The combined effect of inhibiting both ACAT and HMG-CoA reductase may directly induce atherosclerotic lesion regression

We hypothesized that coadministration of avasimibe and simvastatin would limit size, composition and extent of atherosclerotic lesions and potentially promote lesion regression, since bioavailable ACAT inhibitors decrease monocyte-macrophage enrichment and HMG-CoA reductase inhibitors limit smooth muscle cell migration and proliferation. Male New Zealand white rabbits were sequentially fed a 0.5% cholesterol, 3% peanut oil, 3% coconut oil diet for 9 weeks and a chow-fat diet for 6 weeks prior to drug administration. A time zero control group was necropsied prior to drug administration and the progression control was fed various diets but untreated. Avasimibe (10 mg/kg), simvastatin (2.5 mg/kg) or combination of avasimibe (10 mg/kg) with simvastatin (2.5 mg/kg) were administered in the chow-fat diet for 8 weeks. Plasma total cholesterol exposure was unchanged by avasimibe but was reduced 21% by both simvastatin alone and in combination with avasimibe. Combination of avasimibe and simvastatin decreased VLDL-cholesterol exposure by 56%. VLDL+IDL lipid composition was similar in the progression control and simvastatin-treated animals. Administration of avasimibe alone or in combination with simvastatin reduced the cholesteryl ester fraction and increased the triglyceride fraction to comparable extents. Relative to the progression control, avasimibe plus simvastatin markedly decreased thoracic aortic cholesteryl ester content and lesion coverage by 50% and aortic arch lesion size and macrophage area by 75 and 73%, respectively. With respect to lesion regression, avasimibe+simvastatin decreased aortic arch lesion size by 64% and monocyte-macrophage area by 73% when compared to time zero. Based on these data, we conclude that despite changes in plasma total and lipoprotein cholesterol exposure and lipoprotein composition comparable to monotherapy, inhibition of both ACAT and HMG-CoA reductase may not only directly blunt lesion progression but also promote regression of pre-established atherosclerotic lesions.

Reverse cholesterol transport and future pharmacological approaches to the treatment of atherosclerosis

The apparent protective effect of high density lipoprotein cholesterol (HDL) with respect to coronary heart disease (CHD) is generally thought to reside in its ability to transport cholesterol from peripheral cells to the liver for excretion from the body. Knozon as reverse cholesterol transport (RCT), this process involves many key steps and lipoprotein interconversions, and there is no consensus as to which step is most suitable for possible drug intervention. The membrane proteins, scavenger receptor class B, type 1 (SR-B1) and the ATP-binding cassette 1 (ABC1), have been strongly implicated as being important in cholesterol efflux; the former as a bona fide receptor for HDL and the latter as a lipid transporter. Lecithin:cholesterol acyltransferase (LCAT) then esterifies the effluxed cholesterol to form cholesteryl esters (Step 2), which are then transferred to apoB-containing lipoproteins by cholesteryl ester transfer protein (CETP, Step 3). Despite the complexities and uncertainties, drugs should be developed which impact all of the above steps, and short-term endpoints need to be defined for a cautious, systematic approach to clinical evaluation.

Elevated hepatic apolipoprotein A-I transcription is associated with diet-induced hyperalphalipoproteinemia in rabbits

Past studies have shown that a high saturated fatty acid diet containing coconut oil elevates plasma HDL cholesterol and apolipoprotein A-I (apoA-1) in rabbits through a mechanism involving increased synthesis. We have extended those studies by investigating expression of the hepatic apolipoprotein A-I gene and other lipid related genes in that model. Rabbits fed a diet containing 14% coconut oil for 4 weeks showed HDL-C elevations of 170% to 250% over chow-fed controls with peak differences occurring at 1 week. Plasma apoA-I levels were also increased over this time frame (160% to 180%) reflecting the HDL-C changes. After 4 weeks, there were no differences in plasma VLDL-C or LDL-C levels in chow versus coconut oil-fed rabbits. Hepatic levels of apoA-I mRNA in coconut oil-fed animals were elevated 150% after 4 weeks compared to chow-fed controls; hepatic mRNA levels for ten other genes either decreased slightly (apoB, LCAT, hepatic lipase, albumin, ACAT, and HMG CoA reductase) or were unchanged (CETP, apoE, LDL-receptor, and acyl CoA oxidase). Nuclear run-on transcription assays revealed that coconut oil feeding for 4 weeks caused a 220% increase in hepatic apoA-I transcription rate compared to controls; no change was observed for CETP and apoE. Treatment of cultured rabbit liver cells with various saturated fatty acids and sera from chow-fed and coconut oil-fed rabbits did not alter apoA-I mRNA levels as observed in vivo. These data demonstrate that coconut oil elevates plasma HDL-C and apoA-I by increasing hepatic apoA-I transcription while expression of other genes involved in lipid metabolism are reduced or unchanged in response to coconut oil feeding.

The ACAT inhibitor avasimibe reduces macrophages and matrix metalloproteinase expression in atherosclerotic lesions of hypercholesterolemic rabbits

Given the significance of cholesteryl ester (CE) accumulation in macrophage foam cell formation, we hypothesized that inhibitors of acyl-CoA:cholesterol O-acyltransferase (ACAT) would produce a histologically stable lesion by limiting macrophage enrichment and thereby a source of matrix metalloproteinases (MMPs). Male New Zealand White rabbits were sequentially fed a cholesterol/fat diet for 9 weeks, a fat-only diet for 6 weeks, and 25 mg/kg avasimibe for 7 to 8 weeks. Avasimibe had no effect on plasma total cholesterol exposure. Plasma avasimibe maximal concentration and 24-hour area-under-the-curve levels were 178 ng/mL and 2525 ng. h/mL, respectively, after 7 weeks of treatment with 25 mg/kg avasimibe. The median inhibitory concentration against human monocyte-macrophage ACAT was 12 ng/mL when determined in the absence of albumin, and aortic arch avasimibe levels were 25 ng/g of tissue wet weight. Avasimibe reduced thoracic aortic and iliac-femoral CE content by 39%, the extent of thoracic aortic lesions by 41%, aortic arch cross-sectional lesions area by 35%, and monocyte-macrophage area by 27%. The reduction in monocyte-macrophage area reflected a change in cell number and not cell size. In the iliac-femoral artery, avasimibe decreased monocyte-macrophage content by 77% and reduced the macrophage-to-lesion ratio from 0.16 to 0.05. Within the aortic arch, the catalytic activity of latent and active MMP-9 was reduced by 65% and 33%, respectively; latent and active MMP-1 and MMP-3 activity measured collectively was decreased by 52% and 60%, respectively, and MMP-2 was unchanged. Aortic arch MMP-9, tissue inhibitor of matrix metalloproteinase (TIMP)-1, and TIMP-2 mRNA levels were reduced 29% to 39%, and MMP-2 mRNA levels increased. We conclude that the bioavailable ACAT inhibitor avasimibe can directly limit macrophage accumulation, resulting in the histological appearance of mainly fibromuscular lesions, and can potentially stabilize preestablished atherosclerotic lesions by reducing MMP expression within the lesion.

ACAT-2, a second mammalian acyl-CoA:cholesterol acyltransferase. Its cloning, expression, and characterization

The synthesis of cholesterol esters by acyl-CoA:cholesterol acyltransferase (ACAT, EC 2.3.1.26) is an important component of cellular cholesterol homeostasis. Cholesterol ester formation also is hypothesized to be important in several physiologic processes, including intestinal cholesterol absorption, hepatic lipoprotein production, and macrophage foam cell formation in atherosclerotic lesions. Mouse tissue expression studies and the disruption of the mouse ACAT gene (Acact) have indicated that more than one ACAT exists in mammals and specifically that another enzyme is important in mouse liver and intestine. We now describe a second mammalian ACAT enzyme, designated ACAT-2, that is 44% identical to the first cloned mouse ACAT (henceforth designated ACAT-1). Infection of H5 insect cells with an ACAT-2 recombinant baculovirus resulted in expression of a approximately 46-kDa protein in cell membranes that was associated with high levels of cholesterol esterification activity. Both ACAT-1 and ACAT-2 also catalyzed the esterification of the 3beta-hydroxyl group of a variety of oxysterols. Cholesterol esterification activities for ACAT-1 and ACAT-2 exhibited different IC50 values when assayed in the presence of several ACAT-specific inhibitors, demonstrating that ACAT inhibitors can selectively target specific forms of ACAT. ACAT-2 was expressed primarily in mouse liver and small intestine, supporting the hypothesis that ACAT-2 contributes to cholesterol esterification in these tissues. The mouse ACAT-2 gene (Acact2) maps to chromosome 15 in a region containing a quantitative trait locus influencing plasma cholesterol levels. The identification and cloning of ACAT-2 will facilitate molecular approaches to understanding the role of ACAT enzymes in mammalian biology.

