Hypolipidemic effects in monkeys of ML-236B, a competitive inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase

Statins: HMG-CoA Reductase Inhibitors as Potential Anticancer Agents against Malignant Neoplasms in Women

Statins, also known as HMG-CoA inhibitors, are a class of bioactive small molecules that efficiently reduce the levels of cholesterol, and therefore are commonly used to manage and prevent various cardiovascular diseases. With respect to their original medical indications, statins are currently in the group of the most prescribed drugs worldwide. Of note is that statins are perceived actually rather as agents that have pleiotropic activities; in addition to their inhibitory activity on the production of endogenous cholesterol. Statins may also affect cell proliferation, angiogenesis and/or migration (metastasis) of different cancer cells, and play a positive role in the chemoprevention of cancer, thus being the excellent candidates to be repurposed in oncology. Particularly intriguing in this context seems to be the promising role of statins on both the incidence and course of common malignant neoplasms in women. In this article, we review and discuss the effect of the use of statins in the treatment of three types of cancer, i.e., breast, endometrial and ovarian cancer, with the highest mortality among gynecological cancers.

Statins: Then and Now

The discovery of statins (3-hydroxy-3-methylglutaryl CoA reductase inhibitors) is a consequence of the highly targeted, arduous search for naturally occurring compounds that inhibit cholesterol biosynthesis. An enormous amount of basic scientific, genetic, and clinical research substantiated the role of lipoprotein-derived cholesterol in atherogenesis. Quantifying the impact of lipid lowering on cardiovascular event rates became an issue of utmost urgency. Although a variety of nonstatin drugs had been tested in clinical trials, they found limited utility in the clinical setting due to lack of mortality reduction or tolerability issues. As multiple prospective randomized statin trials began publishing their results, it became clear that reducing atherogenic lipoprotein burden with these drugs was highly efficacious, safe, and generally well tolerated. Statins have been shown to reduce risk for nonfatal MI, ischemic stroke, need for revascularization, and cardiovascular and all-cause mortality. They have also been shown to stabilize and even regress established atherosclerotic plaque. For the first 2 decades of their use, statin dosing was largely determined by risk-stratified low-density lipoprotein cholesterol (LDL-C) goals. More recently, there has been a transition away from LDL-C goal attainment with a focus more on cardiovascular risk and percent LDL-C reduction. Unfortunately, long-term adherence rates with statin therapy remain low and, even when used, they tend to be underdosed.

Discovery and Development of Statins

Mevastatin (Compactin) belonging to the statin class is a hypolipidemic agent. It was isolated from the ascomycetous fungus, Penicillium citrinum by A. Endo in the 1970s, and he discovered that it acted as 3-hydroxy-3-methyl-glutaryl (HMG)-CoA reductase inhibitor. Mevastatin is considered the first statin drug. The clinical trials on mevastatin were carried out in the late 1970s in Japan. The first commercial statin drug was lovastatin, the second statin, which was found in Aspergillus terreus by Merc and Endo, independently in 1979. Since lovastatin was commercialized, 10 statins were synthesized among which paravastatin was launched to the market by Sankyo in 1989. Pravastatin is used in the lowering of cholesterol and preventing cardiovascular disease. At present, statins are the largest-selling class of drugs currently taken by patients throughout the world. Sales for this one class of drugs on 2005 were $25 billion. Today an estimated 40 million people worldwide are taking statin drugs.

A historical perspective on the discovery of statins

Cholesterol is essential for the functioning of all human organs, but it is nevertheless the cause of coronary heart disease. Over the course of nearly a century of investigation, scientists have developed several lines of evidence that establish the causal connection between blood cholesterol, atherosclerosis, and coronary heart disease. Building on that knowledge, scientists and the pharmaceutical industry have successfully developed a remarkably effective class of drugs--the statins--that lower cholesterol levels in blood and reduce the frequency of heart attacks.

