Sabitha Papineni

Betulinic Acid Inhibits Prostate Cancer Growth through Inhibition of Specificity Protein Transcription Factors

Betulinic acid is a pentacyclic triterpene natural product initially identified as a melanoma-specific cytotoxic agent that exhibits low toxicity in animal models. Subsequent studies show that betulinic acid induces apoptosis and antiangiogenic responses in tumors derived from multiple tissues; however, the underlying mechanism of action is unknown. Using LNCaP prostate cancer cells as a model, we now show that betulinic acid decreases expression of vascular endothelial growth (VEGF) and the antiapoptotic protein survivin. The mechanism of these betulinic acid-induced antiangiogenic and proapoptotic responses in both LNCaP cells and in tumors is due to activation of selective proteasome-dependent degradation of the transcription factors specificity protein 1 (Sp1), Sp3, and Sp4, which regulate VEGF and survivin expression. Thus, betulinic acid acts as a novel anticancer agent through targeted degradation of Sp proteins that are highly overexpressed in tumors.

Curcumin Decreases Specificity Protein Expression in Bladder Cancer Cells

Curcumin is the active component of tumeric, and this polyphenolic compound has been extensively investigated as an anticancer drug that modulates multiple pathways and genes. In this study, 10 to 25 micromol/L curcumin inhibited 253JB-V and KU7 bladder cancer cell growth, and this was accompanied by induction of apoptosis and decreased expression of the proapoptotic protein survivin and the angiogenic proteins vascular endothelial growth factor (VEGF) and VEGF receptor 1 (VEGFR1). Because expression of survivin, VEGF, and VEGFR1 are dependent on specificity protein (Sp) transcription factors, we also investigated the effects of curcumin on Sp protein expression as an underlying mechanism for the apoptotic and antiangiogenic activity of this compound. The results show that curcumin induced proteasome-dependent down-regulation of Sp1, Sp3, and Sp4 in 253JB-V and KU7 cells. Moreover, using RNA interference with small inhibitory RNAs for Sp1, Sp3, and Sp4, we observed that curcumin-dependent inhibition of nuclear factor kappaB (NF-kappaB)-dependent genes, such as bcl-2, survivin, and cyclin D1, was also due, in part, to loss of Sp proteins. Curcumin also decreased bladder tumor growth in athymic nude mice bearing KU7 cells as xenografts and this was accompanied by decreased Sp1, Sp3, and Sp4 protein levels in tumors. These results show for the first time that one of the underlying mechanisms of action of curcumin as a cancer chemotherapeutic agent is due, in part, to decreased expression of Sp transcription factors in bladder cancer cells.

Oncogenic microRNA-27a is a target for anticancer agent methyl 2-cyano-3,11-dioxo-18β-olean-1,12-dien-30-oate in colon cancer cells

Methyl 2‐cyano‐3,11‐dioxo‐18β‐olean‐1,12‐dien‐30‐oate (CDODA‐Me) is a synthetic derivative of glycyrrhetinic acid, a triterpenoid phytochemical found in licorice extracts. CDODA‐Me inhibited growth of RKO and SW480 colon cancer cells and this was accompanied by decreased expression of Sp1, Sp3 and Sp4 protein and mRNA and several Sp‐dependent genes including survivin, vascular endothelial growth factor (VEGF), and VEGF receptor 1 (VEGFR1 or Flt‐1). CDODA‐Me also induced apoptosis, arrested RKO and SW480 cells at G2/M, and inhibited tumor growth in athymic nude mice bearing RKO cells as xenografts. CDODA‐Me decreased expression of microRNA‐27a (miR‐27a), and this was accompanied by increased expression of 2 miR‐27a‐regulated mRNAs, namely ZBTB10 (an Sp repressor) and Myt‐1 which catalyzes phosphorylation of cdc2 to inhibit progression of cells through G2/M. Both CDODA‐Me and antisense miR‐27a induced comparable responses in RKO and SW480 cells, suggesting that the potent anticarcinogenic activity of CDODA‐Me is due to repression of oncogenic miR‐27a.

