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Updated: Feb 23, 2026

Preparation and Evaluation of 99mTc-labeled Tridentate Chelates for Pre-targeting Using Bioorthogonal Chemistry
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The Low-Affinity Binding of Second Generation Radiotracers Targeting TSPO is Associated with a Unique Allosteric

Camilo Rojas1,2, Marigo Stathis3, Jennifer M Coughlin4

  • 1Johns Hopkins Drug Discovery, Johns Hopkins University School of Medicine, 855 North Wolfe Street, Office 230, Baltimore, MD, 21205, USA. crojas2@jhmi.edu.

Journal of Neuroimmune Pharmacology : the Official Journal of the Society on Neuroimmune Pharmacology
|September 7, 2017
PubMed

[11C]-PK11195 (PK11195) has been widely used with positron emission tomography (PET) to assess levels of the translocator protein 18 kDa (TSPO) as a marker of neuroinflammation. Recent ligands, such as [11C]-PBR28 and [11C]-DPA713, have improved signal-to-noise ratio and specificity for TSPO over PK11195. However, these second generation radiotracers exhibit binding differences due to a single polymorphism (rs6971) that leads to three genotypes: C/C, C/T and T/T associated with high, mixed and low binding affinities, respectively. Here we report that [3H]-DPA-713 in the presence of cholesterol or PK11195 has an accelerated dissociation rate from TSPO in platelets isolated from individuals with the T/T genotype. This allosteric interaction was not observed in platelets isolated from individuals with the C/C or C/T genotype. The results provide a molecular rationale for low binding affinity of T/T TSPO and further support the exclusion of these subjects from PET imaging studies using second generation TSPO ligands.

Keywords:
Allosteric modulationResidence timeTranslocator protein 18 KDa (TSPO)

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