An anticancer Ti(IV) complex increases mitochondrial reactive oxygen species levels in relation with hypoxia and endoplasmic-reticulum stress: A distinct non DNA-related mechanism

Newsights of endoplasmic reticulum in hypoxia

The endoplasmic reticulum (ER) is important to cells because of its essential functions, including synthesizing three major nutrients and ion transport. When cellular homeostasis is disrupted, ER quality control (ERQC) system is activated effectively to remove misfolded and unfolded proteins through ER-phagy, ER-related degradation (ERAD), and molecular chaperones. When unfolded protein response (UPR) and ER stress are activated, the cell may be suffering a huge blow, and the most probable consequence is apoptosis. The membrane contact points between the ER and sub-organelles contribute to communication between the organelles. The decrease in oxygen concentration affects the morphology and structure of the ER, thereby affecting its function and further disrupting the stable state of cells, leading to the occurrence of disease. In this study, we describe the functions of ER-, ERQC-, and ER-related membrane contact points and their changes under hypoxia, which will help us further understand ER and treat ER-related diseases.

Glutathione Depletion and Stalwart Anticancer Activity of Metallotherapeutics Inducing Programmed Cell Death: Opening a New Window for Cancer Therapy

The cellular defense system against exogenous substances makes therapeutics inefficient as intracellular glutathione (GSH) exhibits an astounding antioxidant activity in scavenging reactive oxygen species (ROS) or reactive nitrogen species (RNS) or other free radicals produced by the therapeutics. In the cancer cell microenvironment, the intracellular GSH level becomes exceptionally high to fight against oxidative stress created by the production of ROS/RNS or any free radicals, which are the byproducts of intracellular redox reactions or cellular respiration processes. Thus, in order to maintain redox homeostasis for survival of cancer cells and their rapid proliferation, the GSH level starts to escalate. In this circumstance, the administration of anticancer therapeutics is in vain, as the elevated GSH level reduces their potential by reduction or by scavenging the ROS/RNS they produce. Therefore, in order to augment the therapeutic potential of anticancer agents against elevated GSH condition, the GSH level must be depleted by hook or by crook. Hence, this Review aims to compile precisely the role of GSH in cancer cells, the importance of its depletion for cancer therapy and examples of anticancer activity of a few selected metal complexes which are able to trigger cancer cell death by depleting the GSH level.

Novel Titanocene Y derivative with albumin affinity exhibits improved anticancer activity against platinum resistant cells

The antitumor activity of Ti(IV)-based compounds put them in the spotlight for cancer treatment in the past, but their lack of stability in vivo due to a high rate of hydrolysis has hindered their development as antitumor drugs. As a possible solution for this problem, we have reported a synthesis strategy through which we combined a titanocene fragment, a tridentate ligand, and a long aliphatic chain. This strategy allowed us to generate a titanium compound (Myr-Ti) capable of interacting with albumin, highly stable in water and with cytotoxic activity in tumor cells[1]. Following a similar strategy, now we report the synthesis of a new compound (Myr-TiY) derived from titanocene Y that shows antitumoral activity in a cisplatin resistant model with a 50% inhibitory concentration (IC50) of 41-76 μM. This new compound shows high stability and a strong interaction with human serum albumin. Myr-TiY has a significant antiproliferative and proapoptotic effect on the tested cancer cells and shows potential tumor selectivity when assayed in non-tumor human epithelial cells being more selective (1.3-3.8 times) for tumor cells than cisplatin. These results lead us to think that the described synthesis strategy could be useful to generate compounds for the treatment of both cisplatin-sensitive and cisplatin-resistant cancers.

Synthesis, in vitro antitumor evaluation and structure activity relationship of heptacoordinated amino-bis(Phenolato) Ti(IV) complexes stabilized by 2,6-dipicolinic acid

Eighteen novel Ti(IV) complexes stabilized by different chelating amino-bis(phenolato) (ONNO, ONON, ONOO) ligands and 2,6-dipicolinic acid as a second chelator were synthesized with isolated yields ranging from 79 to 93%. Complexes were characterized by 1H and 13C-NMR spectroscopy, as well as by HRMS and X-Ray diffraction analysis. The good to excellent aqueous stability of these Ti(IV) complexes can be modulated by the substitutions on the 2-position of the phenolato ligands. Most of the synthesized Ti(IV) complexes demonstrated potent inhibitory activity against Hela S3 and Hep G2 tumor cells. Among them, the naphthalenyl based Salan type 2j, 2-picolylamine based [ONON] type 2n and N-(2-hydroxyethyl) based [ONOO] type 2p demonstrated up to 40 folds enhanced cytotoxicity compared to cisplatin together with a significantly reduced activity against healthy AML12 cells. The three Ti(IV) complexes exhibited fast cellular uptake by Hela S3 cells and induced almost exclusively apoptosis. 2j could trigger higher level of ROS generation than 2p and 2n.

