Sprouty2 loss-induced IL6 drives castration-resistant prostate cancer through scavenger receptor B1

Metastatic castration-resistant prostate cancer (mCRPC) is a lethal form of treatment-resistant prostate cancer and poses significant therapeutic challenges. Deregulated receptor tyrosine kinase (RTK) signalling mediated by loss of tumour suppressor Sprouty2 (SPRY2) is associated with treatment resistance. Using pre-clinical human and murine mCRPC models, we show that SPRY2 deficiency leads to an androgen self-sufficient form of CRPC Mechanistically, HER2-IL6 signalling axis enhances the expression of androgen biosynthetic enzyme HSD3B1 and increases SRB1-mediated cholesterol uptake in SPRY2-deficient tumours. Systemically, IL6 elevated the levels of circulating cholesterol by inducing host adipose lipolysis and hepatic cholesterol biosynthesis. SPRY2-deficient CRPC is dependent on cholesterol bioavailability and SRB1-mediated tumoral cholesterol uptake for androgen biosynthesis. Importantly, treatment with ITX5061, a clinically safe SRB1 antagonist, decreased treatment resistance. Our results indicate that cholesterol transport blockade may be effective against SPRY2-deficient CRPC.

Pharmacokinetic and Pharmacodynamic Investigations of ION-353382, a Model Antisense Oligonucleotide: Using Alpha-2-Macroglobulin and Murinoglobulin Double-Knockout Mice

To investigate the pharmacokinetics (PKs) and pharmacodynamics (PDs) for ION-353382, an antisense oligonucleotide (ASO) targeting scavenger receptor class B type I (SRB1) mRNA, using alpha-2-macroglobulin (A2M), murinoglobulin double-knockout (DKO), and wild-type mice. Wild-type and DKO homozygous mice were administered a single subcutaneous injection of ION-353382 at 0, 5, 15, 30, and 60 mg/kg. Mice were sacrificed at 72 h with plasma and organs harvested. Both liquid chromatography-mass spectrometry (LC-MS) and enzyme-linked immunosorbent assay (ELISA) were used to determine ASO exposure with real-time PCR for SRB1 expression. Immunohistochemistry was evaluated to explore hepatic uptake of ASOs. The total plasma protein binding and profiling was assessed. Finally, two-dimensional gel electrophoresis identified protein expression differences. PK exposures were comparable between wild-type and DKO mice in plasma, liver, and kidney, yet a near twofold reduction in EC50 was revealed for DKO mice based on an inhibitory effect liver exposure response model. Total plasma protein binding and profiling revealed no major dissimilarities between both groups. Plasma proteome fingerprinting confirmed protein expression variations related to A2M. Histological examination revealed enhanced ASO distribution into hepatocytes and less nonparenchymal uptake for DKO mice compared to wild-type mice. Knocking out A2M showed improved PD activities without an effect on total plasma and tissue exposure kinetics. Binding to A2M could mediate ASOs to nonproductive compartments, and thus, decreased binding of ASOs to A2M could potentially improve ASO pharmacology.

Novel human anti-claudin 1 mAbs inhibit hepatitis C virus infection and may synergize with anti-SRB1 mAb

Hepatitis C virus (HCV) is a major cause of chronic hepatitis and liver carcinoma and new therapies based on novel targets are needed. The tight junction protein claudin 1 (CLDN-1) is essential for HCV cell entry and spread, and anti-CLDN-1 rat and mouse mAbs are safe and effective in preventing and treating HCV infection in a human liver chimeric mouse model. To accelerate translation of these observations into a novel approach to treat HCV infection and disease in humans, we screened a phage display library of human single-chain antibody fragments by using a panel of CLDN-1-positive and -negative cell lines and identified phage specifically binding to CLDN-1. The 12 clones showing the highest levels of binding were converted into human IgG4. Some of these mAbs displayed low-nanomolar affinity, and inhibited infection of human hepatoma Huh7.5 cells by different HCV isolates in a dose-dependent manner. Cross-competition experiments identified six inhibitory mAbs that recognized distinct epitopes. Combination of the human anti-SRB1 mAb C-1671 with these anti-CLDN-1 mAbs could either increase or reduce inhibition of cell culture-derived HCV infection in vitro. These novel human anti-CLDN-1 mAbs are potentially useful to develop a new strategy for anti-HCV therapy and lend support to the combined use of antibodies targeting the HCV receptors CLDN-1 and SRB1, but indicate that care must be taken in selecting the proper combination.

