Castration-resistant Prostate Cancer Phenotype Research Articles

CDK12-inactivation-induced MYC signaling causes dependency on the splicing kinase SRPK1.

Inactivation of cyclin-dependent kinase 12 (CDK12) characterizes an aggressive sub-group of castration-resistant prostate cancer (CRPC). Hyper-activation of MYC transcription factor is sufficient to confer the CRPC phenotype. Here, we show that loss of CDK12 promotes MYC activity, which renders the cells dependent on the otherwise non-essential splicing regulatory kinase SRSF protein kinase 1 (SRPK1). High MYC expression is associated with increased levels of SRPK1 in patient samples, and overexpression of MYC sensitizes prostate cancer cells to SRPK1 inhibition using pharmacological and genetic strategies. We show that Endovion (SCO-101), a compound currently in clinical trials against pancreatic cancer, phenocopies the effects of the well-characterized SRPK1 inhibitor SRPIN340 on nascent transcription. This is the first study to show that Endovion is an SRPK1 inhibitor. Inhibition of SRPK1 with either of the compounds promotes transcription elongation, and transcriptionally activates the unfolded protein response. In brief, here we discover that CDK12 inactivation promotes MYC signaling in an SRPK1-dependent manner, and show that the clinical grade compound Endovion selectively targets the cells with CDK12 inactivation.

Cholesterol Triggers Nuclear Co-Association of Androgen Receptor, p160 Steroid Coactivators, and p300/CBP-Associated Factor Leading to Androgenic Axis Transactivation in Castration-Resistant Prostate Cancer.

Cholesterol modulates intratumoral androgenic signaling in prostate cancer; however, the molecular mechanisms underlying these changes in castration-resistant prostate cancer (CRPC) are not fully elucidated. Herein, we investigated the effect of cholesterol on androgen receptor (AR) coactivators expression and tumorigenesis in vitro and in vivo. Herein, we monitored the expression of AR coactivators (SRC-1, 2, 3 and PCAF) genes in PC-3 cells exposed to 2µg/mL of cholesterol for 8 hours by qPCR. We also performed cell migration at 0, 8, 24, 48 and 72h and flow cytometry assays (viability, apoptosis, and cell cycle) after a 24h exposure. Immunofluorescence assay was performed to evaluate the protein expression of the AR coactivators. Additionally, in vivo experiments were conducted using 22 male NOD/SCID mice. Mice were fed a standard (Control) or hypercholesterolemic (HCOL) diet for 21 days and then subcutaneously implanted with PC-3 cells. The tumor volume was calculated every two days, and after four weeks, the tumors were resected, weighed, and the serum lipid profile was measured. We also measured the intratumoral lipid profile and AR coactivators gene and protein expression by qPCR and Western Blot, respectively. Intratumor testosterone and dihydrotestosterone (DHT) concentrations were determined using ELISA. Cholesterol up-regulated the gene expression of coactivators SRC-1, SRC-2, SRC-3 and PCAF, increasing AR expression in PC-3 cells. Next, cholesterol-supplemented PC-3 cells exhibited increased cell migration and altered cell cycle phases, leading to changes in proliferation and reduced apoptosis. We found that SRC-1, SRC-2, SRC-3 and PCAF proteins co-localized in the nucleus of cholesterol-supplemented cells and co-associate with AR. In the in vivo model, the hypercholesterolemic (HCOL) group displayed higher serum total and intratumoral cholesterol levels, increased testosterone and dihydrotestosterone concentrations, and up-regulated AR coactivator expression. The tumor volume of the HCOL group was significantly higher than the control group. Our findings revealed that increased nuclear translocation of the coactivators leads to up-regulated AR gene and protein expression, potentially influencing tumor progression. Studies targeting cholesterol-modulated changes in AR coactivator expression may provide insights into the molecular mechanisms associated with the CRPC phenotype.

Identification of the Regulatory Targets of miR-3687 and miR-4417 in Prostate Cancer Cells Using a Proteomics Approach.