Thematic review series: the pathogenesis of atherosclerosis. An interpretive history of the cholesterol controversy, part V: the discovery of the statins and the end of the controversy

The first four reviews in this series (Steinberg, D. 2004. J. Lipid Res. 45: 1583-1593; Steinberg, D. 2005. J. Lipid Res. 46: 179-190; Steinberg, D. 2005. J. Lipid Res. 46: 2037-2051; Steinberg, D. 2006. J. Lipid Res. 47: 1-14) traced the gradual accumulation of evidence, evidence of several different kinds, supporting the lipid hypothesis. They tracked the history from Anitschkow's 1913 classic work on the cholesterol-fed rabbit model to the breakthrough 1984 Coronary Primary Prevention Trial, the first large, randomized, double-blind primary intervention trial showing that decreasing blood cholesterol (using cholestyramine) significantly reduces coronary heart disease events. At that point, for the first time, decreasing blood cholesterol levels became an official national public health goal. Still, only a small fraction of patients at high risk were getting appropriate cholesterol-lowering treatment, and a number of important clinical questions remained unanswered. This final review in the series traces the early studies that led to the discovery of the statins and briefly reviews the now familiar large-scale clinical trials demonstrating their safety and their remarkable effectiveness in reducing coronary heart disease morbidity and mortality.

Influence of simvastatin on bone regeneration of tibial defects and blood cholesterol level in rats

The purpose of this study was to evaluate the effects of simvastatin, by oral or subcutaneous administration, on tibial defects regeneration and blood cholesterol level in rats. A surgical defect was made on the right tibia of 40 male animals assigned to 4 groups (n=10), based on two routes of administration and on the use or not of simvastatin: subcutaneous injection of simvastatin (7 mg/kg) (group AT) or only the vehicle of drug suspension (group AC), above the defect area, for 5 days; and 20 mg/kg of simvastatin macerated on water (group BT) or only water (group BC), orally, daily, during the whole observation period. The animals were sacrificed after 15 or 30 days, when blood samples were analyzed to check plasma cholesterol levels. Tibiae were removed and, after decalcification and routine laboratorial processing, histological and histomorphometrical analyses were carried out. ANOVA was used for statistical analysis at 5% signficance level. The histological and histomorphometrical analyses showed significant differences only between the experimental periods (p<0.05). Animals sacrificed after 30 days showed better bone repair (p<0.05). There was no statistically significant difference (p>0.05) for blood cholesterol levels between the groups. In conclusion, simvastatin administration either orally or subcutaneously did not improve bone repair of experimental tibial defects and did not alter blood cholesterol levels in rats.

Isoprenoids: Remarkable diversity of form and function

The isoprenoid biosynthetic pathway is the source of a wide array of products. The pathway has been highly conserved throughout evolution, and isoprenoids are some of the most ancient biomolecules ever identified, playing key roles in many life forms. In this review we focus on C-10 mono-, C-15 sesqui-, and C-20 diterpenes. Evidence for interconversion between the pathway intermediates farnesyl pyrophosphate and geranylgeranyl pyrophosphate and their respective metabolites is examined. The diverse functions of these molecules are discussed in detail, including their ability to regulate expression of the beta-HMG-CoA reductase and Ras-related proteins. Additional topics include the mechanisms underlying the apoptotic effects of select isoprenoids, antiulcer activities, and the disposition and degradation of isoprenoids in the environment. Finally, the significance of pharmacological manipulation of the isoprenoid pathway and clinical correlations are discussed.

Lovastatin and beyond: the history of the HMG-CoA reductase inhibitors

In the 1950s and 1960s, it became apparent that elevated concentrations of plasma cholesterol were a major risk factor for the development of coronary heart disease, which led to the search for drugs that could reduce plasma cholesterol. One possibility was to reduce cholesterol biosynthesis, and the rate-limiting enzyme in the cholesterol biosynthetic pathway, 3-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) reductase, was a natural target. Here, I describe the discovery and development of lovastatin--the first approved inhibitor of HMG-CoA reductase--and the clinical trials that have provided the evidence for the ability of drugs in this class to reduce the morbidity and mortality associated with cardiovascular disease.

The discovery and development of atorvastatin, a potent novel hypolipidemic agent

The search for potent and efficacious inhibitors of the enzyme HMG-CoA reductase (HMGRI) was the focus of considerable research in the 1980s. Building on the discovery of the fungal metabolite-derived inhibitors, mevastatin, lovastatin, pravastatin and simvastatin, a number of totally synthetic inhibitors were discovered and developed. This manuscript describes the discovery and development of one of those synthetic inhibitors, atovastatin calcium, currently marketed in the United States as LIPITOR. This inhibitor was designed based in part on molecular modeling comparisons of the structures of the fungal metabolites and other synthetically derived inhibitors. In addition to development of the structure-activity relationships which led to atorvastatin calcium, another critical aspect of the development of this area was the parallel improvement in the chemistry required to prepare compounds of the increased synthetic complexity needed to potently inhibit this enzyme. Ultimately, the development of several chiral syntheses of enantiomerically pure atorvastatin calcium was accomplished through a collaborative effort between discovery and development. The impact of the progress of the required chemistry as well as external factors on internal decision-making with regards to the development of atorvastatin calcium will be discussed.

