Renea A. Taylor

Estrogen receptor-beta activated apoptosis in benign hyperplasia and cancer of the prostate is androgen independent and TNFalpha mediated

Prostate cancer (PCa) and benign prostatic hyperplasia (BPH) are androgen-dependent diseases commonly treated by inhibiting androgen action. However, androgen ablation or castration fail to target androgen-independent cells implicated in disease etiology and recurrence. Mechanistically different to castration, this study shows beneficial proapoptotic actions of estrogen receptor–β (ERβ) in BPH and PCa. ERβ agonist induces apoptosis in prostatic stromal, luminal and castrate-resistant basal epithelial cells of estrogen-deficient aromatase knock-out mice. This occurs via extrinsic (caspase-8) pathways, without reducing serum hormones, and perturbs the regenerative capacity of the epithelium. TNFα knock-out mice fail to respond to ERβ agonist, demonstrating the requirement for TNFα signaling. In human tissues, ERβ agonist induces apoptosis in stroma and epithelium of xenografted BPH specimens, including in the CD133+ enriched putative stem/progenitor cells isolated from BPH-1 cells in vitro. In PCa, ERβ causes apoptosis in Gleason Grade 7 xenografted tissues and androgen-independent cells lines (PC3 and DU145) via caspase-8. These data provide evidence of the beneficial effects of ERβ agonist on epithelium and stroma of BPH, as well as androgen-independent tumor cells implicated in recurrent disease. Our data are indicative of the therapeutic potential of ERβ agonist for treatment of PCa and/or BPH with or without androgen withdrawal.

Formation of human prostate tissue from embryonic stem cells.

Rodent models and immortalized or genetically modified cell lines are frequently used—but have limited utility—for studying human prostate development and maturation. Using rodent mesenchyme to establish reciprocal mesenchymal-epithelial cell interactions with human embryonic stem cells (hESCs), we generated human prostate tissue expressing prostate-specific antigen (PSA) within 8–12 weeks. This human prostate model shows species-conserved signalling mechanisms that could extend to integumental, gastrointestinal and genital tissues.

Evidence for Efficacy of New Hsp90 Inhibitors Revealed by Ex Vivo Culture of Human Prostate Tumors

Purpose: Targeting Hsp90 has significant potential as a treatment for prostate cancer, but prototypical agents such as 17-allylamino-17 demethoxygeldanamycin (17-AAG) have been ineffective in clinical trials. Recently, a phase I study aimed at defining a biologically active dose reported the first response to an Hsp90 inhibitor in a patient with prostate cancer, which supports the development of new generation compounds for this disease. Experimental Design: The biological actions of two new synthetic Hsp90 inhibitors, NVP-AUY922 and NVP-HSP990, were evaluated in the prostate cancer cell lines PC-3, LNCaP, and VCaP and in an ex vivo culture model of human prostate cancer. Results: In cell lines, both NVP-AUY922 and NVP-HSP990 showed greater potency than 17-AAG with regard to modulation of Hsp90 client proteins, inhibition of proliferation, and induction of apoptotic cell death. In prostate tumors obtained from radical prostatectomy that were cultured ex vivo, treatment with 500 nmol/L of NVP-AUY922, NVP-HSP990, or 17-AAG caused equivalent target modulation, determined by the pharmacodynamic marker Hsp70, but only NVP-AUY922 and NVP-HSP990 showed antiproliferative and proapoptotic activity. Conclusions: This study provides some of the first evidence that new generation Hsp90 inhibitors are capable of achieving biologic responses in human prostate tumors, with both NVP-AUY922 and NVP-HSP990 showing potent on-target efficacy. Importantly, the ex vivo culture technique has provided information on Hsp90 inhibitor action not previously observed in cell lines or animal models. This approach, therefore, has the potential to enable more rational selection of therapeutic agents and biomarkers of response for clinical trials. Clin Cancer Res; 18(13); 3562–70. ©2012 AACR.

Human Epithelial Basal Cells Are Cells of Origin of Prostate Cancer, Independent of CD133 Status

