Structure-diversity Oriented Synthesis And Biological Evaluation Of Novel Selective Estrogen Receptor Ligands

Estrogens regulate many physiological fuctions,and they play an important role in many cells and tissues,including normal cell growth,development,and tissue-specific gene regulation in the reproductive tract and in the central nervous and skeletal systems.Estrogens' s discorde also can influence the pathological processes of hormone-dependent diseases,such as breast cancer,endometrial cancer,osteoporosis and ovarian cancers,as well as inflammation.The effects of estrogens are mediated by binding to the estrogen receptors(ERs),ER? or ER?.Estrogen Receptor(ER)is a member of the nuclear receptor superfamily of ligand-modulated transcription factors,which egulates the function of estrogens in both reproductive and non-reproductive organs and tissues.The two human ER subtypes(ER? and ER?)are very similar in protein structure and ligand binding pocket,but they have distinct physiological distributions functions.ER? is mainly related in the female reproductive system though ER? is mainly relevant to bone,brain,cardiovascular and immune systems.While the two receptors operate by distinct pathways and the response of cells are dependent on the ER subtypes expressed,resulting in a wide range of physiological and pathological processes,and well established for pharmaceutical targets in contraception,menopausal hormonal therapy,and endocrine therapies for breast cancer.In order to development of antiestrogens ligand and ER? selective ligands,based on ER ligand researches in our lab,we carry out our works into three parts in this paper:1)Base on our privious researches on a novel series of bridged thixabicyclic core arylsulfonamide analogues for ER ligands.We established a competitive fluorometric receptor-binding assay and luciferase reporter gene assays for their ability to stimulate biological activities of ER? and ER?.Some of them give good ER binding affinity and ER agonist activity.Additionally,we find that the methyl group on the phenol ring can increase the binding affinity of ER,while the N-methyl group has critical effect on the ER transcriptional activity.Compounds ???-12 f and ???-12 g showed highest ER ? selectivity,both ratios of ER?/ER? were 333.Compounds ???-11 b,???-11 f and ???-12 f revealed the best ER?agonistic activity.These findings expand our understanding of bridged compounds as ER ligands,and we have elucidated their structure-activity relationships from the docking study,which laying the foundation for the future development of ER ligands.2)Because overcoming the development of resistance to endocrine therapies in breast cancers is a large unmet clinical need,we were motivated to explore a broad range of side chain structures in antiestrogens in a search for new compounds that might have high potency and efficacy as antiproliferative agents and possibly as antiestrogen ligand.The side chain,which is clearly an important functional element in conveying the effectiveness of ER antagonism,has survived over several decades in structurally unaltered form in antiestrogens from GSK,Genentech,Aztra Zeneca,and other pharma companies.In contrast,while many variations have been made in the structures of their core elements,only limited alterations have been made in the acrylate side chain and none have been explored in a systematic fashion.To expedite our investigation,we chose to use a structurally and stereochemically simple,rigid core unit,derived from the cyclofenil class of ER ligands,but having the bridged tricyclic adamantane system in place of the cyclohexane ring of cyclofenil.In place of the acrylic acid side chain,we explored a considerable number and variety of carboxylate analogs(ketones,esters,and amides).Our side chain design was influenced in part by a crystal structure of GW-5638 bound to the ER LBD showing that the acidic side chain interaction with the N-terminus of H12 was assisted by a structural water molecule.In other systems,inhibitors designed to include a polar atom that replaced a structural water had particularly high affinity.Thus,to explore this potential opportunity,we included oxygen or nitrogen atoms in the side chain of in some of our compounds.For each new compound we evaluated ER? binding affinity,and efficacy in suppressing proliferation of ER-positive breast cancer cells and in downregulating ER? levels.We also explored the potency of the most efficacious compounds in these assays and in ER target gene regulation.In the process,we uncovered some rather striking structure-activity relationships(SARs)whereby small structural changes resulted in large changes in activity,and in a number of cases,the inclusion on a polar atom at the terminus of the side chain gave a substantial boost to binding affinity.With this set of compounds,we also made comparisons of the degree to which antiproliferative activity is related to ER?-downregulating activity.The best members(?V-11 a,?V-11m)of this series are as efficacious as fulvestrant in suppressing cell proliferation and compound ?V-11 a nearly as complete in downregulating ER? levels,and they have low nanomolar potencies for both activities.3)We next investigated the discovery,design,synthesis,and characterization of benzoselenazole-core compounds as ER? ligands.Most of the compounds prepared showed good selectivity for ER? in terms of binding affinity and transcriptional potency.In particular,derivatives V-5h and V-5j can be considered the lead compounds of this series(RBA for ER?between 15% and 24%,selectivity of V-5j for ER? binding affinity over 50-fold).In the transcriptional assay,most of the active compounds tested are ER? agonists.In hydrogen peroxide-mediated oxidation assay,compounds V-5g and V-5h processed a neuroprotection effect against oxidative stress.These compounds have some promise as agents for the selective activation of the ER?.As such,they could prove to be useful pharmacological probes to define the biological importance and physiological roles of ER?.Studies are underway in an attempt to produce new benzoselenazole core structures that would retain the ER? binding affinity and selectivity but simultaneously give improved ER?-selective agonist character in transcriptional activity assays.Nevertheless,our generation of this new benzoselenazole series of ER ligands provides important insight into the diversity of structures that function as ER ligands and might lead to improved therapeutics that target the estrogen receptor ?.