The antiandrogen withdrawal syndrome

Targeting the androgen receptor signaling pathway in advanced prostate cancer

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PURPOSE

This article summarizes current androgen receptor (AR)-directed therapies that have received regulatory approval for the treatment of advanced prostate adenocarcinoma (herein referred to as prostate cancer, PC).

SUMMARY

PC is an androgen-dependent malignancy in which ligands including testosterone and dihydrotestosterone bind to AR, initiating androgen-AR complex translocation to the nucleus followed by AR-mediated transcription of target genes. Androgen deprivation therapy (ADT), including gonadotropin hormone-releasing hormone (GnRH) agonists with or without AR antagonists (antiandrogens), GnRH antagonists, or bilateral orchiectomy, forms the backbone of treatment for patients with metastatic castration-naive PC and/or castration-resistant PC (CRPC). ADT is also an option for high-risk, early-stage PC after prostatectomy and/or radiation. While ADT is often very effective as initial therapy, resistance ultimately develops despite suppression of gonadal and/or adrenal androgens, leading to CRCPC, which is characterized by mechanisms such as reactivation of the AR signaling pathway, AR overexpression, and gene mutations in the ligand-binding domain of AR that lead to disease progression, resulting in increased symptom burden and ultimately death. However, disease in patients with CRPC is still dependent on androgen signaling, and these patients continue on ADT to maintain a castrate level of serum testosterone. Novel hormonal therapies including agents that target AR directly (eg, AR antagonists) are often added to ADT in this setting. Targeting the AR signaling pathway led to the development of second-generation AR antagonists, examples of which include enzalutamide, apalutamide, and darolutamide. These agents do not exhibit partial agonism or possess a higher affinity for AR and are not postulated to improve survival outcomes relative to their first-generation counterparts for patients with CRPC. Lastly, the emergence of ADT, including second-generation AR antagonists, has led to the development of supportive care for treatment-related adverse effects.

CONCLUSION

Major advances have been made in targeting the AR signaling pathway in patients with advanced PC. Further studies are warranted to identify the optimal sequencing of therapies to maximize treatment benefit. Mitigation of treatment-related adverse effects presents new opportunities to advance clinical pharmacy practice.

High expression of TROP2 characterizes different cell subpopulations in androgen-sensitive and androgen-independent prostate cancer cells

Progression of castration-resistant tumors is frequent in prostate cancer. Current systemic treatments for castration-resistant prostate cancer only produce modest increases in survival time and self-renewing Tumor-Initiating Cells (TICs) are suspected to play an important role in resistance to these treatments. However it remains unclear whether the same TICs display both chemo-resistance and self-renewing abilities throughout progression from early stage lesions to late, castration resistant tumors. Here, we found that treatment of mice bearing LNCaP-derived xenograft tumors with cytotoxic (docetaxel) and anti-androgen (flutamide) compounds enriched for cells that express TROP2, a putative TIC marker. Consistent with a tumor-initiating role, TROP2^high cells from androgen-sensitive prostate cancer cell lines displayed an enhanced ability to re-grow in culture following treatment with taxane-based chemotherapy with or without androgen blockade. TROP2 down-regulation in these cells reduced their ability to recur after treatment with docetaxel, in the presence or absence of flutamide. Accordingly, in silico analysis of published clinical data revealed that prostate cancer patients with poor prognosis exhibit significantly elevated TROP2 expression level compared to low-risk patients, particularly in the case of patients diagnosed with early stage tumors. In contrast, in androgen-independent prostate cancer cell lines, TROP2^high cells did not exhibit a differential treatment response but were characterized by their high self-renewal ability. Based on these findings we propose that high TROP2 expression identifies distinct cell sub-populations in androgen-sensitive and androgen-independent prostate tumors and that it may be a predictive biomarker for prostate cancer treatment response in androgen-sensitive tumors.

