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

Triphenylphosphine-modified cyclometalated iridiumIII complexes as mitochondria-targeting anticancer agents with enhanced selectivity

This study presents the development and evaluation of triphenylphosphine-modified cyclometalated iridiumIII complexes as selective anticancer agents targeting mitochondria. By leveraging the mitochondrial localization capability of the triphenylphosphine group, these complexes displayed promising cytotoxicity in the micromolar range (3.12-7.24 μM) against A549 and HeLa cancer cells, these complexes exhibit significantly higher activity compared to their unmodified counterparts lacking the triphenylphosphine moiety. Moreover, they demonstrate improved specificity for cancer cells over normal cells, achieving selectivity index in the range of 5.46-14.83. Mechanistic studies confirmed that these complexes selectively target mitochondria rather than DNA, as shown by confocal microscopy and flow cytometry, where they accumulate to induce mitochondrial dysfunction. This disruption leads to mitochondrial membrane depolarization (MMP), elevated reactive oxygen species (ROS) levels, and activation of intrinsic apoptosis pathways. Furthermore, the complexes induce cell cycle arrest at the G2/M phase and suppress the migration of A549 cells.

Anticancer iridium(iii) cyclopentadienyl complexes

A comprehensive review of anticancer iridium(iii) cyclopentadienyl complexes, including a critical discussion of structure–activity relationships and mechanisms of action, is provided.

Significant enhancement of anticancer effect of iridium (III) complexes encapsulated in liposomes

In this study, the ligand EIPP (5-ethoxy-2-(1H-imidazo[4,5-f] [1,10] phenanthrolin-2-yl)phenol) and [Ir(ppy)2(EIPP)](PF6)] (5a, ppy = 2-phenylpyridine) and [Ir(piq)2(EIPP)](PF6)] (5b, piq = 1-phenylisoquinoline) were synthesized and they were entrapped into liposomes to produce 5alipo and 5blipo. 5a and 5b were characterized via HRMS, NMR, UV-vis and IR. The cytotoxicity of 5a, 5b, 5alipo and 5blipo on cancer and non-cancer cells was estimated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). MTT assay demonstrated that 5a and 5b did not show any significant cellular activity but their liposome-encapsulated 5alipo and 5blipo had significant toxic effects. The mechanism of 5alipo, 5blipo-inducing apoptosis was explored by studying cellular uptake, mitochondrial localization, mitochondrial membrane potential, cytochrome C, glutathione (GSH), malondialdehyde (MDA) and protein immunoblotting. The results demonstrated that 5alipo and 5blipo caused a release of cytochrome C, downregulated the expression of Bcl-2, upregulated the expression of BAX, activated caspase 3, and downregulated PARP expression. It was shown that 5alipo and 5blipo could inhibit cancer cell proliferation in G2/M phase by regulating p53 and p21 proteins. Additionally, 5alipo and 5blipo induced autophagy through an adjustment from LC3-I to LC3-II and caused ferroptosis. The in vivo antitumor activity of 5alipo was examined in detail.

Studies of Anticancer Activities In Vitro and In Vivo for Butyltin(IV)-Iridium(III) Imidazole-Phenanthroline Complexes with Aggregation-Induced Emission Properties

Organotin(IV) and iridium(III) complexes have shown good application potential in the field of anticancer; however, the aggregation-caused quenching (ACQ) effect induced by high concentration or dose has limited the research on their targeting and anticancer mechanism. Then, a series of aggregation-induced emission (AIE)-activated butyltin(IV)-iridium(III) imidazole-phenanthroline complexes were prepared in this study. Complexes exhibited significant fluorescence improvement in the aggregated state because of the restricted intramolecular rotation (RIR), accompanied by an absolute fluorescence quantum yield of up to 29.2% (IrSn9). Complexes demonstrated potential in vitro antiproliferative and antimigration activity against A549 cells, following a lysosomal-mitochondrial apoptotic pathway. Nude mouse models further confirmed that complexes had favorable in vivo antitumor and antimigration activity in comparison to cisplatin. Therefore, butyltin(IV)-iridium(III) imidazole-phenanthroline complexes possess the potential as potential substitutes for platinum-based drugs.

Mitochondria-localizing triphenylphosphine-8-hydroxyquinoline Ru complexes induce ferroptosis and their antitumor evaluation

Ruthenium complexes are one of the most promising anticancer drugs and ferroptosis is a novel form of regulated cell death, the study on the effect of Ru complexes on ferroptosis is helpful to find more effective antitumor drugs. Here, the synthesis and characterization of two Ru complexes containing 8-hydroxylquinoline and triphenylphosphine as ligands, [Ru(L1) (PPh3)2Cl2] (Ru-1), [Ru(L2) (PPh3)2Cl2] (Ru-2), were reported. Complexes Ru-1 ∼ Ru-2 showed good anticancer activity in Hep-G2 cells. Researches indicated that complexes Ru-1 ∼ Ru-2 could be enriched and appear as red fluorescence in the mitochondria, arouse dysfunction of mitochondria, induce the accumulation of reactive oxygen species (ROS) and lipid peroxidation (LPO), while the morphology of nuclei and cell apoptosis had no significant change. Further experiments proved that GPX4 and Ferritin were down-regulated, which eventually triggered ferroptosis in Hep-G2 cells. Remarkably, Ru-1 showed high inhibitory activity against xenograft tumor growth in vivo (TGIR = 49%). This study shows that the complex Ru-1 could act as a novel drug candidate by triggering cell ferroptosis.

Design, synthesis, and antitumor mechanism investigation of iridium(III) complexes conjugated with ibuprofen

The design and synthesis of a series of metal complexes formed by non-steroidal anti-inflammatory drugs (NSAIDs) ibuprofen (IBP) and iridium(III), with the molecular formula [Ir(C^N)2bpy(4-CH2OIBP-4'-CH2OIBP)](PF6) (Ir-IBP-1, Ir-IBP-2) (C^N = 2-phenylpyridine (ppy, Ir-IBP-1), 2-(2-thienyl)pyridine (thpy, Ir-IBP-2)) was introduced in this article. Firstly, it was found that the anti-proliferative activity of these complexes was more effective than that of cisplatin. Further research showed that Ir-IBP-1 and Ir-IBP-2 can accumulate in intracellular mitochondria, thereby disrupting mitochondrial membrane potential (MMP), increasing intracellular reactive oxygen species (ROS), blocking the G2/M phase of the cell cycle, and inducing cell apoptosis. In terms of protein expression, the expression of COX-2, MMP-9, NLRP3 and Caspase-1 proteins can be downregulated, indicating their ability to anti-inflammatory and overcome immune evasion. Furthermore, Ir-IBP-1 and Ir-IBP-2 can induce immunogenic cell death (ICD) by triggering the release of cell surface calreticulin (CRT), high mobility group box 1 (HMGB1) and adenosine triphosphate (ATP). Overall, iridium(III)-IBP conjugates exhibit various anti-tumor mechanisms, including mitochondrial damage, cell cycle arrest, inflammatory suppression, and induction of ICD.

