YM-53601, a novel squalene synthase inhibitor, reduces plasma cholesterol and triglyceride levels in several animal species

The mechanism and clinical application of farnesyl diphosphate farnesyltransferase 1 in cancer metabolism

Cancer poses a significant risk to human well-being. Among the crucial characteristics of cancer is metabolic reprogramming. To meet the relentless metabolic needs, cancer cells enhance cholesterol metabolism within the adverse tumor microenvironment. Reprograming cholesterol metabolism includes a series of modifications in the synthesis, absorption, esterification, and metabolites associated with cholesterol. These adjustments have a strong correlation with the proliferation, invasion, metastasis, and other characteristics of malignant tumors. FDFT1, also known as farnesyl diphosphate farnesyltransferase 1, is an enzyme crucial in the process of cholesterol biosynthesis. Its significant involvement in tumor metabolism has garnered considerable interest. The significance of FDFT1 in cancer metabolism cannot be overstated, as it actively interacts with cancer cells. This paper aims to analyze and consolidate the mechanism of FDFT1 in cancer metabolism and explore its clinical application. The goal is to contribute new strategies and targets for the prevention and treatment of cancer metabolism.

Discovery of Novel 11-Membered Templates as Squalene Synthase Inhibitors

Squalene synthase is one of the most promising pharmaceutical targets to treat hyperlipidemia. Inhibition of the squalene synthase causes a decrease in the hepatic cholesterol concentration. We have already reported the design and synthesis of highly potent benzhydrol-type squalene inhibitors. Although these templates showed unique and potent cyclic active conformations via intramolecular hydrogen bonds, the in vivo cholesterol-lowering efficacy was insufficient. We attempted to improve their potential as an orally active medicine. In our medicinal chemistry effort, cyclized 11-membered ring templates were acquired. The novel series of compounds exhibited potent squalene synthase inhibitory activity, and one of the derivatives, isomer A-(1S, 3R)-14i, showed plasma lipid-lowering efficacy in hamster and marmoset repeated-dose studies. Our findings provide valuable insights into the design and development of novel and unique 11-membered ring-type highly potent squalene synthase inhibitors.

Repurposing screen identifies novel candidates for broad-spectrum coronavirus antivirals and druggable host targets

Libraries composed of licensed drugs represent a vast repertoire of molecules modulating physiological processes in humans, providing unique opportunities for the discovery of host-targeting antivirals. We screened the Repurposing, Focused Rescue, and Accelerated Medchem (ReFRAME) repurposing library with approximately 12,000 molecules for broad-spectrum coronavirus antivirals and discovered 134 compounds inhibiting an alphacoronavirus and mapping to 58 molecular target categories. Dominant targets included the 5-hydroxytryptamine receptor, the dopamine receptor, and cyclin-dependent kinases. Gene knock-out of the drugs' host targets including cathepsin B and L (CTSB/L; VBY-825), the aryl hydrocarbon receptor (AHR; Phortress), the farnesyl-diphosphate farnesyltransferase 1 (FDFT1; P-3622), and the kelch-like ECH-associated protein 1 (KEAP1; Omaveloxolone), significantly modulated HCoV-229E infection, providing evidence that these compounds inhibited the virus through acting on their respective host targets. Counter-screening of all 134 primary compound candidates with SARS-CoV-2 and validation in primary cells identified Phortress, an AHR activating ligand, P-3622-targeting FDFT1, and Omaveloxolone, which activates the NFE2-like bZIP transcription factor 2 (NFE2L2) by liberating it from its endogenous inhibitor KEAP1, as antiviral candidates for both an Alpha- and a Betacoronavirus. This study provides an overview of HCoV-229E repurposing candidates and reveals novel potentially druggable viral host dependency factors hijacked by diverse coronaviruses.

Identification of non-conventional small molecule degraders and stabilizers of squalene synthase

Squalene synthase (SQS) is an essential enzyme in the mevalonate pathway, which controls cholesterol biosynthesis and homeostasis. Although catalytic inhibitors of SQS have been developed, none have been approved for therapeutic use so far. Herein we sought to develop SQS degraders using targeted protein degradation (TPD) to lower overall cellular cholesterol content. We found that KY02111, a small molecule ligand of SQS, selectively causes SQS to degrade in a proteasome-dependent manner. Unexpectedly, compounds based on the same scaffold linked to E3 ligase recruiting ligands led to SQS stabilization. Proteomic analysis found KY02111 to reduce only the levels of SQS, while lipidomic analysis determined that KY02111-induced degradation lowered cellular cholesteryl ester content. Stabilizers shielded SQS from its natural turnover without recruiting their matching E3 ligase or affecting enzymatic target activity. Our work shows that degradation of SQS is possible despite a challenging biological setting and provides the first chemical tools to degrade and stabilize SQS.

Unveiling the Therapeutic Potential of Squalene Synthase: Deciphering Its Biochemical Mechanism, Disease Implications, and Intriguing Ties to Ferroptosis

Squalene synthase (SQS) has emerged as a promising therapeutic target for various diseases, including cancers, owing to its pivotal role in the mevalonate pathway and the antioxidant properties of squalene. Primarily, SQS orchestrates the head-to-head condensation reaction, catalyzing the fusion of two farnesyl pyrophosphate molecules, leading to the formation of squalene, which has been depicted as a highly effective oxygen-scavenging agent in in vitro studies. Recent studies have depicted this isoprenoid as a protective layer against ferroptosis due to its potential regulation of lipid peroxidation, as well as its protection against oxidative damage. Therefore, beyond its fundamental function, recent investigations have unveiled additional roles for SQS as a regulator of lipid peroxidation and programmed cell death pathways, such as ferroptosis-a type of cell death characterized by elevated levels of lipid peroxide, one of the forms of reactive oxygen species (ROS), and intracellular iron concentration. Notably, thorough explorations have shed light on the distinctive features that set SQS apart from other members within the isoprenoid synthase superfamily. Its unique biochemical structure, intricately intertwined with its reaction mechanism, has garnered significant attention. Moreover, considerable evidence substantiates the significance of SQS in various disease contexts, and its intriguing association with ferroptosis and lipid peroxidation. The objective of this report is to analyze the existing literature comprehensively, corroborating these findings, and provide an up-to-date perspective on the current understanding of SQS as a prospective therapeutic target, as well as its intricate relationship with ferroptosis. This review aims to consolidate the knowledge surrounding SQS, thereby contributing to the broader comprehension of its potential implications in disease management and therapeutic interventions.

Tapinanthus dodoneifolius leaf inhibits the activity of carbohydrate digesting enzymes and improves the insulin resistance induced in rats by dexamethasone

Background

Tapinanthus dodoneifolius is a plant used in traditional African medicine to treat diabetes mellitus. This study aimed to evaluate the preventive antidiabetic potential of the aqueous extract of T. dodoneifolius leaves (AETD) in insulin resistant rats.

Methods

A quantitative phytochemical study of AETD was carried out to determine the contents of total phenols, tannins, flavonoids, and saponins. AETD was tested in vitro on the activity of α-amylase and α-glucosidase enzymes. Insulin resistance was induced for 10 days by daily subcutaneous injection of dexamethasone (1 mg/kg). One hour before, the rats were divided into 5 groups and treated as follows: group 1 received distilled water (10 mL/kg); group 2 received metformin (40 mg/kg), and groups 3, 4, and 5 were treated with AETD (125, 250, and 500 mg/kg). Body weight, blood sugar, food and water consumption, serum insulin level, lipid profile, and oxidative status were assessed. One-way analysis of variance followed by Turkey's post-test and two-way analysis followed by Bonferroni's post-test were used to analyze univariate and bivariate parameters, respectively.

