IGFBP-3 is a metastasis suppression gene in prostate cancer

The insulin-like growth factor binding protein IGFBP-3 is a proapoptotic and antiangiogenic protein in prostate cancer (CaP). Epidemiologic studies suggest that low IGFBP-3 is associated with greater risk of aggressive, metastatic prostate cancers, but in vivo functional data are lacking. Here we show that mice that are genetically deficient in IGFBP-3 exhibit weaker growth of primary prostate tumors but higher incidence of metastatic disease. Prostates in IGFBP-3 knockout mice (IGFBP-3KO mice) failed to undergo apoptosis after castration. Spontaneous prostate tumors did not develop in IGFBP-3KO mice, but splenic lymphomas occurred in 23% of female IGFBP-3KO mice by 80 weeks of age. To assess the effects of IGFBP-3 deficiency on prostate cancer development, we crossed IGFBP-3KO mice with a c-Myc-driven model of CaP that develops slow-growing, nonmetastatic tumors. By 24 weeks of age, well-differentiated prostate cancers were observed in all mice regardless of IGFBP-3 status. However, by 80 weeks of age IGFBP-3KO mice tended to exhibit larger prostate tumors than control mice. More strikingly, lung metastases were observed at this time in 55% of the IGFBP-3KO mice but none in the control animals. Cell lines established from IGFBP-3KO:Myc tumors displayed more aggressive phenotypes in proliferation, invasion, and colony formation assays, relative to control Myc tumor cell lines. In addition, Myc:IGFBP-3KO cells exhibited evidence of epithelial-mesenchymal transition. Our findings established a function for IGFBP-3 in suppressing metastasis in prostate cancer, and they also offered the first reported transgenic model of spontaneous metastatic prostate cancer for studies of this advanced stage of disease.     

The role of insulin-like growth factor binding protein-3 in the growth inhibitory actions of androgens in LNCaP human prostate cancer cells

Insulin-like growth factor binding protein-3 (IGFBP-3), an antiproliferative and proapoptotic protein, has been shown to be upregulated by growth inhibitory concentrations of androgens in LNCaP human prostate cancer (PCa) cells, but the mechanism of regulation and the role of IGFBP-3 in the modulation of PCa cell proliferation are unknown. In this study, we have examined the effects of a range of concentrations of the synthetic androgen R1881 on IGFBP-3 expression and cell growth in LNCaP cells. We have also investigated the role of androgen-stimulated IGFBP-3 in androgen-induced growth inhibition. We show that low doses of R1881 stimulate LNCaP cell proliferation, but do not induce IGFBP-3 expression, whereas high doses of R1881 that inhibit cell growth, significantly increase expression of IGFBP-3. Importantly, we demonstrate that the combination of calcitriol and androgens not only synergistically upregulates IGFBP-3 expression but also inhibits cell growth better than either hormone alone. siRNA knockdown of IGFBP-3 expression partially reverses the growth inhibition by calcitriol and by androgens. Furthermore, we find that the growth inhibitory dose of R1881 leads to increases in the cyclin dependent kinase inhibitors (CDKIs), p21 and p27 as well as to G1 arrest. These changes can be blocked or partially reversed by IGFBP-3 siRNA, indicating that the induction of CDKIs is downstream of IGFBP-3. Our data suggest, for the first time, that IGFBP-3 is involved in the antiproliferative action of high doses of androgens partly through p21 and p27 pathways and that IGFBP-3 may contribute significantly to androgen-induced changes in LNCaP cell growth.     

