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Mol Imaging Biol. 2017 Dec;19(6):837-845. doi: 10.1007/s11307-017-1070-1.

Synthesis and In Vitro and In Vivo Evaluation of [3H]LRRK2-IN-1 as a Novel Radioligand for LRRK2.

Author information

1
Department of Radiology, New York University School of Medicine, New York, USA.
2
METIS Laboratories, New York, USA.
3
Novandi Chemistry AB, Södertälje, Sweden.
4
Department of Radiology, New York University School of Medicine, New York, USA. yu-shin.ding@nyumc.org.
5
Department of Psychiatry, New York University School of Medicine, New York, USA. yu-shin.ding@nyumc.org.

Abstract

PURPOSE:

LRRK2 (leucine-rich repeat kinase 2) has recently been proven to be a promising drug target for Parkinson's disease (PD) due to an apparent enhanced activity caused by mutations associated with familial PD. To date, there have been no reports in which a LRRK2 inhibitor has been radiolabeled and used for in in vitro or in vivo studies of LRRK2. In the present study, we radiolabeled the LRRK2 ligand, LRRK-IN-1, for the purposes of performing in vitro (IC50, K d , B max, autoradiography) and in vivo (biodistribution, and blocking experiments) evaluations in rodents and human striatum tissues.

PROCEDURES:

[3H]LRRK2-IN-1 was prepared with high radiochemical purity (>99 %) and a specific activity of 41 Ci/mmol via tritium/hydrogen (T/H) exchange using Crabtree's catalyst. For IC50, K d , and B max determination, LRRK2-IN-1 was used as a competing drug for nonspecific binding assessment. The specific binding of the tracer was further evaluated via an in vivo blocking study in mice with a potent LRRK2 inhibitor, Pf-06447475.

RESULTS:

In vitro binding studies demonstrated a saturable binding site for [3H]LRRK2-IN-1 in rat kidney, rat brain striatum and human brain striatum with K d of 26 ± 3 and 43 ± 8, 48 ± 2 nM, respectively. In rat, the density of LRRK2 binding sites (B max) was higher in kidney (6.4 ± 0.04 pmol/mg) than in brain (2.5 ± 0.03 pmol/mg), however, in human brain striatum, the B max was 0.73 ± 0.01 pmol/mg protein. Autoradiography imaging in striatum of rat and human brain tissues gave results consistent with binding studies. In in vivo biodistribution and blocking studies in mice, co-administration with Pf-06447475 (10 mg/kg) reduced the uptake of [3H]LRRK2-IN-1 (%ID/g) by 50-60% in the kidney or brain.

CONCLUSION:

The high LRRK2 brain density observed in our study suggests the feasibility for positron emission tomography imaging of LRRK2 (a potential target) with radioligands of higher affinity and specificity.

KEYWORDS:

Autoradiography; B max; B max/K d; LRRK2; LRRK2-IN-1; PET; Parkinson’s disease

PMID:
28289968
PMCID:
PMC5597475
DOI:
10.1007/s11307-017-1070-1
[Indexed for MEDLINE]
Free PMC Article

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