Normal prostatic epithelium is composed of basal and luminal cells. Prostate cancer can be initiated in both benign basal and luminal stem cells, but because basal cell markers are not expressed in patient tumors, the former result was unexpected. Since the cells of origin of prostate cancer are important therapeutic targets, we sought to provide further proof that basal stem cells have tumorigenic potential. Prostatic basal cells were enriched based on α2β1integrinhi expression and further enriched for stem cells using CD133 in nontumorigenic BPH‐1 cells. Human embryonic stem cells (hESCs) were also used as a source of normal stem cells. To test their tumorigenicity, we used two alternate stromal‐based approaches; (a) recombination with human cancer‐associated fibroblasts (CAFs) or (b) recombination with embryonic stroma (urogenital mesenchyme) and treated host mice with testosterone and 17β‐estradiol. Enriched α2β1integrinhi basal cells from BPH‐1 cells resulted in malignant tumor formation using both assays of tumorigenicity. Surprisingly, the tumorigenic potential did not reside in the CD133+ stem cells but was consistently observed in the CD133− population. CAFs also failed to induce prostatic tumors from hESCs. These data confirmed that benign human basal cells include cells of origin of prostate cancer and reinforced their importance as therapeutic targets. In addition, our data suggested that the more proliferative CD133− basal cells are more susceptible to tumorigenesis compared to the CD133+‐enriched stem cells. These findings challenge the current dogma that normal stem cells and cells of origin of cancer are the same cell type(s). STEM CELLS2012;30:1087–1096

Prostatic Tumor Stroma: A Key Player in Cancer Progression

Although it is evident that prostatic epithelial stem cells are responsible for maintaining normal and malignant tissues, it is well recognized that epithelial cells do not exist independently, but act in concert with the stromal microenvironment. Prostatic stroma is pivotal for normal development and homeostasis. The genetic and morphological changes that occur in prostatic epithelial cells, as they progress from a normal to malignant phenotype, have been well described. However, it is evident that the surrounding microenvironment also plays a major role in cancer cell growth, survival, invasion and metastatic progression. Prostatic tumor stroma provides a niche environment for cancer stem cells and therefore contributes to self-renewal and differentiation. In order to target the tumor microenvironment and develop new therapeutics for prostate cancer, we must understand the role of the tumor stroma, specifically the events mediating the interactions between the cancer stem cell and its immediate microenvironment during cancer initiation and progression. This article presents the rationale and discusses the challenges to targeting prostatic tumor stroma in cancer therapies that will potentially treat prostate cancer.

A preclinical xenograft model of prostate cancer using human tumors

Most cases of prostate cancer are now diagnosed as moderate-grade localized disease. These tumor specimens are important tools in the discovery and translation of prostate cancer research; however, unlike more advanced tumors, they are notoriously difficult to grow in the laboratory. We developed a system for efficiently xenografting localized human prostate cancer tissue, and we adapted this protocol to study the interactions between the specific subsets of epithelial and stromal cells. Fresh prostate tissues or isolated epithelial cells are recombined with mouse seminal vesicle mesenchyme (SVM) and grafted under the renal capsule of immunodeficient mice for optimum growth and survival. Alternatively, mouse mesenchyme can be replaced with human prostate fibroblasts in order to determine their contribution to tumor progression. Grafts can be grown for several months to determine the effectiveness of novel therapeutic compounds when administered to host mice, thereby paving the way for personalizing the treatment of individual prostate cancers.

Stem cells in prostate cancer: treating the root of the problem

Prostate cancer is a hormone-dependent, epithelial-derived tumor, resulting from uncontrolled growth of genetically unstable transformed cells. Stem cells are therapeutic targets for prostate cancer, but as disease progression occurs over decades, the imperative is to identify and target the cancer-repopulating cell (CRC) that maintains malignant clones. In order to achieve this goal, we will review the current knowledge of three specific types of cells, their origins, and their differentiation potential. The first is the normal stem cell, the second is the cancer cell of origin, and the third is the CRC. Specifically, we review three proposed models of stem cell differentiation in normal tissues, including linear, bidirectional, and independent lineages. We consider evidence of the cancer cell of origin arising from both basal and luminal cells. Finally, we discuss the limited data available on the identity and characterization of CRCs in localized and castrate-resistant prostate cancer, which is where we believe the focus of future research efforts should be directed. Ultimately, understanding the intrinsic or extrinsic influences that dictate the behavior of these unique cells will be instrumental in facilitating the development of new therapeutic targets for prostate cancer.

A Preclinical Xenograft Model Identifies Castration-Tolerant Cancer-Repopulating Cells in Localized Prostate Tumors

