Inhibition of prostate carcinogenesis in probasin/SV40 T antigen transgenic rats by raloxifene, an antiestrogen with anti-androgen action, but not nimesulide, a selective cyclooxygenase-2 inhibitor

Oral administration of E-type prostanoid (EP) 1 receptor antagonist suppresses carcinogenesis and development of prostate cancer via upregulation of apoptosis in an animal model

Prostaglandin E2 plays an important role in carcinogenesis and malignant potential of prostate cancer (PC) cells by binding to its specific receptors, E-type prostanoid (EP) receptors. However, anti-carcinogenic effects of the EP receptor antagonist are unclear. In this study, we used a mouse model of PC. The mice were provided standard feed (control) or feed containing the EP1 receptor antagonist and were sacrificed at 10, 15, 30, and 52 weeks of age. Apoptosis was evaluated by immunohistochemical analysis using a cleaved caspase-3 assay. The incidence of cancer in the experimental group was significantly lower than that in the control group at 15, 30, and 52 weeks of age. The percentage of poorly differentiated PC cells was significantly lower in the experimental group than in the control group at 30 and 52 weeks of age. The percentage of apoptotic cells in the experimental group was significantly higher than that in the control group at 15, 30, and 52 weeks of age. These findings indicate that feeding with the addition of EP1 receptor antagonist delayed PC progression via the upregulation of apoptosis. We suggest that the EP1 receptor antagonist may be a novel chemopreventive agent for PC.

Responsiveness of Brca1 and Trp53 Deficiency-Induced Mammary Preneoplasia to Selective Estrogen Modulators versus an Aromatase Inhibitor in Mus musculus

An intervention study initiated at age 4 months compared the impact of tamoxifen (25 mg), raloxifene (22.5 mg), and letrozole (2.5 mg) administered by 60-day release subcutaneous pellet on mammary preneoplasia prevalence at age 6 months in conditional genetically engineered mouse models with different Breast cancer 1 (Brca1) gene dosages targeted to mammary epithelial cells and germline Tumor protein P53 (Trp53) haploinsufficiency (10-16/cohort). The proportion of unexposed control mice demonstrating mammary preneoplasia at age 6 months was highest in Brca1^{fl11/fl11/Cre/p53-/+} (54%) mice followed by Brca1^{WT/fl11/Cre/p53-/+} mice (30%). By age 12 months, invasive mammary cancers appeared in 80% of Brca1^{fl11/fl11/Cre/p53-/+} and 42% of Brca1^{WT/fl11/Cre/p53-/+} control unexposed mice. The spectrum of cancer histology was similar in both models without somatic mutation of the nongenetically engineered Brca1, Trp53, Brca2, or Death-associated protein kinase 3 (Dapk3) alleles. Two-month exposure to tamoxifen, raloxifene, and letrozole significantly reduced estrogen-mediated tertiary branching by 65%, 71%, and 78%, respectively, in Brca1^{fl11/fl11/Cre/p53-/+} mice at age 6 months. However, only letrozole significantly reduced hyperplastic alveolar nodules (HAN) prevalence (by 52%) and number (by 30%) and invasive cancer appeared despite tamoxifen exposure. In contrast, tamoxifen significantly reduced HAN number by 95% in Brca1^{WT/fl11/Cre/p53-/+} mice. Control mice with varying combinations of the different genetically modified alleles and MMTV-Cre transgene demonstrated that the combination of Brca1 insufficiency and Trp53 haploinsufficiency was required for appearance of preneoplasia and no individual genetic alteration confounded the response to tamoxifen. In summary, although specific antihormonal approaches showed effectiveness, with Brca1 gene dosage implicated as a possible modifying variable, more effective chemopreventive approaches for Brca1 mutation-induced cancer may require alternative and/or additional agents. Cancer Prev Res; 10(4); 244-54. ©2017 AACR.

