Antitumor agents. 217. Curcumin analogues as novel androgen receptor antagonists with potential as anti-prostate cancer agents

A number of curcumin analogues were prepared and evaluated as potential androgen receptor antagonists against two human prostate cancer cell lines, PC-3 and DU-145, in the presence of androgen receptor (AR) and androgen receptor coactivator, ARA70. Compounds 4 [5-hydroxy-1,7-bis(3,4-dimethoxyphenyl)-1,4,6-heptatrien-3-one], 20 [5-hydroxy-1,7-bis[3-methoxy-4-(methoxycarbonylmethoxy)phenyl]-1,4,6-heptatrien-3-one], 22 [7-(4-hydroxy-3-methoxyphenyl)-4-[3-(4-hydroxy-3-methoxyphenyl)acryloyl]-5-oxohepta-4,6-dienoic acid ethyl ester], 23 [7-(4-hydroxy-3-methoxyphenyl)-4-[3-(4-hydroxy-3-methoxyphenyl)acryloyl]5-oxohepta-4,6-dienoic acid], and 39 [bis(3,4-dimethoxyphenyl)-1,3-propanedione] showed potent antiandrogenic activities and were superior to hydroxyflutamide, which is the currently available antiandrogen for the treatment of prostate cancer. Structure-activity relationship (SAR) studies indicated that the bis(3,4-dimethoxyphenyl) moieties, the conjugated beta-diketone moiety, and the intramolecular symmetry of the molecules seem to be important factors related to antiandrogenic activity. The data further suggest that the coplanarity of the beta-diketone moiety and the presence of a strong hydrogen bond donor group were also crucial for the antiandrogenic activity, which is consistent with previous SAR results for hydroxyflutamide analogues. When the pharmacophoric elements of dihydrotestosterone (DHT) and compound 4 are superposed, the resulting construct implies that the curcumin analogues may function as a 17alpha-substituted DHT. Compounds 4, 20, 22, 23, and 39 have been identified as a new class of antiandrogen agents, and these compounds or their new synthetic analogues could be developed into clinical trial candidates to control androgen receptor-mediated prostate cancer growth.     

A novel steroidal antiandrogen targeting wild type and mutant androgen receptors

Prostate cancer (PCa) progression is enhanced by androgen and treatment with antiandrogens represents an alternative to castration. While patients initially respond favorably to androgen ablation therapy, most experience a relapse of the disease within 1–2 years by expressing androgen receptor (AR) mutants. Such mutations, indeed, promote unfavorable agonistic behavior from classical antagonists. Here, we have synthesized and screened 37 novel compounds derived from dihydrotestosterone (DHT), cyanolutamide and hydroxyflutamide. These derivatives were tested for their potential antagonistic activity using a luciferase reporter gene assay and binding properties were determined for wild type (WT) and mutant ARs (T877A, W741C, W741L, H874Y). In the absence and presence of antiandrogens, androgen dependent cellular proliferation and prostate specific antigen (PSA) expression were assayed in the prostate cancer cell line LNCaP by crystal violet, real time PCR and by Western blots. Also, cellular proliferation and PSA expression were assayed in 22Rv1. A novel compound RB346, derived from DHT, was found to be an antagonist for all tested AR forms, preventing DHT induced proliferation and PSA expression in LNCaP and 22Rv1 cells. RB346 displayed no agonistic activity, in contrast to the non-steroidal antiandrogen bicalutamide (Casodex^®) with unfavorable agonistic activity for W741L-AR. Additionally, RB346 has a slightly higher binding affinity for WT-AR, T877A-AR and H874Y-AR than bicalutamide. Thus, RB346 is the first potent steroidal antiandrogen with efficacy for WT and various AR mutants.     

Androgen receptor: structure,role in prostate cancer and drug discovery

Androgens and androgen receptors (AR) play a pivotal role in expression of the male phenotype. Several diseases, such as androgen insensitivity syndrome (AIS) and prostate cancer, are associated with alterations in AR functions. Indeed, androgen blockade by drugs that prevent the production of androgens and/or block the action of the AR inhibits prostate cancer growth. However, resistance to these drugs often occurs after 2–3 years as the patients develop castration-resistant prostate cancer (CRPC). In CRPC, a functional AR remains a key regulator. Early studies focused on the functional domains of the AR and its crucial role in the pathology. The elucidation of the structures of the AR DNA binding domain (DBD) and ligand binding domain (LBD) provides a new framework for understanding the functions of this receptor and leads to the development of rational drug design for the treatment of prostate cancer. An overview of androgen receptor structure and activity, its actions in prostate cancer, and how structural information and high-throughput screening have been or can be used for drug discovery are provided herein.     

