Castration-induced up-regulation of insulin-like growth factor binding protein-5 potentiates insulin-like growth factor-I activity and accelerates progression to androgen independence in prostate cancer models

Although insulin-like growth factor binding protein-5 (IGFBP-5) has been shown to be implicated in prostate cancer progression, the functional role of IGFBP-5 in progression to androgen-independence remains largely undefined. Here, we demonstrate substantial up-regulation of IGFBP-5 during castration-induced regression and androgen-independent (AI) progression in the mouse androgen-dependent (AD) Shionogi tumor model. To analyze the functional significance of these changes in IGFBP-5, human AD LNCaP prostate cancer cells were stably transfected with IGFBP-5 gene, and IGFBP-5-overexpressing LNCaP tumors progressed significantly faster to androgen independence after castration compared with controls. Antisense mouse IGFBP-5 oligodeoxynucleotides (ODNs) were then designed that reduced IGFBP-5 expression in Shionogi tumor cells in vitro in a dose-dependent and sequence-specific manner. Growth of Shionogi tumor cells was inhibited by antisense IGFBP-5 ODN treatment in a time- and dose-dependent manner, which could be reversed by exogenous IGF-I. However, antisense IGFBP-5 ODN treatment had no additive inhibitory effect on Shionogi tumor cell growth when IGF-I activity was neutralized by anti-IGF-I antibody. Antisense IGFBP-5 ODN treatment resulted in decreased mitogen-activated protein kinase activity and number of cells in the S + G2-M phases of the cell cycle that directly correlated with reduced proliferation rate of Shionogi tumor cells. Systemic administration of antisense IGFBP-5 ODN in mice bearing Shionogi tumors after castration significantly delayed time to progression to androgen independence and inhibited growth of AI recurrent tumors. These findings suggest that up-regulation of IGFBP-5 after castration serves to enhance IGF bioactivity and raise the possibility that the response of prostate cancer to androgen withdrawal can be enhanced by strategies, such as antisense IGFBP-5 ODN therapy, that target IGF signal transduction.     

Inhibition of tumor growth and progression of LNCaP prostate cancer cells in athymic mice by androgen and liver X receptor agonist

Androgen-dependent human LNCaP 104-S tumor xenografts progressed to androgen-independent relapsed tumors (104-Rrel) in athymic mice after castration. The growth of 104-Rrel tumors was suppressed by testosterone. However, 104-Rrel tumors adapted to androgen and regrew as androgen-stimulated 104-Radp tumors. Androgen receptor expression in tumors and serum prostate-specific antigen increased during progression from 104-S to 104-Rrel but decreased during transition from 104-Rrel to 104-Radp. Expression of genes related to liver X receptor (LXR) signaling changed during progression. LXRalpha, LXRbeta, ATP-binding cassette transporter A1 (ABCA1), and sterol 27-hydroxylase decreased during progression from 104-S to 104-Rrel. These coordinated changes in LXR signaling in mice during progression are consistent with our previous findings that reduction of ABCA1 gene expression stimulates proliferation of LNCaP cells. To test if attenuation of LXR signaling may enhance prostate cancer progression from an androgen-dependent state to an androgen-independent state, castrated mice carrying 104-S tumors were given the synthetic LXR agonist T0901317 by gavage. T0901317 delayed progression from 104-S to 104-Rrel tumors. Based on our in vivo model, androgen is beneficial for the treatment of androgen-independent androgen receptor-rich prostate cancer and modulation of LXR signaling may be a potentially useful therapy for prostate cancer.     