Results

Results showed that the phenol content of AETD (54.13 ± 0.14 mg GAE/g extract) was higher than that of flavonoids (16.73 ± 0.06 mg GAE/g extract), tannins (12.08 ± 0.07 mg GAE/g extract), and saponins (IC₅₀ = 13.56 ± 0.03 mg DE/g extract). AETD showed a higher inhibitory potential on α-glucosidase activity (IC₅₀ = 191.51 ± 5.63 μg/mL) than on α-amylase activity (IC₅₀ = 1774.90 ± 10.32 μg/mL). AETD (250 and/or 500 mg/kg) prevented drastic loss of body weight and reduced food and water consumption in insulin resistant rats. The levels of blood glucose, total cholesterol, triglycerides, low-density lipoprotein cholesterol, and malondialdehyde were also reduced while high-density lipoprotein cholesterol level, reduced glutathion level, and catalase and superoxide dismutase activity increased after administration of AETD (250 and 500 mg/kg) in insulin resistant rats.

Conclusion

AETD has significant antihyperglycemic, antidyslipidemic, and antioxidant potential, thus it can be used for the management of type 2 diabetes mellitus and its complications.

Statins repress needle-like carbon nanotube- or cholesterol crystal-stimulated IL-1β production by inhibiting the uptake of crystals by macrophages

Statins are 3-hydroxy-3-methylglutaryl-CoA reductase inhibitors that lower atherogenic LDL-cholesterol levels. Statins exert clinically relevant anti-inflammatory effects; however, the underlying molecular mechanism remains unclear. Studies have shown that endogenous and exogenous pathogenic crystals, such as cholesterol and monosodium urate (MSU), and needle-like nanomaterials, such as multi-wall carbon nanotubes (MWCNT), induce the production of IL-1β and play a critical role in the development of crystal-associated sterile inflammatory pathologies. In this study, we evaluated the effect of statins on crystal-induced IL-1β production in macrophages. We found that various statins, including pitavastatin, atorvastatin, fluvastatin, and lovastatin, but not squalene synthase inhibitor, repressed IL-1β release upon MWCNT stimulation. In addition, IL-1β production induced by cholesterol crystals and MSU crystals, but not by ATP or nigericin, was diminished. MWCNT-stimulated IL-1β release was dependent on the expression of NLRP3, but not AIM2, NLRC4, or MEFV. Statin-induced repression was accompanied by reduced levels of mature caspase-1 and decreased uptake of MWCNT into cells. Supplementation of mevalonate, geranylgeranyl pyrophosphate, or farnesyl pyrophosphate prevented the reduction in IL-1β release, suggesting a crucial role of protein prenylation, but not cholesterol synthesis. The statin-induced repression of MWCNT-elicited IL-1β release was observed in THP-1-derived and mouse peritoneal macrophages, but not in bone marrow-derived macrophages where statins act in synergy with lipopolysaccharide to enhance the expression of IL-1β precursor protein. In summary, we describe a novel anti-inflammatory mechanism through which statins repress mature IL-1β release induced by pathogenic crystals and nanoneedles by inhibiting the internalization of crystals by macrophages.

Small Molecule Regulators of Ferroptosis

Ferroptosis is a dedicated mode of cell death involving iron, reactive oxygen species and lipid peroxidation. Involved in processes such as glutathione metabolism, lysosomal iron retention or interference with lipid metabolism, leading either to activation or inhibition of ferroptosis. Given the implications of ferroptosis in diseases such as cancer, aging, Alzheimer and infectious diseases, new molecular mechanisms underlying ferroptosis and small molecules regulators that target those mechanisms have prompted a great deal of interest. Here, we discuss the current scenario of small molecules modulating ferroptosis and critically assess what is known about their mechanisms of action.

Roles of Farnesyl-Diphosphate Farnesyltransferase 1 in Tumour and Tumour Microenvironments

Farnesyl-diphosphate farnesyltransferase 1 (FDFT1, squalene synthase), a membrane-associated enzyme, synthesizes squalene via condensation of two molecules of farnesyl pyrophosphate. Accumulating evidence has noted that FDFT1 plays a critical role in cancer, particularly in metabolic reprogramming, cell proliferation, and invasion. Based on these advances in our knowledge, FDFT1 could be a potential target for cancer treatment. This review focuses on the contribution of FDFT1 to the hallmarks of cancer, and further, we discuss the applicability of FDFT1 as a cancer prognostic marker and target for anticancer therapy.

Statin-induced GGPP depletion blocks macropinocytosis and starves cells with oncogenic defects

Cancer cells display novel characteristics which can be exploited for therapeutic advantage. Isolated studies have shown that 1) the mevalonate pathway and 2) increased macropinocytosis are important in tumorigenesis, but a connection between these two observations has not been envisioned. A library screen for compounds that selectively killed Dictyostelium pten ^- cells identified pitavastatin. Pitavastatin also killed human breast epithelial MCF10A cells lacking PTEN or expressing K-Ras^G12V, as well as mouse tumor organoids. The selective killing of cells with oncogenic defects was traced to GGPP (geranylgeranyl diphosphate) depletion. Disruption of GGPP synthase in Dictyostelium revealed that GGPP is needed for pseudopod extension and macropinocytosis. Fluid-phase uptake through macropinocytosis is lower in PTEN-deleted cells and, as reported previously, higher in cells expressing activated Ras. Nevertheless, uptake was more sensitive to pitavastatin in cells with either of these oncogenic mutations than in wild-type cells. Loading the residual macropinosomes after pitavastatin with high concentrations of protein mitigated the cell death, indicating that defective macropinocytosis leads to amino acid starvation. Our studies suggest that the dependence of cancer cells on the mevalonate pathway is due to the role of GGPP in macropinocytosis and the reliance of these cells on macropinocytosis for nutrient uptake. Thus, inhibition of the networks mediating these processes is likely to be effective in cancer intervention.

Discovery of a Small-Molecule-Dependent Photolytic Peptide

We accidentally found that YM-53601, a known small-molecule inhibitor of squalene synthase (SQS), selectively depletes SQS from mammalian cells upon UV irradiation. Further analyses indicated that the photodepletion of SQS requires its short peptide segment located at the COOH terminus. Remarkably, when the 27 amino acid peptide was fused to green fluorescent protein or unrelated proteins at either the NH₂ or COOH terminus, such fusion proteins were selectively depleted when the cells were treated with both YM-53601 and UV exposure. Product analysis and electron spin resonance experiments suggested that the UV irradiation promotes homolytic C-O bond cleavage of the aryl ether group in YM-53601. It is likely that the radical species generated from UV-activated YM-53601 abstract hydrogen atoms from the SQS peptide, leading to the photolysis of the entire protein. The pair of the SQS peptide and YM-53601 discovered in the present study paves the way for the design of a new small-molecule-controlled optogenetic tool.

Hsa-miR-10a-5p downregulation in mutant UQCRB-expressing cells promotes the cholesterol biosynthesis pathway

Ubiquinol cytochrome c reductase binding protein (UQCRB) is known to play crucial roles in the development of various types of diseases. However, the link between UQCRB and microRNAs remains unknown. In the present study, we performed microRNA sequencing of mutant UQCRB-expressing stable cell lines that exhibited pro-oncogenic activities caused by expression of the mutant UQCRB gene. Results showed that hsa-miR-10a-5p was significantly downregulated in the mutant UQCRB-expressing cell lines. Furthermore, mRNA sequencing and gene ontology analysis of differentially expressed genes (DEGs) revealed that the cholesterol biosynthesis pathway might be activation by mutant UQCRB expression. Moreover, inhibition of cholesterol synthesis in mutant UQCRB-expressing cells via treatment with the specific inhibitors suppressed the cell proliferation. Transfection with a hsa-miR-10a-5p mimic validated that lanosterol synthase (LSS) is a target of hsa-miR-10a-5p. In addition, hsa-miR-10a-5p was found to be downregulated in liver cancer cell lines overexpressing UQCRB. Taken together, our findings highlighted the potential use of hsa-miR-10a-5p as a biomarker for UQCRB related diseases.

