Enhancement of Selectivity of an Organometallic Anticancer Agent by Redox Modulation

Iminoamido chelated iridium(III) and ruthenium(II) anticancer complexes with mitochondria-targeting ability and potential to overcome cisplatin resistance

A diverse set of neutral half-sandwich iminoamido iridium and ruthenium organometallic complexes is synthesized through the utilization of Schiff base pro-ligands with N˄N donors. Notably, these metal complexes with varying leaving groups (Cl- or OAc-) are formed by employing different quantities of the deprotonating agent NaOAc, and exhibit promising cytotoxicity against various cancer cell lines such as A549 and cisplatin-resistant A549/DDP lung cancer cells, as well as HeLa cells, with IC50 values spanning from 9.26 to 15.98 μM. Cytotoxicity and anticancer selectivity (SI: 1.9-2.4) of these metal complexes remain unaffected by variations in the metal center, leaving group, and ligand substitution. Further investigations reveal that these metal complexes specifically target mitochondria, leading to the depolarization of the mitochondrial membrane and instigating the production of intracellular reactive oxygen species. Furthermore, the metal complexes are found to induce late apoptosis and disrupt the cell cycle, leading to G2/M cell cycle arrest specifically in A549 cancer cells. In light of these findings, it is evident that the primary mechanism contributing to the anticancer effectiveness of these metal complexes is the redox pathway.

Cu(II) flavonoids as potential photochemotherapeutic agents

Flavonoids, naturally derived polyphenolic compounds, have received significant attention due to their remarkable biochemical properties that offer substantial health benefits to humans. In this work, a series of six Cu(II) flavonoid complexes of the formulation [Cu(L1)(L2)](ClO4) where L1 is 3-hydroxy flavone (HF1, 1 and 4), 4-fluoro-3-hydroxy flavone (HF2, 2 and 5), and 2,6-difluoro-3-hydroxy flavone (HF3, 3 and 6); L2 is 1,10-phenanthroline (phen, 1-3) and 2-(anthracen-1-yl)-1H-imidazo[4,5-f][1,10]phenanthroline (aip, 4-6) were successfully synthesized, fully characterized and also evaluated for their in vitro photo-triggered cytotoxicity in cancer cells. The single-crystal X-ray diffraction structure of complex 2 shows square pyramidal geometry around the Cu(II) center. The complexes 1-6 showed quasi-reversible cyclic voltammetric responses for the Cu(II)/Cu(I) couple at ∼-0.230 V with a very large ΔEp value of ∼350-480 mV against the Ag/AgCl reference electrode in DMF-0.1 M tetrabutylammonium perchlorate (TBAP) at a scan rate of 50 mV s-1. The complexes were found to have considerable binding propensity for human serum albumin (HSA) and calf thymus DNA (ct-DNA). The complexes displayed remarkable dose-dependent photocytotoxicity in visible light (400-700 nm) in both A549 (human lung cancer) and MCF-7 (human breast cancer) cell lines while remaining significantly less toxic in darkness. They were found to be much less toxic to HPL1D (immortalized human peripheral lung epithelial) normal cells compared to A549 and MCF-7 cancer cells. Upon exposure to visible light, they generate reactive oxygen species, which are thought to be the main contributors to the death of cancer cells. In the presence of visible light, the complexes predominantly elicit an apoptotic mode of cell death. Complex 6 preferentially localizes in the mitochondria of A549 cells.

Mitochondria-targeted neutral and cationic iridium(III) anticancer complexes chelating simple hybrid sp2-N/sp3-N donor ligands

Most platinum group-based cyclometalated neutral and cationic anticancer complexes with the general formula [(C^N)2Ir(XY)]0/+ (neutral complex: XY = bidentate anionic ligand; cationic complex: XY = bidentate neutral ligand) are notable owing to their intrinsic luminescence properties, good cell permeability, interaction with some biomolecular targets and unique mechanisms of action (MoAs). We herein synthesized a series of neutral and cationic amine-imine cyclometalated iridium(III) complexes using Schiff base ligands with sp2-N/sp3-N N^NH2 chelating donors. The cyclometalated iridium(III) complexes were identified by various techniques. They were stable in aqueous media, displayed moderate fluorescence and exhibited affinity toward bovine serum albumin (BSA). The complexes demonstrated promising cytotoxicity against lung cancer A549 cells, cisplatin-resistant lung cancer A549/DDP cells, cervical carcinoma HeLa cells and human liver carcinoma HepG2 cells, with IC50 values ranging from 9.98 to 19.63 μM. Unfortunately, these complexes had a low selectivity (selectivity index: 1.62-1.98) towards A549 cells and BEAS-2B normal cells. The charge pattern of the metal center (neutral or cationic) and ligand substituents showed little influence on the cytotoxicity and selectivity of these complexes. The study revealed that these complexes could target mitochondria, cause depolarization of the mitochondrial membrane, and trigger the production of intracellular ROS. Additionally, the complexes were observed to induce late apoptosis and perturb the cell cycle in the G2/M or S phase in A549 cells. Based on these results, it appears that the anticancer efficacy of these complexes was predominantly attributed to the redox mechanism.

Potent Half-Sandwich 16-/18-Electron Iridium(III) and Ruthenium(II) Anticancer Complexes with Readily Available Amine-Imine Ligands

The synthesis and biological evaluation of stable 16-electron half-sandwich complexes have remained scarce. We herein present the different coordination modes (16-electron or 18-electron) between half-sandwich iridium(III) complexes and ruthenium(II) complexes derived from the same amine-imine ligands chelating hybrid sp3-N/sp2-N donors. The 16-electron iridium(III) and 18-electron ruthenium(II) complexes with different counteranions were obtained and identified by various techniques. The promising cytotoxicity of these complexes against A549 lung cancer cells, cisplatin-resistant A549/DPP cells, cervical carcinoma HeLa cells, and human hepatocellular liver carcinoma HepG2 cells was observed with IC50 values ranging from 5.4 to 16.3 μM. Moreover, these complexes showed a certain selectivity (selectivity index: 2.1-3.7) toward A549 cells and BEAS-2B normal cells. The variation of metal center, counteranion, 16/18-electron coordination mode, and ligand substituents showed little influence on the cytotoxicity and selectivity of these complexes. The mechanism of action study showed that these complexes could target mitochondria, induce the depolarization of the mitochondrial membrane, and promote the generation of intracellular reactive oxygen species (ROS). Further, the induction of cell apoptosis and the perturbation of the cell cycle in the G0/G1 phase were also observed for these complexes. Overall, it seems that the redox mechanism dominated the anticancer efficacy of these complexes.

Buthionine sulfoximine and chemoresistance in cancer treatments: a systematic review with meta-analysis of preclinical studies

Buthionine sulfoximine (BSO) is a synthetic amino acid that blocks the biosynthesis of reduced glutathione (GSH), an endogenous antioxidant cellular component present in tumor cells. GSH levels have been associated with tumor cell resistance to chemotherapeutic drugs and platinum compounds. Consequently, by depleting GSH, BSO enhances the cytotoxicity of chemotherapeutic agents in drug-resistant tumors. Therefore, the aim of this study was to conduct a systematic review with meta-analysis of preclinical studies utilizing BSO in cancer treatments. The systematic search was carried out using the following databases: PubMed, Web of Science, Scopus, and EMBASE up until March 20, 2023, in order to collect preclinical studies that evaluated BSO, alone or in association, as a strategy for antineoplastic therapy. One hundred nine investigations were found to assess the cytotoxic potential of BSO alone or in combination with other compounds. Twenty-one of these met the criteria for performing the meta-analysis. The evidence gathered indicated that BSO alone exhibits cytotoxic activity. However, this compound is generally used in combination with other antineoplastic strategies, mainly chemotherapy ones, to improve cytotoxicity to carcinogenic cells and treatment efficacy. Finally, this review provides important considerations regarding BSO use in cancer treatment conditions, which might optimize future studies as a potential adjuvant antineoplastic therapeutic tool.

