Diminished expression of h2-calponin in prostate cancer cells promotes cell proliferation, migration and the dependence of cell adhesion on substrate stiffness

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Calponin is an actin filament-associated protein and its h2 isoform inhibits cell motility.

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H2-calponin expression is strong in prostate epithelial cells and diminished in cancerous cells.

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Low h2-calponin metastatic prostate cancer cells had faster rates of cell proliferation and migration.

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Low h2-calponin metastatic prostate cancer cells showed reduced substrate adhesion.

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Low h2-calponin prostate cancer cells had a higher dependence on substrate stiffness.

Calponin is an actin filament-associated protein and its h2 isoform inhibits cell motility. Here we report significant expression of h2-calponin in prostate epithelial cells, which is diminished in cancerous cells. Comparison between a prostate cancer cell line PC3 and its metastatic derivative PC3-M showed lower levels of h2-calponin in PC3-M, corresponding to faster rates of cell proliferation and migration. Substrate adhesion of PC3 and PC3-M cells was positively correlated to the level of h2-calponin and the adhesion of PC3-M exhibited a higher dependence on substrate stiffness. Such effects of h2-calponin on cell proliferation, migration and substrate adhesion were also seen in normal versus cancerous primary prostate cells. Further supporting the role of h2-calponin in inhibiting cell motility, fibroblasts isolated from h2-calponin knockout mice proliferated and migrated faster than that of wild type fibroblasts. Transfective over-expression of h2-calponin in PC3-M cells effectively inhibited cell proliferation and migration. The results suggest that the diminished expression of h2-calponin in prostate cancer cells increases cell motility, decreases substrate adhesion, and promotes adhesion on high stiffness substrates.

A fluorescence-based thermal shift assay identifies inhibitors of mitogen activated protein kinase kinase 4

Prostate cancer (PCa) is the second highest cause of cancer death in United States males. If the metastatic movement of PCa cells could be inhibited, then mortality from PCa could be greatly reduced. Mitogen-activated protein kinase kinase 4 (MAP2K4) has previously been shown to activate pro-invasion signaling pathways in human PCa. Recognizing that MAP2K4 represents a novel and validated therapeutic target, we sought to develop and characterize an efficient process for the identification of small molecules that target MAP2K4. Using a fluorescence-based thermal shift assay (FTS) assay, we first evaluated an 80 compound library of known kinase inhibitors, thereby identifying 8 hits that thermally stabilized MAP2K4 in a concentration dependent manner. We then developed an in vitro MAP2K4 kinase assay employing the biologically relevant downstream substrates, JNK1 and p38 MAPK, to evaluate kinase inhibitory function. In this manner, we validated the performance of our initial FTS screen. We next applied this approach to a 2000 compound chemically diverse library, identified 7 hits, and confirmed them in the in vitro kinase assay. Finally, by coupling our structure-activity relationship data to MAP2K4's crystal structure, we constructed a model for ligand binding. It predicts binding of our identified inhibitory compounds to the ATP binding pocket. Herein we report the creation of a robust inhibitor-screening platform with the ability to inform the discovery and design of new and potent MAP2K4 inhibitors.

An orthotopic murine model of human prostate cancer metastasis

Our laboratory has developed a novel orthotopic implantation model of human prostate cancer (PCa). As PCa death is not due to the primary tumor, but rather the formation of distinct metastasis, the ability to effectively model this progression pre-clinically is of high value. In this model, cells are directly implanted into the ventral lobe of the prostate in Balb/c athymic mice, and allowed to progress for 4-6 weeks. At experiment termination, several distinct endpoints can be measured, such as size and molecular characterization of the primary tumor, the presence and quantification of circulating tumor cells in the blood and bone marrow, and formation of metastasis to the lung. In addition to a variety of endpoints, this model provides a picture of a cells ability to invade and escape the primary organ, enter and survive in the circulatory system, and implant and grow in a secondary site. This model has been used effectively to measure metastatic response to both changes in protein expression as well as to response to small molecule therapeutics, in a short turnaround time.

