A Kinome-Wide Selective Radiolabeled TrkB/C Inhibitor for in Vitro and in Vivo Neuroimaging: Synthesis, Preclinical Evaluation, and First-in-Human

Abstract

The proto-oncogenes NTRK1/2/3 encode the tropomyosin receptor kinases TrkA/B/C which play pivotal roles in neurobiology and cancer. We describe herein the discovery of [C]-(R)-3 ([C]-(R)-IPMICF16), a first-in-class positron emission tomography (PET) TrkB/C-targeting radiolabeled kinase inhibitor lead. Relying on extensive human kinome vetting, we show that (R)-3 is the most potent and most selective TrkB/C inhibitor characterized to date. It is demonstrated that [C]-(R)-3 readily crosses the blood-brain barrier (BBB) in rodents and selectively binds to TrkB/C receptors in vivo, as evidenced by entrectinib blocking studies. Substantial TrkB/C-specific binding in human brain tissue is observed in vitro, with specific reduction in the hippocampus of Alzheimer's disease (AD) versus healthy brains. We additionally provide preliminary translational data regarding the brain disposition of [C]-(R)-3 in primates including first-in-human assessment. These results illustrate for the first time the use of a kinome-wide selective radioactive chemical probe for endogenous kinase PET neuroimaging in human.

Automated synthesis of PET radiotracers by copper‐mediated 18F‐fluorination of organoborons: Importance of the order of addition and competing protodeborylation

“…This paper reports our efforts to address these two issues and thereby enable the routine automated production of clinical radiotracer doses by using our previously published Cu‐mediated radiofluorination of arylborons. Proof‐of‐concept is demonstrated through the synthesis of [ 18 F]‐( ± )‐IPMICF17 ( 2‐F ), a radiolabeled inhibitor of tropomyosin receptor kinase B/C (TrkB/C) that is currently being developed for PET imaging of TrkB/C …”

“…To challenge the chemistry further, the optimized [ 18 F]KF dissolution/order of addition with KOTf/K 2 CO 3 eluent was applied to the synthesis of [ 18 F]‐( ± )‐IPMICF17 ( 2‐F ), a PET radiotracer for TrkB/C that is currently being developed by the Schirrmacher and Scott groups (Scheme ) . We expected this molecule to be amenable to such labeling because it has been previously demonstrated that the 6‐(pyrrolidin‐1‐yl)imidazo[1,2‐b]pyridazine core does not inhibit Cu‐mediated fluorination reactions .…”

“…Proof-of-concept is demonstrated through the synthesis of [ 18 F]-(±)-IPMICF17 (2-F), a radiolabeled inhibitor of tropomyosin receptor kinase B/C (TrkB/C) that is currently being developed for PET imaging of TrkB/C. 10,11 2 | EXPERIMENTAL Full details of (radio)synthesis procedures and quality control methods, as well as all associated analytical data, can be found in the Supporting Information.…”

Efficient radiosynthesis and preclinical evaluation of [18F]FOMPyD as a positron emission tomography tracer candidate for TrkB/C receptor imaging

“…To further investigate the binding selectivity, we performed heterologous blocking studies on rat and human brain tissues against a panel of kinase inhibitors, including the protodeboronation side product BOMPyD, type‐I pan‐Trk inhibitor ( R )‐IPMICF22 (TrkB/C IC 50 = 0.57/0.37 nM, respectively), type‐II pan‐Trk inhibitor PF‐06273340 (TrkA/B/C IC 50 = 6/4/3 nM, respectively), and CSF‐1R inhibitor BLZ945 (IC 50 = 1.2 nM) . Across all rat brain cortical regions (posterior, medial, and anterior cortices; Figure A) blocking with BOMPyD, a demethoxy analogue of dual Trk/CSF‐1R inhibitor GW2580 was the highest (Δ = 42.1 ± 6.8%; t (28) = 10.574, P < 0.001; n = 15).…”

“…Recently, several positron emission tomography (PET) tracers based on type‐I TrkB/C inhibitors have been developed and evaluated in preclinical and clinical settings . In particular, [ 11 C]IPMICF16 and [ 18 F]TRACK (Figure A) were the first type‐I TKI‐based PET tracers used for endogenous kinase neuroimaging in nonhuman primates and humans . Two putative selective tracers for in vivo imaging of CSF‐1R have been reported to date as attractive candidates for the PET imaging of microglial activation beyond translocator protein (TSPO) (Figure B).…”