Addanki P. Kumar

Single-cell analysis of circulating tumor cells identifies cumulative expression patterns of EMT-related genes in metastatic prostate cancer

Prostate tumors shed circulating tumor cells (CTCs) into the blood stream. Increased evidence shows that CTCs are often present in metastatic prostate cancer and can be alternative sources for disease profiling and prognostication. Here we postulate that CTCs expressing genes related to epithelial–mesenchymal transition (EMT) are strong predictors of metastatic prostate cancer.

Regulation of BRCA1 expression by the Rb-E2F pathway.

Inheritance of a mutant allele of the breast cancer susceptibility gene BRCA1 confers increased risk of developing breast and ovarian cancers. Likewise, inheritance of a mutant allele of the retinoblastoma susceptibility gene (RB1) results in the development of retinoblastoma and/or osteosarcoma, and both alleles are often mutated or inactivated in sporadic forms of these and other cancers. We now demonstrate that the product of the RB1 gene, Rb, regulates the expression of the murine Brca1 and human BRCA1 genes through its ability to modulate E2F transcriptional activity. TheBrca1 gene is identified as an in vivo target of E2F1 in a transgenic mouse model. The Brca1 promoter contains E2F DNA-binding sites that mediate transcriptional activation by E2F1 and repression by Rb. Moreover, ectopic expression of cyclin D1 and Cdk4 can stimulate the Brca1 promoter in an E2F-dependent manner, and this is inhibited by coexpression of the p16 INK4a cyclin-dependent kinase inhibitor. The human BRCA1 promoter also contains a conserved E2F site and is similarly regulated by E2F1 and Rb. This functional link between the BRCA1 and Rb tumor suppressors may provide insight into the mechanism by which BRCA1 inactivation contributes to cancer development.

2-methoxyestradiol blocks cell-cycle progression at G2/M phase and inhibits growth of human prostate cancer cells

2‐Methoxyestradiol (2‐ME), an endogenous metabolite of 17β‐estradiol, is present in human blood and urine. Here we show for the first time that 2‐ME significantly inhibited the growth of normal prostate epithelial cells and androgen‐dependent LNCaP and androgen‐independent DU145 prostate cancer cells. This growth inhibition was accompanied by a twofold increase in the G2/M population, with a concomitant decrease in the G1 population, as shown by cell‐cycle analysis. 2‐ME treatment affected the cell‐cycle progression of prostate cancer cells specifically by blocking cells in the G2 phase. Immunoblot analysis of the key cell‐cycle regulatory proteins in the G2/M phase showed a 14‐fold increase in the expression of p21 and an eightfold increase in the expression of p34 cell division cycle 2 (cdc2). We also found an accumulation of phosphorylated cdc2 after 2‐ME treatment. Furthermore, Wee 1 kinase was detectable after 2‐ME treatment. 2‐ME treatment also led to an increase in the activity of caspase‐3, followed by apoptosis, as shown by terminal deoxynucleotidyl transferase–mediated deoxyuridine 5‐triphosphate–biotin nick end‐labeling and fluorescein isothiocyanate–poly(ADP‐ribose) polymerase assay. Estrogen receptor levels did not change after treatment with 2‐ME. Examination of the signaling pathways that mediate 2‐ME–induced apoptosis showed reduction in the level of p53 expression and its DNA‐binding activity. Given the fact that p53 mutations are common in patients with metastatic prostate cancer, our finding that 2‐ME–mediated growth inhibition of human prostate cancer cells occurred in a p53‐independent manner has considerable clinical significance. These findings, combined with the limited toxicity of 2‐ME, may have significant implications for alternative treatment of advanced prostate cancer.

Akt/cAMP-Responsive Element Binding Protein/Cyclin D1 Network: A Novel Target for Prostate Cancer Inhibition in Transgenic Adenocarcinoma of Mouse Prostate Model Mediated by Nexrutine, a Phellodendron Amurense Bark Extract

Purpose: Development of prostate cancer prevention strategies is an important priority to overcome high incidence, morbidity, and mortality. Recently, we showed that Nexrutine, an herbal extract, inhibits prostate cancer cell proliferation through modulation of Akt and cAMP-responsive element binding protein (CREB)–mediated signaling pathways. However, it is unknown if Nexrutine can be developed as a dietary supplement for the prevention of prostate cancer. In this study, we used the transgenic adenocarcinoma of mouse prostate (TRAMP) model to examine the ability of Nexrutine to protect TRAMP mice from developing prostate cancer. Experimental Design: Eight-week-old TRAMP mice were fed with pelleted diet containing 300 and 600 mg/kg Nexrutine for 20 weeks. Efficacy of Nexrutine was evaluated by magnetic resonance imaging at 18 and 28 weeks of progression and histologic analysis of prostate tumor or tissue at the termination of the experiment. Tumor tissue was analyzed for modulation of various signaling molecules. Results: We show that Nexrutine significantly suppressed palpable tumors and progression of cancer in the TRAMP model. Expression of total and phosphorylated Akt, CREB, and cyclin D1 was significantly reduced in prostate tissue from Nexrutine intervention group compared with tumors from control animals. Nexrutine also inhibited cyclin D1 transcriptional activity in androgen-independent PC-3 cells. Overexpression of kinase dead Akt mutant or phosphorylation-defective CREB inhibited cyclin D1 transcriptional activity. Conclusions: The current study shows that Nexrutine-mediated targeting of Akt/CREB–induced activation of cyclin D1 prevents the progression of prostate cancer. Expression of CREB and phosphorylated CREB increased in human prostate tumors compared with normal tissue, suggesting their potential use as prognostic markers.

