Technetium-99m-Labeled Sulfadiazine: a Targeting Radiopharmaceutical for Scintigraphic Imaging of Infectious Foci Due To Escherichia coli in Mouse and Rabbit Models

Recent Advancements in Radiopharmaceuticals for Infection Imaging

COVID-19 pandemic has heightened the interest toward diagnosis and treatment of infectious diseases. Nuclear medicine, with its powerful scintigraphic, single photon emission computer tomography (SPECT), and positron emission tomography (PET) imaging modalities, has always played an important role in diagnosis of infections and distinguishing them from the sterile inflammation. In addition to the clinically available radiopharmaceuticals, there has been a decades-long effort to develop more specific imaging agents with some examples being radiolabeled antibiotics and antimicrobial peptides for bacterial imaging, radiolabeled antifungals for fungal infections imaging, radiolabeled pathogen-specific antibodies, and molecular engineered constructs. In this chapter, we discuss some examples of the work published in the last decade on developing nuclear imaging agents for bacterial, fungal, and viral infections to generate more interest among nuclear medicine community toward conducting clinical trials of these novel probes, as well as toward developing novel radiotracers for imaging infections.

Highlights of the Latest Developments in Radiopharmaceuticals for Infection Imaging and Future Perspectives

COVID-19 pandemic has heightened the interest toward diagnosis and treatment of infectious diseases. Nuclear medicine with its powerful scintigraphic, single photon emission computer tomography (SPECT) and positron emission tomography (PET) imaging modalities has always played an important role in diagnosis of infections and distinguishing them from the sterile inflammation. In addition to the clinically available radiopharmaceuticals there has been a decades-long effort to develop more specific imaging agents with some examples being radiolabeled antibiotics and antimicrobial peptides for bacterial imaging, radiolabeled anti-fungals for fungal infections imaging, radiolabeled pathogen-specific antibodies and molecular engineered constructs. In this opinion piece, we would like to discuss some examples of the work published in the last decade on developing nuclear imaging agents for bacterial, fungal, and viral infections in order to generate more interest among nuclear medicine community toward conducting clinical trials of these novel probes, as well as toward developing novel radiotracers for imaging infections.

Visualizing and quantifying antimicrobial drug distribution in tissue

The biodistribution and pharmacokinetics of drugs are vital to the mechanistic understanding of their efficacy. Measuring antimicrobial drug efficacy has been challenging as plasma drug concentration is used as a surrogate for tissue drug concentration, yet typically does not reflect that at the intended site(s) of action. Utilizing an image-guided approach, it is feasible to accurately quantify the biodistribution and pharmacokinetics within the desired site(s) of action. We outline imaging modalities used in visualizing drug distribution with examples ranging from in vitro cellular drug uptake to clinical treatment of microbial infections. The imaging modalities of interest are: radio-labeling, magnetic resonance, mass spectrometry imaging, computed tomography, fluorescence, and Raman spectroscopy. We outline the progress, limitations, and future outlook for each methodology. Further advances in these optical approaches would benefit patients and researchers alike, as non-invasive imaging could yield more profound insights with a lower clinical burden than invasive measurement approaches used today.

99m Tc-labeled antibiotics for infection diagnosis: Mechanism, action, and progress

Discovery of penicillin marked a turning point in the history of infection therapy which also led to the emergence of bacterial resistance. It is now 100 years to fight with ever-muted variants of pathogens by developing more and more antibiotics. Since 1987 to todate, no successful class of antibiotic was introduced; this three decade period is known as "the discovery void" period. While, the clinically approved antibiotics are gradually dying in front of bacterial resistance due to which bacterial infections are appearing leading cause of death and disability. Nuclear medicine imaging technique is the strongest modality to diagnose and follow-up of deep-seated and complicated infections. However, the selection of radiolabeled antimicrobial agents plays critical role in gaining sensitivity and specificity of the imaging results. This review comprises of two main sections; first section explains antibiotic targets, and second section explains the imaging efficacy of ^99m Tc-labeled antimicrobial agents against bacterial infection along with the emphasis on progress and update of ^99m Tc-labeled antibiotics as infection imaging probes. The review, in conclusion, could be an acceleration for radiopharmaceutical chemists for designing and developing ^99m Tc-labeled antimicrobial agents to improve infection imaging quality.

