Toward Multi-Targeted Platinum and Ruthenium Drugs-A New Paradigm in Cancer Drug Treatment Regimens?

Half-Sandwich Type Platinum-Group Metal Complexes of C-Glucosaminyl Azines: Synthesis and Antineoplastic and Antimicrobial Activities

While platinum-based compounds such as cisplatin form the backbone of chemotherapy, the use of these compounds is limited by resistance and toxicity, driving the development of novel complexes with cytostatic properties. In this study, we synthesized a set of half-sandwich complexes of platinum-group metal ions (Ru(II), Os(II), Ir(III) and Rh(III)) with an N,N-bidentate ligand comprising a C-glucosaminyl group and a heterocycle, such as pyridine, pyridazine, pyrimidine, pyrazine or quinoline. The sugar-containing ligands themselves are unknown compounds and were obtained by nucleophilic additions of lithiated heterocycles to O-perbenzylated 2-nitro-glucal. Reduction of the adducts and, where necessary, subsequent protecting group manipulations furnished the above C-glucosaminyl heterocycles in their O-perbenzylated, O-perbenzoylated and O-unprotected forms. The derived complexes were tested on A2780 ovarian cancer cells. Pyridine, pyrazine and pyridazine-containing complexes proved to be cytostatic and cytotoxic on A2780 cells, while pyrimidine and quinoline derivatives were inactive. The best complexes contained pyridine as the heterocycle. The metal ion with polyhapto arene/arenyl moiety also impacted on the biological activity of the complexes. Ruthenium complexes with p-cymene and iridium complexes with Cp* had the best performance in ovarian cancer cells, followed by osmium complexes with p-cymene and rhodium complexes with Cp*. Finally, the chemical nature of the protective groups on the hydroxyl groups of the carbohydrate moiety were also key determinants of bioactivity; in particular, O-benzyl groups were superior to O-benzoyl groups. The IC50 values of the complexes were in the low micromolar range, and, importantly, the complexes were less active against primary, untransformed human dermal fibroblasts; however, the anticipated therapeutic window is narrow. The bioactive complexes exerted cytostasis on a set of carcinomas such as cell models of glioblastoma, as well as breast and pancreatic cancers. Furthermore, the same complexes exhibited bacteriostatic properties against multiresistant Gram-positive Staphylococcus aureus and Enterococcus clinical isolates in the low micromolar range.

Triphenyltin(IV) Carboxylates with Exceptionally High Cytotoxicity against Different Breast Cancer Cell Lines

Organotin(IV) carboxylates are a class of compounds explored as alternatives to platinum-containing chemotherapeutics due to propitious in vitro and in vivo results, and distinct mechanisms of action. In this study, triphenyltin(IV) derivatives of non-steroidal anti-inflammatory drugs (indomethacin (HIND) and flurbiprofen (HFBP)) are synthesized and characterized, namely [Ph3Sn(IND)] and [Ph3Sn(FBP)]. The crystal structure of [Ph3Sn(IND)] reveals penta-coordination of the central tin atom with almost perfect trigonal bipyramidal geometry with phenyl groups in the equatorial positions and two axially located oxygen atoms belonging to two distinct carboxylato (IND) ligands leading to formation of a coordination polymer with bridging carboxylato ligands. Employing MTT and CV probes, the antiproliferative effects of both organotin(IV) complexes, indomethacin, and flurbiprofen were evaluated on different breast carcinoma cells (BT-474, MDA-MB-468, MCF-7 and HCC1937). [Ph3Sn(IND)] and [Ph3Sn(FBP)], unlike the inactive ligand precursors, were found extremely active towards all examined cell lines, demonstrating IC50 concentrations in the range of 0.076–0.200 µM. Flow cytometry was employed to examine the mode of action showing that neither apoptotic nor autophagic mechanisms were triggered within the first 48 h of treatment. However, both tin(IV) complexes inhibited cell proliferation potentially related to the dramatic reduction in NO production, resulting from downregulation of nitric oxide synthase (iNOS) enzyme expression.

Development of Novel Pt(IV)-Carbohydrate Derivatives as Targeted Anticancer Agents against Osteosarcoma

Despite the enormous importance of cisplatin as a chemotherapeutic agent, its application is impacted by dose-limiting side effects and lack of selectivity for cancer cells. Researchers can overcome these issues by taking advantage of the pro-drug nature of the platinum(IV) oxidation state, and by modifying the coordination sphere of the metal centre with specific vectors whose receptors are overexpressed in tumour cell membranes (e.g., carbohydrates). In this paper we report the synthesis of four novel carbohydrate-modified Pt(IV) pro-drugs, based on the cisplatin scaffold, and their biological activity against osteosarcoma (OS), a malignant tumour which is most common in adolescents and young adults. The carbohydrate-targeting vectors and Pt scaffold are linked using copper-catalysed azide-alkyne cycloaddition (CuAAC) chemistry, which is synonymous with mild and robust reaction conditions. The novel complexes are characterised using multinuclear 1D-2D NMR (¹H, ¹³C and ¹⁹⁵Pt), IR, HR-MS, Elem. Analyses, and CV. Cytotoxicity on 2D and 3D and cell morphology studies on OS cell lines, as well as non-cancerous human foetal osteoblasts (hFOBs), are discussed.

Novel Indole-Chalcone Derivative-Ligated Platinum(IV) Prodrugs Attenuate Cisplatin Resistance in Lung Cancer through ROS/ER Stress and Mitochondrial Dysfunction

Developing multifunctional platinum(IV) prodrugs via integrating bioactive pharmacophores into one entity is an attractive strategy to ameliorate the defects of platinum(II) drugs. Herein, a series of indole-chalcone derivative-ligated platinum(IV) complexes were synthesized and evaluated for their anticancer activities. Among them, optimal complex 17a exerted superior activity compared to that of cisplatin (CDDP) against the tested cells but showed lower cytotoxicity toward human normal lung cells. Detailed mechanisms demonstrated that 17a significantly enhanced intracellular accumulation, induced DNA damage, and inhibited migration in A549/CDDP cells. Furthermore, 17a efficiently disturbed the tubulin-microtubule system, initiated reactive oxygen species (ROS)-mediated endoplasmic reticulum stress, and activated a mitochondrion-dependent apoptosis signaling pathway. Besides, 17a was superior to free drugs or their combination in inhibiting cancer growth in A549/CDDP xenografts without inducing obvious side effects. The physical mixture of 16a and CDDP was almost identical to 17a but showed apparent systematic side effects. In summary, our studies may provide an efficient treatment regimen for CDDP resistance.

Synthesis, Characterization and Biological Investigation of the Platinum(IV) Tolfenamato Prodrug–Resolving Cisplatin-Resistance in Ovarian Carcinoma Cell Lines

The research on the anticancer potential of platinum(IV) complexes represents one strategy to circumvent the deficits of approved platinum(II) drugs. Regarding the role of inflammation during carcinogenesis, the effects of non-steroidal anti-inflammatory drug (NSAID) ligands on the cytotoxicity of platinum(IV) complexes is of special interest. The synthesis of cisplatin- and oxaliplatin-based platinum(IV) complexes with four different NSAID ligands is presented in this work. Nine platinum(IV) complexes were synthesized and characterized by use of nuclear magnetic resonance (NMR) spectroscopy (1H, 13C, 195Pt, 19F), high-resolution mass spectrometry, and elemental analysis. The cytotoxic activity of eight compounds was evaluated for two isogenic pairs of cisplatin-sensitive and -resistant ovarian carcinoma cell lines. Platinum(IV) fenamato complexes with a cisplatin core showed especially high in vitro cytotoxicity against the tested cell lines. The most promising complex, 7, was further analyzed for its stability in different buffer solutions and behavior in cell cycle and cell death experiments. Compound 7 induces a strong cytostatic effect and cell line-dependent early apoptotic or late necrotic cell death processes. Gene expression analysis suggests that compound 7 acts through a stress-response pathway integrating p21, CHOP, and ATF3.

