Dipyridophenazine iridium(III) complex as a phototoxic cancer stem cell selective, mitochondria targeting agent

Rationally Designed Ir(III) Complex with an Exceptionally Strong Binding to Human Serum Albumin for Targeted Photodynamic Therapy

The application of iridium(III) complexes in photodynamic therapy (PDT) is often limited by their poor selectivity for cancerous cells, necessitating high drug doses that increase the risk of side effects. The development of efficient drug delivery systems such as albumin conjugation is therefore crucial to enhance the tumor-targeted delivery of photosensitizers. To date, the vast majority of metal complexes exhibit weak to moderate binding with human serum albumin, limiting the feasibility of this approach. To overcome this limitation, the rational design through molecular docking and density functional theory calculations of a novel Ir(III) complex as a strong albumin-binding photosensitizer is described. The herein reported compound has the highest albumin binding constant ever reported for an iridium complex, and it showed to photocatalytically produce reactive oxygen species upon blue light irradiation. The presented compound as well as structural derivatives could have high potential in tumor-targeted photodynamic therapy.

The role of ancillary ligands on benzodipyridophenazine-based Ru(II)/Ir(III) complexes in dark and light toxicity against TNBC cells

In this study, we investigated the impact of ancillary ligands on the anticancer activity of benzodipyridophenazine-based Ru(II) and Ir(III) complexes (Ru1, Ru2, Ir1, and Ir2). These metal complexes displayed three significant absorption bands attributed to the ligand-centered (LC) transitions, ligand-to-ligand charge transfer (LLCT), and metal-to-ligand charge transfer (MLCT). Binding studies of biomolecules were performed with the complexes along with the ligand, and it was found that after binding with Ru(II)/Ir(III), the properties of the ligands were enhanced. In vitro screening revealed that complex [(η5-Cp*)IrIIICl(κ2-N,N-benzo[i]dipyrido[3,2-a:2',3'-c])phenazine] (Ir1) exhibited the highest potency and selectivity (IC50 ∼ 2.14 μM, PI > 13) under yellow light irradiation. The photo-toxicity trend was Ir1 > Ru1 > Ir2 ≫ Ru2, which was found to be directly correlated with the singlet oxygen quantum yield (1O2). Chloro-substituted complexes (Ir1 and Ru1) were effective for hypoxic tumor treatment, particularly Ir1, which could generate high amounts of reactive oxygen species (ROS, type I PDT) in cells under photo irradiation. The high value of fluorescence quantum yield (fφ = 0.26) and significant emission at λ = 571 nm of Ir1 were certainly useful for bio-imaging applications. Colocalisation and DCFDA studies of Ir1 revealed that it can accumulate in the mitochondria, leading to depolarization of the mitochondrial membrane. These studies confirm that the complex Ir1 is a promising candidate for TNBC treatment in hypoxic tumors, with efficacy comparable to the current PDT drug Photofrin.

Anticancer activity and mechanism studies of photoactivated iridium(III) complexes toward lung cancer A549 cells

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.

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

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

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.

Photobleaching and phototoxicity of mitochondria in live cell fluorescent super-resolution microscopy

Photobleaching and phototoxicity can induce detrimental effects on cell viability and compromise the integrity of collected data, particularly in studies utilizing super-resolution microscopes. Given the involvement of multiple factors, it is currently challenging to propose a single set of standards for assessing the potential of phototoxicity. The objective of this paper is to present empirical data on the effects of photobleaching and phototoxicity on mitochondria during super-resolution imaging of mitochondrial structure and function using Airyscan and the fluorescent structure dyes Mitotracker green (MTG), 10-N-nonyl acridine orange (NAO), and voltage dye Tetramethylrhodamine, Ethyl Ester (TMRE). We discern two related phenomena. First, phototoxicity causes a transformation of mitochondria from tubular to spherical shape, accompanied by a reduction in the number of cristae. Second, phototoxicity impacts the mitochondrial membrane potential. Through these parameters, we discovered that upon illumination, NAO is much more phototoxic to mitochondria compared to MTG or TMRE and that these parameters can be used to evaluate the relative phototoxicity of various mitochondrial dye-illumination combinations during mitochondrial imaging.

Novel 2-(5-Arylthiophen-2-yl)-benzoazole Cyclometalated Iridium(III) dppz Complexes Exhibit Selective Phototoxicity in Cancer Cells by Lysosomal Damage and Oncosis

A second-generation series of biscyclometalated 2-(5-aryl-thienyl)-benzimidazole and -benzothiazole Ir(III) dppz complexes [Ir(C^N)2(dppz)]+, Ir1-Ir4, were rationally designed and synthesized, where the aryl group attached to the thienyl ring was p-CF3C6H4 or p-Me2NC6H4. These new Ir(III) complexes were assessed as photosensitizers to explore the structure-activity correlations for their potential use in biocompatible anticancer photodynamic therapy. When irradiated with blue light, the complexes exhibited high selective potency across several cancer cell lines predisposed to photodynamic therapy; the benzothiazole derivatives (Ir1 and Ir2) were the best performers, Ir2 being also activatable with green or red light. Notably, when irradiated, the complexes induced leakage of lysosomal content into the cytoplasm of HeLa cancer cells and induced oncosis-like cell death. The capability of the new Ir complexes to photoinduce cell death in 3D HeLa spheroids has also been demonstrated. The investigated Ir complexes can also catalytically photo-oxidate NADH and photogenerate 1O2 and/or •OH in cell-free media.

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

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

Targeting chemotherapy-resistant tumour sub-populations using inorganic chemistry: Anti-cancer stem cell metal complexes

Cancer stem cells (CSC) are a sub-population of tumours linked to metastasis and relapse. Current chemotherapeutic drug options are ineffective against CSCs at their administered doses. New families of cytotoxic agents, and new, highly specific ways of delivering them to CSCs, are needed to provide durable clinical outcomes. Inorganic compounds have recently emerged as a promising class of anti-CSC agents with clinically relevant potencies. In this short review, we present the very latest efforts (post-2020) on the development of anti-CSC metal complexes. The activities of the metal complexes in monolayer and three-dimensional CSC cultures and animal models is documented. The mechanism of action of the metal complexes with respect to their chemical structures is also highlighted.

Mitochondria as a target of third row transition metal-based anticancer complexes

In pursuit of better treatment options for malignant tumors, metal-based complexes continue to show promise as attractive chemotherapeutics due to tunability, novel mechanisms, and potency exemplified by platinum agents. The metabolic character of tumors renders the mitochondria and other metabolism pathways fruitful targets for medicinal inorganic chemistry. Cumulative understanding of the role of mitochondria in tumorigenesis has ignited research in mitochondrial targeting metal-based complexes to overcome resistance and inhibit tumor growth with high potency and selectivity. Here, we discuss recent progress made in third row transition metal-based mitochondrial targeting agents with the goal of stimulating an active field of research toward new clinical anticancer agents and the elucidation of novel mechanisms of action.

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.