Prostate cancer cell growth inhibition by tamoxifen is associated with inhibition of protein kinase C and induction of p21(waf1/cip1)

Research progress on tamoxifen and its analogs associated with nuclear receptors

Tamoxifen, a triphenylethylene-based selective estrogen-receptor modulator, is a landmark drug for the treatment of breast cancer and is also used for treating liver cancer and osteoporosis. Structural studies of tamoxifen have led to the synthesis of more than 20 novel tamoxifen analogs as receptor modulators, including 16 ERα modulators 2-17, an ERRβ inverse agonist 19 and six ERRγ inverse agonists 20-25. This paper summarizes the research progress and structure-activity relationships of tamoxifen analogs modulating these three nuclear receptors reported in the literature, and introduces the relationship between these three nuclear receptor-mediated diseases and tamoxifen analogs to guide the research of novel tamoxifen analogs.

To block or not to block-hormonal signaling in the treatment of cancers

The breast and prostate glands are the two major organs that are highly dependent on the gonadal steroid hormones for their development and homeostasis. The cancers of these organs also show a large dependence on steroid hormones and have formed the basis of endocrine therapy. Estrogen deprivation by oophorectomy has been in active practice since the 1970s, and androgen deprivation therapy for prostate cancer was a major breakthrough in medicine in 1941. Since then, several improvisations have happened in these modes of therapy. However, the development of resistance to this deprivation and the emergence of hormone independence are major problems in both cancers. The lessons learned from rodent models have made it clear that the male hormone has a role in females and vice versa. Also, the metabolic products of these hormones may have unintentional effects including proliferative conditions in both sexes. Hence, administering estrogen as a method of chemical castration in males and administering DHT in females may not be the ideal scenario. It would be important to consider the status of the opposite sex hormone signaling and its effects and come up with a combinatorial regime to strike a balance between androgen and estrogen signaling. This review summarizes the current understanding and developments in this field in the context of prostate cancer.

Tamoxifen and oxidative stress: an overlooked connection

Tamoxifen is the gold standard drug for the treatment of breast cancer in pre and post-menopausal women. Its journey from a failing contraceptive to a blockbuster is an example of pharmaceutical innovation challenges. Tamoxifen has a wide range of pharmacological activities; a drug that was initially thought to work via a simple Estrogen receptor (ER) mechanism was proven to mediate its activity through several non-ER mechanisms. Here in we review the previous literature describing ER and non-ER targets of tamoxifen, we highlighted the overlooked connection between tamoxifen, tamoxifen apoptotic effects and oxidative stress.

Targeted inhibition of ERα signaling and PIP5K1α/Akt pathways in castration-resistant prostate cancer

Selective ERα modulator, tamoxifen, is well tolerated in a heavily pretreated castration-resistant prostate cancer (PCa) patient cohort. However, its targeted gene network and whether expression of intratumor ERα due to androgen deprivation therapy (ADT) may play a role in PCa progression is unknown. In this study, we examined the inhibitory effect of tamoxifen on castration-resistant PCa in vitro and in vivo. We found that tamoxifen is a potent compound that induced a high degree of apoptosis and significantly suppressed growth of xenograft tumors in mice, at a degree comparable to ISA-2011B, an inhibitor of PIP5K1α that acts upstream of PI3K/AKT survival signaling pathway. Moreover, depletion of tumor-associated macrophages using clodronate in combination with tamoxifen increased inhibitory effect of tamoxifen on aggressive prostate tumors. We showed that both tamoxifen and ISA-2011B exert their on-target effects on prostate cancer cells by targeting cyclin D1 and PIP5K1α/AKT network and the interlinked estrogen signaling. Combination treatment using tamoxifen together with ISA-2011B resulted in tumor regression and had superior inhibitory effect compared with that of tamoxifen or ISA-2011B alone. We have identified sets of genes that are specifically targeted by tamoxifen, ISA-2011B or combination of both agents by RNA-seq. We discovered that alterations in unique gene signatures, in particular estrogen-related marker genes are associated with poor patient disease-free survival. We further showed that ERα interacted with PIP5K1α through formation of protein complexes in the nucleus, suggesting a functional link. Our finding is the first to suggest a new therapeutic potential to inhibit or utilize the mechanisms related to ERα, PIP5K1α/AKT network, and MMP9/VEGF signaling axis, providing a strategy to treat castration-resistant ER-positive subtype of prostate cancer tumors with metastatic potential.

Does tamoxifen have a therapeutic role outside of breast cancer? A systematic review of the evidence

INTRODUCTION

Tamoxifen is a widely used hormonal based therapy for breast cancer in the adjuvant and metastatic setting, prolonging overall and recurrence-free survival. There has been increasing interest in the potential for novel "off-target" effects of tamoxifen and its metabolite N-desmethyltamoxifen across a number of cancer types. We aim to review the current literature regarding the potential use of tamoxifen in other primary malignancies.

METHOD

A qualitative systematic review was performed according to the PRISMA guidelines using pre-set search criteria across the PubMed, Cochrane and Scopus databases from 1985 to 2019. Additional results were generated from included papers references.

RESULTS

A total of 324 papers were identified, of which 47 were included; a further 29 articles were obtained from additional referencing to give a total of 76 articles. Clinical trials have demonstrated benefits with the use of tamoxifen in isolation and combination, specifically in patients with advanced non-resectable malignancy, however results are not consistent across the literature. In vivo data consistently suggests that off target effects of tamoxifen are mediated through the ceramide pathway or through inhibition of protein kinase C (PKC).

CONCLUSIONS

With increased focus upon the potential of repurposing drugs, tamoxifen may be a candidate for repurposing in the wider cancer setting. There is evidence to suggest that the ceramide or PKC pathway could act as a therapeutic target for tamoxifen or alternative chemotherapeutics and merits further investigation.

Heat shock protein 27 regulates human prostate cancer cell motility and metastatic progression

Prostate cancer (PCa) is the most common form of cancer in American men. Mortality from PCa is caused by the movement of cancer cells from the primary organ to form metastatic tumors at distant sites. Heat shock protein 27 (HSP27) is known to increase human PCa cell invasion and its overexpression is associated with metastatic disease. The role of HSP27 in driving PCa cell movement from the prostate to distant metastatic sites is unknown. Increased HSP27 expression increased metastasis as well as primary tumor mass. In vitro studies further examined the mechanism of HSP27-induced metastatic behavior. HSP27 did not affect cell detachment, adhesion, or migration, but did increase cell invasion. Cell invasion was dependent upon matrix metalloproteinase 2 (MMP-2), whose expression was increased by HSP27. In vivo, HSP27 induced commensurate changes in MMP-2 expression in tumors. These findings demonstrate that HSP27 drives metastatic spread of cancer cells from the prostate to distant sites, does so across a continuum of expression levels, and identifies HSP27-driven increases in MMP-2 expression as functionally relevant. These findings add to prior studies demonstrating that HSP27 increases PCa cell motility, growth and survival. Together, they demonstrate that HSP27 plays an important role in PCa progression.

Estrogen receptor beta in prostate cancer: friend or foe?

