Dalcetrapib and anacetrapib increase apolipoprotein E-containing HDL in rabbits and humans

The large HDL particles generated by administration of cholesteryl ester transfer protein inhibitors (CETPi) remain poorly characterized, despite their potential importance in the routing of cholesterol to the liver for excretion, which is the last step of the reverse cholesterol transport. Thus, the effects of the CETPi dalcetrapib and anacetrapib on HDL particle composition were studied in rabbits and humans. The association of rabbit HDL to the LDL receptor (LDLr) in vitro was also evaluated. New Zealand White rabbits receiving atorvastatin were treated with dalcetrapib or anacetrapib. A subset of patients from the dal-PLAQUE-2 study treated with dalcetrapib or placebo were also studied. In rabbits, dalcetrapib and anacetrapib increased HDL-C by more than 58% (P < 0.01) and in turn raised large apo E-containing HDL by 66% (P < 0.001) and 59% (P < 0.01), respectively. Additionally, HDL from CETPi-treated rabbits competed with human LDL for binding to the LDLr on HepG2 cells more than control HDL (P < 0.01). In humans, dalcetrapib increased concentrations of large HDL particles (+69%, P < 0.001) and apo B-depleted plasma apo E (+24%, P < 0.001), leading to the formation of apo E-containing HDL (+47%, P < 0.001) devoid of apo A-I. Overall, in rabbits and humans, CETPi increased large apo E-containing HDL particle concentration, which can interact with hepatic LDLr. The catabolism of these particles may depend on an adequate level of LDLr to contribute to reverse cholesterol transport.

Red Blood Cell Membrane Cholesterol May Be a Key Regulator of Sickle Cell Disease Microvascular Complications

Cell membrane lipid composition, especially cholesterol, affects many functions of embedded enzymes, transporters and receptors in red blood cells (RBC). High membrane cholesterol content affects the RBCs' main vital function, O₂ and CO₂ transport and delivery, with consequences on peripheral tissue physiology and pathology. A high degree of deformability of RBCs is required to accommodate the size of micro-vessels with diameters significantly lower than RBCs. The potential therapeutic role of high-density lipoproteins (HDL) in the removal of cholesterol and its activity regarding maintenance of an optimal concentration of RBC membrane cholesterol have not been well investigated. On the contrary, the focus for HDL research has mainly been on the clearance of cholesterol accumulated in atherosclerotic macrophages and plaques. Since all interventions aiming at decreasing cardiovascular diseases by increasing the plasma level of HDL cholesterol have failed so far in large outcome studies, we reviewed the potential role of HDL to remove excess membrane cholesterol from RBC, especially in sickle cell disease (SCD). Indeed, abundant literature supports a consistent decrease in cholesterol transported by all plasma lipoproteins in SCD, in addition to HDL, low- (LDL) and very low-density lipoproteins (VLDL). Unexpectedly, these decreases in plasma were associated with an increase in RBC membrane cholesterol. The concentration and activity of the main enzyme involved in the removal of cholesterol and generation of large HDL particles-lecithin cholesterol ester transferase (LCAT)-are also significantly decreased in SCD. These observations might partially explain the decrease in RBC deformability, diminished gas exchange and tendency of RBCs to aggregate in SCD. We showed that incubation of RBC from SCD patients with human HDL or the HDL-mimetic peptide Fx5A improves the impaired RBC deformability and decreases intracellular reactive oxygen species levels. We propose that the main physiological role of HDL is to regulate the cholesterol/phospholipid ratio (C/PL), which is fundamental to the transport of oxygen and its delivery to peripheral tissues.

Inhibition of the 3CL Protease and SARS-CoV-2 Replication by Dalcetrapib

The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) 3CL protease is a promising target for inhibition of viral replication by interaction with a cysteine residue (Cys145) at its catalytic site. Dalcetrapib exerts its lipid-modulating effect by binding covalently to cysteine 13 of a cholesteryl ester transfer protein. Because 12 free cysteine residues are present in the 3CL protease, we investigated the potential of dalcetrapib to inhibit 3CL protease activity and SARS-CoV-2 replication. Molecular docking investigations suggested that dalcetrapib-thiol binds to the catalytic site of the 3CL protease with a delta G value of -8.5 kcal/mol. Dalcetrapib inhibited both 3CL protease activity in vitro and viral replication in Vero E6 cells with IC₅₀ values of 14.4 ± 3.3 μM and an EC₅₀ of 17.5 ± 3.5 μM (mean ± SD). Near-complete inhibition of protease activity persisted despite 1000-fold dilution after ultrafiltration with a nominal dalcetrapib-thiol concentration of approximately 100 times below the IC₅₀ of 14.4 μM, suggesting stable protease-drug interaction. The inhibitory effect of dalcetrapib on the SARS-CoV-2 3CL protease and viral replication warrants its clinical evaluation for the treatment of COVID-19.

Role of Adenylate Cyclase 9 in the Pharmacogenomic Response to Dalcetrapib: Clinical Paradigm and Molecular Mechanisms in Precision Cardiovascular Medicine

Following the neutral results of the dal-OUTCOMES trial, a genome-wide study identified the rs1967309 variant in the adenylate cyclase type 9 (ADCY9) gene on chromosome 16 as being associated with the risk of future cardiovascular events only in subjects taking dalcetrapib, a CETP (cholesterol ester transfer protein) modulator. Homozygotes for the minor A allele (AA) were protected from recurrent cardiovascular events when treated with dalcetrapib, while homozygotes for the major G allele (GG) had increased risk. Here, we present the current state of knowledge regarding the impact of rs1967309 in ADCY9 on clinical observations and biomarkers in dalcetrapib trials and the effects of mouse ADCY9 gene inactivation on cardiovascular physiology. Finally, we present our current model of the interaction between dalcetrapib and ADCY9 gene variants in the arterial wall macrophage, based on the intracellular role of CETP in the transfer of complex lipids from endoplasmic reticulum membranes to lipid droplets. Briefly, the concept is that dalcetrapib would inhibit CETP-mediated transfer of cholesteryl esters, resulting in a progressive inhibition of cholesteryl ester synthesis and free cholesterol accumulation in the endoplasmic reticulum. Reduced ADCY9 activity, by paradoxically leading to higher cyclic AMP levels and in turn increased cellular cholesterol efflux, could impart cardiovascular protection in rs1967309 AA patients. The ongoing dal-GenE trial recruited 6145 patients with the protective AA genotype and will provide a definitive answer to whether dalcetrapib will be protective in this population.

