy with low side effects and novel mechanisms of action that can combat current drug resistance. 1,8‐Naphthalimides with their extended π system can behave as light‐harvesting groups, fluorescent probes and DNA intercalators. We conjugated N‐(carboxymethyl)‐1,8‐naphthalimide (gly‐R‐Nap) with an R substituent on the naphthyl group to photoactive diazido PtIV complexes to form t,t,t‐[Pt(py)2(N3)2(OH)(gly‐R‐Nap)], R=H (1), 3‐NO2 (2) or 4‐NMe2 (3). They show enhanced photo‐oxidation, cellular accumulation and promising photo‐cytotoxicity in human A2780 ovarian, A549 lung and PC3 prostate cancer cells with visible light activation, and low dark cytotoxicity. Complexes 1 and 2 exhibit pre‐intercalation into DNA, resulting in enhanced photo‐induced DNA crosslinking. Complex 3 has a red‐shifted absorption band at 450 nm, allowing photoactivation and photo‐cytotoxicity with green light., Green to go: Photoactive all‐trans diazido PtIV complexes with an axial 1,8‐naphthalimide ligand that can pre‐intercalate into DNA have been synthesised. They can be photoactivated with visible light to generate PtII DNA interstrand crosslinks and cytotoxic ROS, and are thus promising photo‐chemotherapeutic agents. Notably, a 4‐NMe2 substituent red‐shifted absorption of the naphthalimide ring, giving rise to its green‐light photo‐cytotoxicity.

Several anticancer chemotherapies, while eliminating the bulk of tumor cells, often fail, as they do not obliterate a small fraction of malignant cancer stem cells (CSCs). Thus, developing chemotherapeutics capable of targeting and abrogating CSCs, including inducing immunogenic cell death in CSCs, is essential for developing new anticancer drugs. Herein, we report octahedral Ir(III) complexes based on a benzimidazole backbone containing NH groups. The complexes exhibit low toxicity in the dark against human skin melanoma cells and high phototoxicity with blue light irradiation under both normoxic and hypoxic conditions. Additionally, complex 4 induces secretion of damage-associated molecular patterns characteristic of immunogenic cell death (ICD) in melanoma cells when the cells are irradiated with blue light. The results also suggest that the mechanism of the ICD induced by this complex may involve oxidative damage of intracellular targets by photoinduced ROS generation. This property of 4 may allow targeting the photochemotherapy based on 4 selectively to the tumor.

Complexes [Ru(η6-pcym)(bpydca)Cl]PF6 (Rudca) and [Ir(η5-Cp*)(bpydca)Cl]PF6 (Irdca) were developed as model compounds for the investigation of multi-targeted ester-functionalized half-sandwich ruthenium(II) and iridium(III) complexes; pcym = 1-methyl-4-(propan-2-yl)benzene (p-cymene), bpydca = 2,2′-bipyridine-4,4′-diyldimethanediyl bis(dichloroacetate), Cp* = pentamethylcyclopentadienyl. Aiming to understand the in-solution behaviour of these first-in-class complexes containing the pyruvate dehydrogenase kinase inhibitor dichloroacetate (dca) as the terminal bioactive substituent, several experiments were performed under aqueous conditions for Rudca and Irdca, as well as for compounds [Ru(η6-pcym)(bpyOH)Cl]PF6 (RuOH) and [Ir(η5-Cp*)(bpyOH)Cl]PF6 (IrOH), and acetyl analogues [Ru(η6-pcym)(bpyac)Cl]PF6 (Ruac) and [Ir(η5-Cp*)(bpyac)Cl]PF6 (Irac) bearing a different (biologically inactive) terminal substituent; bpyOH = 2,2′-bipyridine-4,4′-diyldimethanol, bpyac = 2,2′-bipyridine-4,4′-diyldimethanediyl diacetate. The experiments were also conducted in the presence of porcine liver esterase (PLE). All the six complexes were characterized by relevant techniques (e.g., NMR and mass spectrometry), including a single-crystal X-ray analysis of complexes Rudca, Ruac, RuOH and IrOH. Although designed as model compounds, Rudca, Irdca, RuOH and IrOH were also screened for their antiproliferative activity in four human cancer cell lines (HCT116 colon carcinoma, MDA-MB-231 and MCF-7 breast adenocarcinomas, DU145 prostate carcinoma), where the tested complexes did not show any effect (IC50 > 100 μM).

HER2-positive breast cancer is an aggressive subtype that typically responds poorly to standard chemotherapy. To design an anticancer drug selective for HER2-expressing breast cancer, a PtIV prodrug with axial oleate and cinnamate ligands was synthesized. We demonstrate its superior antiproliferative activity in monolayer and 3D spheroid models; the antiproliferative efficiency increases gradually with increasing expression of HER2. The results also suggest that the released PtII compound inhibits the proliferation of cancer cells by a DNA-damage-mediated mechanism. Simultaneously, the released oleic and cinnamic acid can effectively inhibit HER2 expression. To our knowledge, this is the first platinum-based complex inhibiting HER2 expression that does not contain protein or peptide. Moreover, this PtIV prodrug is capable of overcoming the resistance of cancer stem cells (CSCs), inducing death in both CSCs and differentiated cancer cells. Thus, the results substantiate our design strategy and demonstrate the potential of this approach for the development of new, therapeutically relevant compounds.

