LNCaP Tumor-bearing Research Articles

Synthesis and biological evaluation of copper-64 radiolabeled [DUPA-6-Ahx-(NODAGA)-5-Ava-BBN(7-14)NH2], a novel bivalent targeting vector having affinity for two distinct biomarkers (GRPr/PSMA) of prostate cancer

Gastrin-releasing peptide receptors (GRPr) and prostate-specific membrane antigen (PSMA) are two identifying biomarkers expressed in very high numbers on prostate cancer cells and could serve as a useful tool for molecular targeting and diagnosis of disease via positron-emission tomography (PET). The aim of this study was to produce the multipurpose, bivalent [DUPA-6-Ahx-((64)Cu-NODAGA)-5-Ava-BBN(7-14)NH2] radioligand for prostate cancer imaging, where DUPA = (2-[3-(1,3-dicarboxypropyl)-ureido]pentanedioic acid), a small-molecule, PSMA-targeting probe, 6Ahx = 6-aminohexanoic acid, 5-Ava = 5-aminovaleric acid, NODAGA = [2-(4,7-biscarboxymethyl)-1,4,7-(triazonan-1-yl)pentanedioic acid] (a derivative of NOTA (1,4,7-triazacyclononane-1,4,7-triacetic acid)), and BBN(7-14)NH2 = bombesin, a GRPr-specific peptide targeting probe. The PSMA/GRPr dual targeting ligand precursor [DUPA-6-Ahx-K-5-Ava-BBN(7-14)NH2], was synthesized by solid-phase and manual peptide synthesis, after which NODAGA was added via manual conjugation to the ε-amine of lysine (K). The new bivalent GRPr/PSMA targeting vector was purified by reversed-phase high performance liquid chromatography (RP-HPLC), characterized by electrospray-ionization mass spectrometry (ESI-MS), and metallated with (64)CuCl2 and (nat)CuCl2. The receptor binding affinity was evaluated in human, prostate, PC-3 (GRPr-positive) and LNCaP (PSMA-positive) cells and the tumor-targeting efficacy determined in severe combined immunodeficient (SCID) and athymic nude mice bearing PC-3 and LNCaP tumors. Whole-body maximum intensity microPET/CT images of PC-3/LNCaP tumor-bearing mice were obtained 18 h post-injection (p.i.). Competitive binding assays in PC-3 and LNCaP cells indicated high receptor binding affinity for the [DUPA-6-Ahx-((nat)Cu-NODAGA)-5-Ava-BBN(7-14)NH2] conjugate. MicroPET scintigraphy in PC-3/LNCaP tumor-bearing mice indicated that xenografted tumors were visible at 18h p.i. with collateral, background radiation also being observed in non-target tissue. DUPA-6-Ahx-((64)Cu-NODAGA)-5-Ava-BBN(7-14)NH2] targeting vector, as described herein, is the first example of a dual GRPr-/PSMA-targeting radioligand for molecular of imaging prostate tumors. Detailed in vitro studies and microPET molecular imaging investigations of [DUPA-6-Ahx-((64)Cu-NODAGA)-5-Ava-BBN(7-14)NH2 in tumor-bearing mice indicate that further studies are necessary to optimize uptake and retention of tracer in GRPr- and PSMA-positive tissues.

Ericifolin: a novel antitumor compound from allspice that silences androgen receptor in prostate cancer

Silencing of androgen receptor (AR) signaling is a specific and effective mechanism to cure cancer of the prostate (CaP). In this study, the isolation and characterization of a compound from the aromatic berries of Pimenta dioica (allspice) that silences AR is presented. Potential antitumor activities of an aqueous allspice extract (AAE) and a compound purified from the extract were tested on CaP cells. AAE inhibited tumor cell proliferation and colony formation (50% growth inhibition ∼40-85 µg/ml) but not the viability of quiescent normal fibroblasts or non-tumorigenic prostate cells. In tumor cells, AAE inhibited cell cycle progression at G1/S, induced apoptosis or autophagy. Apoptosis was by caspase-dependent poly (ADP ribose) polymerase cleavage. A caspase-independent, apoptosis-inducing factor-mediated mechanism of apoptosis caused cell death in castration-resistant AR-positive or AR-negative CaP cells, such as CWR22RV1, PC-3 or DU145 cells. Treatment with AAE decreased the levels of AR messenger RNA (mRNA), protein and silenced AR activity in AR-positive cells. AR depletion was due to inhibition of AR promoter activity and mRNA stability. Delayed tumor growth (~55%) without measurable systemic toxicity was observed in LNCaP tumor-bearing mice treated with AAE by oral or intraperitoneal routes. LNCaP tumor tissues from AAE-treated mice revealed increased apoptosis as a potential mechanism of antitumor activity of AAE. The chemical identity of bioactive compound in AAE was established through multistep high-performance liquid chromatography fractionation, mass and Nuclear Magnetic Resonance spectroscopies. The compound, eugenol 5-O-β-(6'-galloylglucopyranoside) or ericifolin (EF), showed antiproliferative, pro-apoptosis and anti-AR transcription activities. These results demonstrate a potential use of AAE and EF against prostate cancer.

