Effects of 5α-reductase inhibitors on intraprostatic androgens in the rat

FCE 27837 is a novel inhibitor of 5α-reductase, the enzyme responsible for the conversion of testosterone (T) to 5α-dihydrotestosterone (DHT). The compound caused inhibition of human and rat prostatic enzymes, with IC₅₀ values of 51 and 60 nM, respectively. The in vivo effect of FCE 27837 on 5α-reductase was evaluated in adult male rats, treated orally at 10 mg/kg/day for 10 days. The compound caused 33 and 42% reductions in ventral prostate and seminal vesicle weights, respectively. The prostatic content of DHT, measured 6 h after the 10th dose of FCE 27837, was reduced by 75%, whereas T content increased by 442%. Similar effects were observed with 10 mg/kg/day of finasteride, whereas epristeride, tested at the same oral dose, was found to be the least effective compound, decreasing prostate weight by 22% and DHT content by 46%. Castration caused >90% reductions in prostatic weight and prostatic DHT.     

Human prostatic steroid 5α-reductase isoforms—A comparative study of selective inhibitors

The present study describes the independent expression of the type 1 and 2 isoforms of human 5α-reductase in the baculovirus-directed insect cell expression system and the selectivity of their inhibition. The catalytic properties and kinetic parameters of the recombinant isozymes were consistent with published data. The type 1 isoform displayed a neutral (range 6–8) pH optimum and the type 2 isoform an acidic (5–6) pH optimum. The type 2 isoform had higher affinity for testosterone than did the type 1 isoform (K_m = 0.5 and 2.9 μM, respectively). Finasteride and turosteride were selective inhibitors of the type 2 isoform (K_i (type 2) = 7.3 and 21.7 nM compared to K_i (type 1) = 108 and 330 nM, respectively). 4-MA and the lipido-sterol extract of Serenoa repens (LSESr) markedly inhibited both isozymes (K_i (type 1) = 8.4 nM and 7.2 μg/ml, respectively; K_i (type 2) = 7.4 nM and 4.9 μg/ml, respectively). The three azasteroids were competitive inhibitors vs substrate, whereas LSESr displayed non-competitive inhibition of the type 1 isozyme and uncompetitive inhibition of the type 2 isozyme. These observations suggest that the lipid component of LSESr might be responsible for its inhibitory effect by modulating the membrane environment of 5α-reductase. Partially purified recombinant 5α-reductase type 1 activity was preserved by the presence of lipids indicating that lipids can exert either stimulatory or inhibitory effects on human 5α-reductase.     

Aromatase inhibition and experimental antitumor activity of FCE 24304, MDL 18962 and SH 489

Human placental aromatase inhibitory properties of FCE 24304, MDL 18962, SH 489 and 4-hydroxyandrostenedione (4-OHA) were compared. The compounds caused time-dependent enzyme inactivation with t1/2 values of 13.9, 13.1, 45.3 and 2.1 min and Ki values of 26.0, 0.7, 2.0 and 29.0 nM respectively. The antitumor activity of FCE 24304, MDL 18962 and SH 489 was studied on the DMBA-induced mammary tumor in rats, at daily s.c. doses of 10 and 50 mg/kg. FCE 24304 induced 30 and 73% regressions of established tumors, associated with 86 and 93% decrease in total ovarian aromatase activity. SH 489 and MDL 18962 did not affect tumor growth. FCE 24304, like 4-OHA, was shown to inhibit LH hypersection in castrated rats. A gonadotropin suppressive effect could contribute to the antitumor activity of aromatase inhibitors in intact DMBA-induced tumor bearing rats.     

