Activation of the Wnt Pathway by Small Peptides: Rational Design, Synthesis and Biological Evaluation

A computational analysis of the X-ray structure of the low-density lipoprotein receptor-related protein 6 (LRP6) with the Dickkopf-1 (DKK1) C-terminal fragment has allowed us to rationally design a small set of decapeptides. These compounds behave as agonists of the canonical Wnt pathway in the micromolar range when tested on a dual luciferase Wnt functional assay in glioblastoma cells. Two of the oligopeptides showed a lack of cytotoxicity in human primary osteoblasts isolated from sponge bone tissue (femoral heads or knees of elderly patients). According to the mechanism of action, the studies revealed a dose- and time-dependent increase in the viability of human osteoblasts. These results may indicate a potential therapeutic application of this class of compounds in the treatment of bone diseases related to aging, such as osteoporosis.

Magnetic resonance imaging of infarct-induced canonical wingless/integrated (Wnt)/β-catenin/T-cell factor pathway activation, in vivo

AIMS

Combined magnetic resonance imaging (MRI) of molecular and morpho-functional changes might prove highly valuable for the elucidation of pathological processes involved in the development of cardiac diseases. Our aim was to test a novel MRI reporter gene for in vivo assessment of the canonical Wnt/β-catenin/TCF pathway activation, an important regulator of post-ischaemic cardiac remodelling.

METHODS AND RESULTS

We designed and developed a chimeric construct encoding for both of iron-binding human ferritin heavy chain (hFTH) controlled by the β-catenin-responsive TCF/lymphoid-enhancer binding factor (Lef) promoter and constitutively expressed green fluorescent protein (GFP). It was carried by adeno-associated virus serotype 9 (rAAV9) vectors and delivered to the peri-infarct myocardium of rats subjected to coronary ligation (n = 11). By 1.5 T MRI and a multiecho T2* gradient echo sequence, we detected iron accumulation only in the border zone of the transduced infarcted hearts. In the same cardiac area, post-mortem histological analysis confirmed the co-existence of iron accumulation and GFP. The iron signal was absent when rats (n = 6) were chronically treated with SEN195 (10 mg/kg/day), a small-molecular inhibitor of β-catenin/TCF-dependent gene transcription. Canonical Wnt pathway inhibition attenuated the post-ischaemic remodelling process, as demonstrated by the significant preservation of cardiac function, the 42 ± 1% increase of peri-infarct arteriolar density and 43 ± 3% reduction in infarct scar size compared with untreated animals.

CONCLUSIONS

The TCF/Lef promoter-hFTH construct is a novel and reliable MRI reporter gene for in vivo detection of the canonical Wnt/β-catenin/TCF activation state in response to cardiac injury and therapeutic interventions.

Multimodal molecular imaging system for pathway-specific reporter gene expression

Preclinical imaging modalities represent an essential tool to develop a modern and translational biomedical research. To date, Optical Imaging (OI) and Magnetic Resonance Imaging (MRI) are used principally in separate studies for molecular imaging studies. We decided to combine OI and MRI together through the development of a lentiviral vector to monitor the Wnt pathway response to Lithium Chloride (LiCl) treatment. The construct was stably infected in glioblastoma cells and, after intracranial transplantation in mice, serial MRI and OI imaging sessions were performed to detect human ferritin heavy chain protein (hFTH) and firefly luciferase enzyme (FLuc) respectively. The system allowed also ex vivo analysis using a constitutive fluorescence protein expression. In mice, LiCl administration has shown significantly increment of luminescence signal and a lower signal of T2 values (P<0.05), recorded noninvasively with OI and a 7 Tesla MRI scanner. This study indicates that OI and MRI can be performed in a single in vivo experiment, providing an in vivo proof-of-concept for drug discovery projects in preclinical phase.

The Chaperoning Activity of Amino-oxyacetic Acid on Folding-Defective Variants of Human Alanine:Glyoxylate Aminotransferase Causing Primary Hyperoxaluria Type I

