Sulfatase Inhibitors Research Articles

Microtiter plate cellular assay for human steroid sulfatase with fluorescence readout

Steroid sulfatase (STS; E.C. 3.1.6.2) is an enzyme involved in the local production of estrogens and androgens in target organs. Inhibitors of steroid sulfatase activity are considered novel therapeutic agents for the treatment of different pathologic conditions, including cancers of breast, endometrium, and prostate and disorders of the pilosebaceous unit. Evaluation of steroid sulfatase inhibition in cells up to now has been a cumbersome process, involving the extraction of a radioactive cleavage product into organic solvents. Here, we describe a rapid, nonradioactive cellular assay in microtiter plate format, using 4-methylumbelliferyl sulfate as a substrate. The reaction product, 4-methylumbelliferone, is read in a fluorescence microtiter plate reader. Several cell lines were assayed for sulfatase activity. To increase the sensitivity of the assay, we developed a Chinese hamster ovary (CHO) cell line stably transfected with a cDNA encoding the human steroid sulfatase. The steroid sulfatase activity in transfected cells correlated with the presence of the enzyme in these cells, as determined by immunofluorescence. For most STS inhibitors tested, including estrone-3- O-sulfamate, the results from the CHO cellular assay were in good agreement with those from a standard cell-free assay.

Carbonic anhydrase inhibitors. Inhibition of cytosolic isozymes I and II and transmembrane, tumor-associated isozyme IX with sulfamates including EMATE also acting as steroid sulfatase inhibitors.

A series of sulfamates or bis-sulfamates incorporating aliphatic, aromatic, polycyclic (steroidal), and sugar moieties in their molecules has been synthesized and assayed as inhibitors of the zinc enzyme carbonic anhydrase (CA), and more precisely of the cytosolic isozymes CA I andII, and the transmembrane, tumor-associated isozymes CA IX. Some of these compounds were previously reported to act as inhibitors of steroid sulfatases, among which estrone sulfatase (ES) and dehydroepiandrosterone sulfatase (DHEAS) are the key therapeutic targets for estrogen-dependent tumors. Very potent (nanomolar) inhibitors were detected against the three investigated CA isozymes. Best CA I inhibitors were phenylsulfamate and some of its 4-halogeno derivatives, as well as the aliphatic compound n-octyl sulfamate. Against CA II, low nanomolar inhibitors (1.1-5 nM) were phenylsulfamate and some of its 4-halogeno/nitro derivatives, n-octyl sulfamate, and estradiol 3,17beta-disulfamate among others. All the investigated sulfamates showed efficient CA IX inhibitory properties, with inhibition constants in the range of 18-63 nM. The best CA IX inhibitor detected so far was 4-chlorophenylsulfamate. These data are critical for the design of novel antitumor properties, mainly for hypoxic tumors that overexpress CA IX, which are nonresponsive to radiation or chemotherapy. The antitumor properties of the ES/DHEAS inhibitors in clinical trials may on the other hand also be due to their potent inhibitory properties of CA isozymes involved in tumorigenicity, such as CA II and CA IX.

D-Ring Modified Estrone Derivatives as Novel Potent Inhibitors of Steroid Sulfatase

A series of novel D-ring modified derivatives of estrone was synthesized and tested as inhibitors of steroid sulfatase (STS). The steroidal D-ring was cleaved via an iodoform reaction and thermal condensation of the resulting marrianolic acid derivative gave 16,17- seco-estra-1,3,5(10)-triene-16,17-imide derivatives, where a piperidinedione moiety is in place of the D-ring. This synthetic approach was found to give a higher overall yield than the literature method of Beckmann rearrangement. A range of alkyl side chains have been introduced on the nitrogen atom of the imido-ring and the corresponding 3- O-sulfamates synthesized. The new D-ring modified estrone derivatives bearing a propyl ( 39) and a 1-pyridin-3-ylmethyl ( 46) moiety had IC 50 values of 1 nM when tested in placental microsomes for the inhibition of STS. These compounds are therefore up to 18-fold more potent than EMATE, the very first highly potent irreversible steroidal STS inhibitor.