Solid-phase synthesis of 5'-triantennary N-acetylgalactosamine conjugated antisense oligonucleotides using phosphoramidite chemistry

A convenient solid-phase synthetic method was developed for assembling a triantennary N-acetylgalactosamine (GalNAc) cluster on the 5'-end of antisense oligonucleotide using phosphoramidite chemistry. Conjugation of the 5'-triantennary GalNAc cluster improved potency of the 14 mer ASO 7-fold in mice and more than 50 fold in hepatocytes. The synthetic approach described in this Letter simplifies the synthesis of 5'-triantennary GalNAc cluster conjugated ASOs and helps understand the structure-activity relationship for targeting hepatocytes with oligonucleotide therapeutics.

MicroRNAs 125a and 455 repress lipoprotein-supported steroidogenesis by targeting scavenger receptor class B type I in steroidogenic cells

We sought to identify and characterize microRNA (miRNAs) that posttranscriptionally regulate the expression of scavenger receptor class B type I (SR-BI) and SR-BI-linked selective high-density lipoprotein (HDL) cholesteryl ester (CE) transport and steroidogenesis. Four miRNAs (miRNA-125a, miRNA-125b, miRNA-145, and miRNA-455) with a potential to regulate SR-BI were identified in silico and validated by quantitative real-time PCR (qRT-PCR), Western blot analysis, and SR-BI 3' untranslated region (UTR) reporter assays. In vitro treatment of primary rat granulosa cells and MLTC-1 cells with cyclic AMP (cAMP) or in vivo treatment of rat adrenals with adrenocorticotropic hormone (ACTH) decreased the expression of miRNA-125a, miRNA-125b, and miRNA-455 and reciprocally increased SR-BI expression. Using luciferase constructs containing the 3' untranslated region of SR-BI combined with miRNA overexpression and mutagenesis, we have provided evidence that steroidogenic SR-BI is a direct target of miRNA-125a and miRNA-455. Moreover, the transfection of Leydig tumor cells with precursor miRNA 125a (pre-miRNA-125a) or pre-miRNA-455 resulted in the suppression of SR-BI at both the transcript and protein levels and reduced selective HDL CE uptake and HDL-stimulated progesterone production. Transfection of liver Hepa 1-6 cells with pre-miRNA-125a significantly reduced SR-BI expression and its selective transport function. In contrast, overexpression of miRNA-145 did not affect SR-BI expression or selective HDL CE uptake mediated by SR-BI in steroidogenic cell lines. These data suggest that a trophic hormone and cAMP inversely regulate the expression of SR-BI and miRNA-125a and miRNA-455 in steroidogenic tissues/cells and that both miRNA-125a and miRNA-455, by targeting steroidogenic SR-BI, negatively regulate selective HDL CE uptake and HDL CE-supported steroid hormone production.

Small molecule scavenger receptor BI antagonists are potent HCV entry inhibitors

BACKGROUND AND AIMS

ITX 5061 is a clinical stage small molecule compound that promotes high-density lipoprotein (HDL) levels in animals and patients by targeting the scavenger receptor BI protein pathway. Since SR-BI is a known co-receptor for HCV infection, we evaluated these compounds for their effects on HCV entry.

METHODS

We obtained ITX 5061 and related compounds to characterize their interaction with SR-BI and effects on HCV entry and infection.