Prostate cancer is the commonest, non-cutaneous cancer in men. At present, there is no cure for the advanced, castration-resistant form of the disease. Estrogen has been shown to be important in prostate carcinogenesis, with evidence resulting from epidemiological, cancer cell line, human tissue and animal studies. The prostate expresses both estrogen receptor alpha (ERA) and estrogen receptor beta (ERB). Most evidence suggests that ERA mediates the harmful effects of estrogen in the prostate, whereas ERB is tumour suppressive, but trials of ERB-selective agents have not translated into improved clinical outcomes. The role of ERB in the prostate remains unclear and there is increasing evidence that isoforms of ERB may be oncogenic. Detailed study of ERB and ERB isoforms in the prostate is required to establish their cell-specific roles, in order to determine if therapies can be directed towards ERB-dependent pathways. In this review, we summarise evidence on the role of ERB in prostate cancer and highlight areas for future research.

Effects of flutamide on [methyl-(3)h]-choline uptake in human prostate cancer-3 cells: a pilot study

BACKGROUND

Positron emission tomography using [methyl-(11)C]-choline is effective in imaging many types of cancer, especially prostate cancer (PC). The antiandrogen flutamide is often used as part of the initial treatment of PC. Data on the effect of flutamide on and methylcholine incorporation into PC-3 cells are lacking in the experimental and literature work.

OBJECTIVES

The aims of this study were to assess whether human PC-3 cells are susceptible to flutamide and whether the drug modulates the uptake of [methyl-(3)H]-choline into these cells.

METHODS

PC-3 cells were treated for 3 days with flutamide (≤100 nmol/L), inhibiting growth by 20% to 70% with control cells included. Two viability tests (cytotoxic analyses), the thiazole blue assay and the trypan blue exclusion method, were used to determine the median inhibitory concentration for flutamide (10 nmol/L). Control and flutamide-treated cells were incubated with [methyl-(3)H]-choline for 10 minutes and then in nonradioactive medium for 10 minutes to simulate the rapid blood clearance of [methyl-(11)C]-choline tracer that occurs within 5 to 20 minutes, and then extracted using organic and aqueous solvents to determine the intracellular distribution of the tracer. Protein assay and flow-cytometry analysis were used to determine protein content and DNA synthesis in both control and treated cells. The uptake of [methyl-(3)H]-choline was normalized to protein content and expressed as mean (SD) dpm/1Jg protein (n = 6).

RESULTS

PC-3 cell proliferation was inhibited with flutamide treatment. After treatment of PC-3 cells with flutamide 10 nmol/L for 3 days, cells accumulated DNA during the S phase. Mean (SD) [methyl-(3)H]-choline uptake was found to be significantly lower with flutamide 10-nmol/L-treated cells compared with control cells (65.95 [0.72] vs 114.21 [0.57] dpm/1Jg protein; P < 0.001); the difference between the 5-nmol/L-treated cells and controls was nonsignificant.

CONCLUSIONS

In this pilot study, flutamide inhibited tumor cell growth and proliferation and decreased (modulated) the uptake of [methyl-(3)H]-choline into androgen receptor-negative PC-3 cells. These results suggest that flutamide might inhibit proliferation by an androgen-independent mechanism.

A novel role for raloxifene nanomicelles in management of castrate resistant prostate cancer

Of patients with castrate resistant prostate cancer (CRPC), less than 25-33% survive more than five years. Recent studies have implicated estrogen, acting either alone or synergistically with androgens in the development of castrate resistant prostate cancer. Several in vitro and in vivo studies, as well as a limited number of clinical trials, have highlighted the potential of selective estrogen receptor modulators, such as raloxifene (Ral) for the treatment of castrate resistant prostate cancer. However, the poor oral bioavailability and metabolism of selective estrogen receptor modulators limit their efficiency in clinical application. To overcome these limitations, we have used styrene co-maleic acid (SMA) micelle to encapsulate raloxifene. Compared to free drug, SMA-Ral micelles had 132 and 140% higher cytotoxicity against PC3 and DU 145 prostate cell lines, respectively. SMA-Ral effectively inhibits cell cycle progression, increases apoptosis, and alters the integrity of tumor spheroid models. In addition, the micellar system induced changes in expression and localization of estrogen receptors, epidermal growth factor receptor (EGFR), and downstream effectors associated with cell proliferation and survival. Finally, SMA-Ral treatment decreased migration and invasion of castrate resistant prostate cancer cell lines. In conclusion, SMA-Ral micelles can potentially benefit new strategies for clinical management of castrate resistant prostate cancer.

The strategies to control prostate cancer by chemoprevention approaches

Prostate cancer (PCA) is the most commonly diagnosed cancer in men in the United States with growing worldwide incidence. Despite intensive investment in improving early detection, PCA often escapes timely detection and mortality remains high; this malignancy being the second highest cancer-associated mortality in American men. Collectively, health care costs of PCA results in an immense financial burden that is only expected to grow. Additionally, even in cases of successful treatment, PCA is associated with long-term and pervasive effects on patients. A proactive alternative to treat PCA is to prevent its occurrence and progression prior to symptomatic malignancy. This may serve to address the issue of burgeoning healthcare costs and increasing number of sufferers. One potential regimen in service of this alternative is PCA chemoprevention. Here, chemical compounds with cancer preventive efficacy are identified on the basis of their potential in a host of categories: their historical medicinal use, correlation with reduced risk in population studies, non-toxicity, their unique chemical properties, or their role in biological systems. PCA chemopreventive agents are drawn from multiple broad classes of chemicals, themselves further subdivided based on source or potential effect, with most derived from natural products. Many such compounds have shown efficacy, varying from inhibiting deregulated PCA cell signaling, proliferation, epithelial to mesenchymal transition (EMT), invasion, metastasis, tumor growth and angiogenesis and inducing apoptosis. Overall, these chemopreventive agents show great promise in PCA pre-clinical models, though additional work remains to be done in effectively translating these findings into clinical use.

CB1 and CB2 receptors are novel molecular targets for Tamoxifen and 4OH-Tamoxifen

Tamoxifen (Tam) is classified as a selective estrogen receptor modulator (SERM) and is used for treatment of patients with ER-positive breast cancer. However, it has been shown that Tam and its cytochrome P450-generated metabolite 4-hydroxy-Tam (4OH-Tam) also exhibit cytotoxic effects in ER-negative breast cancer cells. These observations suggest that Tam and 4OH-Tam can produce cytotoxicity via estrogen receptor (ER)-independent mechanism(s) of action. The molecular targets responsible for the ER-independent effects of Tam and its derivatives are poorly understood. Interestingly, similar to Tam and 4OH-Tam, cannabinoids have also been shown to exhibit anti-proliferative and apoptotic effects in ER-negative breast cancer cells, and estrogen can regulate expression levels of cannabinoid receptors (CBRs). Therefore, this study investigated whether CBRs might serve as novel molecular targets for Tam and 4OH-Tam. We report that both compounds bind to CB1 and CB2Rs with moderate affinity (0.9-3 μM). Furthermore, Tam and 4OH-Tam exhibit inverse activity at CB1 and CB2Rs in membrane preparations, reducing basal G-protein activity. Tam and 4OH-Tam also act as CB1/CB2R-inverse agonists to regulate the downstream intracellular effector adenylyl cyclase in intact cells, producing concentration-dependent increases in intracellular cAMP. These results suggest that CBRs are molecular targets for Tam and 4OH-Tam and may contribute to the ER-independent cytotoxic effects reported for these drugs. Importantly, these findings also indicate that Tam and 4OH-Tam might be used as structural scaffolds for development of novel, efficacious, non-toxic cancer drugs acting via CB1 and/or CB2Rs.