Probing the Mechanism of Action of Bis(phenolato) Amine (ONO Donor Set) Titanium(IV) Anticancer Agents

The need for anticancer therapies that overcome metallodrug resistance while minimizing adverse toxicities is targeted, herein, using titanium coordination complexes. Octahedral titanium(IV) trans,mer-[Ti{R1N(CH2-2-MeO-4-R1-C6H2)2}2] [R1 = Et, allyl, n-Pr, CHO, F, CH2(morpholino), the latter from the formyl derivative; R2 = Me, Et; not all combinations] are attained from Mannich reactions of commercial 2-methoxyphenols (27-74% overall yield, 2 steps). These crystalline (four X-ray structures) Ti(IV)-complexes are active against MCF-7, HCT-116, HT-29, PANC-1, and MDA-MB-468 cancer cell lines (GI50 = 0.5-38 μM). Their activity and cancer selectivity (vs nontumor MRC-5 cells) typically exceeds that of cisplatin (up to 16-fold). Proteomic analysis (in MCF-7) supported by other studies (G2/M cell cycle arrest, ROS generation, γH2AX production, caspase activation, annexin positivity, western blot, and kinase screens in MCF-7 and HCT-116) suggest apoptosis elicited by more than one mechanism of action. Comparison of these data to the modes of action proposed for salan Ti(IV) complexes is made.

Hydrolytically Stable TiIV-Hydrazone-Based Metallodrugs: Protein Interaction and Anticancer Potential

In this work, three titanium(IV) [TiIV(L1-3)2] (1-3) complexes have been reported using three different tridentate dibasic ONO donor hydrazone ligands, pyridine-4-carboxylic acid (3-ethoxy-2-hydroxybenzylidene)-hydrazide (H2L1), furan-2-carboxylic acid (3-ethoxy-2-hydroxybenzylidene)-hydrazide (H2L2), and thiophene-2-carboxylic acid (3-ethoxy-2-hydroxybenzylidene)-hydrazide (H2L3) tethered with heterocyclic moieties. Elemental analysis, FT-IR, UV-vis, NMR, HR-ESI-MS, and single-crystal X-ray analysis have been used to characterize H2L1-3 and 1-3. In solid structures of 1-3, two ligand molecules with N2O4 donor sets give distorted octahedral geometries to the metal center. The aqueous stability of 1-3 was investigated and well correlated to their perceived pharmacological results. During the investigation, all three complexes were found to be hydrolytically stable in a 90% DMSO-d6/10% D2O (v/v) medium up to 48 h. Furthermore, the interaction of 1-3 with bovine serum albumin (BSA) was tested using fluorescence and absorption techniques. The complexes showed static quenching with a biomolecular quenching constant of Kq ∼ 1013 proposing a high affinity of complexes for BSA. Finally, the anticancer potential of 1-3 was tested against HeLa, A549, and NIH-3T3 cell lines. Among all, 1 with an IC50 value of 11.6 ± 1.1 μM against HeLa cells was found to be the most cytotoxic in the series. Furthermore, it has been found that the compounds induce an apoptotic mode of cell death, which is confirmed by the live cell confocal microscopy and flow cytometry techniques.

Titanium complexes affect Bacillus subtilis biofilm formation

Biofilms are surface or interface-associated communities of bacterial cells, embedded in a self-secreted extracellular matrix (ECM). Cells in biofilms are 100-1000 times more resistant to antibiotic treatment relative to planktonic cells due to various reasons, including the ECM acting as a diffusion barrier to antibiotic molecules, the presence of persister cells that divide slowly and are less susceptible to cell-wall targeting drugs, and the activation of efflux pumps in response to antibiotic stress. In this study we tested the effect of two titanium(iv) complexes that have been previously reported as potent and non-toxic anticancer chemotherapeutic agents on Bacillus subtilis cells in culture and in biofilm forming conditions. The Ti(iv) complexes tested, a hexacoordinate diaminobis(phenolato)-bis(alkoxo) complex (phenolaTi) and a bis(isopropoxo) complex of a diaminobis(phenolato) "salan"-type ligand (salanTi), did not affect the growth rate of cells in shaken cultures, however they did affect biofilm formation. Surprisingly, while phenolaTi inhibited biofilm formation, the presence of salanTi induced the formation of more mechanically robust biofilms. Optical microscopy images of biofilm samples in the absence and presence of Ti(iv) complexes suggest that Ti(iv) complexes affect cell-cell and/or cell-matrix adhesion, and that these are interfered with phenolaTi and enhanced by salanTi. Our results highlight the possible effect of Ti(iv) complexes on bacterial biofilms, which is gaining interest in light of the emerging relations between bacteria and cancerous tumors.