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

Anticancer behavior of cyclometallated iridium(III)-tributyltin(IV) carboxylate schiff base complexes with aggregation-induced emission

Cyclometallated iridium(III) and organotin(IV) carboxylate complexes have shown potential application value in the field of anticancer. However, the widespread aggregation-caused quenching (ACQ) effect of these complexes is not conducive to the exploration of their targeting and anticancer mechanism, and the idea of aggregation-induced emission (AIE) effect can effectively solve this problem. Then, AIE-activated cyclometallated iridium(III)-tributyltin(IV) carboxylate Schiff base complexes were designed and prepared in this study. Complexes exhibited AIE effect in highly concentrated solution or aggregative state, which facilitated the investigation of subcellular tissue targeting (mitochondria) and cell morphology. Compared with cyclometallated iridium(III) complex and tributyltin(IV) carboxylate monomers, these complexes showed the better in-vitro anti-proliferative activity toward A549 cells, confirming the favorable synergistic anticancer activity. Even for A549/DDP (cisplatin-resistance) cells, these complexes also exhibited the better activity. In addition, complexes showed a mitochondrial apoptotic pathway. Therefore, cyclometallated iridium(III)-tributyltin(IV) carboxylate Schiff base complexes can be used as the potential substitutes for platinum-based drugs and gain further application.

Iridium(III) complexes as novel theranostic small molecules for medical diagnostics, precise imaging at a single cell level and targeted anticancer therapy

Medical applications of iridium (III) complexes include their use as state-of-the-art theranostic agents - molecules that combine therapeutic and diagnostic functions into a single entity. These complexes offer a promising avenue in medical diagnostics, precision imaging at single-cell resolution and targeted anticancer therapy due to their unique properties. In this review we report a short summary of their application in medical diagnostics, imaging at single-cell level and targeted anticancer therapy. The exceptional photophysical properties of Iridium (III) complexes, including their brightness and photostability, make them excellent candidates for bioimaging. They can be used to image cellular processes and the microenvironment within single cells with unprecedented clarity, aiding in the understanding of disease mechanisms at the molecular level. Moreover the iridium (III) complexes can be designed to selectively target cancer cells,. Upon targeting, these complexes can act as photosensitizers for photodynamic therapy (PDT), generating reactive oxygen species (ROS) upon light activation to induce cell death. The integration of diagnostic and therapeutic capabilities in Iridium (III) complexes offers the potential for a holistic approach to cancer treatment, enabling not only the precise eradication of cancer cells but also the real-time monitoring of treatment efficacy and disease progression. This aligns with the goals of personalized medicine, offering hope for more effective and less invasive cancer treatment strategies.

2-Aryl-1H-imidazo[4,5-f][1,10]phenanthroline-Based Binuclear Ru(II)/Ir(III)/Re(I) Complexes as Mitochondria Targeting Cancer Stem Cell Therapeutic Agents

A series of novel Ru(II)/Ir(III)/Re(I)-based organometallic complexes [Ru2L1, Ru2L2, Ir2L1, Ir2L2, Re2L1, and Re2L2] have been synthesized to assess their potency and selectivity against multiple cancer cells A549, HCT-116, and HCT-116 colon CSCs. The cytotoxic screening of the synthesized complexes has revealed that complex Ru2L1 and Ir2L2 are two proficient complexes among all, but Ru2L1 is the most potent complex. A significant binding constant value was observed for DNA and BSA in all complexes. Significant lipophilic properties allow them to penetrate cancer cell membranes, and substantial quantum yield (ϕf) values support bioimaging potential. Again, these complexes are particular for mitochondrial localization and produce a profuse amount of ROS to damage the mitochondrial DNA and then G1 phase cell-cycle arrest. Protein expression analysis unveiled that pro-apoptotic Bax protein overexpressed in Ru2L1-treated cells, whereas antiapoptotic Bcl-2 protein was expressed twofold in Ir2L2-treated cells, which correlated with autophagy reticence.

Novel Re(I) Complexes as Potential Selective Theranostic Agents in Cancer Cells and In Vivo in Caenorhabditis elegans Tumoral Strains

A series of rhenium(I) complexes of the type fac-[Re(CO)3(N^N)L]0/+, Re1-Re9, was synthesized, where N^N = benzimidazole-derived bidentate ligand with an ester functionality and L = chloride or pyridine-type ligand. The new compounds demonstrated potent activity toward ovarian A2780 cancer cells. The most active complexes, Re7-Re9, incorporating 4-NMe2py, exhibited remarkable activity in 3D HeLa spheroids. The emission in the red region of Re9, which contains an electron-deficient benzothiazole moiety, allowed its operability as a bioimaging tool for in vitro and in vivo visualization. Re9 effectivity was tested in two different C. elegans tumoral strains, JK1466 and MT2124, to broaden the oncogenic pathways studied. The results showed that Re9 was able to reduce the tumor growth in both strains by increasing the ROS production inside the cells. Moreover, the selectivity of the compound toward cancerous cells was remarkable as it did not affect neither the development nor the progeny of the nematodes.

Exploring the phototoxicity of GSH-resistant 2-(5,6-dichloro-1H-benzo[d]imidazol-2-yl)quinoline-based Ir(III)-PTA complexes in MDA-MB-231 cancer cells

