Substituted C19 steroid analogs as inhibitors of aromatase.

Various C19-steroidal derivatives have been synthesized and evaluated in biochemical assays for their ability to inhibit the biosynthesis of estrogens. Steroids with substitutions on the A or B ring were prepared by Michael addition of various thiol reagents to appropriate dienone intermediates. An in vitro assay using human placental microsomes was used to evaluate aromatase-inhibitory properties. Synthesized compounds that exhibited high inhibitory activity were further evaluated under initial velocity conditions to determine apparent Ki values. Several 7 alpha-substituted androstenediones were effective competitive inhibitors and have apparent Ki values ranging from 18 to 69 nM, with the apparent Km for androstenedione being 63 nM. The most effective competitive inhibitor tested is 7 alpha-(4'-amino)phenylthioandrost-4-ene-3,17-dione with an apparent Ki of 18 nM. Derivatives of this 7 alpha-thioether compound that contain alkylating moieties have been prepared as potential irreversible enzyme inhibitors and demonstrate varying abilities to inactivate the aromatase enzyme. The results of these studies demonstrate that large chemical functionalities such as an aromatic ring with polar substituents can be accommodated in or near the active site of aromatase and, in some cases, can enhance the affinity of the enzyme for the inhibitors.

Fate of intravenously administered high-density lipoprotein labeled with radioiodinated cholesteryl oleate in normal and hypolipidemic rats.

Radioiodinated cholesteryl oleate (125I-CO) was found to associate rapidly with plasma lipoproteins following intravenous administration to rats. The high-density lipoprotein (HDL) fraction was observed to contain the highest amount of radioiodinated ester. Isolation and purification of this HDL fraction (125I-CO-HDL) and subsequent administration to rats demonstrated a plasma clearance similar to that previously observed for HDL labeled by direct iodination. Moreover, the concentration of radioactivity appearing in the adrenal cortex and ovary 0.5 h after intravenous administration of 125I-CO-HDL was greater than that observed after administration of 125I-CO, and the uptake of radioactivity by these tissues was considerably greater in hypolipidemic rats. These findings are consistent with existing knowledge relating to the metabolic fate of HDL and radioiodinated cholesterol derivatives in the rat, and suggest that radioiodinated cholesteryl esters may become useful probes for labeling lipoproteins.

New inhibitors of steroid 11beta-hydroxylase. Structure--activity relationship studies of metyrapone-like compounds.

A series of metyrapone analogues was synthesized for study as inhibitors of steroid 11beta-hydroxylase. Racemic mixtures of the new compounds were evaluated in vitro. Preliminary results revealed several analogues to be effective inhibitors of deoxycorticosterone hydroxylation. 2-(3-pyridyl)propiophenone (13) and alpha,beta-diphenyl-3-pyridineethanol (16) were the most active new compounds. Each was 65% as potent as metyrapone; 3-Pyridyl alpha-3-pyridylbenzyl ketone (3), 2-phenyl-2-(3-pyridyl)acetophenone (4), alpha-(diphenylmethyl)-3-pyridinemethanol (17), and 1,2-di-3-pyridyl-1-propanol (26) were 52, 32, 25, and 41% as inhibitory as metyrapone, respectively. Diphenylmethyl 3-pyridyl ketone (5), benzyl 3-pyridyl ketone (10), 2-(3-pyridyl)acetophenone (12), 2-phenyl-1-(3-pyridyl)-1-propanone (11), alpha,beta-di-3-pyridylphenethyl alcohol (15), and 1,2-di-3-pyridylethanol (27) had less than 25% the activity of metyrapone. All compounds displaying a metyrapone-like inhibition contained appropriately substituted alcoholic or ketonic functions. A phenyl or methyl group alpha to the carbon bearing the oxygen was necessary for appreciable activity. A 3-phridyl group alpha to the carbonyl carbon could be replaced by a phenyl group. For optimal activity, however, the other 3-pyridyl group of metyrapone could not be exchanged for a phenyl group.

Lipoproteins as potential site-specific delivery systems for diagnostic and therapeutic agents.