Lack of predictability of classical animal models for hypolipidemic activity: a good time for mice?

Hypolipidemic drugs that are efficacious in man are not always active in classical animal models of dyslipidemia. Inhibitors of HMG-CoA reductase (statins) do not lower plasma cholesterol in rats, but yet this species was alone in providing activity for fibrate-type drugs. Nicotinic acid possesses many desirable features with regard to clinical use, but most of these actions are lacking in rats and monkeys. The metabolism of low density lipoproteins in hamsters is widely thought to be similar to that in humans, yet neither statins or fibrates lower plasma lipids in these species. With the advent of mouse models expressing specific human genes (or disruption of genes) it is now possible to re-examine the effect of established drugs and to characterize new hypolipidemic compounds with respect to site and mechanism of action. Drug responses observed in humans are now being seen in such mouse models (e.g. HDL elevation with fenofibrate in mice with the human apo A-I gene). Moreover, mice are now being screened for compounds that lower plasma (human) Lp(a), or lower plasma cholesterol in the absence of LDL receptors. It is proposed that these new genetic mouse models may afford a more focused examination of drug action and provide, for new compounds, better prediction of the human response.

Lipid-lowering effects of WAY-121,898, an inhibitor of pancreatic cholesteryl ester hydrolase

WAY-121,898 is an inhibitor of pancreatic cholesteryl ester hydrolase (pCEH). After confirming its in vitro potency and relative lack of a major effect on acyl-CoA:cholesterol acyltransferase (ACAT), it was found that this compound lowers plasma cholesterol in cholesterol-fed, but not chow-fed, rats. Measures of liver cholesteryl ester content and the direct determination of cholesterol absorption (lymph-fistula model) show that inhibition of cholesterol absorption is at least one mechanism for the observed cholesterol lowering. However, WAY-121,898 was also active when administered parenterally to cholesterol-fed rats, and in cholesterol-fed hamsters cholesterol-lowering occurred with oral dosing despite no change in cholesterol absorption, suggesting other modes of action possibly relating to inhibition of liver CEH. Combination treatment in cholesterol-fed rats with the ACAT inhibitor CI-976 resulted in a greater-than-additive reduction in plasma cholesterol, implying that both pCEH and ACAT may play a role in cholesterol absorption in this species. In rabbits, WAY-121,898 prevented the rise in plasma cholesterol due to the feeding of cholesteryl ester but not in rabbits fed (free) cholesterol. In guinea pigs, the compound induced an increase in adrenal cholesteryl ester mass. Taken together, the overall profile in these animal models suggests that WAY-121,898 inhibits more than just the intestinal (lumenal) pCEH, and that the role of this enzyme in cholesterol metabolism may be different within and across species, the former depending upon the dietary cholesterol load.

The ACAT inhibitor, CI-1011 is effective in the prevention and regression of aortic fatty streak area in hamsters

The hypocholesterolemic and anti-atherogenic properties of sulfamic acid ((2,4,6-tris (1-methylethyl) phenyl) acetyl) 2,6-bis(1-methylethyl) phenyl ester, the ACAT inhibitor, CI-1011, was tested in 120 male F1B hamsters fed a hypercholesterolemic chow-based diet containing 10%, coconut oil and 0.05% cholesterol plus: (i) no drug treatment (HCD); (ii) 3 mg/kg per day (HCD+3): (iii)10 mg/kg per day (HCD+10); (iv) 30 mg/kg per day (HCD+30) of CI-1011; or (v) 500 mg/kg per day of cholestyramine (CSTY). Plasma samples were collected at 8 and 10 weeks for measurement of total cholesterol (TC), very low-density lipoprotein cholesterol (VLDL-C), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C) and triglycerides (TG). For the progression studies, animals were euthanized after 10 weeks for aortic fatty streak area and hepatic cholesterol analysis. For the regression study, a cohort of the HCD was treated with 30 mg/kg per day of CI-1011 (regression) for an additional 8 weeks. The HCD+3, HCD+10, HCD+30 and CSTY lowered plasma TC (25, 32, 34 and 32%, respectively), VLDL-C (62, 74, 71 and 75%, respectively), LDL-C (25, 38, 47 and 46%, respectively) and TG (48, 47, 42 and 45%, respectively). All treatments resulted in a significant lowering of aortic fatty streak area (68, 86, 93 and 94%, respectively) and reduction in hepatic cholesteryl esters (57, 65, 67 and 70%, respectively). Regression of aortic fatty streak area was 90% after 8 weeks of HCD+30 treatment. Also during the regression phase, plasma TC, LDL-C and TG were lowered 23, 33 and 47%, respectively, as well as, hepatic cholesteryl esters (76%). Significant correlations between plasma LDL-C concentration and aortic fatty streak area (r=0.62, P < 0.004) in the HCD+10 group, suggest that CI-1101 altered aortic lipid infiltration primarily by its effect on plasma lipids. However the 30 mg/kg per day dose of CI-1011 which additionally reduced aortic fatty streak area by 51% relative to the 10 mg/kg per day dose was only associated with a 14% further decrease in plasma LDL-C. Finally the 10-fold regression of aortic fatty streak area was associated with only a 35% reduction in plasma LDL-C. These exceptions to the lipid-lesion relationship raise the possibility of additional effects of CI-1011, which may occur independent of or in concert with lipoprotein cholesterol lowering. It is concluded that in hypercholesterolemic hamsters, CI-1011 is approximately 50 times more potent than cholestyramine in cholesterol-lowering, reduction and regression of aortic fatty streak area.

alpha-Substituted malonester amides: tools to define the relationship between ACAT inhibition and adrenal toxicity

We prepared a series of alpha-substituted malonester amides that were evaluated for their ability to inhibit acyl-CoA:cholesterol O-acyl transferase activity in vitro and to lower plasma total cholesterol levels in a variety of cholesterol-fed animal models. Compounds of this series were also useful in examining the relationship between adrenal toxicity and ACAT inhibition. One compound from this series, 9f, was a potent inhibitor of ACAT in both the microsomal and cellular assays. It was also bioavailable as determined by both a bioassay and a HPLC-UV assay. This compound was evaluated in both guinea pig and dog models of adrenal toxicity and compared to tetrazole amide 15. In the most sensitive species, the dog, both of these compounds achieved good plasma levels; however, compound 9f caused adrenal necrosis, whereas compound 15 had no effect on the adrenal gland. This adds to the growing body of evidence that the adrenal toxicity observed with ACAT inhibitors may not be mechanism related.

Inhibitors of acyl-CoA:cholesterol O-acyltransferase (ACAT) as hypocholesterolemic agents: synthesis and structure-activity relationships of novel series of sulfonamides, acylphosphonamides and acylphosphoramidates

Sulfoacetic acid, phosphoramidate, and phosphoramide analogs of the ACAT inhibitors, CI-999 and CI-1011 were synthesized. The structure-activity relationships of these compounds as ACAT inhibitors are described.

Inhibitors of acyl-CoA:cholesterol acyltransferase: novel trisubstituted ureas as hypocholesterolemic agents

Our continued interest in developing novel, potent acyl-CoA:cholesterol acyltransferase (ACAT) inhibitors, and our discovery of several active series of disubstituted urea ACAT inhibitors, have led us to investigate a series of trisubstituted ureas that are structural hybrids of our disubstituted series and of a trisubstituted urea ACAT inhibitor series disclosed by scientists at Lederle. This investigation has led to the discovery of novel trisubstituted ureas, several of which inhibit ACAT in the nanomolar range and effectively lower total plasma cholesterol when administered as a diet admixture in an acute model of hypercholesterolemia in rats. One analogue (35) also lowered total cholesterol as efficaciously as CL 277,082 in our chronic hypercholesterolemic rat model. The most notable finding of this study is that the SAR of the trisubstituted ureas diverges from that seen in our previously disclosed disubstituted urea series. This series showed optimal activity with 2,4-difluoro and 2,4,6-trifluoro substitution on the urea N-phenyl, whereas the disubstituted series showed optimal activity with bulky 2,6-disubstitution on the phenyl ring.

