📚 Article Archive

As the "powerhouse" of a cell, mitochondria maintain energy homeostasis, synthesize ATP via oxidative phosphorylation, generate ROS signaling molecules, and modulate cell apoptosis. Herein, three Re(I) complexes bearing guanidinium derivatives have been synthesized and characterized. All of these complexes exhibit moderate anticancer activity in HepG2, HeLa, MCF-7, and A549 cancer cells. Mechanism studies indicate that complex 3, [Re(CO)3(L)(Im)](PF₆)₂, can selectively localize in the mitochondria and induce cancer cell death through mitochondria-associated pathways. In addition, complex 3 can effectively depress the ability of cell migration, cell invasion, and colony formation. Show less

The synthesis, structural characterization and biological activity of eight ortho-quinone(N-aryl)-oximine rhenium(I) complexes are described. The reaction of the halogenido complexes (CO)(5)ReX (X = Cl (4), Br (5)) with 2-nitroso-N-arylanilines {(C(6)H(3)ClNO)NH(C(6)H(4)R)} (R = p-Cl, p-Me, o-Cl, H) (3a-d) in tetrahydrofurane (THF) yields the complexes fac-(CO)(3)XRe{(C(6)H(3)ClNO)NH(C(6)H(4)R)} (6a-d, 7a-d) with the tautomerized ligand acting as a N,N'-chelate. The substitution of two carbonyl ligands leads to the formation of a nearly planar 5-membered metallacycle. During coordination the amino-proton is shifted to the oxygen of the nitroso group which can be observed in solution for 6 and 7 by (1)H NMR spectroscopy and in solid state by crystal structure analysis. After purification, all compounds have been fully characterized by their (1)H and (13)C NMR, IR, UV/visible (UV/Vis) and mass spectra. The X-ray structure analyses revealed a distorted octahedral coordination of the CO, X and N,N'-chelating ligands for all Re(I) complexes. Biological activity of four oximine rhenium(I) complexes was assessed in vitro in two highly aggressive cancer cell lines: human metastatic melanoma A375 and human chronic myelogenous leukemia K562. Chlorido complexes (6a and 6c) were more efficient than bromido compounds (7d and 7b) in inducing apoptotic cell death of both types of cancer cells. Melanoma cells were more susceptible to tested rhenium(I) complexes than leukemia cells. None of the ligands (3a-d) showed any significant anticancer activity. Show less

Title: Rhenium-guanidine complex as photosensitizer: trigger HeLa cell apoptosis through death receptor-mediated, mitochondria-mediated, and cell cycle arrest pathways. Abstract: The growing evidence over the past few decades has indicated that the photodynamic antitumor activity of transition metal complexes, and Re(I) compounds are potential candidates for photodynamic therapy. This study reports the synthesis, characterization, and anti-tumor activity of three new Re(I)-guadinium complexes. Cytotoxicity tests reveal that complex Re1 increased cytotoxicity by 145-fold from IC50 > 180 μM in the dark to 1.3 ± 0.7 μM following 10 min of light irradiation (425 nm) in HeLa cells. Further, the mechanism by which Re1 induces apoptosis in the presence or absence of light irradiation was investigated, and results indicate that cell death was caused through different pathways. Upon irradiation, Re1 first accumulates on the cell membrane and interacts with death receptors to activate the extrinsic death receptor-mediated signaling pathway, and then is transported into the cell cytoplasm. Most of the intracellular Re1 locates within mitochondria, improving the reactive oxygen species level, and decreasing mitochondrial membrane potential and ATP levels, and inducing the activation of caspase-9 and, thus, apoptosis. Subsequently, the residual Re1 can translocate into the cell nucleus, and activates the p53 pathway, causing cell cycle arrest and eventually cell death. Show less

Complexes of the element Re have recently been shown to possess promising anticancer activity through mechanisms of action that are distinct from the conventional metal-based drug cisplatin. In this study, we report our investigations on the anticancer activity of the complex [Re(CO)₃ (dmphen)(p-tol-ICN)]⁺ (TRIP) in which dmphen=2,9-dimethyl-1,10-phenanthroline and p-tol-ICN=para-tolyl isonitrile. TRIP was synthesized by literature methods and exhaustively characterized. This compound exhibited potent in vitro anticancer activity in a wide variety of cell lines. Flow cytometry and immunostaining experiments indicated that TRIP induces intrinsic apoptosis. Comprehensive biological mechanistic studies demonstrated that this compound triggers the accumulation of misfolded proteins, which causes endoplasmic reticulum (ER) stress, the unfolded protein response, and apoptotic cell death. Furthermore, TRIP induced hyperphosphorylation of eIF2α, translation inhibition, mitochondrial fission, and expression of proapoptotic ATF4 and CHOP. These results establish TRIP as a promising anticancer agent based on its potent cytotoxic activity and ability to induce ER stress. Show less