Modulators of estrogen receptor inhibit proliferation and migration of prostate cancer cells

In the initial stages, human prostate cancer (PC) is an androgen-sensitive disease, which can be pharmacologically controlled by androgen blockade. This therapy often induces selection of androgen-independent PC cells with increased invasiveness. We recently demonstrated, both in cells and mice, that a testosterone metabolite locally synthetized in prostate, the 5α-androstane-3β, 17β-diol (3β-Adiol), inhibits PC cell proliferation, migration and invasion, acting as an anti-proliferative/anti-metastatic agent. 3β-Adiol is unable to bind androgen receptor (AR), but exerts its protection against PC by specifically interacting with estrogen receptor beta (ERβ). Because of its potential retro-conversion to androgenic steroids, 3β-Adiol cannot be used "in vivo", thus, the aims of this study were to investigate the capability of four ligands of ERβ (raloxifen, tamoxifen, genistein and curcumin) to counteract PC progression by mimicking the 3β-Adiol activity. Our results demonstrated that raloxifen, tamoxifen, genistein and curcumin decreased DU145 and PC3 cell proliferation in a dose-dependent manner; in addition, all four compounds significantly decreased the detachment of cells seeded on laminin or fibronectin. Moreover, raloxifen, tamoxifen, genistein and curcumin-treated DU145 and PC3 cells showed a significant decrease in cell migration. Notably, all these effects were reversed by the anti-estrogen, ICI 182,780, suggesting that their actions are mediated by the estrogenic pathway, via the ERβ, the only isoform present in these PCs. In conclusion, these data demonstrate that by selectively activating the ERβ, raloxifen, tamoxifen, genistein and curcumin inhibit human PC cells proliferation and migration favoring cell adesion. These synthetic and natural modulators of ER action may exert a potent protective activity against the progression of PC even in its androgen-independent status.

Purple corn color inhibition of prostate carcinogenesis by targeting cell growth pathways

Purple corn color is a widely used food colorant that was reported to have attenuating effects on hypertension, diabetes, and to have anti-cancer effects on colon and breast cancer. Our study is the first on its possible chemoprevention effects against prostate cancer. For this purpose an androgen-dependent prostate cancer cell line, LNCaP, was used to examine effects in vitro. Purple corn color inhibited the proliferation of LNCaP cells by decreasing the expression of Cyclin D1 and inhibiting the G1 stage of the cell cycle. Thirty-six male transgenic rats for adenocarcinoma of prostate were fed basic diet or diet with purple corn color for 8 weeks. Purple corn color decreased the incidence of adenocarcinoma in the lateral prostate and slowed down the progression of prostate cancer. A lower Ki67 positive rate, a decrease of the expression of Cyclin D1, and downregulation of the activation of Erk1/2 and p38 MAPK were observed in the group consuming purple corn color in the diet. Since purple corn color is a mixture, determining its active component should help in the understanding and usage of purple corn color for prostate cancer chemoprevention. Therefore, the three major anthocyanins in purple corn color, cyanidin-3-glucoside, pelargonidin-3-glucoside and peonidin-3-glucoside, were tested with LNCaP cells. The results suggested that cyanidin-3-glucoside and pelargonidin-3-glucoside are the active compounds.

Raloxifene induces cell death and inhibits proliferation through multiple signaling pathways in prostate cancer cells expressing different levels of estrogen receptor α and β

Raloxifene (RAL), a selective estrogen receptor (ER) modulator (SERM) seems to induce apoptosis in both androgen-dependent and -independent prostate cell (PC) lines via activation of ERβ and an antagonistic effect on ERα. In this study, we evaluated the effects of RAL on epithelial PC growth using the two following in vitro models: the androgen-dependent cell line EPN which expressed both ERs; and a stabilized epithelial cell line derived from a prostate cancer specimen (CPEC), which expressed low levels of ERβ and lacked ERα. In EPN cells, there was an increase in the pre-G1 apoptotic peak and a reduction in the S phase of the cell cycle with G0/G1 arrest after E2 or RAL treatment; bcl-2 mRNA and Bcl-2 protein levels were significantly reduced, while activated caspase-3 and Par-4 levels increased significantly after either E2 or RAL treatment; in addition, c-myc transcript was inhibited after 10(-6)  M RAL treatment. A dose-dependent increase of metallothionein II gene RNA level was also induced by RAL in EPN. In CPEC, there was only a weak apoptotic peak associated with caspase-3 activation and Par-4 increase after either E2 or RAL treatment; while c-myc transcript level increased. RAL induced a rapid but transient phosphorylation of ERK 1/2 in EPN cells but generated a sustained effect in CPEC. These findings suggest that RAL effects on PC growth control in vitro are cell-specific, depending on ERβ or ERβ/ERα relative expression levels. Moreover, this study demonstrated that RAL affected both transcriptional regulation and non-genomic signals, which resulted in the modulation of multiple signaling pathways of apoptosis and of cell cycle progression.

