Acute effects of testicular and adrenal cortical blockade on protein synthesis and dihydrotestosterone content of human prostate tissue

Critical role of antioxidant programs in enzalutamide-resistant prostate cancer

Therapy resistance to second-generation androgen receptor (AR) antagonists, such as enzalutamide, is common in patients with advanced prostate cancer (PCa). To understand the metabolic alterations involved in enzalutamide resistance, we performed metabolomic, transcriptomic, and cistromic analyses of enzalutamide-sensitive and -resistant PCa cells, xenografts, patient-derived organoids, patient-derived explants, and tumors. We noted dramatically higher basal and inducible levels of reactive oxygen species (ROS) in enzalutamide-resistant PCa and castration-resistant PCa (CRPC), in comparison to enzalutamide-sensitive PCa cells or primary therapy-naive tumors respectively. Unbiased metabolomic evaluation identified that glutamine metabolism was consistently upregulated in enzalutamide-resistant PCa cells and CRPC tumors. Stable isotope tracing studies suggest that this enhanced glutamine metabolism drives an antioxidant program that allows these cells to tolerate higher basal levels of ROS. Inhibition of glutamine metabolism with either a small-molecule glutaminase inhibitor or genetic knockout of glutaminase enhanced ROS levels, and blocked the growth of enzalutamide-resistant PCa. The critical role of compensatory antioxidant pathways in maintaining enzalutamide-resistant PCa cells was validated by targeting another antioxidant program driver, ferredoxin 1. Taken together, our data identify a metabolic need to maintain antioxidant programs and a potentially targetable metabolic vulnerability in enzalutamide-resistant PCa.

Development and prevalence of castration-resistant prostate cancer subtypes

BACKGROUND

Castration-resistant prostate cancer (CRPC) occurs when prostate cancer (CaP) progresses under therapy-induced castrate conditions. Several mechanisms have been proposed to explain this acquired resistance, many of which are driven by androgen receptor (AR). Recent findings, however, sub-classified CRPC by downregulation/absence of AR in certain subtypes that consequently do not respond to anti-androgen therapies. To highlight the significance of CRPC sub-classification, we reviewed the development and treatment of CRPC, AR downregulation in CRPC, and summarized recent reports on the prevalence of CRPC subtypes.

METHODS

Using a medline-based literature search, we reviewed mechanisms of CRPC development, current treatment schemes, and assessed the prevalence of AR low/negative subtypes of CRPC. Additionally, we performed immunohistochemical staining on human CRPC specimens to quantify AR expression across CRPC subtypes.

RESULTS

In the majority of cases, CRPC continues to rely on AR signaling, which can be augmented in castrate-conditions through a variety of mechanisms. However, recently low/negative AR expression patterns were identified in a significant proportion of patient samples from a multitude of independent studies. In these AR low/negative cases, we postulated that AR protein may be downregulated by (1) promoter methylation, (2) transcriptional regulation, (3) post-transcriptional regulation by microRNA or RNA-binding-proteins, or (4) post-translational ubiquitination-mediated degradation.

CONCLUSIONS

Here, we discussed mechanisms of CRPC development and summarized the overall prevalence of CRPC subtypes; interestingly, AR low/negative CRPC represented a considerable proportion of diagnoses. Because these subtypes cannot be effectively treated with AR-targeted therapeutics, a better understanding of AR low/negative subtypes could lead to better treatment strategies and increased survival.

The role of adrenal derived androgens in castration resistant prostate cancer

Castration resistant prostate cancer (CRPC) remains androgen dependant despite castrate levels of circulating testosterone following androgen deprivation therapy, the first line of treatment for advanced metstatic prostate cancer. CRPC is characterized by alterations in the expression levels of steroidgenic enzymes that enable the tumour to derive potent androgens from circulating adrenal androgen precursors. Intratumoral androgen biosynthesis leads to the localized production of both canonical androgens such as 5α-dihydrotestosterone (DHT) as well as less well characterized 11-oxygenated androgens, which until recently have been overlooked in the context of CRPC. In this review we discuss the contribution of both canonical and 11-oxygenated androgen precursors to the intratumoral androgen pool in CRPC. We present evidence that CRPC remains androgen dependent and discuss the alterations in steroidogenic enzyme expression and how these affect the various pathways to intratumoral androgen biosynthesis. Finally we summarize the current treatment strategies for targeting adrenal derived androgen biosynthesis.

