Jens Ceder

miR-205 negatively regulates the androgen receptor and is associated with adverse outcome of prostate cancer patients.

Background:The microRNA-205 (miR-205) has been shown to be deregulated in prostate cancer (PCa). Here we continue to investigate the prognostic and therapeutic potential of this microRNA.Methods:The expression of miR-205 is measured by qRT–PCR and in situ hybridisation in a well-documented PCa cohort. An AGO2-based RIP-Chip assay is used to identify targets that are verified with western blots, luciferase reporter assay, ELISA and immunohistochemistry.Results:The expression of miR-205 is inversely correlated to the occurrence of metastases and shortened overall survival, and is lower in castration-resistant PCa patients. The miR-205 expression is mainly localised to the basal cells of benign prostate tissues. Genes regulated by miR-205 are enriched in, for example, the MAPK/ERK, Toll-like receptor and IL-6 signaling pathways. We demonstrate binding of miR-205 to the 3′UTR of androgen receptor (AR) and decrease of both AR transcript and protein levels. This finding was corroborated in the patient cohort were miR-205 expression inversely correlated to AR immunostaining in malignant prostate cells and to serum levels of prostate-specific antigen, an androgen-regulated protein.Conclusion:Taken together, these findings imply that miR-205 might have therapeutic potential, especially for the castration resistant and currently untreatable form of PCa.

REST mediates androgen receptor actions on gene repression and predicts early recurrence of prostate cancer

The androgen receptor (AR) is a key regulator of prostate tumorgenesis through actions that are not fully understood. We identified the repressor element (RE)-1 silencing transcription factor (REST) as a mediator of AR actions on gene repression. Chromatin immunoprecipitation showed that AR binds chromatin regions containing well-characterized cis-elements known to mediate REST transcriptional repression, while cell imaging studies confirmed that REST and AR closely co-localize in vivo. Androgen-induced gene repression also involves modulation of REST protein turnover through actions on the ubiquitin ligase β-TRCP. Androgen deprivation or AR blockage with inhibitor MDV3100 (Enzalutamide) leads to neuroendocrine (NE) differentiation, a phenomenon that is mimicked by REST inactivation. Gene expression profiling revealed that REST not only acts to repress neuronal genes but also genes involved in cell cycle progression, including Aurora Kinase A, that has previously been implicated in the growth of NE-like castration-resistant tumors. The analysis of prostate cancer tissue microarrays revealed that tumors with reduced expression of REST have higher probability of early recurrence, independently of their Gleason score. The demonstration that REST modulates AR actions in prostate epithelia and that REST expression is negatively correlated with disease recurrence after prostatectomy, invite a deeper characterization of its role in prostate carcinogenesis.

Delta-Like 1 (Dlk-1), a Novel Marker of Prostate Basal and Candidate Epithelial Stem Cells, Is Downregulated by Notch Signalling in Intermediate/Transit Amplifying Cells of the Human Prostate

BACKGROUND There is a lack of understanding of the processes that regulate differentiation in the prostate. OBJECTIVE To determine localisation, activity, and regulation of cytodifferentiation-modulatory proteins in the human adult prostate. DESIGN, SETTINGS, AND PARTICIPANTS Eighteen volunteering patients with organ-confined prostate cancer were prospectively enrolled at a single university hospital. INTERVENTION All patients underwent radical prostatectomy, and normal/benign tissue was excised and obtained from the transition zone. MEASUREMENTS Expression and activity of Notch-protein family members, including the Notch-homologous protein Delta-like 1 (Dlk-1/Pref1), were investigated immunohistochemically in normal/benign tissue and explant cultures. The effect of the Notch inhibitor L-685,458 on Dlk-1 expression and cell number was investigated in primary cell cultures, and data were analysed with Student t test. RESULTS AND LIMITATIONS Mature luminal cells were found to co-express Notch-1 and its ligand Jagged1, but epithelia in normal/benign tissue showed no active Notch signalling. The basal cell layer, rare candidate epithelial stem cells, and a subpopulation of neuroendocrine cells expressed the differentiation protein Dlk-1. In explant cultures, luminal cells and Jagged1 expression were lost, whereas intermediate cells downregulated Dlk-1 concomitant with Notch-1 upregulation and activation. Notch inhibition in primary cell cultures led to lower cell densities (p<0.001) and suppressed downregulation of Dlk-1. This is a small study; current results need to be confirmed in larger investigations. CONCLUSIONS We demonstrate that Notch-1 is upregulated in differentiation of prostate epithelia, and that the novel prostate progenitor marker Dlk-1 is downregulated by Notch signalling in intermediate cells. The identification of Dlk-1-expressing candidate stem and neuroendocrine cells suggests a hierarchical relationship.

