Effects of novel 17alpha-hydroxylase/C17, 20-lyase (P450 17, CYP 17) inhibitors on androgen biosynthesis in vitro and in vivo

Targeting the Androgen Signaling Axis in Prostate Cancer

Activation of the androgen receptor (AR) and AR-driven transcriptional programs is central to the pathophysiology of prostate cancer. Despite successful translational efforts in targeting AR, therapeutic resistance often occurs as a result of molecular alterations in the androgen signaling axis. The efficacy of next-generation AR-directed therapies for castration-resistant prostate cancer has provided crucial clinical validation for the continued dependence on AR signaling and introduced a range of new treatment options for men with both castration-resistant and castration-sensitive disease. Despite this, however, metastatic prostate cancer largely remains an incurable disease, highlighting the need to better understand the diverse mechanisms by which tumors thwart AR-directed therapies, which may inform new therapeutic avenues. In this review, we revisit concepts in AR signaling and current understandings of AR signaling-dependent resistance mechanisms as well as the next frontier of AR targeting in prostate cancer.

Engineering C-C Bond Cleavage Activity into a P450 Monooxygenase Enzyme

The cytochrome P450 (CYP) superfamily of heme monooxygenases has demonstrated ability to facilitate hydroxylation, desaturation, sulfoxidation, epoxidation, heteroatom dealkylation, and carbon-carbon bond formation and cleavage (lyase) reactions. Seeking to study the carbon-carbon cleavage reaction of α-hydroxy ketones in mechanistic detail using a microbial P450, we synthesized α-hydroxy ketone probes based on the physiological substrate for a well-characterized benzoic acid metabolizing P450, CYP199A4. After observing low activity with wild-type CYP199A4, subsequent assays with an F182L mutant demonstrated enzyme-dependent C-C bond cleavage toward one of the α-hydroxy ketones. This C-C cleavage reaction was subject to an inverse kinetic solvent isotope effect analogous to that observed in the lyase activity of the human P450 CYP17A1, suggesting the involvement of a species earlier than Compound I in the catalytic cycle. Co-crystallization of F182L-CYP199A4 with this α-hydroxy ketone showed that the substrate bound in the active site with a preference for the (S)-enantiomer in a position which could mimic the topology of the lyase reaction in CYP17A1. Molecular dynamics simulations with an oxy-ferrous model of CYP199A4 revealed a displacement of the substrate to allow for oxygen binding and the formation of the lyase transition state proposed for CYP17A1. This demonstration that a correctly positioned α-hydroxy ketone substrate can realize lyase activity with an unusual inverse solvent isotope effect in an engineered microbial system opens the door for further detailed biophysical and structural characterization of CYP catalytic intermediates.

Preclinical models of prostate cancer - modelling androgen dependency and castration resistance in vitro, ex vivo and in vivo

Prostate cancer is well known to be dependent on the androgen receptor (AR) for growth and survival. Thus, AR is the main pharmacological target to treat this disease. However, after an initially positive response to AR-targeting therapies, prostate cancer will eventually evolve to castration-resistant prostate cancer, which is often lethal. Tumour growth was initially thought to become androgen-independent following treatments; however, results from molecular studies have shown that most resistance mechanisms involve the reactivation of AR. Consequently, tumour cells become resistant to castration - the blockade of testicular androgens - and not independent of AR per se. However, confusion still remains on how to properly define preclinical models of prostate cancer, including cell lines. Most cell lines were isolated from patients for cell culture after evolution of the tumour to castration-resistant prostate cancer, but not all of these cell lines are described as castration resistant. Moreover, castration refers to the blockade of testosterone production by the testes; thus, even the concept of "castration" in vitro is questionable. To ensure maximal transfer of knowledge from scientific research to the clinic, understanding the limitations and advantages of preclinical models, as well as how these models recapitulate cancer cell androgen dependency and can be used to study castration resistance mechanisms, is essential.

Antiandrogenic Effects of a Polyphenol in Carex kobomugi through Inhibition of Androgen Synthetic Pathway and Downregulation of Androgen Receptor in Prostate Cancer Cell Lines

Prostate cancer (PC) represents the most common cancer disease in men. Since high levels of androgens increase the risk of PC, androgen deprivation therapy is the primary treatment; however this leads to castration-resistant PC (CRPC) with a poor prognosis. The progression to CRPC involves ectopic androgen production in the adrenal glands and abnormal activation of androgen signaling due to mutations and/or amplification of the androgen receptor (AR) as well as activation of androgen-independent proliferative pathways. Recent studies have shown that adrenal-derived 11-oxygenated androgens (11-ketotestosterone and 11-ketodihydrotestosterone) with potencies equivalent to those of traditional androgens (testosterone and dihydrotestosterone) are biomarkers of CRPC. Additionally, dehydrogenase/reductase SDR family member 11 (DHRS11) has been reported to be a 17β-hydroxysteroid dehydrogenase that catalyzes the production of the 11-oxygenated and traditional androgens. This study was conducted to evaluate the pathophysiological roles of DHRS11 in PC using three LNCaP, C4-2 and 22Rv1 cell lines. DHRS11 silencing and inhibition resulted in suppression of the androgen-induced expression of AR downstream genes and decreases in the expression of nuclear AR and the proliferation marker Ki67, suggesting that DHRS11 is involved in androgen-dependent PC cell proliferation. We found that 5,7-dihydroxy-8-methyl-2-[2-(4-hydroxyphenyl)ethenyl]-4H-1-benzopyran-4-one (Kobochromone A, KC-A), an ingredient in the flowers of Carex kobomugi, is a novel potent DHRS11 inhibitor (IC₅₀ = 0.35 μM). Additionally, KC-A itself decreased the AR expression in PC cells. Therefore, KC-A suppresses the androgen signaling in PC cells through both DHRS11 inhibition and AR downregulation. Furthermore, KC-A enhanced the anticancer activity of abiraterone, a CRPC drug, suggesting that it may be a potential candidate for the development of drugs for the prevention and treatment of CRPC.

