👤 Silva HD

Title: A Bioactive Benzimidazole-Cyclometalated Iridium(III) Complex as an Epigenetic Regulator through Effectively Interrupting the EED-EZH2 Interaction. Abstract: Epigenetic regulation plays a fundamental role in controlling gene expression and maintaining cellular identity. Among epigenetic processes, the translocation of methyltransferases is critical for the modification of chromatin structure and transcriptional activity. The regulation of these translocation events and the mechanisms involved are complex, yet critical for understanding and manipulating epigenetic states. Therefore, novel strategies are required for detecting and visualizing the movement and interaction of methyltransferases within cells. Using enhancer of zeste homolog 2 (EZH2) methyltransferase as an example, a bifunctional compound capable of both monitoring and disrupting its translocation process is developed by targeting the protein-protein interaction (PPI) between embryonic ectoderm development (EED) and EZH2. The Ir(III) complex 1 bound enthalpically to EED and effectively inhibited the methyltransferase activity of EZH2. Moreover, disruption of the EED-EZH2 PPI led to increased transcriptional activity of P21 and P27, resulting in the suppression of triple-negative breast cancer (TNBC) cell proliferation. Excitingly, 1 suppressed tumor metastasis in a TNBC mouse model in vivo. To our knowledge, complex 1 is the first metal-based bifunctional therapeutic agent designed to probe and inhibit the EED-EZH2 PPI, highlighting the feasibility and significance of using metal complexes to monitor and influence methyltransferase translocations for therapeutic applications. Show less

Ovarian cancer represents a leading cause of cancer-related deaths in women worldwide. Chemotherapeutic agents are usually employed to treat the patients, and Ruthenium(II)-based compounds have been investigated as possible substitutes for platinum drugs. In this work, we studied three different Ru(II)-phosphine-mercapto complexes (1-3) as potential cytotoxic agents against A2780 and A2780-cisR ovarian cancer cells. A time-dependent cytotoxicity was observed for 2, which also exhibited better selectivity than cisplatin control. A similar cytotoxic behavior was observed on 3D tumor spheroids. Although no changes were observed in cell cycle distribution, compound 2 affected the mitochondrial membrane potential on A2780 cells, and caused cell death via apoptotic pathway, which was confirmed by flow cytometry assay. Western blotting experiments revealed that 2 affected the expression of p53, PCNA, γH2AX and cleaved caspase-3, making it a promising anticancer agent for ovarian cancer. Show less

Organoiridium picolinamidate complexes are promising for intracellular applications because of their biocompatibility, activity in living systems, and ease of derivatization. To shield their metal centers from inhibition by biological nucleophiles (e.g., glutathione), attempts were made to increase the steric bulk of the supporting N-(2,6-R₂-phenyl)picolinamidate ligand. It was found that when R = H (Ir1) or methyl (Ir2), the ligand adopts N,N'-coordination to iridium, whereas when R = isopropyl (Ir3) or phenyl (Ir4), N,O-coordination was observed. Based on experimental measurements and density functional theory calculations, it was revealed that the carbon chemical shift of the C(O)NR group can be used as a diagnostic handle to distinguish between the N,N'- and N,O-isomers in solution. Computational studies indicate that the former is favored thermodynamically but the latter is preferred when the R group is overly bulky. Complexes Ir1-Ir4 exhibit differences in lipophilicity, cellular uptake, cytotoxicity, and the propensity to generate reactive oxygen species in living cells. Reaction studies showed that Ir1/Ir2 are more efficient than Ir3/Ir4 in promoting the reduction of aldehydes to alcohols via transfer hydrogenation but both isomer types were susceptible to catalyst poisoning by glutathione. This work has led to new insights into structural isomerism in organoiridium picolinamidate complexes and suggests that steric tuning alone is insufficient to protect the Ir center from poisoning by biological nucleophiles. Show less

In this work, we report on the development of fluorescent half-sandwich iridium complexes using a fluorophore attachment strategy. These constructs consist of pentamethylcyclopentadienyl (Cp*) iridium units ligated by picolinamidate donors conjugated to green-emitting boron-dipyrromethene (bodipy) dyes. Reaction studies in H₂O/THF mixtures showed that the fluorescent Ir complexes were active as catalysts for transfer hydrogenation, with activities similar to that of their non-fluorescent counterparts. The iridium complexes were taken up by NIH-3T3 mouse fibroblast cells, with 50% inhibition concentrations ranging from ~20-70 μM after exposure for 3 h. Visualization of the bodipy-functionalized Ir complexes in cells using fluorescence microscopy revealed that they were localized in the mitochondria and lysosome but not the nucleus. These results indicate that our fluorescent iridium complexes could be useful for future biological studies requiring intracellular catalyst tracking. Show less