Activity of oral VT-464, a selective CYP17-lyase inhibitor, in the LNCaP prostate cancer xenograft.

4671 Background: With the FDA approval of abiraterone acetate, inhibition of CYP17 (17α hydroxylase/C17, 20-lyase) is now a validated approach to the treatment of castration-resistant prostate cancer. VT-464 is a novel, selective CYP17-lyase inhibitor with decreased activity against CYP17 hydroxylase (less mineralcocorticoid and glucocorticoid effects). The study objectives were to observe the effects of VT-464 in a prostate cancer xenograft model and to compare its activity to abiraterone acetate and surgical castration. Methods: SCID mice were implanted subcutaneously with LNCaP cells. When tumors reached 100 mm3, mice were randomized to receive vehicle (0.5% CMC in saline, 5 mL/kg), VT-464 at 15, 50, or 100 mg/kg p.o. b.i.d. A second cohort of LNCaP tumor-bearing mice received vehicle, surgical castration, or VT-464, or abiraterone acetate at 100 mg/kg p.o. b.i.d. for 28 days. Terminal blood and tumor concentrations were analyzed on day 28, four hours after the last dose. Results: In the first LNCaP xenograft cohort, percent growth inhibition (± S.E.) of 9.6 (±15.6), 38.5 (±12.4), and 73.9 (±13.2) was observed on day 21 of treatment for VT-464 doses of 15, 50, and 100 mg/kg, respectively. Growth reduction at 100 mg/kg was statistically significant compared to vehicle control from day 7 to 28. VT-464 was well tolerated with insignificant weight loss at all doses. In the second cohort, VT-464-treated (100 mg/kg) mice had significantly reduced tumor volumes on day 28 compared to control and abiraterone acetate (p<0.05, p<0.01, respectively). Reduction in tumor volumes were similar between VT-464-treated (100 mg/kg) and castrate animals. Plasma and tumor analyses revealed much greater plasma and tumor exposure of VT-464 compared to abiraterone acetate. Conclusions: VT-464 exhibited dose-dependent growth inhibition with significantly reduced tumor volumes at the highest dose compared to abiraterone acetate. The activity in VT-464-treated animals was similar to that of castrate animals. These preclinical results show promising activity of VT-464 in the treatment of prostate cancer.

Activity of VT-464, a selective CYP17 lyase inhibitor, in the LNCaP prostate cancer xenograft model.

64 Background: With the recent FDA approval of abiraterone acetate, CYP17 (17α hydroxylase/C17, 20-lyase) has become a proven target for the treatment of castration- resistant prostate cancer. Inhibition of CYP17-lyase causes a decrease in circulating androgens, severely hampering activation of the androgen receptor signaling pathway that prostate cancer relies on for proliferation. However, inhibition of CYP17-hydroxylase, a second enzymatic activity of CYP17, leads to an increase in upstream steroids that can cause mineralocorticoid excess syndrome as well as a decrease in cortisol production. VT-464 is a novel, selective CYP17 lyase inhibitor with decreased activity against CYP17 hydroxylase. The study objectives were to observe the effects of VT-464 in a prostate cancer xenograft model and to compare its activity to abiraterone acetate and surgical castration. Methods: SCID mice were implanted subcutaneously with LNCaP cells. When tumors reached 100mm3, mice were randomized to receive vehicle (0.5% CMC in saline, 5ml/kg), or VT-464 at 15, 50, or 100mg/kg p.o. bid. A second cohort of LNCaP tumor-bearing mice received vehicle, surgical castration, or VT-464 or abiraterone acetate at 100mg/kg p.o. bid for 28 days. Results: In the LNCaP xenograft model, percent growth inhibition (± S.E.) of 9.6 (±15.6), 38.5(±12.4), and 73.9 (±13.2) was observed on day 21 of treatment for the VT-464 doses of 15, 50, and 100 mg/kg, respectively. VT-464 -treated (100mg/kg) mice had a significantly reduced tumor volume ratio (V/V0) on day 28 compared to control and abiraterone acetate (p<0.05, p<0.01, respectively). Reduction in tumor volume ratios were similar between VT-464-treated (100 mg/kg) and castrate animals. Conclusions: VT-464 exhibited dose-dependent growth inhibition with significantly reduced tumor growth at the highest dose compared to abiraterone acetate. The reduction in tumor growth in VT-464-treated animals was similar to that of castrate animals. These preclinical results show promising activity of VT-464 in the treatment of prostate cancer.

