Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces cell death in various types of cancer cells but has little or no effects on normal cells. Unfortunately, not all cancer cells respond to TRAIL; therefore, TRAIL sensitizing agents are currently being explored. Here, we reported that 6-(4-N,N-dimethylaminophenyltelluro)-6-deoxy-?-cyclodextrin (DTCD), a cyclodextrin-derived diorganyl telluride which has been identified as an excellent inhibitor of thioredoxin reductase (TrxR), could sensitize TRAIL resistant human ovarian cancer cells to undergo apoptosis. In vitro, DTCD enhanced TRAIL-induced cytotoxicity in human ovarian cancer cells through up-regulation of DR5. Luciferase analysis and CHIP assays showed that DTCD increased DR5 promoter activity via Sp1 activation. Additionally, DTCD stimulated extracellular signal-regulated kinase (ERK) activation, while the ERK inhibitor PD98059 blocked DTCD-induced DR5 expression and suppressed binding of Sp1 to the DR5 promoter. We further demonstrated that DTCD could induce the release of ASK1 from its complex with Trx-1, and recovered its kinase activity. Meanwhile, suppression of ASK1 by RNA interference led to decreased ERK phosphorylation induced by DTCD. The underlying mechanisms reveal that Trx-1 is heavily oxidized in response to DTCD treatment, in accordance with the fact that DTCD could inhibit the activity of TrxR that reduces oxidized Trx-1. Moreover, using an A2780 xenograft model, DTCD plus TRAIL significantly inhibited the growth of tumor in vivo. Our results suggest that Trx/TrxR system inhibition may play a critical role in apoptosis by combined treatment with DTCD and TRAIL, and raise the possibility that their combination may be a promising strategy for ovarian carcinoma treatment.
Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) exhibits potent antitumour activity via membrane receptors on cancer cells without deleterious side-effects for normal tissue. Unfortunately, like many other cancer types, breast cancer cells develop resistance to TRAIL; therefore, TRAIL-sensitising agents are currently being explored. In this study, we report that seleno-cyclodextrin (2-selenium-bridged ?-cyclodextrin, 2-SeCD), a seleno-organic compound with glutathione peroxidase (GPx)-mimetic activity, sensitises TRAIL-resistant human breast cancer cells and xenograft tumours to undergo apoptosis. In vitro, 2-SeCD reduces the viability of cancer cells by inducing cell cycle arrest in G(2)/M phase. Furthermore, 2-SeCD efficiently sensitises MDA-MB-468 and T47D cells but not untransformed human mammary epithelial cells to TRAIL-mediated apoptosis, as evidenced by enhanced caspase activity and poly-ADP-ribose-polymerase (PARP) cleavage. From a mechanistic standpoint, we show that 2-SeCD induces the expression of TRAIL receptors DR5 but not DR4 on both mRNA and protein levels in a dose-dependent manner. Moreover, 2-SeCD treatment also suppresses TRAIL-induced nuclear factor-?B (NF-?B) pro-survival pathways by preventing cytosolic I?B? degradation and p65 nuclear translocation. Consequently, the combined administration suppresses anti-apoptotic proteins transcriptionally regulated by NF-?B. In vivo, 2-SeCD and TRAIL are well tolerated in mice, and their combination significantly inhibits the growth of MDA-MB-468 xenografts and promotes apoptosis. Up-regulation of DR5 and down-regulation of NF-?B by dual treatment were also observed in tumour tissues. Overall, 2-SeCD sensitises resistant breast cancer cells to TRAIL-based apoptosis in vitro and in vivo. These findings provide strong evidence for the therapeutic potential of this combination against breast cancers.
Reactive oxygen species (ROS) are involved in cell growth, differentiation, and death. Excessive amounts of ROS (e.g., O(2)(-), H(2)O(2), and HO) play a role in aging as well as in many human diseases. Superoxide dismutase (SOD) and glutathione peroxidase (GPx) are critical antioxidant enzymes in living organisms. SOD catalyzes the dismutation of O(2)(-) to H(2)O(2), and GPx catalyzes the reduction of H(2)O(2) and other harmful peroxides by glutathione (GSH). They not only function in catalytic processes but also protect each other, resulting in more efficient removal of ROS, protection of cells against injury, and maintenance of the normal metabolism of ROS. To imitate the synergism of SOD and GPx, a 65-mer peptide (65P), containing sequences that form the domains of the active center of SOD and the catalytic triad of GPx upon the incorporation of some metals, was designed on the basis of native enzyme structural models; 65P was expressed in the cysteine auxotrophic expression system to obtain Se-65P. Se-65P was converted into Se-CuZn-65P by incorporating Cu(2+) and Zn(2+). Se-CuZn-65P exhibited high SOD and GPx activities because it has a delicate dual-activity center. The synergism of the enzyme mimic was evaluated by using an in vitro model and a xanthine/xanthine oxidase/Fe(2+)-induced mitochondrial damage model system. We anticipate that the peptide enzyme mimic with synergism is promising for the treatment of human diseases and has potential applications in medicine as a potent antioxidant.
Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) exhibits potent antitumor activity via membrane receptors on cancer cells without deleterious side effects for normal tissue. Unfortunately, breast cancer cells, as many other cancer types, develop resistance to TRAIL; therefore, TRAIL sensitizing agents are currently being explored. 2-Tellurium-bridged ?-cyclodextrin (2-TeCD) is a synthetic organotellurium compound, with both glutathione peroxidase-like catalytic ability and thioredoxin reductase inhibitor activity. In the present study, we reported that 2-TeCD sensitized TRAIL-resistant human breast cancer cells and xenograft tumors to undergo apoptosis. In vitro, 2-TeCD efficiently sensitized MDA-MB-468 and T47D cells, but not untransformed human mammary epithelial cells, to TRAIL-mediated apoptosis, as evidenced by enhanced caspase activity and poly (adenosine diphosphate-ribose) polymerase cleavage. From a mechanistic standpoint, we showed that 2-TeCD treatment of breast cancer cells significantly upregulated the messenger RNA and protein levels of TRAIL receptor, death receptor (DR) 5, in a transcription factor Sp1-dependent manner. 2-TeCD treatment also suppressed TRAIL-induced nuclear factor-?B (NF-?B) prosurvival pathways by preventing cytosolic I?B? degradation, as well as p65 nuclear translocation. Consequently, the combined administration suppressed anti-apoptotic molecules that are transcriptionally regulated by NF-?B. In vivo, 2-TeCD and TRAIL were well tolerated in mice and their combination significantly inhibited growth of MDA-MB-468 xenografts and promoted apoptosis. Upregulation of DR5 and downregulation of NF-?B by the dual treatment were also observed in tumor tissues. Overall, 2-TeCD sensitizes resistant breast cancer cells to TRAIL-based apoptosis in vitro and in vivo. These findings provide strong evidence for the therapeutic potential of this combination against breast cancers.
Glutathione peroxidase (GPX), superoxide dismutase (SOD) and catalase (CAT) play crucial roles in the metabolism and homeostasis of reactive oxygen species (ROS) in living organisms. From examination of the steady state and pre-steady state kinetic behavior of natural GPX it was found that, in contrast to accepted theories, the affinity of the enzyme for H(2)O(2) rather than reduced glutathione (GSH) most significantly affects its kinetic behavior. Consequently, an enzyme mimic was produced with a similar affinity for the substrate H(2)O(2). A salicylaldehyde Schiff base containing a dimanganese centre was selected as a precursor, because it has high H(2)O(2)-binding affinity for such a relatively small molecule and similar catalytic activity to that of SOD and CAT. Selenium was also incorporated into the catalytic center to provide activity similar to that of GPX, and thus trifunctional enzymatic activity. The K(mH2O2) of the mimic (7.32×10(-2) mM) was found quite close to that of natural enzyme (1.0×10(-2) mM), indicating that the affinity of the mimic to H(2)O(2) was successfully increased to approach natural GPX. The steady state kinetic performance of the enzyme mimic showed that the ratio between k(cat)/K(mGSH) and k(cat)/ K(mH2O2) was quite similar to that of native GPX, indicating that the Mn(III)(2)(L-Se-SO(3)Na) had the same selectivity for both substrates GSH and H(2)O(2) as native GPX, which put it among the best existing GPX mimics. Moreover, the new mimic was confirmed to strongly inhibit lipid peroxidation and mitochondrial swelling, probably due to the synergism between the three antioxidant enzymatic activities.
The antioxidant enzymes, such as superoxide dismutase, catalase, glutathione peroxidase, and glutathione S-transferase contribute dominatingly to enhance cellular antioxidant defense against oxidative stress. They act cooperatively to scavenge reactive oxygen species, and not one of them can singlehandedly clear all forms of reactive oxygen species. On the basis of the structural understanding for these natural enzymes, many mimics with multifunctional activities had been obtained by chemical synthesis, biosynthesis, and protein fusion techniques. Some of them display remarkable antioxidant cooperative effect in living model which possess potential application in medicine as potent antioxidants. This review summarizes aspects of some multifunctional mimics which have been reported so far.
Apoptosis is known to occur after ultraviolet-B (UV-B) radiation. It was found that UV-B could induce cell apoptosis and change cell cycle progression. After exposure to 100J/m(2) of UV-B, pre-G1 phase thymocytes were increased significantly and S phase thymocytes were decreased significantly. UV-B could also induce lipid peroxidation of thymocytes to have their MDA amount increased. These phenomena could be explained by production of reactive oxygen species (ROS), which were induced by UV-B radiation. In this study, we examined the protective effect of dicyclodextrinyl ditelluride (2-TeCD), the glutathione peroxidase (GPX, EC 188.8.131.52) mimics, on thymocytes apoptosis induced by UV-B radiation. The experimental results showed that 2-TeCD protects thymocytes from apoptosis. Moreover, 2-TeCD inhibits lipid peroxidation of thymocytes and displayed great antioxidant ability. Furthermore, 2-TeCD blocks the accumulation of wild-type-p53 (wt-p53) tumor-suppressor gene product caused by UV-B radiation.