Tamoxifen non-estrogen receptor mediated molecular targets

Recent experimental studies revealing new biological effects of tamoxifen on tumor cells both expressing and not expressing different types of estrogen receptors (ERα and ERβ) show new aspects of a seemingly well known agent. This review describes tamoxifen targets, the blocking of which leads to inhibition of tumor cell growth and angiogenesis, stimulation of programmed cell death (apoptosis, autophagia and necrosis), inhibition of multidrug resistance, invasion and metastasis. Since outcomes of tamoxifen action on cells are prognostically good from the point of view of both tumor growth/metastasis inhibition and tumor response to drug therapy, the authors believe this is an extremely important addition to tamoxifen antiestrogenic effect. Arguments are provided to consider the strategy of long-term tamoxifen treatment proposed by Professor Craig V. Jordan in the 1970s that is also applicable to the treatment of other tumors. This is, first of all, the fact that expression of estrogen receptor-beta that can also be targeted by tamoxifen therapy in solid tumors of practically all known sites and histologies. The authors believe that molecular biological screening of patients with respect to expression of tamoxifen cellular targets other than ERα and ERβ is needed to use to the full all tamoxifen biological activities other than modulation of estrogen receptors during long-term adjuvant therapy for cancers of various sites.

Inhibitory effects of antagonists of growth hormone releasing hormone on experimental prostate cancers are associated with upregulation of wild-type p53 and decrease in p21 and mutant p53 proteins

BACKGROUND

The tumor suppressor gene p53 is implicated in cell cycle control and apoptosis. Antagonists of growth hormone-releasing hormone (GHRH) have been shown to inhibit human experimental prostate cancers.

METHODS

We investigated the involvement of p53 apoptotic pathways in this effect. Nude mice bearing xenografted PC-3, DU-145, and MDA-PCa-2b human prostate cancer lines were treated with a new potent GHRH antagonist MZ-J-7-138. To determine whether tumor inhibition by MZ-J-7-138 involves apoptotic mechanisms such as p53 and p21, we evaluated by Western Blot the expression of mutant mt-p53 in PC-3 and DU-145 and of wild type (wt-p53) in MDA-PCa-2b prostate cancers as well as p21.

RESULTS

MZ-J-7-138 significantly inhibited the growth of PC-3, DU-145, and MDA-PCa-2b xenografts in nude mice. Androgen deprivation with the LHRH antagonist Cetrorelix enhanced the anti-proliferative effect of GHRH antagonist MZ-J-7-138 on MDA-PCa-2b tumors. The expression of mutant (mt-p53) and p21 protein in PC-3 and DU-145 tumors was significantly decreased by treatment with MZ-J-7-138, whereas wild type wt-p53 expression in MDA-PCA-2b tumors was up regulated by treatment with Cetrorelix. All three models investigated expressed specific, high affinity GHRH receptors.

CONCLUSIONS

Our findings indicate that the anti-proliferative effects of GHRH antagonist MZ-J-7-138 and LHRH antagonist Cetrorelix on prostate cancers involve p53 and p21 signaling.

Enhanced formation of 5-oxo-6,8,11,14-eicosatetraenoic acid by cancer cells in response to oxidative stress, docosahexaenoic acid and neutrophil-derived 5-hydroxy-6,8,11,14-eicosatetraenoic acid

The 5-lipoxygenase (5-LO) product 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE), which is a potent chemoattractant for myeloid cells, is known to promote the survival of prostate cancer cells. In the present study, we found that PC3 prostate cancer cells and cell lines derived from breast (MCF7) and lung (A-427) cancers contain 5-hydroxyeicosanoid dehydrogenase (5-HEDH) activity and have the ability to synthesize 5-oxo-ETE from its precursor 5S-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE) when added as an exogenous substrate. H(2)O(2) strongly stimulated the synthesis of 5-oxo-ETE and induced dramatic increases in the levels of both glutathione disulfide and NADP(+). The effects of H(2)O(2) on 5-oxo-ETE and NADP(+) were blocked by N-ethylmaleimide (NEM), indicating that this effect was mediated by the glutathione reductase-dependent generation of NADP(+), the cofactor required by 5-HEDH. 5-Oxo-ETE synthesis was also stimulated by agents that have cytotoxic effects on tumor cells, including 4,7,10,13,16,19-docosahexaenoic acid, tamoxifen and MK-886. Because PC3 cells have only modest 5-LO activity compared with inflammatory cells, we investigated their ability to contribute to the transcellular biosynthesis of 5-oxo-ETE from neutrophil-derived 5-HETE. Stimulation of neutrophils with arachidonic acid and calcium ionophore in the presence of PC3 cells led to a large and selective increase in 5-oxo-ETE synthesis compared with controls in which PC3 cell 5-oxo-ETE synthesis was selectively blocked by pretreatment with NEM. The ability of prostate tumor cells to synthesize 5-oxo-ETE may contribute to tumor cell proliferation as well as the influx of inflammatory cells, which may further induce cell proliferation through the release of cytokines. 5-Oxo-ETE may be an attractive target in cancer therapy.

Phase I clinical trial assessing temozolomide and tamoxifen with concomitant radiotherapy for treatment of high-grade glioma

PURPOSE

The new standard treatment of glioblastoma multiforme is concurrent radiotherapy (RT) and temozolomide. The proliferation of high-grade gliomas might be partly dependent on protein kinase C-mediated pathways. Tamoxifen has been shown in vitro to inhibit protein kinase C through estrogen receptor-independent antineoplastic effects. This Phase I trial was designed to determine the maximal tolerated dose (MTD) of tamoxifen when given with temozolomide and concurrent RT to patients with high-grade gliomas.

METHODS AND MATERIALS

A total of 17 consecutive patients in four cohorts with World Health Organization Grade 3 (n = 2) and 4 (n = 15) gliomas were given tamoxifen twice daily during 6 weeks of concurrent RT and temozolomide. Eligibility included histologic diagnosis, age >18 years old, Karnofsky performance status ≥ 60, and no previous brain RT or chemotherapy. The starting dose was 50 mg/m(2) divided twice daily. If no dose-limiting toxicities (DLTs) occurred in 3 patients, the dose was escalated in 25-mg/m(2) increments until the MTD was reached. When ≥ 2 patients within a cohort experienced a DLT, the MTD had been exceeded. Temozolomide was given with RT at 75 mg/m(2). A dose of 60 Gy in 2 Gy/d fractions to a partial brain field was delivered.

RESULTS

A total of 6 patients in Cohort 4 had received tamoxifen at 125 mg/m(2). One patient was excluded, and the fourth patient developed Grade 4 thrombocytopenia (DLT). Thus, 3 more patients needed to be enrolled. A deep venous thrombosis (DLT) occurred in the sixth patient. Thus, the MTD was 100 mg/m(2).

CONCLUSIONS

The MTD of tamoxifen was 100 mg/m(2) when given concurrently with temozolomide 75 mg/m(2) and RT. Tamoxifen might have a role in the initial treatment of high-grade gliomas and should be studied in future Phase II trials building on the newly established platform of concurrent chemoradiotherapy.

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.

PKC inhibition increases gap junction intercellular communication and cell adhesion in human neuroblastoma

Gap junction intercellular communication and cell-cell adhesion are essential for maintaining a normal cellular phenotype, including the control of growth and proliferation. Loss of either cell-cell adhesion or communication is common in cancers, while restoration of function is associated with tumor suppression. Protein kinase C (PKC) isozymes regulate a broad spectrum of cellular functions including growth and proliferation, and their overexpression has been correlated with carcinogenesis. Consequently, PKC inhibitors are currently undergoing clinical trials as an anti-cancer agents although the precise cellular alterations induced by PKC inhibitors remain to be elucidated. In the current study, the effects of PKC inhibitors on cell interactions were investigated using human neuroblastoma (IMR32, SKNMC, and SHSY-5Y) cell lines. An analysis of intercellular communication revealed an increase in gap junctional coupling with PKC inhibition. The observed increase in coupling was not associated with a change in Connexin 43 distribution or an alteration of phosphorylation status of the protein. There was also an increase in cell-cell adhesion with PKC inhibitor treatment as indicated by a cell aggregation assay. Therefore, the growth suppressive abilities of PKC inhibition on tumors may be due to the cancer suppressive effects of increased gap junction intercellular communication and cell-cell adhesion.

