Pre-clinical imaging of invasive candidiasis using ImmunoPET/MR

This is the final version of the article. Available from Frontiers Media via the DOI in this record.The human commensal yeast Candida is the 4th most common cause of hospital-acquired bloodstream infections, with C. albicans accounting for the majority of the >400,000 life-threatening infections annually. Diagnosis of invasive candidiasis (IC), a disease encompassing candidemia (blood-borne yeast infection) and deep-seated organ infections, is a major challenge since clinical manifestations of the disease are indistinguishable from viral, bacterial and other fungal diseases, and diagnostic tests for biomarkers in the bloodstream such as PCR, ELISA and pan-fungal β-D-glucan lack either standardisation, sensitivity or specificity. Blood culture remains the gold standard for diagnosis, but test sensitivity is poor and turn-around time slow. Furthermore, cultures can only be obtained when the yeast resides in the bloodstream, with samples recovered from hematogenous infections often yielding negative results. Consequently, there is a pressing need for a diagnostic test that allows the identification of metastatic foci in deep-seated Candida infections, without the need for invasive biopsy. Here, we report the development of a highly specific mouse IgG3 monoclonal antibody (MC3) that binds to a putative β-1,2-mannan epitope present in high molecular weight mannoproteins and phospholipomannans on the surface of yeast and hyphal morphotypes of C. albicans, and its use as a [64Cu]NODAGA-labeled tracer for whole-body pre-clinical imaging of deep-seated C. albicans infections using antibody-guided positron emission tomography and magnetic resonance imaging (immunoPET/MRI). When used in a mouse intravenous (i.v.) challenge model that faithfully mimics disseminated C. albicans infections in humans, the [64Cu]NODAGA-MC3 tracer accurately detects infections of the kidney, the principal site of blood-borne candidiasis. Using a strain of the emerging human pathogen Candida auris that reacts with MC3 in vitro, but which is non-infective in i.v. challenged mice, we demonstrate the accuracy of the tracer in diagnosing invasive infections in vivo. This pre-clinical study demonstrates the principle of antibody-guided molecular imaging for detection of deep organ infections in IC, without the need for invasive tissue biopsy.This work was supported, in part, by the European Union Seventh Framework Program FP7/2007-2013 under grant 602820

New pathogen-specific immunoPET/MR tracer for molecular imaging of a systemic bacterial infection

PublishedArticleThe specific and rapid detection of Enterobacteriaceae, the most frequent cause of gram-negative bacterial infections in humans, remains a major challenge. We developed a non-invasive method to rapidly detect systemic Yersinia enterocolitica infections using immunoPET (antibody-targeted positron emission tomography) with [64Cu]NODAGA-labeled Yersinia-specific polyclonal antibodies targeting the outer membrane protein YadA. In contrast to the tracer [18F]FDG, [64Cu]NODAGA-YadA uptake co-localized in a dose dependent manner with bacterial lesions of Yersinia-infected mice, as detected by magnetic resonance (MR) imaging. This was accompanied by elevated uptake of [64Cu]NODAGA-YadA in infected tissues, in ex vivo biodistribution studies, whereas reduced uptake was observed following blocking with unlabeled anti-YadA antibody. We show, for the first time, a bacteria-specific, antibody-based, in vivo imaging method for the diagnosis of a Gram-negative enterobacterial infection as a proof of concept, which may provide new insights into pathogen-host interactions.The research leading to these results has received funding from the European Union Seventh Framework Program (FP7/2007-2013) under grant agreement n°602820, from the European Social Fund Baden-Württemberg (to SEA), and from the Deutsche Forschungsgemeinschaft (grant WI 3777/1-2; to SW)

Evaluation of Positron Emission Tomographic Tracers for Imaging of Papillomavirus-Induced Tumors in Rabbits

In this study, simultaneous positron emission tomography (PET)/magnetic resonance (MR) imaging was employed to evaluate the feasibility of the PET tracers 2-deoxy-2- 18 F-fluoro-D-glucose ( 18 F-FDG), 11 C-choline, and 18 F-fluorothymidine ( 18 F-FLT) to detect papillomavirus-induced tumors in an established rabbit model system. The combined PET/MR allowed the analysis of tracer uptake of the tumors using the morphologic information acquired by MR. New Zealand White rabbits were infected with cottontail rabbit papillomavirus genomes and were imaged for up to 10 months with a simultaneous PET/MR system during the course of infection. The uptake characteristics of the PET tracers 11 C-choline and 18 F-FLT of tumors and reference tissues were examined relative to the clinical standard, 18 F-FDG. Tracer biodistribution of various organs was measured by gamma-counting after the last PET scan and compared to the in vivo PET/MR 18 F-FDG uptake. Increased tracer uptake was found 2 months postinfection in primary tumors with 18 F-FDG and 11 C-choline, whereas 18 F-FLT failed to detect the tumors at all measured time points. Our data show that the PET tracer 18 F-FDG is superior for imaging papillomavirus-induced tumors in rabbits compared to 11 C-choline and 18 F-FLT. However, 11 C-choline imaging, which has previously been applied to detect various tumor entities in patients, appears to be an alternative to 18 F-FDG

Quantitative Correlation at the Molecular Level of Tumor Response to Docetaxel by Multimodal Diffusion-Weighted Magnetic Resonance Imaging and [F-18]FDG/[F-18]FLT Positron Emission Tomography

We aimed to quantitatively characterize the treatment effects of docetaxel in the HCT116 xenograft mouse model, applying diffusion-weighted magnetic resonance imaging (MRI) and positron emission tomography (PET) using 2-deoxy-2-[ 18 F]fluoro-D-glucose ([ 18 F]FDG) and 3′-deoxy-3′-[ 18 F]-fluorothymidine ([ 18 F]FLT). Mice were imaged at four time points over 8 days. Docetaxel (15 mg/kg) was administered after a baseline scan. Voxel-wise scatterplots of PET and apparent diffusion coefficient (ADC) data of tumor volumes were evaluated with a threshold cluster analysis and compared to histology (GLUT1, GLUT3, Ki67, activated caspase 3a). Compared to the extensive tumor growth observed in the vehicle-treated group (from 0.32 ± 0.21 cm 3 to 0.69 ± 0.40 cm 3 ), the administration of docetaxel led to tumor growth stasis (from 0.32 ± 0.20 cm 3 to 0.45 ± 0.23 cm 3 ). The [ 18 F]FDG/ADC cluster analysis and the evaluation of peak histogram values revealed a significant treatment effect matching histology as opposed to [ 18 F]FLT/ADC. [ 18 F]FLT uptake and the Ki67 index were not in good agreement. Our voxel-based cluster analysis uncovered treatment effects not seen in the separate inspection of PET and MRI data and may be used as an independent analysis tool. [ 18 F]FLT/ADC cluster analysis could still point out the treatment effect; however, [ 18 F]FDG/ADC reflected the histology findings in higher agreement