Molecular imaging

Summary

Molecular imaging is a field of medical imaging that focuses on imaging molecules of medical interest within living patients. This is in contrast to conventional methods for obtaining molecular information from preserved tissue samples, such as histology. Molecules of interest may be either ones produced naturally by the body, or synthetic molecules produced in a laboratory and injected into a patient by a doctor. The most common example of molecular imaging used clinically today is to inject a contrast agent (e.g., a microbubble, metal ion, or radioactive isotope) into a patient's bloodstream and to use an imaging modality (e.g., ultrasound, MRI, CT, PET) to track its movement in the body. Molecular imaging originated from the field of radiology from a need to better understand fundamental molecular processes inside organisms in a noninvasive manner. The ultimate goal of molecular imaging is to be able to noninvasively monitor all of the biochemical processes occurring inside an or

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https://en.wikipedia.org/wiki/Molecular_imaging

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Novel Molecular Probes for Non-invasive Optical Imaging of Fatty Acid and Triglyceride Uptake in Living Animals

Grigory Karateev

Molecular imaging allows noninvasive visualization of biological processes in their native environment within living systems. It can give a better understanding of fundamental biology, help in identifying disease mechanisms and visualizing pathological tissues, and enable monitoring disease progression and studying the drug efficacy in intact living organisms. Among various imaging modalities, bioluminescence and fluorescence imaging are powerful techniques that have become essential methods for non-invasive real-time studies of biological processes in vivo. The aim of my thesis was the development of novel fluorescent and bioluminescent probes for in vivo imaging of fatty acid and triglyceride uptake. The goal of my first project was the development of a near infrared fluorescent fatty acid probe for glioma imaging. Some tumors such as glioma may rely on the uptake of extracellular fatty acids. Fatty acids can therefore be considered as targeting molecules for these tumors and could be used to develop tumor-imaging probes. The probe design is based on a near-infrared fluorophore indocyanine green (ICG) that is conjugated to a long-chain fatty acid palmitic acid. The conjugation of ICG to a fatty acid (ICG-FA) was envisioned to improve cell permeability of the fluorophore and its accumulation in glioma. The ICG-FA probe was first evaluated for its ability to mimic the uptake of natural fatty acids in cells and was then applied for glioma imaging studies in vivo, where it showed significant tumor accumulation. As a proof-of-concept, the probe was tested for intraoperative image-guided surgery in a canine patent with mastocytoma, where it allowed intraoperative fluorescence tumor imaging and provided optical guidance for a surgeon during tumor resection. The aim of my second project was the development of bioluminescent triglyceride probes for real-time non-invasive imaging of triglyceride uptake in vivo. Applying an optimized stategy for generating conjugates with luciferin, I developed several bioluminescent triglyceride probes. These imaging tools were validated in cells and mice and were shown to mimic the absorption of natural triglycerides. The developed probes enabled sensitive non-invasive real-time imaging and quantification of triglyceride absorption in living mice. Futhermore, these probes were successfully used to demonstrate the effects of the anti-obesity drug orlistat and the influence of the gut microbiota on the intestinal absorption of triglycerides in vivo. Considering the high importance of triglycerides for human health and nutrition and their implication in several pathologies such as obesity, metabolic syndrome, type 2 diabetes and cancer, the bioluminescent triglyceride probes could offer valuable imaging tools for preclinical research.

EPFL2019

In Vivo Molecular Bioluminescence Imaging: New Tools and Applications

Elena Goun, Hacer Karatas

in vivo bioluminescence imaging (BLi) is an optical molecular imaging technique used to visualize molecular and cellular processes in health and diseases and to follow the fate of cells with high sensitivity using luciferase-based gene reporters. The high sensitivity of this technique arises from efficient photon production, followed by the reaction between luciferase enzymes and luciferin substrates. Novel discoveries and developments of luciferase reporters, substrates, and gene-editing techniques, and emerging fields of applications, promise a new era of deeper and more sensitive molecular imaging.

Elsevier2017

Molecular imaging advances our understanding of cellular and molecular functions within complex biological systems. The development of novel imaging probes that can be applied to answer fundamental biological questions, diagnose and monitor disease progression and the efficacy of therapy in vivo is essential to the field of molecular imaging. Bioluminescence imaging is a powerful technique that allows to study and follow biological processes of interest noninvasively in real-time in living animals. Activatable bioluminescent probes can be designed according to the target of interest and can provide imaging signal in response to the specific stimuli. A strategy called "caged luciferin" can be used to design new bioluminescent probes for imaging of enzymatic activity, the presence of small molecules or metabolite uptake in vivo. In Chapter 1 we present an overview of bioluminescence imaging, with a focus on firefly luciferase-luciferin system. The caged luciferin approach is discussed and examples of existing caged luciferin probes are presented. In Chapter 2 we describe the development of a bioluminescent probe for imaging of bacterial nitroreductase activity and show the potential for its application in different areas of research. Bacterial nitroreductases have been widely utilized in the gene-directed enzyme prodrug therapy (GDEPT) approach for cancer therapy that reached clinical trials. However, both preclinical and clinical development of NTR-based GDEPT systems has been hampered by the lack of imaging tools that allow in vivo evaluation of transgene expression. We developed the NTR caged luciferin (NCL) probe and demonstrated its application for sensitive bioluminescence imaging of NTR in vitro, in bacteria and cancer cells, as well as in vivo in mouse models of bacterial infection and NTR-expressing tumor xenografts. We anticipate that this probe would significantly accelerate the development of cancer therapy approaches based on GDEPT and other fields where evaluation of NTR expression is important. In Chapter 3 we describe the development of a bioluminescent probe for imaging of hydrogen sulfide (H2S) using the caged luciferin approach. The objective of the research was to develop a probe that can detect endogenously produced H2S noninvasively in real-time in living animals. We present a series of caged luciferin probes that were evaluated on their ability to rapidly and selectively detect H2S in in vitro assays, in cells and in bacterial culture. The two selected probes were applied for imaging of exogenous H2S in the gastrointestinal tract in living mice. We anticipate further applications of the best performing probe (Az-CL) for imaging of H2S production by gut microbiota in mice. In Chapter 4 we present the overall conclusion followed by the outlook and future perspectives.

EPFL2016

Novel Molecular Probes for Non-invasive Optical Imaging of Fatty Acid and Triglyceride Uptake in Living Animals

Grigory Karateev

EPFL2019

EPFL2016