Effects of dehydroepiandrosterone on oleic acid formation in the liver of rats, mice and guinea pigs

The purpose of the present study is to answer the question of whether there is a species difference in the effects of a pharmacological dose of dehydroepiandrosterone (DHEA) on the enzymes that participate in oleic acid (18:1) formation in the liver. Feeding a diet containing 0.5% (w/w) DHEA for 14 days markedly increased the activities of acyl-coenzyme A (CoA) synthetase, palmitoyl-CoA chain elongase and stearoyl-CoA desaturase in the liver of rats and mice. These enzyme activities, however, were not changed by DHEA in guinea pigs. The treatments of rats and mice with DHEA markedly increased proportions of 18:1 in hepatic lipids, especially phosphatidylcholine (selectively at C-2 position), triacylglycerol and cholesterol ester. DHEA caused no significant changes in acyl compositions of hepatic lipids of guinea pigs. The levels of DHEA or dehydroepiandrosterone sulfate (DHEAS) were markedly increased in serum and livers by DHEA administration to rats, mice and guinea pigs. High correlations were observed between hepatic levels of DHEA or DHEAS and stearoyl-CoA desaturase activities in rats. These results indicate that there are species differences in the inducing effects of DHEA or DHEAS on hepatic formation of 18:1 and that guinea pigs lack the machinery to induce the enzymes.

Sterol regulatory element binding protein-mediated effect of fluvastatin on cytosolic 3-hydroxy-3-methylglutaryl-coenzyme A synthase transcription

The effects of acute treatment with fluvastatin, a hypocholesteremic drug, on the mRNA levels of several regulatory enzymes of cholesterogenesis and of the LDL receptor were determined in rat liver. Fluvastatin increased the hepatic mRNA levels for HMG-CoA reductase up to 12-fold in 5 weeks of treatment at a daily dose of 6. 3 mg/kg. The effect was less marked in cytosolic HMG-CoA synthase, farnesyl-PP synthase, squalene synthetase, and LDL receptor. SREBP-2 mRNA levels were also increased, but SREBP-1 were not. De novo synthesis of cholesterol in several cultured cells was reduced by increasing concentrations of fluvastatin, and the IC(50) values of fluvastatin in HepG2, CV-1, and CHO cells were respectively 0.01, 0. 05, and 0.1 microM. When CHO cells stably transfected with a chimeric gene composed of the promoter of cytosolic HMG-CoA synthase and the CAT gene as a reporter were incubated with fluvastatin, the CAT gene was overexpressed, an effect which was similar to the cotransfection with the processed form of SREBP-1a. Both ALLN and fluvastatin increased the transcriptional activity of cytosolic HMG-CoA synthase. Mutation in either SRE or NF-Y boxes abolished the increase in transcriptional rate caused by fluvastatin in the promoter of cytosolic HMG-CoA synthase. These results indicate that the increase in transcriptional activity in the HMG-CoA synthase gene attributable to fluvastatin is a consequence of the activation of the proteolytic cleavage of SREBPs by reduced levels of intracellular cholesterol.

Effects of pravastatin and ursodeoxycholic acid on cholesterol and bile acid metabolism in patients with cholesterol gallstones

To investigate the effects of pravastatin and ursodeoxycholic acid (UDCA) on cholesterol and bile acid metabolism in humans, 41 patients with cholesterol gallstone disease were allocated to four groups and treated with pravastatin (20 mg/day), UDCA (600 mg/day), both pravastatin and UDCA, or neither drug (control) for 1-2 weeks prior to elective cholecystectomy. Cholesterol 7 alpha-hydroxylase activity and serum levels of total 7 alpha-hydroxycholesterol were significantly increased by pravastatin and unaffected by UDCA. 3-Hydroxy-3-methylglutaryl coenzyme A reductase activity was markedly increased by pravastatin and decreased by UDCA. UDCA significantly decreased biliary cholesterol concentration and the cholesterol saturation index and prolonged the nucleation time; however, pravastatin alone had little effect on biliary lithogenicity. Serum total and low-density lipoprotein (LDL)-cholesterol levels were reduced most by the combined administration of pravastatin and UDCA. In conclusion, at a dose of 20 mg/day, pravastatin increased bile acid synthesis but did not decrease biliary lithogenicity. UDCA had no significant effect on bile acid synthesis, but markedly decreased biliary lithogenicity.