MicroRNAs (miRNA) are ubiquitous non-coding RNAs that have a prominent role in cellular regulation. The expression of many miRNAs is often found deregulated in prostate cancer (PCa) and castration-resistant prostate cancer (CRPC). Although their expression can be associated with PCa and CRPC, their functions and regulatory activity in cancer development are poorly understood. In this study, we used different proteomics tools to analyze the activity of hsa-miR-3687-3p (miR-3687) and hsa-miR-4417-3p (miR-4417), two miRNAs upregulated in CRPC. PCa and CRPC cell lines were transfected with miR-3687 or miR-4417 to overexpress the miRNAs. Cell lysates were analyzed using 2D gel electrophoresis and proteins were subsequently identified using mass spectrometry (Maldi-MS/MS). A whole cell lysate, without 2D-gel separation, was analyzed by ESI-MS/MS. The expression of deregulated proteins found across both methods was further investigated using Western blotting. Gene ontology and cellular process network analysis determined that miR-3687 and miR-4417 are involved in diverse regulatory mechanisms that support the CRPC phenotype, including metabolism and inflammation. Moreover, both miRNAs are associated with extracellular vesicles, which point toward a secretory mechanism. The tumor protein D52 isoform 1 (TD52-IF1), which regulates neuroendocrine trans-differentiation, was found to be substantially deregulated in androgen-insensitive cells by both miR-3687 and miR-4417. These findings show that these miRNAs potentially support the CRPC by truncating the TD52-IF1 expression after the onset of androgen resistance.

Abstract 397: Mesenchymal stem cell-derived systemic NRG-1 mediates a targetable molecular switch in metastatic prostate cancer

Abstract NRG-1 signals through epidermal growth factor receptor (EGFR) family members. Despite promising preclinical data, HER2 blockade in prostate cancer has failed to improve outcomes in clinical trials.1-4 We have discovered a novel complex systemic role of NRG-1 that drives sensitivity and resistance to androgen deprivation therapy (ADT) in castration-sensitive (CSPC) and castration resistant prostate cancer (CRPC), respectively. Significantly, sensitivity to ADT can be restored in CRPC by manipulating NRG-1 signaling. Our data posit NRG-1 as a systemic “switch” in prostate cancer. Plasma NRG-1 is elevated in our cohort of patients with metastatic CRPC (mean 4.9ng/ml) versus healthy controls (mean 3.2ng/ml, p<0.0001) or metastatic CSPC (mean 3.4ng/ml, p<0.0001). Paradoxically, high systemic NRG-1 predicted superior OS and PFS in CSPC but inferior clinical outcomes in CRPC. Consistently, opposite cell survival between LNCaP (CSPC) vs Du145 & PC3 (CRPC) was observed with recombinant human NRG-1 and enzalutamide (ENZ). ENZ combined with increasing NRG-1 concentration induced LNCaP cell death in an additive manner, but NRG-1 rescued Du145 & PC3 from ENZ-induced death in a dose-dependent manner. We next hypothesized that differential NRG-1 downstream signaling is mediated by engagement with distinct EGFR receptor dimers. While HER2 expression is similar, LNCaP express higher HER3 than Du145 & PC3. High ratio of HER2 to HER3 in Du145 & PC3 mirrors clinical reports of HER2 upregulation in CRPC5,6 and also predicts patient survival in the Stand Up to Cancer cohort.7 Significantly, we recapitulated the CRPC phenotype in LNCaP by inducing HER2 overexpression, HER3 suppression, and chemically-mediated HER2/HER3 dimerization. Conversely, HER2 knockdown sensitized Du145 cells to ENZ. Next, we queried composite single-cell whole human8 and CRPC9 transcriptomes for NRG-1 expression and discovered that the source of NRG-1 is the patients’ own mesenchymal stem cells (MSCs). Bone-derived MSC outgrowth cells produced copious NRG-1, which was increased substantially by coincubation with prostate cancer cell supernatants. Importantly, we were able to manipulate MSCs to reduce their NRG-1 production as a possible clinical translation. Similarly, patients treated with these compounds showed significant reduction in plasma NRG-1 levels after treatment. Additional clinical studies are pending. Together, our observations confirm that NRG-1 has differential signaling: HER3 homodimerization leads to prostate cancer cell death, whereas heterodimerization of HER3 with HER2 leads to prostate cancer cell survival via ADT resistance in a plasma NRG-1 dependent manner. Consequently, HER2 and HER3 receptor availability determine the molecular switch of NRG-1 in prostate cancer. Therefore, NRG-1 can be both a prognostic marker and therapeutic target in CRPC, and multiple clinical trials are pending. Citation Format: Jacob Orme, Roman Thaler, Dejie Wang, Siven Chinniah, Jacob Hirdler, Fernando Quevedo, Lance Pagliaro, Kwon Eugene, Alan Bryce, Brian Costello, Haojie Huang, Sean Park. Mesenchymal stem cell-derived systemic NRG-1 mediates a targetable molecular switch in metastatic 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 397.

