Biomedical subjects

Junxuan Lü

Publications and source records attributed to Junxuan Lü.

12 recordsLinked to original sources

PubMed2006

An oriental herbal cocktail, ka-mi-kae-kyuk-tang, exerts anti-cancer activities by targeting angiogenesis, apoptosis and metastasis.

Rigorous and systematic pre-clinical studies are necessary and essential to establish the efficacy and safety of Oriental herbs and formulas in order to transform traditional herbal practices into evidence-based medicine. Here we evaluated the anti-cancer activities of the ethanol extract of Ka-mi-kae-kyuk-tang (KMKKT), a formula of ten Oriental herbs, with a battery of in vitro and in vivo mechanism-based biomarkers involving angiogenesis, apoptosis and metastasis. The results show that KMKKT suppressed the vascular endothelial responses by inhibiting basic fibroblast growth factor (bFGF)-induced ERK1/2 phosphorylation, cell migration as well as tube formation in the human umbilical vein endothelial cell model, and decreased the hypoxia-induced HIF1alpha and vascular epithelial growth factor (VEGF) expression in the mouse Lewis lung carcinoma (LLC) cells in vitro, and inhibited the bFGF-induced angiogenesis in chick chorioallantoic membrane model, and in the Matrigel plugs in mice. Intraperitoneal delivery of KMKKT potently inhibited the growth of the subcutaneously inoculated LLC cells in syngenic mice. In addition, KMKKT inhibited the invasion ability of the mouse colon 26-L5 cancer cells in vitro and decreased their formation of liver metastasis when intraportally inoculated in syngenic mice. Furthermore, KMKKT suppressed the growth of the human PC-3 prostate cancer xenografts in athymic nude mice and averted the cancer-related body weight loss. The in vivo cancer growth suppression was associated with a decreased microvessel density and VEGF abundance as well as an increased PARP cleavage and the TUNEL-positive apoptosis. Together, our data support broad-spectra in vivo anti-cancer activities of KMKKT targeting angiogenesis, apoptosis and metastasis without any adverse effect on the body weight. This formula merits serious consideration for further evaluation for the chemoprevention and treatment of cancers of multiple organ sites.

Allantois↗

PubMed2006

Enhancement of mammary carcinogenesis in two rodent models by silymarin dietary supplements.

Silymarin is a mixture of polyphenolic flavonoids isolated from milk thistle (Silybum marianum) with anticancer activities reported for several organ sites. The present study tested the efficacy of dietary silymarin against mammary carcinogenesis in two rodent models. In the Sprague-Dawley rat model, female rats were fed a purified diet supplemented with none, 0.03, 0.1, 0.3 or 1% (w/w) of silymarin from 21 days of age (DOA) and carcinogenesis was initiated by a single i.p. injection of 1-methyl-1-nitrosourea (MNU) at 51 DOA. Mammary tumor (MT) development was followed till 110 days after carcinogen injection. In the MMTV-neu/HER2 transgenic mouse mammary carcinogenesis model, homozygous transgenic females were fed a purified diet supplemented with none or 0.3% silymarin, either from 28 or 120 DOA and MT development was followed to approximately 300 DOA. The results showed that dietary silymarin increased the plasma concentration of free and total silibinin, a major component of silymarin, in a dose-dependent manner in the rat, but did not decrease either MT incidence or number. Instead silymarin modestly increased the number of MNU-induced MTs in rats. Similarly, silymarin increased MT incidence and multiplicity and non-MTs in the neu-transgenic mice. In cell culture, treatment of human MCF-7 breast cancer cells with serum-achievable concentrations of silymarin in the rodent models stimulated their growth, in part through an estrogen-like activity. Because silymarin is being used in the treatment of liver cirrhosis and a variety of other human ailments, and is sold as a dietary supplement, our findings add a cautionary note to its application in breast cancer prevention.