High correlation but lack of agreement between direct high-performance gel chromatography analysis and conventional indirect methods for determining lipoprotein cholesterol

Low-density lipoprotein-cholesterol (LDL-C) is currently estimated clinically by using the Friedewald formula, when plasma triglycerides are < 4000 mg/L, or as the difference between infranatant and high-density lipoprotein-cholesterol (HDL-C) values after ultracentrifugation of plasma at native density, when plasma triglycerides are > or = 4000 mg/L (beta quantification). HDL-C is measured by selective precipitation of apolipoprotein B-containing lipoproteins from whole plasma or from the density > 1.006 kg/L infranatant. We compared these conventional methods for LDL-C and HDL-C with "high-performance" gel chromatography (HPGC), a method that directly and simultaneously measures both LDL-C and HDL-C in a single, microliter volume of plasma. Not surprisingly, we found that the results by all these methods were highly correlated. However, LDL-C values were significantly higher and HDL-C values significantly lower by the direct HPGC method than by the conventional methods (paired t-test). In addition, both Bland-Altman plots and concordance correlation analyses indicated lack of agreement between the methods' results in the majority of patients' subgroups.

High correlation but lack of agreement between direct high-performance gel chromatography analysis and conventional indirect methods for determining lipoprotein cholesterol

Low-density lipoprotein-cholesterol (LDL-C) is currently estimated clinically by using the Friedewald formula, when plasma triglycerides are &lt; 4000 mg/L, or as the difference between infranatant and high-density lipoprotein-cholesterol (HDL-C) values after ultracentrifugation of plasma at native density, when plasma triglycerides are &gt; or = 4000 mg/L (beta quantification). HDL-C is measured by selective precipitation of apolipoprotein B-containing lipoproteins from whole plasma or from the density &gt; 1.006 kg/L infranatant. We compared these conventional methods for LDL-C and HDL-C with "high-performance" gel chromatography (HPGC), a method that directly and simultaneously measures both LDL-C and HDL-C in a single, microliter volume of plasma. Not surprisingly, we found that the results by all these methods were highly correlated. However, LDL-C values were significantly higher and HDL-C values significantly lower by the direct HPGC method than by the conventional methods (paired t-test). In addition, both Bland-Altman plots and concordance correlation analyses indicated lack of agreement between the methods' results in the majority of patients' subgroups.

Opposite effects of bezafibrate and gemfibrozil in both normal and hypertriglyceridemic rats

Chow and sucrose-fed rats were used as animal models to study the dose-responses of bezafibrate and gemfibrozil in normolipidemic and hypertriglyceridemic states, respectively. Although both drugs lowered plasma triglycerides (TG) to about the same extent in chow-fed rats, gemfibrozil lowered liver TG as well as plasma total and LDL-cholesterol (LDL-C), but elevated HDL-cholesterol (HDL-C) and plasma apo E concentrations. Bezafibrate produced opposite effects, namely, decreased HDL-C, apo E and liver TG, and tended to increase LDL-C. TG lowering for both drugs in chow-fed rats was not due to changes in TG secretion (production) in normal rats but was associated with enhanced LPL activity. In hypertriglyceridemic rats both drugs modestly reduced TG secretion rates about 40% at a dose producing maximal TG lowering, but again, gemfibrozil elevated and bezafibrate lowered HDL-C and apo E. Unlike gemfibrozil, bezafibrate induced the appearance of LDL-C in hypertriglyceridemic rats which was not detected in control animals, and also tended to increase rather than decrease plasma apo B levels. Finally, changes in liver TG concentration (mg/g) in hypertriglyceridemic rats were opposite for these drugs, resulting in significant drug-related differences in liver TG content (mg/organ). From these data we postulate that, although similar with regard to TG lowering activity and mechanisms thereof, gemfibrozil and bezafibrate produce fundamentally different effects on LDL, HDL and apolipoprotein metabolism (apo B and apo E) in rats which may relate to potential differential effects on reverse cholesterol transport and atherogenesis.

Hypocholesterolemic actions of atorvastatin are associated with alterations on hepatic cholesterol metabolism and lipoprotein composition in the guinea pig

Guinea pigs were fed 15% (w/W) fat, high in lauric and myristic acids, a diet known to produce hypercholesterolemia in these animals. The diet was given alone or in combination with four doses of atorvastatin equivalent to 1, 3, 10, and 20 mg/kg per day. Atorvastatin reduced plasma LDL cholesterol concentrations by 46, 50, 53, and 70%, respectively (P < 0.001). Plasma apoB concentrations were reduced by atorvastatin (P < 0.001) and compositional changes occurred in VLDL and LDL with reductions of the relative proportion of cholesteryl ester and increases in triacylglycerol. A reduction in hepatic cholesteryl ester (66%) was observed only with the highest atorvastatin dose (20 mg/kg per day) while microsomal cholesterol was reduced by 30% with 3-20 mg/kg per day. Hepatic ACAT activity was down-regulated and apoB/E receptor number was increased by atorvastatin. In contrast, HMG-CoA reductase activity and cholesterol 7 alpha-hydroxylase were not affected by the drug. VLDL apoB secretion rates were decreased by atorvastatin treatment 59 and 76% with 3 and 20 mg/kg per day, respectively. Nascent VLDL particles were larger after drug treatment, showing an increased number in triacylglycerol molecules. These results support the hypothesis that the plasma LDL lowering induced by atorvastatin is due to a decreased secretion of apoB in combination with an increase of hepatic apoB/E receptors.

Heterocyclic ureas: inhibitors of acyl-CoA:cholesterol O-acyltransferase as hypocholesterolemic agents

A series of diaryl-substituted heterocyclic ureas was prepared, and their ability to inhibit acyl-CoA: cholesterol O-acyltransferase (ACAT) in vitro and to lower plasma total cholesterol in cholesterol-fed animal models in vivo was examined. N-(2,6-Diisopropylphenyl)-N'-tetrazole or isoxazole-substituted heterocyclic ureas proved optimal. A carbon chain of 11-14 carbons substituted 1,3 with respect to the amine provided the optimal side chain. Substitution of the alkyl chain generally lowered activity. Tetrazole urea 2i dosed at 3 mg/kg lowered plasma total cholesterol (TC) 67% in an acute, cholesterol-fed (C-fed) rat model of hypercholesterolemia and 47% in C-fed dogs. Tetrazole 2i, dosed at 10 mg/kg, also lowered TC 52% and raised HDL cholesterol 113% in rats with pre-established hypercholesterolemia.

Heterocyclic amides: inhibitors of acyl-CoA:cholesterol O-acyl transferase with hypocholesterolemic activity in several species and antiatherosclerotic activity in the rabbit

A series of heterocyclic amides were synthesized and evaluated as inhibitors of acyl-CoA: cholesterol O-acyltransferase (ACAT) in vitro and for cholesterol lowering in cholesterol-fed rats. Compounds were evaluated for cell-based macrophage ACAT inhibition, bioactivity, and adrenal toxicity. Candidates were selected for evaluation in cholesterol-fed dogs and, ultimately, the injured cholesterol-fed rabbit model of atherosclerosis. The heterocyclic amides potently inhibited rabbit liver ACAT (IC50's = 0.014-0.11 microM), and the majority of compounds significantly lowered plasma cholesterol (42-68%) in an acute cholesterol-fed rat model at 3 mg/kg. The most efficacious compounds in the rat were evaluated for bioactivity in vivo and arterial ACAT inhibition in a cell-based macrophage ACAT assay. Two highly bioactive analogs, (+/-)-2-(3-dodecylisoxazol-5-yl)-2-phenyl-N-(2,4,6-trimethoxypheny l) acetamide (13a) and (+/-)-2-(5-dodecylisoxazol-3-yl)-2-phenyl-N-(2,4,6-trimethoxypheny l) acetamide (16a), were selected for further study and were found to be nontoxic in a guinea pig model of adrenal toxicity. Compounds 13a and 16a lowered total cholesterol in the cholesterol-fed rat, rabbit, and dog models of pre-established hypercholesterolemia. Compound 13a in the injured cholesterol-fed rabbit model of atherosclerosis was effective in slowing the development of cholesteryl ester-rich thoracic aortic lesions, reducing lesion coverage by 53% at a dose of 1 mg/kg.

