Castration-induced epithelial cell death in human prostate tissue is related to locally reduced IGF-1 levels

Modelling the distinct roles of epithelial and stromal androgen receptor in the regulation of prostate epithelial dynamics

The prostate is an androgen-responsive organ, but the complex cellular and molecular interactions that mediate these responses remain incompletely defined. Here, I synthesise the existing literature to derive a simple conceptual framework describing the androgen-dependent regulation of prostate epithelial dynamics. In this framework, epithelial androgen receptor (AR) cell-autonomously controls luminal cell height, whereas stromal AR regulates the synthesis of growth factors that promote luminal cell survival and proliferation. With the additional aid of a reanalysis of single-cell RNA-seq data, I also propose that insulin-like growth factor 1 (IGF1) functions as a key androgen-dependent growth factor coordinating stromal-to-epithelial paracrine communication. A novel mathematical model based on this framework was able to quantitatively fit experimental data describing prostate regression and regeneration. Model analysis demonstrates how the luminal cell population can maintain a stable equilibrium size via competition for and degradation of stroma-derived IGF1 and how this population size can be controlled by androgen levels, without a requirement for distinct luminal cell subsets. Moreover, model simulations were able to qualitatively recapitulate experimental observations in inflammatory and cancerous states, thereby providing insights into potential disease mechanisms. This simple model could therefore serve as a foundation for more comprehensive modelling of both the healthy and diseased prostate.

Antagonistic Functions of Androgen Receptor and NF-κB in Prostate Cancer-Experimental and Computational Analyses

Prostate cancer is very frequent and is, in many countries, the third-leading cause of cancer related death in men. While early diagnosis and treatment by surgical removal is often curative, metastasizing prostate cancer has a very bad prognosis. Based on the androgen-dependence of prostate epithelial cells, the standard treatment is blockade of the androgen receptor (AR). However, nearly all patients suffer from a tumor relapse as the metastasizing cells become AR-independent. In our study we show a counter-regulatory link between AR and NF-κB both in human cells and in mouse models of prostate cancer, implying that inhibition of AR signaling results in induction of NF-κB-dependent inflammatory pathways, which may even foster the survival of metastasizing cells. This could be shown by reporter gene assays, DNA-binding measurements, and immune-fluorescence microscopy, and furthermore by a whole set of computational methods using a variety of datasets. Interestingly, loss of PTEN, a frequent genetic alteration in prostate cancer, also causes an upregulation of NF-κB and inflammatory activity. Finally, we present a mathematical model of a dynamic network between AR, NF-κB/IκB, PI3K/PTEN, and the oncogene c-Myc, which indicates that AR blockade may upregulate c-Myc together with NF-κB, and that combined anti-AR/anti-NF-κB and anti-PI3K treatment might be beneficial.

Gut Microbiota-Derived Short-Chain Fatty Acids Promote Prostate Cancer Growth via IGF1 Signaling

Excessive intake of animal fat and resultant obesity are major risk factors for prostate cancer. Because the composition of the gut microbiota is known to change with dietary composition and body type, we used prostate-specific Pten knockout mice as a prostate cancer model to investigate whether there is a gut microbiota-mediated connection between animal fat intake and prostate cancer. Oral administration of an antibiotic mixture (Abx) in prostate cancer-bearing mice fed a high-fat diet containing a large proportion of lard drastically altered the composition of the gut microbiota including Rikenellaceae and Clostridiales, inhibited prostate cancer cell proliferation, and reduced prostate Igf1 expression and circulating insulin-like growth factor-1 (IGF1) levels. In prostate cancer tissue, MAPK and PI3K activities, both downstream of the IGF1 receptor, were suppressed by Abx administration. IGF1 directly promoted the proliferation of prostate cancer cell lines DU145 and 22Rv1 in vitro. Abx administration also reduced fecal levels of short-chain fatty acids (SCFA) produced by intestinal bacteria. Supplementation with SCFAs promoted tumor growth by increasing IGF1 levels. In humans, IGF1 was found to be highly expressed in prostate cancer tissue from obese patients. In conclusion, IGF1 production stimulated by SCFAs from gut microbes influences the growth of prostate cancer via activating local prostate MAPK and PI3K signaling, indicating the existence of a gut microbiota-IGF1-prostate axis. Disrupting this axis by modulating the gut microbiota may aid in prostate cancer prevention and treatment. SIGNIFICANCE: These results suggest that intestinal bacteria, acting through short-chain fatty acids, regulate systemic and local prostate IGF1 in the host, which can promote proliferation of prostate cancer cells.

The potential of tumour microenvironment markers to stratify the risk of recurrence in prostate cancer patients

The tumour micro-environment (TME) plays a crucial role in the onset and progression of prostate cancer (PCa). Here we studied the potential of a selected panel of TME-markers to predict clinical recurrence (CLR) in PCa. Patient cohorts were matched for the presence or absence of CLR 5 years post-prostatectomy. Tissue micro-arrays (TMA) were composed with both prostate non-tumour (PNT) and PCa tissue and subsequently processed for immunohistochemistry (IHC). The IHC panel included markers for cancer activated fibroblasts (CAFs), blood vessels and steroid hormone receptors ((SHR): androgen receptor (AR), progesterone receptor (PR) and estrogen receptor (ER)). Stained slides were digitalised, selectively annotated and analysed for percentage of marker expression with standardized and validated image analysis algorithms. A univariable analysis identified several TME markers with significant impact on CR: expression of CD31 (vascular marker) in PNT stroma, expression of alpha smooth muscle actin (αSMA) in PCa stroma, and PR expression ratio between PCa stroma and PNT stroma. A multivariable model, which included CD31 expression (vascular marker) in PNT stroma and PR expression ratio between PCa stroma and PNT stroma, could significantly stratify patients for CLR, with the identification of a low risk and high-risk subgroup. If validated and confirmed in an independent prospective series, this subgroup might have clinical potential for PCa patient stratification.