Androgen synthesis inhibition increases behavioural flexibility and mPFC tyrosine hydroxylase in gonadectomized male rats

Behavioural flexibility is essential to adapt to a changing environment and depends on the medial prefrontal cortex (mPFC). Testosterone administration decreases behavioural flexibility. It is well known that testosterone is produced in the gonads, but testosterone is also produced in the brain, including the mPFC and other nodes of the mesocorticolimbic system. It is unclear how testosterone produced in the brain versus the gonads influences behavioural flexibility. Here, in adult male rats, we assessed the effects of the androgen synthesis inhibitor abiraterone acetate (ABI) and long-term gonadectomy (GDX) on behavioural flexibility in two paradigms. In Experiment 1, ABI but not GDX reduced the number of errors to criterion and perseverative errors in a strategy set-shifting task. In Experiment 2, with a separate cohort of rats, ABI but not GDX reduced perseverative errors in a reversal learning task. In Experiment 1, we also examined tyrosine hydroxylase immunoreactivity (TH-ir), and ABI but not GDX increased TH-ir in the mPFC. Our findings suggest that neurally-produced androgens modulate behavioural flexibility via modification of dopamine signalling in the mesocorticolimbic system. These results indicate that neurosteroids regulate executive functions and that ABI treatment for prostate cancer might affect cognition.

Abiraterone switches castration-resistant prostate cancer dependency from adrenal androgens towards androgen receptor variants and glucocorticoid receptor signalling

INTRODUCTION

Castration-resistant prostate cancer (CRPC) remains dependent on androgen receptor (AR) signalling, which is largely driven by conversion of adrenal androgen precursors lasting after castration. Abiraterone, an inhibitor of the steroidogenic enzyme CYP17A1, has been demonstrated to reduce adrenal androgen synthesis and prolong CRPC patient survival. To study mechanisms of resistance to castration and abiraterone, we created coculture models using human prostate and adrenal tumours.

MATERIALS AND METHODS

Castration-naïve and CRPC clones of VCaP were incubated with steroid substrates or cocultured with human adrenal cells (H295R) and treated with abiraterone or the antiandrogen enzalutamide. Male mice bearing VCaP xenografts with and without concurrent H295R xenografts were castrated and treated with placebo or abiraterone. Response was assessed by tumour growth and PSA release. Plasma and tumour steroid levels were assessed by LC/MS-MS. Quantitative polymerase chain reaction determined steroidogenic enzyme, nuclear receptor and AR target gene expression.

RESULTS

In vitro, adrenal androgens induced castration-naïve and CRPC cell growth, while precursors steroids for de novo synthesis did not. In a coculture system, abiraterone blocked H295R-induced growth of VCaP cells. In vivo, H295R promoted castration-resistant VCaP growth. Abiraterone only inhibited VCaP growth or PSA production in the presence of H295R. Plasma steroid levels demonstrated CYP17A1 inhibition by abiraterone, whilst CRPC tumour tissue steroid levels showed no evidence of de novo intratumoural androgen production. Castration-resistant and abiraterone-resistant VCaP tumours had increased levels of AR, AR variants and glucocorticoid receptor (GR) resulting in equal AR target gene expression levels compared to noncastrate tumours.

CONCLUSIONS

In our model, ligand-dependent AR-regulated regrowth of CRPC was predominantly supported via adrenal androgen precursor production while there was no evidence for intratumoural androgen synthesis. Abiraterone-resistant tumours relied on AR overexpression, expression of ligand-independent AR variants and GR signalling.

The treatment landscape of metastatic prostate cancer

The treatment landscape of metastatic prostate cancer has evolved significantly over the past two decades. Several landmark phase 3 trials led to new drug approvals and rapid changes in therapy options for patients, including drugs with distinct mechanisms of action (e.g., hormonal, chemotherapy, radionuclide, immunotherapy, and targeted therapies). Therapies initially developed in later stages of the disease (metastatic castration resistant prostate cancer) have started to move earlier in the prostate cancer continuum, with new standards of care for metastatic hormone naive prostate cancer and non-metastatic castration resistant prostate cancer. Overall, patients are living longer with a better quality of life. However, despite these significant advances, prostate cancer remains a leading cause of cancer death globally. Disease heterogeneity and the emergence of therapy resistance remain significant barriers, and the identification and application of molecular biomarkers to guide the choice and sequencing of systemic agents are still in early stages. Here we discuss the current treatment landscape of metastatic prostate cancer, clinical challenges, and the emerging role of molecular biomarkers for targeting biologic subsets of advanced disease and co-targeting heterogenous resistance patterns.