Metal complexes play a crucial role in photo-activated chemotherapy (PACT), which has recently been used to treat specific disorders. Triple-negative breast cancer has an enormously high rate of relapse due to the existence and survival of cancer stem cells (CSCs) characterized by increased amounts of glutathione (GSH). Hence, designing a phototoxic molecule is an enticing area of research to combat triple-negative breast cancer (TNBC) via GSH depletion and DNA photocleavage. Herein, we focus on the application of PTA and non-PTA Ir(III) complexes for phototoxicity in the absence and presence of GSH against MDA-MB-231 TNBC cells. Between these two complexes, [Cp*IrIII(DD)PTA]·2Cl (DDIRP) exhibited better phototoxicity (IC50 ∼ 2.80 ± 0.52 μM) compared to the non-PTA complex [Cp*IrIII(DD)Cl]·Cl (DDIR) against TNBC cells because of the high GSH resistance power of the complex DDIRP. The significant potency of the complex DDIRP under photo irradiation in both normoxia and hypoxia conditions can be attributed to selective transportation, high cellular permeability and uptake towards the nucleus, GSH depletion by GSH-GSSG conversion, the ability of strong DNA binding including intercalation, and oxidative stress. The strong affinity to serum albumin, which serves as a carrier protein, aids in the transport of the complex to its target site while preventing glutathione (GSH) deactivation. Consequently, the complex DDIRP was developed as a suitable phototoxic complex in selective cancer therapy, ruling over the usual chemotherapeutic drug cisplatin and the PDT drug Photofrin. The ability of ROS generation under hypoxic conditions delivers this complex as a hypoxia-efficient selective metallodrug for the treatment of TNBC.

Functional Upgrading of an Organo-Ir(III) Complex to an Organo-Ir(III) Prodrug as a DNA Damage-Responsive Autophagic Inducer for Hypoxic Lung Cancer Therapy

The efficiency of nitrogen mustards (NMs), among the first chemotherapeutic agents against cancer, is limited by their monotonous mechanism of action (MoA). And tumor hypoxia is a significant obstacle in the attenuation of the chemotherapeutic efficacy. To repurpose the drug and combat hypoxia, herein, we constructed an organo-Ir(III) prodrug, IrCpNM, with the composition of a reactive oxygen species (ROS)-inducing moiety (Ir-arene fragment)-a hypoxic responsive moiety (azo linker)-a DNA-alkylating moiety (nitrogen mustard), and realized DNA damage response (DDR)-mediated autophagy for hypoxic lung cancer therapy for the first time. Prodrug IrCpNM could upregulate the level of catalase (CAT) to catalyze the decomposition of excessive H2O2 to O2 and downregulate the expression of the hypoxia-inducible factor (HIF-1α) to relieve hypoxia. Subsequently, IrCpNM initiates the quadruple synergetic actions under hypoxia, as simultaneous ROS promotion and glutathione (GSH) depletion to enhance the redox disbalance and severe oxidative and cross-linking DNA damages to trigger the occurrence of DDR-mediated autophagy via the ATM/Chk2 cascade and the PIK3CA/PI3K-AKT1-mTOR-RPS6KB1 signaling pathway. In vitro and in vivo experiments have confirmed the greatly antiproliferative capacity of IrCpNM against the hypoxic solid tumor. This work demonstrated the effectiveness of the DNA damage-responsive organometallic prodrug strategy with the microenvironment targeting system and the rebirth of traditional chemotherapeutic agents with a new anticancer mechanism.

Ir(III) Half-Sandwich Photosensitizers with a π-Expansive Ligand for Efficient Anticancer Photodynamic Therapy

One approach to reduce the side effects of chemotherapy in cancer treatment is photodynamic therapy (PDT), which allows spatiotemporal control of the cytotoxicity. We have used the strategy of coordinating π-expansive ligands to increase the excited state lifetimes of Ir(III) half-sandwich complexes in order to facilitate the generation of 1O2. We have obtained derivatives of formulas [Cp*Ir(C∧N)Cl] and [Cp*Ir(C∧N)L]BF4 with different degrees of π-expansion in the C∧N ligands. Complexes with the more π-expansive ligand are very effective photosensitizers with phototoxic indexes PI > 2000. Furthermore, PI values of 63 were achieved with red light. Time-dependent density functional theory (TD-DFT) calculations nicely explain the effect of the π-expansion. The complexes produce reactive oxygen species (ROS) at the cellular level, causing mitochondrial membrane depolarization, cleavage of DNA, nicotinamide adenine dinucleotide (NADH) oxidation, as well as lysosomal damage. Consequently, cell death by apoptosis and secondary necrosis is activated. Thus, we describe the first class of half-sandwich iridium cyclometalated complexes active in PDT.

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.

Research Progress of Metal Anticancer Drugs

Cancer treatments, including traditional chemotherapy, have failed to cure human malignancies. The main reasons for the failure of these treatments are the inevitable drug resistance and serious side effects. In clinical treatment, only 5 percent of the 50 percent of cancer patients who are able to receive conventional chemotherapy survive. Because of these factors, being able to develop a drug and treatment that can target only cancer cells without affecting normal cells remains a big challenge. Since the special properties of cisplatin in the treatment of malignant tumors were accidentally discovered in the last century, metal anticancer drugs have become a research hotspot. Metal anticancer drugs have unique pharmaceutical properties, such as ruthenium metal drugs with their high selectivity, low toxicity, easy absorption by tumor tissue, excretion, and so on. In recent years, efficient and low-toxicity metal antitumor complexes have been synthesized. In this paper, the scientific literature on platinum (Pt), ruthenium (Ru), iridium (Ir), gold (Au), and other anticancer complexes was reviewed by referring to a large amount of relevant literature at home and abroad.

Configurationally regulated half-sandwich iridium(III)-ferrocene heteronuclear metal complexes: Potential anticancer agents

Half-sandwich iridium(III) (IrIII) complexes and ferrocenyl (Fc) derivatives are becoming the research hotspot in the field of anticancer because of their good bioactivity and unique anticancer mechanism different from platinum-based drugs. Then, a series of half-sandwich IrIII-Fc pyridine complexes have been prepared through the structural regulation in this study. The incorporation of half-sandwich IrIII complex with Fc unit successfully improves their anticancer activity, and the optimal performance (IrFc5) is almost 3-fold higher than that of cisplatin against A549 cells, meanwhile, which also shows better anti-proliferative activity against A549/DDP cells. Complexes can aggregate in the intracellular lysosome of A549 cells and induce lysosomal damage, disrupt the cell cycle, increase the level of intracellular reactive oxygen species, and eventually lead to cell apoptosis. Half-sandwich IrIII-Fc heteronuclear metal complexes possess a different anticancer mechanism from cisplatin, which can serve as a potential alternative to platinum-based drugs and show a good application prospect.

