Future Diagnostic Agents

Optical imaging of bacterial infection in living mice using deep-red fluorescent squaraine rotaxane probes

Two structurally related fluorescent imaging probes allow optical imaging of bacterial leg infection models in living athymic and immunocompetent mice. Structurally, the probes are comprised of a deep-red fluorescent squaraine rotaxane scaffold with two appended bis(zinc(II)-dicolylamine) (bis(Zn-DPA)) targeting ligands. The bis(Zn-DPA) ligands have high affinity for the anionic phospholipids and related biomolecules that reside within the bacterial envelope, and they are known to selectively target bacterial cells over the nearly uncharged membrane surfaces of healthy mammalian cells. Planar, whole-animal optical imaging studies showed that intravenous dosing of either probe (10 nmol) allowed imaging of localized infections of Gram-positive Staphylococcus aureus and Gram-negative Salmonella enterica serovar typhimurium. High selectivity for the infected target leg (T) over the contralateral nontarget leg (NT) was reflected by T/NT ratios up to six. The infection imaging signal was independent of mouse humoral immune status, and there was essentially no targeting at a site of sterile inflammation induced by injection of lambda-carrageenan. Furthermore, the fluorescent probe imaging signal colocalized with the bioluminescence signal from a genetically engineered strain of S. enterica serovar typhimurium. Although not highly sensitive (the localized infection must contain at least approximately 10(6) colony forming units for fluorescence visualization), the probes are remarkably selective for bacterial cells considering their low molecular weight (<1.5 kDa) and simple structural design. The more hydrophilic of the two probes produced a higher T/NT ratio in the early stages of the imaging experiment and washed out more rapidly from the blood clearance organs (liver, kidney). Therefore, it is best suited for longitudinal studies that require repeated dosing and imaging of the same animal. The results indicate that fluorescent probes based on squaraine rotaxanes should be broadly useful for in vivo animal imaging studies, and they further validate the ability of imaging probes with bis(Zn-DPA) ligands to selectively target bacterial infections in living animals.

Clinical trial of specific imaging of infections

OBJECTIVE

For several decades Ga citrate, technetium-99m ((99m)Tc) or (111)In-labelled leukocytes have been used for imaging the inflammatory process. Unfortunately, these radiopharmaceuticals are not infection-specific markers. In preclinical settings, radiolabelled antimicrobial peptides (AMPs), such as UBI 29-41 seem to be highly infection-specific and even high doses of these peptides have shown neither toxicity nor side effects in animals.

METHODS

In this study we present data of a recent clinical trial carried out with the (99m)Tc labelled antimicrobial peptide UBI 29-41 ((99m)Tc-UBI 29-41) regarding its sensitivity, specificity, and accuracy in detecting various types of infections in 148 patients. The outcome of the trial with (99m)Tc-UBI 29-41 is compared with that of five other trials.

RESULTS

Preparation of (99m)Tc-UBI 29-41 as a kit formulation is an easy, rapid, and reproducible process, and the tracer is very well tolerated by patients. The radiopharmaceutical has proven to be very stable and after injection into patients the biodistribution (renal clearance) and dosimetry seem to be favourable over other infection imaging radiopharmaceuticals. In this preliminary human study, patients with fever of unknown origin, osteomyelitis, diabetic foot, prosthesis infection, septic arthritis, or bacteraemia were successfully imaged with (99m)Tc-UBI 29-41 scintigraphy.

CONCLUSION

(99m)Tc-UBI 29-41 is a promising agent for the specific detection of infections in humans because of its high sensitivity (96.3%), specificity (94.1%), and accuracy (95.3%) with high positive predictive (95.1%) and negative predictive values (95.5%).

(99m)Tc-labeled-1-thio-beta-d-glucose as a new tool to temporomandibular joint inflammatory disorders diagnosis

AIM

The aim of this study was to evaluate early detection of temporomandibular joint (TMJ) inflammatory changes based on 1-thio-beta-d-glucose radiolabeled with technetium-99m.

METHOD

The method applied a TMJ inflammation model in rats followed by radiopharmaceutical synthesis, intravenous administration of (99m)Tc-1-TG and kinetic scintigraphy imaging.

RESULTS

Results show a significant difference of (99m)Tc-1-TG uptake between inflamed TMJ and the control joint. The biodistribution of (99m)Tc-1-TG by images showed the kidneys' excretion.

CONCLUSION

As conclusion, (99m)Tc-1-TG is a helpful tool in TMJ inflammatory process detection.

Expanding role of 18F-fluoro-D-deoxyglucose PET and PET/CT in spinal infections

(18)F-fluoro-D -deoxyglucose positron emission tomography ([(18)F]-FDG PET) is successfully employed as a molecular imaging technique in oncology, and has become a promising imaging modality in the field of infection. The non-invasive diagnosis of spinal infections (SI) has been a challenge for physicians for many years. Morphological imaging modalities such as conventional radiography, computed tomography (CT), and magnetic resonance imaging (MRI) are techniques frequently used in patients with SI. However, these methods are sometimes non-specific, and difficulties in differentiating infectious from degenerative end-plate abnormalities or postoperative changes can occur. Moreover, in contrast to CT and MRI, FDG uptake in PET is not hampered by metallic implant-associated artifacts. Conventional radionuclide imaging tests, such as bone scintigraphy, labeled leukocyte, and gallium scanning, suffer from relatively poor spatial resolution and lack sensitivity, specificity, or both. Initial data show that [(18)F]-FDG PET is an emerging imaging technique for diagnosing SI. [(18)F]-FDG PET appears to be especially helpful in those cases in which MRI cannot be performed or is non-diagnostic, and as an adjunct in patients in whom the diagnosis is inconclusive. The article reviews the currently available literature on [(18)F]-FDG PET and PET/CT in the diagnosis of SI.