Pharmacology of antiandrogens and value of combining androgen suppression with antiandrogen therapy

Mapping actionable pathways and mutations in brain tumours using targeted RNA next generation sequencing

Many biology-based precision drugs are available that neutralize aberrant molecular pathways in cancer. Molecular heterogeneity and the lack of reliable companion diagnostic biomarkers for many drugs makes targeted treatment of cancer inaccurate for many individuals. Identifying actionable hyperactive biological pathways in individual cancers may improve this situation.

To achieve this we applied a novel targeted RNA next generation sequencing (t/RNA-NGS) technique to surgically obtained glioma tissues. The test combines mutation detection with analysis of biological pathway activities that are involved in tumour behavior in many cancer types (e.g. tyrosine kinase signaling, angiogenesis signaling, immune response, metabolism), via quantitative measurement of transcript levels and splice variants of hundreds of genes. We here present proof of concept that the technique, which uses molecular inversion probes, generates a histology-independent molecular diagnosis and identifies classifiers that are strongly associated with conventional histopathology diagnoses and even with patient prognosis. The test not only confirmed known glioma-associated molecular aberrations but also identified aberrant expression levels of actionable genes and mutations that have so far been considered not to be associated with glioma, opening up the possibility of drug repurposing for individual patients. Its cost-effectiveness makes t/RNA-NGS to an attractive instrument to aid oncologists in therapy decision making.

Marine- and plant-derived ω-3 fatty acids differentially regulate prostate cancer cell proliferation

Fish oil contains the marine ω-3 polyunsaturated fatty acids (ω-3 PUFAs) docosahexaenoic (DHA) and eicosapentaenoic acid (EPA). The consumption of diets rich in these fatty acids is associated with a decreased incidence of prostate cancer. However, there is limited knowledge regarding the non-marine ω-3 PUFA α-linolenic acid (ALA). To study which ω-3 PUFAs are more effective in prostate cancer prevention, and whether the mechanisms of action are conserved between them, we investigated the effect of DHA, EPA and ALA on the human prostate cancer cell lines PC-3 and LNCaP. Different trends of inhibition of PC-3 cell proliferation were observed for the three ω-3 PUFA, with DHA having the most pronounced effects on cell proliferation, while ALA had the minimum effects of the three ω-3 PUFAs. All the ω-3 PUFAs decreased fatty acid synthase (FASN) mRNA. Concerning genes involved in inflammation, cell cycle and apoptosis, DHA regulated the most genes in all categories, followed by EPA and then ALA. In addition, DHA and EPA increased the gene expression of the pro-apoptotic protein activating transcription factor 3 mRNA. Moreover, these two fatty acids significantly induced apoptosis. In conclusion, while some mechanisms of cancer cell inhibition are conserved among ω-3 PUFA, the extent, magnitude, and duration of transcriptional changes vary for each individual fatty acid.

New insights into the androgen-targeted therapies and epigenetic therapies in prostate cancer

Prostate cancer is the most common cancer in men in the United States, and it is the second leading cause of cancer-related death in American men. The androgen receptor (AR), a receptor of nuclear family and a transcription factor, is the most important target in this disease. While most efforts in the clinic are currently directed at lowering levels of androgens that activate AR, resistance to androgen deprivation eventually develops. Most prostate cancer deaths are attributable to this castration-resistant form of prostate cancer (CRPC). Recent work has shed light on the importance of epigenetic events including facilitation of AR signaling by histone-modifying enzymes, posttranslational modifications of AR such as sumoylation. Herein, we provide an overview of the structure of human AR and its key structural domains that can be used as targets to develop novel antiandrogens. We also summarize recent findings about the antiandrogens and the epigenetic factors that modulate the action of AR.

Novel, potent anti-androgens of therapeutic potential: recent advances and promising developments

The beneficial effect of androgen ablation has been well established in prostate cancer therapy. Despite the initial response, patients typically relapse with a more aggressive form described as castration-resistant prostate cancer (CRCP), driven by continued androgen receptor (AR) signaling. This review details the current state of anti-androgen therapy, mainly for CRPC, with major emphasis on the most potent and promising compounds under development. Anti-androgen failure has been linked to elevated AR expression, increased expression of coactivator proteins, AR mutations, ligand-independent AR activation and persistent intraprostatic androgens. MDV3100, BMS-641988 and VN/124-1 were developed to overcome these mechanisms. In CRCP, prostate cancer cells still rely on intracellular androgens and, to a greater extent, on active AR for growth and survival. Therefore, potent anti-androgens that efficiently disrupt the functions (signaling) of AR are envisioned to be effective drugs for all types of prostate cancers.