Dalcetrapib and anacetrapib differently impact HDL structure and function in rabbits and monkeys

Inhibition of cholesteryl ester transfer protein (CETP) increases HDL cholesterol (HDL-C) levels. However, the circulating CETP level varies and the impact of its inhibition in species with high CETP levels on HDL structure and function remains poorly characterized. This study investigated the effects of dalcetrapib and anacetrapib, the two CETP inhibitors (CETPis) currently being tested in large clinical outcome trials, on HDL particle subclass distribution and cholesterol efflux capacity of serum in rabbits and monkeys. New Zealand White rabbits and vervet monkeys received dalcetrapib and anacetrapib. In rabbits, CETPis increased HDL-C, raised small and large α-migrating HDL, and increased ABCA1-induced cholesterol efflux. In vervet monkeys, although anacetrapib produced similar results, dalcetrapib caused opposite effects because the LDL-C level was increased by 42% and HDL-C decreased by 48% (P < 0.01). The levels of α- and preβ-HDL were reduced by 16% (P < 0.001) and 69% (P < 0.01), resulting in a decrease of the serum cholesterol efflux capacity. CETPis modulate the plasma levels of mature and small HDL in vivo and consequently the cholesterol efflux capacity. The opposite effects of dalcetrapib in different species indicate that its impact on HDL metabolism could vary greatly according to the metabolic environment.

Cholesteryl ester transfer between lipoproteins does not require a ternary tunnel complex with CETP

The cholesteryl ester transfer protein (CETP) enables the transfer of cholesteryl ester (CE) from high-density lipoproteins (HDL) to low-density lipoproteins (LDL) in the plasma compartment. CETP inhibition raises plasma levels of HDL cholesterol; a ternary tunnel complex with CETP bridging HDL and LDL was suggested as a mechanism. Here, we test whether the inhibition of CETP tunnel complex formation is a promising approach to suppress CE transfer from HDL to LDL, for potential treatment of cardio-vascular disease (CVD). Three monoclonal antibodies against different epitopes of CETP are assayed for their potential to interfere with CE transfer between HDL and/or LDL. Surprisingly, antibodies that target the tips of the elongated CETP molecule, interaction sites sterically required to form the suggested transfer complexes, do not interfere with CETP activity, but an antibody binding to the central region does. We show that CETP interacts with HDL, but not with LDL. Our findings demonstrate that a ternary tunnel complex is not the mechanistic prerequisite to transfer CE among lipoproteins.

Adenylyl Cyclase 9 Polymorphisms Reveal Potential Link to HDL Function and Cardiovascular Events in Multiple Pathologies: Potential Implications in Sickle Cell Disease

Adenylyl cyclase 9 (ADCY9) mediates β2-adrenoceptor (β2-AR) signalling. Both proteins are associated with caveolae, specialized cholesterol-rich membrane substructures. Apolipoprotein A1 (ApoA1), the major protein component of high-density lipoprotein (HDL), removes cholesterol from cell membrane and caveolae and may thereby influence β2-AR signalling, shown in vitro to be modulated by cholesterol. Patients with Sickle Cell Disease (SCD) typically have low HDL and ApoA1 levels. In patients, mainly of African origin, with SCD, β2-AR activation may trigger adhesion of red blood cells to endothelial cells, leading to vascular occlusive events. Moreover, ADCY9 polymorphism is associated with risk of stroke in SCD. In recent clinical trials, ADCY9 polymorphism was found to be a discriminant factor associated with the risk of cardiovascular (CV) events in Caucasian patients treated with the HDL-raising compound dalcetrapib. We hypothesize that these seemingly disparate observations share a common mechanism related to interaction of HDL/ApoA1 and ADCY9 on β2-AR signalling. This review also raises the importance of characterizing polymorphisms that determine the response to HDL-raising and -mimicking agents in the non-Caucasian population at high risk of CV diseases and suffering from SCD. This may facilitate personalized CV treatments.

Pharmacogenomic determinants of the cardiovascular effects of dalcetrapib

BACKGROUND

Dalcetrapib did not improve clinical outcomes, despite increasing high-density lipoprotein cholesterol by 30%. These results differ from other evidence supporting high-density lipoprotein as a therapeutic target. Responses to dalcetrapib may vary according to patients' genetic profile.

METHODS AND RESULTS

We conducted a pharmacogenomic evaluation using a genome-wide approach in the dal-OUTCOMES study (discovery cohort, n=5749) and a targeted genotyping panel in the dal-PLAQUE-2 imaging trial (support cohort, n=386). The primary endpoint for the discovery cohort was a composite of cardiovascular events. The change from baseline in carotid intima-media thickness on ultrasonography at 6 and 12 months was evaluated as supporting evidence. A single-nucleotide polymorphism was found to be associated with cardiovascular events in the dalcetrapib arm, identifying the ADCY9 gene on chromosome 16 (rs1967309; P=2.41×10(-8)), with 8 polymorphisms providing P<10(-6) in this gene. Considering patients with genotype AA at rs1967309, there was a 39% reduction in the composite cardiovascular endpoint with dalcetrapib compared with placebo (hazard ratio, 0.61; 95% confidence interval, 0.41-0.92). In patients with genotype GG, there was a 27% increase in events with dalcetrapib versus placebo. Ten single-nucleotide polymorphism in the ADCY9 gene, the majority in linkage disequilibrium with rs1967309, were associated with the effect of dalcetrapib on intima-media thickness (P<0.05). Marker rs2238448 in ADCY9, in linkage disequilibrium with rs1967309 (r(2)=0.8), was associated with both the effects of dalcetrapib on intima-media thickness in dal-PLAQUE-2 (P=0.009) and events in dal-OUTCOMES (P=8.88×10(-8); hazard ratio, 0.67; 95% confidence interval, 0.58-0.78).

CONCLUSIONS

The effects of dalcetrapib on atherosclerotic outcomes are determined by correlated polymorphisms in the ADCY9 gene.

CLINICAL TRIAL INFORMATION

URL: http://www.clinicaltrials.gov. Unique identifiers: NCT00658515 and NCT01059682.

Will Lipidation of ApoA1 through Interaction with ABCA1 at the Intestinal Level Affect the Protective Functions of HDL?

The relationship between levels of high-density lipoprotein cholesterol (HDL-C) and cardiovascular (CV) risk is well recognized; however, in recent years, large-scale phase III studies with HDL-C-raising or -mimicking agents have failed to demonstrate a clinical benefit on CV outcomes associated with raising HDL-C, casting doubt on the "HDL hypothesis." This article reviews potential reasons for the observed negative findings with these pharmaceutical compounds, focusing on the paucity of translational models and relevant biomarkers related to HDL metabolism that may have confounded understanding of in vivo mechanisms. A unique function of HDL is its ability to interact with the ATP-binding cassette transporter (ABC) A1 via apolipoprotein (Apo) A1. Only recently, studies have shown that this process may be involved in the intestinal uptake of dietary sterols and antioxidants (vitamin E, lutein and zeaxanthin) at the basolateral surface of enterocytes. This parameter should be assessed for HDL-raising drugs in addition to the more documented reverse cholesterol transport (RCT) from peripheral tissues to the liver. Indeed, a single mechanism involving the same interaction between ApoA1 and ABCA1 may encompass two HDL functions previously considered as separate: antioxidant through the intestinal uptake of antioxidants and RCT through cholesterol efflux from loaded cells such as macrophages.