RESULTS

We confirmed that a tritium-labeled compound analog (ITX 7650) binds cells expressing SR-BI, and both ITX 5061 and ITX 7650 compete for HDL-mediated lipid transfer in an SR-BI dependent manner. Both molecules inhibit HCVcc and HCVpp infection of primary human hepatocytes and/or human hepatoma cell lines and have minimal effects on HCV RNA replication. Kinetic studies suggest that the compounds act at an early post-binding step.

CONCLUSIONS

These results suggest that the ITX compounds inhibit HCV infection with a mechanism of action distinct from other HCV therapies under development. Since ITX 5061 has already been evaluated in over 280 patients with good pharmacokinetic and safety profiles, it warrants proof-of-concept clinical studies in HCV infected patients.

Blockade of scavenger receptor class B type I raises high density lipoprotein cholesterol levels but exacerbates atherosclerotic lesion formation in apolipoprotein E deficient mice

Recent accumulating evidence supports the concept that raising high-density lipoprotein (HDL) may represent an additional therapeutic target for prevention of cardiovascular disease. Scavenger receptor class B type I plays a critical role in plasma HDL cholesterol concentration and structure. This study investigated the effect of scavenger receptor class B type I blockade by a synthetic scavenger receptor class B type I blocker on plasma lipids and atherosclerosis lesion formation in apolipoprotein E (apoE)-deficient mice. N-[4-(4-tert-Butoxycarbonylpiperazin-1-yl)phenyl]-(2-chloro-5-nitrophenyl)carboxamide (R-138329), a novel scavenger receptor class B type I blocker, was identified by screening with a half-maximal inhibitory potency (IC50 value) of around 1 μM in scavenger receptor class B type I-expressing COS-1 cells. Male apoE-deficient mice were fed a chow diet with or without R-138329 (0.01-0.10%, approximately 10–100 mg kg−1, n = 9 or 10) for 12 weeks. Compared with control, treatment with R-138329 at 0.10% caused significant (P < 0.05) increases in plasma HDL cholesterol levels, and decreases in non-HDL cholesterol and triglyceride levels. Furthermore, R-138329 at 0.01% significantly increased the extent of atherosclerotic lesion formation in the aorta by 98% (P < 0.05), while favourable changes in plasma lipid parameters were achieved. The results of quantitative analysis of atherosclerosis lesion areas were: control, 102691 ±22871 μm2 (n = 10); R-138329 0.01%, 119792 ± 30842 μm2 (n = 9); R-138329 0.03%, 141346 ± 21934 μm2 (n = 10); and R-138329 0.10% 203732 ± 36326 μm2 (n = 10). To clarify the mechanistic basis underlying this preferential deterioration, we examined the potential impact on closely related cellular functions. Further studies revealed that the active metabolite of R-138329 inhibited scavenger receptor class B type I-mediated cholesterol efflux. This study demonstrates for the first time pharmacological blockade of scavenger receptor class B type I in apoE-deficient mice. Blockade of scavenger receptor class B type I deteriorates atherosclerotic lesion formation in apoE-deficient mice even though it favourably affects plasma lipid parameters such as raising HDL cholesterol and decreasing non-HDL cholesterol. These results provide new insights for pharmaceutical industry research and development issues.

The ability to promote efflux via ABCA1 determines the capacity of serum specimens with similar high-density lipoprotein cholesterol to remove cholesterol from macrophages

OBJECTIVE

We measured efflux from macrophages to apolipoprotein B-depleted serum from 263 specimens and found instances in which serum having similar high-density lipoprotein cholesterol (HDL-C) differed in their efflux capacity. Thus, we wanted to elucidate why efflux capacity could be independent of total HDL-C or apolipoprotein A-I (apoA-I).