Endoglin-mediated suppression of prostate cancer invasion is regulated by activin and bone morphogenetic protein type II receptors

Mortality from prostate cancer (PCa) is due to the formation of metastatic disease. Understanding how that process is regulated is therefore critical. We previously demonstrated that endoglin, a type III transforming growth factor β (TGFβ) superfamily receptor, suppresses human PCa cell invasion and metastasis. Endoglin-mediated suppression of invasion was also shown by us to be dependent upon the type I TGFβ receptor, activin receptor-like kinase 2 (ALK2), and the downstream effector, Smad1. In this study we demonstrate for the first time that two type II TGFβ receptors are required for endoglin-mediated suppression of invasion: activin A receptor type IIA (ActRIIA) and bone morphogenetic protein receptor type II (BMPRII). Downstream signaling through these receptors is predominantly mediated by Smad1. ActRIIA stimulates Smad1 activation in a kinase-dependent manner, and this is required for suppression of invasion. In contrast BMPRII regulates Smad1 in a biphasic manner, promoting Smad1 signaling through its kinase domain but suppressing it through its cytoplasmic tail. BMPRII’s Smad1-regulatory effects are dependent upon its expression level. Further, its ability to suppress invasion is independent of either kinase function or tail domain. We demonstrate that ActRIIA and BMPRII physically interact, and that each also interacts with endoglin. The current findings demonstrate that both BMPRII and ActRIIA are necessary for endoglin-mediated suppression of human PCa cell invasion, that they have differential effects on Smad1 signaling, that they make separate contributions to regulation of invasion, and that they functionally and physically interact.

A phase I trial of aminolevulinic acid-photodynamic therapy for treatment of oral leukoplakia

BACKGROUND

Photodynamic therapy with aminolevulinic acid (ALA PDT) for oral leukoplakia has shown promising effects in regression of oral leukoplakia. Although ALA has been extensively studied and is an ideal photosensitizer, the optimal light dose for treatment of oral leukoplakia has not been determined. We conducted a phase I study to determine MTD and DLT of PDT in patients treated with ALA for leukoplakia.

METHODS

Patients with histologically confirmed oral leukoplakia received a single treatment of ALA PDT in cohorts with escalating doses of light (585nm). Clinical, histologic, and biologic markers were assessed.

RESULTS

Analysis of 11 participants is reported. No significant toxicity from ALA PDT was observed in patients who received ALA with a light dose of up to 4J/cm(2). One participant experienced transient grade 3 transaminase elevation due to ALA. One participant had a partial clinical response 3months after treatment. Biologic mucosal risk markers showed no significant associations. Determination of MTD could not be accomplished within a feasible timeframe for completion of the study.

CONCLUSIONS

ALA PDT could be safely administered with a light dose up to 4J/cm(2) and demonstrated activity. Larger studies are needed to fully elucidate the MTD and efficacy of ALA-PDT.

Abstract 1448: Identifying and subtyping circulating tumor cells from breast, prostate, and pancreatic cancer patients based on distinct morphology

Background: Isolation of circulating tumor cells (CTCs) from peripheral blood based on size exclusion is rapid and straight-forward using precision microfilters. We describe the use of CellSieveTM microfilters to isolate CTCs from the peripheral blood of breast, prostate, and pancreatic cancer patients. It is accepted that CTCs isolated from patient samples represent a highly heterogeneous population with varying degrees of epithelial mesenchymal differentiation. We hypothesized that the CTCs from three different epithelial malignancies can be identified and grouped into distinct subtypes by morphological characterization.

Methods: Prostate, breast, and pancreatic patient blood samples were provided by Northwestern University, Fox Chase Cancer Center, University of Maryland, and Medical College of Wisconsin and analyzed by Creatv MicroTech. The CellSieveTM microfilters have 8 micron diameter pores in a uniform array, with 160,000 pores in a 9 mm diameter area. 7.5 mL of whole blood was diluted in fixative and drawn through a microfilter. CTCs collected by this size exclusion technique were post-fixed, permeabilized, and stained with DAPI, cytokeratin 8, 18 and 19 (FITC), EpCAM (PE), PSMA (Texas Red), and CD45 (Cy5). CTCs were CD45 negative cells identified by their morphology, nuclear profile, and expression of cytokeratin, PSMA, and EpCAM.

Results: Each patient sample was found to have a number of phenotypic CTC subtypes. Distinct morphological patterns emerged in the three malignancies. CTCs from breast cancer patients demonstrated high expression of cytokeratin signal with web-like cytokeratin filamentation. Prostate cancer CTCs had less defined filamentation, but intense PSMA and cytokeratin signal and mottled cytokeratin morphology. Pancreatic CTCs had extremely fine filamentation, with spindle-like morphology and little or no EpCAM expression. Within each cancer, CTCs could be grouped into distinct subtypes. Additional markers, such as vimentin (PE), are used to further analyze the cells after bleaching the original PE.

