Abstract 2802: Establishing and optimizing treatment-naïve prostate cancer patient-derived organoids culture: Implications for personalized medicine

Background: Prostate Cancer (PCa) is a heterogeneous disease. Currently available in vitro and in vivo cancer models fail to recapitulate the spectrum of clinical and biological challenges; accurate models for translational research remain a significant unmet need. Objective: The aim of this work is to employ fresh tissue specimens from a treatment-naïve cohort of patients with prostate cancer to optimize and establish 3D patient-derived organoids as an in vitro disease model for PCa progression and drug response. In addition, acknowledging the difficulty in establishing primary PCa cell lines, our aim was to generate novel PCa patient-derived cell lines.

Methods: Fresh specimens were collected from treatment-naïve patients with prostate cancer during radical prostatectomy (one unaffected and one tumor). Briefly, fresh tissue samples were digested enzymatically, and the resulting cell suspensions were plated in a 3D environment that employs Matrigel as an extracellular matrix. At first, a cocktail of 12 factors, previously recognized, was used to establish organoids. Subsequently, we have optimized the recipe to a minimal 5-factors media for both organoids and cells. Organoids and the corresponding tissue specimens were characterized using immunofluorescent analysis and immunohistochemistry. Furthermore, patient-derived organoids were employed for the assessment of drug response. In addition, PCa patient-derived cell lines were generated and their culture conditions were optimized. These cells were further characterized using immunofluorescent analysis.

Results: Fresh tissues were successfully established as organoids and as 2D cells using the same culture media that contains 12 original factors. The presence of prostate luminal (Cytokeratin 8, Androgen Receptor, and Prostate Specific Antigen) and basal (Cytokeratin 5 and P63) epithelial lineages was confirmed by immunohistochemical and immunofluorescent analyses. Notably, we have identified five essential components (NAC, NOG, A83, B27, and Nicotinamide) that support the establishment of organoids culture in a less expensive, more efficient manner. Moreover, we optimized the culture and maintenance of patient-derived 2D cells by plating on collagen type I and we have reduced the medium requirement to include EGF only as an essential component. Importantly, the results showed differential drug and radiation response between patient samples.

Conclusion: This study provides a repertoire of novel patient-derived organoids and cells from a unique cohort of treatment-naïve patients, as our results demonstrate that we succeeded in delineating the essential components needed to grow prostate organoids and primary cells with a high success rate and long-term maintenance in culture. We hope that we can use this platform in the future to predict treatment response in a personalized fashion leading to better management of the disease.

Citation Format: Katia Cheaito, Hisham Bahmad, Alissar Monzer, Farah Ballout, HIba Msheik, Ola Hadadeh, Christelle Dagher, Nour Saheb, Ayman Tawil, Marwan El-Sabban, Albert El-Hajj, Deborah Mukherji, Wassim G. Abou-Kheir. Establishing and optimizing treatment-naïve prostate cancer patient-derived organoids culture: Implications for personalized medicine [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2802.

Identification of Different Classes of Luminal Progenitor Cells within Prostate Tumors

Primary prostate cancer almost always has a luminal phenotype. However, little is known about the stem/progenitor properties of transformed cells within tumors. Using the aggressive Pten/Tp53-null mouse model of prostate cancer, we show that two classes of luminal progenitors exist within a tumor. Not only did tumors contain previously described multipotent progenitors, but also a major population of committed luminal progenitors. Luminal cells, sorted directly from tumors or grown as organoids, initiated tumors of adenocarcinoma or multilineage histological phenotypes, which is consistent with luminal and multipotent differentiation potentials, respectively. Moreover, using organoids we show that the ability of luminal-committed progenitors to self-renew is a tumor-specific property, absent in benign luminal cells. Finally, a significant fraction of luminal progenitors survived in vivo castration. In all, these data reveal two luminal tumor populations with different stem/progenitor cell capacities, providing insight into prostate cancer cells that initiate tumors and can influence treatment response.