ERRgamma suppresses cell proliferation and tumor growth of androgen-sensitive and androgen-insensitive prostate cancer cells and its implication as a therapeutic target for prostate cancer

Estrogen receptor-related receptors (ERR) are orphan nuclear receptors, which are constitutively activated without estrogen binding. Recent evidence indicates that the ligand-independent ERRs may be involved in similar ER-mediated regulatory pathways and modulate estrogen responsiveness in certain target cells. We recently showed that an ERR subtype, ERRgamma, is coexpressed with ERbeta in normal human prostatic epithelial cells and exhibits reduced expression in many prostate cancer cell lines and clinical neoplastic prostate tissues. Based on this, we hypothesize that ERRgamma may have growth regulatory roles in prostate and prostate cancer. We showed in this study that ERRgamma was expressed in epithelial cell nuclei in fetal and pubertal human prostates, whereas its nuclear expression became reduced in advanced prostate cancer lesions. Stable ERRgamma expression by retroviral transduction suppressed significantly both in vitro cell growth and in vivo tumorigenicity of two prostate cancer cell lines, LNCaP and DU145, as evidenced by a cell-cycle arrest at G(1)-S transition and also induction of two cyclin-dependent kinase inhibitors p21(WAF1/CIP1) and p27(KIP1). We further showed by reporter assay that induction of p21 and p27 by ERRgamma was mediated through direct transactivation of their gene promoters. Moreover, we also showed that a selective ERRgamma-agonist, DY131, could potentiate the ERRgamma-induced growth inhibition in LNCaP-ERRgamma and DU145-ERRgamma cells in a dose-dependent manner compared with respective parental cells. Taken together, our results show that ERRgamma may perform an antiproliferative or tumor-suppressing function in prostate cancer cells. More importantly, our results suggest that ERRgamma could be a novel therapeutic target for prostate cancer treatment.

Novel combination therapy against metastatic and androgen-independent prostate cancer by using gefitinib, tamoxifen and etoposide

In this study, we evaluated, for the first time, the antiproliferative and cytotoxic effects induced by a combination of a selective epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor, gefitinib, with other chemotherapeutic drugs including estrogen receptor-beta (ER-beta) antagonist (tamoxifen) and topoisomerase II inhibitor (etoposide) on some metastatic prostate cancer (PC) cell lines. Immunohistochemial analyses revealed that EGFR expression was enhanced in 38% of primary prostatic adenocarcinomas (Gleason scores 4-10) as compared to the corresponding normal tissues of the same prostate gland from 32 PC patients. The RT-PCR and Western blot data have also indicated the higher expression levels of EGFR and ER-beta transcripts and proteins in metastatic LNCaP, DU145 and PC3 cells relative to nonmalignant normal prostate cells. Moreover, the results from MTT and FACS analyses revealed that the drugs, alone or in combination at lower concentrations, inhibited the growth of 17beta-estradiol (E2) plus EGF and serum-stimulated androgen-responsive LNCaP-C33 and androgen-independent LNCaP-C81, DU145 and PC3 cells. Importantly, the combined gefitinib, tamoxifen and etoposide also caused a higher rate of apoptotic death of PC cells as compared to single agents. The cytotoxic effects induced by these drugs in PC3 cells appear to be mediated through the accumulation of cellular ceramide and activation of caspase cascades via a mitochondrial pathway. These findings indicate that the combined use of inhibitors of EGF-EGFR and E2-ER-beta signaling with etoposide, which act by increasing the cellular ceramide levels and caspase activity, represents a promising strategy for a more effective treatment of metastatic PC forms.

Estrogens and aspects of prostate disease

Estrogens have long been associated with the processes involved in prostate carcinogenesis, particularly in cancer suppression. However, the synergistic influence of low concentrations of estrogens, together with androgens, in promoting aberrant growth of the gland has also been recognized. As new insights into the complex molecular events implicated in growth regulation of the prostate are revealed, the role of the estrogens has become clearer. The present review considers this role in relation to the pathogenesis of prostate cancer and the potential cancer-repressive influence of the dietary estrogens.

Peripheral-type benzodiazepine receptor overexpression and knockdown in human breast cancer cells indicate its prominent role in tumor cell proliferation

The peripheral-type benzodiazepine receptor (PBR), an 18-kDa high affinity drug and cholesterol binding protein, is expressed at high levels in various cancers. Its expression is positively correlated with aggressive metastatic behavior in human breast cancer cells. To determine the role of PBR in tumor progression, two human mammary carcinoma cell lines were utilized: the non-aggressive MCF-7 cell line, which expresses extremely low PBR levels, and the highly aggressive MDA-MB-231 cell line, which has much higher PBR levels. We have generated stably transfected lines of the tetracycline-repressible MCF-7 cell line (MCF-7 Tet-Off) with inducible human PBR cDNA. Induction of PBR expression in MCF-7 Tet-Off cells increased PBR ligand binding and cell proliferation. Transfection of MDA-MB-231 cells with multiple siRNAs complementary to PBR (PBR-siRNAs) led to different levels of PBR mRNA knockdown. Lentiviral-mediated PBR RNA interference in MDA-MB-231 cells decreased PBR levels by 50%. Decreased PBR expression was associated with cell cycle arrest at G2 phase, decreased cell proliferation, and significant increases in the protein levels of the cyclin-dependent kinase inhibitor p21(WAF/CIP1). These changes were accompanied by p53 activation seen as increased p53 phosphorylation (Ser15). In parallel, increased proteolytic activation of caspase-3 was also observed. Taken together these results suggest that PBR protein expression is directly involved in regulating cell survival and proliferation in human breast cancer cells by influencing signaling mechanisms involved in cell cycle control and apoptosis.

Characterization of a method for profiling gene expression in cells recovered from intact human prostate tissue using RNA linear amplification

Coupling array technology to laser capture microdissection (LCM) has the potential to yield gene expression profiles of specific cell populations within tissue. However, remaining problems with linear amplification preclude accurate expression profiling when using the low nanogram amounts of RNA recovered after LCM of human tissue. We describe a novel robust method to reliably amplify RNA after LCM, allowing direct probing of 12K gene arrays. The fidelity of amplification was demonstrated by comparing the ability of amplified RNA (aRNA) versus that of native RNA to identify differentially expressed genes between two different cell lines, demonstrating a 99.3% concordance between observations. Array findings were validated by quantitative polymerase chain reaction analysis of a randomly selected subset of 32 genes. Using LCM to recover normal (N=5 subjects) or cancer (N=3) cell populations from intact human prostate tissue, three differentially expressed genes were identified. Independent investigators have previously identified differential expression of two of these three genes, hepsin and beta-microseminoprotein, in prostate cancer. Taken together, the current study demonstrates that accurate gene expression profiling can readily be performed on specific cell populations present within complex tissue. It also demonstrates that this approach efficiently identifies biologically relevant genes.