The rare disease Primary Hyperoxaluria Type I (PH1) results from the deficit of liver peroxisomal alanine:glyoxylate aminotransferase (AGT), as a consequence of inherited mutations on the AGXT gene frequently leading to protein misfolding. Pharmacological chaperone (PC) therapy is a newly developed approach for misfolding diseases based on the use of small molecule ligands able to promote the correct folding of a mutant enzyme. In this report, we describe the interaction of amino-oxyacetic acid (AOA) with the recombinant purified form of two polymorphic species of AGT, AGT-Ma and AGT-Mi, and with three pathogenic variants bearing previously identified folding defects: G41R-Ma, G170R-Mi, and I244T-Mi. We found that for all these enzyme AOA (i) forms an oxime at the active site, (ii) behaves as a slow, tight-binding inhibitor with KI values in the nanomolar range, and (iii) increases the thermal stability. Furthermore, experiments performed in mammalian cells revealed that AOA acts as a PC by partly preventing the intracellular aggregation of G41R-Ma and by promoting the correct peroxisomal import of G170R-Mi and I244T-Mi. Based on these data, we carried out a small-scale screening campaign. We identified four AOA analogues acting as AGT inhibitors, even if only one was found to act as a PC. The possible relationship between the structure and the PC activity of these compounds is discussed. Altogether, these results provide the proof-of-principle for the feasibility of a therapy with PCs for PH1-causing variants bearing folding defects and provide the scaffold for the identification of more specific ligands.

siRNA screen identifies QPCT as a druggable target for Huntington's disease

Huntington's disease (HD) is a currently incurable neurodegenerative condition caused by an abnormally expanded polyglutamine tract in huntingtin (HTT). We identified new modifiers of mutant HTT toxicity by performing a large-scale 'druggable genome' siRNA screen in human cultured cells, followed by hit validation in Drosophila. We focused on glutaminyl cyclase (QPCT), which had one of the strongest effects on mutant HTT-induced toxicity and aggregation in the cell-based siRNA screen and also rescued these phenotypes in Drosophila. We found that QPCT inhibition induced the levels of the molecular chaperone αB-crystallin and reduced the aggregation of diverse proteins. We generated new QPCT inhibitors using in silico methods followed by in vitro screening, which rescued the HD-related phenotypes in cell, Drosophila and zebrafish HD models. Our data reveal a new HD druggable target affecting mutant HTT aggregation and provide proof of principle for a discovery pipeline from druggable genome screen to drug development.

CXCR4 Antagonists

The CXC chemokine receptor 4 (CXCR4) is a widely expressed G protein–coupled receptor implicated in several diseases. In cancer, an increased number of surface CXCR4 receptors, in parallel with aberrant signaling, have been reported to influence several aspects of malignancy progression. CXCR4 activation by the specific ligand C-X-C motif chemokine 12 (CXCL12) induces several intracellular signaling pathways that have been selectively related to malignancy depending on the tissue or cell type. We developed a panel of CXCR4 screening assays investigating Gαi-mediated cyclic adenosine monophosphate modulation, β-arrestin recruitment, and receptor internalization. All of the assays were set up in recombinant cells and were used to test four reported CXCR4 antagonists. Consequently, a set of hit compounds, deriving from a screening campaign of a 30,000-small-molecule internal library, was profiled with the different assays. We identified several compounds showing a pathway-selective activity: antagonists on a Gαi-dependent pathway; antagonists on both the β-arrestin and Gαi-dependent pathways, some of which induce receptor internalization; and compounds with an antagonist behavior in all of the readouts. The identified biased antagonists induce different functional states on CXCR4 and preferentially affect specific downstream responses from the activated receptor, thus providing an improved therapeutic profile for correction of CXCR4 abnormal signaling.

A Phenotypic Screening Assay for Modulators of Huntingtin-Induced Transcriptional Dysregulation

Huntington’s Disease is a rare neurodegenerative disease caused by an abnormal expansion of CAG repeats encoding polyglutamine in the first exon of the huntingtin gene. N-terminal fragments containing polyglutamine (polyQ) sequences aggregate and can bind to cellular proteins, resulting in several pathophysiological consequences for affected neurons such as changes in gene transcription. One transcriptional pathway that has been implicated in HD pathogenesis is the CREB binding protein (CBP)/cAMP responsive element binding (CREB) pathway. We developed a phenotypic assay to screen for compounds that can reverse the transcriptional dysregulation of the pathway caused by induced mutated huntingtin protein (µHtt). 293/T-REx cells were stably co-transfected with an inducible full-length mutated huntingtin gene containing 138 glutamine repeats and with a reporter gene under control of the cAMP responsive element (CRE). One clone, which showed reversible inhibition of µHtt-induced reporter activity upon treatment with the neuroprotective Rho kinase inhibitor Y27632, was used for the development of a high-throughput phenotypic assay suitable for a primary screening campaign, which was performed on a library of 24,000 compounds. Several hit compounds were identified and validated further in a cell viability adenosine triphosphate assay. The assay has the potential for finding new drug candidates for the treatment of HD.