Biochemistry and pharmacology of 7α-substituted androstenediones as aromatase inhibitors

The inhibition of aromatase, the enzyme responsible for converting androgens to estrogens, is therapeutically useful for the endocrine treatment of hormone-dependent breast cancer. Research by our laboratory has focused on developing competitive and irreversible steroidal aromatase inhibitors, with an emphasis on synthesis and biochemistry of 7α-substituted androstenediones. Numerous 7α-thiosubstituted androst-4-ene-3,17-diones are potent competitive inhibitors, and several 1,4-diene analogs, such as 7α-(4′-aminophenylthio)-androsta-1,4-diene-3,17-dione (7α-APTADD), have demonstrated effective enzyme-activated irreversible inhibition of aromatase in microsomal enzyme assays. One focus of current research is to examine the effectiveness and biochemical pharmacology of 7α-APTADD in vivo. In the hormone-dependent 7,12-dimethylbenz(a)anthracene (DMBA)-induced rat mammary carcinoma model system, 7α-APTADD at a 50 mg/kg/day dose caused an initial decrease in mean tumor volume during the first week, and tumor volume remained unchanged throughout the remaining 5-week treatment period. This agent lowers serum estradiol levels and inhibits ovarian aromatase activity. A second research area has focused on the synthesis of more metabolically stable inhibitors by replacing the thioether linkage at the 7α position with a carbon-carbon linkage. Several 7α-arylaliphatic androst-4-ene-3,17-diones were synthesized by 1,6-conjugate additions of appropriate organocuprates to a protected androst-4,6-diene or by 1,4-conjugate additions to a seco-A-ring steroid intermediate. These compounds were all potent inhibitors of aromatase with apparent K_is ranging between 13 and 19 nM. Extension of the research on these 7α-arylaliphatic androgens includes the introduction of a C₁---C₂ double bond in the A-ring to provide enzyme-activated irreversible inhibitors. The desired 7α-arylaliphatic androsta-1,4-diene-3,17-diones were obtained from their corresponding 7α-arylaliphatic androst-4-ene-3,17-diones by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). These inhibitors demonstrated enzyme-mediated inactivation of aromatase with apparent k_inacts ranging from 4.4 × 10⁻⁴ to 1.90 x 10⁻³ s⁻¹. The best inactivator of the series was 7α-phenpropylandrosta-1,4-diene-3,17-dione, which exhibited a T_1/2 of 6.08 min. Aromatase inhibition was also observed in MCF-7 human mammary carcinoma cell cultures and in JAr human choriocarcinoma cell cultures, exhibiting IC₅₀ values of 64-328 nM. The 7α-arylaliphatic androgens thus demonstrate potent inhibition of aromatase in both microsomal incubations and in choriocarcinoma cell lines expressing aromatase enzymatic activity. Additionally, the results from these studies provide further evidence for the presence of a hydrophobic binding pocket existing near the 7α-position of the steroid in the active site of aromatase. The size of the 7α-substituent influences optimal binding of steroidal inhibitors to the active site and affects the extent of enzyme-mediated inactivation observed with androsta-1,4-diene-3,17-dione analogs.     

Inhibition and inactivation of equine aromatase by steroidal and non-steroid al compounds. A comparison with human aromatase inhibition

Abstract

In order to approach the detailed structure-function relationships of aromatase, we studied the inhibitory and inactivatory potencies of several steroidal androstenedione analogues (1: 4-hydroxyandrostenedione, 2: 4-acetoxyandrostenedione and 3: 7α-(4'-amino)phenylthio-4-androstene-3, 17-dione) and non-steroidal imidazole derivatives (4: ketoconazole, 5: miconazole and 6: fadrozole) on equine aromatase in placental microsomes, a well established mammalian model. Human placental microsomes and the purified enzyme from equine testis were also used to compare inhibition by 1 and 2. In equine microsomes, all compounds tested exhibited a competitive inhibition, with K_i values of 4.1, 26 and 1.8 nM for 1, 2 and 3, and of 2400, 1.4 and 4 nM for 4, 5, and 6, respectively. The K_m for androstenedione, the substrate mainly used in these studies, was 1.8 ± 0.13 nM. The three non-steroidal derivatives did not inactivate equine aromatase, but 1 and 2 acted as comparable inactivators to a much higher degree than 3. Compound 1 inhibited in a similar manner (89–94%) purified or equine and human microsomal aromatases, whereas 2 inhibited microsomal aromatase more efficiently in the horse than in man (92% and 33% inhibition, respectively). There was only a 40% inhibition with 2 on the purified equine enzyme, which is no more in the natural membrane environment. The comparisons between equine and human microsomal aromatases allow precise functional and structural differences to be observed with these enzymes.     