Mesenchymal stem cells and the embryonic reawakening theory of BPH

The prostate is the only organ in a man that continues to grow with age. John McNeal proposed, 40 years ago, that this BPH is characterized by an age-related reinitiation of benign neoplastic growth selectively in developmentally abortive distal ducts within the prostate transition-periurethral zone (TPZ), owing to a reawakening of inductive stroma selectively within these zones. An innovative variant of this hypothesis is that, owing to its location, the TPZ is continuously exposed to urinary components and/or autoantigens, which produces an inflammatory TPZ microenvironment that promotes recruitment of bone marrow-derived mesenchymal stem cells (MSCs) and generates a paracrine-inductive stroma that reinitiates benign neoplastic nodular growth. In support of this hypothesis, MSCs infiltrate human BPH tissue and have the ability to stimulate epithelial stem cell growth. These results provide a framework for defining both the aetiology of BPH in ageing men and insights into new therapeutic approaches.

Comparing the expression profiles of steroid hormone receptors and stromal cell markers in prostate cancer at different Gleason scores

The recent developments in anti-angiogenic and immunomodulatory drugs show that the tumour micro-environment (TME) becomes increasingly important in cancer research. Here we investigated the correlation between the Gleason score (GS) and the TME by comparing tissue expression profiles of steroid hormone receptors, cancer activated fibroblast (CAF) markers and vessel densities between different GS groups. Therefore, matched patient cohorts were composed for different GS (6-7-8). Tissue micro-arrays with 6 samples/patient were processed for immunohistochemistry. Stained slides were digitised, stroma and epithelium were selectively annotated, and all selected areas were quantitatively analysed for marker expression. The most striking findings were decreased stromal expression levels of several steroid hormone receptors, increased CAF-phenotypes and increased vessel densities in high GS prostate cancer compared to low GS prostate cancer and paired prostate non-tumour tissue. The present data reveal a complex correlation between prostate cancer differentiation and TME components and suggest that different GS can be associated with different possible actionable targets in the TME. The use of standardised digital image analysis tools generated robust and reproducible quantitative data, which is novel and more informative compared to the classic semi-quantitative and observer-dependent visual scoring of immunohistochemistry.

Role of Stromal Paracrine Signals in Proliferative Diseases of the Aging Human Prostate

Androgens are essential for the development, differentiation, growth, and function of the prostate through epithelial–stromal interactions. However, androgen concentrations in the hypertrophic human prostate decrease significantly with age, suggesting an inverse correlation between androgen levels and proliferative diseases of the aging prostate. In elderly males, age- and/or androgen-related stromal remodeling is spontaneously induced, i.e., increased fibroblast and myofibroblast numbers, but decreased smooth muscle cell numbers in the prostatic stroma. These fibroblasts produce not only growth factors, cytokines, and extracellular matrix proteins, but also microRNAs as stromal paracrine signals that stimulate prostate epithelial cell proliferation. Surgical or chemical castration is the standard systemic therapy for patients with advanced prostate cancer. Androgen deprivation therapy induces temporary remission, but the majority of patients eventually progress to castration-resistant prostate cancer, which is associated with a high mortality rate. Androgen deprivation therapy-induced stromal remodeling may be involved in the development and progression of castration-resistant prostate cancer. In the tumor microenvironment, activated fibroblasts stimulating prostate cancer cell proliferation are called carcinoma-associated fibroblasts. In this review, we summarize the role of stromal paracrine signals in proliferative diseases of the aging human prostate and discuss the potential clinical applications of carcinoma-associated fibroblast-derived exosomal microRNAs as promising biomarkers.

Clinical relevance of androgen receptor alterations in prostate cancer

Prostate cancer (PC) remains a leading cause of cancer-related deaths among men worldwide, despite continuously improved treatment strategies. Patients with metastatic disease are treated by androgen deprivation therapy (ADT) that with time results in the development of castration-resistant prostate cancer (CRPC) usually established as metastases within bone tissue. The androgen receptor (AR) transcription factor is the main driver of CRPC development and of acquired resistance to drugs given for treatment of CRPC, while a minority of patients have CRPC that is non-AR driven. Molecular mechanisms behind epithelial AR reactivation in CRPC include AR gene amplification and overexpression, AR mutations, expression of constitutively active AR variants, intra-tumoural and adrenal androgen synthesis and promiscuous AR activation by other factors. This review will summarize AR alterations of clinical relevance for patients with CRPC, with focus on constitutively active AR variants, their possible association with AR amplification and structural rearrangements as well as their ability to predict patient resistance to AR targeting drugs. The review will also discuss AR signalling in the tumour microenvironment and its possible relevance for metastatic growth and therapy.

Crosstalk between the Androgen Receptor and PPAR Gamma Signaling Pathways in the Prostate

Nuclear receptors are a superfamily of ligand-activated transcription factors that play critical roles in the regulation of normal biological processes and several disease states. Of the nuclear receptors expressed within the prostate, the androgen receptor (AR) promotes the differentiation of prostatic epithelial cells and stimulates production of enzymes needed for liquefaction of semen. Multiple forms of AR also promote the growth of both early and late stage prostate cancers. As a result, drugs that target the AR signaling pathway are routinely used to treat patients with advanced forms of prostate cancer. Data also suggest that a second member of the nuclear receptor superfamily, the peroxisome proliferator activated receptor gamma (PPARγ), is a tumor suppressor that regulates growth of normal prostate and prostate cancers. Recent studies indicate there is a bidirectional interaction between AR and PPARγ, with each receptor influencing the expression and/or activity of the other within prostatic tissues. In this review, we examine how AR and PPARγ each regulate the growth and development of normal prostatic epithelial cells and prostate cancers. We also discuss interactions between the AR and PPARγ signaling pathways and how those interactions may influence prostate biology.