In vitro and in vivo models for the evaluation of new inhibitors of human steroid sulfatase, devoid of residual estrogenic activity

The goal of our research project is to develop a new class of orally active drugs, estrone sulfatase inhibitors, for the treatment of estrogen-dependent (receptor positive) breast cancer. Several compounds were synthesized and their pharmacological potencies explored. Based on encouraging preliminary results, three of them, TX 1299, TX 1492 and TX 1506 were further studied in vitro as well as in vivo. They proved to be strong inhibitors of estrone sulfatase when measured on the whole human JEG-3 choriocarcinoma and MCF-7 breast cancer cells and their IC 50s found to be in the range of known standard inhibitors. Their residual estrogenic activity was checked as negative in the test of induction of alkaline phosphatase (APase) activity in whole human endometrial adenocarcinoma Ishikawa cells. In addition, their effect on aromatase activity in JEG-3 cells was also examined, since the goal of inhibiting both sulfatase and aromatase activities appears very attractive. However, it has been unsuccessful so far. Then, in vivo potencies of TX 1299, the lead compound in our chemical series, were evaluated in comparison with 6,6,7-COUMATE, a non-steroidal standard, in two different rat models and by oral route. First, the absence of any residual estrogenic activity for these compounds was checked in the uterotrophic model in prepubescent female rats. Second, antiuterotrophic activity in adult ovariectomized rat supplemented with estrone sulfate (E 1S), showed that both compounds were potent inhibitors, the power of TX 1299 relative to 6,6,7-COUMATE being around 80%. This assay was combined with uterine sulfatase level determination and confirmed the complete inhibition of this enzyme within the target organ. Preliminary studies indicated that other non-steroid compounds in the Théramex series were potent in vitro and in vivo inhibitors of estrone sulfatase in rats and further studies are in progress.

Novel D-ring modified steroid derivatives as potent, non-estrogenic, steroid sulfatase inhibitors with in vivo activity

In pursuit of novel steroid sulfatase (STS) inhibitors devoid of estrogenicity, several D-ring modified steroid derivatives were synthesised. In vitro evaluation of the compounds identified two highly potent inhibitors, 4a and 4b, which were 18 times more active than estrone-3- O-sulfamate (EMATE), both having IC 50 values of ca. 1 nM. These 16,17-seco-estra-1,3,5(10)-triene-16,17-imide derivatives were synthesised from estrone, via the intermediate 1, which was easily alkylated, deprotected and sulfamoylated affording the final compounds in high yields. In order to assess their biological profile, the selected inhibitors were tested for their in vivo inhibitory potency and estrogenicity in ovariectomised rats. After an oral dose of 10 mg/kg per day for 5 days, 4a and 4b were found to inhibit rat liver steroid sulfatase by 99%. They were also devoid of estrogenic activity in the uterine weight gain assay, indicating that these two leads have therapeutic potential for the treatment of hormone-dependent breast cancer.

3β-Sulfamate Derivatives of C19 and C21 Steroids Bearing a t -Butylbenzyl or a Benzyl Group: Synthesis and Evaluation as Non-estrogenic and Non-androgenic Steroid Sulfatase Inhibitors

A series of C19 and C21 steroids bearing one or two inhibiting groups (3 β -sulfamate and 17 α - or 20(S)- t -butylbenzyl or benzyl) were synthesized and tested for inhibition of steroid sulfatase activity. When only a sulfamate group was added to dehydroepiandrosterone, androst-5-ene-3 β,17 β -diol, pregnenolone and 20-hydroxy-pregnenolone, no significant inhibition of steroid sulfatase occurred at concentrations of 0.3 and 3 μM. With only a t -butylbenzyl or a benzyl group, a stronger steroid sulfatase inhibition was obtained in the androst-5-ene than in the pregn-5-ene series. Comparative results from the screening tests and the IC 50 values have shown that the effect of a sulfamate moiety as a second inhibiting group can be combined to the t -butylbenzyl or benzyl effect in the C19 and C21 steroid series. The 3 β -sulfamoyloxy-17 α - t -butylbenzyl-5-androsten-17 β -ol (10) was thus found to be the most active compound with IC 50 values of 46 ± 8 and 14 ± 1 nM, respectively for the transformations of E 1 S to E 1 and DHEAS to DHEA. The IC 50 values of compound 10 are similar to that of 17 α - t -butylbenzyl-estradiol, which was previously reported by our group as a good steroid sulfatase reversible inhibitor, but remains higher than that of the potent inactivators estrone-3- O -sulfamate (EMATE) and 17 α - t -butylbenzyl-EMATE. However, contrary to these two latter inhibitors, compound 10 did not induce any proliferative effect on estrogen-sensitive ZR-75-1 cells nor on androgen-sensitive Shionogi cells at concentrations tested, suggesting that this steroid sulfatase inhibitor is non estrogenic and non androgenic.

4,4′‐Benzophenone‐O,O′‐disulfamate: A Potent Inhibitor of Steroid Sulfatase

AbstractFor Abstract see ChemInform Abstract in Full Text.

