Structural basis for the selective inhibition of human 3beta-hydroxysteroid dehydrogenase 1 in human breast tumor MCF-7 cells.

Human 3beta-hydroxysteroid dehydrogenase/isomerase type 1 (3beta-HSD1) is a critical enzyme in the conversion of DHEA to estradiol in breast tumors and may be a target enzyme for inhibition in the treatment of breast cancer in postmenopausal women. Human 3beta-HSD2 participates in the production of cortisol and aldosterone in the human adrenal gland in this population. In our recombinant human breast tumor MCF-7 Tet-off cells that express either 3beta-HSD1 or 3beta-HSD2, trilostane and epostane inhibit the DHEA-induced proliferation of MCF-7 3beta-HSD1 cells with 12- to 16-fold lower IC(50) values compared to the MCF-7 3beta-HSD2 cells. The compounds also competitively inhibit purified human 3beta-HSD1 with 12- to 16-fold lower K(i) values compared to the noncompetitive K(i) values measured for human 3beta-HSD2. Using our structural model of 3beta-HSD1, trilostane or 17beta-acetoxy-trilostane was docked in the active site of 3beta-HSD1, and Arg195 in 3beta-HSD1 or Pro195 in 3beta-HSD2 was identified as a potentially critical residue (one of 23 non-identical residues in the two isoenzymes). The P195R mutant of 3beta-HSD2 were created, expressed and purified. Kinetic analyses of enzyme inhibition suggest that the high affinity, competitive inhibition of 3beta-HSD1 by trilostane and epostane may be related to the presence of Arg195 in 3beta-HSD1 vs. Pro195 in 3beta-HSD2.

Structure/function of the inhibition of human 3beta-hydroxysteroid dehydrogenase type 1 and type 2 by trilostane.

The human type 1 (placenta, breast tumors) and type 2 (gonads, adrenals) isoforms of 3beta-hydroxysteroid dehydrogenase/isomerase (3beta-HSD) are key enzymes in biosynthesis of all active steroid hormones. Human 3beta-HSD1 is a critical enzyme in the conversion of DHEA to estradiol in breast tumors and may be a major target enzyme for the treatment of breast cancer. 3beta-HSD2 participates in the production of cortisol and aldosterone in the human adrenal gland. The goals of this project are to evaluate the role of the 2alpha-cyano group on trilostane (2alpha-cyano-4alpha,5alpha-epoxy-17beta-ol-androstane-3-one) and determine which amino acids may be critical for 3beta-HSD1 specificity. Trilostane without the 2alpha-cyano group, 4alpha,5alpha-epoxy-testosterone, was synthesized. Using our structural model of 3beta-HSD1, trilostane or 4alpha,5alpha-epoxy-testosterone was docked in the active site using Autodock 3.0, and the potentially critical residues (Met187 and Ser124) were identified. The M187T and S124T mutants of 3beta-HSD1 were created, expressed and purified. Dixon analyses of the inhibition of wild-type 3beta-HSD1, 3beta-HSD2, M187T and S124T by trilostane and 4alpha,5alpha-epoxy-testosterone suggest that the 2alpha-cyano group of trilostane is anchored by Ser124 in both isoenzymes. Kinetic analyses of cofactor and substrate utilization as well as the inhibition kinetics of M187T and the wild-type enzymes suggest that the 16-fold higher-affinity inhibition of 3beta-HSD1 by trilostane may be related to the presence of Met187 in 3beta-HSD1 and Thr187 in 3beta-HSD2. This structure/function information may lead to the production of more highly specific inhibitors of 3beta-HSD1 to block the hormone-dependent growth of breast tumors.

Structure-function relationships for the selective inhibition of human 3ß-hydroxysteroid dehydrogenase type 1 by a novel androgen analog.