Iridium(III) complexes conjugated with naproxen exhibit potent anti-tumor activities by inducing mitochondrial damage, modulating inflammation, and enhancing immunity

A series of Ir(III)-naproxen (NPX) conjugates with the molecular formula [Ir(C^N)2bpy(4-CH2ONPX-4'-CH2ONPX)](PF6) (Ir-NPX-1-3) were designed and synthesized, including C^N = 2-phenylpyridine (ppy, Ir-NPX-1), 2-(2-thienyl)pyridine (thpy, Ir-NPX-2) and 2-(2,4-difluorophenyl)pyridine (dfppy, Ir-NPX-3). Cytotoxicity tests showed that Ir-NPX-1-3 exhibited excellent antitumor activity, especially in A549R cells. The cellular uptake experiment showed that the complexes were mainly localized in mitochondria, and induced apoptosis in A549R cells by damaging the structure and function of mitochondria. The main manifestations are a decrease in the mitochondrial membrane potential (MMP), an increase in reactive oxygen species (ROS) levels, and cell cycle arrest. Furthermore, Ir-NPX-1-3 could inhibit the migration and colony formation of cancer cells, demonstrating potential anti-metastatic ability. Finally, the anti-inflammatory and immunological applications of Ir-NPX-1-3 were verified. The downregulation of cyclooxygenase-2 (COX-2) and programmed death-ligand 1 (PD-L1) expression levels and the release of immunogenic cell death (ICD) related signaling molecules such as damage-associated molecular patterns (DAMPs) (cell surface calreticulin (CRT), high mobility group box 1 (HMGB1), and adenosine triphosphate (ATP)) indicate that these Ir(III) -NPX conjugates are novel ICD inducers with synergistic effects in multiple anti-tumor pathways.

(Pentamethylcyclopentadienyl)chloridoiridium(III) Complex Bearing Bidentate Ph2PCH2CH2SPh-κP,κS Ligand

The (pentamethylcyclopentadienyl)chloridoiridium(III) complex bearing a κP,κS-bonded Ph2PCH2CH2SPh ligand ([Ir(η5-C5Me5)Cl(Ph2P(CH2)2SPh-κP,κS)]PF6, (1)] was synthesized and characterized. Multinuclear (1H, 13C and 31P) NMR spectroscopy was employed for the determination of the structure. Moreover, SC-XRD confirmed the proposed structure belongs to the "piano stool" type. The Hirshfeld surface analysis outlined the most important intermolecular interactions in the structure. The crystallographic structure was optimized at the B3LYP-D3BJ/6-311++G(d,p)(H,C,P,S,Cl)/LanL2DZ(Ir) level of theory. The applicability of this level was verified through a comparison of experimental and theoretical bond lengths and angles, and 1H and 13C NMR chemical shifts. The Natural Bond Orbital theory was used to identify and quantify the intramolecular stabilization interactions, especially those between donor atoms and Ir(III) ions. Complex 1 was tested on antitumor activity against five human tumor cell lines: MCF-7 breast adenocarcinoma, SW480 colon adenocarcinoma, 518A2 melanoma, 8505C human thyroid carcinoma and A253 submandibular carcinoma. Complex 1 showed superior antitumor activity against cisplatin-resistant MCF-7, SW480 and 8505C cell lines. The mechanism of tumoricidal action on 8505C cells indicates the involvement of caspase-induced apoptosis, accompanied by a considerable reduction in ROS/RNS and proliferation potential of treated cells.

Anticancer Metallocenes and Metal Complexes of Transition Elements from Groups 4 to 7

With the progression in the field of bioinorganic chemistry, the role of transition metal complexes as the most widely used therapeutics is becoming a more and more attractive research area. The complexes of transition metals possess a great variety of attractive pharmacological properties, including anticancer, anti-inflammatory, antioxidant, anti-infective, etc., activities. Transition metal complexes have proven to be potential alternatives to biologically active organic compounds, especially as antitumor agents. The performance of metal coordination compounds in living systems is anticipated to differ generally from the action of non-metal-containing drugs and may offer unique diagnostic and/or therapeutic opportunities. In this review, the rapid development and application of metallocenes and metal complexes of elements from Groups 4 to 7 in cancer diagnostics and therapy have been summarized. Most of the heavy metals discussed in the current review are newly discovered metals. That is why the use of their metal-based compounds has attracted a lot of attention concerning their organometallic and coordination chemistry. All of this imposes more systematic studies on their biological activity, biocompatibility, and toxicity and presupposes further investigations.

A review on metal complexes and its anti-cancer activities: Recent updates from in vivo studies

Research into cancer therapeutics has uncovered various potential medications based on metal-containing scaffolds after the discovery and clinical applications of cisplatin as an anti-cancer agent. This has resulted in many metallodrugs that can be put into medical applications. These metallodrugs have a wider variety of functions and mechanisms of action than pure organic molecules. Although platinum-based medicines are very efficient anti-cancer agents, they are often accompanied by significant side effects and toxicity and are limited by resistance. Some of the most studied and developed alternatives to platinum-based anti-cancer medications include metallodrugs based on ruthenium, gold, copper, iridium, and osmium, which showed effectiveness against many cancer cell lines. These metal-based medicines represent an exciting new category of potential cancer treatments and sparked a renewed interest in the search for effective anti-cancer therapies. Despite the widespread development of metal complexes touted as powerful and promising in vitro anti-cancer therapeutics, only a small percentage of these compounds have shown their worth in vivo models. Metallodrugs, which are more effective and less toxic than platinum-based drugs and can treat drug-resistant cancer cells, are the focus of this review. Here, we highlighted some of the most recently developed Pt, Ru, Au, Cu, Ir, and Os complexes that have shown significant in vivo antitumor properties between 2017 and 2023.