Androgen cell signaling pathways involved in neuroprotective actions

As a normal consequence of aging in men, testosterone levels significantly decline in both serum and brain. Age-related testosterone depletion results in increased risk of dysfunction and disease in androgen-responsive tissues, including brain. Recent evidence indicates that one deleterious effect of age-related testosterone loss in men is increased risk for Alzheimer's disease (AD). We discuss recent findings from our laboratory and others that identify androgen actions implicated in protecting the brain against neurodegenerative diseases and begin to define androgen cell signaling pathways that underlie these protective effects. Specifically, we focus on the roles of androgens as (1) endogenous negative regulators of beta-amyloid accumulation, a key event in AD pathogenesis, and (2) neuroprotective factors that utilize rapid non-genomic signaling to inhibit neuronal apoptosis. Continued elucidation of cell signaling pathways that contribute to protective actions of androgens should facilitate the development of targeted therapeutic strategies to combat AD and other age-related neurodegenerative diseases.

Impact level of dihydrotestosterone on the hypothalamic-pituitary-leydig cell axis in men

Dihydrotestosterone (DHT) the physiologically most potent androgen cannot be aromatised into oestrogen. DHT is used as a treatment for idiopathic gynaecomastia. In order to investigate the different sites of action of DHT on the hypothalamic-pituitary-testicular axis, two groups of adult men were studied. Group I included 10 gonadotropin-releasing hormone (GnRH)-deficient men who were evaluated before and during a pulsatile infusion of GnRH alone for 2 weeks and then in association with DHT given transdermally at doses used in the treatment of gynaecomastia for further two weeks. Luteinizing hormone (LH) pulsatility was assessed at the end of each step of the study. Plasma LH levels were measured every 15 min. Plasma testosterone (T), DHT, oestradiol (E2), free alpha-subunit (FAS) of glycoproteic hormones and LH bioactivity were measured on pooled plasma samples. Group II included 12 healthy men in whom plasma T, DHT and E2 were measured before and then 24, 48 and 72 h after the injection of 5000 IU hCG alone or in combination with either DHT or the pure anti-androgen nilutamide. Two weeks separated each of the 3 hCG testing. In group I, except for bioactive/immunoreactive (B/I) LH ratio which was unchanged, GnRH treatment induced significant rises (p < 0.01) in all plasma hormone levels, LH pulse amplitude and frequency. During treatment with GnRH+DHT, plasma DHT levels increased up to 16.8 +/- 2.5 nm, while plasma hormone levels, B/I LH ratio, LH pulse amplitude and frequency were similar to those obtained with GnRH alone. In group II, the peak of hCG-induced T rise was not modified by either DHT or nilutamide. In contrast, DHT reduced by 50% (p < 0.01) the E2 peak in response to hCG. These data show that DHT exerts no direct action on the pituitary to retroregulate LH secretion and to modify either B/I LH ratio or FAS secretion. Its reducing effect on LH secretion is likely mediated at the hypothalamic level. DHT does not appear to have a physiological influence on Leydig cells steroidogenesis. Administered at therapeutic doses, DHT directly reduces testicular aromatase activity that combined with its antigonadotropic effect leads to the gain in the symptomatic treatment of gynaecomastia.

Flutamide and cyproterone acetate exert agonist effects: induction of androgen receptor-dependent neuroprotection

Androgens can exert profound effects on the organization, development, and function of the nervous system through activation of androgen receptors (ARs). Nonsteroidal and steroidal antiandrogens antagonize AR-mediated, classic genomic actions of androgens. However, emerging studies in nonneuronal cells indicate that antiandrogens can act as partial agonists for the AR. Here we investigated the effects of the antiandrogens flutamide and cyproterone acetate on neuroprotection induced by dihydrotestosterone (DHT). We observed that, although flutamide and cyproterone acetate blocked androgen-induced gene expression, they failed to inhibit DHT protection against apoptotic insults in cultured hippocampal neurons. Interestingly, flutamide and cyproterone acetate alone, like DHT, significantly reduced apoptosis. Furthermore, the protective actions of flutamide and cyproterone acetate were observed specifically in AR-expressing cell lines, suggesting a role for AR in the agonist effects of antiandrogens. Our results indicate that, in contrast to the classic antiandrogen properties of flutamide and cyproterone acetate, these AR modulators display agonist activities at the level of neuroprotection. These findings provide new insight into the agonist vs. antagonist properties of antiandrogens, information that will be crucial to understanding the neural implications of clinically used AR-modulating drugs.