Quercetin induces p53-independent apoptosis in human prostate cancer cells by modulating Bcl-2-related proteins: a possible mediation by IGFBP-3

Quercetin, a flavonoid found in onion, grapes, green vegetables, etc., has been shown to possess potent antiproliferative effects against various malignant cells. We report insulin-like growth factor-binding protein-3 (IGFBP-3) as an effector of quercetin-induced apoptosis in human prostate cancer cell lines in a p53-independent manner. We evaluated the production of IGFBP-3 in quercetin-treated cells. Apoptosis was studied in quercetin-treated cells to study the IGFBP-3-mediated role with flow cytometry and DNA fragmentation. Protein expressions of Bcl-2, Bcl-x(L), and Bax were studied by Western blot. Increased production of IGFBP-3 was associated with the increased ratio of proapoptotic to antiapoptotic members of the Bcl-2 family. In quercetin-treated PC-3 cells, an increase in Bax protein expression and a decrease in Bcl-x(L) protein and Bcl-2 protein were observed. As PC-3 is a p53-negative cell line, these modulations of proapoptotic proteins and induction of apoptosis were independent of p53. The level of IGFBP-3 on the response of PC-3 cells to quercetin was examined. There was a twofold increase in IGFBP-3 level in conditioned media of 100 microM quercetin-treated cells. Quercetin also brought a peak at sub-G1 in PC-3 cells. Thus, increased level of IGFBP-3 was associated with increased proapoptotic proteins and apoptosis in response to quercetin, suggesting it may be a p53-independent effector of apoptosis in prostate cancer cells via its modulation of the Bax/Bcl-2 protein ratio.     

Endoglin regulates cancer-stromal cell interactions in prostate tumors

Endoglin is an accessory receptor for TGF-β that has been implicated in prostate cancer cell detachment, migration, and invasiveness. However, the pathophysiologic significance of endoglin with respect to prostate tumorigenesis has yet to be fully established. In this study, we addressed this question by investigation of endoglin-dependent prostate cancer progression in a TRAMP (transgenic adenocarcinoma mouse prostate) mouse model where endoglin was genetically deleted. In this model, endoglin was haploinsufficient such that its allelic deletion slightly increased the frequency of tumorigenesis, yet produced smaller, less vascularized, and less metastatic tumors than TRAMP control tumors. Most strikingly, TRAMP:eng(+/-)-derived tumors lacked the pronounced infiltration of carcinoma-associated fibroblasts (CAF) that characterize TRAMP prostate tumors. Studies in human primary prostate-derived stromal cells (PrSC) confirmed that suppressing endoglin expression decreased cell proliferation, the ability to recruit endothelial cells, and the ability to migrate in response to tumor cell-conditioned medium. We found increased levels of secreted insulin-like growth factor-binding proteins (IGFBP) in the conditioned medium from endoglin-deficient PrSCs and that endoglin-dependent regulation of IGFBP-4 secretion was crucial for stromal cell-conditioned media to stimulate prostate tumor cell growth. Together, our results firmly establish the pathophysiologic involvement of endoglin in prostate cancer progression; furthermore, they show how endoglin acts to support the viability of tumor-infiltrating CAFs in the tumor microenvironment to promote neovascularization and growth.     

Oral consumption of green tea polyphenols inhibits insulin-like growth factor-I-induced signaling in an autochthonous mouse model of prostate cancer

We earlier demonstrated that oral infusion of green tea polyphenols inhibits development and progression of prostate cancer in transgenic adenocarcinoma of the mouse prostate (TRAMP) model. Evidence indicates that elevated levels of IGF-I with concomitant lowering of IGF binding protein (IGFBP)-3 are associated with increased risk for prostate cancer development and progression. In this study, we examined the role of IGF/IGFBP-3 signaling and its downstream and other associated events during chemoprevention of prostate cancer by green tea polyphenols in TRAMP mice. Our data demonstrated an increase in the levels of IGF-I, phosphatidylinositol 3'-kinase, phosphorylated Akt (Thr-308), and extracellular signal-regulated kinase 1/2 with concomitant decrease in IGFBP-3 in dorso-lateral prostate of TRAMP mice during the course of cancer progression, i.e., as a function of age. Continuous green tea polyphenol infusion for 24 weeks to these mice resulted in substantial reduction in the levels of IGF-I and significant increase in the levels of IGFBP-3 in the dorso-lateral prostate. This modulation of IGF/IGFBP-3 was found to be associated with an inhibition of protein expression of phosphatidylinositol 3'-kinase, phosphorylated forms of Akt (Thr-308) and extracellular signal-regulated kinase 1/2. Furthermore, green tea polyphenol infusion resulted in marked inhibition of markers of angiogenesis and metastasis most notably vascular endothelial growth factor, urokinase plasminogen activator, and matrix metalloproteinases 2 and 9. Based on our data, we suggest that IGF-I/IGFBP-3 signaling pathway is a prime pathway for green tea polyphenol-mediated inhibition of prostate cancer that limits the progression of cancer through inhibition of angiogenesis and metastasis.     

