Improved Radiosynthesis of [18F]-Labeled Oxazolidinone Antibiotics for Future Clinical Translation

Abstract

The development of radiolabeled antibiotics for positron emission tomography/computed tomography (PET/CT) imaging has the potential to substantially improve our ability to measure compartment-specific antibiotic exposures for various infections. This study focuses on the radiosynthesis and optimization of fluorine-18 [¹⁸F]-labeled oxazolidinone antibiotics, specifically [¹⁸F]linezolid and [¹⁸F]sutezolid, followed by in vivo imaging of the latter. Copper-mediated radiofluorination of boronated precursors was enhanced by variation of the phase-transfer catalysts and base conditions to improve the reaction efficiency. Preclinical evaluation of [¹⁸F]sutezolid in uninfected and Mycobacterium tuberculosis-infected mice demonstrated favorable biodistribution and metabolic stability, with minimal defluorination. Dynamic PET imaging confirmed rapid clearance, predominant renal and hepatobiliary excretion, and consistent tissue uptake across infected and uninfected models. These findings support the feasibility of [¹⁸F]-labeled oxazolidinones as PET tracers for compartment-specific antibiotic exposures, paving the way for optimizing antibiotic dosing and future personalized treatments in patients.

Keywords: antibiotic; copper-mediated radiofluorination; fluorine-18; oxazolidinone; tuberculosis.

Figure 1.

Fluorinated oxazolidinones with known activity against Mycobacterium tuberculosis.

Figure 2.

Dependence of the AY of [¹⁸F]linezolid (2a) as a function of changing precursor (1a) and Cu(OTf)₂(py)₄ amount using two different PTC a) K₂₂₂; b) Et₄N·HCO₃; c) Comparative representation of the AYs using both PTC; d) Comparative AYs as a function of changing the PTC and 1a: Cu(OTf)₂(py)₄ ratios. Filled bars represent AY obtained when using Et₄N·HCO₃ as PTC. Data is presented as Mean± SD (n=3).

Figure 3.

Dependence of the AY of [¹⁸F]sutezolid (2b) as a function of changing precursor (1b) and Cu(OTf)₂(py)₄ amounts using two different PTC a) K₂₂₂; b)Et₄N·HCO₃; c) Comparative representation of the AYs using both PTC; d) Comparative AYs as a function of changing the PTC and 1b: Cu(OTf)₂(py)₄ ratios. Filled bars represent AY obtained when using Et₄N·HCO₃ as PTC. Data is presented as Mean± SD (n=3).

Figure 4.

Preclinical evaluation of [¹⁸F]sutezolid (2b) in mice; panels a-c showing coronal PET/CT (%ID/g, 0– 60 min post injection) in a) uninfected mice; b) Mycobacterium tuberculosis infected mice (2 weeks post infection); c) M. tuberculosis infected mice treated orally with sutezolid containing antibiotic regimen for 2 weeks; d) Time−activity curves (TACs) for blood, brain, lungs, liver, kidneys and bone demonstrating both renal and hepatobiliary excretion in uninfected animals (n = 4, 2 VOIs/organ); e) Collated TACs for blood, brain, lungs, liver, kidneys and bone demonstrate both renal and hepatobiliary excretion (n = 16, 2 VOIs/organ) f) Comparison of AUCratio _{(tissue/blood)} in the three tested animal groups; g) Ex vivo biodistribution at 60 min post-injection using gamma counting (n = 4). Data presented as Median± IQR.

Figure 5.

Representative HPLC radiochromatograms for the purification of [¹⁸F]linezolid (2a) and [¹⁸F]sutezolid (2b); a) Analytical HPLC radiochromatogram for the pure 2a; b) HPLC radiochromatogram of pure 2a co-injected with linezolid standard; c) Analytical HPLC radiochromatogram for the pure 2b; d) HPLC radiochromatogram of pure 2b co-injected with sutezolid standard.

Scheme 1.

Synthetic scheme for obtaining [¹⁸F]linezolid (2a) and [¹⁸F]sutezolid (2b) from their respective boronic acid pinacol ester (1a and 1b).