Swati Dhar

Resveratrol and prostate cancer: promising role for microRNAs.

SCOPE Resveratrol (Res) has anticancer activity in prostate cancer (PCa), which can be attributed to modulation of microRNAs (miRNAs/miRs). miRNAs/miRs are small non-coding RNAs that negatively regulate gene expression. We have analyzed differential miRNA expression in PCa cells treated with Res. METHODS AND RESULTS Using miRNA microarrays we found that 23 miRNAs were significantly down-regulated and 28 miRNAs were significantly up-regulated after Res treatment. The down-regulated miRs included miR-17-92 and miR-106ab clusters with well recognized oncogenic properties while the up-regulated miRs included several tumor suppressors. Selected miRs were verified by qRT-PCR, including miR-17, miR-20a, miR-20b, miR-106a and miR106b. Since these miRNAs target PTEN (phosphatase and tensin homolog deleted on chromosome 10), we performed Western blot to confirm up-regulation of PTEN in PCa cells. In addition, using TargetScan database, we have identified putative mRNA targets for Res-induced down- and up-regulated miRs. Using a bioinformatics approach, we generated gene networks specifically altered by Res-regulated miRNAs. CONCLUSION Our results indicate that the dietary compound Res may play an important role in prostate carcinogenesis through modulation of miRNA expression: Res down-regulated oncogenic miRs and up-regulated tumor suppressor miRs in PCa cells. Further in-depth studies are necessary in order to fully recognize the beneficial miRNA-mediated effects of Res in PCa.

Pterostilbene Acts through Metastasis-Associated Protein 1 to Inhibit Tumor Growth, Progression and Metastasis in Prostate Cancer

The development of natural product agents with targeted strategies holds promise for enhanced anticancer therapy with reduced drug-associated side effects. Resveratrol found in red wine, has anticancer activity in various tumor types. We reported earlier on a new molecular target of resveratrol, the metastasis-associated protein 1 (MTA1), which is a part of nucleosome remodeling and deacetylation (NuRD) co-repressor complex that mediates gene silencing. We identified resveratrol as a regulator of MTA1/NuRD complex and re-activator of p53 acetylation in prostate cancer (PCa). In the current study, we addressed whether resveratrol analogues also possess the ability to inhibit MTA1 and to reverse p53 deacetylation. We demonstrated that pterostilbene (PTER), found in blueberries, had greater increase in MTA1-mediated p53 acetylation, confirming superior potency over resveratrol as dietary epigenetic agent. In orthotopic PCa xenografts, resveratrol and PTER significantly inhibited tumor growth, progression, local invasion and spontaneous metastasis. Furthermore, MTA1-knockdown sensitized cells to these agents resulting in additional reduction of tumor progression and metastasis. The reduction was dependent on MTA1 signaling showing increased p53 acetylation, higher apoptotic index and less angiogenesis in vivo in all xenografts treated with the compounds, and particularly with PTER. Altogether, our results indicate MTA1 as a major contributor in prostate tumor malignant progression, and support the use of strategies targeting MTA1. Our strong pre-clinical data indicate PTER as a potent, selective and pharmacologically safe natural product that may be tested in advanced PCa.

Trimethoxy-Resveratrol and Piceatannol Administered Orally Suppress and Inhibit Tumor Formation and Growth in Prostate Cancer Xenografts

Resveratrol (Res) is recognized as a promising cancer chemoprevention dietary polyphenol with antioxidative, anti‐inflammatory, and anticancer properties. However, the role of its analogues in prostate cancer (PCa) chemoprevention is unknown.

Resveratrol and pterostilbene epigenetically restore PTEN expression by targeting oncomiRs of the miR-17 family in prostate cancer

