Nonclinical investigations of a novel heart-type fatty acid–binding protein ligand, [18F]LUF: three-lot process validation, safety assessment, and radiation dosimetry

Abstract

Background

Heart-type fatty acid–binding protein (FABP3) mediates the intracellular transport of fatty acids and is highly expressed in the myocardium. During myocardial infarction, FABP3 leaks from the myocardial cytoplasm into the blood; thus, detection of FABP3 using positron emission tomography (PET) is useful in identifying the site of myocardial damage. 4-(4-Fluoro-2-(1-phenyl-5-(2-(trifluoromethyl)phenyl)-1H-pyrazol-3-yl)phenoxy)butanoic acid (LUF) is a small-molecule organic compound that specifically binds FABP3. We confirmed that fluorine-18–labeled LUF enables clear, high-quality visualization of the myocardium as well as lesions associated with myocardial injury. In this study, we performed a process validation of [¹⁸F]LUF production for clinical use and evaluated its nonclinical toxicity and radiation dosimetry estimates using mouse biodistribution data.

Results

The activity yield of [¹⁸F]LUF at the end of synthesis was > 8 GBq, with > 99% radiochemical purity, > 500 GBq/μmol molar activity, and < 1.5 μg/185 MBq total chemical content. All process validation batches complied with the product specifications. An extended single-dose intravenous toxicity study in male and female Sprague–Dawley rats indicated a no-observed adverse effect level for LUF and decay-outed [¹⁸F]LUF injection solution of ≥ 25 μg/kg and ≥ 2.5 mL/kg, respectively. These doses are > 100 times the postulated maximum dose of LUF (0.25 μg/kg) and [¹⁸F]LUF injection solution (370 MBq). Reverse mutation tests were negative for LUF and the OH form produced after β-decay of [¹⁸F]LUF. Neither LUF nor the OH form exhibited cardiotoxicity toward cardiomyocytes derived from human induced pluripotent stem cells at > 100 times the postulated maximum dose. Biodistribution study results demonstrated predominantly hepatobiliary excretion of radioactivity. The most critical organ affected was the heart wall (68.6 μGy/MBq). The estimated effective dose was calculated as 10.2 μSv/MBq. These radiation exposure doses are equivalent to 25.4 mGy (heart wall) and 3.78 mSv for a planned maximum dose of 370 MBq.

Conclusions

[¹⁸F]LUF shows acceptable pharmacological safety at the dose required for adequate PET imaging. The potential risks associated with [¹⁸F]LUF injection are well within the acceptable dose limits.