Asako Kaise

Structure–activity relationship study of diphenylamine-based estrogen receptor (ER) antagonists

We have reported the design and synthesis of novel estrogen receptor (ER) agonists with a diphenylamine skeleton, which has several advantages over the formerly used diphenylmethane skeleton for drug development. Here, we confirmed the versatility of the diphenylamine skeleton by designing and synthesizing ER antagonist candidates bearing a basic alkylamino side chain on one of the two phenol groups of the diphenylamine agonist core structure. Among the tested compounds, cyclic alkylamine-containing derivatives showed more potent ER-antagonistic activity than the corresponding acyclic derivatives in cell proliferation assay using the MCF-7 cell line. Compound 5e showed the most potent antiestrogenic activity (IC50: 1.3×10(-7)M), being 10times more potent than tamoxifen.

Enhanced estrogen receptor beta (ERβ) selectivity of fluorinated carborane-containing ER modulators.

We previously showed that fluorination of the carborane-containing selective estrogen receptor modulator (SERM) BE360 altered the agonist/antagonist activity balance and the estrogen receptor (ER) α/β subtype selectivity. Here, we designed and synthesized a series of fluorinated carboranyl phenols as candidate ERβ-selective ligands. Introduction of a fluorine atom onto the carborane cage commonly reduced the binding affinity for ERα, to an extent that depended on the other substituents present. The B-fluorinated m-carboranyl phenol 4a showed fourfold more potent ERβ-binding affinity than the parent non-fluorinated compound 7. 1-Iodo-9-fluoro-m-carboranyl phenol 4f showed high ERβ-binding affinity with an ERβ/ERα selectivity ratio of 8.2. Among the compounds tested, 6 showed the highest ERβ selectivity (10.1-fold) and the highest ER-agonistic activity (EC50: 5.1×10(-10) M) in MCF-7 cell proliferation assay.

Novel estrogen receptor (ER) modulators containing various hydrophobic bent-core structures.

We previously discovered m-carborane-containing estrogen receptor (ER) modulator 4, which exhibits weak ER-agonistic and antagonistic activities in transactivation assays. With the aim of developing novel ER partial agonists, we designed and synthesized various analogues of 4 with a bent-core structure, that is, pseudo cyclic structure (5), tetrahydropyrimidinone (6), m-benzene (7), adamantane (8), and 9,10-dimethyl-m-carborane (9), in place of the m-carborane moiety. Compound 9 showed greater binding affinity than 4 in ER-binding assay using [6,7-(3)H]-17β-estradiol and was a more effective partial agonist than 4 in MCF-7 cell proliferation assay. It appears to be a promising candidate as a selective ER modulator (SERM).

Design and synthesis of carborane-containing estrogen receptor-beta (ERβ)-selective ligands.

Candidates for highly selective estrogen receptor-beta (ERβ) ligands (6a-c, 7a-c, 8a and 8b) were designed and synthesized based on carborane-containing ER ligands 1 and 2 as lead compounds. Among them, p-carboranylcyclohexanol derivatives 8a and 8b exhibited high ERβ selectivity in competitive binding assay: for example, 8a showed 56-fold selectivity for ERβ over ERα. Docking studies of 8a and 8b with the ERα and ERβ ligand-binding domains (LBDs) suggested that the p-carborane cage of the ligands is located close to key amino acid residues that influence ER-subtype selectivity, that is, Leu384 in the ERα LBD and Met336 in the ERβ LBD. The p-carborane cage in 8a and 8b appears to play a crucial role in the increased ERβ selectivity.

