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Background: The urgent demand for innovative theranostic strategies to combat bacterial resistance to antibiotics is evident, with substantial implications for global health. Rapid diagnosis of life-threatening infections can expedite treatment, improving patient outcomes. Leveraging diagnostic modalities i.e., positron emission tomography (PET) and single photon emission computed tomography (SPECT) for detecting focal infections has yielded promising results. Augmenting the sensitivity of current PET and SPECT tracers could enable effective imaging of pathogenic bacteria, including drug-resistant strains.UBI (29–41), an antimicrobial peptide (AMP) fragment recognizes the S. aureus membrane through electrostatic binding. Radiolabeled UBI (29–41) is a promising SPECT and PET-based tracer for detecting focal infections. 2-APBA (2-acetyl-phenyl-boronic acid), a non-natural amino acid, specifically targets lysyl-phosphatidyl-glycerol (lysyl-PG) on the S. aureus membranes, particularly in AMP-resistant strains. We propose that combining UBI with 2-APBA could enhance the diagnostic potential of radiolabeled UBI. Results: Present work aimed to compare the diagnostic potential of two radiolabeled peptides, namely UBI (29–41) and 2-APBA modified UBI (29–41), referred to as UBI and UBI-APBA. APBA modification imparted antibacterial activity to the initially non-bactericidal UBI against S. aureus by inducing a loss of membrane potential. The antibacterial activity demonstrated by UBI-APBA can be ascribed to the synergistic interaction of both UBI and UBI-APBA on the bacterial membrane. To enable PET imaging, we attached the chelator 1,4,7-triazacyclononane 1-glutaric acid 4,7-acetic acid (NODAGA) to the peptides for complexation with the positron emitter Gallium-68 (68Ga). Both NODAGA conjugates were radiolabeled with 68Ga with high radiochemical purity. The resultant 68Ga complexes were stable in phosphate-buffered saline and human serum. Uptake of these complexes was observed in S. aureus but not in mice splenocytes, indicating the selective nature of their interaction. Additionally, the APBA conjugate exhibited superior uptake in S. aureus while preserving the selectivity of the parent peptide. Furthermore, [68Ga]Ga-UBI-APBA demonstrated accumulation at the site of infection in rats, with an improved target-to-non-target ratio, as evidenced by ex-vivo biodistribution and PET imaging. Conclusions: Our findings suggest that linking UBI, as well as AMPs in general, with APBA shows promise as a strategy to augment the theranostic potential of these molecules. [ABSTRACT FROM AUTHOR]

Background: Postsurgical spinal infections are a severe complication and a challenge to the neurosurgeon due to their complex management. Revision surgeries and the removal of hardware are usually necessary. Recently, advances in nuclear medicine have made it possible to employ radiotracers to identify infections. The radiolabeled antimicrobial peptide technetium-99m-ubiquicidin (99mTc-UBI) (29-41) has been demonstrated to detect bacterial infections. UBI 29-41 is a peptide sequence with selective binding to the anionic cell membrane of bacteria, which has recently been used to differentiate between infection and inflammation. Here, we describe the clinical utility of 99mTc-UBI 29-41 single-photon emission computed tomography-computed tomography (SPECT-CT) in a patient suspected of a postoperative infection. Case description: A 54-year-old male who presented with conus medullaris syndrome secondary to T12 spondylodiscitis and multiple abscess collections was initially managed with debridement, corpectomy, and minimally invasive lateral instrumentation. The patient developed postsurgical empyema near the surgical site. The image study avoided the need for a second surgery and hardware removal. Conclusion: The use of 99mTc-UBI 29-41 SPECT-CT served as a tool to avoid a second invasive procedure; instead, conservative management with antibiotics was performed with an effective outcome after two weeks. This radiotracer has utility in cases in which infection is suspected, but the location is not entirely clear, and information is needed to guide the therapeutic approach. [ABSTRACT FROM AUTHOR]

We studied an original radiolabeled complex of antimicrobial peptides UBI29-41 and UBI18-35, ubiquicidin derivatives, for distinguishing between bacterial and aseptic inflammation. For radiolabeling of the peptides with technetium-99m, a bifunctional chelating agent succinimide-1-yl 6-(bis(pyridin-2-ylmethyl)amino)hexanoate was used. The obtained complexes 99mТс-DPAH-UBI29-41 and 99mТс-DPAH-UBI18-35 had radiolabeling yield >80% and radiochemical purity >96%. Accumulation of the complexes in the focus of bacterial inflammation in bone structures and the absence of this complex in the site of aseptic inflammation was confirmed in a rat model of traumatic osteomyelitis by single-photon emission computed tomography. [ABSTRACT FROM AUTHOR]