Additional activation of the AR gene may be involved in the development of the castration resistance phenotype in prostate cancer

IntroductionSeveral studies have already shown that changes in the AR gene may be associated with a more aggressive disease phenotype and even castration-resistant prostate cancer. Thus, we investigated cytogenetic and molecular alterations linked to AR. Materials and methodsTo evaluate AR methylation, we performed a cytogenetic-molecular analysis using fluorescence in situ hybridization that uses specific probes for the AR gene (Xq11.12) and the X chromosome centromere. For AR activity, we performed a qualitative analysis of human androgen receptor activity. To analyze the expression of AR in PC3 and LNCaP cell lines, we used qPCR assays. ResultsIn the qPCR assay, we found downregulation of AR in the PC3 cell line compared with the LNCaP. We found the presence of X chromosome polysomy in PC-3 and LNCaP cell lines by FISH assay. In the HUMARA-Q assay, we found two X chromosomes/cell and the activity of both AR in the PC-3 cell line. In LNCaP cells, we found two X chromosomes/cell and methylation of only one AR. ConclusionCastration-resistant prostate cancer phenotype represents a significant challenge in the setting of urological management. The X chromosomes and AR-linked alterations may contribute to a better understanding of the disease. However, further studies should be performed in an attempt to elucidate as much as possible the role of AR in the castration-resistant prostate cancer phenotype.

Papel de la activación adicional del gen RA en el desarrollo del fenotipo resistente a la castración en el cáncer de próstata

IntroductionSeveral studies have already shown that changes in the AR gene may be associated with a more aggressive disease phenotype and even castration-resistant prostate cancer. Thus, we investigated cytogenetic and molecular alterations linked to AR. Materials and methodsTo evaluate AR methylation, we performed a cytogenetic-molecular analysis using fluorescence in situ hybridization that uses specific probes for the AR gene (Xq11.12) and the X chromosome centromere. For AR activity, we performed a qualitative analysis of human androgen receptor activity. To analyze the expression of AR in PC3 and LNCaP cell lines, we used qPCR assays. ResultsIn the qPCR assay, we found downregulation of AR in the PC3 cell line compared with the LNCaP. We found the presence of X chromosome polysomy in PC-3 and LNCaP cell lines by FISH assay. In the HUMARA-Q assay, we found two X chromosomes/cell and the activity of both AR in the PC-3 cell line. In LNCaP cells, we found two X chromosomes/cell and methylation of only one AR. ConclusionCastration-resistant prostate cancer phenotype represents a significant challenge in the setting of urological management. The X chromosomes and AR-linked alterations may contribute to a better understanding of the disease. However, further studies should be performed in an attempt to elucidate as much as possible the role of AR in the castration-resistant prostate cancer phenotype.

Abstract 5217: RB loss reprograms AR and E2F1 signaling in models of prostate cancer progression

Abstract Prostatic adenocarcinoma (PCa) is the most frequently diagnosed non-cutaneous malignancy, and the third leading cause of cancer death in males in the United States. A crucial component to the development and progression of PCa is the activity of the androgen receptor (AR). As such, targeting the AR-signaling axis through androgen deprivation therapy (ADT) is the first line of therapy for PCa. However, cells invariably become resistant to this therapy and men relapse with the incurable form of the disease termed, castration-resistant prostate cancer (CRPC). In addition to AR, another principal component aiding in the progression of disease is the retinoblastoma tumor suppressor protein (RB). RB functions to repress tumor development by negatively regulating the activity of the E2F family of transcription factors, preventing cell cycle progression. RB is lost in roughly 30% of CRPC tumors and is sufficient to induce a CRPC phenotype in hormone-sensitive cells under ADT conditions. Analyses into the molecular significance of RB loss on disease progression identified a potential cooperation between AR and the RB-E2F1 signaling axis. Biological assessment performed in isogenic RB knockdown (i.e. hormone-sensitive and CRPC models) identified distinct functional consequences of RB loss depending on AR status and disease state. Transcriptome analysis identified divergently regulated gene signatures between disease stages in the presence of AR activation, which were not seen under ADT conditions, implicating a unique role of AR in transcriptional regulation with the loss of RB. Data to be discussed will also include further comparison of the E2F1 and AR cistromes in the absence of RB to identify the mechanism by which the AR-RB-E2F1 signaling axis function in promoting the progression of disease. Citation Format: Amy C. Mandigo, Chris McNair, Matthew J. Schiewer, Karen E. Knudsen. RB loss reprograms AR and E2F1 signaling in models of prostate cancer progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5217.

