Prostate-specific Antigen Protein Levels Research Articles

Abstract 3050: Equol as a radiosensitizer and therapeutic agent in prostate cancer

Abstract The gastrointestinal microbiome and the metabolites it can produce have been linked to response to various cancer treatments, including in prostate cancer. Equol is a microbial metabolite that is exclusively produced by the conversion of soy isoflavones in the diet by specific intestinal bacteria. Interestingly, equol has previously been shown to exhibit anti-androgen effects on prostate cells and likewise may act as a radiosensitizer. We analyzed the microbial composition of fecal samples collected from men receiving stereotactic ablative radiation (SABR) versus observation to treat oligometastatic prostate cancer as part of the ORIOLE trial and found that patients harboring equol-producing bacteria had a lower risk of disease progression. We therefore aimed to study the effect of this compound on prostate cancer cell lines in vitro. MTT assay was used to assess the effects of equol treatment on cell viability in androgen receptor (AR) positive LNCaP cells and AR null PC3 cells over time. We assessed the ability of equol to reduce AR protein levels and/or subcellular localization in LNCaP cells using immunohistochemistry. Finally, western blotting was used to assess the effects of equol treatment on prostate specific antigen (PSA) levels to assess effects on the AR signaling pathway. Cell viability was significantly decreased over time in equol treated cells, but only in prostate cancer cell lines that were AR positive. The effects of equol on LNCaP viability was abrogated in an AR knockdown LNCaP cell line. Interestingly, AR protein levels were found to be markedly decreased upon equol treatment of LNCaP cells. We likewise observed a decrease in PSA protein levels in AR positive cells after equol treatment. Our results support the notion that equol can inhibit prostate cancer growth by inhibition of the androgen receptor. We are currently investigating whether combining equol exposure with radiation treatment produces a synergistic effect on DNA damage and reduction of prostate cancer cell viability and survival in vitro. Our future studies will investigate the effects of equol and equol-producing bacteria on tumor growth in in vivo models. Citation Format: Carli B. Jones, Jonathan B. Coulter, Janielle P. Maynard, Luke A. Mummert, Ryan M. Phillips, Phuoc T. Tran, Karen S. Sfanos. Equol as a radiosensitizer and therapeutic agent in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3050.

Cell-based evidence regarding the role of FSH in prostate cancer

IntroductionConversion of androgen-responsive prostate cancer (CaP) to castration-resistant CaP is associated with an acceleration of the disease that often requires treatment modalities other than androgen deprivation therapy only. Recently, follicle-stimulating hormone (FSH) has been shown to play a role in CaP growth, and clinical data showed that high serum concentration of FSH in chemically castrated CaP patients was associated with a shorter time of progression to castration-resistant CaP. In this study, we sought to investigate if FSH could have direct effects on CaP cells, possibly through the androgen receptor and androgen receptor regulated genes, such as prostate-specific antigen (PSA). Materials and methodsThe human CaP cell lines PC-3, LNCaP and C4-2, and nonmalignant PNT1A cells, were utilized to investigate the effects of FSH. qPCR, Western blotting analysis, and 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymetoxyphenyl)-2-(4-sulfophenyl)-2H tetrazolium assays were performed in order to analyze the FSH effects. ResultsThe FSH receptor was present in all cell lines except PNT1A. FSH significantly increased PSA mRNA (P < 0.01) and protein (P < 0.03) levels in C4-2 cells in a dose-dependent manner. In LNCaP cells, FSH also increased PSA protein level, although to a lesser extent than in C4-2 cells, and the expression was reduced by the antiandrogen enzalutamide. In PC-3 cells, FSH was shown to increase their proliferation (P < 0.03) and β-catenin expression. ConclusionThese findings demonstrate that FSH may have a direct effect in CaP in an androgen-depleted environment. However, further research is needed to understand the significance of direct FSH action in the maintenance of CaP growth at the different phases of transition from androgen dependence to androgen independence.

