Abstract
Orthopedic implant infections (OIIs) present diagnostic and therapeutic challenges, owing to the lack of methods to distinguish between active infection and sterile inflammation. To address this unmet need, d-amino-acid-based radiotracers with unique metabolic profiles in microorganisms have emerged as a novel class of infection-specific imaging agents. Given the pivotal role of d-glutamine in bacterial biofilm formation and virulence, herein, we explored the potential of positron emission tomography (PET) imaging with d-[5-(11)C]-Glutamine (d-[5-(11)C]-Gln) for early detection and treatment monitoring of OIIs. In vitro studies confirmed an active uptake of d-[5-(11)C]-Gln by Staphylococcus aureus (S. aureus) biofilm commonly associated with OIIs. In vivo evaluations included PET imaging comparisons with d-[5-(11)C]-Gln vs l-[5-(11)C]-Gln or 2-deoxy-2-[(18)F]-fluoroglucose ([(18)F]-FDG) in a rat OII model with tibial implantation of sterile or S. aureus-colonized stainless-steel screws before and after treatment. These studies demonstrated that the uptake of d-[5-(11)C]-Gln was significantly higher in the infected screws than that in sterile screws (∼3.4-fold, p = 0.008), which displayed significantly higher infection-to-background muscle uptake ratios (∼2-fold, p = 0.011) with d-[5-(11)C]-Gln as compared to l-[5-(11)C]-Gln. Following a 3 week vancomycin treatment, imaging with d-[5-(11)C]-Gln showed a significant reduction in uptake at the infected sites (∼3-fold, p = 0.0008). Further regression analyses revealed a superior correlation of residual infection-associated radiotracer uptake with the postimaging ex vivo bacterial counts for d-[5-(11)C]-Gln (k = 0.473, R(2) = 0.796) vs [(18)F]-FDG (k = 0.212, R(2) = 0.434), suggesting that d-[5-(11)C]-Gln PET had higher sensitivity for detecting residual bacterial burden than [(18)F]-FDG PET. Our results demonstrate the translational potential of d-[5-(11)C]-Gln PET imaging for noninvasive detection and treatment monitoring of OIIs.