Abstract 5572: An aqueous extract of allspice (Pimenta dioica) suppresses androgen receptor expression and prostate cancer growth

Abstract Background and objective: The aromatic berries of the Jamaican plant Pimenta dioica called Allspice are used in many cuisines for their delectable flavor and as folk remedies for variety of ailments. Despite a rich source of antioxidants the use of Allspice as cancer preventive or anticancer agent has not been reported. Potential anti-cancer activity of an Aqueous Allspice extract (AAE) was tested on prostate cancer (CaP) cells and on tumor models. Methods: AAE was prepared from dried, unripe berries of P. dioica (Certified Organic, Oregon Spices, OR) in water and the extract was lyophilized before testing for biological activity. We tested AAE on growth, survival; response to androgen on human androgen sensitive (AR+) CaP cells (LNCaP, LAPC-4) and in LNCaP xenograft tumors in athymic-nude mice. We used colorimetric MTT-cell survival assay, colony-forming assays, bioluminescence reporter assays, Q-PCR and western blotting to delineate the molecular mechanism of tumor suppressive action of AAE. Results: AAE inhibited tumor cell proliferation (IC50∼100ug/ml) and clonogenic growth (IC50∼40ug/ml) of AR+ CaP cells. AAE was selectively toxic to tumor cells and less toxic to non-tumorigenic cells. AAE blocked cell cycle progression from G1 to S by decreasing cyclin D1, phosphorylated Rb, CDK4 and increased P21 and P27 in AR+ CaP cells. AAE induced apoptosis in LNCaP cells was mediated by intrinsic apoptotic pathway via depolarization of mitochondria, activation of caspase 9, caspase 3/7, cleaved PARP levels, increase in pro-apoptotic protein Bax, decrease in anti-apoptotic protein BID and release of cytochrome C from mitochondria. Importantly, AAE treated AR+ CaP cells showed significant decrease in AR protein level (IC50 50µg/ml) and the proteosome inhibitor MG132 did not rescue the AR protein level decrease by AAE. Transcriptional analysis of androgen receptor (AR) in AR+ CaP cells showed rapid decrease in AR and PSA expression by AAE. Moreover, treatment of LNCaP tumor bearing mice with AAE (100mg/kg, IP, 2x/w) significantly delayed the tumor growth (58%), prolonged the survival period with no systemic toxicity. Ex vivo analyses of LNCaP tumor tissue showed increased apoptosis (70%) in AAE treated mice compared to tissue from vehicle control, with 44% decrease in IGF-1 levels in serum of treated animals. A chemical analysis showed that the major component present on AAE was polyphenol (37% w/v) and devoid of alkaloids and other bioactive compounds. Conclusion: We identified an anticancer product from a New World plant commonly used in cuisines world-over. This extract suppressed the androgen receptor activity in AR+ CaP cells. These studies demonstrate potential use of AAE as a chemotherapeutic or chemopreventive agent against prostate cancer (Funds: NIH1R01 AT 003544 and VA MERIT Grant # 5312.01) Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5572. doi:10.1158/1538-7445.AM2011-5572

Transcription Factor Stat5 Knockdown Enhances Androgen Receptor Degradation and Delays Castration-Resistant Prostate Cancer Progression In vivo

