Androgen levels increase by intratumoral de novo steroidogenesis during progression of castration-resistant prostate cancer

Simvastatin Therapy for Drug Repositioning to Reduce the Risk of Prostate Cancer Mortality in Patients With Hyperlipidemia

Prostate cancer (PCa) is one of the most commonly diagnosed cancers in the western world, and the mortality rate from PCa in Asia has been increasing recently. Statins are potent inhibitors of 3-hydroxy-3-methyl glutaryl coenzyme A (HMG-CoA) reductase and are commonly used for treating hyperlipidemia, with beneficial effects for cardiovascular disease and they also exhibit anti-cancer activity. However, the protective effects of statins against PCa are controversial. In this study, we investigated the effect of two types of statins (simvastatin and lovastatin) and the mortality rate of PCa patients by using the Taiwan National Health Insurance Research Database (NHIRD). A total of 15,264 PCa patients with hyperlipidemia records and medical claims from the Registry of Catastrophic Illness were enrolled. The patients were divided into two cohorts based on their statin use before the diagnosis of PCa: statin users (n = 1,827) and non-statin users (n = 1,826). The results showed that patients who used statins exhibited a significantly reduced risk of mortality from PCa [adjusted hazard ratio (HR) = 0.84, 95% CI = 0.73–0.97]. Analysis of the cumulative defined daily dose (DDD) indicated that patients who were prescribed simvastatin ≥ 180 DDD had a dramatically decreased risk of death from PCa (adjusted HR = 0.63; 95% CI = 0.51–0.77). This population-based cohort study demonstrated that statin use significantly decreased the mortality of PCa patients, and that this risk was inversely associated with the cumulative DDD of simvastatin therapy. The results of this study revealed that statins may be used for drug repositioning and in the development of a feasible approach to prevent death from PCa.

Orphan nuclear receptor TLX contributes to androgen insensitivity in castration-resistant prostate cancer via its repression of androgen receptor transcription

The metastatic castration-resistant prostate cancer (CRPC) is a lethal form of prostate cancer, in which the expression of androgen receptor (AR) is highly heterogeneous. Indeed, lower AR expression and attenuated AR signature activity is shown in CRPC tissues, especially in the subset of neuroendocrine prostate cancer (NEPC) and prostate cancer stem-like cells (PCSCs). However, the significance of AR downregulation in androgen insensitivity and de-differentiation of tumor cells in CRPC is poorly understood and much neglected. Our previous study shows that the orphan nuclear receptor TLX (NR2E1), which is upregulated in prostate cancer, plays an oncogenic role in prostate carcinogenesis by suppressing oncogene-induced senescence. In the present study, we further established that TLX exhibited an increased expression in metastatic CRPC. Further analyses showed that overexpression of TLX could confer resistance to androgen deprivation and anti-androgen in androgen-dependent prostate cancer cells in vitro and in vivo, whereas knockdown of endogenous TLX could potentiate the sensitivity to androgen deprivation and anti-androgen in prostate cancer cells. Our study revealed that the TLX-induced resistance to androgen deprivation and anti-androgen was mediated through its direct suppression of AR gene transcription and signaling in both androgen-stimulated and -unstimulated prostate cancer cells. We also characterized that TLX could bind directly to AR promoter and repress AR transcription by recruitment of histone modifiers, including HDAC1, HDAC3, and LSD1. Together, our present study shows, for the first time, that TLX can contribute to androgen insensitivity in CRPC via repression of AR gene transcription and signaling, and also implicates that targeting the druggable TLX may have a potential therapeutic significance in CRPC management, particularly in NEPC and PCSCs.

Dehydroepiandrosterone (DHEA)-SO4 Depot and Castration-Resistant Prostate Cancer

Dehydroepiandrosterone (DHEA)-SO₄ of adrenal origin is the major C19 steroid in the serum. It is a precursor of intratumoral androgen biosynthesis in patients with advanced prostate cancer following chemical or surgical castration. DHEA is a product of the P450c17 (17α-hydroxylase-17,20-lyase) enzyme. Despite inhibition of P450c17 with new agents, e.g., Abiraterone acetate, Orterenol, and Galeterone, the level of enzyme inhibition rarely exceeds 90% leaving behind a significant depot for androgen biosynthesis within the tumor. For DHEA-SO₄ to be utilized there is uptake by organic anion transporter polypeptides, deconjugation catalyzed by steroid sulfatase, and adaptive upregulation of prostate steroidogenic enzymes that will convert DHEA into either testosterone or dihydrotestosterone. The depot of DHEA-SO₄ that remains after P450c17 inhibition and the adaptive responses that occur within the tumor to promote DHEA utilization contribute to mechanisms of drug resistance observed with P450c17 inhibitors. Knowledge of these mechanisms identify new targets for therapeutics that could be used to surmount drug resistance in prostate cancer.

Modulation of AKR1C2 by curcumin decreases testosterone production in prostate cancer

Intratumoral androgen biosynthesis has been recognized as an essential factor of castration‐resistant prostate cancer. The present study investigated the effects of curcumin on the inhibition of intracrine androgen synthesis in prostate cancer. Human prostate cancer cell lines, LNCaP and 22Rv1 cells were incubated with or without curcumin after which cell proliferation was measured at 0, 24, 48 and 72 hours, respectively. Prostate tissues from the transgenic adenocarcinoma of the mouse prostate (TRAMP) model were obtained after 1‐month oral administration of 200 mg/kg/d curcumin. Testosterone and dihydrotestosterone concentrations in LNCaP prostate cancer cells were determined through LC‐MS/MS assay. Curcumin inhibited cell proliferation and induced apoptosis of prostate cancer cells in a dose‐dependent manner. Curcumin decreased the expression of steroidogenic acute regulatory proteins, CYP11A1 and HSD3B2 in prostate cancer cell lines, supporting the decrease of testosterone production. After 1‐month oral administration of curcumin, Aldo‐Keto reductase 1C2 (AKR1C2) expression was elevated. Simultaneously, decreased testosterone levels in the prostate tissues were observed in the TRAMP mice. Meanwhile, curcumin treatments considerably increased the expression of AKR1C2 in prostate cancer cell lines, supporting the decrease of dihydrotestosterone. Taken together, these results suggest that curcumin's natural bioactive compounds could have potent anticancer properties due to suppression of androgen production, and this could have therapeutic effects on prostate cancer.

Inhibition of dihydrotestosterone synthesis in prostate cancer by combined frontdoor and backdoor pathway blockade

Androgen deprivation therapy (ADT) is palliative and prostate cancer (CaP) recurs as lethal castration-recurrent/resistant CaP (CRPC). One mechanism that provides CaP resistance to ADT is primary backdoor androgen metabolism, which uses up to four 3α-oxidoreductases to convert 5α-androstane-3α,17β-diol (DIOL) to dihydrotestosterone (DHT). The goal was to determine whether inhibition of 3α-oxidoreductase activity decreased conversion of DIOL to DHT. Protein sequence analysis showed that the four 3α-oxidoreductases have identical catalytic amino acid residues. Mass spectrometry data showed combined treatment using catalytically inactive 3α-oxidoreductase mutants and the 5α-reductase inhibitor, dutasteride, decreased DHT levels in CaP cells better than dutasteride alone. Combined blockade of frontdoor and backdoor pathways of DHT synthesis provides a therapeutic strategy to inhibit CRPC development and growth.