4-Hydroxy-3-Methoxybenzoic Acid Methyl Ester: A Curcumin Derivative Targets Akt/NFκB Cell Survival Signaling Pathway: Potential for Prostate Cancer Management

Transcription factor NFkappaB and the serine/threonine kinase Akt play critical roles in mammalian cell survival signaling and have been shown to be activated in various malignancies including prostate cancer (PCA). We have developed an analogue of curcumin called 4-hydroxy-3-methoxybenzoic acid methyl ester (HMBME) that targets the Akt/NFkappaB signaling pathway. Here, we demonstrate the ability of this novel compound to inhibit the proliferation of human and mouse PCA cells. HMBME-induced apoptosis in these cells was tested by using multiple biochemical approaches, in addition to morphologic analysis. Overexpression of constitutively active Akt reversed the HMBME-induced growth inhibition and apoptosis, illustrating the direct role of Akt signaling in HMBME-mediated growth inhibition and apoptosis. Further, investigation of the molecular events associated with its action in LNCaP cells shows that: 1) HMBME reduces the level of activated form of Akt (phosphorylated Akt); and 2) inhibits the Akt kinase activity. Further, the transcriptional activity of NFkappaB, the DNA-binding activity of NFkappaB, and levels of p65 were all significantly reduced following treatment with HMBME. Overexpression of constitutively active Akt, but not the kinase dead mutant of Akt, activated the basal NFkappaB transcriptional activity. HMBME treatment had no influence on this constitutively active Akt-augmented NFkappaB transcriptional activity. These data indicate that HMBME-mediated inhibition of Akt kinase activity may have a potential in suppressing/decreasing the activity of major survival/antiapoptotic pathways. The potential use of HMBME as an agent that targets survival mechanisms in PCA cells is discussed.

Enhanced Sp1 DNA-binding activity in murine keratinocyte cell lines and epidermal tumors

Altered regulation of ornithine decarboxylase (ODC) is frequently observed in epidermal tumors. We have shown that the transcription factor Sp1 is one of the regulators of ODC expression and that Sp3 antagonizes this Sp1-mediated activation of ODC expression. These results led us to examine the levels and binding activity of Sp1 and Sp3 in nuclear extracts prepared from cultured murine keratinocytes, transformed keratinocyte cell lines and epidermal tumors. Here we show that the Sp1 DNA-binding activity is higher in established keratinocyte cell line extracts than in primary keratinocyte extracts. Sp1 message levels and Sp1 DNA-binding activity was found to be low in 20-week papillomas and high in squamous cell carcinomas. These results suggest that increased levels of Sp1 and enhanced Sp1 DNA binding activity are correlated with epidermal tumor progression. Based on these results, we propose that increased Sp1 DNA binding may augment the proliferative capacity of tumor cells through overexpression of Sp1-responsive genes, possibly including ODC.

2-Methoxyestradiol Inhibits Prostate Tumor Development in Transgenic Adenocarcinoma of Mouse Prostate: Role of Tumor Necrosis Factor-α–Stimulated Gene 6

Purpose: 2-Methoxyestradiol, an estrogenic metabolite, is in clinical trials for the treatment of hormone-refractory prostate cancer. However, neither the chemopreventive role nor the mechanism of 2-methoxyestradiol–induced biological activities is fully understood. Experimental Design: Eight- and 24-week-old transgenic adenocarcinoma of mouse prostate (TRAMP) mice were fed a diet containing 50 mg 2-methoxyestradiol/kg body weight for 16 and 8 weeks, respectively. Chemopreventive efficacy was evaluated by magnetic resonance imaging, determining the prostate-seminal vesicle complex volume and histologic analysis of prostate tumor or tissue. Tumor invasion assays were used to show the role of tumor necrosis factor-α–stimulated gene (TSG-6), a 2-methoxyestradiol–up-regulated gene identified by DNA array analysis. Expression of TSG-6 was analyzed in a human tissue array containing different grades of prostate tumors. Results: Dietary administration of 2-methoxyestradiol prevented the development of preneoplastic lesions independent of progression stage. TSG-6 was low or undetectable in prostate cancer cells (LNCaP, PC-3, and DU145) and TRAMP tumors but up-regulated in response to 2-methoxyestradiol. Immunohistochemistry of the human prostate tumor array showed a decrease in TSG-6–positive cells with increasing grade relative to normal prostate (P = 0.0001). Although overexpression of TSG-6 inhibited invasion of androgen-independent cells (P = 0.007), antisense TSG-6 reversed this effect. Conclusions: To the best of our knowledge, this is the first report showing the potential of 2-methoxyestradiol as a chemopreventive agent. We have also identified TSG-6 as a potential marker that could be used for early diagnosis and prognosis of cancerous or precancerous lesions.