Synthesis, characterization, photophysical and electrochemical properties, and biomolecular interaction of 2,2'-biquinoline based phototoxic Ru(II)/Ir(II) complexes

The phototoxic nature of drugs has been seen to convey immense importance in photo activated chemotherapy (PACT) for the selective treatment of disease. Rationally, in order to eradicate the vehemence of cancer in a living body, the design of phototoxic molecules has been of growing interest in research to establish a selective strategy for cancer therapy. Therefore, the present work portrays the synthesis of a phototoxic anticancer agent by incorporating ruthenium(II) and iridium(III) metals into a biologically active 2,2'-biquinoline moiety, BQ. The complexes, RuBQ and IrBQ, have been revealed as effective anticancer agents with remarkable toxicity in the presence of light compared to the dark towards HeLa and MCF-7 cancer cell lines due to the production of a profuse amount of singlet oxygen (1O2) upon irradiation by visible light (400-700 nm). Complex IrBQ exhibited the best toxicity (IC50 = 8.75 μM in MCF-7 and 7.23 μM in HeLa) in comparison to the RuBQ complex under visible light. RuBQ and IrBQ displayed considerable quantum yields (Φf) along with a good lipophilic property, indicating the cellular imaging capability of both complexes upon significant accumulation in cancer cells. Also, the complexes have shown significant binding propensity with biomolecules, viz. deoxyribonucleic acid (DNA) as well as serum albumin (BSA, HSA).

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.

Synthesis, Characterization, and Antitumor Mechanism Investigation of Ruthenium(II)/Rhenium(I)-Daminozide Conjugates

Daminozide, a plant growth regulator, is an effective inhibitor of the Jumonji domain-containing protein (JMJD) histone demethylase. Herein, four ruthenium(II)/rhenium(I)-daminozide conjugates, with molecular formulas [Ru(N-N)2bpy(4-CH2OH-4′-CH2O-daminozide)](PF6)2 (Ru-1/Ru-2) (N-N = 1,10-phenanthroline (phen, in Ru-1) and 4,7-diphenyl-1,10-phenanthroline (DIP, in Ru-2)) and Re(N-N)(CO)3(PyCH2O-daminozide) (Re-1/Re-2) (Py = pyridine, N-N = phen (in Re-1) and DIP (in Re-2)), were synthesized and characterized. Among these complexes, Ru-2 and Re-2 exhibited higher cytotoxicity against tumor cells than cisplatin. Upregulation of H3K9Me3 expression level was found in human cervical cancer cells (HeLa) treated with Ru-2 and Re-2, indicating that these two complexes can inhibit the activity of JMJD histone demethylase. Further investigation revealed that Re-2 can selectively accumulate in the mitochondria of HeLa cells. Both Ru-2 and Re-2 can cause mitochondrial damage, induce apoptosis, and inhibit cell migration and colony formation of HeLa cells. Overall, these complexes exhibit multiple anticancer functions, including inhibiting JMJD, inducing apoptosis, and inhibiting cell invasion, making them promising candidates for anticancer drugs.

Antiproliferative studies of transition metal chelates of a pyrazolone based hydrazone derivative

Pyrazolone derivatives play a significant role in the treatment of cancer. The synergic effect which emerges from the combination of pyrazolone moiety with hydrazone functionality was investigated. The objective of this study was to explore the antiproliferative potential of copper(II), cobalt(II), nickel(II) and zinc(II) metal chelates synthesized from pyrazolone based hydrazone derivative. The ligand and the metal chelates were characterized by various spectroscopic and analytical studies. The ligand was characterized by single crystal X-ray diffraction analysis.The results were in line with the spectroscopic methods. The geometry optimization of ligand and metal chelates were performed using density functional theory (DFT). The invitro cytotoxicity of ligand and metal chelates against different cancer cell lines was investigated by MTT assay. The cell-viability experiments showed that copper(II) complex is an efficient cytotoxic agent against HeLa cell line. Moreover, possible inhibition mechanism of synthesized compounds was evaluated in silico against HPV16-E6 receptor.Communicated by Ramaswamy H. Sarma.

In Vitro and In Vivo Antitumor Assay of Mitochondrially Targeted Fluorescent Half-Sandwich Iridium(III) Pyridine Complexes

Half-sandwich iridium(III) complexes show potential value in the anticancer field. However, complexes with favorable luminescence performance are rare, which limits further investigation of the anticancer mechanism. In this paper, 10 triphenylamine-modified fluorescent half-sandwich iridium(III) pyridine complexes {[(η⁵-Cp^x)Ir(L)Cl₂]} (Ir1-Ir10) were prepared and showed potential antiproliferative activity, effectively inhibiting the migration of A549 cells. Ir6, showing the best activity among these complexes, exhibited excellent fluorescence performance (absolute fluorescence quantum yield of 15.17%) in solution. Laser confocal detection showed that Ir6 followed an energy-dependent cellular uptake mechanism, specifically accumulating in mitochondria (Pearson co-localization coefficient of 0.95). A Western blot assay further confirmed the existence of a mitochondrial apoptotic channel. Additionally, Ir6 could arrest the cell cycle at the G₂/M phase, catalyze NADH oxidation, reduce the mitochondrial membrane potential, induce an increase in the level of intracellular reactive oxygen species, and exhibit a mechanism of oxidation. An in vivo antitumor assay confirmed that Ir6 can effectively inhibit tumor growth and is safer than cisplatin.