Oncology exploration: charting cancer medicinal chemistry space

Approaches for the experimental determination of protein-ligand molecular interactions are reliant on the quality of the compounds being tested. The application of large, randomly designed combinatorial libraries has given way to the creation of more-focused 'drug-like' libraries. Prior to synthesis, we wish to screen the potential compounds to remove undesired chemical moieties and to be within a required range of physiochemical properties. We have used a principal-component analysis (PCA) computational approach to analyze the 3D descriptor space of active and non-active (hit-like) cancer medicinal chemistry compounds. We define hit-like those molecules passing the unmodified OpenEye FILTER program. Our analysis indicates that these compounds occupy quite different regions in space. Cancer-active compounds exist in a much greater volume of space than generic hit-like space and most of them fail the commonly applied filters for orally bioavailable drugs. This is of great significance when designing orally bioavailable cancer target drugs.

Orchiectomy or androgen receptor blockade attenuates baroreflex-mediated bradycardia in conscious rats

BACKGROUND

Previous studies have shown that testosterone enhances baroreflex bradycardia. Therefore, conscious unrestrained rats were used to investigate the role of the androgen receptor in the testosterone-mediated modulation of baroreflex bradycardia. Androgen depletion (3 weeks), and androgen receptor blockade (20-24 h), were implemented to test the hypothesis that testosterone influences baroreflex bradycardia via its activity at the androgen receptor in male rats. Phenylephrine (1-16 microg kg(-1)) was used to assess baroreflex bradycardia.

RESULTS

Androgen depletion attenuated baroreflex bradycardia (P < 0.01). The antiandrogen flutamide (5, 15, or 30 mg kg(-1), s.c.) caused dose-related attenuation of baroreflex bradycardia in spite of a significant (P < 0.05) increase in serum testosterone. The latter did not lead to increased serum 17beta-estradiol level.

CONCLUSION

The data suggest: 1) Androgen depletion or adequate androgen receptor blockade attenuates baroreflex bradycardia. 2) The reflex increase in serum testosterone may counterbalance the action of the lower doses (5 or 15 mg kg(-1)) of flutamide. 3) The absence of a change in serum 17beta-estradiol rules out its contribution to flutamide action on baroreflex bradycardia.

In vitro and in vivo structure-activity relationships of novel androgen receptor ligands with multiple substituents in the B-ring

We recently reported two nonsteroidal androgen receptor (AR) ligands that demonstrate tissue-selective pharmacological activity, identifying these S-3-(phenoxy)-2-hydroxy-2-methyl-N-(4-nitro-3-trifluoromethyl-phenyl)-propionamide analogs as the first members of a new class of drugs known as selective androgen receptor modulators. The purpose of these studies was to explore additional structure-activity relationships of selective androgen receptor modulators to enhance their AR binding affinity, AR-mediated transcriptional activation, and in vivo pharmacological activity. The AR binding affinity (K(i)) of 29 novel synthetic AR ligands was determined by a radioligand competitive binding assay and ranged from 1.0-51 nM. Compounds with electron-withdrawing substituents at the para- and meta-positions of the B-ring demonstrated the highest AR binding affinity. The AR-mediated transcriptional activation was determined using a cotransfection assay in CV-1 cells. Most compounds with two substituents in the B-ring maintained or improved their functional activity in vitro. However, compounds with three halogen substituents exhibited significant regioselectivity. Fifteen compounds were selected to examine their pharmacological activity in castrated rats. In vivo pharmacological activity and selectivity were significantly changed by structural modification in the B-ring. Compounds with halogen groups at the para- and meta-positions of the B-ring displayed the highest pharmacological activity. Incorporating substituents at the ortho-position of the B-ring resulted in poor pharmacological activity. In vitro and in vivo agonist activities were partially correlated. In conclusion, novel selective androgen receptor modulators with improved in vivo pharmacological activity can be designed and synthesized based on the structure-activity relationship identified in these studies.

