FDG-PET imaging to detect and characterize infectious disorders; an unavoidable path for the foreseeable future

Unparalleled and revolutionary impact of PET imaging on research and day to day practice of medicine

Positron emission tomography (PET) imaging is the most quantitative modality for assessing disease activity at the molecular and cellular levels, and therefore, it allows monitoring its course and determining the efficacy of various therapeutic interventions. In this scientific communication, we describe the unparalleled and revolutionary impact of PET imaging on research and day to day practice of medicine. We emphasize the critical importance of the development and synthesis of novel radiotracers (starting from the enormous impact of F-Fluorodeouxyglucose (FDG) introduced by investigators at the University of Pennsylvania (PENN)) and PET instrumentation. These innovations have led to the total-body PET systems enabling dynamic and parametric molecular imaging of all organs in the body simultaneously. We also present our perspectives for future development of molecular imaging by multiphoton PET systems that will enable users to extract substantial information (owing to the evolving role of positronium imaging) about the related molecular and biological bases of various disorders, which are unachievable by the current PET imaging techniques.

Linear Desferrichrome-Linked Silicon-Rhodamine Antibody Conjugate Enables Targeted Multimodal Imaging of HER2 in Vitro and in Vivo

We report the nuclear and optical in vitro and in vivo imaging of SKOV-3 cells by targeting HER2 with a bimodal trastuzumab conjugate. Previously, we have shown that desferrichrome derivatives provide a robust and versatile radiolabeling platform for the radioisotope zirconium-89. Here, we appended silicon-rhodamine functionalized linear desferrichrome to trastuzumab. This construct was radiolabeled and used to image cellular binding and antibody uptake in vitro and in vivo. The robust extinction coefficient of the SiR deep-red emissive fluorophore enables direct quantification of the number of appended chelators and fluorophore molecules per antibody. Subsequent radiolabeling of the multifunctional immunoconjugate with ⁸⁹Zr was achieved with a 64 ± 9% radiochemical yield, while the reference immunoconjugate desferrioxamine (DFO)-trastuzumab exhibited a yield of 84 ± 9%. In vivo PET imaging (24, 48, 72, and 96 h post injection) and biodistribution experiments (96 h post injection) in HER2+ tumor bearing mice revealed no statistically significant difference of the two ⁸⁹Zr-labeled conjugates at each time point evaluated. The bimodal conjugate permitted successful in vivo fluorescence imaging (96 h post injection) and subsequent fluorescence-guided, surgical resection of the tumor mass. This report details the first successful application of a fluorophore-functionalized desferrichrome derivative for targeted imaging, motivating further development and application of this scaffold as a multimodal imaging platform.

Nuclear and Optical Bimodal Imaging Probes Using Sequential Assembly: A Perspective

New, targeted imaging tracers enable improved diagnosis, staging, and planning of treatment of disease and represent an important step toward personalized medicine applications. The combination of radioisotopes for nuclear imaging with fluorophores for fluorescence imaging provides the possibility to noninvasively assess disease burden in a patient using positron emission tomography/single-photon emission computed tomography, followed by fluorescence imaging-assisted surgical intervention in close succession. Probes enabling imaging with both modalities pose a design, synthesis, and pharmacokinetics challenge. In this study, the authors strive to summarize recent efforts toward optimized, discrete, bimodal probes as well as a perspective on future directions of this burgeoning subfield of targeted imaging probe development.