Estradiol-16α-carboxylic Acid Esters as Locally Active Estrogens

Novel Locally Active Estrogens Accelerate Cutaneous Wound Healing-Part 2

Estrogen deprivation is associated with delayed healing, while estrogen replacement therapy (ERT) accelerates acute wound healing and protects against development of chronic wounds. However, current estrogenic molecules have undesired systemic effects, thus the aim of our studies is to generate new molecules for topic administration that are devoid of systemic effects. Following a preliminary study, the new 17β-estradiol derivatives 1 were synthesized. The estrogenic activity of these novel compounds was evaluated in vitro using the cell line ERE-Luc B17 stably transfected with an ERE-Luc reporter. Among the 17β-estradiol derivatives synthesized, compounds 1e and 1f showed the highest transactivation potency and were therefore selected for the study of their systemic estrogenic activity. The study of these compounds in the ERE-Luc mouse model demonstrated that both compounds lack systemic effects when administered in the wound area. Furthermore, wound-healing experiments showed that 1e displays a significant regenerative and anti-inflammatory activity. It is therefore confirmed that this class of compounds are suitable for topical administration and have a clear beneficial effect on wound healing.

Anticancer steroids: linking natural and semi-synthetic compounds

Steroids, a widespread class of natural organic compounds occurring in animals, plants and fungi, have shown great therapeutic value for a broad array of pathologies. The present overview is focused on the anticancer activity of steroids, which is very representative of a rich structural molecular diversity and ability to interact with various biological targets and pathways. This review encompasses the most relevant discoveries on steroid anticancer drugs and leads through the last decade and comprises 668 references.

Estrogen receptor-alpha as a drug target candidate for preventing lung inflammation

Accumulating evidence shows that estrogens are protective factors in inflammatory lung diseases and are involved in the gender-related incidence of these pathologies. The aim of this study was to identify which estrogen receptor (ER), ER-alpha and/or ER beta, mediates hormone antiinflammatory effects in lung and how gender or aging modify this effect. Acute lung inflammation in wild type, ER alpha or ER beta knockout animals was induced by pleural injection of carrageenan; female mice were used and sham operated, ovariectomized, or ovariectomized and treated with 17beta-estradiol (E(2)) before carrageenan. Our data show that ER alpha, and not ER beta, mediates E(2)-induced reduction of the inflammatory response. By real-time PCR and immunohistochemistry assays, we demonstrate ER alpha expression in the resident and infiltrated inflammatory cells of the lung, in which ER beta could not be detected. In these cells, E(2)-mediated reduction in the expression of inflammatory mediators was also due to ER alpha. In parallel, we observed that female mice were more prone to inflammation as compared with males, suggesting a gender-related difference in lung susceptibility to inflammatory stimuli, whereas the effect of E(2) was similar in the two sexes. Interestingly, aging results in a strong increase in the inflammatory response in both sexes and in the disruption E(2)/ER alpha signaling pathway. In conclusion, our data reveal that E(2) is able to regulate lung inflammation in a gender-unrelated, age-restricted manner. The specific involvement of ER alpha in hormone action opens new ways to identify drug targets that limit the inflammatory component of lung pathologies.

Retrometabolic drug design: Principles and recent developments

Retrometabolic drug design incorporates two major systematic approaches: the design of soft drugs (SDs) and of chemical delivery systems (CDSs). Both aim to design new, safe drugs with an improved therapeutic index by integrating structure-activity and -metabolism relationships; however, they achieve it by different means: whereas SDs are new, active therapeutic agents that undergo predictable metabolism to inactive metabolites after exerting their desired therapeutic effect, CDSs are biologically inert molecules that provide enhanced and targeted delivery of an active drug to a particular organ or site through a designed sequential metabolism that involves several steps. General principles and recent developments are briefly reviewed with various illustrative examples from different therapeutic areas with special focus on soft corticosteroids and on brain targeting.