METHODS AND RESULTS

To understand why sera with similar HDL-C or apoA-I could differ in total efflux capacity, we assessed their ability to promote efflux via the pathways expressed in cAMP-treated J774 macrophages. Briefly, macrophages were preincubated with probucol to block ABCA1, with BLT-1 to block SR-BI, and with both inhibitors to measure residual efflux. ABCG1 efflux was measured with transfected BHK-1 cells. We used apolipoprotein B-depleted serum from specimens with similar HDL-C values at the 25(th) and 75(th) percentiles. Specimens in each group were classified as having high or low efflux based on total efflux being above or below the group average. We found that independently of HDL-C, sera with higher efflux capacity had a significant increase in ABCA1-mediated efflux, which was significantly correlated to the concentration of pre beta-1 HDL. The same result was obtained when these sera were similarly analyzed based on similar apoA-I.

CONCLUSIONS

Sera with similar HDL-C or apoA-I differ in their ability to promote macrophage efflux because of differences in the concentration of pre beta-1 HDL.

Plasma-advanced oxidation protein products are potent high-density lipoprotein receptor antagonists in vivo

Advanced oxidation protein products (AOPPs) are carried by oxidized plasma proteins, especially albumin and accumulate in subjects with renal disease and coronary artery disease. AOPPs represent an excellent novel marker of oxidative stress and their roles in the development of cardiovascular disease might be of great importance. Here, we show that in vitro-generated AOPP-albumin binds with high affinity to the high-density lipoprotein (HDL) receptor scavenger receptor class B type I (SR-BI). Already an equimolar concentration of AOPP-albumin to HDL blocked HDL association to SR-BI and effectively inhibited SR-BI-mediated cholesterol ester (CE) uptake. Interestingly, albumin extensively modified by advanced glycation end products (AGE-albumin), which is an established SR-BI ligand known to accumulate in renal disease, only weakly interfered with HDL binding to SR-BI. Furthermore, AOPP-albumin administration increased the plasma half-life of [3H]CE-HDL in control mice 1.6-fold (P=0.01) and 8-fold (P=0.0003) in mice infected with adenoviral vectors encoding human SR-BI. Moreover, albumin isolated from hemodialysis patients, but not albumin isolated from healthy controls, markedly inhibited SR-BI-mediated HDL-CE transfer in vitro dependent on the AOPP content of albumin. These results indicate that AOPP-albumin effectively blocks SR-BI in vitro and in vivo. Thus, depressed plasma clearance of HDL-cholesterol may contribute to the abnormal composition of HDL and the high cardiovascular risk observed in patients with chronic renal failure.

BLT-1, a specific inhibitor of the HDL receptor SR-BI, induces a copper-dependent phenotype during zebrafish development

Block lipid transport-1 (BLT-1) is a small chemical widely used to inhibit the transfer of lipids between high-density lipoproteins (HDL) and cells mediated by scavenger receptor B, type 1 (SR-BI). This study demonstrated that BLT-1 induced in zebrafish (Danio rerio) embryos a copper-dependent phenotype with a twisted notochord, brain ventricle enlargement, and absence of melanisation, phenocopying neocuproine-treated, or calamity mutants. This finding supports an unexpected link between copper availability and SR-BI activity. The copper-chelating activity of BLT-1, revealed by its dramatic effect during embryo development, should be considered in any evaluation of the pharmacological effect of this thiosemicarbazone derivative on SR-BI activity and the potential therapeutic value of this molecule.

Influence of HDL-cholesterol-elevating drugs on the in vitro activity of the HDL receptor SR-BI

Treatment of atherosclerotic disease often focuses on reducing plasma LDL-cholesterol or increasing plasma HDL-cholesterol. We examined in vitro the effects on HDL receptor [scavenger receptor class B type I (SR-BI)] activity of three classes of clinical and experimental plasma HDL-cholesterol-elevating compounds: niacin, fibrates, and HDL376. Fenofibrate (FF) and HDL376 were potent (IC(50) approximately 1 microM), direct inhibitors of SR-BI-mediated lipid transport in cells and in liposomes reconstituted with purified SR-BI. FF, a prodrug, was a more potent inhibitor of SR-BI than an activator of peroxisome proliferator-activated receptor alpha, a target of its active fenofibric acid (FFA) derivative. Nevertheless, FFA, four other fibrates (clofibrate, gemfibrozil, ciprofibrate, and bezafibrate), and niacin had little, if any, effect on SR-BI, suggesting that they do not directly target SR-BI in vivo. However, similarities of HDL376 treatment and SR-BI gene knockout on HDL metabolism in vivo (increased HDL-cholesterol and HDL particle sizes) and structure-activity relationship analysis suggest that SR-BI may be a target of HDL376 in vivo. HDL376 and other inhibitors may help elucidate SR-BI function in diverse mammalian models and determine the therapeutic potential of SR-BI-directed pharmaceuticals.