In utero exposure to antiandrogens alters the responsiveness of the prostate to p,p'-DDE in adult rats and may induce prostatic inflammation

DDE is an environmental pollutant with antiandrogenic properties. Following administration to pregnant rats, DDE was shown to cause feminization in the male offspring at the neonatal stages but did not affect the pubertal growth of accessory sex organs. In this study, we examined the potential of in utero exposure to antiandrogens to alter the responsiveness of the male rats to subsequent DDE challenge. Pregnant Long-Evans rats were dosed by gavage from Gestation Day 14 to 18 at 0, 10 (low dose), or 100 (high dose) mg DDE, or 40 mg flutamide/kg body wt (bw)/day (in utero treatment). At approximately 80 days of age, the male offspring from each of the four in utero treatment groups were divided into two groups. One group received the adult treatment of four daily gavage administrations of DDE at 70 mg/kg bw (adult treatment), while the second group served as the adult treatment control (adult control). The in utero treatment resulted in 18, 31, and 53% reductions of ventral prostate weights at approximately 85 days of age compared to the control for the low- and high-dose DDE and flutamide groups, respectively. These results suggest that the in utero antiandrogen treatments produced a latent effect on prostate growth that became pronounced only in the postpubertal stage. The in utero treatment also altered the responsiveness of the prostate to the adult treatment, indicated by a significant reduction in ventral prostate weight that was seen only in the control group of the in utero treatment but not in the other groups. The in utero treatment was also associated with expression of testosterone-repressed prostatic message-2 in the adult ventral prostate. In addition, a few prostates in the high-dose DDE- and flutamide-treated groups of the in utero treatment were found to have chronic suppurative prostatitis. While other types of hormonal manipulations have been shown to incite similar responses in rat prostate, the possible linkage between in utero antiandrogen treatment and prostatic inflammation needs to be further evaluated.

Nilutamide: an antiandrogen for the treatment of prostate cancer

OBJECTIVE

To review the pharmacology, pharmacokinetics, efficacy, and adverse effects of nilutamide and to compare this agent with the currently marketed nonsteroidal antiandrogens (i.e., bicalutamide, flutamide) by critically analyzing the published literature.

DATA SOURCES

MEDLINE (1980-1995) and CANCERLIT (1991-1995) were searched for English-language publications using the terms nilutamide, bicalutamide, and flutamide alone, and either nilutamide or androgen antagonists in combination with prostatic neoplasms.

STUDY SELECTION AND DATA EXTRACTION

All articles with subject matter on nilutamide, bicalutamide, and flutamide were considered for inclusion. For studies published in more than one journal, the first publication was used unless a subsequent publication included additional or follow-up data, in which case the latter publication was cited instead.

DATA SYNTHESIS

Nilutamide was effective in combination with orchiectomy in improving responses in patients with advanced prostate cancer. However, patient survival was not improved in these trials, and improvements in bone pain did not usually result in improved performance status in these patients. The few trials of nilutamide monotherapy or nilutamide in combination with a luteinizing hormone-releasing hormone analog are too small to draw meaningful conclusions regarding its efficacy or its role in the treatment of advanced prostate cancer. No comparative trials of nilutamide with other antiandrogens and no analysis of the impact of nilutamide on patient quality of life are currently available. Nilutamide appears to produce a higher frequency of adverse effects than the other currently marketed nonsteroidal antiandrogens, bicalutamide and flutamide.

CONCLUSIONS

Nilutamide does not appear to represent a major advance in the treatment of advanced prostate cancer and appears to be somewhat inferior to both flutamide and bicalutamide with regard to adverse effects. Nilutamide should not be considered the antiandrogen of choice in the treatment of advanced prostate cancer.

Is there a role for induction androgen deprivation prior to radical prostatectomy?