Microcapsule biosensors using competitive binding resonance energy transfer assays based on apoenzymes

This paper reports the first demonstration of a fluorescence resonance energy transfer based glucose sensor, wherein a competitive binding (CB) assay is encapsulated into polyelectrolyte microcapsules. The work supports the concept that microcapsules are superior to hydrogel systems or other matrixes for competitive-binding-based system, as they provide free movement of the sensing elements within the capsule interior while constant total sensing assay concentration is maintained. The transduction approach employed in these preliminary experiments is also a novel CB system based on a model apoenzyme, apo-glucose oxidase (AG), which is highly specific to beta-d-glucose, as the model target-binding protein. The glucose sensitivity of the fluorescein isothiocyanate (FITC)-dextran and tetramethylrhodamine isothiocyanate-AG encapsulated in microcapsules showed 5 times greater specificity for beta-D-glucose over other sugars, with sensitivity (change in intensity ratio) in the range of 2-6%/mM. It was observed that the sensitivity and range of the response can be tailored by controlling the assay concentration using different FITC-dextran molecular weight and total capsule concentration. The findings support the concepts of using microcapsules to encapsulate CB assays for reversible and stable sensors and the use of apoenzymes as specific molecular recognition elements in CB assays. Further, characterization results for microcapsule glucose sensors demonstrate their suitability for monitoring physiological glucose levels.

Derivatives of Z-bisdehydrodoisynolic acid provide a new description of the binding-activity paradox and selective estrogen receptor modulator activity

Z-Bisdehydrodoisynolic acid [(+/-)-Z-BDDA], an estrogenic carboxylic acid, is highly active in vivo yet binds poorly to estrogen receptors (ERs). Studies of Z-BDDA and its enantiomers demonstrate therapeutic potential as selective ER modulators; however, the activity vs. binding paradox has remained. One possible explanation is that the carboxylic acid group of Z-BDDA may be modified in vivo to an ester or amide. Synthesis of these derivatives showed the relative binding affinity (RBA) of the methyl ester for ERalpha and ERbeta was increased approximately 14- and 20-fold, respectively, relative to the parent compound. Yet, this increased affinity did not result in increased reporter gene expression. In contrast, the amide showed an unexpected approximately 4-fold decrease in RBA to both ERs compared with the parent. The relationship among the RBAs of ester, acid, and amide is consistent with their predicted polarity, suggesting the carboxylic acid, and not the carboxylate of BDDA, binds to ERs. Studies at pH 6.5, 7.4, and 8.0 were consistent with a simple acid-base equilibrium model, with BDDA binding as the undissociated acid and with affinity equal to or exceeding that of estradiol, consistent with high in vivo potency. Furthermore, the alcohol BDD-OH also demonstrated high affinity and increased activity in gene expression assays. In addition to suggesting a resolution to the decades-old binding/activity paradox, these studies may provide a direction for definitive in vivo metabolic and pharmacokinetic studies and provide additional insight into the chemical and metabolic determinants of BBDA's unique tissue selectivity and selective ER modulator activities.

Focused Libraries of 16-Substituted Estrone Derivatives and Modified E-Ring Steroids: Inhibitors of 17ß-Hydroxysteroid Dehydrogenase Type 1

17beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD1), an oxidoreductase which has a preferential reductive activity using NADPH as cofactor, converts estrone to estradiol and is expressed in many steroidogenic tissues including breast and in malignant breast cells. As estradiol stimulates the growth and development of hormone-dependent breast cancer, inhibition of the final step of its synthesis is an attractive target for the treatment of this disease. The parallel synthesis of novel focused libraries of 16-substituted estrone derivatives and modified E-ring pyrazole steroids as new potent 17beta-HSD1 inhibitors is described. Substituted 3-O-sulfamoylated estrone derivatives were used as templates and were immobilised on 2-chlorotrityl chloride resin to give resin-bound scaffolds with a multi-detachable linker. Novel focused libraries of 16-substituted estrone derivatives and new modified E-ring steroids were assembled from these immobilised templates using solid-phase organic synthesis and solution-phase methodologies. Among the derivatives synthesised, the most potent 17beta-HSD1 inhibitors were 25 and 26 with IC50 values in T-47D human breast cancer cells of 27 and 165 nm, respectively. Parallel synthesis resulting in a library of C5'-linked amides from the pyrazole E-ring led to the identification of 62 with an IC50 value of 700 nM. These potent inhibitors of 17beta-HSD1 have a 2-ethyl substituent which will decrease their estrogenic potential. Several novel 17beta-HSD1 inhibitors emerged from these libraries and these provide direction for further template exploration in this area. A new efficient diastereoselective synthesis of 25 has also been developed to facilitate supply for in vivo evaluation, and an X-ray crystal structure of this inhibitor is presented.