Synthesis and biological activities of drugs for the treatment of osteoporosis

Osteoporosis is an asymptomatic progressive disease. With the improvement of people's living standard and the aging of population, osteoporosis and its fracture have become one of the main diseases threatening the aging society. The serious medical and social burden caused by this has aroused wide public concern. Osteoporosis is listed as one of the three major diseases of the elderly. At present, the drugs for osteoporosis include bone resorption inhibitors and bone formation promoters. The purpose of these anti-osteoporosis drugs is to balance osteoblast bone formation and osteoclast bone resorption. With the development of anti-osteoporosis drugs, new anti osteoporosis drugs have been designed and synthesized. There are many kinds of new compounds with anti osteoporosis activity, but most of them are concentrated on the original drugs with anti osteoporosis activity, or the natural products with anti-osteoporosis activity are extracted from the natural products for structural modification to obtain the corresponding derivatives or analogues. These target compounds showed good ALP activity in vitro and in vivo, promoted osteoblast differentiation and mineralization, or had anti TRAP activity, inhibited osteoclast absorption. This work attempts to systematically review the studies on the synthesis and bioactivity of anti-osteoporosis drugs in the past 10 years. The structure-activity relationship was discussed, which provided a reasonable idea for the design and development of new anti-osteoporosis drugs.

Liver tests increase on abiraterone acetate in men with metastatic prostate cancer: Natural history, management and outcome

BACKGROUND

Abiraterone acetate (abiraterone) combined with prednisone is a standard of care in metastatic castration-resistant prostate cancer. Recently, benefit in overall survival was reported in metastatic castration-sensitive prostate cancer also, and an extension of indication has been granted. Abiraterone is seldom associated with liver toxicity. The clinical management and the outcome of patients with transaminase increase while on abiraterone have not been described.

PATIENTS AND METHOD

We identified 25 men with metastatic prostate cancer and liver function test disorders occurring while on abiraterone treatment from December 2009 to September 2017 in three oncology centres in France.

RESULTS

Forty-six liver disorder events occurred in 25 patients while on abiraterone treatment. The median age at liver function test increase was 67 (55-85) years. The incidence of aspartate aminotransférase (AST) (24 events) and that of alanine aminotransférase (ALT) (22 events) increases were similar. Liver toxicity was of grade 1, 2 and 3 (Common Terminology Criteria for Adverse Events. version 4) in 7 (32%), 6 (27%) and 9 (41%) patients for ALT, and in 12 (50%), 6 (25%) and 6 (25%) for AST, respectively. The median time from abiraterone initiation to the detection of liver toxicity was 7.1 (4-95) weeks. The median time from highest ALT/AST increase to normalisation was 6.2 [2-14] weeks. In 13 patients (52%), liver tests spontaneously returned to baseline values, while abiraterone was continued at full dose.

CONCLUSION

Liver function test increase is a rare event that typically occurs within the first two months on abiraterone. Most patients experience normalisation of the tests, either spontaneously or after dose reduction/discontinuation.

A novel pregnene analogs: synthesis, cytotoxicity on prostate cancer of PC-3 and LNCPa-AI cells and in silico molecular docking study

New pregnene analogs of N-hydroxamic acid 6, imino-propane hydrazides 7 and 8 as well as the aryl amides 9-11, oxadiazole, pyrazole and sulfinyl analogs 13-15, via the hydrazide analog 5 of methyl ((5-pregnen-3β,17β-diol-15α-yl)thio)propanoate (4) were synthesized. The in vitro cytotoxic activities of selected synthesized steroids against two human prostate cancer cell lines (PC-3, and LNCaP-AI) were evaluated by MTT assay. Compound 10 was the most active cytotoxic agent among these steroids against PC-3 and LNCaP-AI cell lines with inhibition of 96.2%, and 93.6% at concentration levels of 10.0 μM and 91.8%, and of 79.8% at concentration of 1.0 μM, respectively. Molecular docking study of 10 showed a hydrogen bonding with the amino acid Asn705 residue of the receptor 1E3G, together with hydrophobic interactions. Therefore, compound 10 can be considered as a promising anticancer agent due to its potent cytotoxic activity.

Prospective computational design and in vitro bio-analytical tests of new chemical entities as potential selective CYP17A1 lyase inhibitors

The development and advancement of prostate cancer (PCa) into stage 4, where it metastasize, is a major problem mostly in elder males. The growth of PCa cells is stirred up by androgens and androgen receptor (AR). Therefore, therapeutic strategies such as blocking androgens synthesis and inhibiting AR binding have been explored in recent years. However, recently approved drugs (or in clinical phase) failed in improving the expected survival rates for this metastatic-castration resistant prostate cancer (mCRPC) patients. The selective CYP17A1 inhibition of 17,20-lyase route has emerged as a novel strategy. Such inhibition blocks the production of androgens everywhere they are found in the body. In this work, a three dimensional-quantitative structure activity relationship (3D-QSAR) pharmacophore model is developed on a diverse set of non-steroidal inhibitors of CYP17A1 enzyme. Highly active compounds are selected to define a six-point pharmacophore hypothesis with a unique geometrical arrangement fitting the following description: two hydrogen bond acceptors (A), two hydrogen bond donors (D) and two aromatic rings (R). The QSAR model showed adequate predictive statistics. The 3D-QSAR model is further used for database virtual screening of potential inhibitory hit structures. Density functional theory (DFT) optimization provides the electronic properties explaining the reactivity of the hits. Docking simulations discovers hydrogen bonding and hydrophobic interactions as responsible for the binding affinities of hits to the CYP17A1 Protein Data Bank structure. 13 hits from the database search (including five derivatives) are then synthesized in the laboratory as different scaffolds. Ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) in vitro experiments reveals three new chemical entities (NCEs) with half maximal inhibitory concentration (IC₅₀) values against the lyase route at mid-micromolar range with favorable selectivity to the lyase over the hydroxylase route (one of them with null hydroxylase inhibition). Thus, prospective computational design has enabled the design of potential lead lyase-selective inhibitors for further studies.