Transition metals in angiogenesis - A narrative review

The aim of this paper is to offer a narrative review of the literature regarding the influence of transition metals on angiogenesis, excluding lanthanides and actinides. To our knowledge there are not any reviews up to date offering such a summary, which inclined us to write this paper. Angiogenesis describes the process of blood vessel formation, which is an essential requirement for human growth and development. When the complex interplay between pro- and antiangiogenic mediators falls out of balance, angiogenesis can quickly become harmful. As it is so fundamental, both its inhibition and enhancement take part in various diseases, making it a target for therapeutic treatments. Current methods come with limitations, therefore, novel agents are constantly being researched, with metal agents offering promising results. Various transition metals have already been investigated in-depth, with studies indicating both pro- and antiangiogenic properties, respectively. The transition metals are being applied in various formulations, such as nanoparticles, complexes, or scaffold materials. Albeit the increasing attention this field is receiving, there remain many unanswered questions, mostly regarding the molecular mechanisms behind the observed effects. Notably, approximately half of all the transition metals have not yet been investigated regarding potential angiogenic effects. Considering the promising results which have already been established, it should be of great interest to begin investigating the remaining elements whilst also further analyzing the established effects.

CuAAC "Click"-Derived Luminescent 2-(2-(4-(4-(Pyridin-2-yl)-1H-1,2,3-triazol-1-yl)butoxy)phenyl)benzo[d]thiazole-Based Ru(II)/Ir(III)/Re(I) Complexes as Anticancer Agents

To enhance the cytoselective behavior of the complexes, we intended to develop a CuAAC "click"-derived synthetic protocol for the preparation of 2-(2-(4-(4-(pyridin-2-yl)-1H-1,2,3-triazol-1-yl)butoxy)phenyl)benzo[d]thiazole-based Ru(II)/Ir(III)/Re(I) complexes, and their cytotoxicity against three different cancer cell lines (MCF-7, HeLa, and U87MG) in consort with one normal cell line (HEK-293) was evaluated. In our detailed investigations, the significant cytotoxic nature of the Ru(II) complex 7a compared to Ir(III) and Re(I) complexes (7b and 7c, respectively) was observed. Complex 7a was capable of MCF-7 cell apoptosis via the inhibition of both S- and G2/M-phase cell cycle arrest in association with a substantial quantity of ROS production and DNA intercalation.

Fine-tuning the cytotoxicity of ruthenium(II) arene compounds to enhance selectivity against breast cancers

Ruthenium-based complexes have been suggested as promising anticancer drugs exhibiting reduced general toxicity compared to platinum-based drugs. In particular, Ru(η6-arene)(PTA)Cl2 (PTA = 1,3,5-triaza-7-phosphaadamantane), or RAPTA, complexes have demonstrated efficacy against breast cancer by suppressing metastasis, tumorigenicity, and inhibiting the replication of the human tumor suppressor gene BRCA1. However, RAPTA compounds have limited cytotoxicity, and therefore comparatively high doses are required. This study explores the activity of a series of RAPTA-like ruthenium(II) arene compounds against MCF-7 and MDA-MB-231 breast cancer cell lines and [Ru(η6-toluene)(PPh3)2Cl]+ was identified as a promising candidate. Notably, [Ru(η6-toluene)(PPh3)2Cl]Cl was found to be remarkably stable and highly cytotoxic, and selective to breast cancer cells. The minor groove of DNA was identified as a relevant target.

Cyclometalated iridium(III) complexes combined with fluconazole: antifungal activity against resistant C. albicans

Candida albicans (C. albicans) is a ubiquitous clinical fungal pathogen. In recent years, combination therapy, a potential treatment method to overcome C. albicans resistance, has gained traction. In this study, we synthesized a series of cyclometalated iridium(III) complexes with the formula [Ir(C-N)2(tpphz)](PF6) (C-N = 2-phenylpyridine (ppy, in Ir1), 2-(2-thienyl)pyridine (thpy, in Ir2), 2-(2,4-difluorophenyl) pyridine (dfppy, in Ir3), tpphz = tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j]phenazine) and polypyridyl ruthenium(II) complexes with the formula [Ru(N-N)2(tpphz)](PF6)2 (N-N = 2,2'-bipyridine (bpy, in Ru1), 1,10-phenanthroline (phen, in Ru2), 4,7-diphenyl-1,10-phenanthroline (DIP, in Ru3)), and investigated their antifungal activities against drug-resistant C. albicans and their combination with fluconazole (FLC). Of which, the combination of the lead iridium(III) complex Ir2 and FLC showed strong antifungal activity against drug-resistant C. albicans. Mechanism studies have shown that they can inhibit the formation of hyphae and biofilm, damage mitochondrial function and accumulate intracellular ROS. Therefore, iridium(III) complexes combined with FLC can be used as a promising treatment to exert anti-drug-resistant C. albicans activity, in order to improve the treatment efficiency of fungal infection.

G2/M-Phase-Inhibitory Mitochondrial-Depolarizing Re(I)/Ru(II)/Ir(III)-2,2'-Bipyrimidine-Based Heterobimetallic Luminescent Complexes: An Assessment of In Vitro Antiproliferative Activity and Bioimaging for Targeted Therapy toward Human TNBC Cells

Triple-negative breast cancer (TNBC) is an extremely vicious subtype of human breast cancer having the worst prognosis along with strong invasive and metastatic competency. Hence, it can easily invade into blood vessels, and presently, no targeted therapeutic approach is available to annihilate this type of cancer. Metal complexes have successfully stepped into the anticancer research and are now being applauded due to their anticancer potency after the discovery of cisplatin. Many of these metal complexes are also well recognized for their activity toward breast cancer. As the TNBC is a very dangerous subtype and has long been a challenging ailment to treat, we have intended to develop a few brand new mixed metallic Ru(II)/Ir(III)/Re(I)-2,2'-bipyrimidine complexes [L'Re2], [L'RuRe], and [L'IrRe] to abate the unbridled proliferation of TNBC cells. The potency of the complexes against TNBC cells has been justified using MDA-MB-468 TNBC cell lines where complex [L'IrRe] has displayed significant potency among all the three complexes with an IC₅₀ value of 24.12 μM. The complex [L'IrRe] has been competent to cause apoptosis of TNBC cells through inhibition of the G2/M phase in the cell cycle in association with a profuse amount of ROS generation and mitochondrial depolarization.