Animals↗

PubMed2006

Inorganic selenium sensitizes prostate cancer cells to TRAIL-induced apoptosis through superoxide/p53/Bax-mediated activation of mitochondrial pathway.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been shown to induce apoptosis in prostate cancer cells through DR4 and DR5 death receptors, but not in normal prostate cells, which do not express these receptors. Therefore, TRAIL has excellent potential to be a selective prostate cancer therapeutic agent with minimal toxic side effects. However, prostate cancer cells, as many other cancer types, develop resistance to TRAIL, and the underlying molecular mechanisms require further investigation. We hypothesize that selenium may sensitize TRAIL-resistant cells to undergo caspase-mediated apoptosis and increase therapeutic efficacy. Here, we report that TRAIL signaling in LNCaP prostate cancer cells stalled at downstream of caspase-8 and BID cleavage, as indicated by the lack of Bax translocation into mitochondria, and no subsequent activation of the caspase-9 cascade. Selenite induced a rapid generation of superoxide and p53 Ser(15) phosphorylation and increased Bax abundance and translocation into the mitochondria. Selenite and TRAIL combined treatment led to synergistic increases of Bax abundance and translocation into mitochondria, loss of mitochondrial membrane potential, cytochrome c release, and cleavage activation of caspase-9 and caspase-3. Inactivating p53 with a dominant-negative mutant abolished apoptosis without affecting superoxide generation, whereas a superoxide dismutase mimetic agent blocked p53 activation, Bax translocation to mitochondria, cytochrome c release, and apoptosis induced by selenite/TRAIL. In support of Bax as a crucial target for cross-talk between selenite and TRAIL pathways, introduction of Bax into p53 mutant DU145 cells enabled selenite to sensitize these cells for TRAIL-induced apoptosis. Taken together, the results indicate that selenite induces a rapid superoxide burst and p53 activation, leading to Bax up-regulation and translocation into mitochondria, which restores the cross-talk with stalled TRAIL signaling for a synergistic caspase-9/3 cascade-mediated apoptosis execution.

Antineoplastic Agents↗

PubMed2005

PKB/AKT and ERK regulation of caspase-mediated apoptosis by methylseleninic acid in LNCaP prostate cancer cells.

Methylselenol has been implicated as an active metabolite for the anticancer effect of selenium in part through the induction of cancer cell apoptosis. Since inactivation of the AKT/protein kinase B negative regulator gene PTEN (phosphatase and tensin homologue deleted on chromosome 10) is common in prostate cancer (PCa), we compared PTEN wild-type DU145 PCa cells (low basal AKT activity) with PTEN-mutant LNCaP PCa cells (high basal AKT activity) for their apoptosis responses to the methylselenol precursor methylseleninic acid (MSeA) and sodium selenite, an inorganic salt. Our results show that LNCaP cells withstood approximately 4 times higher doses of MSeA than DU145 cells, although they were slightly more sensitive than the latter to selenite-induced apoptosis. Treatment by MSeA modestly attenuated AKT phosphorylation and increased phospho-ERK1/2 in LNCaP cells. Selenite treatment increased the phosphorylation of p53 Ser15 and both kinases, but the selenite-induced apoptosis was not influenced by chemical inhibitors of either kinase. In contrast, PI3K/AKT inhibitors greatly sensitized LNCaP cells to apoptosis induced by MSeA, accompanied by increased mitochondrial release of cytochrome c and multiple caspase activation without changing p53 Ser15 phosphorylation. The apoptosis was further accentuated by extracellular signal regulated kinases 1 and 2 (ERK1/2) inhibition without further increase in cytochrome c release. The general caspase inhibitor z-VAD-fmk completely blocked MSeA-induced apoptosis when both kinases were inhibited, whereas a caspase-8 inhibitor exerted a greater protection than did a caspase-9 inhibitor. Transfection of DU145 cells with a constitutively active AKT increased their resistance to MSeA-induced apoptosis. In summary, AKT played an important role in regulating apoptosis sensitivity of LNCaP and DU145 cells to MSeA. An MSeA-induced activation of ERK1/2 in LNCaP cells also contributed to resistance to apoptosis. However, these kinases did not significantly regulate caspase-mediated apoptosis induced by selenite in LNCaP cells. These findings support the differential involvement of these protein kinase pathways in regulating apoptosis induction by different forms of selenium.