Accumulation and toxicity of thiamethoxam and its metabolite clothianidin to the gonads of Eremias argus

The endocrine disrupting effect of pesticides is considered to be an important factor in the decline of reptile populations. The large-scale application of neonicotinoids in the environment poses a potential threat to small farmland lizards Eremias argus. In this study, we evaluated the disruption effects of thiamethoxam and its metabolite clothianidin on the endocrine disruption of Eremias argus during 28 d exposure. Thiamethoxam and clothianidin could accumulate in the testis and ovary. Adequate blood exchange was the main cause of thiamethoxam and clothianidin accumulation in the gonads. The production of clothianidin aggravated the effect of endocrine disruption to lizards. Thiamethoxam/clothianidin exhibited two distinct ways of interfering with the endocrine disruption of the male and female lizards. Thiamethoxam/clothianidin significantly up-regulated the expression of cyp17 and cyp19 genes in the testis, which ultimately led to a significant decrease in testosterone levels and a significant increase in the 17-estradiol concentrations in plasma. The expression of the estrogen receptor gene in the liver was also significantly increased in male lizards. The significant declines in testosterone and prostaglandin D2 levels in the plasma indicated that thiamethoxam and clothianidin could cause androgen deficiency in male lizards. Meanwhile, in female lizards, thiamethoxam/clothianidin increased the expression of hsd17β gene in the ovary, causing an increase in testosterone levels in the plasma and an up-regulation of androgen receptor expression in the liver. The effects of thiamethoxam and clothianidin on male lizards were more pronounced. This study verified the possible endocrine disrupting effects of neonicotinoids and provided a new perspective for the study of global recession of reptiles.

Formation and Cleavage of C-C Bonds by Enzymatic Oxidation-Reduction Reactions

Many oxidation-reduction (redox) enzymes, particularly oxygenases, have roles in reactions that make and break C-C bonds. The list includes cytochrome P450 and other heme-based monooxygenases, heme-based dioxygenases, nonheme iron mono- and dioxygenases, flavoproteins, radical S-adenosylmethionine enzymes, copper enzymes, and peroxidases. Reactions involve steroids, intermediary metabolism, secondary natural products, drugs, and industrial and agricultural chemicals. Many C-C bonds are formed via either (i) coupling of diradicals or (ii) generation of unstable products that rearrange. C-C cleavage reactions involve several themes: (i) rearrangement of unstable oxidized products produced by the enzymes, (ii) oxidation and collapse of radicals or cations via rearrangement, (iii) oxygenation to yield products that are readily hydrolyzed by other enzymes, and (iv) activation of O₂ in systems in which the binding of a substrate facilitates O₂ activation. Many of the enzymes involve metals, but of these, iron is clearly predominant.

Bone-Targeted Therapies in Cancer-Induced Bone Disease

Cancer-induced bone disease is a major source of morbidity and mortality in cancer patients. Thus, effective bone-targeted therapies are essential to improve disease-free, overall survival and quality of life of cancer patients with bone metastases. Depending of the cancer-type, bone metastases mainly involve the modulation of osteoclast and/or osteoblast activity by tumour cells. To inhibit metastatic bone disease effectively, it is imperative to understand its underlying mechanisms and identify the target cells for therapy. If the aim is to prevent bone metastasis, it is essential to target not only bone metastatic features in the tumour cells, but also tumour-nurturing bone microenvironment properties. The currently available bone-targeted agents mainly affect osteoclasts, inhibiting bone resorption (e.g. bisphosphonates, denosumab). Some agents targeting osteoblasts begin to emerge which target osteoblasts (e.g. romosozumab), activating bone formation. Moreover, certain drugs initially thought to target only osteoclasts are now known to have a dual action (activating osteoblasts and inhibiting osteoclasts, e.g. proteasome inhibitors). This review will focus on the evolution of bone-targeted therapies for the treatment of cancer-induced bone disease, summarizing preclinical and clinical findings obtained with anti-resorptive and bone anabolic therapies.

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.

Synthesis and antiproliferative activity evaluation of steroidal imidazo[1,2-a]pyridines

An elegant approach to unknown steroidal imidazo[1,2-a]pyridine hybrids is disclosed. Unique derivatives of androstene and estrane series containing imidazo[1,2-a]pyridine motifs were prepared from 17-ethynyl steroids in good yields via copper-catalyzed cascade aminomethylation/cycloisomerization with imines. The synthesized compounds were screened for cytotoxicity against human breast (MCF-7, MDA-MB-231, HBL-100, MDA-MB-453) and prostate (LNCaP-LN3, PC-3, DU 145) cancer cell lines. The majority of tested compounds showed activities at μM level in breast cancer cells. The hormone-responsive breast cancer cells MCF-7 were more sensitive to novel compounds than ERα-negative cells; in particular, compounds 6a,b exhibited promising cytotoxicity against this cell line with the IC50 values in the range of 3-4μM. Furthermore, compound 4a showed remarkable effects as a selective ERα receptor modulator.