Expression of lncRNA MIR222HG co-transcribed from the miR-221/222 gene promoter facilitates the development of castration-resistant prostate cancer

Mechanisms by which non-coding RNAs contribute to the progression of hormone-sensitive prostate cancer (PCa) (HSPC) to castration-resistant PCa (CRPC) remain largely unknown. We previously showed that microRNA-221/222 is up-regulated in CRPC and plays a critical role in modulating androgen receptor function during CRPC development. With further investigation, we characterized a putative promoter region located 23.3 kb upstream of the miR-221/222 gene, and this promoter is differentially activated in CRPC LNCaP-Abl cells, leading to the up-regulation of miR-221/222. Upon promoter activation, a set of polyadenylated long non-coding RNA (lncRNA) MIR222HGs was transcribed from this promoter region. Over-expression of these MIR222HGs increased androgen-independent cell growth and repressed the expression of androgen receptor-regulated dihydrotestosterone (DHT)-induced KLK3, TMPRSS2, and FKBP5 in HSPC LNCaP cells, hallmarks of the CRPC phenotype. Clinically, increased expression of MIR222HG is associated with PCa progression to CRPC. In primary tumors, expression levels of MIR222HG and miR-221/222 inversely correlate with Gleason score and androgen receptor (AR) pathway activity. Interestingly, MIR222HG is Argonaute 2-bound and its expression is Dicer 1-dependent, suggesting its functional association with the RNA-induced silencing complex. Further studies led to the hypothesis that MIR222HG may potentially affect miR-mediated expression silencing, subsequently leading to AR reprogramming. Our study highlights an essential role of a non-coding RNA in CRPC development and that differential activation of a single promoter can up-regulate two different types of non-coding RNAs, miR-221/222 and lncRNA MIR222HG, in CRPC. Additionally, this study reveals a novel function of lncRNAs as a modulator of Argonaute-mediated RNA-induced silencing complex.

The dark side of glucose transporters in prostate cancer: Are they a new feature to characterize carcinomas?

One of the hallmarks of cancer cells is the increased ability to acquire nutrients, particularly glucose and glutamine. Proliferating cells need precursors for cell growth and NADPH reducing equivalents for survival. The principal responsible for glucose uptake is facilitative glucose transporters (GLUTs), which usually are overexpressed in cancer cells. Besides their role in glucose uptake, GLUT transporters are able to transport other compounds such as dehydroascorbic acid or uric acid. They play a major role in tumor progression and cellular processes such as regulated cell death. The prostate gland has the particular characteristic of being more glycolytic than other non-pathological tissues given an accumulation of citrate in the seminal fluid and the inhibition of m-aconitase that affects to tricarboxylic acid cycle. In prostate cancer (PCa), androgens increase glucose uptake, upregulate GLUT transporters such as GLUT1 and GLUT3 and stimulate AMP-activated protein kinase pathway, suggesting a possible connection between glycolytic and androgenic signaling. Interestingly, diabetes is not a risk factor for PCa, as it is in other cancers, while insulin stimulates progression and insulin-like growth factor 1 pathway plays an important role in PCa progression. It was recently found that PCa cells overexpress GLUT4 and, more importantly, that it seems to be related to the castration-resistant prostate cancer (CRPC) phenotype, although little is known about its participation in tumor progression. This review will focus on the role of GLUT transporters along with PCa progression, and the involvement of GLUT4 on CRPC phenotype transition would be considered.