PTEN Loss Promotes Intratumoral Androgen Synthesis and Tumor Microenvironment Remodeling via Aberrant Activation of RUNX2 in Castration-Resistant Prostate Cancer

Purpose: Intratumoral androgen synthesis (IAS) is a key mechanism promoting androgen receptor (AR) reactivation and antiandrogen resistance in castration-resistant prostate cancer (CRPC). However, signaling pathways driving aberrant IAS remain poorly understood.Experimental Design: The effect of components of the AKT-RUNX2-osteocalcin (OCN)-GPRC6A-CREB signaling axis on expression of steroidogenesis genes CYP11A1 and CYP17A1 and testosterone level were examined in PTEN-null human prostate cancer cell lines. Pten knockout mice were used to examine the effect of Runx2 heterozygous deletion or abiraterone acetate (ABA), a prodrug of the CYP17A1 inhibitor abiraterone on Cyp11a1 and Cyp17a1 expression, testosterone level and tumor microenvironment (TME) remodeling in vivoResults: We uncovered that activation of the AKT-RUNX2-OCN-GPRC6A-CREB signaling axis induced expression of CYP11A1 and CYP17A1 and testosterone production in PTEN-null prostate cancer cell lines in culture. Deletion of Runx2 in Pten homozygous knockout prostate tumors decreased Cyp11a1 and Cyp17a1 expression, testosterone level, and tumor growth in castrated mice. ABA treatment also inhibited testosterone synthesis and alleviated Pten loss-induced tumorigenesis in vivoPten deletion induced TME remodeling, but Runx2 heterozygous deletion or ABA treatment reversed the effect of Pten loss by decreasing expression of the collagenase Mmp9.Conclusions: Abnormal RUNX2 activation plays a pivotal role in PTEN loss-induced IAS and TME remodeling, suggesting that the identified signaling cascade represents a viable target for effective treatment of PTEN-null prostate cancer, including CRPC. Clin Cancer Res; 24(4); 834-46. ©2017 AACR.

Differential gene expression induced by anti-cancer agent plumbagin is mediated by androgen receptor in prostate cancer cells

Treatment of mice harboring PTEN-P2 tumors in the prostate or on prostate tissue in vivo with 5-hydroxy-2-methyl-1,4-naphthoquinone, also known as plumbagin, results in tumor regression in castrated mice, but not in intact mice. This suggested that dihydrotestosterone (DHT) production in the testes may prevent cell death due to plumbagin treatment, but the underlying mechanism is not understood. We performed RNA-seq analysis on cells treated with combinations of plumbagin and DHT, and analyzed differential gene expression, to gain insight into the interactions between androgen and plumbgin. DHT and plumbagin synergize to alter the expression of many genes that are not differentially regulated by either single agent when used alone. These experiments revealed that, for many genes, increases in mRNAs caused by DHT are sharply down-regulated by plumbagin, and that many transcripts change in response to plumbagin in a DHT-dependent manner. This suggests that androgen receptor mediates some of the effects of plumbagin on gene expression.

Nuclear Receptor LRH-1 Functions to Promote Castration-Resistant Growth of Prostate Cancer via Its Promotion of Intratumoral Androgen Biosynthesis

Targeting of steroidogenic enzymes (e.g., abiraterone acetate targeting CYP17A1) has been developed as a novel therapeutic strategy against metastatic castration-resistant prostate cancer (CRPC). However, resistance to steroidal inhibitors inevitably develops in patients, the mechanisms of which remain largely unknown. Liver receptor homolog-1 (LRH-1, NR5A2) is a nuclear receptor, originally characterized as an important regulator of some liver-specific metabolic genes. Here, we report that LRH-1, which exhibited an increased expression pattern in high-grade prostate cancer and CRPC xenograft models, functions to promote de novo androgen biosynthesis via its direct transactivation of several key steroidogenic enzyme genes, elevating intratumoral androgen levels and reactivating AR signaling in CRPC xenografts as well as abiraterone-treated CRPC tumors. Pharmacologic inhibition of LRH-1 activity attenuated LRH-1-mediated androgen deprivation and anti-androgen resistance of prostate cancer cells. Our findings not only demonstrate the significant role of LRH-1 in the promotion of intratumoral androgen biosynthesis in CRPC via its direct transcriptional control of steroidogenesis, but also suggest targeting LRH-1 could be a potential therapeutic strategy for CRPC management.Significance: These findings not only demonstrate the significant role of the nuclear receptor LRH-1 in the promotion of intratumoral androgen biosynthesis in CRPC via its direct transcriptional control of steroidogenesis, but also suggest targeting LRH-1 could be a potential therapeutic strategy for CRPC management. Cancer Res; 78(9); 2205-18. ©2018 AACR.

Lipocalin 2 over-expression facilitates progress of castration-resistant prostate cancer via improving androgen receptor transcriptional activity

BACKGROUND

Castration-resistant prostate cancer (CRPC) is the lethal phenotype of prostate cancer. Lipocalin 2 (LCN2) is aberrantly expressed in many cancers including primary prostate cancer (PCa), but its role in CRPC has not been reported.

RESULTS

LCN2 expression was upregulated in human primary PCa and CRPC tissues. Overexpression of LCN2 promoted C4-2B and 22RV1 cell proliferation while knockdown of LCN2 markedly inhibited C4-2B and 22RV1 cell growth. LCN2 overexpression led to increased AR downstream gene SLC45A3 without upregulating AR expression. In the xenograft model, overexpression of LCN2 significantly promoted tumor growth.

METHODS

LCN2 expression was detected in primary PCa and CRPC tissues and cell lines C4-2B and 22RV1 using immunohistochemistry and western blotting, respectively. Serum LCN2 level was detected vi ELISA. Lentiviruses-mediated over-expression of LCN2 and LCN2 knockdown were performed in CRPC cell lines. Expressions of androgen receptor (AR) downstream genes was examined in cell lines, in CRPC tissues, and in animal models.

CONCLUSION

LCN2 could facilitate cell proliferation of CRPC via AR transcriptional activity. LCN2 could be a novel target in CRPC.

A unifying biology of sex steroid-induced apoptosis in prostate and breast cancers

Prostate and breast cancer are the two cancers with the highest incidence in men and women, respectively. Here, we focus on the known biology of acquired resistance to antihormone therapy of prostate and breast cancer and compare laboratory and clinical similarities in the evolution of the disease. Laboratory studies and clinical observations in prostate and breast cancer demonstrate that cell selection pathways occur during acquired resistance to antihormonal therapy. Following sex steroid deprivation, both prostate and breast cancer models show an initial increased acquired sensitivity to the growth potential of sex steroids. Subsequently, prostate and breast cancer cells either become dependent upon the antihormone treatment or grow spontaneously in the absence of hormones. Paradoxically, the physiologic sex steroids now kill a proportion of selected, but vulnerable, resistant tumor cells. The sex steroid receptor complex triggers apoptosis. We draw parallels between acquired resistance in prostate and breast cancer to sex steroid deprivation. Clinical observations and patient trials confirm the veracity of the laboratory studies. We consider therapeutic strategies to increase response rates in clinical trials of metastatic disease that can subsequently be applied as a preemptive salvage adjuvant therapy. The goal of future advances is to enhance response rates and deploy a safe strategy earlier in the treatment plan to save lives. The introduction of a simple evidence-based enhanced adjuvant therapy as a global healthcare strategy has the potential to control recurrence, reduce hospitalization, reduce healthcare costs and maintain a healthier population that contributes to society.

Identification of valid reference genes for mRNA and microRNA normalisation in prostate cancer cell lines

RT-qPCR offers high sensitivity, for accurate interpretations of qPCR results however, normalisation using suitable reference genes is fundamental. Androgens can regulate transcriptional expression including reference gene expression in prostate cancer. In this study, we evaluated ten mRNA and six non-protein coding RNA reference genes in five prostate cell lines under varied dihydrotestosterone (DHT) treatments. We validated the effects of DHT-treatments using media containing charcoal-stripped serum prior to DHT stimulation on the test samples by Western blot experiments. Reference gene expression stability was analysed using three programs (geNorm, NormFinder and BestKeeper), and the recommended comprehensive ranking is provided. Our results reveal that ACTB and GAPDH, and miR-16 and miR-1228-3p are the most suitable mRNA and miRNA reference genes across all cell lines, respectively. Considering prostate cancer cell types, ACTB/GAPDH and ACTB/HPRT1 are the most suitable reference gene combinations for mRNA analysis, and miR-16/miR-1228-3p and RNU6-2/RNU43 for miRNA analysis in AR+, and AR− and normal cell lines, respectively. Comparison of relative target gene (PCA3 and miR-141) expression reveals different patterns depending on reference genes used for normalisation. To our knowledge, this is the first report on validation of reference genes under different DHT treatments in prostate cancer cells. This study provides insights for discovery of reliable DHT-regulated genes in prostate cells.