The potential advantages of neoadjuvant androgen deprivation include decreased prostatic size, reduced vasculature, and reduced incidence of positive margins. The potential disadvantages are the side effects of hormonal medication, cost, tissue reaction, treatment "delay," and progression of androgen-independent clones. Many theories have been postulated to explain the observed reduction in the incidence of positive margins with neoadjuvant hormonal treatment. It is possible that the reduced prostate size and the frequently found periprostatic tissue reaction facilitate dissection, allowing better cancer clearance. It is possible, however, that the fibrosis may also increase the surgical difficulty, which critics argue may increase the risk of a positive margin. It is difficult to conceive of a research methodology that could resolve this issue. The occurrence of tumor cell death is likely a more significant explanation for the improved results. Whether tumor cells beyond the prostatic capsule are consistently affected to pathologically downstage the disease is unknown. The careful pathologic assessment in the randomized trials discussed previously suggests that pathologic downstaging is not as common as earlier reports have suggested. Difficulty in interpreting pathologic specimens after neoadjuvant treatment must be considered. At this point, neoadjuvant hormonal treatment prior to surgery would appear appropriate for those patients at high risk of having a positive surgical margin. Specifically, this includes clinical stage T2b, PSA elevation greater than 10 to 20 ng/mL, and a high Gleason score on the prostatic biopsy. Research to date suggests that neoadjuvant hormonal therapy prior to radical prostatectomy has a significant effect in reducing the incidence of positive surgical margins. The treatment is well tolerated with minimal side effects. Whether this will translate into improved disease-free survival remains to be determined. Fortunately, the randomized trials have been completed and follow-up data will be forthcoming.

Is disease flare a problem?

When given for the first time to previously untreated patients with advanced prostate cancer, luteinizing hormone-releasing hormone (LHRH) analogs induce a transient rise in pituitary luteinizing hormone levels. As a consequence of this increase of LH, there is, within the first 2 to 3 days, a surge of testosterone, which can cause an exacerbation of the symptoms. First reports concerning this flare have been anecdotal, and in most studies, flare is reported with an incidence of 4-33%. This variance is due mainly to the confusion about the definition of the flare phenomenon. No distinctions have been made between clinical flare, with its manifestations of subjective or objective aggravation of cancer related symptoms, and the biochemical flare that results of the LHRH analog administration and that occurs in a majority of patients and is characterized by increases in testosterone, prostatic acid phosphatase, and prostate specific antigen. As the possible interference of the flare phenomenon on the ultimate aftermath of the patient's response to therapy is not yet known, it seems mandatory that flare prevention should be carried out whenever LHRH analogs are prescribed in monotherapy.

Antiandrogenic agents as monotherapy in advanced prostatic carcinoma

Pure antiandrogens have a quality-of-life advantage over other androgen ablation methods in the treatment of patients with prostatic cancer because they do not reduce the serum testosterone and therefore do not have a marked inhibitory effect on libido and potency. The long half-life of two of the three currently studied pure antiandrogens permits once-a-day administration, which should enhance patient compliance. With continued administration, there is a gradual rise in serum testosterone, and the clinical impact of this requires additional study using randomized Phase III trials. Proper stratification of patients at entry into such studies with documentation of various prognostic factors will add statistical value and enable physicians to draw better conclusion on the relative efficacy of these agents.

Characterization of human androgen receptor overexpressed in the baculovirus system

An essential step in the process of understanding the structure and function of the human androgen receptor (hAR) involves the production of large quantities of the hAR. For this purpose, the full-length hAR has been overproduced in insect cells by using a baculovirus genetic expression system. The recombinant hAR is produced in Sf21 insect cells at approximately 7 pmol/mg of protein (1 x 10(6) AR molecules per cell), which is 70-150 times greater than levels detected in androgen target tissues. Androgen can bind to the baculovirus-expressed hAR with high affinity (Kd = 0.46 nM), and the specificity of hormone binding in baculovirus-expressed hAR is essentially identical to that of bona fide hAR. An anti-AR monoclonal antibody can recognize the baculovirus-expressed hAR at approximately 100 kDa upon Western blot analysis. Sucrose gradient analysis shows that baculovirus-expressed hAR complexes sediment at 4 S in a high salt medium and these complexes can interact with anti-AR monoclonal antibody to form complexes that sediment at 8-10 S. Therefore, production of recombinant hAR from the baculovirus expression system will provide an alternative source of biologically active hAR for studies on the molecular mechanisms of androgen action.