Inhibition of the insulin-like growth factor-1 receptor potentiates acute effects of castration in a rat model for prostate cancer growth in bone

Prostate cancer (PCa) patients with bone metastases are primarily treated with androgen deprivation therapy (ADT). Less pronounced ADT effects are seen in metastases than in primary tumors. To test if acute effects of ADT was enhanced by concurrent inhibition of pro-survival insulin-like growth factor 1 (IGF-1), rats were inoculated with Dunning R3327-G tumor cells into the tibial bone marrow cavity and established tumors were treated with castration in combination with IGF-1 receptor (IGF-1R) inhibitor NVP-AEW541, or by each treatment alone. Dunning R3327-G cells were stimulated by androgens and IGF-1 in vitro. In rat tibia, Dunning R3327-G cells induced bone remodeling, identified through increased immunoreactivity of osteoblast and osteoclast markers. Tumor cells occasionally grew outside the tibia, and proliferation and apoptotic rates a few days after treatment were evaluated by scoring BrdU- and caspase-3-positive tumor cells inside and outside the bone marrow cavity, separately. Apoptosis was significantly induced outside, but unaffected inside, the tibial bone by either castration or NVP-AEW541, and the maximum increase (2.7-fold) was obtained by the combined treatment. Proliferation was significantly reduced by NVP-AEW541, independently of growth site, although the maximum decrease (24%) was observed when NVP-AEW541 was combined with castration. Tumor cell IGF-1R immunoreactivity was evaluated in clinical PCa bone metastases (n = 61), and positive staining was observed in most cases (74%). In conclusion, IGF-1R inhibition may be evaluated in combination with ADT in patients with metastatic PCa, or in combination with therapies for the subsequent development of castration-resistant disease, although diverse responses could be anticipated depending on metastasis site.

Stromal Androgen Receptor in Prostate Cancer Development and Progression

Prostate cancer development and progression is the result of complex interactions between epithelia cells and fibroblasts/myofibroblasts, in a series of dynamic process amenable to regulation by hormones. Whilst androgen action through the androgen receptor (AR) is a well-established component of prostate cancer biology, it has been becoming increasingly apparent that changes in AR signalling in the surrounding stroma can dramatically influence tumour cell behavior. This is reflected in the consistent finding of a strong association between stromal AR expression and patient outcomes. In this review, we explore the relationship between AR signalling in fibroblasts/myofibroblasts and prostate cancer cells in the primary site, and detail the known functions, actions, and mechanisms of fibroblast AR signaling. We conclude with an evidence-based summary of how androgen action in stroma dramatically influences disease progression.

Androgen deprivation in LNCaP prostate tumour xenografts induces vascular changes and hypoxic stress, resulting in promotion of epithelial-to-mesenchymal transition

Background:

When single-agent androgen deprivation therapy (ADT) is administered for locally advanced prostate cancer, men usually relapse within 1–2 years with more malignant castrate-resistant disease. The reason for this is currently unknown. We now hypothesise that an initial treatment response that increases tumour hypoxia drives selection of more malignant tumours.

Methods:

The LNCaP prostate tumour xenografts were analysed for physiological (oxygen and vasculature) and genetic (PCR array) changes during longitudinal treatment with ADT (bicalutamide, 6 or 2 mg kg⁻¹ daily for 28 days).

Results:

Bicalutamide caused an immediate (within 24 h) dose-dependent fall in oxygenation in LNCaP-luc prostate tumours with a nadir of ≤0.1% oxygen within 3–7 days; this was attributed to a significant loss of tumour microvessels (window chamber study). The hypoxic nadir persisted for 10–14 days. During the next 7 days, tumours regrew, oxygenation improved and the vasculature recovered; this was inhibited by the VEGF inhibitor B20.4.1.1. Gene expression over 28 days showed marked fluctuations consistent with the physiological changes. Accompanying the angiogenic burst (day 21) was a particularly striking increase in expression of genes associated with epithelial-to-mesenchymal transition (EMT). In particular, insulin-like growth factor 1 (IGF-1) showed increases in mRNA and protein expression.

Conclusions:

Hypoxic stress caused by ADT promotes EMT, providing a mechanism for the cause of malignant progression in prostate cancer.

Intensity of stromal changes is associated with tumor relapse in clinically advanced prostate cancer after castration therapy

Reactive stromal changes in prostate cancer (PCa) are likely involved in the emergence of castration-resistant PCa (CRPC). This study was designed to investigate stromal changes in patients with clinically advanced PCa and analyze their prognostic significance. Prostate needle biopsies obtained from 148 patients before castration therapy were analyzed by Masson trichrome staining and immunohistochemical analysis of vimentin and desmin. Reactive stroma grading was inversely correlated with Gleason score. Stroma grade (Masson stain 82.8% vs 45.6%, P < 0.001) and vimentin expression (P = 0.005) were significantly higher, and desmin expression (P = 0.004) significantly lower, in reactive stroma of tumors with a Gleason score of 6–7 than in adjacent peritumoral tissue. Kaplan-Meier analysis showed a significant association between reactive stroma grade in tumors and the occurrence of CRPC in patients with a Gleason score of 6–7 (P = 0.009). Furthermore, patients with higher vimentin or lower desmin expression had a shorter disease-free period. In multivariate analysis, only vimentin expression was a significant predictor of tumor relapse (hazard ratio 1.78, 95% confidence interval 1.12–10.26, P = 0.012). These findings indicate that the intensity of reactive stroma is associated with castration responsiveness, especially in patients with a lower Gleason score where the abundant stroma component is most frequently found. High expression of vimentin in tumor stroma was independently associated with poor outcomes in patients with Gleason scores of 6–7, and may serve as a new prognostic marker in daily practice.

Stromal androgen receptor roles in the development of normal prostate, benign prostate hyperplasia, and prostate cancer

The prostate is an androgen-sensitive organ that needs proper androgen/androgen receptor (AR) signals for normal development. The progression of prostate diseases, including benign prostate hyperplasia (BPH) and prostate cancer (PCa), also needs proper androgen/AR signals. Tissue recombination studies report that stromal, but not epithelial, AR plays more critical roles via the mesenchymal-epithelial interactions to influence the early process of prostate development. However, in BPH and PCa, much more attention has been focused on epithelial AR roles. However, accumulating evidence indicates that stromal AR is also irreplaceable and plays critical roles in prostate disease progression. Herein, we summarize the roles of stromal AR in the development of normal prostate, BPH, and PCa, with evidence from the recent results of in vitro cell line studies, tissue recombination experiments, and AR knockout animal models. Current evidence suggests that stromal AR may play positive roles to promote BPH and PCa progression, and targeting stromal AR selectively with AR degradation enhancer, ASC-J9, may allow development of better therapies with fewer adverse effects to battle BPH and PCa.