Organometallic Iridium Complexes with Glucose Based Phosphite Ligands

New organometallic iridium compounds with phosphorus modified glucose ligands containing isopropylidene protection group or bearing uracil, thymine, and 5-fluorouracil (3,5,6-bicyclophosphite-1,2-O-isopropylidene-α-d-glucofuranoside, 3,5,6-bicyclophosphite-1-β-D-glucofuranosyluracil, 3,5,6-bicyclophosphite-1-β-D-glucofuranosylthymine, 3,5,6-bicyclophosphite-1-β-D-glucofuranosyl-5-flurouracil) were prepared. The structure of the new complexes was confirmed by the spectroscopic technique (1H, 31P{1H} NMR) and mass spectrometry, and purity by elemental analysis. The molecular structure of the complex with the isopropylidene protection group was established by the X-ray analysis. The antiproliferative activity of the new iridium compounds was evaluated against several cancer cell lines of human origin, and all compounds showed low toxicity independent of the pyrimidine base nature, attached to the sugar unit.

Bilateral metalloheterocyclic systems based on palladacycle and piperidine-2,4-dione pharmacophores

The design of molecules with effective anticancer properties constructed from both dually active metal complex and organic fragments is a novel trend in medicinal chemistry. This concept suggests the impact of a drug on several biological targets or the synergistic action of both fragments as a single unit. We propose that the combination of a Pd-metallocomplex fragment and an organic unit can be an interesting model for anticancer drug discovery. The first phase in the development of such suggested molecules is the synthesis of bilateral metallosystems containing bioactive 6-substituted piperidin-2-one and a palladated N-phenylpyrazolic fragment. Both fragments were incorporated into one molecule through the fused pyrazole-piperidine-2-one unit followed by pyrazol-directed cyclopalladation of the phenyl-group with Pd(OAc)₂. An effect of acceleration of the rate of the palladation by NH-lactam was observed. The synthesized hybrid palladacycles have been characterized and tested for their cytotoxic activity on three cancerous cell lines as PPh₃ complexes, revealing structures with potential for further development and structural optimization.

Oral Anticancer Heterobimetallic PtIV -AuI Complexes Show High In Vivo Activity and Low Toxicity

Au^I -carbene and Pt^IV -Au^I -carbene prodrugs display low to sub-μM activity against several cancer cell lines and overcome cisplatin (cisPt) resistance. Linking a cisPt-derived Pt^IV (phenylbutyrate) complex to a Au^I -phenylimidazolylidene complex 2, yielded the most potent prodrug. While in vivo tests against Lewis Lung Carcinoma showed that the prodrug Pt^IV (phenylbutyrate)-Au^I -carbene (7) and the 1 : 1 : 1 co-administration of cisPt: phenylbutyrate:2 efficiently inhibited tumor growth (≈95 %), much better than 2 (75 %) or cisPt (84 %), 7 exhibited only 5 % body weight loss compared to 14 % for 2, 20 % for cisPt and >30 % for the co-administration. 7 was much more efficient than 2 at inhibiting TrxR activity in the isolated enzyme, in cells and in the tumor, even though it was much less efficient than 2 at binding to selenocysteine peptides modeling the active site of TrxR. Organ distribution and laser-ablation (LA)-ICP-TOFMS imaging suggest that 7 arrives intact at the tumor and is activated there.

Nature of NMR Shifts in Paramagnetic Octahedral Ru(III) Complexes with Axial Pyridine-Based Ligands

In recent decades, transition-metal coordination compounds have been extensively studied for their antitumor and antimetastatic activities. In this work, we synthesized a set of symmetric and asymmetric Ru(III) and Rh(III) coordination compounds of the general structure (Na+/K+/PPh4+/LH+) [trans-MIIIL(eq)nL(ax)2]- (M = RuIII or RhIII; L(eq) = Cl, n = 4; L(eq) = ox, n = 2; L(ax) = 4-R-pyridine, R = CH3, H, C6H5, COOH, CF3, CN; L(ax) = DMSO-S) and systematically investigated their structure, stability, and NMR properties. 1H and 13C NMR spectra measured at various temperatures were used to break down the total NMR shifts into the orbital (temperature-independent) and hyperfine (temperature-dependent) contributions. The hyperfine NMR shifts for paramagnetic Ru(III) compounds were analyzed in detail using relativistic density functional theory (DFT). The effects of (i) the 4-R substituent of pyridine, (ii) the axial trans ligand L(ax), and (iii) the equatorial ligands L(eq) on the distribution of spin density reflected in the "through-bond" (contact) and the "through-space" (pseudocontact) contributions to the hyperfine NMR shifts of the individual atoms of the pyridine ligands are rationalized. Further, we demonstrate the large effects of the solvent on the hyperfine NMR shifts and discuss our observations in the general context of the paramagnetic NMR spectroscopy of transition-metal complexes.

Influence of the Fatty Acid Metabolism on the Mode of Action of a Cisplatin(IV) Complex with Phenylbutyrate as Axial Ligands

For a variety of cancer types, platinum compounds are still among the best treatment options. However, their application is limited by side effects and drug resistance. Consequently, multi-targeted platinum(IV) prodrugs that target specific traits of the malignant tissue are interesting new candidates. Recently, cisPt(PhB)2 was synthesized which, upon reduction in the malignant tissue, releases phenylbutyrate (PhB), a metabolically active fatty acid analog, in addition to cisplatin. In this study, we in-depth investigated the anticancer properties of this new complex in cell culture and in mouse allograft experiments. CisPt(PhB)2 showed a distinctly improved anticancer activity compared to cisplatin as well as to PhB alone and was able to overcome various frequently occurring drug resistance mechanisms. Furthermore, we observed that differences in the cellular fatty acid metabolism and mitochondrial activity distinctly impacted the drug's mode of action. Subsequent analyses revealed that "Warburg-like" cells, which are characterized by deficient mitochondrial function and fatty acid catabolism, are less capable of coping with cisPt(PhB)2 leading to rapid induction of a non-apoptotic form of cell death. Summarizing, cisPt(PhB)2 is a new orally applicable platinum(IV) prodrug with promising activity especially against cisplatin-resistant cancer cells with "Warburg-like" properties.

Cyclometalated Ru(II)-NHC complexes with phenanthroline ligands induce apoptosis mediated by mitochondria and endoplasmic reticulum stress in cancer cells

The exploration of ruthenium complexes as anticancer drugs has been the focus of intense investigation. In this study, we synthesized and characterized four C,N-cyclometalated ruthenium(II) complexes (Ru1-Ru4) coordinated with pyridine-functionalized N-heterocyclic carbene (NHC) and auxiliary ligands (e.g., acetonitrile, 1,10-phenanthroline, 3,4,7,8-tetramethyl-1,10-phenanthroline, and 4,7-diphenyl-1,10-phenanthroline). X-ray diffraction analysis showed that all of the four cycloruthenated complexes are hexa-coordinated in a typical octahedral geometry. In vitro cytotoxic studies revealed that cyclometalated Ru-NHC complexes Ru3 and Ru4 had stronger anticancer activity than their corresponding Ru-NHC precursor Ru1 and the clinically used cisplatin. For HeLa cells, Ru3 and Ru4 exhibited potent cytotoxicity with the IC₅₀ value of 4.31 ± 0.42 μM and 3.14 ± 0.23 μM, respectively, which was approximately three times lower than that of cisplatin. More interestingly, Ru3 and Ru4 not only effectively inhibited the proliferation of HeLa cells, but also exhibited potential anti-migration activity. In the scratch wound healing assay, Ru3 and Ru4 treatment significantly reduced the wound healing rate of HUVEC cells. Mechanistic studies showed that Ru3 and Ru4 caused a dual action mode of mitochondrial membrane depolarization and endoplasmic reticulum stress and finally induced apoptosis of HeLa cells.