4- and 6-(p-Sulphamoylphenyl)androstenediones: Studies of aromatase inhibitor-based oestrone sulphatase inhibition

4-(p-Sulphamoylphenyl)androstenedione (3) and 6α-p-sulphamoylphenyl analogues 12-14 were synthesised and tested as aromatase inhibitors as well as oestrone sulphatase inhibitors in human placental microsomes. All of the p-sulphamoylphenyl compounds synthesised were powerful inhibitors of aromatase with apparent K_i values ranging between 30 and 97 nM. In addition, the aromatase inhibitory activities of 6α-p-hydroxyphenyl compounds 9-11, which may be produced from their respective sulphamoylphenyl compounds by action of oestrone sulphatase, were also high in a range of 23 and 75 nM of the K_i values. On the other hand, all of the sulphamoylphenyl compounds were poor inhibitors of oestrone sulphatase with more than about 200 μM of IC₂₅ values. Although the present findings of the oestrone sulphatase inhibition are disappointing, such attempts may be valuable to develop a new class of drugs having a dual function, aromatase inhibitor and oestrone sulphatase inhibitor, for the treatment of oestrogen-dependent breast cancer.     

4-Methyl-3-oxo-4-aza-5α-androst-1-ene-17β-N-aryl-carboxamides: an approach to combined androgen blockade [5α-reductase inhibition with androgen receptor binding in vitro]

4-Aza-5α-androstan-3-one 17β-(N-substituted carboxamides) are potent human type 2 5α-reductase (5aR) inhibitors with generally poor binding to the human androgen receptor (hAR). When the 17-amide N-substituent included an aromatic residue, potent dual inhibitors of both type 1 and 2 5aR are produced, but hAR binding remained poor. Tertiary-substituted-17-amides have reduced inhibition of both 5aR isozymes. The addition of an N⁴-methyl substitutent to the A-ring profoundly increased hAR affinity and the addition of unsaturation to the A-ring (Δ¹) modestly augmented hAR binding. The unsubstituted carbanilides in the Δ¹-N⁴-methyl series show some selectivity for type 1 5aR over the type 2 isozyme, whereas addition of aryl substituents, particularly at the 2-position, increased type 2 5aR binding to provide dual inhibitors with excellent hAR binding, e.g. N-(2-chlorophenyl)-3-oxo-4-methyl-4-aza-5α-androst-1-ene-17β-carboxamide (9c). Compounds of this type exhibit low nanomolar IC₅₀s for both human 5aR isozymes as well as the human androgen receptor. Kinetic analysis confirms that the prototype 9c displays reversible, competitive inhibition of both human isozymes of 5aR with K_i values of less than 10 nM. Furthermore, this compound binds to the androgen receptor with an IC₅₀ equal to 8 nM. Compounds in this series are projected to be powerful antagonists of testosterone and dihydrotestosterone action in vivo, with potential utility in the treatment of prostatic carcinoma (PC).     