Abstract 1585: Endostatin inhibits androgen-independent prostate cancer growth by suppressing nuclear receptor-mediated oxidative stress

Abstract Androgen-deprivation therapy has been identified to induce oxidative stress in prostate cancer (PCa), leading to re-activation of androgen receptor (AR) signaling in a hormone-refractory manner. Thus, antioxidant therapies have gained attention as adjuvants for castration-resistant PCa (CRPC). Here, we report for the first time that human endostatin (ES) prevents androgen-independent growth phenotype in PCa cells through its molecular targeting of AR and glucocorticoid receptor (GR), and downstream pro-oxidant signaling. This reversal following ES treatment significantly decreased PCa cell proliferation through downregulation of GR, and upregulation of manganese superoxide dismutase and reduced glutathione levels. Proteome and biochemical analyses of ES-treated PCa cells further indicated a significant upregulation of enzymes in major ROS scavenging machinery, including catalase, glutathione synthetase, glutathione reductase, NADPH-cytochrome P450 reductase, biliverdin reductase and thioredoxin reductase, resulting in a concomitant reduction of intracellular ROS. ES further augmented antioxidant system through upregulation of glucose influx, pentose phosphate pathway (PPP) and NAD salvaging pathway. This shift in cancer cell redox homeostasis by ES significantly decreased the effect of protumorigenic oxidative machinery on androgen-independent PCa growth, suggesting that ES can suppress GR-induced CRPC phenotype upon AR antagonism, and dual targeting action of ES on AR and GR can be further translated to PCa therapy. Citation Format: Joo Hyoung Lee, Minsung Kang, Gurudatta Naik, James A. Mobley, Guru Sonpavde, W. Timothy Garvey, Victor M. Darley-Usmar, Selvarangan Ponnazhagan. Endostatin inhibits androgen-independent prostate cancer growth by suppressing nuclear receptor-mediated oxidative stress [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1585. doi:10.1158/1538-7445.AM2017-1585

Abstract LB-087: Stage specific re-calibration of E2F1 function after RB loss

Abstract Prostate cancer (PCa) is the most frequently diagnosed non-cutaneous malignancy, and the third leading cause of cancer death in males in the United States. The development of the disease is reliant on the activity of the androgen receptor (AR), which promotes proliferation and is required for cell growth and survival. Deregulation of AR leads to the progression of PCa to the incurable form of disease termed castration-resistant prostate cancer (CRPC). One of the underlying mechanisms of AR deregulation is the loss of function of the retinoblastoma (RB) tumor suppressor protein. RB loss is almost exclusively seen in CRPC and is sufficient to induce a CRPC phenotype in primary PCa models. However, RB function is only lost in roughly 30% of tumors. The remaining 70% of tumors that progress to CRPC do so via other mechanisms and retain RB function. A subset of RB positive CRPC tumors progress to lose RB function even in this post-CRPC transition stage of disease. Biological assessment performed in isogenic RB knockdown, both hormone-sensitive and CRPC models, identified distinct functional consequences of RB loss depending on disease state. Transcriptome analysis identified opposing regulated gene signatures between disease stages. Further investigation of the E2F1 cistrome revealed differential E2F1 binding with RB loss in hormone sensitive and CRPC models, identifying distinct roles of E2F1, in the absence of RB, in different disease states. Data to be discussed reveal the stage-specific molecular pathways driven by E2F1 upon RB loss with the potential to promote disease progression. Citation Format: Amy C. Mandigo, Christopher McNair, Kexin Xu, Fugen Li, Matthew J. Schiewer, Myles Brown, Karen E. Knudsen. Stage specific re-calibration of E2F1 function after RB loss [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-087. doi:10.1158/1538-7445.AM2017-LB-087

Abstract A10: LncRNA MIR222HG transcribed from the miR-221/222 promoter are associated with the development of castration resistant prostate cancer

Abstract We previously found that microRNA-221 and 222 play a crucial role in regulating the AR function during the castration resistant prostate cancer (CRPC) development. We further investigated mechanisms involved in the differential expression of miR-221/222 in prostate cancer cell lines. Based on transcriptome and histone modification data, we recognized a putative promoter region located at 23.3 kb upstream of the miR-221/222. By further characterizing transcriptional events occurred in this promoter region, we identified a two- exonic, polyadenylated long non-coding RNA (lncRNA), MIR222HG. Forced over-expression MIR222HG significantly increased androgen-independent cell growth and repressed DHT induced PSA expression in LNCaP cells, a hallmark of CRPC phenotype. Expression level of MIR222HG is significantly associated with human prostate cancer progression from localized hormone sensitive prostate cancer (HSPC) to CRPC. Taken together, lncRNA MIR222HG, which is co-transcribed from miR-221/222 promoter region, mediated AR transcriptional regulation and may involved in transformation process from HSPC to CRPC. Further study on MIR222HG may help understand the CRPC development processes. Citation Format: Fangfang Qu, Tong Sun, Xiaodong Wang, Gwo-Shu Mary Lee, Philip W. Kantoff. LncRNA MIR222HG transcribed from the miR-221/222 promoter are associated with the development of castration resistant prostate cancer. [abstract]. In: Proceedings of the AACR Special Conference on Noncoding RNAs and Cancer: Mechanisms to Medicines ; 2015 Dec 4-7; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2016;76(6 Suppl):Abstract nr A10.

