Theranostic Lysosomal Targeting Anticancer and Antimetastatic Agents: Half-Sandwich Iridium(III) Rhodamine Complexes

Metal complexes with a twist: modified rhodamines as a promising theranostic approach for combating cancer

Rhodamines have been recognized for their exceptional optical properties, making them suitable for detection, imaging, and disease diagnosis. However, their use as photosensitizers in Photodynamic Therapy (PDT) has been limited by their low singlet oxygen production and limited tissue penetration. The development of rhodamine-metal complexes has overcome these limitations, offering a promising new approach for cancer treatment. These complexes in combination with structural and optical tuning of rhodamines, have been engineered to enhance tumour cell selectivity, improve reactive oxygen species (ROS) generation, and mitochondrial-targeted delivery. Notably, a variety of metal ions, including iridium(III), ruthenium(II) and platinum(II/IV) can form complexes with bright rhodamines with excellent optical responses and remarkable ROS generation. These breakthroughs have the potential to improve cancer diagnosis and therapeutic applications. Photophysical properties, photostability, and targeting agents, particularly in the near-infrared (NIR) range, will be discussed, with a focus on their applications in cancer detection, localization, and cytotoxicity.

A comprehensive survey of cytotoxic active half-sandwich Ir(III) complexes: structural perspective, and mechanism of action

Iridium(III) complexes, particularly those with piano-stool structures, have drawn a lot of interest recently as possible anticancer drugs. These complexes, which have displayed enhanced cytotoxicity and cytoselectivity compared with clinically approved drugs like cisplatin, oxaliplatin, and carboplatin, hold promising prospects for further anticancer research. Our review aims to explore the complex interplay between cytotoxic properties, cellular uptake efficiency, and intracellular distribution properties of this class of Ir(III) complexes, considering the variation of the coordination site atoms. We provide an overview of the majority of research on mono- and polynunclear half-sandwich Ir(III) complexes with mono- and bidentate ligands, focusing on the impact of altering the leaving group, tethers, substituents on the cyclopentadienyl ring and ligand, spacers, and counter ions on the cytotoxicity and mode of action.

RuIII-Morpholine-Derived Thiosemicarbazone-Based Metallodrugs: Lysosome-Targeted Anticancer Agents

The idea of coordinating biologically active ligand systems to metal centers to exploit their synergistic effects has gained momentum. Therefore, in this report, three RuIII complexes 1-3 of morpholine-derived thiosemicarbazone ligands have been prepared and characterized by spectroscopy and HRMS along with the structure of 2 through a single-crystal X-ray diffraction study. The solution stability of 1-3 was tested using conventional techniques such as UV-vis and HRMS. Further, the anticancer activity of 1-3 was tested in HT-29 and HeLa cancer cell lines. To gain insight into their mechanism of action, the cytotoxicity, hydrophobicity, and the interaction of 1-3 with DNA and HSA were evaluated by different conventional methods such as absorption, fluorescence, and circular dichroism studies. Along with favorable biomolecule interaction, 1-3 revealed potent selectivity toward cancer cells, which is a prerequisite for the generation of an anticancer drug. According to cell viability results, 1 has the highest cytotoxicity among all in the group, against both cells, respectively. Additionally, the fluorescence-active ruthenium complexes selectively target lysosomes, which is evaluated by live-cell imaging. 1-3 disrupt the lysosome membrane potential by generating an excessive amount of reactive oxygen species, which results in an apoptotic mode of cell death.

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.

Synthesis of novel rhodamine type Anthrone Spiro-lactam (ASL) analogues and evaluation of antiviral activity against dengue and chikungunya viruses

A series of Rhodamine type Anthrone-Spirolactam (ASL) derivatives Benzylimin-Anthrone-Spirolactam (ASL-1 to ASL-10) and Benzamide-Anthrone-Spirolactam (ASL-11 and ASL-12) were synthesized via a simple condensation reaction between Anthrone Spiro-lactamine (2) and various aromatic aldehyde and acyl chlorides respectively. Since rhodamine-based compounds were reported to have antiviral activity, the ASL derivatives were examined for in vitro antiviral activity against dengue and chikungunya viruses. Among all the analogues, ASL-3, ASL-6, ASL-7, ASL-8, ASL-9 and ASL-10 were the most potent against dengue virus (DENV) and exerted around one log reduction in virus titre under post-treatment conditions. At the same time ASL-3 was effective under co-treatment conditions. Two analogues ASL-6 and ASL-12 exerted anti-chikungunya virus (CHIKV) activity under post-treatment conditions. In silico docking studies revealed that the ASL derivatives interacted with the proteins of DENV and CHIKV. Together, the results suggest the anti-DENV and CHIKV activity of ASL derivatives which may be exploited further for therapeutic purposes.

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.