Published methods for radiolabelling of 1,4,7-triazacyclononane-1,4,7-triacetic acid ubiquicidin (NOTA-UBI) 29–41 to date describe manual or kit-based procedures. The purpose of this study was to develop an automated synthesis method for the synthesis of [68Ga]Ga-NOTA-UBI. NOTA-UBI was successfully labelled with gallium-68 using three different automated procedures. The use of radical scavengers to improve radiochemical purity is also discussed. The automated procedures showed a high degree of robustness and repeatability. The validated automated synthesis protocols using a Scintomics GRP Module will contribute to provide GMP-compliant [68Ga]Ga-NOTA-UBI for clinical infection imaging. [ABSTRACT FROM AUTHOR]

Purpose: Detection of osteomyelitis beneath a diabetic foot ulcer is imperative for proper management; however, accurate and noninvasive diagnosis of osteomyelitis remains a challenge. Ubiquicidin 29-41 (UBI 29-41) is a synthetic antimicrobial peptide fragment reported to be highly infection-specific. Tc-UBI 29-41 has recently been reported to be a promising radiotracer for infection imaging. The aim of this prospective study was to evaluate the utility of Tc-UBI 29-41 scintigraphy in diabetic patients with suspected osteomyelitis of the foot. Methods: Included in the study were 65 patients with type 2 diabetes mellitus and foot ulcer and with clinical suspicion of osteomyelitis . Each patient had a three-phase bone scan and a Tc-UBI scan at 30 and 60 min after injection. The scan was considered to be consistent with osteomyelitis when the Tc-UBI 29-41 uptake was concordant with the Tc-MDP uptake. It was considered negative for osteomyelitis if there was no uptake of Tc-UBI 29-41 or if Tc-UBI 29-41 accumulated in an area not concordant with the abnormal uptake of Tc-MDP on the bone scan. In the latter case a diagnosis of soft-tissue infection was made. Bone infection was confirmed by bone biopsy/culture and by clinical and radiological follow-up. Results: Final analysis was done in 55 patients. Osteomyelitis was confirmed in 37 patients, and 18 patients were free of bone infection. Tc-UBI 29-41 was positive in all 37 patients and with the bone scan as the reference for the bone identified all osteomyelitic foci (68 in total). Tc-UBI 29-41 was negative for osteomyelitis in all 18 patients, and 17 of these patients were diagnosed with soft-tissue infection (Tc-UBI 29-41 accumulation without concordant abnormal uptake on bone scintigraphy). The sensitivity, specificity and accuracy of Tc-UBI 29-41 scan in combination with three-phase bone scan for the diagnosis of osteomyelitis in diabetic foot was 100 %. Accuracy for soft-tissue infection was also 100 %. Maximum accumulation of the Tc-UBI 29-41 with maximum target to background activity was observed in the infectious foci at 30 min after injection. Conclusion: Tc-UBI 29-41 may be a useful agent for the accurate diagnosis of bone infection in diabetic foot because of the high accuracy demonstrated in this pilot study. It was able to differentiate between bone and soft-tissue involvement effectively in combination with a bone scan. [ABSTRACT FROM AUTHOR]

Introduction: Ubiquicidin (UBI) 29-41 is a synthetic antimicrobial peptide that binds with the microbial cell membrane at the location of infection. This study was conducted to evaluate its probable efficacy as an infection- imaging agent with potential to differentiate bacterial infection from sterile inflammation in humans. Methods: Fifteen diabetic foot patients (10 males and 5 females) with suspected bacterial infection, prior to starting antibiotic treatment, were selected for this study. First a routine three phase bone scan and later a 99mTc-UBI scan was performed for all the patients. 555-740 MBq of 99mTc-UBI was injected intravenously. A 10 minute dynamic study was followed by spot views of the suspected region of infection and corresponding normal areas (liver and kidneys) at 60 and 120 mm. Whole-body anterior and posterior images were also acquired. To interpret the studies as positive or negative, visual score (0-3) was used, with scores of 0 (minimal or no uptake; equivalent to soft tissue) and 1 (mild; less uptake than in liver) being considered negative and scores of 2 (moderate; uptake equal to or greater than that in liver) and 3 (intense uptaike equal to or greater than that in kidneys) being considered positive. Results: Of 15 studies performed with 99mTc-UBI, all had positive bacterial cultures. The result of bone scan was positive for osteomyelitis in 12 patients (80%). 99mTc-UBI Scintigraphy was positive in 6 patients, but negative in nine. The sensitivity of 99mTc-UBI for detection of infection was therefore 40%. From 12 patients who had positive bone scans, only 6 had a positive 99mTc-UBI (50%) indicating the sensitivity of 50% for 99~Tc-UBI in osteomyelitis cases. 99mTc-UBI was not positive in any patient who had evidence of soft tissue infection in the bone scan. Conclusion: Although 99mTc-UBl 29-41 was well tolerated by all the patients without any side effects, considering low sensitivity of this agent, this radiopharmaceutical is not of great value for diabetic foot infection diagnosis. [ABSTRACT FROM AUTHOR]