Toremifene--a promising therapy for the prevention of prostate cancer and complications of androgen deprivation therapy

Deregulation of the estrogen axis in humans prompts a series of tissue-specific events. In the breast and prostate, alterations in estrogen signalling lead to genotypic and phenotypic molecular alterations that result in dysplastic cellular appearance, deregulated cell growth and carcinoma. In bone, decreased estrogen leads to increased osteoclastogenesis and bone resorption, decreased bone mineral density and a significant fracture risk. Toremifene is a selective estrogen receptor modulator that exerts pharmacological activity in the breast, bone and prostate. An intense interest in developing this agent for prostate cancer chemoprevention is based on the reduction of premalignant and malignant prostate lesions in a transgenic model of prostate cancer. Biological and clinical activity was demonstrated in Phase II trials by the prevention of progression to prostate cancer in men with high-grade prostate intraepithelial neoplasia and through suppression of bone turnover biomarkers and increased bone mineral density in men on androgen deprivation therapy for prostate cancer.

Tumour plasticity and extravascular circulation in ECV304 human bladder carcinoma cells

BACKGROUND

The concepts of vasculogenic mimicry and mosaic vessels have been proposed as novel modes of tumour neovascularisation. However, the presence and significance of these types of neovascularisation remain unclear.

MATERIALS AND METHODS

ECV304 human bladder carcinoma cells were used to determine how tumour cells take part in tumour neovascularisation.

RESULTS

Subcutaneous ECV304 xenografts in mice showed various vessel types, including angiogenic vessels, tumour cell-related vessels and extracellular matrix networks. A tracer experiment demonstrated perfusion of beads in these structures. ECV304 cells, cultured on collagen I gels, formed tube networks with expressions of several endothelial-related markers. In coculture models of ECV304 cells and human umbilical vein endothelial cells, the two cells collaborated to form sprouts or networks.

CONCLUSION

ECV304 cells possess an endothelial character which confers the ability to mimic and collaborate with vascular endothelial cells and facilitates the acquisition of tumour microcirculation.

Inhibition of human androgen-independent PC-3 and DU-145 prostate cancers by antagonists of bombesin and growth hormone releasing hormone is linked to PKC, MAPK and c-jun intracellular signalling

Bombesin/gastrin-releasing peptide (BN/GRP) antagonists RC-3940-II and RC-3940-Et, and growth hormone-releasing hormone (GHRH) antagonists MZ-J-7-118 and RC-J-29-18 inhibit the growth of human androgen-independent PC-3 and DU-145 prostate cancers in nude mice. Additive inhibitory effects were observed after treatment with both classes of analogs. In the present study, we investigated the effects of these antagonists on intracellular signalling pathways of protein kinase C (PKC), mitogen activated protein kinases (MAPK) and c-fos and c-jun oncogenes that are involved in tumour cell proliferation. In PC-3 tumours, antagonists of BN/GRP and GHRH decreased significantly the expression of PKC isoforms alpha (alpha), eta (eta) and zeta (zeta) and increased that of delta (delta) PKC protein. MAPK was not detectable. In DU-145 tumours, which constitutively express MAPK, all treatments strongly decreased the levels of p42/44 MAPK. Treatment with the antagonists tended to reduce m-RNA for c-jun in both tumour models. In proliferation assays in vitro, inhibitors of PKC and MAPK diminished growth of DU-145 and PC-3 cells. These findings suggest that antagonists of BN/GRP and GHRH inhibit the growth of androgen-independent prostate cancer by affecting intracellular signalling mechanisms of PKC, MAPK and c-jun.

Apoptosis of human carcinoma cells in the presence of inhibitors of glycosphingolipid biosynthesis: I. Treatment of Colo-205 and SKBR3 cells with isomers of PDMP and PPMP

Apoptosis, or programmed cell death, plays an important role in many physiological and diseased conditions. Induction of apoptosis in cancer cells by anti-cancer drugs and biosynthetic inhibitors of cells surface glycolipids in the human colon carcinoma cells (Colo-205) are of interest in recent years. In our present studies, we have employed different stereoisomers of PPMP and PDMP (inhibit GlcT-glycosyltransferase (GlcT-GLT)) to initiate apoptosis in Colo-205 cells grown in culture in the presence of (3)H-TdR and (3)H/or (14)C-L-Serine. Our analysis showed that the above reagents (between 1 to 20 microM) initiated apoptosis with induction of Caspase-3 activities and phenotypic morphological changes in a dose-dependent manner. We have observed an increase of radioactive ceramide formation in the presence of a low concentration (1-4 microM) of these reagents in these cell lines. However, high concentrations (4-20 microM) inhibited incorporation of radioactive serine in the higher glycolipids. Colo-205 cells were treated with L-threo-PPMP (0-20 microM) and activities of different GSL: GLTs were estimated in total Golgi-pellets. The cells contained high activity of GalT-4 (UDP-Gal: LcOse3Cer beta 1-4galactosyltransferase), whereas negligible activity of GalT-3 (UDP-Gal: GM2 beta 1-3galactosyltransferase) or GM2-synthase activity of the ganglioside pathway was detected. Previously, GLTs involved in the biosynthetic pathway of SA-Le(x) formation had been detected in these colon carcinoma (or Colo-205) cells (Basu M et al. Glycobiology 1, 527-35 (1991)). However, during progression of apoptosis in Colo-205 cells with increasing concentrations of L-PPMP, the GalT-4 activity was decreased significantly. These changes in the specific activity of GalT-4 in the total Golgi-membranes could be the resultant of decreased gene expression of the enzyme.

Can we prevent prostate cancer? Rationale and current status of prostate cancer chemoprevention

Prostate cancer has been one of the most frequent cancers among men in Western countries for the past decade. Investigation of prostate cancer prevention is very attractive, because prostate cancer has a high incidence, long-term natural history, regional difference in incidence, and is effected by sex steroids. Chemoprevention is defined as the use of specific agents to suppress or reverse carcinogenesis and to prevent the development of cancer. The development of chemoprevention strategies against prostate cancer would be of medical and economic importance. Basic and clinical research of chemoprevention of prostate cancer are under active investigation. This article aims to summarize and review the basic evidence and clinical trials on prostate cancer chemoprevention. Recent research has demonstrated that many agents, such as agents altering sex steroid signaling, drugs inducing antiproliferation/differentiation, retinoids, anti-inflammatory drugs, and antioxidants, could be potential preventatives for prostate cancer. Large-scale clinical trials have suggested that 5alpha-reductase inhibitor finasteride, selenium, and vitamin E can function as a chemopreventive agent. Although no definitely effective strategies of prostate cancer prevention have been identified yet, increasing evidence will provide effective and safe strategies that bring clinical benefits.

Genistein inhibits p38 map kinase activation, matrix metalloproteinase type 2, and cell invasion in human prostate epithelial cells

Epidemiologic studies associate consumption of genistein, in the form of dietary soy, with lower rates of metastatic prostate cancer. We have previously shown that genistein inhibits prostate cancer cell detachment in vitro, that it is well tolerated in an older cohort of men with prostate cancer, and that it alters cell signaling in that same cohort. We have also shown that p38 mitogen-activated protein kinase (MAPK) is necessary for transforming growth factor beta (TGF-beta)-mediated increases in prostate cancer adhesion. Although cell invasion is closely linked to metastatic behavior, little is known about how this process is regulated in prostate cancer or what effect, if any, genistein has on associated processes. We now show that genistein inhibits matrix metalloproteinase type 2 (MMP-2) activity in six of seven prostate cell lines tested, blocks MMP-2 induction by TGF-beta, and inhibits cell invasion. Efficacy was seen at low nanomolar concentrations, corresponding to blood concentrations of free genistein attained after dietary consumption. Inhibition of p38 MAPK by either SB203580 or dominant-negative construct blocked induction of MMP-2 and cell invasion by TGF-beta. Genistein exerted similar effects and was found to block activation of p38 MAPK by TGF-beta. This study shows that p38 MAPK is necessary for TGF-beta-mediated induction of MMP-2 and cell invasion in prostate cancer and that genistein blocks activation of p38 MAPK, thereby inhibiting processes closely linked to metastasis, and does so at concentrations associated with dietary consumption. Any potential causal link to epidemiologic findings will require further investigation.