Monosaccharides are added to the hydrophilic face of a self‐assembled asymmetric FeII metallohelix, using CuAAC chemistry. The sixteen resulting architectures are water‐stable and optically pure, and exhibit improved antiproliferative selectivity against colon cancer cells (HCT116 p53+/+) with respect to the non‐cancerous ARPE‐19 cell line. While the most selective compound is a glucose‐appended enantiomer, its cellular entry is not mainly glucose transporter‐mediated. Glucose conjugation nevertheless increases nuclear delivery ca 2.5‐fold, and a non‐destructive interaction with DNA is indicated. Addition of the glucose units affects the binding orientation of the metallohelix to naked DNA, but does not substantially alter the overall affinity. In a mouse model, the glucose conjugated compound was far better tolerated, and tumour growth delays for the parent compound (2.6 d) were improved to 4.3 d; performance as good as cisplatin but with the advantage of no weight loss in the subjects., Asymmetric triplex metallohelices can be conjugated with sugars using post‐assembly CuAAC chemistry, to give optically pure architectures with anti‐cancer activity and marked selectivity with respect to non‐cancerous cell lines. Glucose‐appended structures exhibit improved nuclear uptake in vitro and supress tumour growth in vivo.

The adverse side effects and acquired resistance associated with the clinical application of traditional platinum-based anticancer drugs have forced investigation of alternative transition metal-based compounds and their cytostatic properties. Over the last years, the anticancer potential of cobalt complexes has been extensively studied, and in-depth analyses of their mode of action have been conducted. In this work, we present antiproliferative activity against human cancer cells of the dinuclear Co(III) complexes bearing the quinizarin ligand and tris(2-aminoethyl)amine (tren, compound 1) or tris(2-pyridylmethyl)amine (tpa, compound 2) co-ligands. To contribute the understanding mechanisms of biological action of these compounds, their association with DNA in the cells, DNA binding in cell-free media, and DNA cleavage capability were investigated in detail. The results demonstrate that both complexes interact with DNA in tumor cells. However, their mechanism of antiproliferative action is different, and this difference is mirrored by distinct antiproliferative activity. The antiproliferative effect of 1 is connected with its ability to intercalate into DNA and subsequently to inhibit activities of DNA processing enzymes. In contrast, the total antiproliferative efficiency of 2, thanks to its redox properties, appears to be connected with its ability to form radicals and, consequently, with the ability of 2 to cleave DNA. Hence, the findings presented in this study may significantly contribute to understanding the antitumor potential of cobalt complexes. Dinuclear Co(III) complexes containing the bioactive quinizarin ligand exhibit antiproliferative activity based on distinct mechanism.

A series of four new 3,6,9-trisubstituted acridine derivatives (two with fluorine substituents on phenyl ring) were synthesized and their interaction with calf thymus DNA and HSA was investigated using a combination of biochemical, biophysical and biological techniques. Analysis using fluorescent spectra provided valuable information about the formation of the acridine–DNA complex, while several other experiments suggest that acridine may bind to DNA through intercalation. These observations are further supported by LD spectral analysis, viscosity measurements and DNA melting studies. The interaction between HSA and four compounds were studied by fluorescence quenching spectra. In addition, the method was used for the calculation of characteristic binding parameters. These result and result obtained by synchronous fluorescence spectra of acridines with HSA determined that compounds create complexes with HSA and induce conformational changes. KB values were found to be of 1.51–7.34 × 106 M−1. The studied 8c compound were the most sensitive against S. epidermidis ATCC 12228.

This work studied the mechanism of action of a Pt(IV) complex 2 bearing two axial lonidamine ligands, which are selective inhibitors of aerobic glycolysis. The presence of two lonidamine ligands in 2 compared to the parent Pt(II) complex increased its antiproliferative activity, cellular accumulation, and changed its cell cycle profile and mechanism of cell death. In 3D cell culture, 2 showed exceptional antiproliferative activity with IC50 values as low as 1.6 μM in MCF7 cells. The study on the influence of the lonidamine ligands in the Pt complex on glycolysis showed only low potency of ligands to affect metabolic processes in cancer cells, making the investigated complex, not a dual- or multi-action prodrug. However, the Pt(IV) prodrug effectively delivers the cytotoxic Pt(II) complex into cancer cells.

While ruthenium arene complexes have been widely investigated for their medicinal potential, studies on homologous compounds containing a tridentate tris(1-pyrazolyl)methane ligand are almost absent in the literature. Ruthenium(II) complex 1 was obtained by a modified reported procedure; then, the reactions with a series of organic molecules (L) in boiling alcohol afforded novel complexes 2-9 in 77-99% yields. Products 2-9 were fully structurally characterized. They are appreciably soluble in water, where they undergo partial chloride/water exchange. The antiproliferative activity was determined using a panel of human cancer cell lines and a noncancerous one, evidencing promising potency of 1, 7, and 8 and significant selectivity toward cancer cells. The tested compounds effectively accumulate in cancer cells, and mitochondria represent a significant target of biological action. Most notably, data provide convincing evidence that the mechanism of biological action is mediated by the inhibiting of mitochondrial calcium intake.

In this work, gallium(III) complex with cloxyquin (5-chloro-8-quinolinol, HClQ) ligands is shown to effectively inhibit proliferation of rhabdomyosarcoma cells, the frequent, aggressive, and poorly treatable cancer of children. It offers striking selectivity to cancer cells compared to noncancerous human fibroblasts. The data reveal that the complex induces ferroptosis in rhabdomyosarcoma cells, likely due to interfering with iron metabolism. Importantly, it can kill both bulk and stem rhabdomyosarcoma cells. To the best of our knowledge, this is the first compound based on metal other than Fe capable of inducing ferroptosis in cancer cells.

2-Amino-5,10-dihydro-5,10-dioxo-4(pyridine-3-yl)-4H-benzo[g]chromene-3-carbonitrile 5, a cytotoxic lawsone derivative, was reacted with [Ru(p-cymene)Cl2]2 to afford a new Ru(II) 'piano-stool' complex 6 which differed from its ligand 5 by a greater selectivity for highly invasive 518A2 melanoma cells over human dermal fibroblasts in MTT cytotoxicity assays, and by inducing senescence rather than apoptosis in the former. DNA is a likely cellular target of complex 6 as it bound, presumably non-covalently, to linear and circular double-stranded DNA in vitro and as ruthenium was found in the lysate of nuclei of treated 518A2 melanoma cells. It also caused a fivefold increase of reactive oxygen species in these cells, originating from a more persistent redox cycling as visualised by cyclic voltammetry.

