Yum-Shing Wong

Ruthenium Polypyridyl Complexes That Induce Mitochondria-Mediated Apoptosis in Cancer Cells

The limitations of cisplatin-based chemotherapy, including high toxicity, undesirable side effects, and drug resistance, have motivated extensive investigations into alternative metal-based cancer therapies. Ruthenium (Ru) possesses several favorable properties suited to rational anticancer drug design and biological applications. In the present study, we synthesized a series of ruthenium polypyridyl complexes containing N,N-chelating ligands, examined their anticancer activities, and elucidated the molecular mechanisms through which they caused the cancer cell death. The results demonstrated that [Ru(phen)(2)-p-MOPIP](PF(6))(2).2H(2)O (RuPOP), a complex with potent antiproliferative activity, is able to induce mitochondria-mediated and caspase-dependent apoptosis in human cancer cells. On the basis of these results, we suggest that RuPOP may be a candidate for further evaluation as a chemopreventive and chemotherapeutic agent for human cancers, especially for melanoma.

Selenocystine induces caspase-independent apoptosis in MCF-7 human breast carcinoma cells with involvement of p53 phosphorylation and reactive oxygen species generation

The role of selenium as potential cancer chemopreventive and chemotherapeutic agents has been supported by epidemiological, preclinical and clinical studies. Although cell apoptosis has been evidenced as a critical mechanism mediating the anticancer activity of selenium, the underlying molecular mechanisms remain elusive. In the present study, we showed that selenocystine (SeC), a naturally occurring selenoamino acid, induced caspase-independent apoptosis in MCF-7 breast carcinoma cells, which was accompanied by poly(ADP-ribose) polymerase (PARP) cleavage, caspase activation, DNA fragmentation, phosphatidylserine exposure and nuclear condensation. Moreover, SeC induced the loss of mitochondrial membrane potential (DeltaPsi(m)) by regulating the expression and phosphorylation of Bcl-2 family members. Loss of DeltaPsi(m) led to the mitochondrial release of cytochrome c and apoptosis-inducing factor (AIF) which subsequently translocated into the nucleus and induced chromatin condensation and DNA fragmentation. MCF-7 cells exposed to SeC shown increase in total p53 and phosphorylated p53 on serine residues of Ser15, Ser20, and Ser392 prior to mitochondrial dysfunction. Silencing and attenuating of p53 activation with RNA interference and pifithrin-alpha treatment, respectively, partially suppressed SeC-induced cell apoptosis. Furthermore, generation of reactive oxygen species and subsequent induction of DNA strand breaks were found to be upstream cellular events induced by SeC. The thiol-reducing antioxidants, N-acetylcysteine and glutathione, completely blocked the occurrence of cell apoptosis. Taken together, these results suggest that SeC, as a promising anticancer selenocompound, induces MCF-7 cell apoptosis by activating ROS-mediated mitochondrial pathway and p53 phosphorylation.

Selenium nanoparticles fabricated in Undaria pinnatifida polysaccharide solutions induce mitochondria-mediated apoptosis in A375 human melanoma cells.

Selenium nanoparticle (Nano-Se) is a novel Se species with novel biological activities and low toxicity. In the present study, we demonstrated a simple method for synthesis of size-controlled Nano-Se by adding Undaria pinnatifida polysaccharides to the redox system of selenite and ascorbic acid. A panel of four human cancer cell lines was shown to be susceptible to Nano-Se, with IC(50) values ranging from 3.0 to 14.1 microM. Treatment of A375 human melanoma cells with the Nano-Se resulted in dose-dependent cell apoptosis as indicated by DNA fragmentation and phosphatidylserine translocation. Further investigation on intracellular mechanisms found that Nano-Se treatment triggered apoptotic cell death in A375 cells with the involvement of oxidative stress and mitochondrial dysfunction. Our results suggest that Nano-Se may be a candidate for further evaluation as a chemopreventive and chemotherapeutic agent for human cancers, especially melanoma cancer.