Treatment of low HDL-C subjects with the CETP modulator dalcetrapib increases plasma campesterol only in those without ABCA1 and/or ApoA1 mutations

We investigated the effect of dalcetrapib treatment on phytosterol levels in patients with familial combined hyperlipidemia (FCH) or familial hypoalphalipoproteinemia (FHA) due to mutations in apolipoprotein A1 (ApoA1) or ATP-binding cassette transporter A1 (ABCA1). Patients (n = 40) with FCH or FHA received dalcetrapib 600 mg or placebo in this 4-week, double-blind, crossover study. Lipids, apolipoproteins, cholesteryl ester transfer protein (CETP) activity and mass, and phytosterols were assessed. Dalcetrapib increased high-density lipoprotein cholesterol (HDL-C) and ApoA1 levels to a similar extent in FHA (+22.8, +13.9%) and FCH (+18.4, +12.1%), both p < 0.001 vs. placebo. Changes in CETP activity and mass were comparable for FHA (-31.5, +120.9%) and FCH (-26.6, +111.9%), both p < 0.0001 vs. placebo. Campesterol and lathosterol were unchanged in FHA (+3.8, +3.0%), but only campesterol was markedly increased in FCH (+25.0%, p < 0.0001 vs. placebo). Campesterol increased with dalcetrapib treatment in FCH but not in FHA, despite comparable HDL-C and ApoA1 increases, suggesting that ApoA1 and/or ABCA1 is essential for HDL lipidation by enterocytes in humans.

Abstract 235: Atorvastatin Has No Impact on the Effects of CETP Inhibitors on HDL Structure and Cholesterol Efflux Capacity in Chow-Fed Rabbits

Introduction: In the dal-OUTCOMES trial, cholesteryl ester transfer protein (CETP) inhibition by dalcetrapib increased HDL-C but had a neutral effect on CV risk. However, these patients were also treated with standard-of-care therapies including statins, a drug class shown to reduce ABCA1 mRNA expression in human peripheral blood mononuclear cells (PBMC).

Hypothesis: Given the role of ABCA1 in cholesterol efflux and HDL biogenesis, we determined the impact of atorvastatin on the potential beneficial effects provided by dalcetrapib and anacetrapib, two CETP inhibitors.

Methods: Dalcetrapib (300 mg/kg) or anacetrapib (30 mg/kg) were administered to New Zealand White rabbits receiving or not atorvastatin (2.5 mg/kg) for 14 days. Lipid profiles were measured biochemically. ApoA-I distribution in HDL subclasses was evaluated by 1D-non-denaturing gradient gel electrophoresis (1D-NDGGE). BHK cells with inducible expression of human ABCA1 and HepG2 hepatocytes were used to measure ABCA1- and SR-BI-dépendent cholesterol efflux. Human THP-1 macrophages and PBMC isolated from rabbits were also used for efflux assays.

Results: Dalcetrapib increased HDL-C by +81% (p<0.01) and total apoA-I (1D-NDGGE) by 1.5-fold (p<0.01). This was associated with an increase in both large and small α-migrating HDL (+52%, p<0.05; +74%, p<0.05). Cholesterol efflux showed that ABCA1- and SR-BI-dependent effluxes to apoB-depleted serum were increased in dalcetrapib-treated rabbits (+31%, p<0.01; +38%, p<0.001). Atorvastatin had no impact on all these parameters. Moreover, treatment of THP-1 with atorvastatin did not inhibit the increase of cholesterol efflux (+24%, p<0.01) induced by depleted serum from dalcetrapib-treated rabbits. Efflux capacity of PBMC isolated from rabbits treated with atorvastatin was also unchanged compared to the other groups. The absence of effect of atorvastatin on cholesterol efflux was also observed with anacetrapib.

Conclusion: CETP inhibition increased HDL-C, apoA-I levels and cholesterol efflux from different cell types. Atorvastatin had no effect on these parameters, suggesting that the increased cholesterol efflux capacity induced by CETPi is not hampered by statins.

The effect of cholesteryl ester transfer protein inhibition on lipids, lipoproteins, and markers of HDL function after an acute coronary syndrome: the dal-ACUTE randomized trial

AIMS

The effects of cholesteryl ester transfer protein (CETP) inhibition on lipids, inflammation, and markers of high-density lipoprotein (HDL) function, following an acute coronary syndrome (ACS), are unknown.

METHODS AND RESULTS

The dal-ACUTE study randomized 300 patients (1 : 1) to dalcetrapib 600 mg/day or placebo within 1 week of an ACS. The primary endpoint was per cent change in HDL-cholesterol (HDL-C) after 4 weeks. Secondary endpoints included apolipoprotein levels, markers of HDL function, and inflammation. Dalcetrapib treatment increased HDL-C and apolipoprotein A1 by 33.7 and 11.8%, respectively (both P < 0.001) and total cholesterol efflux by 9.5% (P = 0.003) after 4 weeks, principally via an increase in non-ATP-binding cassette transporter (ABC) A1-mediated efflux, without statistically significant changes in pre-β1-HDL levels. The increase in total efflux with dalcetrapib correlated most strongly with increases in apolipoprotein A1 and HDL-C (r = 0.46 and 0.43, respectively) rather than the increase in pre-β1-HDL (r = 0.32). Baseline and on-treatment ABCA1-mediated efflux correlated most strongly with pre-β1-HDL levels; in contrast, non-ABCA1-mediated efflux correlated better with apolipoprotein A1 and HDL-C levels.

CONCLUSIONS

High-density lipoprotein raised through CETP inhibition with dalcetrapib improves cholesterol efflux, principally via a non-ABCA1-mediated pathway. While HDL-C was increased by one-third, apolipoprotein A1 and total efflux were increased only by one-tenth, supporting the concept of dissociation between improvements in HDL function and HDL-C levels, which may be of relevance to ongoing trials and the development of therapeutic interventions targeting HDL.

Differential effects of fenofibrate and extended-release niacin on high-density lipoprotein particle size distribution and cholesterol efflux capacity in dyslipidemic patients

BACKGROUND

The effectiveness of therapies that raise high-density lipoprotein cholesterol (HDL-C) to lower cardiovascular disease risk is currently under debate, and further research into the relationship between HDL-C and function is required.

OBJECTIVE

o investigate whether 2 established HDL-C-raising therapies had differential effects on parameters of high-density lipoprotein (HDL) quality and function, such as HDL particle profile and cholesterol efflux capacity (CEC), in patients with dyslipidemia.

METHODS AND RESULTS

Sixty-six patients with dyslipidemia, 24 with low HDL-C levels (<40 mg/dL) and 42 with normal HDL-C levels (40-59 mg/dL), were treated for 6 weeks with fenofibrate (160 mg/d) or extended-release (ER) niacin (0.5 g/d for 3 weeks, then 1 g/d) with 4 weeks of washout between treatments. Lipoprotein particle size distribution was determined using nuclear magnetic resonance, and pathway-specific serum CECs were assessed in J774 macrophages, hepatoma, and Chinese hamster ovary-human adenosine triphosphate-binding cassette transporter G1 cells. Comparable increases in HDL-C and apolipoprotein A-I levels were seen with fenofibrate and ER niacin. There was a shift toward larger HDL, predominantly to medium-size HDL particles for fenofibrate (+209%) and to large HDL particles for ER niacin (+221%). Minor changes in serum CECs were observed with fenofibrate and ER niacin for all the efflux pathways measured. Small increases in plasma cholesteryl ester transfer protein and lecithin: cholesterol acyltransferase concentrations, and decreases in cholesteryl ester transfer protein activity were seen with both drugs.