Despite the paucity of literature dealing with the effect of plasma lipoproteins upon drug disposition, evidence is accumulating that shows that these macromolecular complexes can play important roles in the absorption and transport of lipid-soluble agents. Moreover, preliminary studies have demonstrated that radiotracers can be directed to specific tissues by prior incorporation into the hydrophobic core of specific lipoproteins. Although these studies offer encouragement for the possible use of lipoproteins in the site-specific delivery of radiopharmaceuticals that are used in tracer doses, the use of lipoproteins in the transport of drugs at pharmacological concentrations represents a much greater challenge. Nothing is known at this time about the saturation kinetics of drug incorporation into lipoproteins or partially delipidated lipoproteins. Nor is there any assurance that drug-laden lipoproteins will participate in receptor-mediated uptake processes similar to native lipoproteins. Moreover, receptor-mediated uptake of lipoproteins is a saturable process and may not permit attainment of sufficient drug concentrations within cells. It could be argued, however, that receptor-mediated uptake could be enhanced by prior treatment with hypocholesterolemic drugs as has been shown for cholestyramine. In any event, the possible use of lipoproteins for the site-specific delivery of intravenously administered radiodiagnostics or highly potent drugs (e.g., anticancer agents) appears promising. Only the results of ongoing studies will determine the practicality of this approach.

Potential organ- or tumor-imaging agents. 18. Radioiodinated diamines and bisquaternaries.

The purpose of this research was to employ diamines and their quaternary derivatives as carrier molecules for gamma-emitting radiation. The diamine putrescine is widespread in nature and has been reported to selectively concentrate in the rat ventral prostate and pancreas. This study confirms the selective uptake of radioactivity in the rat ventral prostate, but not in the pancreas, following administration of [14C]putrescine. The radioiodinated analogues of putrescine showed no predilection for either of these organs. On the other hand, radioactivity associated with a radioidinated quaternary derivative (3) was found to accumulate incartilaginous tissues such as trachea, intervertebral disks, and chondrosarcoma tumor in a manner simular to hexamethonium.

Radioiodinated p-iodoclonidine: a high-affinity probe for the alpha 2-adrenergic receptor.

The chemical synthesis of 2-[(2,6-dichloro-4-iodophenyl)imino]imidazolidine (PIC) and its radioiodinated analogue [125I]PIC is described. PIC was synthesized from 2,6-dichloroaniline in five synthetic steps. This agent displayed a high affinity for the alpha 2-adrenergic receptor (IC50 = 1.5 nM) in competitive binding assays conducted with purified human platelet plasma membrane fractions. For the synthesis of radioiodinated PIC the triazene intermediate 11 was synthesized from 2,6-dichloro-4-nitroaniline in five synthetic steps. Acid-catalyzed decomposition of 11 with no-carrier-added Na125I afforded high specific activity [125I]PIC. In view of its high affinity for the alpha 2-adrenergic receptor, [125I]PIC is a potentially useful probe for studies in adrenergic pharmacology.

Synthesis and biochemical evaluation of inhibitors of estrogen biosynthesis.

The synthesis and biochemical evaluation of various C19-steroidal derivatives as inhibitors of estrogen biosynthesis are described. Steroids with substitutions on the A or B ring were synthesized by Michael addition of various thiol reagents to appropriate dienone intermediates. An in vitro assay employing the microsomal fraction isolated from human term placenta was used to evaluate aromatase inhibitory properties. Agents exhibiting high inhibitory activity were further evaluated in inital velocity studies (low product formation) to determine apparent Ki values. Several 7alpha-substituted androst-4-ene-3,17-diones were effective competitive inhibitors and have apparent Ki values equal to or less than the apparent Km of 0.063 microM for the substrate androstenedione.

Carbocyclic prostaglandin analogs. 1. Steroid carboxylic acids.