P,p′-Dichlorodiphenyltrichloroethane (p,p′-DDT) and p,p′-dichlorodiphenyldichloroethylene (p,p′-DDE) repress prostate specific antigen levels in human prostate cancer cell lines

Despite stringent restrictions on their use by many countries since the 1970s, the endocrine disrupting chemicals, DDT and DDE are still ubiquitous in the environment. However, little attention has been directed to p,p′-DDT and the anti-androgen, p,p′-DDE on androgen receptor (AR) target gene transcription in human cells. Inhibitors of androgenic activity may have a deleterious clinical outcome in prostate cancer screens and progression, therefore we determined whether environmentally relevant concentrations of p,p′-DDT and p,p′-DDE negatively impact AR-regulated expression of prostate-specific antigen (PSA), and other AR target genes in human LNCaP and VCaP prostate cancer cells. Quantitative real-time PCR and immuno-blotting techniques were used to measure intracellular PSA, PSMA and AR mRNA and protein levels. We have shown for the first time that p,p′-DDT and p,p′-DDE repressed R1881-inducible PSA mRNA and protein levels in a dose-dependent manner. Additionally, we used the fully automated COBAS PSA detection system to determine that extracellular PSA levels were also significantly repressed. These chemicals achieve this by blocking the recruitment of AR to the PSA promoter region at 10μM, as demonstrated by the chromatin immunoprecipitation (ChIP) in LNCaP cells. Both p,p′-DDT and p,p′-DDE repressed R1881-inducible AR protein accumulation at 10μM. Thus, we conclude that men who have been exposed to either DDT or DDE may produce a false-negative PSA test when screening for prostate cancer, resulting in an inaccurate clinical diagnosis. More importantly, prolonged exposure to these anti-androgens may mimic androgen ablation therapy in individuals with prostate cancer, thus exacerbating the condition by inadvertently forcing adaptation to this stress early in the disease.

Increased expression of GCNT1 is associated with altered O-glycosylation of PSA, PAP, and MUC1 in human prostate cancers.

Protein glycosylation is a common posttranslational modification and glycan structural changes have been observed in several malignancies including prostate cancer. We hypothesized that altered glycosylation could be related to differences in gene expression levels of glycoprotein synthetic enzymes between normal and malignant prostate tissues. We interrogated prostate cancer gene expression data for reproducible changes in expression of glycoprotein synthetic enzymes. Over-expression of GCNT1 was validated in prostate samples using RT-PCR. ELISA was used to measure core 2 O-linked glycan sialyl Lewis X (sLe(x) ) of prostate specific antigen (PSA), Mucin1 (MUC1), and prostatic acidic phosphatase (PAP) proteins. A key glycosyltransferase, GCNT1, was consistently over-expressed in several prostate cancer gene expression datasets. RT-PCR confirmed increased transcript levels in cancer samples compared to normal prostate tissue in fresh-frozen prostate tissue samples. ELISA using PSA, PAP, and MUC1 capture antibodies and a specific core 2 O-linked sLe(x) detection antibody demonstrated elevation of this glycan structure in cancer compared to normal tissues for MUC1 (P = 0.01), PSA (P = 0.03) and near significant differences in PAP sLe(x) levels (P = 0.06). MUC1, PSA and PAP protein levels alone were not significantly different between paired normal and malignant prostate samples. GCNT1 is over-expressed in prostate cancer and is associated with higher levels of core 2 O-sLe(x) in PSA, PAP and MUC1 proteins. Alterations of O-linked glycosylation could be important in prostate cancer biology and could provide a new avenue for development of prostate cancer specific glycoprotein biomarkers.