Adhesion molecules play an important role in the pathogenesis of atherogenesis. They are expressed on endothelial cells surface in response to various inflammatory stimuli. In this paper, we examined the effect of 2-tellurium-bridged beta-cyclodextrin (2-TeCD), a GPx mimic, on the expression of adhesion molecules in human umbilical vein endothelial cells (HUVECs) under tumor necrosis factor-alpha (TNF-alpha) stimulation. Experimental results indicated that 2-TeCD suppressed the TNF-alpha-induced the expression of vascular adhesion molecule-1 (VCAM-1) and intercellular cell adhesion molecule-1 (ICAM-1) on HUVECs surface in a dose-dependent manner. 2-TeCD also reduced the level of mRNA expression of VCAM-1 and ICAM-1. Furthermore, 2-TeCD inhibited THP-1 monocyte adhesion to HUVECs stimulated by TNF-alpha. Nuclear factor-kappaB (NF-kappaB) could regulate transcription of VCAM-1 and ICAM-1 genes. Western blot analysis showed that 2-TeCD inhibited the translocation of the p65 subunit of NF-kappaB into the nucleus. In short, these results indicated that 2-TeCD inhibits TNF-alpha-stimulated VCAM-1 and ICAM-1 expression in HUVECs partly due to suppressing translocation of NF-kappaB.
Glutathione peroxidase (GPX) is one of the important members of the antioxidant enzyme family. It can catalyze the reduction of hydroperoxides with glutathione to protect cells against oxidative damage. In previous studies, we have prepared the human catalytic antibody Se-scFv-B3 (selenium-containing single-chain Fv fragment of clone B3) with GPX activity by incorporating a catalytic group Sec (selenocysteine) into the binding site using chemical mutation; however, its activity was not very satisfying. In order to try to improve its GPX activity, structural analysis of the scFv-B3 was carried out. A three-dimensional (3D) structure of scFv-B3 was constructed by means of homology modeling and binding site analysis was carried out. Computer-aided docking and energy minimization (EM) calculations of the antibody-GSH (glutathione) complex were also performed. From these simulations, Ala44 and Ala180 in the candidate binding sites were chosen to be mutated to serines respectively, which can be subsequently converted into the catalytic Sec group. The two mutated protein and wild type of the scFv were all expressed in soluble form in Escherichia coli Rosetta and purified by Ni(2+)-immobilized metal affinity chromatography (IMAC), then transformed to selenium-containing catalytic antibody with GPX activity by chemical modification of the reactive serine residues. The GPX activity of the mutated catalytic antibody Se-scFv-B3-A180S was significantly increased compared to the original Se-scFv-B3.
A rival to native peroxidase! An existing binding site for glutathione was combined with the catalytic residue tellurocysteine by using an auxotrophic expression system to create an engineered enzyme that functions as a glutathione peroxidase from the scaffold of a glutathione transferase (see picture). The catalytic activity of the telluroenzyme in the reduction of hydroperoxides by glutathione is comparable to that of native glutathione peroxidase.
By combining computational design and site-directed mutagenesis, we have engineered a new catalytic ability into the antibody scFv2F3 by installing a catalytic triad (Trp(29)-Sec(52)-Gln(72)). The resulting abzyme, Se-scFv2F3, exhibits a high glutathione peroxidase (GPx) activity, approaching the native enzyme activity. Activity assays and a systematic computational study were performed to investigate the effect of successive replacement of residues at positions 29, 52, and 72. The results revealed that an active site Ser(52)/Sec substitution is critical for the GPx activity of Se-scFv2F3. In addition, Phe(29)/Trp-Val(72)/Gln mutations enhance the reaction rate via functional cooperation with Sec(52). Molecular dynamics simulations showed that the designed catalytic triad is very stable and the conformational flexibility caused by Tyr(101) occurs mainly in the loop of complementarity determining region 3. The docking studies illustrated the importance of this loop that favors the conformational shift of Tyr(54), Asn(55), and Gly(56) to stabilize substrate binding. Molecular dynamics free energy and molecular mechanics-Poisson Boltzmann surface area calculations estimated the pK(a) shifts of the catalytic residue and the binding free energies of docked complexes, suggesting that dipole-dipole interactions among Trp(29)-Sec(52)-Gln(72) lead to the change of free energy that promotes the residual catalytic activity and the substrate-binding capacity. The calculated results agree well with the experimental data, which should help to clarify why Se-scFv2F3 exhibits high catalytic efficiency.
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