CONCLUSIONS

Fenofibrate and ER niacin increased plasma HDL-C level similarly, but modulated HDL particle size distribution differently; however, these changes did not result in differential effects on serum CECs.

Lipid and apoprotein composition of HDL in partial or complete CETP deficiency

Hyperalphalipoproteinemia, as observed in patients who are either homozygous or heterozygous for cholesteryl ester transfer protein (CETP) deficiency, has been shown to be associated with striking changes in apolipoprotein size distribution, namely, of high-density lipoprotein (HDL) and HDL-like particles. We compared the effect of varying degrees of CETP activity on the HDL apolipoprotein profile in Caucasian CETP-deficient subjects and following pharmacological decrease in CETP activity, using Size Exclusion Chromatography followed by Reverse Phase Protein Array (SEC RPA). The main HDL-associated apolipoproteins (Apo), i.e. ApoA-I, ApoA-II, ApoC-I, and ApoC-III, co-eluted with the HDL peak. The presence of a HDL-like peak migrating between the ApoB-LDL and ApoA-I-HDL was identified in a Caucasian patient with homozygosity for a point mutation in exon 2 of the CETP gene (c.109 C > T) resulting in a premature termination codon (R37X) and complete CETP deficiency. This HDL-like peak was not observed either in healthy volunteers treated with the CETP modulator dalcetrapib, patients heterozygous for the same mutation, or in patients heterozygous with G165X mutations. SEC RPA offers the possibility to investigate the distribution of a large number of apolipoproteins simultaneously under non-denaturing separation in normal and dyslipidemic subjects. This is only limited by the availability of antibodies against specific apolipoproteins to be investigated.

Abstract 319: Dalcetrapib-Mediated Modulation of Cholesteryl Ester Transfer Protein Activity Increases HDL-Cholesterol, Apolipoprotein A-I Levels and Cholesterol Efflux Capacity in Chow-Fed Rabbits

Introduction: A potential approach to reduce CV risk is to increase HDL-C levels. This could be achieved by reducing cholesteryl ester transfer protein (CETP) activity. Dalcetrapib, which modulates CETP activity by changing its conformation and raises HDL-C without inhibiting CETP-induced pre-β-HDL formation in humans, was shown to decrease progression of atherosclerosis in rabbits.

Hypothesis: Investigate the modifications of HDL particle size distribution and cholesterol efflux capacity of serum produced by dalcetrapib in normocholesterolemic rabbits.

Methods: New Zealand white rabbits were treated with dalcetrapib (300 mg/kg as food admix) or placebo for 14 days. We evaluated CETP conformation and mass by ELISAs (including antibodies sensitive to conformational change), CETP activity by fluorescent lipid transfer, lipid profile and apoA-I distribution in HDL subclasses by 2D-non denaturing gradient gels (2D-NDGGE). Cholesterol efflux capacity of rabbit sera was determined after loading cells with 3 H-free cholesterol, using HepG2 hepatocytes to measure SR-BI-dependent efflux and by inducing ABCA1 or ABCG1 expression in BHK cells.

Results: Dalcetrapib modified the conformation of rabbit CETP in vitro and in vivo and, after 14 days, this was associated with increased CETP mass (+50%, p<0.001) and reduced CETP activity (-86%, p<0.001). Total cholesterol was increased with dalcetrapib (+178%, p<0.001), due to a higher HDL-C level. In contrast, dalcetrapib reduced LDL-C and triglycerides by 41% (p<0.01) and 48% (p<0.001). Serum analysis by 2D-NDGGE showed that total rabbit apoA-I was increased 1.7- fold in animals treated with dalcetrapib. This was associated with an increase in large HDL but also in small α-migrating HDL with pre-β-HDL size. Cholesterol efflux assays showed that ABCA1-, ABCG1- and SR-BI-dependent efflux were all increased in dalcetrapib-treated rabbits (+24%, p=0.038; +21%, p=0.021; +44%, p<0.001).

Conclusion: Modulation of CETP activity and conformation by dalcetrapib increases HDL-C and apoA-I levels and affects apoA-I distribution in HDL subclasses. These changes are associated with increased cholesterol efflux capacity, suggesting that HDL functionality is preserved in dalcetrapib-treated chow-fed rabbits.

Abstract 69: The Increase in Dalcetrapib-Induced HDL Remodeling Is Dependent on Cysteine 13 of Cholesteryl Ester Transfer Protein and Does Not Involve Phospholipid Transfer Protein

Introduction: Inhibition of the cholesteryl ester transfer between HDL and apoB-containing lipoproteins by dalcetrapib requires cysteine 13 (C13) of CETP. In contrast to the CETP inhibitors torcetrapib or anacetrapib, the CETP modulator dalcetrapib stimulates CETP-dependent generation of pre-β-HDL in human plasma or isolated HDL in vitro .

Hypothesis: We hypothesized that the effects of dalcetrapib on CETP-dependent HDL remodeling also require C13 of CETP and are not the result of interaction with the other cysteine-containing phospholipid transfer protein (PLTP).

Results: The CETP C13S mutant was as active as wild-type (wt) CETP both i) in transferring cholesteryl ester between HDL and apoB-containing lipoproteins and ii) in generating pre-β1-HDL. Dalcetrapib inhibited the transfer of cholesteryl ester between HDL and apoB-containing lipoproteins by wtCETP (IC 50 = 200 nM) but increased pre-β1-HDL formation from isolated HDL, and ABCA1-mediated efflux (3-fold and 2.5-fold increase at 10 μM, respectively, p<0.01). These properties of dalcetrapib were not observed with the CETP C13S mutant. Native HDL was remodeled by wtCETP as evidenced by the formation of large and small particles; a process further enhanced by dalcetrapib.

When reconstituted HDL (rHDL), containing only apoA-I and phospholipids, was substituted for isolated HDL, dalcetrapib did not increase wtCETP-induced pre-β1-HDL or ABCA1-dependent efflux (0.9-fold at 10 μM). PLTP induced pre-β1-HDL generation and ABCA1 efflux from native HDL and rHDL. PLTP-dependent HDL remodeling was not affected by dalcetrapib (0.9- and 1-fold at 10 μM for HDL and rHDL respectively).

Conclusions: The enhanced generation of pre-β1-HDL by wtCETP and dalcetrapib was associated with an increase in ABCA1-specific efflux and HDL remodeling. As observed for cholesteryl ester transfer activity, dalcetrapib effects on CETP-dependent HDL remodeling required C13 of CETP and dalcetrapib had no effect on PLTP-dependent HDL remodeling.