Multifunctional organometallic compounds for the treatment of Chagas disease: Re(I) tricarbonyl compounds with two different bioactive ligands

Chagas' disease (American Trypanosomiasis) is an ancient and endemic illness in Latin America caused by the protozoan parasite Trypanosoma cruzi. Although there is an urgent need for more efficient and less toxic chemotherapeutics, no new drugs to treat this disease have entered the clinic in the last decades. Searching for metal-based prospective antichagasic drugs, in this work, multifunctional Re(I) tricarbonyl compounds bearing two different bioactive ligands were designed: a polypyridyl NN derivative of 1,10-phenanthroline and a monodentate azole (Clotrimazole CTZ or Ketoconazol KTZ). Five fac-[Re(CO)₃(NN)(CTZ)](PF₆) compounds and a fac-[Re(CO)₃(NN)(KTZ)](PF₆) were synthesized and fully characterized. They showed activity against epimastigotes (IC₅₀ 3.48-9.42 μM) and trypomastigotes of T. cruzi (IC₅₀ 0.61-2.79 μM) and moderate to good selectivity towards the parasite compared to the VERO mammalian cell model. In order to unravel the mechanism of action of our compounds, two potential targets were experimentally and theoretically studied, namely DNA and one of the enzymes involved in the parasite ergosterol biosynthetic pathway, CYP51 (lanosterol 14-α-demethylase). As hypothesized, the multifunctional compounds shared in vitro a similar mode of action as that disclosed for the single bioactive moieties included in the new chemical entities. Additionally, two relevant physicochemical properties of biological interest in prospective drug development, namely lipophilicity and stability in solution in different media, were determined. The whole set of results demonstrates the potentiality of these Re(I) tricarbonyls as promising candidates for further antitrypanosomal drug development.

Interaction between [(η6-p-cym)M(H2O)3]2+ (MII = Ru, Os) or [(η5-Cp*)M(H2O)3]2+ (MIII = Rh, Ir) and Phosphonate Derivatives of Iminodiacetic Acid: A Solution Equilibrium and DFT Study

The pH-dependent binding strengths and modes of the organometallic [(η⁶-p-cym)M(H₂O)₃]²⁺ (M^II = Ru, Os; p-cym = 1-methyl-4-isopropylbenzene) or [(η⁵-Cp*)M(H₂O)₃]²⁺ (M^III = Rh, Ir; Cp* = pentamethylcyclopentadienyl anion) cations towards iminodiacetic acid (H₂Ida) and its biorelevant mono- and diphosphonate derivatives N-(phosphonomethyl)-glycine (H₃IdaP) and iminodi(methylphosphonic acid) (H₄Ida2P) was studied in an aqueous solution. The results showed that all three of the ligands form 1:1 complexes via the tridentate (O,N,O) donor set, for which the binding mode was further corroborated by the DFT method. Although with IdaP^3- and Ida2P^4- in mono- and bis-protonated species, where H⁺ might also be located at the non-coordinating N atom, the theoretical calculations revealed the protonation of the phosphonate group(s) and the tridentate coordination of the phosphonate ligands. The replacement of one carboxylate in Ida^2- by a phosphonate group (IdaP^3-) resulted in a significant increase in the stability of the metal complexes; however, this increase vanished with Ida2P^4-, which was most likely due to some steric hindrance upon the coordination of the second large phosphonate group to form (5 + 5) joined chelates. In the phosphonate-containing systems, the neutral 1:1 complexes are the major species at pH 7.4 in the millimolar concentration range that is supported by both NMR and ESI-TOF-MS.

State of art in the chemistry of nucleoside-based Pt(II) complexes

After the fortuitous discovery of the anticancer properties of cisplatin, many Pt(II) complexes have been synthesized, to obtain less toxic leads which could overcome the resistance phenomena. Given the importance of nucleosides and nucleotides as antimetabolites, studying their coordinating properties towards Pt(II) ions is challenging for bioorganic and medicinal chemistry. This review aims to describe the results achieved so far in the aforementioned field, paying particular attention to the synthetic aspects, the chemical-physical characterization, and the biological activities of the nucleoside-based Pt(II) complexes.

Platinum glycoconjugates: "Sweet bullets" for targeted cancer therapy?

Cancer, which is characterized by uncontrolled proliferation of abnormal cells, is a leading cause of morbidity and mortality worldwide. Cytotoxic chemotherapy, especially with platinum drugs, remains the mainstay of cancer treatment in the clinical setting. Despite phenomenal success, small-molecule chemotherapeutic drugs suffer from some serious drawbacks. Lack of cancer selectivity and the ensuing side effects mar the therapeutic potential of these drugs. Glycoconjugation has emerged as an attractive strategy for imparting selectivity and improving pharmacokinetics of cytotoxic agents. In this review, we provide an overview of the glycoconjugation strategy and then illustrate the application of this strategy with the help of some concrete examples of platinum based glycoconjugates. At the end we discuss a few important aspects of these glycoconjugates which merit further investigations.

Platinum(terpyridine) complexes with N-heterocyclic carbene co-ligands: high antiproliferative activity and low toxicity in vivo

Pt(terpyridine) complexes are well-known DNA intercalators. The introduction of an NHC co-ligand rendered such a complex highly antiproliferative in cancer cells compared to its chlorido derivative. Despite the high potency, zebrafish embryos tolerated the compound well, especially compared to cisplatin. DNA interaction studies support a mode of action related to intercalation.

Half sandwich-type osmium, ruthenium, iridium and rhodium complexes with bidentate glycosyl heterocyclic ligands induce cytostasis in platinum-resistant ovarian cancer cells and bacteriostasis in Gram-positive multiresistant bacteria

The toxicity of and resistance to platinum complexes as cisplatin, oxaliplatin or carboplatin calls for the replacement of these therapeutic agents in clinical settings. We have previously identified a set of half sandwich-type osmium, ruthenium and iridium complexes with bidentate glycosyl heterocyclic ligands exerting specific cytostatic activity on cancer cells but not on non-transformed primary cells. The apolar nature of the complexes, conferred by large, apolar benzoyl protective groups on the hydroxyl groups of the carbohydrate moiety, was the main molecular feature to induce cytostasis. We exchanged the benzoyl protective groups to straight chain alkanoyl groups with varying length (3 to 7 carbon units) that increased the IC50 value as compared to the benzoyl-protected complexes and rendered the complexes toxic. These results suggest a need for aromatic groups in the molecule. The pyridine moiety of the bidentate ligand was exchanged for a quinoline group to enlarge the apolar surface of the molecule. This modification decreased the IC50 value of the complexes. The complexes containing [(η6-p-cymene)Ru(II)], [(η6-p-cymene)Os(II)] or [(η5-Cp*)Ir(III)] were biologically active unlike the complex containing [(η5-Cp*)Rh(III)]. The complexes with cytostatic activity were active on ovarian cancer (A2780, ID8), pancreatic adenocarcinoma (Capan2), sarcoma (Saos) and lymphoma cell lines (L428), but not on primary dermal fibroblasts and their activity was dependent on reactive oxygen species production. Importantly, these complexes were cytostatic on cisplatin-resistant A2780 ovarian cancer cells with similar IC50 values as on cisplatin-sensitive A2780 cells. In addition, the quinoline-containing Ru and Os complexes and the short chain alkanoyl-modified complexes (C3 and C4) proved to be bacteriostatic in multiresistant Gram-positive Enterococcus and Staphylococcus aureus isolates. Hereby, we identified a set of complexes with submicromolar to low micromolar inhibitory constants against a wide range of cancer cells, including platinum resistant cells and against multiresistant Gram-positive bacteria.