Selenocystine induces apoptosis of A375 human melanoma cells by activating ROS-mediated mitochondrial pathway and p53 phosphorylation

Abstract.Selenocystine (SeC), a naturally occurring selenoamino acid, has been shown to be a novel compound with broad-spectrum anticancer activity. In this study, we showed that SeC triggered time- and dose-dependent apoptosis in A375 human melanoma cells by activating the mitochondria-mediated and death receptor-mediated apoptosis pathways. Pretreatment of cells with a general caspase inhibitor z-VAD-fmk significantly prevented SeC-induced apoptosis. A375 cells exposed to SeC showed an increase in levels of total p53 and phosphorylated p53 (serine-15). Silencing of p53 expression with RNA interference significantly suppressed SeC-induced p53 phosphorylation, caspase activation and apoptotic cell death. Moreover, generation of reactive oxygen species and subsequent induction of DNA strand breaks were found to be upstream mediators of p53 activation induced by SeC. In a nude mice xenograft experiment, SeC significantly inhibited the tumor growth of A375 cells via induction of apoptosis. Taken together, these results suggest the potential applications of SeC in cancer chemoprevention.

Selenocystine induces reactive oxygen species-mediated apoptosis in human cancer cells.

Epidemiological and clinical studies have demonstrated that dietary supplementation of selenium (Se) could reduce the incidence of human cancers. In this study, selenocystine, a nutritionally available selenoamino acid, was identified as a novel agent with broad-spectrum antitumor activity. A panel of eight human cancer cell lines was shown to be susceptible to selenocystine, with IC(50) values ranging from 3.6 to 37.0 microM. Selenocystine induced dose-dependent apoptosis in A375, HepG2 and MCF7 cells was evaluated by flow cytometric analysis and annexin-V staining assay. Mechanistic studies showed time- and dose-dependent increases in intracellular reactive oxygen species (ROS) in susceptible cancer cells (MCF7 and HepG2 cells) treated with selenocystine. However, selenocystine-induced ROS overproduction was not observed in non-susceptible normal human fibroblast Hs68 cells. Significant DNA strand breaks were observed in selenocystine-treated MCF7 and HepG2 cells as examined by single-cell gel electrophoresis (Comet assay). The thiol-reducing antioxidants, glutathione and N-acetylcysteine, inhibited intracellular ROS generation, DNA strand breaks and accumulation of sub-G1 population in MCF7 cells exposed to selenocystine. Our results suggest a possible role of ROS as a mediator of the signaling pathway of selenocystine-induced, DNA damage-mediated apoptosis in susceptible cancer cells.

Selenocystine Induces S-Phase Arrest and Apoptosis in Human Breast Adenocarcinoma MCF-7 Cells by Modulating ERK and Akt Phosphorylation

Selenocystine (SeC) is a nutritionally available selenoamino acid with selective anticancer effects on a number of human cancer cell lines. The present study shows that SeC inhibited the proliferation of human breast adenocarcinoma MCF-7 cells in a time- and dose-dependent manner, through the induction of cell cycle arrest and apoptotic cell death. SeC-induced S-phase arrest was associated with a marked decrease in the protein expression of cyclins A, D1, and D3 and cyclin-dependent kinases (CDKs) 4 and 6, with concomitant induction of p21waf1/Cip1, p27Kip1, and p53. Exposure of MCF-7 cells to SeC resulted in apoptosis as evidenced by caspase activation, PARP cleavage, and DNA fragmentation. SeC treatment also triggered the activation of JNK, p38 MAPK, ERK, and Akt. Inhibitors of ERK (U0126) and Akt (LY294002), but not JNK (SP600125) and p38 MAPK (SB203580), suppressed SeC-induced S-phase arrest and apoptosis in MCF-7 cells. The findings establish a mechanistic link between the PI3K/Akt pathway, MAPK pathway, and SeC-induced cell cycle arrest and apoptosis in MCF-7 cells.

The reversal of cisplatin-induced nephrotoxicity by selenium nanoparticles functionalized with 11-mercapto-1-undecanol by inhibition of ROS-mediated apoptosis.

