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Preclinical In Vitro and In Vivo Characterization of Synaptic Vesicle 2A–Targeting Compounds Amenable to F-18 Labeling as Potential PET Radioligands for Imaging of Synapse Integrity

  • Shil PatelEmail author
  • Ashley Knight
  • Stephen Krause
  • Tyler Teceno
  • Cedric Tresse
  • Songye Li
  • Zhengxin Cai
  • Alexandra Gouasmat
  • Vincent M. Carroll
  • Olivier Barret
  • Vijay Gottmukkala
  • Wenjie Zhang
  • Xianhong Xiang
  • Thomas Morley
  • Yiyun Huang
  • Jan Passchier
Research Article
  • 96 Downloads

Abstract

Purpose

Current synaptic vesicle 2A (SV2A) positron emission tomography (PET) imaging agents include the nanomolar affinity probes [11C]UCB-J and [18F]UCB-H derived from the anti-epileptic drug levitaracetam (Keppra®). An industry-utilized “de-risking” approach was used to carry out initial pharmacological characterization and to assess potential next-generation candidates amenable to F-18 radiolabeling for preliminary evaluation.

Procedures

Radioligand binding methods were employed in mammalian brain homogenates to determine the SV2A affinity (Kd) and maximal binding capacity (Bmax) of [3H]UCB-J. Novel leads were then screened to identify compounds minimally with comparable binding affinities with UCB-J in order to select a F-18-labeled candidate for subsequent in vivo assessment in rat. In parallel, mammalian brain tissue section autoradiography was performed to assess specific SV2A distribution.

Results

[3H]UCB-J bound with high affinity to a single population of sites in the rat brain (Kd = 2.6 ± 0.25 nM; Bmax = 810 ± 25 fmol/mg protein) and control human cortex (Kd = 2.9 ± 0.54 nM; Bmax = 10,000 ± 640 fmol/mg protein). Distribution of specific SV2A binding was shown to be homogeneous throughout the rodent brain and primarily in gray matter regions of rodent and human brain sections. Analog screening identified MNI-1038, MNI-1126/SDM-8, and SDM-2 as having comparable binding affinities with the currently available PET ligands. Subsequent [18F]MNI-1126/[18F]SDM-8 dynamic micro-PET imaging in rats revealed in vivo uptake and accumulation in the brain with favorable kinetics. Chase studies using 30 mg/kg levetiracetam confirmed that in vivo brain uptake of [18F]MNI-1126/[18F]SDM-8 was reversible.

Conclusions

Taken together, these data suggest [18F]MNI-1126/[18F]SDM-8 (since renamed as [18F]SynVesT-1) characterized via an in vitro screening cascade provided a measurable in vivo SV2A specific signal in the rodent brain. This tracer as well as the close analog [18F]SDM-2 (since renamed as [18F]SynVesT-2) is currently undergoing further evaluation in preclinical and clinical studies.

Key words

PET radioligand Preclinical characterization SV2A Micro-PET imaging Radioligand binding 

Notes

Compliance with Ethical Standards

Conflict of Interest

The authors declare that they have no conflict of interest.

Supplementary material

11307_2019_1428_MOESM1_ESM.pdf (342 kb)
ESM 1 (PDF 341 kb)

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Copyright information

© World Molecular Imaging Society 2019

Authors and Affiliations

  • Shil Patel
    • 1
    Email author
  • Ashley Knight
    • 2
  • Stephen Krause
    • 3
  • Tyler Teceno
    • 3
  • Cedric Tresse
    • 4
  • Songye Li
    • 5
  • Zhengxin Cai
    • 5
  • Alexandra Gouasmat
    • 4
  • Vincent M. Carroll
    • 4
  • Olivier Barret
    • 4
  • Vijay Gottmukkala
    • 4
  • Wenjie Zhang
    • 6
  • Xianhong Xiang
    • 7
  • Thomas Morley
    • 4
  • Yiyun Huang
    • 5
  • Jan Passchier
    • 4
  1. 1.Codiak BiosciencesCambridgeUSA
  2. 2.Centre for Addiction and Mental HealthUniversity of TorontoTorontoCanada
  3. 3.Eisai Inc.Woodcliff LakeUSA
  4. 4.Invicro, LLCBostonUSA
  5. 5.PET Center, Department of Radiology and Biomedical ImagingYale University School of MedicineNew HavenUSA
  6. 6.Department of Nuclear Medicine, West China HospitalSichuan UniversityChengduChina
  7. 7.Department of Interventional RadiologyThe First Affiliated Hospital of Sun Yat-Sen UniversityGuangzhouChina

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