Inhibitors of acyl-CoA:cholesterol O-acyltransferase. synthesis and pharmacological activity of (+/-)-2-dodecyl-alpha-phenyl-N-(2,4,6-trimethoxyphenyl)-2H-tetrazole-5- acetamide and structurally related tetrazole amide derivatives

A series of tetrazole amide derivatives of (+/-)-2-dodecyl-alpha-phenyl-N-(2,4,6-trimethoxyphenyl)-2H-tetrazole-5- acetamide (1) was prepared and evaluated for their ability to inhibit acyl-CoA: cholesterol O-acyltransferase (ACAT) in vitro and to lower plasma total cholesterol in vivo. For this series of compounds, our objective was to systematically replace substituents appended to the amide and tetrazole moieties of 1 with structurally diverse functionalities and assess the effect that these changes have on biological activity. The ensuing structure-activity relationship (SAR) studies identified aryl (7b) and heteroaryl (7f,g) replacements for 2,4,6-trimethoxyphenyl that potently inhibit liver microsomal and macrophage ACAT in vitro and exhibit good cholesterol lowering activity (56-66% decreases in plasma total cholesterol at 30 mg/kg), relative to 1, when compared in the acute rat model of hypercholesterolemia. Replacement of the alpha-phenyl moiety with electron-withdrawing substituents (13e-h), however, significantly reduced liver microsomal ACAT inhibitory activity (IC50 > 1 microM). This is in contrast to electron-donating substituents (13ij,m-q), which produce IC50 values ranging from 5 to 75 nM in the hepatic microsomal assay. For selected tetrazole amides (1, 7b, 13n,o), reversing the order of substituents appended to the 2- and 5-positions in the tetrazole ring (36a-d), in general, improved macrophage ACAT inhibitory activity and provided excellent cholesterol-lowering activity (ranging from 65% to 77% decreases in plasma total cholesterol at 30 mg/kg) in the acute rat screen. The most potent isomeric pair in this set of unsubstituted methylene derivatives (13n and 36a) caused adrenocortical cell degeneration in guinea pigs treated with these inhibitors. In contrast, adrenal glands taken from guinea pigs treated with the corresponding alpha-phenyl-substituted analogs (7b and 36c) were essentially unchanged compared to untreated controls. Subsequent evaluation of 7b and 36c in a rabbit bioassay showed that both compounds and/or their metabolities were present in plasma after oral dosing. Unlike 7b and 36c, compound 1 and related 2,4,6-trimethoxyanilides (13j, 30c,d) showed poor oral activity in the rabbit bioassay. Nevertheless, in cholesterol-fed rabbits, both systemically available (7b, 36c) and poorly absorbed inhibitors (1, 36d) were more effective in lowering plasma total cholesterol than the fatty acid amide CI-976.

Inhibitors of acyl-CoA:cholesterol O-acyltransferase. 17. Structure-activity relationships of several series of compounds derived from N-chlorosulfonyl isocyanate

Several series of acyl-CoA:cholesterol O-acyltransferase inhibitors were prepared by the stepwise addition of nitrogen, oxygen, and sulfur nucleophiles to N-chlorosulfonyl isocyanate. The (aminosulfonyl)ureas 3-44 were the most potent inhibitors in vitro, with several compounds having IC50 values < 1 microM. Although the other series of compounds were not as potent in vitro, many compounds did display good in vivo activity in cholesterol-fed rats. Several of the oxysulfonyl carbamates (including CI-999, 115) showed excellent lipid-lowering activity in the chronic in vivo screen, demonstrating significant cholesterol lowering in a pre-established hypercholesterolemic state.

Hypolipidemic activity of select fibrates correlates to changes in hepatic apolipoprotein C-III expression: a potential physiologic basis for their mode of action

For the last 30 years fibrates have been widely prescribed to treat human dyslipidemia. However, the primary mechanism by which they lower plasma lipid levels is still unknown. Studies with transgenic mice have suggested that changes in apoC-III expression levels have a dramatic influence on plasma triglyceride levels. These results suggested that fibrates could reduce lipid levels by lowering apoC-III gene expression. In the current studies, we sought to determine whether the selected fibrates, bezafibrate, clofibrate, fenofibrate, and gemfibrozil, could reduce hepatic apoC-III mRNA and plasma apoC-III levels. Chow-fed rats were orally gavaged daily with a dosing vehicle alone or with 100 mg/kg of each of the fibrates for 1 week and in addition with gemfibrozil for 2 weeks. Bezafibrate and fenofibrate lowered plasma triglyceride by approximately half and dramatically reduced hepatic apoC-III mRNA and plasma apoC-III levels. In contrast, clofibrate did not reduce plasma triglyceride levels and only partially reduced apoC-III mRNA and plasma protein levels. Gemfibrozil strongly reduced plasma triglyceride levels and had an intermediate but significant effect on apoC-III mRNA and plasma apoC-III levels. Some of the fibrates, especially gemfibrozil also reduced plasma apoC-II levels, an effect that could contribute to the observed triglyceride-lowering effect. In addition, the ratio of plasma apoE to plasma apoC-II plus apoC-III was strongly and inversely correlated with plasma triglyceride levels. As plasma apoE levels were not reduced in gemfibrozil-treated animals, this could also have contributed to the triglyceride-lowering effect of this fibrate. Fibrate-mediated triglyceride lowering was not the result of a decreased apoB or VLDL production and, therefore, suggested an enhanced VLDL remnant catabolism. Our results suggest that the mechanism by which fibrates lower plasma triglycerides is by reducing the level of hepatic apoC-III expression.

Lipid-lowering activity of atorvastatin and lovastatin in rodent species: triglyceride-lowering in rats correlates with efficacy in LDL animal models

Since inhibitors of HMG-CoA reductase lower plasma triglycerides rather than cholesterol in rats, we compared the triglyceride-lowering activity of lovastatin in rats to that of atorvastatin, a more potent synthetic inhibitor, prior to evaluating these drugs in established animal models in which low density lipoproteins (LDL) rather than high density lipoproteins (HDL) are the major transporters of plasma cholesterol. Atorvastatin was more efficacious than lovastatin in normal, chow-fed rats, and more potent in rats with endogenous hypertriglyceridemia (sucrose-fed). In hypertriglyceridemic rats plasma apoB concentrations decreased only with atorvastatin (30 mg/kg), and VLDL-triglyceride secretion (Triton method) was also decreased more by atorvastatin. The inactive enantiomer of atorvastatin did not lower plasma triglycerides. Thus, triglyceride-lowering was dependent upon inhibition of HMG-CoA reductase. Liver unesterified cholesterol and cholesteryl esters (mg/g) were increased by both drugs in normal rats but remained unchanged in hypertriglyceridemic rats. In normal, chow-fed guinea pigs atorvastatin was a more potent cholesterol-lowering drug, and unlike lovastatin, lowered plasma triglycerides and VLDL-cholesterol. In casein-fed rabbits with endogenous hypercholesterolemia and in chow-fed rabbits atorvastatin lowered LDL-cholesterol more potently than lovastatin, but in chow-fed rabbits neither drug had an effect on the in vivo rate of VLDL-lipid secretion, suggesting that efficacy was due to inhibition of direct LDL production and/or enhanced LDL clearance. We conclude that normal rats can be used as a preclinical tool to assess the efficacy of HMG-CoA reductase inhibitors since triglyceride-lowering correlates with cholesterol-lowering in LDL animal models. In this regard atorvastatin is a more potent hypolipidemic agent than lovastatin in animals. A common but not sole mechanism for these drugs may be direct inhibition of the hepatic production of the major apoB-containing lipoprotein in a given species, e.g. VLDL in rats and LDL in guinea pigs and rabbits.

Comparative effects of HMG-CoA reductase inhibitors on apo B production in the casein-fed rabbit: atorvastatin versus lovastatin

Rabbits fed a diet enriched in casein develop an endogenous hypercholesterolemia (EH) due both to an increased low density lipoprotein (LDL) synthetic rate and decreased LDL receptor activity. Pre-established EH in this model was used to assess the ability and mechanism by which atorvastatin lowers total plasma cholesterol (TPC) compared to the reference agent lovastatin. Rabbits were fed a casein diet for 6 weeks, obtaining average TPC levels above 200 mg/dl. To ensure equivalent mean cholesterol concentrations, animals were randomized into treatment groups based on the 6-week TPC levels, and fed the casein diet alone or in combination with either atorvastatin or lovastatin for an additional 6 weeks. Under these conditions, new steady-state cholesterol values were established. Lipoprotein concentrations and distributions were determined at this point. Compared to pretreatment values, TPC were similar in untreated animals. Atorvastatin, however, significantly reduced TPC by 38%, 45%, and 54% at the 1, 3, and 10 mg/kg doses, respectively. Statistically significant lowering of TPC (35%) by lovastatin was only achieved at the 10 mg/kg dose. To determine the mechanism by which atorvastatin lowered TPC in the EH rabbits, kinetic studies using human [125I]-LDL were performed in a subset of animals maintained on the casein diet alone (n = 5), or those treated with 3 mg/kg of atorvastatin (n = 5) or lovastatin (n = 7). In this set of studies, atorvastatin significantly lowered TPC compared to control and lovastatin-treated rabbits by 57% and 46%, respectively. Lovastatin treatment resulted in a 20% decrease in TPC as compared to untreated controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Tissue specific changes in acyl-CoA: cholesterol acyltransferase (ACAT) mRNA levels in rabbits