Rhenium and ruthenium complexes containing N-heterocylic carbene (NHC) ligands and conjugated to indomethacin were prepared. The anticancer properties were probed against pancreatic cell lines, revealing a remarkable activity of the rhenium fragment as anticancer agent. The ruthenium complexes were found to be inactive against the same pancreatic cancer cell lines, either alone or in conjugation with indomethacin. An in-depth biological study revealed the origin of the anticancer properties of the rhenium tricarbonyl fragment, of which a complete elucidation had yet to be achieved. It was found that the rhenium complexes induce cell cycle arrest at the G2/M phase by inhibiting the phosphorylation of Aurora-A kinase. A preliminary study on the structure-activity relationship on a large family of these complexes revealed that the anticancer properties are mainly associated with the lability of the ancillary ligand, with inert complexes showing limited to no anticancer properties. Show less

A series of N,N-disubstituted salicylaldehyde semicarbazones (SSCs), HOC(6)H(4)CHN-NHCONR(2), and their rhenium(I) tricarbonyl complexes, [ReBr(CO)(3)(SSC)], have been synthesised and characterised by IR and (1)H NMR spectroscopy. Crystallographic analysis of the complex [ReBr(CO)(3)(H(2)Bu(2))] (H(2)Bu(2)=SSC where R=Bu(n)) showed that the SSC acts as a bidentate ligand via its imino nitrogen and carbonyl oxygen atoms. The [ReBr(CO)(3)(SSC)] complexes exhibit moderate to high cytotoxicities towards MOLT-4 cells (IC(50)=1-24μM, cf. 18μM for cisplatin), and the majority of them are virtually non-toxic against non-cancerous human fibroblasts. Apoptotic assays of [ReBr(CO)(3)(H(2)Bnz(2))] (Bnz=benzyl) revealed that it mediates cytotoxicity in MOLT-4 cells via apoptosis. The complex [ReBr(CO)(3)(H(2)Bnz(2))] reacts with guanosine by proton transfer from the phenolic OH group to N(7) of guanosine. In (CD(3))(2)SO, [ReBr(CO)(3)(H(2)Bnz(2))] undergoes facile conversion to the dimeric complex, [Re(CO)(3)(HBnz(2))](2), via bromide dissociation. Show less

Title: Comparative Study of Sonodynamic and Photoactivated Cancer Therapies with Re(I)-Tricarbonyl Complexes Comprising Phenanthroline Ligands. Abstract: Herein, we have compared the effectivity of light-based photoactivated cancer therapy and ultrasound-based sonodynamic therapy with Re(I)-tricarbonyl complexes (Re1-Re3) against cancer cells. The observed photophysical and TD-DFT calculations indicated the potential of Re1-Re3 to act as good anticancer agents under visible light/ultrasound exposure. Re1 did not display any dark- or light- or ultrasound-triggered anticancer activity. However, Re2 and Re3 displayed concentration-dependent anticancer activity upon light and ultrasound exposure. Interestingly, Re3 produced 1O2 and OH• on light/ultrasound exposure. Moreover, Re3 induced NADH photo-oxidation in PBS and produced H2O2. To the best of our knowledge, NADH photo-oxidation has been achieved here with the Re(I) complex for the first time in PBS. Additionally, Re3 released CO upon light/ultrasound exposure. The cell death mechanism revealed that Re3 produced an apoptotic cell death response in HeLa cells via ROS generation. Interestingly, Re3 showed slightly better anticancer activity under light exposure compared to ultrasound exposure. Show less