Vitamin E succinate suppresses prostate tumor growth by inducing apoptosis

Prostate cancer is a major cause of cancer death and morbidity in western countries. However, because of its intrinsic nature of chemoresistance, there is only limited systemic therapy available for the patients. Vitamin E (VE) has been under intensive study as a chemopreventive agent for various types of cancers. Preclinical studies suggest that vitamin E succinate (VES) is the most effective antitumor analogue of VE, yet there are scarce studies of VES in prostate cancer. In this study, we investigated the effects of VES on a panel of prostate cancer cells, and a xenograft model of prostate cancer. Our results indicate that VES significantly inhibited proliferation and induced apoptosis of prostate cancer cell lines in a dose and time dependent manner. The results of microarray analysis followed by real-time RT-PCR and inhibitor analyses indicated that the VES-induced apoptosis is mediated by caspase-4 in prostate tumor cells. In our animal model of prostate cancer in SCID mouse, daily injection of VES significantly suppressed tumor growth as well as lung metastases. These results suggest a potential therapeutic utility of VES for patients with prostate cancer.     

Chemopreventive efficacy of inositol hexaphosphate against prostate tumor growth and progression in TRAMP mice.

PURPOSE: Herein, for the first time, we evaluated the in vivo chemopreventive efficacy of inositol hexaphosphate (IP6), a major constituent of high-fiber diets, against prostate tumor growth and progression in the transgenic adenocarcinoma of the mouse prostate (TRAMP) model. EXPERIMENTAL DESIGN: Beginning at 4 weeks of age, male TRAMP mice were fed 2% (w/v) IP6 in drinking water or only drinking water till 24 weeks of age, and then sacrificed. Prostate tissue was subjected to histopathologic analysis and to immunohistochemical analyses for proliferation and apoptosis. RESULTS: IP6 feeding did not show any adverse effect on fluid and diet consumption and body weight. There was a significant reduction (40%; P < 0.01) in lower urogenital tract weight in IP6-fed mice. IP6 inhibited prostate cancer progression at prostatic intraepithelial neoplasia stage and strongly reduced the incidence of adenocarcinoma (prostatic intraepithelial neoplasia/adenocarcinoma, 75:25% in the IP6 group versus 39:61% in the control group; P < 0.05). The incidences of well-differentiated and poorly differentiated adenocarcinomas in the IP6-fed group were reduced by 44% and 62%, respectively. Immunohistochemical analysis of prostate tissue showed a 26% decrease (P < 0.05) in proliferation cell nuclear antigen-positive cells and a 3.5-fold increase in apoptotic cells with no effect on Tag expression by IP6. CONCLUSIONS: These findings are both novel and highly significant in establishing for the first time that oral IP6, without any toxicity, suppresses prostate tumor growth and progression at the neoplastic stage, thereby reducing the incidence of adenocarcinoma through its antiproliferative and proapoptotic effects, and thus indicating that IP6 could have potential chemopreventive effects against human prostate cancer.     

