Non-invasive detection of adeno-associated viral gene transfer using a genetically encoded CEST-MRI reporter gene in the murine heart

Abstract

Research into gene therapy for heart failure has gained renewed interest as a result of improved safety and availability of adeno-associated viral vectors (AAV). While magnetic resonance imaging (MRI) is standard for functional assessment of gene therapy outcomes, quantitation of gene transfer/expression relies upon tissue biopsy, fluorescence or nuclear imaging. Imaging of gene expression through the use of genetically encoded chemical exchange saturation transfer (CEST)-MRI reporter genes could be combined with clinical cardiac MRI methods to comprehensively probe therapeutic gene expression and subsequent outcomes. The CEST-MRI reporter gene Lysine Rich Protein (LRP) was cloned into an AAV9 vector and either administered systemically via tail vein injection or directly injected into the left ventricular free wall of mice. Longitudinal in vivo CEST-MRI performed at days 15 and 45 after direct injection or at 1, 60 and 90 days after systemic injection revealed robust CEST contrast in myocardium that was later confirmed to express LRP by immunostaining. Ventricular structure and function were not impacted by expression of LRP in either study arm. The ability to quantify and link therapeutic gene expression to functional outcomes can provide rich data for further development of gene therapy for heart failure.

A brief review of reporter gene imaging in oncolytic virotherapy and gene therapy

“… 117 Another study generated an AAV-9 vector encoding LRP to longitudinally track cardiac transduction in mice, with robust imaging achieved 90 days post infection. 104 The sustained expression and lack of observed toxicity bode well for LRP CEST MRI. However, LRP imaging and CEST MRI suffer from low sensitivity and high specific absorption rate (SAR), limiting its clinical use.…”

“…(C) From Meier et al. 104 and reproduced under CC Attribution 4.0 International License ( https://creativecommons.org/licenses/by/4.0/ ). …”

Cellular and molecular imaging for stem cell tracking in neurological diseases

“…The current report genes used in MRI include lacZ, transferrin gene and ferritin gene. 14 To visualise cells from the host cell background and increase their sensitivity, MRI-based cell imaging requires contrast agents to label the cells. Superparamagnetic iron oxide (SPIOs) is a kind of iron oxide nanoparticles exhibiting superparamagnetism.…”

Redesigned Reporter Gene for Improved Proton Exchange-based Molecular MRI Contrast

“…(iii) The reporter contrast can be switched on/off by the use of a selective MR RF saturation pulse, allowing the acquisition of additional and uncontaminated anatomical/functional MRI information at the same imaging session. Of particular promise was the development of the lysine-rich protein (LRP) reporter gene 23 , with demonstrated applicability for imaging cells in tumors 29 , oncolytic virus delivery and spread 5 , and cardiac viral vector expression 30 . However, thus far, the gap between the promise of MR reporters and actual clinical use has not been bridged due to the low sensitivity and specificity of the detection.…”