Introduction: Ubiquicidin 29-41 (UBI) is a fragment of the cationic antimicrobial peptide that is present in various species including humans. The purpose of this study was to investigate radiochemical and biological characteristics of [6-hydrazinopyridine-3-carboxylic acid (HYNIC)]-UBI 29-41 designed for the labeling with 99mTc using tricine as coligand. Methods: Synthesis was preformed on a solid phase using a standard Fmoc strategy and HYNIC precursor coupled at the N-terminus. Purified peptide conjugate was labeled with 99mTc at 100°C for 10 min, Radiochemical analysis involved ITLC and high-performance liquid chromatography methods. Peptide conjugate stability and affinity to human serum was challenged for 24 hours and its in vitro binding to bacteria was assessed. Biodistribution and accumulation of radiopeptide in staphylococcus aureus infected mice were studied using scintigraphy and ca- vivo counting. Results: Radiolabeling was performed at high specific activities, and radiochemical purity was >95%. The stability of radiolabeled peptide in human serum was excellent. In vitro studies showed 70% of radioactivity was bound to bacteria. After injection into mice with a bacterial infection, removing from the circulation occurred mainly by renal clearance and site of infection was rapidly detected within 30 rain. Target to nontarget muscle ratio was 2.099 ± 0.05% at 30 rain post injection. Conclusion: [99mTc-HYNIC]-UBI 29-41 showed favorable radiochemical and biological characteristics which permitted detection of the infection with optimal visualization within 30 min. [ABSTRACT FROM AUTHOR]

The uptake of 99mTc-UBI (29–41) was evaluated at sites of bacterial infections in rabbits before and after treatment with ciprofloxacin. Staphylococcus aureus susceptible to ciprofloxacin was used to induce a focal infection in each rabbit of group 1 (G1), group 2 (G2), and group 3 (G3) with 2 × 104, 2 × 106, and 2 × 108 colony forming units (CFU), respectively. After 24 h, images of infected thighs (target: T) and contralateral thighs (nontarget: NT) were acquired. Animals then received ciprofloxacin intramuscularly for 5 days followed by imaging on the third and fifth days. The control group 4 (G4) was imaged at days 1, 3, and 5 under the same acquisition parameters. Group 5 (G5) was employed to study biodistribution of the peptide. Increases in (T/NT) ratios in G1, G2, and G3 were observed from 5 min onwards with maximum values at 60 min. G3 revealed the highest accumulation of the peptide. Growth of the same strain of S. aureus on blood agar medium was visualized after fine needle aspiration. After ciprofloxacin treatment, the images for G1–G3 resulted in significantly decreased ( P < 0.05) T/NT values on the third and fifth days that correlated with reduction in number of viable bacteria. No significant difference ( P < 0.05) in left to right thigh ratios in the control group (G4) was observed. Biodistribution of the peptide showed rapid removal of tracer from circulation through the kidneys. 99m Tc-UBI (29–41) accumulation directly correlates with the number of viable bacteria. This infection localization agent can be utilized for monitoring efficacy and duration of antibiotic treatment. [ABSTRACT FROM AUTHOR]

Introduction: Radiotracers are widely used in medical imaging, using techniques of gamma-camera imaging (scintigraphy and SPECT) or positron emission tomography (PET). In bone marrow infection, there is no single routine test available that can detect infection with sufficiently high diagnostic accuracy. Here, we review radiotracers used for imaging of bone marrow infection, also known as osteomyelitis, with a focus on why these molecules are relevant for the task, based on their physiological uptake mechanisms. The review comprises [67Ga]Ga-citrate, radiolabelled leukocytes, radiolabelled nanocolloids (bone marrow) and radiolabelled phosphonates (bone structure), and [18F]FDG as established radiotracers for bone marrow infection imaging. Tracers that are under development or testing for this purpose include [68Ga]Ga-citrate, [18F]FDG, [18F]FDS and other non-glucose sugar analogues, [15O]water, [11C]methionine, [11C]donepezil, [99mTc]Tc-IL-8, [68Ga]Ga-Siglec-9, phage-display selected peptides, and the antimicrobial peptide [99mTc]Tc-UBI29-41 or [68Ga]Ga-NOTA-UBI29-41. Conclusion: Molecular radiotracers allow studies of physiological processes such as infection. None of the reviewed molecules are ideal for the imaging of infections, whether bone marrow or otherwise, but each can give information about a separate aspect such as physiology or biochemistry. Knowledge of uptake mechanisms, pitfalls, and challenges is useful in both the use and development of medically relevant radioactive tracers. [ABSTRACT FROM AUTHOR]