Signal transducer and activator of transcription 5 (Stat5) plays an important role in the transition of prostate cancer (PCa) to its castrate-resistant state. Pharmacologic targeting of Stat5 is a rational approach to delay castrate-resistant progression, in part, because Stat5 cooperates with the androgen receptor (AR) to promote PCa progression. Immunostaining of tissue microarrays was used to correlate Stat5 expression with Gleason grade and to characterize changes in treatment-naive and androgen-deprived human PCa. Potency of a Stat5 antisense oligonucleotide (ASO) on Stat5 knockdown, cell growth, and apoptosis was assessed in LNCaP, C4-2, and DU145 cells. Effects of Stat5 knockdown on AR activity and stability was assessed using a PSA transactivation-luciferase assay and cyclohexamide plus MG132 treatment, respectively. LNCaP tumor-bearing mice were castrated and randomly assigned to treatment with Stat5-ASO or controls. Here, we show that the frequency of Stat5 expression is significantly increased in high Gleason grade as well as in hormone-treated PCa. Also, specific knockdown of Stat5 with ASO abrogates androgen-induced AR nuclear translocation and PSA transactivation despite R1881 stimulation. Moreover, Stat5 knockdown destabilizes AR, which leads to AR degradation via the proteasome. Shown for the first time as a preclinical proof-of-principle, Stat5 knockdown with Stat5-ASO significantly delays CRPC tumor progression in vivo. Thereby, we are able to recapitulate our in vitro results by reducing serum PSA and expression levels of target proteins in the xenograft tumors.

Human prostate cancer xenografts in lit/lit mice exhibit reduced growth and androgen‐independent progression

The growth hormone/insulin-like growth factor I (GH/IGF-I) axis has been linked to prostate cancer (PCa) risk. Although previous studies indicate that human breast cancers and a murine PCa model develop more slowly in murine hosts homozygous for a missense mutation in the GH-releasing hormone receptor (lit/lit) whose "little" dwarfed phenotype is caused by suppressed GH and IGF-I production, the role of these two hormones remains controversial. To assess how the GH/IGF-I axis influences androgen-responsive, castration-resistant (CR), and androgen-independent (AI) growth of human PCa, we compared xenograft growth of the androgen-responsive human PCa cells, LNCaP, and AI human PCa cells, PC3, in intact and castrate Nod/SCID lit/lit and lit/+ mice, and in vitro growth of these cell lines in lit/lit and lit/+ serum-containing media supplemented with GH or IGF-I. Tumor growth and PSA accumulation rates were suppressed in LNCaP tumor-bearing lit/lit mice pre- and post-castration. Growth of PC3 xenografts in lit/lit mice was also suppressed. In vitro proliferation of LNCaP and PC3 cells cultured in media containing lit/lit mouse serum was decreased as compared to growth in media containing lit/+ serum. Suppressed growth in lit/lit serum could be restored by the addition of IGF-I, and to a lesser extent, GH. Differences in growth correlated with differences in steady-state AKT and ERK1/2 activation. This study demonstrates that circulating GH and IGF-I can promote androgen-responsive growth, CR progression, and AI expansion of PTEN-deficient human PCa cell xenografts and indicates that IGF-I can promote PCa growth in a suppressed GH environment.

681 REDUCED ANDROGEN DEPENDENT AND INDEPENDENT GROWTH OF HUMAN PROSTATE CANCER XENOGRAFTS IN GROWTH HORMONE RELEASING HORMONE RECEPTOR MUTANT HOSTS