Estrogen receptor signaling in prostate cancer: Implications for carcinogenesis and tumor progression

BACKGROUND

The androgen receptor (AR) is the classical target for prostate cancer prevention and treatment, but more recently estrogens and their receptors have also been implicated in prostate cancer development and tumor progression.

METHODS

Recent experimental and clinical data were reviewed to elucidate pathogenetic mechanisms how estrogens and their receptors may affect prostate carcinogenesis and tumor progression.

RESULTS

The estrogen receptor beta (ERβ) is the most prevalent ER in the human prostate, while the estrogen receptor alpha (ERα) is restricted to basal cells of the prostatic epithelium and stromal cells. In high grade prostatic intraepithelial neoplasia (HGPIN), the ERα is up-regulated and most likely mediates carcinogenic effects of estradiol as demonstrated in animal models. The partial loss of the ERβ in HGPIN indicates that the ERβ acts as a tumor suppressor. The tumor promoting function of the TMPRSS2-ERG fusion, a major driver of prostate carcinogenesis, is triggered by the ERα and repressed by the ERβ. The ERβ is generally retained in hormone naïve and metastatic prostate cancer, but is partially lost in castration resistant disease. The progressive emergence of the ERα and ERα-regulated genes (eg, progesterone receptor (PR), PS2, TMPRSS2-ERG fusion, and NEAT1) during prostate cancer progression and hormone refractory disease suggests that these tumors can bypass the AR by using estrogens and progestins for their growth. In addition, nongenomic estrogen signaling pathways mediated by orphan receptors (eg, GPR30 and ERRα) has also been implicated in prostate cancer progression.

CONCLUSIONS

Increasing evidences demonstrate that local estrogen signaling mechanisms are required for prostate carcinogenesis and tumor progression. Despite the recent progress in this research topic, the translation of the current information into potential therapeutic applications remains highly challenging and clearly warrants further investigation.

Integrative molecular network analysis identifies emergent enzalutamide resistance mechanisms in prostate cancer

Recent work demonstrates that castration-resistant prostate cancer (CRPC) tumors harbor countless genomic aberrations that control many hallmarks of cancer. While some specific mutations in CRPC may be actionable, many others are not. We hypothesized that genomic aberrations in cancer may operate in concert to promote drug resistance and tumor progression, and that organization of these genomic aberrations into therapeutically targetable pathways may improve our ability to treat CRPC. To identify the molecular underpinnings of enzalutamide-resistant CRPC, we performed transcriptional and copy number profiling studies using paired enzalutamide-sensitive and resistant LNCaP prostate cancer cell lines. Gene networks associated with enzalutamide resistance were revealed by performing an integrative genomic analysis with the PAthway Representation and Analysis by Direct Reference on Graphical Models (PARADIGM) tool. Amongst the pathways enriched in the enzalutamide-resistant cells were those associated with MEK, EGFR, RAS, and NFKB. Functional validation studies of 64 genes identified 10 candidate genes whose suppression led to greater effects on cell viability in enzalutamide-resistant cells as compared to sensitive parental cells. Examination of a patient cohort demonstrated that several of our functionally-validated gene hits are deregulated in metastatic CRPC tumor samples, suggesting that they may be clinically relevant therapeutic targets for patients with enzalutamide-resistant CRPC. Altogether, our approach demonstrates the potential of integrative genomic analyses to clarify determinants of drug resistance and rational co-targeting strategies to overcome resistance.

Randomized phase 2 therapeutic equivalence study of abiraterone acetate fine particle formulation vs. originator abiraterone acetate in patients with metastatic castration-resistant prostate cancer: The STAAR study

BACKGROUND

This multicenter, randomized, open-label, active-controlled study evaluated therapeutic equivalence, steady-state pharmacokinetics, and safety of a novel abiraterone acetate fine particle formulation (AAFP) 500mg plus methylprednisolone vs. the originator AA (OAA) 1000mg plus prednisone in men with metastatic castrate-resistant prostate cancer (mCRPC). The primary endpoint was a comparison of average of serum testosterone levels on treatment days 9 and 10 between groups.

METHODS

Men with progressive mCRPC, receiving gonadotropin-releasing hormone agonist or antagonist therapy, and with a serum testosterone level of <50ng/dl were randomized 1:1 to either AAFP 500mg daily plus 4mg methylprednisolone orally twice daily (BID), or OAA 1000mg daily plus 5mg prednisone BID for 84 days. Serum testosterone, serum prostate-specific antigen (PSA), steady-state (trough) abiraterone pharmacokinetics, and safety were evaluated.

RESULTS

Fifty-three patients were enrolled (n = 24, AAFP; n = 29, OAA). Mean age was 75.1 years and 54.7% had Gleason>7. Over 90% of patients in each group achieved absolute testosterone levels of ≤1ng/dl during the study. The averaged absolute testosterone levels ≤0.1ng/dl were achieved in 25% of AAFP-treated patients and 17% of OAA-treated patients. A PSA-50 response was observed in>65% of patients in both groups on days 28, 56, and 84 (P = NS, all timepoints). Days 9 and 10 averaged rounded-up least squares (LS) mean (SE) serum testosterone levels were comparable (1.05ng/dl [0.04], AAFP; 1.02ng/dl [0.03], OAA; P = 0.4703 for LS mean difference). The geometric mean ratio between groups was 1.021 (90% CI: 0.965-1.081); the 90% CI fell within 80.0% to 125.0% equivalence limits. The LS mean differences in abiraterone trough plasma concentrations were not statistically significant at any visit. Adverse event frequency was comparable between arms (75.0%, AAFP; 82.8%, OAA). Musculoskeletal events were more common among OAA-treated patients (37.9% vs. 12.5%).

CONCLUSION

Therapeutic equivalence between AAFP 500mg daily and OAA 1000mg daily based on serum testosterone levels was confirmed in mCRPC patients. Both agents led to similar PSA-50 response rates. Abiraterone trough levels were similar between treatments. No new safety concerns were observed.

Antiandrogens Reduce Intratumoral Androgen Concentrations and Induce Androgen Receptor Expression in Castration-Resistant Prostate Cancer Xenografts

The development of castration-resistant prostate cancer (CRPC) is associated with the activation of intratumoral androgen biosynthesis and an increase in androgen receptor (AR) expression. We recently demonstrated that, similarly to the clinical CRPC, orthotopically grown castration-resistant VCaP (CR-VCaP) xenografts express high levels of AR and retain intratumoral androgen concentrations similar to tumors grown in intact mice. Herein, we show that antiandrogen treatment (enzalutamide or ARN-509) significantly reduced (10-fold, P < 0.01) intratumoral testosterone and dihydrotestosterone concentrations in the CR-VCaP tumors, indicating that the reduction in intratumoral androgens is a novel mechanism by which antiandrogens mediate their effects in CRPC. Antiandrogen treatment also altered the expression of multiple enzymes potentially involved in steroid metabolism. Identical to clinical CRPC, the expression levels of the full-length AR (twofold, P < 0.05) and the AR splice variants 1 (threefold, P < 0.05) and 7 (threefold, P < 0.01) were further increased in the antiandrogen-treated tumors. Nonsignificant effects were observed in the expression of certain classic androgen-regulated genes, such as TMPRSS2 and KLK3, despite the low levels of testosterone and dihydrotestosterone. However, other genes recently identified to be highly sensitive to androgen-regulated AR action, such as NOV and ST6GalNAc1, were markedly altered, which indicated reduced androgen action. Taken together, the data indicate that, besides blocking AR, antiandrogens modify androgen signaling in CR-VCaP xenografts at multiple levels.

