Targeting FOXA1-mediated repression of TGF-β signaling suppresses castration-resistant prostate cancer progression

Prostate cancer (PC) progressed to castration resistance (CRPC) is a fatal disease. CRPC tumors develop resistance to new-generation antiandrogen enzalutamide through lineage plasticity, characterized by epithelial-mesenchymal transition (EMT) and a basal-like phenotype. FOXA1 is a transcription factor essential for epithelial lineage differentiation. Here, we demonstrate that FOXA1 loss leads to remarkable upregulation of transforming growth factor beta 3 (TGFB3), which encodes a ligand of the TGF-β pathway. Mechanistically, this is due to genomic occupancy of FOXA1 on an upstream enhancer of the TGFB3 gene to directly inhibit its transcription. Functionally, FOXA1 downregulation induces TGF-β signaling, EMT, and cell motility, which is effectively blocked by the TGF-β receptor I inhibitor galunisertib (LY2157299). Tissue microarray analysis confirmed reduced levels of FOXA1 protein and a concordant increase in TGF-β signaling, indicated by SMAD2 phosphorylation, in CRPC as compared with primary tumors. Importantly, combinatorial LY2157299 treatment sensitized PC cells to enzalutamide, leading to synergistic effects in inhibiting cell invasion in vitro and xenograft CRPC tumor growth and metastasis in vivo. Therefore, our study establishes FOXA1 as an important regulator of lineage plasticity mediated in part by TGF-β signaling, and supports a novel therapeutic strategy to control lineage switching and potentially extend clinical response to antiandrogen therapies.

Movember GAP1 PDX project: An international collection of serially transplantable prostate cancer patient-derived xenograft (PDX) models

BACKGROUND

While it has been challenging to establish prostate cancer patient-derived xenografts (PDXs), with a take rate of 10-40% and long latency time, multiple groups throughout the world have developed methods for the successful establishment of serially transplantable human prostate cancer PDXs using a variety of immune deficient mice. In 2014, the Movember Foundation launched a Global Action Plan 1 (GAP1) project to support an international collaborative prostate cancer PDX program involving eleven groups. Between these Movember consortium members, a total of 98 authenticated human prostate cancer PDXs were available for characterization. Eighty three of these were derived directly from patient material, and 15 were derived as variants of patient-derived material via serial passage in androgen deprived hosts. A major goal of the Movember GAP1 PDX project was to provide the prostate cancer research community with a summary of both the basic characteristics of the 98 available authenticated serially transplantable human prostate cancer PDX models and the appropriate contact information for collaborations. Herein, we report a summary of these PDX models.

METHODS

PDX models were established in immunocompromised mice via subcutaneous or subrenal-capsule implantation. Dual-label species (ie, human vs mouse) specific centromere and telomere Fluorescence In Situ Hybridization (FISH) and immuno-histochemical (IHC) staining of tissue microarrays (TMAs) containing replicates of the PDX models were used for characterization of expression of a number of phenotypic markers important for prostate cancer including AR (assessed by IHC and FISH), Ki67, vimentin, RB1, P-Akt, chromogranin A (CgA), p53, ERG, PTEN, PSMA, and epithelial cytokeratins.

RESULTS

Within this series of PDX models, the full spectrum of clinical disease stages is represented, including androgen-sensitive and castration-resistant primary and metastatic prostate adenocarcinomas as well as prostate carcinomas with neuroendocrine differentiation. The annotated clinical characteristics of these PDXs were correlated with their marker expression profile.

CONCLUSION

Our results demonstrate the clinical relevance of this series of PDXs as a platform for both basic science studies and therapeutic discovery/drug development. The present report provides the prostate cancer community with a summary of the basic characteristics and a contact information for collaborations using these models.

Abstract IA21: AR is ablated: Now what? Targeting the double-negative phenotype

Background/Introduction: Androgen receptor (AR) signaling is a distinctive feature of prostate cancer (PC) and represents the major therapeutic target for treating metastatic prostate cancer (mPC). Though highly effective, AR antagonism can produce tumors that bypass a functional requirement for AR, often through neuroendocrine (NE) transdifferentiation. Through the molecular assessment of mPCs over two decades, we find that a phenotypic shift has occurred in mPC with the emergence of an AR-null NE-null phenotype. We sought to identify drivers of these “double-negative” PCs (DNPC), with the ultimate objective of developing therapeutic strategies.

Methods: We used genome-wide profiling of copy number (array CGH), mutations (whole-exome sequencing-WES), and gene expression (RNA-seq) to compare the molecular landscapes of AR-active PC (ARPC), NEPC, and DNPC in tumors obtained from 84 consecutive men with mPC undergoing a rapid autopsy. We developed model systems including DNPC patient-derived xenografts (PDX) and cell lines that are devoid of AR activity and lack NE features. Using these models, we tested therapeutics hypothesized to inhibit the activity of pathways preferentially active in DNPC.

Results: In the era prior to the approval of the AR pathway antagonists enzalutamide and abiraterone, most CRPCs were ARPCs (85%) with rare NEPCs (10%) and rarer DNPCs (5%). In the contemporary era (2012-2016), we observed a shift in tumor phenotypes with a higher representation of DNPCs. Gene expression programs of the tumors classified by IHC supported these distinct subtypes. DNPCs did not exhibit GR activity or PI3K/AKT activation but were notable for high MAPK and FGF pathway activity. Models systems recapitulated these findings. FGFR antagonists differentially repressed the growth of DNPC tumors in vitro and in vivo.

Conclusions: Though the majority of mPCs that resist AR targeting retain AR signaling, an increasingly common subtype of mPC exhibits a DNPC phenotype. Our results indicate that at least a subset of these DNPCs are driven by FGF signaling and MAPK activation. Targeting the FGF axis may represent a therapeutic approach for those cancers resistant to AR-directed therapies and may circumvent treatment resistance if combined with initial AR pathway blockade.

Citation Format: Colm Morrissey, Eric G. Bluemn, Ilsa M. Coleman, Jared M. Lucas, Roger T. Coleman, Robin Tharakan, Daniella Bianchi-Frias, Ruth F. Dumpit, Arja Kaipainen, Alexandra N. Corella, Yu Chi Yang, Michael D. Nyquist, Elahe Mostaghel, Xiaotun Zhang, Eva Corey, Lisha G. Brown, Holly M. Nguyen, Michael Schweizer, Lawrence D. True, Paul S. Rennie, Robert L. Vessella, Peter S. Nelson. AR is ablated: Now what? Targeting the double-negative phenotype [abstract]. In: Proceedings of the AACR Special Conference: Prostate Cancer: Advances in Basic, Translational, and Clinical Research; 2017 Dec 2-5; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(16 Suppl):Abstract nr IA21.

Multicenter Evaluation of the Performance and Clinical Utility in Longitudinal Monitoring of the Bayer Immuno 1™ Complexed PSA Assay

We conducted a multicenter evaluation of the analytical and clinical performance of the automated Bayer Immuno 1™ complexed PSA (cPSA) assay, and compared assay performance to the Bayer Immuno 1™ PSA assay. We sought to determine whether measurements of cPSA could be of clinical utility in the management of patients with prostate cancer. Results of the 10–day imprecision across three evaluation sites produced total CV < 2.50% and an analytical sensitivity of 0.02μg/L. There was an increased trend in clinical sensitivity for prostate cancer with increasing stage of disease (71–86%). Clinical specificity for patients with benign urogenital disease was 74.8%, and for other nonprostate diseases ranged from 91.1–100%. Retrospective serial monitoring of 155 patients with prostate cancer demonstrated concordance of cPSA measurements to clinical status for 97% of the patients analyzed. Results from the clinical studies using the Bayer Immuno 1 cPSA assay were comparable to results obtained with the Bayer Immuno 1 PSA assay. The Bayer Immuno 1 cPSA assay demonstrates analytical performance and clinical effectiveness in the management of prostate cancer patients during the course of disease and therapy.

s-SHIP expression identifies a subset of murine basal prostate cells as neonatal stem cells

Isolation of prostate stem cells (PSCs) is crucial for understanding their biology during normal development and tumorigenesis. In this aim, we used a transgenic mouse model expressing GFP from the stem cell-specific s-SHIP promoter to mark putative stem cells during postnatal prostate development. Here we show that cells identified by GFP expression are present transiently during early prostate development and localize to the basal cell layer of the epithelium. These prostate GFP+ cells are a subpopulation of the Lin- CD24+ Sca-1+ CD49f+ cells and are capable of self-renewal together with enhanced growth potential in sphere-forming assay in vitro, a phenotype consistent with that of a PSC population. Transplantation assays of prostate GFP+ cells demonstrate reconstitution of prostate ducts containing both basal and luminal cells in renal grafts. Altogether, these results demonstrate that s-SHIP promoter expression is a new marker for neonatal basal prostate cells exhibiting stem cell properties that enables PSCs in situ identification and isolation via a single consistent parameter. Transcriptional profiling of these GFP+ neonatal stem cells showed an increased expression of several components of the Wnt signaling pathway. It also identified stem cell regulators with potential applications for further analyses of normal and cancer stem cells.

Plasma Fatty Acids as Surrogate for Prostate Levels

Inconsistent results from epidemiologic studies of circulating fatty acids and prostate cancer risk may be partly due to use of blood concentrations as surrogate biomarkers of prostate tissue concentrations. To determine whether blood concentrations reflect prostate tissue fatty acid profiles, we evaluated associations between phospholipid fatty acid (PLFA) profiles measured in plasma and prostate tissue from 20 patients who underwent prostatectomy. For each patient, three prostate tissue specimens varying in size and location were collected. Correlations were calculated between a) tissue specimens by size ( ≤ 20 mg, > 20 mg); b) individual tissue samples [Intraclass Correlation Coefficient (ICC)]; and c) plasma and mean tissue PLFA concentrations. PLFA concentrations from ≤ 20 mg and > 20 mg tissues were nearly identical. For most PLFAs, intra-individual correlations between tissue specimens were moderate to strong (linoleic acid = 0.66, eicosapentaenoic acid = 0.96), with only one ICC below 0.50 (trans-fatty acid 18:2, ICC = 0.28). Most correlations of mean tissue and plasma concentrations were moderate to strong (α-linoleic acid = 0.47, eicosapentaenoic acid = 0.93). PLFA concentrations are largely homogeneous within the prostate and can be reliably measured in small quantities of tissue. The overall strong correlations between plasma and tissue suggest that for most individual PLFAs, plasma concentrations are adequate surrogate markers of prostate tissue concentrations.

Androgen Receptor Pathway-Independent Prostate Cancer Is Sustained through FGF Signaling

Androgen receptor (AR) signaling is a distinctive feature of prostate carcinoma (PC) and represents the major therapeutic target for treating metastatic prostate cancer (mPC). Though highly effective, AR antagonism can produce tumors that bypass a functional requirement for AR, often through neuroendocrine (NE) transdifferentiation. Through the molecular assessment of mPCs over two decades, we find a phenotypic shift has occurred in mPC with the emergence of an AR-null NE-null phenotype. These "double-negative" PCs are notable for elevated FGF and MAPK pathway activity, which can bypass AR dependence. Pharmacological inhibitors of MAPK or FGFR repressed the growth of double-negative PCs in vitro and in vivo. Our results indicate that FGF/MAPK blockade may be particularly efficacious against mPCs with an AR-null phenotype.