3ß-Hydroxysteroid dehydrogenase type 1 (3ß-HSD1) is selectively expressed in human placenta, mammary glands and breast tumors in women. Human 3ß-HSD2 is selectively expressed in adrenal glands and ovaries. Based on AutoDock 3 and 4 results, we have exploited key differences in the amino acid sequences of 3ß-HSD1 (Ser194, Arg195) and 3ß-HSD2 (Gly194, Pro195) by designing a selective inhibitor of 3ß-HSD1. 2,16-Dicyano-4,5-epoxy-androstane-3,17-dione (16-cyano-17-keto-trilostane or DiCN-AND) was synthesized in a 4-step procedure from androstenedione. In purified 3ß-HSD inhibition studies, DiCN-AND competitively inhibited 3ß- HSD1 with Ki=4.7µM and noncompetitively inhibited 3ß-HSD2 with a 6.5-fold higher Ki=30.7µM. We previously reported similar isoenzyme-specific inhibition profiles for trilostane. Based on our docking results, we created, expressed and purified the chimeric S194G-1 mutant of 3ß-HSD1. Trilostane inhibited S194G-1 (Ki=0.67µM) with a noncompetitive mode compared to its 6.7-fold higher affinity, competitive inhibition of 3ß-HSD1 (Ki=0.10µM). DiCN-AND inhibited S194G-1 with a 6.3-fold higher Ki (29.5µM) than measured for 3ß-HSD1 (Ki=4.7µM) but with the same competitive mode for both enzyme species. Since DiCN-AND noncompetitively inhibits 3ß-HSD2, which has the Gly194 and Pro195 of 3ß-HSD2 in place of the Ser194 and Arg195 in 3ß-HSD1, this suggests that Arg195 alone in 3ß-HSD1 or S194G-1 is required to bind DiCN-AND in the substrate binding site (competitive inhibition). However, both Ser194 and Arg195 are required to bind trilostane in the 3ß-HSD1 substrate site based on its noncompetitive inhibition of S194G-1 and 3ß-HSD2. In support of this hypothesis, DiCN-AND inhibited our chimeric R195P-1 mutant noncompetitively with a Ki=41.3µM (similar to the 3ß-HSD2 inhibition profile). Since DiCN-AND competitively inhibited S194G-1 that still contains R195 but noncompetitively inhibited R195P-1 that still contains S194, our data provides strong evidence that the Arg195 being mutated to Pro195 (as present in 3ß-HSD2) shifts the inhibition mode from competitive to noncompetitive in 3ß-HSD1. This supports the key role of Arg195 in 3ß-HSD1 for the high affinity, competitive binding of the trilostane analogs. Our new structure/function information for the design of targeted 3ß-HSD1 inhibitors may lead to important new treatments for the prevention of spontaneous premature birth.

Self-selection in olefin cross-metathesis: the effect of remote functionality.

Olefin cross-metathesis (CM) is potentially an attractive method for generating dynamic combinatorial libraries (DCLs). In order for the CM reaction to be useful for DCL production, the course of the reaction and product distribution must be relatively insensitive to functionality remote from the reacting centers. We report on the CM of a series of allyl- and homoallylamides that are strongly dependent on remote functionality. This includes an unusual example of a cis-selective CM. [Reaction: see text]

Selective inhibition of human 3ß-hydroxysteroid dehydrogenase type 1 as a potential treatment for breast cancer.