Half-Sandwich Iridium(III), Rhodium(III), and Ruthenium(II) Complexes Chelating Hybrid sp2-N/sp3-N Donor Ligands to Achieve Improved Anticancer Selectivity

The biological efficacy of half-sandwich platinum group organometallic complexes of the formula [(η5-Cpx)/(η6-arene)M(XY)Cl]0/+ (XY = bidentate ligands; Cpx = functionalized cyclopentadienyl; M = Ir, Rh, Ru, Os) has received considerable attention due to the significance of the metal center, chelating ligand, and Cpx/arene moieties in defining their anticancer potency and selectivity. With a facile access to the BIAN-derived imine-amine ligands using alkylaluminum as the reductant, we herein described the preparation and characterization of 16 half-sandwich Ir(III), Rh(III), and Ru(II) complexes chelating the hybrid sp2-N/sp3-N donor ligand. A nonplanar five-member metallacycle was confirmed by X-ray single-crystal structures of Ir1-Ir3, Ir7, Rh1, Ru1, and Ru4. The attempt to prepare imine-amido complexes using a base as the deprotonating agent led to the mixture of imine-amine complexes, within which the leaving group Cl- was displaced, and 16-electron imine-amido complexes without Cl-. The half-sandwich imine-amine complexes in this system underwent rapid hydrolysis in aqueous solution, exhibited weak photoluminescence, and showed the ability of binding to CT-DNA and BSA. The cytotoxicity of all imine-amine complexes against A549 lung cancer cell lines, HeLa cervical cancer cell lines, and 4T1 mouse breast cancer cells was determined by an MTT assay. The IC50 values of these complexes were in a range of 5.71-67.28 μM. Notably, most of these complexes displayed improved selectivity toward A549 cancer cells versus noncancerous BEAS-2B cells in comparison with the corresponding α-diimine complexes chelating the sp2-N/sp2-N donor ligand, which have been shown no selectivity in our previous report. The anticancer selectivity of these complexes appeared to be related to the redox-based mechanism including the catalytic oxidation of NADH to NAD+, reactive oxygen species (ROS) generation, and depolarization of the mitochondrial membrane. Further, inducing apoptosis of these complexes in A549 cancer cells and BEAS-2B normal cells also correlated with their anticancer selectivity, indicating the apoptosis mode of cell death in this system. In addition, these complexes could enter A549 cells via energy-dependent pathway and were able to impede the in vitro migration of A549 cells.

Ru(II) CONTAINING PHOTOSENSITIZERS FOR PHOTODYNAMIC THERAPY: A CRITIQUE ON REPORTING AND AN ATTEMPT TO COMPARE EFFICACY

Ruthenium(II)-based coordination complexes have emerged as photosensitizers (PSs) for photodynamic therapy (PDT) in oncology as well as antimicrobial indications and have great potential. Their modular architectures that integrate multiple ligands can be exploited to tune cellular uptake and subcellular targeting, solubility, light absorption, and other photophysical properties. A wide range of Ru(II) containing compounds have been reported as PSs for PDT or as photochemotherapy (PCT) agents. Many studies employ a common scaffold that is subject to systematic variation in one or two ligands to elucidate the impact of these modifications on the photophysical and photobiological performance. Studies that probe the excited state energies and dynamics within these molecules are of fundamental interest and are used to design next-generation systems. However, a comparison of the PDT efficacy between Ru(II) containing PSs and 1st or 2nd generation PSs, already in clinical use or preclinical/clinical studies, is rare. Even comparisons between Ru(II) containing molecular structures are difficult, given the wide range of excitation wavelengths, power densities, and cell lines utilized. Despite this gap, PDT dose metrics quantifying a PS's efficacy are available to perform qualitative comparisons. Such models are independent of excitation wavelength and are based on common outcome parameters, such as the photon density absorbed by the Ru(II) compound to cause 50% cell kill (LD50) based on the previously established threshold model. In this focused photophysical review, we identified all published studies on Ru(II) containing PSs since 2005 that reported the required photophysical, light treatment, and in vitro outcome data to permit the application of the Photodynamic Threshold Model to quantify their potential efficacy. The resulting LD50 values range from less than 1013 to above 1020 [hν cm-3], indicating a wide range in PDT efficacy and required optical energy density for ultimate clinical translation.

Copper(ii) curcumin complexes for endoplasmic reticulum targeted photocytotoxicity

Three copper(ii) complexes viz. [Cu(cur)(L)(ClO4)] (1-3), where Hcur is curcumin and L is 1,10-phenanthroline (phen, 1), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq, 2), or dipyrido[3,2-a:2',3'-c]phenazine (dppz, 3) were synthesized, fully characterized by various physicochemical methods and evaluated for their light-assisted chemotherapeutic potential. The complexes [Cu(acac)(L)(ClO4)] (4-6), where Hacac is acetylacetone and L is phen (in 4), dpq (in 5) and dppz (in 6), were synthesized and used as controls. The solid state structures of complexes 4 and 5 were determined by single crystal X-ray diffraction. The curcumin complexes (1-3) were redox inactive at the copper centre, whereas the acetylacetonato complexes (4-6) displayed a Cu(ii)/Cu(i) couple at ∼0.1 V vs. Ag/AgCl reference electrode in DMF. Complexes 1-3 showed an intense curcumin-based band at ∼440 nm in DMF-Tris-HCl buffer (pH = 7.2) (1 : 9 v/v) which masks the copper based d-d band. The complexes bind to human serum albumin (HSA) with moderate efficacy. They also displayed significant binding affinity for calf-thymus (CT) DNA. The lipophilic curcumin complexes show remarkable visible light induced cytotoxicity (IC50 = ∼4 μM) with high phototoxic indices (PI) with low dark toxicity in human cervical carcinoma (HeLa) and human lung carcinoma (A549) cells. The corresponding acetylacetonato controls (4-6) did not show significant cytotoxicity in the dark or light. DCFDA and annexin V-FITC/PI assays using flow cytometry confirm the induction of significant apoptosis in cancer cells via generation of cytotoxic reactive oxygen species upon photoactivation. Confocal microscopic images using complex 3 demonstrate localization of the complexes predominantly in the endoplasmic reticulum of HeLa cells.

