Efficacy of adeno-associated virus gene therapy in a MNGIE murine model enhanced by chronic exposure to nucleosides

Abstract

Background: Preclinical studies have shown that gene therapy is a feasible approach to treat mitochondrial neurogastrointestinal encephalomyopathy (MNGIE). However, the genetic murine model of the disease (Tymp/Upp1 double knockout, dKO) has a limited functional phenotype beyond the metabolic imbalances, and so the studies showing efficacy of gene therapy have relied almost exclusively on demonstrating correction of the biochemical phenotype. Chronic oral administration of thymidine (dThd) and deoxyuridine (dUrd) to dKO mice deteriorates the phenotype of the animals, providing a better model to test therapy approaches. Methods: dKO mice were treated with both dThd and dUrd in drinking water from weaning until the end of the study. At 8-11 weeks of age, mice were treated with several doses of adeno-associated virus (AAV) serotype 8 vector carrying the human TYMP coding sequence under the control of different liver-specific promoters (TBG, AAT, or HLP). The biochemical profile and functional phenotype were studied over the life of the animals. Findings: Nucleoside exposure resulted in 30-fold higher plasma nucleoside levels in dKO mice compared with non-exposed wild type mice. AAV-treatment provided elevated TP activity in liver and lowered systemic nucleoside levels in exposed dKO mice. Exposed dKO mice had enlarged brain ventricles (assessed by magnetic resonance imaging) and motor impairment (rotarod test); both were prevented by AAV treatment. Among all promoters tested, AAT showed the best efficacy. Interpretation: Our results show that AAV-mediated gene therapy restores the biochemical homeostasis in the murine model of MNGIE and, for the first time, demonstrate that this treatment improves the functional phenotype. Funding: This work was funded in part by the Spanish Instituto de Salud Carlos III, and the Generalitat de Catalunya. The disclosed funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Therapy Prospects for Mitochondrial DNA Maintenance Disorders

“…The comparison of different promoters showed that the one of the alpha-1-antitrypsin gene provided the best efficacy as compared to other liver or constitutive promoters [ 194 ]. Recently, the use of an enhanced animal model showed that this treatment also has a therapeutic effect on the neuromotor function of the mice [ 195 ].…”

“…Some of the murine models recapitulate, at least partially, the clinical phenotype of the diseases [ 171 , 176 , 187 , 210 , 211 , 212 ], but in some other cases, the phenotype is barely biochemical or molecular, with no or little effect on the functional life of the animals [ 90 , 184 ]. Sometimes, the models can be stressed to show enhanced phenotypes that result as useful to show the efficacy of the experimental therapies [ 188 , 195 , 213 ]. In any case, testing in these models those treatments that have shown promising results in cell culture or other in vitro models should be encouraged in order to accelerate the implementation of clinical programs for them.…”

AAV-vector based gene therapy for mitochondrial disease: progress and future perspectives

“…Liver-specific promoters resulted in the longest supression of dThd levels Vila-Julia et al (2020). EBioMed [ 88 ] AAV8 5 × 10 11 , 1 × 10 12 , 2 × 10 12 , 1 × 10 13 vg/kg (TBG) 2 × 10 12 , 1 × 10 13 vg/kg (AAT, HLP) 8–11 weeks (IV) Sustained lowering of plasma dThd and dUrd levels, modestly improved motor performance, and modestly decreased ventricular volume MPV17 Bottani et al . (2014).…”

“…Though dThd and dUrd levels were increased in the tissues of Tymp/Upp1 -DKO mice exposed to exogenous nucleosides, no gastrointestinal pathology developed [ 87 ]. AAV vector-mediated delivery of hTYMP under a liver-specific promoter (AAT, TBG, HLP) to dThd and dUrd exposed mice 8–11 weeks of age resulted in decreased nucleoside levels in tissue and serum, and modest improvement in motor function as measured by rotarod performance at 25 weeks of age [ 88 ]. AAV gene therapy also resulted in a modest reduction of ventricular volume in treated animals compared to untreated animals at 84 weeks old [ 88 ].…”

Circulating miRNAs as Biomarkers for Mitochondrial Neuro-Gastrointestinal Encephalomyopathy

“…Although there is currently no universally established treatment to prevent or reverse the inexorable fatal clinical deterioration in patients with MNGIE, a number of experimental therapeutic approaches have been investigated over the past two decades [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ]. Unique challenges face the translation of candidate therapeutics into approved treatments for rare diseases, and MNGIE is no exception.…”