Modification of estrone at the 6, 16, and 17 positions: novel potent inhibitors of 17beta-hydroxysteroid dehydrogenase type 1

The 17beta-hydroxysteroid dehydrogenases (17beta-HSDs) catalyze the interconversion between the oxidized and reduced forms of androgens and estrogens at the 17 position. The 17beta-HSD type 1 enzyme (17beta-HSD1) catalyzes the reduction of estrone to estradiol and is expressed in malignant breast cells. Inhibitors of this enzyme thus have potential as treatments for hormone dependent breast cancer. Here we report the syntheses and biological evaluation of novel inhibitors based on the estrone or estradiol template. These have been investigated by modification at the 6, 16 or 17 positions or combinations of these in order to gain information about structure-activity relationships by probing different areas in the enzyme active site. Activity data have been incorporated into a QSAR with predictive power, and the X-ray crystal structures of compounds 15 and 16c have been determined. Compound 15 has an IC50 of 320 nM for 17beta-HSD1 and is selective for 17beta-HSD1 over 17beta-HSD2. Three libraries of amides are also reported that led to the identification of inhibitors 19e and 20a, which have IC50 values of 510 and 380 nM respectively, and 20 h which, having an IC50 value of 37 nM, is the most potent inhibitor of 17beta-HSD1 reported to date. These amides are also selective for 17beta-HSD1 over 17beta-HSD2.

Novel and potent 17beta-hydroxysteroid dehydrogenase type 1 inhibitors

Structure-based drug design using the crystal structure of human 17beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD1) led to the discovery of novel, selective, and the most potent inhibitors of 17beta-HSD1 reported to date. Compounds 1 and 2 contain a side chain with an m-pyridylmethyl-amide functionality extended from the 16beta position of a steroid scaffold. A mode of binding is proposed for these inhibitors, and 2 is a steroid-based 17beta-HSD1 inhibitor with the potential for further development.

Nonpolar and Short Side Chain Groups at C-11β of Estradiol Result in Antiestrogens

We have previously found that esters of 11beta-estradiol carboxylates are transformed from an estrogen into an antiestrogen when the 11beta-side chain is increased in length from four to five non-hydrogen atoms (n > or = 5). To understand the structural requirements for this transformation and obtain metabolically stable analogues that are not susceptible to esterase cleavage, we have synthesized other compounds having an 11beta-side chain composed of other functional groups: ketones, amides, ethers, and thiono esters. With the exception of amides, which bind poorly to the estrogen receptor (ER), all of these compounds exhibit antiestrogenic action when the side chain length is n > or = 5. Ethers (n > or = 5), studied in more detail, inhibit the action of estradiol with either ERalpha or ERbeta. In rat uteri they are estrogen antagonists/weak agonists and decrease the concentration of cholesterol in blood (an hepatic estrogenic action). Thus, these short chain and nonpolar 11beta-analogues of estradiol have tissue specific antiestrogenic/estrogenic actions, characteristics of selective estrogen receptor modulators.

Estrogen to antiestrogen with a single methylene group resulting in an unusual steroidal selective estrogen receptor modulator

Selective estrogen receptor (ER) modulators (SERMs) are important therapeutic agents for breast cancer prevention and treatment. We have synthesized two analogs, E11-2,1 [methyl-(3,17beta-dihydroxyestra-1,3,5(10)-triene-11beta-yl)acetate] and E11-2,2 [ethyl-(3,17beta-dihydroxyestra-1,3,5(10)-triene-11beta-yl)acetate], the methyl and ethyl esters of an estradiol analog, substituted in the B ring at C-11beta with a carboxymethyl group. The shorter methyl ester, E11-2,1, has high ER affinity and high estrogenic potency in the Ishikawa estrogen cell bioassay, whereas the longer ethyl ester, E11-2,2, has even higher ER affinity, but little or no estrogenic activity. We found that this minor change of one methylene group transforms a potent estrogenic agonist into an antagonist in vitro with either ER alpha or beta. In the rat, E11-2,2 acts as a SERM in the uterus, where it inhibits estradiol-induced proliferation, and as an estrogen agonist in the liver and skeleton, where it decreases plasma cholesterol and increases bone growth. The characteristic feature of antiestrogens, including SERMs, is a long and polar side-chain that prevents agonist-induced conformation of helix 12 of ER. E11-2,2 with its short, nonpolar side-chain, lacks this critical structure, presenting the possibility that it might act through a unique mechanism.