Effect of dutasteride on castration-resistant prostate cancer

It has previously been demonstrated that the intratumoral generation of the potent androgen dihydrotestosterone (DHT), contributes critically to the progression of prostate cancer and its castration-resistant form, castration-resistant prostate cancer (CRPC). Circulating testosterone is converted into DHT by 5α-reductase (SRD5A). Dutasteride is a dual inhibitor of type I and II SRD5A. The present study assessed the effectiveness of dutasteride in the treatment of CRPC. Between 2010 and 2013, CRPC was diagnosed in 41 patients at the Tokyo Metropolitan Tama Medical Center. Following diagnosis, the patients received 0.5 mg dutasteride daily. The patients' median age was 77.3 years (range, 63-90). Bone metastases were recognized in 12 patients. All the patients received dexamethasone. Twenty-four (59%) patients had previously undergone chemotherapy, while 11 (27%) received docetaxel, and 24 (59%) estramustine. The prostatic-specific antigen (PSA) level declined in 17 (41%) patients from the baseline value, following dutasteride treatment. The median value for the PSA decrease was 23% (range, 4.3-89.8%), and the median duration of the response was 4 months (range, 1-10). The PSA response rate (defined as >50% decline in PSA from the baseline value) was recognized in 7 (17%) patients. The median duration of the response was 3 months (range, 2-10). Dutasteride was efficacious against CRPC in certain patients and may be a promising option in CRPC treatment. A prospective randomized trial is necessary to verify the efficacy of dutasteride.

Circulating steroid hormone variations throughout different stages of prostate cancer

Steroid hormones play a central role in the maintenance and progression of prostate cancer. The androgen receptor is the primary driver of tumor cell proliferation and is activated by the androgens testosterone and 5α-dihydrotestosterone. Inhibition of this pathway through medical or surgical castration improves survival in the majority of advanced prostate cancer patients. However, conversion of adrenal androgen precursors and alternative steroidogenic pathways have been found to contribute to tumor progression and resistance to treatment. The emergence of highly accurate detection methods allows us to study steroidogenic mechanisms in more detail, even after treatment with potent steroidogenic inhibitors such as the CYP17A1 inhibitor abiraterone. A clear overview of steroid hormone levels in patients throughout the local, metastatic and castration-resistant stages of prostate cancer and treatment modalities is key toward a better understanding of their role in tumor progression and treatment resistance. In this review, we summarize the currently available data on steroid hormones that have been implicated in the various stages of prostate cancer. Additionally, this review addresses the implications of these findings, highlights important studies in this field and identifies current gaps in literature.

CYP17A1-independent production of the neurosteroid-derived 5α-pregnan-3β,6α-diol-20-one in androgen-responsive prostate cancer cell lines under serum starvation and inhibition by Abiraterone

CYP17A1-independent intratumoral steroid hormone synthesis is regarded as one possible explanation for resistance to treatment with the CYP17-inhibitor Abiraterone (Abi). The aim of our study was therefore to investigate the steroid metabolism of prostate cancer cells under serum starvation and the effects of Abi treatment. We assessed steroid metabolism in a panel of prostate cancer cells under serum starvation by radioactivity detector-coupled HPLC and HPLC-ESI-ToF-mass spectrometry after treatment with pregnenolone, progesterone and allopregnanolone. We further evaluated the effects of Abi on steroid metabolism of testosterone, dihydrotestosterone (DHT) and dehydroepiandrosterone (DHEA) by enzyme immunoassays (EIAs). Androgen-responsive cell lines metabolized pregnenolone primarily to mitogenic steroid 5α-pregnan-3β,6α-diol-20-one under serum starvation. Co-administration of Abi lead to detectable concentrations of the Abi metabolite Δ⁴-Abi (D4A), known to inhibit enzymes other than CYP17A1 in steroid metabolism. In addition, co-administration of Abi abrogated pregnenolone metabolism and resulted in a CYP17A1-independent significant increase of DHEA (13- to >100-fold) and DHT (2.5-fold) in androgen-responsive cells. Our results demonstrate the CYP17A1-independent formation of 5α-pregnan-3β,6α-diol-20-one by androgen-responsive prostate cancer cells under serum starvation and its inhibition by Abi. Its metabolism from pregnenolone suggests a major steroidogenesis shift in these cells, hinting at a neuroendocrine transdifferentiation phenomenon. The marked increase of DHEA levels by Abi resembles the steroidogenic pathways in nervous tissue, in a manner that precludes CYP17A1 activity. To which extent these processes are responsible or involved in the development of resistance to Abi, needs to be further elucidated.

ACSL3 promotes intratumoral steroidogenesis in prostate cancer cells

Long‐chain acyl‐coenzyme A (CoA) synthetase 3 (ACSL3) is an androgen‐responsive gene involved in the generation of fatty acyl‐CoA esters. ACSL3 is expressed in both androgen‐sensitive and castration‐resistant prostate cancer (CRPC). However, its role in prostate cancer remains elusive. We overexpressed ACSL3 in androgen‐dependent LNCaP cells and examined the downstream effectors of ACSL3. Furthermore, we examined the role of ACSL3 in the androgen metabolism of prostate cancer. ACSL3 overexpression led to upregulation of several genes such as aldo‐keto reductase 1C3 (AKR1C3) involved in steroidogenesis, which utilizes adrenal androgen dehydroepiandrosterone sulfate (DHEAS) as substrate, and downregulated androgen‐inactivating enzyme UDP‐glucuronosyltransferase 2 (UGT2B). Exposure to DHEAS significantly increased testosterone levels and cell proliferative response in ACSL3‐overexpressing cells when compared to that in control cells. A public database showed that ACSL3 level was higher in CRPC than in hormone‐sensitive prostate cancer. CRPC cells showed an increased expression of ACSL3 and an expression pattern of AKR1C3 and UGT2B similar to ACSL3‐overexpressing cells. DHEAS stimulation significantly promoted the proliferation of CRPC cells when compared to that of LNCaP cells. These findings suggest that ACSL3 contributes to the growth of CRPC through intratumoral steroidogenesis (i.e. promoting androgen synthesis from DHEAS and preventing the catabolism of active androgens).

Clinical utility of emerging liquid biomarkers in advanced prostate cancer

The therapeutic landscape of advanced prostate cancer (PCa) has rapidly expanded in recent years. Despite significant improvements in patient overall survival, it remains challenging to determine the optimal therapy and sequence of therapies for individual patients. The development of molecular biomarkers will be key for patient stratification, and for monitoring response and resistance to therapy. In this context, minimally-invasive blood-based "liquid" biopsies are attractive as a practical surrogate for solid tumor tissue, providing a window into metastatic disease. Circulating tumor cells and circulating cell-free tumor DNA in particular have demonstrated remarkable potential to inform on PCa patient outcomes through the detection of specific genomic and transcriptomic alterations. This review covers recent advances in the development of clinically-informative liquid biomarkers for advanced PCa.

Androgen Receptor and Beyond, Targeting Androgen Signaling in Castration-Resistant Prostate Cancer

The development of metastatic castration-resistant prostate cancer (mCRPC) signals the terminal disease phase. The preceding hormone-dependent disease setting is effectively managed with androgen deprivation therapy. This foundation of treatment has a high rate of biochemical and clinical response and meaningful clinical benefit but is finite in duration as most cancers will progress to castration resistance. Historically, treatment for mCRPC entailed androgen receptor (AR) inhibitors (nilutamide, flutamide, bicalutamide), nonspecific steroidal biosynthesis inhibitors (ketoconazole, itraconazole), steroids (prednisone, diethylstilbesterol, dexamethasone), or palliative chemotherapy (mitoxantrone, estramustine), but none of these strategies impacted survival. Docetaxel was the first agent to demonstrate a survival improvement in this population, and other therapies followed (cabazitaxel, sipuleucel-T and radium-223). Understanding how prostate cancer cells grow in a systemic androgen-deprived environment further changed this clinical landscape. Deciphering what steroidogenic enzymes are overactive and required for testosterone/dihydrotestosterone synthesis has yielded therapies directed toward both adrenal and tumor-derived androgens. All androgens normally act through AR, and this fact remains true in mCRPC. The cancer accomplishes this by overexpressing the receptor (by genomic copy-number gains or RNA amplification), mutating it directly to lose its selectivity for testosterone/dihydrotestosterone, or selecting for splice variants that do not require ligand at all. These resistance mechanisms result in persistent AR-mediated signaling. Through this understanding, drugs targeting non-ligand-binding aspects of AR functioning (e.g., nuclear translocation, cofactor recruitment) have been developed. Finally, how AR interacts with other signaling pathway is being explored, and new combinations of targets to test are being proposed. Multiple compounds remain in various stages of clinical development based on targeting these resistance pathways, and hopefully, they will further the armamentarium for mCRPC. This review visits these mechanisms of resistance, how they are targeted, and remaining challenges in implementing these therapies into clinical practice among the other approved treatments.