Ketoconazole-induced estrogen deficiency causes transient decrease in placental blood flow associated with hypoxia and later placental weight gain in rats

This study investigated the relationship among estrogen, placental blood flow and placental weight gain in rats treated with ketoconazole. Oral administration of ketoconazole (25mg/kg/day) on Days 12-14 of pregnancy induced reduction of plasma estradiol-17β (E2) concentration, transient decrease in placental blood flow and increased intensity of a hypoxia-related marker in the placenta on Day 14 of pregnancy. On Day 20 of pregnancy, placental weights of ketoconazole-treated rats increased when compared to controls. Histologically, maternal sinusoidal area of the placenta decreased on Day 14 of pregnancy and the total area of maternal and fetal sinusoids increased on Day 20. All the changes disappeared by concomitant subcutaneous infusion of E2. These results indicate that ketoconazole-induced E2 deficiency causes transient decrease in placental blood flow associated with hypoxia and later placental weight gain in rats.

New biaryl-chalcone derivatives of pregnenolone via Suzuki-Miyaura cross-coupling reaction. Synthesis, CYP17 hydroxylase inhibition activity, QSAR, and molecular docking study

A new class of steroids is being synthesized for its ability to prevent intratumoral androgen production by inhibiting the activity of CYP17 hydroxylase enzyme. The scheme involved the synthesis of chalcone derivative of pregnenolone 5 which was further modified to the corresponding biaryl-chalcone pregnenolone analogs 16-25 using Suzuki-Miyaura cross-coupling reaction. The synthesized compounds were tested for activity using human CYP17α hydroxylase expressed in Escherichia coli. Compounds 21 was the most active inhibitor in this series, with IC50 values of 0.61μM and selectivity profile of 88.7% inhibition of hydroxylase enzyme. Molecular docking study of 21 was performed and showed the hydrogen bonds and hydrophobic interaction with the amino acid residues of the active site of CYP17.

A new pregnenolone analogues as privileged scaffolds in inhibition of CYP17 hydroxylase enzyme. Synthesis and in silico molecular docking study

A new series of 17-(N-(arylimino)-5-pregnen-3β-ol derivatives 19-32 as well as carboxylate and acrylate analogues of pregnenolone 37-40 were synthesized and evaluated for their inhibitory activity against human CYP17 hydroxylase expressed in Escherichia coli. Compounds 32 and 37 were the most potent analogues in this series, showing inhibition activity with IC50 = 2.11 and 1.29 μM, respectively. However, the analogue 37 revealed a better selectivity profile (83.21% inhibition of hydroxylase), which is a leading candidate for further development. Molecular docking study of 37 showed binding with the amino acid residues of CYP17 through hydrogen bonds and hydrophobic interaction.

Differential response to abiraterone acetate and di-n-butyl phthalate in an androgen-sensitive human fetal testis xenograft bioassay

In utero exposure to antiandrogenic xenobiotics such as di-n-butyl phthalate (DBP) has been linked to congenital defects of the male reproductive tract, including cryptorchidism and hypospadias, as well as later life effects such as testicular cancer and decreased sperm counts. Experimental evidence indicates that DBP has in utero antiandrogenic effects in the rat. However, it is unclear whether DBP has similar effects on androgen biosynthesis in human fetal testis. To address this issue, we developed a xenograft bioassay with multiple androgen-sensitive physiological endpoints, similar to the rodent Hershberger assay. Adult male athymic nude mice were castrated, and human fetal testis was xenografted into the renal subcapsular space. Hosts were treated with human chorionic gonadotropin for 4 weeks to stimulate testosterone production. During weeks 3 and 4, hosts were exposed to DBP or abiraterone acetate, a CYP17A1 inhibitor. Although abiraterone acetate (14 d, 75 mg/kg/d po) dramatically reduced testosterone and the weights of androgen-sensitive host organs, DBP (14 d, 500 mg/kg/d po) had no effect on androgenic endpoints. DBP did produce a near-significant trend toward increased multinucleated germ cells in the xenografts. Gene expression analysis showed that abiraterone decreased expression of genes related to transcription and cell differentiation while increasing expression of genes involved in epigenetic control of gene expression. DBP induced expression of oxidative stress response genes and altered expression of actin cytoskeleton genes.

Targeting the adrenal gland in castration-resistant prostate cancer: a case for orteronel, a selective CYP-17 17,20-lyase inhibitor

Androgen and the androgen receptor (AR) pathway remain the key targets for emerging new therapies against castration-resistant prostate cancer (CRPC). Adrenal androgens and intratumoral testosterone production appear to be sufficient to activate AR in the castration-resistant setting. This process re-engages AR and allows it to continue to be the primary target responsible for prostate cancer progression. Adrenal androgen production can be blocked by inhibiting cytochrome P450 17α-hydroxylase/17,20-lyase (CYP17), a key enzyme for androgen synthesis in adrenal glands and peripheral tissues. Therapeutic CYP17 inhibition by ketoconazole or by the recently approved adrenal inhibitor abiraterone acetate is the only available choice to target this pathway in CRPC. A new CYP17 inhibitor, with more selective inhibition of 17,20-lyase over 17α-hydroxylase, orteronel (TAK-700), is currently undergoing phase III clinical trials in pre- and postchemotherapy CRPC. In a completed phase II trial in CRPC patients, orteronel demonstrated its efficacy by lowering the levels of circulating androgens, reducing prostate-specific antigen (PSA) levels, and decreasing the levels of circulating tumor cells. Ongoing studies evaluating orteronel in CRPC will further define its safety and role in the management of this disease.