Human 3ß-hydroxysteroid dehydrogenase/isomerase type 1 (3ß-HSD1) is a critical enzyme in the conversion of DHEA to estradiol in breast tumors and may be a target enzyme for inhibition in the treatment of breast cancer in postmenopausal women. Human 3ß-HSD2 participates in the production of cortisol and aldosterone in the human adrenal gland in this population. In our recombinant human breast tumor MCF-7 Tet-off cells that express either 3ß-HSD1 or 3ß-HSD2, trilostane and epostane inhibit the DHEA-induced proliferation of MCF-7 3ß-HSD1 cells with 12-16-fold lower IC(50) values compared to the MCF-7 3ß-HSD2 cells. Trilostane and epostane also competitively inhibit purified human 3ß-HSD1 with 12-16-fold lower K(i) values compared to the noncompetitive K(i) values measured for human 3ß-HSD2. Using our structural model of 3ß-HSD1, trilostane was docked in the active site of 3ß-HSD1, and Arg195 in 3ß-HSD1 or Pro195 in 3ß-HSD2 was identified as a potentially critical residue. The R195P-1 mutant of 3ß-HSD1 and the P195R-2 mutant of 3ß-HSD2 were created, expressed and purified. Kinetic analyses of enzyme inhibition suggest that the high-affinity, competitive inhibition of 3ß-HSD1 by trilostane may be related to the presence of Arg195 in 3ß-HSD1 versus Pro195 in 3ß-HSD2. In addition, His156 in 3ß-HSD1 may play a role in the higher affinity of 3ß-HSD1 for substrates and inhibitors compared to 3ß-HSD2 containing Try156. Structural modeling of the 3ß-HSD1 dimer identified a possible interaction between His156 on one subunit and Gln105 on the other. Kinetic analyses of the H156Y-1, Q105M-1 and Q105M-2 support subunit interactions that contribute to the higher affinity of 3ß-HSD1 for the inhibitor, epostane, compared to 3ß-HSD2. Article from the Special issue on Targeted Inhibitors.

The functions of key residues in the inhibitor, substrate and cofactor sites of human 3beta-hydroxysteroid dehydrogenase type 1 are validated by mutagenesis.

In postmenopausal women, human 3beta-hydroxysteroid dehydrogenase type 1 (3beta-HSD1) is a critical enzyme in the conversion of DHEA to estradiol in breast tumors, while 3beta-HSD2 participates in the production of cortisol and aldosterone in the human adrenal gland. The goals of this project are to determine if Arg195 in 3beta-HSD1 vs. Pro195 in 3beta-HSD2 in the substrate/inhibitor binding site is a critical structural difference responsible for the higher affinity of 3beta-HSD1 for inhibitor and substrate steroids compared to 3beta-HSD2 and whether Asp61, Glu192 and Thr8 are fingerprint residues for cofactor and substrate binding using site-directed mutagenesis. The R195P-1 mutant of 3beta-HSD1 and the P195R-2 mutant of 3beta-HSD2 have been created, expressed, purified and characterized kinetically. Dixon analyses of the inhibition of the R195P-1 mutant, P195R-2 mutant, wild-type 3beta-HSD1 and wild-type 3beta-HSD2 by trilostane has produced kinetic profiles that show inhibition of 3beta-HSD1 by trilostane (K(i)=0.10microM, competitive) with a 16-fold lower K(i) and different mode than measured for 3beta-HSD2 (K(i)=1.60microM, noncompetitive). The R195P-1 mutation shifts the high-affinity, competitive inhibition profile of 3beta-HSD1 to a low-affinity (trilostane K(i)=2.56microM), noncompetitive inhibition profile similar to that of 3beta-HSD2 containing Pro195. The P195R-2 mutation shifts the low-affinity, noncompetitive inhibition profile of 3beta-HSD2 to a high-affinity (trilostane K(i)=0.19microM), competitive inhibition profile similar to that of 3beta-HSD1 containing Arg195. Michaelis-Menten kinetics for DHEA, 16beta-hydroxy-DHEA and 16alpha-hydroxy-DHEA substrate utilization by the R195P-1 and P195R-2 enzymes provide further validation for higher affinity binding due to Arg195 in 3beta-HSD1. Comparisons of the Michaelis-Menten values of cofactor and substrate for the targeted mutants of 3beta-HSD1 (D61N, D61V, E192A, T8A) clarify the functions of these residues as well.

Synthesis and evaluation of the first cis-cyclobutane-containing receptor for lipid A.

The first example of a designed receptor containing a cis-1,3-disubstituted cyclobutane ring has been synthesized. This molecule binds diphosphoryl lipid A (a conserved portion of the Gram-(-) bacterial cell membrane, and the causative agent of septic shock) with an affinity comparable to previously described ter-cycloalkane based lipid A-binding compounds.