LuCaP Prostate Cancer Patient-Derived Xenografts Reflect the Molecular Heterogeneity of Advanced Disease an--d Serve as Models for Evaluating Cancer Therapeutics

BACKGROUND

Metastatic prostate cancer is a common and lethal disease for which there are no therapies that produce cures or long-term durable remissions. Clinically relevant preclinical models are needed to increase our understanding of biology of this malignancy and to evaluate new agents that might provide effective treatment. Our objective was to establish and characterize patient-derived xenografts (PDXs) from advanced prostate cancer (PC) for investigation of biology and evaluation of new treatment modalities.

METHODS

Samples of advanced PC obtained from primary prostate cancer obtained at surgery or from metastases collected at time of death were implanted into immunocompromised mice to establish PDXs. Established PDXs were propagated in vivo. Genomic, transcriptomic, and STR profiles were generated. Responses to androgen deprivation and docetaxel in vivo were characterized.

RESULTS

We established multiple PDXs (LuCaP series), which represent the major genomic and phenotypic features of the disease in humans, including amplification of androgen receptor, PTEN deletion, TP53 deletion and mutation, RB1 loss, TMPRSS2-ERG rearrangements, SPOP mutation, hypermutation due to MSH2/MSH6 genomic aberrations, and BRCA2 loss. The PDX models also exhibit variation in intra-tumoral androgen levels. Our in vivo results show heterogeneity of response to androgen deprivation and docetaxel, standard therapies for advanced PC, similar to the responses of patients to these treatments.

CONCLUSIONS

The LuCaP PDX series reflects the diverse molecular composition of human castration-resistant PC and allows for hypothesis-driven cause-and-effect studies of mechanisms underlying treatment response and resistance. Prostate 77: 654-671, 2017. © 2017 The Authors. The Prostate Published by Wiley Periodicals, Inc.

Radium-223 Inhibits Osseous Prostate Cancer Growth by Dual Targeting of Cancer Cells and Bone Microenvironment in Mouse Models

Purpose: Radium-223 dichloride (radium-223, Xofigo), a targeted alpha therapy, is currently used for the treatment of patients with castration-resistant prostate cancer (CRPC) with bone metastases. This study examines the mode-of-action and antitumor efficacy of radium-223 in two prostate cancer xenograft models.Experimental Design: Mice bearing intratibial LNCaP or LuCaP 58 tumors were randomized into groups (n = 12-17) based on lesion grade and/or serum PSA level and administered radium-223 (300 kBq/kg) or vehicle, twice at 4-week intervals. X-rays and serum samples were obtained biweekly. Soft tissue tumors were observed macroscopically at sacrifice. Tibiae were analyzed by gamma counter, micro-CT, autoradiography and histology.Results: Radium-223 inhibited tumor-induced osteoblastic bone growth and protected normal bone architecture, leading to reduced bone volume in LNCaP and abiraterone-resistant LuCaP 58 models. Furthermore, radium-223 resulted in lower PSA values and reduced total tissue and tumor areas, indicating that treatment constrains prostate cancer growth in bone. In addition, radium-223 suppressed abnormal bone metabolic activity as evidenced by decreased number of osteoblasts and osteoclasts and reduced level of the bone formation marker PINP. Mode-of-action studies revealed that radium-223 was deposited in the intratumoral bone matrix. DNA double-strand breaks were induced in cancer cells within 24 hours after radium-223 treatment, and PSA levels were significantly lower 72 hours after treatment, providing further evidence of the antitumor effects.Conclusions: Taken together, radium-223 therapy exhibits a dual targeting mode-of-action that induces tumor cell death and suppresses tumor-induced pathologic bone formation in tumor microenvironment of osseous CRPC growth in mice. Clin Cancer Res; 23(15); 4335-46. ©2017 AACR.

Src promotes castration-recurrent prostate cancer through androgen receptor-dependent canonical and non-canonical transcriptional signatures

Progression of prostate cancer (PC) to castration-recurrent growth (CRPC) remains dependent on sustained expression and transcriptional activity of the androgen receptor (AR). A major mechanism contributing to CRPC progression is through the direct phosphorylation and activation of AR by Src-family (SFK) and ACK1 tyrosine kinases. However, the AR-dependent transcriptional networks activated by Src during CRPC progression have not been elucidated. Here, we show that activated Src (Src527F) induces androgen-independent growth in human LNCaP cells, concomitant with its ability to induce proliferation/survival genes normally induced by dihydrotestosterone (DHT) in androgen-dependent LNCaP and VCaP cells. Src induces additional gene signatures unique to CRPC cell lines, LNCaP-C4-2 and CWR22Rv1, and to CRPC LuCaP35.1 xenografts. By comparing the Src-induced AR-cistrome and/or transcriptome in LNCaP to those in CRPC and LuCaP35.1 tumors, we identified an 11-gene Src-regulated CRPC signature consisting of AR-dependent, AR binding site (ARBS)-associated genes whose expression is altered by DHT in LNCaP[Src527F] but not in LNCaP cells. The differential expression of a subset (DPP4, BCAT1, CNTNAP4, CDH3) correlates with earlier PC metastasis onset and poorer survival, with the expression of BCAT1 required for Src-induced androgen-independent proliferation. Lastly, Src enhances AR binding to non-canonical ARBS enriched for FOXO1, TOP2B and ZNF217 binding motifs; cooperative AR/TOP2B binding to a non-canonical ARBS was both Src- and DHT-sensitive and correlated with increased levels of Src-induced phosphotyrosyl-TOP2B. These data suggest that CRPC progression is facilitated via Src-induced sensitization of AR to intracrine androgen levels, resulting in the engagement of canonical and non-canonical ARBS-dependent gene signatures.

Characterization of an Abiraterone Ultraresponsive Phenotype in Castration-Resistant Prostate Cancer Patient-Derived Xenografts

Purpose: To identify the molecular signature associated with abiraterone acetate (AA) response and mechanisms underlying AA resistance in castration-resistant prostate cancer patient-derived xenografts (PDXs).Experimental Design: SCID mice bearing LuCaP 136CR, 77CR, 96CR, and 35CR PDXs were treated with AA. Tumor volume and prostate-specific antigen were monitored, and tumors were harvested 7 days after treatment or at end of study for gene expression and immunohistochemical studies.Results: Three phenotypic groups were observed based on AA response. An ultraresponsive phenotype was identified in LuCaP 136CR with significant inhibition of tumor progression and increased survival, intermediate responders LuCaP 77CR and LuCaP 96CR with a modest tumor inhibition and survival benefit, and LuCaP 35CR with minimal tumor inhibition and no survival benefit upon AA treatment. We identified a molecular signature of secreted proteins associated with the AA ultraresponsive phenotype. Upon resistance, AA ultraresponder LuCaP 136CR displayed reduced androgen receptor (AR) signaling and sustainably low nuclear glucocorticoid receptor (nGR) localization, accompanied by steroid metabolism alteration and epithelial-mesenchymal transition phenotype enrichment with increased expression of NF-κB-regulated genes; intermediate and minimal responders maintained sustained AR signaling and increased tumoral nGR localization.Conclusions: We identified a molecular signature of secreted proteins associated with AA ultraresponsiveness and sustained AR/GR signaling upon AA resistance in intermediate or minimal responders. These data will inform development of noninvasive biomarkers predicting AA response and suggest that further inhibition along the AR/GR signaling axis may be effective only in AA-resistant patients who are intermediate or minimal responders. These findings require verification in prospective clinical trials. Clin Cancer Res; 23(9); 2301-12. ©2016 AACR.

Restoration of tumor suppression in prostate cancer by targeting the E3 ligase E6AP

Restoration of tumor suppression is an attractive onco-therapeutic approach. It is particularly relevant when a tumor suppressor is excessively degraded by an overactive oncogenic E3 ligase. We previously discovered that the E6-associated protein (E6AP; as classified in the human papilloma virus context) is an E3 ligase that has an important role in the cellular stress response, and it directly targets the tumor-suppressor promyelocytic leukemia protein (PML) for proteasomal degradation. In this study, we have examined the role of the E6AP-PML axis in prostate cancer (PC). We show that knockdown (KD) of E6AP expression attenuates growth of PC cell lines in vitro. We validated this finding in vivo using cell line xenografts, patient-derived xenografts and mouse genetics. We found that KD of E6AP attenuates cancer cell growth by promoting cellular senescence in vivo, which correlates with restoration of tumor suppression by PML. In addition, we show that KD of E6AP sensitizes cells to radiation-induced death. Overall, our findings demonstrate a role for E6AP in the promotion of PC and support E6AP targeting as a novel approach for PC treatment, either alone or in combination with radiation.

GRM1 is An Androgen-Regulated Gene and its Expression Correlates with Prostate Cancer Progression in Pre-Clinical Models

PURPOSE

We recently demonstrated that glutamate receptor GRM1 was expressed at high levels in castration-resistant prostate cancer (CR-PCa) tissues and cells. Herein, we determined the relationship between GRM1 and AR, PSA, and tumor growth, remission, and recurrence in preclinical PCa models. The effect of alterations in GRM1 expression was also investigated on PCa cell growth, migration and invasion.

EXPERIMENTAL DESIGN

We used quantitative gene expression and immunohistochemistry to define the temporal association between GRM1 expression and AR, PSA, and tumor growth during CR progression in CWR22 (n = 59) and LuCaP 35 (n = 12) PCa xenografts. The effect of alterations in GRM1 expression levels on growth, migration, and invasion was investigated in GRM1-overexpressed or -silenced PCa cell lines. The effect of DHT on GRM1 expression was determined in the presence or absence of the antiandrogen bicalutamide.

RESULTS

We found that GRM1 transcript and tissue expression directly correlated with growth and AR and PSA expression in hormone-sensitive (HS), castrated, and CR tumor xenografts. GRM1 overexpression or silencing directly correlated with PCa cell proliferation, migration, and invasion. DHT increased GRM1 expression via an AR-dependent manner in HS- and CR-PCa cell lines.

CONCLUSIONS

This is a first report of GRM1 as an androgen and AR-target gene. GRM1 expression directly correlated with tumor growth, regression, and recurrence and may contribute to CR-progression of PCa in preclinical models. Further studies are needed to define the utility of GRM1 as a druggable target or biomarker for PCa.

Characterizing the molecular features of ERG-positive tumors in primary and castration resistant prostate cancer

BACKGROUND

The TMPRSS2-ERG gene fusion is detected in approximately half of primary prostate cancers (PCa) yet the prognostic significance remains unclear. We hypothesized that ERG promotes the expression of common genes in primary PCa and metastatic castration-resistant PCa (CRPC), with the objective of identifying ERG-associated pathways, which may promote the transition from primary PCa to CRPC.

METHODS

We constructed tissue microarrays (TMA) from 127 radical prostatectomy specimens, 20 LuCaP patient-derived xenografts (PDX), and 152 CRPC metastases obtained immediately at time of death. Nuclear ERG was assessed by immunohistochemistry (IHC). To characterize the molecular features of ERG-expressing PCa, a subset of IHC confirmed ERG+ or ERG- specimens including 11 radical prostatectomies, 20 LuCaP PDXs, and 45 CRPC metastases underwent gene expression analysis. Genes were ranked based on expression in primary PCa and CRPC. Common genes of interest were targeted for IHC analysis and expression compared with biochemical recurrence (BCR) status.