Evaluation of synthesized coumarin derivatives on aromatase inhibitory activity

In women across the world, the most common type of cancer is breast cancer. Among medical treatments, endocrine therapy based on aromatase inhibitors (AI) is expected to be effective against not only post-menopausal but also pre-menopausal breast cancer. In this study, we examined the structure–activity relationship between the aromatase inhibitory effects of 7-diethylaminocoumarin derivatives with a substituent at position 3 and coumarin derivatives with a substituent at position 7. Consequently, we found that 7-(pyridin-3-yl)coumarin (IC₅₀ values 30.3 nM) and 7,7′-diethylamino-3,3′-biscoumarin (28.7 nM) are the most potent inhibitors of aromatase. These inhibitors were found to be comparable to the existing CYP19 inhibitor exemestane (42.5 nM).     

Exemestane (FCE 24304), a new steroidal aromatase inhibitor.

Exemestane (FCE 24304; 6-methylenandrosta-1,4-diene-3,17-dione) is a novel orally active irreversible aromatase inhibitor. Its in vitro and in vivo pharmacological properties have been compared to 4-hydroxyandrostenedione (4-OHA). In preincubation studies with human placental aromatase, exemestane, like 4-OHA, showed enzyme inactivating properties with a similar affinity (Ki 26 vs 29 nM) and a lower rate of inactivation (t1/2 13.9 vs 2.1 min). Conversely, when tested in pregnant mares' serum gonadotropin-treated rats, exemestane was more potent in reducing microsomal ovarian aromatase activity than 4-OHA, after both subcutaneous (ED50 1.8 vs 3.1 mg/kg) and oral dosing (ED50 3.7 vs greater than 100 mg/kg). No interference of exemestane on desmolase or 5 alpha-reductase activity was found. The compound did not show any relevant binding affinity to steroidal receptors, but slight binding to the androgen receptor (approximately 0.2% of dihydrotestosterone), like 4-OHA. In the first phase I trial, healthy postmenopausal volunteers were given single oral doses of exemestane, ranging from 0.5 to 800 mg, and plasma [estrone (E1), estradiol (E2) and estrone sulphate (E1S)] and urinary estrogens (E1 and E2) were measured up to 5-8 days. The minimal effective dose in decreasing estrogens was 5 mg. At 25 mg the maximal suppression was observed at day 3: plasma estrogens fell to 35 (E1), 39 (E2) and 28% (E1S), and urinary estrogens fell to 20 (E1) and 25% (E2) of basal values, these effects still persisting on day 5. No effects on plasma levels of cortisol, aldosterone, 17-hydroxyprogesterone, DHEAS, LH and FSH, and no significant adverse events were observed up to the highest tested dose of 800 mg exemestane.     

Indole and benzimidazole derivatives as steroid 5α-reductase inhibitors in the rat prostate

A novel series of indole and benzimidazole derivatives were synthesized and evaluated for their inhibitory activity of rat prostatic 5α-reductase. Among these compounds, 4-{2-[1-(4,4′-dipropylbenzhydryl)indole-5-carboxamido]phenoxy}butyric acid (15) and its benzimidazole analogue 25 showed potent inhibitory activities for rat prostatic 5α-reductase (IC₅₀ values of 9.6 ± 1.0 and 13 ± 1.5nM, respectively), with the potency very close to that of finasteride. Compound 30, in which the moiety between the benzene ring and amide bond was replaced by quinolin-4-one ring, showed almost equipotent activity (IC₅₀ = 19 ± 6.2nM) with the correspondent amide derivative 13. This result was consistent with the previous observation that the coplanarity of this moiety might contribute to the potent inhibitory activity.     

Inhibitory effects of some steroidal 6-methylene derivatives on 5α-reductase activity in human and rat prostate