Apoptosis↗

PubMed2005

Methylseleninic acid potentiates apoptosis induced by chemotherapeutic drugs in androgen-independent prostate cancer cells.

PURPOSE: To test whether and how selenium enhances the apoptosis potency of selected chemotherapeutic drugs in prostate cancer (PCA) cells. EXPERIMENTAL DESIGN: DU145 and PC3 human androgen-independent PCA cells were exposed to minimal apoptotic doses of selenium and/or the topoisomerase I inhibitor 7-ethyl-10-hydroxycamptothecin (SN38), the topoisomerase II inhibitor etoposide or the microtubule inhibitor paclitaxel/taxol. Apoptosis was measured by ELISA for histone-associated DNA fragments, by flow cytometric analysis of sub-G(1) fraction, and by immunoblot analysis of cleaved poly(ADP-ribose)polymerase. Pharmacologic inhibitors were used to manipulate caspases and c-Jun-NH(2)-terminal kinases (JNK). RESULTS: The methylselenol precursor methylseleninic acid (MSeA) increased the apoptosis potency of SN38, etoposide, or paclitaxel by several folds higher than the expected sum of the apoptosis induced by MSeA and each drug alone. The combination treatment did not further enhance JNK1/2 phosphorylation that was induced by each drug in DU145 cells. The JNK inhibitor SP600125 substantially decreased the activation of caspases and apoptosis induced by MSeA combination with SN38 or etoposide and completely blocked these events induced by MSeA/paclitaxel. The caspase-8 inhibitor zIETDfmk completely abolished apoptosis and caspase-9 and caspase-3 cleavage, whereas the caspase-9 inhibitor zLEHDfmk significantly decreased caspase-3 cleavage and apoptosis but had no effect on caspase-8 cleavage. None of these caspase inhibitors abolished JNK1/2 phosphorylation. A JNK-independent suppression of survivin by SN38 and etoposide, but not by paclitaxel, was also observed. In contrast to MSeA, selenite did not show any enhancing effect on the apoptosis induced by these drugs. CONCLUSIONS: MSeA enhanced apoptosis induced by cancer therapeutic drugs in androgen-independent PCA cells. In DU145 cells, the enhancing effect was primarily through interactions between MSeA and JNK-dependent targets to amplify the caspase-8-initiated activation cascades. The results suggest a novel use of methyl selenium for improving the chemotherapy of PCA.

Androgens↗

PubMed2004

Methyl selenium-induced vascular endothelial apoptosis is executed by caspases and principally mediated by p38 MAPK pathway.

The induction of vascular endothelial cell apoptosis and inhibition of tumor-associated angiogenesis by selenium may contribute to its cancer chemopreventive effects. Here we examined the stress-activated/mitogen-activated protein kinases (p38 MAPK, ERK1/2) and protein kinase B/AKT as potential signaling mediators for apoptosis induction by a methylselenol precursor methylseleninic acid (MSeA) in human umbilical vein endothelial cells (HUVEC). Time course experiments showed that p38 MAPK hyperphosphorylation and ERK1/2 dephosphorylation occurred before the cleavage of procaspase-3 and poly(ADP-ribose) polymerase (PARP), whereas AKT dephosphorylation occurred after caspase activation. The p38 MAPK inhibitor SB202190 attenuated the MSeA-induced morphological changes and decreased DNA fragmentation and the cleavage of procaspase-3 and PARP in concordant proportions. The general caspase inhibitor zVADfmk completely blocked the MSeA-induced PARP cleavage and DNA fragmentation, whereas zDEVDfmk, an inhibitor for caspase-3-like activities, was nearly as effective for inhibiting apoptosis. In comparison, apoptosis induced by selenite in HUVECs was observed in the complete absence of an activation of the major caspases. Taken together, the data support p38 MAPK as a key upstream mediator for the methylselenol-specific induction of vascular endothelial caspase-dependent apoptosis, which is principally executed by caspase-3-like activities.

