In Vitro and In Vivo Evaluation of 99mTc-Polymyxin B for Specific Targeting of Gram-Bacteria

Abstract

Background: Infectious diseases are one of the main causes of morbidity and mortality worldwide. Nuclear molecular imaging would be of great help to non-invasively discriminate between septic and sterile inflammation through available radiopharmaceuticals, as none is currently available for clinical practice. Here, we describe the radiolabeling procedure and in vitro and in vivo studies of 99mTc-polymyxin B sulfate (PMB) as a new single photon emission imaging agent for the characterization of infections due to Gram-negative bacteria. Results: Labeling efficiency was 97 ± 2% with an average molar activity of 29.5 ± 0.6 MBq/nmol. The product was highly stable in saline and serum up to 6 h. In vitro binding assay showed significant displaceable binding to Gram-negative bacteria but not to Gram-positive controls. In mice, 99mTc-HYNIC-PMB was mainly taken up by liver and kidneys. Targeting studies confirmed the specificity of 99mTc-HYNIC-PMB obtained in vitro, showing significantly higher T/B ratios for Gram-negative bacteria than Gram-positive controls. Conclusions: In vitro and in vivo results suggest that 99mTc-HYNIC-PMB has a potential for in vivo identification of Gram-negative bacteria in patients with infections of unknown etiology. However, further investigations are needed to deeply understand the mechanism of action and behavior of 99mTc-HYNIC-PMB in other animal models and in humans.

Radiolabelled FGF-2 for Imaging Activated Fibroblasts in the Tumor Micro-Environment

“…The affinity of the radiopharmaceutical and the capacity of the 99m Tc-FGF-2 to bind the receptor after the radiolabeling process was assessed in vitro using a competitive binding assay. The measurements were obtained using a LigandTracer™ (Ridgeview Instruments AB, Uppsala, Sweden) [21]. Two different cell lines were used: a human keratinocyte (HEK001) cell line (CRL-2404, ATCC, Manassas, VA, USA), which stably overexpress FGFR-2c (2C cells), and EV cells overexpressing FGFR-2b.…”

Recently developed radiopharmaceuticals for bacterial infection imaging

“…P. aeruginosa and A. baumanii infections. Auletta et al ( 2021 ) radiolabelled polymyxin B sulphate with 99m Tc using succinimidyl-6-hydrazinonicotinate hydrochloride (HYNIC) as a bifunctional chelating agent. [ 99m Tc]Tc-HYNIC-PMB was obtained at a labelling efficiency of approximately 97% using a HYNIC:PMB molar ratio of 1.5:1 and demonstrated stability in human serum and saline over 6 h. In vitro bacterial uptake studies demonstrated specific [ 99m Tc]Tc-HYNIC-PMB uptake in Gram-negative bacterial cell cultures ( E. coli , P. aeruginosa and A. baumanii ) and generally lower uptake in Gram-positive bacterial cell cultures ( K. pneumoniae , S. aureus and E. faecalis ).…”

The Development and Validation of Radiopharmaceuticals Targeting Bacterial Infection

“…When tracer sensitivity to different pathogens is being compared, a dual infection model (e.g., a mouse infected with 2 pathogens) (38) or separate carefully generated cohorts (e.g., in comparing [ 99m Tc]hydrazinonicotinamide polymyxin B accumulation in Pseudomonas aeruginosa and Staphylococcus aureus) may be used (Fig. 3) (54). The volume of distribution, metabolism, excretion, vascular leakage, etc., are also key variables that should be considered before choosing a specific model.…”