RESULTS

IHC revealed that 43% of primary PCa, 35% of the LuCaP PDXs, and 18% of the CRPC metastases were ERG+ (12 of 48 patients [25%] had at least one ERG+ metastasis). Based on gene expression data and previous literature, two proteins involved in calcium signaling (NCALD, CACNA1D), a protein involved in inflammation (HLA-DMB), CD3 positive immune cells, and a novel ERG-associated protein, DCLK1 were evaluated in primary PCa and CRPC metastases. In ERG+ primary PCa, a weak association was seen with NCALD and CACNA1D protein expression. HLA-DMB association with ERG was decreased and CD3 cell number association with ERG was changed from positive to negative in CRPC metastases compared to primary PCa. DCLK1 was upregulated at the protein level in unpaired ERG+ primary PCa and CRPC metastases (P = 0.0013 and P < 0.0001, respectively). In primary PCa, ERG status or expression of targeted proteins was not associated with BCR-free survival. However, for primary PCa, ERG+DCLK1+ patients exhibited shorter time to BCR (P = 0.06) compared with ERG+DCLK1- patients.

CONCLUSIONS

This study examined ERG expression in primary PCa and CRPC. We have identified altered levels of inflammatory mediators associated with ERG expression. We determined expression of DCLK1 correlates with ERG expression and may play a role in primary PCa progression to metastatic CPRC. Prostate 76:810-822, 2016. © 2016 Wiley Periodicals, Inc.

Amplification of the 9p13.3 chromosomal region in prostate cancer

Amplification of the 9p13.3 chromosomal region occurs in a subset of prostate cancers (PCs); however, the target gene or genes of this amplification have remained unidentified. The aim of this study was to investigate the 9p13.3 amplification in more detail to identify genes that are potentially advantageous for cancer cells. We narrowed down the minimally amplified area and assessed the frequency of the 9p13.3 amplification. Of the clinical samples from untreated PCs that were examined (n = 134), 9.7% showed high-level amplification, and 32.1% showed low-level amplification. Additionally, in clinical samples from castration-resistant PCs (n = 70), high- and low-level amplification was seen in 14.3% and 44.3% of the samples, respectively. We next analyzed the protein-coding genes in this chromosomal region for both their expression in clinical PC samples as well as their potential as growth regulators in PC cells. We found that the 9p13.3 amplification harbors several genes that are able to affect the growth of PC cells when downregulated using siRNA. Of these, UBAP2 was the most prominently upregulated gene in the clinical prostate tumor samples. © 2016 Wiley Periodicals, Inc.

Substantial interindividual and limited intraindividual genomic diversity among tumors from men with metastatic prostate cancer

Tumor heterogeneity may reduce the efficacy of molecularly guided systemic therapy for cancers that have metastasized. To determine whether the genomic alterations in a single metastasis provide a reasonable assessment of the major oncogenic drivers of other dispersed metastases in an individual, we analyzed multiple tumors from men with disseminated prostate cancer through whole-exome sequencing, array comparative genomic hybridization (CGH) and RNA transcript profiling, and we compared the genomic diversity within and between individuals. In contrast to the substantial heterogeneity between men, there was limited diversity among metastases within an individual. The number of somatic mutations, the burden of genomic copy number alterations and aberrations in known oncogenic drivers were all highly concordant, as were metrics of androgen receptor (AR) activity and cell cycle activity. AR activity was inversely associated with cell proliferation, whereas the expression of Fanconi anemia (FA)-complex genes was correlated with elevated cell cycle progression, expression of the E2F transcription factor 1 (E2F1) and loss of retinoblastoma 1 (RB1). Men with somatic aberrations in FA-complex genes or in ATM serine/threonine kinase (ATM) exhibited significantly longer treatment-response durations to carboplatin than did men without defects in genes encoding DNA-repair proteins. Collectively, these data indicate that although exceptions exist, evaluating a single metastasis provides a reasonable assessment of the major oncogenic driver alterations that are present in disseminated tumors within an individual, and thus may be useful for selecting treatments on the basis of predicted molecular vulnerabilities.

Addition of PSMA ADC to enzalutamide therapy significantly improves survival in in vivo model of castration resistant prostate cancer

BACKGROUND

Despite multiple new therapies available to patients with advanced castration-resistant prostate cancer (CRPC), the overall survival benefit still remains relatively short. Therefore, it is important to investigate additional treatment options that could achieve greater efficacy. Because of tumor heterogeneity and the development of resistance to treatment with single agents, combination therapies using existing drugs with new agents can potentially broaden individual therapeutic windows and achieve improved efficacy and safety profiles. The objective of the current studies was to evaluate the efficacy of combination of enzalutamide (ENZ) with prostate specific membrane antigen antibody drug conjugate (PSMA ADC) to inhibit CRPC patient-derived xenografts (PDX) in a preclinical setting.

METHODS

Subcutaneous LuCaP 96CR prostate cancer PDX bearing mice were treated with a single dose of PSMA ADC (2.0 mg/kg) or 5 days a week ENZ (50 mg/kg) as monotherapy or with a combination of these two agents. The effects of the PSMA ADC+ENZ combination were compared to PSMA ADC alone, ENZ alone, and placebo control. IHC analyses were performed to determine PSMA, AR, ARV7, and GR expression and effects on proliferation.

RESULTS

All treatments inhibited tumor progression but with different efficacy. At 6 weeks, in the control and ENZ groups all tumors were progressing, while in the PSMA ADC group only 5/11 were progressing, two remained unchanged and four tumors had decreased tumor volume. Moreover, all animals in the PSMA ADC+ENZ group had smaller tumors at week 6 when compared to their size at enrollment (week 0). A 14-week followup showed that all three treatments resulted in significant survival benefits but the combination effects were the most pronounced resulting in PSMA ADC+ENZ versus ENZ HR = 0.093 (P = 0.0045) and PSMA ADC+ENZ versus PSMA ADC HR = 0.051 (P = <0.0001) with no deaths observed in the combination group.

CONCLUSIONS

Our results clearly indicate that the combination of PSMA ADC+ENZ possesses strong antitumor activity and significantly improves survival over ENZ monotherapy using the LuCaP 96CR PDX model. These results provide a strong rationale for clinical testing of PSMA ADC in combination with ENZ and/or other androgen-directed treatment strategies.

Conversion of Prostate Adenocarcinoma to Small Cell Carcinoma-Like by Reprogramming

The lineage relationship between prostate adenocarcinoma and small cell carcinoma was studied by using the LuCaP family of xenografts established from primary neoplasm to metastasis. Expression of four stem cell transcription factor (TF) genes, LIN28A, NANOG, POU5F1, SOX2, were analyzed in the LuCaP lines. These genes, when force expressed in differentiated cells, can reprogram the recipients into stem-like induced pluripotent stem (iPS) cells. Most LuCaP lines expressed POU5F1, while LuCaP 145.1, representative of small cell carcinoma, expressed all four. Through transcriptome database query, many small cell carcinoma genes were also found in stem cells. To test the hypothesis that prostate cancer progression from "differentiated" adenocarcinoma to "undifferentiated" small cell carcinoma could involve re-expression of stem cell genes, the four TF genes were transduced via lentiviral vectors into five adenocarcinoma LuCaP lines-70CR, 73CR, 86.2, 92, 105CR-as done in iPS cell reprogramming. The resultant cells from these five transductions displayed a morphology of small size and dark appearing unlike the parentals. Transcriptome analysis of LuCaP 70CR* ("*" to denote transfected progeny) revealed a unique gene expression close to that of LuCaP 145.1. In a prostate principal components analysis space based on cell-type transcriptomes, the different LuCaP transcriptome datapoints were aligned to suggest a possible ordered sequence of expression changes from the differentiated luminal-like adenocarcinoma cell types to the less differentiated, more stem-like small cell carcinoma types, and LuCaP 70CR*. Prostate cancer progression can thus be molecularly characterized by loss of differentiation with re-expression of stem cell genes. J. Cell. Physiol. 231: 2040-2047, 2016. © 2016 Wiley Periodicals, Inc.

Epithelial mesenchymal-like transition occurs in a subset of cells in castration resistant prostate cancer bone metastases

TGFβ is a known driver of epithelial-mesenchymal transition (EMT) which is associated with tumor aggressiveness and metastasis. However, EMT has not been fully explored in clinical specimens of castration-resistant prostate cancer (CRPC) metastases. To assess EMT in CRPC, gene expression analysis was performed on 149 visceral and bone metastases from 62 CRPC patients and immunohistochemical analysis was performed on 185 CRPC bone and visceral metastases from 42 CRPC patients. In addition, to assess the potential of metastases to seed further metastases the mitochondrial genome was sequenced at different metastatic sites in one patient. TGFβ was increased in bone versus visceral metastases. While primarily cytoplasmic; nuclear and cytoplasmic Twist were significantly higher in bone than in visceral metastases. Slug and Zeb1 were unchanged, with the exception of nuclear Zeb1 being significantly higher in visceral metastases. Importantly, nuclear Twist, Slug, and Zeb1 were only present in a subset of epithelial cells that had an EMT-like phenotype. Underscoring the relevance of EMT-like cells, mitochondrial sequencing revealed that metastases could seed additional metastases in the same patient. In conclusion, while TGFβ expression and EMT-associated protein expression is present in a considerable number of CRPC visceral and bone metastases, nuclear Twist, Slug, and Zeb1 localization and an EMT-like phenotype (elongated nuclei and cytoplasmic compartment) was only present in a small subset of CRPC bone metastases. Mitochondrial sequencing from different metastases in a CRPC patient provided evidence for the seeding of metastases from previously established metastases, highlighting the biological relevance of EMT-like behavior in CRPC metastases.

Abstract A109: Radium-223 dichloride inhibits tumor growth and tumor-induced bone growth in osteoblastic prostate cancer models

Radium-223 dichloride (radium-223), an alpha particle-emitting calcium-mimetic, improves overall survival in prostate cancer patients with symptomatic bone metastases. We have defined radium-223 mode-of-action and efficacy in two clinically relevant prostate cancer xenograft models demonstrating PSA expression and osteoblastic growth upon intratibial inoculation of cancer cells. Immunocompromised male mice were inoculated with human LNCaP or patient-derived LuCaP 58 prostate cancer cells in the intratibial compartment and subsequently stratified into treatment groups based on lesion grade and/or serum PSA levels. Radium-223 (300 kBq/kg) or vehicle was administered intravenously, two times at 4-week intervals during the experiment. X-rays and serum samples were obtained biweekly and at sacrifice. Soft tissue tumors were examined macroscopically at sacrifice and tissue samples were collected and processed for γ-counter measurements, micro-CT, autoradiography and histology. Radium-223 treatment inhibited tumor-induced osteoblastic bone growth as indicated by reduced bone volume and surface in LNCaP and LuCaP 58 prostate cancer mouse models. In addition, radium-223 treatment suppressed metabolic activity in bone as evidenced by decreased number of osteoblasts and osteoclasts relative to bone surface and reduced levels of the bone formation marker PINP. Radium-223 resulted in lower PSA values as early as two weeks after the first dose, indicating constrained tumor growth following treatment. This phenomenon was further supported by reduced total bone lesion tissue and tumor area in LNCaP and LuCaP 58 models and increased percentage of necrotic tumor area in the LuCaP 58 model in radium-223-treated mice as compared to vehicle-treated mice. Moreover, DNA double-strand breaks were increased in cancer cells 24 hours post radium-223 treatment in the LuCaP 58 model providing further evidence of anti-tumor effects. Radium-223-treated mice exhibited less visceral metastases in the LuCaP 58 model (not significant). Based on autoradiography, radium-223 was deposited in the intratumoral bone matrix and in conjunction with osteoblasts in osteoblastic metastases. Our results demonstrate that radium-223 dichloride is successfully incorporated into the intratumoral bone matrix and inhibits tumor growth in both cell line- and patient-derived osteoblastic prostate cancer metastasis models. Given the α-particle range of 50-80 μm, potent radiation effects on the tumor microenvironment are evident whereas relevant effects on the more distant bone marrow are not expected. Taken together, radium-223 therapy exhibits a dual mode-of-action that impacts tumor growth and tumor-induced bone reaction, both important players in the destructive vicious cycle of osteoblastic bone metastasis in prostate cancer.