Using a short-term organ culture assay, some 6-methylene derivatives of progesterone and testosterone have been evaluated for their effects on testosterone metabolism in rat and human prostatic tissues, and on DNA synthesis in explants from 7-day castrated rats. Comparative studies showed that the ability to inhibit 5α-reductase activity was fairly specific with respect to structural requirements. Methylene substitution at the C₆ position of the progesterone molecule was associated with high inhibitory activity. In explants prepared from human prostates, 6-methylene progesterone (II) had 70–85% (mean of 79% for 4 BPH tissues) of the potency of unmodified progesterone (I). Its 17α-acetoxy-6-methylene analog (III), however, had only 32–73% (mean of 53% for 5 BPH specimens) of the activity of (I). The degrees of inhibition in rat and human prostatic tissues were similar. Inhibition of 5α-reductase activity in cultured explants by 6-methylene progesterone (II) could not be reversed by change in media. The 6-methylene derivatives had little or no effect on DNA synthesis. Histological examination confirmed a lack of effect on basal cell proliferation. However, morphological alterations affecting epithelial cell height and secretory activity were clearly evident. These results indicate that, under our experimental conditions, the main effect of inhibition of 5α-reductase activity in prostatic tissues by 6-methylene derivatives of progesterone is related to suppression of differentiated function.     

Comparison of Aromatase Activity in Human Prostatic,Testicular and Placental Tissues

Abstract

The aromatase enzyme was quantified by the release of tritiated water from [1β-³H] androstenedione. Tritiated water was released by the crude homogenates in 4 of 18 samples of benign prostatic hyperplasia tissue and one of 5 samples of prostate carcinoma tissue. However, this apparent aromatase activity was not inhibited by 4-hydroxyandrostenedione (0.5 and 5.0μM), and none of the particulate fractions (100,000 g pellet) prepared from each of the prostatic tissues exhibited aromatase activity. Particulate fractions from rat ovary (n = 3) and human testes (n = 6) displayed significant aromatase activity (mean values of 9.9 and 0.033 nmol estrone formed/g protein/h, respectively). The testicular aromatase was inhibited by aminoglutethimide, 4-hydroxyandrostenedione and CGS 16949A with IC₅₀ values of 6.4, 0.17 and 0.0017 μM. respectively. These are of a similar order to values obtained with the aromatase enzyme from human placental microsomes (14, 0.43 and 0.0075μM, respectively).     

Role of 5α-reduction in progesterone's ability to release FSH in estrogen-primed ovariectomized rats

In ovariectomized estrogen-primed rats, progesterone as well as 5α-dihydroprogesterone (5α-DHP) are capable of inducing the release of gonadotropins. This study examined the need of 5α-reduction as a prerequisite for the action of progesterone. The 5α-reductase inhibitor, N,N-diethyl-4-methyl-3-oxo-4-aza-5α-androstane-17β-carboxamide was injected at a 1 or 2 mg dose/rat 2 h prior to an injection of 0.4 or 0.8 mg progesterone/kg body weight at 0900 h to immature ovariectomized, estrogen-primed rats and serum was analyzed for LH and FSH at 1500 h. Pituitary and hypothalamic 5α-reductase activity was measured at the time of progesterone administration and at the time of the surge by incubating tissue homogenates with [³H]progesterone. Substrate, ([³H]progesterone) and product ([³H]5α-DHP), were separated by reverse phase HPLC. The pituitary 5α-reductase activity was not blocked at 1500 h. However, both pituitary and hypothalamic 5α-reductase was blocked at the time of progesterone administration. No effect was seen by acute administration of the 5α-reductase inhibitor upon either the 0.4 or 0.8 mg progesterone/kg-induced release of LH and FSH. There was, however, a specific, significant inhibition of progesterone-induced FSH but not LH release when the 5α-reductase inhibition was sustained throughout the afternoon of the gonadotropin surge. These results indicate a biologically significant role for the irreversible 5α-reduction of progesterone in the modulation of the release of FSH.     