Abstract 508: Plasma Kinetics of 3H-Cholesterol from Labeled Macrophages in Hamsters Treated with Dalcetrapib, Torcetrapib and Anacetrapib

Introduction: A model using hamsters injected intraperitoneally with cholesterol-labeled macrophages has been developed for the study of reverse cholesterol transport following treatment with compounds affecting CETP activity e.g., the CETP modulator dalcetrapib or the CETP inhibitors torcetrapib and anacetrapib.

Hypothesis: Contrary to torcetrapib and anacetrapib, dalcetrapib allows CETP-induced remodeling of HDL and the formation of pre-β-HDL in vitro ; these compounds may differentially alter the kinetics of efflux of 3 H-cholesterol ( 3 H-C) from macrophages to plasma HDL and elimination from plasma HDL.

Methods: Male Golden Syrian hamsters were fed a chow diet and received dalcetrapib 150 mg/kg bid, n=10; torcetrapib 30 mg/kg qd, n=10; anacetrapib 30 mg/kg qd, n=10; or vehicle (0.5% HPMC), n=8, for 10 days. On Day 7, all animals were administered ip 3 H-C-labeled J774 macrophages and treated as above for a further 3 days. The appearance of 3 H-C in plasma HDL (24, 48 and 72 h), liver and in feces was measured and 3 H-C specific activity (SA) calculated.

Results: Compared to vehicle, torcetrapib and dalcetrapib raised plasma total cholesterol by 14% and anacetrapib by 21% with a similar trend for HDL-C. At 24, 48 and 72 h, HDL 3 H-C SA was -22.3, +4.9 and -0.5% (p<0.01, NS, NS) for torcetrapib, -16.7, -1.7 and -3.0% (p<0.05, NS, NS) for anacetrapib and +35.3, +36.4 and +8.7% (p<0.007, 0.012, NS) for dalcetrapib compared to vehicle. At sacrifice the percentage of injected dose in liver did not differ between treatment and vehicle for torcetrapib, anacetrapib and dalcetrapib. The SA of 3 H-C in fecal cholesterol was +19.8, +0.5 and +44.8% (NS, NS, p<0.05 vs vehicle) and in fecal bile acids was +49.7, +7.8 and +56.0% (p<0.03, NS, NS vs vehicle) respectively.

Conclusions: The SA of HDL 3 H-C from labeled macrophages is significantly higher for dalcetrapib at 24 and 48 h but lower for torcetrapib and anacetrapib at 24 h in treated hamsters compared to vehicle. A comparable SA to vehicle at later time points suggests an active mechanism of 3 H-C removal from macrophages and elimination for dalcetrapib, while 3 H-C for torcetrapib and anacetrapib is initially diluted in the HDL-C pool followed by attainment of equilibrium in this pool.

Effect of dalcetrapib plus pravastatin on lipoprotein metabolism and high-density lipoprotein composition and function in dyslipidemic patients: results of a phase IIb dose-ranging study

BACKGROUND

Cholesteryl ester transfer protein (CETP) is involved in high-density lipoprotein (HDL) remodeling and transfer of lipids between HDL particles and other lipoproteins. Epidemiologic studies show that both elevated HDL-cholesterol (HDL-C) and reduced CETP activity attenuate cardiovascular risk, making inhibition or modulation of CETP a potential therapeutic target. This study analyzed the effect of dalcetrapib on lipoprotein profile, CETP activity, and cellular cholesterol efflux when co-administered with pravastatin in patients with low or average HDL-C.

METHODS

Patients were randomized in a double-blind fashion to receive placebo or dalcetrapib 300, 600, or 900 mg once daily for 12 weeks. All patients were concomitantly treated to their low-density lipoprotein cholesterol target with pravastatin. Lipoprotein profile was analyzed by nuclear magnetic resonance spectroscopy and polyacrylamide gradient gel electrophoresis. Composition of the HDL fraction was assessed after polyethylene glycol precipitation. Contribution of this fraction to cholesterol efflux was assessed using radiolabeled donor cells.

RESULTS

Co-administration of dalcetrapib with pravastatin increased HDL-C, apolipoproteins (apo) A-I and A-II, and CETP mass, and decreased CETP activity. A relative increase in large HDL and low-density lipoprotein subparticle fractions was observed. High-density lipoprotein composition showed increased association of esterified cholesterol, free cholesterol, phospholipids, apo A-I, and apo E. Adenosine 5'-triphosphate-binding cassette A1- and scavenger receptor type BI-mediated cholesterol efflux increased.

CONCLUSIONS

Dalcetrapib up to 600 mg, combined with pravastatin, increased HDL-C and altered lipoprotein profile, HDL composition, and HDL function, with little further change at a 900-mg dose. The impact on cardiovascular events in dyslipidemic patients is being evaluated.

Multidimensional profiling of plasma lipoproteins by size exclusion chromatography followed by reverse-phase protein arrays

The composition of lipoproteins and the association of proteins with various particles are of much interest in the context of cardiovascular disease. Here, we describe a technique for the multidimensional analysis of lipoproteins and their associated apolipoproteins. Plasma is separated by size exclusion chromatography (SEC), and fractions are analyzed by reverse-phase arrays. SEC fractions are spotted on nitrocellulose slides and incubated with different antibodies against individual apolipoproteins or antibodies against various apolipoproteins. In this way, tens of analytes can be measured simultaneously in 100 μl of plasma from a single SEC separation. This methodology is particularly suited to simultaneous analysis of multiple proteins that may change their distribution to lipoproteins or alter their conformation, depending on factors that influence circulating lipoprotein size or composition. We observed changes in the distribution of exchangeable apolipoproteins following addition of recombinant apolipoproteins or interaction with exogenous compounds. While the cholesteryl ester transfer protein (CETP)-dependent formation of pre-β-HDL was inhibited by the CETP inhibitors torcetrapib and anacetrapib, it was not reduced by the CETP modulator dalcetrapib. This finding was elucidated using this technique.

Different effects of compounds decreasing cholesteryl ester transfer protein activity on lipoprotein metabolism

PURPOSE OF REVIEW

Review literature on the effect of decreasing cholesteryl ester transfer protein (CETP) activity through pharmacological inhibition or modulation in preclinical and clinical settings compared to human CETP deficiency on lipoprotein characteristics, HDL remodelling and function.

RECENT FINDINGS

Torcetrapib, anacetrapib and dalcetrapib inhibited the heterotypic transfer of cholesteryl ester from HDL to LDL and/or VLDL with similar potency, although the potency of dalcetrapib was time dependent. Homotypic transfer of cholesteryl ester from HDL3 to HDL2 via recombinant human CETP was inhibited by torcetrapib and anacetrapib (CETP inhibitors, CETPi) but not by dalcetrapib (CETP modulator, CETPm). In a hamster model of reverse cholesterol transport, only dalcetrapib increased efflux of fecal sterols from macrophages to feces. In clinical studies, dose-responses of CETPi and CETPm demonstrate qualitative and quantitative changes in HDL and LDL particle composition and distribution.