Synergy of ruthenium metallo-intercalator, [Ru(dppz)2(PIP)]2+, with PARP inhibitor Olaparib in non-small cell lung cancer cells

Poly(ADP-ribose) polymerase (PARP) are critical DNA repair enzymes that are activated as part of the DNA damage response (DDR). Although inhibitors of PARP (PARPi) have emerged as small molecule drugs and have shown promising therapeutic effects, PARPi used as single agents are clinically limited to patients with mutations in germline breast cancer susceptibility gene (BRCA). Thus, novel PARPi combination strategies may expand their usage and combat drug resistance. In recent years, ruthenium polypyridyl complexes (RPCs) have emerged as promising anti-cancer candidates due to their attractive DNA binding properties and distinct mechanisms of action. Previously, we reported the rational combination of the RPC DNA replication inhibitor [Ru(dppz)₂(PIP)]²⁺ (dppz = dipyrido[3,2-a:2',3'-c]phenazine, PIP = 2-(phenyl)-imidazo[4,5-f][1,10]phenanthroline), "Ru-PIP", with the PARPi Olaparib in breast cancer cells. Here, we expand upon this work and examine the combination of Ru-PIP with Olaparib for synergy in lung cancer cells, including in 3D lung cancer spheroids, to further elucidate mechanisms of synergy and additionally assess toxicity in a zebrafish embryo model. Compared to single agents alone, Ru-PIP and Olaparib synergy was observed in both A549 and H1975 lung cancer cell lines with mild impact on normal lung fibroblast MRC5 cells. Employing the A549 cell line, synergy was confirmed by loss in clonogenic potential and reduced migration properties. Mechanistic studies indicated that synergy is accompanied by increased double-strand break (DSB) DNA damage and reactive oxygen species (ROS) levels which subsequently lead to cell death via apoptosis. Moreover, the identified combination was successfully able to inhibit the growth of A549 lung cancer spheroids and acute zebrafish embryos toxicity studies revealed that this combination showed reduced toxicity compared to single-agent Ru-PIP.

Impact of Hydrophobic Chains in Five-Coordinate Glucoconjugate Pt(II) Anticancer Agents

This study describes new platinum(II) cationic five-coordinate complexes (1-R,R') of the formula [PtR(NHC)(dmphen)(ethene)]CF₃SO₃ (dmphen = 2,9-dimethyl-1,10-phenanthroline), containing in their axial positions an alkyl group R (methyl or octyl) and an imidazole-based NHC-carbene ligand with a substituent R' of variable length (methyl or octyl) on one nitrogen atom. The Pt-carbene bond is stable both in DMSO and in aqueous solvents. In DMSO, a gradual substitution of dmphen and ethene is observed, with the formation of a square planar solvated species. Octanol/water partitioning studies have revealed the order of hydrophobicity of the complexes (1-Oct,Me > 1-Oct,Oct > 1-Me,Oct > 1-Me,Me). Their biological activity was investigated against two pairs of cancer and non-cancer cell lines. The tested drugs were internalized in cancer cells and able to activate the apoptotic pathway. The reactivity of 1-Me,Me with DNA and protein model systems was also studied using UV-vis absorption spectroscopy, fluorescence, and X-ray crystallography. The compound binds DNA and interacts in various ways with the model protein lysozyme. Remarkably, structural data revealed that the complex can bind lysozyme via non-covalent interactions, retaining its five-coordinate geometry.

Synthesis, structure, properties, and cytotoxicity of a (quinoline)RuCp+ complex

A rare example of a structurally characterized metal quinoline complex was prepared using a non-covalent quinoline-based proteasome inhibitor (Quin1), and a related complex bearing an inactive quinoline ligand (Quin2) was also synthesized. The quinolines are prepared by a one-pot procedure involving titanium-catalyzed alkyne iminoamination and are bound to ruthenium by reaction with CpRu(NCMe)₃⁺ PF₆^- in CH₂Cl₂. The arene of the quinoline is η⁶-bonded to the ruthenium metal center. The kinetics of quinoline displacement were investigated, and reactivity with deuterated solvents follows the order acetonitrile > DMSO > water. Quinolines with more methyl groups on the arene are more kinetically stable, and RuCp(Quin1)⁺ PF₆^- (1), which has two methyl groups on the arene, is stable for days in DMSO. In contrast, a very similar complex (2) made with Quin2 having no methyl groups on the arene was readily displaced by DMSO. Both 1 and 2 are stable in 9 : 1 water/DMSO for days with no measurable displacement of the quinoline. The cytotoxicity of the quinolines, their CpRu⁺-complexes, and CpRu(DMSO)₃⁺ PF₆^- was investigated towards two multiple myeloma cell lines: MC/CAR and RPMI 8226. To determine whether the activity of the complexes was related to the nature of the quinoline ligands, two structurally similar quinoline ligands with vastly different biological properties were investigated. Quin1 is a cytotoxic proteasome inhibitor, whereas Quin2 is not a proteasome inhibitor and showed no discernable cytotoxicity. The ruthenium complexes showed poor cellular proteasome inhibition. However, both 1 and 2 showed good cytotoxicity towards RPMI 8226 and MC/CAR, with 1 being slightly more cytotoxic. For example, 1 has a CC₅₀ = 2 μM in RPMI 8226, and 2 has a CC₅₀ = 5 μM for the same cell line. In contrast, CpRu(DMSO)₃⁺ PF₆^- was quite active towards MC/CAR with CC₅₀ = 2.8 μM but showed no discernible cytotoxicity toward RPMI 8226. The mechanism of action responsible for the observed cytotoxicity is not known, but the new Ru(Cp)(Quin)⁺ PF₆^- complexes do not cross-link DNA as found for platinum-based drugs. It is concluded that the Ru(Cp)(Quin)⁺ PF₆^- complexes remain intact in the cellular assays and constitute a new class of cytotoxic metal complexes.

Synthesis and Antiparasitic Activity of New Trithiolato-Bridged Dinuclear Ruthenium(II)-arene-carbohydrate Conjugates

Eight novel carbohydrate-tethered trithiolato dinuclear ruthenium(II)-arene complexes were synthesized using CuAAC ‘click’ (Cu(I)-catalyzed azide-alkyne cycloaddition) reactions, and there in vitro activity against transgenic T. gondii tachyzoites constitutively expressing β-galactosidase (T. gondii β-gal) and in non-infected human foreskin fibroblasts, HFF, was determined at 0.1 and 1 µM. When evaluated at 1 µM, seven diruthenium-carbohydrate conjugates strongly impaired parasite proliferation by >90%, while HFF viability was retained at 50% or more, and they were further subjected to the half-maximal inhibitory concentration (IC50) measurement on T. gondii β-gal. Results revealed that the biological activity of the hybrids was influenced both by the nature of the carbohydrate (glucose vs. galactose) appended on ruthenium complex and the type/length of the linker between the two units. 23 and 26, two galactose-based diruthenium conjugates, exhibited low IC50 values and reduced effect on HFF viability when applied at 2.5 µM (23: IC50 = 0.032 µM/HFF viability 92% and 26: IC50 = 0.153 µM/HFF viability 97%). Remarkably, compounds 23 and 26 performed significantly better than the corresponding carbohydrate non-modified diruthenium complexes, showing that this type of conjugates are a promising approach for obtaining new antiparasitic compounds with reduced toxicity.

Antioxidant conjugated metal complexes and their medicinal applications

Antioxidants are naturally available and man-made substances have the ability to protect cells from damage due to a number of intracellular redox activities. Moreover, Antioxidants such as α-lipoic acid, curcumin and catechin are good anticancer agents. In recent years, the usage of metal complexes as therapeutic agents is gaining importance due to their useful biological properties. Most of the metal ions act as the essential components in building drug molecules that serve as medicines for cancer and neurodegenerative diseases. In particular, metals like copper, gold, ruthenium, and platinum have adequate anticancer properties at both micro- and nano-levels. Hence, conjugation of antioxidants with metals and metal-based compounds results in hybrid bioactive materials with improved anticancer properties. In this chapter, medicinal applications of antioxidant conjugated metal complexes are reviewed and discussed.