Betulinic acid inhibits colon cancer cell and tumor growth and induces proteasome- dependent and -independent downregulation of specificity proteins (Sp) transcription factors

BackgroundBetulinic acid (BA) inhibits growth of several cancer cell lines and tumors and the effects of BA have been attributed to its mitochondriotoxicity and inhibition of multiple pro-oncogenic factors. Previous studies show that BA induces proteasome-dependent degradation of specificity protein (Sp) transcription factors Sp1, Sp3 and Sp4 in prostate cancer cells and this study focused on the mechanism of action of BA in colon cancer cells.MethodsThe effects of BA on colon cancer cell proliferation and apoptosis and tumor growth in vivo were determined using standardized assays. The effects of BA on Sp proteins and Sp-regulated gene products were analyzed by western blots, and real time PCR was used to determine microRNA-27a (miR-27a) and ZBTB10 mRNA expression.ResultsBA inhibited growth and induced apoptosis in RKO and SW480 colon cancer cells and inhibited tumor growth in athymic nude mice bearing RKO cells as xenograft. BA also decreased expression of Sp1, Sp3 and Sp4 transcription factors which are overexpressed in colon cancer cells and decreased levels of several Sp-regulated genes including survivin, vascular endothelial growth factor, p65 sub-unit of NFκB, epidermal growth factor receptor, cyclin D1, and pituitary tumor transforming gene-1. The mechanism of action of BA was dependent on cell context, since BA induced proteasome-dependent and proteasome-independent downregulation of Sp1, Sp3 and Sp4 in SW480 and RKO cells, respectively. In RKO cells, the mechanism of BA-induced repression of Sp1, Sp3 and Sp4 was due to induction of reactive oxygen species (ROS), ROS-mediated repression of microRNA-27a, and induction of the Sp repressor gene ZBTB10.ConclusionsThese results suggest that the anticancer activity of BA in colon cancer cells is due, in part, to downregulation of Sp1, Sp3 and Sp4 transcription factors; however, the mechanism of this response is cell context-dependent.

Structure-dependent activity of glycyrrhetinic acid derivatives as peroxisome proliferator–activated receptor γ agonists in colon cancer cells

Glycyrrhizin, a pentacyclic triterpene glycoside, is the major phytochemical in licorice. This compound and its hydrolysis product glycyrrhetinic acid have been associated with the multiple therapeutic properties of licorice extracts. We have investigated the effects of 2-cyano substituted analogues of glycyrrhetinic acid on their cytotoxicities and activity as selective peroxisome proliferator–activated receptor γ (PPARγ) agonists. Methyl 2-cyano-3,11-dioxo-18β-olean-1,12-dien-30-oate (β-CDODA-Me) and methyl 2-cyano-3,11-dioxo-18α-olean-1,12-dien-30-oate (α-CDODA-Me) were more cytotoxic to colon cancer cells than their des-cyano analogues and introduction of the 2-cyano group into the pentacyclic ring system was necessary for the PPARγ agonist activity of α-CDODA-Me and β-CDODA-Me isomers. However, in mammalian two-hybrid assays, both compounds differentially induced interactions of PPARγ with coactivators, suggesting that these isomers, which differ only in the stereochemistry at C18 which affects conformation of the E-ring, are selective receptor modulators. This selectivity in colon cancer cells was shown for the induction of two proapoptotic proteins, namely caveolin-1 and the tumor-suppressor gene Krüppel-like factor-4 (KLF-4). β-CDODA-Me but not α-CDODA-Me induced caveolin-1 in SW480 colon cancer cells, whereas caveolin-1 was induced by both compounds in HT-29 and HCT-15 colon cancer cells. The CDODA-Me isomers induced KLF-4 mRNA levels in HT-29 and SW480 cells but had minimal effects on KLF-4 expression in HCT-15 cells. These induced responses were inhibited by cotreatment with a PPARγ antagonist. This shows for the first time that PPARγ agonists derived from glycyrrhetinic acid induced cell-dependent caveolin-1 and KLF-4 expression through receptor-dependent pathways. [Mol Cancer Ther 2007;6(5):1588–98]

Tolfenamic acid inhibits esophageal cancer through repression of specificity proteins and c-Met