Castration-induced increases in insulin-like growth factor-binding protein 2 promotes proliferation of androgen-independent human prostate LNCaP tumors

Activation of alternative growth factor pathways after androgen withdrawal is one mechanism mediating androgen-independent (AI) progression in advanced prostate cancer. Insulin-like growth factor (IGF) I activation is modulated by a family of IGF binding proteins (IGFBPs). Although IGFBP-2 is one of the most commonly overexpressed genes in hormone refractory prostate cancer, the functional significance of changes in IGF-I signaling during AI progression remains poorly defined. In this article, we characterize changes in IGFBP-2 in the LNCaP tumor model after androgen withdrawal and evaluate its functional significance in AI progression using gain-of-function and loss-of-function analyses. IGFBP-2 mRNA and protein levels increase 2-3-fold after androgen withdrawal in LNCaP cells in vitro in LNCaP tumors during AI progression in vivo. Increased IGFBP-2 levels after castration were also identified using a human prostate tissue microarray of untreated and posthormone therapy-treated prostatectomy specimens. LNCaP cell transfectants that stably overexpressed IGFBP-2 progressed more rapidly after castration than control tumors. Antisense oligonucleotides (ASOs) targeting the translation initiation site of IGFBP-2 reduced IGFBP-2 mRNA and protein expression by >70% in a dose-dependent and sequence-specific manner. ASO-induced decreases in IGFBP-2-reduced LNCaP cell growth rates and increased apoptosis 3-fold. LNCaP tumor growth and serum prostate-specific antigen levels in mice treated with castration plus adjuvant IGFBP-2 ASOs were significantly reduced compared with mismatch control oligonucleotides. Increased IGFBP-2 levels after androgen ablation may represent an adaptive response that helps potentiate IGF-I-mediated survival and mitogenesis and promote androgen-independent tumor growth. Inhibiting IGFBP-2 expression using ASO technology may offer a treatment strategy to delay AI progression.     

Chemosensitization and delayed androgen-independent recurrence of prostate cancer with the use of antisense Bcl-2 oligodeoxynucleotides

BACKGROUND: Increased expression of the bcl-2 gene has been observed in prostate cancer cells after androgen withdrawal and has been associated with the development of androgen independence and chemoresistance. The objective of this study was to determine whether antisense Bcl-2 oligodeoxynucleotides could enhance paclitaxel cytotoxicity and delay androgen-independent progression. METHODS: Northern and western blot analyses were used to measure changes in Bcl-2 expression in mouse Shionogi tumor cells after treatment with antisense Bcl-2 oligodeoxynucleotides and/or paclitaxel. Growth inhibition and induction of apoptotic cell death were assessed with the use of standard methods. All P values are two-sided. RESULTS: Treatment of Shionogi tumor cells with 500 nM antisense Bcl-2 oligodeoxynucleotides decreased expression of Bcl-2 messenger RNA (mRNA) by approximately 85%. Paclitaxel treatment induced Bcl-2 protein phosphorylation but did not alter Bcl-2 mRNA expression. Antisense Bcl-2 oligodeoxynucleotide treatment substantially enhanced paclitaxel chemosensitivity in a dose-dependent manner. Characteristic apoptotic DNA laddering and cleavage of poly(adenosine diphosphate-ribose) polymerase were demonstrated only after combined treatment. Adjuvant in vivo administration of antisense Bcl-2 oligodeoxynucleotides and micellar paclitaxel following castration resulted in a statistically significant delay of androgen-independent, recurrent tumors compared with administration of either agent alone (P<.001, Mantel-Cox log-rank test). Combination therapy also statistically significantly inhibited the growth of established hormone-refractory tumors compared with treatment with either agent alone (P<.001, Student's t test). CONCLUSIONS. Combined treatment with antisense Bcl-2 oligodeoxynucleotides and paclitaxel could be a novel and attractive strategy to inhibit progression to androgen-independent disease as well as growth of hormone-refractory prostate cancer through deprivation of Bcl-2 function.     

Effect of isocaloric low-fat diet on prostate cancer xenograft progression to androgen independence

An isocaloric low-fat diet has been shown to slow androgen-sensitive Los Angeles Prostate Cancer-4 (LAPC-4) tumor growth in a mouse xenograft model. LAPC-4 cells were injected into male severe combined immunodeficient mice. After palpable tumors developed, the mice were divided into three groups, high-fat intact, high-fat castration, and low-fat castration. Tumor latency (18 versus 9 weeks; P < 0.001) and mouse survival (20.8 +/- 1.3 versus 13 +/- 0.7 weeks; P < 0.01) were significantly longer in the low-fat castration versus high-fat castration group. Reduced dietary fat intake delayed conversion from androgen-sensitive to -insensitive prostate cancer and significantly prolonged survival of severe combined immunodeficient mice bearing LAPC-4 xenografts.     