Although cyclometalated IrIII complexes have emerged as promising photosensitizers for photodynamic therapy, some key drawbacks still hamper clinical translation, such as operability in the phototherapeutic window and reactive oxygen species (ROS) production efficiency and selectivity. In this work, a cyclometalated IrIII complex conjugated to a far-red-emitting coumarin, IrIII -COUPY, is reported with highly favourable properties for cancer phototherapy. IrIII -COUPY was efficiently taken up by HeLa cells and showed no dark cytotoxicity and impressive photocytotoxicity indexes after irradiation with green and blue light, even under hypoxia. Importantly, a clear correlation between cell death and intracellular generation of superoxide anion radicals after visible light irradiation was demonstrated. This strategy opens the door to novel fluorescent photodynamic therapy agents with promising applications in theragnosis.

The substitution inert platinum agent [Pt(1 S,2 S-diaminocyclohexane)(5,6-dimethyl-1,10-phenanthroline)]2+ (56MeSS, 5) is a potent cytotoxic metallodrug. In contrast to conventional cisplatin or oxaliplatin, the mechanism of action (MoA) of 5 is fundamentally different. However, details of the mechanism by which the 5,6-dimethyl-1,10-phenanthroline ligand contributes to the cytotoxicity of 5 and its derivatives have not been sufficiently clarified so far. Here, we show that 5 and its Pt(IV) derivatives exhibit an intriguing potency in the triple-negative breast cancer cells MDA-MB-231. Moreover, we show that the Pt(IV) derivatives of 5 act by multimodal MoA resulting in the global biological effects, that is, they damage nuclear DNA, reduce the mitochondrial membrane potential, induce the epigenetic processes, and last but not least, the data provide evidence that changes in the organization of cytoskeleton networks are functionally important for 5 and its derivatives, in contrast to clinically used platinum cytostatics, to kill cancer cells.

Dual- or multi-action PtIV prodrugs represent a new generation of platinum anticancer drugs. The important property of these PtIV prodrugs is that their antitumor action combines several different mechanisms owing to the presence of biologically active axial ligands. This work describes the synthesis and some biological properties of a "triple-action" prodrug that releases in cancer cells cisplatin and two different epigenetically acting moieties, octanoate and phenylbutyrate. It is demonstrated, with the aid of modern methods of molecular and cellular biology and pharmacology, that the presence of three different functionalities in a single molecule of the PtIV prodrug results in a selective and high potency in tumor cells including those resistant to cisplatin [the IC50 values in the screened malignant cell lines ranged from as low as 9 nm (HCT-116) to 74 nm (MDA-MB-231)]. It is also demonstrated that cellular activation of the PtIV prodrug results in covalent modification of DNA through the release of the platinum moiety accompanied by inhibition of the activity of histone deacetylases caused by phenylbutyrate and by global hypermethylation of DNA by octanoate. Thus, the PtIV prodrug introduced in this study acts as a true "multi-action" prodrug, which is over two orders of magnitude more active than clinically used cisplatin, in both 2D monolayer culture and 3D spheroid cancer cells.

The platinum drugs belong to prevailing chemotherapeutics used in the treatment of cancer. At present, however, the search for new anticancer metal-based drugs that operate by the mechanisms distinct from those of the conventional chemotherapeutics is very active. Furthermore, it has been demonstrated that cytotoxic chemotherapy and immunotherapy may exert a highly synergistic anticancer activity. Thus, the development of antitumor platinum and other metal-based drugs that exhibit cytostatic effects and concurrently elicit immunogenic cell death (ICD) has shown promise for cancer treatment. Notably, conventional platinum drug oxaliplatin ([Pt(1R,2R-DACH)(oxalate)], DACH = diaminocyclohexane) is a well-known agent that displays both cytostatic and immune responses. Moreover, it was also demonstrated that even minor derivatization of the unleaving cycloalkyl moiety in oxaliplatin might have a pronounced effect on its immunomodulatory activity. Here, we investigated how replacing the 1R,2R- diaminocyclohexane ring by 1,3-diaminocycloalkane (alkane = butane, pentane, or hexane) affects the ability to evoke secretion of damage-associated molecular patterns characteristic of ICD in model murine colorectal carcinoma cell line CT26. The results indicate that among the investigated [Pt(cis-1,3-diaminocycloalkane)Cl

A cyclometalated Ir

In this work, the mechanism underlying the anticancer activity of a photoactivatable Ir(III) compound of the type [Ir(C^N)

A cyclometalated IrIII complex conjugated to a far-red-emitting coumarin, IrIII -COUPY (3), was recently shown as a very promising photosensitizer suitable for photodynamic therapy of cancer. Therefore, the primary goal of this work was to deepen knowledge on the mechanism of its photoactivated antitumor action so that this information could be used to propose a new class of compounds as drug candidates for curing very hardly treatable human tumors, such as androgen resistant prostatic tumors of metastatic origin. Conventional anticancer chemotherapies exhibit several disadvantages, such as limited efficiency to target cancer stem cells (CSCs), which are considered the main reason for chemotherapy resistance, relapse, and metastasis. Herein, we show, using DU145 tumor cells, taken as the model of hormone-refractory and aggressive prostate cancer cells resistant to conventional antineoplastic drugs, that the photoactivated conjugate 3 very efficiently eliminates both prostate bulk (differentiated) and prostate hardly treatable CSCs simultaneously and with a similar efficiency. Notably, the very low toxicity of IrIII -COUPY conjugate in the prostate DU145 cells in the dark and its pronounced selectivity for tumor cells compared with noncancerous cells could result in low side effects and reduced damage of healthy cells during the photoactivated therapy by this agent. Moreover, the experiments performed with the 3D spheroids formed from DU145 CSCs showed that conjugate 3 can penetrate the inner layers of tumor spheres, which might markedly increase its therapeutic effect. Also interestingly, this conjugate induces apoptotic cell death in prostate cancer DU145 cells associated with calcium signaling flux in these cells and autophagy. To the best of our knowledge, this is the first study demonstrating that a photoactivatable metal-based compound is an efficient agent capable of killing even hardly treatable CSCs.