Novel Nickel(II), Palladium(II), and Platinum(II) Complexes with O,S Bidendate Cinnamic Acid Ester Derivatives: An In Vitro Cytotoxic Comparison to Ruthenium(II) and Osmium(II) Analogues

(1) Background: Since the discovery of cisplatin’s cytotoxic properties, platinum(II) compounds have attracted much interest in the field of anticancer drug development. Over the last few years, classical structure−activity relationships (SAR) have been broken by some promising new compounds based on platinum or other metals. We focus on the synthesis and characterization of 17 different complexes with β-hydroxydithiocinnamic acid esters as O,S bidendate ligands for nickel(II), palladium(II), and platinum(II) complexes. (2) Methods: The bidendate compounds were synthesized and characterized using classical methods including NMR spectroscopy, MS spectrometry, elemental analysis, and X-ray crystallography, and their cytotoxic potential was assessed using in vitro cell culture assays. Data were compared with other recently reported platinum(II), ruthenium(II), and osmium(II) complexes based on the same main ligand system. (3) Results: SAR analyses regarding the metal ion (M), and the alkyl-chain position (P) and length (L), revealed the following order of the effect strength for in vitro activity: M > P > L. The highest activities have Pd complexes and ortho-substituted compounds. Specific palladium(II) complexes show lower IC50 values compared to cisplatin, are able to elude cisplatin resistance mechanisms, and show a higher cancer cell specificity. (4) Conclusion: A promising new palladium(II) candidate (Pd3) should be evaluated in further studies using in vivo model systems, and the identified SARs may help to target platinum-resistant tumors.

Lysosomal Targeted Cyclometallic Iridium(Ⅲ) Salicylaldehyde-Coumarin Schiff Base Complexes and Anticancer Application

Natural coumarin derivatives and cyclometallic iridium (Ⅲ) (Ir^Ⅲ) complexes have attracted much attention in the field of anticancer. In this study, six coumarin-modified cyclometallic Ir^Ⅲ salicylaldehyde Schiff base complexes ([(ppy)₂Ir(O^N)]/[(ppy-CHO)₂Ir(O^N)]) were designed and synthesized. Compared with coumarin and Ir^Ⅲ complex monomers, target complexes exhibited favorable cytotoxic activity toward A549 and BEAS-2B cells. These complexes could induce extensive apoptosis of A549 cell (late apoptosis), which was represented by the disturbance of cell cycle (G₁-phase) and the accumulation of intracellular reactive oxygen species, exhibiting an anticancer mechanism of oxidation. With the help of suitable fluorescence of these complexes, no conflict with the probes, confocal detection confirmed that complexes showed an energy-dependent cellular uptake mechanism and triggered lysosome-mediated apoptosis in A549 cell line. Above all, our findings reveal the design of a lysosomal targeting cyclometallic Ir^Ⅲ Schiff base complexes and provide a new idea for the design of integrated drugs for diagnosis and treatment.

Effect of cysteine thiols on the catalytic and anticancer activity of Ru(II) sulfonyl-ethylenediamine complexes

We have synthesized a series of novel substituted sulfonyl ethylenediamine (en) Ru^II arene complexes 1-8 of [(η⁶-arene)Ru(R¹-SO₂-EnBz)X], where the arene is benzene, HO(CH₂)₂O-phenyl or biphenyl (biph), X = Cl or I, and R¹ is phenyl, 4-Me-phenyl, 4-NO₂-phenyl or dansyl. The 'piano-stool' structure of complex 3, [(η⁶-biph)Ru(4-Me-phenyl-SO₂-EnBz)I], was confirmed by X-ray crystallography. The values of their aqua adducts were determined to be high (9.1 to 9.7). Complexes 1-8 have antiproliferative activity against human A2780 ovarian, and A549 lung cancer cells with IC₅₀ values ranging from 4.1 to >50 μM, although, remarkably, complex 7 [(η⁶-biph)Ru(phenyl-SO₂-EnBz)Cl] was inactive towards A2780 cells, but as potent as the clinical drug cisplatin towards A549 cells. All these complexes also showed catalytic activity in transfer hydrogenation (TH) of NAD⁺ to NADH with sodium formate as hydride donor, with TOFs in the range of 2.5-9.7 h^-1. The complexes reacted rapidly with the thiols glutathione (GSH) and N-acetyl-L-cysteine (NAC), forming dinuclear bridged complexes [(η⁶-biph)₂Ru₂(GS)₃]^2- or [(η⁶-biph)₂Ru₂(NAC-H)₃]^2-, with the liberation of the diamine ligand which was detected by LC-MS. In addition, the switching on of fluorescence for complex 8 in aqueous solution confirmed release of the chelated DsEnBz ligand in reactions with these thiols. Reactions with GSH hampered the catalytic TH of NAD⁺ to NADH due to the decomposition of the complexes. Co-administration to cells of complex 2 [(η⁶-biph)Ru(4-Me-phenyl-SO₂-EnBz)Cl] with L-buthionine sulfoximine (L-BSO), an inhibitor of GSH synthesis, partially restored the anticancer activity towards A2780 ovarian cancer cells. Complex 2 caused a concentration-dependent G1 phase cell cycle arrest, and induced a significant level of reactive oxygen species (ROS) in A2780 human ovarian cancer cells. The amount of induced ROS decreased with increase in GSH concentration, perhaps due to the formation of the dinuclear Ru-SG complex.

Reactive Oxygen Species Production Is Responsible for Antineoplastic Activity of Osmium, Ruthenium, Iridium and Rhodium Half-Sandwich Type Complexes with Bidentate Glycosyl Heterocyclic Ligands in Various Cancer Cell Models

Platinum complexes are used in chemotherapy, primarily as antineoplastic agents. In this study, we assessed the cytotoxic and cytostatic properties of a set of osmium(II), ruthenium(II), iridium(III) and rhodium(III) half-sandwich-type complexes with bidentate monosaccharide ligands. We identified 5 compounds with moderate to negligible acute cytotoxicity but with potent long-term cytostatic activity. These structure-activity relationship studies revealed that: (1) osmium(II) p-cymene complexes were active in all models, while rhodium(III) and iridium(III) Cp* complexes proved largely inactive; (2) the biological effect was influenced by the nature of the central azole ring of the ligands—1,2,3-triazole was the most effective, followed by 1,3,4-oxadiazole, while the isomeric 1,2,4-oxadiazole abolished the cytostatic activity; (3) we found a correlation between the hydrophobic character of the complexes and their cytostatic activity: compounds with O-benzoyl protective groups on the carbohydrate moiety were active, compared to O-deprotected ones. The best compound, an osmium(II) complex, had an IC₅₀ value of 0.70 µM. Furthermore, the steepness of the inhibitory curve of the active complexes suggested cooperative binding; cooperative molecules were better inhibitors than non-cooperative ones. The cytostatic activity of the active complexes was abolished by a lipid-soluble antioxidant, vitamin E, suggesting that oxidative stress plays a major role in the biological activity of the complexes. The complexes were active on ovarian cancer, pancreatic adenocarcinoma, osteosarcoma and Hodgkin’s lymphoma cells, but were inactive on primary, non-transformed human fibroblasts, indicating their applicability as potential anticancer agents.

Oxidative stress in cancer therapy: Friend or enemy?