Steroidal 5α-reductase and 17α-hydroxylase/17,20-lyase (CYP17) inhibitors useful in the treatment of prostatic diseases

The role of steroidal inhibitors of androgen biosynthesis as potential weapons in the treatment of prostatic diseases, such as benign prostatic hyperplasia and prostatic cancer will be reviewed. Two enzymes have been targeted in the development of inhibitors that potentially could be useful in the management of such conditions. 5α-Reductase is primarily of interest in benign prostatic disease, though some role in the chemoprevention of prostatic carcinoma have been considered, whereas the 17α-hydroxylase/17,20-lyase (CYP17) enzyme is of interest in the treatment of malignant disease. An overview of the main achievements obtained during the past years will be presented, however special focus will be made on steroidal molecules that reached clinical trials or have been commercially launched. Relevant examples of such drugs are finasteride, dutasteride, abiraterone acetate and galeterone (TOK-001, formerly known as VN/124-1). This article is part of a Special Issue entitled "Synthesis and biological testing of steroid derivatives as inhibitors".

The European medicines agency review of abiraterone for the treatment of metastatic castration-resistant prostate cancer in adult men after docetaxel chemotherapy and in chemotherapy-naive disease: summary of the scientific assessment of the committee for medicinal products for human use

On September 5, 2011, abiraterone was approved in the European Union in combination with prednisone or prednisolone for the treatment of metastatic castration-resistant prostate cancer (CRPC) in adult men whose disease has progressed on or after a docetaxel-based chemotherapy regimen. On December 18, 2012, the therapeutic indication was extended to include the use of abiraterone in combination with prednisone or prednisolone for the treatment of metastatic CRPC in adult men who are asymptomatic or mildly symptomatic after failure of androgen deprivation therapy in whom chemotherapy is not yet clinically indicated. Abiraterone is a selective, irreversible inhibitor of cytochrome P450 17α, an enzyme that is key in the production of androgens. Inhibition of androgen biosynthesis deprives prostate cancer cells from important signals for growth, even in cases of resistance to castration. At the time of European Union approval and in a phase III trial in CRPC patients who had failed at least one docetaxel-based chemotherapy regimen, median overall survival for patients treated with abiraterone was 14.8 months versus 10.9 months for those receiving placebo (hazard ratio, 0.65; 95% confidence interval 0.54-0.77; p < .0001). In a subsequent phase III trial in a similar but chemotherapy-naïve patient population, median radiographic progression-free survival was 16.5 months for patients in the abiraterone treatment arm versus 8.3 months for patients in the placebo arm (hazard ratio, 0.53; 95% confidence interval, 0.45-0.62; p < .0001). Abiraterone was most commonly associated with adverse reactions resulting from increased or excessive mineralocorticoid activity. These were generally manageable with basic medical interventions. The most common side effects (affecting more than 10% of patients) were urinary tract infection, hypokalemia, hypertension, and peripheral edema.

The effect of prior androgen synthesis inhibition on outcomes of subsequent therapy with docetaxel in patients with metastatic castrate-resistant prostate cancer: results from a retrospective analysis of a randomized phase 3 clinical trial (CALGB 90401) (Alliance)

BACKGROUND

Preliminary data suggest a potential decreased benefit of docetaxel in patients with metastatic, castration-resistant prostate cancer (mCRPC) who previously received abiraterone acetate, a novel androgen synthesis inhibitor (ASI). Cancer and Leukemia Group B (CALGB) trial 90401 (Alliance), a phase 3 trial in patients with mCRPC who received docetaxel-based chemotherapy, offered the opportunity to evaluate effect of prior ketoconazole, an earlier generation ASI, on clinical outcomes after docetaxel.

METHODS

In CALGB trial 90401, 1050 men with chemotherapy-naive mCRPC were randomized to receive treatment with docetaxel and prednisone that included either bevacizumab or placebo. In total, 1005 men (96%) had data available regarding prior ketoconazole therapy. The observed effects of prior ketoconazole on overall survival (OS), progression-free survival (PFS), prostate-specific antigen (PSA) decline, and the objective response rate (ORR) were assessed using proportional hazards and Poisson regression methods adjusted for validated prognostic factors and treatment arm.

RESULTS

Baseline characteristics between patients who did (N=277) and did not (N=728) receive prior ketoconazole therapy were similar. There were no statistically significant differences between patients who did and those who did not receive prior ketoconazole therapy with respect to OS (median OS, 21.1 months vs 22.3 months, respectively; stratified log-rank P=.635), PFS (median PFS, 8.1 months vs 8.6 months, respectively; stratified log-rank P=.342), the proportion achieving a decline ≥ 50% in PSA (61% vs 66%, respectively; relative risk, 1.09; adjusted P=.129), or ORR (39% vs 43%, respectively; relative risk, 1.11; adjusted P=.366).

CONCLUSIONS

As measured by OS, PFS, PSA, and the ORR, there was no evidence that prior treatment with ketoconazole had an impact on the clinical outcomes of patients with mCRPC who received subsequent docetaxel-based therapy. The current results highlight the need for prospective studies to assess for potential cross-resistance with novel ASIs and to define the optimal sequence of therapy in mCRPC.

Optimal management of recurrent prostate cancer in older patients

With a large, aging population in the USA and continued prolongation of life expectancy, treatment of cancer in the elderly will continue to be of importance. The most common cancer in men is prostate cancer, which is most often diagnosed in those over the age of 65 years. Initial therapies for prostate cancer are local treatments in those with localized disease and for whom definitive therapy is appropriate. Optimal treatment of an older patient with recurrent prostate cancer now involves more of a decision process than treatment has in the past, with the recent approval of several new medical agents for advanced prostate cancer. Through this article we will focus on treatment options for recurrent prostate cancer, keeping in mind the unique characteristics of the elderly population. A majority of the discussion will focus on many of the newly approved agents used to treat castration-resistant prostate cancer, and exciting agents currently under investigation. Improved androgen blockade has improved overall survival in patients with metastatic disease but carries many of the same adverse effects as previous agents. Newer approaches with immunotherapy, radiopharmaceuticals, or second-generation androgen receptor blockers introduce a different adverse-effect profile for older patients. As data matures, these too may improve survival for patients with metastatic disease. Throughout all stages of disease, one must keep in mind the unique needs of an older patient population.