Susceptibility of 99mTc-Ciprofloxacin for Common Infection Causing Bacterial Strains Isolated from Clinical Samples: an In Vitro and In Vivo Study

^99mTc-ciprofloxacin scintigraphy is useful in the detection of gram-positive and gram-negative bacterial infections and also for differentiating the infection from aseptic inflammation. However, due to growing bacterial resistance to antibiotics, the ^99mTc-ciprofloxacin no longer can be effective in broad-spectrum infection imaging as it is gradually losing specificity. In this study, we are presenting our findings regarding the in vitro and in vivo susceptibility of ^99mTc-ciprofloxacin for multi-drug-resistant Staphylococcus aurous, Escherichia coli, and Pseudomonas aeruginosa bacterial strains which were isolated from clinical samples. The results of radiosynthesis of ^99mTc-ciprofloxacin showed more the 95% radiochemical purity and less than 5% radioactive impurities. In vitro ^99mTc-ciprofloxacin susceptibility test showed that E. coli offered more resistant to ^99mTc-ciprofloxacin as compared to S. aurous and P. aeruginosa. In vivo study using bacterial infection induced rabbit model also revealed lowest uptake by E. coli lesion. The T/NT values were obtained 1.96 ± 0.15 in the case of E. coli; 2.81 ± 0.51 in the case of S. aurous; and 2.32 ± 0.66 in the case of P. aeruginosa at 4 h post-injection. The SPECT infection imaging of S. aurous, E. coli, and P. aeruginosa bacterial infection induced rabbit models also indicated the clear accumulation in S. aurous and P. aeruginosa lesions while negligible uptake by E. coli lesion further verify the in vitro and in vivo susceptibility profile. On the bases of the results obtained, the ^99mTc-ciprofloxacin showed selective and poor broad spectrum SPECT infection imaging.

Technetium-99m radiolabeling and biological study of epirubicin for in vivo imaging of multi-drug-resistant Staphylococcus aureus infections via single photon emission computed tomography

The development of functional imaging is a promising strategy for diagnosis and treatment of infectious and cancerous diseases. In this study, epirubicin was developed as a [^99m Tc]-labeled radiopharmaceutical for the imaging of multi-drug-resistant Staphylococcus aureus infections. The labeling was carried out using sodium pertechnetate (Na^99m TcO₄ ; ~370 MBq). The other parameters such as amount of ligand, reducing agent (SnCl₂ .2H₂ O), and pH were optimized. The highest labeling yield ≥96.98% was achieved when 0.3 mg epirubicin, 13 μg SnCl₂ .2H₂ O, and ~370 MBq Na^99m TcO₄ were incubated at pH 7 for 15 min in the presence of ascorbic acid at room temperature. Radiochemical purity, stability, charge, and glomerular filtration rate were studied to evaluate the biological compatibility for in vivo administration. Biodistribution investigations showed radiotracer uptake (13.89 ± 1.56% ID/gm organ) by liver and 7.79 ± 0.38% ID/gm organ by kidneys at 30 min post-injection which promisingly wash out at 24 hr post-injection. Scintigraphy study showed selective uptake in S. aureus-infected tissues in contrast to turpentine oil-induced inflamed tissues. Target-to-non-target ratio (6.7 ± 0.05) was calculated at 1 hr post-injection using SPECT gamma camera. The results of this study reveal that the [^99m Tc]-epirubicin can be a choice of imaging and monitoring the treatment process of multi-drug resistant S. aureus bacterial infections.