Abstract 3061: In vivo role of miR-32 in prostate cancer

The androgen receptor (AR) signaling pathway is central to the emergence of castration-resistant prostate cancer (CRPC). We set out to identify androgen-regulated microRNAs (miRNAs) that may contribute to the development of CRPC. We found miR-32 to be an androgen regulated miRNA which is differentially expressed in CRPC compared to benign prostatic hyperplasia (BPH) and able to provide a significant growth advantage to LNCaP cells by reducing apoptosis

To study how increased miR-32 expression contributes to prostate cancer formation and/or progression in vivo, and to search for in vivo targets of miR-32 in the prostate tissue, we have established transgenic mice expressing miR-32 specifically in the prostate. FVB/N mouse strain was used to create transgenic mice with probasin promoter (ARR2PB) driving expression of miR-32 androgen-responsively in prostate epithelium post-puberty. The mice develop and breed normally, and express the transgene specifically in the ventral and dorsolateral lobes of the prostate, with no transgene expression detected in anterior prostate or seminal vesicles up to six months of age. To provoke lesions in prostate epithelium, the miR-32 mice were cross-bred with mice heterozygous for tumor suppressor Pten. Histological analysis of the prostates of ARR2PB-miR-32xPten+/- mice shows increased number of prostatic intraepithelial neoplasia (PIN) lesions in the dorsal prostate compared to Pten+/- mice. In addition, transgenic miR-32 can induce goblet cell metaplasia in prostate epithelium in lateral to ventral prostate, in addition to stromal responses, in the prostate in the Pten+/- background.

In search for in vivo targets of miR-32, we have performed a gene expression microarray analysis comparing the wild type and ARR2PB-miR-32 prostate tissue. Several candidate targets have been identified, and will be discussed further for their potential cancer relevance.

We find that miR-32 is potentially an important gene in the progression of prostate cancer and a putative drug target. We are currently analyzing histology of the miR-32 transgenic mouse prostates further, and assessing tissue targets of miR-32. With the transgenic mouse model, we aim to determine whether miR-32 is an oncomiR for prostate cancer in vivo, and will assess the potency of miR-32 as a therapeutic target.

Citation Format: Leena Latonen, Mauro Scaravilli, Fuping Zhang, Pekka Ruusuvuori, Matti Poutanen, Tapio Visakorpi. In vivo role of miR-32 in prostate cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3061. doi:10.1158/1538-7445.AM2015-3061

Abstract 3883: Clonal evolution of a lethal prostate cancer: Integrated whole genome analysis case study

Prostate cancer (PC) is prevalent in both indolent and lethal forms. Although many PC patients diagnosed today have organ-confined disease curable by prostatectomy or radiation therapy, 20-30% of PCs will relapse to lethal disease within 5-years of treatment. Relatively little attention has been paid to distinguishing the molecular characteristics of proven lethal metastatic PC from non-lethal cancers. A better understanding of the origins and evolution of lethal cancers should allow screening and treatment to be better tailored to the needs of each patient. To this end, we performed an integrative molecular profiling of a lethal PC from one patient (A21). High-coverage whole genome sequence, transcriptome sequence, and methylation analysis was performed on 9 anatomically separate metastases obtained by autopsy, and targeted sequencing was performed in multiple cancerous and noncancerous foci within the radical prostatectomy specimen removed 5 years prior to death. Molecular results were analyzed in relation to detailed clinical data. Integrated whole genome sequence analysis revealed convergent evolution of AR gene amplification events, and inception of p.L702H mutation in the AR present only in liver metastases. In addition, the analysis showed parallel increases in AR regulated transcripts in the liver metastases, suggesting a dominant effect by the mutation. Mutation of PI3/PI4 kinase member PIK3CG was found in all metastases but in no primary tumor foci studied. The study demonstrated the power of an integrated approach to interrogate clonal evolution of cancer suggesting that such studies are valuable on the individual level and could lead the way towards personalized treatment. In the individual studied, cessation of corticosteroid treatment and/or therapeutic manipulation of PI3K/AKT/mTOR activity theoretically could have provided a personalized benefit. These findings suggest that similar integrated analysis in large cohorts of patients with metastatic cancer could accelerate progress in establishing effective personalized cancer medicine.