Multifactorial activities of nonsteroidal antiestrogens against leukemia

The antileukemic activity of nonsteroidal antiestrogens was investigated. Tamoxifen, clomiphene and nafoxidine caused a decrease in viability of the estrogen receptor-negative T-lymphoblastic leukemia cell line CCRF/CEM, nafoxidine being the most active. A combination of clomiphene and genistein resulted in a synergistic cytotoxic effect when applied to Molt-3, another T-lymphblastic leukemic cell line. The antiestrogens arrested the cells at G(0)/G(1) phase and induced apoptosis. Using the CCRF/VCR(1000) cell line, which is resistant to vincristine, it was observed that the effect of nafoxidine on modulating drug resistance was manifested at a lower concentration than that causing a direct cytotoxic effect. Nafoxidine inhibited the Pgp pump activity as measured by rhodamine 123 efflux. Combination with verapamil was found to be more effective in abrogating the pump activity. This study points to the multifactorial activities of nonsteroidal antiestrogens against lymphoblastic leukemia and implies their potential use in clinical treatment as antileukemic drugs.

Effect of anti-estrogens on the androgen receptor activity and cell proliferation in prostate cancer cells

Although some anti-estrogens have been reported to inhibit the proliferation of prostate cancer cells, few studies on the mechanism by which they suppress the growth of prostate cancer have been reported. We investigated, for the first time, whether anti-estrogens modulate the transactivation activity of the androgen receptor (AR) in prostate cancer cells. In DU-145 cells transfected with AR, the transactivation activity of AR was inhibited by tamoxifen and toremifene, even in the presence of 10 nM of DHT. On the other hand, in LNCaP cells having an endogenous AR mutation at codon 877, the activity of AR was suppressed by faslodex in the presence of 10 nM DHT, whereas it was not inhibited by tamoxifen nor toremifene. In PC-3 cells, both the cell growth and the AR activity were remarkably inhibited by tamoxifen at 50 microM. Faslodex and toremifene inhibited AR activity to some extent, but they seemed to function as agonists at higher concentrations. In PC-3 cells, the inhibition of cell growth by flutamide, faslodex and toremifene was much less than their suppression of AR activity. We also demonstrated that a synthetic estrogen diethylstilbestrol and progesterone-related drugs such as chlormadinone acetate and allylestrenol dose-dependently inhibited the activity of AR in DU-145 and PC-3 cells. These results highlight the anti-androgenic aspect of anti-estrogens and estrogens in regard to the AR-mediated transcription of the relevant genes in prostate cancer.

Silencing expression of the clusterin/apolipoprotein j gene in human cancer cells using small interfering RNA induces spontaneous apoptosis, reduced growth ability, and cell sensitization to genotoxic and oxidative stress

Clusterin/Apolipoprotein J (CLU) is a heterodimeric ubiquitously expressed secreted glycoprotein that is implicated in several physiological processes and is differentially expressed in many severe physiological disturbances, including tumor formation and in vivo cancer progression. Despite extensive efforts, clarification of CLU's biological role has been exceptionally difficult and its precise function remains elusive. Short RNA duplexes, referred to as small interfering RNAs (siRNAs), provide a new approach for the elucidation of gene function in human cells. Here, we describe siRNA-mediated CLU gene silencing in osteosarcoma and prostate human cancer cells and illustrate that CLU mRNA is amenable to siRNA-mediated degradation. Our data demonstrate that CLU knockdown in human cancer cells induces significant reduction of cellular growth and higher rates of spontaneous endogenous apoptosis. Moreover, CLU knockdown cancer cells were significantly sensitized to both genotoxic and oxidative stress induced by chemotherapeutic drugs and H(2)O(2), respectively. These effects were more pronounced in cell lines that express high endogenous steady-state levels of the CLU protein and occur through hyperactivation of the cellular apoptotic machinery. Overall, our results reveal that, in the distinct cellular contexts of the osteosarcoma and prostate cancer cells assayed, CLU is a central molecule in cell homeostasis that exerts a cytoprotective function. The described CLU-specific siRNA oligonucleotides that can potently silence CLU gene expression may thus prove valuable agents during antitumor therapy or at other pathological conditions where CLU has been implicated.

p38 MAP kinase modulates Smad-dependent changes in human prostate cell adhesion

Transforming growth factor beta (TGFbeta) regulates cell adhesion, proliferation, and differentiation in a variety of cells. Smad proteins are receptor-activated transcription factors that translocate to the nucleus in response to TGFbeta. We demonstrate here that TGFbeta increases cell adhesion in metastatic PC3-M prostate cancer cells. TGFbeta treatment of PC3-M cells leads to nuclear translocation of R-Smad proteins. We show that Smad proteins are necessary, but not sufficient, for TGFbeta-mediated cell adhesion. After showing that TGFbeta upregulated p38 MAP kinase activity in PC3-M cells, we show that inhibition of p38 MAP kinase partially blocked TGFbeta-mediated increase in cell adhesion, as well as nuclear translocation of Smad3. Finally, we show that Smad3 is phosphorylated by p38 MAP kinase in vitro. These findings implicate crosstalk between the MAP kinase and Smad signaling pathways in TGFbeta's regulation of cell adhesion in human prostate cells. This represents a mechanism by which the pleiotropic effects of TGFbeta may be channeled to modulate cell adhesion.

Antiestrogens and selective estrogen receptor modulators reduce prostate cancer risk

The development of chemoprevention strategies against prostate cancer would have the greatest overall impact both medically and economically against prostate cancer. Estrogens are required for prostate carcinogenesis. Estrogenic stimulation through estrogen receptor alpha in a milieu of decreasing androgens contributes significantly to the genesis of benign prostatic hyperplasia, prostate dysplasia, and prostate cancer. The ability of antiestrogens and selective estrogen receptor modulators (SERMs) to delay and to suppress prostate carcinogenesis is supported by preclinical, clinical, and epidemiological studies. SERMs have many features that make them attractive candidates for prostate cancer chemoprevention including their favorable safety profile and efficacy in preclinical prostate cancer models. The true clinical benefits of SERMs for chemoprevention to prevent prostate cancer, however, should continue to be investigated through human clinical trials. A phase IIb/III human clinical trial is currently evaluating safety and efficacy of toremifene, a SERM, in men who have high-grade prostatic intraepithelial neoplasia.