Discovery and development of ODM-204: A Novel nonsteroidal compound for the treatment of castration-resistant prostate cancer by blocking the androgen receptor and inhibiting CYP17A1

We report the discovery of a novel nonsteroidal dual-action compound, ODM-204, that holds promise for treating patients with castration-resistant prostate cancer (CRPC), an advanced form of prostate cancer characterised by high androgen receptor (AR) expression and persistent activation of the AR signaling axis by residual tissue androgens. For ODM-204, has a dual mechanism of action. The compound is anticipated to efficiently dampen androgenic stimuli in the body by inhibiting CYP17A1, the prerequisite enzyme for the formation of dihydrotestosterone (DHT) and testosterone (T), and by blocking AR with high affinity and specificity. In our study, ODM-204 inhibited the proliferation of androgen-dependent VCaP and LNCaP cells in vitro and reduced significantly tumour growth in a murine VCaP xenograft model in vivo. Intriguingly, after a single oral dose of 10-30 mg/kg, ODM-204 dose-dependently inhibited adrenal and testicular steroid production in sexually mature male cynomolgus monkeys. Similar results were obtained in human chorionic gonadotropin-treated male rats. In rats, leuprolide acetate-mediated (LHRH agonist) suppression of the circulating testosterone levels and decrease in weights of androgen-sensitive organs was significantly and dose-dependently potentiated by the co-administration of ODM-204. ODM-204 was well tolerated in both rodents and primates. Based on our data, ODM-204 could provide an effective therapeutic option for men with CRPC.

Canonical and Noncanonical Androgen Metabolism and Activity

Androgens are critical drivers of prostate cancer. In this chapter we first discuss the canonical pathways of androgen metabolism and their alterations in prostate cancer progression, including the classical, backdoor and 5α-dione pathways, the role of pre-receptor DHT metabolism, and recent findings on oncogenic splicing of steroidogenic enzymes. Next, we discuss the activity and metabolism of non-canonical 11-oxygenated androgens that can activate wild-type AR and are less susceptible to glucuronidation and inactivation than the canonical androgens, thereby serving as an under-recognized reservoir of active ligands. We then discuss an emerging literature on the potential non-canonical role of androgen metabolizing enzymes in driving prostate cancer. We conclude by discussing the potential implications of these findings for prostate cancer progression, particularly in context of new agents such as abiraterone and enzalutamide, which target the AR-axis for prostate cancer therapy, including mechanisms of response and resistance and implications of these findings for future therapy.

Combined blockade of testicular and locally made androgens in prostate cancer: a highly significant medical progress based upon intracrinology

Recently two drugs, namely the antiandrogen MDV-3100 and the inhibitor of 17α-hydroxylase abiraterone have been accepted by the FDA for the treatment of castration-resistant prostate cancer (CRPC) with or without previous chemotherapy, with a prolongation of overall survival of 2.2-4.8 months. While medical (GnRH agonist) or surgical castration reduces the serum levels of testosterone by about 97%, an important concentration of testosterone and dihydrotestosterone remains in the prostate and activates the androgen receptor (AR), thus offering an explanation for the positive data obtained in CRPC. In fact, explanation of the response observed with MDV-3100 or enzalutamide in CRPC is essentially a blockade of the action or formation of intraprostatic androgens. In addition to the inhibition of the action or formation of androgens made locally by the mechanisms of intracrinology, increased AR levels and AR mutations can be involved, especially in very advanced disease. Future developments look at more efficient inhibitors of the action or formation of intraprostatic androgens and starting treatment earlier when blockade of androgens can exert long-term control and even cure prostate cancer treated at a stage before the appearance of metastases. This article is part of a Special Issue entitled 'Essential role of DHEA'.