Targeting the mevalonate pathway is a novel therapeutic approach to inhibit oncogenic FoxM1 transcription factor in human hepatocellular carcinoma

Dysregulation of cell metabolism is a hallmark of cancer. The mevalonate pathway in lipid metabolism has been implicated as a potential target of cancer therapy for hepatocellular carcinoma (HCC). The role of the Forkhead Box M1 (FoxM1) transcription factor in HCC development has been well documented, however, its involvement in cancer metabolism of HCC has not been fully determined. Here, we hypothesized that FoxM1 is involved in the mevalonate pathway of cholesterol biosynthesis in HCC. Inhibition of the mevalonate pathway by statins, inhibitors of 3-hydroxy-3-methylglutaryl CoA reductase (HMGCR), resulted in reduced expression of FoxM1 and increased cell death in human hepatoma cells. Re-exposure of mevalonate, a product of HMGCR, restored these effects. Likewise, knockdown of HMGCR reduced FoxM1 expression, indicating that FoxM1 expression was regulated by the mevalonate pathway in HCC. Mechanistically, protein geranylgeranylation was found to be responsible for FoxM1 expression and geranylgeranylated proteins, including RhoA, Rac1 or Cdc42, were shown to be involved in this process. In surgically resected human HCC tissues, the gene expression of FoxM1 had a positive correlation with that of the mevalonate pathway-related genes, such as HMGCR or sterol regulatory element-binding protein 2 (SREBP2). Furthermore, the gene expression of FoxM1 along with that of HMGCR or SREBP2 defined prognosis of HCC patients, suggesting the clinical significance of the mevalonate-FoxM1 pathway in human HCC. Our data indicate that FoxM1 links the mevalonate pathway to oncogenic signals in HCC. Thus, we propose a novel therapeutic approach to inhibit FoxM1 by targeting the mevalonate pathway for HCC.

A Genomic DNA Reporter Screen Identifies Squalene Synthase Inhibitors That Act Cooperatively with Statins to Upregulate the Low-Density Lipoprotein Receptor

Hypercholesterolemia remains one of the leading risk factors for the development of cardiovascular disease. Many large double-blind studies have demonstrated that lowering low-density lipoprotein (LDL) cholesterol using a statin can reduce the risk of having a cardiovascular event by approximately 30%. However, despite the success of statins, some patient populations are unable to lower their LDL cholesterol to meet the targeted lipid levels, due to compliance or potency issues. This is especially true for patients with heterozygous familial hypercholesterolemia who may require additional upregulation of the low-density lipoprotein receptor (LDLR) to reduce LDL cholesterol levels below those achievable with maximal dosing of statins. Here we identify a series of small molecules from a genomic DNA reporter screen that upregulate the LDLR in mouse and human liver cell lines at nanomolar potencies (EC₅₀ = 39 nM). Structure-activity relationship studies carried out on the lead compound, OX03771 [(E)-N,N-dimethyl-3-(4-styrylphenoxy)propan-1-amine], led to the identification of compound OX03050 [(E)-3-(4-styrylphenoxy)propan-1-ol], which had similar potency (EC₅₀ = 26 nM) but a much-improved pharmacokinetic profile and showed in vivo efficacy. Compounds OX03050 and OX03771 were found to inhibit squalene synthase, the first committed step in cholesterol biosynthesis. These squalene synthase inhibitors were shown to act cooperatively with statins to increase LDLR expression in vitro. Overall, we demonstrated here a novel series of small molecules with the potential to be further developed to treat patients either alone or in combination with statins.

Differential Regulation of Gene Expression by Cholesterol Biosynthesis Inhibitors That Reduce (Pravastatin) or Enhance (Squalestatin 1) Nonsterol Isoprenoid Levels in Primary Cultured Mouse and Rat Hepatocytes

Squalene synthase inhibitors (SSIs), such as squalestatin 1 (SQ1), reduce cholesterol biosynthesis but cause the accumulation of isoprenoids derived from farnesyl pyrophosphate (FPP), which can modulate the activity of nuclear receptors, including the constitutive androstane receptor (CAR), farnesoid X receptor, and peroxisome proliferator-activated receptors (PPARs). In comparison, 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors (e.g., pravastatin) inhibit production of both cholesterol and nonsterol isoprenoids. To characterize the effects of isoprenoids on hepatocellular physiology, microarrays were used to compare orthologous gene expression from primary cultured mouse and rat hepatocytes that were treated with either SQ1 or pravastatin. Compared with controls, 47 orthologs were affected by both inhibitors, 90 were affected only by SQ1, and 51 were unique to pravastatin treatment (P < 0.05, ≥1.5-fold change). When the effects of SQ1 and pravastatin were compared directly, 162 orthologs were found to be differentially coregulated between the two treatments. Genes involved in cholesterol and unsaturated fatty acid biosynthesis were up-regulated by both inhibitors, consistent with cholesterol depletion; however, the extent of induction was greater in rat than in mouse hepatocytes. SQ1 induced several orthologs associated with microsomal, peroxisomal, and mitochondrial fatty acid oxidation and repressed orthologs involved in cell cycle regulation. By comparison, pravastatin repressed the expression of orthologs involved in retinol and xenobiotic metabolism. Several of the metabolic genes altered by isoprenoids were inducible by a PPARα agonist, whereas cytochrome P450 isoform 2B was inducible by activators of CAR. Our findings indicate that SSIs uniquely influence cellular lipid metabolism and cell cycle regulation, probably due to FPP catabolism through the farnesol pathway.

Statins inhibit blastocyst formation by preventing geranylgeranylation

STUDY HYPOTHESIS

Statins, inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase of the mevalonate pathway and prescription drugs that treat hypercholesterolemia, compromise preimplantation mouse development via modulation of HIPPO signaling.

STUDY FINDING

HMG-CoA reductase activity is required for trophectoderm specification, namely blastocyst cavity formation and Yes-associated protein (YAP) nuclear localization, through the production of isoprenoid geranylgeranyl pyrophosphate (GGPP) and the action of geranylgeranyl transferase.

WHAT IS KNOWN ALREADY

Previous studies have shown that treatment of mouse embryos with mevastatin prevents blastocyst formation, but how HMG-CoA reductase is involved in preimplantation development is unknown. HIPPO signaling regulates specification of the trophectoderm lineage of the mouse blastocyst by controlling the nuclear localization of YAP. In human cell lines, the mevalonate pathway regulates YAP to mediate self-renewal and survival through geranylgeranylation of RHO proteins. These studies suggest that in preimplantation development, statins may act through HIPPO pathway to interfere with trophectoderm specification and thereby inhibit blastocyst formation.

STUDY DESIGN, SAMPLES/MATERIALS, METHODS

Eight-cell stage (E2.5) mouse embryos were treated in hanging drop culture with chemical agents, namely statins (lovastatin, atorvastatin, cerivastatin and pravastatin), mevalonic acid (MVA), cholesterol, squalene, farnesyl pyrophosphate (FPP), geranylgeranyl pyrophosphate (GGPP), geranylgeranyltransferase inhibitor GGTI-298, RHO inhibitor I, and squalene synthase inhibitor YM-53601, up to the late blastocyst stage (E4.5). Efficiency of blastocyst formation was assessed based on gross morphology and the measurement of the cavity size using an image analysis software. Effects on cell lineages and HIPPO signaling were analyzed using immunohistochemistry with confocal microscopy based on the expression patterns of the lineage-specific markers and the nuclear accumulation of YAP. Effects on cell lineages were also examined by quantitative RT-PCR based on the transcript levels of the lineage-specific marker genes. Data were analyzed using one-way ANOVA and two-sample t-test.