Conclusions: In addition to enumeration and identification, the phenotypic analysis of CTCs provides new information that can be used to characterize disease status for personalized treatment of cancer patients. We have shown that CTCs can have multiple distinct phenotypes. These phenotypic morphologies may implicate definable traits which can be exploited while tracking site directed treatment of metastatic cancer patients.

Citation Format: Daniel Adams, R. Katherine Alpaugh, Massimo Cristofanilli, Stuart Martin, Saranya Chumsri, Monica Charpentier, Raymond C. Bergan, Irene May Ogden, Susan Tsai, Peixuan Zhu, Olga V. Makarova, Shuhong Li, Platte T. Amstutz, Cha-Mei Tang. Identifying and subtyping circulating tumor cells from breast, prostate, and pancreatic cancer patients based on distinct morphology. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1448. doi:10.1158/1538-7445.AM2013-1448

Androgen receptor-independent function of FoxA1 in prostate cancer metastasis

FoxA1 (FOXA1) is a pioneering transcription factor of the androgen receptor (AR) that is indispensible for the lineage-specific gene expression of the prostate. To date, there have been conflicting reports on the role of FoxA1 in prostate cancer progression and prognosis. With recent discoveries of recurrent FoxA1 mutations in human prostate tumors, comprehensive understanding of FoxA1 function has become very important. Here, through genomic analysis, we reveal that FoxA1 regulates two distinct oncogenic processes via disparate mechanisms. FoxA1 induces cell growth requiring the AR pathway. On the other hand, FoxA1 inhibits cell motility and epithelial-to-mesenchymal transition (EMT) through AR-independent mechanism directly opposing the action of AR signaling. Using orthotopic mouse models, we further show that FoxA1 inhibits prostate tumor metastasis in vivo. Concordant with these contradictory effects on tumor progression, FoxA1 expression is slightly upregulated in localized prostate cancer wherein cell proliferation is the main feature, but is remarkably downregulated when the disease progresses to metastatic stage for which cell motility and EMT are essential. Importantly, recently identified FoxA1 mutants have drastically attenuated ability in suppressing cell motility. Taken together, our findings illustrate an AR-independent function of FoxA1 as a metastasis inhibitor and provide a mechanism by which recurrent FoxA1 mutations contribute to prostate cancer progression.

Abstract 4752: Selective inhibition of cancer metastasis with a novel small therapeutic molecule

Prostate cancer (PCa) is the second most common cause of cancer death in US males. Death is typically caused by metastasis. Naturally occurring isoflavanones have been reported to be a class of compounds that effectively inhibit PCa motility and metastasis. This led us to use these compounds as a synthetic scaffold starting point. By integrating fragment-based diversification synthesis with chemi-driven biological selection, we discovered novel small molecule therapeutics with increased selectivity and potent efficacy. We thereby efficiently synthesized a new class of bioactive compounds that inhibit cell motility in vitro and inhibit human PCa metastasis in a murine model at low nanomolar concentrations. Extensive investigations indicate high specificity at the molecular and cellular levels, and failed to identify toxicity, even at high doses administered over extended periods. Importantly, efficacy against several cancer types was also demonstrated. Target validation studies used our lead as a chemical probe, and point to inhibition of ATM/ATR interaction with specific substrate proteins as important. Together, these studies indicate that we have successfully discovered a novel compound, acting upon a novel pharmacologic target, which selectively inhibits human PCa metastasis. Taken with our favorable preclinical toxicological data, these findings support movement of our lead compound into early phase human trials.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4752. doi:1538-7445.AM2012-4752

Abstract 491: Endoglin suppresses prostate cancer invasion through two distinct type II TGF-β receptors