Abstract 941: Suppression of the androgen receptor function by c-Jun in prostate cancer via a dual mechanism

Abstract Androgen receptor (AR) signaling plays a pivotal role in growth and survival of prostate cancer cells. Upon ligand binding, AR translocates into the nucleus and regulates expression of multiple genes through binding their promoter regions. Thus, altered expression and activity of AR contribute to disease progression. Consequently, significant effort has been undertaken to identify and characterize numerous coactivators and corepressors of AR. Here we report that the transcription factor c-Jun, a basic region leucine zipper (bZIP) transcription factor and is an important member of the AP-1 family, acts as a transcriptional repressor to inhibit the AR transcriptional activity. Furthermore, we have found that c-Jun also represses the transcription of AR. Overexpression of c-Jun in LNCaP prostate cancer cells inhibited luciferase reporters driven by the androgen-induced prostate-specific antigen (PSA) promoter, probasin promoter, mouse mammary tumor virus (MMTV) promoter and tandem repeats of androgen response elements in a dose-dependent manner. Conversely, knockdown of c-Jun enhanced androgen-stimulated AR activity in LNCaP cells. To further confirm the results, we generated a doxycycline-inducible c-Jun overexpression LNCaP stable cell line using lentivrial system. Consistent with the results of promoter activity assay, induction of c-Jun by doxycycline inhibited both steady state and androgen-induced PSA mRNA and protein levels. Interestingly, the protein and mRNA of AR were also downregulated when c-Jun was induced, suggesting that c-Jun suppresses AR expression at the transcriptional level. Moreover, c-Jun induction resulted in a significant reduction in cell number, suggesting that c-Jun suppresses LNCaP cell proliferation by antagonizing AR signaling. In summary, our results suggest that c-Jun negatively regulates the AR signaling by a dual mechanism. Future identification of negative regulators of c-Jun expression will provide a new opportunity to develop novel therapeutics. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 941. doi:1538-7445.AM2012-941

Abstract C133: The use of exosomal mRNA for noninvasive transcriptional analysis of the prostate.

Abstract Background: Prostate cancer studies have used urine as a non-invasive source of nucleic acids for biomarker analysis. These studies have been limited by the need for a digital rectal exam (DRE) or prostate massage prior to urine collection to enable enough cellular material for RNA analysis. Such manipulations can potentially lead to variability in assay performance depending on DRE intensity and may also reduce compliance. Here we investigate the novel use of RNA in urinary exosomes, small lipid bilayer vesicles released from cells into bodily fluids, to analyze previously identified prostate cancer mRNA biomarkers without a prostate massage. Methods: Random urine samples (&amp;gt;20ml) were collected from 207 consecutive patients under a Columbia University IRB approved prospective protocol. Patients were stratified into 5 groups: TRUS biopsy negative (Bx Neg, n=39), TRUS biopsy positive (Bx Pos, n=47), post-radical prostatectomy (RP, n=37), no TRUS biopsy (No Bx, n=44) and control (healthy males &amp;lt;35 yrs, n=40). Due to the unique stability of exosomal RNA (exoRNA), urine samples were stored at 4°C and 0.8 um filtration was used to remove whole cells and debris. Urinary exoRNA was isolated using our in-house technique. RT-qPCR was used to analyze GAPDH, prostate-specific antigen (PSA), prostate cancer antigen 3 (PCA3), androgen receptor (AR), survivin, nuclear receptor co-activator 2 (NCOA2), RAD21, transmembrane protease serine 2 (TMPRSS2), ERG and TMPRSS2:ERG fusion. Results: All groups were age matched except for control males (&amp;lt;35 yrs)(P&amp;lt;0.001). Serum PSA protein was significantly lower in the No Bx and RP groups versus the Bx Neg and Bx Pos groups (P&amp;lt;0.001). Relative quantitation (RQ) of genes standardized to GAPDH revealed that ERG and PCA3 expression levels were significantly increased in the Bx Pos versus Bx Neg groups (ERG P&amp;lt;0.01, PCA3 P&amp;lt;0.05). Further, RQ analysis standardized to the prostate related gene, PSA, revealed that survivin (P&amp;lt;0.005), ERG (P&amp;lt;0.005), PCA3 (P&amp;lt;0.005), TMPRSS2:ERG fusion (P&amp;lt;0.05), and TMPRSS2 (P&amp;lt;0.05) were significantly increased in the Bx Pos versus Bx Neg group. Analysis of the TMPRSS2:ERG fusion revealed 44% of Bx Neg and 68% of Bx Pos had a positive fusion event. Analysis of the RP group revealed that no patients had positive TMPRSS2:ERG detection; this finding was further supported by the loss of TMPRSS2:ERG expression experienced by 4 Bx Pos patients following prostatectomy suggesting specificity of the fusion event for the prostate. Interestingly, the control group (males &amp;lt;35yrs) had a much lower TMPRSS2:ERG fusion incidence of 5% compared to the No Bx group's fusion incidence of 41%, which was similar to the Bx Neg group despite having significantly lower serum PSA protein levels. Conclusion: This study confirms that urinary exosomes are a novel source of high quality RNA to examine prostate gene expression. We demonstrate that expression levels of ERG, PCA3, TMPRSS2:ERG, TMPRSS2 and survivin are significantly higher in cases of confirmed prostate cancer, consistent with previous studies using prostate biopsies and/or urinary cells collected after DRE/prostate massage. The unique stability and yield of urinary exoRNA collected without the need for a prostatic massage will hopefully simplify sample handing, obviate sample variability and patient discomfort inherent to prostate massage, and broaden the role of exosomes in future diagnostic testing. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C133.