Citation Format: Heini M.L. Kallio, Matti Annala, Kati Kivinummi, Gunilla Högnäs, Gunes Gundem, David C. Wedge, Peter Van Loo, Holger Heyn, Michael R. Emmert-Buck, William B. Isaacs, Manel Esteller, Ultan McDermott, Matti Nykter, Tapio Visakorpi, G. Steven Bova. Clonal evolution of a lethal prostate cancer: Integrated whole genome analysis case study. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3883. doi:10.1158/1538-7445.AM2015-3883

Construction of therapeutically relevant human prostate epithelial fate map by utilising miRNA and mRNA microarray expression data

Background:

Objective identification of key miRNAs from transcriptomic data is difficult owing to the inherent inconsistencies within miRNA target-prediction algorithms and the promiscuous nature of miRNA-mRNA target relationship.

Methods:

An integrated database of miRNAs and their ‘relevant' mRNA targets was generated from validated miRNA and mRNA microarray data sets generated from patient-derived prostate epithelial normal and cancer stem-like cells (SCs) and committed basal (CB) cells. The effect of miR-542-5p inhibition was studied to provide proof-of-principle for database utility.

Results:

Integration of miRNA-mRNA databases showed that signalling pathways and processes can be regulated by a single or relatively few miRNAs, for example, DNA repair/Notch pathway by miR-542-5p, P=0.008. Inhibition of miR-542-5p in CB cells (thereby achieving miR-542-5p expression levels similar to SCs) promoted efficient DNA repair and activated expression of Notch reporters, HES1 and Survivin, without inducing dedifferentiation into SCs.

Conclusions:

Our novel framework impartially identifies therapeutically relevant miRNA candidates from transcriptomic data sets.

Epigenetically altered miR-193b targets cyclin D1 in prostate cancer

Micro-RNAs (miRNA) are important regulators of gene expression and often differentially expressed in cancer and other diseases. We have previously shown that miR-193b is hypermethylated in prostate cancer (PC) and suppresses cell growth. It has been suggested that miR-193b targets cyclin D1 in several malignancies. Here, our aim was to determine if miR-193b targets cyclin D1 in prostate cancer. Our data show that miR-193b is commonly methylated in PC samples compared to benign prostate hyperplasia. We found reduced miR-193b expression (P < 0.05) in stage pT3 tumors compared to pT2 tumors in a cohort of prostatectomy specimens. In 22Rv1 PC cells with low endogenous miR-193b expression, the overexpression of miR-193b reduced CCND1 mRNA levels and cyclin D1 protein levels. In addition, the exogenous expression of miR-193b decreased the phosphorylation level of RB, a target of the cyclin D1-CDK4/6 pathway. Moreover, according to a reporter assay, miR-193b targeted the 3'UTR of CCND1 in PC cells and the CCND1 activity was rescued by expressing CCND1 lacking its 3'UTR. Immunohistochemical analysis of cyclin D1 showed that castration-resistant prostate cancers have significantly (P = 0.0237) higher expression of cyclin D1 compared to hormone-naïve cases. Furthermore, the PC cell lines 22Rv1 and VCaP, which express low levels of miR-193b and high levels of CCND1, showed significant growth retardation when treated with a CDK4/6 inhibitor. In contrast, the inhibitor had no effect on the growth of PC-3 and DU145 cells with high miR-193b and low CCND1 expression. Taken together, our data demonstrate that miR-193b targets cyclin D1 in prostate cancer.

MiR-1247-5p is overexpressed in castration resistant prostate cancer and targets MYCBP2

BACKGROUND

Recently, there has been increasing attention on the role of microRNAs (miRNAs) in cancer development. Several expression profiling studies have provided evidence of aberrant expression of miRNAs in prostate cancer and have highlighted the potential use of specific miRNA expression signatures as prognostic or predictive markers. Here we report an expression analysis of miR-1247-5p, miR-1249, miR-1269a, miR-1271-5p, miR-1290, miR-1291, and miR-1299.

METHODS

qRT-PCR was performed to validate the differential expression of miRNAs in clinical samples, and the effect of miR-1247-5p was studied in prostate cancer cell lines transiently transfected with a miR-1247-5p mimic. The expression of miR-1247-5p's putative target MYCBP2 was evaluated by qRT-PCR and Western blotting, and the interaction of the miRNA with the target gene was assessed using a luciferase assay.

RESULTS

We found a significant up-regulation of miR-1247-5p in castration-resistant prostate cancer (CRPC) samples compared to non-malignant prostate. The expression of miR-1247-5p was subsequently studied in prostate cancer (PC) cell lines where an up-regulation of miR-1247-5p was observed in the androgen-independent PC-3 model. Target prediction analysis for miR-1247-5p performed online revealed that MYCBP2 (myc-binding protein 2) was a high-scoring potential target. Functional studies in vitro performed using PC-3 and LNCaP models confirmed the down-regulation of MYCBP2 at the mRNA and protein levels, and a luciferase assay showed interaction between the miRNA and target gene.