TMPRSS2- driven ERG expression in vivo increases self-renewal and maintains expression in a castration resistant subpopulation

Genomic rearrangements commonly occur in many types of cancers and often initiate or alter the progression of disease. Here we describe an in vivo mouse model that recapitulates the most frequent rearrangement in prostate cancer, the fusion of the promoter region of TMPRSS2 with the coding region of the transcription factor, ERG. A recombinant bacterial artificial chromosome including an extended TMPRSS2 promoter driving genomic ERG was constructed and used for transgenesis in mice. TMPRSS2-ERG expression was evaluated in tissue sections and FACS-fractionated prostate cell populations. In addition to the anticipated expression in luminal cells, TMPRSS2-ERG was similarly expressed in the Sca-1^hi/EpCAM⁺ basal/progenitor fraction, where expanded numbers of clonogenic self-renewing progenitors were found, as assayed by in vitro sphere formation. These clonogenic cells increased intrinsic self renewal in subsequent generations. In addition, ERG dependent self-renewal and invasion in vitro was demonstrated in prostate cell lines derived from the model. Clinical studies have suggested that the TMPRSS2-ERG translocation occurs early in prostate cancer development. In the model described here, the presence of the TMPRSS2-ERG fusion alone was not transforming but synergized with heterozygous Pten deletion to promote PIN. Taken together, these data suggest that one function of TMPRSS2-ERG is the expansion of self-renewing cells, which may serve as targets for subsequent mutations. Primary prostate epithelial cells demonstrated increased post transcriptional turnover of ERG compared to the TMPRSS2-ERG positive VCaP cell line, originally isolated from a prostate cancer metastasis. Finally, we determined that TMPRSS2-ERG expression occurred in both castration-sensitive and resistant prostate epithelial subpopulations, suggesting the existence of androgen-independent mechanisms of TMPRSS2 expression in prostate epithelium.

Abstract B28: TMPRSS2- driven ERG in primary prostate epithelium demonstrates castration-resistant expression and expands a unique population of progenitor cells

It has become increasingly appreciated that recurrent genomic rearrangements contribute to the genesis of solid tumors. The genomic rearrangement of the Ets transcription factor, Ets related gene (ERG), with the promoter of the highly expressed Transmembrane protease serine 2 (TMPRSS2) gene, has been demonstrated in 20-65% of prostate adenocarcinoma precursor lesions, implying that ERG may contribute a function selected early in cancer formation. However, the functional role of ERG in developing prostate cancer is unclear. This study utilized bacterial artificial chromosome transgenesis, to produce a mouse model that recapitulates the genetic regulatory features of the genomic TMPRSS2-ERG translocation, where exon 1 and 2 of TMPRSS2 is fused to the region downstream of ERG exon 8. This model allows mechanistic investigations into the function and regulation of expression for TMPRSS2 promoter-driven ERG in the earliest initiating phase of tumorigenesis.

Using QRT-PCR, TMPRSS2-ERG was expressed in the progenitor containing, Sca-1hi fraction of FACS-separated primary prostate cells. In addition, the fusion gene functioned to expand a unique subpopulation of prostate epithelial progenitors when compared to wild type, as demonstrated by serially passaged in vitro sphere forming assays. Androgen regulation of TMPRSS2 has been shown in a limited number of androgen receptor positive luminal prostate cancer cell lines. In this study, TMPRSS2-ERG expression demonstrated a significant castration-resistant component, suggesting mechanisms of AR-independent transcriptional regulation for the TMPRSS2 promoter in the setting of primary prostate epithelial cells. Introduction of the TMPRSS2-ERG fusion alone did not result in histological change, where prostate sections from mice up to 15 months of age were examined. However, the functionality of the model was shown as TMPRSS2-ERG synergized with heterozygous Pten loss to promote PIN. No apparent genetic interaction was observed between TMPRSS2-ERG and Nkx3.1 loss.

These studies demonstrate the potential for androgen independent TMPRSS2-ERG expression in primary prostate epithelium and show that TMPRSS2-ERG expression promotes increased self-renewal of prostate progenitors. These data support a model whereby TMPRSS2-ERG regulates progenitor cell de-differentiation or survival, including within a population of castration-resistant progenitors.

Citation Format: Orla M. Casey, Paul G. Hynes, Lei Fang, Wassim G. Abou-Kheir, Philip L. Martin, Heather S. Tillman, Hibah O. Awwad, Luhua Zhang, Kathleen Kelly. TMPRSS2- driven ERG in primary prostate epithelium demonstrates castration-resistant expression and expands a unique population of progenitor cells [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr B28.