Title: Re(I)[2-aryl-1 Abstract: Recently, achieving selective cancer therapy with trifling side effects has been a great challenge in the eradication of cancer. Thus, to amplify the cytoselective approach of complexes, herein, we developed a series of Re(I)[2-aryl-1H-imidazo[4,5-f][1,10]phenanthroline] tricarbonyl chloride complexes and screened their potency against HeLa and MCF-7 cell lines together with the evaluation of their toxicity towards a normal kidney cell line (HEK-293). On meticulous investigation, complex [ReI(CO)3Cl(K2-N,N-(2c))] (3c) was found to be the most potent anticancer entity among other complexes. Complex 3c also showed competency to induce apoptosis in MCF-7 cells through G2/M phase cell-cycle arrest in association with the generation of ample reactive oxygen species (ROS), eventually leading to DNA intercalation and internucleosomal cleavage. The order of the cytotoxicity of these complexes depended on their lipophilic character and the electron-withdrawing halogen substitution at the para-position of the phenyl ring in the imidazophenanthroline ligand. Show less

The established platinum-based drugs form covalent DNA adducts to elicit their cytotoxic response. Although they are widely employed, these agents cause toxic side-effects and are susceptible to cancer-resistance mechanisms. To overcome these limitations, alternative metal complexes containing the rhenium(I) tricarbonyl core have been explored as anticancer agents. Based on a previous study ( Chem. Eur. J. 2019, 25, 9206), a series of highly active tricarbonyl rhenium isonitrile polypyridyl (TRIP) complexes of the general formula fac-[Re(CO)₃(NN)(ICN)]⁺, where NN is a chelating diimine and ICN is an isonitrile ligand, that induce endoplasmic reticulum (ER) stress via activation of the unfolded protein response (UPR) pathway are investigated. A total of 11 of these TRIP complexes were synthesized, modifying both the equatorial polypyridyl and axial isonitrile ligands. Complexes with more electron-donating equatorial ligands were found to have greater anticancer activity, whereas the axial ICN ligands had a smaller effect on their overall potency. All 11 TRIP derivatives trigger a similar phenotype that is characterized by their abilities to induce ER stress and activate the UPR. Lastly, we explored the in vivo efficacy of one of the most potent complexes, fac-[Re(CO)₃(dmphen)(ptolICN)]⁺ (TRIP-1a), where dmphen = 2,9-dimethyl-1,10-phenanthroline and ptolICN = para-tolyl isonitrile, in mice. The ^99mTc congener of TRIP-1a was synthesized, and its biodistribution in BALB/c mice was investigated in comparison to the parent Re complex. The results illustrate that both complexes have similar biodistribution patterns, suggesting that ^99mTc analogues of these TRIP complexes can be used as diagnostic partner agents. The in vivo antitumor activity of TRIP-1a was then investigated in NSG mice bearing A2780 ovarian cancer xenografts. When administered at a dose of 20 mg/kg twice weekly, this complex was able to inhibit tumor growth and prolong mouse survival by 150% compared to the vehicle control cohort. Show less

Elucidation of relationship among chemical structure, cellular uptake, localization, and biological activity of anticancer metal complexes is important for the understanding of their mechanisms of action. Organometallic rhenium(I) tricarbonyl compounds have emerged as potential multifunctional anticancer drug candidates that can integrate therapeutic and imaging capabilities in a single molecule. Herein, two mononuclear phosphorescent rhenium(I) complexes (Re1 and Re2), along with their corresponding dinuclear complexes (Re3 and Re4), were designed and synthesized as potent anticancer agents. The subcellular accumulation of Re1-Re4 was conveniently analyzed by confocal microscopy in situ in live cells by utilizing their intrinsic phosphorescence. We found that increased lipophilicity of the bidentate ligands could enhance their cellular uptake, leading to improved anticancer efficacy. The dinuclear complexes were more potent than the mononuclear counterparts. The molecular anticancer mechanisms of action evoked by Re3 and Re4 were explored in detail. Re3 with a lower lipophilicity localizes to lysosomes and induces caspase-independent apoptosis, whereas Re4 with higher lipophilicity specially accumulates in mitochondria and induces caspase-independent paraptosis in cancer cells. Our study demonstrates that subcellular localization is crucial for the anticancer mechanisms of these phosphorescent rhenium(I) complexes. Show less