CONCLUSION

miR-1247-5p is overexpressed in CRPC and targets MYCBP2.

The evolutionary history of lethal metastatic prostate cancer

Cancers emerge from an ongoing Darwinian evolutionary process, often leading to multiple competing subclones within a single primary tumour. This evolutionary process culminates in the formation of metastases, which is the cause of 90% of cancer-related deaths. However, despite its clinical importance, little is known about the principles governing the dissemination of cancer cells to distant organs. Although the hypothesis that each metastasis originates from a single tumour cell is generally supported, recent studies using mouse models of cancer demonstrated the existence of polyclonal seeding from and interclonal cooperation between multiple subclones. Here we sought definitive evidence for the existence of polyclonal seeding in human malignancy and to establish the clonal relationship among different metastases in the context of androgen-deprived metastatic prostate cancer. Using whole-genome sequencing, we characterized multiple metastases arising from prostate tumours in ten patients. Integrated analyses of subclonal architecture revealed the patterns of metastatic spread in unprecedented detail. Metastasis-to-metastasis spread was found to be common, either through de novo monoclonal seeding of daughter metastases or, in five cases, through the transfer of multiple tumour clones between metastatic sites. Lesions affecting tumour suppressor genes usually occur as single events, whereas mutations in genes involved in androgen receptor signalling commonly involve multiple, convergent events in different metastases. Our results elucidate in detail the complex patterns of metastatic spread and further our understanding of the development of resistance to androgen-deprivation therapy in prostate cancer.

miR-25 Modulates Invasiveness and Dissemination of Human Prostate Cancer Cells via Regulation of αv- and α6-Integrin Expression

Altered microRNA (miRNA; miR) expression is associated with tumor formation and progression of various solid cancers. A major challenge in miRNA expression profiling of bulk tumors is represented by the heterogeneity of the subpopulations of cells that constitute the organ, as well as the tumor tissue. Here, we analyzed the expression of miRNAs in a subpopulation of epithelial stem/progenitor-like cells in human prostate cancer [prostate cancer stem cell (PCSC)] and compared their expression profile to more differentiated cancer cells. In both cell lines and clinical prostate cancer specimens, we identified that miR-25 expression in PCSCs was low/absent and steadily increased during their differentiation into cells with a luminal epithelial phenotype. Functional studies revealed that overexpression of miR-25 in prostate cancer cell lines and selected subpopulation of highly metastatic and tumorigenic cells (ALDH(high)) strongly affected the invasive cytoskeleton, causing reduced migration in vitro and metastasis via attenuation of extravasation in vivo. Here, we show, for the first time, that miR-25 can act as a tumor suppressor in highly metastatic PCSCs by direct functional interaction with the 3'-untranslated regions of proinvasive αv- and α6-integrins. Taken together, our observations suggest that miR-25 is a key regulator of invasiveness in human prostate cancer through its direct interactions with αv- and α6-integrin expression.

Hypermethylation of the GABRE~miR-452~miR-224 promoter in prostate cancer predicts biochemical recurrence after radical prostatectomy

PURPOSE

Available tools for prostate cancer diagnosis and prognosis are suboptimal and novel biomarkers are urgently needed. Here, we investigated the regulation and biomarker potential of the GABRE∼miR-452∼miR-224 genomic locus.

EXPERIMENTAL DESIGN

GABRE/miR-452/miR-224 transcriptional expression was quantified in 80 nonmalignant and 281 prostate cancer tissue samples. GABRE∼miR-452∼miR-224 promoter methylation was determined by methylation-specific qPCR (MethyLight) in 35 nonmalignant, 293 prostate cancer [radical prostatectomy (RP) cohort 1] and 198 prostate cancer tissue samples (RP cohort 2). Diagnostic/prognostic biomarker potential of GABRE∼miR-452∼miR-224 methylation was evaluated by ROC, Kaplan-Meier, uni- and multivariate Cox regression analyses. Functional roles of miR-224 and miR-452 were investigated in PC3 and DU145 cells by viability, migration, and invasion assays and gene-set enrichment analysis (GSEA) of posttransfection transcriptional profiling data.

