[show abstract][hide abstract] ABSTRACT: PurposeThis study examines the role of cell survival/apoptosis related proteins involved in NFκB signaling pathways and its associated
events in GTP-induced chemoprevention of prostate cancer in TRAMP mice.
MethodsMice were given 0.1% GTP as drinking fluid. Western blot and immunohistochemical analysis performed to examine NFκB and its
regulated pathway in response to GTP.
ResultsOur data demonstrated increased expression of NFκB, IKKα, IKKβ, RANK, NIK and STAT-3 in dorso-lateral prostate of TRAMP mice
as a function of age and tumor growth and continuous GTP infusion for 32 weeks resulted in substantial reduction in these
proteins. The levels of transcription factor osteopontin, a non-collagenous extracellular matrix protein, were also downregulated.
Inhibition of NFκB signaling is known to activate apoptotic and inhibit anti-apoptotic proteins. Therefore, we analyzed Bax
and Bcl2 levels in the dorsolateral prostate of TRAMP mice fed GTP and observed a shift in balance between Bax and Bcl2 favoring apoptosis.
ConclusionsBased on the data we suggest that oral consumption of GTP might inhibit osteopontin and NFκB signaling that may contribute
to induction of apoptosis observed in GTP fed TRAMP mice.
Pharmaceutical Research 04/2012; 25(9):2135-2142. · 4.74 Impact Factor
[show abstract][hide abstract] ABSTRACT: The activated androgen receptor (AR) promotes prostate cancer (PCa) growth. AR antagonists repress the AR by recruitment of corepressors. Not much is known about the inactivation of AR by corepressors in the presence of agonists (androgens). Here we show that the corepressor LCoR acts as an androgen-dependent corepressor that represses human PCa growth in vivo. In line with this, progressive decrease of ligand-dependent corepressor expression was observed in the PCa TRAMP mouse model with increasing age. LCoR interacts with AR and is recruited to chromatin in an androgen-induced manner. Unexpectedly, the LXXLL motif of LCoR is dispensable for interaction with the AR. Rather, the data indicate that LCoR interacts with the AR DNA binding domain on DNA. Interestingly, the interaction of LCoR with AR is inhibited by signaling pathways that are associated with androgen-independent PCa. Here we also show that the Src kinase inactivates the corepressive function of LCoR. Interfering with endogenous Src function by a dominant negative Src mutant, the growth inhibitory activity of LCoR is enhanced in vivo in a xenograft mouse model system. Thus, our studies indicate a role of LCoR as an AR corepressor and a tumor suppressor. Further, the decreased expression or inactivation of LCoR is as an important step toward PCa carcinogenesis in vivo.
Journal of Biological Chemistry 08/2011; 286(43):37108-17. · 4.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: The activated androgen receptor (AR) promotes prostate cancer (PCa) growth. AR- antagonists repress the AR by recruitment
of corepressors. Not much is known about the inactivation of AR by corepressors in the presence of agonists (androgens). Here
we show that the corepressor LCoR acts as an androgen-dependent corepressor that represses human PCa growth in vivo. In line
with this, progressive decrease of LCoR expression was observed in the PCa TRAMP mouse model with increasing age. LCoR interacts
with AR and is recruited to chromatin in an androgen-induced manner. Unexpectedly, the LXXLL motif of LCoR is dispensable
for interaction with the AR, rather the data indicate that LCoR interacts with the AR-DBD on DNA. Interestingly, the interaction
of LCoR with AR is inhibited by signaling pathways that are associated with androgen-independent PCa. Here we also show that
the Src kinase inactivates the corepressive function of LCoR. Interfering with endogenous Src function by a dominant negative
Src mutant, the growth inhibitory activity of LCoR is enhanced in vivo in xenograft mouse model system. Thus, our studies
indicate the role of LCoR as an AR corepressor and a tumor suppressor. Further, the decreased expression or inactivation of
LCoR is as an important step towards PCa carcinogenesis in vivo.
Journal of Biological Chemistry 08/2011; · 4.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: Androgen deprivation therapy is the major treatment for advanced prostate cancer (PCa). However, it is a temporary remission, and the patients almost inevitably develop hormone refractory prostate cancer (HRPC). HRPC is almost incurable, although most HRPC cells still express androgen receptor (AR) and depend on the AR for growth, making AR a prime drug target. Here, we provide evidence that epigallocatechin-3-gallate (EGCG), the major polyphenol in green tea, is a direct antagonist of androgen action. In silico modeling and FRET-based competition assay showed that EGCG physically interacts with the ligand-binding domain of AR by replacing a high-affinity labeled ligand (IC(50) 0.4 μM). The functional consequence of this interaction was a decrease in AR-mediated transcriptional activation, which was due to EGCG mediated inhibition of interdomain N-C termini interaction of AR. Treatment with EGCG also repressed the transcriptional activation by a hotspot mutant AR (T877A) expressed ectopically as well as the endogenous AR mutant. As the physiological consequence of AR antagonism, EGCG repressed R1881-induced PCa cell growth. In a xenograft model, EGCG was found to inhibit AR nuclear translocation and protein expression. We also observed a significant down-regulation of androgen-regulated miRNA-21 and up-regulation of a tumor suppressor, miRNA-330, in tumors of mice treated with EGCG. Taken together, we provide evidence that EGCG functionally antagonizes androgen action at multiple levels, resulting in inhibition of PCa growth.