You have accessJournal of UrologyProstate Cancer: Basic Research V1 Apr 2010681 REDUCED ANDROGEN DEPENDENT AND INDEPENDENT GROWTH OF HUMAN PROSTATE CANCER XENOGRAFTS IN GROWTH HORMONE RELEASING HORMONE RECEPTOR MUTANT HOSTS Kiyoshi Takahara, Howard Tearle, Tabitha Tombe, Martin E. Gleave, and Michael E. Cox Kiyoshi TakaharaKiyoshi Takahara More articles by this author , Howard TearleHoward Tearle More articles by this author , Tabitha TombeTabitha Tombe More articles by this author , Martin E. GleaveMartin E. Gleave More articles by this author , and Michael E. CoxMichael E. Cox More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2010.02.1080AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Signaling through the growth hormone/insulin-like growth factor (GH/IGF) axis has been linked to prostate cancer (PCa) risk. Previous studies have indicated that human breast cancer xenografts and murine PCa models develop more slowly in little murine hosts. The little (lit/lit) phenotype is due to a D60G missense mutation in the GH-releasing hormone receptor (GHRHR) resulting in loss of pituitary GHRHR function and suppression of GH and IGF-1 expression. We hypothesized that the GH/IGF axis influences PCa growth and castration-resistant (CR) progression of human PCa xenografts. METHODS To determine whether PCa growth in vivo models is influenced by the host GH/IGF axis, we performed in vivo growth studies using the androgen-responsive human PCa cell line, LNCaP, and CR human PCa cell line, PC3, in Nod/SCID lit/lit mice and compared them to growth and CR progression in mice heterozygous for the lit allele (lit/+). To assess whether suppressed GH/IGF levels affected androgen-responsive growth of PCa xenografts, we monitored tumor size and serum PSA levels before and after castration of LNCaP tumor-bearing lit/lit and lit/+ mice. We also monitored growth rate of PC3 xenografts in intact mice to assess the impact of GH/IGF axis deficiencies on CR PCa. Growth of LNCaP and PC3 cells in vitro using serum from lit/lit mice or lit/+ mice serum was examined to complement the in vivo experiments. RESULTS In intact mice, androgen-responsive growth rate of LNCaP xenografts was significantly reduced in lit/lit mice as compared to lit/+ mice [mm3/day (mean±SD) 56.0±8.5 vs 93.2±16.3, p < 0.05]. CR progression of LNCaP xenografts was also significantly delayed in lit/lit mice as compared to lit/+ mice [mm3/day (mean±SD) 65.2±12.8 vs 147.2±47.3, p < 0.1]. After castration, serum PSA levels in lit/lit mice was significantly lower than in lit/+ mice [ng/ml/day (mean±SD) 18.0±6.5 vs 60.0±33.0, p < 0.1]. Growth of CR PC3 xenografts was significantly delayed in lit/lit mice (n=19) as compared to lit/+ mice (n=17) [mm3/day (mean±SD) 234.5±24.1 vs 441.6±42.4, p < 0.001]. LNCaP and PC3 cells grown in vitro with serum from lit/lit mice showed decreased proliferation as compared with serum from lit/+ mice. CONCLUSIONS The GH/IGF axis appears to be an important stimulator of both androgen-responsive growth and CR progression of these PCa xenograft models. The results motivate clinical trials of novel hormonal treatment strategies that target the GH/IGF axis for PCa patients. Vancouver, Canada© 2010 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 183Issue 4SApril 2010Page: e266 Advertisement Copyright & Permissions© 2010 by American Urological Association Education and Research, Inc.MetricsAuthor Information Kiyoshi Takahara More articles by this author Howard Tearle More articles by this author Tabitha Tombe More articles by this author Martin E. Gleave More articles by this author Michael E. Cox More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

177Lu-AMBA Biodistribution, Radiotherapeutic Efficacy, Imaging, and Autoradiography in Prostate Cancer Models with Low GRP-R Expression

(177)Lu-DO3A-CH(2)CO-G-4-aminobenzoyl-Q-W-A-V-G-H-L-M-NH(2) ((177)Lu-AMBA) is a radiolabeled bombesin derivative that is bound and internalized by cells expressing the G-protein-coupled gastrin-releasing peptide receptor (GRP-R) and is currently in phase I clinical trials. In previous radiotherapy studies with PC-3 xenografted mice, (177)Lu-AMBA treatment significantly increased survival and reduced tumor growth rates. The PC-3 tumor cell line has an elevated expression of GRP-Rs (2.5 x 10(5)/cell), whereas LNCaP--a prostate cancer metastatic cell line representing the early androgen-sensitive stage of prostate cancer--and DU145--an androgen-insensitive metastatic line--express lower receptor numbers (5.9 x 10(3) and 1.2 x 10(4)/cell, respectively). Because of tumor heterogeneity, the high number of receptors in the PC-3 line may not represent the clinical situation, and little definitive work on the GRP-R status of primary prostate tumors and metastases exists. We sought to evaluate the tumor binding and imaging potential of (177)Lu-AMBA in low GRP-R models of prostate cancer and determine how reduced expression affects (177)Lu-AMBA radiotherapy efficacy. The LNCaP and DU145 cell lines were used to determine the binding (K(d)), retention, and efflux of (177)Lu-AMBA. Biodistribution radiotherapy, imaging, and autoradiography studies were performed in LNCaP, DU145, or PC-3 tumor-bearing male nude mice. Immunohistochemistry was used to determine the proliferative state in LNCaP and DU145 models and the vascular phenotype of LNCaP radiotherapy tumors. (177)Lu-AMBA binds to GRP-R in these cell lines with high affinity (K(d) of LNCaP, 0.65 +/- 0.2 nM; K(d) of DU145, 0.53 +/- 0.1 nM). The uptake of (177)Lu-AMBA is at least 10-fold less in LNCaP and DU145 cell lines than it is in the PC-3 cell line. Autoradiography identifies activity concentrated in areas of viable tumor tissue, and gamma-images of (177)Lu-AMBA identify tumors in vivo. Despite having lower uptake, (177)Lu-AMBA demonstrated radiotherapeutic efficacy and decreased proliferation in the LNCaP and DU145 xenografts; in the LNCaP model, (177)Lu-AMBA normalized the phenotype of microvasculature, reducing tumoral blood pooling. (177)Lu-AMBA is a single radiolabeled agent that combines targeted radiotherapy after imaging dosimetry with the potential for single-agent or multimodality therapy for prostate cancer.