This study uses a preclinical xenograft model to reveal prostate cancer cells that exist in untreated localized disease, survive androgen withdrawal, and are potential therapeutic targets. The Enemy Within Prostate cancer is one of the most common types of cancer in men. In advanced stages, it is typically treated with medications that mimic castration, depriving the tumor of androgen stimulation. Unfortunately, these cancers eventually become castration-resistant and begin to grow even in the absence of hormonal input. What isn’t known is how these cancer cells develop the ability to survive androgen deprivation, and whether some types of stem-like castration-resistant cells are already present in prostate cancer from early stages or evolve later during the course of treatment. Now, Toivanen and colleagues shed some light on this mystery, with a report of castration-tolerant cells derived from early localized tumors that had not yet been exposed to anti-androgen therapy. The authors used primary prostate tumors from 12 men with localized cancer, implanting them in a mouse xenograft model to study the effects of androgen deprivation on the tumors’ survival. Castration of the host mice led to rapid regression, but not disappearance of the tumors. Even after a prolonged period of castration (4 weeks), some residual tumor foci persisted. When testosterone stimulation was restored in the host animals, these residual cells rebounded, regenerating masses that were histologically similar to the original tumors. This work by Toivanen et al. indicates that some prostate cancer cells can survive castration and later repopulate the tumor when androgen stimulation is available. Thus far, there is no indication that these castration-tolerant cells can proliferate in the absence of androgens, unlike the cells found in more advanced “castration-resistant” prostate cancer. Additional work will be needed to clarify whether these might be a type of prostate cancer stem cells, and what makes them different from the population of “androgen-sensitive” cancer cells that do not survive androgen depletion. Although there are many questions that must still be answered about the biology of these castration-tolerant cells, this work raises the intriguing possibility that we may eventually be able to specifically target and eradicate them, thus preventing prostate cancer recurrence in patients. A lack of clinically relevant experimental models of human prostate cancer hampers evaluation of potential therapeutic agents. Currently, androgen deprivation therapy is the gold standard treatment for advanced prostate cancer, but inevitably, a subpopulation of cancer cells survives and repopulates the tumor. Tumor cells that survive androgen withdrawal are critical therapeutic targets for more effective treatments, but current model systems cannot determine when they arise in disease progression and are unable to recapitulate variable patient response to treatment. A model system was developed in which stromal-supported xenografts from multiple patients with early-stage localized disease can be tested for response to castration. The histopathology of these xenografts mimicked the original tumors, and short-term host castration resulted in reduced proliferation and increased apoptosis in tumor cells. After 4 weeks of castration, residual populations of quiescent, stem-like tumor cells remained. Without subsequent treatment, these residual cells displayed regenerative potential, because testosterone readministration resulted in emergence of rapidly proliferating tumors. Therefore, this model may be useful for revealing potential cellular targets in prostate cancer, which exist before the onset of aggressive incurable disease. Specific eradication of these regenerative tumor cells that survive castration could then confer survival benefits for patients.

A bioengineered microenvironment to quantitatively measure the tumorigenic properties of cancer-associated fibroblasts in human prostate cancer

Stromal-epithelial cell interactions play an important role in cancer and the tumor stroma is regarded as a therapeutic target. In vivo xenografting is commonly used to study cellular interactions not mimicked or quantified in conventional 2D culture systems. To interrogate the effects of tumor stroma (cancer-associated fibroblasts or CAFs) on epithelia, we created a bioengineered microenvironment using human prostatic tissues. Patient-matched CAFs and non-malignant prostatic fibroblasts (NPFs) from men with moderate (Gleason 7) and aggressive (Gleason 8-9 or castrate-resistant) prostate cancer were cultured with non-tumorigenic BPH-1 epithelial cells. Changes in the morphology, motility and phenotype of BPH-1 cells in response to CAFs and NPFs were analyzed using immunofluorescence and quantitative cell morphometric analyses. The matrix protein gene expression of CAFs, with proven tumorigenicity in vivo, had a significantly different gene expression profile of matrix proteins compared to patient matched NPFs. In co-culture with CAFs (but not NPFs), BPH-1 cells had a more invasive, elongated phenotype with increased motility and a more directed pattern of cell migration. CAFs from more aggressive tumors (Gleason 8-9 or CRPC) were not quantitatively different to moderate grade CAFs. Overall, our bioengineered microenvironment provides a novel 3D in vitro platform to systematically investigate the effects of tumor stroma on prostate cancer progression.

Breaking through a roadblock in prostate cancer research: An update on human model systems

Prostate cancer is a prevalent disease that affects the aging male population. Whilst there have been significant advances of our biological understanding of the disease, clinical translation of promising agents continues to lag behind. In part, this is due to a paucity of relevant experimental and pre-clinical models required to further develop effective prevention and therapeutic strategies. Genetically modified cell lines fail to entirely represent the genetic and molecular diversity of primary human specimens, particularly from localised disease. Furthermore, primary prostate cancer tissues are extremely difficult to grow in the laboratory and virtually all human models, whether they grow as xenografts in immune-deficient animals or as cell cultures, are genetically modified by the investigator or derived from patients with advanced metastatic disease. In this review, we discuss the latest advances and improvements to current methods of xenografting human primary prostate cancer, and their potential application to translational research.