Eight rhenium(I) tricarbonyl aqua complexes with the general formula fac-[Re(CO)₃(N,N'-bid)(H₂O)][NO₃] (1-8), where N,N'-bid is (2,6-dimethoxypyridyl)imidazo[4,5-f]1,10-phenanthroline (L1), (indole)imidazo[4,5-f]1,10-phenanthroline (L2), (5-methoxyindole)-imidazo[4,5-f]1,10-phenanthroline (L3), (biphenyl)imidazo[4,5-f]1,10-phenanthroline (L4), (fluorene)imidazo[4,5-f]1,10-phenanthroline (L5), (benzo[b]thiophene)imidazo[4,5-f]1,10-phenanthroline (L6), (5-bromothiazole)imidazo[4,5-f]1,10-phenanthroline (L7), and (4,5-dimethylthiophene)imidazo[4,5-f]1,10-phenanthroline (L8), were synthesized and characterized using ¹H and ¹³C{¹H} NMR, FT-IR, UV/Vis absorption spectroscopy, and ESI-mass spectrometry, and their purity was confirmed by elemental analysis. The stability of the complexes in aqueous buffer solution (pH 7.4) was confirmed by UV/Vis spectroscopy. The cytotoxicity of the complexes (1-8) was then evaluated on prostate cancer cells (PC3), showing a low nanomolar to low micromolar in vitro cytotoxicity. Worthy of note, three of the Re(I) tricarbonyl complexes showed very low (IC₅₀ = 30-50 nM) cytotoxic activity against PC3 cells and up to 26-fold selectivity over normal human retinal pigment epithelial-1 (RPE-1) cells. The cytotoxicity of both complexes 3 and 6 was lowered under hypoxic conditions in PC3 cells. However, the compounds were still 10 times more active than cisplatin in these conditions. Additional biological experiments were then performed on the most selective complexes (complexes 3 and 6). Cell fractioning experiments followed by ICP-MS studies revealed that 3 and 6 accumulate mostly in the mitochondria and nucleus, respectively. Despite the respective mitochondrial and nuclear localization of 3 and 6, 3 did not trigger the apoptosis pathways for cell killing, whereas 6 can trigger apoptosis but not as a major pathway. Complex 3 induced a paraptosis pathway for cell killing while 6 did not induce any of our other tested pathways, namely, necrosis, paraptosis, and autophagy. Both complexes 3 and 6 were found to be involved in mitochondrial dysfunction and downregulated the ATP production of PC3 cells. To the best of our knowledge, this report presents some of the most cytotoxic Re(I) carbonyl complexes with exceptionally low nanomolar cytotoxic activity toward prostate cancer cells, demonstrating further the future viability of utilizing rhenium in the fight against cancer. Show less

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. Show less

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

Title: Mitochondria-targeted cyclometalated iridium-β-carboline complexes as potent non-small cell lung cancer therapeutic agents. Abstract: Natural products and metals play a crucial role in cancer research and the development of antitumor drugs. We designed and synthesized three new carboline-based cyclometalated iridium complexes [Ir(C-N)2(PPβC)](PF6), where PPβC = N-(1,10-phenanthrolin-5-yl)-1-phenyl-9H-pyrido[3,4-b]indole-3-carboxamide, C-N = 2-phenylpyridine (ppy, Ir1), 2-(2,4-difluorophenyl) pyridine (dfppy, Ir2), 7,8-benzoquinoline (bzq, Ir3), by combining iridium with β-carboline derivative. These iridium complexes exhibited high potential antitumor effects after being promptly taken up by A549 cells. Accumulating in mitochondria rapidly and preferentially, Ir1-3 caused a series of changes in mitochondrial events, including the loss of mitochondrial membrane potential, the depletion of cellular ATP, and the elevation of reactive oxygen species, leading to significant death of A549 cells. Moreover, the activation of intracellular caspase pathway and apoptosis was further validated to contribute to iridium complexes-induced cytotoxicity. These novel iridium complexes exerted a prominent inhibitory effect on tumor growth in a three-dimensional multicellular tumor spheroid model. Show less

Title: Cyclometalated iridium(III) tetrazine complexes for mitochondria-targeted two-photon photodynamic therapy. Abstract: The fast-moving field of photodynamic therapy (PDT) has provided fresh opportunities to expand the potential of metallodrugs to combat cancers in a light-controlled manner. As such, in the present study, a series of cyclometalated Ir(III) complexes modified with a tetrazine functional group (namely, Ir-ppy-Tz, Ir-pbt-Tz, and Ir-dfppy-Tz) are developed as potential two-photon photodynamic anticancer agents. These complexes target mitochondria but exhibit low toxicity towards HLF primary lung fibroblast normal cells in the dark. When receiving a low-dose one- or two-photon PDT, they become highly potent towards A549 lung cancer cells (with IC50 values ranging from 24.0 nM to 96.0 nM) through the generation of reactive oxygen species (ROS) to induce mitochondrial damage and subsequent apoptosis. Our results indicated that the incorporation of tetrazine with cyclometalated Ir(III) matrices would increase the singlet oxygen (1O2) quantum yield (ΦΔ) and, meanwhile, enable a type I PDT mechanism. Ir-pbt-Tz, with the largest two-photon absorption (TPA) cross-section (σ2 = 102 GM), shows great promise in serving as a two-photon PDT agent for phototherapy. Show less

