Akihiro Tasaka

Discovery of orteronel (TAK-700), a naphthylmethylimidazole derivative, as a highly selective 17,20-lyase inhibitor with potential utility in the treatment of prostate cancer.

A novel naphthylmethylimidazole derivative 1 and its related compounds were identified as 17,20-lyase inhibitors. Based on the structure-activity relationship around the naphthalene scaffold and the results of a docking study of 1a in the homology model of 17,20-lyase, the 6,7-dihydro-5H-pyrrolo[1,2-c]imidazole derivative (+)-3c was synthesized and identified as a potent and highly selective 17,20-lyase inhibitor. Biological evaluation of (+)-3c at a dose of 1mg/kg in a male monkey model revealed marked reductions in both serum testosterone and dehydroepiandrosterone concentrations. Therefore, (+)-3c (termed orteronel [TAK-700]) was selected as a candidate for clinical evaluation and is currently in phase III clinical trials for the treatment of castration-resistant prostate cancer.

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.

Optically Active Antifungal Azoles. V. Synthesis and Antifungal Activity of Stereoisomers of 3-Azolyl-2-(substituted phenyl)-1-(1H-1,2,4-triazol-1-yl)-2-butanols

The (2S,3S)-, (2R,3S)- and (2S,3R)-stereoisomers of (2R,3R)-3-azolyl-2-(substituted phenyl)-1-(1H-1,2,4-triazol-1-yl)-2-butanols [(2R,3R)-1a--d] were prepared and evaluated for antifungal activity against Candida albicans in vitro and in vivo to clarify the relationships between stereochemistry and biological activities. The results revealed that the in vitro antifungal activity in each set of the four stereoisomers [(2R,3R)-, (2S,3S)-, (2R,3S)- and (2S,3R)-1a--d] definitely paralleled the in vivo antifungal activity against candidosis in mice, and the order of potency was (2R,3R) >> (2R,3S) > or = (2S,3S) > or = (2S,3R). In addition, the four stereoisomers in each set were assessed for sterol biosynthesis-inhibitory activities in C. albicans and rat liver. The (2R,3R)-isomer was found to exert a strong and selective inhibitory effect on the sterol synthesis in C. albicans as compared with that in rat liver.

Design, synthesis, and biological evaluation of 4-phenylpyrrole derivatives as novel androgen receptor antagonists

A series of 4-phenylpyrrole derivatives D were designed, synthesized, and evaluated for their potential as novel orally available androgen receptor antagonists therapeutically effective against castration-resistant prostate cancers. 4-Phenylpyrrole compound 1 exhibited androgen receptor (AR) antagonistic activity against T877A and W741C mutant-type ARs as well as wild-type AR. An arylmethyl group incorporated into compound 1 contributed to enhancement of antagonistic activity. Compound 4n, 1-{[6-chloro-5-(hydroxymethyl)pyridin-3-yl]methyl}-4-(4-cyanophenyl)-2,5-dimethyl-1H-pyrrole-3-carbonitrile exhibited inhibitory effects on tumor cell growth against the bicalutamide-resistant LNCaP-cxD2 cell line as well as the androgen receptor-dependent JDCaP cell line in a mouse xenograft model. These results demonstrate that this series of pyrrole compounds are novel androgen receptor antagonists with efficacy against prostate cancer cells, including castration-resistant prostate cancers such as bicalutamide-resistant prostate cancer.

Synthesis and biological evaluation of novel selective androgen receptor modulators (SARMs). Part I

To develop effective drugs for hypogonadism, sarcopenia, and cachexia, we designed, synthesized, and evaluated selective androgen receptor modulators (SARMs) that exhibit not only anabolic effects on organs such as muscles and the central nervous system (CNS) but also neutral or antagonistic effects on the prostate. Based on the information obtained from a docking model with androgen receptor (AR), we modified a hit compound A identified through high-throughput screening. Among the prepared compounds, 1-(4-cyano-1-naphthyl)-2,3-disubstituted pyrrolidine derivatives 17h, 17m, and 17j had highly potent AR agonistic activities in vitro and good tissue selectivity in vivo. These derivatives increased the weight of the levator ani muscle without influencing the prostate and seminal vesicle. In addition, these compounds induced sexual behavior in castrated rats, indicating that the compounds could also act as agonists on the CNS.