Significance of microRNAs in Androgen Signaling and Prostate Cancer Progression

The androgen receptor (AR) plays important roles in prostate cancer development and prostate tumor growth. After binding to androgens, AR functions as a nuclear receptor and translocates to the nucleus to bind to specific AR-binding sites (ARBSs). AR regulates epigenetic factor recruitments to activate its downstream signaling. Although androgen deprivation therapy (ADT) is initially useful for prostate cancer patients, most patients eventually show resistance with hormone-refractory prostate cancers (HRPCs) or castration-resistant prostate cancers (CRPCs). Thus, new therapeutic strategies targeting HRPCs/CRPCs should be very important for clinical medicine as well as prostate cancer biology. Past studies have shown that mechanisms such as AR overexpression, hypersensitivity, variants and reprograming are responsible for developing HRPCs/CRPCs. These findings suggest that AR target genes will be major key factors. In this review article, we focus mainly on the androgen-regulated microRNAs (miRNAs) to summarize the contribution of miRNA-mediated pathways for prostate cancer progression.

Circulating tumor cells in prostate cancer: Precision diagnosis and therapy

The primary cause of tumor-associated mortality in prostate cancer (PCa) remains distant metastasis. The dissemination of tumor cells from the primary tumor to distant sites through the bloodstream cannot be detected early by standard imaging methods. Circulating tumor cells (CTCs) represent an effective prognostic and predictive biomarker, which are able to monitor efficacy of adjuvant therapies, detect early development of metastases, and finally, assess therapeutic responses of advanced disease earlier than traditional diagnostic methods. In addition, since repeated tissue biopsies are invasive, costly and not always feasible, the assessment of tumor characteristics on CTCs, by a peripheral blood sample as a liquid biopsy, represents an attractive opportunity. The implementation of molecular and genomic characterization of CTCs may contribute to improve the treatment selection and thus, to move toward more precise diagnosis and therapy in PCa. The present study summarizes the current advances in CTC enrichment and detection strategies and reviews how CTCs may contribute to significant insights in the metastatic process, as well as how they may be utilized in clinical application in PCa. Although it is proposed that CTCs may offer insights into the prognosis and management of PCa, there are a number of challenges in the study of circulating tumor cells, and their clinical utility remains under investigation.

Androgen Receptor Regulation of Local Growth Hormone in Prostate Cancer Cells

Prostate cancer (PCa) growth is mainly driven by androgen receptor (AR), and tumors that initially respond to androgen deprivation therapy (ADT) or AR inhibition usually relapse into a more aggressive, castration-resistant PCa (CRPC) stage. Circulating growth hormone (GH) has a permissive role in PCa development in animal models and in human PCa xenograft growth. As GH and GH receptor (GHR) are both expressed in PCa cells, we assessed whether prostatic GH production is linked to AR activity and whether GH contributes to the castration-resistant phenotype. Using online datasets, we found that GH is highly expressed in human CRPC. We observed increased GH expression in castration-resistant C4-2 compared with castration-sensitive LNCaP cells as well as in enzalutamide (MDV3100)-resistant (MDVR) C4-2B (C4-2B MDVR) cells compared with parental C4-2B. We describe a negative regulation of locally produced GH by androgens/AR in PCa cells following treatment with AR agonists (R1881) and antagonists (enzalutamide, bicalutamide). We also show that GH enhances invasive behavior of CRPC 22Rv1 cells, as reflected by increased migration, invasion, and anchorage-independent growth, as well as expression of matrix metalloproteases. Moreover, GH induces expression of the AR splice variant 7, which correlates with antiandrogen resistance, and also induces insulinlike growth factor 1, which is implicated in PCa progression and ligand-independent AR activation. In contrast, blockade of GH action with the GHR antagonist pegvisomant reverses these effects both in vitro and in vivo. GH induction following ADT or AR inhibition may contribute to CRPC progression by bypassing androgen growth requirements.

CLDN8, an androgen-regulated gene, promotes prostate cancer cell proliferation and migration

The proliferation of prostate cancer cells is controlled by the androgen receptor (AR) signaling pathway. However, the function of AR target genes has not been fully elucidated. In previous studies, we have identified global AR binding sites and AR target genes in prostate cancer cells. Here, we focused on Claudin 8 (CLDN8), a protein constituting tight junctions in cell membranes. We found one AR binding site in the promoter region and two functional androgen‐responsive elements in the sequence. Reporter assay revealed that transcriptional activation of the CLDN8 promoter by androgen is dependent on these androgen‐responsive elements. Furthermore, CLDN8 mRNA is induced by androgen time‐dependently and the induction is blocked by AR inhibitor, suggesting that AR is involved in the transcriptional activation. In addition, our functional analyses by overexpression and knockdown of CLDN8 mRNA indicate that CLDN8 promotes prostate cancer cell proliferation and migration. Claudin 8 was overexpressed in prostate cancer clinical samples compared to benign tissues. Furthermore, we found that CLDN8 regulates intracellular signal transduction and stabilizes the cytoskeleton. Taken together, these results indicate that CLDN8 functions as an AR downstream signal to facilitate the progression of prostate cancer. Claudin 8 may be a novel molecular target for prostate cancer therapy.

Androgen receptor antagonism drives cytochrome P450 17A1 inhibitor efficacy in prostate cancer

The clinical utility of inhibiting cytochrome P450 17A1 (CYP17), a cytochrome p450 enzyme that is required for the production of androgens, has been exemplified by the approval of abiraterone for the treatment of castration-resistant prostate cancer (CRPC). Recently, however, it has been reported that CYP17 inhibitors can interact directly with the androgen receptor (AR). A phase I study recently reported that seviteronel, a CYP17 lyase-selective inhibitor, ædemonstrated a sustained reduction in prostate-specific antigen in a patient with CRPC, and another study showed seviteronel's direct effects on AR function. This suggested that seviteronel may have therapeutically relevant activities in addition to its ability to inhibit androgen production. Here, we have demonstrated that CYP17 inhibitors, with the exception of orteronel, can function as competitive AR antagonists. Conformational profiling revealed that the CYP17 inhibitor-bound AR adopted a conformation that resembled the unliganded AR (apo-AR), precluding nuclear localization and DNA binding. Further, we observed that seviteronel and abiraterone inhibited the growth of tumor xenografts expressing the clinically relevant mutation AR-F876L and that this activity could be attributed entirely to competitive AR antagonism. The results of this study suggest that the ability of CYP17 inhibitors to directly antagonize the AR may contribute to their clinical efficacy in CRPC.

Development of 17β-hydroxysteroid dehydrogenase type 3 as a target in hormone-dependent prostate cancer therapy

17β-Hydroxysteroid dehydrogenase type 3 (17β-HSD3) is expressed almost exclusively in the testes and specifically converts the weak androgenic androstenedione to active testosterone (T) in the presence of NADPH. Additionally, studies have demonstrated that 17β-HSD3 is over-expressed in hormone-dependent prostate cancer. T, which interacts with the androgen receptor (AR), eventually stimulates the growth of prostate cancer cells. Defects in T synthesis or action impair the development of the male phenotype during embryogenesis and cause the autosomal recessive disorder male pseudohermaphroditism. Affected individuals are often born with female-appearing external genitalia and are reared as females. Since 17β-HSD3 plays a central role in T production, it has been recognized as a promising therapeutic target to reduce the circulating level of androgens and to suppress androgen-sensitive tumor proliferation. In recent decades, improvements have been made in the development of 17β-HSD3 inhibitors. Herein, we give an overview of the main structure and function of human 17β-HSD3 and summarize steroidal and non-steroidal inhibitors of 17β-HSD3, which can be a potential target for prostate cancer.