The FASEB Journal 12/2010; 25(4):1198-207. · 5.70 Impact Factor
[show abstract][hide abstract] ABSTRACT: Prostate cancer is one of the most prominent malignancies of elderly males. The growth of normal prostate and prostate cancer (PCa) cells depend on functional androgen receptor (AR), a ligand controlled transcription factor and member of the nuclear receptor superfamily. Binding of agonistic ligand enhances the transactivation function of AR and hence promotes the growth of prostate epithelial cells. We have earlier shown that AR antagonistic ligands such as cyproterone acetate (CPA) promote the recruitment of transcriptional corepressors such as silencing mediator of retinoid and thyroid receptor (SMRT) leading to repression of AR transactivation in non-PCa cells. Unfortunately, however, in LNCaP PCa cells, CPA functions as an agonist and thereby increases AR transactivation function. Here, we show that activated MEK signaling cascade inhibits functional recruitment of corepressor SMRT to CPA-bound AR in PCa cells. Chemical blockade of MEK kinase using a specific inhibitor U0126 increases the interaction and hence repression of AR by the corepressor SMRT in LNCaP PCa cells. This inhibition also results in enhanced antagonistic behavior of CPA as assessed by reporter and cell-growth assays. Moreover, the growth of LNCaP cells stably overexpressing SMRT was more robustly inhibited in the presence of CPA and U1026. In line with this, the growth rate of LNCaP cells was decelerated in the presence of both CPA and U0126. This suggests that activated MEK signaling pathway attenuates the functional recruitment of corepressor SMRT to AR induced by antagonists and thus indicates the important role of corepressors in mediating repression of both AR transactivation and PCa cell growth by antagonists. Furthermore, these findings suggest that combining receptor antagonists with signaling inhibitors could be a beneficial approach for PCa treatment.
Journal of Molecular Endocrinology 03/2009; 42(5):429-35. · 3.58 Impact Factor
[show abstract][hide abstract] ABSTRACT: Chemoprevention, especially through the use of naturally occurring phytochemicals capable of impeding the process of one or more steps of carcinogenesis process, is a promising approach for cancer management. Despite promising results in preclinical settings, its applicability to humans has met with limited success largely due to inefficient systemic delivery and bioavailability of promising chemopreventive agents. Here, we introduce the concept of nanochemoprevention, which uses nanotechnology for enhancing the outcome of chemoprevention. We encapsulated green tea polyphenol epigallocatechin-3-gallate (EGCG) in polylactic acid-polyethylene glycol nanoparticles and observed that encapsulated EGCG retains its biological effectiveness with over 10-fold dose advantage for exerting its proapoptotic and angiogenesis inhibitory effects, critically important determinants of chemopreventive effects of EGCG in both in vitro and in vivo systems. Thus, this study could serve as a basis for the use of nanoparticle-mediated delivery to enhance bioavailability and limit any unwanted toxicity of chemopreventive agents, such as EGCG.
Cancer Research 03/2009; 69(5):1712-6. · 8.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: Notch, a type 1 transmembrane protein, plays a key role in the development of many tissues and organ types. Aberrant Notch signaling, found in a wide variety of human cancers, contributes to tumor development. Because Notch1 was found to be overexpressed in prostate cancer (PCa) cells and human PCa tissue, we therefore tested our hypothesis that overexpression of Notch1 in PCa promotes tumor invasion.
Notch1 expression was evaluated in human PCa cells and human PCa tissues. PCa cells were transiently transfected with Notch1-specific small interfering RNAs in concentrations ranging from 30 to 120 nmol/L and subsequently evaluated for effects on invasion and expression analysis for molecules involved in invasion.
Small interfering RNA-mediated knockdown of Notch1 in PC3 and 22Rnu1 PCa cells dramatically decreased their invasion. Focused cDNA array revealed that Notch1 knockdown resulted in significant reduction in the expression of urokinase plasminogen activator (uPA) and matrix metalloproteinase-9 (MMP9) gene transcripts. These data were further verified by reverse transcription-PCR, real-time reverse transcription-PCR, and immunoblot analysis. Knockdown of Notch1 was also observed to significantly reduce the mRNA expression and protein levels of uPA and its receptor uPAR. A significant reduction in MMP9 expression in Notch1 knockdown cells suggested a role for Notch1 in augmenting MMP9 transcription.