Title: Anticancer activity and mechanism studies of photoactivated iridium(III) complexes toward lung cancer A549 cells. Abstract: Cyclometalated iridium(III) compounds have been widely explored due to their outstanding photo-physical properties and multiple anticancer activities. In this paper, three cyclometalated iridium(III) compounds [Ir(ppy)2(DBDIP)]PF6 (5a), [Ir(bzq)2(DBDIP)]PF6 (5b), and [Ir(piq)2(DBDIP)]PF6 (5c) (ppy: 2-phenylpyridine; bzq: benzo[h]quinoline; piq: 1-phenylisoquinoline, and DBDIP: 2-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-1H-imidazo[4,5-f][1,10]phenanthroline) were synthesized and the mechanism of antitumor activity was investigated. Compounds photoactivated by visible light show strong cytotoxicity against tumor cells, especially toward A549 cells. Biological experiments such as migration, cellular localization, mitochondrial membrane potential and permeability, reactive oxygen species (ROS) and calcium ion level detection were performed, and they demonstrated that the compounds induced the apoptosis of A549 cells through a mitochondrial pathway. At the same time, oxidative stress caused by ROS production increases the release of damage-related molecules and the expression of porogen gasdermin D (GSDMD), and the content of LDH released from damaged cell membranes also increased. Besides, the content of the lipid peroxidation product, malondialdehyde (MDA), increased and the expression of GPX4 decreased. These indicate that the compounds promote cell death by combining ferroptosis and pyroptosis. The results reveal that cyclometalated iridium(III) compounds 5a-5c may be a potential chemotherapeutic agent for photodynamic therapy of cancers. Show less

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

Title: Lysosome-targeted cyclometalated iridium(III) complexes: JMJD inhibition, dual induction of apoptosis, and autophagy. Abstract: A series of cyclometalated iridium(III) complexes with the formula [Ir(C^N)2 L](PF6) (C^N = 2-phenylpyridine (ppy, in Ir-1), 2-(2-thienyl)pyridine (thpy, in Ir-2), 2-(2,4-difluorophenyl)pyridine (dfppy, in Ir-3), L = 2-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)quinolin-8-ol) were designed and synthesized, which utilize 8-hydroxyquinoline derivative as N^N ligands to chelate the cofactor Fe2+ of the Jumonji domain-containing protein (JMJD) histone demethylase. As expected, the results of UV/Vis titration analysis confirm the chelating capabilities of Ir-1-3 for Fe2+, and molecular docking studies also show that Ir-1-3 can interact with the active pocket of JMJD protein, and treatment of cells with Ir-1-3 results in significant upregulation of trimethylated histone 3 lysine 9 (H3K9Me3), indicating the inhibition of JMJD activity. Meanwhile, Ir-1-3 exhibit much higher cytotoxicity against the tested tumor cell lines compared with the clinical chemotherapeutic agent cisplatin. And Ir-1-3 can block the cell cycle at the G2/M phase and inhibit cell migration and colony formation. Further studies show that Ir-1-3 can specifically accumulate in lysosomes, damage the integrity of lysosomes, and induce apoptosis and autophagy. Reduction of mitochondrial membrane potential and elevation of reactive oxygen species also contribute to the antitumor effects of Ir-1-3. Finally, Ir-1 can inhibit tumor growth effectively in vivo and increase the expression of H3K9Me3 in tumor tissues. Our study demonstrates that these iridium(III) complexes are promising anticancer agents with multiple functions, including the inhibition of JMJD and induction of apoptosis and autophagy. Show less