Prostate-Specific Antigen Gene Expression and Telomerase Activity in Breast Cancer Patients: Possible Relationship to Steroid Hormone Receptors

Breast cancer, the most prevalent cancer among women, is a steroid hormone receptor-dependent cancer. Recently, it has been shown that telomerase and prostate-specific antigen (PSA) gene expressions are under control of steroid hormone receptors. The aim of this study was to investigate the relationship between telomerase activity and PSA gene expression with steroid hormone receptors in breast cancer patients. This study consisted of 50 women with breast benign tumors and 50 malignant (invasive) tumors. Telomerase activity was measured in tumor cytosol of samples by telomeric repeat amplification protocol (TRAP) assay. PSA protein and its mRNA expression were measured using ultrasensitive immunoassay and RT-PCR technique in all tumor tissues, respectively. Estrogen and progesterone receptors were stained using immunohistochemistry in tumor tissues. Telomerase activity was detected in all of the invasive breast cancer tissues. The difference of relative telomerase activity (RTA) values between stages and grades were statistically significant (p < 0.05). The PSA mRNA was detected only in benign tumors and stage I and grade I malignant tumor cytosol. Difference of tumor cytosol PSA levels between the cases and control groups and also between all grades and stages of diseases were significant (p < 0.05). There was an inverse significant correlation between the RTA and PSA protein levels in the case groups (r = -0.42, p < 0.05). There was a statistically significant difference between ER/PR with PSA level and telomerase activity in tumor tissues (p < 0.05). It is speculated that differential expression of PSA and telomerase genes in breast tumors are under control of steroid hormone receptors and could be used as a target for treatment in the future.

Antiandrogenic and growth inhibitory effects of ring‐substituted analogs of 3,3′‐diindolylmethane (Ring‐DIMs) in hormone‐responsive LNCaP human prostate cancer cells