In Vivo Biodistribution, PET Imaging, and Tumor Accumulation of 86Y- and 111In-Antimindin/RG-1, Engineered Antibody Fragments in LNCaP Tumor–Bearing Nude Mice

To optimize in vivo tissue uptake kinetics and clearance of engineered monoclonal antibody (mAb) fragments for radiotherapeutic and radiodiagnostic applications, we compared the biodistribution and tumor localization of four (111)In- and (86)Y-labeled antibody formats, derived from a single antimindin/RG-1 mAb, in a prostate tumor model. The IgG, diabody, single-chain variable domain (scFv), and novel miniantibody formats, composed of the human IgE-C(H)4 and a modified IgG1 hinge linked to scFv domains, were compared. Antibodies were first derivatized with the bifunctional chelator CHX-A''-diethylenetriamine pentaacetic acid and then bound to the radiometal to create radiolabeled immunoconjugates. Human LNCaP xenografts were grown in nude mice, and (111)In- or (86)Y-labeled antibodies were administered intravenously. Tissues were harvested at different times, and the level of antibody deposition was determined by measuring radioactivity. Whole-body small-animal PET of mice receiving (86)Y-labeled antibodies was performed at 6 time points and colocalized with simultaneous micro-CT imaging. The biodistributions of (111)In and (86)Y antibodies were quite similar. The blood, tumor, kidney, and liver tissues contained varying levels of radioactivity. The antibody accumulation in the tumor correlated with molecular size. The IgG steadily increased with time to 24.1 percentage injected dose per gram (%ID/g) at 48 h. The miniantibody accumulated at a similar rate to reach a lower level (14.2 %ID/g) at 48 h but with a higher tumor-to-blood ratio than the IgG. Tumor accumulation of the diabody peaked at 3 h, reaching a much lower level (3.7 %ID/g). A combination of rapid clearance and lower relative affinity of the scFv precluded deposition in the tumor. Small-animal PET results correlated well with the biodistribution results, with similar tumor localization patterns. The larger antibody formats (IgG and miniantibody) gave higher tumor uptake levels than did the smaller formats (diabody and scFv). These larger formats may be more suitable for radioimmunotherapy applications, evidenced by the preclinical efficacy previously shown by a report on the IgG format. The smaller formats were rapidly cleared from circulation, and the diabody, which accumulated in the tumor, may be more suitable for radiodiagnostic applications.

1-11C-Acetate as a PET Radiopharmaceutical for Imaging Fatty Acid Synthase Expression in Prostate Cancer

Although it is accepted that the metabolic fate of 1-(11)C-acetate is different in tumors than in myocardial tissue because of different clearance patterns, the exact pathway has not been fully elucidated. For decades, fatty acid synthesis has been quantified in vitro by the incubation of cells with (14)C-acetate. Fatty acid synthase (FAS) has been found to be overexpressed in prostate carcinomas, as well as other cancers, and it is possible that imaging with 1-(11)C-acetate could be a marker for its expression. In vitro and in vivo uptake experiments in prostate tumor models with 1-(11)C-acetate were performed both with and without blocking of fatty acid synthesis with either C75, an inhibitor of FAS, or 5-(tetradecyloxy)-2-furoic acid (TOFA), an inhibitor of acetyl-CoA carboxylase (ACC). FAS levels were measured by Western blot and immunohistochemical techniques for comparison. In vitro studies in 3 different prostate tumor models (PC-3, LNCaP, and 22Rv1) demonstrated blocking of 1-(11)C-acetate accumulation after treatment with both C75 and TOFA. This was further shown in vivo in PC-3 and LNCaP tumor-bearing mice after a single treatment with C75. A positive correlation between 1-(11)C-acetate uptake into the solid tumors and FAS expression levels was found. Extensive involvement of the fatty acid synthesis pathway in 1-(11)C-acetate uptake in prostate tumors was confirmed, leading to a possible marker for FAS expression in vivo by noninvasive PET.