Hormones and the neuromuscular control of courtship in the golden-collared manakin (Manacus vitellinus)

Many animals engage in spectacular courtship displays, likely recruiting specialized neural, hormonal and muscular systems to facilitate these performances. Male golden-collared manakins (Manacus vitellinus) of Panamanian rainforests perform physically elaborate courtship displays that include novel forms of visual and acoustic signaling. We study the behavioral neuroendocrinology of this male's courtship, combining field behavioral observations with anatomical, biochemical and molecular laboratory-based studies. Seasonally, male courtship is activated by testosterone with little correspondence between testosterone levels and display intensity. Females prefer males whose displays are exceptionally frequent, fast and accurate. The activation of androgen receptors (AR) is crucial for optimal display performance, with AR expressed at elevated levels in several neuromuscular tissues. Apparently, courtship enlists an elaborate androgen-dependent network that includes spinal motoneurons, skeletal muscles and somatosensory systems. This work highlights the value of studying non-traditional species to illuminate physiological adaptations and, hopefully, stimulates future research on other species with complex behaviors.

Key targets of hormonal treatment of prostate cancer. Part 1: the androgen receptor and steroidogenic pathways

OBJECTIVE

Knowledge of the molecular and cellular changes that occur during the transition of hormone-naïve to castration-resistant prostate cancer (CRPC) is increasing rapidly. This might provide a window of opportunity for (future) drug development, and for treating patients with these potential devastating states of disease. The objective of this review is to provide an understanding of the mechanisms that prostate cancer cells use to bypass androgen-deprived conditions.

METHODS

We searched PubMed for experimental and clinical studies that describe the molecular changes that lead to CRPC.

RESULTS

CRPC remains dependent on a functional androgen receptor (AR), AR-mediated processes, and on the availability of intraprostatic intracellular androgens. CRPCs might acquire different (molecular) mechanisms that enable them to use intracellular androgens more efficiently (AR amplification, AR protein overexpression, AR hypersensitivity), use alternative splice variants of the AR protein to mediate androgen-independent AR functioning, and have altered co-activator and co-repressor gene and protein expression. Furthermore, CRPCs might have the ability to synthesise androgens de novo from available precursors through a renewed and up-regulated synthesis of steroid-hormone converting enzymes. Blocking of enzymes key to de novo androgen synthesis could be an alternative means to treat patients with advanced and/or metastatic disease.

CONCLUSION

In CRPC, prostate cancer cells still rely on intracellular androgens and on an active AR for growth and survival. CRPCs have gained mechanisms that enable them to use steroids from the circulation more efficiently through altered gene expression, and through a renewed and up-regulated synthesis of steroid hormone-converting enzymes. Additionally, CRPCs might synthesise AR isoforms that enable AR mediated processes independent from available androgens.

Discovery and structure–activity relationships of new steroidal compounds bearing a carboxy-terminal side chain as androgen receptor pure antagonists

Lead optimization of CH4892280 (4), an androgen receptor (AR) pure antagonist, was investigated. Compounds 6 and 7, which have a carboxylic acid at the end of the side chain at the position 7alpha of dihydrotestosterone (DHT), showed partial agonistic activities in reporter gene assay (RGA). Conversion of the steroidal core structure to 17alpha-methyltestosterone gave compound 14, which showed weak pure antagonistic activity. Optimization of the side chain by the insertion of a phenyl ring led to compounds 22 and 28-30, which showed pure antagonistic activities at submicromolar concentrations. The structure-activity relationships were clarified.

Androgen and the elaborate courtship behavior of a tropical lekking bird

In most bird species, male courtship behavior is controlled by testosterone (T) and its metabolites. In species breeding in temperate and arctic regions T circulates at high levels during a relatively short courtship period because high levels of T can be costly in terms of immunocompetence and parental care. Few studies have investigated androgen modulation of courtship behavior in tropical birds. Male golden-collared manakins (Manacus vitellinus) aggregate in leks for several months and perform spectacular, acrobatic courtship displays. Here we examined whether T is elevated in golden-collared manakins during the displaying period and if courtship behavior is modulated by androgen action on androgen receptors. We measured T levels in displaying males at the beginning of the breeding season and again, one month later. In addition, both wild and captive males were treated with the anti-androgen, flutamide, and their courtship behavior was recorded for several weeks. T levels were relatively high shortly after leks were established but decreased substantially a month later, even though the amount of courtship did not change. Flutamide reduced male courtship activity for one week, but display behavior then increased after two weeks of flutamide treatment. Our studies show that androgens modulate male manakin courtship, but the amount of courtship is not directly correlated with the concentration of circulating T. These results suggest that the relationships between androgen and courtship might differ between tropical and temperate birds.