Prostate cancer (PCa) is the most common cancer of American men and the second leading cause of cancer-related death. Death from PCa results from the development of metastatic disease, yet the processes underlying progression from localized to invasive and ultimately metastatic disease remain poorly understood. Our group has previously shown that endoglin, an auxiliary TGF-β superfamily receptor, is lost with PCa progression. Restoration of endoglin expression inhibits PCa cell migration, invasion, and metastasis in pre-clinical models. Endoglin-mediated suppression of PCa invasion (EMSI) is mediated through the type I TGF-β receptor ALK2 and the downstream effector Smad1. Given that TGF-β signaling minimally requires both a type I and a type II TGF-β receptor (RII), we sought to determine the RII(s) involved in EMSI. We now show that silencing of either the type IIA activin receptor (ActRII) or the type II bone morphogenic protein receptor (BMPRII) abrogates endoglin's invasion suppressive effects. Surprisingly, ActRII and BMPR2 have opposite effects on downstream Smad1 signaling: ActRII promotes basal and endoglin-mediated Smad1 transcriptional activity dependent on its kinase domain, while BMPR2 suppresses Smad1 transcriptional activity independent of its kinase domain but dependent on its cytoplasmic tail. Moreover, we show that engagement of distinct BMP-responsive R-Smads (i.e. Smad1, Smad5, & Smad8) does not account for differential signaling and confirm that Smad1 is the main mediator downstream of endoglin. We posit the existence of two parallel pathways that are required for EMSI: an ActRII / ALK2 / Smad1 pathway and a second, as-yet-uncharacterized pathway involving BMPR2.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 491. doi:1538-7445.AM2012-491

Abstract 615: Apigenin regulates prostate cancer matrix composition and cell attachment through an integrin alpha 1 dependent pathway

Prostate cancer (PCa) mortality is primarily attributed to metastatic rather than primary, organ-confined disease. Acquiring a motile and invasive phenotype is an important step in the development of metastasis. This step involves remodeling of the extracellular matrix (ECM) and of cell-matrix interactions, cell movement mediated by the actin cytoskeleton, and activation of focal adhesion kinase (FAK)/Src signaling. Epidemiologic studies suggest that the metastatic behavior of PCa may be an ideal target for chemoprevention. The natural flavone apigenin is known to have chemopreventive properties against many cancers, including PCa. Building upon our previous findings showing that apigenin inhibits cell motility and invasion of PCa cells through the FAK/Src signaling pathway, here we study the effect of apigenin on integrin receptors, cell attachment, and ECM composition. By using an alpha/beta integrin-mediated cell adhesion array, we found that integrin alpha 1 (ITGA1) was the only integrin subunit to be down-regulated by apigenin in PC3-M cells. ITGA1, whose only binding partner is integrin beta 1, is a receptor for collagen and laminin. Integrin α1α1 gives cells the ability to attach to collagenous substrata. As collagen and laminin are important regulators of PCa cell survival, growth and metastasis to bone, we next elucidated the effect of apigenin on PC3-M cell attachment to laminin 1 and collagen IV. We found that apigenin decreases cell attachment to both of these ECM molecules, suggesting a potential anti-tumorigenic mechanism. It has been shown that integrin α1α1 can regulate the synthesis of collagen. So we next tested whether apigenin can alter the ECM deposited by PC3-M cells. We first tested whether ECM deposited by apigenin-treated cells provided the same adhesive support to PCa cells as the ECM deposited by the untreated cells. Interestingly, even cells not treated with apigenin did not attach and spread well on the ECM deposited by apigenin-treated cells, indicating that apigenin treatment changes the composition of the ECM. Using Western blot to evaluate differences in the composition of matrix deposited by control cells and apigenin-treated cells, we found that apigenin-treated cells produce much less collagen I and IV, thus correlating with the decrease in adhesion and spreading. These results demonstrate that the chemopreventive bioflavonoid apigenin may inhibit PCa cell adhesion through a combined effect on integrin α1α1 cell surface expression and ECM deposition.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 615. doi:1538-7445.AM2012-615

Soy isoflavone supplementation for breast cancer risk reduction: a randomized phase II trial

Soy isoflavone consumption may protect against breast cancer development. We conducted a phase IIB trial of soy isoflavone supplementation to examine its effect on breast epithelial proliferation and other biomarkers in the healthy high-risk breast. One hundred and twenty-six consented women underwent a random fine-needle aspiration (rFNA); those with 4,000 or more epithelial cells were randomized to a double-blind 6-month intervention of mixed soy isoflavones (PTIG-2535) or placebo, followed by repeat rFNA. Cells were examined for Ki-67 labeling index and atypia. Expression of 28 genes related to proliferation, apoptosis, and estrogenic effect was measured using quantitative reverse transcriptase PCR. Hormone and protein levels were measured in nipple aspirate fluid (NAF). All statistical tests were two-sided. Ninety-eight women were evaluable for Ki-67 labeling index. In 49 treated women, the median Ki-67 labeling index was 1.18 at entry and 1.12 post intervention, whereas in 49 placebo subjects, it was 0.97 and 0.92 (P for between-group change: 0.32). Menopausal stratification yielded similar results between groups, but within premenopausal soy-treated women, Ki-67 labeling index increased from 1.71 to 2.18 (P = 0.04). We saw no treatment effect on cytologic atypia or NAF parameters. There were significant increases in the expression of 14 of 28 genes within the soy, but not the control group, without significant between-group differences. Plasma genistein values showed excellent compliance. A 6-month intervention of mixed soy isoflavones in healthy, high-risk adult Western women did not reduce breast epithelial proliferation, suggesting a lack of efficacy for breast cancer prevention and a possible adverse effect in premenopausal women.