Conversion of androgen receptor signaling from a growth suppressor in normal prostate epithelial cells to an oncogene in prostate cancer cells involves a gain of function in c-Myc regulation

In normal prostate, androgen-dependent androgen receptor (AR) signaling within prostate stromal cells induces their secretion of paracrine factors, termed “andromedins” which stimulate growth of the epithelial cells. The present studies demonstrate that androgen-dependent andromedin-driven growth stimulation is counter-balanced by androgen-induced AR signaling within normal adult prostate epithelial cells resulting in terminal G₀ growth arrest coupled with terminal differentiation into ΔNp63-negative, PSA-expressing secretory luminal cells. This cell autonomous AR-driven terminal differentiation requires DNA-binding of the AR protein, is associated with decreases in c-Myc m-RNA and protein, are coupled with increases in p21, p27, and SKP-2 protein expression, and does not require functional p53. These changes result in down-regulation of Cyclin D₁ protein and RB phosphoryation. shRNA knockdown documents that neither RB, p21, p27 alone or in combination are required for such AR-induced G₀ growth arrest. Transgenic expression of a constitutive vector to prevent c-Myc down-regulation overrides AR-mediated growth arrest in normal prostate epithelial cells, which documents that AR-induced c-Myc down-regulation is critical in terminal growth arrest of normal prostate epithelial cells. In contrast, in prostate cancer cells, androgen-induced AR signaling paradoxically up-regulates c-Myc expression and stimulates growth as documented by inhibition of both of these responses following exposure to the AR antagonist, bicalutamide. These data document that AR signaling is converted from a growth suppressor in normal prostate epithelial cells to an oncogene in prostate cancer cells during prostatic carcinogenesis and that this conversion involves a gain of function for regulation of c-Myc expression.

Inhibition of the insulin-like growth factor-1 receptor enhances effects of simvastatin on prostate cancer cells in co-culture with bone

Prostate cancer (PC) bone metastases show weak responses to conventional therapies. Bone matrix is rich in growth factors, with insulin-like growth factor-1 (IGF-1) being one of the most abundant. IGF-1 acts as a survival factor for tumor cells and we speculate that bone-derived IGF-1 counteracts effects of therapies aimed to target bone metastases and, consequently, that therapeutic effects could be enhanced if given in combination with IGF-1 receptor (IGF-1R) inhibitors. Simvastatin inhibits the mevalonate pathway and has been found to induce apoptosis of PC cells. The aims of this study were to confirm stimulating effects of bone-derived IGF-1 on PC cells and to test if IGF-1R inhibition enhances growth inhibitory effects of simvastatin on PC cells in a bone microenvironment. The PC-3 and 22Rv1 tumor cell lines showed significantly induced cell growth when co-cultured with neonatal mouse calvarial bones. The tumor cell IGF-1R was activated by calvariae-conditioned media and neutralization of bone-derived IGF-1 abolished the calvarium-induced PC-3 cell growth. Treatment of PC-3 and 22Rv1 cells with simvastatin, or the IGF-1R inhibitor NVP-AEW541, reduced tumor cell numbers and viability, and induced apoptosis. Combined simvastatin and NVP-AEW541 treatment resulted in enhanced growth inhibitory effects compared to either drug given alone. Effects of simvastatin involved down-regulation of IGF-1R in PC-3 and of constitutively active androgen receptor variants in 22Rv1 cells. In conclusion, we suggest that IGF-1 inhibition may be a way to strengthen effects of apoptosis-inducing therapies on PC bone metastases; a possibility that needs to be further tested in pre-clinical models.

Activation of FGF2-FGFR signaling in the castrated mouse prostate stimulates the proliferation of basal epithelial cells

The prostate gland is unique in that it undergoes rapid regression following castration but regenerates completely once androgens are replaced. Residual ductal components play an important role in the regeneration of a fully functional prostate. In this study, to examine how androgen status affects prostate structure and components, we conducted histopathological studies of the involuted and regenerated mouse dorsolateral prostate (DLP). In the castrated mouse DLP, the number of luminal epithelial cells decreased in a time-dependent manner. On Day 14 postandrogen replacement, the number of luminal epithelial cells was completely restored to the baseline level. In contrast, the number of basal epithelial cells gradually increased in the castrated mouse prostate. The Ki67-labeling index of prostate basal epithelial cells was significantly increased after castration. The number of basal epithelial cells decreased to baseline after androgen replacement. After castration, mRNA expression levels of specific growth factors, such as Fgf2, Fgf7, Hgf, Tgfa, and Tgfb, were relatively abundant in whole mouse DLPs. In organ culture experiments, basal epithelial proliferation was recapitulated in the absence of dihydrotestosterone (DHT). The proliferation of basal epithelial cells in the absence of DHT was suppressed by treatment with an FGF receptor inhibitor (PD173074). Moreover, FGF2 treatment directly stimulated the proliferation of basal epithelial cells. Taken together, these data indicated that the FGF2-FGF receptor signal cascade in the prostate gland may be one of the pathways stimulating the proliferation of basal epithelial cells in the absence of androgens.

The stroma-a key regulator in prostate function and malignancy

Prostate cancer is a very common and highly unpredictable form of cancer. Whereas many prostate cancers are slow growing and could be left without treatment, others are very aggressive. Additionally, today there is no curative treatment for prostate cancer patients with local or distant metastasis. Identification of new, improved prognostic and diagnostic biomarkers for prostate cancer and the finding of better treatment strategies for metastatic prostate cancer is therefore highly warranted. Interactions between epithelium and stroma are known to be important already during prostate development and this interplay is critical also in development, progression of primary tumors and growth of metastases. It is therefore reasonable to expect that future biomarkers and therapeutic targets can be identified in the prostate tumor and metastasis stroma and this possibility should be further explored.