Involvement of activator protein-1 (AP-1) in induction of apoptosis by vitamin E succinate in human breast cancer cells

The purpose of this study was to document induction of apoptosis by vitamin E succinate (VES; RRR-α-tocopheryl succinate) in human breast cancer cells in culture and to characterize potential c-jun involvement. VES at 18.8 μM (10 μg/mL) induced DNA synthesis arrest, reduced total cell numbers, and induced apoptosis in estrogen receptor–positive and estrogen-responsive MCF-7 human breast cancer cells. VES at 10 μg/mL induced apoptosis in greater than 60% of cells within 3 d of treatment. Apoptosis was documented by detection of fragmented or condensed nuclei in 4′,6-diamindino-2-phenylindole–stained cells, detection of terminal deoxynucleotidyl transferase–mediated dUTP-biotin nick-end labeled DNA, and DNA laddering. Analyses of mRNA and protein levels of candidate molecules involved in apoptosis showed that MCF-7 cells treated with VES exhibited elevated and persistent expression of c-jun. MCF-7 cells stably transfected with a dominant-negative interfering mutant c-jun, TAM-67, and expressing high levels of mutant jun exhibited approximately 50% blockage of VES-mediated apoptosis. In addition to increased c-jun expression after VES treatment, VES-treated MCF-7 cells exhibited elevated activator protein-1 (AP-1) binding activity. Comparisons of AP-1 binding factors by super-shift analyses with jun-specific antibodies in cells sensitive to VES-induced apoptosis (empty-vector control 7-1 cells) and cells resistant to VES-induced apoptosis (TAM-67–containing TAM-9 cells) showed that the sensitive cells expressed c-jun and jun D and the resistant cells TAM-67 AP-1 binding proteins after VES treatment. These studies suggested that c-jun may be involved in the apoptotic process initiated by VES treatment of human MCF-7 breast cancer cells. Mol. Carcinog. 19:180–190, 1997. © 1997 Wiley-Liss, Inc.     

Insulin-like growth factor-binding protein-3 suppresses tumor growth via activation of caspase-dependent apoptosis and cross-talk with NF-κB signaling

Nuclear factor-kappaB (NF-κB) is constitutively activated in a variety of human cancers including prostate cancer and involved in tumorigenesis, tumor progression and chemo-resistance. Insulin-like growth factor-binding protein-3 (IGFBP-3) is a potent tumor suppressor and is significantly suppressed in a variety of cancers. Diverse biological effects of IGFBP-3 have been reported to be both dependent and independent of the IGF/IGF-I receptor (IGF-IR) axis. The precise underlying mechanisms of IGF/IGF-IR-independent, antiproliferative actions of IGFBP-3 are yet to be elucidated. We found an inverse correlation between NF-κB activity and IGFBP-3 expression during prostate cancer progression using an in vitro prostate cancer progression model. Restoration of IGFBP-3 resulted in significant inhibition of constitutively elevated NF-κB activity in prostate cancer cells. IGFBP-3 further inhibited the expression of NF-κB-regulated angiogenic factors such as VEGF and IL-8, and cell adhesion molecules, ICAM-1 and VCAM-1. This inhibitory action of IGFBP-3 was IGF/IGF-IR-independent since IGFBP-3 mutant devoid of IGF binding affinity had a similar inhibitory effect. We identified that IGFBP-3 degrades the key NF-κB regulatory molecules-IκBα and p65-NF-κB proteins through activation of caspase-8 and -3/-7, thereby inhibiting elevated NF-κB activity in prostate cancer. Finally intratumoral administration of IGFBP-3 resulted in significant tumor suppression as well as sensitization of antitumor effect of doxorubicin. Our findings indicate that IGFBP-3 exerts antitumor effects via IGF-independent mechanisms which involve activation of caspase-dependent apoptosis and cross-talk with NF-κB signaling. The use of IGFBP-3 as a cancer therapeutic with this distinctive suppression mechanism may offer alternate means to treat chemotherapy resistant tumors.     