Animals↗

PubMed2004

Methyl selenium metabolites decrease prostate-specific antigen expression by inducing protein degradation and suppressing androgen-stimulated transcription.

Prostate-specific antigen (PSA) is widely used clinically for prostate cancer diagnostics and as an indicator of therapeutic efficacy and recurrence. Several human chemoprevention trials are being conducted to validate the prostate cancer prevention efficacy of selenium and PSA is used in these trials as a biomarker of response. A better understanding of the effects of selenium metabolites on the kinetics of PSA turnover and secretion in prostate cancer cells treated with selenium at concentrations which are achievable physiologically will be important for interpreting the results of these trials. This study addresses whether the putative active anticancer selenium metabolite methylselenol or its precursor methylseleninic acid (MSeA) specifically inhibits PSA expression in the androgen-responsive LNCaP prostate cancer cell model. The results show that exposure to sub-apoptotic concentrations of MSeA and methylselenol inhibited PSA protein expression and secretion, whereas sodium selenite and selenomethionine lacked inhibitory effect. The inhibition was detectable at 3 h of exposure and required a threshold level of MSeA to sustain. Turnover experiments showed that MSeA caused rapid PSA degradation, which was partially blocked by lysosomal inhibitors, but not by a proteasomal inhibitor. Furthermore, MSeA treatment reduced PSA mRNA level, down-regulated androgen receptor protein expression, and inhibited androgen-stimulated PSA promoter transcription. In summary, methylselenol or MSeA specifically and rapidly inhibited PSA expression through two mechanisms of action: inducing PSA protein degradation and suppressing androgen-stimulated PSA transcription. These findings may have important mechanistic implications for the prostate specific cancer chemopreventive action of selenium.

Androgens↗

PubMed2004

Selenite-induced p53 Ser-15 phosphorylation and caspase-mediated apoptosis in LNCaP human prostate cancer cells.

The issue of p53 requirement for the caspase-mediated apoptosis induced by selenium in a cancer chemoprevention or chemotherapy context has not been critically addressed. We and others have shown that selenite induces apoptotic DNA laddering in the p53-mutant DU145 prostate cancer cells and the p53-null HL60 leukemia cells without the cleavage of poly(ADP-ribose) polymerase (PARP; i.e., caspase-independent apoptosis), whereas selenium compounds leading to the formation of methylselenol induce caspase-mediated apoptosis in these cells. Because selenite induces DNA single strand breaks, and because certain types of DNA damage activate p53, we investigated whether the human LNCaP prostate cancer cells, which contain a wild-type p53, execute selenite-induced apoptosis through caspase pathways. The results showed that exposure of LNCaP cells for 24 hours to lower micromolar concentrations of selenite led to DNA laddering, and to the cleavage of PARP and several pro-caspases. In contrast to this apoptosis sensitivity, LNCaP cells were rather resistant to similar concentrations of the methylselenol precursor methylseleninic acid. Selenite treatment led to a significant increase in p53 phosphorylation on Ser-15 (Ser15P). Time course experiments showed that p53 Ser15P occurred several hours before caspase activation and PARP cleavage. The general caspase inhibitor zVADfmk completely blocked PARP cleavage, and significantly decreased DNA laddering, but did not affect p53 Ser15P. An inhibitor for caspase-8 was equally as protective as that for caspase-9 against the selenite-induced apoptosis. Attenuating p53 by a chemical inhibitor pifithrin-alpha decreased the selenite-induced p53 Ser15P and led to concordant reductions of PARP cleavage and apoptosis. In summary, selenite-induced p53 Ser15P appeared to be important for activating the caspase-mediated apoptosis involving both the caspase-8 and the caspase-9 pathways in the LNCaP cells.