The non-steroidal anti-inflammatory drug tolfenamic acid (TA) inhibits proliferation of SEG-1 and BIC-1 esophageal cancer cells with half-maximal growth inhibitory concentration values of 36 and 48 muM, respectively. TA also increased Annexin V staining in both cell lines, indicative of proapoptotic activity. Treatment of SEG-1 and BIC-1 cells with TA for up to 72 h decreased expression of specificity protein (Sp) transcription factors Sp1, Sp3 and Sp4 and this was accompanied by decreased expression of the well-characterized Sp-regulated genes cyclin D1, vascular endothelial growth factor and survivin. TA also decreased hepatocyte growth factor receptor, (c-Met), a receptor tyrosine kinase that is overexpressed in esophageal cancer cells and tumors and is an important drug target. Knockdown of Sp1, Sp3 and Sp4 by RNA interference in SEG-1 and BIC-1 cells also decreased c-Met expression, demonstrating that c-Met is an Sp-regulated gene in esophageal cancer cells. Sp1 was overexpressed in esophageal cancer cells and tumors and increased Sp1 staining was observed in esophageal tumors from patients. TA (20 mg/kg/day) also decreased tumor growth and weight in athymic nude mice bearing SEG-1 cells as xenografts and this was accompanied by increased apoptosis and decreased Sp1 and c-Met staining in tumors from treated mice. Thus, TA-dependent downregulation of Sp transcription factors and c-Met defines a novel chemotherapeutic approach for treatment of esophageal cancer.

1,1-Bis(3′-indolyl)-1-(p-chlorophenyl)methane activates the orphan nuclear receptor Nurr1 and inhibits bladder cancer growth

Nurr1 is an orphan nuclear receptor and a member of the nerve growth factor I-B subfamily of transcription factors with no known endogenous ligand or stimulator. We show, for the first time, evidence that Nurr1 is expressed in a panel of 11 human bladder cancer cell lines. A new class of methylene-substituted diindolylmethanes (C-DIM) were screened and 1,1-bis(3′-indolyl)-1-(p-chlorophenyl)methane (DIM-C-pPhCl) activated the ligand-binding domain of Nurr1. Treatment of bladder cancer cells with Nurr1-active C-DIM resulted in decreased cell survival (MTT assay) and induction of cell death pathways, resulting in poly(ADP-ribose) polymerase cleavage and DNA fragmentation. The specificity of the Nurr1-active compound was shown using RNA interference in 253J B-V cells, whereby small interfering RNA against Nurr1 attenuated ligand-dependent activation of Nurr1 and poly(ADP-ribose) polymerase cleavage. Furthermore, activation of Nurr1 resulted in stimulation of tumor necrosis factor-related apoptosis-inducing ligand and small interfering RNA experiments attenuated tumor necrosis factor-related apoptosis-inducing ligand production. In an orthotopic model of human bladder tumors established in nude mice, administration of a Nurr1-active C-DIM suppressed bladder cancer growth. These results identify Nurr1 as a potential target for bladder cancer therapy and also identify a novel agent for activating Nurr1. [Mol Cancer Ther 2008;7(12):3825–33]

1,1-Bis(3′-indolyl)-1-(p-substituted phenyl)methanes inhibit colon cancer cell and tumor growth through PPARγ-dependent and PPARγ-independent pathways

1,1-Bis(3′-indolyl)-1-(p-substituted phenyl)methanes containing p-trifluoromethyl, t-butyl, and phenyl [1,1-bis(3′-indolyl)-1-(p-phenyl)methane (DIM-C-pPhC6H5)] substituents induce peroxisome proliferator-activated receptor γ (PPARγ)–mediated transactivation in SW480 colon cancer cells. These PPARγ-active compounds also inhibit cell proliferation and modulate some cell cycle proteins. At concentrations from 2.5 to 7.5 μmol/L, the PPARγ agonists induce caveolin-1 and phosphorylation of Akt and cotreatment with the PPARγ antagonist GW9662 inhibited the induction response. In contrast, higher concentrations (10 μmol/L) of 1,1-bis(3′-indolyl)-1-(p-substituted phenyl)methanes containing 1,1-bis(3′-indolyl)-1-(p-trifluoromethyl)methane and DIM-C-pPhC6H5 induce apoptosis, which is PPARγ independent. This was accompanied by loss of caveolin-1 induction but induction of proapoptotic nonsteroidal anti-inflammatory drug activated gene-1. In athymic nude mice bearing SW480 cell xenografts, DIM-C-pPhC6H5 inhibits tumor growth at doses of 20 and 40 mg/kg/d and immunohistochemical staining of the tumors showed induction of apoptosis and nonsteroidal anti-inflammatory drug activated gene-1 expression. Thus, the indole-derived PPARγ-active compounds induce both receptor-dependent and receptor-independent responses in SW480 cells, which are separable over a narrow range of concentrations. This dual mechanism of action enhances their antiproliferative and anticancer activities. [Mol Cancer Ther 2006;5(5):1362–70]