Low Testosterone Alters the Activity of Mouse Prostate Stem Cells

BACKGROUND

Low serum testosterone (low T) has been repeatedly linked to worse outcomes in men with newly diagnosed prostate cancer (PC). How low T contributes to these outcomes is unknown. Here we demonstrate that exposure to low T causes significant changes in the mouse prostate and prostate stem cells.

METHODS

Mice were castrated and implanted with capsules to achieve castrate, normal, or sub-physiological levels of T. After 6 weeks of treatment, LC-MS/MS was used to quantify the levels of T and dihydrotestosterone (DHT) in serum and prostate tissue. FACS was used to quantify the percentages of purported prostate stem and transit amplifying (TA) cells in mouse prostates. Prostate tissues were also stained for the presence of CD68+ cells and RNA was extracted from prostate tissue or specific cell populations to measure changes in transcript levels with low T treatment.

RESULTS

Despite having significantly different levels of T and DHT in the serum, T and DHT concentrations in prostate tissue from different T treatment groups were similar. Low T treatment resulted in significant alterations in the expression of androgen biosynthesis genes, which may be related to maintaining prostate androgen levels. Furthermore, the expression of androgen-regulated genes in the prostate was similar among all T treatment groups, demonstrating that the mouse prostate can maintain functional levels of androgens despite low serum T levels. Low T increased the frequency of prostate stem and TA cells in adult prostate tissue and caused major transcriptional changes in those cells. Gene ontology analysis suggested that low T caused inflammatory responses and immunofluorescent staining indicated that low T treatment led to the increased presence of CD68+ macrophages in prostate tissue.

CONCLUSIONS

Low T alters the AR signaling axis which likely leads to maintenance of functional levels of prostate androgens. Low T also induces quantitative and qualitative changes in prostate stem cells which appear to lead to inflammatory macrophage infiltration. These changes are proposed to lead to an aggressive phenotype once cancers develop and may contribute to the poor outcomes in men with low T. Prostate 77:530-541, 2017. © 2016 Wiley Periodicals, Inc.

Berberine inhibits androgen synthesis by interaction with aldo-keto reductase 1C3 in 22Rv1 prostate cancer cells

Aldo-keto reductase family 1 member C3 has recently been regarded as a potential therapeutic target in castrate-resistant prostate cancer. Herein, we investigated whether berberine delayed the progression of castrate-resistant prostate cancer by reducing androgen synthesis through the inhibition of Aldo-keto reductase family 1 member C3. Cell viability and cellular testosterone content were measured in prostate cancer cells. Aldo-keto reductase family 1 member C3 mRNA and protein level were detected by RT-PCR and Western bolt analyses, respectively. Computer analysis with AutoDock Tools explored the molecular interaction of berberine with Aldo-keto reductase family 1 member C3. We found that berberine inhibited 22Rv1 cells proliferation and decreased cellular testosterone formation in a dose-dependent manner. Berberine inhibited Aldo-keto reductase family 1 member C3 enzyme activity, rather than influenced mRNA and protein expressions. Molecular docking study demonstrated that berberine could enter the active center of Aldo-keto reductase family 1 member C3 and form p-p interaction with the amino-acid residue Phe306 and Phe311. In conclusion, the structural interaction of berberine with Aldo-keto reductase family 1 member C3 is attributed to the suppression of Aldo-keto reductase family 1 member C3 enzyme activity and the inhibition of 22Rv1 prostate cancer cell growth by decreasing the intracellular androgen synthesis. Our result provides the experimental basis for the design, research, and development of AKR1C3 inhibitors using berberine as the lead compound.

Serum testosterone level predicts the effective time of androgen deprivation therapy in metastatic prostate cancer patients

Androgen deprivation therapy (ADT) is the standard of care for patients with metastatic prostate cancer. However, whether serum testosterone levels, using a cut-off point of 50 ng dl⁻¹, are related to the effective time of ADT in newly diagnosed prostate cancer patients remains controversial. Moreover, recent studies have shown that some patients may benefit from the addition of upfront docetaxel chemotherapy. To date, no studies have been able to distinguish patients who will benefit from the combination of ADT and docetaxel chemotherapy. This study included 206 patients who were diagnosed with metastatic prostate cancer and showed progression to castrate-resistance prostate cancer (CRPC). Serum testosterone levels were measured prospectively after ADT for 1, 3, and 6 months. The endpoint was the time to CRPC. In univariate and multivariate analyses, testosterone levels <50 ng dl⁻¹ were not associated with the effective time of ADT. Receiver operating characteristic and univariate analysis showed that testosterone levels of ≤25 ng dl⁻¹ after the first month of ADT offered the best overall sensitivity and specificity for prediction of a longer time to CRPC (adjusted hazard ratio [HR], 1.46; 95% confidence interval [95% CI], 1.08–1.96; P = 0.013). Our results show that serum testosterone level of 25 ng dl⁻¹ plays a prognostic role in prostate cancer patients receiving ADT. A testosterone value of 25 ng dl⁻¹ after the first month of ADT can distinguish patients who benefit from ADT effectiveness for only a short time. These patients may need to receive ADT and concurrent docetaxel chemotherapy.

CDK4/6 Therapeutic Intervention and Viable Alternative to Taxanes in CRPC

Resistance to second-generation androgen receptor (AR) antagonists and CYP17 inhibitors in patients with castration-resistant prostate cancer (CRPC) develops rapidly through reactivation of the androgen signaling axis and has been attributed to AR overexpression, production of constitutively active AR splice variants, or the selection for AR mutants with altered ligand-binding specificity. It has been established that androgens induce cell-cycle progression, in part, through upregulation of cyclin D1 (CCND1) expression and subsequent activation of cyclin-dependent kinases 4 and 6 (CDK4/6). Thus, the efficacy of the newly described CDK4/6 inhibitors (G1T28 and G1T38), docetaxel and enzalutamide, was evaluated as single agents in clinically relevant in vitro and in vivo models of hormone-sensitive and treatment-resistant prostate cancer. CDK4/6 inhibition (CDK4/6i) was as effective as docetaxel in animal models of treatment-resistant CRPC but exhibited significantly less toxicity. The in vivo effects were durable and importantly were observed in prostate cancer cells expressing wild-type AR, AR mutants, and those that have lost AR expression. CDK4/6i was also effective in prostate tumor models expressing the AR-V7 variant or the AR F876L mutation, both of which are associated with treatment resistance. Furthermore, CDK4/6i was effective in prostate cancer models where AR expression was lost. It is concluded that CDK4/6 inhibitors are a viable alternative to taxanes as therapeutic interventions in endocrine therapy-refractory CRPC.Implications: The preclinical efficacy of CDK4/6 monotherapy observed here suggests the need for near-term clinical studies of these agents in advanced prostate cancer. Mol Cancer Res; 15(6); 660-9. ©2017 AACR.

Epithelial-mesenchymal-transition regulators in prostate cancer: Androgens and beyond

Castration resistant prostate cancer (CRPC) remains one of the leading causes of cancer deaths among men. Conventional therapies targeting androgen signaling driven tumor growth have provided limited survival benefit in patients. Recent identification of the critical molecular and cellular events surrounding tumor progression, invasion, and metastasis to the bone as well as other sites provide new insights in targeting advanced disease. Epithelial mesenchymal transition (EMT) is a process via which epithelial cells undergo morphological changes to a motile mesenchymal phenotype, a phenomenon implicated in cancer metastasis but also therapeutic resistance. Therapeutic targeting of EMT has the potential to open a new avenue in the treatment paradigm of CRPC through the reversion of the invasive mesenchymal phenotype to the well differentiated tumor epithelial tumor phenotype. Overcoming therapeutic resistance in metastatic prostate cancer is an unmet need in today's clinical management of advanced disease. This review outlines our current understanding of the contribution of EMT and its reversal to MET in prostate cancer progression and therapeutic resistance, and the impact of selected targeting of mechanisms of resistance via EMT towards a therapeutic benefit in patients with CRPC.