RESULTS

GABRE∼miR-452∼miR-224 was significantly downregulated in prostate cancer compared with nonmalignant prostate tissue and had highly cancer-specific aberrant promoter hypermethylation (AUC = 0.98). Functional studies and GSEA suggested that miR-224 and miR-452 inhibit proliferation, migration, and invasion of PC3 and DU145 cells by direct/indirect regulation of pathways related to the cell cycle and cellular adhesion and motility. Finally, in uni- and multivariate analyses, high GABRE∼miR-452∼miR-224 promoter methylation was significantly associated with biochemical recurrence in RP cohort 1, which was successfully validated in RP cohort 2.

CONCLUSION

The GABRE∼miR-452∼miR-224 locus is downregulated and hypermethylated in prostate cancer and is a new promising epigenetic candidate biomarker for prostate cancer diagnosis and prognosis. Tumor-suppressive functions of the intronic miR-224 and miR-452 were demonstrated in two prostate cancer cell lines, suggesting that epigenetic silencing of GABRE∼miR-452∼miR-224 may be selected for in prostate cancer.

Prevalence and prognostic significance of TMPRSS2-ERG gene fusion in lymph node positive prostate cancers

BACKGROUND

TMPRSS2-ERG gene fusion is the most frequent genetic alteration in prostate cancer. However, information about its distribution in lymph node positive prostate cancers and the prognostic significance in these advanced tumors is unknown.

METHODS

Gene fusion status was determined by fluorescence in situ hybridization on a tissue-microarray constructed from 119 hormone-naïve nodal positive, surgically treated prostate cancers containing samples from the primary tumors and corresponding lymph node metastases. Data were correlated with various tumor features (Gleason score, stage, cancer volume, nodal tumor burden) and biochemical recurrence-free, disease-specific, and overall survival.

RESULTS

TMPRSS2-ERG fusion was detected in 43.5% of the primary tumors. Conversely, only 29.9% of the metastasizing components showed the fusion. Concordance in TMPRSS2-ERG status between primary tumors and metastases was 70.9% (Kappa 0.39); 20.9% and 8.1% of the patients showed the mutation solely in their primary tumors and metastases, respectively. TMPRSS2-ERG fusion was not correlated with specific histopathological tumor features but predicted favorable biochemical recurrence-free, disease-specific and overall survival independently when present in the primary tumor (P < 0.05 each).

CONCLUSION

TMPRSS2-ERG fusion is more frequent in primary prostate cancer than in corresponding metastases suggesting no selection of fusion-positive cells in the metastatic process. The gene fusion in primary tumors independently predicts favorable outcome.

Different gDNA content in the subpopulations of prostate cancer extracellular vesicles: apoptotic bodies, microvesicles, and exosomes

BACKGROUND

Extracellular vesicles (EVs) are cell-derived membrane vesicles. EVs contain several RNAs such as mRNA, microRNAs, and ncRNAs, but less is known of their genomic DNA (gDNA) content. It is also unknown whether the DNA cargo is randomly sorted or if it is systematically packed into specific EV subpopulations. The aim of this study was to analyze whether different prostate cancer (PCa) cell-derived EV subpopulations (apoptotic bodies, microvesicles, and exosomes) carry different gDNA fragments.

METHODS

EV subpopulations were isolated from three PCa cell lines (LNCaP, PC-3, and RC92a/hTERT) and the plasma of PCa patients and healthy donors, and characterized by transmission electron microscopy, nanoparticle tracking analysis and total protein content. gDNA fragments of different genes were detected by real time quantitative PCR and confirmed by DNA sequencing.

RESULTS

We report that the concentration of EVs was higher in the cancer patients than in the healthy controls. EV subpopulations differed from each other in terms of total protein and DNA content. Analysis of gDNA fragments of MLH1, PTEN, and TP53 genes from the PCa cell-derived EV subpopulations showed that different EVs carried different gDNA content, which could even harbor specific mutations. Altogether, these results suggest that both nucleic acids and proteins are selectively and cell-dependently packed into the EV subtypes.

CONCLUSIONS

EVs derived from PCa cell lines and human plasma samples contain double-stranded gDNA fragments which could be used to detect specific mutations, making EVs potential biomarkers for cancer diagnostics and prognostics.