Luminescent 11-{Naphthalen-1-yl}dipyrido[3,2-a:2',3'-c]phenazine-Based Ru(II)/Ir(III)/Re(I) Complexes for HCT-116 Colorectal Cancer Stem Cell Therapy

Due to a number of unpleasant considerations, marketed drugs have steadily lost their importance in the treatment of cancer. In order to find a viable cancer cell diagnostic agent, we therefore focused on metal complexes that displayed target adequacy, permeability to cancer cells, high standard water solubility, cytoselectivity, and luminescent behavior. In this aspect, luminescent 11-{naphthalen-1-yl} dipyrido [3,2-a:2',3'-c] phenazine based Ru(II)/Ir(III)/Re(I) complexes have been prepared for HCT-116 colorectal cancer stem cell therapy. Our study successfully established the possible cytotoxicity of IrL complex at different doses on HCT-116 colorectal cancer stem cells (CRCSCs). Additionally, an immunochemistry analysis of the complex IrL showed that the molecule was subcellularly localized in the nucleus and other regions of the cytoplasm, where it caused nuclear DNA damage and mitochondrial dysfunction. The level of BAX and Bcl-2 was further quantified by qRT-PCR. The expression of proapoptotic BAX showed increased expression in the complex IrL-treated cell compared to the control, indicating the potential of complex IrL for apoptotic induction. Upon further validation, complex IrL was developed as an inhibitor of autophagy for the eradication of cancer stem cells.

Half-Sandwich Rhodium Complexes with Releasable N-Donor Monodentate Ligands: Solution Chemical Properties and the Possibility for Acidosis Activation

Cancer chemotherapeutics usually have serious side effects. Targeting the special properties of cancer and activation of the anticancer drug in the tumor microenvironment in situ may decrease the intensity of the side effects and improve the efficacy of therapy. In this study, half-sandwich Rh complexes are introduced, which may be activated at the acidic, extracellular pH of the tumor tissue. The synthesis and aqueous stability of mixed-ligand complexes with a general formula of [Rh(η⁵-Cp*)(N,N/O)(N)]^2+/+ are reported, where (N,N/O) indicates bidentate 8-quinolate, ethylenediamine and 1,10-phenanthroline and (N) represents the releasable monodentate ligand with a nitrogen donor atom. UV-visible spectrophotometry, ¹H NMR, and pH-potentiometry were used to determine the protonation constants of the monodentate ligands, the proton dissociation constants of the coordinated water molecules in the aqua complexes, and the formation constants of the mixed-ligand complexes. The obtained data were compared to those of the analogous Ru(η⁶-p-cymene) complexes. The developed mixed-ligand complexes were tested in drug-sensitive and resistant colon cancer cell lines (Colo205 and Colo320, respectively) and in four bacterial strains (Gram-positive and Gram-negative, drug-sensitive, and resistant) at different pH values (5-8). The mixed-ligand complexes with 1-methylimidazole displayed sufficient stability at pH 7.4, and their activation was found in cancer cells with decreasing pH; moreover, the mixed-ligand complexes demonstrated antimicrobial activity in Gram-positive and Gram-negative bacteria, including the resistant MRSA strain. This study proved the viability of incorporating releasable monodentate ligands into mixed-ligand half-sandwich complexes, which is supported by the biological assays.

Increasing Anticancer Activity with Phosphine Ligation in Zwitterionic Half-Sandwich Iridium(III), Rhodium(III), and Ruthenium(II) Complexes

The synthesis and biological assessment of neutral or cationic platinum group metal-based anticancer complexes have been extremely studied, whereas there are few reports on the corresponding zwitterionic complexes. Herein, the synthesis, characterization, and bioactivity of zwitterionic half-sandwich phosphine-imine iridium(III), rhodium(III), and ruthenium(II) complexes were presented. The sulfonated phosphine-imine ligand and a group of zwitterionic half-sandwich P,N-chelating organometallic complexes were fully characterized by nuclear magnetic resonance (NMR), mass spectrum (electrospray ionization, ESI), elemental analysis, and X-ray crystallography. The solution stability of these complexes and their spectral properties were also determined. Notably, almost all of these complexes showed enhanced anticancer activity against model HeLa and A549 cancer cells than the corresponding zwitterionic pyridyl-imine N,N-chelating iridium(III) and ruthenium(II) complexes, which have exhibited inactive or low active in our previous work. The increase in the lipophilic property and intracellular uptake levels of these zwitterionic P,N-chelating complexes appeared to be associated with their superior cytotoxicity. In addition, these complexes showed biomolecular interactions with bovine serum albumin (BSA). The flow cytometry studies indicated that the representative complex Ir1 could induce early-stage apoptosis in A549 cells. Further, confocal microscopy imaging analysis displayed that Ir1 entered A549 cells through the energy-dependent pathway, targeted lysosome, and could cause lysosomal damage. In particular, these complexes could impede cell migration in A549 cells.

Current status of iridium-based complexes against lung cancer

Lung cancer is one of the most common malignant tumors, with the highest mortality rate in the world, and its incidence is second only to breast cancer. It has posed a serious threat to human health. Cisplatin, a metal-based drug, is one of the most widely used chemotherapeutic agents for the treatment of various cancers. However, its clinical efficacy is seriously limited by numerous side effects and drug resistance. This has led to the exploration and development of other transition metal complexes for the treatment of malignant tumors. In recent years, iridium-based complexes have attracted extensive attention due to their potent anticancer activities, limited side effects, unique antitumor mechanisms, and rich optical properties, and are expected to be potential antitumor drugs. In this review, we summarize the recent progress of iridium complexes against lung cancer and introduce their anti-tumor mechanisms, including apoptosis, cycle arrest, inhibition of lung cancer cell migration, induction of immunogenic cell death, etc.