Comparison of serum testosterone levels in prostate cancer patients receiving LHRH agonist therapy with or without the removal of the prostate

INTRODUCTION

: The prostate secretes enzymes and nutrients to promote sperm motility. Recent reports suggest that the prostate may also secrete testosterone, which is believed to be a fuel for prostate tumour growth. The aim of this study was to determine if a difference in serum testosterone levels exists between men on luteinizing hormone releasing-hormone (LHRH) agonists who have undergone radical prostatectomy, radiation or hormone therapy as primary prostate cancer treatment.

METHODS

: Serum testosterone levels were evaluated in 165 consecutive prostate cancer patients using LHRH analogues for >3 months. We excluded patients receiving either radiation or chemotherapy at time of time of testosterone measurement. Patients were classified based on primary treatment: (1) radical prostatectomy; (2) radiation; or (3) primary hormone therapy. We used one-way ANOVA to compare testosterone levels. Pearson correlation was used to correlate testosterone with prostate-specific antigen (PSA) and time on LHRH agonists. Multivariable linear regression was used to predict serum testosterone levels.

RESULTS

: The median (interquartile range) serum testosterone levels were 1.4 (1-1.9), 1.3 (1-1.625) and 1.25 (0.9-1.525) nmol/L for radical prostatectomy, radiation and primary hormone therapy groups, respectively. There was no statistically significant difference in testosterone levels between the groups (p = 0.3). No correlation was found between testosterone and PSA levels or time on LHRH (r = 0.02 and r = 0.01), respectively. Multivariable linear regression showed that none of the clinical variables were predictors of serum testosterone levels.

CONCLUSION

: Our study suggests that primary treatment does not affect serum testosterone levels among men using LHRH analogues.

Genomic and epigenomic alterations in prostate cancer

Prostate cancer (PC) is the second most frequently diagnosed cancer and the second leading cause of cancer deaths in man. The treatment of localized PC includes surgery or radiation therapy. In case of relapse after a definitive treatment or in patients with locally advanced or metastatic disease, the standard treatment includes the androgen-deprivation therapy (ADT). By reducing the levels of testosterone and dihydrotestosterone under the castration threshold, the ADT acts on the androgen receptor (AR), even if indirectly. The effects of the ADT are usually temporary and nearly all patients, initially sensitive to the androgen ablation therapy, have a disease progression after an 18-24 months medium term. This is probably due to the selection of the cancer cell clones and to their acquisition of critical somatic genome and epigenomic changes. This review aims to provide an overview about the genetic and epigenetic alterations having a crucial role in the carcinogenesis and in the disease progression toward the castration resistant PC. We focused on the role of the AR, on its signaling cascade and on the clinical implications that the knowledge of these aspects would have on hormonal therapy, on its failure and its toxicity.

Castration-resistant prostate cancer: targeting androgen metabolic pathways in recurrent disease

Emerging evidence suggests that despite testicular androgen ablation, residual androgens, likely of adrenal--though potentially of prostatic--origin, play a critical role in the progression of prostate cancer to recurrent "castration-resistant" disease. Thus, a reassessment of the concept of total androgen deprivation is warranted. Current treatment strategies may not only lack optimal efficacy, but may actually contribute to the selection of neoplastic clones adapted to exist and proliferate in a low (but not zero) androgen environment. Moreover, the adequacy of androgen receptor (AR) pathway inhibition cannot be surmised from serum or plasma androgen levels, but must be ascertained at the tissue and molecular level prior to drawing conclusions regarding clinical efficacy or failure. Recent studies by our group and others indicate that prostate cancers undergo an adaptive response to castration that is associated with the up-regulation of transcripts encoding enzymes involved in the biosynthesis of androgens. Targeting these metabolic enzymes either individually or using combinations of agents to inhibit testicular, adrenal, and intracrine sources may provide enhanced clinical responses in the setting of both localized and metastatic disease.