Certain structural similarities between prostaglandins with close-packed side chains and the perhydrocyclopentanophenanthrene nucleus of steroids prompted the synthesis and biological evaluation of 6beta, 17 beta-dihydroxy-5alpha-androstane-2alpha-carboxylic acid (30), its 6-deoxy derivative 28, and the corresponding 6-deoxy-2beta derivative 29 in an attempt to evaluate carbocyclic acids as potential prostaglandin analogs. Preliminary in vitro studies on isolated guinea pig ileum have shown weakly specific, prostaglandin-stimulated smooth muscle antagonism for 28 when compared with antagonism of bradykinin- and acetylcholine-induced contractions. Complete dose-response curves for 28 on prostaglandin-stimulated guinea pig ileum have shown a reduction in the maxium response and a decrease in the slope of the curve, indicating a noncompetitive type of inhibition for this type of derivative.

Potential organ or tumor imaging agents. 16. Fluorinated androstanes and the prostate.

A series of substituted 5alpha-androstan-17beta-ols was synthesized and evaluated for their potential use in the development of a prostate imaging agent. The ability of the synthesized compounds to compete with [3H]-5alpha-dihydrotestosterone for rat prostate androgen receptor protein served as the screening assay. For 3-substituted derivatives, the order of binding to the androgen receptor protein was =O greater than -OH greater than H approximately or equal to F. 3beta-Fluoro-5alpha-androstan-17beta-ol was found to have approximately 5% the androgenic activity of testosterone propionate in the castrated rat. The low biological activity for the 3beta-fluoro derivatives, coupled with the synthetic obstacles associated with introducing fluorine-18, has led us to search for more suitable halo steroids as potential radiodiagnostics.

Inhibition of cholesterol side-chain cleavage. 4. Synthesis of A or B ring modified azacholesterols.

A number of A or B ring modified 20- and 22-azacholesterol analogues (1 and 2, respectively) were synthesized in an attempt to ascertain the structural requirements for inhibition of the cholesterol side-chain cleavage reaction in bovine adrenocortical mitochondrial acetone powder preparations. The inhibition studies of these analogues revealed that (1) the 3-methyl ethers were as active as the parent compounds and that (2) reduction of the delta 5 double bond greatly lessened the inhibitory activity. These studies demonstrated a crucial role of the delta 5 double bond for inhibitory activity, while a free hydroxyl group at C-3 is not essential for this action. Furthermore, as in the parent compounds, 22-azacholesterol analogues were more potent than their 20-azacholesterol counterparts.

Potential tumor- or organ-imaging agents. 29. Radioiodinated esters and amides of 20-hydroxy- and 20-aminopregn-5-en-3 beta-ols.

Radioiodinated benzoyl esters and amides of epimeric 20-hydroxy- and 20-aminopregn-5-en-3 beta-ols were synthesized in an effort to find an agent that would be rapidly and selectively taken up by adrenal cortical tissue. Achievement of such a goal would provide a basis for the development of adrenal imaging agents superior to those currently available for clinical use. The iodobenzoyl derivatives were obtained by treating the appropriate epimer with 2-iodobenzoic acid in the presence of dicyclohexylcarbodiimide and 4-(dimethylamino)pyridine. The resulting esters and amides were readily labeled with radioiodine by isotope exchange with sodium iodide-125 in pivalic acid. Tissue distribution studies in female rats revealed that only the esters displayed appreciable adrenal specificity, and the ester having the same configuration at C-20 as cholesterol was significantly better than the corresponding C-20 epimer.

Potential tumor or organ-imaging agents. 30. Radioiodinated phospholipid ethers.

A radioiodinated analogue of a naturally occurring alkyl lysophospholipid (ALP) was synthesized for evaluation as a potential tumor-localizing imaging agent. rac-1-[12-(m-Iodophenyl)dodecyl]-2-methylglycero-3-phosphocholine (ET-12IP-OMe, 14) was radiolabeled with iodine-125 via an isotope-exchange procedure. Tissue distribution studies with [125I]ET-12IP-OMe in tumor-bearing rats revealed an immediate tumor uptake of radioactivity. Although radioactivity was also present in nontarget tissues at this time, clearance of tracer from the tumor was much slower and thus provided a suitable tumor to nontarget tissue ratio at 24 h. As a result of this selective accumulation, it was possible to clearly delineate the tumor with gamma-camera scintigraphy.