Post-complexation Functionalization of Cyclometalated Iridium(III) Complexes and Applications to Biomedical and Material Sciences

Cyclometalated iridium(III) (Ir(III)) complexes exhibit excellent photophysical properties that include large Stokes shift, high emission quantum yields, and microsecond-order emission lifetimes, due to low-lying metal-to-ligand charge transfer (spin-forbidden singlet-triplet (³MLCT) transition). As a result, analogs have been applied for research not only in the material sciences, such as the development of organic light-emitting diodes (OLEDs), but also for photocatalysts, bioimaging probes, and anticancer reagents. Although a variety of methods for the synthesis and the applications of functionalized cyclometalated iridium complexes have been reported, functional groups are generally introduced to the ligands prior to the complexation with Ir salts. Therefore, it is difficult to introduce thermally unstable functional groups such as peptides and sugars due to the harsh reaction conditions such as the high temperatures used in the complexation with Ir salts. In this review, the functionalization of Ir complexes after the formation of cyclometalated Ir complexes and their biological and material applications are described. These methods are referred to as "post-complexation functionalization (PCF)." In this review, applications of PCF to the design and synthesis of Ir(III) complexes that exhibit blue -red and white color emissions, luminescence pH probes, luminescent probes of cancer cells, compounds that induce cell death in cancer cells, and luminescent complexes that have long emission lifetimes are summarized.

Formation of Iridium(III) and Rhodium(III) Amine, Imine, and Amido Complexes Based on Pyridine-Amine Ligands: Structural Diversity Arising from Reaction Conditions, Substituent Variation, and Metal Centers

Herein, we present the different coordination modes of half-sandwich iridium(III) and rhodium(III) complexes based on pyridine-amine ligands. The pyridyl-amine iridium(III) and rhodium(III) complexes, the corresponding oxidation pyridyl-imine products, and 16-electron pyridyl-amido complexes can be obtained through the change in reaction conditions (nitrogen/adventitious oxygen atmosphere, reaction time, and solvents) and structural variations in the metal and ligand. Overall, the reaction of pyridine-amine ligands with [(η⁵-C₅(CH₃)₅)MCl₂]₂ (M = Ir or Rh) in the presence of adventitious oxygen afforded the oxidized pyridyl-imine complexes. The possible mechanism for the oxidation of iridium(III) and rhodium(III) amine complexes was confirmed by the detection of the byproduct hydrogen peroxide. Moreover, the formation of pyridyl-amine complexes was favored when nonpolar solvent CH₂Cl₂ was used instead of CH₃OH. The rarely reported complex with [(η⁵-Cp*)IrCl₃] anions can also be obtained without the addition of NH₄PF₆. The introduction of the sterically bulky i-Bu group on the bridge carbon of the ligand led to the formation of stable 16-electron pyridyl-amido complexes. The pyridyl-amine iridium(III) and rhodium(III) complexes were also synthesized under a N₂ atmosphere, and no H₂O₂ was detected in the whole process. In particular, the aqueous solution stability and in vitro cytotoxicity toward A549 and HeLa human cancer cells of these complexes were also evaluated. No obvious selectivity was observed for cancer cells versus normal cells with these complexes. Notably, the represented complex 5a can promote an increase in the reactive oxygen species level and induce cell death via apoptosis.

Synthesis and biological evaluation of zwitterionic half-sandwich Rhodium(III) and Ruthenium(II) organometallic complexes

Herein we present the synthesis and characterization of a panel of structurally related zwitterionic piano-stool rhodium(III) and ruthenium(II) complexes. The identities of these novel complexes have been determined by NMR spectroscopy, mass spectrometry, elemental analysis and single-crystal X-ray crystallography. The stability and fluorescence property of these zwitterionic complexes were also confirmed. Zwitterionic rhodium(III) complexes Rh1-Rh4 displayed potent cytotoxic activity against A549 and HeLa human cancer cells. On the contrary, zwitterionic ruthenium(II) complexes Ru1-Ru4 presented no obvious cytotoxic activity to the test cell lines. Moreover, the trend that the introduction of fluorinated substituent and phenyl ring in the η⁵-Cp^R ring and N,N-chelating ligand, respectively, could enhance the cytotoxicity of these zwitterionic rhodium(III) complexes, were observed. The exploration of mechanism using flow cytometry displayed that the cytotoxicity of these rhodium(III) complexes was associated with the perturbation of the cell cycle and the induction of cell apoptosis. Furthermore, microscopic analysis using confocal microscopy indicated that the representative rhodium(III) complex Rh4 entered A549 cells via energy-dependent pathway and predominantly accumulated in lysosomes, thus leading to the disruption of lysosomal integrity.

Insights into the antiproliferative mechanism of (C^N)-chelated half-sandwich iridium complexes

Transition metal-based anticancer compounds, as an alternative to platinum derivatives, are raising scientific interest as they may present distinct although poorly understood mechanisms of action. We used a structure-activity relationship-based methodology to investigate the chemical and biological features of a series of ten (C^N)-chelated half-sandwich iridiumIII complexes of the general formula [IrCp*(phox)Cl], where (phox) is a 2-phenyloxazoline ligand forming a 5-membered metallacycle. This series of compounds undergoes a fast exchange of their chlorido ligand once solubilised in DMSO. They were cytotoxic to HeLa cells with IC50 values in the micromolar range and induced a rapid activation of caspase-3, an apoptosis marker. In vitro, the oxidative power of all the complexes towards NADH was highlighted but only the complexes bearing substituents on the oxazoline ring were able to produce H2O2 at the micromolar range. However, we demonstrated using a powerful HyPer protein redox sensor-based flow cytometry assay that most complexes rapidly raised intracellular levels of H2O2. Hence, this study shows that oxidative stress can partly explain the cytotoxicity of these complexes on the HeLa cell line and gives a first entry to their mechanism of action.

Ru(ii), Ir(iii), Re(i) and Rh(iii) based complexes as next generation anticancer metallopharmaceuticals

Several anticancer drugs such as cisplatin, and its analogues, epirubicin, and doxorubicin are well known for their anticancer activity but the therapeutic value of these drugs comes with certain side effects and they cannot distinguish between normal and cancer cells. Thus, a major challenge for researchers around the world is to develop an anticancer drug with the least toxicity and more target specificity. With the successful reporting of NAMI-A and KP1019, a new path has emerged in the anticancer field. Recently, several Ru(ii) complexes have been reported for their anticancer activity due to their enhanced cellular uptake and selectivity towards cancer cells. Apart from the Ru(ii) complexes, a large amount of research has been carried out with Ir(iii), Re(i), and Rh(iii) based complexes, which exhibited promising anticancer activity. The present review reports various Ru(ii), Ir(iii), Re(i), and Rh(iii) based complexes for their anticancer activity based on their cytotoxicity profiles, biological targets and mechanism of action.

