Receptor crosstalk: haloperidol treatment enhances A2A adenosine receptor functioning in a transfected cell model

A(2A) adenosine receptors are considered an excellent target for drug development in several neurological and psychiatric disorders. It is noteworthy that the responses evoked by A(2A) adenosine receptors are regulated by D(2) dopamine receptor ligands. These two receptors are co-expressed at the level of the basal ganglia and interact to form functional heterodimers. In this context, possible changes in A(2A) adenosine receptor functional responses caused by the chronic blockade/activation of D(2) dopamine receptors should be considered to optimise the therapeutic effectiveness of dopaminergic agents and to reduce any possible side effects. In the present paper, we investigated the regulation of A(2A) adenosine receptors induced by antipsychotic drugs, commonly acting as D(2) dopamine receptor antagonists, in a cellular model co-expressing both A(2A) and D(2) receptors. Our data suggest that the treatment of cells with the classical antipsychotic haloperidol increased both the affinity and responsiveness of the A(2A) receptor and also affected the degree of A(2A)-D(2) receptor heterodimerisation. In contrast, an atypical antipsychotic, clozapine, had no effect on A(2A) adenosine receptor parameters, suggesting that the two classes of drugs have different effects on adenosine-dopamine receptor interaction. Modifications to A(2A) adenosine receptors may play a significant role in determining cerebral adenosine effects during the chronic administration of antipsychotics in psychiatric diseases and may account for the efficacy of A(2A) adenosine receptor ligands in pathologies associated with dopaminergic system dysfunction. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11302-010-9201-z) contains supplementary material, which is available to authorized users.     

Assessing cytotoxicity of boron nitride nanotubes: Interference with the MTT assay

Thanks to a non-covalent wrapping with glycol-chitosan, highly biocompatible and highly concentrated dispersions of boron nitride nanotubes were obtained and tested on human neuroblastoma cells. A systematic investigation of the cytotoxicity of these nanovectors with several complementary qualitative and quantitative assays allowed a strong interference with the MTT metabolic assay to be highlighted, similar to a phenomenon already observed for carbon nanotubes, that would wrongly suggest toxicity of boron nitride nanotubes. These results confirm the high complexity of these new nanomaterials, and the needing of extensive investigations on their exciting potential applications in the biomedical field.     

Anti-PlGF inhibits growth of VEGF(R)-inhibitor-resistant tumors without affecting healthy vessels

Novel antiangiogenic strategies with complementary mechanisms are needed to maximize efficacy and minimize resistance to current angiogenesis inhibitors. We explored the therapeutic potential and mechanisms of alphaPlGF, an antibody against placental growth factor (PlGF), a VEGF homolog, which regulates the angiogenic switch in disease, but not in health. alphaPlGF inhibited growth and metastasis of various tumors, including those resistant to VEGF(R) inhibitors (VEGF(R)Is), and enhanced the efficacy of chemotherapy and VEGF(R)Is. alphaPlGF inhibited angiogenesis, lymphangiogenesis, and tumor cell motility. Distinct from VEGF(R)Is, alphaPlGF prevented infiltration of angiogenic macrophages and severe tumor hypoxia, and thus, did not switch on the angiogenic rescue program responsible for resistance to VEGF(R)Is. Moreover, it did not cause or enhance VEGF(R)I-related side effects. The efficacy and safety of alphaPlGF, its pleiotropic and complementary mechanism to VEGF(R)Is, and the negligible induction of an angiogenic rescue program suggest that alphaPlGF may constitute a novel approach for cancer treatment.     