Tissue selectivity of hydroxymethylglutaryl coenzyme A (HMG CoA) reductase inhibitors

Hydroxymethylglutaryl coenzyme A (HMG CoA) reductase inhibitors are a class of lipid-lowering medications, with a major activity on plasma cholesterol levels, now enjoying a vast popularity among physicians and patients. These drugs, affecting a very early and key step of sterol biosynthesis, differ to a large extent in their physicochemical properties, tissue distribution and side effects in animals, possibly in humans. Some of these agents (namely lovastatin and simvastatin) are strikingly lipophilic and require enzymatic conversion from the lactone to the open-ring forms, whereas pravastatin, active per se, is hydrophilic. Liver uptake of pravastatin is regulated by a carrier-mediated mechanism. Other HMG CoA reductase inhibitors have been designed, with the objective of obtaining high levels of hepato-selectivity. Evaluation of available data in terms of potential advantages in tissue, namely liver selectivity, of HMG CoA reductase inhibitors, suggests, that, indeed, altered sterol biosynthesis in a number of tissues may potentially result in the appearance of significant side effects. While there is no clear-cut relationship between tissue selectivity and lipophilicity, the presence of this latter feature seems, in general, to dictate a lesser absorption to peripheral tissues vs the liver. At present, the toxicological profile of major HMG CoA reductase inhibitors appears safe; it is, however, possible that in selected patient groups liver selectivity may offer a considerable therapeutic advantage.

Effects of lovastatin and leupeptin on ceroidogenesis of vitamin E-deficient and -supplemented young rats

Previous studies in young normal rats have shown that intracerebral administration of the proteinase inhibitor, leupeptin, caused a rapid accumulation of lipofuscin-like pigment in lysosomes of brain cells (Ivy et al., 1984a). On the other hand, we have recently found that the administration of lovastatin, an inhibitor of HMG-CoA reductase, reduced the ceroid-like pigment and dolichol contents in the crushed epididymal fat pad of rats (Porta et al., 1988). In order to study now the possible modulating effects of these enzyme inhibitors on ceroidogenesis associated with vitamin E deficiency, two main groups of weanling Wistar female rats were respectively fed ad libitum a vitamin E-deficient basal diet, or the same diet supplemented with 16 mg% of dl-alpha-tocopherol acetate. The vitamin E-deficient and -supplemented rats were further subdivided and received for 8 weeks their diets alone or with 2, 1, or 0.5 g of lovastatin/kg of diet. Other subgroups were treated with constant peritoneal infusion of 0.5 mg/day of leupeptin by means of osmotic minipumps (Alzet 2002) consecutively implanted at days 15, 30, and 45. Lovastatin treatment to vitamin E-deficient rats was associated with dose-dependent toxicity, resulting in 100%, 75%, and 50% mortality at concentrations of 2, 1, and 0.5 g/kg diet, respectively. This mortality was mainly due to extensive hepatic necrosis. Food intake and growth rates were reduced, while the relative weights of liver, kidneys, spleen, heart and brain, as well as the serum levels of GPT and GOT were significantly increased over the values of the untreated vitamin E-deficient control rats. The volumetric densities of ceroid pigment and the dolichol contents in liver and kidneys were not significantly modified. Lovastatin toxicity was partially prevented by vitamin E supplementation. However, in these supplemented rats, lovastatin treatment did not modify the volumetric densities of hepatic and renal ceroid, although the contents of hepatic and renal dolichol were significantly increased. No correlations could be found between levels of hepatic or renal ceroid and total dolichol content in vitamin E-deficient and supplemented rats. Leupeptin treatment to vitamin E-deficient rats only slightly reduced food intake and growth rates, and did not significantly modify the relative organ weights or the serum levels of cholesterol, GOT and GPT. Although in both vitamin E-deficient and -supplemented rats the leupeptin treatment consistently showed a tendency to increase the volumetric densities of hepatic and renal ceroid pigment, the differences with the control untreated rats were not statistically significant.(ABSTRACT TRUNCATED AT 400 WORDS)

Treatment of hypercholesterolemia with the HMG CoA reductase inhibitor, simvastatin