Self-assembled nanoparticles based on cationic mono-/AIE tetra-nuclear Ir(III) complexes: long wavelength absorption/near-infrared emission photosensitizers for photodynamic therapy

Cyclometalated Ir(III) complexes as photosensitizers (PSs) have attracted widespread attention because of their good photostability and efficient ¹O₂ production ability. However, their strong absorption in the UV-vis region severely limits their applications in photodynamic therapy (PDT) because the short wavelength illuminating light can be easily absorbed by the skin and subcutaneous adipose tissue causing damage to the patient's normal tissue. Herein, mono- and tetra-nuclear Ir(III) complex-porphyrin conjugates are rationally designed and synthesized, especially [TPP-4Ir]4+ exhibits obvious aggregation-induced emission (AIE) characteristics. PSs comprising Ir(III) complex-porphyrin conjugates self-assembled as nanoparticles (NPs) are successfully achieved. The obtained [TPP-Ir]+ NPs and [TPP-4Ir]4+ NPs exhibit long wavelength absorption (500-700 nm) and near-infrared emission (635-750 nm), successfully overcoming the inherent defects of short wavelength absorption of traditional Ir(III) complexes. Moreover, [TPP-4Ir]4+ NPs exhibit good biocompatibility, high ¹O₂ generation ability, low half-maximal inhibitory concentration (IC₅₀) (0.47 × 10^-6 M), potent cytotoxicity toward cancer cells and superior cellular uptake under white light irradiation. This work extends the scope for transition metal complex PSs with promising clinical applications.

N-Heterocyclic Carbene-Iridium Complexes as Photosensitizers for In Vitro Photodynamic Therapy to Trigger Non-Apoptotic Cell Death in Cancer Cells

A series of seven novel iridium complexes were synthetized and characterized as potential photosensitizers for photodynamic therapy (PDT) applications. Among them, four complexes were evaluated in vitro for their anti-proliferative activity with and without irradiation on a panel of five cancer cell lines, namely PC-3 (prostate cancer), T24 (bladder cancer), MCF7 (breast cancer), A549 (lung cancer) and HeLa (cervix cancer), and two non-cancerous cell models (NIH-3T3 fibroblasts and MC3T3 osteoblasts). After irradiation at 458 nm, all tested complexes showed a strong selectivity against cancer cells, with a selectivity index (SI) ranging from 8 to 34 compared with non-cancerous cells. The cytotoxic effect of all these complexes was found to be independent of the anti-apoptotic protein Bcl-xL. The compound exhibiting the best selectivity, complex 4a, was selected for further investigations. Complex 4a was mainly localized in the mitochondria. We found that the loss of cell viability and the decrease in ATP and GSH content induced by complex 4a were independent of both Bcl-xL and caspase activation, leading to a non-apoptotic cell death. By counteracting the intrinsic or acquired resistance to apoptosis associated with cancer, complex 4a could be an interesting therapeutic alternative to be studied in preclinical models.

Synthesis, characterization and biological evaluation of two cyclometalated iridium(III) complexes containing a glutathione S-transferase inhibitor

The cyclometalated iridium(III) compounds have been intensively studied for health-related applications due to their outstanding luminescent properties and multiple anticancer modes of action. Herein, two iridium(III) compounds Ir-1 and Ir-3 containing glutathione S-transferase inhibitor (GSTi) were developed and studied together with two unfunctionalized compounds Ir-2 and Ir-4 as a comparison. Biological study indicated that GSTi-bearing complexes Ir-1 and Ir-3 exert a synergistic effect on the inhibition of cancer cells. The photophysical properties of Ir-1 ∼ Ir-4 were investigated by UV/vis absorption and fluorescence spectroscopy and rationalized with TD-DFT calculations. As expected, GSTi-bearing complexes Ir-1 and Ir-3 exhibited considerable cytotoxicity against both A549 and cisplatin-resistant A549/cis cancer cells, much higher than the unfunctionalized iridium compounds Ir-2 and Ir-4. Further study indicated that Ir-1 and Ir-3 mainly localize in the mitochondria of tumor cells, and exert their cytotoxicity via generating ROS and inhibiting GST activity. The flow cytometry investigations demonstrated that Ir-1 and Ir-3 can arrest the cell cycle in S phase and induce the cell death through apoptosis process. Overall, the complexation of GST inhibitors with cyclometalated iridium(III) agents provides an effective way for potentiating the cytotoxicity of iridium(III) anticancer agents and resensitizing the efficacy against cisplatin resistant cancer cells.

Targets, Mechanisms and Cytotoxicity of Half-Sandwich Ir(III) Complexes Are Modulated by Structural Modifications on the Benzazole Ancillary Ligand

Cancers are driven by multiple genetic mutations but evolve to evade treatments targeting specific mutations. Nonetheless, cancers cannot evade a treatment that targets mitochondria, which are essential for tumor progression. Iridium complexes have shown anticancer properties, but they lack specificity for their intracellular targets, leading to undesirable side effects. Herein we present a systematic study on structure-activity relationships of eight arylbenzazole-based Iridium(III) complexes of type [IrCl(Cp*)], that have revealed the role of each atom of the ancillary ligand in the physical chemistry properties, cytotoxicity and mechanism of biological action. Neutral complexes, especially those bearing phenylbenzimidazole (HL1 and HL2), restrict the binding to DNA and albumin. One of them, complex 1[C,NH-Cl], is the most selective one, does not bind DNA, targets exclusively the mitochondria, disturbs the mitochondria membrane permeability inducing proton leak and increases ROS levels, triggering the molecular machinery of regulated cell death. In mice with orthotopic lung tumors, the administration of complex 1[C,NH-Cl] reduced the tumor burden. Cancers are more vulnerable than normal tissues to a treatment that harnesses mitochondrial dysfunction. Thus, complex 1[C,NH-Cl] characterization opens the way to the development of new compounds to exploit this vulnerability.

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.

Polymeric Nanosystems Applied for Metal-Based Drugs and Photosensitizers Delivery: The State of the Art and Recent Advancements

Nanotechnology-based approaches for targeting the delivery and controlled release of metal-based therapeutic agents have revealed significant potential as tools for enhancing the therapeutic effect of metal-based agents and minimizing their systemic toxicities. In this context, a series of polymer-based nanosized systems designed to physically load or covalently conjugate metal-based therapeutic agents have been remarkably improving their bioavailability and anticancer efficacy. Initially, the polymeric nanocarriers were applied for platinum-based chemotherapeutic agents resulting in some nanoformulations currently in clinical tests and even in medical applications. At present, these nanoassemblies have been slowly expanding for nonplatinum-containing metal-based chemotherapeutic agents. Interestingly, for metal-based photosensitizers (PS) applied in photodynamic therapy (PDT), especially for cancer treatment, strategies employing polymeric nanocarriers have been investigated for almost 30 years. In this review, we address the polymeric nanocarrier-assisted metal-based therapeutics agent delivery systems with a specific focus on non-platinum systems; we explore some biological and physicochemical aspects of the polymer–metallodrug assembly. Finally, we summarize some recent advances in polymeric nanosystems coupled with metal-based compounds that present potential for successful clinical applications as chemotherapeutic or photosensitizing agents. We hope this review can provide a fertile ground for the innovative design of polymeric nanosystems for targeting the delivery and controlled release of metal-containing therapeutic agents.