Cruciferous vegetables protect against prostate cancer. Indole-3-carbinol (I3C) and its major metabolite 3,3'-diindolylmethane (DIM), exhibit antitumor activities in vitro and in vivo. Several synthetic ring-substituted dihaloDIMs (ring-DIMs) appear to have increased anticancer activity. Inhibition of LNCaP prostate cancer cell growth was measured by a WST-1 cell viability assay. Cytoplasmic and nuclear proteins were analyzed by immunoblotting and immunofluorescence. Androgen receptor (AR) activation was assessed by measuring prostate-specific antigen (PSA) expression and using LNCaP cells containing human AR and an AR-dependent probasin promoter-green fluorescent protein (GFP) construct. Like DIM, several ring-substituted dihaloDIM analogs, namely 4,4'-dibromo-, 4,4'-dichloro-, 7,7'-dibromo-, and 7,7'-dichloroDIM, significantly inhibited DHT-stimulated growth of LNCaP cells at concentrations ≥1 µM. We observed structure-dependent differences for the effects of the ring-DIMs on AR expression, nuclear AR accumulation and PSA levels in LNCaP cells after 24 hr. Both 4,4'- and 7,7'-dibromoDIM decreased AR protein and mRNA levels, whereas 4,4'- and 7,7'-dichloroDIM had minimal effect. All four dihaloDIMs (10 and 30 µM) significantly decreased PSA protein and mRNA levels. Immuofluorescence studies showed that only the dibromoDIMs increased nuclear localization of AR. All ring-DIMs caused a concentration-dependent decrease in fluorescence induced by the synthetic androgen R1881 in LNCaP cells transfected with wild-type human AR and an androgen-responsive probasin promoter-GFP gene construct, with potencies up to 10-fold greater than that of DIM. The antiandrogenic effects of ring-DIMs suggest they may form the basis for the development of novel agents against hormone-sensitive prostate cancer, alone or in combination with other drugs.

Simultaneous analysis of glycosylated and sialylated prostate-specific antigen revealing differential distribution of glycosylated prostate-specific antigen isoforms in prostate cancer tissues.

Aberrant protein glycosylation has been shown to be associated with disease progression and can be potentially useful as a biomarker if disease-specific glycosylation can be identified. However, high-throughput quantitative analysis of protein glycosylation derived from clinical specimens presents technical challenges due to the typically high complexity of biological samples. In this study, a mass spectrometry-based analytical method was developed to measure different glycosylated forms of glycoproteins from complex biological samples by coupling glycopeptide extraction strategy for specific glycosylation with selected reaction monitoring (SRM). Using this method, we monitored glycosylated and sialylated prostate-specific antigen (PSA) in prostate cancer and noncancer tissues. Results of this study demonstrated that the relative abundance of glycosylated PSA isoforms were not correlated with total PSA protein levels measured in the same prostate cancer tissue samples by clinical immunoassay. Furthermore, the sialylated PSA was differentially distributed in cancer and noncancer tissues. These data suggest that differently glycosylated isoforms of glycoproteins can be quantitatively analyzed and may provide unique information for clinically relevant studies.

Abstract 3804: Transcriptional repression of androgen receptor in human prostate cancer cells by plant flavone apigenin

Abstract Accumulating evidence suggest that androgen receptor (AR)-mediated signaling plays an important role in the development and progression of prostate cancer. Although Prostate Cancer Prevention Trial (PCPT) showed controversial results however manipulation of AR signaling pathway reduced the incidence of prostate cancer. Safer agents are needed that can modulate AR signaling pathways with effective suppression of prostate cancer. Plant flavonoids have been shown to possess weak oestrogenic and anti-androgen activity. Apigenin, a naturally occurring plant flavone, has shown promising anticancer activity by modulating several signaling pathways that have relevance to prostate cancer. However, the effect of apigenin on AR signaling has not been fully investigated. Using androgen-responsive human prostate cancer LNCaP and 22Rv1cells, we determine the effect of apigenin on androgen receptor signaling. Exposure of these cells with 5-40μM apigenin suppressed cell proliferation and arrested cells in sub G0-G1 phase of the cell cycle after 5nM dihydrotestosterone (DHT) stimulation. Apigenin inhibited endogenous prostate-specific antigen (PSA) transcription and reduced intracellular and secreted PSA protein levels induced by DHT in these cells. In LNCaP cells apigenin inhibited AR expression in a concentration-dependent manner by restricting its translocation into the nucleus. Co-transfection of PC-3 cells with wild-type AR-GFP-tag plasmid demonstrated that apigenin has ability to inhibit DHT-induced AR translocation into the nucleus. Additionally, receptor binding assays indicated that apigenin is a strong competitive inhibitor of DHT binding to the AR. These observations matched with the results of structural modeling studies exhibiting that apigenin is remarkably similar in conformational geometry and surface charge distribution to synthetic AR antagonist, flutamide, although the atomic compositions of the two substances were quite different. Taken together, our results indicate that apigenin exhibits potent anti-proliferative and anti-androgenic properties and may be developed as useful and safer agent for prevention/therapy of prostate cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3804.

