Sorlin Alexandre M, López-Álvarez Marina, Biboy Jacob, Gray Joe, Rabbitt Sarah J, Rahim Junaid Ur, Lee Sang Hee, Bobba Kondapa Naidu, Blecha Joseph, Parker Mathew F L, Flavell Robert R, Engel Joanne, Ohliger Michael, Vollmer Waldemar, Wilson David M
Department of Radiology, Biomedical Imaging University of California, San Francisco, San Francisco, California 94158, United States.
The Centre for Bacterial Cell Biology, Newcastle University Newcastle, Newcastle upon Tyne NE2 4AX, United Kingdom.
JACS Au. 2024 Feb 26;4(3):1039-1047. doi: 10.1021/jacsau.3c00776. eCollection 2024 Mar 25.
Imaging is increasingly used to detect and monitor bacterial infection. Both anatomic (X-rays, computed tomography, ultrasound, and MRI) and nuclear medicine ([In]-WBC SPECT, [F]FDG PET) techniques are used in clinical practice but lack specificity for the causative microorganisms themselves. To meet this challenge, many groups have developed imaging methods that target pathogen-specific metabolism, including PET tracers integrated into the bacterial cell wall. We have previously reported the d-amino acid derived PET radiotracers d-methyl-[C]-methionine, d-[3-C]-alanine, and d-[3-C]-alanine-d-alanine, which showed robust bacterial accumulation and . Given the clinical importance of radionuclide half-life, in the current study, we developed [F]3,3,3-trifluoro-d-alanine (d-[F]-CF-ala), a fluorine-18 labeled tracer. We tested the hypothesis that d-[F]-CF-ala would be incorporated into bacterial peptidoglycan given its structural similarity to d-alanine itself. NMR analysis showed that the fluorine-19 parent amino acid d-[F]-CF-ala was stable in human and mouse serum. d-[F]-CF-ala was also a poor substrate for d-amino acid oxidase, the enzyme largely responsible for mammalian d-amino acid metabolism and a likely contributor to background signals using d-amino acid derived PET tracers. In addition, d-[F]-CF-ala showed robust incorporation into peptidoglycan, as detected by HPLC/mass spectrometry. Based on these promising results, we developed a radiosynthesis of d-[F]-CF-ala via displacement of a bromo-precursor with [F]fluoride followed by chiral stationary phase HPLC. Unexpectedly, the accumulation of d-[F]-CF-ala by bacteria was highest for Gram-negative pathogens in particular . In a murine model of acute bacterial infection, d-[F]-CF-ala could distinguish live from heat-killed , with low background signals. These results indicate the viability of [F]-modified d-amino acids for infection imaging and indicate that improved specificity for bacterial metabolism can improve tracer performance.
成像技术越来越多地用于检测和监测细菌感染。解剖学成像技术（X射线、计算机断层扫描、超声和磁共振成像）和核医学技术（[铟]-白细胞单光子发射计算机断层扫描、[氟]-脱氧葡萄糖正电子发射断层扫描）都应用于临床实践，但对致病微生物本身缺乏特异性。为应对这一挑战，许多研究团队开发了针对病原体特异性代谢的成像方法，包括整合到细菌细胞壁中的正电子发射断层扫描示踪剂。我们之前报道了源自d-氨基酸的正电子发射断层扫描放射性示踪剂d-甲基-[碳]-蛋氨酸、d-[3-碳]-丙氨酸和d-[3-碳]-丙氨酸-d-丙氨酸，它们在细菌中具有显著的积聚。鉴于放射性核素半衰期的临床重要性，在本研究中，我们开发了[氟]3,3,3-三氟-d-丙氨酸（d-[氟]-CF-ala），一种氟-18标记的示踪剂。鉴于其与d-丙氨酸本身的结构相似性，我们检验了d-[氟]-CF-ala会被整合到细菌肽聚糖中的假设。核磁共振分析表明，氟-19母体氨基酸d-[氟]-CF-ala在人血清和小鼠血清中是稳定的。d-[氟]-CF-ala也是d-氨基酸氧化酶的不良底物，该酶在很大程度上负责哺乳动物d-氨基酸代谢，并且可能是使用源自d-氨基酸的正电子发射断层扫描示踪剂时背景信号的一个来源。此外，通过高效液相色谱/质谱检测发现，d-[氟]-CF-ala能有效地整合到肽聚糖中。基于这些有前景的结果，我们通过用[氟]氟化物取代溴前体，然后进行手性固定相高效液相色谱，开发了d-[氟]-CF-ala的放射性合成方法。出乎意料的是，d-[氟]-CF-ala在细菌中的积聚尤其在革兰氏阴性病原体中最高。在急性细菌感染的小鼠模型中，d-[氟]-CF-ala能够区分活菌和热杀死菌，背景信号较低。这些结果表明[氟]修饰的d-氨基酸用于感染成像的可行性，并表明提高对细菌代谢的特异性可以改善示踪剂性能。