We report the results of a two center study on the use of the HMG Co A reductase inhibitor, simvastatin, in 44 patients suffering from familial hypercholesterolemia or from primary hypercholesterolemia of unknown etiology. The study included two separate phases: Phase I was part of a multicenter, 4-week, placebo-controlled trial; phase II was a 6-month, open extension trial, the object of which was to reduce low density lipoprotein (LDL) cholesterol levels to below the 50th percentile by increasing the dose of simvastatin, by the use of additional lipid-lowering medication, or both. Our phase I results were commensurate with those reported for the entire international cohort of 272 patients, indicating a clear dose-response relationship, with approximately 75% of the maximum reduction in LDL-C levels being achieved with 20 mg/day and over 90% of the maximum being achieved with 40 mg of simvastatin per day. In the open extension trial, the results from the 2 centers were essentially similar. Total cholesterol fell by 29% on the 20 mg/day dose and by 34% on the full dose of 40 mg/day. LDL-C levels were reduced by 40% on the 40 mg/day schedule, and triglycerides also fell to between 20% and 40% below baseline values. HDL-C concentration rose by 14% and 17.6%. The effects of simvastatin were uniform, both within and between the two cohorts. The addition of cholestyramine caused a further substantial reduction in LDL-cholesterol to below 55% of the initial value in four patients, whereas bezafibrate further enhanced the fall in triglycerides and the increase in high-density lipoprotein cholesterol, but had only a slight effect on LDL-C levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Biochemical aspect of HMG CoA reductase inhibitors

Subsequent to the discovery of compactin (ML-236B) as a specific inhibitor of HMG CoA reductase, a series of compactin analogs have been either isolated or synthesized. Several of these compounds, which include compactin, mevinolin (monacolin K) and CS-514, have been extensively studied. The inhibition of HMG CoA reductase by these compounds is reversible and competitive (Ki = approximately 1 nM). The 3', 5'-dihydroxypentanoic acid portion of the acid form of compactin analogs, which resembles the HMG portion of HMG CoA, plays a crucial role in inhibitory activity. These inhibitors block sterol synthesis both in cultured mammalian cells and in animals. Strong inhibition of sterol synthesis results in a marked increase in HMG CoA reductase activity both in vitro and in vivo. These compounds strongly lower plasma LDL-cholesterol levels in animals and humans. The lowering of LDL-cholesterol levels occurs by an inhibition of LDL synthesis and/or by an elevation of the receptor-mediated LDL catabolism in the liver.

Discovery, biochemistry and biology of lovastatin

Cholesterol is a 27-carbon steroid that is an essential component of the cell membrane, the immediate precursor of steroid hormones, the substrate for the formation of bile acids, and is required for the assembly of very low density lipoprotein in the liver. Because as much as two-thirds of total body cholesterol in patients is of endogenous origin, an effective means to control cholesterogenesis may occur by inhibition of its biosynthesis. Cholesterol is biosynthesized in a series of more than 25 separate enzymatic reactions that initially involve the formation of 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA). Early attempts to pharmacologically block cholesterol synthesis focused only on steps later in the biosynthetic pathway and resulted in compounds with unacceptable toxicity. Recent research had identified that HMG CoA reductase is a key rate-limiting enzyme in this pathway and is responsible for the conversion of HMG CoA to mevalonate. Additional research with fungal metabolites identified a series of compounds with potent inhibiting properties for this target enzyme, from which lovastatin was selected for clinical development. A reduction in cholesterol synthesis by lovastatin has been subsequently confirmed in cell culture, animal studies and in humans. A resultant decrease in circulating total and low-density lipoprotein (LDL) cholesterol has also been demonstrated in animals and humans. Because hepatic LDL receptors are the major mechanism of LDL clearance from the circulation, further animal research has confirmed that these declines in cholesterol are accompanied by an increase in hepatic LDL receptor activity. Lovastatin effectively diminishes endogenous cholesterol synthesis providing useful therapeutic properties for patients with hypercholesterolemia.