MAIN RESULTS AND THE ROLE OF CHANCE

All four statins examined inhibited blastocyst formation. The adverse impact of statins was rescued by supplementation of MVA (P < 0.01) or GGPP (P < 0.01) but not squalene nor cholesterol. Blastocyst formation was also prevented by GGTI-298 (P < 0.01). These results indicate that HMG-CoA reductase activity is required for blastocyst formation mainly through the production of GGPP but not cholesterol. Inhibition of RHO proteins, known targets of geranylgeranylation, impaired blastocyst formation, which was not reversed by GGPP supplementation. Nuclear localization of YAP was diminished by statin treatment but fully restored by supplementation of MVA (P < 0.01) or GGPP (P < 0.01). This suggests that HIPPO signaling is regulated by GGPP-dependent mechanisms, possibly geranylgeranylation of RHO, to enable trophectoderm formation. YM-53601 prevented blastocyst formation (P < 0.01), but its adverse impact was not rescued by supplementation of squalene or cholesterol, suggesting that squalene synthesis inhibition was not the cause of blastocyst defects.

LIMITATIONS, REASONS FOR CAUTION

Analyses were conducted on embryos cultured ex vivo, but they enable the determination of specific concentrations that impair embryo development which can be compared with drug concentrations in the reproductive tract when testing in vivo impact of statins through animal experimentations. Also, analyses were conducted in only one species, the mouse. Epidemiological studies on the effects of various types of statins on the fertility of women are necessary.

WIDER IMPLICATIONS OF THE FINDINGS

Our study reveals how the mevalonate pathway is required for blastocyst formation and intersects with HIPPO pathway to provide a mechanistic basis for the embryotoxic effect of statins. This bears relevance for women who are taking statins while trying to conceive, since statins have potential to prevent the conceptus from reaching the blastocyst stage and to cause early conceptus demise.

LARGE SCALE DATA

Not applicable.

STUDY FUNDING AND COMPETING INTERESTS

This study was supported by grants from the George F. Straub Trust of the Hawaii Community Foundation (13ADVC-60315 to V.B.A.) and the National Institutes of Health, USA (P20GM103457 to V.B.A.). The authors have no conflict of interest to declare.

Targeting cellular squalene synthase, an enzyme essential for cholesterol biosynthesis, is a potential antiviral strategy against hepatitis C virus

Hepatitis C virus (HCV) exploits host membrane cholesterol and its metabolism for progeny virus production. Here, we examined the impact of targeting cellular squalene synthase (SQS), the first committed enzyme for cholesterol biosynthesis, on HCV production. By using the HCV JFH-1 strain and human hepatoma Huh-7.5.1-derived cells, we found that the SQS inhibitors YM-53601 and zaragozic acid A decreased viral RNA, protein, and progeny production in HCV-infected cells without affecting cell viability. Similarly, small interfering RNA (siRNA)-mediated knockdown of SQS led to significantly reduced HCV production, confirming the enzyme as an antiviral target. A metabolic labeling study demonstrated that YM-53601 suppressed the biosynthesis of cholesterol and cholesteryl esters at antiviral concentrations. Unlike YM-53601, the cholesterol esterification inhibitor Sandoz 58-035 did not exhibit an antiviral effect, suggesting that biosynthesis of cholesterol is more important than that of cholesteryl esters for HCV production. YM-53601 inhibited transient replication of a JFH-1 subgenomic replicon and entry of JFH-1 pseudoparticles, suggesting that at least suppression of viral RNA replication and entry contributes to the antiviral effect of the drug. Collectively, our findings highlight the importance of the cholesterol biosynthetic pathway in HCV production and implicate SQS as a potential target for antiviral strategies against HCV.

IMPORTANCE

Hepatitis C virus (HCV) is known to be closely associated with host cholesterol and its metabolism throughout the viral life cycle. However, the impact of targeting cholesterol biosynthetic enzymes on HCV production is not fully understood. We found that squalene synthase, the first committed enzyme for cholesterol biosynthesis, is important for HCV production, and we propose this enzyme as a potential anti-HCV target. We provide evidence that synthesis of free cholesterol is more important than that of esterified cholesterol for HCV production, highlighting a marked free cholesterol dependency of HCV production. Our findings also offer a new insight into a role of the intracellular cholesterol pool that is coupled to its biosynthesis in the HCV life cycle.

Targeting cholesterol synthesis increases chemoimmuno-sensitivity in chronic lymphocytic leukemia cells

Background

Cholesterol plays an important role in cancer development, drug resistance and chemoimmuno-sensitivity. Statins, cholesterol lowering drugs, can induce apoptosis, but also negatively interfere with CD-20 and rituximab-mediated activity. Our goal is to identify the alternative targets that could reduce cholesterol levels but do not interfere with CD-20 in chemo immunotherapy of chronic lymphocytic leukemia (CLL).

Methods

MEC-2 cells, a CLL cell line, and the peripheral blood mononuclear cells (PBMCs) from CLL patients were treated with cholesterol lowering agents, and analyzed the effect of these agents on cholesterol levels, CD-20 expression and distribution, and cell viability in the presence or absence of fludarabine, rituximab or their combinations.

Results

We found that MEC-2 cells treated with cholesterol lowering agents (BIBB-515, YM-53601 or TAK-475) reduced 20% of total cellular cholesterol levels, but also significantly promoted CD-20 surface expression. Furthermore, treatment of cells with fludarabine, rituximab or their combinations in the presence of BIBB-515, YM-53601 or TAK-475 enhanced MEC-2 cell chemoimmuno-sensitivity measured by cell viability. More importantly, these cholesterol lowering agents also significantly enhanced chemoimmuno-sensitivity of the PBMCs from CLL patients.

Conclusion

Our data demonstrate that BIBB-515, YM53601 and TAK-475 render chemoimmuno-therapy resistant MEC-2 cells sensitive to chemoimmuno-therapy and enhance CLL cell chemoimmuno-sensitivity without CD-20 epitope presentation or its downstream signaling. These results provide a novel strategy which could be applied to CLL treatment.

Triglyceride-lowering agents

This review is the first attempt at systematization of the literature data on the structures and activities of triglyceride-lowering agents which used in medical practice or are in development. The effects and mechanisms of action of statins, squalene synthase inhibitors, fibrates, PPARα and PPARα/γ agonists, nicotinic acid, omega-3 fatty acids and some other molecular targets were considered. Unfortunately, to date, harmless and effective triglyceride-lowering drug still does not exist and there is still need for development of better triglyceride-lowering agents.

Design, synthesis and biological evaluation of WC-9 analogs as antiparasitic agents

As a part of our project pointed at the search of new safe chemotherapeutic and chemoprophylactic agents against parasitic diseases, several compounds structurally related to 4-phenoxyphenoxyethyl thiocyanate (WC-9), which were modified at the terminal aromatic ring, were designed, synthesized and evaluated as antiproliferative agents against Trypanosoma cruzi, the parasite responsible of American trypanosomiasis (Chagas disease) and Toxoplasma gondii, the etiological agent of toxoplasmosis. Most of the synthetic analogs exhibited similar antiparasitic activity being slightly more potent than the reference compound WC-9. For example, the nitro derivative 13 showed an ED₅₀ value of 5.2 μM. Interestingly, the regioisomer of WC-9, compound 36 showed similar inhibitory action than WC-9 indicating that para-phenyl substitution pattern is not necessarily required for biological activity. The biological evaluation against T. gondii was also very promising. The ED₅₀ values corresponding for 13, 36 and 37 were at the very low micromolar level against tachyzoites of T. gondii.