Excessive cellular oxidative stress is widely perceived as a key factor in pathophysiological conditions and cancer development. Healthy cells use several mechanisms to maintain intracellular levels of reactive oxygen species (ROS) and overall redox homeostasis to avoid damage to DNA, proteins, and lipids. Cancer cells, in contrast, exhibit elevated ROS levels and upregulated protective antioxidant pathways. Counterintuitively, such elevated oxidative stress and enhanced antioxidant defence mechanisms in cancer cells provide a therapeutic opportunity for the development of drugs with different anticancer mechanisms of action (MoA). In this review, oxidative stress and the role of ROS in cells are described. The tumour-suppressive and tumour-promotive functions of ROS are discussed to compare these two different therapeutic strategies (increasing or decreasing ROS to fight cancer). Clinically approved drugs with demonstrated oxidative stress anticancer MoAs are highlighted before describing examples of metal-based anticancer drug candidates causing oxidative stress in cancer cells via novel MoAs.

In Vitro Anticancer Activity of Novel Co(II) and Ni(II) Complexes of Non-steroidal Anti-inflammatory Drug Niflumic Acid Against Human Breast Adenocarcinoma MCF-7 Cells

Herein, we report the synthesis, characterization and anticancer activity of six novel complexes of non-steroidal anti-inflammatory drug niflumic acid with Co(II) and Ni(II). In vitro cytotoxicity screening in MCF-7, HepG2 and HT-29 cancer cell lines showed that the complex 3 [Co(nif)2(met)(4-pic)] and complex 6 [Ni(nif)2(met)(4-pic)] among all the complexes exhibited the highest cytotoxicity against MCF-7 cells with IC50 values of 11.14 µM and, 41.47 µM, respectively. Besides, all the complexes exhibited significantly higher selectivity towards mouse fibroblast 3T3L1 cells. Further mechanistic studies with both complexes on MCF-7 cells revealed their cytotoxic action through the mitochondrial-dependent apoptotic pathway causing an increase oxidative/nitrosative stress, decrease in mitochondrial membrane potential (ΔΨm), inducing the multicaspase activation and arresting the cell cycle at S phase. q-PCR analysis resulted in an increase in the expression of the apoptotic marker proteins bax, p53 and caspase-3 and -8 in MCF-7 cells, but a decrease in the expression of antiapoptotic bcl-2 gene. Moreover, both complexes induced the apoptosis through the inhibition of PI3K/Akt signaling pathway by decreasing the expression of PI3K and increasing dephosphorylation form of Akt protein. These results provide a significant contribution to the explanation of the anticancer mechanisms of these complexes in MCF-7 cells.

In Vitro and In Vivo of Triphenylamine-Appended Fluorescent Half-Sandwich Iridium(III) Thiosemicarbazones Antitumor Complexes

Half-sandwiched structure iridium(III) complexes appear to be an attractive organometallic antitumor agents in recent years. Here, four triphenylamine-modified fluorescent half-sandwich iridium(III) thiosemicarbazone (TSC) antitumor complexes were developed. Because of the "enol" configuration of the TSC ligands, these complexes formed a unique dimeric configuration. Aided by the appropriate fluorescence properties, studies found that complexes could enter tumor cells in an energy-dependent mode, accumulate in lysosomes, and result in the damage of lysosome integrity. Complexes could block the cell cycle, improve the levels of intrastitial reactive oxygen species, and lead to apoptosis, which followed an antitumor mechanism of oxidation. Compared with cisplatin, the antitumor potential in vivo and vitro confirmed that Ir4 could effectively inhibit tumor growth. Meanwhile, Ir4 could avoid detectable side effects in the experiments of safety evaluation. Above all, half-sandwich iridium(III) TSC complexes are expected to be an encouraging candidate for the treatment of malignant tumors.

NMR studies of group 8 metallodrugs: 187Os-enriched organo-osmium half-sandwich anticancer complex

We report the synthesis of the organo-osmium anticancer complex [Os(η⁶-p-cym)(N,N-azpy-NMe₂)Br]PF₆ (1) containing natural abundance ¹⁸⁷Os (1.96%), and isotopically-enriched (98%) [¹⁸⁷Os]-1. Complex 1 and [¹⁸⁷Os]-1 contain a π-bonded para-cymene (p-cym), a chelated 4-(2-pyridylazo)-N,N-dimethylaniline (azpy-NMe₂), and a monodentate bromide as ligands. The X-ray crystal structure of 1 confirmed its half-sandwich 'piano-stool' configuration. Complex 1 is a member of a family of potent anticancer complexes, and exhibits sub-micromolar activity against A2780 human ovarian cancer cells (IC₅₀ = 0.40 μM). Complex [¹⁸⁷Os]-1 was analysed by high-resolution ESI-MS, 1D ¹H and ¹³C NMR, and 2D ¹H COSY, ¹³C-¹H HMQC, and ¹H-¹⁸⁷Os HMBC NMR spectroscopy. Couplings of ¹H and ¹³C nuclei from the azpy/p-cym ligands to ¹⁸⁷Os were observed with J-couplings (¹J to ⁴J) ranging between 0.6-8.0 Hz. The ¹⁸⁷Os chemical shift of [¹⁸⁷Os]-1 (-4671.3 ppm, determined by 2D ¹H-¹⁸⁷Os HMBC NMR) is discussed in relation to the range of values reported for related Os(II) arene and cyclopentadienyl complexes (-2000 to -5200 ppm).

Co(II) complexes of curcumin and a ferrocene-based curcuminoid: a study on photo-induced antitumor activity

Co(II) complexes having a ferrocene-based curcuminoid (Fc-curH) ligand viz. [Co(L)₂(Fc-cur)]ClO₄ (1, 2), where L is phenanthroline base, namely, 1,10-phenanthroline (phen in 1) and dipyrido[3,2-a:2',3'-c]phenazine (dppz in 2) have been synthesized, characterized and evaluated as photochemotherapeutic agents in vitro. The corresponding Co(II) complexes of the naturally occurring polyphenol curcumin (curH), namely, [Co(L)₂(cur)]ClO₄ (3, 4), where L is phen (in 3) and dppz (in 4) were synthesized and their photo-induced anticancer activities compared with their ferrocene containing counterparts 1 and 2. The Co(II) acetylacetonato complex viz. [Co(phen)₂(acac)]ClO₄ (5) was structurally characterized through X-ray crystallography and used as control for cellular experiments. The Co(II) complexes having ferrocene-based curcuminoid are remarkably stable at physiological condition with higher lipophilicity compared to their curcumin analogues. The complexes display significant binding propensity to calf thymus (ct) DNA and human serum albumin (HSA). The complexes 1-4 display remarkable visible light induced cytotoxicity with the ferrocenyl analogues showing more phototoxic index (PI). The Co(II) curcumin complexes localize in the nucleus and mitochondria of A549 cells. The primary cell death mechanism is believed to be apoptotic in nature induced by light assisted generation of reactive oxygen species (ROS).Graphic abstract.

Evaluating the mechanisms of action and subcellular localization of ruthenium(II)-based photosensitizers

The identification of ruthenium(II) polypyridyl complexes as photosensitizers in photodynamic therapy (PDT) for the treatment of cancer is progressing rapidly. Due to their favorable photophysical and photochemical properties, Ru(II)-based photosensitizers have absorption in the visible spectrum, can be irradiated via one- and two-photon excitation within the PDT window, and yield potent oxygen-dependent and/or oxygen-independent photobiological activities. Herein, we present a current overview of the mechanisms of action and subcellular localization of Ru(II)-based photosensitizers in the treatment of cancer. These photosensitizers are highlighted from a medicinal chemistry and chemical biology perspective. However, although this field is burgeoning, challenges and limitations remain in the photosensitization strategies and clinical translation.