Androgen deprivation therapy: progress in understanding mechanisms of resistance and optimizing androgen depletion

Androgen deprivation therapy remains a critical component of treatment for men with advanced prostate cancer, and data support its use in metastatic disease and in conjunction with surgery or radiation in specific settings. Alternatives to standard androgen deprivation therapy, such as intermittent androgen suppression and estrogen therapy, hold the potential to improve toxicity profiles while maintaining clinical benefit. Current androgen deprivation strategies seem to incompletely suppress androgen levels and androgen-receptor-mediated effects at the tissue level. Advances in the understanding of mechanisms that contribute to castration-resistant prostate cancer are leading to rationally designed therapies targeting androgen metabolism and the androgen receptor. The results of large trials investigating the optimization of primary androgen deprivation therapy, including evaluation of intermittent androgen suppression and phase III studies of novel androgen synthesis inhibitors, such as abiraterone acetate, are eagerly awaited.

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

Although systemic androgen deprivation prolongs life in advanced prostate cancer, remissions are temporary because patients almost uniformly progress to a state of a castration-resistant prostate cancer (CRPC) as indicated by recurring PSA. This complex process of progression does not seem to be stochastic as the timing and phenotype are highly predictable, including the observation that most androgen-regulated genes are reactivated despite castrate levels of serum androgens. Recent evidence indicates that intraprostatic levels of androgens remain moderately high following systemic androgen deprivation therapy, whereas the androgen receptor (AR) remains functional, and silencing the AR expression following castration suppresses tumor growth and blocks the expression of genes known to be regulated by androgens. From these observations, we hypothesized that CRPC progression is not independent of androgen-driven activity and that androgens may be synthesized de novo in CRPC tumors leading to AR activation. Using the LNCaP xenograft model, we showed that tumor androgens increase during CRPC progression in correlation to PSA up-regulation. We show here that all enzymes necessary for androgen synthesis are expressed in prostate cancer tumors and some seem to be up-regulated during CRPC progression. Using an ex vivo radiotracing assays coupled to high-performance liquid chromatography-radiometric/mass spectrometry detection, we show that tumor explants isolated from CRPC progression are capable of de novo conversion of [(14)C]acetic acid to dihydrotestosterone and uptake of [(3)H]progesterone allows detection of the production of six other steroids upstream of dihydrotestosterone. This evidence suggests that de novo androgen synthesis may be a driving mechanism leading to CRPC progression following castration.

Intracrine androgen metabolism in prostate cancer progression: mechanisms of castration resistance and therapeutic implications

Residual tissue androgens are consistently detected within the prostate tumors of castrate individuals and are thought to play a critical role in facilitating the androgen receptor-mediated signaling pathways leading to disease progression. The source of residual tumor androgens is attributed in part to the uptake and conversion of circulating adrenal androgens. Whether the de novo biosynthesis of androgens from cholesterol or earlier precursors occurs within prostatic tumors is not known, but it has significant implications for treatment strategies targeting sources of androgens exogenous to the prostate versus 'intracrine' sources within the prostatic tumor. Moreover, increased expression of androgen-metabolizing genes within castration-resistant metastases suggests that up-regulated activity of endogenous steroidogenic pathways may contribute to the outgrowth of 'castration-adapted' tumors. These observations suggest that a multi-targeted treatment approach designed to simultaneously ablate testicular, adrenal and intracrine contributions to the tumor androgen signaling axis will be required to achieve optimal therapeutic efficacy.

Na+,K(+)-ATPase: the actual androgen receptor of the prostate?

While the nucleus may play a secondary role in androgen regulation of prostatic functional and structural development, I propose that, in the fully developed gland, the pace of all metabolism, biosynthesis, secretion and reparative proliferation in the gland is coupled to and set by the action of androgen on the Na+,K(+)-ATPase of the plasma membrane. This report identifies the three questions which must be asked and affirmatively answered to verify this hypothesis: 1. Straightforward procedures for the unambiguous demonstration of the coupling of (Na+,K+)-ATPase activity to glycolysis, oxidative metabolism, protein synthesis, cell alkalinization and citrate synthesis/secretion and that addition of androgen in vitro boosts the rates of the enzyme and all its coupled processes. 2. Demonstration that the stimulatory effect of the androgen is on the specific catalytic activity of each (Na+,K+)-ATPase molecule, not on the number of these enzyme units present. 3. Provision of means to show a likely mechanism for this activation; viz. shift in enzyme conformation.