Androgen-induced PSA expression requires not only activation of AR but also endogenous IGF-I or IGF-I/PI3K/Akt signaling in human prostate cancer epithelial cells

BACKGROUND

Prostate cancer (PrCa) risk is positively associated with levels of insulin-like growth factor I (IGF-I) and prostate specific antigen (PSA), both androgen receptor (AR) signaling target genes in PrCa cells. Although activated AR is required for androgen-induction of expression of both genes, effects of the IGF-I signaling pathways on the androgen-induction of PSA have not been studied.

METHODS

Human prostate stromal and epithelial cancer cells were treated alone or in coculture with steroid hormone and/or inhibitors. Gene or protein expression was analyzed by real time RT-PCR or Western blotting of lysates, nuclear extracts, or immunoprecipitated products.

RESULTS

In PrCa epithelial cells, endogenous IGF-I, significantly induced by R1881, was required for R1881-induction of PSA. Increased IGF-I correlated with accumulation of cytoplasmic dephospho β-catenin (CPDP β-catenin), a co-activator of AR signaling. Exogenous IGF-I enhanced R1881-induced PSA and accumulation of CPDP β-catenin in LAPC-4 cells. Functional depletion of IGF-I or IGF-I receptor diminished PSA induction. Induction of IGF-I reached a plateau while PSA consecutively increased. Inhibiting PI3K abolished R1881-induced Akt phosphorylation, CPDP and nuclear β-catenin and nuclear association of AR/β-catenin, consequently abrogating R1881-induced expression of IGF-I and/or PSA.

CONCLUSIONS

By integrating androgen, IGF-I and β-catenin signaling pathways, these data reveal that androgen-induced PSA expression requires activation of AR and endogenous IGF-I or IGF-I/PI3K/Akt signaling, suggesting a positive feedback cycle for increased production of PSA associated with PrCa.

Diabetes, growth hormone-insulin-like growth factor pathways and association to benign prostatic hyperplasia

Diabetes significantly increases the risk of benign prostatic hyperplasia (BPH) and low urinary tract symptoms (LUTS). The major endocrine aberration in connection with the metabolic syndrome is hyperinsulinemia. Insulin is an independent risk factor and a promoter of BPH. Insulin resistance may change the risk of BPH through several biological pathways. Hyperinsulinemia stimulates the liver to produce more insulin-like growth factor (IGF), another mitogen and an anti-apoptotic agent which binds insulin receptor/IGF receptor and stimulates prostate growth. The levels of IGFs and IGF binding proteins (IGFBPs) in prostate tissue and in blood are associated with BPH risk, with the regulation of circulating androgen and growth hormone. Stromal-epithelial interactions play a critical role in the development and growth of the prostate gland and BPH. Previously, we have shown that the expression of c-Jun in the fibroblastic stroma can promote secretion of IGF-I, which stimulates prostate epithelial cell proliferation through activating specific target genes. Here, we will review the epidemiologic, clinical, and molecular findings which have evaluated the relation between diabetes and development of BPH.

Altered prostate epithelial development and IGF-1 signal in mice lacking the androgen receptor in stromal smooth muscle cells

BACKGROUND

Androgens and the androgen receptor (AR) play critical roles in the prostate development via mesenchymal-epithelial interactions. Smooth muscle cells (SMC), differentiated from mesenchyme, are one of the basic components of the prostate stroma. However, the roles of smooth muscle AR in prostate development are still obscure.

METHODS

We established the smooth muscle selective AR knockout (SM-ARKO) mouse model using the Cre-loxP system, and confirmed the ARKO efficiency at RNA, DNA and protein levels. Then, we observed the prostate morphology changes, and determined the epithelial proliferation, apoptosis, and differentiation. We also knocked down the AR in a prostate smooth muscle cell line (PS-1) to confirm the in vivo findings and to probe the mechanism.

RESULTS

The AR was selectively and efficiently knocked out in the anterior prostates of SM-ARKO mouse. The SM-ARKO prostates have defects with loss of infolding structures, and decrease of epithelial proliferation, but with little change of apoptosis and differentiation. The mechanism studies showed that IGF-1 expression level decreased in the SM-ARKO prostates and AR-knockdown PS-1 cells. The decreased IGF-1 expression might contribute to the defective development of SM-ARKO prostates.

CONCLUSIONS

The AR in SMCs plays important roles in the prostate development via the regulation of IGF-1 signal.

Local insulin-like growth factor-I of ventral prostate was upregulated during long-term castration and may function through the autocrine system

The insulin-like growth factor I (IGF-I) is one of the main mitogens and anti-apoptotic factors, which has an important role in cell proliferation, inhibiting cell death in prostate cancer (PCa), and may act as a replacement for androgen after castration. Characterizing the changes in local IGF-I levels in the prostate after castration, is therefore of great importance for doctors to guide and select therapy models after surgical castration in men with PCa. The present study was performed to detect IGF-I of local ventral prostate (VP) at intervals up to 24 weeks after castration by a combination of reverse transcriptase PCR, western-blot, immunohistochemistry and immunofluorescence. We found IGF-I to be decreased sharply after castration and that mRNA and protein levels reached their minimum at 2 days and 5 days, respectively. The level of IGF-I increased gradually and although mRNA levels remained high for longer than 2 weeks, protein levels remained high for longer than 4 weeks. The epithelium cells of VP express IGF-I and its receptor longer than 2 weeks after castration. These findings suggested that although IGF-I of local VP decreases sharply in short-stage castration, its levels increase gradually and remain at high levels at least until 24 weeks. IGF-I synthesized mainly from epithelial cells, which may function through the autocrine system longer than 2 weeks castration.