Mechanisms of Therapeutic Resistance in Prostate Cancer

Prostate cancer is the second leading cause of cancer deaths in the USA. The challenge in managing castration-resistant prostate cancer (CRPC) stems not from the lack of therapeutic options but from the limited duration of clinical and survival benefit offered by treatments in this setting due to primary and acquired resistance. The remarkable molecular heterogeneity and tumor adaptability in advanced prostate cancer necessitate optimization of such treatment strategies. While the future of CRPC management will involve newer targeted therapies in deliberately biomarker-selected patients, interventions using current approaches may exhibit improved clinical benefit if employed in the context of optimal sequencing and combinations. This review outlines our current understanding of mechanisms of therapeutic resistance in progression to and after the development of castration resistance, highlighting targetable and reversible mechanisms of resistance.

A Tale of Two Signals: AR and WNT in Development and Tumorigenesis of Prostate and Mammary Gland

Prostate cancer (PCa) is one of the most common cancers and among the leading causes of cancer deaths for men in industrialized countries. It has long been recognized that the prostate is an androgen-dependent organ and PCa is an androgen-dependent disease. Androgen action is mediated by the androgen receptor (AR). Androgen deprivation therapy (ADT) is the standard treatment for metastatic PCa. However, almost all advanced PCa cases progress to castration-resistant prostate cancer (CRPC) after a period of ADT. A variety of mechanisms of progression from androgen-dependent PCa to CRPC under ADT have been postulated, but it remains largely unclear as to when and how castration resistance arises within prostate tumors. In addition, AR signaling may be modulated by extracellular factors among which are the cysteine-rich glycoproteins WNTs. The WNTs are capable of signaling through several pathways, the best-characterized being the canonical WNT/β-catenin/TCF-mediated canonical pathway. Recent studies from sequencing PCa genomes revealed that CRPC cells frequently harbor mutations in major components of the WNT/β-catenin pathway. Moreover, the finding of an interaction between β-catenin and AR suggests a possible mechanism of cross talk between WNT and androgen/AR signaling pathways. In this review, we discuss the current knowledge of both AR and WNT pathways in prostate development and tumorigenesis, and their interaction during development of CRPC. We also review the possible therapeutic application of drugs that target both AR and WNT/β-catenin pathways. Finally, we extend our review of AR and WNT signaling to the mammary gland system and breast cancer. We highlight that the role of AR signaling and its interaction with WNT signaling in these two hormone-related cancer types are highly context-dependent.

Neuropilin-1 is upregulated in the adaptive response of prostate tumors to androgen-targeted therapies and is prognostic of metastatic progression and patient mortality

Recent evidence has implicated the transmembrane co-receptor neuropilin-1 (NRP1) in cancer progression. Primarily known as a regulator of neuronal guidance and angiogenesis, NRP1 is also expressed in multiple human malignancies, where it promotes tumor angiogenesis. However, non-angiogenic roles of NRP1 in tumor progression remain poorly characterized. In this study, we define NRP1 as an androgen-repressed gene whose expression is elevated during the adaptation of prostate tumors to androgen-targeted therapies (ATTs), and subsequent progression to metastatic castration-resistant prostate cancer (mCRPC). Using short hairpin RNA (shRNA)-mediated suppression of NRP1, we demonstrate that NRP1 regulates the mesenchymal phenotype of mCRPC cell models and the invasive and metastatic dissemination of tumor cells in vivo. In patients, immunohistochemical staining of tissue microarrays and mRNA expression analyses revealed a positive association between NRP1 expression and increasing Gleason grade, pathological T score, positive lymph node status and primary therapy failure. Furthermore, multivariate analysis of several large clinical prostate cancer (PCa) cohorts identified NRP1 expression at radical prostatectomy as an independent prognostic biomarker of biochemical recurrence after radiation therapy, metastasis and cancer-specific mortality. This study identifies NRP1 for the first time as a novel androgen-suppressed gene upregulated during the adaptive response of prostate tumors to ATTs and a prognostic biomarker of clinical metastasis and lethal PCa.

Achieving resistance specificity in prostate cancer

Prostate (CaP) cancer is the second-leading cause of cancer-related mortality in men in Western societies. Androgen receptor (AR) signaling is a critical survival pathway for prostate cancer cells, and androgen-deprivation therapy (ADT) remains the principal treatment for patients with locally advanced and metastatic disease. Although a majority of patients initially respond to ADT, most will eventually develop castrate resistance. The recent discovery that AR signaling persists during systemic castration via intratumoral production of androgens led to the development of novel anti-androgen therapies. Although these therapies effectively palliate symptoms and prolong life, metastatic castration-resistant prostate cancer remains incurable. Recent studies suggest that epithelial plasticity, which covers a range of changes in differentiation and cell behavior, with full epithelial integrity at one end and epithelial-mesenchymal Transition (EMT) as the full realization of a plasticity is regulated by microRNAs (miRNAs). MicroRNAs are involved in human tumourigenesis and are aberrantly expressed in CaP cell lines, xenografts and clinical tissues and is associated with enhanced survival signaling, proliferation, migration, invasion, integrin-mediated adhesion, EMT, and drug resistance. Due to the oncogenic or tumor suppressive properties of CaP-related miRNAs, they are likely to be of clinical use as therapeutic targets for prostate cancer treatment in the near future. This review summarizes our current understanding of CaP and castration-recurrent CaP (CR-CaP) to earlier studies that characterized ADT and the molecular mechanisms that facilitate the transition from androgen-stimulated CaP to CR-CaP.

Contemporary agents in the management of metastatic castration-resistant prostate cancer

Docetaxel-based chemotherapy has been the standard of care for metastatic castration-resistant prostate cancer (mCRPC) since 2004. Over the past few years, there has been a significant paradigm shift in the treatment landscape of this disease. A deeper understanding of prostate cancer biology, along with the development of novel agents has created hope towards treating chemotherapy-naïve and resistant disease. Following the implementation of docetaxel as the first-line therapy for mCRPC, five novel therapies have demonstrated survival benefit in mCRPC. Cabazitaxel, abiraterone acetate, and enzalutamide are three agents recently approved for the treatment of mCRPC, having shown overall survival benefit in patients previously treated with docetaxel, while both abiraterone acetate and enzalutamide have also shown promise in the pre-docetaxel setting. Sipuleucel-T has shown overall survival benefit in asymptomatic mCRPC, while radium-223 provides survival benefit to patients with mCRPC who are symptomatic from their skeletal metastases in both docetaxel-naïve patients and post-docetaxel patients. Denosumab, an anti-RANKL antibody, has been approved for the prevention of skeletal-related events in patients with prostate cancer bone metastases. This review examines the phase 3 trials supporting the use of theses novel agents in the treatment of mCRPC. While these agents provide incremental increases in patient survival, further study to determine the best choice, combination, and/or sequencing of administration is still necessary.

The Molecular Evolution of Castration-resistant Prostate Cancer

CONTEXT

Androgen deprivation therapy (ADT) is the backbone of treatment for advanced prostate cancer. However, castration-resistant prostate cancer (CRPC) nearly invariably develops through a range of different molecular mechanisms accompanied by progression to a more aggressive phenotype.

OBJECTIVE

To understand the key molecular mechanisms leading to CRPC and the functional implications of this progression. Understanding molecular evolutionary mechanisms in CRPC is essential for the development of novel curative therapeutic approaches.

EVIDENCE ACQUISITION

A systematic literature search to identify relevant original articles was conducted using PubMed. Findings verified in independent studies and supported by in vivo data were prioritised. From the eligible collection, 50 papers were selected.

