Real-time MR tracking of AAV gene therapy with βgal-responsive MR probe in a murine model of GM1-gangliosidosis

Toloo Taghian,Ana Rita Batista,Sarah Kamper,Michael Caldwell,Laura Lilley,Hao Li,Paola Rodriguez,Katerina Mesa,Shaokuan Zheng,Robert M King,Matthew J Gounis,Sophia Todeasa,Anne Maguire,Douglas R Martin,Miguel Sena-Esteves,Thomas J Meade,Heather L Gray-Edwards

doi:10.1016/j.omtm.2021.08.003

Abstract

Transformative results of adeno-associated virus (AAV) gene therapy in patients with spinal muscular atrophy and Leber’s congenital amaurosis led to approval of the first two AAV products in the United States to treat these diseases. These extraordinary results led to a dramatic increase in the number and type of AAV gene-therapy programs. However, the field lacks non-invasive means to assess levels and duration of therapeutic protein function in patients. Here, we describe a new magnetic resonance imaging (MRI) technology for real-time reporting of gene-therapy products in the living animal in the form of an MRI probe that is activated in the presence of therapeutic protein expression. For the first time, we show reliable tracking of enzyme expression after a now in-human clinical trial AAV gene therapy (ClinicalTrials.gov: NTC03952637) encoding lysosomal acid beta-galactosidase (βgal) using a self-immolative βgal-responsive MRI probe. MRI enhancement in AAV-treated enzyme-deficient mice (GLB-1−/−) correlates with βgal activity in central nervous system and peripheral organs after intracranial or intravenous AAV gene therapy, respectively. With >1,800 gene therapies in phase I/II clinical trials (ClinicalTrials.gov), development of a non-invasive method to track gene expression over time in patients is crucial to the future of the gene-therapy field.

Highlights

We and others[1–20] have shown dramatic efficacy of adeno-associated virus (AAV) gene therapy in animal models including encouraging results in patients
The real-time tracking of bgal activity is tantamount to evaluation of a therapeutic response in GM1 and in the case of magnetic resonance (MR) contrast agents,[32,33] can be spatially resolved to any organ in the body, including the brain
In this report, we show detection of lysosomal acid bgal activity using MR imaging (MRI) in bgal-deficient GM1 mice after AAV gene transfer and correlation of enhancement with enzymatic activity ex vivo

Summary

Introduction

We and others[1–20] have shown dramatic efficacy of adeno-associated virus (AAV) gene therapy in animal models including encouraging results in patients. For a number of these AAV genetherapy clinical trials, initial dosing has yielded modest results, with increased dosing required for maximal benefit. This situation is a significant hindrance, leaving physicians guessing which organs or tissues are effectively treated. Without an effective real-time diagnostic, the disconnect between dosage control and therapeutic response threatens the clinical progress and approval of urgently needed gene-based therapeutics. The real-time tracking of bgal activity is tantamount to evaluation of a therapeutic response in GM1 and in the case of magnetic resonance (MR) contrast agents,[32,33] can be spatially resolved to any organ in the body, including the brain

Methods

Results

Conclusion