A human cDNA clone (K1) was recently isolated that encodes functional acyl-CoA:cholesterol acyltransferase (ACAT) protein (Chang et al. J. Biol. Chem. 1993. 268: 20747-20755). We used the K1 clone to screen a rabbit liver cDNA library and isolated a 919 base pair partial rabbit cDNA (ACAT14b) that was greater than 90% homologous with the human nucleotide sequence. Northern blotting using the rabbit ACAT cDNA14b revealed the existence of at least six related mRNA species (ranging from 6.2 to 1.7 kb) in various rabbit tissues. Using an RNAse protection assay, ACAT mRNA14b was detected in twelve separate rabbit organs. Adrenal gland contained the highest concentrations of ACAT mRNA14b (per microgram of total RNA) being 20-, 30-, and 50-fold higher than small intestine, aorta, and liver, respectively. Additional studies with isolated liver cell populations revealed that rabbit hepatic nonparenchymal cells contained 30-fold more ACAT mRNA14b (per microgram of total RNA) than parenchymal cells. To determine whether ACAT mRNA14b levels are regulated in vivo, rabbits were fed for 4 weeks a high fat/high cholesterol diet (HFHC; 0.5% cholesterol, 3% coconut oil, 3% peanut oil) at which point they were either kept for an additional 4 weeks on the HFHC-diet or switched to the HFHC-diet plus CI-976 (50 mg/kg), a potent and specific ACAT inhibitor; another group of rabbits was fed a chow diet for the entire 8 weeks. The HFHC-diet caused a 2- and 3-fold increase in hepatic and aortic ACAT mRNA14b levels, respectively, in comparison to chow-fed animals; there was no change in adrenal or small intestine levels. CI-976 treatment lowered ACAT mRNA14b levels by 60% and 40% in liver and aorta, respectively, in comparison to the HFHC controls; again there was no change in adrenal or small intestine levels. These data indicate that ACAT mRNA14b levels increase in a tissue specific manner in response to dietary fat and cholesterol.

Hepatic microsomal induction profile of carbamic acid [[2,6-bis(1- methylethyl)phenoxy] sulfonyl]-2,6-bis(1-methylethyl) phenyl ester, monosodium salt (PD138142-15), a novel lipid regulating agent

Induction of hepatic microsomal cytochrome P450 produced by carbamic acid [2,6-bis(1-methylethyl)phenoxy]sulfonyl]-2,6-bis(1-methylethyl) phenyl ester, monosodium salt (PD138142-15), a novel water-soluble inhibitor of acyl-CoA: cholesterol acyltransferase, was examined in male and female rats, dogs, and monkeys, and in male guinea pigs. Relative to control, PD138142-15 increased hepatic microsomal total spectral P450 in all species examined. Hepatic microsomal ethoxyresorufin-O-deethylase, pentoxyresorufin-O-dealkylase, and peroxisomal carnitine acetyltransferase activities and cyanide-insensitive Beta-oxidation were affected only marginally. Erythromycin-N-demethylase activity was increased (2- to 6-fold) in all three species in which it was examined (rat, dog and pig). Marked increases in immunoreactive P450 3A were noted in the rats and dogs, while slight increases were seen in monkeys. Pharmacokinetic studies of PD138142-15 in rats and dogs revealed pronounced decreases (80-90%) in plasma Cmax and AUC within 2 weeks of initiation of daily dosing. In spite of the marked decline in plasma drug levels, efficacy in dogs, as determined by serum cholesterol levels, was maintained for up to 6 weeks with continued dosing. Potential acid (gastric) breakdown products of PD 138142-15 were examined for their hepatic cytochrome P450 induction profiles in rats adn were found to differ both quantitatively and qualitatively from profiles produced by the parent compound. This suggested that induction observed in rats was due to parent PD138142-15 and not to any of the known potential acid breakdown products. The cumulative data establish that PD 138142-15 is an inducer of P450 3A in rats and dogs. The results also suggest that P450 3A is induced in monkeys and pigs as well, although the data are less definitive. Decreases in plasma drug levels imply that the compound may be an autoinducer in dogs and rats. The maintenance of efficacy in spite of decreased drugs levels in dogs suggests that the effects on serum cholesterol are due to a metabolite or that cholesterol lowering effects occur before the compound is metabolized by the liver.

Bioisosterism in drug design: identification of and structure-activity relationships in a series of glycine anilide ACAT inhibitors

To examine the effects of bioisosteric replacement on the biological activity of our previously disclosed disubstituted urea inhibitors of the enzyme acyl-CoA:cholesterol acyltransferase (ACAT), we prepared a series of N'-substituted and N',N'-disubstituted glycine anilides. These compounds were tested for the ability to inhibit ACAT in vitro and lower plasma total cholesterol in cholesterol-fed rats given a single high-fat, high-cholesterol meal. ACAT inhibitory potency was greatest in compounds containing 2,6-diisopropyl substituents in the anilide portion with the glycine nitrogen substituted by a 1,1-diphenylmethyl moiety. Small improvements in potency in vitro were obtained by substitution of electron donating groups in the 2-, 3- or 5-positions of the aryl rings of the 1,1-diphenylmethyl moiety, but not by substitution in the 4-position. In vitro potency was maintained, but not improved by acylation of the glycine nitrogen. Through a QSAR analysis of in vitro ACAT inhibition for this set of compounds, an equation could be derived which accounted for 85% of the variance in the dataset. An optimal clogp of 6.65 was found, comparable to that found for other series of ACAT inhibitors. In general, compounds from this series displayed inhibitory potency against ACAT in vitro and hypocholesterolemic activity in the in vivo rat model of hypercholesterolemia comparable to that found with the ureas.

Inhibitors of acyl-CoA:cholesterol O-acyltransferase. 11. Structure-activity relationships of several series of compounds derived from N-(chlorocarbonyl) isocyanate

Five series of compounds (4-9) derived from N-(chlorocarbonyl) isocyanate have been synthesized and evaluated for their ability to inhibit the enzyme acyl-CoA:cholesterol O-acyltransferase and lower plasma cholesterol levels in cholesterol-fed rats. Structure-activity relationships indicate that the imino dicarboxylates (6 and 7) and the oxycarbonyl thiocarbamates (8) are the most potent and efficacious series. In these series, the combination of a 2,6-diisopropylphenyl group and an aliphatic alkyl group with a chain length between 6 and 14 carbon atoms gives good activity in vitro and in vivo. In addition, a hydrogen donor is required to maintain good in vitro activity, and the acidic proton on the central nitrogen in these series appears to be important for in vivo activity.

Inhibitors of acyl-CoA:cholesterol O-acyl transferase (ACAT) as hypocholesterolemic agents. 8. Incorporation of amide or amine functionalities into a series of disubstituted ureas and carbamates. Effects on ACAT inhibition in vitro and efficacy in vivo

A series of disubstituted ureas containing amide or amine groups was prepared and evaluated for their ability to inhibit acyl-CoA:cholesterol O-acyl transferase in vitro and to lower plasma total cholesterol in a variety of cholesterol-fed rat models in vivo. The presence of polar or ionizable functionalities within this class of compounds may impart greater aqueous solubility to those compounds and thus allow improved transport to the enzyme location within the intestinal enterocyte. Compounds from this class exhibit good cholesterol lowering in a chronic cholesterol-fed rat model of hypercholesterolemia even when dosed in an aqueous vehicle. In general, the amine-containing compounds were more potent and efficacious than the amides in the acute rat model of hypercholesterolemia. Further structure-activity relationship studies showed that the preferred position of the amide/amine group was beta to the urea moiety and not alpha, and that in this series, the presence of a secondary amine (or amide) proton is required for good in vitro potency. One of these compounds, 9n(-), lowered plasma total cholesterol (-47%) and elevated high-density lipoprotein cholesterol (+256%) when dosed in an aqueous vehicle to rats with preestablished hypercholesterolemia.