Hepatocyte growth factor-like protein is required for prostate tumor growth in the TRAMP mouse model

The Ron receptor is deregulated in a variety of cancers. Hepatocyte growth factor-like protein (HGFL) is the ligand for Ron and is constitutively secreted from hepatocytes into the circulation. While a few recent reports have emerged analyzing ectopic HGFL overexpression in cancer cells, no studies have examined the effect of host-produced HGFL in tumorigenesis. To examine HGFL function in prostate cancer, the TRAMP mouse model, which is predisposed to develop prostate tumors, was utilized. Prostate tumors from TRAMP mice exhibit elevated levels of HGFL, which correlated with upregulation in human prostate cancer. To directly implicate HGFL in prostate tumorigenesis, TRAMP mice deficient in HGFL (HGFL-/-TRAMP+) were generated. HGFL-/- TRAMP+ mice developed significantly smaller prostate tumors compared to controls. Analysis of HGFL-/- tumors revealed reduced tumor vascularization. No differences in cancer cell proliferation were detected between HGFL-/- TRAMP+ and HGFL+/+ TRAMP+ mice. However, a significant increase in cancer cell death was detected in HGFL-/- TRAMP+ prostates which correlated with decreased pro-survival targets. In vitro analysis demonstrated robust STAT3 activation resulting in Bcl2-dependent survival following treatment of prostate cancer cells with HGFL. These data document a novel function for endogenous HGFL in prostate cancer by imparting a critical survival signal to tumor cells.     

Calcitriol-induced prostate-derived factor: autocrine control of prostate cancer cell growth

Calcitriol (1alpha,25-dihydroxycholecalciferol) seems to play an important role in the complex control of prostate cell growth. It inhibits proliferation and induces differentiation and apoptosis in prostate cancer cells. However, the molecular mechanisms of the antiproliferative activity of calcitriol are not completely understood. The expression of prostate-derived factor (PDF), a member of the transforming growth factor-beta (TGF-beta) superfamily, has been shown to be associated with proapoptotic and antimitotic activities. We show that calcitriol induces PDF expression in LNCaP human prostate cancer cells in a concentration- and time-dependent manner. In LNCaP cells, the suppression of cell growth by calcitriol is accompanied by stimulation of PDF mRNA and protein synthesis. Human recombinant PDF inhibits LNCaP cell growth. We do not detect any effect of PDF-specific antibody on the basal growth of LNCaP cells, but this antibody partially reverses the suppression of LNCaP cell growth by calcitriol, suggesting that the effect of calcitriol on cell growth is at least partially mediated by PDF. In PC-3 cells, which are less responsive to the growth-inhibitory effect of calcitriol, it has no effect on PDF expression. We do not detect an effect of recombinant PDF on SMAD phosphorylation in LNCaP cells, but ERK1/2 kinases are transiently phosphorylated in response to PDF, which suggests that in LNCaP cells PDF may exert its action through pathway alternative to the classical TGF-beta signaling pathway. The present study describes the regulation of PDF, the proapoptotic protein of the TGF-beta superfamily, by calcitriol in androgen-responsive prostate cancer cells. This is a new link between calcitriol and growth factors of TGF-beta superfamily in the control of prostate cell growth.     

Vitamin E succinate (VES) induces Fas sensitivity in human breast cancer cells: role for Mr 43,000 Fas in VES-triggered apoptosis