Ruthenium(II) complexes (Ru1-Ru5), with the general formula [Ru(N-S)(dppe)₂]PF₆, bearing two 1,2-bis(diphenylphosphino)ethane (dppe) ligands and a series of mercapto ligands (N-S), have been developed. The combination of these ligands in the complexes endowed hydrophobic species with high cytotoxic activity against five cancer cell lines. For the A549 (lung) and MDA-MB-231 (breast) cancer cell lines, the IC₅₀ values of the complexes were 288- to 14-fold lower when compared to cisplatin. Furthermore, the complexes were selective for the A549 and MDA-MB-231 cancer cell lines compared to the MRC-5 nontumor cell line. The multitarget character of the complexes was investigated by using calf thymus DNA (CT DNA), human serum albumin, and human topoisomerase IB (hTopIB). The complexes potently inhibited hTopIB. In particular, complex [Ru(dmp)(dppe)₂]PF₆ (Ru3), bearing the 4,6-diamino-2-mercaptopyrimidine (dmp) ligand, effectively inhibited hTopIB by acting on both the cleavage and religation steps of the catalytic cycle of this enzyme. Molecular docking showed that the Ru1-Ru5 complexes have binding affinity by active sites on the hTopI and hTopI-DNA, mainly via π-alkyl and alkyl hydrophobic interactions, as well as through hydrogen bonds. Complex Ru3 displayed significant antitumor activity against murine melanoma in mouse xenograph models, but this complex did not damage DNA, as revealed by Ames and micronucleus tests. Show less

Nitric oxide (NO) is an intra- and extracellular messenger with important functions during human physiology process. A long-lived luminescent iridium(III) complex probe 1 has been designed and synthesized for the monitoring of NO controllably released from sodium nitroprusside (SNP). Probe 1 displayed a 15-fold switch-on luminescence in the presence of SNP at 580 nm. The probe exhibited a linear response towards SNP between 5 to 25 μM with detection limit at 0.18 μM. Importantly, the luminescent switch-on detection of NO in HeLa cells was demonstrated. Overall, complex 1 has the potential to be applied for NO tracing in complicated cellular environment. Show less

The aim of this work was the synthesis, characterization, and cytotoxicity evaluation of three new Ru(II) complexes with a general formula [Ru(Spy)(bipy)(P-P)]PF₆ [Spy = pyridine-6-thiolate; bipy = 2,2'-bipyridine; P-P = 1,2-bis(diphenylphosphine)ethane (1); 1,3-bis(diphenylphosphine) propane (2); and 1,1'-bis(diphenylphosphino)ferrocene] (4). Complex (3) with the 1,4-bis(diphenylphosphine)butane ligand, already known from the literature, was also synthesized, to be better studied here. The cytotoxicities of the complexes toward two kinds of cancerous cells (K562 and S-180 cells) were evaluated and compared to normal cells (L-929 and PBMC) by MTT assay. The complex [Ru(Spy)(bipy)(dppb)]PF₆ (3) was selected to study both the cellular and molecular mechanisms underlying its promising anticancer action in S-180 cells. The results obtained from this study indicated that complex (3) induces cell cycle arrest in the G0/G1 phase in S-180 cells associated with a decrease in the number of cells in S phase. After 24 and 48 h of exposure to complex (3), the cell viability decreased when compared to the negative control. Complex (3) does not appear to be involved in the DNA damage, but induced changes in the mitochondrial membrane potential in S-180 cells. Furthermore, there was also an increase in the gene expression of Bax, Caspase 9, and Tp53. According to our results, complex (3) induces cell apoptosis through p53/Bax-dependent intrinsic pathway and suppresses the expression of active antiapoptotic Bcl-2 protein. Show less

Targeting protein-protein interactions (PPIs) offers tantalizing opportunities for therapeutic intervention for the treatment of human diseases. Modulating PPI interfaces with organic small molecules has been found to be exceptionally challenging, and few candidates have been successfully developed into clinical drugs. Meanwhile, the striking array of distinctive properties exhibited by metal compounds renders them attractive scaffolds for the development of bioactive leads. Here, we report the identification of iridium(iii) compounds as inhibitors of the H-Ras/Raf-1 PPI. The lead iridium(iii) compound 1 exhibited potent inhibitory activity against the H-Ras/Raf-1 interaction and its signaling pathway in vitro and in vivo, and also directly engaged both H-Ras and Raf-1-RBD in cell lysates. Moreover, 1 repressed tumor growth in a mouse renal xenograft tumor model. Intriguingly, the Δ-enantiomer of 1 showed superior potency in the biological assays compared to Λ-1 or racemic 1. These compounds could potentially be used as starting scaffolds for the development of more potent Ras/Raf PPI inhibitors for the treatment of kidney cancer or other proliferative diseases. Show less