The choice of μ-vinyliminium ligand substituents is key to optimize the antiproliferative activity of related diiron complexes

Diiron vinyliminium complexes constitute a large family of organometallics displaying a promising anticancer potential. The complexes [Fe2Cp2(CO)(μ-CO){μ-η1:η3-C(R3)C(R4)CN(R1)(R2)}]CF3SO3 (2a-c, 4a-d) were synthesized, assessed for their behavior in aqueous solutions (D2O solubility, Log Pow, stability in D2O/Me2SO-d6 mixture at 37°C over 48 h) and investigated for their antiproliferative activity against A2780 and A2780cisR ovarian cancer cell lines and the nontumoral one Balb/3T3 clone A31. Cytotoxicity data collected for 50 vinyliminium complexes were correlated with the structural properties (i.e. the different R1-R4 substituents) using the partial least squares methodology. A clear positive correlation emerged between the octanol-water partition coefficient and the relative antiproliferative activity on ovarian cancer cell lines, both of which appear as uncorrelated to the cancer cell selectivity. However, the different effects played by the R1-R4 substituents allow tracing guidelines for the development of novel, more effective compounds. Based on these results, three additional complexes (4p-r) were designed, synthesized and biologically investigated, revealing their ability to hamper thioredoxin reductase enzyme and to induce cancer cell production of reactive oxygen species.

Ruthenium(II)-Dithiocarbazates as Anticancer Agents: Synthesis, Solution Behavior, and Mitochondria-Targeted Apoptotic Cell Death

The reaction of the Ru(PPh₃ )₃ Cl₂ with HL^1-3 -OH (-OH stands for the oxime hydroxyl group; HL¹ -OH=diacetylmonoxime-S-benzyldithiocarbazonate; HL² -OH=diacetylmonoxime-S-(4-methyl)benzyldithiocarbazonate; and HL³ -OH=diacetylmonoxime-S-(4-chloro)benzyl-dithiocarbazonate) gives three new ruthenium complexes [Ru^II (L^1-3 -H)(PPh₃ )₂ Cl] (1-3) (-H stands for imine hydrogen) coordinated with dithiocarbazate imine as the final products. All ruthenium(II) complexes (1-3) have been characterized by elemental (CHNS) analyses, IR, UV-vis, NMR (¹ H, ¹³ C, and ³¹ P) spectroscopy, HR-ESI-MS spectrometry and also, the structure of 1-2 was further confirmed by single crystal X-ray crystallography. The solution/aqueous stability, hydrophobicity, DNA interactions, and cell viability studies of 1-3 against HeLa, HT-29, and NIH-3T3 cell lines were performed. Cell viability results suggested 3 being the most cytotoxic of the series with IC₅₀ 6.9±0.2 μM against HeLa cells. Further, an apoptotic mechanism of cell death was confirmed by cell cycle analysis and Annexin V-FITC/PI double staining techniques. In this regard, the live cell confocal microscopy results revealed that compounds primarily target the mitochondria against HeLa, and HT-29 cell lines. Moreover, these ruthenium complexes elevate the ROS level by inducing mitochondria targeting apoptotic cell death.

Assessing the role of membrane lipids in the action of ruthenium(III) anticancer compounds

This work addresses the possible role of the cell membrane in the molecular mechanism of action of two salan-type ruthenium complexes that were previously shown to be active against human tumor cells, namely [Ru(III)(L1)(PPh₃)Cl] and [Ru(III)(L2)(PPh₃)Cl] (where L1 is 6,6'-(1R,2R)-cyclohexane-1,2-diylbis(azanediyl)bis(methylene)bis(3-methoxyphenol); and L2 is 2,2'-(1R,2R)-cyclohexane-1,2-diylbis(azanediyl)bis(methylene)bis(4-methoxyphenol)). One-component membrane models were first used, a disordered fluid bilayer of dioleoylphosphatodylcholine (DOPC), and an ordered rigid gel bilayer of dipalmitoylphosphatidylcholine. In addition, two quaternary mixtures of phosphatidylcholine, phosphatidylethanolamine, sphingomyelin and cholesterol were used to mimic the lipid composition either of mammalian plasma membrane (1:1:1:1 mol ratio) or of a cancer cell line membrane (36.2:23.6:6.8:33.4 mol ratio). The results show that both salan ligands L1 and L2 bind relatively strongly to DOPC bilayers, but without significantly affecting their structure. The ruthenium complexes have moderate affinity for DOPC. However, their impact on the membranes was notable, leading to a significant increase in the permeability of the lipid vesicles. None of the compounds compromised liposome integrity, as revealed by dynamic light scattering. Fluorescence spectroscopy studies revealed changes in the biophysical properties of all membrane models analyzed in the presence of the two complexes, which promoted an increased fluidity and water penetration into the lipid bilayer in the one-component systems. In the quaternary mixtures, one of the complexes had an analogous effect (increasing water penetration), whereas the other complex reorganized the liquid ordered and liquid disordered domains. Thus, small structural differences in the metal ligands may lead to different outcomes. To better understand the effect of these complexes in cancer cells, the membrane dipole potential was also measured. For both Ru complexes, an increase in the dipole potential was observed for the cancer cell membrane model, while no alteration was detected on the non-cancer plasma membrane model. Our results show that the action of the Ru(III) complexes tested involves changes in the biophysical properties of the plasma membrane, and that it also depends on membrane lipid composition, which is frequently altered in cancer cells when compared to their normal counterparts.

Synthesis, structural characterization and study of antioxidant and anti-PrPSc properties of flavonoids and their rhenium(I)-tricarbonyl complexes

This study aims at the synthesis and initial biological evaluation of novel rhenium-tricarbonyl complexes of 3,3',4',5,7-pentahydroxyflavone (quercetin), 3,7,4΄-trihydroxyflavone (resokaempferol), 5,7-dihydroxyflavone (chrysin) and 4΄,5,7-trihydroxyflavonone (naringenin) as neuroprotective and anti-PrP agents. Resokaempferol was synthesized from 2,2΄,4-trihydroxychalcone by H₂O₂/NaOH. The rhenium-tricarbonyl complexes of the type fac-[Re(CO)₃(Fl)(sol)] were synthesized by reacting the precursor fac-[Re(CO)₃(sol)₃]⁺ with an equimolar amount of the flavonoids (Fl) quercetin, resokaempferol, chrysin and naringenin and the solvent (sol) was methanol or water. The respective Re-flavonoid complexes were purified by semi-preparative HPLC and characterized by spectroscopic methods. Furthermore, the structure of Re-chrysin was elucidated by X-ray crystallography. Initial screening of the neuroprotective properties of these compounds included the in vitro assessment of the antioxidant properties by the DPPH assay as well as the anti-lipid peroxidation of linoleic acid in the presence of AAPH and their ability to inhibit soybean lipoxygenase. From the above studies, it was concluded that the complexes' properties are mainly correlated with the structural characteristics and the presence of the flavonoids. The flavonoids and their respective Re-complexes were also tested in vitro for their ability to inhibit the formation and aggregation of the amyloid-like abnormal prion protein, PrP^Sc, by employing the real-time quaking-induced conversion assay with recombinant PrP seeded with cerebrospinal fluid from patients with Creutzfeldt-Jakob disease. All the compounds blocked de novo abnormal PrP formation and aggregation.

A new strategy for improving cytotoxicity of a copper complex toward metastatic melanoma cells unveiled by EPR spectroscopy†

A novel strategy of improving cytotoxicity against metastatic melanoma cells using an oxindolimine copper(ii) complex immobilized and dimerized on a modified Polyhedral Oligomeric Silsesquioxane (POSS) matrix was developed, as revealed by electron paramagnetic resonance (EPR) spectroscopy. An assured correlation between continuous-wave (CW) and pulsed EPR spectroscopies provided a complete characterization of the actual active species, its coordination environment, as well as the efficiency/selectivity of the bioconjugate materials.