Osmium-arene complexes with high potency towards Mycobacterium tuberculosis

The treatment of tuberculosis (TB) poses a major challenge as frontline therapeutic agents become increasingly ineffective with the emergence and spread of drug-resistant strains of Mycobacterium tuberculosis (Mtb). To combat this global health problem, new antitubercular agents with novel modes of action are needed. We have screened a close family of 17 organometallic half-sandwich Os(II) complexes [(arene)Os(phenyl-azo/imino-pyridine)(Cl/I)]+Y- containing various arenes (p-cymene, biphenyl, or terphenyl), and NMe2, F, Cl, or Br phenyl or pyridyl substituents, for activity towards Mtb in comparison with normal human lung cells (MRC5). In general, complexes with a monodentate iodido ligand were more potent than chlorido complexes, and the five most potent iodido complexes (MIC 1.25-2.5 µM) have an electron-donating Me2N or OH substituent on the phenyl ring. As expected, the counter anion Y (PF6-, Cl-, I-) had little effect on the activity. The pattern of potency of the complexes towards Mtb is similar to that towards human cells, perhaps because in both cases intracellular thiols are likely to be involved in their activation and their redox mechanism of action. The most active complex against Mtb is the p-cymene Os(II) NMe2-phenyl-azopyridine iodido complex (2), a relatively inert complex that also exhibits potent activity towards cancer cells. The uptake of Os from complex 2 by Mtb is rapid and peaks after 6 h, with temperature-dependence studies suggesting a major role for active transport. Significance to Metallomics Antimicrobial resistance is a global health problem. New advances are urgently needed in the discovery of new antibiotics with novel mechanisms of action. Half-sandwich organometallic complexes offer a versatile platform for drug design. We show that with an appropriate choice of the arene, an N,N-chelated ligand, and monodentate ligand, half-sandwich organo-osmium(II) complexes can exhibit potent activity towards Mycobacterium tuberculosis (Mtb), the leading cause of death from a single infectious agent. The patterns of activity of the 17 azo- and imino-pyridine complexes studied here towards Mtb and normal lung cells suggest a common redox mechanism of action involving intracellular thiols.

An intramolecular photoswitch can significantly promote photoactivation of Pt(iv) prodrugs

Selective activation of prodrugs at diseased tissue through bioorthogonal catalysis represents an attractive strategy for precision cancer treatment. Achieving efficient prodrug photoactivation in cancer cells, however, remains challenging. Herein, we report two Pt(iv) complexes, designated as rhodaplatins {rhodaplatin 1, [Pt(CBDCA-O,O)(NH3)2(RhB)OH]; rhodaplatin 2, [Pt(DACH)ox(RhB)(OH)], where CBDCA is cyclobutane-1,1-dicarboxylate, RhB is rhodamine B, DACH is (1R,2R)-1,2-diaminocyclohexane, and ox is oxalate}, that bear an internal photoswitch to realize efficient accumulation, significant co-localization, and subsequent effective photoactivation in cancer cells. Compared with the conventional platform of external photocatalyst plus substrate, rhodaplatins presented up to 4.8 104-fold increased photoconversion efficiency in converting inert Pt(iv) prodrugs to active Pt(ii) species under physiological conditions, due to the increased proximity and covalent bond between the photoswitch and Pt(iv) substrate. As a result, rhodaplatins displayed increased photocytotoxicity compared with a mixture of RhB and conventional Pt(iv) compound in cancer cells including Pt-resistant ones. Intriguingly, rhodaplatin 2 efficiently accumulated in the mitochondria and induced apoptosis without causing genomic DNA damage to overcome drug resistance. This work presents a new approach to develop highly effective prodrugs containing intramolecular photoswitches for potential medical applications.

Dose- and time-dependent tolerability and efficacy of organo-osmium complex FY26 and its tissue pharmacokinetics in hepatocarcinoma-bearing mice

The organo-osmium complex [OsII(ɳ6-p-cym)(PhAzPy-NMe2)I]+ (FY26) exhibits promising in vitro antitumour activity against mouse hepatocarcinoma Hepa1-6 and other mouse or human cancer cell lines. Here, we drastically enhance water solubility of FY26 through the replacement of the PF6- counter-anion with chloride using a novel synthesis method. FY26⋅PF6 and FY26⋅Cl displayed similar in vitro cytotoxicity in two cancer cell models. We then show the moderate and late anticancer efficacy of FY26⋅PF6 and FY26⋅Cl in a subcutaneous murine hepatocarcinoma mouse model. Both efficacy and tolerability varied according to FY26 circadian dosing time in hepatocarcinoma tumour-bearing mice. Tumour and liver uptake of the drug were determined over 48 h following FY26⋅Cl administration at Zeitgeber time 6 (ZT6), when the drug is least toxic (in the middle of the light span when mice are resting). Our studies suggest the need to administer protracted low doses of FY26 at ZT6 in order to optimize its delivery schedule, for example through the use of chrono-releasing nanoparticles.

Exploring the binding and cleavage activities of nickelII complexes towards DNA and proteins

Three novel nickel(ii) complexes with cis octahedral geometry display excellent binding and cleavage affinity towards DNA and proteins. Furthermore, all complexes show superior cytotoxicity against human lung (A549) and breast (MCF-7) tumor cells.

Bakalova RB, Semkova S, Zhelev Z. The antimalaria drug artemisinin displays strong cytotoxic effect on leukaemia lymphocytes in combination with vitamin C and pro-vitamin K3

This study investigated the anticancer effect of the anti-parasitic drug artemisinin in combination with two redox modulators: vitamin C and pro-vitamin K3 (C/K3) The experiments were conducted on leukaemia cells Jurkat. Cells were treated with either artemisinin or C/K3 alone and with all three compounds. Cell proliferation and viability were analysed using trypan blue stating and automated cell counting. The results showed that artemisinin (>10 mM) suppressed cell proliferation activity, but did not induce cell death up to 500 mM. The drug demonstrated a clear cytostatic effect at concentrations 250- 500 mM – Jurkat cells did not proliferate, but were alive. The combination C/K3 (200:2, 300:3 mM/mM) applied alone did not affect cell proliferation and viability. Vitamins C/K3 in concentration ratio 500:5 (μM/mM) decreased cell proliferation activity by ~10%. The triple combination artemisinin/C/K3 manifested synergistic anti-proliferative effects at all concentration ratios analysed. This synergistic effect increased with increasing C/K3 concentration. Based on literature data, it was assumed that the anti-proliferative effect of the triple combination was mediated by changes in the redox-homeostasis of cancer cells. The C/K3 redox system likely acted on cancer mitochondria and increased superoxide production and activation of pro-apoptotic signals, specific for cancer cells. On the other hand, artemisinin could generate hydroxyl radicals as a result of activation of Fenton reactions, depleting intracellular reducing equivalents. Both redox mechanisms lead to activation of signal pathways for induction of cancer cell death.