Synthesis and evaluation of 19-aza- and 19-aminoandrostenedione analogues as potential aromatase inhibitors.

Derivatives of 19- azaandrostenedione (10 beta-amino-4- estrene -3,17-dione, 2) and 19-amino-4-androstene-3,17-dione (3) were synthesized as potential inhibitors of aromtase (estrogen synthetase). Compound 2 and its derivatives were synthesized from 3,17-dioxo-4-androsten-19-oic acid (5) via a Curtius rearrangement. Derivatives of 3 were synthesized from the intermediate 3,17-bis(ethylenedioxy)-5-androsten-19-al oxime (14), which was reduced to the corresponding amine (16) with Raney nickel. However, attempts to synthesize the parent compound, 3, from 16 by several different methods were unsuccessful. The compounds obtained were tested for inhibitory activity in the tritiated water assay for aromatase, with human placental microsomes as the enzyme source and [1-3H]-androst-4-ene-3,17-dione (83% 3H 1 beta) as the substrate. All of the compounds caused less than 20% inhibition of enzyme activity when tested at one and five times the substrate concentration (0.25 microM, 1.25 microM) and were poorer inhibitors than two known inhibitors, 7 alpha-[(p-aminophenyl)thio] androstenedione (7- APTA ) and 4-hydroxy-4-androstene-3,17-dione (4-OHA).

Potential tumor- or organ-imaging agents. 26. Polyiodinated 2-substituted triacylglycerols as hepatographic agents.

A series of omega-(3-amino-2,4,6-triiodophenyl)alkanoic acids and the corresponding 1,3-dipalmitoylglycerol 2-[omega-(3-amino-2,4,6-triiodophenyl)alkanoates] were synthesized, radioiodinated with iodine-125, and evaluated for their ability to selectively localize in the liver for potential use as hepatographic imaging agents. Acid analogues 1d and 1e afforded relatively high levels of radioactivity in the liver (45 and 49% injected dose) 5 min after intravenous administration to rats. These acids displayed a marked propensity to become bound to plasma albumin. In contrast, triacylglycerol analogues 10a and 10c did not become immediately associated with plasma albumin but instead rapidly became associated with plasma lipoproteins and showed a different tissue distribution profile than free acids 1a and 1c. Although long-chain triacylglycerol analogues 10d and 10e exhibited some capacity to accumulate in the liver at 5 and 30 min, respectively, analysis of the plasma revealed significant in vivo ester hydrolysis. It would thus appear that liver radioactivity following administration of 10d and 10e was due to uptake of the free acid and not the intact triacylglycerol. Triacylglycerol analogues 10a and 10c, on the other hand, were taken up intact and showed liver accumulations of 25 and 35% of the administered dose at 30 min.

Potential tumor- or organ-imaging agents. 27. Polyiodinated 1,3-disubstituted and 1,2,3-trisubstituted triacylglycerols.

A series of glyceryl 1,3-bis- and 1,2,3-tris[omega-(3-amino-2,4,6-triiodophenyl)alkanoates] were synthesized, radioiodinated with iodine-125, and evaluated for their ability to selectively localize in the liver for potential use as hepatographic imaging agents. Of the nine target compounds synthesized and evaluated in rats, glyceryl 1,2,3-tris[3-(3-amino-2,4,6-triiodophenyl)propionate] (5b) displayed rapid and sustained liver specificity. This agent was found to accumulate in the liver in concentrations of 60, 75, and 86% of the administered dose at 5 min, 30 min, and 24 h, respectively. Moreover, the 24-h liver-to-blood ratio of 235 justifies further studies in higher animal species.

Aromatic amino acid hydroxylase inhibitors. 4. 3-Substituted alpha-methyltyrosines.

In the present study a series of 3-alkenyl-alpha-methyltyrosines and their corresponding 3-alkyl-and dihydrobenzofuran analogs was synthesized for potential tyrosine hydroxylase (TH) inhibitory activity. The appropriately substituted hydantoins IIIa and IIIb, which were prepared from the corresponding allyloxybenzylhydantoins IIa and IIb through Claisen rearrangement, served as intermediates for the synthesis of these amino acids. TH inhibition was reduced upon either saturation of the double bond in the side chain or cyclization to form the dihydrobenzofuran analogs. Formation of the epoxide had a similar effect. The inhibitory activity of these compounds against aromatic amino acid decarboxylase (AADC) and dopamine beta-hydroxylase (DBH) was also investigated. Unsaturation, in both cases, decreases the inhibitory activity; however, the presence of a free phenolic group appears to be essential for AACD inhibitory activity.