Effect of treatment sequence with radiotherapy and the antiestrogen EM 800 on the growth of ZR 75 1 human mammary carcinoma in nude mice

We demonstrated previously that continuous administration of EM-800, a SERM having pure antiestrogenic activity in the mammary gland and endometrium in combination with monthly radiotherapy caused a greater inhibition of human ZR 75 1 tumor growth in nude mice than either therapy used alone. To further optimize therapy, we have now examined the effect of various treatment sequences to determine the optimal treatment regimen in the same model. EM 800 was given at the maximally effective oral dose of 300 microg daily. External beam radiation therapy (RTX) was carried out (2 Gy/tumor/day, 5 days per week for 3 weeks) for a total of 30 Gy/tumor delivered directly to the tumor while shielding the rest of the animal body. There was no evidence of RTX-related morbidity. Continuous treatment with EM 800 was initiated either 3 weeks before or at the same time as RTX, immediately after RTX, or 3 weeks before and immediately after RTX. After 156 days of treatment, EM 800 alone caused a 75% decrease in average tumor area, an effect equivalent to that achieved by ovariectomy. RTX alone, on the other hand, caused a transient 30% decrease in tumor area regardless of treatment sequence, whereas combined treatment with EM 800 and RTX was superior to either treatment alone. Combined treatment with EM 800 and RTX both started on Day 1 caused the greatest (88%), most rapid (50% in 2 weeks) and sustained decrease in tumor size. The present data indicate that optimal reduction in breast tumor size is achieved by continuous administration of EM 800 and RTX started simultaneously on Day 1.

Prostate cancer chemoprevention agents exhibit selective activity against early stage prostate cancer cells

Preclinical models for the identification of prostate cancer chemoprevention agents are lacking. Based upon the notion that clinically useful chemoprevention agents should exhibit selective activity against early stage disease, studies were undertaken to assess whether chemoprevention agents selectively inhibited the growth of early stage prostate cancer, as compared to late stage cancer. First, a series of cell and molecular studies were performed, which, when taken together, validated the use of a panel of prostate cell lines as a model of the different stages of carcinogenesis. Next, therapeutic responsiveness to ten different cytotoxic or chemoprevention agents was evaluated. Chemoprevention agents exhibited selective activity against normal and early transformed prostate tissue, whereas cytotoxic agents were non-specific. Selective activity against early versus advanced prostate cancer cells is identified as a potential screening method for chemoprevention agents.Prostate Cancer and Prostatic Diseases (2001) 4, 81-91

Resveratrol induces apoptosis in LNCaP cells and requires hydroxyl groups to decrease viability in LNCaP and DU 145 cells

BACKGROUND

This study was conducted to determine the effects of resveratrol on prostate cancer cell viability through apoptosis induction and the significance of the three hydroxyl groups on resveratrol to the measured effect.

METHODS

Hormone-sensitive LNCaP cells and hormone-insensitive DU 145 cells were treated with resveratrol, tri-methoxy-resveratrol, or diethylstilbestrol (DES; the positive control for toxicity and apoptosis). Cell viability was determined by using an MTS assay. Apoptosis was determined by the appearance of apoptotic morphology, annexin V-FITC-positive intact cells, and caspase activation.

RESULTS

Resveratrol and DES decreased viability in LNCaP cells, but only resveratrol-treated cells expressed apoptotic morphology, annexin V-FITC-positive cells, and caspase activation. Tri-methoxy-resveratrol had no effect on DU 145 cell-viability and was less toxic to LNCaP cells than resveratrol.

CONCLUSION

Resveratrol was toxic to cells regardless of whether the cells were hormone-responsive or -unresponsive. This finding suggests that the cell's hormone responsive status is not an important determinant of the response to resveratrol. Furthermore, the hydroxyl-groups on resveratrol are required for cell toxicity. Finally resveratrol but not DES induced caspase-mediated apoptosis.

Selective estrogen receptor modulators for the chemoprevention of prostate cancer

The ability to interfere with prostate carcinogenesis, and as a consequence, prevent prostate cancer with drugs is the basis for chemoprevention. The prostate contains estrogen receptors in both the stroma and epithelium. Both animal models and human epidemiologic studies have implicated estrogens as an initiator of prostate cancer. In the aging male, prostate cancer occurs in an environment of rising estrogen and decreasing androgen levels. Selective estrogen receptor modulators (SERMs) have shown the ability to prevent (GTx-006 [acapodene]) and treat (GTx-006 and arzoxifene) prostate cancer, suggesting that they may be used in prostate cancer chemoprevention. A phase 2 clinical trial using GTx-006 for prostate cancer chemoprevention is currently being conducted.

Improved intracellular delivery of oligonucleotides by square wave electroporation

Prior studies have shown that electroporation is a simple and effective method for the introduction of oligonucleotides (ODN) into cells. In ex vivo bone marrow purging models, electroporation of ODN into cells has been associated with selective killing of human neoplastic cells while sparing hematopoietic stem cells. Prior studies used conventional electroporation methods (i.e., exponential decay) to introduce ODN into cells. Square wave electroporation allows the delivery of a more defined and regulated electrical pulse and is associated with high transfection efficiencies in a variety of systems. The current study was undertaken to determine whether square wave electroporation was more effective than exponential decay electroporation for the delivery of ODN into hematopoietic cells. Using fluorescein-tagged ODN and K562, chronic myelogenous leukemia (CML) cells, higher transfection rates were observed after square wave electroporation. In addition, c-myc antisense ODN were more effective in reducing c-myc protein when introduced by square wave electroporation, as compared with introduction by exponential decay electroporation. Square wave electroporation is thus identified as the optimal method for delivering ODN into hematopoietic cells.

Low-dose genistein induces cyclin-dependent kinase inhibitors and G(1) cell-cycle arrest in human prostate cancer cells

Genistein, a naturally occurring isoflavone found chiefly in soy products, reportedly has antiprostate cancer effects, but the mechanisms underlying these effects are unknown. We studied the antiproliferative and apoptosis-inducing effects of genistein in the androgen-sensitive human prostate cancer cell line LNCaP. Viable cell number was assessed by the 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay; cell-cycle progression and apoptosis were evaluated by flow cytometry; apoptosis was also assessed by a histone enzyme-linked immunosorbent assay; and the expression of several cell-cycle- and apoptosis-related genes and their gene products was determined by northern blot analysis, western blot analysis, and/or assays based on polymerase chain reaction. Physiologic concentrations of genistein (< or = 20 microM) decreased LNCaP viable cell number in a dose-dependent manner, induced a G(1) cell-cycle block, decreased prostate-specific antigen mRNA expression, and increased p27(KIP1) and p21(WAF1) (mRNA and protein) but had no effect on apoptosis or the mRNA expression of the apoptosis- and cell-cycle-related markers bcl-2, bax, Rb, and proliferating cell nuclear antigen. Higher concentrations of genistein (> 20 microM) did induce apoptosis. We conclude that genistein (at physiologic concentrations) exerts potent antiproliferative effects on LNCaP cells by inducing a G(1) cell-cycle block. The antiproliferative effects of genistein may be mediated by increased levels of p27(KIP1) and p21(WAF1), which are negative cell-cycle regulators that act as cyclin-dependent kinase inhibitors and that have been recently linked with prostate carcinogenesis. These findings may provide insights into the mechanisms underlying the apparent antiprostate cancer effects of soy consumption observed in epidemiologic studies.