Mechanisms for Tuning Engineered Nanomaterials to Enhance Radiation Therapy of Cancer

Engineered nanomaterials that produce reactive oxygen species on exposure to X- and gamma-rays used in radiation therapy offer promise of novel cancer treatment strategies. Similar to photodynamic therapy but suitable for large and deep tumors, this new approach where nanomaterials acting as sensitizing agents are combined with clinical radiation can be effective at well-tolerated low radiation doses. Suitably engineered nanomaterials can enhance cancer radiotherapy by increasing the tumor selectivity and decreasing side effects. Additionally, the nanomaterial platform offers therapeutically valuable functionalities, including molecular targeting, drug/gene delivery, and adaptive responses to trigger drug release. The potential of such nanomaterials to be combined with radiotherapy is widely recognized. In order for further breakthroughs to be made, and to facilitate clinical translation, the applicable principles and fundamentals should be articulated. This review focuses on mechanisms underpinning rational nanomaterial design to enhance radiation therapy, the understanding of which will enable novel ways to optimize its therapeutic efficacy. A roadmap for designing nanomaterials with optimized anticancer performance is also shown and the potential clinical significance and future translation are discussed.

Metallodrugs are unique: opportunities and challenges of discovery and development

Metals play vital roles in nutrients and medicines and provide chemical functionalities that are not accessible to purely organic compounds. At least 10 metals are essential for human life and about 46 other non-essential metals (including radionuclides) are also used in drug therapies and diagnostic agents. These include platinum drugs (in 50% of cancer chemotherapies), lithium (bipolar disorders), silver (antimicrobials), and bismuth (broad-spectrum antibiotics). While the quest for novel and better drugs is now as urgent as ever, drug discovery and development pipelines established for organic drugs and based on target identification and high-throughput screening of compound libraries are less effective when applied to metallodrugs. Metallodrugs are often prodrugs which undergo activation by ligand substitution or redox reactions, and are multi-targeting, all of which need to be considered when establishing structure-activity relationships. We focus on early-stage in vitro drug discovery, highlighting the challenges of evaluating anticancer, antimicrobial and antiviral metallo-pharmacophores in cultured cells, and identifying their targets. We highlight advances in the application of metal-specific techniques that can assist the preclinical development, including synchrotron X-ray spectro(micro)scopy, luminescence, and mass spectrometry-based methods, combined with proteomic and genomic (metallomic) approaches. A deeper understanding of the behavior of metals and metallodrugs in biological systems is not only key to the design of novel agents with unique mechanisms of action, but also to new understanding of clinically-established drugs.

Preparation and Bioactivity of Iridium(III) Phenanthroline Complexes with Halide Ions and Pyridine Leaving Groups

A series of half-sandwich structural iridium(III) phenanthroline (Phen) complexes with halide ions (Cl^- , Br^- , I^- ) and pyridine leaving groups ([(η⁵ -Cp^X )Ir(Phen)Z](PF₆ )_n , Cp^x : electron-rich cyclopentadienyl group, Z: leaving group) have been prepared. Target complexes, especially the Cp^xbiph (biphenyl-substituted cyclopentadienyl)-based one, showed favourable anticancer activity against human lung cancer (A549) cells; the best one (Ir8) was almost five times that of cisplatin under the same conditions. Compared with complexes involving halide ion leaving groups, the pyridine-based one did not display hydrolysis but effectively caused lysosomal damage, leading to accumulation in the cytosol, inducing an increase in the level of intracellular reactive oxygen species and apoptosis; this indicated an anticancer mechanism of oxidation. Additionally, these complexes could bind to serum albumin through a static quenching mechanism. The data highlight the potential value of half-sandwich iridium(III) phenanthroline complexes as anticancer drugs.

Improvement of the Anticancer Activities of Telmisartan by Zn(II) Complexation and Mechanisms of Action

To improve the anticancer activity of telmisartan, its structure has been modified by Zn(II) complexation giving [Zn(Telm)₂(H₂O)₂]·2H₂O (ZnTelm). The cytotoxic effect was measured on the human lung cancer cells (A549) and on the lung fibroblast cells (MRC-5). The complex markedly improved anticancer activity (IC₅₀ 75 μM) of telmisartan (IC₅₀ 125 μM) or ZnSO₄ (IC₅₀ 225 μM) and did not show toxicity on non-cancer cells, inducing oxidative stress with cellular ROS generation and GSH/GSSG decrease. Apoptosis was the dominant form of cell death for the complex. The Bax/Bcl-XL ratio was significantly increased as well as caspase-3 activation. Both the complex and the ligand bind to bovine serum albumin (BSA) and can be stored and transported by the protein but the interaction with the complex is greater. Telmisartan binds BSA by hydrophobic interactions while the interaction of ZnTelm occurs through van der Waals forces and hydrogen bonding. Therefore, it can be shown that the coordination complex ZnTelm improved the anticancer activity of the antihypertensive drug telmisartan (IC₅₀ 75 μM and 125 μM, respectively) and the interaction with BSA. Graphical Abstract Improvement of the anticancer activities of telmisartan by Zn(II) complexation and mechanisms of action. Intrinsic apoptotic pathway: induction ofoxidative stress and regulation of proteins related to apoptosis. The complex interacted with bovine serum albumin (BSA) and can be stored and transported by the protein.

Ni(II) curcumin complexes for cellular imaging and photo-triggered in vitro anticancer activity

Nickel(II) complexes [Ni(cur)(L)₂](OAc) (1-3) where L is N,N-donor heterocyclic bases namely 1,10-phenanthroline (phen in 1), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq in 2), dipyrido[3,2-a:2',3'-c]phenazine (dppz in 3) and Hcur is curcumin were prepared, fully characterized and light-induced in vitro anticancer activity studied. Three nickel(II) complexes containing acetylacetonato (Hacac) ligand, viz.[Ni(acac)(L)₂](OAc) (4-6) where L is phen (in 4), dpq (in 5), dppz (in 6) were prepared and used as controls. Complex 4 was structurally characterized by single crystal X-ray diffraction technique, which revealed an octahedral NiN₄O₂ geometry around the metal centre. Complexes 1-3 showed an intense curcumin-based band at ∼440 nm in DMSO-Tris-HCl buffer (pH = 7.2) (1:4 v/v) which masks the nickel based d-d band. The curcumin comlexes (1-3) were redox inactive at the nickel centre, whereas the acetylacetonato complexes (4-6) displayed an irreversible voltammetric response at ∼1.00 V vs. Ag/AgCl reference electrode in DMF. The complexes bind to calf thymus DNA (ct-DNA) with considerable affinity and interacted with human serum albumin (HSA) with moderate affinity. The Ni(II) curcumin complexes display significant in vitro light-induced cytotoxicity in HeLa (human cervical carcinoma) and A549 (lung cancer cells) involving reactive oxygen species (ROS), with very low dark toxicity. The complexes were found to be much less toxic to immortalized lung epithelial normal cells (HPL1D). Confocal microscopic images using complex 2 and 3 showed that they primarily localize in the cytosol of A549 cells. The mechanism of cell death is mainly apoptosis in nature showing arrest of sub-G1 phase of cell cycle progression in A549 cells under visible light exposure and involves significant loss of mitochondrial membrane potential as observed from JC-1 assay.