Title: Synthesis, biological evaluation of novel iridium(III) complexes targeting mitochondria toward melanoma B16 cells. Abstract: A new ligand 2-(1E,3E,5E,7E)-2,6-dimethyl-8-(2,6,6-trimethylcyclohex-1-yl)octa-1,2,5,7-tetraen-1-yl)-1H-imidazo[4,5-f][1,10]phenanthroline (DTOIP) was synthesized and combined with [Ir(ppy)2Cl]2·2H2O (ppy = deprotonated Hppy: 2-phenylpyridine), [Ir(piq)2Cl]2·2H2O (piq = deprotonated Hpiq: 1-phenylisoquinoline) and [Ir(bzq)2Cl]2·2H2O (bzq = deprotonated Hbzq: benzo[h]quinolone) to form [Ir(ppy)2(DTOIP)](PF6) (Ir1), [Ir(piq)2(DTOIP)](PF6) (Ir2), and [Ir(bzq)2(DTOIP)](PF6) (Ir3), respectively. The complexes were characterized by elemental analysis, high-resolution mass spectrometry (HRMS), 1H NMR and 13C NMR. The antiproliferative activity of the complexes toward B16, BEL-7402, Eca-109 and normal LO2 cells was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. Complexes Ir1, Ir2 and Ir3 showed high antiproliferative activity against B16 cells with a low IC50 values of 0.4 ± 0.1, 2.0 ± 0.1 and 1.4 ± 0.09 μM, respectively. Three-dimensional (3D) in vitro cell models also demonstrated that the iridium(III) complexes have a remarkable cytotoxicity to B16 cells. The experiments of cellular uptake, mitochondrial localization, and intracellular distribution of the drugs proved that the three iridium(III) complexes can enter the mitochondria, leading to the loss of mitochondrial membrane potential (MMP), decreased glutathione (GSH) levels, causing an increase of intracellular ROS content, and DNA damage, finally inducing apoptosis. RNA-sequence and bioinformatics analyses were used to analyze the differentially expressed genes and enriched biology processes. Antitumor in vivo demonstrated that complex Ir1 (5 mg/kg) exhibits a high efficacy to inhibit the tumor growth with an inhibitory rate of 71.67%. These results show that the complexes may be potent anticancer candidate drugs. Show less

The development of anticancer drugs to treat triple-negative breast cancer (TNBC) is an ongoing challenge. Immunogenic cell death (ICD) has garnered considerable interest worldwide as a promising synergistic modality for cancer chemoimmunotherapy. However, only few drugs or treatment modalities can trigger an ICD response and none of them exert a considerable clinical effect against TNBC. Therefore, new agents with potentially effective chemoimmunotherapeutic response are required. In this study, five new cyclometalated Ir(III) complexes containing isoquinoline alkaloid CˆN ligands were designed and synthesized. Among them, Ir-1 exhibited the highest in vitro cytotoxicity. Mechanistically, Ir-1 could trigger autophagy-dependent ferroptosis and a subsequent ferroptosis-dependent ICD response as well as indoleamine 2,3-dioxygenase (IDO) inhibition via reactive oxygen species (ROS)-mediated endoplasmic reticulum (ER) stress in MDA-MB-231 cells. When immunocompetent BALB/c mice were vaccinated with Ir-1-treated dying TNBC cells, antitumor CD8⁺ T-cell response and Foxp3⁺ T-cell depletion were induced, resulting in long-lasting antitumor immunity in TNBC cells. Moreover, combination therapy with Ir-1 and anti-PD1 could substantially augment in vivo therapeutic effects. Based on these results, Ir-1 is a promising candidate for chemoimmunotherapy against TNBC and its effects are mediated synergistically via ICD induction and IDO blockage. Show less

Title: Cyclometalated iridium(III) complexes induce immunogenic cell death in HepG2 cells via paraptosis. Abstract: Immunotherapy has been shown to provide superior antitumor efficacy by activating the innate immune system to recognize, attack and eliminate tumor cells without seriously harming normal cells. Herein, we designed and synthesized three new cyclometalated iridium(III) complexes (Ir1, Ir2, Ir3) then evaluated their antitumor activity. When co-incubated with HepG2 cells, the complex Ir1 localized in the lysosome, where it induced paraptosis and endoplasmic reticulum stress (ER stress). Notably, Ir1 also induced immunogenic cell death (ICD), promoted dendritic cell maturation that enhanced effector T cell chemotaxis to tumor tissues, down-regulated proportions of immunosuppressive regulatory T cells within tumor tissues and triggered activation of antitumor immunity throughout the body. To date, Ir1 is the first reported iridium(III) complex-based paraptosis inducer to successfully induce tumor cell ICD. Furthermore, Ir1 induced ICD of HepG2 cells without affecting cell cycle or reactive oxygen species levels. Show less

