Mitochondria-targeted cyclometalated iridium (III) complexes: Dual induction of A549 cells apoptosis and autophagy

Cyclometalated iridium(III)-lonidamine conjugates: Mitochondrial targeting and pyroptosis induction

A series of cyclometalated Ir(III)-lonidamine (LND) complexes (Ir-LND-1-6) with the formula [Ir(C^N)2bpy(4-CH3-4'-CH2OLND)](PF6) (Ir-LND-1-3) and [Ir(C^N)2bpy(4-CH2OLND-4'-CH2OLND)](PF6) (Ir-LND-4-6) (C^N = 2-phenylpyridine (ppy, in Ir-LND-1 and Ir-LND-4), 2-(2-thienyl) pyridine (thpy, in Ir-LND-2 and Ir-LND-5) and 2-(2,4-difluorophenyl) pyridine (dfppy, in Ir-LND-3 and Ir-LND-6)), were designed and synthesized. 3-(4,5-dimethylthiazol-2-yl)-2,5-biphenyltetrazolium bromide (MTT) assay data showed that the cytotoxicity of Ir-LND-1-3 carry one LND moiety was superior to that of Ir-LND-4-6 with two LND moieties. Therefore, we selected Ir-LND-1-3 as model compounds to investigate the anti-tumor mechanism of the Ir(III)-LND system. The results showed that Ir-LND-1-3 could inhibit cancer cell migration and colony formation. In addition, Ir-LND-1-3 could penetrate into HeLa cells and localized to mitochondria, further disrupting mitochondrial membrane potential (MMP), increasing intracellular reactive oxygen species (ROS), and reducing intracellular adenosine triphosphate (ATP). Further exploration of anti-tumor mechanisms showed that pyroptosis was the main mode of Ir-LND-1-3 induced cell death, manifested as membrane perforation and swelling, activation of caspase-3 and cleavage of Gasdermin E (GSDME), as well as release of lactic dehydrogenase (LDH) and ATP. The pyroptosis induced by Ir-LND-1-3 also initiated immunogenic cell death (ICD) by triggering the release of calreticulin (CRT) and high mobility group protein b1 (HMGB1) on the cell surface.

Designing novel tridentate iridium(III) complexes comprising functionalized benzothiazole ligands to improve anticancer activity by targeting mitochondria

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.

Preparation of ferrocene‑iridium(III) acylhydrazone complexes and their anticancer application against A549 cell line

Two ferrocene‑iridium(III) acylhydrazone complexes (Fe-Ir1 and Fe-Ir2) were designed and synthesized, which showed excellent anti-proliferative activity against A549 human lung adenocarcinoma and A549/DDP (cisplatin-resistant) cell lines, especially for Fe-Ir1 (IC50 = 10.2 ± 0.4 μM, twice that of cisplatin). Meanwhile, Fe-Ir1 showed low toxicity to BEAS-2B cells (normal dividing human bronchial epithelial cells), indicating its favorable selectivity. Fe-Ir1 entered A549 cells following an non-energy-dependent pathway, targeted lysosomes, induced changes in lysosomal membrane permeability, reduced glycolytic stress, arrested cell cycle, then promoted early-stage apoptosis and effectively inhibited cell migration. Western blotting also showed that the Fe-Ir1 could promote the expression of Bax protein and inhibited Bcl-2 and PARP protein in A549 cells. In vivo experiments demonstrated that Fe-Ir1 had significant capabilities in inhibiting tumor growth, cancer cell metastasis and spread. In conclusion, Fe-Ir1 holds promise as a potential alternative to platinum-based drugs and warrants further research, offering more hope and vitality to cancer patients.

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

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

Photoactivatable, mitochondria targeting dppz iridium(III) complex selectively interacts and damages mitochondrial DNA in cancer cells

Cyclometalated Ir(III) complex [Ir(L)2(dppz)]PF6 (where L = 1-methyl-2-(thiophen-2-yl)-1H-benzo[d]imidazole and dppz = dipyrido [3,2-a:2',3'-c]phenazine) (Ir1) is potent anticancer agent whose potency can be significantly increased by irradiation with blue light. Structural features of the cyclometalated Ir(III) complex Ir1 investigated in this work, particularly the presence of dppz ligand possessing an extended planar area, suggest that this complex could interact with DNA. Here, we have shown that Ir1 accumulates predominantly in mitochondria of cancer cells where effectively and selectively binds mitochondrial (mt)DNA. Additionally, the results demonstrated that Ir1 effectively suppresses transcription of mitochondria-encoded genes, especially after irradiation, which may further affect mitochondrial (and thus also cellular) functions. The observation that Ir1 binds selectively to mtDNA implies that the mechanism of its biological activity in cancer cells may also be connected with its interaction and damage to mtDNA. Further investigations revealed that Ir1 tightly binds DNA in a cell-free environment, with sequence preference for GC over AT base pairs. Although the dppz ligand itself or as a ligand in structurally similar DNA-intercalating Ru polypyridine complexes based on dppz ligand intercalates into DNA, the DNA binding mode of Ir1 comprises surprisingly a groove binding rather than an intercalation. Also interestingly, after irradiation with visible (blue) light, Ir1 was capable of cleaving DNA, likely due to the production of superoxide anion radical. The results of this study show that mtDNA damage by Ir1 plays a significant role in its mechanism of antitumor efficacy. In addition, the results of this work are consistent with the hypothesis and support the view that targeting the mitochondrial genome is an effective strategy for anticancer (photo)therapy and that the class of photoactivatable dipyridophenazine Ir(III) compounds may represent prospective substances suitable for further testing.

Mitochondria-targeted ruthenium(II) complexes for photodynamic therapy and GSH detection in living cells

Photodynamic therapy is an emerging tumor therapy that kills tumor cells by activating reactive oxygen species (ROS) produced by photosensitizers. Mitochondria, as an important organelle, are the main generator of cellular ROS. Therefore, the development of photosensitizers capable of targeting mitochondria could significantly enhance the efficacy of photodynamic therapy. In this study, two novel ruthenium(II) complexes, Ru-1 and Ru-2, were designed and synthesized, both of which were functionalized with α,β-unsaturated ketones for sensing of glutathione (GSH). The crystal structures of the two complexes were determined and they exhibited good recognition of GSH by off-on luminescence signals. The complex Ru-2 containing aromatic naphthalene can enter the cells and react with GSH to generate a strong luminescence signal that can be used to monitor intracellular GSH levels through imaging. Ru-2 also has an excellent mitochondrial localization ability with a Pearson's coefficient of 0.95, which demonstrates that it can efficiently target the mitochondria of tumor cells to enhance the effectiveness of photodynamic therapy as a photosensitizer.