Steroidal oxathiazine inhibitors of estrone sulfatase

The presence of estrone sulfatase in breast tumors and the high levels of circulating estrone sulfate may contribute the major portion of estrogen synthesized locally in breast tissues through conversion of estrone sulfate to estrone by the enzyme. Using inhibitors of estrone sulfatase for the treatment of estrogen-dependent (estrogen receptor positive, ER +) breast cancer could be a very effective therapeutic strategy for the treatment of estrogen-dependent breast tumors in postmenopausal women. Therefore, we designed and synthesized several steroidal 2′,3′-oxathiazines that inhibit estrone sulfatase and have greatly reduced estrogenic side effects. Our in vitro studies indicate that the oxathiazine compounds have inhibitory activity on estrone sulfatase in MCF-7 human breast cancer cells. These estrone sulfatase inhibitors (ESIs) also inhibit the growth of MCF-7 cells induced by estrone sulfate. In addition, our in vivo experiments demonstrate that our ESIs have moderate antitumor activity against MCF-7 breast cancer xenografts in Balb/c athymic nude mice. The synthesis and biological activity of a number of these unique steroidal ESIs are described.

Estrone 3-sulfate mimics, inhibitors of estrone sulfatase activity: homology model construction and docking studies.

Steroid sulfatase (STS) is a new target for the endocrine therapy of breast cancer. To ascertain some of the requirements for inhibition of estrone sulfatase activity, a number of novel analogues of estrone 3-O-sulfate possessing sulfate surrogates were synthesized and evaluated as inhibitors of estrone sulfatase (STS) in comparison to a lead inhibitor, estrone-3-O-methylthiophosphonate (E1-3-MTP). Using a selective enzyme digestion, one of the diastereoisomers of this compound, (R(p))-E1-3-MTP, could be prepared and evaluated. From structure-activity studies, we show that chirality at the phosphorus atom, hydrophobicity, basicity, size, and charge all influence the ability of a compound to inhibit estrone sulfatase activity. Of these, hydrophobicity seems to be the most important since simple, active nonsteroidal inhibitors, based on 5,6,7,8-tetrahydronaphth-2-ol (THN), can be prepared, provided that they are lipophilic enough to partition into a nonpolar environment. Also, a negatively charged group is favorable for optimal binding, although it appears that the presence of a potentially cleavable group can compensate for lack of charge in certain cases. A homology model of STS has been constructed from the STS sequence, and molecular docking studies of inhibitors have been performed to broaden the understanding of enzyme/inhibitor interactions. This model clearly shows the positions of the key amino acid residues His136, His290, Lys134, and Lys368 in the putative catalytic region of the formylglycine at position 75, with residues Asp35, Asp36, Asp342, and Gln343 as ligands in the coordination sphere of the magnesium ion. Docking studies using the substrate and estrone-3-sulfate mimics that are active inhibitors indicate they are positioned in the area of proposed catalysis, confirming the predictive power of the model.

Design, synthesis and biochemical evaluation of AC ring mimics as novel inhibitors of the enzyme estrone sulfatase (ES)

We report the results of our study into a series of 4′- O-sulfamoyl-4-biphenyl based compounds as novel inhibitors of the enzyme estrone sulfatase (ES). From the results of the molecular modeling design process, it was suggested that these compounds would be able to mimic both the A and C rings of the steroid backbone, and thus possess inhibitory activity against ES. The results of the biochemical evaluation study show that these compounds are indeed good inhibitors, possessing greater inhibitory activity than COUMATE, but weaker inhibitory activity than EMATE or the tricyclic derivative of COUMATE, namely 667-COUMATE. Furthermore, the compounds are observed to be irreversible inhibitors.

Design, Synthesis and Biochemical Evaluation of AC Ring Mimics as Novel Inhibitors of the Enzyme Estrone Sulfatase (ES).

AbstractFor Abstract see ChemInform Abstract in Full Text.