Identification of Androgen Receptor Splice Variants in the Pten Deficient Murine Prostate Cancer Model.

Androgen receptor (AR) variants are associated with resistance to anti androgen therapy both in human prostate cancer cell lines and clinical samples. These observations support the hypothesis that AR isoform accumulation is a consequence of selective therapeutic pressure on the full length AR. The Pten deficient prostate cancer model proceeds with well-defined kinetics including progression to castration resistant prostate cancer (CRPC). While surgical castration and enzalutamide treatments yield an initial therapeutic response, Pten-/-epithelia continue to proliferate yielding locally invasive primary tumor pathology. That most epithelium remains AR positive, but ligand independent, suggests the presence of oncogenic AR variants. To address this hypothesis, we have used a panel of recently described Pten-/- tumor cell lines derived from both from hormone intact (E4, E8) and castrated Pten mutants (cE1, cE2) followed by RACE PCR to identify and characterize three novel truncated, amino terminus containing AR variants (mAR-Va, b, c). Variants appear not only conserved throughout progression but are correlated with nearly complete loss of full length AR (AR-FL) at castrate androgen levels. The overexpression of variants leads to enhanced transcriptional activity of AR while knock down studies show reduced transcriptional output. Collectively, the identification of truncated AR variants in the conditional PTEN deletion model supports a role for maintaining the CRPC phenotype and provides further therapeutic applications of this preclinical model.

MiR-221 promotes the development of androgen independence in prostate cancer cells via downregulation of HECTD2 and RAB1A

Hormone-sensitive prostate cancer typically progresses to castration resistant prostate cancer (CRPC) after the androgen deprivation therapy. We investigated the impact of microRNAs (miRs) in the transition of prostate cancer to CRPC. MiR-221/-222 was highly expressed in bone metastatic CRPC tumor specimens. We previously demonstrated that transient overexpression of miR-221/-222 in LNCaP promoted the development of the CRPC phenotype. In current study, we show that stably overexpressing miR-221 confers androgen independent (AI) cell growth in LNCaP by rescuing LNCaP cells from growth arrest at G1 phase due to the lack of androgen. Overexpressing of miR-221 in LNCaP reduced the transcription of a subgroup of androgen-responsive genes without affecting the androgen receptor (AR) or AR-androgen integrity. By performing systematic biochemical and bioinformatical analyses, we identified two miR-221 targets, HECTD2 and RAB1A, which could mediate the development of CRPC phenotype in multiple prostate cancer cell lines. Downregulation of HECTD2 significantly affected the androgen-induced and AR-mediated transcription, and downregulation of HECTD2 or RAB1A enhances AI cell growth. As a result of the elevated expression of miR-221, expression of many cell cycle genes was altered and pathways promoting epithelial to mesenchymal transition/tumor metastasis were activated. We hypothesize that a major biological consequence of upregulation of miR-221 is reprogramming of AR signaling, which in turn may mediate the transition to the CRPC phenotype.

Abstract LB-136: Creation of androgen independent prostate cancer cell lines using targeting nucleases.