The platinum((IV)) prodrug trans,trans,trans-[Pt(N(3))(2)(OH)(2)(py)(2)] (1) is stable and non-toxic in the dark, but potently cytotoxic to cancer cells when irradiated by visible light, including cisplatin-resistant cells. On irradiation with visible light, it generates reactive Pt(II) species which can attack DNA, and produces reactive oxygen species (ROS) and reactive nitrogen species (RNS) which exert unusual effects on biochemical pathways. We now show that its novel mechanism of action includes induction of immunogenic cell death (ICD). Treatment of cancer cells with 1 followed by photoirradiation with visible light induces calreticulin (CRT) expression at the surface of dying cancer cells. This is accompanied by release of high mobility group protein-1B (HMGB1) and the secretion of ATP. Autophagy appears to play a key role in this chemotherapeutically-stimulated ICD. The observed uneven distribution of ecto-CRT promotes phagocytosis, confirmed by the observation of engulfment of photoirradiated CT26 colorectal cancer cells treated with 1 by J774.A1 macrophages. The photoactivatable prodrug 1 has a unique mechanism of action which distinguishes it from other platinum drugs due to its immunomodulating properties, which may enhance its anticancer efficacy.

The search for more effective platinum anticancer drugs has led to the design, synthesis, and preclinical testing of hundreds of new platinum complexes. This search resulted in the recognition and subsequent FDA approval of the third-generation Pt(II) anticancer drug, [Pt(1,2-diaminocyclohexane)(oxalate)], oxaliplatin, as an effective agent in treating colorectal and gastrointestinal cancers. Another promising example of the class of anticancer platinum(II) complexes incorporating the Pt(1,n-diaminocycloalkane) moiety is kiteplatin ([Pt(cis-1,4-DACH)Cl

The phototoxicity in cancer cells of three series of octahedral Ir(III) complexes of the general formula [Ir(C^N)2(N^N)][PF6], where the N^N ligand is dipyrido[3,2-a:2′,3′-c]phenazine (dppz) and the C^N ligands are deprotonated 2-phenyl-, 2-(naphthalen-2-yl)- or 2-(thiophen-2-yl)-benzimidazole derivatives (series 1, 2 and 3, respectively) with different substituents (H, methyl or 4-(trifluoromethyl)benzyl) on the imidazole units, has been studied. The 1-methyl benzimidazole compounds 2b and 3b were found to be the most photoactive in model human cervical cancer HeLa cells (IC50 about 20 nM under irradiation conditions, λexc = 420 nm), inducing a substantial formation of apoptotic bodies as shown by flow cytometry, whereas the 4-(trifluoromethyl)benzyl derivatives 1c–3c showed the highest phototoxic indexes of the three series. Notably, the antiproliferative activity of the photoactivated Ir(III) compounds was also significant under hypoxic conditions (2% O2). Fluorescence confocal microscopy investigation for 1c, 2c and 3c was undertaken, showing a significant subcellular localization of 3c in mitochondria, whereas 1c and 2c were located preferentially in the endoplasmic reticulum (ER). Further investigations on series 3 compounds using CellRox® (oxidative stress deep red reagent) have shown, after pretreatment with Tiron, that molecular superoxide radical (O2˙−) generation is mainly responsible for the oxidative stress induced by irradiation of the cells treated with the 2-(thiophen-2-yl)benzimidazole derivatives 3a–c. The photopotentiation of 3a and 3c also involves the formation of singlet oxygen (1O2), but this does not occur with 3b, due to pretreatment with sodium azide. The ROS generation was also studied by standard droethidium (DHE) and singlet oxygen sensor green (SOSG) staining assays under both normoxic and hypoxic conditions. The results showed that in tumor HeLa cells, the generation of superoxide radicals competed with singlet oxygen production in cells in normoxia, but became dominant under hypoxia.

Four gallium(III) complexes, [Ga(ClQ)3]⋅MeOH (1 – MeOH), [Ga(ClQ)3] (1), [Ga(BrQ)3] (2), [Ga(dIQ)3] (3) and [Ga(CQ)3] (4), were prepared (H-ClQ = 5-chloro-8-quinolinol, H-BrQ = 7-bromo-8-quinolinol, H-dIQ = 5,7-diiodo-8-quinolinol, H-CQ = 5-chloro-7-iodo-8-quinolinol) and characterised by elemental analysis, IR and NMR spectroscopy. Single crystal structure analysis of 1 – MeOH confirmed that the complex has a molecular structure with gallium(III) metal ion coordinated in mer-fashion by N- and O-donor atoms of three ClQ ligands. Stability of all complexes in DMSO was proved by 1H NMR spectroscopy. The in vitro antiproliferative activity of 1 was evaluated against the A2780, MBA-MB-231 and HCT116 cell lines. Complex 1 displays higher antiproliferative activity (IC50 values in the range 2.1–6 μ m ) compared to the ClQ ligand and cisplatin; and a significant selective antiproliferative potency (IC50 = 136 μ m , for normal MRC5pd30 cell line). Radical scavenging experiments revealed that complex 1 exhibits the highest antioxidant activity of the prepared complexes as well as the ligands.