SUMMARY

Recent studies of the CETPi torcetrapib and anacetrapib and the CETPm dalcetrapib have shown differences in the resulting increase in HDL-cholesterol and in the level of HDL remodelling and potential for effective reverse cholesterol transport. Results from ongoing clinical outcomes studies with anacetrapib and dalcetrapib will clarify the relevance of CETP inhibition versus modulation towards HDL remodelling in the treatment of cardiovascular diseases.

Modulating cholesteryl ester transfer protein activity maintains efficient pre-β-HDL formation and increases reverse cholesterol transport

The mechanism by which cholesteryl ester transfer protein (CETP) activity affects HDL metabolism was investigated using agents that selectively target CETP (dalcetrapib, torcetrapib, anacetrapib). In contrast with torcetrapib and anacetrapib, dalcetrapib requires cysteine 13 to decrease CETP activity, measured as transfer of cholesteryl ester (CE) from HDL to LDL, and does not affect transfer of CE from HDL3 to HDL2. Only dalcetrapib induced a conformational change in CETP, when added to human plasma in vitro, also observed in vivo and correlated with CETP activity. CETP-induced pre-β-HDL formation in vitro in human plasma was unchanged by dalcetrapib ≤3 µM and increased at 10 µM. A dose-dependent inhibition of pre-β-HDL formation by torcetrapib and anacetrapib (0.1 to 10 µM) suggested that dalcetrapib modulates CETP activity. In hamsters injected with [³H]cholesterol-labeled autologous macrophages, and given dalcetrapib (100 mg twice daily), torcetrapib [30 mg once daily (QD)], or anacetrapib (30 mg QD), only dalcetrapib significantly increased fecal elimination of both [³H]neutral sterols and [³H]bile acids, whereas all compounds increased plasma HDL-[³H]cholesterol. These data suggest that modulation of CETP activity by dalcetrapib does not inhibit CETP-induced pre-β-HDL formation, which may be required to increase reverse cholesterol transport.

Dalcetrapib: no off-target toxicity on blood pressure or on genes related to the renin-angiotensin-aldosterone system in rats

BACKGROUND AND PURPOSE

The association between torcetrapib and its off-target effects on blood pressure suggested a possible class-specific effect. The effects of dalcetrapib (RO4607381/JTT-705) and torcetrapib on haemodynamics and the renin-angiotensin-aldosterone system (RAAS) were therefore assessed in a rat model.

EXPERIMENTAL APPROACH

Arterial pressure (AP) and heart rate were measured by telemetry in normotensive and spontaneously hypertensive rats (SHR) receiving torcetrapib 10, 40 or 80 mg kg(-1) day(-1); dalcetrapib 100, 300 or 500 mg(-1) kg day(-1); or vehicle (placebo) for 5 days. Expression of RAAS genes in adrenal gland, kidney, aorta and lung from normotensive rats following 5 days' treatment with torcetrapib 40 mg kg(-1) day(-1), dalcetrapib 500 mg kg(-1) day(-1) or vehicle was measured by quantitative polymerase chain reaction.

KEY RESULTS

Torcetrapib transiently increased mean AP in normotensive rats (+3.7 +/- 0.1 mmHg), whereas treatment in SHR resulted in a dose-dependent and sustained increase [+6.5 +/- 0.6 mmHg with 40 mg kg(-1) day(-1) at day 1 (P < 0.05 versus placebo)], which lasted over the treatment period. No changes in AP or heart rate were observed with dalcetrapib. Torcetrapib, but not dalcetrapib, increased RAAS-related mRNAs in adrenal glands and aortas.

CONCLUSIONS AND IMPLICATIONS

In contrast to torcetrapib, dalcetrapib did not increase blood pressure or RAAS-related gene expression in rats, suggesting that the off-target effects of torcetrapib are not a common feature of all compounds acting on cholesteryl ester transfer protein.

Safety and tolerability of dalcetrapib

Efficacy and safety data for dalcetrapib (RO4607381/JTT-705) are presented, following a report of increased mortality and cardiac events with another cholesteryl ester transfer protein inhibitor, torcetrapib, associated with off-target adverse effects (hypertension and the activation of the renin-angiotensin-aldosterone system). The efficacy and clinical safety of dalcetrapib 300, 600, and 900 mg or placebo were assessed (n = 838) in 4 pooled 4-week phase IIa trials (1 monotherapy, n = 193; 3 statin combination, n = 353) and 1 12-week phase IIb trial (with pravastatin, n = 292). Nonclinical safety, assessed by the induction of aldosterone production and aldosterone synthase (cytochrome P450 11B2) messenger ribonucleic acid, was measured in human adrenocarcinoma (H295R) cells exposed to dalcetrapib or torcetrapib. Dalcetrapib increased high-density lipoprotein cholesterol by up to 36% and apolipoprotein A-I by up to 16%. The incidence of adverse events (AEs) was similar between placebo (42%) and dalcetrapib 300 mg (50%) and 600 mg (42%), with more events with dalcetrapib 900 mg (58%) (p <0.05, pooled 4-week studies). Six serious AEs (3 with placebo, 1 with dalcetrapib 300 mg, and 2 with dalcetrapib 600 mg) were considered "unrelated" to treatment. Cardiovascular AEs were similar across treatment groups, with no dose-related trends and no clinically relevant changes in blood pressure or electrocardiographic results. Findings were similar in the 12-week study. In vitro, torcetrapib but not dalcetrapib increased aldosterone production and cytochrome P450 11B2 messenger ribonucleic acid levels. In conclusion, dalcetrapib alone or in combination with statins was effective at increasing high-density lipoprotein cholesterol and was well tolerated, without clinically relevant changes in blood pressure or cardiovascular AEs and no effects on aldosterone production as assessed nonclinically.

Apomine, an inhibitor of HMG-CoA-reductase, promotes apoptosis of myeloma cells in vitro and is associated with a modulation of myeloma in vivo

Apomine, a novel 1,1 bisphosphonate ester, increases the rate of degradation of HMG-CoA reductase, inhibiting the mevalonate pathway and thereby blocking cholesterol biosynthesis. We have investigated whether Apomine can induce myeloma cell apoptosis in vitro and modulate myeloma disease in vivo. Apomine induced a dose-dependent increase in apoptosis in NCI H929, RPMI 8226 and JJN-3 human myeloma cells. Apomine, unlike the bisphosphonate, alendronate, had no measurable effect on osteoclastic bone resorption in vitro. To investigate the effect of Apomine in vivo, 5T2MM murine myeloma cells were injected into C57BL/KaLwRij mice. After 8 weeks all animals had a serum paraprotein and were treated with Apomine (200 mg/kg), or vehicle, for 4 weeks. Animals injected with 5T2MM cells and treated with vehicle developed osteolytic bone lesions, reduced cancellous bone area, decreased bone mineral density (BMD) and increased osteoclast number. Apomine caused a decrease in serum paraprotein and a decrease in tumor burden. Apomine inhibited the development of osteolytic lesions and prevented the tumor-induced decreases in BMD. Apomine had no effect on osteoclast number in contrast to what had been seen previously with the bisphosphonate, zoledronic acid, suggesting that these are direct effects of Apomine on myeloma cells. This demonstrates that Apomine is able to promote myeloma cell apoptosis in vitro and inhibit the development of multiple myeloma and lytic bone disease in vivo. The use of bisphosphonate esters such as Apomine represents a novel therapeutic approach in the treatment of myeloma and, indirectly, the associated bone disease.