Mutant p53 disrupts mammary tissue architecture via the mevalonate pathway

p53 is a frequent target for mutation in human tumors, and mutant p53 proteins can actively contribute to tumorigenesis. We employed a three-dimensional culture model in which nonmalignant breast epithelial cells form spheroids reminiscent of acinar structures found in vivo, whereas breast cancer cells display highly disorganized morphology. We found that mutant p53 depletion is sufficient to phenotypically revert breast cancer cells to a more acinar-like morphology. Genome-wide expression analysis identified the mevalonate pathway as significantly upregulated by mutant p53. Statins and sterol biosynthesis intermediates reveal that this pathway is both necessary and sufficient for the phenotypic effects of mutant p53 on breast tissue architecture. Mutant p53 associates with sterol gene promoters at least partly via SREBP transcription factors. Finally, p53 mutation correlates with highly expressed sterol biosynthesis genes in human breast tumors. These findings implicate the mevalonate pathway as a therapeutic target for tumors bearing mutations in p53.

Squalene monooxygenase – a target for hypercholesterolemic therapy

Squalene monooxygenase catalyzes the epoxidation of C-C double bond of squalene to yield 2,3-oxidosqualene, the key step of sterol biosynthesis pathways in eukaryotes. Sterols are essential compounds of these organisms and squalene epoxidation is an important regulatory point in their synthesis. Squalene monooxygenase downregulation in vertebrates and fungi decreases synthesis of cholesterol and ergosterol, respectively, which makes squalene monooxygenase a potent and attractive target of hypercholesterolemia and antifungal therapies. Currently some fungal squalene monooxygenase inhibitors (terbinafine, naftifine, butenafine) are in clinical use, whereas mammalian enzymes’ inhibitors are still under investigation. Research on new squalene monooxygenase inhibitors is important due to the prevalence of hypercholesterolemia and the lack of both sufficient and safe remedies. In this paper we (i) review data on activity and the structure of squalene monooxygenase, (ii) present its inhibitors, (iii) compare current strategies of lowering cholesterol level in blood with some of the most promising strategies, (iv) underline advantages of squalene monooxygenase as a target for hypercholesterolemia therapy, and (v) discuss safety concerns about hypercholesterolemia therapy based on inhibition of cellular cholesterol biosynthesis and potential usage of squalene monooxygenase inhibitors in clinical practice. After many years of use of statins there is some clinical evidence for their adverse effects and only partial effectiveness. Currently they are drugs of choice but are used with many restrictions, especially in case of children, elderly patients and women of childbearing potential. Certainly, for the next few years, statins will continue to be a suitable tool for cost-effective cardiovascular prevention; however research on new hypolipidemic drugs is highly desirable. We suggest that squalene monooxygenase inhibitors could become the hypocholesterolemic agents of the future.

Squalene monooxygenase - a target for hypercholesterolemic therapy

Squalene monooxygenase catalyzes the epoxidation of C-C double bond of squalene to yield 2,3-oxidosqualene, the key step of sterol biosynthesis pathways in eukaryotes. Sterols are essential compounds of these organisms and squalene epoxidation is an important regulatory point in their synthesis. Squalene monooxygenase downregulation in vertebrates and fungi decreases synthesis of cholesterol and ergosterol, respectively, which makes squalene monooxygenase a potent and attractive target of hypercholesterolemia and antifungal therapies. Currently some fungal squalene monooxygenase inhibitors (terbinafine, naftifine, butenafine) are in clinical use, whereas mammalian enzymes' inhibitors are still under investigation. Research on new squalene monooxygenase inhibitors is important due to the prevalence of hypercholesterolemia and the lack of both sufficient and safe remedies. In this paper we (i) review data on activity and the structure of squalene monooxygenase, (ii) present its inhibitors, (iii) compare current strategies of lowering cholesterol level in blood with some of the most promising strategies, (iv) underline advantages of squalene monooxygenase as a target for hypercholesterolemia therapy, and (v) discuss safety concerns about hypercholesterolemia therapy based on inhibition of cellular cholesterol biosynthesis and potential usage of squalene monooxygenase inhibitors in clinical practice. After many years of use of statins there is some clinical evidence for their adverse effects and only partial effectiveness. Currently they are drugs of choice but are used with many restrictions, especially in case of children, elderly patients and women of childbearing potential. Certainly, for the next few years, statins will continue to be a suitable tool for cost-effective cardiovascular prevention; however research on new hypolipidemic drugs is highly desirable. We suggest that squalene monooxygenase inhibitors could become the hypocholesterolemic agents of the future.

Emerging options in the treatment of dyslipidemias: a bright future?

INTRODUCTION

Hypercholesterolemia is a major risk factor for cardiovascular disease (CVD). Low-density lipoprotein cholesterol (LDL-C) reduction has been demonstrated to decrease CVD-related morbidity and mortality. However, several patients do not reach LDL-C target levels with the currently available lipid lowering agents, particularly statins. Lipid and non-lipid parameters other than LDL-C may account for the residual CVD risk after adequate LDL-C lowering with statins.

AREAS COVERED

This review focuses on the efficacy and safety of emerging drugs aiming at high-density lipoprotein cholesterol (HDL-C) elevation (i.e., recombinant or plasma-derived wild-type apolipoprotein (apo) A-I, apo A-I mimetic peptides, reconstituted mutant HDL, partially delipidated HDL and cholesterol ester transfer protein inhibitors), microsomal triglyceride transfer protein inhibitors and antisense oligonucleotides.

EXPERT OPINION

Several lipid modifying agents in development may potently reduce the residual CVD risk. Ongoing and future studies with clinical outcomes will clarify their efficacy in clinical practice.

Pharmacologic inhibition of squalene synthase and other downstream enzymes of the cholesterol synthesis pathway: a new therapeutic approach to treatment of hypercholesterolemia

Hypercholesterolemia is a major risk factor for the development of atherosclerotic vascular diseases. The most popular agents for cholesterol reduction are the statin drugs, which are competitive inhibitors of hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase, the primary rate-limiting enzyme in the hepatic biosynthesis of cholesterol. Although relatively safe and effective, the available statins can cause elevations in liver enzymes and myopathy. Squalene synthase is another enzyme that is downstream to HMG-CoA reductase in the cholesterol synthesis pathway and modulates the first committed step of hepatic cholesterol biosynthesis at the final branch point of the cholesterol biosynthetic pathway. Squalene epoxidase and oxidosqualene cyclase are other enzymes that act distally to squalene synthase. Pharmacologic inhibitors of these downstream enzymes have been developed, which may reduce low-density lipoprotein cholesterol and reduce the myopathy side effect seen with upstream inhibition of HMG-CoA. At this juncture, one squalene synthase inhibitor, lapaquistat (TAK-475) is in active clinical trials as a monotherapy, but there have been suggestions of increased hepatotoxicity with the drug.

Other therapies for reducing low-density lipoprotein cholesterol: medications in development

Although the past 30 years have been fruitful and productive in lipid research, from basic science to drug development to demonstration of clinical benefit, cardiovascular disease remains the major cause of mortality and morbidity in industrialized societies. With the rapid industrialization of countries, such as India and China, cardiovascular disease rapidly is becoming the leading cause of global death and disability. Although most of the effective lipid-lowering drugs, the statins, have become generic and inexpensive, there remains a need for effective and safe agents. Hopefully, some of those discussed in this article will fill that need.

