TY - JOUR
T1 - Evaluation of TSPO PET Ligands [18F]VUIIS1009A and [18F]VUIIS1009B
T2 - Tracers for Cancer Imaging
AU - Tang, Dewei
AU - Li, Jun
AU - Buck, Jason R.
AU - Tantawy, Mohamed Noor
AU - Xia, Yan
AU - Harp, Joel M.
AU - Nickels, Michael L.
AU - Meiler, Jens
AU - Manning, H. Charles
N1 - Publisher Copyright:
© 2016, World Molecular Imaging Society.
PY - 2017/8/1
Y1 - 2017/8/1
N2 - Purpose: Positron emission tomography (PET) ligands targeting translocator protein (TSPO) are potential imaging diagnostics of cancer. In this study, we report two novel, high-affinity TSPO PET ligands that are 5,7 regioisomers, [18F]VUIIS1009A ([18F]3A) and [18F]VUIIS1009B ([18F]3B), and their initial in vitro and in vivo evaluation in healthy mice and glioma-bearing rats. Procedures: VUIIS1009A/B was synthesized and confirmed by X-ray crystallography. Interactions between TSPO binding pocket and novel ligands were evaluated and compared with contemporary TSPO ligands using 2D 1H-15N heteronuclear single quantum coherence (HSQC) spectroscopy. In vivo biodistribution of [18F]VUIIS1009A and [18F]VUIIS1009B was carried out in healthy mice with and without radioligand displacement. Dynamic PET imaging data were acquired simultaneously with [18F]VUIIS1009A/B injections in glioma-bearing rats, with binding reversibility and specificity evaluated by radioligand displacement. In vivo radiometabolite analysis was performed using radio-TLC, and quantitative analysis of PET data was performed using metabolite-corrected arterial input functions. Imaging was validated with histology and immunohistochemistry. Results: Both VUIIS1009A (3A) and VUIIS1009B (3B) were found to exhibit exceptional binding affinity to TSPO, with observed IC50 values against PK11195 approximately 500-fold lower than DPA-714. However, HSQC NMR suggested that VUIIS1009A and VUIIS1009B share a common binding pocket within mammalian TSPO (mTSPO) as DPA-714 and to a lesser extent, PK11195. [18F]VUIIS1009A ([18F]3A) and [18F]VUIIS1009B ([18F]3B) exhibited similar biodistribution in healthy mice. In rats bearing C6 gliomas, both [18F]VUIIS1009A and [18F]VUIIS1009B exhibited greater binding potential (k3/k4)in tumor tissue compared to [18F]DPA-714. Interestingly, [18F]VUIIS1009B exhibited significantly greater tumor uptake (VT) than [18F]VUIIS1009A, which was attributed primarily to greater plasma-to-tumor extraction efficiency. Conclusions: The novel PET ligand [18F]VUIIS1009B exhibits promising characteristics for imaging glioma; its superiority over [18F]VUIIS1009A, a regioisomer, appears to be primarily due to improved plasma extraction efficiency. Continued evaluation of [18F]VUIIS1009B as a high-affinity TSPO PET ligand for precision medicine appears warranted.
AB - Purpose: Positron emission tomography (PET) ligands targeting translocator protein (TSPO) are potential imaging diagnostics of cancer. In this study, we report two novel, high-affinity TSPO PET ligands that are 5,7 regioisomers, [18F]VUIIS1009A ([18F]3A) and [18F]VUIIS1009B ([18F]3B), and their initial in vitro and in vivo evaluation in healthy mice and glioma-bearing rats. Procedures: VUIIS1009A/B was synthesized and confirmed by X-ray crystallography. Interactions between TSPO binding pocket and novel ligands were evaluated and compared with contemporary TSPO ligands using 2D 1H-15N heteronuclear single quantum coherence (HSQC) spectroscopy. In vivo biodistribution of [18F]VUIIS1009A and [18F]VUIIS1009B was carried out in healthy mice with and without radioligand displacement. Dynamic PET imaging data were acquired simultaneously with [18F]VUIIS1009A/B injections in glioma-bearing rats, with binding reversibility and specificity evaluated by radioligand displacement. In vivo radiometabolite analysis was performed using radio-TLC, and quantitative analysis of PET data was performed using metabolite-corrected arterial input functions. Imaging was validated with histology and immunohistochemistry. Results: Both VUIIS1009A (3A) and VUIIS1009B (3B) were found to exhibit exceptional binding affinity to TSPO, with observed IC50 values against PK11195 approximately 500-fold lower than DPA-714. However, HSQC NMR suggested that VUIIS1009A and VUIIS1009B share a common binding pocket within mammalian TSPO (mTSPO) as DPA-714 and to a lesser extent, PK11195. [18F]VUIIS1009A ([18F]3A) and [18F]VUIIS1009B ([18F]3B) exhibited similar biodistribution in healthy mice. In rats bearing C6 gliomas, both [18F]VUIIS1009A and [18F]VUIIS1009B exhibited greater binding potential (k3/k4)in tumor tissue compared to [18F]DPA-714. Interestingly, [18F]VUIIS1009B exhibited significantly greater tumor uptake (VT) than [18F]VUIIS1009A, which was attributed primarily to greater plasma-to-tumor extraction efficiency. Conclusions: The novel PET ligand [18F]VUIIS1009B exhibits promising characteristics for imaging glioma; its superiority over [18F]VUIIS1009A, a regioisomer, appears to be primarily due to improved plasma extraction efficiency. Continued evaluation of [18F]VUIIS1009B as a high-affinity TSPO PET ligand for precision medicine appears warranted.
KW - Cancer imaging
KW - PET
KW - Precision medicine
KW - TSPO
KW - VUIIS1009A
KW - VUIIS1009B
UR - http://www.scopus.com/inward/record.url?scp=84995485065&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84995485065&partnerID=8YFLogxK
U2 - 10.1007/s11307-016-1027-9
DO - 10.1007/s11307-016-1027-9
M3 - Article
C2 - 27853987
AN - SCOPUS:84995485065
SN - 1536-1632
VL - 19
SP - 578
EP - 588
JO - Molecular Imaging and Biology
JF - Molecular Imaging and Biology
IS - 4
ER -