A New Strategy to Fight Metallodrug Resistance: Mitochondria-Relevant Treatment through Mitophagy to Inhibit Metabolic Adaptations of Cancer Cells

Metabolic adaptations can help cancer cells to escape from chemotherapeutics, mainly involving autophagy and ATP production. Herein, we report a new rhein-based cyclometalated Ir^III complex, Ir-Rhein, that can accurately target mitochondria and effectively inhibit metabolic adaptations. The complex Ir-Rhein induces severe mitochondrial damage and initiates mitophagy to reduce the number of mitochondria and subsequently inhibit both mitochondrial and glycolytic bioenergetics, which eventually leads to ATP starvation death. Moreover, Ir-Rhein can overcome cisplatin resistance. Co-incubation experiment, 3D tumor spheroids experiment and transcriptome analysis reveal that Ir-Rhein shows promising antiproliferation performance for cisplatin-resistant cancer cells with the regulation of platinum resistance-related transporters. To our knowledge, this is a new strategy to overcome metallodrug resistance with a mitochondria-relevant treatment.

Synthesis, Characterization and Antitumor Mechanism Investigation of Heterometallic Ru(Ⅱ)-Re(Ⅰ) Complexes

The development of heteronuclear metal complexes as potent anticancer agents has received increasing attention in recent years. In this study, two new heteronuclear Ru(Ⅱ)-Re(Ⅰ) metal complexes, [Ru(bpy)₂LRe(CO)₃(DIP)](PF₆)₃ and [Ru(phen)₂LRe(CO)₃(DIP)](PF₆)₃ [RuRe-1 and RuRe-2, L = 2-(4-pyridinyl)imidazolio[4,5-f][1,10]phenanthroline, bpy = 2,2′-bipyridine, DIP = 4,7-diphenyl-1,10-phenanthroline, phen = 1,10-phenanthroline], were synthesized and characterized. Cytotoxicity assay shows that RuRe-1 and RuRe-2 exhibit higher anticancer activity than cisplatin, and exist certain selectivity toward human cancer cells over normal cells. The anticancer mechanistic studies reveal that RuRe-1 and RuRe-2 can induce apoptosis through the regulation of cell cycle, depolarization of mitochondrial membrane potential (MMP), elevation of intracellular reactive oxygen species (ROS), and caspase cascade. Moreover, RuRe-1 and RuRe-2 can effectively inhibit cell migration and colony formation. Taken together, heteronuclear Ru(Ⅱ)-Re(Ⅰ) metal complexes possess the prospect of developing new anticancer agents with high efficacy.

Brominated cyclometalated iridium(III) complexes for mitochondrial immobilization as potential anticancer agents

Mitochondria-targeted iridium complexes for anticancer studies have received increasing attention in recent years. Herein, three cyclometalated iridium(III) complexes Ir1-Ir3 [Ir(N^C)₂(N^N)](PF₆) (N^N = 2,2'-bipyridine (bpy)) or 2-(5-bromopyridin-2-yl)benzo[d]thiazole (bpybt); [N^C = 2-phenylpyridine (ppy) or 2-phenylquinoline (pq) or 2-(4-bromophenyl)benzo[d]thiazole (bpbt)] had been explored as potential mitochondria-targeted anticancer agents. All of the complexes mainly localized in the mitochondria and could be fixed on the mitochondria through a nucleophilic reaction with reactive mitochondrial proteins. Further studies revealed that these complexes showed high anticancer activity, induced mitochondrial depolarization, elevated intracellular reactive oxygen species (ROS) levels, restrained thioredoxin reductase (TrxR) activity, and inhibited the formation of tumor cell colonies and angiogenesis. Further mechanistic studies showed that complex Ir2 could markedly stimulate the activation of caspase-3, regulate the expression of Bax and KI67, and trigger apoptosis.

Bioactivity and Development of Small Non-Platinum Metal-Based Chemotherapeutics

Countless expectations converge in the multidisciplinary endeavour for the search and development of effective and safe drugs in fighting cancer. Although they still embody a minority of the pharmacological agents currently in clinical use, metal-based complexes have great yet unexplored potential, which probably hides forthcoming anticancer drugs. Following the historical success of cisplatin and congeners, but also taking advantage of conventional chemotherapy limitations that emerged with applications in the clinic, the design and development of non-platinum metal-based chemotherapeutics, either as drugs or prodrugs, represents a rapidly evolving field wherein candidate compounds can be fine-tuned to access interactions with druggable biological targets. Moving in this direction, over the last few decades platinum family metals, e.g., ruthenium and palladium, have been largely proposed. Indeed, transition metals and molecular platforms where they originate are endowed with unique chemical and biological features based on, but not limited to, redox activity and coordination geometries, as well as ligand selection (including their inherent reactivity and bioactivity). Herein, current applications and progress in metal-based chemoth are reviewed. Converging on the recent literature, new attractive chemotherapeutics based on transition metals other than platinum—and their bioactivity and mechanisms of action—are examined and discussed. A special focus is committed to anticancer agents based on ruthenium, palladium, rhodium, and iridium, but also to gold derivatives, for which more experimental data are nowadays available. Next to platinum-based agents, ruthenium-based candidate drugs were the first to reach the stage of clinical evaluation in humans, opening new scenarios for the development of alternative chemotherapeutic options to treat cancer.