Docetaxel plus prednisone or mitoxantrone plus prednisone for advanced prostate cancer

BACKGROUND

Mitoxantrone plus prednisone reduces pain and improves the quality of life in men with advanced, hormone-refractory prostate cancer, but it does not improve survival. We compared such treatment with docetaxel plus prednisone in men with this disease.

METHODS

From March 2000 through June 2002, 1006 men with metastatic hormone-refractory prostate cancer received 5 mg of prednisone twice daily and were randomly assigned to receive 12 mg of mitoxantrone per square meter of body-surface area every three weeks, 75 mg of docetaxel per square meter every three weeks, or 30 mg of docetaxel per square meter weekly for five of every six weeks. The primary end point was overall survival. Secondary end points were pain, prostate-specific antigen (PSA) levels, and the quality of life. All statistical comparisons were against mitoxantrone.

RESULTS

As compared with the men in the mitoxantrone group, men in the group given docetaxel every three weeks had a hazard ratio for death of 0.76 (95 percent confidence interval, 0.62 to 0.94; P=0.009 by the stratified log-rank test) and those given weekly docetaxel had a hazard ratio for death of 0.91 (95 percent confidence interval, 0.75 to 1.11; P=0.36). The median survival was 16.5 months in the mitoxantrone group, 18.9 months in the group given docetaxel every 3 weeks, and 17.4 months in the group given weekly docetaxel. Among these three groups, 32 percent, 45 percent, and 48 percent of men, respectively, had at least a 50 percent decrease in the serum PSA level (P<0.001 for both comparisons with mitoxantrone); 22 percent, 35 percent (P=0.01), and 31 percent (P=0.08) had predefined reductions in pain; and 13 percent, 22 percent (P=0.009), and 23 percent (P=0.005) had improvements in the quality of life. Adverse events were also more common in the groups that received docetaxel.

CONCLUSIONS

When given with prednisone, treatment with docetaxel every three weeks led to superior survival and improved rates of response in terms of pain, serum PSA level, and quality of life, as compared with mitoxantrone plus prednisone.

Ectopic expression of the amino-terminal peptide of androgen receptor leads to androgen receptor dysfunction and inhibition of androgen receptor-mediated prostate cancer growth

Androgen receptor (AR) is a ligand-activated transcription factor that requires androgen binding to initiate a series of molecular events leading to specific gene activation. AR has been suggested to form an antiparallel homodimer based on the characteristics of high affinity interaction between the amino (N) and carboxyl (C) termini of it. Recently, it is suggested that AR N-to-C interaction is critical for the ability of this receptor to up-regulate the transcription of androgen-responsive genes, and may be a new target for treatment of prostate cancer (PCa). In this study, we investigated the effect of N-terminal (1-34) peptide of AR (ARN34) on androgen-dependent function in PCa cell. Ectopic expression of ARN34 suppressed both androgen-dependent AR N-to-C interaction and prostate specific antigen transcription. Ectopic expression of ARN34 also caused delaying translocation to the nucleus and the decreasing stability of the AR. Stable expression of ARN34 suppressed androgen-dependent cell growth of LNCaP cells. Moreover, transactivation and cell growth of the AR variant in LNCaP cells by the AR antagonist, hydroxyflutamide, were also inhibited by ARN34. Although treatment of LNCaP cells with androgen drove transition of cells from G1 to S-phase, the cells expressing ARN34 were inhibited to enter into S phase in the presence of androgen. This cell cycle arrest was attended by decrease in cyclin E levels and cyclin-dependent-kinase 2 activity, and increase in p27 levels. Our results demonstrated that disruption of AR N-to-C interaction caused by ARN34 leads to AR dysfunction and inhibition of AR-mediated prostate cancer cell growth. This approach is thus considered to provide a useful therapeutic opinion for blocking AR-mediated PCa growth.