Abstract Understanding mechanisms by which advanced prostate cancer (PCa) progresses to a castration resistant PCa (CRPC) phenotype is crucial for tailoring targeted therapies for individual patients. Constitutively active androgen receptor (AR) splice variants that lack the ligand binding domain drive androgen independent growth in cell lines and xenograft models of PCa and their overexpression in CRPC metastases is associated with poor prognosis. However, the mechanism of AR splice variant overexpression in CRPC is not completely understood. We have shown that diverse genomic rearrangements within the AR gene are linked to AR splicing alterations in PCa cell lines, xenografts, and CRPC metastases. To test whether these AR gene rearrangements drive AR splice variant synthesis and a CRPC phenotype, we developed transcription activator-like effector nucleases (TALENs) for precision genome engineering in androgen-sensitive PCa cells. Engineering of specific AR gene rearrangements induced splicing alterations and efficient expression of AR splice variants. Functionally, these genome-engineered cells displayed constitutive, ligand-independent AR transcriptional activity and an androgen-independent growth profile. These fundamental properties of CRPC were blocked following siRNA-mediated knock-down of truncated AR variants. Overall, these data demonstrate that AR gene rearrangements induce fundamental aspects of the CRPC phenotype including constitutive, ligand-independent, AR splice variant activity. Overall, these data advance the concept of AR splice variants as key drivers of advanced disease, and provide new genome-engineered models that could be used to develop agents targeted to these AR-derived species. Citation Format: Michael D. Nyquist, Yingming Li, Scott M. Dehm. Creation of androgen independent prostate cancer cell lines using targeting nucleases. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-136. doi:10.1158/1538-7445.AM2013-LB-136

Inhibition of p53 expression modifies the specificity of chromatin binding by the androgen receptor

The androgen receptor (AR) is known to play a critical role in prostate cancer (PC). p53 likely also plays a role given that p53 mutations are commonly found in advanced PC, and loss of wild-type protein function contributes to the phenotype of castration-resistant prostate cancer (CRPC). Nevertheless, the extent of the contribution of p53 dysfunction to PC remains unclear. Here we analyze the effects of p53 inhibition in PC cells and show that it has significant consequences for both the interaction between AR, and chromatin and the proliferative capacity of these cells. Inhibition of p53 expression enabled LNCaP cells to proliferate independently of androgens. Moreover, it modified the genome-wide binding pattern of AR. ChIP-sequnce analyis (ChIP-seq) revealed that fewer AR-binding sites were present in the context of p53 inhibition, suggesting that wild-type p53 is required for stable binding of AR to certain chromatin regions. Further analysis revealed that a lower AR occupancy was accompanied by a reduction in FoxA1 binding at regulatory regions of AR-dependent genes. Our study also identifies a pool of genes that may be transcriptionally regulated by AR only in the absence of p53, and that may contribute to the CRPC phenotype. Overall, our results point to p53 playing an important role in regulating AR activity across the genome.

The altered expression of MiR‐221/‐222 and MiR‐23b/‐27b is associated with the development of human castration resistant prostate cancer

We have previously identified seven miRs-miR-221, -222, -23b, -27b, -15a, -16-1, and -203, that are differentially expressed in the hormone sensitive LNCaP cell line and the hormone resistant LNCaP-abl cell line and hypothesized that these miRs may characterize certain subtypes of human castration resistant prostate cancer (CRPC). Functional studies in cell culture systems have been performed to determine the effect of alternated expression level on cellular response to androgen treatment. To determine the clinical relevance of the expression patterns of these miRs, we compared the expression levels of these seven miRs in normal prostate tissues from 86 individuals, prostate tumor tissues from 34 individuals with localized hormone naïve disease, and bone-derived metastatic CRPC tissues from 17 individuals. The altered expression of miR-221/-222 (as previously described) or miR-203 affected the cellular response to androgen treatment, suggesting their potential involvement in the transition to CRPC. However, the expression of miR-23b, -27b, -15a, and -16-1 did not have a significant influence in the cellular response to androgen treatment, suggesting that these miRs may not play a causative role in the CRPC phenotype. Comparison of the expression levels of these miRs in tissue samples revealed that strikingly, ∼90% of the analyzed metastatic CRPC tumors could be characterized by the increased miR-221/-222 expression and the down-regulated miR-23b/-27b expression. This finding suggests that altered miR-221/-222 and miR-23b/-27b expression may be associated with the CRPC process.