An oxindolimine-copper(ii) complex with antitumor properties was immobilized in a silica matrix, and verified to be more active and selective due the formation of a dinuclear species, unveiled by continuous wave and pulsed EPR spectroscopy.

Competitive binding studies of the nucleosomal histone targeting drug, [Ru(η6-p-cymene)Cl2(pta)] (RAPTA-C), with oligonucleotide-peptide mixtures

Protein crystallography and biochemical assays reveal that the organometallic drug, [Ru(η⁶-p-cymene)Cl₂(pta)] (RAPTA-C), preferentially binds to nucleosomal histone proteins in chromatin. To better understand the binding mechanism we report here a mass spectrometric-based competitive binding study between a model peptide from the acidic patch region of the H2A histone protein (the region where RAPTA-C is known to bind) and an oligonucleotide. In contrast to the protein crystallography and biochemical assays, RAPTA-C preferentially binds to the oligonucleotide, confirming that steric factors, rather than electronic effects, primarily dictate binding of RAPTA-C to histone proteins within the nucleosome.

The Strange Case: The Unsymmetric Cisplatin-Based Pt(IV) Prodrug [Pt(CH3COO)Cl2(NH3)2(OH)] Exhibits Higher Cytotoxic Activity with respect to Its Symmetric Congeners due to Carrier-Mediated Cellular Uptake

The biological behavior of the axially unsymmetric antitumor prodrug (OC-6-44)-acetatodiamminedichloridohydroxidoplatinum(IV), 2, was deeply investigated and compared with that of analogous symmetric Pt(IV) complexes, namely, dihydroxido 1 and diacetato 3, which have a similar structure. The complexes were tested on a panel of human tumor cell lines. Complex 2 showed an anomalous higher cytotoxicity (similar to that of cisplatin) with respect to their analogues 1 and 3. Their reduction potentials, reduction kinetics, lipophilicity, and membrane affinity are compared. Cellular uptake and DNA platination of Pt(IV) complexes were deeply investigated in the sensitive A2780 human ovarian cancer cell line and in the corresponding resistant A2780cisR subline. The unexpected activity of 2 appears to be related to its peculiar cellular accumulation and not to a different rate of reduction or a different efficacy in DNA platination and/or efficiency in apoptosis induction. Although the exact mechanism of cell uptake is not fully deciphered, a series of naïve experiments indicates an energy-dependent, carrier-mediated transport: the organic cation transporters (OCTs) are the likely proteins involved.

Synthesis, Crystallographic Structure, Theoretical Analysis, Molecular Docking Studies, and Biological Activity Evaluation of Binuclear Ru(II)-1-Naphthylhydrazine Complex

Ruthenium(II)-arene complexes have gained significant research interest due to their possible application in cancer therapy. In this contribution two new complexes are described, namely [{RuCl(η⁶-p-cymene)}₂(μ-Cl)(μ-1-N,N'-naphthyl)]X (X = Cl, 1; PF₆, 2), which were fully characterized by IR, NMR, and elemental microanalysis. Furthermore, the structure of 2 in the solid state was determined by a single crystal X-ray crystallographic study, confirming the composition of the crystals as 2·2MeOH. The Hirshfeld surface analysis was employed for the investigation of interactions that govern the crystal structure of 2·2MeOH. The structural data for 2 out of 2·2MeOH was used for the theoretical analysis of the cationic part [{RuCl(η⁶-p-cymene)}₂(μ-Cl)(μ-1-N,N'-naphthyl)]⁺ (2a) which is common to both 1 and 2. The density functional theory, at B3LYP/6-31+G(d,p) basis set for H, C, N, and Cl atoms and LanL2DZ for Ru ions, was used for the optimization of the 2a structure. The natural bond orbital and quantum theory of atoms in molecules analyses were employed to quantify the intramolecular interactions. The reproduction of experimental IR and NMR spectra proved the applicability of the chosen level of theory. The binding of 1 to bovine serum albumin was examined by spectrofluorimetry and molecular docking, with complementary results obtained. Compound 1 acted as a radical scavenger towards DPPH^• and HO^• radicals, along with high activity towards cancer prostate and colon cell lines.

Potent Ruthenium-Ferrocene Bimetallic Antitumor Antiangiogenic Agent That Circumvents Platinum Resistance: From Synthesis and Mechanistic Studies to In Vivo Evaluation in Zebrafish

Emergence of resistance in cancer cells and dose-limiting side effects severely limit the widespread use of platinum (Pt) anticancer drugs. Multi-action hybrid anticancer agents that are constructed by merging two or more pharmacophores offer the prospect of circumventing issues of Pt drugs. Herein, we report the design, synthesis, and in-depth biological evaluation of a ruthenium-ferrocene (Ru-Fc) bimetallic agent [(η6-p-cymene)Ru(1,1,1-trifluoro-4-oxo-4-ferrocenyl-but-2-en-2-olate)Cl] and its five analogues. Along with aquation/anation chemistry, we evaluated the in vitro antitumor potency, Pt cross-resistance profile, and in vivo antiangiogenic properties. A structure activity analysis was performed to understand the impact of Fc, CF3, and p-cymene groups on the anticancer potency of the Ru-Fc hybrid. Finally, in addition to assessing cellular uptake and intracellular distribution, we demonstrated that the Ru-Fc hybrid binds to nucleophilic biomolecules and produces reactive oxygen species, which causes mitochondrial dysfunction and induces ER stress, leading to poly(ADP-ribose) polymerase-mediated necroptotic cell death.

Development of Mitochondria Targeting AIE-Active Cyclometalated Iridium Complexes as Potent Antimalarial Agents

The emergence of resistance to conventional antimalarial treatments remains a major cause for concern. New drugs that target the distinct development stages of Plasmodium parasites are required to address this risk. Herein, water-soluble aggregation-induced emission active cyclometalated iridium(III) polypyridyl complexes (Ir1-Ir12) are developed for the elimination of malaria parasites. Remarkably, these complexes show potent antimalarial activity in low nanomolar range against 3D7 (chloroquine and artemisinin sensitive strain), RKL9 (chloroquine resistant strain), and R539T (artemisinin resistant strains) strains of Plasmodium falciparum with faster killing rate of malaria parasites. Concomitantly, these complexes exhibit efficient in vivo antimalarial activity against both the asexual and gametocyte stages of Plasmodium berghei malaria parasite, suggesting promising transmission-blocking potential. The complexes tend to localize into mitochondria of P. falciparum determined by image and cell-based assay. The mechanistic studies reveal that these complexes exert their antimalarial activity by increasing reactive oxygen species levels and disrupting its mitochondrial membrane potential. Furthermore, the mitochondrial-dependent antimalarial activity of these complexes is confirmed in yeast model. Thus, this study for the first time highlights the potential role of targeting P. falciparum mitochondria by iridium complexes in discovering and developing the next-generation antimalarial agents for treating multidrug resistant malaria parasites.