Chemistry, biochemistry, and pharmacology of HMG-CoA reductase inhibitors

After an extensive searching for a microbial product that inhibits cholesterol synthesis, compactin and a series of related metabolites like monacolin K (mevinolin) have been isolated from molds as active agents. These compounds, which were structurally related to hydroxymethylglutaryl coenzyme A, were potent competitive inhibitors of hydroxymethylglutaryl coenzyme A reductase, the rate-limiting enzyme in cholesterol synthesis. The inhibition was reversible and the inhibitor constant Ki for compactin was around 10(-9) M. Compactin inhibited cholesterol synthesis in mammalian cells at 10(-9) M. Sterol synthesis in vivo was also reduced when compactin was given orally to rats at a dose of 50 mg/kg. Hydroxymethylglutaryl coenzyme A reductase activity of both cultured cells and rat liver was elevated when sterol synthesis was strongly inhibited by compactin. Both the growth inhibition and reductase induction could be overcome by the presence of mevalonate. A compactin-resistant cell line of mouse FM3A cells, called CR200, was developed by stepwise selection. CR200-cells had an abnormally high level of reductase activity and amplified reductase gene. Compactin was not able to lower plasma cholesterol levels in mice, rats, and hamsters. However, it was highly effective in rabbits, dogs, and monkeys; plasma cholesterol of dogs was reduced by 30%-40% at a dose of 20-50 mg/kg. The low-density lipoprotein cholesterol, which is responsible for atherosclerosis, was preferentially lowered. Compactin was also highly effective in hypercholesterolemic patients at a small dose. The results of the current studies have proved that compactin and related compounds are far more effective in lowering plasma cholesterol than any other drugs available.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of mevinolin on cholesterol metabolism in obese and lean Zucker rats

Mevinolin is a potent competitive inhibitor of HMG-CoA reductase, the enzyme catalyzing the major rate-limiting step in cholesterol synthesis. In this study the drug was administered as an intragastric dose at 2.5 mg/kg/day to 10 to 12-week-old lean and obese Zucker female rats over a 5-day period. Mevinolin showed no effect on plasma cholesterol levels in the lean rat; however, in the obese rat there was a significant decrease in plasma cholesterol (about a 40% decrease from initial levels). Although there was a difference in effect on plasma cholesterol levels in obese and lean rats, hepatocytes isolated from both fed lean and obese rats incubated with various concentrations of mevinolin exhibited similar levels of inhibition of cholesterol synthesis and showed no effects on the other metabolic processes studied. These results indicate that the drug was effective acutely on cholesterol synthesis in hepatocytes isolated from both lean and obese rats, but on a chronic treatment basis the hypocholesterolemic effect was observed only in the obese Zucker rat. This study supports the idea that the naturally occurring hypercholesterolemic obese Zucker rat may be a good model for testing potential new cholesterol lowering agents.

The effect of CS-514, an inhibitor of HMG-CoA reductase, on serum lipids in healthy volunteers

CS-514 is a competitive inhibitor of HMG-CoA reductase. The effect of this agent on serum lipids and lipoproteins was studied in 10 healthy normocholesterolemic male volunteers by giving 20 mg of CS-514 or placebo twice a day for 7 days under double-blind conditions. The mean total serum cholesterol level decreased by 18.6% in the CS-514 group, whereas it increased by 7.4% in the placebo group and the difference between the two groups was statistically significant (P less than 0.01). LDL cholesterol and LDL apo B values were reduced by 22.6% and 23.2%, respectively. Serum triglyceride level did not change significantly. No clinical or laboratory abnormalities were observed.

Effects of an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase on serum lipoproteins and ubiquinone-10-levels in patients with familial hypercholesterolemia

We studied the effects of ML-236B, a competitive inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, on serum levels of lipoproteins and ubiquinone-10-in seven heterozygous patients with familial hypercholesterolemia. ML-236B was given at doses of 30 to 60 mg per day for 24 weeks. Serum cholesterol decreased from 390 +/- 9 to 303 +/- 8 mg per deciliter (101 +/- 0.2 to 7.88 +/- 0.2 mmol per liter, mean +/- S.E.M.; p less than 0.001) and serum triglyceride decreased from 137 +/- 18 to 87 +/- 9 mg per deciliter (1.55 +/- 0.20 to 0.98 +/- 0.01 mmol per liter; p less than 0.05). Intermediate-density-lipoprotein (DL) cholesterol, IDL triglyceride, low-density-lipoprotein (LDL) cholesterol, and LDL triglyceride decreased significantly (p less than 0.01, P less than 0.001, and P less than 0.001, respectively). However, there were no significant changes in very-low-density-lipoprotein (VLDL) cholesterol and triglyceride or high-density-lipoprotein (HDL) cholesterol. Serum ubiquinone-10 levels did not change, and LDL levels of ubiquinone-10 decreased by 50 per cent, from 0.39 +/- 0.07 to 0.20 +/- 0.01 microgram per milliliter (P less than 0.05). No adverse effects were observed. We conclude that ML-236B is effective in lowering serum cholesterol without lowering serum ubiquinone-10 in heterozygous patients with familial hypercholesterolemia.