In recent years, not only has the role of miRNAs in cancer become increasingly clear but also their utilization as potential biomarkers and therapeutic targets has gained ground. Although the importance of dietary stilbenes such as resveratrol and pterostilbene as anti-cancer agents is well recognized, our understanding of their miRNA-targeting capabilities is still limited. In our previous study, we reported that resveratrol downregulates PTEN-targeting members of the oncogenic miR-17 family, which are overexpressed in prostate cancer. This study investigates the resveratrol and pterostilbene induced miRNA-mediated regulation of PTEN in prostate cancer. Here, we show that both compounds decrease the levels of endogenous as well as exogenously expressed miR-17, miR-20a and miR-106b thereby upregulating their target PTEN. Using functional luciferase reporter assays, we demonstrate that ectopically expressed miR-17, miR-20a and miR-106b directly target PTEN 3′UTR to reduce its expression, an effect rescued upon treatment with resveratrol and pterostilbene. Moreover, while stable lentiviral expression of miR-17/106a significantly decreased PTEN mRNA and protein levels and conferred survival advantage to the cells, resveratrol and more so pterostilbene was able to dramatically suppress these effects. Further, pterostilbene through downregulation of miR-17-5p and miR-106a-5p expression both in tumors and systemic circulation, rescued PTEN mRNA and protein levels leading to reduced tumor growth in vivo. Our findings implicate dietary stilbenes as an attractive miRNA-mediated chemopreventive and therapeutic strategy, and circulating miRNAs as potential chemopreventive and predictive biomarkers for clinical development in prostate cancer.

Resveratrol regulates PTEN/Akt pathway through inhibition of MTA1/HDAC unit of the NuRD complex in prostate cancer.

Metastasis associated protein 1 (MTA1) is a component of the nucleosome remodeling and deacetylating (NuRD) complex which mediates gene silencing and is overexpressed in several cancers. We reported earlier that resveratrol, a dietary stilbene found in grapes, can down-regulate MTA1. In the present study, we show that PTEN is inactivated by MTA1 in prostate cancer cells. Further, we show that resveratrol promotes acetylation and reactivation of PTEN via inhibition of the MTA1/HDAC complex, resulting in inhibition of the Akt pathway. In addition, we show that MTA1 knockdown is sufficient to augment acetylation of PTEN indicating a crucial role of MTA1 itself in the regulation of PTEN acetylation contributing to its lipid phosphatase activity. Acetylated PTEN preferentially accumulates in the nucleus where it binds to MTA1. We also show that MTA1 interacts exclusively with PTEN acetylated on Lys¹²⁵ and Lys¹²⁸, resulting in diminished p-Akt levels. Finally, using orthotopic prostate cancer xenografts, we demonstrate that both resveratrol treatment and MTA1 knockdown enhance PTEN levels leading to a decreased p-Akt expression and proliferation index. Taken together, our results indicate that MTA1/HDAC unit is a negative regulator of PTEN which facilitates survival pathways and progression of prostate cancer and that resveratrol can reverse this process through its MTA1 inhibitory function.

Nuclear MTA1 overexpression is associated with aggressive prostate cancer, recurrence and metastasis in African Americans

Metastasis-associated protein 1 (MTA1), a negative epigenetic modifier, plays a critical role in prostate cancer (PCa) progression. We hypothesized that MTA1 overexpression in primary tumor tissues can predict PCa aggressiveness and metastasis. Immunohistochemical staining of MTA1 was done on archival PCa specimens from University of Mississippi Medical Center and University of Iowa. We found that nuclear MTA1 overexpression was positively correlated with the severity of disease progression reaching its highest levels in metastatic PCa. Nuclear MTA1 overexpression was significantly associated with Gleason > 7 tumors in African Americans but not in Caucasians. It was also a predictor of recurrent disease. We concluded that MTA1 nuclear overexpression may be a prognostic indicator and a future therapeutic target for aggressive PCa in African American men. Our findings may be useful for categorizing African American patients with a higher probability of recurrent disease and metastasis from those who are likely to remain metastasis-free.

Dietary pterostilbene is a novel MTA1-targeted chemopreventive and therapeutic agent in prostate cancer

Overexpression of the epigenetic modifier metastasis-associated protein 1 (MTA1) is associated with aggressive human prostate cancer. The purpose of this study was to determine MTA1- targeted chemopreventive and therapeutic efficacy of pterostilbene, a natural potent analog of resveratrol, in pre-clinical models of prostate cancer. Here, we show that high levels of MTA1 expression in Pten-loss prostate cooperate with key oncogenes, including c-Myc and Akt among others, to promote prostate cancer progression. Loss-of-function studies using human prostate cancer cells indicated direct involvement of MTA1 in inducing inflammation and epithelial-to-mesenchymal transition. Importantly, pharmacological inhibition of MTA1 by pterostilbene resulted in decreased proliferation and angiogenesis and increased apoptosis. This restrained prostatic intraepithelial neoplasia (PIN) formation in prostate-specific Pten heterozygous mice and reduced tumor development and progression in prostate-specific Pten-null mice. Our findings highlight MTA1 as a key upstream regulator of prostate tumorigenesis and cancer progression. More significantly, it offers pre-clinical proof for pterostilbene as a promising lead natural agent for MTA1-targeted chemopreventive and therapeutic strategy to curb prostate cancer.