Citation Format: Mari I. Suominen, Katja M. Fagerlund, Dominik Mumberg, Karl Ziegelbauer, Sanna-Maria Käkönen, Jussi M. Halleen, Robert L. Vessella, Arne Scholz. Radium-223 dichloride inhibits tumor growth and tumor-induced bone growth in osteoblastic prostate cancer models. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A109.

High-Resolution Genomic Profiling of Disseminated Tumor Cells in Prostate Cancer

Circulating tumor cells and disseminated tumor cells (DTCs) are of great interest because they provide a minimally invasive window for assessing aspects of cancer biology, including tumor heterogeneity, a means to discover biomarkers of disease behavior, and a way to identify and prioritize therapeutic targets in the emerging era of precision oncology. However, the rarity of circulating tumor cells and DTCs poses a substantial challenge to the consistent success in analyzing their molecular features, including genomic aberrations. Herein, we describe optimized and robust methods to reproducibly detect genomic copy number alterations in samples of 2 to 40 cells after whole-genome amplification with the use of a high-resolution single-nuclear polymorphism-array platform and refined computational algorithms. We have determined the limit of detection for heterogeneity within a sample as 50% and also demonstrated success in analyzing single cells. We validated the genes in genomic regions that are frequently amplified or deleted by real-time quantitative PCR and nCounter copy number quantification. We further applied these methods to DTCs isolated from individuals with advanced prostate cancer to confirm their highly aberrant nature. We compared copy number alterations of DTCs with matched metastatic tumors isolated from the same individual to gain biological insight. These developments provide high-resolution genomic profiling of single and rare cell populations and should be applicable to a wide-range of sample sources.

The biology and clinical implications of prostate cancer dormancy and metastasis

Disseminated tumor cells (DTCs) are detected early in the disease process in prostate cancer (PCa) patients and can persist after radical prostatectomy. DTCs can remain dormant in patients with no evidence of disease for a prolonged period of time only to recur 10 or more years later. Recent advances in single-cell genomics and transcriptomics have provided much needed insight into DTC biology and cancer dormancy in patients. With the development of new in vitro and preclinical models, researchers recapitulate the clinical events in patients and therefore allow further elucidation of the molecular mechanisms underlying cancer dormancy and escape. In this review, we explore novel ideas on the detection, heterogeneous transcriptomic profiles, molecular and cellular mechanisms of dormancy, and potential mechanisms underlying dormancy escape by DTCs. As such, there is hope that identifying and targeting novel dormancy-associated pathways in patients with residual disease will have significant clinical implications for the treatment of PCa patients in the future.

Cyclin D1 Loss Distinguishes Prostatic Small-Cell Carcinoma from Most Prostatic Adenocarcinomas

PURPOSE

Small-cell neuroendocrine differentiation in prostatic carcinoma is an increasingly common resistance mechanism to potent androgen deprivation therapy (ADT), but can be difficult to identify morphologically. We investigated whether cyclin D1 and p16 expression can inform on Rb functional status and distinguish small-cell carcinoma from adenocarcinoma.

EXPERIMENTAL DESIGN

We used gene expression data and immunohistochemistry to examine cyclin D1 and p16 levels in patient-derived xenografts (PDX), and prostatic small-cell carcinoma and adenocarcinoma specimens.

RESULTS

Using PDX, we show proof-of-concept that a high ratio of p16 to cyclin D1 gene expression reflects underlying Rb functional loss and distinguishes morphologically identified small-cell carcinoma from prostatic adenocarcinoma in patient specimens (n = 13 and 9, respectively). At the protein level, cyclin D1, but not p16, was useful to distinguish small-cell carcinoma from adenocarcinoma. Overall, 88% (36/41) of small-cell carcinomas showed cyclin D1 loss by immunostaining compared with 2% (2/94) of Gleason score 7-10 primary adenocarcinomas at radical prostatectomy, 9% (4/44) of Gleason score 9-10 primary adenocarcinomas at needle biopsy, and 7% (8/115) of individual metastases from 39 patients at autopsy. Though rare adenocarcinomas showed cyclin D1 loss, many of these were associated with clinical features of small-cell carcinoma, and in a cohort of men treated with adjuvant ADT who developed metastasis, lower cyclin D1 gene expression was associated with more rapid onset of metastasis and death.

CONCLUSIONS

Cyclin D1 loss identifies prostate tumors with small-cell differentiation and may identify a small subset of adenocarcinomas with poor prognosis. Clin Cancer Res; 21(24); 5619-29. ©2015 AACR.

Characterization of single disseminated prostate cancer cells reveals tumor cell heterogeneity and identifies dormancy associated pathways

Cancer dormancy refers to the prolonged clinical disease-free time between removal of the primary tumor and recurrence, which is common in prostate cancer (PCa), breast cancer, esophageal cancer, and other cancers. PCa disseminated tumor cells (DTC) are detected in both patients with no evidence of disease (NED) and advanced disease (ADV). However, the molecular and cellular nature of DTC is unknown. We performed a first-in-field study of single DTC transcriptomic analyses in cancer patients to identify a molecular signature associated with cancer dormancy. We profiled eighty-five individual EpCAM⁺/CD45⁻ cells from the bone marrow of PCa patients with NED or ADV. We analyzed 44 DTC with high prostate-epithelial signatures, and eliminated 41 cells with high erythroid signatures and low prostate epithelial signatures. DTC were clustered into 3 groups: NED, ADV_1, and ADV_2, in which the ADV_1 group presented a distinct gene expression pattern associated with the p38 stress activated kinase pathway. Additionally, DTC from the NED group were enriched for a tumor dormancy signature associated with head and neck squamous carcinoma and breast cancer. This study provides the first clinical evidence of the p38 pathway as a potential biomarker for early recurrence and an attractive target for therapeutic intervention.

Abstract 1718: The importance of clinically relevant rapid autopsy specimens and LuCaP patient-derived xenograft models to interrogate the heterogeneous and evolving treatment resistance of castration-resistant prostate cancer

Recent advances in our understanding of metastatic castration-resistant prostate cancer (mCRPC) biology have led to the approval and use of multiple novel drugs, including abiraterone, enzalutamide, cabazitaxel, sipuleucel-T and radium-223. Although these agents all provide improvement in survival, resistance always develops after an initial response. To understand the biology of responses and resistance, clinically relevant specimens and preclinical models are needed. To address this critical need, our objectives are: 1) to collect samples of metastases prior to and after treatment for evaluation of potential biomarkers of responses and resistance and 2) to generate patient-derived xenografts (PDXs) that are representative of these novel phenotypes of advanced mCRPC.

A Rapid Autopsy Program (RAP) was established at the University of Washington to study the lethal phenotype of mCRPC. Through the RAP we have collected more than 3000 tissue specimens, including bone and visceral metastases from over 110 patients who died of mCRPC. The samples were processed for paraffin embedding and frozen for future histological and molecular analyses. All samples are tracked in a relational database and cross-linked to clinical and pathologic data.

To provide clinically relevant preclinical models for studies of late stage advanced prostate cancer, we also implant tissues acquired during the RAP into immunocompromised mice in order to establish novel CRPC PDXs. At present we have 28 primary PDXs (the LuCaP series), and 10 castration-resistant sublines of the primary lines. The LuCaP models have been extensively characterized by light microscopy, immunohistochemistry, expression arrays, RNASeq, IHC, exome sequencing and other methodologies. We have also determined responses of these PDXs to castration and docetaxel. To address the need for models representing the current tumor phenotypes that exist in patients who develop resistance to secondary androgen-targeting therapy, we have also evaluated responses to abiraterone and enzalutamide, and are experimentally developing abiraterone- and enzalutamide-resistant LuCaP PDXs. In addition, we are continuing to generate novel PDXs using abiraterone- and enzalutamide-resistant patient samples, and have four models that were established from abiraterone-resistant tumors.

In summary, we have established a large biorepository of mCRPC specimens and PDXs. Moreover, due to the constant evolution of the advanced PCa phenotype we continue to acquire mCRPC specimens and establish novel PDXs that are refractory to the most recent treatments which allow us to investigate biology of late stage mCRPC and to provide valuable clinical specimens and LuCaP PDXs to the PCa research community.

Citation Format: Colm Morrissey, Ming H. Lam, Tia S. Higano, Lawrence D. True, Martine Roudier, Robert B. Montgomery, Peter S. Nelson, Paul H. Lange, Evan Y. Yu, Robert L. Vessella, Eva Corey. The importance of clinically relevant rapid autopsy specimens and LuCaP patient-derived xenograft models to interrogate the heterogeneous and evolving treatment resistance of castration-resistant 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 1718. doi:10.1158/1538-7445.AM2015-1718

Abstract 4313: Abiraterone acetate (AA) treatment of prostate cancer patient-derived xenografts (PDX) demonstrates heterogeneity of responses and identifies potential biomarkers of adaptive resistance

AA, a prodrug of the CYP17A1 inhibitor abiraterone, is the first second-line hormonal agent shown to improve survival in metastatic castration-resistant prostate cancer (CRPC); however, as with all available treatments, responding tumors eventually develop resistance. This highlights the importance of identification of mechanisms involved in tumor response and resistance to AA. We evaluated the efficacy of AA in LuCaP CRPC PDXs and investigated mechanisms of response and/or resistance, focusing on androgen receptor (AR) and glucocorticoid receptor (GR) signaling.

Mice bearing CRPC LuCaP 35CR, 96CR, 77CR, and 136CR PDXs were treated with AA (0.5 mmol/kg/d), and tumor responses and body weights were monitored. Tumors were harvested 7 days after the beginning of the treatment (d7) and at end of study (EOS) (sacrifice when tumor &gt; 1000 mg). Gene expression analyses using Affymetrix HG-U219 gene array and qPCR were performed to evaluate the validity of established biomarkers and identify novel biomarkers related to AA response.

