Design, synthesis, and metabolite identification of Tamoxifen esterase-activatable

Tamoxifen (TAM) is used in treatment of hormonal dependent breast cancer, both in premenopausal and post-menopausal women. TAM is intrinsically metabolized by CYP450 enzymes to more active metabolites. Recent reports identified CYP2D6, an enzyme involved in the conversion of TAM to the more potent 4-OH-TAM, is encoded by the CYP2D6 gene, which is highly polymorphic. Women with inactive alleles are poor metabolizers; in many cases they suffer acquired TAM resistance. Herein we report synthesis and biological evaluation of novel TAM analogues. The novel analogues are designed to elude CYP2D6 metabolism. Hydrolysis of the carbamate moiety on ring C is mediated via carboxylesterases. Compound 3d [E/Z Benzyl-carbamic acid4-{2-benzyl-1-[4-(2-pyrrolidin-1-yl-ethoxy)-phenyl]-but-1-enyl}-phenyl ester] showed GI50 = 0.09 mu M on MCF-7 and GI50 = 1.84 mu M on MDA-MB231 cell lines. To further validate our hypothesis, metabolites of selected novel analogues were determined in vitro under different incubation conditions. The hydroxylated analogues were obtained under non CYP2D6 dependent conditions. Compound 8d, a benzyl carbamate derivative, was the least-stable analog and showed the highest rate of metabolism among all tested analogues. Our in silico model showed the novel flexible analogues can still adopt an antiestrogenic binding profile occupying the same pocket as 4-OH-TAM.

Automated summary

Tamoxifen (TAM) is a commonly used drug for treating hormonal dependent breast cancer. However, some patients develop resistance to TAM due to their genetic makeup. In this study, novel TAM analogues were designed to bypass the metabolic pathway involving CYP2D6 enzyme. The most promising analogue, compound 3d, showed strong anti-cancer activity against MCF-7 and MDA-MB231 cell lines. Further analysis of the metabolites confirmed that the hydroxylated analogues were produced through non CYP2D6 dependent mechanisms. Our findings suggest that these novel analogues could potentially be used as alternative treatments for TAM-resistant breast cancer.