Current and future pharmacologic options for the management of patients unable to achieve low-density lipoprotein-cholesterol goals with statins

Low-density lipoprotein-cholesterol (LDL-C) lowering is the mainstay of the current treatment guidelines in the management of cardiovascular risk. HMG-CoA reductase inhibitors (statins) are currently the most effective LDL-C-lowering drugs. However, a substantial number of patients do not reach treatment targets with statins. Therefore, an unmet medical need exists for lipid-lowering drugs with novel mechanisms of action to reach the recommended cholesterol target levels, either by monotherapy or combination therapy. Upregulation of the LDL receptor with squalene synthase inhibitors has shown promising results in animal studies but the clinical development of the lead compound lapaquistat (TAK-475) has recently been discontinued. Ezetimibe combined with statins allowed significantly more patients to reach their LDL-C targets. Other inhibitors of intestinal cholesterol absorption such as disodium ascorbyl phytostanol phosphate (FM-VP4) and bile acid transport inhibitors have shown positive results in early development trials, whereas the prospect of acyl coenzyme A: cholesterol acyltransferase inhibition in cardiovascular prevention is dire. Selective inhibition of messenger RNA (mRNA) by antisense oligonucleotides is a new approach to modify cholesterol levels. The inhibition of apolipoprotein B mRNA is in advanced development and mipomersen sodium (ISIS 301012) has shown striking results in phase II studies both as monotherapy as well as in combination with statins.

Hepatitis B virus infection is dependent on cholesterol in the viral envelope

The viral and cellular determinants leading to binding and entry of hepatitis B virus (HBV) are still not fully understood. We found that HBV infection of primary hepatocyte cultures is dependent on the presence of cholesterol in the viral envelope. Extraction of cholesterol from HBV purified from plasma of HBV-infected patients with methyl-beta-cyclodextrin (MbetaCD) leads to a strongly reduced level of infection. The cholesterol-depleted virions showed higher buoyant density (1.23 versus 1.17 g ml(-1)), a smaller diameter (39 versus 48 nm), but maintained particle integrity, antigenicity and ability to bind to hepatocytes. Although addition of exogenous cholesterol and cholesterol analogues restored the physical appearance of cholesterol-depleted virions, infectivity was only regained by cholesterol add-back. Infectivity of HBV produced from cell culture in the presence of inhibitors of cholesterol-synthesis is severely impaired. Interestingly, cholesterol extraction from cellular membranes, incubation with filipin and the protein tyrosine kinase inhibitor genistein showed no effect on HBV infection, excluding a role of lipid rafts for the infection process of HBV. In summary, presence of cholesterol within the viral envelope is not important for viral binding, but indispensable for the entry process of HBV and might be important for a later step in viral uptake, e.g. fusion in a yet unknown compartment.

Regulation of cholesterologenesis by the oxysterol receptor, LXRalpha

Cholesterol is required for normal cellular and physiological function, yet dysregulation of cholesterol metabolism is associated with diseases such as atherosclerosis. Cholesterol biosynthesis is regulated by end product negative feedback inhibition where the levels of sterols and oxysterols regulate the expression of cholesterologenic enzymes. Sterol regulatory element-binding protein-2 is responsive to both sterols and oxysterols and has been shown to mediate the transcriptional response of the cholesterologenic enzymes to these lipids. Here, we show that the nuclear hormone receptor for oxysterols, the liver X receptor alpha (LXRalpha), regulates cholesterol biosynthesis by directly silencing the expression of two key cholesterologenic enzymes (lanosterol 14alpha-demethylase (CYP51A1), and squalene synthase (farnesyl diphosphate farnesyl transferase 1)) via novel negative LXR DNA response elements (nLXREs) located in each of these genes. Examination of the CYP51A1 gene revealed that both the SRE and nLXRE are required for normal oxysterol-dependent repression of this gene. Thus, these data suggest that LXRalpha plays an important role in the regulation of cholesterol biosynthesis.

Farnesol decreases serum triglycerides in rats: identification of mechanisms including up-regulation of PPARalpha and down-regulation of fatty acid synthase in hepatocytes

Obesity is associated with impaired fatty acid (FA) oxidation and increased de novo hepatic lipogenesis that may contribute to the development of hypertriglyceridemia, an important risk factor for the development of cardiovascular disease. Strategies to improve hepatocyte FA metabolism, including dietary interventions, are therefore important for the prevention of obesity-associated co-morbidities. Farnesol is consumed in the diet as a component of plant products. In the present study, we administered farnesol orally to rats for seven days and found significantly reduced serum triglyceride concentrations compared with controls. Potential mechanisms underlying the hypotriglyceridemic effect of farnesol were investigated using clone-9 cultured rat hepatocytes. Farnesol significantly upregulated expression of peroxisome proliferator-activated receptor alpha (PPARalpha) and the PPARalpha-regulated genes fatty acyl-CoA oxidase and carnitine palmitoyl transferase 1a, suggesting that increased hepatic FA oxidation may contribute to serum triglyceride lowering in rats. Farnesol did not change SREBP-1c mRNA levels, but significantly down-regulated fatty acid synthase (FAS) mRNA and protein levels and activity, indicating that attenuated lipogenesis may also contribute to hypotriglyceridemic effects of farnesol in vivo. Rescue experiments revealed that down-regulation of FAS by farnesol was not related to activation of PPARalpha, but rather was caused by a 9-cis retinoic acid mediated mechanism that involved down-regulation of retinoid X receptor beta. Diets rich in plant products are associated with a lower risk of cardiovascular disease. Our findings suggest that farnesol may contribute to this protective effect by lowering serum TG levels.

Identification of a chromosome 8p locus for early-onset coronary heart disease in a French Canadian population

Susceptibility to coronary heart disease (CHD) has long been known to exhibit familial aggregation, with heritability estimated to be greater than 50%. The French Canadian population of the Saguenay-Lac Saint-Jean region of Quebec, Canada is descended from a founder population that settled this region 300-400 years ago and this may provide increased power to detect genes contributing to complex traits such as CHD. Probands with early-onset CHD, defined by angiographically determined coronary stenosis, and their relatives were recruited from this population (average sibship size of 6.4). Linkage analysis was performed following a genome-wide microsatellite marker scan on 42 families with 284 individuals. Nonparametric linkage (NPL) analysis provided suggestive evidence for a CHD susceptibility locus on chromosome 8 with an NPL score of 3.14 (P=0.001) at D8S1106. Linkage to this locus was verified by fine mapping in an enlarged sample of 50 families with 320 individuals. This analysis provided evidence of linkage at D8S552 (NPL score=3.53, P=0.0003), a marker that maps to the same location as D8S1106. Candidate genes in this region, including macrophage scavenger receptor 1, farnesyl-diphosphate farnesyltransferase 1, fibrinogen-like 1, and GATA-binding protein 4, were resequenced in all coding exons in both affected and unaffected individuals. Association studies with variants in these and five other genes did not identify a disease-associated mutation. In conclusion, a genome-wide scan and additional fine mapping provide evidence for a locus on chromosome 8 that contributes to CHD in a French Canadian population.

The biology and chemistry of hyperlipidemia

Coronary arterial diseases are responsible for more deaths than all other associated causes combined. Elevated serum cholesterol levels leading to atherosclerosis can cause coronary heart disease (CHD). Reduction in serum cholesterol levels reduces the risk for CHD, substantially. Medicinal chemists all around the world have been designing, synthesizing, and evaluating a variety of new bioactive molecules for lowering lipid levels. This review summarizes the disorders associated with elevation of lipids in blood and the current strategies to control them. The emphasis has been laid in particular on the new potential biological targets and the possible treatments as well as the current ongoing research status in the field of lipid lowering agents.

Visceral obesity is associated with high levels of serum squalene

OBJECTIVE

To investigate the impact of visceral obesity on cholesterol metabolism in normoglycemic offspring of patients with type 2 diabetes.