Fas (CD95/APO-1) is an important mediator of apoptosis. We show that Fas-resistant MCF-7, MDA-MB-231, and MDA-MB-435 human breast cancer cells become responsive to anti-Fas (CD95) agonistic antibody-triggered apoptosis after pretreatment or cotreatment with vitamin E succinate (VES; RRR-alpha-tocopheryl succinate). In contrast, no enhancement of anti-Fas agonistic antibody-triggered apoptosis was observed following VES pretreatment or cotreatment with Fas-sensitive primary cultures of human mammary epithelial cells, immortalized MCF-10A cells, or T47D human breast cancer cells. Although VES is itself a potent apoptotic triggering agent, the 6-h pretreatment procedure for Fas sensitization did not initiate VES-mediated apoptosis. The combination of VES plus anti-Fas in pretreatment protocols was synergistic, inducing 2.8-, 3.0-, and 6.3-fold enhanced apoptosis in Fas-resistant MCF-7, MDA-MB-231, and MDA-MB-435 cells, respectively. Likewise, cotreatment of Fas-resistant MCF-7, MDA-MB-231, and MDA-MB-435 cells with VES plus anti-Fas enhanced apoptosis 1.9-, 2.0-, and 2.6-fold, respectively. Functional knockout of Fas-mediated signaling with either Fas-neutralizing antibody (MCF-7-, MDA-MB-231-, and MDA-MB-435-treated cells) or Fas antisense oligomers (MDA-MB-435-treated cells only), reduced VES-triggered apoptosis by approximately 50%. Analyses of whole cell extracts from Fas-sensitive cells revealed high constitutive expression of Mr 43,000 Fas, whereas Fas-resistant cells expressed low levels that were confined to the cytosolic fraction. VES treatment of the Fas-resistant cells caused a depletion of cytosolic Mr 43,000 Fas with a concomitant increase in Mr 43,000 membrane Fas. These data show that VES can convert Fas-resistant human breast cancer cells to a Fas-sensitive phenotype, perhaps by translocation of cytosolic Mr 43,000 Fas to the membrane and show that VES-mediated apoptosis involves Mr 43,000 Fas signaling.     

Bitter melon extract impairs prostate cancer cell-cycle progression and delays prostatic intraepithelial neoplasia in TRAMP model

Prostate cancer remains the second leading cause of cancer deaths among American men. Earlier diagnosis increases survival rate in patients. However, treatments for advanced disease are limited to hormone ablation techniques and palliative care. Thus, new methods of treatment and prevention are necessary for inhibiting disease progression to a hormone refractory state. One of the approaches to control prostate cancer is prevention through diet, which inhibits one or more neoplastic events and reduces the cancer risk. For centuries, Ayurveda has recommended the use of bitter melon (Momordica charantia) as a functional food to prevent and treat human health related issues. In this study, we have initially used human prostate cancer cells, PC3 and LNCaP, as an in vitro model to assess the efficacy of bitter melon extract (BME) as an anticancer agent. We observed that prostate cancer cells treated with BME accumulate during the S phase of the cell cycle and modulate cyclin D1, cyclin E, and p21 expression. Treatment of prostate cancer cells with BME enhanced Bax expression and induced PARP cleavage. Oral gavage of BME, as a dietary compound, delayed the progression to high-grade prostatic intraepithelial neoplasia in TRAMP (transgenic adenocarcinoma of mouse prostate) mice (31%). Prostate tissue from BME-fed mice displayed approximately 51% reduction of proliferating cell nuclear antigen expression. Together, our results suggest for the first time that oral administration of BME inhibits prostate cancer progression in TRAMP mice by interfering cell-cycle progression and proliferation.     

The Ron receptor promotes prostate tumor growth in the TRAMP mouse model

The Ron receptor tyrosine kinase (TK) is overexpressed in many cancers, including prostate cancer. To examine the significance of Ron in prostate cancer in vivo, we utilized a genetically engineered mouse model, referred to as TRAMP mice, that is predisposed to develop prostate tumors. In this model, we show that prostate tumors from 30-week-old TRAMP mice have increased Ron expression compared with age-matched wild-type prostates. Based on the upregulation of Ron in human prostate cancers and in this murine model of prostate tumorigenesis, we hypothesized that this receptor has a functional role in the development of prostate tumors. To test this hypothesis, we crossed TRAMP mice with mice that are deficient in Ron signaling (TK-/-). Interestingly, TK-/- TRAMP+ mice show a significant decrease in prostate tumor mass relative to TRAMP mice containing functional Ron. Moreover, TK-/- TRAMP+ prostate tumors exhibited decreased tumor vascularization relative to TK+/+ TRAMP+ prostate tumors, which correlated with reduced levels of the angiogenic molecules vascular endothelial growth factor and CXCL2. Although Ron loss did not alter tumor cell proliferation, a significant decrease in cell survival was observed. Similarly, murine prostate cancer cell lines containing a Ron deficiency exhibited decreased levels of active nuclear factor-κB, suggesting that Ron may be important in regulating prostate cell survival at least partly through this pathway. In total, our data show for the first time that Ron promotes prostate tumor growth, prostate tumor angiogenesis and prostate cancer cell survival in vivo.     