Androgen metabolism and biotransformation in nontumoral and malignant human liver tissues and cells

There is indirect multiple evidence that hints at a potential role of sex steroids in development and progression of human hepatocellular carcinoma (HCC). In the present study, we have investigated androgen metabolism in a panel of human liver cancer cell lines (HA22T, Huh7, HepG2) and in normal, cirrhotic and malignant human liver tissues aiming to dissect the potential impact of individual enzyme activities and their products in normal and diseased human liver, both in vivo and in vitro. Using our intact cell analysis we were able to assess rates and pathways of androgen metabolism in living conditions. Overall, incubation of cultured cells or tissue minces with either testosterone (T) or androstenedione (Ad) used as precursor resulted in a large extent of 17βoxidation of T to Ad (cells: 28–77%; tissues: 35–50%). In malignant liver cell lines, both HA22T and Huh7 cells showed consistent amounts of the 5α-reductase enzyme products (18% and 15%, respectively), while 5β-reductase activity was more pronounced in Huh7 cells (18%) than in HA22T cells (1.8%). Interestingly, a significant extent of estrogen formation could be observed in Huh7 cells (5.4–11.5%), while no aromatase activity could be detected in HA22T cells. In HepG2 cells, along with a relatively high proportion of Ad, estrogens represented the most prominent (50–55%) end product of androgen metabolism, regardless of the precursor used. In liver tissues, equivalent results could be obtained, with a consistent proportion of 17βoxidation of T to Ad (35–50%) being observed in the majority of samples. However, while normal liver tissue samples exhibited a minor proportion of bioactive androgens (3.4%) with no aromatase products, HCC tissues showed a significant extent of aromatase activity (nearly 20%) with estrogen representing the most prominent metabolic product after 24 h incubation with either T or Ad. HCV and alcoholic cirrhotic tissues displayed different patterns of androgen metabolism. The former produced limited amounts of bioactive androgens (5.3%) and considerable levels of the intermediate aromatase product 19OH-Ad (up to 28%), the latter exhibited a prevalence of androgen degradation through the 5β-reductase pathway (9.8%) and a significant extent of aromatase activity (16% as a whole). In conclusion, three major metabolic states could be depicted, depending on prevalent pathways of androgen metabolism and steroid receptor status: estrogenic, androgenic, and mixed. This model supports the idea that local estrogen biosynthesis may be implicated in human HCC and provides a basis for the exploitation of aromatase inhibitors and/or ER antagonists or selective estrogen receptor modulators (SERMs) as a new therapeutic strategy in HCC patients.     

6β,19-Bridged androstenedione analogs as aromatase inhibitors

Inhibition of aromatase is an efficient approach for the prevention and treatment of breast cancer. New 6β,19-bridged steroid analogs of androstenedione, 6β,19-epithio- and 6β,19-methano compounds 11 and 17, were synthesized starting from 19-hydroxyandrostenedione (6) and 19-formylandrost-5-ene-3β,17β-yl diacetate (12), respectively, as aromatase inhibitors. All of the compounds including known steroids 6β,19-epoxyandrostenedione (4) and 6β,19-cycloandrostenedione (5) tested were weak to poor competitive inhibitors of aromatase and, among them, 6β,19-epoxy steroid 4 provided only moderate inhibition (K_i: 2.2 μM). These results show that the 6β,19-bridged groups of the inhibitors interfere with binding in active site of aromatase.     

Aromatase inactivation by 2-substituted derivatives of the suicide substrate androsta-1,4-diene-3,17-dione

To gain the structure–activity relationship of Δ¹-androstenediones (Δ¹-ADs) as mechanism-based inactivator of aromatase, series of 2-alkyl- and 2-alkoxy-substitiuted Δ¹-ADs (6 and 9) as well as 2-bromo-Δ¹-AD (14) were synthesized and tested. All of the inhibitors examined blocked aromatase in human placental microsomes in a competitive manner. In a series of 2-alkyl-Δ¹-ADs (6), n-hexyl compound 6f was the most powerful inhibitor with an apparent K_i value of 31 nM. The inhibitory activities of 2-alkoxy steroids 9 decreased in relation to length of the alkyl chain up to n-hexyloxy group (K_i: 95 nM for methoxy 9a). All of the alkyl steroids 6 along with the alkoxy steroid 9, except for the ethyl and n-propyl compounds 6b and 6c, caused a time-dependent inactivation of aromatase. The inactivation rates (k_inact: 0.020–0.084 min⁻¹) were comparable to that of the parent compound Δ¹-AD. The inactivation was prevented by the substrate AD, and no significant effect of l-cysteine on the inactivation was observed in each case. The results indicate that the 2-hexyl compound 6f act as the most powerful mechanism-based inactivator of aromatase among Δ¹-AD analogs and may be submitted to the preclinical study in estrogen-dependent breast cancer.     