Our data show the involvement of Notch1 in human PCa invasion and that silencing of Notch1 inhibits invasion of human PCa cells by inhibiting the expression of MMP9 and uPA. Thus, targeting of Notch1 could be an effective therapeutic approach against PCa.
Clinical Cancer Research 02/2009; 15(2):452-9. · 7.84 Impact Factor
[show abstract][hide abstract] ABSTRACT: In a recent publication, we have shown that delphinidin, an anthocyanidin induces apoptosis and cell cycle arrest in highly metastatic human prostate cancer (PCa) PC3 cells. Extending these studies, we provide additional evidence that delphinidin induces apoptosis and cell cycle arrest in androgen refractory human PCa 22Rnu1 cells and that these effects are concomitant with inhibition of NFkappaB. We observed that delphinidin treatment to 22Rnu1 cells resulted in a dose-dependent (i) G(2)/M phase cell cycle arrest, (ii) induction of apoptosis (iii) and inhibition of NFkappaB signaling. The induction of apoptosis by delphinidin was mediated via activation of caspases since a general caspase inhibitor Z-VAD-FMK significantly reversed this effect. Delphinidin treatment to cells resulted in a dose-dependent decrease in (i) phosphorylation of IKKgamma (NEMO), (ii) phosphorylation of NFkappaB inhibitory protein IkappaBalpha, (iii) phosphorylation of NFkappaB/p65 at Ser(536) and NFkappaB/p50 at Ser529, (iv) NFkappaB/p65 nuclear translocation, and (v) NFkappaB DNA binding activity. Taken together, our data show that delphinidin induces apoptosis of both androgen independent and androgen refractory human PCa cells via activation of caspases and in addition, this effect might be due to inhibition of NFkappaB signaling. We suggest that delphinidin could be developed as a novel agent against PCa.
[show abstract][hide abstract] ABSTRACT: Delphinidin, a major anthocyanidin present in many pigmented fruits and vegetables, possesses antioxidant, anti-inflammatory, and antiangiogenic properties. In this study, we provide evidence that it could be developed as a novel agent against human prostate cancer (PCa). We observed that delphinidin treatment to human PCa LNCaP, C4-2, 22Rnu1, and PC3 cells resulted in a dose-dependent inhibition of cell growth without having any substantial effect on normal human prostate epithelial cells. We selected PC3 cells as a test model system because of their highly aggressive proliferative nature. Delphinidin treatment of cells resulted in a dose-dependent induction of apoptosis and arrest of cells in G(2)-M phase. This induction of apoptosis seems to be mediated via activation of caspases because N-benzyloxycarbonyl-Val-Ala-Asp(OMe)-fluromethylketone significantly reduced apoptosis induced by delphinidin. We also observed that delphinidin treatment of cells resulted in a dose-dependent decrease in (a) phosphorylation of IkappaB kinase gamma (NEMO), (b) phosphorylation of nuclear factor-kappaB (NF-kappaB) inhibitory protein IkappaBalpha, (c) phosphorylation of NF-kappaB/p65 at Ser(536) and NF-kappaB/p50 at Ser(529), (d) NF-kappaB/p65 nuclear translocation, and (e) NF-kappaB DNA binding activity. Delphinidin administration (2 mg, i.p. thrice weekly) to athymic nude mice implanted with PC3 cells resulted in a significant inhibition of tumor growth. Analysis of tumors from delphinidin-treated mice showed significant decrease in the expression of NF-kappaB/p65, Bcl2, Ki67, and PCNA. Taken together, our data suggest that delphinidin could be developed as an agent against human PCa.
Cancer Research 11/2008; 68(20):8564-72. · 8.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: Androgen receptor (AR)-mediated signaling plays an important role in the development and progression of prostate cancer (PCa). Hormonal therapies, mainly with combinations of antiandrogens and androgen deprivation, are the mainstay treatment for advanced disease. However, emergence of androgen resistance largely due to inefficient antihormone action limits their therapeutic usefulness. Here, we report that fisetin, a novel dietary flavonoid, acts as a novel AR ligand by competing with the high-affinity androgen to interact with the ligand binding domain of AR. We show that this physical interaction results in substantial decrease in AR stability and decrease in amino-terminal/carboxyl-terminal (N-C) interaction of AR. This results in blunting of AR-mediated transactivation of target genes including prostate-specific antigen (PSA). In addition, treatment of LNCaP cells with fisetin decreased AR protein levels, in part, by decreasing its promoter activity and by accelerating its degradation. Fisetin also synergized with Casodex in inducing apoptosis in LNCaP cells. Treatment with fisetin in athymic nude mice implanted with AR-positive CWR22Rupsilon1 human PCa cells resulted in inhibition of tumor growth and reduction in serum PSA levels. These data identify fisetin as an inhibitor of AR signaling axis and suggest that it could be a useful chemopreventive and chemotherapeutic agent to delay progression of PCa.