A meta-analysis of 87,040 individuals identifies 23 new susceptibility loci for prostate cancer

Genome-wide association studies (GWAS) have identified 76 variants associated with prostate cancer risk predominantly in populations of European ancestry. To identify additional susceptibility loci for this common cancer, we conducted a meta-analysis of > 10 million SNPs in 43,303 prostate cancer cases and 43,737 controls from studies in populations of European, African, Japanese and Latino ancestry. Twenty-three new susceptibility loci were identified at association P < 5 × 10(-8); 15 variants were identified among men of European ancestry, 7 were identified in multi-ancestry analyses and 1 was associated with early-onset prostate cancer. These 23 variants, in combination with known prostate cancer risk variants, explain 33% of the familial risk for this disease in European-ancestry populations. These findings provide new regions for investigation into the pathogenesis of prostate cancer and demonstrate the usefulness of combining ancestrally diverse populations to discover risk loci for disease.

Origins and functional consequences of somatic mitochondrial DNA mutations in human cancer

Recent sequencing studies have extensively explored the somatic alterations present in the nuclear genomes of cancers. Although mitochondria control energy metabolism and apoptosis, the origins and impact of cancer-associated mutations in mtDNA are unclear. In this study, we analyzed somatic alterations in mtDNA from 1675 tumors. We identified 1907 somatic substitutions, which exhibited dramatic replicative strand bias, predominantly C > T and A > G on the mitochondrial heavy strand. This strand-asymmetric signature differs from those found in nuclear cancer genomes but matches the inferred germline process shaping primate mtDNA sequence content. A number of mtDNA mutations showed considerable heterogeneity across tumor types. Missense mutations were selectively neutral and often gradually drifted towards homoplasmy over time. In contrast, mutations resulting in protein truncation undergo negative selection and were almost exclusively heteroplasmic. Our findings indicate that the endogenous mutational mechanism has far greater impact than any other external mutagens in mitochondria and is fundamentally linked to mtDNA replication.

Mapping of the chromosomal amplification 1p21-22 in bladder cancer

Background

The aim of the study was to characterize a recurrent amplification at chromosomal region 1p21-22 in bladder cancer.

Methods

ArrayCGH (aCGH) was performed to identify DNA copy number variations in 7 clinical samples and 6 bladder cancer cell lines. FISH was used to map the amplicon at 1p21-22 in the cell lines. Gene expression microarrays and qRT-PCR were used to study the expression of putative target genes in the region.

Results

aCGH identified an amplification at 1p21-22 in 10/13 (77%) samples. The minimal region of the amplification was mapped to a region of about 1 Mb in size, containing a total of 11 known genes. The highest amplification was found in SCaBER squamous cell carcinoma cell line. Four genes, TMED5, DR1, RPL5 and EVI5, showed significant overexpression in the SCaBER cell line compared to all the other samples tested. Oncomine database analysis revealed upregulation of DR1 in superficial and infiltrating bladder cancer samples, compared to normal bladder.

Conclusions

In conclusions, we have identified and mapped chromosomal amplification at 1p21-22 in bladder cancer as well as studied the expression of the genes in the region. DR1 was found to be significantly overexpressed in the SCaBER, which is a model of squamous cell carcinoma. However, the overexpression was found also in a published clinical sample cohort of superficial and infiltrating bladder cancers. Further studies with more clinical material are needed to investigate the role of the amplification at 1p21-22.

Mobile DNA in cancer. Extensive transduction of nonrepetitive DNA mediated by L1 retrotransposition in cancer genomes

Long interspersed nuclear element-1 (L1) retrotransposons are mobile repetitive elements that are abundant in the human genome. L1 elements propagate through RNA intermediates. In the germ line, neighboring, nonrepetitive sequences are occasionally mobilized by the L1 machinery, a process called 3' transduction. Because 3' transductions are potentially mutagenic, we explored the extent to which they occur somatically during tumorigenesis. Studying cancer genomes from 244 patients, we found that tumors from 53% of the patients had somatic retrotranspositions, of which 24% were 3' transductions. Fingerprinting of donor L1s revealed that a handful of source L1 elements in a tumor can spawn from tens to hundreds of 3' transductions, which can themselves seed further retrotranspositions. The activity of individual L1 elements fluctuated during tumor evolution and correlated with L1 promoter hypomethylation. The 3' transductions disseminated genes, exons, and regulatory elements to new locations, most often to heterochromatic regions of the genome.