17α-Methyl testosterone is a competitive inhibitor of aromatase activity in Jar choriocarcinoma cells and macrophage-like THP-1 cells in culture

17α-Methyl testosterone is a synthetic androgen with affinity for the androgen receptor. 17α-Methyl testosterone is used widely as a component of hormone replacement therapy. Previous reports have indicated that contrary to testosterone, 17α-methyl testosterone is not aromatized. However, 17α-methyl testosterone still could affect local estrogen formation by regulating aromatase expression or by inhibiting aromatase action. Both possibilities have important clinical implications. To evaluate the effect of 17α-methyl testosterone on the expression and activity of aromatase, we tested the choriocarcinoma Jar cell line, a cell line that express high levels of P₄₅₀ aromatase, and the macrophage-like THP-1 cells, which express aromatase only after undergoing differentiation. We found that in both cell lines, 17α-methyl testosterone inhibits aromatase activity in a dose-related manner. The curve of inhibition parallels that of letrozole and gives complete inhibition at 10⁻⁴ M 17α-methyl testosterone, determined by the tritium release assay. 17α-Methyl testosterone does not have detectable effects on aromatase RNA and protein expression by Jar cells. Undifferentiated THP-1 cells had no aromatase activity and showed no effect of 17α-methyl testosterone, but differentiated THP-1 (macrophage-like) cells had a similar inhibition of aromatase activity by 17α-methyl testosterone to that seen in Jar cells. The Lineweaver–Burke plot shows 17α-methyl testosterone to be a competitive aromatase inhibitor. Our results show for the first time that 17α-methyl testosterone acts as an aromatase inhibitor. These findings are relevant for understanding the effects of 17α-methyl testosterone as a component of hormone replacement therapy. 17α-Methyl testosterone may, as a functional androgen and orally active steroidal inhibitor of endogenous estrogen production, also offer special possibilities for the prevention/treatment of hormone-sensitive cancers.     

The human carbonic anhydrase isoenzymes I and II inhibitory effects of some hydroperoxides,alcohols, and acetates

The carbonic anhydrases (CAs, EC 4.2.1.1) represent a superfamily of widespread enzymes, which catalyze a crucial biochemical reaction, the reversible hydration of carbon dioxide to bicarbonate and protons. Human CA isoenzymes I and II (hCA I and hCA II) are ubiquitous cytosolic isoforms. In this study, a series of hydroperoxides, alcohols, and acetates were tested for the inhibition of the cytosolic hCA I and II isoenzymes. These compounds inhibited both hCA isozymes in the low nanomolar ranges. These compounds were good hCA I inhibitors (K_is in the range of 24.93–97.99?nM) and hCA II inhibitors (K_is in the range of 26.04–68.56?nM) compared to acetazolamide as CA inhibitor (K_i: 34.50?nM for hCA I and K_i: 28.93?nM for hCA II).     

Pyrrolylbenzothiazole Derivatives as Aldose Reductase Inhibitors

Abstract

2,2-Dimethyl-4-hydroxy-4-androstene-3,17-dione (4) has been synthesized and has been shown to be a powerful competitive inhibitor of aromatase (K_i = 11.4nM). However, compound 4 does not cause time-dependent loss of enzyme activity, in contrast to the unmethylated parent compound, 4-OHA.