Blockade of beta-catenin signaling by plant flavonoid apigenin suppresses prostate carcinogenesis in TRAMP mice

Deregulation of beta-catenin signaling is an important event in the genesis of several human malignancies including prostate cancer. We investigated the effects of apigenin, a naturally occurring plant flavone, on prostate carcinogenesis in TRAMP mice and further elucidated its mechanism of action. Oral intake of apigenin by gavage at doses of 20 and 50 microg/mouse/d, 6 days per week for 20 weeks, significantly decreased tumor volumes of the prostate as well as completely abolished distant-site metastases to lymph nodes, lungs, and liver in TRAMP mice. Apigenin-treated mice had significantly diminished weights of their genitourinary apparatuses and dorsolateral and ventral prostate lobes, compared with the control group, and showed reduced proliferation and increased apoptosis in the dorsolateral prostates, which correlated with elevated plasma apigenin levels. Continuous intake of apigenin up to 50 weeks by TRAMP mice significantly improved their overall survival. P.o. administration of apigenin further resulted in increased levels of E-cadherin and decreased levels of nuclear beta-catenin, c-Myc, and cyclin D1 in the dorsolateral prostates of TRAMP mice. Similar effects were noted in TRAMP mice with established tumors. Treatment of DU145 human prostate cancer cells with 10 and 20 micromol/L apigenin also increased protein levels of E-cadherin by 27% to 74%, inhibited nuclear translocation of beta-catenin and its retention in the cytoplasm, and decreased c-Myc and cyclin D1 levels, an effect similar to the exposure of cells to beta-catenin small interfering RNA. Our results indicate that apigenin effectively suppressed prostate carcinogenesis in TRAMP mice, at least in part, by blocking beta-catenin signaling.     

RRR-alpha-tocopheryl succinate inhibits human prostate cancer cell invasiveness

RRR-alpha-tocopheryl succinate (alpha-vitamin E succinate, VES), one of the vitamin E derivatives, can effectively inhibit the proliferation of human prostate cancer cells. However, little is known about its effect on prostate cancer cell invasive ability. Tumor metastasis is a complex process and the extracellular matrix (ECM) is the first barrier that tumor cells encounter. Therefore, we tested the effect of VES on the invasion of different prostate tumor cells, PC-3, DU-145, and LNCaP, through Matrigel, a reconstituted ECM, using an in vitro cell invasion assay. The invasion of PC-3 and DU-145 cells through Matrigel was inhibited by 20 microM VES after treating for 24 h. The condition did not alter cell survival, cell cycle, cell adhesion or cell motility. We further investigated whether the ability of VES to inhibit prostate cancer cell invasiveness was associated with its ability to inhibit the activity of matrix metalloproteinases (MMPs), the key enzymes in the proteolysis of basement membrane during invasion. PC-3 and DU-145 cells that were treated with VES showed a significant reduction in the levels of MMP-9 in the culture medium. In contrast, LNCaP cells, which did not secrete MMP-9, were poorly invasive in Matrigel and were hardly affected by treatment with VES. This is the first report suggesting that VES inhibits human prostate cancer cell invasiveness and the reduction of secreted MMP-9 activity could be one of the contributory factors, which points to the potential use of VES in the prevention and therapy of prostate cancer invasion.