Design and synthesis of aptamer-cyclometalated iridium(III) complex conjugate targeting cancer cells

Targeted therapy showed broad application prospects in the treatment of various types of cancer. Through carriers such as aptamers, antibodies, proteins and peptides, targeted therapy can selectively deliver drugs into tumor cells. Compared with traditional treatment methods such as chemo- and radiotherapy, targeted drug delivery systems can reduce the toxic effects of drugs on normal cells and avoid adverse reactions. Herein, an aptamer-cyclometalated iridium(III) complex conjugate (ApIrC) has been designed and developed as a targeted anticancer agent. Owing to the targeting ability of aptamers, ApIrC specifically bound to nucleolin over-expressed on the surface of cancer cells and showed strong fluorescence signal for tumor imaging and diagnosis. ApIrC had more substantial cellular uptake in cancer cells than the iridium complex alone and exhibited favorable low toxicity to normal cells. After uptake by cells through endocytosis, ApIrC can selectively accumulated in mitochondria and induced caspase-3/7-dependent cell death. Remarkably, ApIrC can also specifically target 3D multicellular spheroids (MCSs) and show excellent tumor permeability. So, it can effectively reach the interior of MCSs and cause cell damage. To our knowledge, this is the first report of the aptamer-cyclometalated iridium(III) complex conjugate which studied for cancer targeted therapy. The developed conjugate has great potential to be developed as novel therapeutics for effective and low-toxic cancer treatment.

Nanomedicines in the treatment of colon cancer: a focus on metallodrugs

Worldwide, colon cancer (CC) represents the fourth most common type of cancer and the fifth major cause of cancer-associated deaths. Surgical resection is considered the standard therapeutic choice for CC in early stages. However, in latter stages of the disease, adjuvant chemotherapy is essential for an appropriate management of this pathology. Metal-based complexes displaying cytotoxic properties towards tumor cells emerge as potential chemotherapeutic options. One metallodrug, oxaliplatin, was already approved for clinical use, playing an important role in the treatment of CC patients. Unfortunately, most of the newly designed metal-based complexes exhibit lack of selectivity against cancer cells, low solubility and permeability, high dose-limiting toxicity, and emergence of resistances. Nanodelivery systems enable the incorporation of metallodrugs at adequate payloads, solving the above-referred drawbacks. Moreover, drug delivery systems, depending on their physicochemical properties, are able to release the incorporated material preferentially at affected tissues/organs, enhancing the therapeutic activity in vivo, with concomitant fewer side effects. In this review, the general features and therapeutic management of CC will be addressed, with a special focus on preclinical or clinical studies using metal-based compounds. Furthermore, the use of different nanodelivery systems will also be described as tools to potentiate the therapeutic index of metallodrugs for the management of CC.

V, Kar B, Das U, Paira P. Target-specific mononuclear and binuclear rhenium(i) tricarbonyl complexes as upcoming anticancer drugs

Metal complexes have gradually been attracting interest from researchers worldwide as potential cancer therapeutics. Driven by the many side effects of the popular platinum-based anticancer drug cisplatin, the tireless endeavours of researchers have afforded strategies for the design of appropriate metal complexes with minimal side effects compared to cisplatin and its congeners to limit the unrestricted propagation of cancer. In this regard, transition metal complexes, especially rhenium-based complexes are being identified and highlighted as promising cancer theranostics, which are endowed with the ability to detect and annihilate cancer cells in the body. This is attributed the amazing photophysical properties of rhenium complexes together with their ability to selectively attack different organelles in cancer cells. Therefore, this review presents the properties of different rhenium-based complexes to highlight their recent advances as anticancer agents based on their cytotoxicity results.

In this review, rhenium-based complexes are highlighted as promising cancer theranostics, which are endowed with the ability to detect and annihilate cancer cells in the body.

Metal complexes against breast cancer stem cells

With the highest incidence, breast cancer is the leading cause of cancer deaths among women in the world. Tumor metastasis is the major contributor of high mortality in breast cancer, and the existence of cancer stem cells (CSCs) has been proven to be the cause of tumor metastasis. CSCs are a small proportion of tumor cells, and they are associated with self-renewal and tumorigenic potential. Given the significance of CSCs in tumor initiation, expansion, relapse, resistance, and metastasis, studies should investigate and discover effective anticancer agents that can not only inhibit the proliferation of differentiated tumor cells but also reduce the tumorigenic capability of CSCs. Thus, new therapies must be discovered to treat and prevent this severely hazardous disease of human beings. The success of platinum complexes in cancer treatment has laid the basic foundation for the utilization of metal complexes in the treatment of malignant cancers, in particular the highly aggressive triple-negative breast cancer. Importantly, metal complexes currently have diverse and versatile competences in the therapeutic targeting of CSCs. The anti-CSC properties provide a strong impetus for the development of novel metal-based compounds for the targeting of CSCs and treatment of chemotherapy-resistant and relapsed tumors. In this review, we provide the latest advances in metal complexes including platinum, ruthenium, osmium, iridium, manganese, cobalt, nickel, copper, zinc, palladium, and tin complexes against breast CSCs obtained over the past decade, with pertinent literature including those published until 2021.

The Development of Ru(II)-Based Photoactivated Chemotherapy Agents

Photoactivated chemotherapy (PACT) is a novel cancer treatment method that has drawn increasing attention due to its high selectivity and low side effects by spatio-temporal control of irradiation. Compared with photodynamic therapy (PDT), oxygen-independent PACT is more suitable for treating hypoxic tumors. By finely tuning ligand structures and coordination configurations, many Ru(II) complexes can undergo photoinduced ligand dissociation, and the resulting Ru(II) aqua species and/or free ligands may have anticancer activity, showing their potential as PACT agents. In this mini-review, we summarized the progress in Ru(II)-based PACT agents, as well as challenges that researchers in this field still face.

Mitochondria-targeted artesunate conjugated cyclometalated iridium(iii) complexes as potent anti-HepG2 hepatocellular carcinoma agents

Hepatocellular carcinoma (HCC) poses a serious threat to people's health worldwide. Artesunate (ART), one of the classical antimalarial drugs, has recently been shown to exert significant cytotoxicity in various cancers, but its bioavailability is low. Cyclometalated iridium(iii) complexes have emerged as a promising class of anticancer therapeutic agents. Herein, through conjugation of two of them, three novel Ir(iii)-ART conjugates, [Ir(C-N)2(bpy-ART)](PF6) (bpy = 2,2'-bipyridine, C-N = 2-phenylpyridine (ppy, Ir-ART-1), 2-(2-thienyl)pyridine (thpy, Ir-ART-2), and 2-(2,4-difluorophenyl)pyridine (dfppy, Ir-ART-3)) have been synthesized, and their potential as anti-HCC agents was evaluated. We demonstrate that Ir-ART-1-3 display higher cytotoxicity against HCC cell lines than normal liver cells, and they can especially locate to mitochondria of HepG2 cells and induce a series of mitochondria-mediated apoptosis events. Moreover, Ir-ART-1-3 can regulate the cell cycle and inhibit metastasis of HepG2 cells. Finally, in vivo antitumor evaluation also demonstrates the inhibitory activity of Ir-ART-1 on tumor growth. Taken together, these Ir(iii)-ART conjugates have the potential to become drug candidates for future anti-HCC treatments.