Structure-activity relationships for osmium(II) arene phenylazopyridine anticancer complexes functionalised with alkoxy and glycolic substituents

Twenty-four novel organometallic osmium(II) phenylazopyridine (AZPY) complexes have been synthesised and characterised; [Os(η⁶-arene)(5-RO-AZPY)X]Y, where arene = p-cym or bip, AZPY is functionalized with an alkoxyl (O-R, R = Me, Et, ⁿPr, ⁱPr, ⁿBu) or glycolic (O-{CH₂CH₂O}_nR*, n = 1-4, R* = H, Me, or Et) substituent on the pyridyl ring para to the azo-bond, X is a monodentate halido ligand (Cl, Br or I), and Y is a counter-anion (PF₆^-, CF₃SO₃^- or IO₃^-). X-ray crystal structures of two complexes confirmed their 'half-sandwich' structures. Aqueous solubility depended on X, the AZPY substituents, arene, and Y. Iodido complexes are highly stable in water (X = I ⋙ Br > Cl), and exhibit the highest antiproliferative activity against A2780 (ovarian), MCF-7 (breast), SUNE1 (nasopharyngeal), and OE19 (oesophageal) cancer cells, some attaining nanomolar potency and good cancer-cell selectivity. Their activity and distinctive mechanism of action is discussed in relation to hydrophobicity (RP-HPLC capacity factor and Log P_o/w), cellular accumulation, electrochemical reduction (activation of azo bond), cell cycle analysis, apoptosis and induction of reactive oxygen species (ROS). Two complexes show ca. 4× higher activity than cisplatin in the National Cancer Institute (NCI) 60-cell line five-dose screen. The COMPARE algorithm of their datasets reveals a strong correlation with one another, as well as anticancer agents olivomycin, phyllanthoside, bouvardin and gamitrinib, but only a weak correlation with cisplatin, indicative of a different mechanism of action.

Kinetic analysis of the accumulation of a half-sandwich organo-osmium pro-drug in cancer cells

The organo-osmium half-sandwich complex [(η6-p-cymene)Os(Ph-azopyridine-NMe2)I]+ (FY26) exhibits potent antiproliferative activity towards cancer cells and is active in vivo. The complex is relatively inert, but rapidly activated in cells by displacement of coordinated iodide. Here, we study time-dependent accumulation of FY26 in A2780 human ovarian cancer cells at various temperatures in comparison with the chlorido metabolite [(η6-p-cymene)Os(Ph-azopyridine-NMe2)Cl]+ (FY25). Mathematical models described the time evolution of FY26 and FY25 intracellular and extracellular concentrations taking into account both cellular transport (influx and efflux) and the intracellular conversion of FY26 to FY25. Uptake of iodide complex FY26 at 37 °C was 17× faster than that of chloride complex FY25, and efflux 1.4× faster. Osmium accumulation decreased markedly after 24 h of exposure. Modelling revealed that this phenomenon could be explained by complex-induced reduction of osmium uptake, rather than by a model involving enhanced osmium efflux. The intracellular osmium concentration threshold above which reduction in drug uptake was triggered was estimated as 20.8 μM (95% confidence interval [16.5, 30]). These studies provide important new insight into the dynamics of transport of this organometallic anticancer drug candidate.

Ruthenium(II)-Arene Thiocarboxylates: Identification of a Stable Dimer Selectively Cytotoxic to Invasive Breast Cancer Cells

Ru^II -arene complexes provide a versatile scaffold for novel anticancer drugs. Seven new Ru^II -arene-thiocarboxylato dimers were synthesized and characterized. Three of the complexes (2 a, b and 5) showed promising antiproliferative activities in MDA-MB-231 (human invasive breast cancer) cells, and were further tested in a panel of fifteen cancerous and noncancerous cell lines. Complex 5 showed moderate but remarkably selective activity in MDA-MB-231 cells (IC₅₀ =39±4 μm Ru). Real-time proliferation studies showed that 5 induced apoptosis in MDA-MB-231 cells but had no effect in A549 (human lung cancer, epithelial) cells. By contrast, 2 a and b showed moderate antiproliferative activity, but no apoptosis, in either cell line. Selective cytotoxicity of 5 in aggressive, mesenchymal-like MDA-MB-231 cells over many common epithelial cancer cell lines (including noninvasive breast cancer MCF-7) makes it an attractive lead compound for the development of specifically antimetastatic Ru complexes with low systemic toxicity.

Lysosome-targeted chemotherapeutics: Anticancer mechanism of N-heterocyclic carbene iridium(III) complex

N-heterocyclic carbenes-modified half-sandwich iridium(III) complex [(η⁵-C₅Me₄C₆H₄C₆H₅)Ir(C^C)Cl]PF₆ (C1) (where C^C is a N-heterocyclic carbene ligand) can effectively prevent the proliferation of human cervical cancer cells. Here, this study aims to investigate the in-deep anticancer effects of this complex on non-small cell lung cancer cells and explore the underlying molecular mechanism. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay showed that iridium(III) complex had potent cytotoxicity studies towards non-small cell lung cancer cells (A549), human lung squamous cells (L78), human cervical cancer cells (Hela) and human bronchial epithelial cells (BEAS-2B). Colocalization and cellular uptake studies were analyzed by confocal microscopy. Notably, C1 targeted lysosomes and entered the cancer cells partially through an energy-dependent pathway, inducing the release of cathepsins and other proteins. These proteins regulated lysosomal-mitochondrial dysfunction, thus leading to the release of cytochrome c (cyt c), which amplified apoptotic signals by activating many downstream pathways such as caspase pathways to promote cell apoptosis. The results showed that the inhibitory mechanism of this organometallic iridium(III) complex may involve caspase-associated apoptosis initiated by the lysosomal-mitochondrial pathway.

Dual functions of iridium(III) 2-phenylpyridine complexes: Metastasis inhibition and lysosomal damage

Six N-phenylcarbazole/triphenylamine-appended half-sandwich iridium(III) 2-phenylpyridine complexes ([(η⁵-Cp*)Ir(C^N)Cl]) were prepared and characterized. Compared with cisplatin, these complexes exhibited potential antitumor activity against A549 and HeLa tumor cells, with IC₅₀ values (half-maximum inhibitory concentration) that changed from 2.8 ± 0.8 μM to 39.5 ± 2.7 μM, and could block the migration of tumor cells. These complexes also effectively bound to protein (binding constant: ~10⁴ M^-1) and were transported through serum proteins, catalyzed the oxidation of coenzyme nicotinamide-adenine dinucleotide. Additionally, laser confocal microscopy and flow cytometry confirmed that these complexes possessed a non-energy-dependent cellular uptake mechanism, effectively accumulated in lysosomes (Pearson colocalization coefficient: ~0.74), damaged the integrity of acidic lysosomes, led to a change in the mitochondrial membrane potential, disrupted the cell cycle (G₀/G₁ phase), and eventually induced apoptosis. Above all, these complexes are potential antitumor agents with dual functions: metastasis inhibition and lysosomal damage.

Lysosome-targeted iridium(iii) compounds with pyridine-triphenylamine Schiff base ligands: syntheses, antitumor applications and mechanisms

Half-sandwiched iridium(iii) Schiff base complexes showed potential antitumor activity and could induce apoptosis through metastasis inhibition and lysosomal damage.

Fluorescent iridium(iii) coumarin-salicylaldehyde Schiff base compounds as lysosome-targeted antitumor agents

Fluorescent iridium(iii) coumarin-salicylaldehyde Schiff base antitumor compounds change the ROS and ΔΨ_m, induce lysosomal damage, and lead to apoptosis.