Cancer Research 11/2008; 68(20):8555-63. · 8.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: Poor prognosis of metastatic melanoma mandates the development of novel strategies for its treatment and prevention. In this study, the effect of lupeol, a diet-based triterpene, was determined on the growth and tumorigenicity of human melanoma cells in vitro and in vivo.
Normal human melanocytes, and human metastatic (451Lu) and nonmetastatic (WM35) cells were treated with lupeol; its effect on growth, proliferation, and apoptosis were evaluated. Further athymic nude mice bearing 451Lu cell-originated tumors were administered with lupeol thrice a week, and its effect on tumor growth and surrogate biomarkers was evaluated.
Lupeol significantly decreased the viability of 451Lu and WM35 melanoma cells but had only a marginal effect on normal human melanocyte cells at similar doses. Lupeol treatment of 451Lu cells caused (a) G(1)-S phase cell cycle arrest and apoptosis; (b) down-regulation of Bcl2 and up-regulation of Bax; (c) activation of caspase-3 and induction of poly(ADP)ribose polymerase cleavage; (d) decreased expression of cyclin D1, cyclin D2, and cdk2; and (e) increased expression of p21 protein. Next, lupeol significantly reduced 451Lu tumor growth in athymic nude mice and modulated the expression of proliferation markers, apoptotic markers, and cell cycle regulatory molecules in tumor xenografts.
Our findings showed the anticancer efficacy of lupeol with mechanistic rationale against metastatic human melanoma cells. We suggest that lupeol, alone or as an adjuvant to current therapies, could be useful for the management of human melanoma.
Clinical Cancer Research 05/2008; 14(7):2119-27. · 7.84 Impact Factor
[show abstract][hide abstract] ABSTRACT: Androgens play a central role in prostate development and prostate cancer proliferation. Induction of telomerase is an early event in prostate carcinogenesis and is considered as a marker for both primary tumors and metastases. Interestingly, several reports suggest that telomerase activity is regulated by androgens in vivo. Here, we show that the wild-type (WT) human androgen receptor (AR) inhibits the expression of the human telomerase reverse transcriptase (hTERT) and telomerase activity via inhibition of hTERT promoter activity in the presence of androgen receptor agonists. However, pure androgen antagonists failed to repress hTERT transcription. The androgen-mediated repression of hTERT is abrogated in a human prostate cancer cell line exhibiting hormone-dependent growth, which expresses a mutant AR (T877A) frequently occurring in prostate cancer. We reveal that this single amino acid exchange is sufficient for the lack of transrepression. Interestingly, chromatin immunoprecipitation data suggest that, in contrast to the WT AR, the mutant AR is recruited less efficiently to the hTERT promoter in vivo, indicating that loss of transrepression results from reduced chromatin recruitment. Thus, our findings suggest that the WT AR inhibits expression of hTERT, which is indicative of a protective mechanism, whereas the T877A mutation of AR not only broadens the ligand spectrum of the receptor but abrogates this inhibitory mechanism in prostate cancer cells. This novel role of AR mutations in prostate cancer development suggests the benefit to a search for new AR antagonists that inhibit transactivation but allow transrepression.
The FASEB Journal 05/2008; 22(4):1258-67. · 5.70 Impact Factor
[show abstract][hide abstract] ABSTRACT: Prostate cancer (PCa) is the most frequently diagnosed malignancy and the second leading cause of cancer-related deaths in American males with similar trends in many western countries. The existing treatment approaches and surgical intervention have not been able to effectively cope with this dreaded disease. For these reasons, it is necessary to intensify our efforts for a better understanding of the disease process and for the development of novel approaches for its prevention and treatment. Based on considerable evidence from in vivo and in vitro data and epidemiological studies, in recent years the beverage tea has gained considerable attention for reducing the risk of several cancers. Much of the cancer preventive effects of tea, especially green tea appear to be mediated by the polyphenols present therein. Geographical evidence suggests that the incidence and occurrence of PCa is lower in populations that consume tea regularly. This evidence suggests that tea polyphenols could be extrapolated to optimize their chemopreventive properties against PCa. PCa represents an excellent candidate disease for chemoprevention because it is typically diagnosed in men over 50 years of age and therefore, even a modest delay in neoplastic development achieved through pharmacological or nutritional intervention could result in a substantial reduction in the incidence of clinically detectable disease. In this review we address the issue of possible use of tea, especially green tea, for the prevention as well as treatment of PCa.