Amino Acid Chloromethyl Ketones↗

PubMed2002

Induction of caspase-mediated apoptosis and cell-cycle G1 arrest by selenium metabolite methylselenol.

Previous work based on mono-methyl selenium compounds that are putative precursors of methylselenol has strongly implicated this metabolite in the induction of caspase-mediated apoptosis of human prostate carcinoma and leukemia cells and G1 arrest in human vascular endothelial and cancer epithelial cells. To test the hypothesis that methylselenol itself is responsible for exerting these cellular effects, we examined the apoptotic action on DU145 human prostate cancer cells and the G1 arrest effect on the human umbilical vein endothelial cells (HUVECs) of methylselenol generated with seleno-L-methionine as a substrate for L-methionine-alpha-deamino-gamma-mercaptomethane lyase (EC4.4.1.11, also known as methioninase). Exposure of DU145 cells to methylselenol so generated in the sub-micromolar range led to caspase-mediated cleavage of poly(ADP-ribose) polymerase, nucleosomal DNA fragmentation, and morphologic apoptosis and resulted in a profile of biochemical effects similar to that of methylseleninic acid (MSeA) exposure as exemplified by the inhibition of phosphorylation of protein kinase AKT and extracellularly regulated kinases 1/2. In HUVEC, methylselenol exposure recapitulated the G1 arrest action of MSeA in mitogen-stimulated G1 progression during mid-G1 to late G1. This stage specificity was mimicked by inhibitors of phosphatidylinositol 3-kinase. The results support methylselenol as an active selenium metabolite for inducing caspase-mediated apoptosis and cell-cycle G1 arrest. This cell-free methylselenol-generation system is expected to have significant usefulness for studying the biochemical and molecular targeting mechanisms of this critical metabolite and may constitute the basis of a novel therapeutic approach for cancer, using seleno-L-methionine as a prodrug.

Apoptosis↗

PubMed2002

Distinct effects of methylseleninic acid versus selenite on apoptosis, cell cycle, and protein kinase pathways in DU145 human prostate cancer cells.

Selenium has been implicated as a promising chemopreventive agent for prostate cancer. Whereas the anticancer mechanisms have not been clearly defined, one hypothesis relates to selenium metabolites, especially the monomethyl selenium pool, generated under supranutritional selenium supplementation. To explore potential molecular targets for mediating the chemopreventive activity, we contrasted the effects of methylseleninic acid (MSeA), a novel precursor of methylselenol, versus sodium selenite, a representative of the hydrogen selenide metabolite pool, on apoptosis execution, cell cycle distribution, and selected protein kinases in DU145 human prostate cancer cells. Exposure of DU145 cells to 3 microM MSeA led to a profound G1 arrest at 24 h, and exposure to greater concentrations led to not only G1 arrest, but also to DNA fragmentation and caspase-mediated cleavage of poly(ADP-ribose) polymerase (PARP), two biochemical hallmarks of apoptosis. Immunobiot analyses indicated that G1 arrest induced by the subapoptogenic doses of MSeA was associated with increased expression of p27kip1 and p21cip1, but apoptosis was accompanied by dose-dependent decreases of phosphorylation of protein kinase AKT and extracellular signal-regulated kinase (ERK1/2) in the absence of any phosphorylation change in p38 mitogen-activated protein kinase (p38MAPK) and c-Jun NH2-terminal kinase (JNK1/2). In contrast, selenite exposure caused S-phase arrest and caspase-independent apoptotic DNA fragmentation, which were associated with decreased expression of p27kip1 and p21cip1 and increased phosphorylation of AKT, JNK1/2, and p38MAPK. Although apoptosis induction by MSeA exposure was not sensitive to superoxide dismutase added into the cell culture medium, cell detachment and DNA nucleosomal fragmentation induced by selenite exposure were greatly attenuated by this enzyme, supporting a chemical mediator role of superoxide for these processes. Despite a temporal relationship of AKT and ERK1/2 de-phosphorylation changes before the onset of PARP cleavage in MSeA-exposed cells, experiments with phosphatidylinositol 3-kinase inhibitors wortmannin and LY294002 did not show an enhancing effect of specific blocking of AKT on MSeA-induction of PARP cleavage. Taken together, exposure of DU145 cells to MSeA versus selenite induced differential patterns of cell cycle arrest and apoptosis execution as well as distinct patterns of effects on AKT, ERK1/2, JNK1/2, and p38MAPK phosphorylation and p27kip1 and p21cip1 expression. Multiple molecular pathways are likely differentially targeted by selenium metabolite pools to mediate cancer chemoprevention.