Ruthenium complexes exhibit a broad variety of biological and biomedical activities including anticancer efficiency. The reason is that the octahedral bonding of both Ru(II) and Ru(III) complexes affords an extensive repertoire of three-dimensional architectures, giving the potential for a high degree of site selectivity for binding to their biological targets. The mechanism of biological and biomedical action of ruthenium compounds is connected with their interactions with biomacromolecules. A lot of mechanistic studies revealed disposition of many ruthenium complexes to operate via mechanisms of action involving interactions with DNA, but distinctly different from those of the approved platinum anticancer drugs. In this Review, we discuss major DNA binding modes hitherto identified for ruthenium complexes of biological or biomedical significance and provide some typical examples. The introduction provides the reader with a brief overview of the approaches in the search for the new, transition metal-based agents of biological or biomedical significance to provide the context in which more recent research of DNA binding of ruthenium complexes has been evolved. We then describe main categories of binding modes between DNA and ruthenium compounds, such as coordinative, intercalative, minor groove binding, sequence specificity of DNA binding, the ability of ruthenium compounds to condense and cleave DNA, binding to A- and Z-DNA, DNA quadruplexes and other unusual DNA structures. A number of complexes based on ruthenium(II) centers have been reported to have excellent photophysical and radiosensitizing properties so that DNA photocleavage and synergistic enhancement of DNA damage due to a combined action of ruthenium complexes and ionizing radiation is also discussed. Finally, inhibition of DNA processing enzymes is reviewed as well. We believe that such a synthesis of disparate DNA binding modes of ruthenium complexes will help to generate new ruthenium complexes of improved biological and biomedical significance.

The half-sandwich iridium(III) complexes [Ir(η5-Cpx)(phaza–)Cl] (1, 2), [Ir(η5-Cpx)(thaza–)Cl] (3, 4), and [Ir(η5-Cpx)(pyaza)Cl]PF6 (5, 6) containing deprotonated 1-phenyl-7-azaindole (phaza–) and 1-(thiophen-2-yl)-7-azaindole (thaza–) and electroneutral 1-(pyridin-2-yl)-7-azaindole (pyaza), were prepared; Cpx = pentamethylcyclopentadienyl (Cp*; for 1, 3, and 5) or 1,2,3,4-tetramethyl-5-phenylcyclopentadienyl (Cpph; for 2, 4, and 6). The complexes were thoroughly characterized, including a single-crystal X-ray analysis of complexes 1, 5, and 6. All of the complexes were screened for their in vitro cytotoxicity at the A2780 human ovarian carcinoma cell line and its A2780R cisplatin-resistant variant (2D culture cells). The best-performing complex 6 was further studied against the human DU-145 prostatic carcinoma, A549 lung carcinoma, HCT116 colon carcinoma, HeLa cervix adenocarcinoma, and MCF7 breast adenocarcinoma cell lines (2D culture cells). Complex 6 showed a cytotoxic profile different from that of c...

Combination regiments involving platinum anticancer drugs and agents with unrelated mechanisms of action are a subject of widespread interest. Here, we show that synergistic toxic action in cancer cells of combinations of antitumor platinum drug carboplatin and effective PARP inhibitor olaparib is considerably improved if these combined drugs are encapsulated into liposomes. Notably, the formation of such nano-formulations, called OLICARB, leads to a marked enhancement of activity in human cancer cell lines (including those resistant to conventional platinum antitumor drugs) and selectivity towards tumor cells. We used immunofluorescence analysis of γH2AX expression and examined DNA damage in cancerous cells treated with the investigated compounds. We find that the synergistic toxic effects in cancer cells of both drugs used in combination, nonencapsulated or embedded in the OLICARB nanoparticles, positively correlates with DNA damage. These results also suggest that the enhancement of the toxic effects of carboplatin by olaparib in cancer cells is a consequence of an accumulation of cytotoxic lesions in DNA due to the inhibition of repair of platinated DNA augmented by the synergistic action of olaparib as an effective PARP inhibitor. Our findings also reveal that the combination of olaparib with carboplatin encapsulated in the OLICARB nanoparticles is particularly effective to inhibit the growth of 3D mammospheres. Collectively, the data provide convincing evidence that the encapsulation of carboplatin and olaparib into liposomal constructs to form the OLICARB nanoparticles may represent the viable approach for the treatment of tumors with the aim to eliminate the possible effects of acquired resistance.

The design of photosensitive platinum antitumor drugs has been shown to be a very promising approach to enhance the low selectivity of antitumor platinum drugs towards cancer tissues. Here, we show that UVA irradiation can substantially potentiate the toxicity of a cisplatin derivative, cis-[PtCl2(NH3)(1-methyl-7-azaindole)], in tumor cells. We used methods of molecular biophysics and cellular biology to investigate the mechanism underlying this effect. We find that the enhanced phototoxicity of cis-[PtCl2(NH3)(1-methyl-7-azaindole)] is connected with the capability of this complex to cleave DNA strands. We demonstrate that production of reactive singlet oxygen, conditioned by the presence of the 1-methyl-7-azaindole ligand, is responsible for the cleavage of DNA strands not only in vitro but also in living cells. Our findings also reveal that UVA irradiation of DNA modified by cis-[PtCl2(NH3)(1-methyl-7-azaindole)] may result in a significant increase in the number of more toxic interstrand cross-links in DNA. Collectively, these data provide convincing evidence that the replacement of the ammine in the molecule of cisplatin by the 1-methyl-7-azaindole ligand might lead to a new potential candidate for photoactivated chemotherapy (PACT) against some types of cancer.