Characterizing the contribution of stem/progenitor cells to tumorigenesis in the Pten-/-TP53-/- prostate cancer model

Loss of PTEN is one of the most common mutations in prostate cancer, and loss of wild-type TP53 is associated with prostate cancer progression and castrate resistance. Modeling prostate cancer in the mouse has shown that while Pten deletion in prostate epithelial cells leads to adenocarcinoma, combined loss of Pten and TP53 results in rapidly developing disease with greater tumor burden and early death. TP53 contributes significantly to the regulation of stem cell self-renewal, and we hypothesized that loss of Pten/TP53 would result in measurable changes in prostate cancer stem/progenitor cell properties. Clonogenic assays that isolate progenitor function in primary prostate epithelial cells were used to measure self-renewal, differentiation, and tumorigenic potential. Pten/TP53 null as compared with wild-type protospheres showed increased self-renewal activity and modified lineage commitment. Orthotopic transplantation of Pten/TP53 null cells derived from protospheres produced invasive Prostatic Intraepithelial Neoplasia (PIN)/adenocarcinoma, recapitulating the pathology seen in primary tumors. Pten/TP53 null progenitors relative to wild type also demonstrated increased dependence on the AKT/mammalian target of rapamycin complex 1 (mTORC1) and androgen receptor (AR) pathways for clonogenic and tumorigenic growth. These data demonstrate roles for Pten/TP53 in prostate epithelial stem/progenitor cell function, and moreover, as seen in patients with castrate-resistant prostate cancer, suggest for the involvement of an AR-dependent axis in the clonogenic expansion of prostate cancer stem cells.

Abstract 4227: Pten and P53 control self-renewal ability and differentiation potential of prostate epithelial stem/progenitor cells

Pten and P53 tumor suppressors are among the most commonly inactivated genes in prostate cancer. Pten deletion in the mouse prostate epithelium results in the development of carcinoma in situ which eventually progresses to adenocarcinoma, while loss of P53 alone does not result in an obvious phenotype. The combination of PTEN and P53 loss leads to significantly more rapid and extensive development of prostate tumors and death due to urinary outflow obstruction. Pten and P53 together have been implicated as co-regulators of neural and glioma stem/progenitor cell renewal and differentiation. We hypothesize that Pten and P53 play a crucial role in regulating self-renewal and differentiation ability, two defining hallmarks of stem/progenitor cells. In order to test our hypothesis, cells were isolated from Pten−/−P53−/− adenocarcinomas and employed in a variety of assays. Clonogenic 2D colony and 3D sphere formation in minimal media measure progenitor activity. Colony and sphere formation activity was monitored over at least 4 generations of serial propagation in vitro. Protospheres generated from Pten−/−P53−/− single cell suspensions were approximately 3 times larger than wild type (wt) spheres and demonstrated significant heterogeneity in morphology, displaying less uniform cell shapes. Sphere forming units (SFU) in single cell suspensions from Pten−/−P53−/− prostates showed a 50%-80% increase when compared to wt. Pten−/−P53−/− SFU activity was maintained upon serial passage of single cell suspensions for 4 generations, while a reduction in SFU activity was observed over the same 4 generations in wt. Similar findings were obtained from analyzing the colony forming ability of cells taken from wt and Pten−/−P53−/− spheres. Pten and P53 deletion significantly affects the differentiation profile of colonies and spheres generated from knockout as compared to wt cells. Pten−/−P53−/− and wt protospheres (3D) and colonies (2D) were stained for markers of all prostate epithelial cell lineages using CK5, CK8, p63 and neuroendocrine markers. Interestingly, an increased number of luminal, transit-amplifying and neuroendocrine cells with a relative reduction in the number of basal cells were observed in the Pten−/−P53−/− spheres and colonies compared to wt. In addition to increased progenitor cell numbers and alterations in differentiation potential, Pten−/−P53−/− progenitor cells demonstrated dependence upon distinct signal transduction pathways for survival as revealed by their sensitivity to drugs against mTOR (Rapamycin), AKT (Triciribine) and androgen receptor (Nilutamide and Bicalutamide). In conclusion, our findings to date confirm the presence of an amplified stem/progenitor cell population in Pten−/−P53−/− prostates that generates morphologically abnormal protospheres displaying changes in the relative production of differentiated progeny.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4227.