Progression to androgen-independent LNCaP human prostate tumors: cellular and molecular alterations

Lethal phenotypes of human prostate cancer are characterized by progression to androgen-independence and metastasis. For want of a clinically relevant animal model, mechanisms behind this progression remain unclear. Our study used an in vivo model of androgen-sensitive LNCaP human prostate cancer cell xenografts in male SCID mice to study the cellular and molecular biology of tumor progression. Primary tumors were established orthotopically, and the mice were then surgically castrated to withdraw androgens. Five generations of androgen-independent tumors were developed using castrated host mice. Tumor samples were used to determine expressions of cellular and molecular markers. Androgen-independent tumors had increased proliferation and decreased apoptosis compared to androgen-sensitive tumors, outcomes associated with elevated expression of p53, p21/waf1, bcl-2, bax and the bcl-2/bax ratio. Blood vessel growth in androgen-independent tumor was associated with increased expression of vascular endothelial growth factor. Overexpression of androgen receptor mRNA and reduced expression of androgen receptor protein in androgen-independent tumors suggest that the androgen receptor signaling pathway may play an important role in the progression of human prostate cancer to androgen-independence. The in vivo orthotopic LNCaP tumor model described in our study mimics the clinical course of human prostate cancer progression. As such, it can be used as a model for defining the molecular mechanisms of prostate cancer progression to androgen-independence and for evaluating the effect of preventive or therapeutic regimens for androgen-independent human prostate cancer.     

Short hairpin RNA knockdown of the androgen receptor attenuates ligand-independent activation and delays tumor progression

Progression to androgen independence is the lethal end stage of prostate cancer. We used expression of androgen receptor (AR)-targeted short hairpin RNAs (shRNA) to directly test the requirement for AR in ligand-independent activation of androgen-regulated genes and hormone-independent tumor progression. Transient transfection of LNCaP human prostate cancer cells showed that AR shRNA decreased R1881 induction of the prostate-specific antigen (PSA)-luciferase reporter by 96%, whereas activation by forskolin, interleukin-6, or epidermal growth factor was inhibited 48% to 75%. Whereas the antiandrogen bicalutamide provided no further suppression, treatment with the mitogen-activated protein kinase (MAPK) inhibitor U0126 completely abrogated the residual activity, indicating a MAPK-dependent, AR-independent pathway for regulating the PSA promoter. Expression of doxycycline-inducible AR shRNA expression in LNCaP cells resulted in decreased levels of AR and PSA as well as reduced proliferation in vitro. When these cells were grown as xenografts in immunocompromised mice, induction of AR shRNA decreased serum PSA to below castration nadir levels and significantly retarded tumor growth over the entire 55-day experimental period. This is the first demonstration that, by inducibly suppressing AR expression in vivo, there is an extensive delay in progression to androgen independence as well as a dramatic inhibition of tumor growth and decrease in serum PSA, which exceeds that seen with castration alone. Based on these findings, we propose that suppressing AR expression may provide superior therapeutic benefit in reducing tumor growth rate than castration and may additionally be very effective in delaying progression to androgen independence.     

Smad3 is overexpressed in advanced human prostate cancer and necessary for progressive growth of prostate cancer cells in nude mice.