EVIDENCE SYNTHESIS

The majority of CRPC tumours harbour alterations in the androgen receptor (AR) at the DNA, RNA, and/or protein level, and/or other alterations involving the AR signalling pathway, so this central molecule is the focus of this review. To survive and resume growth despite low levels of circulating androgens, prostate cancer cells can also adapt androgen synthesis or induce alternative pathways.

CONCLUSIONS

Despite more efficient ADT strategies, most evidence points to persistent AR signalling as a major mechanism of progression to CRPC. Resistance due to transdifferentiation or AR independence is also emerging as a mechanism of resistance. The diversity of potential resistance mechanisms supports the need for combination treatment and serial monitoring for adaptive treatment strategies.

PATIENT SUMMARY

In this review, we summarise how prostate cancer cells evade androgen deprivation therapy and become more aggressive. Defining the molecular mechanisms will be critical for the development of new treatment approaches and hence improved survival.

[2.2.1]-Bicyclic sultams as potent androgen receptor antagonists

This letter describes the discovery, synthesis, SAR, and biological activity of [2.2.1]-bicyclic sultams as potent antagonists of the androgen receptor. Optimization of the series led to the identification of compound 25, which displayed robust pharmacodynamic effects in rats after oral dosing.

Targeting the N-Terminal Domain of the Androgen Receptor: A New Approach for the Treatment of Advanced Prostate Cancer

: Despite the recent approval and widespread use of abiraterone acetate and enzalutamide for the treatment of castration-resistant prostate cancer (CRPC), this disease still poses significant management challenges because of various tumor escape mechanisms, including those that allow androgen receptor (AR) signaling to remain active. These AR-related resistance mechanisms include AR gene amplification or overexpression, constitutively active ligand-independent AR splice variants, and gain-of-function mutations involving the AR ligand-binding domain (LBD), among others. Therefore, the development of AR-targeted therapies that function independently of the LBD represents an unmet medical need and has the potential to overcome many of these resistance mechanisms. This article discusses N-terminal domain (NTD) inhibition as a novel concept in the field of AR-directed therapies for prostate cancer. AR NTD-targeting agents have the potential to overcome shortcomings of current hormonal therapies by inhibiting all forms of AR-mediated transcriptional activity, and as a result, may affect a broader AR population including mutational and splice variant ARs. Indeed, the first clinical trial of an AR NTD inhibitor is now underway.

IMPLICATIONS FOR PRACTICE

Because of emerging resistance mechanisms that involve the ligand-binding domain of the androgen receptor (AR), there is currently no effective treatment addressing tumor escape mechanisms related to current AR-targeted therapies. Many patients still demonstrate limited clinical response to current hormonal agents, and castration-resistant prostate cancer remains a lethal disease. Intense research efforts are under way to develop therapies to target resistance mechanisms, including those directed at other parts of the AR molecule. A novel small-molecule agent, EPI-506, represents a new pharmaceutical class, AR N-terminal domain inhibitors, and shows preclinical promise to overcome many known resistance mechanisms related to novel hormonal therapies.

Androgen deprivation therapy with Leuprolide acetate for treatment of advanced prostate cancer

INTRODUCTION

Hormone sensitive advanced prostate cancer (PCa) is an incurable disease that is treated with a variety of hormonal therapies targeting the androgen/androgen receptor signaling axis. For decades androgen deprivation therapy (ADT) by surgical or chemical castration is the gold standard for the treatment of advanced PCa. Areas covered: This review discusses the pharmacological features of Leuprolide, a luteinizing hormone-releasing hormone (LHRH) agonists/analog and the most commonly used drug in ADT. Expert opinion: Although Leuprolide has been on the market for more than 30 years it is still the leading option for ADT and serves as a basis for most multimodal therapy concepts. The fact that with the onset of castration-resistance in late stage metastatic disease, a prolongation of ADT in combination with a second line hormonal manipulation is recommended supports the importance of the compound for daily clinical practice.

The interplay between cell signalling and the mevalonate pathway in cancer

The mevalonate (MVA) pathway is an essential metabolic pathway that uses acetyl-CoA to produce sterols and isoprenoids that are integral to tumour growth and progression. In recent years, many oncogenic signalling pathways have been shown to increase the activity and/or the expression of MVA pathway enzymes. This Review summarizes recent advances and discusses unique opportunities for immediately targeting this metabolic vulnerability in cancer with agents that have been approved for other therapeutic uses, such as the statin family of drugs, to improve outcomes for cancer patients.

Inhibition of AKR1C3 Activation Overcomes Resistance to Abiraterone in Advanced Prostate Cancer

Abiraterone suppresses intracrine androgen synthesis via inhibition of CYP17A1. However, clinical evidence suggests that androgen synthesis is not fully inhibited by abiraterone and the sustained androgen production may lead to disease relapse. In the present study, we identified AKR1C3, an important enzyme in the steroidogenesis pathway, as a critical mechanism driving resistance to abiraterone through increasing intracrine androgen synthesis and enhancing androgen signaling. We found that overexpression of AKR1C3 confers resistance to abiraterone while downregulation of AKR1C3 resensitizes resistant cells to abiraterone treatment. In abiraterone-resistant prostate cancer cells, AKR1C3 is overexpressed and the levels of intracrine androgens are elevated. In addition, AKR1C3 activation increases intracrine androgen synthesis and enhances androgen receptor (AR) signaling via activating AR transcriptional activity. Treatment of abiraterone-resistant cells with indomethacin, an AKR1C3 inhibitor, overcomes resistance and enhances abiraterone therapy both in vitro and in vivo by reducing the levels of intracrine androgens and diminishing AR transcriptional activity. These results demonstrate that AKR1C3 activation is a critical mechanism of resistance to abiraterone through increasing intracrine androgen synthesis and enhancing androgen signaling. Furthermore, this study provides a preclinical proof-of-principle for clinical trials investigating the combination of targeting AKR1C3 using indomethacin with abiraterone for advanced prostate cancer. Mol Cancer Ther; 16(1); 35-44. ©2016 AACR.

Efficacy of Therapies After Galeterone in Patients With Castration-resistant Prostate Cancer

BACKGROUND

Galeterone is a multi-targeted agent with activity as a CYP17 inhibitor, androgen receptor antagonist, and also causes androgen receptor degradation. It has shown meaningful anti-tumor activity with a well-tolerated safety profile in patients with castration-resistant prostate cancer (CRPC) in phase I and II studies; however, the efficacy of currently approved CRPC therapies after treatment with galeterone is unknown. In this study, we evaluate prostate specific antigen (PSA) response of non-protocol therapies following galeterone in a subset of patients treated on the Androgen Receptor Modulation Optimized for Response (ARMOR) 2 study.

PATIENTS AND METHODS

Patients who received any subsequent treatment were included. PSA response and treatment duration were summarized by line and type of subsequent therapy.

RESULTS

Overall, 27 of 40 patients received ≥ 1 post-galeterone treatment, of whom 18 (67%) discontinued galeterone for progression, 14 (52%) received ≥ 2 treatments, and 6 (22%) received ≥ 3 treatments. PSA changed by a median of -36%, -35%, and +60% in patients receiving first-line, second-line, and third-line therapy, respectively. Overall, 18 (67%) received subsequent enzalutamide, 12 (44%) received docetaxel, 9 (33%) received abiraterone, and 5 (19%) received cabazitaxel. PSA changed by a median of -27%, -34%, -39%, and 17% for patients receiving subsequent enzalutamide, docetaxel, abiraterone, and cabazitaxel, respectively, at any line.

CONCLUSION

We demonstrate that CRPC therapies exhibit differential anti-tumor activity following galeterone. In this small cohort, abiraterone demonstrates the highest PSA response post-galeterone, whereas enzalutamide and chemotherapy have more modest activity. Larger clinical studies are warranted to fully evaluate the efficacy and safety of second-generation hormonal agents and chemotherapy post-galeterone. Predictive biomarkers will be critical to optimizing patient selection for sequential therapies.