Linear regression model analyses showed that AA inhibited tumor progression in 3 of 4 LuCaP PDXs (96CR, 77CR, 136CR), but the initial response was followed by development of resistance. Corresponding analyses of serum prostate-specific antigen (PSA) levels demonstrated a decrease post AA (96CR: p = 0.051; 77CR: p = 0.001; 136CR: undetectable at baseline). AA improved median survival (77CR: 7 vs 9.5 weeks, p = 0.022; and 136CR: 6.8 vs 21.6 weeks, p &lt; 0.0001), and highly variable responses were observed for 96CR (5.75 vs 10 weeks, p = 0.25). 35CR did not exhibit significant growth inhibition, reduction in PSA, or decreased median survival on AA. Evaluation of gene signatures revealed a negative association of proliferation-associated genes with AA at d7 for 35CR and 136CR, while at EOS these signatures were negatively associated with AA for 96CR and 136CR. Signatures of AR-regulated genes were negatively associated with AA at d7 for 35CR and 136CR, while at EOS they were negatively associated with AA for 96CR and 136CR. Targeted sequencing of the AR ligand binding domain coding sequence did not detect any mutations in any PDX at EOS. Trends toward increased expression of full length AR (ARFL) and splice variant ARv7 were associated with AA at d7 for 136CR. At EOS, trends toward increased ARFL and ARv7 expression were associated with AA for 35CR and 96CR. Significantly increased GR expression was associated with AA at EOS for 96CR and 77CR, and a trend was observed for 136CR.

Our results demonstrate model-specific heterogeneity of physiological and molecular responses to AA in CRPC. However, our data indicate that increased ARFL, ARv7, and/or GR could be biomarkers of adaptive resistance and potentially play functional roles in conferring resistance.

Citation Format: Hung-Ming Lam, Ryan McMullin, Holly M. Nguyen, Michael Gormley, Roman Gulati, Weimin Li, Deborah Ricci, Karin Verstraeten, Shibu Thomas, Elahe A. Mostaghel, Peter S. Nelson, Robert L. Vessella, Eva Corey. Abiraterone acetate (AA) treatment of prostate cancer patient-derived xenografts (PDX) demonstrates heterogeneity of responses and identifies potential biomarkers of adaptive resistance. [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 4313. doi:10.1158/1538-7445.AM2015-4313

Abstract 3447: Radium-223 dichloride exhibits dual mode-of-action inhibiting both tumor and tumor-induced bone growth in two osteoblastic prostate cancer models

Radium-223 dichloride (radium-223), an alpha particle-emitting calcium-mimetic, improves overall survival in prostate cancer patients with symptomatic bone metastases. Here, we define radium-223 mode-of-action and efficacy in two clinically relevant prostate cancer xenograft models demonstrating PSA expression and osteoblastic growth upon intratibial inoculation of cancer cells.

Immunocompromized male mice were inoculated with human LNCaP or patient-derived LuCaP 58 prostate cancer cells in the intratibial compartment and subsequently stratified into treatment groups based on lesion grade and/or serum PSA levels. Radium-223 (300 kBq/kg) or vehicle was administered intravenously, two times at 4-week intervals during the experiment. X-rays and serum samples were obtained biweekly and at sacrifice. Soft tissue tumors were examined macroscopically at sacrifice and tissue samples were collected and processed for γ-counter measurements, micro-CT, autoradiography and histology.

Radium-223 treatment inhibited tumor-induced osteoblastic bone growth as indicated by reduced bone volume and surface in LNCaP and LuCaP 58 prostate cancer mouse models. In addition, radium-223 treatment suppressed metabolic activity in bone as evidenced by decreased number of osteoblasts and osteoclasts relative to bone surface and reduced levels of the bone formation marker PINP. Radium-223 resulted in lower PSA values as early as two weeks after the first dose, indicating constrained tumor growth following treatment. This phenomenon was further supported by reduced total tissue and tumor area in tibia in LNCaP and LuCaP 58 models and increased percentage of necrotic tumor area in the LuCaP 58 model in radium-223-treated mice as compared to vehicle-treated mice. Moreover, DNA double-strand breaks were increased in cancer cells 24 hours post radium-223 treatment in the LuCaP 58 model providing further evidence of anti-tumor effects. Radium-223-treated mice exhibited less visceral metastases in the LuCaP 58 model (not significant). Based on autoradiography, radium-223 was deposited in the intratumoral bone matrix and in conjunction with osteoblasts in osteoblastic metastases.

We demonstrate that radium-223 dichloride is successfully incorporated into the intratumoral bone matrix and inhibits tumor growth in both cell line- and patient-derived osteoblastic prostate cancer metastasis models. Given the α-particle range of 50-80 μm, potent radiation effects on the tumor microenvironment are evident whereas relevant effects on the more distant bone marrow are not expected. Taken together, radium-223 therapy exhibits a dual mode-of-action that impacts tumor growth and tumor-induced bone reaction, both important players in the destructive vicious cycle of osteoblastic bone metastasis in prostate cancer.

Citation Format: Mari I. Suominen, Katja M. Fagerlund, Jukka P. Rissanen, Yvonne Konkol, Jukka Morko, Zhiqi Peng, Esa Alhoniemi, Dominik Mumberg, Karl Ziegelbauer, Sanna-Maria Käkönen, Jussi M. Halleen, Robert L. Vessella, Arne Scholz. Radium-223 dichloride exhibits dual mode-of-action inhibiting both tumor and tumor-induced bone growth in two osteoblastic prostate cancer models. [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 3447. doi:10.1158/1538-7445.AM2015-3447

Reprogramming of prostate cancer cells--technical challenges

Prostate cancer progression is characterized by tumor dedifferentiation. Cancer cells of less differentiated tumors have a gene expression/transcriptome more similar to that of stem cells. In dedifferentiation, cancer cells may follow a specific program of gene expression changes to a stem-like state. In order to treat cancer effectively, the stem-like cancer cells and cancer differentiation pathway need to be identified and studied. Due to the very low abundance of stem-like cancer cells, their isolation from fresh human tumors is technically challenging. Induced pluripotent stem cell technology can reprogram differentiated cells into stem-like, and this may be a tool to generate sufficient stem-like cancer cells.

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.

Cellular Adhesion Promotes Prostate Cancer Cells Escape from Dormancy

Dissemination of prostate cancer (PCa) cells to the bone marrow is an early event in the disease process. In some patients, disseminated tumor cells (DTC) proliferate to form active metastases after a prolonged period of undetectable disease known as tumor dormancy. Identifying mechanisms of PCa dormancy and reactivation remain a challenge partly due to the lack of in vitro models. Here, we characterized in vitro PCa dormancy-reactivation by inducing cells from three patient-derived xenograft (PDX) lines to proliferate through tumor cell contact with each other and with bone marrow stroma. Proliferating PCa cells demonstrated tumor cell-cell contact and integrin clustering by immunofluorescence. Global gene expression analyses on proliferating cells cultured on bone marrow stroma revealed a downregulation of TGFB2 in all of the three proliferating PCa PDX lines when compared to their non-proliferating counterparts. Furthermore, constitutive activation of myosin light chain kinase (MLCK), a downstream effector of integrin-beta1 and TGF-beta2, in non-proliferating cells promoted cell proliferation. This cell proliferation was associated with an upregulation of CDK6 and a downregulation of E2F4. Taken together, our data provide the first clinically relevant in vitro model to support cellular adhesion and downregulation of TGFB2 as a potential mechanism by which PCa cells may escape from dormancy. Targeting the TGF-beta2-associated mechanism could provide novel opportunities to prevent lethal PCa metastasis.

SRRM4 Expression and the Loss of REST Activity May Promote the Emergence of the Neuroendocrine Phenotype in Castration-Resistant Prostate Cancer

PURPOSE

The neuroendocrine phenotype is associated with the development of metastatic castration-resistant prostate cancer (CRPC). Our objective was to characterize the molecular features of the neuroendocrine phenotype in CRPC.

EXPERIMENTAL DESIGN

Expression of chromogranin A (CHGA), synaptophysin (SYP), androgen receptor (AR), and prostate-specific antigen (PSA) was analyzed by IHC in 155 CRPC metastases from 50 patients and in 24 LuCaP prostate cancer patient-derived xenografts (PDX). Seventy-one of 155 metastases and the 24 LuCaP xenograft lines were analyzed by whole-genome microarrays. REST splicing was verified by PCR.

RESULTS

Coexpression of CHGA and SYP in >30% of cells was observed in 22 of 155 metastases (9 patients); 11 of the 22 metastases were AR(+)/PSA(+) (6 patients), 11/22 were AR-/PSA- (4 patients), and 4/24 LuCaP PDXs were AR(-)/PSA(-). By IHC, of the 71 metastases analyzed by whole-genome microarrays, 5 metastases were CHGA(+)/SYP(+)/AR(-), and 5 were CHGA(+)/SYP(+)/AR(+). Only CHGA(+)/SYP(+) metastases had a neuroendocrine transcript signature. The neuronal transcriptional regulator SRRM4 transcript was associated with the neuroendocrine signature in CHGA(+)/SYP(+) metastases and all CHGA(+)/SYP(+) LuCaP xenografts. In addition, expression of SRRM4 in LuCaP neuroendocrine xenografts correlated with a splice variant of REST that lacks the transcriptional repressor domain.

CONCLUSIONS

(i) Metastatic neuroendocrine status can be heterogeneous in the same patient, (ii) the CRPC neuroendocrine molecular phenotype can be defined by CHGA(+)/SYP(+) dual positivity, (iii) the neuroendocrine phenotype is not necessarily associated with the loss of AR activity, and (iv) the splicing of REST by SRRM4 could promote the neuroendocrine phenotype in CRPC.

Efficacy studies of an antibody-drug conjugate PSMA-ADC in patient-derived prostate cancer xenografts

BACKGROUND

It is timely and important to develop new treatment modalities for advanced prostate cancer, because even the newly FDA approved treatments, despite providing significant survival benefits, do not constitute cure of this disease. Antibody drug conjugates (ADCs) represent a promising approach to cancer therapy. Prostate-specific membrane antigen (PSMA) is expressed in advanced prostate cancer and targeting this protein is used for imaging of advanced prostate cancer as well as development of targeting strategies. The objective of our studies was to evaluate the efficacy of PSMA ADC against a series of patient-derived prostate cancer xenografts (LuCaP 58, LuCaP 77, LuCaP 96CR, and LuCaP 105) with different characteristics, including varying levels of PSMA expression and responses to androgen suppression.

METHODS

Mice bearing subcutaneous LuCaP prostate cancer-derived xenografts received PSMA antibody monomethyl auristatin E (MMAE) drug conjugate (PSMA ADC) in which the antibody and MMAE are linked via a protease-cleavable linker. PSMA ADC dose ranged from 1 to 6 mg/kg. Unmodified PSMA mAb + free MMAE at the amount equivalent to those contained in 6 mg/kg PSMA ADC was used as control. All treatments were administered once a week via tail-vein injections and repeated four times once a week and tumor responses were monitored for 10 weeks. IHC analyses were performed to determine PSMA and AR expression and effects on proliferation.

RESULTS

Treatment responses varied widely across the tumor models, from complete tumor regressions in LuCaP 96CR to largely unimpeded tumor progression of LuCaP 58, which had the lowest baseline level of PSMA expression. Intermediate antitumor effects were seen for LuCaP 77 and LuCaP 105 tumors, despite their having similar basal expression of PSMA as LuCaP 96CR. Interestingly, we detected substantial differences in responses even within the same model, indicating that PSMA expression is not the only factor involved in treatment outcomes.

CONCLUSIONS

Our results show high efficacy of PSMA ADC in advanced prostate cancer but also considerable variability in effects despite PSMA expression. Further studies to identify tumor characteristics that are predictive of treatment response are ongoing.