Ruthenium Complexes as Promising Candidates against Lung Cancer

Lung cancer is one of the most common malignancies with the highest mortality rate and the second-highest incidence rate after breast cancer, posing a serious threat to human health. The accidental discovery of the antitumor properties of cisplatin in the early 1960s aroused a growing interest in metal-based compounds for cancer treatment. However, the clinical application of cisplatin is limited by serious side effects and drug resistance. Therefore, other transition metal complexes have been developed for the treatment of different malignant cancers. Among them, Ru(II/III)-based complexes have emerged as promising anticancer drug candidates due to their potential anticancer properties and selective cytotoxic activity. In this review, we summarized the latest developments of Ru(II/III) complexes against lung cancer, focusing mainly on the mechanisms of their biological activities, including induction of apoptosis, necroptosis, autophagy, cell cycle arrest, inhibition of cell proliferation, and invasion and metastasis of lung cancer cells.

Interaction between DNA, Albumin and Apo-Transferrin and Iridium(III) Complexes with Phosphines Derived from Fluoroquinolones as a Potent Anticancer Drug

A group of cytotoxic half-sandwich iridium(III) complexes with aminomethyl(diphenyl)phosphine derived from fluoroquinolone antibiotics exhibit the ability to (i) accumulate in the nucleus, (ii) induce apoptosis, (iii) activate caspase-3/7 activity, (iv) induce the changes in cell cycle leading to G2/M phase arrest, and (v) radicals generation. Herein, to elucidate the cytotoxic effects, we investigated the interaction of these complexes with DNA and serum proteins by gel electrophoresis, fluorescence spectroscopy, circular dichroism, and molecular docking studies. DNA binding experiments established that the complexes interact with DNA by moderate intercalation and predominance of minor groove binding without the capability to cause a double-strand cleavage. The molecular docking study confirmed two binding modes: minor groove binding and threading intercalation with the fluoroquinolone part of the molecule involved in pi stacking interactions and the Ir(III)-containing region positioned within the major or minor groove. Fluorescence spectroscopic data (HSA and apo-Tf titration), together with molecular docking, provided evidence that Ir(III) complexes can bind to the proteins in order to be transferred. All the compounds considered herein were found to bind to the tryptophan residues of HSA within site I (subdomain II A). Furthermore, Ir(III) complexes were found to dock within the apo-Tf binding site, including nearby tyrosine residues.

Evaluation of anticancer effects in vitro of new iridium(III) complexes targeting the mitochondria

Iridium(III) complexes have the potential to serve as novel therapeutic drugs for treating tumor. In this work, three new complexes [Ir(ppy)₂(cdppz)](PF₆) (1) (ppy = 2-phenylpyridine, cdppz = 11-chlorodipyrido[3,2-a,2',3'-c]phenazine), [Ir(bzq)₂(cdppz)](PF₆) (2) (bzq = benzo[h]quinolone) and [Ir(piq)₂(cdppz)](PF₆) (3) (piq = 1-phenylisoquinoline) were prepared as well as characterized. MTT (3-(4,5-dimethylthiazole)-2,5-diphenyltetraazolium bromide) assay revealed that the complex 2 exerted potent cytotoxicity against to various cancer cells lines and particularly for SGC-7901 cells. Meanwhile, the complexes could suppress cell colonies formation and migration ability. Apoptosis assays of AO/EB staining as well as flow cytometry revealed that the synthesized complexes may cause apoptosis of SGC-7901 cells. Moreover, the decline of mitochondrial membrane potential (MMP), elevation of intracellular reactive oxygen species (ROS) levels and release of cytochrome c demonstrated the complexes could cause apoptosis mainly through the mitochondrial death pathway and arrest cell at G0/G1 phase. Additionally, the complexes have significant influence on the expression of proteins which is interrelated to cell apoptosis. In summary, our studies provided fundamental information regarding the further study of the possible anticancer mechanisms of iridium (III) complexes.

New iridium bis-terpyridine complexes: synthesis, characterization, antibiofilm and anticancer potentials

This study represents synthesis, characterization, screening of antibiofilm efficacy, and cytotoxicity of iridium bis-terpyridine complexes. The complexes were characterized by NMR, MS, FTIR, UV/Visible, and fluorescence spectroscopies. The efficacy of biofilm inhibition and eradication of iridium complexes was evaluated using a crystal violet assay test and verified by fluorescence microscopy. Cytotoxicity and apoptosis analysis of iridium complexes were determined in this study. The results of our study revealed that three iridium complexes had the potential to inhibit biofilm formation and moderate the ability to destroy pre-formed biofilm of S. aureus ATCC 29,213. 250 µM concentration of synthesized complexes showed the highest antibiofilm activity (75% for Ir1, 90% for Ir2, and 71% for Ir3). The significant inhibition obtained at 6.25 µM concentration of Ir2 and Ir3 revealed the potential of our samples. Also, Ir1 and Ir2 complexes had a good capacity to destroy pre-formed biofilm. The results clearly showed that iridium complexes have cytotoxic activity towards colon cancer (Caco-2) and liver cancer (HepG2) cell lines without affecting non-cancerous cells (HEK293) at applied doses. Moreover, tested compounds induced apoptosis in these cancer cells. All of these results showed that iridium complexes had possessed the ability to inhibit or destroy pre-formed biofilm and could be developed as an effective agent against bacterial biofilms. Moreover, these pure substances may have valuable anti-cancer activity and it should be confirmed with further studies for therapeutic effects.

Mitochondria and Endoplastic Reticulum Targeting Strategy for Enhanced Phototherapy

To ensure improved efficacy and minimized toxicity of therapeutic molecules, it is generally accepted that specifically delivering them to the subcellular site of their action will be attractive. Phototherapy has received considerable attention because of its noninvasiveness, high temporal-spatial resolution, and minimal drug resistance. As important functional organelles in cells, mitochondria and endoplasmic reticulum (ER) participate in fundamental cellular processes, which make them much more sensitive to reactive oxygen species (ROS) and hyperthermia. Thus, mitochondria- or ER-targeted phototherapy will be rational strategies for synergetic cancer therapy. In this review, we focus on the latest advances in molecules and nanomaterials currently used for mitochondria- and ER-targeted phototherapy.