Immunisation with a Novel Hepatitis B Vaccine

The most critical problem in the treatment of prostate cancer is the emergence of hormone-refractory tumour during hormonal therapy. Although the vast majority of patients initially have an excellent response to androgen withdrawal, disease will often return later. There is no effective treatment for such hormone-refractory prostate cancer. Despite the fact that the mechanisms leading to transition from androgen-dependent to androgen-independent disease have been extensively studied, they have mostly remained unclear. It was earlier considered that the growth of hormone-refractory tumour is independent of androgens and androgen receptor (AR) signalling pathways. Recently, however, several studies have indicated that aberrations in the AR signalling pathway could actually be key mechanisms in androgen independence. For example, the revelations of AR gene amplification, mutations and cross-talk with the ERBB2 pathway suggest that AR is still operational in hormone-refractory tumours. Thus, AR is a putative new-old target for novel treatment modalities.     

Pharmacokinetics and Pharmacodynamics of Nonsteroidal Androgen Receptor Ligands

Testosterone and structurally related anabolic steroids have been used to treat hypogonadism, muscle wasting, osteoporosis, male contraception, cancer cachexia, anemia, and hormone replacement therapy in aging men or age-related frailty; while antiandrogens may be useful for treatment of conditions like acne, alopecia (male-pattern baldness), hirsutism, benign prostatic hyperplasia (BPH) and prostate cancer. However, the undesirable physicochemical and pharmacokinetic properties of steroidal androgen receptor (AR) ligands limited their clinical use. Nonsteroidal AR ligands with improved pharmacological and pharmacokinetic properties have been developed to overcome these problems. This review focuses on the pharmacokinetics, metabolism, and pharmacology of clinically used and emerging nonsteroidal AR ligands, including antagonists, agonists, and selective androgen receptor modulators.     

The androgen receptor as putative therapeutic target in hormone-refractory prostate cancer

The androgen receptor (AR) plays a central role in the initiation and growth of prostate cancer. Androgen deprivation therapy (ADT) has been a gold standard for advanced prostate cancer for decades. Unfortunately, suppressive effects of ADT do not last long and hormone-refractory prostate cancer develops within several years. In spite of extensive research on mechanisms of hormone-independent growth of prostate cancer, there are few effective treatment options for recurrent tumors and most patients die from the disease in a short period of time. Accumulating evidence suggests that the AR signaling system remains intact and activated despite low levels of androgens in hormone-resistant prostate cancer. Currently, modifications to the AR via mutations, amplification and phosphorylation have been proposed as underlying mechanisms of hormone-resistance of prostate cancer cells. In addition, changes in AR cofactors are implicated in ligand-independent activation of AR signaling. Thus, the development of novel and more effective treatment modalities targeting the AR and AR-related molecules may provide better management of androgen-independent prostate cancer. Although recent patents on the AR related to prostate cancer are focused on antiandrogens, future trend will be shifted to agents or methods suppressing molecules or pathways that activate AR signaling in low androgen environments.     

雄激素受体抑制剂的研究进展

雄激素受体与前列腺癌的发生、发展密切相关,是配体依赖的转录因子,其与雄激素结合后发生构象转化形成二聚体而活化,并进入细胞核中与相应的 DNA 反应元件结合,促进靶基因的转录,进而促进细胞的增殖。在前列腺癌组织中,雄激素受体的增殖或突变能使其对血清中较低含量的雄激素敏感,是前列腺癌恶化的主要原因。设计合成对野生型及突变型雄激素受体具有较好抑制活性的药物是治疗前列腺癌的首要策略。该文综述了雄激素受体的结构、功能及其抑制剂的研究进展,期望为新型抗前列腺癌药物的设计研究提供参考。     

Structural basis for the glucocorticoid response in a mutant human androgen receptor (AR(ccr)) derived from an androgen-independent prostate cancer

The crystal structure of a mutant androgen receptor (AR) ligand-binding domain (LBD) in complex with the agonist 9alpha-fluorocortisol has been determined at 1.95 A resolution. This mutant AR contains two mutations (L701H and T877A) and was previously reported as a high-affinity cortisol/cortisone responsive AR (AR(ccr)) isolated from the androgen-independent human prostate cancer cell lines MDA PCa 2a and 2b (Zhao et al. Nature Med. 2000, 6, 703-6). The three-dimensional structure of the AR(ccr) LBD complexed with 9alpha-fluorocortisol shows the typical conformation of an agonist-bound nuclear receptor in which helix 12 is precisely positioned as a "lid" for the ligand-binding pocket. Binding of 9alpha-fluorocortisol to the AR(ccr) involves favorable hydrogen bond patterns on the C17 and C21 substituents of the ligand due to the mutations at 701 and 877 in the AR(ccr). Our studies provide the first structural explanation for the glucocorticoid activation of AR(ccr), which is important for the development of new therapeutic treatments for androgen-independent prostate cancer.     