CH5137291, an androgen receptor nuclear translocation-inhibiting compound, inhibits the growth of castration-resistant prostate cancer cells

Resistance of prostate cancer to castration is currently an unavoidable problem. The major mechanisms underlying such resistance are androgen receptor (AR) overexpression, androgen-independent activation of AR, and AR mutation. To address this problem, we developed an AR pure antagonist, CH5137291, with AR nuclear translocation-inhibiting activity, and compared its activity and characteristics with that of bicalutamide. Cell lines corresponding to the mechanisms of castration resistance were used: LNCaP-BC2 having AR overexpression and LNCaP-CS10 having androgen-independent AR activation. VCaP and LNCaP were used as hormone-sensitive prostate cancer cells. In vitro functional assay clearly showed that CH5137291 inhibited the nuclear translocation of wild-type ARs as well as W741C- and T877A-mutant ARs. In addition, it acted as a pure antagonist on the transcriptional activity of these types of ARs. In contrast, bicalutamide did not inhibit the nuclear translocation of these ARs, and showed a partial/full agonistic effect on the transcriptional activity. CH5137291 inhibited cell growth more strongly than bicalutamide in VCaP and LNCaP cells as well as in LNCaP-BC2 and LNCaP-CS10 cells in vitro. In xenograft models, CH5137291 strongly inhibited the tumor growth of LNCaP, LNCaP-BC2, and LNCaP-CS10, whereas bicalutamide showed a weaker effect in LNCaP and almost no effect in LNCaP-BC2 and LNCaP-CS10 xenografts. Levels of prostate-specific antigen (PSA) in plasma correlated well with the antitumor effect of both agents. CH5137291 inhibited the growth of LNCaP tumors that had become resistant to bicalutamide treatment. A docking model suggested that CH5137291 intensively collided with the M895 residue of helix 12, and therefore strongly inhibited the folding of helix 12, a cause of AR agonist activity, in wild-type and W741C-mutant ARs. In cynomolgus monkeys, the serum concentration of CH5137291 increased dose-dependently and PSA level decreased 80% at 100 mg/kg. CH5137291 is expected to offer a novel therapeutic approach against major types of castration-resistant prostate cancers.

The role of the microenvironment-dormant prostate disseminated tumor cells in the bone marrow

Disseminated tumor cells (DTC) leave the primary tumor and reside in distant sites (e.g. bone) early in prostate cancer. Patients may harbor dormant DTC which develop into clinically overt metastasis years after radical prostatectomy. We will describe recent evidence suggesting high p38/ERK ratio, bone morphogenetic proteins, and tumor growth factor-beta 2 promote dormancy in solid tumors. Furthermore, we will discuss the possible regulation of dormancy by hematopoietic stem cell and vascular niches, and describe novel models recapitulating bone marrow metastatic latency and out- growth, 3D microvascular networks, and 3D biomatrix supportive niches in the studies of tumor cell dormancy.

Prostate cancer characteristics associated with response to pre-receptor targeting of the androgen axis

BACKGROUND

Factors influencing differential responses of prostate tumors to androgen receptor (AR) axis-directed therapeutics are poorly understood, and predictors of treatment efficacy are needed. We hypothesized that the efficacy of inhibiting DHT ligand synthesis would associate with intra-tumoral androgen ratios indicative of relative dependence on DHT-mediated growth.

METHODS

We characterized two androgen-sensitive prostate cancer xenograft models after androgen suppression by castration in combination with the SRD5A inhibitor, dutasteride, as well as a panel of castration resistant metastases obtained via rapid autopsy.

RESULTS

In LuCaP35 tumors (intra-tumoral T:DHT ratio 2:1) dutasteride suppressed DHT to 0.02 ng/gm and prolonged survival vs. castration alone (337 vs.152 days, HR 2.8, p = 0.0015). In LuCaP96 tumors (T:DHT 10:1), survival was not improved despite similar DHT reduction (0.02 ng/gm). LuCaP35 demonstrated higher expression of steroid biosynthetic enzymes maintaining DHT levels (5-fold higher SRD5A1, 41 fold higher, 99-fold higher RL-HSD, p<0.0001 for both), reconstitution of intra-tumoral DHT (to ∼30% of untreated tumors), and ∼2 fold increased expression of full length AR. In contrast, LuCaP96 demonstrated higher levels of steroid catabolizing enzymes (6.9-fold higher AKR1C2, 3000-fold higher UGT2B15, p = 0.002 and p<0.0001 respectively), persistent suppression of intra-tumoral DHT, and 6-8 fold induction of full length AR and the ligand independent V7 AR splice variant. Human metastases demonstrated bio-active androgen levels and AR full length and AR splice-variant expression consistent with the range observed in xenografts.

CONCLUSIONS

Intrinsic differences in basal steroidogenesis, as well as variable expression of full length and splice-variant AR, associate with response and resistance to pre-receptor AR ligand suppression. Expression of steroidogenic enzymes and AR isoforms may serve as potential biomarkers of sensitivity to potent AR-axis inhibition and should be validated in additional models.

Abstract 735: Evaluation of cabozantinib in combination with abiraterone, enzalutamide or docetaxel in a castration-resistant prostate cancer xenograft in vivo

New second-generation hormonal therapy agents abiraterone (abi) and enzalutamide (enz), and standard chemotherapy docetaxel (doc) provide survival benefits for patients with castration-resistant prostate cancer (CRPC). However, despite these survival benefits, CRPC is still an incurable disease. Therefore, combination treatments with other agents are under consideration to potentially improve patient outcome. Cabozantinib (cabo), an inhibitor of tyrosine kinases including MET, VEGFR2, RET, KIT and AXL, has shown activity as monotherapy in clinical investigations in CRPC. Our objective was to evaluate effects of cabo in combination with abi, enz or doc on a CRPC xenograft tumors in vivo.

Mice with subcutaneous LuCaP 35CR CRPC patient-derived xenograft tumors were treated with abi (0.5 mmol/kg), enz (50 mg/kg), doc (10 mg/kg) or cabo (10 mg/kg) monotherapies or with combinations of cabo with abi, enz or doc. Mice were treated for 4 weeks (wks) and followed for additional 6 wks. After 4 wks of treatment abi and enz exhibited limited activity in this model (∼20% inhibition of tumor volume (TV), not significant), doc exhibited ∼40% TV inhibition (P=0.017), and cabo exhibited ∼60% TV inhibition (P&lt;0.001) vs untreated tumors. Combination of cabo with each of these agents provided reduction in TV vs single agent treatments: ∼40% inhibition vs abi only, P=0.0039; ∼60% inhibition vs enz only, P&lt;0.0001; and ∼70% inhibition vs doc only, P&lt;0.0001. When the tumors were followed for 6 wks after discontinuation of the treatment, all treated tumors started to grow at rates similar to the untreated tumors, indicating presence of viable tumor cells. At the end of the study (10 wks) there were survival benefits for monotherapies, and further survival benefits were detected for combination of enz+cabo vs enz as a monotherapy (medium survival 5.7 vs 3.5 wks, P=0.0087) and doc+cabo vs doc as monotherapy (medium survival 4.75 vs 3.5 wks, P=0.0003), however survival of animals treated with the combinations was not significantly different from the survival of animals treated with cabo monotherapy. In the second study, where mice were treated for up to 18 wks, there were significant survival benefits detected for enz+cabo vs enz (median survival 15.5 vs 6.5 wks; P=0.0039), and for doc+cabo vs doc (median survival 15 vs 6.8 wks; P=0.0008); however, the cabo combinations with enz and doc had survival times similar to cabo monotherapy (16 wks). No significant effects on survival were detected for abi+cabo vs abi as monotherapy. Cabo at 10 mg/kg administered long term did not result in decreased body weight in comparison to non-treated mice. These preliminary data indicate that combinations of cabo with enz, doc or abi are active in the subcutaneous LuCaP 35CR xenograft model. Further analyses of the data and tumors are ongoing.

Citation Format: Holly M. Nguyen, Lisha G. Brown, Jessica L. Olson, Dana T. Aftab, Robert L. Vessella, Eva Corey. Evaluation of cabozantinib in combination with abiraterone, enzalutamide or docetaxel in a castration-resistant prostate cancer xenograft in vivo. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 735. doi:10.1158/1538-7445.AM2014-735

Abstract 1214: Preclinical models of prostate cancer: New patient-derived xenografts for preclinical studies and evaluation of prostate cancer biology

Prostate cancer (PCa) is a heterogeneous disease and in order to increase our understanding of PCa biology and evaluate efficacy of novel pipeline agents, clinically relevant models are needed. It is well known that PCa xenografts are difficult to establish and propagate with approximate take rates of only 20%. During past the 20 years we have established and characterized a large series of LuCaP prostate cancer patient-derived xenografts (PDXs). Herein, we present a summary of the biological and molecular characterization of these PDX LuCaP models.

LuCaP PCa PDX models were derived from primary PCa and various sites of metastases. The histology of the LuCaP PDXs is similar to the originating clinical specimen, and the unsupervised gene expression array clustering analyses revealed an association between the xenograft and the originating specimen. Twenty four of the lines are adenocarcinoma and four exhibit a neuroendocrine phenotype. Characterization of the LuCaP PDX tumors includes expression arrays, RNASeq, exome sequencing, and IHC for multiple markers. Some of the models show Rb deletion, TMPRSS2/ERG translocation, PTEN deletion, PI3K activation and other critical characteristics detected in clinical specimens and associated with PCa progression. In vivo characterizations show responses to androgen suppression spanning the range of responses to this therapy seen in patients; differential levels of serum PSA, tumor-doubling time, and responses to docetaxel. Furthermore, seven of our models elicit an osteoblastic reaction when implanted in the bone.

In summary the diversity of phenotypes and responses of the LuCaP PDXs to therapy are representative of responses seen in the clinical setting. Therefore, the LuCaP PCa PDXs are highly clinically relevant models to study PCa biology and evaluate new treatment modalities. These models are available to researchers worldwide for studies aiming to improve survival of PCa patients and quality of life of men suffering from this disease.

Citation Format: Holly M. Nguyen, Colm Morrissey, Peter S. Nelson, Xiaotun Zhang, Paul H. Lange, Robert L. Vessella, Eva Corey. Preclinical models of prostate cancer: New patient-derived xenografts for preclinical studies and evaluation of prostate cancer biology. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1214. doi:10.1158/1538-7445.AM2014-1214

Abstract 737: Assessment of cabozantinib activity in diverse prostate cancer xenograft models

Cabozantinib (cabo), an inhibitor of tyrosine kinases including MET, VEGFR2, RET, KIT, and AXL, is undergoing clinical investigation in patients with castration-resistant prostate cancer (CRPC). A phase II randomized discontinuation trial of cabo showed clinical activity in CRPC patients. However, not all patients responded to cabo, and most of the responding patients eventually experienced disease progression. The objective of our study was to evaluate the efficacy of cabo in a preclinical setting using xenograft models of CRPC with differential phenotypes to obtain insight into which tumor types might be sensitive to cabo, and to investigate mechanisms of action of this agent.

