Synthesis and Preclinical Evaluation of a Novel Fluorine-18-Labeled Tracer for Positron Emission Tomography Imaging of Bruton’s Tyrosine Kinase

Abstract

Bruton’s tyrosine kinase (BTK) is a target for treating B-cell malignancies and autoimmune diseases. To aid in the discovery and development of BTK inhibitors and improve clinical diagnoses, we have developed a positron emission tomography (PET) radiotracer based on a selective BTK inhibitor, remibrutinib. [18F]PTBTK3 is an aromatic, 18F-labeled tracer that was synthesized in 3 steps with a 14.8 ± 2.4% decay-corrected radiochemical yield and ≥99% radiochemical purity. The cellular uptake of [18F]PTBTK3 was blocked up to 97% in JeKo-1 cells using remibrutinib or non-radioactive PTBTK3. [18F]PTBTK3 exhibited renal and hepatobiliary clearance in NOD SCID (non-obese diabetic/​severe combined immunodeficiency) mice, and the tumor uptake of [18F]PTBTK3 in BTK-positive JeKo-1 xenografts (1.23 ± 0.30% ID/cc) was significantly greater at 60 min post injection compared to the tumor uptake in BTK-negative U87MG xenografts (0.41 ± 0.11% ID/cc). In the JeKo-1 xenografts, tumor uptake was blocked up to 62% by remibrutinib, indicating the BTK-dependent uptake of [18F]PTBTK3 in tumors.

Preliminary PET imaging of [11C]evobrutinib in mouse models of colorectal cancer, SARS‐CoV‐2, and lung damage: Radiosynthesis via base‐aided palladium‐NiXantphos‐mediated 11C‐carbonylation

“…While the preliminary imaging studies herein did not show [ 11 C]evobrutinib to be a promising PET radiotracer for imaging the SARS‐CoV‐2 pseudovirus infection or LPS lung injury in mouse models, the development of BTK inhibitors for drug development and PET imaging remains an active area of interest. It is noteworthy that [ 18 F]BTK‐1 and [ 18 F]PTBTK 3 have recently been reported; however, both radiotracers revealed very high abdominal uptake in kidney, liver, and gastrointestinal organs in mice 38,39 …”

“…It is noteworthy that [ 18 F]BTK-1 and [ 18 F]PTBTK 3 have recently been reported; however, both radiotracers revealed very high abdominal uptake in kidney, liver, and gastrointestinal organs in mice. 38,39 4 | CONCLUSIONS [ 11 C]Evobrutinib was successfully synthesized in comparative RCYs using a base-aided palladium-NiXantphos-mediated 11 C-carbonylation. Our ex vivo results were promising, with the visualization of tumors with [ 11 C]evobrutinib and its displacement in the presence of excess unlabeled evobrutinib.…”

Synthesis and Biological Evaluation of Fluorine-18 and Deuterium Labeled l-Fluoroalanines as Positron Emission Tomography Imaging Agents for Cancer Detection

“…The method was slightly adapted from a previously published protocol. 53 The athymic nude mice were then subcutaneously injected with 4 × 10 6 U87MG cells (0.1 mL of 1:1 Matrigel/PBS) in the left flank. The mice were monitored closely until a palpable tumor was present.…”

Diagnostic and Therapeutic Radiopharmaceuticals: A “Hot” Topic

“…Blocking studies demonstrated that [ 18 F]17 uptake in cells was consistent with a BTK-dependent mechanism. 22 Windhorst et al describe the synthesis and preclinical evaluation of [ 11 C]18 (Figure 2) as a PET tracer targeting both mutated epidermal growth factor receptor and anaplastic lymphoma kinase for non-small-cell lung cancer (NSCLC) imaging. 23 Another target for anticancer drug development is the C− X−C motif chemokine receptor 4 (CXCR4).…”

“…Tonge et al reported [ 18 F] 17 (Figure ) for PET imaging of BTK expression levels and target occupancy in vivo . Blocking studies demonstrated that [ 18 F] 17 uptake in cells was consistent with a BTK-dependent mechanism …”