In Vitro Evaluation of Radiolabeled Amphotericin B for Molecular Imaging of Mold Infections

Lukas Page; Andrew J Ullmann; Fabian Schadt; Sebastian Wurster; Samuel Samnick

doi:10.1128/AAC.02377-19

In Vitro Evaluation of Radiolabeled Amphotericin B for Molecular Imaging of Mold Infections

Antimicrob Agents Chemother. 2020 Jun 23;64(7):e02377-19. doi: 10.1128/AAC.02377-19. Print 2020 Jun 23.

Authors

Lukas Page^{1

2}, Andrew J Ullmann¹, Fabian Schadt², Sebastian Wurster^#^{3

4}, Samuel Samnick^#²

Affiliations

¹ Department of Internal Medicine II, Division of Infectious Diseases, University Hospital of Wuerzburg, Wuerzburg, Germany.
² Department of Nuclear Medicine, University Hospital of Wuerzburg, Wuerzburg, Germany.
³ Department of Internal Medicine II, Division of Infectious Diseases, University Hospital of Wuerzburg, Wuerzburg, Germany stwurster@mdanderson.org.
⁴ Department of Infectious Diseases, University of Texas MD Anderson Cancer Center, Houston, Texas, USA.

^# Contributed equally.

Abstract

Invasive pulmonary aspergillosis and mucormycosis are life-threatening complications in immunocompromised patients. A rapid diagnosis followed by early antifungal treatment is essential for patient survival. Given the limited spectrum of biomarkers for invasive mold infections, recent studies have proposed the use of radiolabeled siderophores or antibodies as molecular probes to increase the specificity of radiological findings by nuclear imaging modalities. While holding enormous diagnostic potential, most of the currently available molecular probes are tailored to the detection of Aspergillus species, and their cost-intensive and sophisticated implementation restricts their accessibility at less specialized centers. In order to develop cost-efficient and broadly applicable tracers for pulmonary mold infections, this study established streamlined and high-yielding protocols to radiolabel amphotericin B (AMB) with the gamma emitter technetium-99m (^99mTc-AMB) and the positron emitter gallium-68 (⁶⁸Ga-AMB). The radiochemical purity of the resulting tracers consistently exceeded 99%, and both probes displayed excellent stability in human serum (>98% after 60 to 240 min at 37°C). The uptake kinetics by representative mold pathogens were assessed in an in vitro Transwell assay using infected endothelial cell layers. Both tracers accumulated intensively and specifically in Transwell inserts infected with Aspergillus fumigatus, Rhizopus arrhizus, and other clinically relevant mold pathogens compared with their accumulation in uninfected inserts and inserts infected with bacterial controls. Inoculum-dependent enrichment was confirmed by gamma counting and autoradiographic imaging. Taken together, this pilot in vitro study proposes ^99mTc-AMB and ⁶⁸Ga-AMB to be facile, stable, and specific probes, meriting further preclinical in vivo evaluation of radiolabeled amphotericin B for molecular imaging in invasive mycoses.

Keywords: antifungals; aspergillosis; biomarker; mucormycosis; nuclear imaging; tracer.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Amphotericin B*
Antifungal Agents / therapeutic use
Aspergillus fumigatus
Humans
Molecular Imaging
Mucormycosis* / drug therapy

Substances

Antifungal Agents
Amphotericin B