Effects of ML-236b (compactin) on sterol synthesis and low density lipoprotein receptor activities in fibroblasts of patients with homozygous familial hypercholesterolemia

We studied biochemical genetics of low density lipoprotein (LDL) receptor mutations in fibroblasts from six homozygous and five heterozygous patients with familial hypercholesterolemia (FH). Three of six homozygotes are receptor-negative type and the other three homozygotes are receptor-defective type. In the cells from three receptor-negative homozygotes, the receptor binding, internalization, and degradation of (125)I-LDL were 0.5+/-0.3 ng/mg protein (mean+/-SEM), 14+/-8 and 8+/-6 ng/mg protein per 6 h (four normal cells; 44+/-3, 386+/-32, and 1,335+/-214 ng/mg protein per 6 h), respectively. In the cells from three receptor-defective homozygotes, the receptor binding, internalization, and degradation of (125)I-LDL were 6+/-2, 29+/-8, and 90+/-32 ng/mg protein per 6 h, respectively. In these six homozygotes, two pairs of siblings are included. Two siblings in the same family were classified as receptor-negative and two siblings in another family were classified as receptor-defective. The receptor-negative phenotypes and the receptor-defective phenotypes bred true in individual families. The cells from five heterozygotes showed approximately 46% of the normal activities of receptor.ML-236B, competitive inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase), completely inhibited the incorporation of [(14)C]acetate into digitonin-precipitable sterols in fibroblasts from normal subjects and heterozygous and homozygous patients with FH with the concentration of 0.5 mug/ml. However, at 0.05 mug/ml of ML-236B sterol synthesis in fibroblasts from homozygotes was not completely suppressed in contrast to normal and heterozygous cells. Moreover, after preincubation with 0.05 mug/ml of ML-236B for 24 h in medium containing lipoproteins, sterol synthesis in the cells from receptor-negative homozygote showed 75% of the initial activity compared with that of 25% without preincubation. In the cells from a normal subject and a heterozygote, sterol synthesis was inhibited even after preincubation. These results suggest that (a) the inhibitory effect of ML-236B is overcome in homozygote cells by their high intracellular levels of HMG-CoA reductase and (b) that a higher dose of ML-236B may be required to lower serum cholesterol levels in FH homozygotes than in heterozygotes.

Hypolipidemic effects of CS-500 (ML-236B) in WHHL-rabbit, a heritable animal model for hyperlipidemia

Oral administration of CS-500, a competitive inhibitor of 3-hydroxy-3-methylglutaryl CoA reductase, lowered the serum cholesterol level of both normal and WHHL-rabbits (the first example of heritable hyperlipidemic animals) at doses higher than 5 mg/kg/day. Phospholipids decreased concomitantly, whereas triglycerides did not in either normal or WHHL-rabbits.

Feedback regulation of 3-hydroxy-3-methylglutaryl coenzyme A reductase in livers of mice treated with mevinolin, a competitive inhibitor of the reductase

Compactin (ML-236B) and the related compound, mevinolin, are competitive inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG CoA reductase), the rate-controlling enzyme in cholesterol synthesis. Previous studies have shown that administration of compactin to cultured cells elicits a compensatory increase in the amount of HMG CoA reductase in the cells. A similar increase in HMG CoA reductase has been reported in livers of rats and mice that have been treated with compactin. In this study, we explore the mechanism for the mevinolin-mediated increase in hepatic HMG CoA reductase in mice that have been fed a control diet and a 2% cholesterol diet. Administration of mevinolin to mice on a control diet produced a 6- to 10-fold increase in the amount of HMG CoA reductase in liver microsomes. When mice were fed the cholesterol-enriched diet, cholesterol accumulated in the liver and HMG CoA reductase declined by 90%. The administration of mevinolin to cholesterol-fed mice produced a three to eightfold increase in HMG CoA reductase. Despite the abundant amount of cholesterol that was already present in the livers of the mevinolin-treated, cholesterol-fed animals, their elevated HMG CoA reductase could be rapidly suppressed by the subcutaneous injection of small amounts of mevalonate, the product of HMG CoA reductase. These data are compatible with the existence in mouse liver of a multivalent feedback regulatory mechanism for HMG CoA reductase in which suppression of the enzyme requires both a sterol and a nonsterol substance derived from mevalonate. By blocking mevalonate synthesis, mevinolin activates this regulatory mechanism, and this in turn causes an increase in hepatic HMG CoA reductase. The ability to suppress the elevated HMG CoA reductase with mevalonate may prove useful in potentiating the effectiveness of mevinolin as a hypocholesterolemic agent.