A novel compound, R-138329, increases plasma HDL cholesterol via inhibition of scavenger receptor BI-mediated selective lipid uptake

High-density lipoprotein (HDL) has a protective effect against atherosclerosis. Therefore, a compound that elevates the plasma HDL cholesterol (HDL-C) levels is expected to be a promising anti-atherosclerotic agent. We discovered a novel compound, R-138329, that increased HDL-C by 41% in normolipidemic hamsters at a dose of 100mg/kg. To investigate the mechanism of action of R-138329, we examined the effect of R-138329 on the clearance of [(3)H]cholesterol ether ([(3)H]COE)-labeled and [(125)I]-labeled HDL in mice. R-138329 delayed the clearance of [(3)H]COE-labeled HDL and reduced accumulation of tracer HDL in the liver, whereas the clearance of [(125)I]-labeled HDL particles was unaffected by the compound. In vitro analysis showed that R-154716, a metabolite of R-138329, dramatically inhibited the uptake of [(3)H]COE-labeled HDL in McA-RH 7777 rat hepatoma cells. Furthermore, 100 nM of R-154716 completely inhibited [(3)H]COE-labeled HDL uptake induced by overexpression of scavenger receptor BI (SR-BI) in HEK293 cells. Taken together, these findings suggest that the mechanism by which R-138329 elevates HDL-C in vivo is principally involved in the inhibition of SR-BI-mediated selective lipid uptake in the liver.

Involvement of mitogen-activated protein kinases in class B scavenger receptor type I-induced phagocytosis of apoptotic cells

Class B scavenger receptor type I (SR-BI) is a multiligand membrane protein expressed in a variety of cell types. This receptor is responsible for the incorporation of lipids from high density lipoprotein (HDL) by steroidogenic cells, as well as for the phosphatidylserine (PS)-mediated phagocytosis of apoptotic cells by some phagocytic cell types, such as testicular Sertoli cells. Although SR-BI directly binds to PS present on the surface of apoptotic cells, as to whether SR-BI transmits signals to induce engulfment has not been clear. In the present study, we examined this issue using a monoclonal antibody that neutralizes SR-BI activity and a chemical known to be an inhibitor of the SR-BI-mediated incorporation of HDL lipids. The chemical compound inhibited the incorporation of HDL lipids and PS-containing liposomes by an SR-BI-expressing culture cell line, with no effect on the binding of these targets. Similarly, the phagocytosis of PS-exposing apoptotic cells by primary cultured rat Sertoli cells was inhibited in the presence of either reagent, not at the recognition but at the engulfment step. The addition of apoptotic cells or PS-containing liposomes caused a temporal increment of the phosphorylation of all three mitogen-activated protein kinases, p38, extracellular-signal-regulated kinase (ERK) and c-Jun amino-terminal kinase (JNK), in Sertoli cells. The increase of phosphorylated p38 and ERK, but not of phosphorylated JNK, was cancelled in the presence of the monoclonal antibody. Furthermore, the level of Sertoli cell phagocytosis of PS-exposing apoptotic cells, as well as that of PS-containing liposomes, was reduced only when the actions of p38 and ERK were simultaneously repressed. In conclusion, these results indicate that SR-BI, when it binds to PS, transmits signals to activate the mitogen-activated protein kinase pathway, which leads to the induction of the engulfment of PS-exposing apoptotic cells by phagocytic cells.