Abstract 4556: AR intragenic rearrangement and altered androgen receptor mRNA splicing in castration-resistant prostate cancer

Abstract Androgen depletion for advanced prostate cancer (PCa) targets activity of the androgen receptor (AR), a steroid receptor transcription factor required for PCa growth. The emergence of lethal castration-resistant PCa (CRPCa) is marked by aberrant re-activation of the AR despite ongoing androgen depletion. Recently, alternative splicing has been described as a mechanism giving rise to COOH-terminally truncated, constitutively active AR isoforms that can support the CRPCa phenotype. However, the pathologic origin of these truncated AR isoforms has not been described. The goal of this study was to investigate alterations in AR expression arising in a cell-based model of PCa progression driven by truncated AR isoform activity. We demonstrate that stable, high-level expression of truncated AR isoforms in 22Rv1 CRPCa cells coincides with intragenic rearrangement of a ∼35kb AR genomic segment, which contains several alternative AR exons. Analysis of metastatic CRPCa tissues indicated that related AR copy number alterations are frequent and often occur in conjunction with high-level AR amplification. Nucleotide-level resolution of the break fusion junction in 22Rv1 cells revealed a DNA repair signature consistent with a microhomology-mediated, replication-based mechanism of origin. Together, these data provide the first report of AR intragenic rearrangements in CRPCa and a link with pathologic expression of truncated AR isoforms in a cell-based model of PCa progression. 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 4556. doi:10.1158/1538-7445.AM2011-4556

IL-6/IL-6R as a potential key signaling pathway in prostate cancer development

Interleukin-6 (IL-6) is a pleiotropic cytokine involved in prostate regulation and in prostate cancer (PC) development/progression. IL-6 acts as a paracrine and autocrine growth stimulator in benign and tumor prostate cells. The levels of IL-6 and respective receptors are increased during prostate carcinogenesis and tumor progression. Several studies reported that increased serum and plasma IL-6 and soluble interleukin-6 receptor levels are associated with aggressiveness of the disease and are associated with a poor prognosis in PC patients. In PC treatment, patients diagnosed with advanced stages are frequently submitted to hormonal castration, although most patients will eventually fail this therapy and die from recurrent castration-resistant prostate cancer (CRPC). Therefore, it is important to understand the mechanisms involved in CRPC. Several pathways have been proposed to be involved in CRPC development, and their understanding will improve the way to more effective therapies. In fact, the prostate is known to be dependent, not exclusively, on androgens, but also on growth factors and cytokines. The signaling pathway mediated by IL-6 may be an alternative pathway in the CRPC phenotype acquisition and cancer progression, under androgen deprivation conditions. The principal goal of this review is to evaluate the role of IL-6 pathway signaling in human PC development and progression and discuss the interaction of this pathway with the androgen recepto pathway. Furthermore, we intend to evaluate the inclusion of IL-6 and its receptor levels as a putative new class of tumor biomarkers.The IL-6/IL-6R signaling pathway may be included as a putative molecular marker for aggressiveness in PC and it may be able to maintain tumor growth through the AR pathway under androgen-deprivation conditions. The importance of the IL-6/IL-6R pathway in regulation of PC cells makes it a good candidate for targeted therapy.

The role of microRNA-221 and microRNA-222 in androgen-independent prostate cancer cell lines.

Androgen-dependent prostate cancer typically progresses to castration-resistant prostate cancer (CRPC) after the androgen deprivation therapy. MicroRNAs (miR) are noncoding small RNAs (19-25nt) that play an important role in the regulation of gene expression. Recent studies have shown that miR expression patterns are significantly different in normal and neoplastic prostate epithelial cells. However, the importance of miRs in the development of CRPC has not yet been explored. By performing genome-wide expression profiling of miRs, we found that expression levels of several miRs, in particular miR-221 and miR-222, were significantly increased in CRPC cells (the LNCaP-derived cell line LNCaP-Abl), compared with those in the androgen-dependent prostate cancer cell line (LNCaP). Overexpression of miR-221 or miR-222 in LNCaP or another androgen-dependent cell line, LAPC-4, significantly reduced the level of the dihydrotestosterone (DHT) induced up-regulation of prostate-specific antigen (PSA) expression and increased androgen-independent growth of LNCaP cells. Knocking down the expression level of miR-221 and miR-222 with antagonist miRs in the LNCaP-Abl cell line restored the response to the DHT induction of PSA transcription and also increased the growth response of the LNCaP-Abl cells to the androgen treatment. Changing the expression level of p27/kip1, a known target of miR-221 and miR-222, alone in LNCaP cells affected the DHT-independent cell growth but did not significantly influence the response of PSA transcription to the DHT treatment. In conclusion, our data suggest the involvement of miR-221 and miR-222 in the development or maintenance of the CRPC phenotype.