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

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. 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. 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. 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.

Antitumor activity of the histone deacetylase inhibitor MS‐275 in prostate cancer models

Histone deacetylase (HDAC) inhibitors represent a novel class of therapeutic agents with antitumor activity currently in clinical development. In this study, we tested the biological effects of the HDAC inhibitor MS-275 in various pre-clinical prostate cancer models both in'vitro and in vivo. In vitro cell proliferation XTT assay and protein expression analysis by Western blot were performed. In vivo tumor growth assessment in subcutaneous, orthotopic, and transgenic mouse models were conducted. MS-275 significantly upregulated histone H3 acetylation and p21 gene expression in human prostate cancer cell lines. MS-275 exerted growth arrest in PC-3 and LNCaP cells, and induced cell death in DU-145 cells. Prostate specific antigen protein levels were increased by MS-275 in LAPC4 cell line. In vivo, MS-275 inhibited the growth of DU-145, LNCaP, and PC-3 in subcutaneous xenografts. MS-275 had also a significant inhibition of PC-3 cells growth in a mouse intratibial model. Molecular analysis showed increased histone acetylation and p21 expression in tumor samples from MS-275-treated mice. In transgenic adenocarcinoma of mouse prostate (TRAMP) mice, long-term treatment of MS-275 slowed the progression of prostate carcinomas with significant reduction in cell proliferation. Taken together, these data support the clinical testing of MS-275 for the treatment of prostate cancer.

Prostate Specific Antigen Expression Does Not Necessarily Correlate With Prostate Cancer Cell Growth

The antiproliferative effects of pharmacological agents used for androgen ablative therapy in prostate cancer, including goserelin, bicalutamide and cyproterone acetate (Fluka Chemie, Buchs, Switzerland), were tested in vitro. It was determined whether they affected prostate specific antigen mRNA and protein expression independent of growth inhibition. Goserelin, bicalutamide (AstraZeneca, Zug, Switzerland) and cyproterone acetate were added to prostate specific antigen expressing, androgen dependent LNCaP and androgen independent C4-2 cell line (Urocor, Oklahoma City, Oklahoma) cultures. Proliferation was determined by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazoliumbromide assay (Roche, Mannheim, Germany). Prostate specific antigen mRNA expression was assessed by quantitative real-time polymerase chain reaction. Secreted prostate specific antigen protein levels were quantified by microparticle enzyme-immunoassay. Goserelin inhibited cell growth and prostate specific antigen protein secretion in LNCaP and C4-2 cells. Prostate specific antigen mRNA expression was not decreased. Bicalutamide did not affect cell growth or prostate specific antigen mRNA expression in LNCaP or C4-2 cells, although it significantly decreased prostate specific antigen protein secretion in LNCaP and to a lesser extent in C4-2 cells. Cyproterone acetate decreased the growth of C4-2 but not of LNCaP cells. It did not affect prostate specific antigen mRNA or protein expression in either cell line. Prostate specific antigen expression does not necessarily correlate with cell growth. Without a substantial effect on cell growth bicalutamide lowers prostate specific antigen synthesis, whereas cyproterone acetate decreases cell growth with no effect on prostate specific antigen secretion. Prostate specific antigen expression may be influenced by growth inhibition but also by altered mRNA and protein levels depending on the agent, its concentration and the cell line evaluated. For interpreting clinical trials prostate specific antigen is not necessarily a surrogate end point marker for a treatment effect on prostate cancer cell growth.