Mevinolin: a highly potent competitive inhibitor of hydroxymethylglutaryl-coenzyme A reductase and a cholesterol-lowering agent

Mevinolin, a fungal metabolite, was isolated from cultures of Aspergillus terreus. The structure and absolute configuration of mevinolini and its open acid form, mevinolinic acid, were determined by a combination of physical techniques. Mevinolin was shown to be 1,2,6,7,8,8a-hexahydro-beta, delta-dihydroxy-2,6-dimethyl-8-(2-methyl-1-oxobutoxy)-1-naphthalene-hepatanoic acid delta-lactone. Mevinolin in the hydroxy-acid form, mevinolinic acid, is a potent competitive inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A reductase [mevalonate: NADP+ oxidoreductase (CoA-acylating), EC 1.1.1.34]; its Ki of 0.6 nM can be compared to 1.4 nM for the hydroxy acid form of the previously described related inhibitor, ML-236B (compactin, 6-demethylmevinolin). In the rat, orally administered sodium mevinolinate was an active inhibitor of cholesterol synthesis in an acute assay (50% inhibitory dose = 46 microgram/kg). Furthermore, it was shown that mevinolin was an orally active cholesterol-lowering agent in the dog. Treatment of dogs for 3 weeks with mevinolin at 8 mg/kg per day resulted in a 29.3 +/- 2.5% lowering of plasma cholesterol.

The effect of compactin, a potent inhibitor of 3-hydroxy-3-methylglutaryl coenzyme-A reductase activity, on cholesterogenesis and serum cholesterol levels in rats and chicks

Compactin, [7-(1,2,6,7,8,8a-hexahydro-2-methyl-8-(2-methylbutyrylox)naphthyl)-3-hydroxyheptan-5-olide], a potent competitive inhibitor of the rate-determining step in cholesterol biosynthesis, was used to study the influence of changes in cholesterogenesis on serum cholesterol levels. Up to 3 h after a single oral dose (20 or 50 mg/kg) or after the last of a series of daily oral doses (50 mg/kg for 7 or 28 days) to young, male normolipidaemic rats, compactin consistently inhibited cholesterogenesis measured using 3H20 in liver, ileum and other extrahepatic tissues without affecting fatty acid synthesis. Compactin did not reduce serum or tissue cholesterol nor affect the serum concentration of other lipids nor the ratio between lipoprotein classes. A diurnal variation in the effect of compactin on cholesterogenesis was observed. For example, by 12--20 h after dosing, cholesterogenesis at all sites was increased above the comparable control value, indicating the induction of enzyme synthesis and overall there was little effect on the mass of cholesterol synthesized per day. Similar results were obtained using male chicks. Inhibition of cholesterogenesis by compactin was also observed in cholestyramine-treated rats, in which cholesterol turnover was markedly increased, and even in cholesterol-fed rats, in which cholesterogenesis already was repressed. In neither case, however, was inhibition of cholesterogenesis accompanied by a hypocholesterolaemic effect. It is concluded that a more persistent suppression of cholesterogenesis, than that observed with compactin in the rat, may be required in order to affect serum cholesterol concentrations.

Therapeutic effects of ML-236B in primary hypercholesterolemia

ML-236B, a competitive inhibitor of 3-hydroxy-3-methylglutaryl CoA reductase, was administered to 11 patients with primary hypercholesterolemia. After 4--8 weeks of drug treatment at doses of 50--150 mg/day, serum cholesterol levels were reduced by 11--37% (27% on average) in cases of heterozygous familial hypercholesterolemia and combined hyperlipidemia. A marked reduction in tuberous xanthomas was noticed in a homozygous case of familial hypercholesterolemia, but here the drug was less effective in reducing the serum cholesterol level and a higher dose was required for treatment. Softening of Achilles tendon xantomas was observed in a case of combined hyperlipidemia.