Investigation into antiproliferative activity and apoptosis mechanism of new arene Ru(ii) carbazole-based hydrazone complexes

Ruthenium complexes with bioactive ligands are becoming promising substitutes for platinum complexes due to their precise action against various cancers. In the present study, the synthesis of three new arene Ru(ii) complexes containing new carbazole-based hydrazone ligands of general formula [(η6-benzene)Ru(L)Cl] (1-3; L = carbazolone benzhydrazone ligands), and their anticancer properties are described. The structural characterization of the ligands and their ruthenium complexes has been realized with the aid of elemental analysis, IR, UV-vis, NMR and HR-MS techniques. The molecular structures of all three complexes have been elucidated by single crystal X-ray crystallography and reveal the existence of pseudo-octahedral geometry around the ruthenium. The in vitro cancer cell growth inhibition property of the complexes against A549 (lung carcinoma), A2780 (ovarian adenocarcinoma) and non-cancerous 16HBE (human lung bronchial epithelium) cells were examined by MTT assay. All the complexes display good cytotoxicity towards both of these types of cancer cell compared to the standard drug cisplatin, with low IC50 values. Remarkably, complex 3, which contains an electron-donating substituent, induces a significant reduction of viability in A2780 cells. The inhibition capacity of the complexes towards A2780 cells proliferation was further confirmed using 5-ethynyl-2-deoxyuridine (EdU) assay via minimal DNA synthesis. The result of the acridine orange-ethidium bromide (AO-EB) fluorescent staining assay establishes that the cytotoxicity of the complexes was mediated by apoptosis in cancer cells. Furthermore, flow cytometry using Annexin V-FITC/propidium iodide (PI) double staining determines the quantitative discrimination of early apoptosis by the externalization of phosphatidylserine. In addition, cell cycle distribution indicates that the complexes block the cell cycle progression in the S-phase. The outcome of our investigation shows the promising scope and potency of tailored arene ruthenium complexes for precise cancer chemotherapy beyond platinum drugs.

Synthesis of NNN Chiral Ruthenium Complexes and Their Cytotoxicity Studies

The synthesis and characterization of chiral pincer-ruthenium complexes of the type (^R2NNN)RuCl₂ (PPh₃) (R = 3-methylbutyl and 3,3-dimethylbutyl) is reported here. The cytotoxicity studies of these complexes were studied and compared with the corresponding activity of achiral complexes. The cytotoxic effect of pincer-ruthenium complexes on human dermal fibroblasts and human tongue carcinoma cells assessed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay displayed an inhibition of normal and cancer cell growth in a dose-dependent manner. Intracellular reactive oxygen species (ROS) level measurement, lactate dehydrogenase assay, DNA fragmentation, and necrosis studies revealed that treatment with pincer-ruthenium complexes induced a redox imbalance in SAS cells by upregulating ROS generation and caused necrotic cell death by disrupting the cellular membrane integrity.

Development and validation of DGT passive samplers for the quantification of Ir, Pd, Pt, Rh and Ru: A challenging application in waters impacted by urban activities

Platinum group elements (PGEs) are among the least abundant in the continental crust. They have become excellent tracers of anthropogenic activities, particularly due to their use in catalytic converters or in the medical industry. However, their quantification in environmental matrices is still problematic because of their low concentrations combined with the presence of interfering elements. Preconcentration methods are therefore necessary to measure accurate concentrations. In this study, the quantification of Ir, Rh, Ru, Pd and Pt was studied in depth by focusing on two resins: AG MP-1 (anion exchange) and Purolite® S-920 (chelating) with the aim of developing passive Diffusive Gradients in Thin films (DGT) samplers as in-situ pre-concentration tools. The characteristics of both resins (e.g. adsorption, elution, selectivity, etc.) were studied and the diffusion coefficients of PGEs in different matrices were determined. For the first time, carcinostatic platinum-based drugs were also studied. Better rates and percentages of adsorption were observed for S-920 while AG MP-1 was more selective with regard to spectral interferents and easier to elute. The diffusion coefficients of PGEs were resin-dependent, particularly for carcinostatic platinum-based drugs. For the first time, the applicability of these DGT samplers dedicated to PGEs was demonstrated in the field after their deployment in two wastewater treatment plants in Northern France for which concentrations were found to range from few pg L^-1 (Ir, Ru) to few ng L^-1 (Pt).

Synthesis, characterization and photodynamic activity of half-sandwich rhodium(III) complexes with curcuminoids

Half-sandwich Cp*-Rh complexes containing curcuminoids ([Rh(η⁵-Cp*)(L)(Py)]PF₆, 1-3, L = curcuminoid ligands L¹-L³) were prepared, characterized and studied for anticancer activity. Complex 1 was structurally characterized by single-crystal X-ray crystallography. Complex 3 presented excellent photodynamic anticancer effect in light (>400 nm) showing IC₅₀ values of 7.5 and 4.3 μM against HepG2, SKOV3 and HeLa, respectively, along with the 12.4, 7.9 and 4.7-fold lower toxicity in the dark. Confocal fluorescence images show that the complex primarily targeted mitochondrial localization. These results suggest that the complex 3 was a valuable agent with higher efficacy for chemotherapy and photodynamic therapy, which can achieve real-time image guidance in cancer therapy for the fluorescence of the complex as imaging signals. This investigation provides a valuable route to design novel half-sandwich Cp*-Rh complexes with higher efficacy for photodynamic anticancer chemotherapy.

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.