A series of neutral pseudo-octahedral RuII sulfonamidoethylenediamine complexes [(η6-p-cym)Ru(N, N’)Cl] where N, N’ is N-(2-(R1,R2-amino)ethyl)-4-toluenesulfonamide (TsEn(R1,R2)) R1,R2 = Me,H (1); Me,Me (2); Et,H (3); benzyl,H (Bz, 4); 4-fluorobenzyl,H (4-F-Bz, 5) or naphthalen-2-ylmethyl,H (Naph, 6), were synthesised and characterised including the X-ray crystal structure of 3. These complexes catalyse the reduction of NAD+ regioselectively to 1, 4-NADH by using formate as hydride source. The catalytic efficiency depends markedly on the steric and electronic effects of the N-substitutent, with turnover frequencies (TOFs) increasing in the order: 1 < 2 < 3, 6 < 4, 5, achieving a TOF of 7.7 h-1 for 4 with a 95% yield of 1, 4-NADH. The reduction rate was highest between pH* (deuterated solvent) 6 and 7.5 and improved with an increase in formate concentration (TOF of 18.8 h-1, 140 mM formate). The calculations suggested initial substitution of an aqua ligand by formate, followed by hydride transfer to RuII and then to NAD+, and indicated specific interactions between the aqua complex and both NAD+ and NADH, the former allowing a preorganisation involving interaction between the aqua ligand, formate anion and the pyridine ring of NAD+. The complexes exhibited antiproliferative activity towards A2780 human ovarian cancer cells with IC50 values ranging from 1 to 31 μM, the most potent complex, [(η6-p-cym)Ru(TsEn(Bz,H))Cl] (4, IC50 = 1.0 ± 0.1 μM), having a potency similar to the anticancer drug cisplatin. Co-administration with sodium formate (2 mM), increased the potency of all complexes towards A2780 cells by 20-36%, with the greatest effect seen for complex 6.

Despite the widespread use of antineoplastic platinum drugs, a number of accompanying disadvantages exist. In connection with attempts to circumvent these problems new platinum compounds have been prepared and mechanisms underlying their biological activity have been extensively investigated. These mechanistic investigations involve research focused on understanding interactions of platinum agents with DNA since DNA binding and recognition of DNA modified by these metallodrugs are the important processes responsible for their anticancer properties. In this review, we discuss how various classes of platinum(II) complexes, which can interact with DNA by coordination, intercalation and other noncovalent modes of binding or by combination of these DNA binding modes, can alter the cellular response induced by conventional platinum drugs. We describe that these alterations can be achieved by changing: (i) the nature and structure of the DNA lesion induced; (ii) conformational alterations induced in DNA by these lesions; and (iii) various cellular signaling pathways initiated by platinum-DNA damage. We anticipate that summarization of the results on DNA binding of cytotoxic platinum compounds may help to shed light on their potency and will make it possible to create new strategies to design rationally new anticancer platinum compounds and/or combine platinum drugs with other cytotoxic agents.

To evaluate the 5-substituted tetrazolate (5R-tetrazolate) ligand for the development of novel antitumor active Pt(II) and Pt(IV) diamines, eight analogues of transplatin bearing 5-phenyltetrazolato and 5-(phenol)tetrazolato ligands were prepared by reacting transplatin with the 5-substituted tetrazolate in DMF in the presence of trimethylamine. Coordination to platinum was through the N2 position of the tetrazolato ligand, as evidenced by a X-ray crystal structure of trans-diamminobis[5-(phenyl-4-ol)tetrazolato-κN2]platinum(II). Attempts to synthesize the corresponding cis-coordinated analogues from cisplatin were unsuccessful due to isomerization to the more stable trans isomers. Hydrogen peroxide was used to oxidize trans-diamminobis(5-phenyltetrazolato) and trans-diamminobis(5-phenoltetrazolato)platinum(II) complexes to the trans-dihydroxo-Pt(IV) analogues; the hydroxo ligands were then further acylated. The binding of Pt to calf thymus DNA for trans,trans,trans-diamminodihydroxidobis(5-phenyltetrazolato-κN2)platinum(IV) was dependent on the presence of ascorbate; however, the Pt(II) analogue trans-diamminobis(5-phenyltetrazolato-κN2)platinum(II) itself bond only very weakly to DNA, indicating that this is not the product of the ascorbate induced reduction of the Pt(IV) complex. Evaluation of the antiproliferative activity on eight human cancer cells in vitro showed the Pt(IV) complexes to be more potent than the Pt(II) analogues but all complexes were still much less active than cisplatin. No cross resistance to cisplatin was observed in the A2870 ovarian cancer cell line.

The adverse side effects and acquired resistance associated with the clinical application of traditional platinum-based anticancer drugs have forced investigation of alternative transition metal-based compounds and their cytostatic properties. Over the last years, the anticancer potential of cobalt complexes has been extensively studied, and in-depth analyses of their mode of action have been conducted. In this work, we present antiproliferative activity against human cancer cells of the dinuclear Co(III) complexes bearing the quinizarin ligand and tris(2-aminoethyl)amine (tren, compound 1) or tris(2-pyridylmethyl)amine (tpa, compound 2) co-ligands. To contribute the understanding mechanisms of biological action of these compounds, their association with DNA in the cells, DNA binding in cell-free media, and DNA cleavage capability were investigated in detail. The results demonstrate that both complexes interact with DNA in tumor cells. However, their mechanism of antiproliferative action is different, and this difference is mirrored by distinct antiproliferative activity. The antiproliferative effect of 1 is connected with its ability to intercalate into DNA and subsequently to inhibit activities of DNA processing enzymes. In contrast, the total antiproliferative efficiency of 2, thanks to its redox properties, appears to be connected with its ability to form radicals and, consequently, with the ability of 2 to cleave DNA. Hence, the findings presented in this study may significantly contribute to understanding the antitumor potential of cobalt complexes. Dinuclear Co(III) complexes containing the bioactive quinizarin ligand exhibit antiproliferative activity based on distinct mechanism.