Inhibitors of acyl-CoA:cholesterol acyltransferase (ACAT). 7. Development of a series of substituted N-phenyl-N'-[(1-phenylcyclopentyl)methyl]ureas with enhanced hypocholesterolemic activity

We recently described our initial structure-activity relationship (SAR) studies on a series of N-phenyl-N'-aralkyl- and N-phenyl-N'-(1-phenylcycloalkyl)ureas as inhibitors of acyl-CoA: cholesterol acyltransferase (ACAT). From this series of analogs, compound 1 (PD 129337) was identified as a potent inhibitor of ACAT with an IC50 value of 17 nM. It was also shown to dose-dependently lower plasma cholesterol in cholesterol-fed rats. However, further investigation led to the suggestion that this compound was poorly absorbed, due to a lack of efficacy when administered by gavage in an aqueous vehicle. To overcome this deficiency, we continued our SAR study on this novel series of ACAT inhibitors using an acute in vivo screen in which the compounds are administered to rats in an aqueous, CMC/Tween suspension vehicle. Modification of the N'-phenyl moiety by incorporating functional groups which were amenable to forming salts and/or polar groups to reduce lipophilicity led to the identification of several inhibitors which displayed excellent efficacy employing this protocol. Overall, substitution on the phenyl ring in the ortho, meta, or para positions led to inhibitors with only a slight decrease in potency in vitro compared to the parent unsubstituted compound. Bulkier groups in the para position tended to lower the ACAT inhibitory activity in vitro. Polar groups, such as carboxyl (33,34), lowered in vitro activity significantly, suggesting that polar-ionic interactions are disfavored for the enzyme activity. From this series, compound 28 was evaluated further in secondary in vivo screens. In a chronic cholesterol-fed rat model of hypercholesterolemia, compound 28 dose-dependently reduced nonHDL cholesterol and significantly elevated HDL cholesterol. It showed significantly greater aqueous solubility than the parent compound 1. However, it was shown to cause adrenal toxicity in guinea pigs. This led us to design a series of homologs (44-51) with increased basicity and lower lipophilicity. Some of these compounds were more potent ACAT inhibitors in vitro and demonstrated excellent hypocholesterolemic activity in vivo. Interestingly, compound 45, unlike 28, did not produce adrenal toxicity in guinea pigs and demonstrated excellent lipid-modulating activity in the chronic model of preestablished dyslipidemia in rats.

Comparison of lifibrol to other lipid-regulating agents in experimental animals

In vitro data suggests that lifibrol lowers plasma cholesterol by inhibiting cholesterol synthesis. We report that lifibrol is far less potent in vitro and in vivo than lovastatin for inhibiting 14C-acetate incorporation into sterols. Moreover, several major differences between lifobrol and lovastatin were noted in various animal models. In contrast, lifibrol exhibited several activities in common with gemfibrozil, another phenoxy-acid-type drug. Specifically, in normal rats lifibrol, like gemfibrozil, lowered plasma non-HDL-cholesterol and triglycerides, and increased liver weight and hepatic peroxisomal marker enzyme activities. Lovastatin only lowered plasma triglycerides. In cholesterol-fed rats lifibrol and gemfibrozil lowered non-HDL-cholesterol and elevated HDL-cholesterol while lovastatin was inactive. Finally, lovastatin but not lifibrol exhibited hypocholesterolemic activity in normal guinea pigs and resin-primed dogs. Our interpretation is that these data do not support the notion that lifibrol lowers plasma cholesterol in vivo by inhibiting cholesterol synthesis.

ACAT inhibition decreases LDL cholesterol in rabbits fed a cholesterol-free diet. Marked changes in LDL cholesterol without changes in LDL receptor mRNA abundance

Rabbits fed low-fat, cholesterol-free diets containing casein as the sole protein source develop endogenous hypercholesterolemia (EH). To test the hypothesis that lipoprotein cholesteryl esters in EH rabbits are acyl coenzyme A:cholesterol acyltransferase (ACAT) derived, we treated EH rabbits with CI-976, a potent and selective ACAT inhibitor. In addition, since cholesterol and bile acid synthesis as well as low-density lipoprotein (LDL) receptor activity are reduced in EH rabbits, we determined whether changes in gene expression for 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, 7 alpha-hydroxylase, and the LDL receptor might be associated with the efficacy due to ACAT inhibition. Compared with EH controls, CI-976-treated rabbits (50 mg/kg per day for 5 weeks) had decreased plasma total cholesterol (-43%), very-low-density lipoprotein (VLDL) cholesterol (-62%), LDL cholesterol (-43%), plasma apolipoprotein B (-23%), liver cholesteryl esters (-39%), LDL size, VLDL and LDL cholesteryl ester content (percent of total lipids), cholesteryl oleate/cholesteryl linoleate ratios in VLDL and LDL (25% to 30%), and ex vivo liver ACAT activity. The triglyceride/cholesteryl ester ratio increased twofold to fourfold in these apolipoprotein B-containing lipoproteins. Endogenous cholesterol absorption appeared to be unaffected by drug treatment. CI-976 failed to alter specific hepatic mRNAs involved in cholesterol metabolism, but comparisons among dietary control groups revealed a marked reduction in 7 alpha-hydroxylase mRNA, no change in LDL receptor mRNA, and an increase in HMG-CoA reductase mRNA in EH rabbits compared with normal chow-fed controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Atherosclerotic lesion development in hypercholesterolemic Japanese quail following probucol treatment: a biochemical and morphologic evaluation

Probucol, a cholesterol-lowering agent which possesses antioxidant properties, was evaluated in hypercholesterolemic Japanese quail in order to assess the significance of antioxidant therapy on the development of atherosclerosis. Forty quail were fed a 0.5% cholesterol diet containing 0, 100, 200 or 500 mg kg-1 probucol for 2 months. At necropsy, plasma total and lipoprotein cholesterol and lipoprotein distribution were unchanged despite plasma probucol levels of 50 to 59 micrograms ml-1. The cholesteryl ester content of the liver and blood vasculature (brachiocephalic artery and aortic arch combined) was reduced by 33% and 62%, respectively, in animals given 500 mg kg-1 probucol. The vascular free cholesterol content was also reduced by 43 to 60% over the probucol dose range. Morphometric analysis of the brachiocephalic artery revealed that probucol reduced the incidence of lesions containing esterase-positive cells from 62% in untreated animals to 26% and 13% in animals administered 200 and 500 mg kg-1 probucol, respectively. No difference in mean wall thickness or area of the bracheocephalic artery was noted between the groups. Thus, we conclude that probucol can blunt the cholesteryl ester and macrophage enrichment of atherosclerotic lesions and this activity appears to be mediated by the compound's antioxidant properties since the changes noted were seen in the absence of alterations in plasma total and lipoprotein cholesterol levels.

Divergent pharmacologic activities of PD 132301-2 and CL 277,082, urea inhibitors of acyl-CoA:cholesterol acyltransferase

The in vitro potencies and hypocholesterolemic properties of CL 277,082 and PD 132301-2, two urea inhibitors of acyl-CoA:cholesterol acyltransferase (ACAT) were compared. PD 132301-2 was several-fold more potent at inhibiting ACAT in microsomes from rat and rabbit tissues and in cultured cells (murine macrophages and the human HepG2 cell line). This disubstituted urea was also relatively specific for ACAT as other cholesterol esterifying enzymes (e.g., lecithin:cholesterol acyltransferase, pancreatic cholesterol ester hydrolase), as well as intestinal diglyceride synthesis (acyl-CoA:monoglyceride acyltransferase), were unaffected in vitro at relevant concentrations. In normal chow-fed rats, both compounds reduced plasma triglycerides at doses > 50 mg/kg, but only PD 132301-2 reduced plasma cholesterol. In rat and rabbit models of hypercholesterolemia the greater in vitro potency of PD 132301-2 translated into greater in vivo efficacy (i.e., ED50 values 2- to 3-fold higher for CL 277,082 in both acute and chronic rate models). Of particular note was the greater elevation of high-density lipoprotein-cholesterol and parenteral activity of PD 132301-2 compared to CL 277,082 in the chronic rat model. Inhibition of cholesterol absorption in rats was also greater with PD 132301-2. In guinea pigs, in which 77% of plasma cholesterol was transported in low-density lipoprotein, PD 132301-2 potently reduced plasma total cholesterol (lowest significant dose = 1 mg/kg) as well as plasma triglycerides. CL 277,082 only reduced cholesterol at doses > 100 mg/kg in this low-density lipoprotein model. In a canine model of hypercholesterolemia CL 277,082 was inactive at doses up to 50 mg/kg, but PD 132301-2 was active at 3 mg/kg. Moreover, efficacy in dogs with PD 132301-2 was positively correlated with plasma drug concentration, an observation not previously demonstrated for other hypolipidemic drugs. The combined data illustrate that pharmacologic activities can vary widely among ACAT inhibitors of the same general class. In addition, the unique observation of proportionality between efficacy and blood drug levels in nonrodent animal models may not only help to simplify early stages in drug development but also may help to predict or monitor a direct action of the drug on vascular disease.