17,20-Lyase inhibitors. Part 4: Design, synthesis and structure–activity relationships of naphthylmethylimidazole derivatives as novel 17,20-lyase inhibitors

A novel series of naphthylmethylimidazole derivatives and related compounds have been investigated as selective 17,20-lyase inhibitors. Optimization of the substituent at the 6-position on the naphthalene ring was performed to yield a methylcarbamoyl derivative, which exhibited potent inhibitory activity against human 17,20-lyase and promising selectivity (>200-fold) for 17,20-lyase over CYP3A4. Further modifications of the methylcarbamoyl derivative led to the discovery of the corresponding tricyclic compound, which showed highly potent activity against human 17,20-lyase (IC(50) 19 nM) and good selectivity (>1000-fold) for inhibition of 17,20-lyase over CYP3A4. Additional biological evaluation revealed that the tricyclic compound had potent in vivo efficacy in monkeys and favorable pharmacokinetic profiles when administered in rats. Asymmetric synthesis of the selective tricyclic inhibitor was also achieved using a chiral α-hydroxy ketone.

17,20-Lyase inhibitors. Part 3: Design, synthesis, and structure–activity relationships of biphenylylmethylimidazole derivatives as novel 17,20-lyase inhibitors

A novel series of biphenylylmethylimidazole derivatives and related compounds were synthesized as inhibitors of 17,20-lyase, a key enzyme in the production of steroid hormones, and their biological activities were evaluated. In an attempt to identify potent and selective inhibitors of 17,20-lyase over the related CYP3A4 enzyme, a homology model for human 17,20-lyase was developed using the X-ray crystallographic structure of the mammalian CYP2C5 enzyme. With the aid of molecular modeling, optimization of the biphenyl moiety was performed to give an acetamide derivative, which was resolved by HPLC to give the active (-)-enantiomer. The obtained active enantiomer showed not only potent inhibition of both rat and human 17,20-lyase,with IC(50) values of 14 and 26 nM, respectively, but also excellent selectivity (>300-fold) for inhibition of 17,20-lyase over CYP3A4. Moreover, the active enantiomer significantly reduced both serum testosterone and DHEA concentrations in a monkey model after single oral administration. Asymmetric synthesis of the active enantiomer was also developed via a chiral intermediate using a diastereoselective Grignard reaction.

Effect of an investigational CYP17A1 inhibitor, orteronel (TAK-700), on estrogen- and corticoid-synthesis pathways in hypophysectomized female rats and on the serum estradiol levels in female cynomolgus monkeys

Orteronel (TAK-700) is an investigational, non-steroidal inhibitor of CYP17A1 with preferential inhibition of 17,20-lyase in NCI-H295 cells. Estrogen is synthesized from androgen by aromatase activity, and the effect of orteronel on estrogen synthesis was therefore evaluated. First, it was confirmed that orteronel does not directly inhibit aromatase activity. Second, the specific decline of serum estradiol and androgen levels in hypophysectomized female rats by orteronel in comparison with aromatase inhibitor anastrozole was evaluated; orteronel at doses ≥3mg/kg significantly suppressed serum estradiol, testosterone, androstenedione and 17-hydroxyprogesterone levels, and increased progesterone levels in the estrogen-synthesis pathway. Orteronel, at a dose of 300mg/kg, suppressed serum estradiol concentrations to a similar degree as 0.1mg/kg anastrozole. In contrast, in the corticoid-synthesis pathway, serum aldosterone, corticosterone, and progesterone levels did not change significantly following administration of 300mg/kg of orteronel. Third, the effect of multiple oral administration of orteronel on serum estradiol levels in regularly cycling female cynomolgus monkeys was evaluated. Orteronel at 15mg/kg/day (7.5mg/kg/treatment, twice daily [bid]) continued to suppress the estradiol surge prior to the start of luteal phase for 1.5-times the average duration of three consecutive, pre-treatment menstrual cycles, while serum progesterone was maintained at levels almost equal to those in the luteal phase although a certain portion of this increased level of progesterone could be of adrenal-origin. This suppressive effect on estradiol surge was thought to be reversible since serum estradiol levels started to rise immediately after the discontinuation of orteronel. Estradiol surge was not abrogated by treatment with anastrozole 0.2mg/kg/day (0.1mg/kg/treatment, bid). In summary, orteronel can suppress serum estradiol concentrations in hypophysectomized female rats and monkeys through selective inhibition of CYP17A1 activity, suggesting that orteronel might be effective for hormone-dependent breast cancers and estrogen-dependent diseases.