Copper(ii) complexes containing enoxacin and heterocyclic ligands: synthesis, crystal structures and their biological perspectives

Two copper-based complexes with a distorted square pyramidal geometry show excellent binding and cleavage affinity towards DNA and proteins. Also, these complexes have potential cytotoxicity against MCF-7 cancer cells.

Triphenylamine/carbazole-modified ruthenium(ii) Schiff base compounds: synthesis, biological activity and organelle targeting

N-phenylcarbazole/triphenylamine modified Schiff base half-sandwich ruthenium(ii) compounds showed potential anticancer activity against A549 and HeLa cells.

Iridium(III) Complexes Targeting Apoptotic Cell Death in Cancer Cells

Targeting apoptosis is a principal strategy in the design of anticancer drugs. In recent years, non-platinum-based scaffolds have been exploited as viable candidates for the exploitation of anticancer agents with potentially lower toxicity than the widely used cisplatin analogues. This review highlights the latest advances in developing iridium(III) complexes as anticancer agents that act particularly via targeting apoptotic cell death in cancer cells.

Pharmaco-genomic investigations of organo-iridium anticancer complexes reveal novel mechanism of action

Resistance to platinum drugs (used in >50% of cancer chemotherapies) is a clinical problem. Other precious metal complexes with distinct mechanisms of action might overcome this. Half-sandwich organometallic complexes containing arene or cyclopentadienyl (Cp) ligands show promise. We screened two iridium(iii) complexes [Ir(Cp^Xbiph)(ppy)Cl] (ZL49, 1, ppy = phenylpyridine) and [Ir(Cp^Xph)(azpyNMe₂)Cl]PF₆ (ZL109, 2, azpyNMe₂ = N,N-dimethylphenylazopyridine) in 916 cancer cell lines from 28 tissue types. On average, complex 2 was 78× more potent than 1, 36× more active than cisplatin (CDDP), and strongly active (nanomolar) in patient-derived ovarian cancer cell lines. RNA sequencing of A2780 ovarian cells revealed upregulation of antioxidant responses (NRF2, AP-1) consistent with observed induction of reactive oxygen species (ROS). Protein microarrays, high content imaging and cell cycle analysis showed S/G2 arrest, and late-stage DNA damage response without p53 requirement. The triple-negative breast cancer cell line OCUB-M was highly sensitive to 2 as were cell lines with KIT mutations. Complex 2 exhibits a markedly different pattern of antiproliferative activity compared to the 253 drugs in the Sanger Cancer Genome database, but is most similar to osmium(ii) arene complexes which share the same azopyridine ligand. Redox modulation and DNA damage can provide a multi-targeting strategy, allowing compounds such as 2 to overcome cellular resistance to platinum anticancer drugs.

Nanofocused synchrotron X-ray absorption studies of the intracellular redox state of an organometallic complex in cancer cells

Synchrotron nanoprobe X-ray absorption studies of an osmium metallodrug in cancer cells show hetereogeneous intracellular distribution of Os^II and Os^III species.

Triphenyltin(IV) acylhydrazone compounds: Synthesis, structure and bioactivity

Four new triphenyltin(IV) acylhydrazone compounds of the type Ph₃SnCH₂CH₂CONHN=R (where Ph = phenyl; R = isopropyl, isobutyl, cyclopentyl and cyclooctyl) were synthesized and characterized by elemental analysis, infrared spectrum (IR), nuclear magnetic resonance spectrum (NMR) and mass spectrum (MS). The crystal structures were determined and showed that tin atoms were four-coordinated and adopted a pseudo-tetrahedron configuration. Tin(IV) compounds show excellent bovine serum albumin (BSA) binding properties, and can oxidize nicotinamide-adenine dinucleotid (NADH) to generate reactive oxygen species (ROS), which inducing apoptosis effectively. Bioassay results indicated that tin(IV) compounds have stronger cytotoxic activity against A549 human lung cancer cells compared with cis-platin used clinically, and showing some selectivity.

A new C,N-cyclometalated osmium(ii) arene anticancer scaffold with a handle for functionalization and antioxidative properties

A series of six osmium(ii) complexes of the type [(η6-p-cymene)Os(C^N)X] (X = chlorido or acetato) containing benzimidazole C^N ligands with an ester group as a handle for further functionalization have been synthesized. They exhibit IC50 values in the low micromolar range in a panel of cisplatin (CDDP)-resistant cancer cells (approximately 10× more cytotoxic than CDDP in MCF-7), decrease the levels of intracellular ROS and reduce the NAD+ coenzyme, and inhibit tubulin polymerization. This discovery could open the door to a new large family of osmium(ii)-based bioconjugates with diverse modes of action.

In Vivo Selectivity and Localization of Reactive Oxygen Species (ROS) Induction by Osmium Anticancer Complexes That Circumvent Platinum Resistance

Platinum drugs are widely used for cancer treatment. Other precious metals are promising, but their clinical progress depends on achieving different mechanisms of action to overcome Pt-resistance. Here, we evaluate 13 organo-Os complexes: 16-electron sulfonyl-diamine catalysts [(η6-arene)Os( N, N')], and 18-electron phenylazopyridine complexes [(η6-arene)Os( N, N')Cl/I]+ (arene = p-cymene, biphenyl, or terphenyl). Their antiproliferative activity does not depend on p21 or p53 status, unlike cisplatin, and their selective potency toward cancer cells involves the generation of reactive oxygen species. Evidence of such a mechanism of action has been found both in vitro and in vivo. This work appears to provide the first study of osmium complexes in the zebrafish model, which has been shown to closely model toxicity in humans. A fluorescent osmium complex, derived from a lead compound, was employed to confirm internalization of the complex, visualize in vivo distribution, and confirm colocalization with reactive oxygen species generated in zebrafish.

Novel half-sandwich iridium(iii) imino-pyridyl complexes showing remarkable in vitro anticancer activity

Seven novel half-sandwich Ir^III cyclopentadienyl complexes, [(η⁵-Cp^x)Ir(N^N)Cl]PF₆, have been prepared and characterized, where Cp^x is Cp* or the biphenyl derivative Cp^xbiph (C₅Me₄C₆H₄C₆H₅), and the N^N-chelating ligands are imino-pyridyl Schiff-bases. The X-ray crystal structures of complexes 2A, 2B, and 3A have been determined. Excitingly, most of the complexes show potent antiproliferative activity towards A549 and HeLa cancer cells, except for Cp* complex 1A towards HeLa cells. Cp^xbiph complex 2B displayed the highest potency, about 19 and 6 times more active than the clinically used drug cisplatin toward A549 and HeLa cells, respectively. These complexes undergo hydrolysis, and the kinetics data have been calculated. DNA binding has been studied by interaction with nucleobases 9-ethylguanine and 9-methyladenine, cleavage of plasmid DNA, and interaction with ctDNA. Interaction with DNA does not appear to be the major mechanism of action. Protein binding (bovine serum albumin, BSA) has been established by UV-Vis, fluorescence and synchronous spectroscopic studies. The stability of complex 2B in the presence of GSH was evaluated. The complexes catalytically convert coenzyme NADH to NAD⁺via hydride transfer. Cp^xbiph complexes 2B and 4B induce cell apoptosis and arrest cell cycles at the S and G₂/M phases towards A549 cancer cells and increase the reactive oxygen species dramatically, which appear to contribute to the remarkable anticancer activity.