Effect of a novel 17,20-lyase inhibitor, orteronel (TAK-700), on androgen synthesis in male rats

Endogenous androgens play a role in the development and progression of prostate cancer (PC), thus androgen suppression may offer an effective therapeutic strategy for this disease. Orteronel (TAK-700), 6-[(7S)-7-hydroxy-6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-7-yl]-N-methyl-2-naphthamide, is a novel, non-steroidal, selective inhibitor of the 17,20-lyase activity of CYP17A--a key enzyme in the production of steroidal hormones--and is being developed as a therapy for PC. The purpose of this study was to elucidate the inhibitory activity of orteronel, in particular its specificity for androgen synthesis enzymes, in male rats--an androgen-synthesis model that largely reflects this pathway in humans. Orteronel inhibited 17,20-lyase activity in rats with an IC(50) of 1200 nM but did not inhibit 17α-hydroxylase or 11β-hydroxylase (CYP11B1) activity in rats at concentrations up to 10 μM. In cellular steroidogenesis assays using rat testicular cells, orteronel suppressed testosterone and androstenedione production with an IC(50) of 640 nM and 210 nM, respectively, but did not suppress either corticosterone or aldosterone production in rat adrenal cells at concentrations up to 30 μM. In addition, serum testosterone and androstenedione levels in human chorionic gonadotropin-injected hypophysectomized rats were significantly reduced by single oral administration of orteronel at a dose of 30 mg/kg (both p ≤ 0.01); serum corticosterone and aldosterone levels in ACTH-injected hypophysectomized rats did not result in significant differences compared with controls, following orteronel administration at doses up to 300 mg/kg. Serum testosterone levels in intact male rats were significantly reduced by orteronel 4h after dosing at 100mg/kg (p ≤ 0.01); testosterone levels showed a tendency to recover afterward. In intact male rats, the weight of the prostate glands and seminal vesicles was decreased in a dose-dependent manner following multiple doses of orteronel at 37.5, 150, and 600 mg/kg, TID for 4 days. The reversibility of orteronel was further confirmed using a human adrenocortical tumor cell line. In summary, orteronel is a selective and reversible 17,20-lyase inhibitor, and decreases the weight of androgen-dependent organs in male rats. Our data suggests that orteronel would therefore be effective for androgen-dependent disorders such as PC.

Current and emerging treatments in the management of castration-resistant prostate cancer

Historically, patients diagnosed with castration-resistant prostate cancer (CRPC) have had poor survival rates. In recent years there have been significant advances in the treatment of CRPC. In addition to cytotoxic chemotherapy, treating physicians and their patients now have the option of several new agents that target not only androgen- and cytotoxic-mediated pathways, but also the patient's own immune system. In this review, we discuss the existing US FDA-approved therapies, a wide range of experimental treatments that are currently in development, and also palliative options for patients with symptoms secondary to metastatic disease. We also discuss the progression-free survival, overall survival, PSA levels and other end points used in clinical trials in order to evaluate and compare novel therapeutic options for CRPC. Currently, docetaxel and sipuleucel-T are the first line treatment options for patients with CRPC; approved second-line treatments for first line treatment failure are limited to cabazitaxel and abiraterone acetate. Recently, a few experimental agents, MDV3100 and radium-223, have demonstrated efficacy in improving overall survival in patients who had previously failed chemotherapy. These agents, and possibly others introduced in this review, are positioned to change the treatment landscape for CRPC.

Abiraterone acetate for the treatment of prostate cancer

INTRODUCTION

Prostate cancer is the second leading cause of cancer death in men in the United States. The disease is driven by androgen receptor (AR) signaling, and the majority of patients initially respond to androgen deprivation therapies. The lethal form of this disease occurs when metastatic lesions progress in the setting of low testosterone levels, in what is conventionally referred to as castration-resistant prostate cancer (CRPC). Recent insights suggest that CRPC continues to rely on an active AR pathway for cell survival and growth.

AREAS COVERED

This review summarizes the rationale, mechanism of action and relevant clinical data of abiraterone acetate , an oral androgen biosynthesis inhibitor, in the management of CRPC.

EXPERT OPINION

Abiraterone acetate is an oral, well-tolerated drug that targets a newly elucidated paradigm of continued AR activation in CRPC. Abiraterone acetate is approved in CRPC patients who have received docetaxel, and recent data suggest that the drug will also be effective and utilized in the pre-chemotherapy setting. Significant areas of scientific investigation remain in the optimization and further understanding of the therapy.

3-Pyridyl substituted aliphatic cycles as CYP11B2 inhibitors: aromaticity abolishment of the core significantly increased selectivity over CYP1A2

Aldosterone synthase (CYP11B2) is a promising therapeutic target for the treatment of cardiovascular diseases related to abnormally high aldosterone levels. On the basis of our previously identified lead compounds I–III, a series of 3-pyridinyl substituted aliphatic cycles were designed, synthesized and tested as CYP11B2 inhibitors. Aromaticity abolishment of the core was successfully applied to overcome the undesired CYP1A2 inhibition. This study resulted in a series of potent and selective CYP11B2 inhibitors, with compound 12 (IC₅₀ = 21 nM, SF = 50) as the most promising one, which shows no inhibition toward CYP1A2 at 2 µM. The design conception demonstrated in this study can be helpful in the optimization of CYP inhibitor drugs regarding CYP1A2 selectivity.