Title: Endocytic Uptake of Self-Assembled Iridium(III) Nanoaggregates for Holistic Treatment of Metastatic 3D Triple-Negative Breast Tumor Spheroids. Abstract: Triple-negative breast cancer (TNBC) presents a formidable challenge due to its aggressive behavior and limited array of treatment options available. This study focuses on employing nanoaggregate material of organometallic Ir(III) complexes for treating TNBC cell line MDA-MB-231. In this approach, Ir(III) complexes with enhanced cellular permeability are strategically designed and achieved through the incorporation of COOMe groups into their structure. The lead compound, IrL1, exhibits promiscuous nanoscale aggregation in RPMI cell culture media, characterized by a stable hydrodynamic effective diameter ranging from 190 to 202 nm over 48 h. With excellent photo-responsive contrast-enhanced cell imaging properties IrL1 exhibits an outstanding IC50, 48h value of 36.05± 0.03 nm when irradiated with 390 nm light in MDA-MB-231 (IC50, 48 h of Cisplatin is 5.29 µµ). In cell, investigation confirms that IrL1 nanoaggregates internalization via energy-dependent endocytosis undergo ferroptosis and ROS mediated cell death in MDA-MB-231 cells. Further, these in vivo studies using NOD-SCID mice confirmed that IrL1 exhibits a tendency to ablate tumors inoculated in mice models at therapeutically relevant doses. Thus, this comprehensive approach holds promise for expanding the repertoire of organometallic Ir(III) nanoaggregates with adaptable characteristics, thereby advancing their clinical utility of nanomedicine in the holistic treatment of metastatic 3D triple-negative breast tumor spheroids. Show less

Title: Designing novel tridentate iridium(III) complexes comprising functionalized benzothiazole ligands to improve anticancer activity by targeting mitochondria. Abstract: In recent years, organo‑iridium anticancer agents have shown promising antitumor activity toward cancer cells. In this paper, two benzothiazole-based tridentate ligands, 2,2'-(5-(tert-butyl)-1,3-phenylene)bis(benzo[d]thiazole) (L1) and 2,2'-(5-(methyl)-1,3-phenylene)bis(benzo[d]thiazole) (L2), have been designed and synthesized, and then combined with 2,2'-bipyridine (bipy) and 1,10-phenanthroline (phen) ancillary ligands to form a series of novel [Ir(N^C^N)(N^N)Cl]+-type iridium(III) complexes (Ir1-Ir4). The phosphorescence properties of these complexes facilitate the visualization of their subcellular localization and interactions with other biomolecules. Among them, complex Ir2 has the best cytotoxicity activity toward A549 cells and its antitumor activity was further evaluated. Laser confocal assay reveals that Ir2 followed an energy-dependent cellular uptake mechanism and specifically accumulates in mitochondria (Pearson colocalization coefficient: 0.89). The anticancer mechanism has been explored through apoptosis, cell cycle arrest, western blotting (WB), reactive oxygen species (ROS) levels and mitochondrial membrane potential (MMP) changes. The antitumor activity in vivo confirms that Ir2 could effectively inhibit tumor growth with an inhibitory rate of 71.60 %, which is superior to cisplatin. To the best of our knowledge, Ir2 is a rare example of [Ir(N^C^N)(N^N)Cl]+-type complexes as potential anticancer agents. Show less

Colon cancer is one of the most commonly diagnosed cancers and is recognized as the most aggressive tumor of the digestive system. Aberrant activation of signal transducer and activator of transcription 3 (STAT3) is associated with proliferation, metastasis and immunosuppression of the tumor cells. Here, to inhibit the STAT3 pathway and suppress metastasis in colon cancer cells, the half-sandwich iridium complex Ir-ART containing an artesunate-derived ligand was synthesized. The complex showed remarkable antiproliferative activity against human colon cancer HCT-116 cells and exhibited a concentration-dependent reduction in STAT3 protein expression. Mechanism study demonstrates that Ir-ART is located mainly in the nucleus and mitochondria, causing γ-H2AX and cyclin B1 reduction and reactive oxygen species accumulation and mitochondrial membrane potential loss, ultimately leading to autophagic cell death. The migration of cancer cells was also inhibited via metalloproteinase 9 downregulation. Furthermore, Ir-ART could initiate antitumor immune responses by eliciting immunogenic cell death and downregulating immunosuppressive cytokine cyclooxygenase-2. Taken together, Ir-ART is expected to be further applied to chemotherapy and immunotherapy for colon cancer. Show less