RESEARCH METHODS AND PROCEDURES

The proportion of intra-abdominal fat (IAF) was measured by abdominal computer tomography, and serum cholesterol synthesis and absorption markers were determined by gas-liquid chromatography in 109 normoglycemic offspring of patients with type 2 diabetes. Insulin action was measured with the hyperinsulinemic euglycemic clamp. The gene encoding squalene synthase (farnesyl-diphosphate farnesyltransferase 1) was screened with the single-strand conformation polymorphism analysis and direct sequencing.

RESULTS

Cholesterol synthesis markers correlated positively with IAF (r = 0.213 to 0.309, p < or = 0.027) and negatively with the rates of insulin-stimulated whole-body glucose uptake (r = -0.372 to -0.248, p < or = 0.010). However, serum squalene, the first measured precursor of cholesterol synthesis, showed a positive correlation with IAF (r = 0.309, p = 0.001) without any association with subcutaneous fat or insulin sensitivity. Variation in the farnesyl-diphosphate farnesyltransferase 1 gene did not explain elevated serum squalene levels in viscerally obese subjects. From the cholesterol absorption markers, cholestanol was associated negatively with IAF and positively with whole-body glucose uptake (p < 0.05).

DISCUSSION

High serum squalene levels are associated with visceral obesity but not with subcutaneous obesity. Whether this finding is causally connected to visceral obesity remains to be established.

Pharmacological characterization in vitro of EP2306 and EP2302, potent inhibitors of squalene synthase and lipid biosynthesis

We investigated the effects of EP2306 and EP2302, two novel 2-biphenylmorpholine derivatives, on squalene synthase activity in rabbit and human liver microsomes, lipid biosynthesis, low-density lipoprotein (LDL) receptor expression and LDL protein uptake as well as apoB secretion in HepG2 cells. Both EP2306 and EP2302 inhibited squalene synthase activity dose-dependently. In rabbit liver microsomes, the IC50 values were 33 microM for EP2306 and 0.6 microM for EP2302 whereas in human liver microsomes, they were 63 microM for EP2306 and 1 microM for EP2302. Both EP2300 compounds inhibited cholesterol production by HepG2 cells dose dependently with IC50 values of 13.3 microM for EP2306 and 3 microM for EP2302. Furthermore, both EP2300 compounds and simvastatin significantly reduced triglyceride synthesis and apoB secretion and increased LDL receptor expression and LDL uptake in HepG2 cells. In summary, we have shown that EP2300 compounds are potent inhibitors of squalene synthase activity in rabbit and human liver microsomes and also they are effective inhibitors of cholesterol and triglyceride biosynthesis in HepG2 cells. These results suggest that EP2306 and EP2302 might prove to be useful for lipid-lowering and treatment of atherosclerosis in vivo.

New lipid-lowering agents

Lipid-lowering is established as a proven intervention to reduce atherosclerosis and its complications. This article summarises imminent developments in lipid-lowering therapy, including new statins and cholesterol absorption inhibitors currently undergoing investigation for licensing. It also discusses other therapeutic targets such as squalene synthase, microsomal transfer protein (MTP), acyl-cholesterol acyl transferase (ACAT), cholesterol ester transfer protein (CETP), peroxosimal proliferator activating receptors (PPARs) and lipoprotein (a) (LP(a)), for which compounds have been developed and have at least reached trials in animal models. Lipid-lowering drugs are likely to prove a fast-developing area for novel treatments, as possible synergies exist between new and established compounds for the treatment of atherosclerosis.

Lipid-lowering therapies in development

Lipid lowering is established as a proven intervention to reduce atherosclerosis and its complications. This article summarises novel developments in the lipid-altering therapies under development, including combination therapies, squalene synthase inhibitors, microsomal transfer protein inhibitors, acyl-cholesterol acyl transferase inhibitors, cholesterol ester transfer protein antagonists, peroxisome proliferator-activated receptor agonists, high-density lipoprotein-derived peptides and inflammation inhibitors, which have at least reached trials in animal models. Lipid-altering drugs are likely to to be a fast-developing area for novel treatments as possible synergies exist between new and established compounds for the treatment of atherosclerosis. New agents will have to show significant advantage in tolerability or efficacy over existing agents and have the potential to be used in combination therapy as is well established for bile acid sequestrants, nicotinic acid or fibrates and statins. Any new drugs will also have to be assessed in clinical end-point trials against current compounds with proven outcome benefits.

Lipid-altering agents: the future

Lipid-lowering is established as proven intervention to reduce atherosclerosis and its complications. This article summarises novel developments in the lipid-altering therapies under development. It also discusses other therapeutic targets, such as squalene synthase, microsomal transfer protein, acyl-cholesterol acyl transferase, cholesterol ester transfer protein, peroxosimal proliferator-activating receptors and lipoprotein (a), for which compounds have been developed and have at least reached trials in animal models. Lipid-altering drugs are likely to prove a fast-developing area for novel treatments, as possible synergies exist between new and established compounds for the treatment of atherosclerosis.

Guinea pigs as models to study the hypocholesterolemic effects of drugs

Guinea pigs are useful models to investigate the mechanisms of the hypocholesterolemic effects of drugs. Like humans, guinea pigs are one of the few species that carry the majority of cholesterol in LDL. This animal model has also been shown to develop atherosclerosis when challenged with hypercholesterolemic diets. In addition, plasma lipid profiles in males, females and ovariectomized guinea pigs, a model for menopause, follow similar patterns to those observed in humans. In this report, drugs aimed at lowering plasma cholesterol and triglycerides in hyperlipidemic individuals are reviewed. Studies analyzing the hypolipidemic effect of HMG-CoA reductase inhibitors, acyl CoA cholesterol acyltransferase inhibitors, fibrates, bile acid resins, apical sodium bile acid transporter inhibitors, and others show that guinea pigs and humans have comparable responses to drug therapy. In addition, results from the limited clinical reports addressing specific effects of drugs on LDL catabolism or VLDL synthesis are in agreement with observations in guinea pigs. From the review of these studies, it is apparent that the guinea pig is a useful animal model to further explore the mechanisms of action of lipid lowering drugs including effects on specific receptors and regulatory enzymes involved in cholesterol metabolism and on early atherosclerosis development.

ABBREVIATIONS

ACAT, acyl-CoA:cholesterol acyltransferase; ASBT, apical sodium co-dependent bile acid transporter; ApoB, apolipoprotein B; CHD, coronary heart disease; CYP7, cholesterol 7alpha-hydroxylase; HDL, high density lipoprotein; HMG-CoA, 3-hydroxy-3-methylglutaryl coenzyme A; FCR, free catabolic rate; LDL, low density lipoprotein; PPAR, peroxisome proliferators-activated receptor; TC, total cholesterol; TG, triglycerides; VLDL, very low density lipoprotein.

In vitro and in vivo activities of E5700 and ER-119884, two novel orally active squalene synthase inhibitors, against Trypanosoma cruzi

Chagas' disease is a serious public health problem in Latin America, and no treatment is available for the prevalent chronic stage. Its causative agent, Trypanosoma cruzi, requires specific endogenous sterols for survival, and we have recently demonstrated that squalene synthase (SQS) is a promising target for antiparasitic chemotherapy. E5700 and ER-119884 are quinuclidine-based inhibitors of mammalian SQS that are currently in development as cholesterol- and triglyceride-lowering agents in humans. These compounds were found to be potent noncompetitive or mixed-type inhibitors of T. cruzi SQS with K(i) values in the low nanomolar to subnanomolar range in the absence or presence of 20 microM inorganic pyrophosphate. The antiproliferative 50% inhibitory concentrations of the compounds against extracellular epimastigotes and intracellular amastigotes were ca. 10 nM and 0.4 to 1.6 nM, respectively, with no effects on host cells. When treated with these compounds at the MIC, all of the parasite's sterols disappeared from the parasite cells. In vivo studies indicated that E5700 was able to provide full protection against death and completely arrested the development of parasitemia when given at a concentration of 50 mg/kg of body weight/day for 30 days, while ER-119884 provided only partial protection. This is the first report of an orally active SQS inhibitor that is capable of providing complete protection against fulminant, acute Chagas' disease.