USP22 regulates oncogenic signaling pathways to drive lethal cancer progression

Increasing evidence links deregulation of the ubiquitin-specific proteases 22 (USP22) deubitiquitylase to cancer development and progression in a select group of tumor types, but its specificity and underlying mechanisms of action are not well defined. Here we show that USP22 is a critical promoter of lethal tumor phenotypes that acts by modulating nuclear receptor and oncogenic signaling. In multiple xenograft models of human cancer, modeling of tumor-associated USP22 deregulation demonstrated that USP22 controls androgen receptor accumulation and signaling, and that it enhances expression of critical target genes coregulated by androgen receptor and MYC. USP22 not only reprogrammed androgen receptor function, but was sufficient to induce the transition to therapeutic resistance. Notably, in vivo depletion experiments revealed that USP22 is critical to maintain phenotypes associated with end-stage disease. This was a significant finding given clinical evidence that USP22 is highly deregulated in tumors, which have achieved therapeutic resistance. Taken together, our findings define USP22 as a critical effector of tumor progression, which drives lethal phenotypes, rationalizing this enzyme as an appealing therapeutic target to treat advanced disease.

Loss of PTEN is associated with aggressive behavior in ERG-positive prostate cancer

BACKGROUND

The associations of ERG overexpression with clinical behavior and molecular pathways of prostate cancer are incompletely known. We assessed the association of ERG expression with AR, PTEN, SPINK1, Ki-67, and EZH2 expression levels, deletion, and mutations of chromosomal region 3p14 and TP53, and clinicopathologic variables.

METHODS

The material consisted of 326 prostatectomies, 166 needle biopsies from men treated primarily with endocrine therapy, 177 transurethral resections of castration-resistant prostate cancers (CRPC), and 114 CRPC metastases obtained from 32 men. Immunohistochemistry, FISH, and sequencing was used for the measurements.

RESULTS

ERG expression was found in about 45% of all patient cohorts. In a multivariate analysis, ERG expression showed independent value of favorable prognosis (P = 0.019). ERG positivity was significantly associated with loss of PTEN expression in prostatectomy (P = 0.0348), and locally recurrent CRPCs (P = 0.0042). Loss of PTEN expression was associated (P = 0.0085) with shorter progression-free survival in ERG-positive, but not in negative cases. When metastases in each subject were compared, consistent ERG, PTEN, and AR expression as well as TP53 mutations were found in a majority of subjects.

CONCLUSIONS

A similar frequency of ERG positivity from early to late stage of the disease suggests lack of selection of ERG expression during disease progression. The prognostic significance of PTEN loss solely in ERG-positive cases indicates interaction of these pathways. The finding of consistent genetic alterations in different metastases suggests that the major genetic alterations take place in the primary tumor.

IMPACT

Interaction of PTEN and ERG pathways warrants further studies.

Chk1 targeting reactivates PP2A tumor suppressor activity in cancer cells

Checkpoint kinase Chk1 is constitutively active in many cancer cell types and new generation Chk1 inhibitors show marked antitumor activity as single agents. Here we present a hitherto unrecognized mechanism that contributes to the response of cancer cells to Chk1-targeted therapy. Inhibiting chronic Chk1 activity in cancer cells induced the tumor suppressor activity of protein phosphatase protein phosphatase 2A (PP2A), which by dephosphorylating MYC serine 62, inhibited MYC activity and impaired cancer cell survival. Mechanistic investigations revealed that Chk1 inhibition activated PP2A by decreasing the transcription of cancerous inhibitor of PP2A (CIP2A), a chief inhibitor of PP2A activity. Inhibition of cancer cell clonogenicity by Chk1 inhibition could be rescued in vitro either by exogenous expression of CIP2A or by blocking the CIP2A-regulated PP2A complex. Chk1-mediated CIP2A regulation was extended in tumor models dependent on either Chk1 or CIP2A. The clinical relevance of CIP2A as a Chk1 effector protein was validated in several human cancer types, including neuroblastoma, where CIP2A was identified as an NMYC-independent prognostic factor. Because the Chk1-CIP2A-PP2A pathway is driven by DNA-PK activity, functioning regardless of p53 or ATM/ATR status, our results offer explanative power for understanding how Chk1 inhibitors mediate single-agent anticancer efficacy. Furthermore, they define CIP2A-PP2A status in cancer cells as a pharmacodynamic marker for their response to Chk1-targeted therapy.

DNA methylation signatures for prediction of biochemical recurrence after radical prostatectomy of clinically localized prostate cancer

PURPOSE

Diagnostic and prognostic tools for prostate cancer (PC) are suboptimal, causing overtreatment of indolent PC and risk of delayed treatment of aggressive PC. Here, we identify six novel candidate DNA methylation markers for PC with promising diagnostic and prognostic potential.