Inhibitors of acyl-Coa:cholesterol acyltransferase. 4. A novel series of urea ACAT inhibitors as potential hypocholesterolemic agents

We have synthesized a series of N-phenyl-N'-aralkyl and N-phenyl-N'-(1-phenylcycloalkyl)ureas as inhibitors of acyl-CoA:cholesterol acyltransferase (ACAT). This intracellular enzyme is thought to be responsible for the esterification of dietary cholesterol; hence inhibition of this enzyme could reduce diet-induced hypercholesterolemia. For this series of compounds, the in vitro ACAT inhibitory activity was improved by increasing the bulk of the 2,6-substituents on the phenyl ring. Additionally, we found that spacing of the aromatic rings was critical for ACAT inhibitory activity. A phenyl ring five atoms away from the requisite 2,6-diisopropylphenyl moiety was optimal for in vitro activity. Substitution alpha to the N'-phenyl moiety enhanced in vitro potency. In the case of phenylcycloalkyl ureas, ACAT inhibitory activity was independent of the size of the cycloalkyl ring. From this series of analogs, compound 25, which had excellent in vitro potency for inhibiting ACAT, was found to lower plasma cholesterol by 73% in vivo when administered in the diet at 50 mg/kg in an animal model of hypercholesterolemia. In this model, compound 25 lowered plasma cholesterol dose dependently and was as efficacious as the Lederle ACAT inhibitor CL 277082.

Inhibitors of acyl-CoA:cholesterol acyltransferase. 5. Identification and structure-activity relationships of novel beta-ketoamides as hypocholesterolemic agents

A study of structure-activity relationships of substituted beta-ketoamide ACAT inhibitors I and II was performed. The results of this study suggest that whereas the beta-keto group was tolerated with no loss in activity, beta-hydroxy and oxime moieties led to significantly reduced activity in vitro and in vivo. The most potent inhibitor from the acyclic series (I) (11, IC50 = 0.006 microM) contained a C-13 alkyl chain. This compound reduced plasma total cholesterol by 38% and 66% at 3 and 30 mg/kg, respectively, in cholesterol-fed rats. Dimethylation alpha to the anilide core (5) and subsequent N-methylation of the amide NH (6) decreased in vitro potency significantly. It was also found that high potency was retained with inhibitors which incorporated the carbonyl into a lactam ring (II).

A hardware-independent data acquisition package incorporating a simulation driver and simulation description language

Device drivers for commercial data acquisition boards (DASH-16, DT2801) and a device driver for a virtual data acquisition board have been developed and incorporated in a single package for a multiple station anesthesia research laboratory. The package provides a compiler for a simulation description language which is used to program the virtual board. The package, written in C for the IBM PC, was designed to be easily extended with additional drivers. Applications using the package can control all supported devices without the programmer having to learn the details of the hardware.

Inhibitors of acyl-CoA:cholesterol acyltransferase (ACAT). 2. Modification of fatty acid anilide ACAT inhibitors: bioisosteric replacement of the amide bond

In order to further define the structural features necessary for potent inhibition of acyl-coenzyme A:cholesterol acyltransferase (ACAT) in vitro and cholesterol lowering in vivo, systematic study of bioisosteric replacements for the amide bond in our previously identified series of fatty acid anilide ACAT inhibitors was undertaken. Only replacement of amide bonds with isosterases having both hydrogen bond donor and acceptor functionalities yielded compounds retaining ACAT inhibitory activity. Replacement of the amide bond with the urea bioisostere yielded compounds that were potent ACAT inhibitors in vitro and efficacious hypocholesterolemic agents in vivo. Examination of the structure activity relationships in the phenyl ring and alkyl portion of the N-phenyl-N'-alkylureas revealed that 2,6-diisopropyl substitution was optimal in the phenyl ring. When the 2,6-diisopropyl moiety was kept constant, potency in vitro and in vivo was maintained with straight and branched alkyl groups from 6 to 18 carbons in length.

In vivo evidence that the lipid-regulating activity of the ACAT inhibitor CI-976 in rats is due to inhibition of both intestinal and liver ACAT

CI-976, a new trimethoxy fatty acid anilide, is a potent and specific inhibitor of liver and intestinal acyl coenzyme A:cholesterol acyltransferase (ACAT) in vitro. Several in vivo approaches were used to determine the efficacy and sites of action of this compound in rats. CI-976 decreased non-high density lipoprotein (HDL)-cholesterol and increased HDL-cholesterol in rats with pre-established dyslipidemia. High performance gel chromatographic separation of plasma lipoproteins also revealed that CI-976, but not CL 277,082, lowered low density lipoprotein (LDL)-cholesterol and elevated HDL-cholesterol. Bay o 2752, octimibate, melinamide, and SaH 58-035 were all less potent in vivo compared to CI-976 and CL 277,082, and CI-976 produced the greatest decrease in liver cholesteryl esters. Subcutaneous (SC) administration of CI-976 was also efficacious in cholesterol-fed animals. In sucrose-fed rats, oral and SC CI-976 administration potently lowered plasma triglycerides. Hepatic cholesteryl ester accumulation in the ethinyl estradiol-treated rat was also diminished by orally administered CI-976. ACAT activity and cholesteryl ester mass were dose-dependently decreased in the livers from cholesterol-fed rats treated with CI-976, suggesting a direct effect on the liver. In both hypercholesterolemic and hypertriglyceridemic models, CI-976 also decreased plasma apoB concentrations. In other experiments radiolabeled CI-976 accumulated in the liver after multiple doses. Time-dependent changes in biliary lipid and bile acid secretion suggested that free cholesterol did not accumulate in the liver but instead was excreted as such or as bile acid. Finally, inhibition of endogenous and exogenous intestinal cholesterol absorption was demonstrated using several in vivo techniques. The combined data strongly supports the hypothesis that orally administered CI-976 inhibits both intestinal and hepatic ACAT, and that both of these enzymes may be determinants of plasma lipid concentrations in the rat.

Effect of the ACAT inhibitor CI-976 on plasma cholesterol concentrations and distribution in hamsters fed zero- and low-cholesterol diets

The overall objective of the present study was to determine if the ACAT inhibitor CI-976 can lower plasma cholesterol in hamsters fed zero or low, "human-like" levels of cholesterol. With a purified diet containing zero dietary cholesterol, CI-976 significantly lowered VLDL cholesterol (VLDL-C), but not total plasma cholesterol (TPC). When 0.06% cholesterol was added to this diet, reductions in both VLDL and LDL cholesterol (LDL-C) lowered TPC. Efficacy was still greater with 0.2% dietary cholesterol, but not potency. Mixing CI-976 into the purified diet resulted in greater decreases in VLDL-C compared to gavage administration, but LDL-C reductions with 0.2% cholesterol were optimal with gavage. With nonpurified, chow-based diets efficacy was markedly greater with diet-admix administration, regardless of the amount of dietary cholesterol. CI-976 inhibited cholesterol absorption with chow-based diets more potently compared to nonabsorbable agents (e.g., beta-sitosterol, tigogenin cellobioside), and the lowering of LDL-C was greatest when inhibition of cholesterol absorption was maximal. We conclude that the ACAT inhibitor CI-976 is efficacious in hamster models which utilize human-like levels of dietary cholesterol. Moreover, the data suggest that the pharmacologic responses to lipophilic ACAT inhibitors in the hamster, or even other lipid-regulating drugs, are likely to depend not only on the type of basal diet but also on the mode of drug administration.

Inhibitors of cholesterol biosynthesis. 6. trans-6-[2-(2-N-heteroaryl-3,5-disubstituted- pyrazol-4-yl)ethyl/ethenyl]tetrahydro-4-hydroxy-2H-pyran-2-ones

A series of N-heteroaryl-substituted mevalonolactones were prepared and evaluated for their ability to inhibit the enzyme HMG-CoA reductase both in vitro and in vivo, and to lower plasma cholesterol in a hypercholesterolemic dog model. The goal of the strategy employed was to design an inhibitor which possessed the pharmacological properties of lovastatin (1), and the physicochemical properties (increased hydrophilicity) of pravastatin (2). Two compounds 20a and 20b, were more potent than lovastatin at inhibiting cholesterol biosynthesis both in vitro and in vivo. In terms of plasma cholesterol lowering, 20a was much more efficacious than lovastatin. In addition to possessing increased biological activity, these compounds are significantly less lipophilic than lovastatin, in fact, 20b has a CLOGP value comparable to pravastatin.