PURPOSE: The purpose of this study was to investigate the potential role of Smad3, a key mediator of transforming growth factor-beta signaling, in progression of prostate cancer. EXPERIMENTAL DESIGN: Expression of Smad proteins was determined in human prostate cancer tissue array and cell lines. Growth and metastasis of cells overexpressing dominant-negative Smad3 (Smad3D) were studied to determine its role in tumor progression in mice. Cell growth, apoptosis, and expression of angiogenic molecules in tumor lesions were studied to determine potential pathways that Smad3 promotes tumor progression. RESULTS: Smad3 was overexpressed in human prostate cancer, which correlated with Gleason score and expression of proliferating cell nuclear antigen. Androgen-independent PC-3MM2 and DU145 cells expressed much higher levels of Smad3 than did androgen-dependent LNCaP, 22Rv1, and LAPC-4 cells. Overexpression of Smad3D in PC-3MM2 cells (PC-3MM2-Smad3D) had minimal direct effects on cell growth but attenuated effects of transforming growth factor-beta1 on gene expression and cell growth. Overexpression of Smad3D did not significantly alter tumor incidence but reduced tumor growth rate and metastasis incidence. Most cells in the control tumors, but not PC-3MM2-Smad3D tumors, were positively stained by an antibody to proliferating cell nuclear antigen. Microvessels and expression of angiogenic molecule interleukin-8 were significantly reduced in tumors from PC-3MM2-Smad3D cells. PC-3MM2-Smad3D tumors also expressed lower levels of vascular endothelial growth factor and platelet-derived growth factor. CONCLUSIONS: These data suggest that Smad3, through regulating angiogenic molecule expression in tumor cells, is critical for progression of human prostate cancer.     

Docetaxel followed by castration improves outcomes in LNCaP prostate cancer-bearing severe combined immunodeficient mice.

PURPOSE: Androgen ablation is the standard initial treatment for advanced prostate cancer; however, tumors eventually develop androgen independence and become incurable. Chemotherapy is commonly used after hormone treatment fails but has not shown significant survival benefit. Studies suggest that androgen ablation can select for a population of hormone-independent cells that are also relatively chemotherapy resistant. Thus, it may be therapeutically advantageous to target prostate cancer with chemotherapy before hormone ablation. This study was undertaken to determine the relative efficacy of such an approach in a preclinical model of prostate cancer. EXPERIMENTAL DESIGN: Severe combined immunodeficient mice bearing human LNCaP prostate tumors were treated with docetaxel and/or surgical castration applied singly, concurrently, or in different sequences. Treatment efficacy was determined by tumor volume and growth delay measurements. The extent of apoptosis in tumors in response to treatments was assessed via terminal deoxynucleotidyl transferase-mediated nick-end labeling (TUNEL) assays. In addition, Western blots were done to study the relative expression of Bcl-2 and Bax in the tumors. RESULTS: Docetaxel followed by castration showed the most potent antitumor effects. In contrast, with the exception of castration alone, castration followed by docetaxel produced the least antitumor activity. TUNEL assays confirmed that the density of apoptotic tumor cells was significantly greater for docetaxel followed by castration than for any other treatment. In tumors of mice treated with single modality therapies, Bax to Bcl-2 ratios decreased significantly after castration, whereas this ratio remained high after docetaxel treatment. CONCLUSION: A treatment sequence of docetaxel followed by hormone ablation may be more effective in treating prostate cancer than concurrent docetaxel/hormone therapy or hormone ablation followed by docetaxel.     

膀胱移行细胞癌中p53突变、bcl-2和PCNA表达的临床意义(英文)