METHODS

Microarray-based screening and bisulfite sequencing of 20 nonmalignant and 29 PC tissue specimens were used to identify new candidate DNA hypermethylation markers for PC. Diagnostic and prognostic potential was evaluated in 35 nonmalignant prostate tissue samples, 293 radical prostatectomy (RP) samples (cohort 1, training), and 114 malignant RP samples (cohort 2, validation) collected in Denmark, Switzerland, Germany, and Finland. Sensitivity and specificity for PC were evaluated by receiver operating characteristic analyses. Correlations between DNA methylation levels and biochemical recurrence were assessed using log-rank tests and univariate and multivariate Cox regression analyses.

RESULTS

Hypermethylation of AOX1, C1orf114, GAS6, HAPLN3, KLF8, and MOB3B was highly cancer specific (area under the curve, 0.89 to 0.98). Furthermore, high C1orf114 methylation was significantly (P < .05) associated with biochemical recurrence in multivariate analysis in cohort 1 (hazard ratio [HR], 3.10; 95% CI, 1.89 to 5.09) and was successfully validated in cohort 2 (HR, 3.27; 95% CI, 1.17 to 9.12). Moreover, a significant (P < .05) three-gene prognostic methylation signature (AOX1/C1orf114/HAPLN3), classifying patients into low- and high-methylation subgroups, was trained in cohort 1 (HR, 1.91; 95% CI, 1.26 to 2.90) and validated in cohort 2 (HR, 2.33; 95% CI, 1.31 to 4.13).

CONCLUSION

We identified six novel candidate DNA methylation markers for PC. C1orf114 hypermethylation and a three-gene methylation signature were independent predictors of time to biochemical recurrence after RP in two PC patient cohorts.

The mutational landscape of prostate cancer

CONTEXT

Prostate cancer (PCa) is a clinically heterogeneous disease with marked variability in patient outcomes. Molecular characterization has revealed striking mutational heterogeneity that may underlie the variable clinical course of the disease.

OBJECTIVE

In this review, we discuss the common genomic alterations that form the molecular basis of PCa, their functional significance, and the potential to translate this knowledge into patient care.

EVIDENCE ACQUISITION

We reviewed the relevant literature, with a particular focus on recent studies on somatic alterations in PCa.

EVIDENCE SYNTHESIS

Advances in sequencing technology have resulted in an explosion of data regarding the mutational events underlying the development and progression of PCa. Heterogeneity is the norm; few abnormalities in specific genes are highly recurrent, but alterations in certain signaling pathways do predominate. These alterations include those in pathways known to affect tumorigenesis in a wide spectrum of tissues, such as the phosphoinositide 3-kinase/phosphatase and tensin homolog/Akt pathway, cell cycle regulation, and chromatin regulation. Alterations more specific to PCa are also observed, particularly gene fusions of ETS transcription factors and alterations in androgen signaling. Mounting data suggest that PCa can be subdivided based on a molecular profile of genetic alterations.

CONCLUSIONS

Major advances have been made in cataloging the genomic alterations in PCa and understanding the molecular mechanisms underlying the disease. These findings raise the possibility that PCa could soon transition from being a poorly understood, heterogeneous disease with a variable clinical course to being a collection of homogenous subtypes identifiable by molecular criteria, associated with distinct risk profiles, and perhaps amenable to specific management strategies or targeted therapies.

STAT5A/B gene locus undergoes amplification during human prostate cancer progression

The molecular mechanisms underlying progression of prostate cancer (PCa) to castrate-resistant (CR) and metastatic disease are poorly understood. Our previous mechanistic work shows that inhibition of transcription factor Stat5 by multiple alternative methods induces extensive rapid apoptotic death of Stat5-positive PCa cells in vitro and inhibits PCa xenograft tumor growth in nude mice. Furthermore, STAT5A/B induces invasive behavior of PCa cells in vitro and in vivo, suggesting involvement of STAT5A/B in PCa progression. Nuclear STAT5A/B protein levels are increased in high-grade PCas, CR PCas, and distant metastases, and high nuclear STAT5A/B expression predicts early disease recurrence and PCa-specific death in clinical PCas. Based on these findings, STAT5A/B represents a therapeutic target protein for advanced PCa. The mechanisms underlying increased Stat5 protein levels in PCa are unclear. Herein, we demonstrate amplification at the STAT5A/B gene locus in a significant fraction of clinical PCa specimens. STAT5A/B gene amplification was more frequently found in PCas of high histologic grades and in CR distant metastases. Quantitative in situ analysis revealed that STAT5A/B gene amplification was associated with increased STAT5A/B protein expression in PCa. Functional studies showed that increased STAT5A/B copy numbers conferred growth advantage in PCa cells in vitro and as xenograft tumors in vivo. The work presented herein provides the first evidence of somatic STAT5A/B gene amplification in clinical PCas.