Targeting prostate cancer stem cells with alpha-particle therapy

Modern molecular and radiopharmaceutical development has brought the promise of tumor-selective delivery of antibody–drug conjugates to tumor cells for the diagnosis and treatment of primary and disseminated tumor disease. The classical mode of discourse regarding targeted therapy has been that the antigen targeted must be highly and homogenously expressed in the tumor cell population, and at the same time exhibit low expression in healthy tissue. However, there is increasing evidence that the reason cancer patients are not cured by current protocols is that there exist subpopulations of cancer cells that are resistant to conventional therapy including radioresistance and that these cells express other target antigens than the bulk of the tumor cells. These types of cells are often referred to as cancer stem cells (CSCs). The CSCs are tumorigenic and have the ability to give rise to all types of cells found in a cancerous disease through the processes of self-renewal and differentiation. If the CSCs are not eradicated, the cancer is likely to recur after therapy. Due to some of the characteristics of alpha particles, such as short path length and high density of energy depositions per distance traveled in tissue, they are especially well suited for use in targeted therapies against microscopic cancerous disease. The characteristics of alpha particles further make it possible to minimize the irradiation of non-targeted surrounding healthy tissue, but most importantly, make it possible to deliver high-absorbed doses locally and therefore eradicating small tumor cell clusters on the submillimeter level, or even single tumor cells. When alpha particles pass through a cell, they cause severe damage to the cell membrane, cytoplasm, and nucleus, including double-strand breaks of DNA that are very difficult to repair for the cell. This means that very few hits to a cell by alpha particles are needed in order to cause cell death, enabling killing of cells, such as CSCs, exhibiting cellular resistance mechanisms to conventional therapy. This paper presents and evaluates the possibility of using alpha-particle emitting radionuclides in the treatment of prostate cancer (PCa) and discusses the parameters that have to be considered as well as pros and cons of targeted alpha-particle therapy in the treatment of PCa. By targeting and eradicating the CSCs responsible of tumor recurrence in patients who no longer respond to conventional therapies, including androgen deprivation and castration, it may be possible to cure the disease, or prolong survival significantly.

Label retention and stem cell marker expression in the developing and adult prostate identifies basal and luminal epithelial stem cell subpopulations

BackgroundProstate cancer is the second most frequent cancer among males worldwide, and most patients with metastatic disease eventually develop therapy-resistant disease. Recent research has suggested the existence of cancer stem-like cells, and that such cells are behind the therapy resistance and progression.MethodsHere, we have taken advantage of the relatively quiescent nature of stem cells to identify the slow-cycling label-retaining stem cell (LRC) populations of the prostate gland. Mice were pulsed with bromodeoxyuridine (BrdU) during prostate organogenesis, and the LRC populations were then identified and characterized in 5-day-old and in 6-month-old adult animals using immunohistochemistry and immunofluorescence.ResultsQuantification of LRCs in the adult mouse prostate showed that epithelial LRCs were significantly more numerous in prostatic ducts (3.7 ± 0.47% SD) when compared to the proximal (1.4 ± 0.83%) and distal epithelium (0.48 ± 0.08%) of the secretory lobes. LRCs were identified in both the basal and epithelial cell layers of the prostate, and LRCs co-expressed several candidate stem cell markers in a developmental and duct/acini-specific manner, including Sca-1, TROP-2, CD133, CD44, c-kit, and the novel prostate progenitor marker cytokeratin-7. Importantly, a significant proportion of LRCs were localized in the luminal cell layer, the majority in ducts and the proximal prostate, that co-expressed high levels of androgen receptor in the adult prostate.ConclusionsOur results suggest that there are separate basal and luminal stem cell populations in the prostate, and they open up the possibility that androgen receptor-expressing luminal stem-like cells could function as cancer-initiating and relapse-responsible cells in prostate cancer.

Targeting the Mechanisms of Progression in Castration-resistant Prostate Cancer

Until recently, few treatment options were available for metastatic castration-resistant prostate cancer (mCRPC). However, in recent years, there has been a rapid increase in the number of therapeutic options in addition to docetaxel. Novel therapies include the androgen synthesis inhibitor abiraterone, the antiandrogen enzalutamide, the taxane cabazitaxel, immunotherapeutic sipuleucel-T, and bonetargeting radium 223. Although these new therapies have shown an improvement in overall survival for patients with mCRPC, and although clinical trials optimising their sequence with one another may further increase survival values, death from mCRPC is invariably due to resistance to contemporary treatment modalities. Understanding the biology behind mCRPC is of crucial importance if we are to develop new and better treatment regimens for this patient group. In this month’s issue of European Urology, Karantanos et al provide an updated and in-depth review of issues pertaining to mechanisms behind development of resistance in mCRPC [1]. While the molecular basis implicated in the development of CRPC is complex and varied, it is clear that androgen receptor (AR) signalling remains an important driver of mCRPC despite systemic androgen deprivation and the new therapeutic options available today. Schweizer et al recently showed that docetaxel has only limited antitumor activity in CRPC patients previously treated with abiraterone [2], and this cross-resistance is likely due to interference of taxanes with the AR pathway [3]. Likewise, it has been reported that there is crossresistance between abiraterone and enzalutamide therapy, although a proportion of patients benefit from sequential treatment therapy [4]. Such resistance may be associated