Exploring Structure-Activity Relationships in Photodynamic Therapy Anticancer Agents Based on Ir(III)-COUPY Conjugates.

Photodynamic therapy holds great promise as a non-invasive anticancer tool against drug-resistant cancers. However, highly effective, non-toxic, and reliable photosensitizers with operability under hypoxic conditions remain to be developed. Herein, we took the advantageous properties of COUPY fluorophores and cyclometalated Ir(III) complexes to develop novel PDT agents based on Ir(III)-COUPY conjugates with the aim of exploring structure-activity relationships. The structural modifications carried out within the coumarin scaffold had a strong impact on the photophysical properties and cellular uptake of the conjugates. All Ir(III)-COUPY conjugates exhibited high phototoxicity under green light irradiation, which was attributed to the photogeneration of ROS, while remaining non-toxic in the dark. Among them, two hit conjugates showed excellent phototherapeutic indexes in cisplatin-resistant A2780cis cancer cells, both in normoxia and in hypoxia, suggesting that photoactive therapy approaches based on the conjugation of far-red/NIR-emitting COUPY dyes and transition metal complexes could effectively tackle in vitro acquired resistance to cisplatin.

Novel valproate half-sandwich rhodium and iridium conjugates to fight against multidrug-resistant Gram-positive bacteria.

New valproate Ir(III) and Rh(III) half-sandwich conjugates containing a C,N-phenylbenzimidazole chelated ligand have been synthesized and characterized. The valproic acid conjugation to organometallic fragments seems to switch on the antibacterial activity of the complexes towards Enterococcus faecium and Staphylococcus aureus Gram-positive bacteria.

Potent anticancer activity of a novel iridium metallodrug via oncosis.

Oncosis (from Greek ónkos, meaning "swelling") is a non-apoptotic cell death process related to energy depletion. In contrast to apoptosis, which is the main form of cell death induced by anticancer drugs, oncosis has been relatively less explored but holds potential to overcome drug resistance phenomena. In this study, we report a novel rationally designed mitochondria-targeted iridium(III) complex (OncoIr3) with advantageous properties as a bioimaging agent. OncoIr3 exhibited potent anticancer activity in vitro against cancer cells and displayed low toxicity to normal dividing cells. Flow cytometry and fluorescence-based assays confirmed an apoptosis-independent mechanism involving energy depletion, mitochondrial dysfunction and cellular swelling that matched with the oncotic process. Furthermore, a Caenorhabditis elegans tumoral model was developed to test this compound in vivo, which allowed us to prove a strong oncosis-derived antitumor activity in animals (with a 41% reduction of tumor area). Indeed, OncoIr3 was non-toxic to the nematodes and extended their mean lifespan by 18%. Altogether, these findings might shed new light on the development of anticancer metallodrugs with non-conventional modes of action such as oncosis, which could be of particular interest for the treatment of apoptosis-resistant cancers.

Inert cationic iridium(III) complexes with phenanthroline-based ligands: application in antimicrobial inactivation of multidrug-resistant bacterial strains.

The antimicrobial activity of a new series of heteroleptic iridium(III) complexes of the type [Ir(C^N)2(N^N)][PF6] (C^N = deprotonated 2-phenylbenzimidazole-κN, κC; N^N = phen (Ir1), dpq (Ir2), dppz (Ir3), dppn (Ir4), and dppz-idzo (Ir5)) was studied towards two Gram positive (vancomycin-resistant Enterococcus faecium and a methicillin-resistant Staphylococcus aureus) and two Gram negative (Acinetobacter baumanii and Pseudomonas aeruginosa) multidrug-resistant bacterial strains of clinical interest. Although the complexes were inactive towards Gram negative bacteria, their effectiveness against Gram positive strains was remarkable, especially for Ir1 and Ir2, the most bactericidal complexes that were even more active (10 times) than the fluoroquinolone antibiotic norfloxacin and displayed no toxicity in human kidney cells (HEK293). Mechanistic studies revealed that the cell wall and membrane of MRSA S. aureus remained intact on treatment with these compounds and that DNA was not their main target. It is important to note that the complexes were able to induce ROS generation, this being the feature key to their antimicrobial activity.