Light activation of iridium(III) complexes driving ROS production and DNA damage enhances anticancer activity in A549 cells

The work aimed to synthesize and characterize two iridium(III) complexes [Ir(ppy)₂(IPPH)](PF₆) (Ir1, IPPH = (2S,3R,5S,6R)-2-(2-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)phenoxy)-6-(hydroxymethyl)tetrahydro-2H-pyran-3,4,5-triol, ppy = 2-phenylpyridine), [Ir(piq)₂(IPPH)](PF₆) (Ir2, piq = 1-phenylisoquinoline). The cytotoxicity of the complexes against BEL-7402, A549, HCT-116, B16 cancer cells and normal LO2 was evaluated through 3-(4,5-dimethylthiazole-2-yl)-2,5-biphenyl tetrazolium bromide (MTT) method. The complexes show no cytotoxic activity (IC₅₀ > 100 μM) against these cancer cells, while their cytotoxicity can significantly be elevated upon illumination. The IC₅₀ values range from 0.2 ± 0.05 to 35.5 ± 3.5 μM. The cellular uptake, endoplasmic reticulum and mitochondria localization, reactive oxygen species, the change of mitochondrial membrane potential, γ-H2AX levels, cycle arrest, apoptosis and the expression of B-cell lymphoma-2 were investigated. The calreticulin (CRT), heat shock protein 70 (HSP70), high mobility group box 1 (HMGB1) were explored. This study demonstrates that photoactivatable complexes induce cell death in A549 through ROS-mediated endoplasmic reticulum stress-mitochondrial pathway, DNA damage pathways, immunogenic cell death (ICD), activation of PI3K/AKT signaling pathway and inhibit the cell growth at S phase.

Metal Complexes in Target-Specific Anticancer Therapy: Recent Trends and Challenges

Cancer is characterized by abnormal cell differentiation in or on the part of the body. The most commonly used chemotherapeutic drugs are developed to target rapidly dividing cells, such as cancer cells, but they also damage healthy epithelial cells. This has serious consequences for normal cells and become responsible for the development of various disorders. Several strategies for delivering the cytotoxic drugs to cancerous sites that limit systemic toxicity and other adverse effects have recently been evolved. Among them, biomolecule-conjugated metal complexes-based cancer targeting strategies have shown tremendous advantages in cancer therapy. This review focuses on several chemoselective biomolecules-bound metal complexes as prospective cancer therapy-targeted agents. In this review, we presented the details of the various extra- and intracellular targeting mechanisms in cancer therapy. We also addressed the current clinical issues and recent therapeutic strategies in targeted cancer therapy that may pave a way for the future direction of metal complexes-based targeted cancer therapy.

Iridium(III) complexes entrapped in liposomes trigger mitochondria-mediated apoptosis and GSDME-mediated pyroptosis

In this report, a new ligand TFBIP (TFBIP = 2-(4'-trifluoromethyl)-[1,1'-biphenyl]-4-yl)-1H-imidazo[4,5-f][1,10]phenanthroline) and its three iridium (III) complexes [Ir(ppy)₂(TFBIP)](PF₆) (Ir1, ppy = 2-phenylpyridine), [Ir(bzq)₂(TFBIP)](PF₆) (Ir2, bzq = benzo[h]quinolone) and [Ir(piq)₂(TFBIP)](PF₆) (Ir3, piq = 1-phenylisoquinoline) were synthesized and characterized. The cytotoxicity in vitro of the complexes toward several cancer cells was evaluated by 3-(4,5-dimethylthiazole-2-yl)-2,5-biphenyl tetrazolium bromide (MTT) methods. The complexes show no cytotoxicity (IC₅₀ > 100 μM) against these cancer cells. To enhance anticancer activity, these complexes were trapped in liposomes to form Ir1Lipo, Ir2Lipo and Ir3Lipo. The liposomes Ir1Lipo, Ir2Lipo and Ir3Lipo exhibit high or moderate cytotoxic activity. In particular, Ir1Lipo can effectively inhibit the cell growth with a low IC₅₀ value (< 10 μM) toward A549, HepG2, BEL-7402, B16, HeLa and SGC-7901 cells. Surprisingly, Ir1Lipo has no cytotoxic activity against the normal cell LO2 (IC₅₀ > 100 μM). The apoptosis and pyroptosis were investigated. Ir3Lipo induces apoptosis with a high early apoptotic number of 37%. The reactive oxygen species (ROS) levels, mitochondrial permeability transition pore open and mitochondrial membrane potential were detected. The intracellular Ca²⁺ concentration and release of cytochrome c were investigated. The expression of Bcl-2 (B-cell lymphoma-2) family proteins was explored by western blot. The antitumor activity in vivo of Ir1Lipo was evaluated with an inhibitory rate of 53%.