We used LuCaP 35CR, a PTEN- ERG+ Rb+ CRPC patient-derived xenograft (PDX) that exhibits amplification of the androgen receptor (AR); LuCaP 96CR, a PTEN+ ERG- Rb+ CRPC PDX with high levels of intra-tumoral androgens; LuCaP 86.2, a PTEN- ERG+ Rb- CRPC PDX that expresses the AR v5-7 variant and is not responsive to endocrine therapy; and LuCaP 93, a PTEN- ERG- Rb- neuroendocrine CRPC PDX. Expression of cabo targets in these models was determined by qPCR. Animals were treated with 30 mg/kg cabo p.o. for six weeks (5d on/2d off), and tumor volume (TV), serum PSA and body weights were monitored. IHC and expression arrays were used to analyze effects of cabo. Cabo was effective in halting tumor growth in all four PDXs. Significant inhibition of TV was evident after one week of cabo treatment compared to control groups. PSA values were also significantly lower after one week of the treatment in all three adenocarcinomas. Furthermore, cabo treatment resulted in significant survival benefits in LuCaP 35CR, LuCaP 96CR and LuCaP 93 without significant decreases in body weight. IHC analysis showed decreased microvessel density in all cabo-treated groups vs control groups, suggesting effects on tumor environment. qPCR analysis showed that all models expressed some cabo targets though at different levels, but we did not observe any associations between magnitude of cabo effects and levels of the its targets in the tumors; inhibition of LuCaP 93, which expresses the highest levels of cabo targets, was similar to that of LuCaP 96CR, which expresses low levels of cabo targets. Our analyses of expression profiles of tumors following cabo treatment showed very little overlap between the models. However, E2F1 signaling, was inhibited by cabo in Rb- PDXs LuCaP 93 and LuCaP 86.2, but not in the Rb+ PDXs LuCaP 35CR and LuCaP 96CR. Also, expression of genes regulated by androgen was increased in the Rb- tumors and decreased (LuCaP 35CR) or was not altered (LuCaP 96CR) in the Rb+ tumors, and the levels of nuclear AR showed a similar pattern. Further investigations are ongoing to obtain more detailed insight into mechanisms of cabo effects.

Citation Format: Lisha G. Brown, Holly M. Nguyen, Ilsa M. Coleman, Peter S. Nelson, Robert L. Vessella, Dana T. Aftab, Eva Corey. Assessment of cabozantinib activity in diverse prostate cancer xenograft models. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 737. doi:10.1158/1538-7445.AM2014-737

Abstract 4011: Single cell transcriptomic analysis identified a potential dormant signature in prostate cancer disseminated tumor cells

Prostate cancer (PCa) disseminates before radical prostatectomy and can remain in the bone marrow for a prolonged period of time (&gt;10 years) until lethal metastasis develops. These cells are referred to as disseminated tumor cells (DTC). Dormant DTC are resistant to current chemotherapy targeting cell division, therefore understanding the nature of DTC will allow the development of novel drug target to prevent overt cancer metastases.

DTC were isolated from the bone marrow aspirates of PCa patients with no evidence of disease (NED, undetectable PSA level after 7-18 years after radical prostatectomy) or advanced diseases (ADV, disease progression after treatment or existing distant metastases). Eighty-five EpCAM+/CD45- individual cells were subjected to microarray gene expression analyses and two populations of cells were identified: erythroid progenitor-like and prostate epithelial cells. We utilized a dual signature method to identify EpCAM+/CD45- cells that are of prostatic origin. Comparison among prostate DTC showed that the DTC population within each patient was heterogeneous. Importantly, comparison between DTC from NED and ADV patients revealed that DTC from NED patients were enriched in a dormancy-associated signature identified in the head and neck squamous cell carcinoma, supporting the dormant nature of DTC from NED patients. Global clustering analysis and Ingenuity Pathway Analysis further identified a potential PCa dormancy signature, and this signature is significantly suppressed in a subpopulation of DTC isolated from ADV patients.

We reported a single cell transcriptomic analysis to reveal for the first time clinically heterogeneous DTC population in PCa patients and a dual signature method to identify cells of prostatic origin from erythroid-progenitor cells that harbored the same epithelial (EpCAM) surface marker in the bone marrow. The proposed gene signature associated with PCa dormancy may allow development of possible biomarkers to predict prognosis and therapeutic targets to promote PCa dormancy or prevent dormancy escape.

Citation Format: Hung-Ming Lam, Lisly Chéry, Ilsa Coleman, Bryce Lakely, Sandy Larson, Roger Coleman, Julio Aguirre-Ghiso, Jing Xia, Roman Gulati, Peter S. Nelson, Bruce Montgomery, Paul H. Lange, Linda A. Snyder, Robert L. Vessella, Colm Morrissey. Single cell transcriptomic analysis identified a potential dormant signature in prostate cancer disseminated tumor cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4011. doi:10.1158/1538-7445.AM2014-4011

Spheroid culture of LuCaP 147 as an authentic preclinical model of prostate cancer subtype with SPOP mutation and hypermutator phenotype

LuCaP serially transplantable xenografts are valuable preclinical models of locally advanced or metastatic prostate cancer. For the first time, we recently succeeded in establishing and serially passaging spheroid cultures of several LuCaP xenografts. Here, we characterized in depth the molecular and cellular phenotype of LuCaP 147 cultures and found faithful retention of the characteristics of the original xenograft, including immunophenotype, genetic fidelity, gene expression profile and responsiveness to androgen. Furthermore, we demonstrated capabilities for high-throughput drug screening and that anti-cancer agents induced cell cycle arrest and apoptosis in spheroid cultures. Finally, we showed that cells formed tumors when re-introduced into mice, providing an authentic in vitro-in vivo preclinical model of a subtype of prostate cancer with a hypermutator phenotype and an SPOP mutation.

Androgen receptor splice variants determine taxane sensitivity in prostate cancer

Prostate cancer growth depends on androgen receptor signaling. Androgen ablation therapy induces expression of constitutively active androgen receptor splice variants that drive disease progression. Taxanes are a standard of care therapy in castration-resistant prostate cancer (CRPC); however, mechanisms underlying the clinical activity of taxanes are poorly understood. Recent work suggests that the microtubule network of prostate cells is critical for androgen receptor nuclear translocation and activity. In this study, we used a set of androgen receptor deletion mutants to identify the microtubule-binding domain of the androgen receptor, which encompasses the DNA binding domain plus hinge region. We report that two clinically relevant androgen receptor splice variants, ARv567 and ARv7, differentially associate with microtubules and dynein motor protein, thereby resulting in differential taxane sensitivity in vitro and in vivo. ARv7, which lacks the hinge region, did not co-sediment with microtubules or coprecipitate with dynein motor protein, unlike ARv567. Mechanistic investigations revealed that the nuclear accumulation and transcriptional activity of ARv7 was unaffected by taxane treatment. In contrast, the microtubule-interacting splice variant ARv567 was sensitive to taxane-induced microtubule stabilization. In ARv567-expressing LuCap86.2 tumor xenografts, docetaxel treatment was highly efficacious, whereas ARv7-expressing LuCap23.1 tumor xenografts displayed docetaxel resistance. Our results suggest that androgen receptor variants that accumulate in CRPC cells utilize distinct pathways of nuclear import that affect the antitumor efficacy of taxanes, suggesting a mechanistic rationale to customize treatments for patients with CRPC, which might improve outcomes.

Targeting GPR30 with G-1: a new therapeutic target for castration-resistant prostate cancer

Castration-resistant prostate cancer (CRPC) is an advanced-stage prostate cancer (PC) associated with high mortality. We reported that G-1, a selective agonist of G protein-coupled receptor 30 (GPR30), inhibited PC cell growth by inducing G2 cell cycle arrest and arrested PC-3 xenograft growth. However, the therapeutic actions of G-1 and their relationships with androgen in vivo are unclear. Using the LNCaP xenograft to model PC growth during the androgen-sensitive (AS) versus the castration-resistant (CR) phase, we found that G-1 inhibited growth of CR but not AS tumors with no observable toxicity to the host. Substantial necrosis (approximately 65%) accompanied by marked intratumoral infiltration of neutrophils was observed only in CR tumors. Global transcriptome profiling of human genes identified 99 differentially expressed genes with 'interplay between innate and adaptive immune responses' as the top pathway. Quantitative PCR confirmed upregulation of neutrophil-related chemokines and inflammation-mediated cytokines only in the G-1-treated CR tumors. Expression of murine neutrophil-related cytokines also was elevated in these tumors. GPR30 (GPER1) expression was significantly higher in CR tumors than in AS tumors. In cell-based experiments, androgen repressed GPR30 expression, a response reversible by anti-androgen or siRNA-induced androgen receptor silencing. Finally, in clinical specimens, 80% of CRPC metastases (n=123) expressed a high level of GPR30, whereas only 54% of the primary PCs (n=232) showed high GPR30 expression. Together, these results provide the first evidence, to our knowledge, that GPR30 is an androgen-repressed target and G-1 mediates the anti-tumor effect via neutrophil-infiltration-associated necrosis in CRPC. Additional studies are warranted to firmly establish GPR30 as a therapeutic target in CRPC.

Prostate cancer derived prostatic acid phosphatase promotes an osteoblastic response in the bone microenvironment

Approximately 90 % of patients who die of prostate cancer (PCa) have bone metastases, often promoting osteoblastic lesions. We observed that 88 % of castration-resistant PCa (CRPC) bone metastases express prostatic acid phosphatase (PAP), a soluble secreted protein expressed by prostate epithelial cells in predominately osteoblastic (n = 18) or osteolytic (n = 15) lesions. Additionally, conditioned media (CM) of an osteoblastic PCa xenograft LuCaP 23.1 contained significant levels of PAP and promoted mineralization in mouse and human calvaria-derived cells (MC3T3-E1 and HCO). To demonstrate that PAP promotes mineralization, we stimulated MC3T3-E1 cells with PAP and observed increased mineralization, which could be blocked with the specific PAP inhibitor, phosphonic acid. Furthermore, the mineralization promoted by LuCaP 23.1 CM was also blocked by phosphonic acid, suggesting PAP is responsible for the mineralization promoting activity of LuCaP 23.1. In addition, gene expression arrays comparing osteoblastic to osteolytic CRPC (n = 14) identified betacellulin (BTC) as a gene upregulated during the osteoblastic response in osteoblasts during new bone formation. Moreover, BTC levels were increased in bone marrow stromal cells in response to LuCaP 23.1 CM in vitro. Because new bone formation does occur in osteoblastic and can occur in osteolytic CRPC bone metastases, we confirmed by immunohistochemistry (n = 36) that BTC was highly expressed in osteoblasts involved in new bone formation occurring in both osteoblastic and osteolytic sites. These studies suggest a role for PAP in promoting the osteoblastic reaction in CRPC bone metastases and identify BTC as a novel downstream protein expressed in osteoblasts during new bone formation.