Indole-3-carbinol inhibition of androgen receptor expression and downregulation of androgen responsiveness in human prostate cancer cells

Indole-3-carbinol (I3C), a naturally occurring compound found in vegetables of the Brassica genus, such as broccoli and cabbage, is a promising anticancer agent previously shown to induce a G(1) cell-cycle arrest in the cells of human lymph node carcinoma of prostate (LNCaP) through regulation of specific G(1)-acting cell-cycle components. Since the androgen receptor (AR) mediates proliferation and differentiation in the prostate and is expressed in nearly all human prostate cancers, the effects of I3C on AR expression and function were examined in LNCaP cells. Immunoblot and quantitative RT-PCR assays revealed that I3C inhibited the expression of AR protein and mRNA levels within 12 h of indole treatment. I3C downregulated the reporter activity of LNCaP cells transiently transfected with an AR promoter-luciferase plasmid, demonstrating that a unique response to I3C is the inhibition of AR promoter activity. In contrast to I3C, the natural I3C dimerization product 3,3'-diindolylmethane, which acts as an androgen antagonist, had no effect on AR expression. To determine the functional significance of the I3C-inhibited expression of AR, the AR-regulated prostate specific antigen (PSA) was utilized as a downstream indicator. I3C downregulated the expression of PSA transcripts and protein levels and inhibited PSA promoter activity, as well as that of a minimal androgen responsive element containing reporter plasmid. Expression of exogenous AR prevented the I3C disruption of androgen-induced PSA expression. Taken together, our results demonstrate that I3C represses AR expression and responsiveness in LNCaP cells as a part of its antiproliferative mechanism.

Changes in prostate-specific antigen (PSA) level correlate with growth inhibition of prostate cancer cells treated in vitro with a novel anticancer drug, irofulven.

Irofulven (hydroxymethylacylfulvene, HMAF, MGI 114) is a novel agent with alkylating activity and a potent inducer of apoptosis. It is currently undergoing Phase II clinical trials for several tumor types, including hormone-refractory prostate cancer. Reduction of serum prostate-specific antigen (PSA) levels has been proposed as a generally useful endpoint for evaluating the antitumor efficacy of treatments for prostate cancer. However, the utility of PSA as a marker of tumor cell burden could be compromised, if drugs directly affected PSA secretion and/or expression. In these studies, we evaluated the effects of irofulven on PSA protein and mRNA levels during the course of treatment of prostate tumor cells in vitro. The rate of PSA secretion (normalized per equal cell number) by control and drug treated cells was similar, as determined by a solid phase, two-site immunoradiometric assay. Consistent with the lack of effect of irofulven on PSA protein level, the drug does not appear to affect the expression of PSA mRNA (on a per cell basis) as assessed by RT-PCR. Thus, changes in PSA secretion and expression appear to reflect irofulven-induced cell growth inhibition rather than reflecting a direct effect of the drug on PSA. These results suggest that PSA should be a reasonable marker of tumor burden in irofulven-treated prostate cancer patients.

Secretion of prostate-specific antigen-suppressing activity by two human prostate carcinoma cell lines

The well-differentiated human prostatic carcinoma cell line LNCaP has often been used as a model to study the modulation of prostate-specific antigen (PSA) expression. In this study, we examined the effect of conditioned medium from two androgen-unresponsive, PSA-negative human prostatic carcinoma cell lines, PC-3 and DU-145, on PSA expression by the LNCaP cells. Our results show, for the first time, that the undifferentiated PC-3 and DU-145 cells secrete a factor that lowers PSA mRNA and protein levels in LNCaP cells. Further characterization of the PSA-suppressing activity indicated that it was trypsin as well as acid sensitive, heat-stable, and ammonium sulfate precipitable. The activity was present in the 30–100-kd fraction of PC-3 and DU-145 conditioned media. This PSA-suppression factor could act in an autocrine manner to render undifferentiated prostatic carcinoma cells PSA negative. It may also be responsible for the lack of increase in serum PSA levels observed in a subset of patients with hormone-resistant prostatic carcinoma.