Effect of combined hormonal and insulin therapy on the steroid hormone receptors and growth factors signalling in diabetic mice prostate

Diabetes causes harmful effects on prostatic morphology and function. However, there still are doubts about the occurrence of various diseases in the prostate, as well as abnormal angiogenesis in relation to diabetes. Thus, the aim of this study was to correlate and quantify the level of the steroid hormone receptors and the angiogenic and antiangiogenic factors in non-obese diabetic mice (Nod) after combined hormonal and insulin therapy. Sixty mice were divided into six groups after 20 days of diabetes: the control group received 0.9% NaCl, as did the diabetic group. The diabetic-insulin group received insulin, the diabetic-testosterone group received testosterone cypionate, the diabetic-oestrogen group received 17β-oestradiol, and the diabetic-insulin-testosterone-oestrogen group received insulin, testosterone and oestrogen simultaneously. After 20 days, the ventral lobe was processed for immunocytochemical and hormonal analyses. The results showed that the lowest serum testosterone and androgen receptor levels were found in the diabetic group and the highest testosterone and androgen receptor levels in the diabetic-insulin-testosterone-oestrogen group. The serum oestrogen level and its receptor showed changes opposite to those of testosterone and its receptor. The endostatin reactivity was mainly decreased in diabetic mice. The greatest IGFR-1 and VEGF reactivities occurred in diabetic mice. Thus, diabetes led to the prostatic hormonal imbalance, affecting molecular dynamics and angiogenesis in this organ. Combined insulin and steroid hormone therapy partially restored the hormonal and angiogenic imbalance caused by diabetes.

Proliferative, structural and molecular features of the Mdx mouse prostate

The prostate is fundamental to the male reproductive process, and the stroma-epithelium interaction has an important role in prostate maintenance. Studies suggest that dystroglycan (DG) plays a role in cancer development in various organs. Thus, the aims of this work were to characterize morphological and proliferative features of the prostatic stroma and epithelium of mdx mice; to verify the immunolocalization of the α and β DG, IGF-1 and laminin α3 receptors; and to relate those structural and molecular events to prostate pathogenesis and to verify the viability of this experimental model in prostate studies. Thirty male mice (mdx and C57BL10/Uni) were divided into control and mdx groups. Samples from the ventral prostate were collected for immunological, Western Blotting, transmission electron microscopy and morphometric analyses. Oestradiol and testosterone measurements were verified. The results showed diminished testosterone and increased oestradiol levels in the mdx group. Atrophied cells and hypertrophied stroma were seen in the mdx mice. Weak α and β DG and laminin α3 immunolocalization was demonstrated in the mdx group. Intense insulin-like growth factor receptor α-1 (IGFRα-1) localization was identified in the mdx animals. Thus, mdx animals showed changes in molecular and structural integrity and proliferation signals, leading to glandular homoeostasis imbalance, and compromise of prostate function. Also, the steroid hormone imbalance and the increased IGF-1 receptor level detected in mdx mice could be considered as a crucial factor in the pathogenesis of prostatic disorders.

Mast cells are novel independent prognostic markers in prostate cancer and represent a target for therapy

Mast cells affect growth in various human tumors, but their role in prostate cancer (PC) is unclear. Here, we identify mast cells as independent prognostic markers in PC using a large cohort of untreated PC patients with a long follow-up. By analyzing mast cells in different tissue compartments, our data indicate that intratumoral and peritumoral mast cells have anti- opposed to protumor properties. Intratumoral mast cells negatively regulate angiogenesis and tumor growth, whereas peritumoral mast cells stimulate the expansion of human prostate tumors. We also observed mast cell recruitment particularly to the peritumoral compartment in men during the formation of castrate-resistant prostate tumors. In our ortothopic rat model, mast cells accumulated in the peritumoral tissue where they enhanced angiogenesis and tumor growth. In line with this, prostate mast cells expressed high levels of the angiogenic factor FGF-2. Similar to the situation in men, mast cells infiltrated rat prostate tumors that relapsed after initially effective castration treatment, concurrent with a second wave of angiogenesis and an up-regulation of FGF-2. We conclude that mast cells are novel independent prognostic markers in PC and affect tumor progression in animals and patients. In addition, peritumoral mast cells provide FGF-2 to the tumor micro environment, which may contribute to their stimulating effect on angiogenesis.

Characterization and functional role of the stroma compartment in prostate tumors

Evaluation of: Dakhova O, Ozen M, Creighton CJ et al.: Global gene expression analysis of reactive stroma in prostate cancer. Clin. Cancer Res. 15, 3979–3989 (2009). Prostate tumors are composed of many cell types, yet the biological significances of the different nonepithelial cells have been largely overlooked. According to recent studies, however, the stroma, which constitutes a substantial part of the tumor volume, plays an important role during the initiation, progression, metastasis and metastatic growth of prostate cancers. To explore this further, Dakhova and co-workers compared gene expression in laser microdissected normal peripheral zone stroma with stroma in peripheral zone cancers (only those with reactive stroma grade 3). A total of 544 genes were upregulated and 606 genes downregulated in tumor stroma. The cancer stroma showed signs of formation of nerves, increased number of stem cells, and responses to DNA damage. Further studies are needed to explore the functional consequences of this, particularly the role of nerves. If these stroma changes can be used as prognostic markers, as targets for therapy, and if similar changes occur in metastases also need to be explored.

The prostatic environment suppresses growth of androgen-independent prostate cancer xenografts: an effect influenced by testosterone

BACKGROUND

Interactions between prostate cancer cells and their surrounding stroma play an important role in the growth and maintenance of prostate tumors. To elucidate this further, we investigated how growth of androgen-dependent (AD) LNCaP and androgen-independent (AI) LNCaP-19 prostate tumors was affected by different microenvironments and androgen levels.

METHODS

Tumor cells were implanted subcutaneously and orthotopically in intact and castrated immunodeficient mice. Orthotopic tumor growth was followed by magnetic resonance imaging (MRI). Gene expression in the tumors was evaluated by means of microarray analysis and microvessel density (MVD) was analyzed using immunohistochemistry.