Abstract C177: Chemical-driven biological probing: Discovery of a novel antimetastatic drug

Chemicals constitute richly informative probes, have high resolving potential and are able to uncover complex biological processes. Harnessing this potential provides an avenue for the discovery of new therapeutics that act via novel mechanisms. We focused these principles upon an intractable problem: cancer metastasis. We started with a chemical scaffold with broad bioactivity, with desirable drug-like properties and that would support synthetic diversification. Initially focusing upon human prostate cancer (PCa) we then coupled fragment-diversification and novel synthetic routes to upfront positive selection screens (inhibition of cell motility) and negative selection screens (cell toxicity) in an iterative fashion. We thereby efficiently synthesized a new class of bioactive compounds that inhibits systemic PCa metastasis at low nanomolar concentrations. Efficacy against other cancer types was demonstrated. Extensive investigations indicate high specificity and no toxicity. Target validation studies point to inhibition of protein-protein interaction motifs. Together, these studies support the notion that this approach is powerful, can be broadly applied across biological systems, and constitutes a paradigm. Specifically, they have led to the discovery of a novel acting drug that inhibits human cancer metastasis.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C177.

The Ninth Annual American Association of cancer research international conference on frontiers in cancer prevention research

The Ninth Annual AACR Frontiers in Cancer PREVENTION Research conference was held in Philadelphia in November 7-10, 2010. Its thematic focus was "

PREVENTION

From Basic Science to Public Health Benefit." Telomere plasticity, the microenvironment, inflammation, transformation to the metastatic phenotype, and pathways to obesity were highlighted as important elements of carcinogenesis amenable to intervention. The integration of information from novel technologies related to physical biology, molecular and genetic profiles, and imaging along with behavioral and clinical parameters have advanced risk stratification and early detection. Cancer prevention represents a powerful testing ground for the development of individually tailored intervention and for increasing the efficiency of drug discovery. Advances in clinical trials relate to more efficient design strategies, have shown first-in-human targeting capabilities, and have developed powerful strategies to overcome accrual barriers. Tailored intervention strategies now show high efficacy on large cohorts across several cancer types. These successes are expected to increase.

Abstract 1407: Mitogen-activated protein kinase kinase 4 (MEK4) is a key regulator of prostate cancer progression

Mitogen-activated protein kinase kinase 4 (MEK4) is a dual-specificity kinase that has been implicated in cancer progression in multiple cancer types, including prostate cancer (PCa). MEK4 is upregulated in invasive PCa lesions in human tissue. We hypothesize that increased MEK4 promotes PCa invasion and metastasis. Our group has created PC3-M cells stably transfected with either constitutively-active or increased levels of wild-type MEK4. In a Matrigel Boyden chamber assay, constitutively-active or wild-type MEK4 was shown to increase PCa invasion. Cancer cell invasion requires the coupling of cell migration with increased production of proteases. We hypothesized that MEK4 promoted invasion via production of proteases, but not via cell migration. Using an uncoated boyden chamber, MEK4 was shown not to affect migration. Using quantitative real time polymerase chain reaction (qRT/PCR), we went on to demonstrate that MEK4 increased MMP-2 and MMP-9 transcript expression, but did not affect MMP-10 expression. In addition to these studies, we have also looked at the effect of increased or constitutively-active MEK4 on an orthotopic mouse model of PCa. In this model, PCa cells are injected into the prostates of nude mice and tumor size, circulating tumor cells, and lung metastasis are quantified. Preliminary data shows that constitutively-active MEK4 causes an increase in primary tumor size as well as an increase in circulating tumor cells in both the blood and the bone marrow. In summary, we demonstrated that chronic high expression of MEK4 increases human PCa invasion, that this is not due to increased migration, but is associated with increases in MMP-2 and MMP-9. Further, constitutively-active MEK4 appears to have different biological effects than high levels of wild type MEK4 in vivo. Ongoing studies are evaluating the effect of wild type MEK4 and of constitutively-active MEK4 on the formation of distant soft tissue metastasis in the above murine model. In related studies we are seeking to identify downstream proteins critical for MEK4's effects on cell invasion and metastasis both in vitro and in vivo. We are also seeking to examine the effects of sustained MEK4 knockdown on PCa invasion and metastasis.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1407. doi:10.1158/1538-7445.AM2011-1407

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.