Sulfamoyloxy-substituted 2-phenylindoles: Antiestrogen-based inhibitors of the steroid sulfatase in human breast cancer cells

Estrone sulfate (E1S) is an endogenous prodrug that delivers estrone and, subsequently, estradiol to the target cells following the hydrolysis by the enzyme estrone sulfatase which is active in various tissues including hormone dependent breast cancer cells. Blockade of this enzyme should reduce the estrogen level in breast cancer cells and prevent hormonal growth stimulation. Sulfamates of a variety of phenolic compounds have been shown to be inhibitors of estrone sulfatase. Our rational is based on findings that these inhibitors can undergo hydrolysis and the pharmacological effects of the free hydroxy compounds contribute to the bioactivity of the sulfamates. A desirable action of the metabolites would be an estrogen antagonism to block stimulatory effects of residual amounts of estrogens. Thus, we synthesized a number of sulfamoyloxy-substituted 2-phenylindoles with side chains at the indole nitrogen that guarantee antiestrogenic activity. All of the new sulfamates were studied for their inhibitory effects on the enzyme estrone sulfatase from human breast cancer cells and their (anti)hormonal activities in stably transfected human MCF-7/2a mammary carcinoma cells. The hormonal profile of the sulfamates was partly reflected by the properties of the corresponding hydroxy precursors. Some of the sulfamoylated antiestrogens strongly inhibited estrone sulfatase activity with IC 50 values in the submicromolar range. They were devoid of agonist activity and suppressed estrone sulfate-stimulated gene expression mainly by blocking the enzyme. Examples are the disulfamates of the indoles ZK 119, 010 and ZK 164, 015. Their IC 50s for sulfatase inhibition were 0.3 and 0.2 μM, respectively, and 50 and 80 nM, respectively, for the inhibition of E1S-stimulated luciferase expression in transfected MCF-7 cells. With some of the new sulfamates an additional direct antiestrogenic effect was noticed which might be due to a partial hydrolysis during incubation and would improve the growth inhibitory effect on estrogen-sensitive breast cancer cells.

Inhibition of estrone sulfatase (ES) by derivatives of 4-[(aminosulfonyl)oxy] benzoic acid

In our search for potent inhibitors of the enzyme estrone sulfatase (ES), we have undertaken the synthesis and biochemical evaluation of a range of straight chain alkyl esters of 4-[(aminosulfonyl)oxy] benzoic acid. The results of the study show that the synthesised compounds possess greater inhibitory activity when compared to COUMATE, although they were all found to possess lower inhibitory activity with respect to EMATE. Furthermore, the data suggest a strong correlation between logP and IC 50 and therefore adds further support to our previous report where we suggested a link between inhibitory activity and hydrophobicity.

4,4′-Benzophenone- O,O′-disulfamate: a potent inhibitor of steroid sulfatase

We investigated whether the benzophenone moiety can be used as core element of steroid sulfatase (STS) inhibitors. While 4- and 3-benzophenone- O-sulfamates inhibit STS with IC 50 values between 5 and 7 μM irrespective of additional hydroxy and methoxy substituents at the second phenyl ring, benzophenone- O,O′-disulfamates show increased activity. With an IC 50 value of 190 nM the 4,4′-derivative is the first small monocyclic STS inhibitor coming close to the potency of the steroidal standard estrone sulfamate.

Inhibition of steryl sulfatase activity in LNCaP human prostate cancer cells

The enzyme steryl sulfatase may help support the growth of hormone-dependent tumors, including prostate cancers, by facilitating the conversion of circulating precursor steroids to active hormones. We sought to determine the presence of steryl sulfatase activity in the androgen-dependent human prostate cancer cell line LNCaP, and to determine if this activity was inhibited by known steryl sulfatase inhibitors. Intact LNCaP cultures had steryl sulfatase activity, as determined by conversion of [3H]estrone sulfate (E(1)S) to unconjugated steroids. The level of steryl sulfatase activity was relatively low (4.6 pmol/18 h/million cells) compared to MDA-MB-231 breast cancer cells (284.0 pmol/18 h/million cells). The observed activity in both cell lines was blocked by addition of 1 microM estrone sulfamate (EMATE), an active-site-directed, steroidal inhibitor of steryl sulfatase. Steryl sulfatase activity was also inhibited by Danazol, and by (p-O-sulfamoyl)-tetradecanoyl tyramine (C2-14), a non-steroidal inhibitor. Microsomes prepared from LNCaP cultures also showed steryl sulfatase activity, as determined by hydrolysis of [3H]E(1)S and [3H]dehydroepiandrosterone sulfate (DHEAS) to unconjugated forms. LNCaP and MDA-MB-231 microsomes both hydrolyzed E(1)S about two times faster than DHEAS. Hydrolysis of E(1)S in LNCaP and MDA-MB-231 microsomes was blocked by steryl sulfatase inhibitors with the following relative potencies: EMATE>C2-14>Danazol. These data demonstrate that LNCaP prostate cancer cells contain a steryl sulfatase with properties similar to that found in human breast cancer cells, and that the activity of this enzyme can be blocked by known steryl sulfatase inhibitors. Steryl sulfatase inhibitors may be useful as an adjuvant to androgen deprivation therapy for prostate cancer.

