Structure-activity relationship study of estrogen receptor down-regulators with a diphenylmethane skeleton

Selective estrogen receptor (ER) down-regulators (SERDs) are pure ER antagonists that also induce ER degradation upon binding to the receptor. Although SERDs have been developed for the treatment of ER-positive breast cancers for nearly a decade, their precise mechanism(s) of action and structure-activity relationship are still unclear. Generally, Western blotting is used to examine the effects of SERDs on ER protein levels, but the methodology is low-throughput and not quantitative. Here, we describe a quantitative, high-throughput, luciferase-based assay for the evaluation of SERDs activity. For this purpose, we established stable recombinant HEK-293 cell lines expressing ERα fused with emerald luciferase. We also designed and synthesized new diphenylmethane derivatives as candidate SERDs, and evaluated their SERDs activity using the developed system in order to examine their structure-activity relationship, taking EC₅₀ as a measure of potency, and E_max as a measure of efficacy.

Design and synthesis of novel selective estrogen receptor degradation inducers based on the diphenylheptane skeleton

Estrogen receptors (ERs) are a family of nuclear receptors (NRs) that regulate physiological effects such as reproduction and bone homeostasis. It has been reported that approximately 70% of human breast cancers are hormone-dependent and ERα-positive. Recently, novel anti-breast cancer drugs based on different mechanisms of action have received significant attention. In this article, we have designed and synthesized a selective ER degradation inducer based on the diphenylheptane skeleton. Western blotting analysis revealed that PBP-NC10 degraded ERα through the ubiquitin-proteasome system. We also performed computational docking analysis to predict the binding mode of PBP-NC10 to ERα.

Synthesis and evaluation of raloxifene derivatives as a selective estrogen receptor down-regulator

Estrogen receptors (ERs) play a major role in the growth of human breast cancer cells. A selective estrogen receptor down-regulator (SERD) that acts as not only an inhibitor of ligand binding, but also induces the down-regulation of ER, would be useful for the treatment for ER-positive breast cancer. We previously reported that tamoxifen derivatives, which have a long alkyl chain, had the ability to down-regulate ERα. With the aim of expanding range of the currently available SERDs, we designed and synthesized raloxifene derivatives, which had various lengths of the long alkyl chains, and evaluated their SERD activities. All compounds were able to bind ERα, and RC10, which has a decyl group on the amine moiety of raloxifene, was shown to be the most potent compound. Our findings suggest that the ligand core was replaceable, and that the alkyl length was important for controlling SERD activity. Moreover, RC10 showed antagonistic activity and its potency was superior to that of 4,4'-(heptane-4,4-diyl)bis(2-methylphenol) (18), a competitive antagonist of ER without SERD activity. These results provide information that will be useful for the development of promising SERDs candidates.

Discovery and structure-activity relationship studies of N6-benzoyladenine derivatives as novel BRD4 inhibitors

Bromodomain and extra-terminal domain (BET) proteins are epigenetic readers that bind to acetylated lysines in histones. Among them, BRD4 is a candidate target molecule of therapeutic agents for diverse diseases, including cancer and inflammatory disease. As a part of our continuing structural development studies of thalidomide to obtain a broad spectrum of biological modifiers based on the 'multi-template' approach, in this work we focused on BRD4-inhibitory activity, and discovered that N6-benzoyladenine derivatives exhibit this activity. Structure-activity relationship studies led to N6-(2,4,5-trimethoxybenzoyl)adenine (29), which exhibits potent BRD4 bromodomain1 inhibitory activity with an IC50 value of 0.427μM. N6-Benzoyladenine appears to be a new chemical scaffold for development of BRD4 inhibitors.

Design and synthesis of silicon-containing steroid sulfatase inhibitors possessing pro-estrogen antagonistic character

Steroid sulfatase (STS) is a potential target for treatment of postmenopausal hormone-dependent breast cancer. Several steroidal STS inhibitors have been reported, but steroidal compounds are difficult to optimize and may interact with other targets. On the other hand, we have shown that diphenylmethane (DPM) derivatives act as estrogen receptor (ER) agonists and antagonists. Here, we aimed to design and synthesize non-steroidal DPM-type STS inhibitors that would also serve as pro-estrogen antagonists, releasing a metabolite with ERα-antagonistic activity upon hydrolysis by STS. We synthesized a series of compounds and evaluated their biological activities by means of STS-inhibitory activity assay and ER reporter gene assay. Among them, silicon-containing compound 16a showed strong STS-inhibitory activity (IC50=0.17μM). Further, its putative metabolite (12a) exhibited potent ERα-antagonistic activity (IC50=29.7nM).

Structure-activity relationships of bisphenol A analogs at estrogen receptors (ERs): discovery of an ERα-selective antagonist

Our multi-template approach for drug discovery, focusing on protein targets with similar fold structures, has yielded lead compounds for various targets. We have also shown that a diphenylmethane skeleton can serve as a surrogate for a steroid skeleton. Here, on the basis of those ideas, we hypothesized that the diphenylmethane derivative bisphenol A (BPA) would bind to the ligand-binding domain of estrogen receptors (ERs) in a similar manner to estradiol and act as a steroid surrogate. To test this idea, we synthesized a series of BPA analogs and evaluated their structure-activity relationships, focusing on agonistic/antagonistic activities at ERs and ERα/ERβ subtype selectivity. Among the compounds examined, 18 was found to be a potent ERα-antagonist with high selectivity over ERβ and androgen receptor under our assay conditions. A computational docking study suggested that 18 would bind to the antagonistic conformation of ERα. ERα-selective antagonists, such as 18, are candidate agents for treatment of breast cancer.