Genistein and resveratrol, alone and in combination, suppress prostate cancer in SV-40 tag rats

BACKGROUND

Chemoprevention utilizing dietary agents is an effective means to slow the development of prostate cancer. We evaluated the potential additive and synergistic effects of genistein and resveratrol for suppressing prostate cancer in the Simian Virus-40 T-antigen (SV-40 Tag) targeted probasin promoter rat model, a transgenic model of spontaneously developing prostate cancer.

METHODS

Rats were fed genistein or resveratrol (250 mg/kg AIN-76A diet) alone and in combination, and a low-dose combination (83 mg genistein + 83 mg resveratrol/kg diet). Histopathology and mechanisms of action studies were conducted at 30 and 12 weeks of age, respectively.

RESULTS

Genistein, resveratrol, and the high-dose combination treatments suppressed prostate cancer. The low-dose combination did not elicit protection against prostate cancer and was most likely below the effective dose for causing significant histopathological changes. Total genistein and resveratrol concentrations in the blood reached 2,160 and 211 nM, respectively in rats exposed to the single treatments. Polyphenol treatments decreased cell proliferation and insulin-like growth factor-1 (IGF-1) protein expression in the prostate. In addition, genistein as a single agent induced apoptosis and decreased steroid receptor coactivator-3 (SRC-3) in the ventral prostate (VP).

CONCLUSIONS

Genistein and resveratrol, alone and in combination, suppress prostate cancer development in the SV-40 Tag model. Regulation of SRC-3 and growth factor signaling proteins are consistent with these nutritional polyphenols reducing cell proliferation and increasing apoptosis in the prostate.

Characterization of SV-40 Tag rats as a model to study prostate cancer

Background

Prostate cancer is the second most frequently diagnosed cancer in men. Animal models that closely mimic clinical disease in humans are invaluable tools in the fight against prostate cancer. Recently, a Simian Virus-40 T-antigen (SV-40 Tag) targeted probasin promoter rat model was developed. This model, however, has not been extensively characterized; hence we have investigated the ontogeny of prostate cancer and determined the role of sex steroid receptor and insulin-like growth factor-1 (IGF-1) signaling proteins in the novel SV-40 Tag rat.

Methods

The SV-40 Tag rat was histopathologically characterized for time to tumor development, incidence and multiplicity and in the ventral, dorsal, lateral and anterior lobes of the prostate. Immunoassay techniques were employed to measure cell proliferation, apoptosis, and sex steroid receptor and growth factor signaling-related proteins. Steroid hormone concentrations were measured via coated well enzyme linked immunosorbent assay (ELISA) kits.

Results

Prostatic intraepithelial neoplasia (PIN) and well-differentiated prostate cancer developed as early as 2 and 10 weeks of age, respectively in the ventral prostate (VP) followed by in the dorsolateral (DLP). At 8 weeks of age, testosterone and dihydrotestosterone (DHT) concentrations in SV-40 Tag rats were increased when compared to non-transgenic rats. High cell proliferation and apoptotic indices were found in VP and DLP of transgenic rats. Furthermore, we observed increased protein expression of androgen receptor, IGF-1, IGF-1 receptor, and extracellular signal-regulated kinases in the prostates of SV-40 Tag rats.

Conclusion

The rapid development of PIN and prostate cancer in conjunction with the large prostate size makes the SV-40 Tag rat a useful model for studying prostate cancer. This study provides evidence of the role of sex steroid and growth factor proteins in prostate cancer development and defines appropriate windows of opportunity for preclinical trials and aids in the rational design of chemoprevention, intervention, regression, and therapeutic studies using prostate cancer rodent models.

Effect of raloxifene on cerebral vasospasm following experimental subarachnoid hemorrhage in rats

The effect of raloxifene on cerebral vasospasm following experimental subarachnoid hemorrhage (SAH) was investigated in a rat model. Seven groups of seven rats underwent no SAH, no treatment; SAH only; SAH plus vehicle; SAH plus 3 days intraperitoneal raloxifene treatment; SAH plus 4 days intraperitoneal raloxifene treatment; SAH plus 3 days intrathecal raloxifene treatment; and SAH plus 4 days intrathecal raloxifene treatment. The basilar artery cross-sectional areas were measured at 72 or 96 hours following SAH. The results showed raloxifene decreased SAH-induced cerebral vasospasm in all treatment groups, and suggested no difference between intraperitoneal and intrathecal application, or between 3 days and 4 days of raloxifene treatment. The present study demonstrates that raloxifene is a potential therapeutic agent against cerebral vasospasm after SAH.