The bile acid nuclear receptor FXR and the bile acid binding protein IBABP are differently expressed in colon cancer

Bile acids have been implicated in the development of colorectal cancers. We investigated the expression of the transcription factor regulated by bile acids, farnesoid X receptor (FXR), as well as other components of this pathway in human colorectal tumors and cell lines. The most significant changes were a decrease in FXR mRNA levels in adenomas (5-fold average) and carcinomas (10 fold average) and an increase in peroxisome proliferator activated receptor-gamma (2-fold average). FXR was not expressed in undifferentiated colon adenocarcinoma SW480 cells and metastasis derived SW620 cells. In Caco-2 and HT-29 cells, the level of FXR expression increased with the degree of differentiation. Intestinal bile acid binding protein was activated by chenodeoxycholic acid and the synthetic FXR agonist GW4064 in Caco-2 and HT-29 but not in SW cells unless FXR was transfected. The down-regulation of the nuclear receptor FXR in colon cancer might be of clinical and pharmacological importance.

The Nuclear Oxysterol Receptor LXRα Is Expressed in the Normal Human Breast and in Breast Cancer

The liver X> or = receptor alpha (LXRalpha) is a nuclear receptor with a key role in bile acid biosynthesis and cholesterol metabolism. The present study investigated the expression and function of LXRalpha in the normal and malignant human breast. LXRalpha mRNA transcripts were detected by RT-PCR in nine breast carcinoma cell lines. The nucleotide sequence of the cloned PCR product was identical to the corresponding human LXRalpha cDNA sequence. Expression of LXRalpha protein was confirmed by immunoblot analysis of breast cancer cell lysates. LXRalpha mRNA was expressed in 14/15 (93%) of normal human breast mammoplasty specimens and in 11/15 (73%) of primary breast carcinomas. Oxysterol and nonsteroidal LXRalpha agonists at low micromolar concentrations inhibited proliferation of breast carcinoma cell lines in culture. The importance of LXRalpha signaling in cholesterol homeostasis and the observed expression of LXRalpha in normal breast tissue suggest that this nuclear oxysterol receptor has an important physiological function in the breast. LXRalpha gene expression is regulated by dietary fatty acids implicated in breast carcinogenesis and detection of LXRalpha expression in breast cancer cell lines and breast tumors in the present study indicates that LXRalpha may also be important in breast carcinogenesis. Inhibition of breast cancer cell proliferation suggests that pharmacological LXRalpha agonists may have potential preventive and/or therapeutic antitumor activity in breast cancer.

Apomine, a novel hypocholesterolemic agent, accelerates degradation of 3-hydroxy-3-methylglutaryl-coenzyme A reductase and stimulates low density lipoprotein receptor activity

Apomine, a novel 1,1-bisphosphonate ester, has been shown to lower plasma cholesterol concentration in several species. Here we show that Apomine reduced the levels of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR), the rate-limiting enzyme in the mevalonate pathway, both in rat liver and in cultured cells. Apomine resembles sterols such as 25-hydroxycholesterol in its ability to potently accelerate the rate of HMGR degradation by the ubiquitin-proteasome pathway, a process that depends on the transmembrane domain of the enzyme. The similarity between Apomine and sterols in promoting rapid HMGR degradation extends to its acute requirements for ongoing protein synthesis and mevalonate-derived non-sterol product(s) as a co-regulator. Yet, at suboptimal concentrations, sterols potentiated the effect of Apomine in stimulating HMGR degradation, indicating that these agents act via distinct modes. Furthermore, unlike sterols, Apomine inhibited the activity of acyl-CoA:cholesterol acyltransferase in intact cells but not in cell-free extracts. Apomine stimulated the cleavage of the precursor of sterol-regulatory element-binding protein-2 and increased the activity of low density lipoprotein receptor pathway. This Apomine-enhanced activation of sterol-regulatory element-binding protein-2 was prevented by sterols or mevalonate. Taken together, our results provide a molecular mechanism for the hypocholesterolemic activity of Apomine.

Expression of nuclear receptors and apo E secretion during the differentiation of monocytic THP-1 cells into macrophages

The human monocytic THP-1 cell line differentiates into macrophage-like cells that secrete apo E after addition of PMA. Using this model, we studied the time course of apo E transcriptional activation and secretion in relation with the expression of nuclear receptors. Upon treatment with PMA, apo E mRNA and protein secretion were triggered with the concomitant increase of LXRalpha, PPARgamma, and PPARbeta mRNA expression levels. PPARalpha was downregulated, RXRalpha expression was unchanged, and RARalpha and VDR showed only transient increases. FXR and SXR transcripts were not detectable. Specific agonists were used to investigate the functional role of these nuclear receptors upon apo E secretion. The LXRalpha ligands T0901317 and 22(R)-hydroxycholesterol were the most potent apo E inducers, followed by the PPARgamma agonist BRL49653. The PPARalpha agonist Wy14,643 was inactive and 1alpha,25-dihydroxyvitamin D3, 9-cis-retinoic acid and all-trans-retinoic acid decreased apo E secretion. Thus, during PMA-induced THP-1 differentiation, there is a sequential and coordinate regulation of apo E and nuclear receptor transcription.

Phase I pharmacokinetic trial and correlative in vitro phase II tumor kinetic study of Apomine (SR-45023A), a novel oral biphosphonate anticancer drug

PURPOSE

To study the human pharmacokinetics and in vitro cytotoxicity of Apomine, an p.o. administered, nonmyelosuppressive agent that selectively inhibits cell proliferation and induces tumor cell apoptosis through the farnesoid X receptor.

EXPERIMENTAL DESIGN

Seven solid cancer patients who participated in an ongoing Phase I study of Apomine and received the starting dose level of 125 mg/m(2)/day x 14 days every 3 weeks underwent a pharmacokinetic study on day 14 of the first course. Plasma concentrations of Apomine were assayed with a Hewlett Packard gas chromatograph using a nitrogen phosphorus detector and HP-5 15m x 0.32-mm column. Fresh human ovarian cancer tumor samples were obtained during initial exploratory laparotomy from 35 chemotherapy-naive, advanced stage epithelial ovarian cancer patients. Tumor samples were tested for sensitivity to Apomine, carboplatin, cisplatin, paclitaxel, and topotecan using an in vitro clonogenic [(3)H]thymidine end point assay.

RESULTS

Pharmacokinetic analysis revealed a mean Apomine plasma C(max) of 16.4 +/- 9.1 microg/ml (29.1 microM), a mean plasma AUC(0--12 h) of 173.4 +/- 105 microg. h/ml (308 microM. h), and a mean t(1/2 (24--192 h)) of 156.2 +/- 42.9 h. In vitro assay results showed that 63 and 91% of the ovarian cancers were sensitive (i.e., >70% inhibition of tumor cell growth) to Apomine at concentrations of 10 and 20 microM. The sensitivity rates were 91% for carboplatin (270 microM), 88% for cisplatin (33 microM), 41% for paclitaxel (5.9 microM), and 85% for topotecan (2.2 microM).