Establishment of a highly tumorigenic LNCaP cell line having inflammatory cytokine resistance

Human androgen-dependent prostate cancer LNCaP cells are low tumorigenic even in immunodeficient mice and were killed by the synergistic effect of inflammatory cytokines, IL-β and IL-6. To establish a highly tumorigenic LNCaP cell line, we isolated the cytokine-resistant LNCaP-CR cell line and examined the phenotypes. The parental LNCaP cells were induced to commit apoptosis by the addition of IL-1β and IL-6, but LNCaP-CR cells showed strong resistance against the cytokine action. However, LNCaP-CR cells did not exhibit any resistance to various antitumor drugs investigated. While LNCaP cells formed only palpable tumors in SCID mice, LNCaP-CR cells readily made tumors and their growth was significantly higher than that of LNCaP cells. Moreover, LNCaP tumor-bearing mice gained the weight gradually, but LNCaP-CR tumor-bearing mice significantly lost their body weight. LNCaP-CR cells still responded to androgen action and expressed AR, erbB2, IL-1R, IL-6R, gp130, STAT3, p21, Bcl-2 and caspase-3 as well as LNCaP cells. These results indicate that LNCaP-CR cell line is a new type of tumorigenic LNCaP cell lines and should be useful for identifying responsible genes of tumorigenicity, cytokine resistance, and also cachexia.

Nitroxide tempo, a small molecule, induces apoptosis in prostate carcinoma cells and suppresses tumor growth in athymic mice

In previous studies, nitroxide tempo (2, 2, 6, 6-tetramethyl-piperidine-1-oxyl), a small molecule, induced cell death in cancer cells. The current study examined the antineoplastic properties of tempo in the human hormone-dependent/hormone-independent prostate carcinoma models (LNCaP, DU-145, and PC-3). The apoptotic effects of tempo were examined by the flow cytometric analysis of cells labeled with fluorescein isothiocyanate-conjugated annexin-V, and by electron microscopy. Enzymatic assays were performed to measure the activities of 2 cysteine proteases, i.e., caspase-9 and caspase-3, in tempo-treated cells. The effects of tempo on cell proliferation and on cell cycle distribution profiles were measured by the flow cytometric assay using immunofluorescent staining of incorporated 5'-bromo-2'-deoxyuridine (BrdU) coupled with 7-amino-actinomycin D (7-AAD) staining of total DNA. The number of proliferating cells was also determined independently by enzyme-linked immunosorbent assay using chemiluminescent detection of incorporated BrdU. Subcutaneous growth of human prostate carcinoma in athymic mice was monitored after intratumoral administration of tempo into tumor-bearing mice. In addition, cell viability assays were performed to compare the cytotoxic effect of a combination of doxorubicin or mitoxantrone and tempo with single agents. Tempo treatment of prostate carcinoma cells caused a significant increase in the number of apoptotic cells compared with control groups (tempo, 2.5 mM, 24 hours: DU-145, approximately 3.4-fold; PC-3, approximately 6-7-fold; tempo 1 mM, 24 hours: LNCaP, approximately 12-fold). Tempo-induced loss of cell viability was blocked partially or completely after pretreatment of cells with actinomycin-D or cycloheximide, suggesting a de novo macromolecule synthesis-dependent mechanism of cell death. Electron microscopy revealed aggregation and marginalization of chromatin in the nuclei of a large number of tempo-treated LNCaP cells. Tempo treatment of LNCaP cells resulted in enhanced activities of caspase-9 (tempo, 5 mM, 15 hours: approximately 2-fold) and caspase-3 (tempo, 2.5 mM, 24 hours: approximately 12-fold). Tempo treatment also led to an enhanced number of cells in G2/M phase of the cell cycle (tempo, 5.0 mM, 24 hours: DU-145, approximately 1.6-fold; PC-3, approximately 1.5-fold; LNCaP, approximately 5.3-fold), and decreased BrdU incorporation indicative of a decline in the number of proliferating cells (tempo, 2.5 mM, 24 or 48 hours; DU-145, approximately 2-3-fold; PC-3, approximately 1.2-fold; LNCaP, approximately 5-10-fold). Administration of tempo into LNCaP tumor-bearing mice resulted in a significant inhibition of tumor growth (percent initial tumor volume [Day 30, n = 4]: vehicle, 845.35 +/- 272.83; tempo, 9.72 +/- 9.72; tempo vs. vehicle, P < 0.02). In hormone-refractory prostate carcinoma cells, a combination of relatively low doses of tempo and doxorubicin or mitoxantrone caused enhanced cytotoxicity as compared with single agents. These data demonstrated that nitroxide tempo induced apoptosis and activated a caspase-mediated signaling pathway in prostate carcinoma cells. Tempo treatment also caused cell cycle arrest in G2/M phase and decreased the number of proliferating cells (S phase). Tempo treatment of tumor-bearing mice led to inhibition of tumor growth, suggesting that tempo is a novel member of the small-molecule family of antineoplastic agents.