Inhibition of SULT2B1b expression alters effects of 3beta-hydroxysteroids on cell proliferation and steroid hormone receptor expression in human LNCaP prostate cancer cells

BACKGROUND

Sulfation is an important steroid inactivation in human tissues. Sulfotransferase (SULT) 2B1b selectively conjugates 3beta-hydroxysteroids and is expressed in epithelial cells of normal and cancerous prostate tissues. Dehydroepiandrosterone (DHEA) and Delta(5)-androstenediol (Delta(5)-Adiol) sulfation prevents their conversion to more potent androgens and estrogens in tissues although both compounds may also be biologically active.

METHODS

SULT2B1b expression and activity were inhibited >85% in human LNCaP prostate adenocarcinoma cells using short interference RNA (siRNA). The effects of treating control and SULT2B1b-deficient LNCaP cells with DHEA, Delta(5)-Adiol, and 5alpha-androstane-3beta-17beta-diol (Anstane-diol) on cellular proliferation, estrogen receptors (ERs), androgen receptor (AR), and prostate specific antigen protein levels were examined.

RESULTS

Physiological concentrations of DHEA and Delta(5)-Adiol increased proliferation of control cells and the proliferative effects were significantly increased in SULT2B1b-siRNA cells. DHEA, but not Delta(5)-Adiol increased AR levels at concentrations >/=1,000 nM in SULT2B1b-siRNA cells but not in control LNCaP cells. ER-alpha levels were not affected with any of the compounds tested. Physiological concentrations of DHEA and Delta(5)-A-diol decreased ER-beta levels in control cells and had significantly greater effects in SULT2B1b-siRNA cells. In contrast, Anstane-diol had no effect on AR or ER-alpha levels but induced more elevation of ER-beta levels in SULT2B1b-siRNA cells at concentrations >/=1,000 nM.

CONCLUSIONS

SULT2B1b is involved in regulating prostate cell responsiveness to DHEA and Delta(5)-Adiol. Inhibition of SULT2B1b increased cell proliferation and ER-beta repression after treatment with physiological levels of DHEA and Delta(5)-Adiol indicating that SULT2B1b has an inhibitory effect on DHEA and Delta(5)-Adiol activity.

Inhibition of androgen-independent prostate cancer by estrogenic compounds is associated with increased expression of immune-related genes

The clinical utility of estrogens for treating prostate cancer (CaP) was established in the 1940s by Huggins. The classic model of the anti-CaP activity of estrogens postulates an indirect mechanism involving the suppression of androgen production. However, clinical and preclinical studies have shown that estrogens exert growth-inhibitory effects on CaP under low-androgen conditions, suggesting additional modes whereby estrogens affect CaP cells and/or the microenvironment. Here we have investigated the activity of 17beta estradiol (E2) against androgen-independent CaP and identified molecular alterations in tumors exposed to E2. E2 treatment inhibited the growth of all four androgen-independent CaP xenografts studied (LuCaP 35V, LuCaP 23.1AI, LuCaP 49, and LuCaP 58) in castrated male mice. The molecular basis of growth suppression was studied by cDNA microarray analysis, which indicated that multiple pathways are altered by E2 treatment. Of particular interest are changes in transcripts encoding proteins that mediate immune responses and regulate androgen receptor signaling. In conclusion, our data show that estrogens have powerful inhibitory effects on CaP in vivo in androgen-depleted environments and suggest novel mechanisms of estrogen-mediated antitumor activity. These results indicate that incorporating estrogens into CaP treatment protocols could enhance therapeutic efficacy even in cases of advanced disease.

Fulvestrant (ICI 182,780) down-regulates androgen receptor expression and diminishes androgenic responses in LNCaP human prostate cancer cells