Targeting Cancer with PCPA‐Drug Conjugates: LSD1 Inhibition‐Triggered Release of 4‐Hydroxytamoxifen

Targeting cancer with small molecule prodrugs should help overcome problems associated with conventional cancer-targeting methods. Herein, we focused on lysine-specific demethylase 1 (LSD1) to trigger the controlled release of anticancer drugs in cancer cells, where LSD1 is highly expressed. Conjugates of the LSD1 inhibitor trans-2-phenylcyclopropylamine (PCPA) were used as novel prodrugs to selectively release anticancer drugs by LSD1 inhibition. As PCPA-drug conjugate (PDC) prototypes, we designed PCPA-tamoxifen conjugates 1 a and 1 b, which released 4-hydroxytamoxifen in the presence of LSD1 in vitro. Furthermore, 1 a and 1 b inhibited the growth of breast cancer cells by the simultaneous inhibition of LSD1 and the estrogen receptor without exhibiting cytotoxicity toward normal cells. These results demonstrate that PDCs provide a useful prodrug method that may facilitate the selective release of drugs in cancer cells.

Synthesis and biological evaluation of novel m-carborane-containing estrogen receptor partial agonists as SERM candidates

We designed and synthesized novel m-carborane-containing selective estrogen receptor modulator (SERM) candidates using previously reported m-carborane-containing ER partial agonist 1 as the lead compound. Biological activities were evaluated by means of ERα competitive binding assay and MCF-7 cell proliferation assay. Re-positioning the N,N-dimethylaminoethyloxy group at the para position of 1 to the meta position enhanced the ERα-binding affinity, and 4c showed the highest relative binding affinity (RBA: 83 vs 17β-estradiol = 100) among the tested compounds. Compound 4b showed the most potent ER-agonist activity (EC50: 1.4 nM) and the lowest maximal efficacy (Emax: 50%) in MCF-7 cell proliferation assay. Inhibition of 0.1 nM 17β-estradiol-induced MCF-7 cell proliferation by 4b (IC50: 0.4 μM) was at least 10 times more potent than that of the lead compound 1.

Novel p-carborane-containing multitarget anticancer agents inspired by the metabolism of 17β-estradiol

The female hormone 17 β-estradiol (E2) is synthesized from estrone by steroid sulfatase (STS), and metabolized into 2-methoxyestradiol (2-ME), whereby the biological activity of the latter is substantially different from that of E2. Based on the metabolic pathways of E2, a carborane-containing 2-ME mimic (1c) and its derivatives (1 and 2) were designed and synthesized as novel multitarget anticancer agents. Bissulfamate 1f exhibited potent STS-inhibitory activity and tubulin-polymerization-inhibitory activity. Moreover, the cell-growth-inhibitory (CGI) activity of 1f was similar to that of 2-ME in a panel screening against 39 human cancer cell lines. Accordingly, 1f should be a promising perspective therapeutic agent for hormone-dependent breast tissue.

Design and synthesis of p-carborane-containing sulfamates as multitarget anti-breast cancer agents

The development of multitarget anticancer agents is of high interest to medicinal chemists in terms of overcoming drug resistance and preventing cancer-cell migration. Based on the structure of the potent carborane-containing estrogen BE120, non-steroidal multitarget anti-breast cancer agent candidates 1a-1j were designed and synthesized. Compound 1f shows potent STS-inhibitory activity (IC50 = 1.8 μM), cell-growth-inhibitory (CGI) activity against 39 human cancer cell lines (MG-MID = 2.8 μM), and tubulin-polymerization-inhibitory (TPI) activity. An analysis of the DNA content for MDA-MB-453 breast cancer cells revealed that 1f arrests the cell cycle in the G2/M phase and induces apoptosis. Accordingly, 1f should be a promising therapeutic agent for hormone-dependent breast cancer.

Novel androgen receptor full antagonists: Design, synthesis, and a docking study of glycerol and aminoglycerol derivatives that contain p-carborane cages

Based on the co-crystal structure of bicalutamide with a T877A-mutated androgen receptor (AR), glycerol and aminoglycerol derivatives were designed and synthesized as a novel type of carborane-containing AR modulators. The (R)-isomer of 6c, whose chirality is derived from the glycerol group, showed 20 times more potent cell inhibitory activity against LNCaP cell lines expressing T877A-mutated AR than the corresponding (S)-isomer. Docking studies of both isomers with AR suggested that (R)-6c is in closer spatial proximity to helix-12 of the AR than (S)-6c, which is the most important common motif in the secondary structure of AR for the expression of antagonistic activity.