RNA and DNA binding properties of HIV-1 Vif protein: a fluorescence study

The HIV-1 viral infectivity factor (Vif) is a small basic protein essential for viral fitness and pathogenicity. Some "non-permissive" cell lines cannot sustain replication of Vif(-) HIV-1 virions. In these cells, Vif counteracts the natural antiretroviral activity of the DNA-editing enzymes APOBEC3G/3F. Moreover, Vif is packaged into viral particles through a strong interaction with genomic RNA in viral nucleoprotein complexes. To gain insights into determinants of this binding process, we performed the first characterization of Vif/nucleic acid interactions using Vif intrinsic fluorescence. We determined the affinity of Vif for RNA fragments corresponding to various regions of the HIV-1 genome. Our results demonstrated preferential and moderately cooperative binding for RNAs corresponding to the 5'-untranslated region of HIV-1 (5'-untranslated region) and gag (cooperativity parameter omega approximately 65-80, and K(d) = 45-55 nM). In addition, fluorescence spectroscopy allowed us to point out the TAR apical loop and a short region in gag as primary strong affinity binding sites (K(d) = 9.5-14 nM). Interestingly, beside its RNA binding properties, the Vif protein can also bind the corresponding DNA oligonucleotides and their complementary counterparts with an affinity similar to the one observed for the RNA sequences, while other DNA sequences displayed reduced affinity. Taken together, our results suggest that Vif binding to RNA and DNA offers several non-exclusive ways to counteract APOBEC3G/3F factors, in addition to the well documented Vif-induced degradation by the proteasome and to the Vif-mediated repression of translation of these antiviral factors.     

Aminoglycoside binding to the HIV-1 RNA dimerization initiation site: thermodynamics and effect on the kissing-loop to duplex conversion

Owing to a striking, and most likely fortuitous, structural and sequence similarity with the bacterial 16 S ribosomal A site, the RNA kissing-loop complex formed by the HIV-1 genomic RNA dimerization initiation site (DIS) specifically binds 4,5-disubstituted 2-deoxystreptamine (2-DOS) aminoglycoside antibiotics. We used chemical probing, molecular modeling, isothermal titration calorimetry (ITC) and UV melting to investigate aminoglycoside binding to the DIS loop–loop complex. We showed that apramycin, an aminoglycoside containing a bicyclic moiety, also binds the DIS, but in a different way than 4,5-disubstituted 2-DOS aminoglycosides. The determination of thermodynamic parameters for various aminoglycosides revealed the role of the different rings in the drug–RNA interaction. Surprisingly, we found that the affinity of lividomycin and neomycin for the DIS (K_d ~ 30 nM) is significantly higher than that obtained in the same experimental conditions for their natural target, the bacterial A site (K_d ~ 1.6 µM). In good agreement with their respective affinity, aminoglycoside increase the melting temperature of the loop–loop interaction and also block the conversion from kissing-loop complex to extended duplex. Taken together, our data might be useful for selecting new molecules with improved specificity and affinity toward the HIV-1 DIS RNA.     

Design, synthesis, and biological evaluation of new (2E,6E)-10-(dimethylamino)-3,7-dimethyl-2,6-decadien-1-ol ethers as inhibitors of human and Trypanosoma cruzi oxidosqualene cyclase

New dimethylamino truncated squalene ether derivatives containing a different aromatic moiety (phenyl, naphthyl, and biphenyl) or a simple alkyl (n-hexylic) group were synthesized as inhibitors of the oxidosqualene cyclase (OSC) and of the sterol biosynthetic pathway. The activity against human OSC was compared with the activity against the OSCs of pathogenic organisms such as Pneumocystis carinii and Trypanosoma cruzi. The phenyl derivative was the most potent inhibitor of T. cruzi OSC.     

Synthesis and biological evaluation of non-peptide alpha(v)beta(3)/alpha(5)beta(1) integrin dual antagonists containing 5,6-dihydropyridin-2-one scaffolds

Small constrained non-peptidic molecules consisting of a polyfunctionalized rigid core, carrying appendages corresponding to arginine and aspartic acid side chains, have been recently reported to be promising for drug development. In this work, the 5,6-dihydropyridin-2-one was envisaged as a scaffold to turn into potential integrin ligands, introducing a carboxylic acid and a basic appendage. The synthesis and the antiadhesion activity of a small library of peptidomimetics capable to recognize alpha(v)beta(3) and alpha(5)beta(1) integrins has been herein reported.