Modulateurs du métabolisme du cholestérol et avenir du traitement de l’athérosclérose

Atherosclerosis is a disease characterized by lipid accumulation in the vascular wall leading to myocardial infarction or stroke. Hypercholesterolemia is an important risk factor and current treatments are largely based on cholesterol lowering. In spite of proven efficacy of existing drugs, like statins, cardiovascular diseases still remain the most common cause of death in industrialised countries. Many new molecular targets are being studied to improve atherosclerosis treatment and reduce the number of deaths. The action on these targets could lead to a decrease of blood cholesterol levels or produce a direct anti-atherosclerotic effect on the vascular wall. A cholesterol lowering effect could be achieved by reducing cholesterol synthesis (squalene synthase inhibitors), intestinal cholesterol absorption as well as intestinal and liver lipoprotein secretion (microsomal transfer protein inhibitors, acyl-coenzyme A-cholesterol acyltransferase inhibitors) or by increasing fecal excretion of bile acids (ileal sodium-dependent bile acid transporter inhibitors). An anti-atherosclerotic effect on the vascular wall could be achieved by reducing the inflammation via activation of peroxisome proliferator activated receptors, or, more particularly, could consist of decreased expression of adhesion molecules and chemoattractant proteins. Increasing the adenosine triphosphate-binding cassette A1 protein and inhibiting acyl-coenzyme A :cholesterol acyltransferase 1 activity could slow down formation of foam cells, which are a hallmark of atherosclerosis. Finally, the cholesterol fraction carried by high density lipoproteins, which is inversely correlated to cardiovascular risk, could be increased by cholesterol ester transfer protein inhibitors. All of these new classes of compounds are currently studied by pharmaceutical companies and are in different phases of development (preclinical or clinical).

Syntheses of 3-ethylidenequinuclidine derivatives as squalene synthase inhibitors. Part 2: enzyme inhibition and effects on plasma lipid levels

Squalene synthase (E.C. 2.5.1.21) is a microsomal enzyme which catalyzes the reductive dimerization of two molecules of farnesyl diphosphate to form squalene, and is involved in the first committed step in cholesterol biosynthesis. It is an attractive target for hypocholesterolemic and hypotriglyceridemic strategies. We synthesized a series of 3-ethylidenequinuclidine derivatives, and evaluated their ability to inhibit squalene synthase in vitro and to lower non-HDL cholesterol levels in hamsters. 3-Ethylidenequinuclidine derivatives incorporating an unsubstituted 9H-carbazole moiety reduced plasma non-HDL cholesterol levels and did not affect plasma transaminase levels, indicating a lack of hepatotoxicity. Among the novel compounds, (Z)-2-[2-(quinuclidin-3-ylidene)ethoxy]-9H-carbazole hydrochloride 8 (YM-53579) and (E)-2-[2-fluoro-2-(quinuclidin-3-ylidene)ethoxy]-9H-carbazole hydrochloride 28 (YM-53601) were potent inhibitors of squalene synthase derived from human hepatoma cells, with IC(50) values of 160 and 79 nM, respectively. They also reduced plasma non-HDL cholesterol levels in hamsters by approximately 50 and 70%, respectively, at an oral dose of 50 mg/kg/day for 5 days.

Lipid-lowering properties of TAK-475, a squalene synthase inhibitor, in vivo and in vitro

1. Squalene synthase is the enzyme that converts farnesyl pyrophosphate to squalene in the cholesterol biosynthesis pathway. We examined the lipid-lowering properties of 1-[[(3R,5S)-1-(3-acetoxy-2,2-dimethylpropyl)-7-chloro-5-(2,3-dimethoxyphenyl)-2-oxo-1,2,3,5-tetrahydro-4,1-benzoxazepin-3-yl]acetyl]piperidine-4-acetic acid (TAK-475), a novel squalene synthase inhibitor. 2. TAK-475 inhibited hepatic cholesterol biosynthesis in rats (ED(50), 2.9 mg kg(-1)) and showed lipid-lowering effects in beagle dogs, marmosets, cynomolgus monkeys and Wistar fatty rats. 3. In marmosets, TAK-475 (30, 100 mg kg(-1), p.o., for 4 days) lowered both plasma non-high-density lipoprotein (HDL) cholesterol and triglyceride, but did not affect plasma HDL cholesterol. On the other hand, atorvastatin (10, 30 mg kg(-1), p.o., for 4 days) lowered the levels of all these lipids. A correlation between decrease in triglyceride and increase in HDL cholesterol was observed, and TAK-475 increased HDL cholesterol with a smaller decrease in triglyceride than did atorvastatin. 4. TAK-475 (60 mg kg(-1), p.o., for 15 days) suppressed the rate of triglyceride secretion from the liver in hypertriglyceridemic Wistar fatty rats, which show an enhanced triglyceride secretion rate from the liver compared with their lean littermates. 5. In HepG2 cells, TAK-475 and its pharmacologically active metabolite, T-91485, increased the binding of (125)I-low-density lipoprotein (LDL) to LDL receptors. 6. These results suggest that TAK-475 has clear hypolipidemic effects in animals via inhibition of hepatic triglyceride secretion and upregulation of LDL receptors, and that TAK-475 might increase HDL cholesterol by decreasing triglyceride. Thus, TAK-475 is expected to be useful for the treatment of dyslipidemia.

Mechanism of action of 4-phenoxyphenoxyethyl thiocyanate (WC-9) against Trypanosoma cruzi, the causative agent of Chagas' disease

We investigated the molecular basis of the activity of 4-phenoxyphenoxyethyl thiocyanate (WC-9) against Trypanosoma cruzi, the etiological agent of Chagas' disease. We found that growth inhibition of T. cruzi epimastigotes induced by this compound was associated with a reduction in the content of the parasite's endogenous sterols due to a specific blockade of their de novo synthesis at the level of squalene synthase.

YM-53601, a novel squalene synthase inhibitor, suppresses lipogenic biosynthesis and lipid secretion in rodents

1. To better understand how it decreases plasma cholesterol and triglyceride levels, we evaluated the effect of (E)-2-[2-fluoro-2-(quinuclidin-3-ylidene)ethoxy]-9H-carbazole monohydrochloride(YM-53601) on lipogenic biosynthesis in the liver and lipid secretion from the liver in rats and hamsters. 2. Single administration of YM-53601 in cholestyramine-treated rats inhibited triglyceride and free fatty acid (FFA) biosynthesis at a similar dose range to that at which it inhibited cholesterol biosynthesis. YM-53601 inhibited both triglyceride and FFA biosynthesis in hamsters treated with cholestyramine. 3. YM-53601 by single oral administration decreased the enhanced plasma triglyceride levels in hamsters induced by an injection of protamine sulfate, which inhibits lipoprotein lipase (LPL) and consequently increases plasma very low-density lipoprotein (VLDL) triglyceride levels. YM-53601 also decreased the enhanced plasma triglyceride and cholesterol levels in hamsters treated with Triton WR1339, which also inhibits the degradation of VLDL. Plasma cholesterol was significantly decreased as soon as 1 h after single administration of YM-53601 in hamsters fed a normal diet. 4. This is the first report that a squalene synthase inhibitor suppresses lipogenic biosynthesis in the liver and cholesterol and triglyceride secretion from the liver in vivo. We therefore suggest that the mechanism by which YM-53601 decreases plasma triglyceride might include these effects. The finding that YM-53601 rapidly decreased plasma cholesterol suggests that this compound may be effective in decreasing plasma cholesterol levels early in the course of treatment of hypercholesterolemia in humans.