Although cisplatin is still one of the most effective chemotherapy agents for human cancers, its clinical use is limited by serious side effects, especially nephrotoxicity. Oxidative stress is an important mediator of cisplatin-induced nephrotoxicity. In the present study, a simple method for functionalization of selenium nanoparticles by self-assembly of 11-mercapto-1-undecanol (Se@MUN) to achieve enhanced antioxidant activity and antagonis against cisplatin-induced nephrotoxicity has been demonstrated. The chemical structure of the nanoparticles was characterized by various microscopic and spectroscopic methods. The results revealed that the spherical nanoparticles were capped with MUN on the surface through formation of Se-S bond. The in vitro protective effects of Se@MUN on HK-2 proximal tubular cells against cisplatin-induced nephrotoxicity and the underlying mechanisms were also investigated. Se@MUN exhibited free radical scavenging activity and higher cellular uptake in human normal cells by comparing with SeNPs. Se@MUN significantly attenuated cisplatin-induced reduction in cell viability, appearance of Sub-G1 peak, nuclear condensation and DNA fragmentation in HK-2 cells. Activation of caspase-3 in cells exposed to cisplatin was also effectively blocked by Se@MUN. Moreover, Se@MUN significantly prevented the cisplatin-induced overproduction of intracellular ROS. Our findings suggest that Se@MUN is a promising selenium species with potential application in prevention of cisplatin-induced renal injury.

Enhancement of Auranofin-Induced Apoptosis in MCF-7 Human Breast Cells by Selenocystine, a Synergistic Inhibitor of Thioredoxin Reductase

Thioredoxin system plays an important role in regulation of intracellular redox balance and various signaling pathways. Thioredoxin reductase (TrxR) is overexpressed in many cancer cells and has been identified as a potential target of anticancer drugs. Auranofin (AF) is potent TrxR inhibitor with novel in vitro and in vivo anticancer activities. Selenocystine (SeC) is a nutritionally available selenoamino acid with selective anticancer effects through induction of apoptosis. In the present study, we demonstrated the synergistic effects and the underlying molecular mechanisms of SeC in combination with AF on MCF-7 human breast cancer cells. The results showed that SeC and AF synergistically inhibited the cancer cell growth through induction of ROS-dependent apoptosis with the involvement of mitochondrial dysfunction. DNA damage-mediated p53 phosphorylation and down-regulation of phosphorylated AKT and ERK also contributed to cell apoptosis. Moreover, we demonstrated the important role of TrxR activity in the synergistic action of SeC and AF. Taken together, our results suggest the strategy to use SeC and AF in combination could be a highly efficient way to achieve anticancer synergism by targeting TrxR.

Mitochondria-mediated apoptosis in human breast carcinoma MCF-7 cells induced by a novel selenadiazole derivative

The role of organoselenium compounds as potent cancer chemopreventive and chemotherapeutic agents has been supported by epidemiological, preclinical and clinical studies. In this study, a novel selenadiazole derivative, 1,2,5-selenadiazolo-[3,4-d]pyrimidine-5,7-(4H,6H)-dione (SPO), is identified as a potent antiproliferative agent against human breast adrenocarcinoma MCF-7 cells, human hepatoma HepG2 cells and human melanoma A375 cells. Induction of apoptosis in MCF-7 and A375 cells by SPO was evidenced by accumulation of sub-G1 cell population, DNA fragmentation and nuclear condensation. Further investigation on intracellular mechanisms found that SPO treatments induced activation of caspase-8 and caspase-9, overproduction of reactive oxygen species, and depletion of mitochondrial membrane potential (Delta Psi m) through regulating the expression of pro-survival and pro-apoptotic Bcl-2 family members. Our findings suggest that SPO is a promising novel organoselenium compound with potential in the treatment of human cancers.

Effects of cooking on content of amino acids and antinutrients in three Chinese indigenous legume seeds

The effects of domestic cooking on the content of amino acids and antinutrients of Phaseolus angularis, Phaseolus calcaratus and Dolichos lablab seeds were evaluated. Heat treatment (30 min) caused significant declines (P<0·05) in the apparent recovery of most of the essential amino acids except leucine and phenylalanine for P angularis, and except phenylalanine for P calcaratus. Cooking D lablab seeds (60 min) also resulted in a significant reduction (P<0·05) in the apparent recovery of all the essential amino acids except leucine, histidine, lysine and threonine. Increased cooking time for P angularis (60 min), P calcaratus (60 min) and D lablab (120 min) led to a lower apparent recovery of methionine (28·9–31·6%) and cystine (17·1–19·3%). Even with increased cooking times, the total essential amino acid levels in all three cooked seeds remained higher than that of the FAO/WHO requirement, except for methionine and cystine. Cooking (60 min) was found to be effective in reducing the tannin contents of P angularis, P calcaratus and D lablab seeds by 70·6, 64·6 and 74·6%, respectively. Upon cooking, phytate and trypsin inhibitory activity in different seeds were also reduced to different extents depending on the cooking times. ©1997 SCI