Inhibition of cancer cell invasion and metastasis by genistein

Genistein is a small, biologically active flavonoid that is found in high amounts in soy. This important compound possesses a wide variety of biological activities, but it is best known for its ability to inhibit cancer progression. In particular, genistein has emerged as an important inhibitor of cancer metastasis. Consumption of genistein in the diet has been linked to decreased rates of metastatic cancer in a number of population-based studies. Extensive investigations have been performed to determine the molecular mechanisms underlying genistein’s antimetastatic activity, with results indicating that this small molecule has significant inhibitory activity at nearly every step of the metastatic cascade. Reports have demonstrated that, at high concentrations, genistein can inhibit several proteins involved with primary tumor growth and apoptosis, including the cyclin class of cell cycle regulators and the Akt family of proteins. At lower concentrations that are similar to those achieved through dietary consumption, genistein can inhibit the prometastatic processes of cancer cell detachment, migration, and invasion through a variety of mechanisms, including the transforming growth factor (TGF)-β signaling pathway. Several in vitro findings have been corroborated in both in vivo animal studies and in early-phase human clinical trials, demonstrating that genistein can both inhibit human cancer metastasis and also modulate markers of metastatic potential in humans, respectively. Herein, we discuss the variety of mechanisms by which genistein regulates individual steps of the metastatic cascade and highlight the potential of this natural product as a promising therapeutic inhibitor of metastasis.

Abstract CN02-04: Phase II study of genistein in men with prostate cancer

Progression of cells to a metastatic phenotype begins in the primary organ and represents an important chemoprevention target. In preclinical studies, genistein induces reversion of human prostate cancer (PCa) cells to a less metastatic phenotype. In a phase II study, men with localized PCa were randomized between genistein treatment versus not prior to radical prostatectomy. Analysis of prostate epithelial cells within harvested organs revealed that genistein had the following effects: 1) it decreased matrix metalloproteinase 2 (MMP-2) expression; 2) it induced nuclear spreading; a surrogate marker of inhibition of cell detachment; and 3) gene expression profiling demonstrated selective modulation of genes associated with regulation of cell motility in other cell types. By engineering the expression of these genes in cell lines, we demonstrated that they were important regulators of human PCa cell invasion. Genistein increased the expression of genes that suppress invasion and decreased the expression of genes that enhance invasion. Together, this study demonstrates that genistein induces reversion of human prostate cells in man to a less metastatic phenotype. Importantly, this study demonstrates the proof-of-principal concept that the conduct of molecular screens in human chemoprevention trials has the ability to identify the mechanism of action of investigational agents.

Citation Information: Cancer Prev Res 2010;3(12 Suppl):CN02-04.

Concise syntheses of the abyssinones and discovery of new inhibitors of prostate cancer and MMP-2 expression

Hydrogen-bonding catalysis is an emerging field that facilitates rapid access to medicinally relevant enantioenriched small molecules. Here, we report the first asymmetric total syntheses of four members of the abyssinone class of natural products (I, II, III, and IV 4´-OMe) via quinine- or quinidine-derived thiourea-catalyzed intramolecular conjugate additions of β-keto ester alkylidenes. This concise strategy includes a tandem deprotection/decarboxylation final step that delivers all four natural products and their corresponding antipodes. A preliminary evaluation of all of these small molecules against a metastatic human prostate cancer cell line has identified that these compounds selectively and differentially inhibit cell growth and downregulate the expression of matrix metalloproteinase-2 (MMP-2) at non-toxic concentrations.