New multifunctional Ru(II) organometallic compounds show activity against Trypanosoma brucei and Leishmania infantum

Human African trypanosomiasis (sleeping sickness) and leishmaniasis are prevalent zoonotic diseases caused by genomically related trypanosomatid protozoan parasites (Trypanosoma brucei and Leishmania spp). Additionally, both are co-endemic in certain regions of the world. Only a small number of old drugs exist for their treatment, with most of them sharing poor safety, efficacy, and pharmacokinetic profiles. In this work, new multifunctional Ru(II) ferrocenyl compounds were rationally designed as potential agents against these trypanosomatid parasites by including in a single molecule 1,1'-bis(diphenylphosphino)ferrocene (dppf) and two bioactive bidentate ligands: 8-hydroxyquinoline derivatives (8HQs) and polypyridyl ligands (NN). Three [Ru(8HQs)(dppf)(NN)](PF₆) compounds were synthesized and fully characterized. They showed in vitro activity on bloodstream Trypanosoma brucei (IC₅₀ 140-310 nM) and on Leishmania infantum promastigotes (IC₅₀ 3.0-4.8 μM). The compounds showed good selectivity towards T. brucei in respect to J774 murine macrophages as mammalian cell model (SI 15-38). Changing hexafluorophosphate counterion by chloride led to a three-fold increase in activity on both parasites and to a two to three-fold increase in selectivity towards the pathogens. The compounds affect in vitro at least the targets of the individual bioactive moieties included in the new chemical entities: DNA and generation of ROS. The compounds are stable in solution and are more lipophilic than the free bioactive ligands. No clear correlation between lipophilicity, interaction with DNA or generation of ROS and activity was detected, which agrees with their overall similar anti-trypanosoma potency and selectivity. These compounds are promising candidates for further drug development.

Photocatalytic Pt(IV)-Coordinated Carbon Dots for Precision Tumor Therapy

Rapid, efficient, and precise cancer therapy is highly desired. Here, this work reports solvothermally synthesized photoactivatable Pt(IV)-coordinated carbon dots (Pt-CDs) and their bovine serum albumin (BSA) complex (Pt-CDs@BSA) as a novel orange light-triggered anti-tumor therapeutic agent. The homogeneously distributed Pt(IV) in the Pt-CDs (Pt: 17.2 wt%) and their carbon cores with significant visible absorption exhibit excellent photocatalytic properties, which not only efficiently releases cytotoxic Pt(II) species but also promotes hydroxy radical generation from water under orange light. When triggered with a 589 nm laser, Pt-CDs@BSA possesses the ultrastrong cancer cell killing capacities of intracellular Pt(II) species release, hydroxyl radical generation, and acidification, which induce powerful immunogenic cell death. Activation of Pt-CDs@BSA by a single treatment with a 589 nm laser effectively eliminated the primary tumor and inhibited distant tumor growth and lung metastasis. This study thus presents a new concept for building photoactivatable Pt(IV)-enriched nanodrug-based CDs for precision cancer therapy.

Dichloro[N-[(η6-phenyl)methyl]-4-(1-(3,5,5,8,8-pentamethyl-5,6,7,8tetrahydronaphthalen-2-yl)vinyl)benzamide](1,3,5-triaza-7-phosphatricyclo [3.3.1.13,7]decane-κP7)ruthenium

Bexarotene-tethered RuII(arene) compounds with 1,3,5-triaza-7-phosphatricyclo[3.3.1.1]decane (PTA) were prepared as an analog of RAPTA antitumor complexes in order to evaluate their in vitro antiproliferative activity against human cancer cell lines.

New Nucleic Base-Tethered Trithiolato-Bridged Dinuclear Ruthenium(II)-Arene Compounds: Synthesis and Antiparasitic Activity

Aiming toward compounds with improved anti-Toxoplasma activity by exploiting the parasite auxotrophies, a library of nucleobase-tethered trithiolato-bridged dinuclear ruthenium(II)-arene conjugates was synthesized and evaluated. Structural features such as the type of nucleobase and linking unit were progressively modified. For comparison, diruthenium hybrids with other type of molecules were also synthesized and assessed. A total of 37 compounds (diruthenium conjugates and intermediates) were evaluated in a primary screening for in vitro activity against transgenic Toxoplasma gondii tachyzoites constitutively expressing β-galactosidase (T. gondii β-gal) at 0.1 and 1 µM. In parallel, the cytotoxicity in non-infected host cells (human foreskin fibroblasts, HFF) was determined by alamarBlue assay. Twenty compounds strongly impairing parasite proliferation with little effect on HFF viability were subjected to T. gondii β-gal half maximal inhibitory concentration determination (IC₅₀) and their toxicity for HFF was assessed at 2.5 µM. Two promising compounds were identified: 14, ester conjugate with 9-(2-oxyethyl)adenine, and 36, a click conjugate bearing a 2-(4-(hydroxymethyl)-1H-1,2,3-triazol-1-yl)methyl substituent, with IC₅₀ values of 0.059 and 0.111 µM respectively, significantly lower compared to pyrimethamine standard (IC₅₀ = 0.326 µM). Both 14 and 36 exhibited low toxicity against HFF when applied at 2.5 µM and are candidates for potential treatment options in a suitable in vivo model.

Ruthenium-based antitumor drugs and delivery systems from monotherapy to combination therapy

Ruthenium complex is an important compound group for antitumor drug research and development. NAMI-A, KP1019, TLD1433 and other ruthenium complexes have entered clinical research. In recent years, the research on ruthenium antitumor drugs has not been limited to single chemotherapy drugs; other applications of ruthenium complexes have emerged such as in combination therapy. During the development of ruthenium complexes, drug delivery forms of ruthenium antitumor drugs have also evolved from single-molecule drugs to nanodrug delivery systems. The review summarizes the following aspects: (1) ruthenium complexes from monotherapy to combination therapy, including the development of single-molecule compounds, carrier nanomedicine, and self-assembly of carrier-free nanomedicine; (2) ruthenium complexes in the process of ADME in terms of absorption, distribution, metabolism and excretion; (3) the applications of ruthenium complexes in combination therapy, including photodynamic therapy (PDT), photothermal therapy (PTT), photoactivated chemotherapy (PACT), immunotherapy, and their combined application; (4) the future prospects of ruthenium-based antitumor drugs.

Integrative Metallomics Studies of Toxic Metal(loid) Substances at the Blood Plasma–Red Blood Cell–Organ/Tumor Nexus

Globally, an estimated 9 million deaths per year are caused by human exposure to environmental pollutants, including toxic metal(loid) species. Since pollution is underestimated in calculations of the global burden of disease, the actual number of pollution-related deaths per year is likely to be substantially greater. Conversely, anticancer metallodrugs are deliberately administered to cancer patients, but their often dose-limiting severe adverse side-effects necessitate the urgent development of more effective metallodrugs that offer fewer off-target effects. What these seemingly unrelated events have in common is our limited understanding of what happens when each of these toxic metal(loid) substances enter the human bloodstream. However, the bioinorganic chemistry that unfolds at the plasma/red blood cell interface is directly implicated in mediating organ/tumor damage and, therefore, is of immediate toxicological and pharmacological relevance. This perspective will provide a brief synopsis of the bioinorganic chemistry of AsIII, Cd2+, Hg2+, CH3Hg+ and the anticancer metallodrug cisplatin in the bloodstream. Probing these processes at near-physiological conditions and integrating the results with biochemical events within organs and/or tumors has the potential to causally link chronic human exposure to toxic metal(loid) species with disease etiology and to translate more novel anticancer metal complexes to clinical studies, which will significantly improve human health in the 21st century.

Biomolecular Interactions of Cytotoxic Ruthenium Compounds with Thiosemicarbazone or Benzothiazole Schiff Base Chelates

Herein we illustrate the formation and characterization of new paramagnetic ruthenium compounds, trans-P-[RuCl(PPh3 )2 (pmt)]Cl (1) (Hpmt=1-((pyridin-2-yl)methylene)thiosemicarbazide), trans-P-[RuCl(PPh3 )2 (tmc)]Cl (2) (Htmc=1-((thiophen-2-yl)methylene)thiosemicarbazide) and a diamagnetic ruthenium complex, cis-Cl, trans-P-[RuCl2 (PPh3 )2 (btm)] (3) (btm=2-((5-hydroxypentylimino)methyl)benzothiazole). Agarose gel electrophoresis experiments of the metal compounds illustrated dose-dependent binding to gDNA by 1-3, while methylene blue competition assays suggested that 1 and 2 are also DNA intercalators. Assessment of the effects of the compounds on topoisomerase function indicated that 1-3 are capable of inhibiting topoisomerase I activity in terms of the ability to nick supercoiled plasmid DNA. The cytotoxic activities of the metal complexes were determined against a range of cancer cell lines versus a non-tumorigenic control cell line, and the complexes were, in general, more cytotoxic towards the cancer cells, displaying IC50 values in the low micromolar range. Time-dependent stability studies showed that in the presence of strong nucleophilic species (such as DMSO), the chloride co-ligands of 1-3 are rapidly substituted by the former as proven by the suppression of the substitution reactions in the presence of an excess amount of chloride ions. The metal complexes are significantly stable in both DCM and an aqueous phosphate buffer containing 2 % DMSO.