目的探讨膀胱癌中 bcl-2、p53、PCNA 表达与细胞增殖、凋亡和临床病理学参数之间的关系。方法 SABC 免疫组化分折62例(T1G1-G339例,T2-T4aG3 NOM023例)甲醛固定和石蜡包埋的膀胱癌标本 bcl-2、p53和 PCNA 蛋白的免疫反应性。平均随访37个月,24例复发。增殖指数(PI)表示肿瘤细胞中 PCNA 阳性细胞百分比。TUNEL 法检测细胞凋亡,凋亡指数(AI)表示肿瘤细胞中凋亡细胞的百分比。结果 62例膀胱癌中,50例(80.0%)发生 p53突变,与 G1(72.7%)和 G2(78.5%)相比较 G3(91.3%)更多见(P<0.05);pT2期(95.7%)p53突变率较 pTa-1期(74.3%)高(P<0.01)。14例(22.5%)发现有 bcl-2表达,bcl-2表达阳性率 G3明显高于 G1和 G2(P<0.05),与分期无关(P>0.05)。Bcl-2表达与 p53突变无关。在膀胱癌中,PI 为17.2%～41.8%(平均为22.4%),AI 为1.9%～3.5%(平均为2.9%)。统计分析显示 PI 与肿瘤分级、分期关系密切,AI 与肿瘤的分级有明显关系。结论结果表明,p53突变与浸润性行为呈正相关。在膀胱癌中 p53和 PCNA 过表达可能能提供有价值的预后信息。随着肿瘤的进展,肿瘤细胞过度增殖可能伴有频繁的凋亡,但增殖指数的增加明显强于凋亡指数的增加。     

膀胱移行细胞癌中p53突变、bcl-2和PCNA表达的临床意义

To correlate the frequency of p53 mutations, bcl-2 expression and the proliferation status (proliferating cell nuclear antigen, PCNA) in patients with bladder cancer with cell proliferation, apoptosis and their clinico-pathologic findings. Paraffin-embedded sections from 39 superficial (T1G1-G3) and 23 invasive (T2-T4a G3 N0M0) primary transitional cell carcinomas (TCC) in the bladder were investigated immunohistochemically for p53, bcl-2 and PCNA. The median follow-up was 37 months; 24 had recurrences. The proliferation index (PI) was expressed as a percentage of the PCNA-positive cells in the tumor cells. Apoptosis was detected by terminal deoxy-nucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL), and the apoptotic index (AI) was expressed as a percentage of the TUNEL-positive tumor cells. p53 mutation was identified in 50 patients (80.6%). The mutation was most common in tumors grade 3 (91.3%) as compared to grade 2 (78.5%) and grade 1 (72.7%, P<0.05). Stage pT2 tumors had a higher frequency of p53 mutation (95.7%) as compared to pTa-1 tumors (74.3%, P<0.01). Only 14 tumors (22.5%) expressed bcl-2; grade 3 tumors expressed bcl-2 significantly more frequently (P<0.05); there was no correlation between bcl-2 and tumor stage. There was no interrelation between p53 mutation and bcl-2 expression (P>0.05). The PI ranged from 17.2% to 41.8% (median 22.4%) and the AI from 1.9% to 3.5% (median 2.9%) in bladder cancer. Statistical analyses revealed a close associations between PI, AI and tumor grade and stage of bladder cancer. p53 mutation correlates with invasion. p53 and PCNA overexpression may offer valuable additional prognostic information in bladder tumors. With the progression of the tumor grade, cell proliferation may be accompanied by frequent apoptosis in bladder cancer, but the PI increased much more than the AI.     

NE-10 neuroendocrine cancer promotes the LNCaP xenograft growth in castrated mice

Increases in neuroendocrine (NE) cells and their secretory products are closely correlated with tumor progression and androgen-independent prostate cancer. However, the mechanisms by which NE cells influence prostate cancer growth and progression, especially after androgen ablation therapy, are poorly understood. To investigate the role of NE cells on prostate cancer growth, LNCaP xenograft tumors were implanted into nude mice. After the LNCaP tumors were established, the NE mouse prostate allograft (NE-10) was implanted on the opposite flank of these nude mice to test whether NE tumor-derived systemic factors can influence LNCaP growth. Mice bearing LNCaP tumors with or without NE allografts were castrated 2 weeks after NE tumor inoculation, and changes in LNCaP tumor growth rate and gene expression were investigated. After castration, LNCaP tumor growth decreased in mice bearing LNCaP tumors alone, and this was accompanied by a loss of nuclear androgen receptor (AR) localization. In contrast, in castrated mice bearing both LNCaP and NE-10 tumors, LNCaP tumors continued to grow, had increased levels of nuclear AR, and secreted prostate-specific antigen. Therefore, in the absence of testicular androgens, NE secretions were sufficient to maintain LNCaP cell growth and androgen-regulated gene expression in vivo. Furthermore, in vitro experiments showed that NE secretions combined with low levels of androgens activated the AR, an effect that was blocked by the antiandrogen bicalutamide. Because an increase in AR level has been reported to be sufficient to account for hormone refractory prostate cancers, the NE cell population ability to increase AR level/activity can be another mechanism that allows prostate cancer to escape androgen ablation therapy.     