Inhibitors of acyl-CoA:cholesterol acyltransferase. 1. Identification and structure-activity relationships of a novel series of fatty acid anilide hypocholesterolemic agents

A series of fatty acid anilides was prepared, and compounds were tested for their ability to inhibit the enzyme acyl-CoA:cholesterol acyltransferase (ACAT) in vitro and to lower plasma total cholesterol and elevate high-density lipoprotein cholesterol in cholesterol-fed rats in vivo. The compounds reported were found to fall into two subclasses with different anilide SAR. For nonbranched acyl analogues, inhibitory potency was found to be optimal with bulky 2,6-dialkyl substitution. For alpha-substituted acyl analogues, there was little dependence of in vitro potency on anilide substitution and 2,4,6-trimethoxy was uniquely preferred. Most of the potent inhibitors (IC50 less than 50 nM) were found to produce significant reductions in plasma total cholesterol in cholesterol-fed rats. Additionally, in vivo activity could be improved significantly by the introduction of alpha,alpha-disubstitution into the fatty acid portion of the molecule. A narrow group of alpha,alpha-disubstituted trimethoxyanilides, exemplified by 2,2-dimethyl-N-(2,4,6-trimethoxyphenyl)dodecanamide (39), was found to not only lower plasma total cholesterol (-60%) in cholesterol-fed rats but also elevate levels of high-density lipoprotein cholesterol (+94%) in this model at the screening dose of 0.05% in the diet (ca. 50 mg/kg).

Hepatic and nonhepatic sterol synthesis and tissue distribution following administration of a liver selective HMG-CoA reductase inhibitor, CI-981: comparison with selected HMG-CoA reductase inhibitors

Since cholesterol biosynthesis is an integral part of cellular metabolism, several HMG-CoA reductase inhibitors were systematically analyzed in in vitro, ex vivo and in vivo sterol synthesis assays using [14C]acetate incorporation into digitonin precipitable sterols as a marker of cholesterol synthesis. Tissue distribution of radiolabeled CI-981 and lovastatin was also performed. In vitro, CI-981 and PD134967-15 were equipotent in liver, spleen, testis and adrenal, lovastatin was more potent in extrahepatic tissues than liver and BMY21950, pravastatin and PD135023-15 were more potent in liver than peripheral tissues. In ex vivo assays, all inhibitors except lovastatin preferentially inhibited liver sterol synthesis; however, pravastatin and BMY22089 were strikingly less potent in the liver. CI-981 inhibited sterol synthesis in vivo in the liver, spleen and adrenal while not affecting the testis, kidney, muscle and brain. Lovastatin inhibited sterol synthesis to a greater extent than CI-981 in the spleen, adrenal and kidney while pravastatin and BMY22089 primarily affected liver and kidney. The tissue distribution of radiolabeled CI-981 and lovastatin support the changes observed in tissue sterol synthesis. Thus, we conclude that a spectrum of liver selective HMG-CoA reductase inhibitors exist and that categorizing agents as liver selective is highly dependent upon method of analysis.

Comparison of CI-976, an ACAT inhibitor, and selected lipid-lowering agents for antiatherosclerotic activity in iliac-femoral and thoracic aortic lesions. A biochemical, morphological, and morphometric evaluation

Due to the potential importance of acyl-coenzyme A:cholesterol O-acyltransferase (ACAT) in the generation of lipid-filled monocytes-macrophages, the ACAT inhibitor CI-976 (2,2-dimethyl-N-(2,4,6-trimethoxyphenyl)dodecanamide) was evaluated relative to selected lipid-lowering agents for their effect on atherosclerotic lesion regression and progression. Atherosclerotic lesions comparable in composition to human fatty streaks were induced by chronic endothelial denudation in the iliac-femoral artery of hypercholesterolemic New Zealand White rabbits before intervention, while naturally occurring fatty streaks developed in the thoracic aorta. CI-976 administered in a hypercholesterolemic diet at a dose that did not lower plasma cholesterol prevented the accumulation of monocytes-macrophages within the preestablished iliac-femoral lesion and reduced the foam cell area by 27-29% relative to the initiation of intervention. CI-976 also blunted the development of thoracic aortic fatty streak-like lesions and decreased the cholesteryl ester enrichment by 46%. CI-976 had no effect on plasma triglycerides and, more importantly, had no effect or decreased liver, iliac-femoral, and thoracic aortic free cholesterol content. Dietary intervention alone increased monocyte-macrophage involvement in the iliac-femoral lesion despite reductions in plasma, liver, and thoracic aortic cholesterol content. Conventional lipid-lowering therapy such as cholestyramine or cholestyramine/niacin required substantial decreases in plasma cholesterol levels to achieve comparable vascular changes. We conclude that inhibition of ACAT within the arterial wall by the potent and specific ACAT inhibitor CI-976, even in the absence of plasma cholesterol lowering, can result in the inhibition of atherosclerotic lesion progression and can enhance regression.

Rapid on-line determination of cholesterol distribution among plasma lipoproteins after high-performance gel filtration chromatography

A high-performance gel chromatography (HPGC) system has been developed which allows the unattended on-line determination of lipoprotein cholesterol distribution (VLDL-C, LDL-C, HDL-C), within 40 min, in microliter quantities of plasma using a single, relatively inexpensive column (Superose 6HR). The FAST cholesterol reagent (Sclavo) and a knitted PFTE Kratos reaction coil (Applied Biosystems) were found to provide optimal sensitivity, linearity, resolution, and dispersion characteristics. Validation is provided by comparison to target values for human quality control reference sera, and by comparing the values obtained by HPGC to the beta-quant method (LRC). The utility of the system is illustrated by comparing profiles from seven different species with normal or elevated plasma cholesterol concentrations. This technique allows rapid analysis of samples, regardless of species, without the use of precipitating agents or the ultracentrifuge. It could also be applied for the direct clinical determination of LDL-cholesterol.

Inhibitors of cholesterol biosynthesis. 4. trans-6-[2-(substituted-quinolinyl)ethenyl/ethyl]tetrahydro-4-hydroxy-2 H-pyran-2-ones, a novel series of HMG-CoA reductase inhibitors

A series of substituted quinoline mevalonolactones were prepared and evaluated for their ability to inhibit the enzyme HMG-CoA reductase both in vitro and (cholesterol biosynthesis) in vivo. Since previous studies suggested that the 4-(4-fluorophenyl) and 2-(1-methylethyl) substituents afforded optimum potency, attention was focused on variations at position 6 of the quinoline ring. Biological evaluation of a small number of analogues bearing a variety of 6-substituents showed that modification at this position had little effect on potency. Several compounds (8b, 8e, and 11) were identified that showed comparable potency to compactin and mevinolin in both the in vitro and in vivo assays.

Hep-G2 cells and primary rat hepatocytes differ in their response to inhibitors of HMG-CoA reductase

CI-981, a novel synthetic inhibitor of HMG-CoA reductase, was previously reported to be highly liver-selective using an ex vivo approach. In order to determine liver-selectivity at the cellular level, CI-981 was evaluated in cell culture and compared to lovastatin, pravastatin, fluvastatin and BMY-21950. Using human cell lines, none of the compounds tested showed liver-selectivity, i.e. strong inhibition of cholesterol synthesis in Hep-G2 cells (liver model) but weak inhibition in human fibroblasts (peripheral cell model). In contrast, all drugs tested produced equal and potent inhibition of sterol synthesis in primary cultures of rat hepatocytes, and CI-981, pravastatin and BMY-21950 were more than 100-fold more potent in rat hepatocytes compared to human fibroblasts. Since all compounds were also equally potent at inhibiting sterol synthesis in a rat subcellular system and in vivo, the data suggest that the use of Hep-G2 cells may not be the cell system of choice in which to study inhibition of hepatic cholesterogenesis or to demonstrate liver selectivity of inhibitors of HMG-CoA reductase.

Quantitative whole-body autoradiographic analysis of the tissue distribution of orally-administered [14C]cholesterol in hypercholesterolemic rats

The cholesterol-fed rat model has been used to examine the distribution of radiolabeled cholesterol by whole-body autoradiographic and quantitative videodensitometric methods. Animals were fed a hypercholesterolemic diet for 7 days, and were subsequently killed at 3, 6, 12, 24, or 72 h following a single oral dose of [14C]cholesterol. Maximum blood and tissue levels were observed at 12 h, while liver and adrenals were the most intensely labeled tissues. Liver maintained consistently high levels over the course of the study, while activity in other tissues declined moderately by 72 h, indicating the long half-life of cholesterol radioequivalents in tissue. The results of these experiments suggest that autoradiographic examination of cholesterol distribution in animals treated with pharmaceutical agents designed to modify cholesterol absorption or clearance will be useful in providing supplemental or confirmatory information on the drugs' mode of action.