Dietary Resveratrol prevents development of high-grade prostatic intraepithelial neoplastic lesions: Involvement of SIRT1/S6K axis

SIRT1 (mammalian ortholog of the yeast silent information regulator 2) is a NAD-dependent histone deacetylase belonging to the multigene family of sirtuins. Anecdotal and epidemiologic observations provide evidence for beneficial effects of the calorie restriction mimetic resveratrol (RES), a SIRT1 activator in preventing cardiovascular diseases and cancer. Although SIRT1 possesses both tumorigenic and antitumorigenic potential, the molecular mechanisms underlying SIRT1-mediated tumor progression or inhibition are poorly understood. In this study, we investigated the role of SIRT1 in multiple human prostate cancer cell lines and prostate-specific PTEN knockout mouse model using resveratrol. Androgen-independent prostate cancer cell lines (C42B, PC3, and DU145) express higher levels of SIRT1 than androgen-responsive (LNCaP) and nontumorigenic prostate cells (RWPE-1). Resveratrol enhanced this expression without any significant effect on SIRT1 enzymatic activity. Inhibition of SIRT1 expression using shRNA enhanced cell proliferation and inhibited autophagy by repressing phosphorylation of S6K and 4E-BP1. These biologic correlates were reversed in the presence of resveratrol. Analysis of prostates from dietary intervention with resveratrol showed a significant reduction in prostate weight and reduction in the incidence of high-grade prostatic intraepithelial neoplastic (HGPIN) lesions by approximately 54% with no significant change in body weight. Consistent with the in vitro findings, resveratrol intervention in the PTEN knockout mouse model was associated with reduction in the prostatic levels of mTOR complex 1 (mTORC1) activity and increased expression of SIRT1. These data suggest that SIRT1/S6K-mediated inhibition of autophagy drives prostate tumorigenesis. Therefore, modulation of SIRT1/S6K signaling represents an effective strategy for prostate cancer prevention. Cancer Prev Res; 6(1); 27–39. ©2012 AACR.

Butanol fraction containing berberine or related compound from Nexrutine® inhibits NFκB signaling and induces apoptosis in prostate cancer cells

Epidemiological and laboratory studies support the hypothesis that several plant components influence prostate carcinogenesis and holds promise for disease prevention. Previously we reported that Nexrutine® (bark extract from Phellodendron amurense) inhibits proliferation of prostate cancer cells and prostate tumor development in the transgenic adenocarcinoma of mouse prostate (TRAMP) model through modulation of Akt signaling pathway. In the present investigation we conducted studies to further define the mechanism of action of Nexrutine® and to identify the active component associated with its biological activity.

Cell cycle block and apoptosis induction in a human melanoma cell line following treatment with 2-methoxyoestradiol: therapeutic implications?

&NA; Due to minimal success with non‐surgical treatment options for melanoma, it is imperative that other compounds be tested for potential preventive/therapeutic use. We have tested the ability of the endogenous oestrogenic metabolite 2‐methoxyestradiol (2‐ME) to inhibit the growth of human melanoma cells in culture. 2‐ME inhibited the growth of all the melanoma cells tested, without inhibiting the growth of non‐tumorigenic cells. Microscopic observations showed that treated cells exhibit the characteristic features of apoptosis. Examination of the molecular mechanism in WM98–1 cells, using biochemical assays such as a modified TUNEL staining and DNA fragmentation, confirmed the induction of apoptosis following 2‐ME treatment. Flow cytometry analysis showed that, following treatment, cells are arrested in the G2/M phase of the cell cycle. Western blot analysis of the G2/M regulatory proteins suggests that cdc2 is involved in the cell cycle block by Myt1 phosphorylation following 2‐ME treatment. Furthermore, examination of the levels of apoptosis regulatory proteins showed that, while levels of p53, Bax and p21 are higher, that of anti‐apoptotic Bcl‐2 is undetectable in cells treated with 2‐ME compared with untreated controls. Taken together these results have major implications for the use of 2‐ME for melanoma management.