Abstract 5217: Integrative sequencing reveals novel alterations in untreated and castration resistant prostate cancer

Prostate cancer is the third most common source of male cancer deaths in developed countries. The standard of care for aggressive prostate cancer is androgen ablation, which prolongs survival until the tumor acquires a castration resistant phenotype. The molecular pathology underlying prostate cancer progression is not yet fully understood. We used integrative high throughput sequencing to study cancer-associated alterations in 53 prostate cancer related neoplasia at the DNA, RNA and epigenetic levels. The cohort included both hormone-naive and castration resistant prostate cancers, along with two neuroendocrine prostate cancers. We identified two new fusion genes, one of which associated with neuronal differentiation and castration resistance. We also identified a number of novel prostate cancer associated transcripts, including transcripts specific to castration resistant tumors. Based on ChIP-seq data from prostate cancer cell lines, many of the novel transcripts were regulated by known oncogenes such as ERG and AR. Methylation sequencing revealed a near-identical pattern of promoter hypermethylation in both hormone-naive and castration resistant tumors. Enrichment of hypermethylation was observed at EZH2 binding sites, supporting the role of EZH2 in the recruitment of DNA methyltransferase in prostate cancer. Promoter hypermethylation suppressed the expression of hundreds of genes, but a subset of genes characterized by promoter H3K27 trimethylation responded to hypermethylation with increased expression.

Citation Format: Matti J. Annala, Kati K. Waltering, Antti Ylipää, Kimmo Kartasalo, Kirsi Tuppurainen, Serdar Karakurt, Leena Latonen, Outi Saramäki, Simo-Pekka Leppänen, Janne Seppälä, Hanna E. Rauhala, Teuvo LJ Tammela, Olli Yli-Harja, Wei Zhang, Tapio Visakorpi, Matti Nykter. Integrative sequencing reveals novel alterations in untreated and castration resistant prostate cancer. [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 5217. doi:10.1158/1538-7445.AM2013-5217

Abstract 3576: USP22 modulates AR activity to critically regulate prostate cancer progression

Recently, the deubiquitylase Ubiquitin-specific protease 22 (USP22) was identified as a member of the 11 gene ‘death-from-cancer’ signature, which can predict poor response to therapy and/or propensity toward metastasis of multiple tumor types, including breast and prostate. However, the mechanism for how USP22 impacts cancer is currently unknown. Our new data implicate a specific role for USP22 in hormone-dependent cancers, especially prostate cancer (PCa) where USP22 expression is elevated in primary and metastatic PCa. USP22 has an established role in regulating oncogenic c-Myc activity as it is recruited by c-Myc for transcriptional activation through deubiquitylation of histones, and is necessary for c-Myc-mediated cell transformation. Similarly, our data in PCa cells demonstrates that USP22 controls c-Myc activity but does not affect expression levels.

Additional data has also identified USP22 as a critical effector of androgen receptor (AR) levels and output. This is of great clinical relevance since PCa is intricately dependent on AR signaling for disease initiation and progression to castrate resistant disease (CRPC). First, USP22 overexpression in hormone-dependent and CRPC cell lines increased AR protein expression and activity, but did not perturb transcript. Second, in the absence of ligand, USP22 upregulation resulted in enhanced AR recruitment to target genes, as determined by chromatin immunoprecipitation, which corresponded with significant enhancement of cell proliferation and BrdU incorporation. Third, USP22 depletion resulted in attenuated AR activity and caused a significant reduction in AR protein levels that could be attributed to protein stability. Importantly, in the CRPC setting, USP22 depletion dramatically inhibited in vivo tumor growth while expression correlated with decreased time for tumor regression.

In sum, the data suggest that USP22 upregulation is sufficient for aberrant c-Myc activity, altered AR expression and activity, and establishment of a CRPC phenotype. We propose that modulation of UPS22 expression and/or activity may present a novel platform to achieve combinatorial suppression of AR and c-Myc function, and therefore could be potentially developed as a novel approach for treatment of PCa.

Citation Format: Randy Schrecengost, Jeffry Dean, Tim Stanek, Ruth Birbe, Jessica Hicks, Tapio Visakorpi, Angelo DeMarzo, Steve McMahon, Karen Knudsen. USP22 modulates AR activity to critically regulate prostate cancer progression. [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 3576. doi:10.1158/1538-7445.AM2013-3576