Endoglin suppresses human prostate cancer metastasis

Endoglin is a transmembrane receptor that suppresses human prostate cancer (PCa) cell invasion. Small molecule therapeutics now being tested in humans can activate endoglin signaling. It is not known whether endoglin can regulate metastatic behavior, PCa tumor growth, nor what signaling pathways are linked to these processes. This study sought to investigate the effect of endoglin on these parameters. We used a murine orthotopic model of human PCa metastasis, designed by us to measure effects at early steps in the metastatic cascade, and implanted PCa cells stably engineered to express differing levels of endoglin. We now extend this model to measure cancer cells circulating in the blood. Progressive endoglin loss led to progressive increases in the number of circulating PCa cells as well as to the formation of soft tissue metastases. Endoglin was known to suppress invasion by activating the Smad1 transcription factor. We now show that it selectively activates specific Smad1-responsive genes, including JUNB, STAT1, and SOX4. Increased tumor growth and increased Ki67 expression in tissue was seen only with complete endoglin loss. By showing that endoglin increased TGFβ-mediated suppression of cell growth in vitro and TGFβ-mediated signaling in tumor tissue, loss of this growth-suppressive pathway appears to be implicated at least in part for the increased size of endoglin-deficient tumors. Endoglin is shown for the first time to suppress cell movement out of primary tumor as well as the formation of distant metastasis. It is also shown to co-regulate tumor growth and metastatic behavior in human PCa.

Endoglin phosphorylation by ALK2 contributes to the regulation of prostate cancer cell migration

Endoglin, a transmembrane glycoprotein that acts as a transforming growth factor-beta (TGF-beta) coreceptor, is downregulated in PC3-M metastatic prostate cancer cells. When restored, endoglin expression in PC3-M cells inhibits cell migration in vitro and attenuates the tumorigenicity of PC3-M cells in SCID mice, though the mechanism of endoglin regulation of migration in prostate cancer cells is not known. The current study indicates that endoglin is phosphorylated on cytosolic domain threonine residues by the TGF-beta type I receptors ALK2 and ALK5 in prostate cancer cells. Importantly, in the presence of constitutively active ALK2, endoglin did not inhibit cell migration, suggesting that endoglin phosphorylation regulated PC3-M cell migration. Therefore, our results suggest that endoglin phosphorylation is a mechanism with relevant functional consequences in prostate cancer cells. These data demonstrate for the first time that TGF-beta receptor-mediated phosphorylation of endoglin is a Smad-independent mechanism involved in the regulation of prostate cancer cell migration.

MEK4 function, genistein treatment, and invasion of human prostate cancer cells

BACKGROUND

Dietary intake of genistein by patients with prostate cancer has been associated with decreased metastasis and mortality. Genistein blocks activation of p38 mitogen-activated protein kinase and thus inhibits matrix metalloproteinase-2 (MMP-2) expression and cell invasion in cultured cells and inhibits metastasis of human prostate cancer cells in mice. We investigated the target for genistein in prostate cancer cells.

METHODS

Prostate cell lines PC3-M, PC3, 1532NPTX, 1542NPTX, 1532CPTX, and 1542CPTX were used. All cell lines were transiently transfected with a constitutively active mitogen-activated protein kinase kinase 4 (MEK4) expression vector (to increase MEK4 expression), small interfering RNA against MEK4 (to decrease MEK4 expression), or corresponding control constructs. Cell invasion was assessed by a Boyden chamber assay. Gene expression was assessed by a quantitative reverse transcription-polymerase chain reaction. Protein expression was assessed by Western blot analysis. Modeller and AutoDock programs were used for modeling of the structure of MEK4 protein and ligand docking, respectively. MMP-2 transcript levels were assessed in normal prostate epithelial cells from 24 patients with prostate cancer from a phase II randomized trial comparing genistein treatment with no treatment. Statistical significance required a P value of .050 or less. All statistical tests were two-sided.

RESULTS

Overexpression of MEK4 increased MMP-2 expression and cell invasion in all six cell lines. Decreased MEK4 expression had the opposite effects. Modeling showed that genistein bound to the active site of MEK4. Genistein inhibited MEK4 kinase activity with a half maximal inhibitory concentration of 0.40 microM (95% confidence interval [CI] = 0.36 to 0.45 muM). The MMP-2 transcript level in normal prostate epithelial cells was statistically significantly higher in the untreated group (100%) than in the genistein-treated group (24%; difference = 76%, 95% CI = 38% to 115%; P = .045).

CONCLUSIONS

We identified MEK4 as a proinvasion protein in six human prostate cancer cell lines and the target for genistein. We showed, to our knowledge for the first time, that genistein treatment, compared with no treatment, was associated with decreased levels of MMP-2 transcripts in normal prostate cells from prostate cancer-containing tissue.