RESULTS

The results showed that LNCaP-19 tumors grew more rapidly at the subcutaneous site than in the prostate, where tumors were obviously inhibited. Castration of the mice did not affect ectopic tumors but did result in increased tumor growth in the prostatic environment. This effect was reversed by testosterone treatment. In contrast to LNCaP-19, the LNCaP cells grew rapidly in the prostate and castration reduced tumor development. Gene expression analysis of LNCaP-19 tumors revealed an upregulation of genes, inhibiting tumor growth (including ADAMTS1, RGS2 and protocadherin 20) and a downregulation of genes, promoting cell adhesion and metastasis (including N-cadherin and NRCAM) in the slow-growing orthotopic tumors from intact mice.

CONCLUSIONS

The results show that the prostatic environment has a varying impact on AD and AI tumor xenografts. Data indicate that the androgen-stimulated prostatic environment limits growth of orthotopic AI tumors through induction of genes that inhibit tumor growth and suppression of genes that promote cell adhesion and metastasis.

Low stroma androgen receptor level in normal and tumor prostate tissue is related to poor outcome in prostate cancer patients

BACKGROUND

The role of androgen receptors (ARs) in the prostate tumor cell environment is largely unknown.

METHODS

AR immunostaining was evaluated in relation to stroma morphology, expression of AR co-activator ARA55, tumor characteristics and clinical outcome in normal and prostate cancer (PCa) tissue obtained at transurethral resection in men treated with expectancy, and in diagnostic transrectal core biopsies in men treated with surgical castration. Stroma composition was studied by Masson-trichrome and desmin staining. Levels of AR and ARA55 mRNA were quantified by laser micro-dissection and RT-PCR.

RESULTS

The percentage of cells with positive nuclear AR immunostaining in the tumor and normal stroma was inversely related to Gleason score, tumor size, tumor stage, metastasis, response to castration therapy, and cancer-specific survival. The AR staining in the normal stroma provided independent prognostic information in Cox multiple linear regression analysis. Loss of stroma AR staining was linked to low expression of ARA55 in stroma smooth muscle cells, and in tumors also to gradual disappearance of this cell type.

CONCLUSIONS

PCa aggressiveness and efficacy of castration therapy are related to AR levels in the tumor stroma and importantly to AR levels in the surrounding normal prostate tissue stroma. .

Stroma-epithelium crosstalk in prostate cancer

The critical role played by stroma-epithelium crosstalk in carcinogenesis and progression of prostate cancer has been increasingly recognized. These interactions are mediated by a variety of paracrine factors secreted by cancer cells and/or stromal cells. In human prostate cancer, reactive stroma is characterized by an increase in myofibroblasts and a corresponding amplification of extracellular matrix production and angiogenesis. Permanent genetic mutations have been reported in stromal cells as well as in tumour cells. Transforming growth factor-beta, vascular endothelial growth factor, platelet-derived growth factor and fibroblast growth factor signalling pathways are involved in the process of angiogenesis, whereas hepatocyte growth factor, insulin-like growth factor-1, epidermal growth factor, CXC12 and Interleukin-6 play active roles in the progression, androgen-independent conversion and distal metastasis of prostate cancer. Some soluble factors have reciprocal interactions with androgens and the androgen receptor (AR), and can even activate AR in the absence of the androgen ligand. In this article, we review the complex interactions between cancer cells and the surrounding microenvironment, and discuss the potential therapeutic targets in the stromal compartment of prostate cancer.

Androgen receptor and growth factor signaling cross-talk in prostate cancer cells

Androgens promote the growth and differentiation of prostate cells through ligand activation of the androgen receptor (AR). Sensitization of the androgenic response by multifunctional growth factor signaling pathways is one of the mechanisms via which AR contributes to the emergence of androgen-independent prostate tumors. The ability of AR to cross-talk with key growth factor signaling events toward the regulation of cell cycle, apoptosis, and differentiation outcomes in prostate cancer cells is established. In this paper, we review the functional interaction between AR and an array of growth factor signal transduction events (including epidermal growth factor; fibroblast growth factor; IGF1; vascular endothelial growth factor; transforming growth factor-beta) in prostate tumors. The significance of this derailed cross-talk between androgens and key signaling networks in prostate cancer progression and its value as a therapeutic forum targeting androgen-independent metastatic prostate cancer is discussed.

Prosaposin is an AR-target gene and its neurotrophic domain upregulates AR expression and activity in prostate stromal cells

Recent studies have introduced prosaposin (PSAP) as a pleiotrophic growth factor for prostate cancer (PCa). We have previously reported that PSAP or one of its known active molecular derivatives, saposin C functions as an androgen-agonist and androgen-regulated gene (ARG) for androgen-sensitive (AS) PCa cell lines. Due to the potential significance of androgen receptor (AR)-expressing stroma in PCa, we evaluated a possible bi-directional paracrine regulatory interactions between DHT and PSAP in AR-positive prostate stromal (PrSt) cells. We report that saposin C in a ligand-independent manner increased AR expression, its nuclear content, and tyrosine phosphorylation. DHT treatment of PrSt cells increased PSAP expression. We also demonstrated both serum- and androgen-inducibility of a previously characterized hormone-responsive element (HRE) located in the proximal region of PSAP promoter. In addition, conditioned-media derived from PrSt cells and bone fibroblasts (i.e., MSF) differentially increased PSAP-promoter activity in androgen-independent (AI) PC-3 and AS LNCaP cells. Our data for the first time demonstrate that not only saposin C or PSAP regulates AR expression/activity, but also function as an ARG in PrSt. Ligand-independent activation of AR by PSAP or saposin C in PCa and stromal cells may contribute not only to prostate carcinogenesis at an early stage, but also in AI progression of the disease in an androgen-deprived tumor microenvironment.