Experimental and theoretical characterization of the strong effects on DNA stability caused by half-sandwich Ru(II) and Ir(III) bearing thiabendazole complexes

The synthesis and characterization of two half-sandwich complexes of Ru(II) and Ir(III) with thiabendazole as ancillary ligand and their DNA binding ability were investigated using experimental and computational methods. ¹H NMR and acid-base studies have shown that aquo-complexes are the reactive species. Kinetic studies show that both complexes bind covalently to DNA through the metal site and non covalently through the ancillary ligand. Thermal stability studies, viscosity, circular dichroism measurements and quantum chemical calculations have shown that the covalent binding causes breaking of the H-bonding between base pairs, bringing about DNA denaturation and compaction. Additionally, molecular dynamics (MD) simulations and quantum mechanics/molecular mechanics (QM/MM) calculations shed light into the binding features of the Ru(II) and Ir(III) complexes and their respective enantiomers toward double-helical DNA, highlighting the important role played by the NˆN ancillary ligand once the complexes are covalently linked to DNA. Moreover, metal quantification in the nucleus of SW480 colon adenocarcinoma cells were carried out by inductively coupled plasma-mass spectrometry (ICP-MS), both complexes are more internalized than cisplatin after 4 h of exposition. However, in spite of the dramatic changes in the helicity of the DNA secondary structure induced by these complexes and their nuclear localization, antiproliferative studies have revealed that both, Ru(II) and Ir(III) complexes, cannot be considered cytotoxic. This unexpected behavior can be justified by the fast formation of aquo-complexes, which may react with components of the cell culture medium or the cytoplasm compartment in such a way that they may become deactivated before reaching DNA.

Potent half-sandwich Ru(Ⅱ) N^N (aryl-BIAN) complexes: Lysosome-mediated apoptosis, in vitro and in vivo anticancer activities

Herein a new series of organometallic half-sandwich Ru(Ⅱ) complexes bearing aryl-BIAN chelating ligands with various electron-withdrawing and electron-donating substituents have been developed as theranostic agents. All the complexes display much higher anti-proliferative potency than the clinical chemotherapeutic drug cisplatin towards seven cancer cell lines. The anti-proliferative efficacy of these complexes is correlated to their electron-withdrawing ability. Interestingly, complex Ru1 also potently suppresses cancer cell migration in vitro and effectively inhibit tumor growth in vivo in a CT26 colon cancer mouse xenograft model. Mechanisms of action studies display that Ru1 can favorably accumulate in lysosome and exerts anti-cancer potency by inducing a series of events related to lysosomal dysfunction in CT26 cells. Interestingly, inhibition of lysosomal enzymes leads to suppression of cytotoxicity and apoptosis induced by Ru1. Our results elucidate that complex Ru1 can elicit cytotoxicity through lysosome-mediated apoptosis in vitro and suppress tumor growth in vivo.

Ligand-centred redox activation of inert organoiridium anticancer catalysts

Organometallic complexes with novel activation mechanisms are attractive anticancer drug candidates. Here, we show that half-sandwich iodido cyclopentadienyl iridium(iii) azopyridine complexes exhibit potent antiproliferative activity towards cancer cells, in most cases more potent than cisplatin. Despite their inertness towards aquation, these iodido complexes can undergo redox activation by attack of the abundant intracellular tripeptide glutathione (GSH) on the chelated azopyridine ligand to generate paramagnetic intermediates, and hydroxyl radicals, together with thiolate-bridged dinuclear iridium complexes, and liberate reduced hydrazopyridine ligand. DFT calculations provided insight into the mechanism of this activation. GS- attack on the azo bond facilitates the substitution of iodide by GS-, and leads to formation of GSSG and superoxide if O2 is present as an electron-acceptor, in a largely exergonic pathway. Reactions of these iodido complexes with GSH generate Ir-SG complexes, which are catalysts for GSH oxidation. The complexes promoted elevated levels of reactive oxygen species (ROS) in human lung cancer cells. This remarkable ligand-centred activation mechanism coupled to redox reactions adds a new dimension to the design of organoiridium anticancer prodrugs.

Structurally Strained Half-Sandwich Iridium(III) Complexes As Highly Potent Anticancer Agents

Six complexes of formula [Ir(η⁵:κ¹-C₅Me₄CH₂py)(C,N)]PF₆, where C₅Me₄CH₂py is 2-((2,3,4,5-tetramethylcyclopentadienyl)methyl)pyridine, and C,N is 2-phenylpyridine (1), 7,8-benzoquinoline (2), 1-phenylisoquinoline (3), 2-(p-tolyl)pyridine (4), 4-chloro-2-phenylquinoline (5), or 2-(2,4-difluorophenyl)pyridine (6), have been synthesized. The cyclopentadienyl ligand bears a tethered pyridine that binds to the metal center, resulting in an Ir(η⁵:κ¹-C₅Me₄CH₂pyN) tether-ring structure, as confirmed by the X-ray crystal structures of 1, 2, 4, 5, and 6. Nontether versions of 1 and 2 were synthesized to aid unambiguous correlation between structure and activity. While nontether complexes are highly potent toward MCF7 cancer cells (similar to cisplatin), complexes bearing the tether-ring structure, 1-6, are exceptionally more potent (1-2 orders of magnitude). Additionally, 1-6 disrupt mitochondrial membrane potential (ΔΨ_m) and induce oxidative stress. Internalization studies strongly correlate intracellular accumulation and anticancer activity in tether and nontether complexes. We present a new class of organo-iridium drug candidates bearing a structural feature that results in a leap in anticancer potency.

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.

Transition Metal-Based Prodrugs for Anticancer Drug Delivery

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Transition metal complexes, of which the platinum(II) complex cisplatin is an example, have been used in medicine to treat cancer for more than 40 years. Although many successes have been achieved, there are problems associated with the use of these drugs, such as side effects and drug resistance. Converting them into prodrugs, to make them more inert, so that they can travel to the tumour site unchanged and release the drug in its active form only there, is a strategy which is the subject of much research nowadays. The new prodrugs may be activated and release the cytotoxic agent by differences in oxygen concentration or in pH, by the action of overexpressed enzymes, by differences in metabolic rates, etc., which characteristically distinguish cancer cells from normal ones, or even by the input of radiation, which can be visible light. Converting a metal complex into a prodrug may also be used to improve its pharmacological properties. In some cases, the metal complex is a carrier which transports the active drug as a ligand. Some platinum prodrugs have reached clinical trials. So far platinum, ruthenium and cobalt have been the most studied metals. This review presents the recent developments in this area, including the types of complexes used, the mechanisms of drug action and in some cases the techniques applied to monitor drug delivery to cells.