1,1-Bis(3′-Indolyl)-1-(p-substitutedphenyl)methanes Inhibit Growth, Induce Apoptosis, and Decrease the Androgen Receptor in LNCaP Prostate Cancer Cells through Peroxisome Proliferator-Activated Receptor γ-Independent Pathways

1,1-Bis(3′-indolyl)-1-(p-substitutedphenyl)methanes (C-DIMs) containing para-trifluoromethyl, t-butyl, and phenyl groups are a novel class of peroxisome proliferator-activated receptor (PPAR)γ agonists. In LNCaP prostate cancer cells, these compounds induce PPARγ-dependent transactivation, inhibit cell proliferation, and induce apoptosis. In addition, these PPARγ agonists modulate a number of antiproliferative and proapoptotic responses, including induction of p27, activating transcription factor 3, and nonsteroidal anti-inflammatory drug-activated gene-1 and down-regulation of cyclin D1 and caveolin-1. Moreover, the PPARγ antagonist 2-chloro-5-nitrobenzanilide (GW9662) does not inhibit these effects. The C-DIM compounds also abrogate androgen receptor (AR)-mediated signaling and decrease prostate-specific antigen (PSA) and AR protein expression, and these responses were PPARγ-independent. The effects of C-DIMs on AR and PSA were due to decreased AR and PSA mRNA expression in LNCaP cells. Thus, this series of methylene-substituted diindolylmethane derivatives simultaneously activate multiple pathways in LNCaP cells, including ablation of androgen-responsiveness and down-regulation of caveolin-1. Both of these responses are associated with activation of proapoptotic pathways in this cell line.

Induction of apoptosis and nonsteroidal anti‐inflammatory drug‐activated gene 1 in pancreatic cancer cells by a glycyrrhetinic acid derivative

Methyl 2‐cyano‐3,11‐dioxo‐18β‐olean‐1,12‐dien‐30‐oate (CDODA‐Me) is a synthetic triterpenoid derived from glycyrrhetinic acid, a bioactive phytochemical in licorice, CDODA‐Me inhibits growth of Panc1 and Panc28 pancreatic cancer cell lines and activates peroxisome proliferator‐activated receptor γ (PPARγ)‐dependent transactivation in these cells. CDODA‐Me also induced p21 and p27 protein expression and downregulates cyclin D1; however, these responses were receptor‐independent. CDODA‐Me induced apoptosis in Panc1 and Panc28 cells, and this was accompanied by receptor‐independent induction of the proapoptotic proteins early growth response‐1 (Egr‐1), nonsteroidal anti‐inflammatory drug‐activated gene‐1 (NAG‐1), and activating transcription factor‐3 (ATF3). Induction of NAG‐1 and Egr‐1 by CDODA‐Me was dependent on activation of phosphatidylinositol‐3‐kinase (PI3‐K) and/or p42 and p38 mitogen‐activated protein kinase (MAPK) pathways but there were differences between Panc28 and Panc1 cells. Induction of NAG‐1 in Panc28 cells was p38‐MAPK‐ and PI3‐K‐dependent but Egr‐1‐independent, whereas induction in Panc1 cells was associated with activation of p38‐MAPK, PI3‐K, and p42‐MAPK and was only partially Egr‐1‐dependent. This is the first report of the induction of the proapoptotic protein NAG‐1 in pancreatic cancer cells.