AAV9fyhr gene replacement therapy for PDHA1 deficiency in the E75A mouse model

About This Grant

PROJECT SUMMARY/ABSTRACT Primary Pyruvate Dehydrogenase Complex Deficiency (PDCD) is a rare but severe mitochondrial disorder, with an estimated incidence of 1 in 50,000 to 75,000 live births in North America. The majority of cases are caused by mutations in the X-linked PDHA1 gene. There is currently no curative therapy for PDHA1 deficiency, and the prognosis remains very poor, with death occurring in approximately 90% of affected individuals before the age of four. Adeno-associated virus (AAV)-mediated gene delivery has emerged as a well-established approach for treating neuromuscular and neurodevelopmental disorders. Lumbar intrathecal (IT) injection of AAV9 into the cerebrospinal fluid (CSF) has been used successfully in animal models to rescue multiple CNS diseases. Our laboratory has over 20 years of experience in developing gene therapies for more than two dozen neurological conditions. Notably, 8 gene therapy candidates originating from our lab have progressed to clinical trials, two of which (CLN7 and SPG50) entered the clinic since 2021 and are currently ongoing within the Gene Therapy Program at UT Southwestern Medical Center. We propose to use a novel AAV9 variant (AAV9fyhr) vector to deliver the PDHA1 gene to the central nervous system (CNS) in a newly developed and characterized E75A mouse model to identify the potential efficacy, as well as toxicity, of the AAV9fyhr/PDHA1 vector. Our central hypothesis is that AAV9fyhr-mediated PDHA1 gene replacement therapy will restore proper protein function and ameliorate disease phenotypes in the E75A mouse model, with the degree of benefit driven by dose and age of treatment. We will test this hypothesis by pursuing two specific aims: Aim 1. Evaluate the efficacy of AAV9fyhr/PDHA1 in the E75A mouse model of PDHA1 deficiency. E75A mice will be treated with a range of doses by lumbar IT injection, at either young or older ages. Mice will be monitored for treatment benefit by longitudinal behavioral tests and biochemical assessment of metabolic correction. Aim 2. Determine the safety of AAV9fyhr/PDHA1 in wild-type (WT) C57BL/6J mice. WT mice will receive lumbar IT injections of escalating doses of AAV9fyhr/PDHA1. Mice will be monitored in life and post-mortem for short and long term adverse effects, including comprehensive histopathology, with special attention to the assessment of dorsal root ganglia (DRG) toxicity and hepatotoxicity, two known risks associated with AAV-based therapies. If these proof-of- concept studies demonstrate favorable efficacy and no detectable toxicity, the resulting data will serve as pivotal IND-enabling efficacy evidence and supportive safety data. Building on the precedent set by our work advancing 8 gene therapies into clinical trials, in future studies we intend to leverage our extensive experience to design and carry out the remaining IND-enabling studies. If successful, these efforts are designed to ultimately support the translation of this gene therapy approach into a human treatment. This will be of great significance to not only offer a potential life-saving treatment for patients with PDHA1 deficiency, but also providing broader proof- of-concept for AAV9fyhr as a CNS-targeting platform for other neurological disorders.