Towards Novel Photodynamic Anticancer Agents Generating Superoxide Anion Radicals: A Cyclometalated IrIII Complex Conjugated to a Far-Red Emitting Coumarin.

Although cyclometalated IrIII complexes have emerged as promising photosensitizers for photodynamic therapy, some key drawbacks still hamper clinical translation, such as operability in the phototherapeutic window and reactive oxygen species (ROS) production efficiency and selectivity. In this work, a cyclometalated IrIII complex conjugated to a far-red-emitting coumarin, IrIII -COUPY, is reported with highly favourable properties for cancer phototherapy. IrIII -COUPY was efficiently taken up by HeLa cells and showed no dark cytotoxicity and impressive photocytotoxicity indexes after irradiation with green and blue light, even under hypoxia. Importantly, a clear correlation between cell death and intracellular generation of superoxide anion radicals after visible light irradiation was demonstrated. This strategy opens the door to novel fluorescent photodynamic therapy agents with promising applications in theragnosis.

Exploring the Effect of Polypyridyl Ligands on the Anticancer Activity of Phosphorescent Iridium(III) Complexes: From Proteosynthesis Inhibitors to Photodynamic Therapy Agents.

A series of five kinetically inert bis-cyclometalated IrIII complexes of general formula [Ir(C^N)2 (N^N)][PF6 ] [C^N=2-phenyl-1-[4-(trifluoromethyl)benzyl]-1H-benzo[d]imidazol-κN,C; N^N=1,10-phenanthroline (phen, 1), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq, 2), dipyrido[3,2-a:2',3'-c]phenazine (dppz, 3), benzo[i]dipyrido[3,2-a:2',3'-c]phenazine (dppn, 4), and dipyrido[3,2-a:2',3'-c]phenazine-10,11-imidazolone (dppz-izdo, 5)] were designed and synthesized to explore the effect of the degree of π conjugation of the polypyridyl ligand on their toxicity in cancer cells. We show that less-lipophilic complexes 1 and 2 exhibit the highest toxicity [sub-micromolar inhibitory concentration (IC50 ) values] in A2780, HeLa, and MCF-7 cancer cells, and they are markedly more efficient than clinically used platinum drugs. It is noteworthy that the investigated Ir agents display the capability to overcome acquired and inherent resistance to conventional cisplatin (in A2780cisR and MCF-7 cells, respectively). We demonstrate that the Ir complexes, unlike clinically used platinum antitumor drugs, do not kill cells through DNA-damage response. Rather, they kill cells by inhibiting protein translation by targeting preferentially the endoplasmic reticulum. Our findings also reveal that the toxic effect of the Ir complexes can be significantly potentiated by irradiation with visible light (by more than two orders of magnitude). The photopotentiation of the investigated Ir complexes can be attributed to a marked increase (≈10-30-fold) in intracellular reactive oxygen species. Collectively, these data highlight the functional diversity of antitumor metal-based drugs and the usefulness of a mechanism-based rationale for selecting candidate agents that are effective against chemoresistant tumors for further preclinical testing.

Highly potent extranuclear-targeted luminescent iridium(iii) antitumor agents containing benzimidazole-based ligands with a handle for functionalization.

A series of 6 substitutionally inert and luminescent iridium(iii) antitumor agents of the type [Ir(C∧N)2(N∧N)][PF6] containing a benzimidazole N∧N ligand with an ester group as a handle for further functionalization has been prepared. They exhibit IC50 values in the high nanomolar range in some ovarian and breast cancer cell lines (approximately 100× more cytotoxic than cisplatin (CDDP) in MDA-MB-231) and are located in the actin cortex predominantly as shown by confocal luminescence microscopy. This discovery could open the door to a new large family of drug bioconjugates with diverse and simultaneous functions.