Synthesis, receptor binding, molecular modeling, and proliferative assays of a series of 17alpha-arylestradiols

A series of new derivatives of estradiol substituted at position 17alpha by various aryls has been synthesized. This was made possible by efficient activation methods for the addition of aryllithiums to the carbonyl group at position 17 of estrone by using tetramethylethylenediamine (TMEDA) or BF3 x OEt2. Their relative binding affinity (RBA) for the alpha and the beta forms of the estrogen receptor (ER) have been measured. All except one of the compounds synthesized had an RBA value of around 10 % which indicates a level of tolerance towards the bulky substituent at position 17. The lipophilicity values measured for these compounds are higher than that found for estradiol (E2). A study of their proliferative/antiproliferative effects was carried out on hormone-dependent (MCF7) and hormone-independent (MDA-MB231) breast cancer cell lines. It is interesting to note that all the compounds are estrogenic. The possibility of easily attaching an iodine at the end of a phenyl spacer opens up a route to new radiopharmaceuticals for use in radioimaging.

Synthesis and evaluation of B-, C-, and D-ring-substituted estradiol carboxylic acid esters as locally active estrogens

We have synthesized derivatives of estradiol that are structurally modified to serve as "soft" estrogens and act within a geographically limited area of the body; estrogens without systemic action. We have previously shown with 16alpha-substituted analogues of estradiol that carboxylates proximal to the steroid ring neither bind to the estrogen receptor nor activate estrogen-responsive genes. However, when the carboxylic acid is masked as an ester, they bind to the receptor and stimulate estrogenic responses. Enzymatic hydrolysis through nonspecific esterases can inactivate these estrogens and thereby limit their area of action. Here, we describe our continued studies to design "soft" estrogens by synthesizing carboxylic acid esters of estradiol at the 7alpha-, 11beta-, and 15alpha-positions in the steroid nucleus at which bulky substituents are accommodated by the estrogen receptor. These compounds were tested for estrogen receptor binding (estrogen receptors alpha and beta), stimulation of an estrogen sensitive gene in Ishikawa cells in culture, and as substrates for enzymatic hydrolysis. Likely candidates were tested in in vivo assays for systemic and local estrogenic action. The biological studies showed that regardless of the point of attachment, all of the short-chain carboxylic acids, C-1 to C-3, were devoid of hormonal action, while many of the esters were estrogenic. The site on the steroid nucleus had great influence on hormonal activity and esterase hydrolysis. Formate esters at 7alpha and 15alpha were good estrogens, but lengthening the chain to acetate dramatically decreased hormonal activity. However, the 7alpha-formate esters were not enzymatically hydrolyzed. At 11beta, the acetate (methyl ester) was an effective estrogen, but increasing the chain length to propionate dramatically reduced hormonal activity. In general, the length of the alcohol from methyl to butyl had only a small effect on receptor binding, and as the size of the alcohol increased, so did esterase hydrolysis. One exception was the 11beta-acetate esters where increasing the alcohol moiety from methyl to ethyl eliminated estrogenic activity (Ishikawa cells) without affecting estrogen receptor binding. Several of the esters were tested in vivo, and two, the methyl and ethyl esters of estradiol-15alpha-formate, appeared to have the requisite properties (high local and low systemic activity) of superior "soft" estrogens.

Prodrug and antedrug: two diametrical approaches in designing safer drugs

The prodrug and antedrug concepts, which were developed to overcome the physical and pharmacological shortcomings of various therapeutic classes of agents, employ diametrically different metabolic transformations. The prodrug undergoes a predictable metabolic activation prior to exhibiting its pharmacological effects in a target tissue while the antedrug undergoes metabolic deactivation in the systemic circulation upon leaving a target tissue. An increased therapeutic index is the aspiration for both approaches in designing as well as evaluation criteria. The recent research endeavors of prodrugs include the gene-directed and antibody-directed enzymatic activation of a molecule in a targeted tissue, organ specific delivery, improved bioavailabilities of nucleosides and cellular penetration of nucleotides. As for antedrugs, emphasis in research has been based upon the design and synthesis of systemically inactive molecule by incorporating a metabolically labile functional group into an active molecule.