Progression to androgen independence is delayed by adjuvant treatment with antisense Bcl-2 oligodeoxynucleotides after castration in the LNCaP prostate tumor model.

Bcl-2 has emerged as a critical regulator of apoptosis in a variety of cell systems and is up-regulated during progression to androgen independence in prostate cancer cells. The objectives of this study were to characterize changes in Bcl-2 after androgen withdrawal and during progression to androgen independence in the human prostate LNCaP tumor model and determine whether adjuvant use of antisense Bcl-2 oligodeoxynucleotides (ODNs) with androgen ablation delays progression to androgen independence. Bcl-2 expression in LNCaP cells is down-regulated to undetectable levels by androgen in vitro and up-regulated after castration in vivo. Antisense Bcl-2 ODN treatment reduced LNCaP cell Bcl-2 messenger RNA and protein levels by >90% in a sequence-specific and dose-dependent manner at concentrations >50 nM. Bcl-2 mRNA levels returned to pretreatment levels by 48 h after discontinuing treatment. Athymic male mice bearing SQ LNCaP tumors were castrated and injected i.p. with 12.5 mg/kg/day with two-base mismatch ODN control, reverse polarity ODN control, or antisense Bcl-2 ODN. Tumor volume in control mice gradually increased 5-fold (range, 3-6) by 12 weeks after castration compared to a 10-50% decrease in precastrate tumor volume in mice treated with antisense Bcl-2 ODN. Changes in serum PSA paralleled changes in tumor volume, increasing 4-fold faster above nadir in controls than in mice treated with antisense Bcl-2 ODN. After decreasing 70% by 1 week after castration, PSA increased 1.6-fold above precastrate levels by 11 weeks in controls while staying 30% below precastrate levels in antisense-treated mice. In a second group of experiments, LNCaP tumor growth and serum PSA levels were 90% lower (P<0.01) in mice treated with antisense Bcl-2 ODN compared with mismatch or reverse polarity ODN controls. These results support the hypothesis that Bcl-2 helps mediate progression to androgen independence and is an appropriate target for antisense therapy.     

NDRG2 acts as a negative regulator downstream of androgen receptor and inhibits the growth of androgen-dependent and castration-resistant prostate cancer

Castration resistance is a major issue during castration therapy for prostate cancer and thus more effective treatment are needed for castration-resistant prostate cancer (CRPC). NDRG2 (N-Myc downstream regulated gene 2), a recently identified tumor suppressor, was previously shown to inhibit the proliferation and invasion of prostate cancer, but whether NDRG2 is involved in CRPC remains to be known. Because androgen receptor (AR) axis plays an important role in castration resistance, we evaluate the role of NDRG2 in AR signaling and CRPC. Immunohistochemistry examination of prostate cancer tissues demonstrated that the expression of NDRG2 is negatively correlated with that of AR and c-Myc. Furthermore, AR negatively regulates NDRG2, as well as alters levels of c-Myc and prostate specific antigen (PSA). Forced expression of NDRG2 significantly inhibits the in vitro growth of androgen-dependent and castration-resistant prostate cancer cells; this was accompanied by alterations in PSA, but not by those of AR and c-Myc. Finally, by mimicking castration therapy in a xenograft mouse model, we showed that lentivirus-mediated NDRG2 overexpression efficiently overcomes castration resistance. Thus, by acting as a negative regulator downstream of AR, NDRG2 may emerge as a potential therapy molecule for CRPC.