Epigenetic potential of resveratrol and analogs in preclinical models of prostate cancer

Lifestyle, particularly diet, is a risk factor for prostate cancer. Dietary polyphenols such as resveratrol possess anticancer properties and therefore have chemopreventive and therapeutic potential. Resveratrol has pleiotropic effects, exerting its biological activity through multiple pathways and targets, including those associated with cancer. Numerous studies have demonstrated the anticancer effects of resveratrol and, to a lesser extent, its analogs, in tissue culture, while in vivo observations are limited. Here, we provide a concise summary of our results on epigenetic mechanisms of resveratrol and analogs mediated through regulation of chromatin modifier metastasis‐associated protein 1 (MTA1) and microRNAs (miRNAs), and highlight the anticancer effects of these compounds in preclinical models of prostate cancer. We suggest that the identified stilbene responsive mechanism–based biomarkers, such as MTA1 and oncogenic miRNAs, may become indicative of treatment efficacy in prostate cancer. Resveratrol analogs with better bioavailability, conferring superior pharmacological potencies and greater anticancer effects, may become stronger candidates for clinical development.

MTA1‐activated Epi‐microRNA‐22 regulates E‐cadherin and prostate cancer invasiveness

We have previously shown that metastasis‐associated protein 1 (MTA1), a chromatin remodeler, plays an important role in prostate cancer invasiveness, likely through regulation of epithelial‐to‐mesenchymal transition. Here, we identified miR‐22 as an epigenetic‐microRNA (Epi‐miR) directly induced by MTA1 and predicted to target E‐cadherin. Loss‐of‐function and overexpression studies of MTA1 reinforced its regulatory role in miR‐22 expression. MiR‐22 directly targets the 3′‐untranslated region of E‐cadherin, and ectopic overexpression of miR‐22 diminishes E‐cadherin expression. Overexpression of miR‐22 in prostate cancer cells promotes cell invasiveness and migration. Meta‐analysis of patient tumor samples indicates a positive correlation between MTA1 and miR‐22, supporting their inhibitory effect on E‐cadherin expression. Our findings implicate the MTA1/Epi‐miR‐22/E‐cadherin axis as a new epigenetic signaling pathway that promotes tumor invasion in prostate cancer.

Stilbenes Inhibit Androgen Receptor Expression in 22Rv1 Castrate-resistant Prostate Cancer Cells

Androgen receptor (AR) signaling plays an important role in the development and progression of prostate cancer (PCa). Importantly, AR continues to be expressed in advanced stages of castrate-resistant PCa (CRPC), where it can have ligand- independent activity. Identification of naturally occurring substances which can inhibit AR expression holds promise for PCa chemoprevention and therapy. We have previously shown that resveratrol (Res) inhibits androgen-promoted growth, AR expression and transactivation in androgen-responsive non-metastatic LNCaP PCa cells. In the current study, we investigated the effects of Res and its three natural analogs: trimethoxy-resveratrol (3M-Res), pterostilbene (Pter) and piceatannol (Pic) on growth of 22Rv1 castrate-resistant cells, which express wild type (AR114/110) and truncated form (AR80) of AR. We found that although all the stilbenes inhibited the proliferation of 22Rv1 cells in a dose-dependent manner, 3M-Res was the most potent inhibitor. We also found that while AR114/110 responded to the synthetic androgen agonist methyltrienolone (R1881) as well as to antiandrogen Flutamide AR80, which lacks ligand-binding domain, did not respond to R1881 but was inhibited by Flutamide. Interestingly, Res, Pter and Pic but not 3M-Res, like Flutamide, inhibited both AR114/110 and AR80, with the effect on AR80 being more prominent when high concentrations of the stilbenes were used. Taken together, these data indicate both AR-independent (3M-Res) and possible AR-dependent (Res, Pter, Pic) mechanisms of cell growth inhibition by these stilbenes. These findings provide evidence for the potential use of these stilbenes in arresting the progression of CRPC.