Title: Mitochondrial Viscosity Probes: Iridium(III) Complexes Induce Apoptosis in HeLa Cells. Abstract: Mitochondrial viscosity has emerged as a promising biomarker for diseases such as cancer and neurodegenerative disorders, yet accurately measuring viscosity at the subcellular level remains a significant challenge. In this study, we synthesized and characterized three cyclometalated iridium(III) complexes (Ir1-Ir3) containing 5-fluorouracil derivatives as ligands. Among these, Ir1 selectively induced apoptosis in HeLa cells by increasing mitochondrial production of reactive oxygen species (ROS), which triggered a cascade of events leading to mitochondrial dysfunction. Additionally, the fluorescence lifetime of Ir1 demonstrated high sensitivity to intracellular viscosity changes, enabling real-time fluorescence lifetime imaging microscopy (FLIM) of cellular micro-viscosity during apoptosis. These findings underscore the potential of cyclometalated Ir(III) complexes for both therapeutic and diagnostic applications at the subcellular level. Show less

Title: Mitochondrial-targeted iridium(III) complexes suppress tumor growth through inducting immunogenic cell death to activate immune response. Abstract: A new ligand, 2-(2-hydroxyl-4-methyl)phenyl-1H-imidazo[4,5-f][1,10]phenanthroline (IPMP), and [Ir(ppy)2(IPMP)]PF6 (7a), [Ir(bzq)2(IPMP)]PF6 (7b), and [Ir(piq)2(IPMP)]PF6 (7c) have been prepared and characterized by HRMS, NMR spectra. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays revealed that 7b exhibited excellent activity (IC50 = 4.5 ± 0.4 μM), while 7a and 7c showed good cytotoxicity (IC50 = 8.5 ± 0.9 μM and 8.9 ± 2.2 μM) against non-small cell lung cancer A549 cells. The experiments of cellular uptake and mitochondrial localization demonstrate that these new iridium(III) complexes are readily taken up by A549 cells and accumulate in the mitochondria and damage the structure of the mitochondria, which results in the loss of mitochondrial membrane potential (MMP), elevated lipid peroxidation, as well as DNA damage, the inhibition of microtubule polymerization, hindrance of the cell cycle in the G0/G1 phase, and release of cytochrome c, collectively leading to apoptosis. Furthermore, upregulation of Beclin-1, overexpression of NF-κB and downregulation of GPX4 protein were observed, which resulted in the activation of autophagy, pyroptosis and ferroptosis, respectively. In the C57BL/6 mouse model, the 7b demonstrated promising in vivo antitumor efficacy, with a tumor inhibitory rate of 66.9 %. Additionally, the complexes induce an immunogenic cell death to activate immune response, further enhance CD8+ T cells and efficiently inhibit tumor growth. Collectively, we consider that the complexes may be utilized as potential candidate agents for the treatment of A549 cancer. Show less

Modulating mitochondrial activity to regulate cancer cell homeostatic recycling presents a promising approach to overcome tumor resistance. Consequently, there is an urgent need for novel mitochondria-targeting agents and innovative strategies. We have developed [((η⁵-Cp∗)Ir(rhod)]²⁺2PF₆^- (Ir-rhod), a new mitochondria-targeted iridium complex that exhibits greater cytotoxicity towards A549R (cisplatin-resistant human lung cancer) cells compared to the ligand rhod. Ir-rhod's mitochondrial targeting ability stems from both rhodamine's inherent mitochondrial affinity and the complex's positive bivalent nature. The positively charged Ir-rhod enters cells and is drawn to mitochondria due to the high transmembrane potential in tumor cells. Notably, rhodamine enables real-time observation of Ir-rhod's dynamic distribution in vivo. Ir-rhod influences mitochondrial function, triggering tumor cell ferroptosis and apoptosis by modulating ACSL4 and GPX4. The targeting effect of Ir-rhod reduces its systemic toxicity in vivo, enhancing its biosafety profile. To our knowledge, Ir-rhod is an effective mitochondria-targeted Ir complex capable of inducing tumor cell death by disrupting mitochondrial function, offering a potent strategy to suppress cisplatin resistance in non-small cell lung cancer. Show less