Niphatenones, glycerol ethers from the sponge Niphates digitalis block androgen receptor transcriptional activity in prostate cancer cells: structure elucidation, synthesis, and biological activity

Extracts of the marine sponge Niphates digitalis collected in Dominica showed strong activity in a cell-based assay designed to detect antagonists of the androgen receptor (AR) that could act as lead compounds for the development of a new class of drugs to treat castration recurrent prostate cancer (CRPC). Assay-guided fractionation showed that niphatenones A (3) and B (4), two new glycerol ether lipids, were the active components of the extracts. The structures of 3 and 4 were elucidated by analysis of NMR and MS data and confimed via total synthesis. Biological evaluation of synthetic analogues of the niphatenones has shown that the enantiomers 7 and 8 are more potent than the natural products in the screening assay and defined preliminary SAR for the new AR antagonist pharmacophore, including the finding that the Michael acceptor enone functionality is not required for activity. Niphatenone B (4) and its enantiomer 8 blocked androgen-induced proliferation of LNCaP prostate cancer cells but had no effect on the proliferation of PC3 prostate cancer cells that do not express functional AR, consistent with activity as AR antagonists. Use of the propargyl ether 44 and Click chemistry showed that niphatenone B binds covalently to the activation function-1 (AF1) region of the AR N-terminus domain (NTD).     

Development of potential antiandrogens: N-(4-nitro-3-trifluoromethyl-phenyl)-cyclohexanoylamides and -benzamides, N-(3,4-diochlorophenyl)- and N-(3,4,5-trichlorophenyl)-benzamides

Development of potential nonsteroidal antiandrogens: N-(4-nitro-3-trifluoromethylphenyl)-cyclohexanoylamides and -benzamides and N-(3,4-dichlorophenyl)- and N-(3,4,5-trichlorophenyl)-benzamides For the development of potential nonsteroidal antiandrogens, N-(4-nitro-3-trifluoromethylphenyl)-cyclohexanoylamides and -benzamides, and N-(3,4-dichlorophenyl)- and N-(3,4,5-trichlorophenyl)-benzamides were synthesized. The hydroxycyclohexane analog 3 exerted a higher binding affinity to the androgen receptor (AR) than hydroxyflutamide. Changing the α-hydroxycyclohexane ring of 3 to a hydroxyphenyl moiety led to a strong decrease in AR affinity. Compounds showing AR affinity were further tested for antiandrogenic and androgenic activity.     

Sesquiterpenoids from myrrh inhibit androgen receptor expression and function in human prostate cancer cells

Aim:

To examine whether two naturally occurring sesquiterpenoids (ST1 and ST2) with anti-proliferative activity in prostate cancer cells inhibit androgen receptor (AR) signaling.

Methods:

Human prostate cancer cell lines LNCaP and PC3 were used. The expression of AR, AR translocation into the nucleus, and expression levels of AR coactivators ARA70 and steroid receptor coactivator-1 (SRC-1) in LNCaP cells were examined using real-time PCR and Western blot. Changes in prostate-specific antigen (PSA) protein levels, PSA promoter activity, and androgen response element (ARE)-mediated reporter gene activity were examined using enzyme-linked immunoabsorbent assay (ELISA) and transient transfection assays. Co-immunoprecipitation was performed to analyze the interaction between AR and the AR coactivators in ST1- and ST2-treated cells.

Results:

In LNCaP cells, ST1 and ST2 (40 μmol/L) led to a significant decrease in the expression of AR as well as a reduction of AR translocation into the nucleus, but had no effect on AR protein translation. ST1 and ST2 treatment also resulted in a significant decrease in the level of PSA protein secreted into the medium and was able to suppress PSA promoter-dependent and ARE-dependent luciferase activity. Furthermore, decreased expression of ARA70 and SRC-1 was observed when LNCaP cells were exposed to ST1 and ST2, which interfered with their ability to interact with AR.

Conclusion:

The observations suggest that suppression of AR transactivation by ST1 and ST2 may be mediated, in part, by inhibiting AR nuclear translocation and/or interfering with the interaction between AR and its coactivators ARA70 and SRC-1. Therefore, sesquiterpenoids could be developed as novel therapeutic agents for treating prostate cancer.     

Targeting CYP17: established and novel approaches in prostate cancer

There is a growing body of evidence that although medical or surgical castration blocks the generation of gonadal testosterone in prostate cancer, androgens originating from other sources may continue to drive androgen receptor (AR) signaling. Recent studies have demonstrated high intratumoral levels of androgens and continued AR signaling in castration-resistant prostate cancer (CRPC), suggesting that androgens may also be synthesized de novo. Inhibiting the systemic biosynthesis of androgens in CRPC by targeting CYP17 may thus represent a rational therapeutic approach since this enzyme catalyses two key steroid reactions involving 17alpha-hydroxylase and C(17,20)-lyase in the androgen biosynthesis pathway. This review will discuss the rationale for and implications of targeting CYP17 in CRPC and focus on established and novel CYP17 inhibitors, including ketoconazole, abiraterone acetate, and VN/124-1, which are agents currently at different stages of development.