Cytotoxic BODIPY-Appended Half-Sandwich Iridium(III) Complex Forms Protein Adducts and Induces ER Stress

Half-sandwich complexes of iridium(III) are currently being developed as anticancer drug candidates. In this context, we introduce IrBDP for which the C^N chelating phenyloxazoline ligand carries a fluorescent and lipophilic BODIPY reporter group, designed for intracellular tracking and hydrophobic compartment tropism. High-resolution analysis of cells cultured with IrBDP showed that it quickly permeates the plasma membrane and accumulates in the mitochondria and endoplasmic reticulum (ER), generating ER stress, dispersal of the Golgi apparatus, cell proliferation arrest and apoptotic cell death. Moreover, IrBDP forms fluorescent adducts with a subset of amino acids, namely histidine and cysteine, via coordination of N or S donor atoms of their side chains. Consistently, in vivo formation of covalent adducts with specific proteins is demonstrated, providing a molecular basis for the observed cytotoxicity and cellular response. Collectively, these results provide a new entry to the development of half-sandwich iridium-based anticancer drugs.

Development of pH/Glutathione-Responsive Theranostic Agents Activated by Glutathione S-Transferase π for Human Colon Cancer

Two novel theranostic agents HJTA and HJTB have been designed and synthesized by covalently linking a β-carboline derivative, with antitumor activities and pH-responsive fluorescence, with a 2-exomethylenecyclohexanone moiety, which can be activated by the tumor-targeting glutathione (GSH)/glutathione S-transferase π (GSTπ). These agents showed pH- and GSH-dual-responsive fluorescence in tumor cells but not in normal cells. Importantly, HJTA selectively illuminated tumor tissue for up to 7 h and generated precise visualization of orthotopic colonic tumors through the blood circulation system in intraoperative mice. Furthermore, HJTA exhibited potent and selective antiproliferative activities and colonic tumor inhibition in mice. Finally, HJTA induced great cancer cell apoptosis and autophagy by regulating the expression of apoptotic and autophagic proteins. Therefore, this pH/GSH-dual-responsive fluorescent probe with cancer-targeting therapeutic activity provides a novel tool for precise diagnosis and tumor treatment, therefore broadening the impact of multifunctional agents as theranostic precision medicines.

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

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

Liposomes encapsulated iridium(III) polypyridyl complexes enhance anticancer activity in vitro and in vivo

Three iridium(III) complexes [Ir(ppy)₂(CPIP)](PF₆) (Ir-1, ppy = 2-phenylpyridine, CPIP = 2-(4-chlorophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline), [Ir(ppy)₂(DCPIP)](PF₆) (Ir-2, DCPIP = 2-(3,4-dichlorophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline) and [Ir(ppy)₂(TCPIP)](PF₆) (Ir-3, TCPIP = 2,3,5-trichlorophenyl)-1H-imidazo[4,5-f][1,10]phenanthroline) were synthesized and characterized. The complexes Ir-1, Ir-2 and Ir-3 were encapsulated in liposomes to form Ir-1-Lipo, Ir-2-Lipo and Ir-3-Lipo. Morphology, size distribution, and zeta potential of liposomes were examined by transmission electron microscopy (TEM) and Zetasizer. The cytotoxic activity in vitro of Ir-1, Ir-2 and Ir-3 against cancer A549, HTC-116, HepG2, BEL-7402, Eca-109, B16, HeLa SGC-7901 and normal NIH3T3 cells was evaluated by 3-(4,5-dimethylthiazole-2-yl)-2,5-biphenyl tetrazolium bromide (MTT) method. Ir-2 and Ir-3 show no cytotoxic activity against the selected cancer cells, and Ir-1 displays moderate cytotoxic effect on the cell growth in A549 cells. However, Ir-1, Ir-2 and Ir-3 were encapsulated in liposomes, the cytotoxic activity was greatly enhanced. In particular, Ir-1-Lipo and Ir-2-Lipo can effectively inhibit the cell growth in A549 cells with a low IC₅₀ value of 3.1 ± 0.3 and 1.2 ± 0.4 μM. The apoptosis was assayed by flow cytometry. Ir-1, Ir-2 and Ir-3 reveal weak apoptotic effect, whereas Ir-1-Lipo, Ir-2-Lipo and Ir-3-Lipo induce an apoptotic percentage of 55.6%, 69.3% and 16.7% in A549 cells, respectively. Specially, in the assay of antitumor activity in vivo, the inhibiting percentage of tumor growth induced by Ir-2 is 27.65%, while inhibiting percentage of tumor growth caused by Ir-2-Lipo is 57.45%. Obviously, the liposomes can enhance anticancer activity in vitro and in vivo compared with the complexes. The results show that the iridium(III) complexes encapsulated liposomes induce apoptosis in A549 cells through ROS-mediated lysosome-mitochondria dysfunction pathway and target the microtubules.

Novel cyclometalated iridium(iii) phosphine-imine (P^N) complexes: highly efficient anticancer and anti-lung metastasis agents in vivo

Iridium(iii)-based complexes with phosphine-imine (P^N) ligands are synthesized and authenticated. The combined treatment with Ir(iii) and BIX01294 potently inhibited tumour growth and lung metastasis in vitro and in vivo.