Induction of p21WAF1 expression via Sp1-binding sites by tamoxifen in estrogen receptor-negative lung cancer cells

Although originally synthesized as an anti-estrogen, tamoxifen (Tam) was found to be able to inhibit proliferation of estrogen receptor (ER)-negative cancer cells in vitro. However, the molecular basis of such ER-independent growth inhibition is largely unknown. We have previously demonstrated that Tam induces p21WAF1 and p27KIP1 expression in human lung cancer cells which lack ER-alpha and -beta. We found that Tam induced p21WAF1 expression via transcriptional activation. In order to determine the molecular mechanism responsible for p21WAF1 induction by Tam, we performed a deletion analysis on the p21WAF1 promoter. The minimal region in the p21WAF1 promoter required for Tam-activated induction was mapped to a contiguous stretch of 10 bp located 83 bases upstream of the transcription initiation site. Our results showed that transcription factor Sp1 and Sp3 bound to this GC-rich region and mutation of Sp1-binding sites dramatically attenuated Tam-induced p21WAF1 promoter activity. We also tried to elucidate the signaling pathway that mediated the activation of p21WAF1 by Tam. Inhibition of mitogen-activated protein kinase pathways did not block Tam-induced p21WAF1. Similarly, protein kinase C inhibitor calphostin C could not suppress Tam-induced p21WAF1. Conversely, pretreatment of a specific protein kinase A inhibitor H89 significantly attenuated the induction of p21WAF1 by Tam. Furthermore, PKA activators forskolin and dibutyryl-cAMP activated p21WAFI promoter activity and increased p21wAF1 protein level in lung cancer cells. Taken together, these results demonstrate that Tam activates the p21WAF1 promoter via Sp1-binding sites and suggest that PKA may be involved in the induction of p21wAF1 by Tam in ER-negative lung cancer cells.

Mechanical strain-induced Ca(2+) waves are propagated via ATP release and purinergic receptor activation

Mechanical strain applied to prostate cancer cells induced an intracellular Ca(2+) (Ca(i)(2+)) wave spreading with a velocity of 15 microm/s. Ca(i)(2+) waves were not dependent on extracellular Ca(2+) and membrane potential because propagation was unaffected in high-K(+) and Ca(2+)-free solution. Waves did not depend on the cytoskeleton or gap junctions because cytochalasin B and nocodazole, which disrupt microfilaments and microtubules, respectively, and 1-heptanol, which uncouples gap junctions, were without effects. Fluorescence recovery after photobleaching experiments revealed an absence of gap junctional coupling. Ca(i)(2+) waves were inhibited by the purinergic receptor antagonists basilen blue and suramin; by pretreatment with ATP, UTP, ADP, UDP, 2-methylthio-ATP, and benzoylbenzoyl-ATP; after depletion of ATP by 2-deoxyglucose; and after ATP scavenging by apyrase. Waves were abolished by the anion channel inhibitors 5-nitro-2-(3-phenylpropylamino)benzoic acid, tamoxifen, 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid, niflumic acid, and gadolinium. ATP release following strain was significantly inhibited by anion channel blockers. Hence, ATP is secreted via mechanosensitive anion channels and activates purinergic receptors on the same cell or neighboring cells in an autocrine and paracrine manner, thus leading to Ca(i)(2+) wave propagation.

Antiestrogens--tamoxifen, SERMs and beyond

Estrogens play a central role in reproductive physiology. The cellular effects of estrogens are mediated by binding to nuclear receptors (ER) which activate transcription of genes involved in cellular growth control. At least two such receptors, designated ERalpha and ERbeta, mediate these effects in conjunction with a number of coactivators. These receptors can directly interact with other members of the steroid receptor superfamily. A complex cross-talk exists between the estrogen-signaling pathways and the downstream signaling events initiated by growth factors, such as epidermal growth factor and insulin-like growth factors. Estrogens are also a causative factor in the pathogenesis of a variety of neoplastic and non-neoplastic diseases, including breast cancer, endometrial cancer, endometriosis, and uterine fibroids, among others. Antiestrogens, such as tamoxifen, are widely used for the treatment of breast cancer. Tamoxifen produces objective tumor shrinkage in advanced breast cancer, reduces the risk of relapse in women treated for invasive breast cancer, and prevents breast cancer in high-risk women. Although, initially developed as an antiestrogen, tamoxifen can also prevent postmenopausal osteoporosis as well as reduce cholesterol, due to its estrogen-agonist effects. Its estrogen-agonist activity, however, can lead to significant side-effects such as endometrial cancer and thromboembolic phenomena. This has led to the concept of "ideal" selective estrogen receptor modulators (SERMs), drugs that would have the desired, tissue selective, estrogen-agonist or -antagonist effects. Raloxifene is a SERM which has the desirable mixed agonist/antagonist effects of tamoxifen but does not cause uterine stimulation. "Pure" antiestrogens may provide very potent estrogen-antagonist drugs, but are likely to be devoid of beneficial effects on bone and lipids. Future drug development efforts should focus on developing superior SERMs that have a greater efficacy against ER-positive tumors and do not cause hot flashes or thromboembolism, and explore combination strategies to simultaneously target hormone-dependent as well as hormone-independent breast cancer.

Ziskind-Somerfeld Research Award. Protein kinase C signaling in the brain: molecular transduction of mood stabilization in the treatment of manic-depressive illness

Understanding the biology of the pharmacological stabilization of mood will undoubtedly serve to provide significant insight into the pathophysiology of manic-depressive illness (MDI). Accumulating evidence from our laboratories and those of other researchers has identified the family of protein kinase C isozymes as a shared target in the brain for the long-term action of both lithium and valproate. In rats chronically treated with lithium, there is a reduction in the hippocampus of the expression of two protein kinase isozymes, alpha and epsilon, as well as a reduction in the expression of a major PKC substrate, MARCKS, which has been implicated in long-term neuroplastic events in the developing and adult brain. In addition, we have been investigating the down-stream impact of these mood stabilizers on another kinase system, GSK-3 beta and on the AP-1 family of transcription factors. Further studies have generated promising preliminary data in support of the antimanic action of tamoxifen, and antiestrogen that is also a PKC inhibitor. Future studies must address the therapeutic relevance of these protein targets in the brain using innovative strategies in both animal and clinical investigations to ultimately create opportunities for the discovery of the next generations of mood stabilizers for the treatment of MDI.

Tamoxifen induces p21WAF1 and p27KIP1 expression in estrogen receptor-negative lung cancer cells

Tamoxifen (Tam), besides its action as an anti-estrogen, also inhibits cell proliferation of estrogen receptor (ER)-negative cancer cells by an unknown mechanism. In this study, we used ER-negative lung cancer cells to clarify such ER-independent inhibitory effect of Tam. We found that Tam induced G1 growth arrest in these cells. However, our results indicated that the expression of G1 cyclins (including D1, 2, 3 and E) was not regulated by Tam in these lung cancer cells. Additionally, the protein levels of G1 acting cyclin-dependent kinases (CDKs), CDK2, 4 and 6, was unaltered in Tam-treated lung cancer cells with the exception of CDK2 expression in H322 cells which was attenuated by Tam in a cell line-specific manner. We next examined the effect of Tam on the expression of cyclin-dependent kinase inhibitors (CDKIs) and our results demonstrated that the expression of p21WAF1 and p27KIP1, but not p57KIP2, was strongly activated by Tam in these cells. The amounts of p21WAF1 and p27KIP1 co-immunoprecipitated with cyclin E were obviously increased after Tam treatment and reduced activity of cyclin E-associated kinases and accumulation of hypo-phosphorylated retinoblastoma (Rb) protein were clearly detected in Tam-incubated cells. No consentaneous induction of CDKIs was found when ER-negative lung cancer cells were incubated with cytotoxic drugs, cisplatin and etoposide, this indicates that enhancement of CDKI expression is not a non-specific effect of Tam. We also found that Tam may up-regulate p21WAF1 expression via transcription activation. Considered together, these results suggest that Tam-induced growth inhibition in ER-negative lung cancer cells is associated with induction of p21WAF1 and p27KIP1.