The androgen receptor (AR) plays a key role in the development and progression of prostate cancer. Targeting the AR for down-regulation would be a useful strategy for treating prostate cancer, especially hormone-refractory or androgen-independent prostate cancer. In the present study, we showed that the antiestrogen fulvestrant [ICI 182,780 (ICI)] effectively suppressed AR expression in several human prostate cancer cells, including androgen-independent cells. In LNCaP cells, ICI (10 micromol/L) treatment decreased AR mRNA expression by 43% after 24 hours and AR protein expression by approximately 50% after 48 hours. We further examined the mechanism of AR down-regulation by ICI in LNCaP cells. ICI did not bind to the T877A-mutant AR present in the LNCaP cells nor did it promote proteasomal degradation of the AR. ICI did not affect AR mRNA or protein half-life. However, ICI decreased the activity of an AR promoter-luciferase reporter plasmid transfected into LNCaP cells, suggesting a direct repression of AR gene transcription. As a result of AR down-regulation by ICI, androgen induction of prostate-specific antigen mRNA and protein expression were substantially attenuated. Importantly, LNCaP cell proliferation was significantly inhibited by ICI treatment. Following 6 days of ICI treatment, a 70% growth inhibition was seen in androgen-stimulated LNCaP cells. These data show that the antiestrogen ICI is a potent AR down-regulator that causes significant inhibition of prostate cancer cell growth. Our study suggests that AR down-regulation by ICI would be an effective strategy for the treatment of all prostate cancer, especially AR-dependent androgen-independent prostate cancer.

2-Methoxyestradiol inhibits prostate tumor development in transgenic adenocarcinoma of mouse prostate: role of tumor necrosis factor-alpha-stimulated gene 6

PURPOSE

2-Methoxyestradiol, an estrogenic metabolite, is in clinical trials for the treatment of hormone-refractory prostate cancer. However, neither the chemopreventive role nor the mechanism of 2-methoxyestradiol-induced biological activities is fully understood.

EXPERIMENTAL DESIGN

Eight- and 24-week-old transgenic adenocarcinoma of mouse prostate (TRAMP) mice were fed a diet containing 50 mg 2-methoxyestradiol/kg body weight for 16 and 8 weeks, respectively. Chemopreventive efficacy was evaluated by magnetic resonance imaging, determining the prostate-seminal vesicle complex volume and histologic analysis of prostate tumor or tissue. Tumor invasion assays were used to show the role of tumor necrosis factor-alpha-stimulated gene (TSG-6), a 2-methoxyestradiol-up-regulated gene identified by DNA array analysis. Expression of TSG-6 was analyzed in a human tissue array containing different grades of prostate tumors.

RESULTS

Dietary administration of 2-methoxyestradiol prevented the development of preneoplastic lesions independent of progression stage. TSG-6 was low or undetectable in prostate cancer cells (LNCaP, PC-3, and DU145) and TRAMP tumors but up-regulated in response to 2-methoxyestradiol. Immunohistochemistry of the human prostate tumor array showed a decrease in TSG-6-positive cells with increasing grade relative to normal prostate (P = 0.0001). Although overexpression of TSG-6 inhibited invasion of androgen-independent cells (P = 0.007), antisense TSG-6 reversed this effect.

CONCLUSIONS

To the best of our knowledge, this is the first report showing the potential of 2-methoxyestradiol as a chemopreventive agent. We have also identified TSG-6 as a potential marker that could be used for early diagnosis and prognosis of cancerous or precancerous lesions.

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.

Raloxifene, an oestrogen-receptor-beta-targeted therapy, inhibits androgen-independent prostate cancer growth: results from preclinical studies and a pilot phase II clinical trial

OBJECTIVES

To determine, in preclinical in vivo animal and in clinical studies, whether raloxifene (a selective oestrogen-receptor (ER) modulator that targets ER-beta and induces apoptosis in vitro in androgen-independent prostate cancer, AIPC cells) affects prostate cell differentiation, proliferation and carcinogenesis, and in the pilot phase II clinical trial, the response rate and duration of patients with AIPC treated with a daily oral dose of raloxifene.

PATIENTS, MATERIALS AND METHODS

Tumour proliferation rate in response to raloxifene treatment, and molecular markers of cell cycle and apoptosis, were evaluated in established ER-beta-positive androgen-dependent (AD) CWR22 and AI CWRSA9 human xenograft prostate cancer models. Twenty-one patients with AIPC and evidence of disease progression were enrolled into the clinical trial and given daily oral raloxifene.

RESULTS

There was significant growth inhibition by raloxifene in the ADPC and AIPC xenograft models (CWR22 68%, P < 0.010; CWRSA9 64%, P < 0.001), with no tumour regression. There was evidence of G1 arrest by increased p27kip1 expression in the raloxifene-treated group. Eighteen patients comprised the efficacy analysis, as three withdrew before the first evaluation. At the first evaluation, five men had stable disease and continued on the study for a median of five cycles. The longest response was 17 cycles. Drug related toxicity was minimal.

CONCLUSION

Raloxifene has activity in xenograft models, slowing disease progression. This translated to possible disease stabilization in patients with AIPC. Further studies are warranted.