Metallo-Drugs in Cancer Therapy: Past, Present and Future

Cancer treatments which include conventional chemotherapy have not proven very successful in curing human malignancies. The failures of these treatment modalities include inherent resistance, systemic toxicity and severe side effects. Out of 50% patients administrated to chemotherapy, only 5% survive. For these reasons, the identification of new drug designs and therapeutic strategies that could target cancer cells while leaving normal cells unaffected still continues to be a challenge. Despite advances that have led to the development of new therapies, treatment options are still limited for many types of cancers. This review provides an overview of platinum, copper and ruthenium metal based anticancer drugs in clinical trials and in vitro/in vivo studies. Presumably, copper and ruthenium complexes have greater potential than Pt(II) complexes, showing reduced toxicity, a new mechanism of action, a different spectrum of activity and the possibility of non-cross-resistance. We focus the discussion towards past, present and future aspects.

Antitumor effects of new glycoconjugated PtII agents dual-targeting GLUT1 and Pgp proteins

A novel and highly efficient dual-targeting Pt^II system was designed to improve the drug delivery capacity and selectivity in cancer treatment. The dual-targeting monofunctional Pt^II complexes (1-8) having glycosylated pendants as tridentated ligand were achieved by introducing glycosylation modification in the thioaminocarbazone compounds with potential lysosomal targeting ability. The structures and stability of 1-8 were further established by various techniques. Molecular docking studies showed that 2 was efficiently docked into glucose transporters protein 1 (GLUT1) and P-glycoprotein (Pgp) proteins with the optimal CDocker-interaction-energy of -64.84 and -48.85 kcal mol^-1. Complex 2 with higher protein binding capacity demonstrated significant and broad-spectrum antitumor efficacy in vitro, even exhibiting a half maximal inhibitory concentration (IC₅₀) value (∼10 μM) than cisplatin (∼17 μM) against human lung adenocarcinoma cells (A549). The inhibitor experiment revealed GLUT-mediated uptake of 2, and the subcellular localization experiment in A549 also proved that 2 could be localized in the lysosome, thereby causing cell apoptosis. Moreover, cellular thermal shift assay (CETSA) confirmed the binding of 2 with the target proteins of GLUT1 and Pgp. The above results indicated that 2 represents a potential anticancer candidate with dual-targeting functions.

Platinum(IV) Complexes of the 1,3,5-Triamino Analogue of the Biomolecule Cis-Inositol Designed as Innovative Antineoplastic Drug Candidates

Metal complexes occupy a special place in the field of treatment and diagnostics. Their main advantages stem from the possibility of fine-tuning their thermodynamic properties and kinetic behavior in the biological milieu by applying different approaches such as properly constructed inner coordination sphere, appropriate choice of ligands, metal oxidation state, redox potential, etc., which are specific to these compounds. Here we discuss the design and synthesis of two octahedral cationic Pt(IV) complexes of the tridentate ligand all-cis-2,4,6-triaminocyclohexane-1,3,5-triol (taci) with composition, fac-[Pt(taci)I3]+, 1 and bis-[Pt(taci)2]4+, 2 as well as the potential for their application as antineoplastic agents. The complexes have been isolated in a solid state as: fac-[Pt(taci)I3]I·3H2O (1A), fac-[Pt(taci)I3]I (1B), fac-[Pt(taci)I3]I·2DMF (1C), bis-[Pt(taci)2](CO3)2·6H2O (2A) by changing the acidity of the reaction systems, the molar ratios of the reagents and the counterions, and by re-crystallization. The ligand taci is coordinated through the NH2-groups, each molecule occupying three coordination places in the inner coordination sphere of Pt(IV). Monitoring of the hydrolysis processes of 1A and 2A at different acidity showed that while 2A remained stable over the study period, the I--ions in 1A were successively substituted, with the main product under physiologically mimetic conditions being fac,cis-[Pt(taci)I(OH)2]+ (h2). The antiproliferative tests involved eight cancer cell models, among which chemosensitive (derived from leukemias and solid tumors) and chemoresistant human Acute myeloid leukemia lines (HL-60/Dox, HL-60/CDDP), as well as the non-malignant kidney' cells HEK-293T showed that the complexes 1A and 2A are characterized by a fundamentally different profile of chemosensitivity and spectrum of cytotoxic activity compared to cisplatin. The new Pt(IV) complexes were shown to be more effective in selectively inhibiting the proliferation of human malignant cells compared to cisplatin. Remarkable activity was recorded for 1A, which showed an effect (IC50 = 8.9 ± 2.4) at more than 16-fold lower concentration than cisplatin (IC50 = 144.4 ± 9.8) against the resistant cell line HL-60/CDDP. In parallel, 1A exhibited virtually the same cytotoxic effect against the parental HL-60 cells (IC50 = 9.0 ± 1.2), where cisplatin displays comparable chemosensitivity (IC50 = 8.3 ± 0.8). The determined resistance indices (RI~1) show unequivocally that the resistant lines are sensitive to both compounds tested; therefore, they are capable of overcoming the mechanisms of cisplatin resistance. The structural features of these compounds and their promising pharmacological properties justify their inclusion in the group of "non-classical metal-based antitumor compounds" and are a prerequisite for the admission of alternative mechanisms of action.

Design and Syntheses of Ruthenium ENE (E = S, Se) Pincer Complexes: A Versatile System for Catalytic and Biological Applications

This report describes synthesis of two ruthenium(II) ENE pincer complexes (E = S, C1 and E = Se, C2 ) by the reaction of bis(2-(phenylchalcogenyl)ethyl)amine ( L1 , L2 ) with RuCl 2 (PPh 3 ) 3 . The complexes were characterized with the help of 1 H and 13 C{ 1 H} NMR, FTIR, HRMS, cyclic voltammetry and elemental analysis techniques. The structure and bonding mode of ligand with ruthenium in C2 was established with the help of single crystal X-ray diffraction. The complex showed distorted octahedral geometry with two chlorine atoms trans to each other. The Ru-Se bond distances (Å) are 2.4564(3)-2.4630(3), Ru-N distance is 2.181(2), Ru-P distance is 2.2999(6), and Ru-Cl distances are 2.4078(6)-2.4314(6). The complexes showed good to excellent catalytic activity for the N -alkylation of 1,2-phenylenediamine with benzyl alcohol derivatives to synthesize 1,2-disubstituted benzimidazole derivatives. The complexes were also found to be efficient for aerobic oxidation of benzyl alcohols to corresponding aldehydes which are precursors to the bisimines generated in situ during the synthesis of 1,2-disubstituted benzimidazole derivatives. Complex C2 where selenium is coordinated with ruthenium was found to be more efficient as compared to sulfur coordinated ruthenium complex C1 . Since ruthenium complexes are getting increasing attention for developing new anticancer agents, the preliminary studies like binding behavior of both the complexes towards CT-DNA were studied by competitive binding with ethidium bromide (EthBr) using emission spectroscopy. In addition, the interactions of C1-C2 were also studied with bovine serum albumin (BSA) using steady state fluorescence quenching and synchronous fluorescence studies. A good stability of Ru(II) state was observed by cyclic voltammetric studies of C1-C2 . Overall these molecules are good examples of bio-organometallic systems for catalytic and biological applications.