Biological activity and photocatalytic properties of a naphthyl-imidazo phenanthroline (HNAIP) ligand and its [Ir(ppy)2(HNAIP)]Cl and [Rh(ppy)2(HNAIP)]Cl complexes

The synthesized 2-(hydroxy-1-naphtyl)imidazo-[4,5-f][1,10]phenanthroline (HNAIP) ligand and its new iridium ([Ir(ppy)₂(HNAIP)]Cl) and rhodium ([Rh(ppy)₂(HNAIP)]Cl) complexes, being ppy = 2-phenylpiridinate, show cytotoxic effects in SW480 (colon adenocarcinoma) and A549 (epithelial lung adenocarcinoma) cells. They all are cytotoxic in the tested cell lines. HNAIP and [Rh(ppy)₂(HNAIP)]⁺ are the most cytotoxic, whereas [Ir(ppy)₂(HNAIP)]⁺ displays negligible cytotoxicity towards A549 cells and moderate activity towards SW480. The interaction of all three compounds with Bovine Serum Albumin (BSA), l-glutathione reduced (GSH), nicotinamide adenine dinucleotide (NADH) and DNA was studied to explain the differences found in terms of cytotoxicity. None of them are able to interact with BSA, thus excluding bioavailability due to plasma protein interaction as the possible differentiating factor in their biological activity. By contrast, small differences have been observed regarding DNA interaction. In addition, taking advantage of the emission properties of these molecules, they have been visualized in the cytoplasmic region of A549 cells. Inductively coupled plasma mass spectrometry (ICP-MS) experiments show, in turn, that the internalization ability follow the sequence [Rh(ppy)₂(HNAIP)]⁺ > [Ir(ppy)₂(HNAIP)]⁺ > cisplatin. Therefore, it seems clear that the cellular uptake by tumour cells is the key factor affecting the different cytotoxicity of the metal complexes and that this cellular uptake is influenced by the hydrophobicity of the studied complexes. On the other hand, preliminary catalytic experiments performed on the photo-oxidation of GSH and some amino acids such as l-methionine (Met), l-cysteine (Cys) and l-tryptophan (Trp) provide evidence for the photocatalytic activity of the Ir(III) complex in this type of reactions.

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.

Novel half-sandwich rhodium(III) and iridium(III) photosensitizers for dual chemo- and photodynamic therapy

BACKGROUND AND OBJECTIVE

Photodynamic therapy has emerged as a promising treatment for cancer and other malignancies. Design of photosensitizers with two different action mechanisms may be an essential strategy for the improvement of the efficacy of phototherapeutic drugs. The objective of this study was to evaluate the anticancer photo- and chemocytotoxic effects of the novel half-sandwich rhodium(III) and iridium(III) photosensitizers.

MATERIALS AND METHODS

A series of novel half-sandwich Cp*-Rh(III) and Cp*-Ir(III) complexes containing 9-anthraldehyde thiosemicarbazones, (Cp*)M(L)Cl (M = Rh or Ir, L = 9-anthraldehyde thiosemicarbazones), were compared for cell uptake and photo- and chemocytotoxic effects against human prostate carcinoma (PC3) and human ovarian carcinoma (SKOV3) cell lines.

RESULTS

Cp*-Ir(III) complexes, (Cp*)Ir(L)Cl, showed remarkable phototoxic behavior against human ovarian adenocarcinoma SKOV3 cells (IC₅₀ = 2.7 and 2.3 μM, respectively, λ_irr > 400 nm), as well as the 7.4 and 5.3-fold lower toxicity in the dark, implying possibility of dual action as chemo- and phototherapeutic agents.

CONCLUSION

The complexes, which present a synergistic effect with good properties of both the Cp*-Rh(III) and Cp*-Ir(III) chemotherapeutic effect and the anthracene photodynamic therapy efficiency, show great potential as a new generation of light activated dual-action anticancer agents for photodynamic therapy.

Mitochondria-Targeting Anticancer Metal Complexes

Background:

Since the serendipitous discovery of the antitumor activity of cisplatin there has been a continuous surge in studies aimed at the development of new cytotoxic metal complexes. While the majority of these complexes have been designed to interact with nuclear DNA, other targets for anticancer metallodrugs attract increasing interest. In cancer cells the mitochondrial metabolism is deregulated. Impaired apoptosis, insensitivity to antigrowth signals and unlimited proliferation have been linked to mitochondrial dysfunction. It is therefore not surprising that mitochondria have emerged as a major target for cancer therapy. Mitochondria-targeting agents are able to bypass resistance mechanisms and to (re-) activate cell-death programs.

Methods:

Web-based literature searching tools such as SciFinder were used to search for reports on cytotoxic metal complexes that are taken up by the mitochondria and interact with mitochondrial DNA or mitochondrial proteins, disrupt the mitochondrial membrane potential, facilitate mitochondrial membrane permeabilization or activate mitochondria-dependent celldeath signaling by unbalancing the cellular redox state. Included in the search were publications investigating strategies to selectively accumulate metallodrugs in the mitochondria.

Results:

This review includes 241 references on antimitochondrial metal complexes, the use of mitochondria-targeting carrier ligands and the formation of lipophilic cationic complexes.

Conclusion:

Recent developments in the design, cytotoxic potency, and mechanistic understanding of antimitochondrial metal complexes, in particular of cyclometalated Au, Ru, Ir and Pt complexes, Ru polypyridine complexes and Au-N-heterocyclic carbene and phosphine complexes are summarized and discussed.