Investigation of 6-[¹⁸F]-Fluoromaltose as a Novel PET Tracer for Imaging Bacterial Infection

<div><p></p><p>Despite advances in the field of nuclear medicine, the imaging of bacterial infections has remained a challenge. The existing reagents suffer from poor sensitivity and specificity. In this study we investigate the potential of a novel PET (positron emission tomography) tracer that overcomes these limitations.</p><p>Methods</p><p>6-[¹⁸F]-fluoromaltose was synthesized. Its behavior <i>in vitro</i> was evaluated in bacterial and mammalian cultures. Detailed pharmacokinetic and biodistribution profiles for the tracer were obtained from a murine model.</p><p>Results</p><p>6-[¹⁸F]-fluoromaltose is taken up by multiple strains of pathogenic bacteria. It is not taken up by mammalian cancer cell lines. 6-[¹⁸F]-fluoromaltose is retained in infected muscles in a murine model of bacterial myositis. It does not accumulate in inflamed tissue.</p><p>Conclusion</p><p>We have shown that 6-[¹⁸F]-fluoromaltose can be used to image bacterial infection <i>in vivo</i> with high specificity. We believe that this class of agents will have a significant impact on the clinical management of patients.</p></div

<i>In vivo</i> characterization of 6-[¹⁸F]-fluoromaltose.

<p>A) 3D color map from a PET/CT scan of a mouse bearing <i>E.coli</i> induced infection on the left thigh (red arrow) 1 hr after tail-vein injection of 7.4MBq of 6-[¹⁸F]-fluoromaltose. B) Region of interest analysis (ROIs) from PET/CT images at the indicated time points (n = 4 for each time point) * indicates statistical significance with p<0.05. C) Time activity curve showing accumulation of 6-[¹⁸F]-fluoromaltose in the infected muscle (n = 3).</p

<i>In vitro</i> characterization of 6-[¹⁸F]-fluoromaltose.

<p>A) Uptake of 6-[¹⁸F]-fluoromaltose in the indicated strains of bacteria for 60 minutes. B) 1 hour uptake of 6-[¹⁸F]-fluoromaltose in the mammalian cell lines, MDA MB231 and HeLa and its uptake in <i>E.coli</i> in the presence of 1 mM maltose. C) Bioluminescence imaging of a macrophage cell line J774 infected with a bioluminescent strain of <i>Listeria monocytogenes.</i> D) 1 hour uptake of 6-[¹⁸F]-fluoromaltose in the bioluminescent strain of <i>Listeria monocytogenes</i> and in macrophage cell line J774 with and without intracellular <i>Listeria</i> infections.</p

Specificity of 6-[¹⁸F]-fluoromaltose for viable bacteria.

<p>A) A coronal slice from a PET/CT image of a mouse bearing 10⁸ CFU of viable bioluminescent <i>E.coli</i> on the right thigh (red arrow) and 10⁸ CFU of heat-inactivated <i>E.coli</i> on the left thigh, 1hr after tail-vein injection of 7.4MBq of 6-[¹⁸F]-fluoromaltose B) A transverse slice from the same mouse shown in A), with arrows indicating sites of viable and heat inactivated bacteria. C) Bioluminescent image of the mouse shown in A). D) ROI analysis from PET/CT scan of mice (n = 3). * indicates statistical significance.</p

Uptake of 6-[¹⁸F]-fluoromaltose in infection versus inflammation.

<p>A) Ex-vivo biodistribution of 6-[¹⁸F]-fluoromaltose in mice bearing E.coli induced myositis, 2 h and 4 h after tail-vein injection of 7.4MBq of tracer. B) Ex-vivo biodistribution of 6-[¹⁸F]-fluoromaltose in mice bearing turpentine oil induced sterile abscess, 2 h after tail-vein injection of 7.4MBq of tracer. C) Representative gram stained muscle sections with a black arrow indicating presence of <i>E.coli</i> in the infected muscle section. D) Representative H&E stained muscle sections showing neutrophil infiltration in inflamed muscle.</p

A ¹⁸F‑Labeled Saxitoxin Derivative for <i>in Vivo</i> PET-MR Imaging of Voltage-Gated Sodium Channel Expression Following Nerve Injury

Both chronic and neuropathic pain conditions are associated with increased expression of certain voltage-gated sodium ion channel (Na_V) isoforms in peripheral sensory neurons. A method for noninvasive imaging of these channels could represent a powerful tool for investigating aberrant expression of Na_V and its role in pain pathogenesis. Herein, we describe the synthesis and evaluation of a positron emission tomography (PET) radiotracer targeting Na_Vs, the design of which is based on the potent, Na_V-selective inhibitor saxitoxin. Both autoradiography analysis of sciatic nerves excised from injured rats as well as whole animal PET-MR imaging demonstrate that a systemically administered [¹⁸F]-labeled saxitoxin derivative concentrates at the site of nerve injury, consistent with upregulated sodium channel expression following axotomy. This type of PET agent has potential use for serial monitoring of channel expression levels at injured nerves throughout wound healing and/or following drug treatment. Such information may be correlated with pain behavioral analyses to help shed light on the complex molecular processes that underlie pain sensation

Additional file 2: of [18F]FSPG-PET reveals increased cystine/glutamate antiporter (xc-) activity in a mouse model of multiple sclerosis

Dynamic PET imaging of [18F]FSPG uptake in the spinal cords (a) and brains (b). Time-activity curves represent average counts from a dynamic 90-min scan in EAE and naïve mice. Data are mean ± SEM (n = 3–7 animals per group). (DOCX 119 kb

Additional file 7: of [18F]FSPG-PET reveals increased cystine/glutamate antiporter (xc-) activity in a mouse model of multiple sclerosis

xCT protein levels in CNS tissues do not differ between control and naïve mice. SC = spinal cord. Data are represented as mean xCT/Na,K-ATPase signal ± SD (n = 3–5). Significance determined by Mann-Whitney test with NS = not significant. (DOCX 65 kb

Additional file 3: of [18F]FSPG-PET reveals increased cystine/glutamate antiporter (xc-) activity in a mouse model of multiple sclerosis

[18F]FSPG and [18F]FDG ex vivo autoradiography of EAE versus naïve mice. Representative autoradiography images of whole spinal cords and sagittal brain sections from EAE (score 3.0–3.5) versus naïve mice collected ~ 110 min after injection of (a) [18F]FSPG and (b) [18F]FDG. The same brain sections were stained with Nissl and overlayed with the corresponding autoradiographic images. Cb—cerebellum, Ctx—cortex, HC—hippocampus, Med—medulla, Ob—olfactory bulb, Thal—thalamus. Dotted lines highlight region containing the optic chiasm. (DOC 184 kb

Additional file 5: of [18F]FSPG-PET reveals increased cystine/glutamate antiporter (xc-) activity in a mouse model of multiple sclerosis

Ex vivo biodistribution of [18F]FSPG in EAE versus control mice (a) with magnified views of the brain (b) and spinal cord (c) data (n = 8–10, mean %ID/g ± SD). Data was collected 110 min after injection of radiotracer and mean score of EAE mice was 2.4 ± 0.8. Significance determined Mann-Whitney test with ****p < 0.0001, ***p 0.0001–0.001, **p 0.001–0.01, *p 0.01–0.05. (DOCX 128 kb