Novel CEST MRI-suitable Reporter Genes to Non-Invasively Monitor Distribution and Migration of Biotherapeutics

Unmet Need
Green Fluorescent Protein (GFP) reporter genes and PET (positron-emission tomography) imagining are two techniques which have been widely used to monitor the movement and distribution of specific molecules in cells or animals. Imaging GFP-tagged molecules is often destructive to the sample and is limited by the degree that light can penetrate the tissue. PET imaging is dependent on administering an exogenous radionuclide-labeled agent that can have difficulty reaching and specifically binding to its target—an especially difficult task if crossing the blood-brain barrier. The method of chemical exchange saturation transfer (CEST) magnetic resonance imaging (MRI) is recognized as another powerful non-invasive imaging modality offering near-cellular spatial resolution permitting single-cell imaging. To optimally utilize CEST-MRI, there remains a need for reporter genes that are detectable by CEST-MRI with high sensitivity without the need of exogenous probes or substrates.
 
Technology Overview
Johns Hopkins researchers have created artificial reporter proteins that demonstrate substantial contrast enhancement on magnetic resonance images by CEST-MRI. The overall concept of CEST reporter genes is similar to existing reporter GFP genes. CEST reporter genes encoding artificial proteins rich in lysine or arginine were generated and demonstrated to substantially enhance contrast in CEST MR imaging, without altering cellular metabolism. Using specific radiofrequencies, the CEST-MRI reporter system allows double- or triple-labeling and detection strategies using combinations of different artificial proteins. Inventors showed that CEST MRI can be used to image hematopoietic cells, stem cells and tumor cells stably transfected with such an artificial reporter gene(s). The invention also solves the problems of tracking labeled cells as an exogenous label dilutes with cell division and discriminating between live and dead cells. More recently, evidence was presented for the use of the CEST reporter gene in monitoring oncolytic virus therapy. Importantly, CEST reporter genes permit non-invasive and repetitive monitoring with 3D whole body imaging without dependence on light penetration. Together, this technology presents a powerful new tool that may be broadly useful to non-invasively label and track biodistribution and migration of single cells for purposes of evaluating efficacy of gene therapy and monitoring cell therapy.
 
Stage of Development
Cellular and animal data are available.
 
Publications
Nat Biotechnol. 2007 Feb;25(2):217-9.
Radiology. 2015 Jun;275(3):746-54.
 

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