Sensing living P. aeruginosa using D-alanine derived radiotracers

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PROJECT SUMMARY: This application addresses a major challenge that radiologists and other physicians encounter frequently, namely distinguishing active infection from other processes in the human body. Specifically, the proposed work is motivated by the difficulty in diagnosing and treating pneumonias in cystic fibrosis patients, especially those caused by P. aeruginosa. Clinically available imaging tools either (1) are limited by their background accumulation in the lungs or (2) image the host response to infection rather than the living bacteria themselves. To address this challenge, we have developed several PET radiotracers that exploit metabolic pathways specific to bacteria, including D-amino acid derived probes most recently D-[3-11C]alanine. When D-[3-11C]alanine was applied to several compelling preclinical models of infection, we found that it was exquisitely sensitive to P. aeruginosa, which is not the case for the vast majority of reported radiotracers. We further showed that D-[3-11C]alanine is a radiotracer with (1) a simple, high-yield radiosynthesis (2) good in vivo stability (3) appropriate mimicry of the endogenous substrate (4) high rate of incorporation into both gram- negative and gram-positive bacteria and (5) low uptake in background tissues. These studies demonstrate the outstanding potential of D-[3-11C]alanine, with the proposed work necessary to further validate and understand this tracer. We will first expand our radiochemical methods, synthesizing the D-[1-11C]alanine isotopomer and structurally related 18F probes (Specific Aim 1). We will then further investigate the lead 11C isotopomer in vitro, analyzing its performance in clinical P. aeruginosa strains and validated biofilm models (Specific Aim 2). In Specific Aim 3, we will extend these concepts in vivo employing both acute and chronic models of P. aeruginosa infection.