Conventional chemotherapy is mostly effective in the treatment of rapidly-dividing differentiated tumor cells but has limited application toward eliminating cancer stem cell (CSC) population. The presence of a very small number of CSCs may contribute to the development of therapeutic resistance, metastases, and relapse. Thus, treatment failure by developing novel anticancer drugs capable of effective targeting of CSCs is at present a major challenge for research focused on chemotherapy of cancer. Here, we show that Os(II) complex 2 [Os(η6-pcym)(bphen)(dca)]PF6 (pcym = p-cymene, bphen = bathophenanthroline, and dca = dichloroacetate), is capable of efficient and selective killing CSCs in heterogeneous populations of human breast cancer cells MCF-7 and SKBR-3. Notably, its remarkable submicromolar potency to kill CSCs is considerably higher than that of its Ru analog, [Ru(η6-pcym)(bphen)(dca)]PF6 (complex 1) and salinomycin, one of the most selective CSC-targeting compounds hitherto identified. Furthermore, Os(II) complex 2 reduces the formation, size, and viability of three-dimensional mammospheres which more closely reflect the tumor microenvironment than cells in traditional two-dimensional cultures. The antiproliferation studies and propidium iodide staining using flow cytometry suggest that Os(II) complex 2 induces human breast cancer stem cell death predominantly by necroptosis, a programmed form of necrosis. The results of this study demonstrate the promise of Os(II) complex 2 in treating human breast tumors. They also represent the foundation for further preclinical and clinical studies and applications of Os(II) complex 2 to comply with the emergent need for human breast CSCs-specific chemotherapeutics capable to treat chemotherapy-resistant and relapsed human breast tumors.

One concept how to improve anticancer effects of conventional metallodrugs consists in conjugation of these compounds with other biologically (antitumor) active agents, acting by a different mechanism. Here, we present synthesis, biological effects, and mechanisms of action of new Pt(II) derivatives containing one or two nonsteroidal anti-inflammatory diclofenac (DCF) ligands also known for their antitumor effects. The antiproliferative properties of these metallic conjugates show that these compounds are potent and cancer cell selective cytotoxic agents exhibiting activity in cisplatin resistant and the COX-2 positive tumor cell lines. One of these compounds, compound 3, in which DCF molecules are coordinated to Pt(II) through their carboxylic group, is more potent than parental conventional Pt(II) drug cisplatin, free DCF and the congeners of 3 in which DCF ligands are conjugated to Pt(II) via a diamine. The potency of 3 is due to several factors including enhanced internalization that correlates with enhanced DNA binding and cytotoxicity. Mechanistic studies show that 3 combines multiple effects. After its accumulation in cells, it releases Pt(II) drug capable of binding/damaging DNA and DCF ligands, which affect distribution of cells in individual phases of the cell cycle, inhibit glycolysis and lactate transport, collapse mitochondrial membrane potential, and suppress the cellular properties characteristic of metastatic progression.

The DNA interstrand cross-links of the antitumor drug {[cis-Pt(NH3)2Cl]2(4,4′-methylenedianiline)}2+ (1) play a prevalent role in its antitumor effects. Complex 1 forms DNA long-range interstrand cross-links uniquely in the 3′–3′ direction. Conformational distortions induced by these interstrand cross-links in DNA represent a potential structural motif for recognition by high-mobility-group proteins.

One of the promising new antitumor platinum complexes is a large-ring chelate complex [PtCl2(cis-1,4-DACH)] (DACH = diaminocyclohexane) (kiteplatin). Recently, new platinum(II) derivatives of kiteplatin with pyrophosphate as a carrier ligand have been synthesized and tested on a panel of human cancer cell lines. These derivatives of kiteplatin were found to be more effective than clinically used anticancer platinum drugs. The design of kiteplatin pyrophosphate derivatives was based on the concept of pyrophosphate coordinated platinum complexes, phosphaplatins. Phosphaplatins have been shown to function without binding to DNA and hence DNA has been excluded as the target of phosphaplatins in contrast to conventional antitumor platinum drugs. Cytotoxicity, major cellular targets and DNA interactions of the new anticancer platinum drug were characterized by standard biochemical methods and methods of molecular and cellular biology. We demonstrate that, in contrast to what has been reported on closely related phosphaplatins, the derivatives of kiteplatin with the pyrophosphate carrier ligand are activated in the cellular environment. This activation, which yields species capable of platination of DNA, very likely comprises the hydrolytic release of the pyrophosphate ligand that could be enzymatically catalyzed. Collectively, these data provide convincing evidence that unexpectedly DNA is an important target for the biological activity of the kiteplatin pyrophosphate derivatives, although the overall mechanism of action might be different from those of conventional platinum drugs.

We report DNA cleavage by ruthenium(II) arene anticancer complex [(η(6)-p-terp)Ru(II)(en)Cl](+) (p-terp=para-terphenyl, en=1,2-diaminoethane, complex 1) after its photoactivation by UVA and visible light, and the toxic effects of photoactivated 1 in cancer cells. It was shown in our previous work (T. Bugarcic et al., J. Med. Chem. 51 (2008) 5310-5319) that this complex exhibits promising toxic effects in several human tumor cell lines and concomitantly its DNA binding mode involves combined intercalative and monofunctional (coordination) binding modes. We demonstrate in the present work that when photoactivated by UVA or visible light, 1 efficiently photocleaves DNA, also in hypoxic media. Studies of the mechanism underlying DNA cleavage by photoactivated 1 reveal that the photocleavage reaction does not involve generation of reactive oxygen species (ROS), although contribution of singlet oxygen ((1)O2) to the DNA photocleavage process cannot be entirely excluded. Notably, the mechanism of DNA photocleavage by 1 appears to involve a direct modification of mainly those guanine residues to which 1 is coordinatively bound. As some tumors are oxygen-deficient and cytotoxic effects of photoactivated ruthenium compounds containing {Ru(η(6)-arene)}(2+) do not require the presence of oxygen, this class of ruthenium complexes may be considered potential candidate agents for improved photodynamic anticancer chemotherapy.