Abstract 3240: A transgenic mouse model of a common genetic aberration in prostate cancer: Chromosomal rearrangement of TMPRSS2:ERG

The most prevalent gene fusion identified in prostate cancer (PC) to date is the recurrent fusion of the 5’ region of Transmembrane Serine Protease 2 (TMPRSS2) to the transcription factor Ets related gene (ERG). The fusion occurs in ∼50% of PC and has been identified in malignant cells preceding the development of prostate adenocarcinoma. This has led to the hypothesis that the rearrangement is an early and critical event in PC. The purpose of this study is to generate a novel mouse model to investigate the role of the transgene in development of PC, and to examine the biological and molecular properties of prostate epithelial cells carrying a translocation of the ERG oncogene.

The fusion is a result of deletion in the genomic region between TMPRSS2 and ERG, which are both located on chromosome 21. Several fusion variants have been described and the focus of this study is the TMPRSS2 exon 2 and ERG exon 4 variant which has been associated with aggressive disease. Importantly, expression of the fusion gene initiates from the TMPRSS2 promoter which is primarily expressed in the prostate and regulated by androgen receptor (AR), which is central to PC development. The objectives of this study included the generation of a novel model that maintains regulation and processing of the translocation. This was achieved by using the complete promoter region, including androgen regulatory regions, and the human genomic sequence thus maintaining the intron/exon arrangement and facilitating alternative splicing. Transgenic mice in the FVB and C57/BL6 background were produced using a 230 Kb construct generated by recombineering technology, where ∼25Kb of the TMPRSS2 promoter region and its first two exons were fused to the entire genomic ERG locus following exon 4.

Two splice variants of the transgene have been identified in mouse prostates corresponding to the presence and absence of a 72bp exon, replicating the pattern in human PC, where this has been associated with aggressive disease. No distinct histological phenotypic change has been observed in the murine prostate of transgenic animals at six to twelve months. Towards the aim of determining the role of this fusion in PC - further in vitro and in vivo assays are currently in progress with the objectives of 1) determining the role of AR in regulation of the promoter and 2) investigating alterations in gene expression profiles in distinct cell populations of the prostate harboring the transgene. Additional crosses with other mice carrying mutations significant to prostate cancer, e.g. Nkx 3.1 and PTEN mice are being performed thus allowing the investigation of the phenotypic effect of this fusion when combined with other common genetic events.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3240.

Abstract 4226: A luminal epithelial cell line isolated from PTEN−/−;P53−/− mouse protospheres forms adenocarcinoma in vivo

Pten deletion in the mouse prostate epithelium results in the expansion of a prostatic stem/progenitor cell subpopulation, which co-fractionates with basal epithelial cells. Progenitor cells in the luminal layer of Pten null prostates also have been suggested as tumor initiating cells. Here we describe the isolation of a protosphere-derived, androgen independent cell line with a luminal epithelial phenotype that displays properties of prostate progenitor cells and forms adenocarcinoma in-vivo. The cell line was generated from Rosa26-CreERPtenfl/flP53fl/fl prostate cells. Cells were plated to form protospheres, which originate from stem/progenitor cells, and the deletion of Pten and p53 was induced by tamoxifen. After spheres were serially passaged for 3 generations, a monolayer cell line capable of growth in minimal serum-free media was established. A clonal line also was generated from the parental cell line. In order to determine the differentiated cell phenotype of the parental and the clonal cell lines, cells were stained over multiple generations for markers of epithelial (CK5, CK8, CK14) and neuroendocrine (beta 3 tubulin) cell lineages. The cell line is entirely CK8 positive with a minor component of CK8/CK14 double positive cells. Cells are capable of forming protospheres both in Matrigel and in suspension, a property of stem/progenitor cells. In addition, based on lentiviral reporter assays, a minor population of cells in the parental and the clonal cell line expressed Nanog, Oct4 and Notch dependent activity. Interestingly, Nanog and Oct4 positive cells showed higher sphere forming ability as compared to negative cells. In order to investigate their tumorigenic potential, the parental and the cloned lines were injected subcutaneously into athymic nude mice. Visible tumor formation was observed after 2 weeks, and histological analysis revealed adenocarcinoma and poorly differentiated carcinoma. In addition to CK8+ cells within the tumors, there were rare CK5+ and neuroendocrine cells, suggesting plasticity in the differentiation potential. In conclusion, we have isolated a prostate luminal epithelial cell line and derivative clones with a defined background (Pten and p53 null) that have stem-like and tumor initiating properties in vitro and in vivo. Future experiments are aimed at deciphering the molecular mechanisms regulating growth and differentiation downstream of Pten and p53 loss.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4226.