CONCLUSIONS

These in vitro assay results, taken together with our preliminary plasma pharmacokinetic data, suggest that Apomine should be clinically active at the 125 mg/m(2) dose level.

The nuclear receptors FXR and LXRalpha: potential targets for the development of drugs affecting lipid metabolism and neoplastic diseases

The orphan nuclear receptors FXR and LXRalpha have become challenging targets for the discovery of new therapeutic agents. Bile acids and hydroxysterol intermediates are the respective natural ligands of these two structurally and functionally closely related receptors. Both FXR and LXRalpha; are thought to play a major role in the control of cholesterol catabolism by regulating the expression of cholesterol 7alpha-hydroxylase, the rate limiting enzyme of bile acid synthesis. Reverse cholesterol transport might also be affected by FXR and LXR since they control the expression of PLTP and CETP, two proteins involved in the transfer of phospholipid, cholesterol and cholesteryl esters among plasma lipoproteins. A new class of potent synthetic activators of FXR, the 1,1-bisphosphonate esters, has been discovered which up regulate the Intestinal Bile Acid Binding Protein gene (I-BABP) as demonstrated for chenodeoxycholic acid, however there are no known synthetic activators yet identified for LXRalpha. The evaluation of FXR as a potential target for the development of drugs affecting plasma cholesterol can take advantage of the fact that the activators of FXR (farnesol, bile acids and the 1,1-bisphosphonate esters) have been studied in various in vitro and in vivo models. Administration of chenodeoxycholic acid to animals and man did not result in the increase in plasma cholesterol expected from a decrease in cholesterol 7alpha-hydroxylase expression. Like farnesol, the 1,1-bisphosphonate esters increase the rate of degradation of HMGCoA reductase and have the unexpected property of inducing hypocholesterolemia in normal animals. The natural and synthetic FXR agonists trigger differentiation, inhibit cell proliferation and are potent inducers of apoptosis. The 1,1-bisphosphonate ester SR-45023A (Apomine) is presently being developed as an antineoplastic drug.

The mevalonate/isoprenoid pathway inhibitor apomine (SR-45023A) is antiproliferative and induces apoptosis similar to farnesol

Apomine (SR-45023A) is a new antineoplastic compound which is currently in clinical trials and representative of the family of cholesterol synthesis inhibitors 1,1-bisphosphonate esters. Apomine inhibits growth of a wide variety of tumor cell lines with IC(50) values ranging from 5 to 14 microM. The antiproliferative activity of apomine was studied in comparison with that of other inhibitors of the mevalonate/isoprenoid pathway of cholesterol synthesis, simvastatin, farnesol, and 25-hydroxycholesterol. All these compounds inhibit 3-hydroxy-3-methylglutaryl-coenzyme A reductase activity. Apomine (IC(50) = 14 microM), simvastatin (IC(50) = 3 microM), farnesol (IC(50) = 60 microM), and 25-hydroxycholesterol (IC(50) = 2 microM) inhibited HL60 cell growth. Growth inhibition due to simvastatin was reverted by mevalonate, whereas the antiproliferative activity of apomine, farnesol, and 25-hydroxycholesterol was not. Apomine triggered apoptosis in HL60 cells in less than 2 h. Apomine and farnesol induced caspase-3 activity at concentrations similar to their IC(50) values for cell proliferation, whereas a 10-fold excess of simvastatin was necessary to trigger apoptosis compared to its potency on proliferation. Caspase-3 activity was not induced by 25-hydroxycholesterol. The overall similar profile on mevalonate synthesis inhibition, cell growth inhibition, and apoptosis suggests that apomine acts as a synthetic mimetic of farnesol.

A new class of calcium entry blockers defined by 1,3-diphosphonates. Interactions of SR-7037 (belfosdil) with receptors for calcium channel ligands

Tetrabutyl-2(2-phenoxyethyl)-1,3-propylidene diphosphonate (SR-7037) completely displaced dihydropyridine [( 3H]PN200-110), phenylalkylamine [( 3H]D888), and benzothiazepine [( 3H]diltiazem) ligands from brain L-type calcium channels. Half-maximal inhibition of [3H]PN200-110 binding occurred at 19 nM with a Hill coefficient of 0.96. SR-7037 primarily decreased the affinity for [3H]PN200-110 with a small, but significantly, effect on the maximal binding capacity. Kinetic studies showed that this was due to an increased radioligand dissociation rate from 0.04 min-1 to 0.43 min-1 in the presence of the diphosphonate. Displacement of [3H]D888 by SR-7037 was biphasic with respective IC50 of 44 and 8400 nM. Likewise, unlabeled (-)-D888 identified two sites with IC50 values of 0.9 and 27 nM. Both SR-7037 (1000 nM) and D888 (200 nM) accelerated radioligand dissociation about 2-fold. [3H]Diltiazem binding was inhibited by SR-7037 with an IC50 value of 29 nM. The inhibition of dihydropyridine binding by SR-7037 is enhanced by most divalent cations at millimolar concentrations with the following potency: Mn2+ greater than Mg2+ greater than Ca2+ greater than Co2+. Barium has the opposite effect. The half-maximal effect of calcium occurred at 6 microM free ion. Specific binding of [3H]D888 was antagonized in the presence of 1 mM CaCl2. It is concluded that SR-7037 has allosteric interactions with the dihydropyridine receptor of the L-type calcium channel. The differential effect of Ca2+ on the potency of D888 and diltiazem relative to that of SR-7037 indicates that the three drugs may bind to nonequivalent sites. These results support specific calcium channel inhibition, possibly at a novel site, as the primary mechanism of the diphosphonate's pharmacological actions.

Establishment of rat pancreatic endocrine cell lines by infection with simian virus 40

The feasibility of infection and transformation by SV40 (simian virus 40) of primary cell cultures derived from newborn-rat pancreas was investigated. As judged by the presence of intranuclear SV40 T-antigen, exposure to the virus resulted specifically in infection and transformation of epithelioid (predominantly endocrine) cells. The transformed cells were subcultured (more than 64 passages) and cloned. Culture medium and acid/ethanol extracts of the cells did not contain detectable amounts of immunoreactive insulin after the third subculture. However, inoculation of such SV40-transformed pancreatic cells into immunodeficient rats results in tumours in which insulin production was partially restored through the passage in vivo, since the tumour cells contained and synthesized small amounts of immunoreactive insulin which co-migrated with an insulin marker on gel chromatography. Interestingly, the transformed cells maintained under tissue-culture conditions produced a protein immunologically related to insulin, soluble in aqueous buffer but insoluble in acid/ethanol. This 3000-dalton protein is too large to be a translation product of the rat preproinsulin 9S mRNA. SV40-transformed pancreatic cells might prove useful in the investigation of the factors controlling and maintaining insulin biosynthesis.