68 Ga-labeled phage-display selected peptides as tracers for positron emission tomography imaging of Staphylococcus aureus biofilm-associated infections: Selection, radiolabelling and preliminary biological evaluation

Preclinical evaluation of potential infection‐imaging probe [68Ga]Ga‐DOTA‐K‐A9 in sterile and infectious inflammation

“…As seen in the first line of Table , when using the traditional purification setup: C18 cartridge preconditioning with first a 50% EtOH aq solution then isotonic saline; product rinse by isotonic saline; and final a product elution with first a 50% EtOH aq solution followed by isotonic saline for formulation, half of the radioactivity remained on the C18‐cartridge, including retained [ 68 Ga]Ga‐DOTA‐K‐A9. During the investigation of the similar issue with [ 68 Ga]Ga‐DOTA‐KGSG‐A11 on the C18 cartridge, we observed no improvement in the elution of the radio‐peptide when increasing the ethanol concentration in the product elution step . However, the [ 68 Ga]Ga‐DOTA‐KGSG‐A11 peptide was most efficiently eluted when using a 50% EtOH/PBS (2%) solution as eluent, and the radio‐peptide was subsequently stable in that formulation up to 2 hours.…”

“…In this method, the HEPES is necessary in the product formulation where it acts as radical scavenger to prevent radiolysis of the radio‐peptide. In a previous evaluation of the A9 68 Ga‐labelling, the use of HEPES aq solutions lower than 0.1 M resulted in a slightly improved radiochemical purity, potentially due to reduced [ 68 Ga]Ga‐HEPES complexation, while the stability of [ 68 Ga]Ga‐DOTA‐K‐A9 deceased most likely as a consequence of increased radiolysis …”

“…The different bacteria used in the study are listed in Table . The S aureus isolate originating from a clinical prosthesis infection, which was used to prepare the biofilm applied in the preceding phage‐display selection of the A9 peptide, was also used in both the murine SC infection model and in vitro evaluation of TAMRA‐K‐A9. The bacteria were grown overnight from a single colony in tryptic soy broth (TSB) at 37°C while being gently shaken at 200 rpm on an incubator shaker (IKA KS 4000i control, from VWR).…”

“…The [ 68 Ga]Ga‐DOTA‐K‐A9 for the mice pilot infection study was prepared as previously described . Briefly, approx 1.0 GBq [ 68 Ga]GaCl 3 was eluted from the generator with 0.1 M HCl (10 mL) and trapped on a Strata‐X‐C cartridge, before it was eluted with a 0.02 M HCl/acetone (97.6%) solution (600 μL).…”

“…Staphylococcus aureus is a major cause of soft tissue, endovascular, bone, and postsurgical infections and is often associated with abscess and biofilm formation . We have earlier reported the identification of the dodecapeptide A9 by phage‐display selection against S aureus biofilm, as well as the gallium‐68 labelling, and initial biological evaluation of the 1,4,7,10‐tetraazacyclododecane‐N,N′,N″,N‴‐tetraacetic acid (DOTA) conjugated peptide DOTA‐K‐A9 (Figure A) as a potentially bacteria‐specific PET‐tracer …”