The design, synthesis, and biochemical evaluation of derivatives of biphenyl sulfamate-based compounds as novel inhibitors of estrone sulfatase

We report the initial results of our study into the use of a potential transition state (TS) of the reaction catalyzed by the enzyme estrone sulfatase (ES) in the design of a series of simple 4 ′- O-sulfamoyl-4-biphenyl-based compounds as novel inhibitors of ES. The results of the study show that these compounds are: potent inhibitors, possessing greater inhibitory activity than 4-methylcoumarin-7- O-sulfamate (COUMATE); weaker inhibitors than the tricyclic derivative of COUMATE, namely 667-COUMATE and the steroidal inhibitor estrone-3- O-sulfamate (EMATE), and irreversible inhibitors of ES.

Design, synthesis and biochemical evaluation of aC ring mimics as novel inhibitors of the enzyme estrone sulfatase (ES)

We report the initial results of our study into a series of simple 4′- O-sulfamoyl-4-biphenyl based compounds as novel inhibitors of the enzyme estrone sulfatase (ES). The results of the study show that these compounds are potent inhibitors, possessing greater inhibitory activity than COUMATE, but weaker inhibitory activity than EMATE or the tricyclic derivative of COUMATE, namely 667-COUMATE. Furthermore, the compounds are observed to be irreversible inhibitors.

A novel type of nonsteroidal estrone sulfatase inhibitors

Madurahydroxylactone (MHL) is a secondary metabolite produced by the soil bacterium Nonomuria rubra and belongs to the family of benzo[ a]naphthacenequinones. We report the initial results and structure–activity relationships of our study into a series of thiosemicarbazone derivatives of madurahydroxylactone as potential nonsteroidal inhibitors of the enzyme estrone sulfatase. The most active compound, the cyclohexylthiosemicarbazone, was shown to be a non-competitive inhibitor with a K i of 0.35 μM. This compound is devoid of estrogenic properties and showed low acute toxicity in the hen's fertile egg screening test.

The mechanism of the irreversible inhibition of estrone sulfatase (ES) through the consideration of a range of methane- and amino-sulfonate-based compounds

We report the results of our study into a series of simple phenyl and alkyl sulfamates and alkyl methanesulfonates as potential inhibitors of the enzyme estrone sulfatase (ES). The results of the study show that the substituted phenyl sulfamates are good irreversible inhibitors; the alkyl sulfamate compounds were found to lack inhibitory activity; whilst the large alkyl chain containing methanesulfonate-based compounds were found to possess weak reversible inhibitory activity. Using the results of the inhibition study, we postulate the probable mechanism for ES and suggest that an attack by the gem-diol is a major requirement prior to the hydrolysis of the sulfamate group, following which, attack on the active site CO occurs and which therefore leads to the production of an imine type functionality, resulting in irreversible inhibition.

Nonsteroidal compounds designed to mimic potent steroid sulfatase inhibitors

Chemical synthesis and enzyme inhibition results are reported for a series of nonsteroidal sulfatase inhibitors, 1-( p-sulfamoyloxyphenyl)-5-( p- t-butylbenzyl)-5-alkanols and the lower active phenolic analogues. These compounds conserve some structural elements from the previously reported potent steroidal inhibitor 3- O-sulfamate-17α-( p- t-butylbenzyl)-17β-hydroxy-estra-1,3,5(10)-triene, while the C18-methyl group and the hydrocarbon backbone represented by the steroid rings B, C, and D were replaced with a free conformational chain. Using estrone sulfate (100 μM) as substrate and homogenate of transfected HEK-293 cells as source of steroid sulfatase activity, the IC 50 values of the best inhibitors, the undecanol derivatives, were 0.4±0.1 and >300 nM, respectively, in the sulfamate and phenolic series. Although these sulfamoylated nonsteroidal inhibitors appear a bit less active than their steroidal analogues, they are however more potent than known inhibitors estrone-3- O-sulfamate and p-( O-sulfamoyl)- N-tetradecanoyl tyramine. The optimal side-chain length for the inhibition of steroid sulfatase activity was found to be six carbons, which corresponds to the number of carbons that mimic the B, C and D steroid rings, between C6 and C17. Furthermore, compounds with only the t-butylbenzyl group or the alkyl chain of six carbons are less potent inhibitors compared to the one that include both of these hydrophobic substituents. Such results suggest that compound from this later category better mimic the steroidal inhibitor.