The fabrication of nanoparticles using different formulations, and which can be used for the delivery of chemotherapeutics, has recently attracted considerable attention. We describe herein an innovative approach that may ultimately allow for the selective delivery of anticancer drugs to tumor cells by using an external magnet. A conventional antitumor drug, cisplatin, has been incorporated into new carboxymethylcellulose-stabilized magnetite nanoparticles conjugated with the fluorescent marker Alexa Fluor 488 or folic acid as targeting agent. The magnetic nanocarriers possess exceptionally high biocompatibility and colloidal stability. These cisplatin-loaded nanoparticles overcome the resistance mechanisms typical of free cisplatin. Moreover, experiments aimed at the localization of the nanoparticles driven by an external magnet in a medium that mimics physiological conditions confirmed that this localization can inhibit tumor cell growth site-specifically.

The molecular and cellular mechanisms of enhanced toxic effects in tumor cells of the Pt(IV) derivatives of antitumor oxaliplatin containing axial dichloroacetate (DCA) ligands were investigated. DCA ligands were chosen because DCA has shown great potential as an apoptosis sensitizer and anticancer agent reverting the Wartburg effect. In addition, DCA reverses mitochondrial changes in a wide range of cancers, promoting tumor cell apoptosis in a mitochondrial-dependent pathway. We demonstrate that (i) the transformation of oxaliplatin to its Pt(IV) derivatives containing axial DCA ligands markedly enhances toxicity in cancer cells and helps overcome inherent and acquired resistance to cisplatin and oxaliplatin; (ii) a significant fraction of the intact molecules of DCA conjugates with Pt(IV) derivative of oxaliplatin accumulates in cancer cells where it releases free DCA; (iii) mechanism of biological action of the Pt(IV) derivatives of oxaliplatin containing DCA ligands is connected with the effects of DCA released in cancer cells from the Pt(IV) prodrugs on mitochondria and metabolism of glucose; (iv) treatments with the Pt(IV) derivatives of oxaliplatin containing DCA ligands activate an autophagic response in human colorectal cancer cells; (v) the toxic effects in cancer cells of the Pt(IV) derivatives of oxaliplatin containing DCA ligands can be potentiated if cells are treated with these prodrugs in combination with 5-fluorouracil. These properties of the Pt(IV) derivatives of oxaliplatin containing DCA ligands provide opportunities for further development of new platinum-based agents with the capability of killing cancer cells resistant to conventional antitumor platinum drugs used in the clinic.

Three gallium(III) complexes, [Ga(NQ)3] (1), Na3[Ga(SQ)3]·7H2O·3NaCl (2) and [Ga(ClNQ)3]·MeOH (3) were synthesised as possible anticancer agents (H-NQ = 5-nitro-8-quinolinol, H-SQH = 5-sulfo-8-quinolinol, H-ClNQ = 5-chloro-7-nitro-8-quinolinol) and characterised by elemental analysis, IR and NMR spectroscopy. Single crystal structure analysis of 1 revealed two crystallographically independent [Ga(NQ)3] molecules in the asymmetric part of the unit cell. Stability of the complexes 1 and 2 in solution was determined by 1H NMR spectroscopy. Complex 3 was not further studied due to the low solubility. Antiproliferative activity of complexes 1 and 2 was studied using in vitro MTT assay against the A2780, HCT116 and MDA-MB-231 cancer cell lines and the selectivity of the complexes was verified on noncancerous MRC5 pd30 cell line. Complex 1 showed high antiproliferative potency (IC50 = 3.6 ± 0.8 μM for HCT116) and noticeable selectivity of 1 against the cancer cell lines (IC50 = 32 ± 4 μM for normal MRC5 pd30 cell line) was also found. The complex 2 displayed the highest antioxidant activity of all tested complexes and free ligands.

A novel ambidentate type hydroxamic acid derivative (phenhaH, 1) containing an (O,O) and a 1,10-phenantroline (phen) based (N,N) donoratom set together with its heterobimetallic complexes incorporating an octahedral [Co(4 N)]3+ (4 N = tris(2-aminoethyl)amine (tren) or tris(2-methylpyridyl)amine (tpa)) and a half-sandwich type [(η6-p-cym)Ru]2+ entity have been synthesized and characterized using various analytical techniques. Reaction of [Co(4 N)Cl]Cl2 with 1 proved the exclusive (O,O) coordination of the ligand to the [Co(4 N)]3+ core to yield [Co(tpa)(phenha)](ClO4)2, (2). Subsequent treatment of 1 with [Ru(η6-p-cym)Cl2]2 and [Co(4 N)Cl]Cl2 in a one-pot reaction resulted in the formation of [(η6-p-cym)Ru(Cl)(phenha)Co(tren)]Cl(PF6)2 (3) and [(η6-p-cym)Ru(Cl)(phenha)Co(tpa)](PF6)3 (4) in which the organometallic Ru core is coordinated by the phen part while the Co entity by the hydroxamate part of 1. Cyclic voltammetry revealed that 4 could be reduced at a less negative potential and exhibits a reversible Co(III)/Co(II) redox process compared to 3 due to the π-back bonding interaction between the Co(III) centre and the pyridyl-N donors of tpa in 4. Complexes 2–4 were tested for their in vitro cytotoxicity using human-derived cancer cell lines (HeLa, MCF-7, HCT116 and MDA-MB-231) and showed moderate anti-proliferative activity in the double digit micromolar concentration range, 4 being the most active. Complex 4 displayed better activity against MDA-MB-231 cells than cisplatin.

Although cyclometalated Ir