Androgen receptor signalling in prostate: effects of stromal factors on normal and cancer stem cells

The prostate gland is the most common site for cancer in males within the developed world. Androgens play a vital role in prostate development, maintenance of tissue function and pathogenesis of prostate disease. The androgen receptor signalling pathway facilitates that role in both the epithelial compartment and in the underlying stroma. Stroma is a key mediator of androgenic effects upon the epithelium and can regulate both the fate of the epithelial stem cell and potentially the initiation and progression of prostate cancer. Different groups of growth factors are expressed by stroma, which control proliferation, and differentiation of prostate epithelium demonstrating a critical role for stroma in epithelial growth and homeostasis. Paracrine stromal proteins may offer the possibility to control tumour stem cell growth and could permit prostate specific targeting of both therapies and of androgen responsive proteins. The effect of 5alpha-dihydrotestosterone, the more potent metabolite of testosterone, on expression of androgen-regulated genes in stroma from benign prostatic hyperplasia is a key mediator of epithelial cell fate. Global gene expression arrays have recently identified new candidate genes in androgen responsive stroma, some of which have androgen receptor binding sites in their promoter regions. Some of these genes have direct androgen receptor binding ability.

Prostate stem cells and benign prostatic hyperplasia

Pharmacological approaches are available to medically-managed patients with symptomatic BPH before surgical intervention is required. These include daily treatment with alpha-blockers and 5-alpha-reductase inhibitors alone or in combination. These medical approaches have two major problems. First, treatments are chronic and must be taken daily. Second, there are significant financial costs and quality of life issues for such chronic treatments. Is it possible to develop effective acute therapy for symptomatic BPH without the long-term androgen deprivation-induced side effects? Two seminal but rarely cited studies of Walsh [Peters, Walsh: N Engl J Med 317:599-604, 1987] and Coffey et al. [Sufrin et al.: Invest Urol 13:418-423, 1976], combined with the growing understanding of the stem cell organization of the prostate stromal (S) and epithelial (E) compartments and their reciprocal paracrine and autocrine interactions provides the rationale for an acute approach.The Walsh study documents that: (1) androgen deprivation disrupts the reciprocal interaction between the prostate S and E thereby decreasing the weight of both compartments and (2) once BPH develops, androgen deprivation does not decrease the number of stem cell units in either the S or E compartments since subsequent androgen restoration fully restores the enlarged gland. The Coffey study documents that acute androgen deprivation sensitizes S-E interactions to radiation induced disruptions so that following radiation, androgen restoration does not induce full gland regrowth. Therefore, effective therapy for symptomatic BPH should be achievable by acute treatment with reversible androgen deprivation for a limited period followed by a single dose of conformal external beam radiation before allowing the man to recovery his normal serum testosterone.

A stroma targeted therapy enhances castration effects in a transplantable rat prostate cancer model

BACKGROUND

Castration results in a major involution of the normal prostate gland. This process is initiated by effects in the prostate stroma and vasculature. Castration-induced regression of androgen sensitive prostate tumors is however less prominent and hypothetically this could be related to a limited stromal/vascular response. We therefore used animal tumor models to explore the importance of stroma and vascular effects, and if castration effects could be enhanced by a simultaneous therapy targeting the tumor stroma.

METHODS

Using rats with Dunning PAP and H tumors, stereological methods, immunohistochemistry, and Western blotting, we studied the tumor response 7 and 28 days after castration and after the addition of stroma targeted therapies.

RESULTS

In the normal ventral prostate (VP) nuclear androgen receptors (AR) were rapidly downregulated after castration. In contrast, the Dunning tumors downregulated the AR in the cancerous epithelium, but not in the surrounding stroma. Vascular regulators such as the angiopoietins, tie 2, and PDGF-Rbeta were not decreased in the stroma after castration, as observed in the VP, creating an environment that prevents vascular involution. When a tumor stroma targeted therapy inhibiting the tie 2 receptor and the PDGF-Rbeta simultaneously was added to castration it resulted in a decreased vascular density, increased tumor cell apoptosis and decreased tumor growth compared to castration alone.

CONCLUSIONS

The stroma in highly differentiated androgen sensitive Dunning tumors is apparently androgen insensitive. If this unresponsive stroma is targeted the effects of castration can be enhanced.

Nuclear androgen receptors recur in the epithelial and stromal compartments of malignant and non-malignant human prostate tissue several months after castration therapy

BACKGROUND

As changed paracrine support from androgen receptor (AR)-positive cells in the prostate stroma contribute to castration-induced glandular involution, we examined if the subsequent relapse to androgen-independent epithelial cell growth could be related to reactivation of AR signaling in the stroma.

MATERIALS AND METHODS

Human prostate tissue taken before, within 14 days, and at suspected local tumor relapse after surgical castration therapy was immunostained for AR.

RESULTS

Castration initially decreased nuclear AR staining in epithelial and stroma cells, in both tumor and non-malignant tissue, but after some months, it reappeared.

CONCLUSIONS

Local tumor relapse was associated with reappearance of nuclear AR not only in tumor epithelial cells but also in the tumor stroma. Reappearance of nuclear AR in non-malignant prostate cells may be a physiological response to long-term systemic androgen ablation that could influence tumor growth.

The basic biochemistry and molecular events of hormone therapy

Data regarding the molecular response of prostate cancer to hormone therapy continue to emerge, identifying a complex network of autocrine and paracrine signaling events mediating the tumor response to androgen suppression. Emerging data provide insight into cellular pathways important in the apoptotic response to therapy, including the transforming growth factor-beta, insulin-like growth factor-1, and vascular endothelial growth factor signaling axes. They also reveal mechanisms of direct antitumor cytotoxicity mediated by various hormonal agents and highlight the importance of developing antiandrogens capable of irreversibly inhibiting the androgen receptor. Accumulated data emphasize the presence of residual androgens and persistent activation of androgen receptor signaling in advanced prostate tumors despite castration. These factors suggest that a multitargeted treatment approach designed to ablate all contributions to the androgen receptor signaling axis within the prostate tumor microenvironment will be required in order for hormonal therapy to achieve optimal antitumor efficacy.