Variation in Binding Affinity of the Novel Anxiolytic XBD173 for the 18 kDa Translocator Protein in Human Brain

ArticleinSynapse 65(3):257-9 · March 2011with24 Reads
DOI: 10.1002/syn.20884 · Source: PubMed


    • "The results also could help to better understand pharmacokinetic–pharmacodynamic relationships for drugs targeting TSPO, as we have suggested previously based on data from direct binding affinity assays with XBD173 (AC-5216) (Owen et al, 2011b). This binding affinity variation has greatest impact for studies of Caucasians, for whom the rs6971 polymorphism has a reported minor allele (Thr147) frequency of 30% and a major allele (Ala147) frequency of 70% (11). "
    [Show abstract] [Hide abstract] ABSTRACT: [(11)C]PBR28 binds the 18-kDa Translocator Protein (TSPO) and is used in positron emission tomography (PET) to detect microglial activation. However, quantitative interpretations of signal are confounded by large interindividual variability in binding affinity, which displays a trimodal distribution compatible with a codominant genetic trait. Here, we tested directly for an underlying genetic mechanism to explain this. Binding affinity of PBR28 was measured in platelets isolated from 41 human subjects and tested for association with polymorphisms in TSPO and genes encoding other proteins in the TSPO complex. Complete agreement was observed between the TSPO Ala147Thr genotype and PBR28 binding affinity phenotype (P value=3.1 × 10(-13)). The TSPO Ala147Thr polymorphism predicts PBR28 binding affinity in human platelets. As all second-generation TSPO PET radioligands tested hitherto display a trimodal distribution in binding affinity analogous to PBR28, testing for this polymorphism may allow quantitative interpretation of TSPO PET studies with these radioligands.
    Full-text · Article · Jan 2012
  • [Show abstract] [Hide abstract] ABSTRACT: The mitochondrial translocator protein (TSPO) mediates the synthesis of neurosteroids in the CNS, which have been demonstrated to enhance the neurotransmitter GABA response, exhibiting related behavioural properties. Selective TSPO ligands are able to stimulate steroidogenesis with great efficacy, thus representing potential anxiolytic agents. This review describes the development of a class of high affinity ligands to TSPO, N,N-dialkylindol-3-ylglyoxylamides (IGA), from the initial stages of design to the pharmacological characterization of selected compounds for their anxiolytic activity. Affinity data and SARs of the new class of ligands are discussed; the potential applications of compounds characterized by the indolylglyoxylyl scaffold in diagnostic imaging are also pointed out.
    Article · Feb 2012
  • [Show abstract] [Hide abstract] ABSTRACT: The translocator protein (TSPO) is a potential drug target for the treatment of CNS diseases, with TSPO ligands being able to modulate steroidogenesis, apoptosis, and cell proliferation. While there exist multiple TSPO binding sites, the nature of these sites--either overlapping or allosterically linked--remains largely uncharacterized. Furthermore, while evidence suggests that microglial activation and polymerization result in changes to TSPO binding sites, these changes are poorly understood. While current pharmacophoric models can be used to synthesize TSPO ligands with high affinity and selectivity, these models are unable to predict ligands with desirable functional effects. Better characterization of TSPO binding sites in health and disease may provide insight into particular sites which mediate promising therapeutic profiles, thus refining the TSPO pharmacophore.
    Full-text · Article · Feb 2012
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