A homogeneous HTRF assay for the identification of inhibitors of the TWEAK-Fn14 protein interaction

The TWEAK-Fn14 pathway is upregulated in models of inflammation, autoimmune diseases, and cancer. Both TWEAK and Fn14 show increased expression also in the CNS in response to different stimuli, particularly astrocytes, microglia, and neurons, leading to activation of NF-κB and release of proinflammatory cytokines. Although neutralizing antibodies against these proteins have been shown to have therapeutic efficacy in animal models of inflammation, no small-molecule therapeutics are yet available. Here, we describe the development of a novel homogeneous time-resolved fluorescence (HTRF)-based screening assay together with several counterassays for the identification of small-molecule inhibitors of this protein-protein interaction. Recombinant HIS-TWEAK and Fn14-Fc proteins as well as FLAG-TWEAK and Fn14-FLAG proteins and an anti-Fn14 antibody were used to establish and validate these assays and to screen a library of 60 000 compounds. Two HTRF counterassays with unrelated proteins in the same assay format, an antiaggregation assay and a redox assay, were applied to filter out potential false-positive compounds. The novel assay and associated screening cascade should be useful for the discovery of small-molecule inhibitors of the TWEAK-Fn14 protein interaction.

Antioxidant properties of propargylamine derivatives: assessment of their ability to scavenge peroxynitrite

A series of arylpropargylamines, variously substituted in the hydrogen in p-position and in the propargyl moiety, were studied as potential peroxynitrite scavengers. The scavenging activity of these compounds was evaluated through peroxynitrite (ONOO−)-mediated oxidation of dichlorofluorescin and linoleic acid by measuring the dichlorofluorescein formation and oxygen consumption, respectively. Among tested compounds, only 1-phenylpropargylamine (AP3) promoted concentration-dependent inhibition of ONOO−-induced dichlorofluorescin and linoleic acid oxidation with IC50 values of 637 and 63 μm, respectively. The AP3 spectral changes in UV-visible absorbance properties in the presence of peroxynitrite suggested the formation of a new compound. This was identified by gas-chromatograph-mass spectrometer analysis as phenylpropargyl alcohol. Structure—activity relationship analysis indicated that the scavenging activity of AP3 was due to the aminopropargyl moiety and availability of the nitrogen electron pair. This data suggested that AP3 could be considered a lead compound for the synthesis of new ONOO− scavenger derivatives.

Internationally adopted children: a new challenge for pediatricians

Children adopted from abroad by Italian families have increased during the last years. Since 2001 to 2004 they have been more than 10,000, mainly from Eastern Europe, and all indications suggest that they will continue to increase. Most of the internationally adopted children reside in orphanage before adoption where they may experience malnutrition, exposure to infectious diseases, environmental deprivation, neglect. Moreover, their pre-adoptive records are scarcely reliable and their immunization status is not always adequate. The most common long-term problems of internationally adopted children concern developmental and scholastic delay especially if they come from a long and severely deprived institutional setting, precocious puberty and, during adolescence, depressive disorders as well as antisocial behaviours. Inter-country adopted children are at increased risk for health and social problems and have to be recognized as a group of subjects requiring special medical attentions. Specialized centres for internationally adopted children where they could receive medical evaluations upon arrival and a prolonged health follow-up should be set up.

A Continuous Time-Resolved Fluorescence Assay for Identification of BACE1 Inhibitors

The aspartic protease beta-site amyloid precursor protein cleaving enzyme 1 (BACE1) mediates the production of the neurotoxic amyloid beta peptide and is therefore considered an important drug target for treatment of Alzheimer's disease. We describe a new homogeneous time-resolved fluorescence quenching assay for the identification of BACE1 inhibitors that is characterized by minimal compound interference and allows both kinetic and end-point measurements. A fluorescent Eu-chelate as fluorescent donor, coupled to the N-terminus of a peptide containing the amyloid precursor protein Swedish mutation with a quenching molecule at the C-terminus as acceptor, is used as substrate. Upon peptide cleavage by BACE1, the energy transfer between donor and acceptor molecules is interrupted, leading to increased fluorescence emission of the donor. Compound interference, a common problem in fluorescence assays, is minimized with this technology because of the large Stoke's shift and the time-resolved fluorescence emission of the Eu-chelate. The assay reproduced IC50 values of known inhibitors and detected them also as hits in a screening campaign. A high signal-to-noise ratio of 289 and a Z' factor of 0.76 make this assay suitable for high-throughput screening.