Effects of castration compared with total androgen blockade on tissue dihydrotestosterone (DHT) concentration in benign prostatic hyperplasia (BPH)

We compared the effect of a variety of drug regimens to lower prostate DHT concentration. Patients with BPH were treated for one week prior to surgery with either tamoxifen, flutamide, megestrol acetate, megestrol acetate plus tamoxifen and megestrol acetate plus DES or ketoconazole. DHT concentration in the surgically resected tissue was compared with tissues obtained from untreated patients. We also obtained prostate tissue at the time of relapse in patients with prostate cancer who had been treated with orchiectomy with or without estrogen therapy. Megestrol acetate plus the mini-dose of DES (0.1 mg) and megestrol acetate plus ketoconazole both decreased DHT concentrations in prostate tissue to levels (0.79 ng/g) significantly below those noted with orchiectomy (1.16 ng/g). The difference between the DHT concentration in the two groups (orchiectomy vs. total androgen blockade) represents the contribution of adrenal androgens to prostate tissue DHT. This small amount of DHT (approximately 0.4 ng/g) may be biologically important in stimulating prostate epithelial cell growth.

Effect of antiandrogen and/or antiestrogen blockade on human prostate epithelial and stromal cell protein synthesis

To evaluate the role of small amounts of DHT in prostate tissue as a stimulus to epithelial cell growth (protein synthesis) we studied tissue from patients given various androgen-blocking drugs prior to transurethral resection of the prostate (TURP) and measured epithelial protein synthesis and DHT in the tissue specimens. We also studied the effects on stromal cell protein synthesis of an antiestrogen, tamoxifen. Test drugs prior to TURP included Megace 160 mg per day, Megace 160 mg per day plus Tamoxifen 40 mg per day, Megace 160 mg a day plus ketoconazole 1200 mg per day and tamoxifen 40 mg/day. The tissue was processed immediately and epithelial and stromal cells separated by digestion of tissue with 0.5% collagenase. After separation, epithelial cells were labeled with either [3H]leucine or L-[35S]methionine. Stromal cells were labelled with [3H]proline. DHT was measured in whole prostate tissue. Megace alone and Megace plus tamoxifen significantly decreased both [3H]leucine incorporation into protein and tissue concentration of DHT; Megace plus ketoconazole significantly decreased L-[35S]methionine incorporation into protein and DHT. Tamoxifen significantly decreased stromal protein synthesis. When the data correlating DHT with epithelial protein synthesis using both labeling techniques were combined, the curves were parallel and a strong correlation was noted between DHT and protein synthesis over a wide range of values (P less than 0.001). These results suggest that in hormone-dependent prostate cancer even small amounts of prostate DHT such as may occur from adrenal androgens following castration may significantly stimulate growth of the tumor epithelial cells. Since tamoxifen decreased stromal protein synthesis, estrogen is likely a significant growth stimulus to the increased stromal mass characteristic of benign prostatic hypertrophy.

Effects of androgen blockade with ketoconazole and megestrol acetate on human prostatic protein patterns

We studied the effects of megestrol acetate (MA) and ketoconazole (KC) on protein synthesis of epithelial and stromal cells of human prostate. Patients with benign prostatic hypertrophy (BPH) were treated with MA (160 mg/day) plus KC (1,200 mg/day) for 7 days. Prostate tissues obtained from transurethral resection (TURP) were separated into epithelial and stromal cells with 0.5% collagenase. The separated cells were incubated with L-35S-methionine in methionine-free MEM at 37 degrees C for 3 hr. The protein synthesis in both epithelial and stromal cells was significantly inhibited in the group treated with MA and KC when compared to a control group (p less than 0.05). The proteins incorporated with L-35S-methionine were analyzed by SDS-PAGE and autoradiography. The molecular weights of the epithelial and stromal proteins inhibited ranged between 35-55K.