The role of abiraterone in the management of metastatic castration-resistant prostate cancer

Prostate cancer is the most common solid-organ cancer affecting the male population. Men with metastatic prostate cancer treated with androgen ablation therapy often respond rapidly, with improvement in bone pain and decreases in serum prostate-specific antigen. However, almost all patients progress to the castrate-resistant state and until recently chemotherapy was the only treatment available with proven survival benefit. Abiraterone is a new class of anti-androgen with proven survival benefit post-chemotherapy. In this review we discuss the characteristics of abiraterone and the clinical trials that led to its approval for the treatment of patients with prostate cancer.

Synthesis of D-ring-substituted (5'R)- and (5'S)-17β-pyrazolinylandrostene epimers and comparison of their potential anticancer activities

Various steroidal benzylidenes were synthetized from pregnenolone with benzaldehyde and p-substituted benzaldehydes. The resulting 17β-chalconyl derivatives of pregnenolone were reacted with hydrazine hydrate in acetic acid solution. Regardless of the starting material, the ring-closure reaction afforded (in contrast with the literature data) a mixture of two steroidal pyrazoline epimers. The epimers were critical isomer pairs, which could be separated only in their acetylated form; their structures were investigated by NMR techniques. The in vitro inhibition of rat testicular C(17,20)-lyase activity and the antiproliferative effects on four human cancer cell lines were measured, and the results obtained from the two epimer series were compared.

Optimization of hydroxybenzothiazoles as novel potent and selective inhibitors of 17β-HSD1

17β-HSD1 is a novel target for the treatment of estrogen-dependent diseases, as it catalyzes intracellular estradiol formation. Starting from two recently described compounds, highly active and selective inhibitors were developed. Benzoyl 6 and benzamide 17 are the most selective compounds toward 17β-HSD2 described so far. They also showed a promising profile regarding activity in T47-D cells, selectivity toward ERα and ERβ, inhibition of hepatic CYP enzymes, metabolic stability, and inhibition of marmoset 17β-HSD1 and 17β-HSD2.

Development and clinical utility of abiraterone acetate as an androgen synthesis inhibitor

In April 2011, abiraterone acetate (AA) was approved by the US Food and Drug Administration (FDA) for the treatment of metastatic castration-resistant prostate cancer (CRPC) after chemotherapy. The development of AA is the direct result of our increased understanding of the intricacies of the androgen receptor (AR) pathway and its natural evolution in prostate cancer cells over the course of treatment. In this paper we review the biology of the AR and how it led to the rational design of AA. We also examine the clinical development of AA, its current use, and questions to be addressed for future development.

Progress of molecular targeted therapies for prostate cancers

Prostate cancer remains the most commonly diagnosed malignancy and the second leading cause of cancer-related deaths in men in the United States. The current standard of care consists of prostatectomy and radiation therapy, which may often be supplemented with hormonal therapies. Recurrence is common, and many develop metastatic prostate cancer for which chemotherapy is only moderately effective. It is clear that novel therapies are needed for the treatment of the malignant forms of prostate cancer that recur after initial therapies, such as hormone refractory (HRPC) or castration resistant prostate cancer (CRPC). With advances in understanding of the molecular mechanisms of cancer, we have witnessed unprecedented progress in developing new forms of targeted therapy. Several targeted therapeutic agents have been developed and clinically used for the treatment of solid tumors such as breast cancer, non-small cell lung cancer, and renal cancer. Some of these reagents modulate growth factors and/or their receptors, which are abundant in cancer cells. Other reagents target the downstream signal transduction, survival pathways, and angiogenesis pathways that are abnormally activated in transformed cells or metastatic tumors. We will review current developments in this field, focusing specifically on treatments that can be applied to prostate cancers. Finally we will describe aspects of the future direction of the field with respect to discovering biomarkers to aid in identifying responsive prostate cancer patients.

Triazole ring-opening leads to the discovery of potent nonsteroidal 17β-hydroxysteroid dehydrogenase type 2 inhibitors

17β-Hydroxysteroid dehydrogenase type 2 (17β-HSD2) catalyzes the oxidation of the highly potent steroids: the estrogen estradiol (E2) and the androgen testosterone (T) to the less active estrone and androstenedione, respectively. Inhibition of this enzyme may help maintain the local E2 level in bone tissue when the circulating E2 level drops and is therefore a novel and promising approach for the treatment of osteoporosis. In this work, a series of new nonsteroidal and achiral 17β-HSD2 inhibitors, namely N-benzyl-diphenyl-3(or 4)-carboxamide and N-benzyl-5-phenyl-thiophene-2-carboxamide was designed and the compounds were synthesized in a two to three steps reaction. A small library was built applying parallel synthesis. Highly potent 17β-HSD2 inhibitors could be identified in the thiophene-2-carboxamide class with IC(50) in the low nanomolar range. These compounds also showed a good selectivity profile toward 17β-HSD1 and toward the estrogen receptors α and β. The most interesting 17β-HSD2 inhibitor identified in this study is the 5-(2-fluoro-3-methoxyphenyl)-N-(3-hydroxybenzyl)-N-methylthiophene-2-carboxamide 6w displaying an IC(50) of 61 nM and a selectivity factor of 73 toward 17β-HSD1.