Antineoplastic Agents↗

PubMed2002

Selenium compounds inhibit I kappa B kinase (IKK) and nuclear factor-kappa B (NF-kappa B) in prostate cancer cells.

Selenium compounds are potential chemopreventive agents for prostate cancer. There are several proposed mechanisms for their anticancer effect, including enhanced apoptosis of transformed cells. Because the transcription factor nuclear factor-kappa B (NF-kappa B) is often constitutively activated in tumors and is a key antiapoptotic factor in mammalian cells, we tested whether selenium inhibited NF-kappa B activity in prostate cancer cells. In our work, we used sodium selenite and a novel synthetic compound, methylseleninic acid (MSeA), that served as a precursor of the putative active monomethyl metabolite methylselenol. We found that both selenium forms inhibited cell growth and induced apoptosis in DU145 and JCA1 prostate carcinoma cells. Sodium selenite and MeSeA, at the concentrations that induced apoptosis, inhibited NF-kappa B DNA binding induced by tumor necrosis factor-alpha and lipopolysaccharide in DU145 and JCA1 prostate cells. Both compounds also inhibited kappa B. Luciferase reporter activity in prostate cells. A key to NF-kappa B regulation is the inhibitory kappa B (I kappa B) proteins that in response to diverse stimuli are rapidly phosphorylated by I kappa B kinase complex, ubiquitinated, and undergo degradation, releasing NF-kappa B factor. We showed that sodium selenite and MSeA inhibited I kappa B kinase activation and I kappa B-alpha phosphorylation and degradation induced by TNF-alpha and lipopolysaccharide in prostate cells. NF-kappa B blockage by I kappa B-alpha d.n. mutant resulted in the sensitization of prostate carcinoma cells to apoptosis induced by selenium compounds. These results suggest that selenium may target the NF-kappa B activation pathway to exert, at least in part, its cancer chemopreventive effect in prostate.

Active Transport, Cell Nucleus↗

PubMedDate not supplied

Selenium and cancer chemoprevention: hypotheses integrating the actions of selenoproteins and selenium metabolites in epithelial and non-epithelial target cells.

The trace element nutrient selenium (Se) discharges its well-known nutritional antioxidant activity through the Se-dependent glutathione peroxidases. It also regulates nuclear factor activities by redox mechanisms through the selenoprotein thioredoxin reductases. Converging data from epidemiological, ecological, and clinical studies have shown that Se can decrease the risk for some types of human cancers, especially those of the prostate, lung, and colon. Mechanistic studies have indicated that the methylselenol metabolite pool has many desirable attributes of chemoprevention, targeting both cancer cells and vascular endothelial cells, whereas the hydrogen selenide pool in excess of selenoprotein synthesis can lead to DNA single strand breaks, which may be mediated by some reactive oxygen species. We propose a new paradigm based on a consideration of the post-initiation biology of avascular early lesion expansion microenvironment, physiochemistry of Se delivery, and the obligatory need for angiogenesis to sustain lesion progression. Our model integrates the roles of selenoproteins and specific Se metabolites to account for cancer risk reduction or enhancement. For future studies, speciation (profiling) methods for Se metabolites and for Se forms in foods and supplements are much needed for hypothesis testing and for the development of mechanism-based Se status markers for cancer prevention. Randomized cancer prevention trials are necessary to test the efficacy of methyl selenium compounds.

Animals↗