7 alpha-substituted derivatives of androstenedione as inhibitors of estrogen biosynthesis.

In an effort to obtain more information on the structure-activity relationship among the 7 alpha-(phenylthio)androstenedione inhibitors of the enzyme aromatase, a series of compounds containing both electron-donating and electron-withdrawing ring substituents was synthesized and tested for aromatase inhibitory activity. No linear correlation between substituent electronic effects and inhibitory activity was observed. The halogen-containing compounds, particularly 8, appeared to be quite potent inhibitors. The 125I analogue of 8 was synthesized in order to evaluate the possibility of side-chain elimination under the assay conditions. Approximately 90% of [125I]-8 remained intact for up to 1 h under assay conditions.

Potential organ- or tumor-imaging agents. 22. Acyl-labeled cholesterol esters.

A series of cholesteryl phenylalkanoic esters was synthesized in which the acyl moiety served as the carrier for radioiodine. Tissue distribution studies in rats revealed that several of these radioiodinated esters selectively accumulated in steroid-secreting tissues, such as the adrenal cortex and ovary. Furthermore, this selective uptake was shown to correlate with the stability of these esters to in vivo hydrolysis. An unexpected finding was the unusually high propensity of some of these esters to localize in the ovary and thus afford a possible approach to ovarian imaging agents.

Synthesis and evaluation of iodinated analogues of diacylglycerols as potential probes for protein kinase C.

Analogues of diacylglycerol containing a 3-(3-amino-2,4,6-triiodophenyl)-2-ethylpropanoyl or 3-(3-amino-2,4,6-triiodophenyl)propanoyl group in the 2-position (1a and 1b, respectively) were synthesized and shown to compete with [3H]phorbol dibutyrate [( 3H]PDBu) for binding in a crude rat brain preparation. Phorbol diesters have been shown to bind specifically to protein kinase C and the PDBu receptor has been copurified with protein kinase C activity. The four diastereomers of 1a (1c-f) were synthesized from chiral starting material and studied in the same assay. The affinities for the [3H]PDBu binding site of 1a, 1b, and two isomers of 1a with naturally occurring L configuration were comparable to that of 1-oleoyl-2-acetyl-rac-glycerol (OAG), but the D isomers of 1a were essentially inactive. The chirality of the side chain did not influence the binding affinity. Activation of protein kinase C by 1a, 1c, and 1e demonstrated the same stereochemical requirements, but none were as active as OAG. For the 1,3-isomers 2, 2a, and 2b, the competitive binding studies gave different results. The racemic mixture and the D isomer, 2b, were able to compete for binding, but the L isomer, 2a, did not compete. These studies demonstrate that diacylglycerol binding to and activation of protein kinase C is stereospecific for the glycerol backbone, but not the side chain. Furthermore, the D-1,3-isomer must exist in a conformation such that the acyl and hydroxyl oxygens assume a spatial relationship similar to that in the L-1,2-isomers.

Iodoaryl analogues of dioctanoylglycerol and 1-oleoyl-2-acetylglycerol as probes for protein kinase C.

Analogues of dioctanoylglycerol (diC8) and 1-oleoyl-2-acetylglycerol (OAG) containing an iodoaryl group have been synthesized and shown to compete with [3H]phorbol dibutyrate [( ([3H]PDBu) for binding to protein kinase C in a crude rat brain preparation. Phorbol diesters have been shown to bind specifically to protein kinase C and the PDBu receptor has been copurified with protein kinase C activity. All three diacylglycerol analogues were comparable to OAG in binding affinity. In an assay of protein kinase C activation, the diC8 analogue was more active than the OAG analogues, thus demonstrating greater structural specificity under the conditions of this assay.