合成香豆素-7-胺基磺酸衍生物作為類固醇硫酸酯酶抑制劑及其用於荷爾蒙依賴型乳癌治療之活性評估

Abstract

類固醇硫酸酯酶(steroid sulfatase, STS)為雌激素生合成中的關鍵酵素，催化雌酮硫酸鹽(estrone sulfate, E1S)和硫酸脫氫表雄酮(dehydroepiandrosterone sulfate, DHEAS)轉化為具雌激素活性之雌激素酮(estrone, E1)和脫氫表雄酮(dehydroepiandrosterone, DHEA)。而在雌激素受體陽性型(ER+)乳癌組織中，類固醇硫酸酯酶過度表現引起雌激素濃度升高，誘導癌細胞增生並抑制細胞凋亡。因此，抑制類固醇硫酸酯酶的活性可以降低類固醇雌激素水平，繼而減緩乳房腫瘤的生長。

Irosustat (STX-64, 32c)為首個進入臨床2期試驗的類固醇硫酸酯酶抑制劑，具有香豆素胺基磺酸(coumarin-based sulfamate)骨架，其臨床試驗因副作用而中止。基於STX-64與類固醇硫酸酯酶的分子模擬研究，我們保留了其香豆素-7-胺基磺酸骨架，設計並合成了一系列的芐基衍生物。先前的研究發現，香豆素3號位芐基衍生物如3-(2,3-dimethoxybenzyl)-aminocoumarin-7-sulfamate (52c)對STS具有良好活性。進一步，將香豆素3、4號位擴環以增加平面性，其芐基衍生物如化合物55b對人類胎盤類固醇硫酸酯酶具有理想的抑制活性和分配係數(Log P)值。因此，本研究將針對這個系列進行更深入的構效關係探討。

結果顯示，增加苯環對位的親脂性可以提升對STS的抑制效果，異丙基修飾的化合物60e對人類胎盤及MCF-7細胞類固醇硫酸酯酶之IC50分別為0.25 nM及0.38 μM。苯環的間位含有氯亦可以增加抑制活性，而苯環鄰位修飾甲基的化合物(60d)活性最強，對人類胎盤及MCF-7細胞類固醇硫酸酯酶之IC50分別為0.15 nM及3.31 μM。這些化合物具可以應用於乳癌之荷爾蒙療法，未來將於(ER+)乳癌動物模型中進一步測試。

Steroid sulfatase (STS) plays a major role in estrogen biosynthesis that catalyzes the conversion of inactive estrone 3-sulfate (E1S) to estrogenic estrone (E1) and dehydroepiandrosterone sulfate (DHEAS) to dehydroepiandrosterone (DHEA). The STS is overexpressed in estrogen receptor-positive (ER+) breast cancer which causes estrogen levels raising, resulting in cell proliferation and anti-apoptosis. Therefore, inhibition of STS is a promising approach to reduce estrogenic steroid level which in turn halts breast tumorigenesis.

Irosustat (STX-64, 32c), a coumarin-based sulfamate, was the first potent STS inhibitor to enter phase II trial but which was halted. Inspired by the docking investigation of STX-64 and STS, a series of STS inhibitors with coumarin skeleton were designed and synthesized. In was found earlier that 3-benzylaminocoumarin-7- sulfamate (52c) was capable of inhibiting STS activity, and a series of substituents at adjacent phenyl ring were synthesized and evaluated. Moreover, ring expansion at 3,4-position of coumarin resulted in compound 55b which displayed improved inhibitory activity against STS of both human placenta and MCF-7 cells, and it also showed good partition coefficient (Log P). Intensive investigation on this series were then conducted.

In this study, conformational restricted derivatives with hydrophobic group at para-position of phenyl ring (60e) had IC50 of 0.25 nM and 0.38 μM against STS of human placenta and MCF-7 cell line, respectively. The phenyl ring bearing meta-chloro substituents enhanced inhibitory activity and the ortho-methyl substituted derivative 60d was the most potent compound with an IC50 value of 0.15 nM and 3.31 μM in STS of placental microsome and MCF-7 cell line, respectively. These compounds are potential agents for breast cancer as adjuvant endocrine therapy (AET), which will be tested in animal model of (ER+) breast cancer in the future.