Sensing Living Bacteria in Vivo Using d‑Alanine-Derived 11C Radiotracers

• Published in: ACS central science Vol. 6; no. 2; pp. 155 - 165
• Main Authors: Parker, Matthew F. L, Luu, Justin M, Schulte, Brailee, Huynh, Tony L, Stewart, Megan N, Sriram, Renuka, Yu, Michelle A, Jivan, Salma, Turnbaugh, Peter J, Flavell, Robert R, Rosenberg, Oren S, Ohliger, Michael A, Wilson, David M
• Format: Journal Article
• Language: English
• Published: American Chemical Society 26-02-2020
• ISSN: 2374-7943; 2374-7951
• DOI: 10.1021/acscentsci.9b00743

Incorporation of d-amino acids into peptidoglycan is a unique metabolic feature of bacteria. Since d-amino acids are not metabolic substrates in most mammalian tissues, this difference can be exploited to detect living bacteria in vivo. Given the prevalence of d-alanine in peptidoglycan muropeptides, as well as its role in several antibiotic mechanisms, we targeted this amino acid for positron emission tomography (PET) radiotracer development. d-[3-11C]­Alanine and the dipeptide d-[3-11C]­alanyl-d-alanine were synthesized via asymmetric alkylation of glycine-derived Schiff-base precursors with [11C]­methyl iodide in the presence of a cinchonidinium phase-transfer catalyst. In cell experiments, both tracers showed accumulation by a wide variety of both Gram-positive and Gram-negative pathogens including Staphylococcus aureus and Pseudomonas aeruginosa. In a mouse model of acute bacterial myositis, d-[3-11C]­alanine was accumulated by living microorganisms but was not taken up in areas of sterile inflammation. When compared to existing clinical nuclear imaging tools, specifically 2-deoxy-2-[18F]­fluoro-d-glucose and a gallium citrate radiotracer, d-alanine showed more bacteria-specific uptake. Decreased d-[3-11C]­alanine uptake was also observed in antibiotic-sensitive microbes after antimicrobial therapy, when compared to that in resistant organisms. Finally, prominent uptake of d-[3-11C]­alanine uptake was seen in rodent models of discitis-osteomyelitis and P. aeruginosa pneumonia. These data provide strong justification for clinical translation of d-[3-11C]­alanine to address a number of important human infections.