Mitochondria specific highly cytoselective iridium(iii)-Cp* dipyridophenazine (dppz) complexes as cancer cell imaging agents

Cancer is the most incurable pernicious disease to date after cardiovascular disease with an immeasurable rate of mortality. However, effective cancer medication and therapy are still castles in the sky to researchers. Therefore, in search of an appropriate strategy to annihilate cancer, we have designed a set of Ir(iii)-Cp* dipyridophenazine complexes as luminescent anticancer agents combining the cancer inhibiting potency of the planar dipyridophenazine (dppz) moiety through DNA interaction and mitochondrial dysfunction with the wonderful photoluminescence ability and target specificity of iridium metal. Hence, with the synergy of these dual aspects in the same system, we have aspired to emphasize the theranostic approach of cancer treatment in the present study by preparing effective, aqueous-soluble, mitochondria-targeting, highly cytoselective, luminescent, cancer cell-permeable scaffolds, enabling diagnosis as well as the healing of cancer cells in the body. Here, the presence of the cyclopentadienyl (Cp*) moiety in association with the fluorine group has boosted the lipophilic character of the complexes. Also, the cytotoxicity screening of the prepared Cp*Ir(iii)-dipyridophenazine complexes (IrL1-IrL7) against colorectal adenocarcinoma cells (Caco-2) and human epitheloid cervix carcinoma cells (HeLa) clearly identified them as potential anticancer agents and imaging studies unveiled their superb cellular imaging properties. Among them, the complex [(η⁵-Cp*)IrCl(11-fluorodipyrido[3,2-a:2',3'-c]phenazine)] (IrL6) achieved the best cytoselectivity. However, the superiority of the anticancer potency of [(η⁵-Cp*)IrCl(benzo[i]dipyrido[3,2-a:2',3'-c]phenazine)] (IrL3) was also corroborated by its activity against the most aggressive colorectal carcinoma cell line (HT-29), whereas (η⁵-Cp*)IrCl(11-(trifluoromethyl)dipyrido[3,2-a:2',3'-c]phenazine (IrL5) came into the limelight as the best theranostic agent as it showed remarkable cytoselectivity as well as significant cellular imaging properties, endowing it with the highest quantum yield value among all the complexes.

Phosphorescent metal complexes as theranostic anticancer agents: combining imaging and therapy in a single molecule

Phosphorescent metal complexes are a new kind of multifunctional antitumor compounds that can integrate imaging and antitumor functions in a single molecule. In this minireview, we summarize the recent research progress in this field, concentrating on the theranostic applications of phosphorescent iridium(iii), ruthenium(ii) and rhenium(i) complexes. The molecular design that affords these complexes with tumour- or subcellular organelle-targeting properties is elucidated. The potential of these complexes to induce and monitor the dynamic behavior of subcellular organelles and the changes in microenvironment during the process of therapy is demonstrated. Moreover, the potential and advantages of applying new technologies, such as super-resolution imaging and phosphorescence lifetime imaging, are also described. Finally, the challenges faced in the development of novel theranostic metallo-anticancer complexes for possible clinical translation are proposed.

Half-sandwich organometallic Ru and Rh complexes of (N,N) donor compounds: effect of ligand methylation on solution speciation and anticancer activity

A series of half-sandwich polypyridyl complexes was synthesized and compared focusing on structural, cytotoxic and aqueous solution behaviour. The formula of the synthesized complexes is [M(arene)(N,N)Cl]Cl, where M: Ru or Rh, arene: p-cymene, toluene or C5Me5-, (N,N): 2,2'-bipyridine (bpy), 4,4'-dimethyl-2,2'-bipyridine (dmb), 1,10-phenanthroline (phen) or 2,9-dimethyl-1,10-phenanthroline (neo). The structures of five half-sandwich complexes were determined by X-ray crystallography. It was found that introducing methyl groups next to the coordinating nitrogen atoms of the bidentate ligand causes steric congestion around the metal centre which changes the angle between ligand planes. The ligands and the Rh complexes showed significant cytotoxicity in A2780 and MES-SA cancer cell lines (IC50 = 0.1-56 μM) and in the cisplatin-resistant A2780cis cells. Paradoxically, phen and dmb as well as their half-sandwich Rh complexes showed increased toxicity against multidrug resistant MES-SA/Dx5 cells. In contrast, coordination to Ru caused loss of toxicity. Solution equilibrium constants showed that the studied metal complexes have high stability, and no dissociation was found for Ru and Rh complexes even at micromolar concentrations in a wide pH range. However, in the case of Ru complexes a slow and irreversible decomposition, namely arene loss, was also observed, which was more pronounced in light exposure in aqueous solution. In the case of neo, the methyl groups next to the nitrogen atoms significantly decrease the stability of complexes. For Rh complexes, the order of the stability constants corrected with ligand basicity (log K*): 9.78 (phen) > 9.01 (dmb) > 8.89 (bpy) > 3.93 (neo). The coordinated neo resulted in an enormous decrease in the chloride ion affinity of Ru compounds. Based on the results, a universal model was introduced for the prediction of chloride ion capability of half-sandwich Rh and Ru complexes. It combines the effects of the bidentate ligand and the M(arene) part using only two terms, performing multilinear regression procedure.

Structure-tuned membrane active Ir-complexed oligoarginine overcomes cancer cell drug resistance and triggers immune responses in mice

The development of chemotherapy, an important cancer treatment modality, is hindered by the frequently found drug-resistance phenomenon. Meanwhile, researchers have been enthused lately by the synergistic use of chemotherapy with emerging immunotherapeutic treatments. In an effort to address both of the two unmet needs, reported herein is a study on a series of membrane active iridium(iii) complexed oligoarginine peptides with a new cell death mechanism capable of overcoming drug resistance as well as stimulating immunological responses. A systematic structure-activity relationship study elucidated the interdependent effects of three structural factors, i.e., hydrophobicity, topology and cationicity, on the regulation of the cytotoxicity of the Ir(iii)-oligoarginine peptides. With the most prominent toxicities, Ir-complexed octaarginines (R8) were found to display a progressive oncotic cell death featuring cell membrane-penetration and eruptive cytoplasmic content release. Consequently, this membrane-centric death mechanism showed promising potential in overcoming multiple chemical drug-resistance of cancer cells. More interestingly, the eruptive mode of cell death proved to be immunogenic by stimulating the dendritic cell maturation and inflammatory factor accumulation in mice tumours. Taking these mechanisms together, this work demonstrates that membrane active compounds may become the next generation chemotherapeutics because of their combined advantages.