11C]Choline as a PET biomarker for assessment of prostate cancer tumor models

[ 11C]Choline has been evaluated as a positron emission tomography (PET) biomarker for assessment of established human prostate cancer tumor models. [ 11C]Choline was prepared by the reaction of [ 11C]methyl triflate with 2-dimethylaminoethanol (DMAE) and isolated and purified by solid-phase extraction (SPE) method in 60–85% yield based on [ 11C]CO 2, 15–20 min overall synthesis time from end of bombardment (EOB), 95–99% radiochemical purity and specific activity >0.8 Ci/μmol at end of synthesis (EOS). The biodistribution of [ 11C]choline was determined at 30 min post iv injection in prostate cancer tumor models C4-2, PC-3, CWR22rv, and LNCaP tumor-bearing athymic mice. The results showed the accumulation of [ 11C]choline in these tumors was 1.0% dose/g in C4-2 mouse, 0.4% dose/g in PC-3 mice, 3.2% dose/g in CWR22rv mice, and 1.4% dose/g in LNCaP mice; the ratios of tumor/muscle (T/M) and tumor/blood (T/B) were 2.3 (T/M, C4-2), 1.4 (T/M, PC-3), 2.5 (T/M, CWR22rv), 1.2 (T/M, LNCaP) and 2.6 (T/B, C4-2), 2.6 (T/B, PC-3), 7.8 (T/B, CWR22rv), 3.2 (T/B, LNCaP), respectively. The micro-PET imaging of [ 11C]choline in prostate cancer tumor models was acquired from a C4-2, PC-3, CWR22rv, or LNCaP implanted mouse at 30 min post iv injection of 1 mCi of the tracer using a dedicated high resolution (<3 mm full-width at half-maximum) small FOV (field-of-view) PET imaging system, IndyPET-II scanner, developed in our laboratory, which showed the accumulation of [ 11C]choline in C4-2, PC-3, CWR22rv, or LNCaP tumor implanted in a nude athymic mouse. The initial dynamic micro-PET imaging data indicated the average T/M ratios were approximately 3.0 (C4-2), 2.1 (PC-3), 3.5 (CWR22rv), and 3.3 (LNCaP), respectively, which showed the tumor accumulation of [ 11C]choline in all four tumor models is high. These results suggest that there are significant differences in [ 11C]choline accumulation between these different tumor types, and these differences might offer some useful measure of tumor biological process.

Inhibition of LNCaP prostate tumor growth in vivo by an antisense oligonucleotide directed against the human androgen receptor.

We have shown recently that a 15-mer phosphorothioate oligodeoxynucleotide (ODNas750/15) that hybridizes to the (CAG)n polyglutamine region of mRNA encoding human androgen receptor (AR) inhibits the expression of AR in LNCaP prostate cancer cells in vitro. This AR downregulation was accompanied by significant cell growth inhibition and reduced PSA secretion. In the present study we investigated the effects of this antisense AR ODN on prostate tumor growth in vivo using a mouse xenograft model. Via subcutaneously implanted diffusion pumps, either ODNas750/15 or a scrambled control sequence ODNsr750/15 was continuously administered into LNCaP tumor-bearing male nude mice for 7 weeks. Compared with untreated control animals, treatment with ODNas750/15 resulted in significant tumor growth inhibition. Retardation of tumor growth was also significant in castrated mice, whereas the scrambled control ODN did not exert any effects. No side effects such as loss of body weight were observed at any time of treatment. ODN treatment was well tolerated and, in contrast to castration, did not induce shrinkage of mouse prostates. Both AR expression in the tumor and PSA levels in mouse serum correlated with tumor size. However, we failed to demonstrate a correlation between tumor retardation and Ki-67 antigen expression and the number of apoptotic cells, respectively. Testing of antisense-treated LNCaP cells revealed that expression levels of other proteins that contain shorter polyglutamine sequence stretches such as HDAC2, TFIID, and c-jun were not affected. The present study demonstrates that downregulation of AR with antisense ODNas750/15 causes prostate tumor growth inhibition. These results further point out the important role of the AR in prostate tumors and support further testing of AR downregulation for treatment of prostate cancer.