This material is available free of charge via the Internet at binding sites have been identified4 and the binding sites for substrates/inhibitors have been characterized. Aberrant expression and action of AKR1C enzymes can lead to different pathophysiological conditions.5,6 For instance, in the endometrium, both AKR1C1 and AKR1C3 prevent the progestational and pro-differentiating effect of progesterone in the uterus and the ectopic endometrium.7,8 Thus inhibitors of these enzymes could help maintain pregnancy and may have a role in the treatment of endometriosis. Increased expression of AKR1C3 can result in high levels of the potent androgens, testosterone and dihydrotestosterone RWJ-51204 in the prostate or the potent estrogen estradiol in the breast, leading to enhanced proliferation of prostate or breast cells.9,10 Thus inhibitors of AKR1C3 could be used in anti-hormonal therapy of prostate and breast cancer. In the prostate on the other hand, AKR1C1 and AKR1C2 convert the most potent androgen 5-dihydrotestosterone to pro-apoptotic 5-androstane-3,17-diol, and 5-androstane-3,17-diol, respectively.11,12 These data suggest a need for selective inhibitors for AKR1C1 and AKR1C3. Inhibition of AKR1C2 and liver specific AKR1C4, which are both involved in inactivation of steroid hormones and their elimination from the body, is not desirable. In the last decade, steroidal and non-steroidal AKR1C inhibitors have been reported.4,13,14 Several compounds with Ki values in the nanomolar range for AKR1C1 and AKR1C3 have been recently found based on the observation that salicylates were potent and selective inhibitors for AKR1C1 and that Rabbit Polyclonal to SEC16A to one another, and an electron-withdrawing group was placed in the evaluation. Among these hits RWJ-51204 there were some new inhibitors, anthranilic acid and salicylic acid derivatives, with scaffolds that are known to inhibit AKR1C enzymes,16,23,29 which validates our method and is supported by the successful re-docking of co-crystallized inhibitors with high scores. Biochemical Evaluation of Hits Against AKR1C1-AKR1C4 Out of 70 obtained compounds, 11 compounds were insoluble. For RWJ-51204 the other 59 compounds, the percentage of inhibition of AKR1C1 and AKR1C3 at compound concentrations of 400 M was first determined. All compounds, regardless of the virtual screen in which they were identified, were assayed on both AKR1C1 and AKR1C3 enzymes because these enzymes share 88 % identical amino acid residues, and thus have a common fold and similar active site. In addition, we were interested to learn if it is possible to discover isoform selective AKR1C inhibitors by virtual screening. For compounds that showed more than 55% inhibition of AKR1C1 and/or 55% inhibition of AKR1C3, IC50 values were determined and selectivity towards AKR1C2 was measured. The complete results of the biochemical characterization are presented in Supporting Information-Table 1. In the case of the most promising compounds, further kinetic analysis was pursued. Salicylic acid and aminobenzoic acid derivatives In a series of salicylic acid derivatives (Figure 1, Box A), compounds 1, 2 and 3 are 5-aminosalicylates with different acyl substituents on the amino group. Compound 1, 5-(2-fluorobenzamido)salicylic acid, shows only low and moderate inhibition of AKR1C1 and AKR1C3, respectively. Replacement of 2-fluorobenzoyl moiety with dimethylfurancarboxyl as in compounds 2 and 3 significantly improved AKR1C1-3 inhibition. It appears that the methylation pattern of the furan ring together with the position of carbonyl substituent influences inhibition and selectivity. Compound 2, 5-(2,5-dimethylfuran-3-carboxamido)-salicylic acid, is a nonselective AKR1C1-3 inhibitor, with Ki values of 50, 90 and 118 M on AKR1C1, AKR1C2 and AKR1C3, respectively. On the other hand, compound 3, 5-(4,5-dimethylfuran-2-carboxamido)-salicylic acid, is a selective AKR1C3 inhibitor with Ki value of 82 M on AKR1C3, very low inhibition of AKR1C2 and no observable inhibition of AKR1C1. Another salicylic acid derivative, compound 4 (4-((2-carbamoylphenoxy)methyl)-5-methylfuran-2- carboxamide) is partially selective towards AKR1C1 with Ki value of 122 M and a moderate inhibitor of AKR1C2 and AKR1C3. Open in a separate window Figure 1 Structures and AKR1C1-3 inhibitory activities of salicylic acid (box A) and aminobenzoic acid (box B) derivatives. Percent inhibition was determined at 400 M inhibitor concentration. Compounds 5C10 (Figure 1, Box B) belong to the group of 2-aminobenzoic acids (anthranilic acid derivatives). Compounds 5 and 6 are both 2-(benzylideneamino)benzamides which differ only by one aromatic hydroxyl group. Compound 5, 2-(3-hydroxybenzylideneamino)benzamide, is a selective AKR1C3 inhibitor, whereas substance 6, 2-(2,3-dihydroxybenzylideneamino)benzamide, inhibits AKR1C1-AKR1C3 towards the same degree in the reduced micromolar focus range. With Ki = 12 M, compound 6 can be the very best AKR1C3 inhibitor through the salicylic and aminobenzoic acidity series. The testing.