Tumor necrosis factor receptor associated factor-4: an adapter protein overexpressed in metastatic prostate cancer is regulated by microRNA-29a

The tumor necrosis factor receptor (TNFR)-associated factor 4 (TRAF4) is a member of TRAF family proteins that act as major signal transducers of the TNF receptor and the interleukin-1 receptor/Toll-like receptor (IL-1R/TLR) superfamily. TRAF4 has been reported to be overexpressed in various human cancers. However, the exact mechanisms that regulate the expression of TRAF4 still remain elusive. The objective of the present study was to investigate the regulatory mechanism of TRAF4 expression in prostate cancer. We initially identified microRNA-29a (miR‑29a) as a possible candidate to bind TRAF4 3' untranslated region (3'UTR) by the algorithm, TargetScan. The expression of TRAF4 mRNA and protein was inversely associated with miR-29a expression in prostate cancer cell lines (LNCaP, DU145 and PC3). TRAF4 expression was reduced by the introduction of mimic miR-29a in LNCaP cells. Luciferase activity from the construct harboring wild-type TRAF4 3'UTR was reduced by the mimic miR-29a and this reduction was diminished by introducing mutations at the predicted miR-29a binding site. On the other hand, TRAF4 was upregulated when transfected with the inhibitor of miR-29a in DU145 and PC3 cells. TRAF4 was significantly upregulated in patients with metastatic prostate cancer compared to those with localized prostate cancer. Furthermore, there was a significant inverse correlation between TRAF4 and miR-29a expression in tumor tissues from radical prostatectomy. Considered together, our results suggest that the tumor suppressor microRNA, miR-29a, is one of the regulators of TRAF4 expression in metastatic prostate cancer.

Establishment and serial passage of cell cultures derived from LuCaP xenografts

BACKGROUND

LuCaP serially transplantable xenografts derived from primary and metastatic human prostate cancer encompass the molecular and cellular heterogeneity of the disease and are an invaluable resource for in vivo preclinical studies. A limitation of this model, however, has been the inability to establish and passage cell cultures derived from the xenografts. Here, we describe a novel spheroid culture system that supports long-term growth of LuCaP cells in vitro.

METHODS

Xenografts were minced and digested with collagenase. Tissue dissociation was terminated while the majority of cells remained as clusters rather than single cells. The cell clusters were suspended in StemPro medium supplemented with R1881 and Y-27632, a Rho kinase inhibitor, and placed in ultralow attachment dishes for spheroid culture. Serial passage was achieved by partial digestion to small clusters with trypsin/EDTA in the presence of Y-27632. Cell viability, growth and phenotype were monitored with LIVE/DEAD®, MTS, qRT-PCR, and immunocytochemical assays.

RESULTS

Cells from six LuCaP xenografts formed proliferating spheroids that were serially passaged a minimum of three times and cryopreserved. Two of the cell lines, LuCaP 136 and LuCaP 147, were further passaged and characterized. Both expressed biomarkers characteristic of the xenografts of origin, were determined to be of independent origin by STR fingerprinting, and were free of mycoplasma. LuCaP 147 formed tumors similar to the original xenograft when injected into mice.

CONCLUSIONS

The ability to culture LuCaP cells affords new opportunities for fast, cheap, and efficient preclinical studies and extends the value of the LuCaP xenograft models.

Absolute quantification by droplet digital PCR versus analog real-time PCR

Nanoliter-sized droplet technology paired with digital PCR (ddPCR) holds promise for highly precise, absolute nucleic acid quantification. Our comparison of microRNA quantification by ddPCR and real-time PCR revealed greater precision (coefficients of variation decreased by 37–86%) and improved day-to-day reproducibility (by a factor of seven) of ddPCR but with comparable sensitivity. When we applied ddPCR to serum microRNA biomarker analysis, this translated to superior diagnostic performance for identifying individuals with cancer.

Tumour cell survival mechanisms in lethal metastatic prostate cancer differ between bone and soft tissue metastases

The complexity of survival mechanisms in cancer cells from patients remains poorly understood. To obtain a comprehensive picture of tumour cell survival in lethal prostate cancer metastases, we examined five survival proteins that operate within three survival pathways in a cohort of 185 lethal metastatic prostate metastases obtained from 44 patients. The expression levels of BCL-2, BCL-XL, MCL-1, cytoplasmic survivin, nuclear survivin, and stathmin were measured by immunohistochemistry in a tissue microarray. Simultaneous expression of three or more proteins occurred in 81% of lethal prostate cancer metastases and BCL-2, cytoplasmic survivin and MCL-1 were co-expressed in 71% of metastatic sites. An unsupervised cluster analysis separated bone and soft tissue metastases according to patterns of survival protein expression. BCL-2, cytoplasmic survivin and MCL-1 had significantly higher expression in bone metastases (p < 10(-5)), while nuclear survivin was significantly higher in soft tissue metastases (p = 3 × 10(-14)). BCL-XL overexpression in soft tissue metastases almost reached significance (p = 0.09), while stathmin expression did not (p = 0.28). In addition, the expression of MCL-1 was significantly higher in AR-positive tumours. Neuroendocrine differentiation was not associated with specific survival pathways. These studies show that bone and soft tissue metastases from the same patient differ significantly in expression of a panel of survival proteins and that with regard to survival protein expression, expression is associated with the metastatic site and not the patient. Altogether, this suggests that optimal therapeutic inhibition may require combinations of drugs that target both bone and soft tissue-specific survival pathways.

5α-reductase inhibition suppresses testosterone-induced initial regrowth of regressed xenograft prostate tumors in animal models

Androgen deprivation therapy (ADT) is the standard treatment for patients with prostate-specific antigen progression after treatment for localized prostate cancer. An alternative to continuous ADT is intermittent ADT (IADT), which allows recovery of testosterone during off-cycles to stimulate regrowth and differentiation of the regressed prostate tumor. IADT offers patients a reduction in side effects associated with ADT, improved quality of life, and reduced cost with no difference in overall survival. Our previous studies showed that IADT coupled with 5α-reductase inhibitor (5ARI), which blocks testosterone conversion to DHT could prolong survival of animals bearing androgen-sensitive prostate tumors when off-cycle duration was fixed. To further investigate this clinically relevant observation, we measured the time course of testosterone-induced regrowth of regressed LuCaP35 and LNCaP xenograft tumors in the presence or absence of a 5ARI. 5α-Reductase inhibitors suppressed the initial regrowth of regressed prostate tumors. However, tumors resumed growth and were no longer responsive to 5α-reductase inhibition several days after testosterone replacement. This finding was substantiated by bromodeoxyuridine and Ki67 staining of LuCaP35 tumors, which showed inhibition of prostate tumor cell proliferation by 5ARI on day 2, but not day 14, after testosterone replacement. 5α-Reductase inhibitors also suppressed testosterone-stimulated proliferation of LNCaP cells precultured in androgen-free media, suggesting that blocking testosterone conversion to DHT can inhibit prostate tumor cell proliferation via an intracrine mechanism. These results suggest that short off-cycle coupled with 5α-reductase inhibition could maximize suppression of prostate tumor growth and, thus, improve potential survival benefit achieved in combination with IADT.

Characterization of osteoblastic and osteolytic proteins in prostate cancer bone metastases

BACKGROUND

Approximately 90% of patients who die of Prostate Cancer (PCa) have bone metastases, which promote a spectrum of osteoblastic, osteolytic or mixed bone responses. Numerous secreted proteins have been reported to promote osteoblastic or osteolytic bone responses. We determined whether previously identified and/or novel proteins were associated with the osteoblastic or osteolytic response in clinical specimens of PCa bone metastases.

METHODS

Gene expression was analyzed on 14 PCa metastases from 11 patients by microarray profiling and qRT-PCR, and protein expression was analyzed on 33 PCa metastases from 30 patients by immunohistochemistry on highly osteoblastic and highly osteolytic bone specimens.

RESULTS

Transcript and protein levels of BMP-2, BMP-7, DKK-1, ET-1, and Sclerostin were not significantly different between osteoblastic and osteolytic metastases. However, levels of OPG, PGK1, and Substance P proteins were increased in osteoblastic samples. In addition, Emu1, MMP-12, and sFRP-1 were proteins identified with a novel role of being associated with either the osteoblastic or osteolytic bone response.

CONCLUSIONS

This is the first detailed analysis of bone remodeling proteins in human specimens of PCa bone metastases. Three proteins not previously shown to be involved may have a role in the PCa bone response. Furthermore, our data suggests that the relative expression of numerous, rather than a single, bone remodeling proteins determine the bone response in PCa bone metastases.

Abstract 406: Characterizing the molecular features of the neuroendocrine phenotype in castration resistant prostate cancer

Metastatic castration-resistant prostate cancer (CRPC) has a poor prognosis and remains a significant therapeutic challenge. Understanding the conversion from hormone sensitive to castration resistance may promote the development of more effective therapies. Recent findings suggest that neuroendocrine (NE) differentiation may be associated with the development of CRPC. Our objective was to characterize the NE phenotype in CRPC.

Using specimens obtained at radical prostatectomy and rapid autopsy at the University of Washington, 2 sets of tissue microarrays were made from 50 radical prostatectomies and 155 metastatic sites from 50 autopsy patients who died from CRPC (with up to 4 metastatic sites from each patient). NE markers, including Chromogranin A (CHGA), Neuron specific enolase (NSE) and Synaptophysin (SYN), as well as androgen receptor (AR) and prostate specific antigen (PSA) were analyzed by immunohistochemistry (IHC). To characterize the molecular features of the NE phenotype in CRPC, 78 corresponding metastatic sites were also assessed by Agilent gene expression analysis.

IHC revealed that only 2 of 50 primary prostate cancers had &gt;10% CHGA positive cells whereas 7 of 50 primary prostate cancers 1-10% of cells expressed CHGA and all 50 were AR positive. By contrast, 29 of 50 CRPC autopsy patients had at least 1 CHGA+ metastasis; 53 of 155 metastatic sites had &gt;10% CHGA positive cells (11 sites were AR negative), and 7 had 1-10% CHGA positive cells. Compared to primary prostate carcinomas, CRPC metastases had an increase in the frequency of CHGA+ expression (4% vs. 58%, p&lt;0.001). Two other NE markers were also highly expressed by &gt;10% of cells in each of the CRPC metastases. Of 155 CRPC metastases: 28 were positive for SYN and 47 were positive for NSE. Co-expression of CHGA and SYN was observed in 22 sites from 10 patients (10 sites did not express AR) and co-expression of CHGA, SYN and NSE was observed in 12 sites from 6 patients (6 sites did not express AR). PSA, a surrogate of AR activity, was absent in all NE CRPC tumors that did not express AR. All AR negative sites (12/155) expressed at least one NE marker. Gene expression data were generated from 78 laser captured metastases, which were grouped into 4 categories: 21 CHGA+ sites, 6 CHGA+, SYN+ and AR- sites, 5 CHGA+, SYN+ and AR+ sites, and 40 CHGA-, SYN-, NSE- and AR+ sites.

This study is the first extensive analysis of the NE features of CRPC. Our data suggest that a) the NE phenotype (as defined by CHGA expression) is significantly more common in CRPC than in hormone sensitive primary disease, b) NE status from different sites in the same patient can be heterogeneous, and c) the NE phenotype is not necessarily associated with the loss of AR. These molecular studies suggest that evolution from hormone sensitive to castration resistant disease involves emergence of NE characteristics over time that may explain the behavior of true “androgen independent” disease.

Citation Format: Xiaotun Zhang, Ilsa Coleman, Roger Coleman, Khanhthy Doan, Martine Roudier, Lisly Chéry, Jennifer Noteboom, Celestia Higano, Lawrence D. True, Paul H. Lange, Peter S. Nelson, Robert L. Vessella, Colm Morrissey. Characterizing the molecular features of the neuroendocrine phenotype in 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 406. doi:10.1158/1538-7445.AM2013-406