Elevated levels of prostate-specific antigen (PSA) in prostate cancer cells expressing mutant p53 is associated with tumor metastasis

The underlying basis for rising levels of prostate-specific antigen (PSA) in prostate cancer is not fully understood, but attention has turned to the possibility that loss of normal p53 function might be directly involved. We have investigated the relationship between p53 function and PSA expression using in vitro and in vivo approaches. Three prostate cancer-derived p53 mutants (F134L, M237L, R273H) were introduced into LNCaP prostate cancer cells and stable transfectants established. Expression of mutant p53 was demonstrated by Western blot analysis, inactivation of wtp53 function, and a loss of p53-dependent responses to DNA damage induced by UV-irradiation and cisplatin. Levels of PSA mRNA and secreted protein were determined by RT-PCR and Western blotting, respectively. Serine protease activity was assessed using an esterase assay. In vivo effects of mutant p53 expression were examined after orthotopic implantation into prostates of nude mice. Expression of all p53 mutants was associated with elevated PSA mRNA and secreted PSA protein. In a representative line, mutant p53 was also associated with increased PSA protease-like activity compared with a control line expressing wildtype p53. Overall PSA levels, and PSA levels in serum from mice bearing tumors derived from cells expressing mutant p53, were increased compared with levels in mice bearing tumors derived from control cells. In addition, the tumors derived from cells with mutant p53 had increased vascularization and induced lymph node metastases. These data provide in vitro and in vivo support for the notion that p53 mutations directly contribute to increased levels of serum PSA, and are associated with more aggressive tumors.

The androgen receptor: structure, mutations, and antiandrogens

Androgens play a critical role not only in the physiological development of the prostate but also in the genesis of prostate cancer. The effects of androgen on the prostate gland and on the other tissues of the body are mediated by activation of the androgen receptor. The androgen receptor is a member of the superfamily of hormone receptors with a DNA-binding site, two zinc finger domains, and a hormone-binding site. Mutations in this receptor can be associated with loss of function or chronic endogeneous activation, depending upon the site of change. Androgens effect a conformal change in the structure of the androgen receptor associated with a change in protein phosphorylation. The androgen receptor can be activated by additional ligands affecting the hormone-binding site besides androgens. Activators and repressors of the androgen receptor modify this protein's function and are very delicately balanced such that disruptions of either function are associated with a disease state. Antiandrogens, which bind to the receptor and thus down-regulate the effects of endogeneous circulating androgens, remain the first line treatment for palliation of advanced prostate cancer. Mutations in the receptor are associated with a change in function of such compounds from antagonist to agonist in vitro. Newer evidence suggests there may be a role of intermittent androgen suppression rather than continuous suppression, perhaps by preventing overgrowth of hormone independent tumor cells. Future research focuses on the development of drugs directed at suppressing the androgen drive of the androgen sensitive clone of the tumor and making the nonsensitive subset more susceptible to cytotoxics.

Promotion of agonist activity of antiandrogens by the androgen receptor coactivator, ARA70, in human prostate cancer DU145 cells

Although hormone therapy with antiandrogens has been widely used for the treatment of prostate cancer, some antiandrogens may act as androgen receptor (AR) agonists that may result in antiandrogen withdrawal syndrome. The molecular mechanism of this agonist response, however, remains unclear. Using mammalian two-hybrid assay, we report that antiandrogens, hydroxyflutamide, bicalutamide (casodex), cyproterone acetate, and RU58841, and other compounds such as genistein and RU486, can promote the interaction between AR and its coactivator, ARA70, in a dose-dependent manner. The chloramphenicol acetyltransferase assay further demonstrates that these antiandrogens and related compounds significantly enhance the AR transcriptional activity by cotransfection of AR and ARA70 in a 1:3 ratio into human prostate cancer DU145 cells. Our results suggest that the agonist activity of antiandrogens might occur with the proper interaction of AR and ARA70 in DU145 cells. These findings may provide a good model to develop better antiandrogens without agonist activity.