FDA Grants Fast Track Designation to Pretzel's PX578 for POLG-Mediated Primary Mitochondrial Disorders
核心洞察
The FDA has granted Fast Track Designation to Pretzel Therapeutics (搜索)' PX578 (搜索) for POLG-mediated primary mitochondrial disorders (搜索), a progressive genetic condition with no approved disease-modifying therapies.
PX578 (搜索) is a CNS-penetrant small molecule designed to activate mutant mitochondrial DNA polymerase gamma, increasing mtDNA levels to address the underlying cause of disease.
The designation follows FDA clearance in August 2026 of the IND application for a first-in-patient trial, supported by a completed Phase 1 healthy volunteer study in New Zealand.
Pretzel Therapeutics (搜索) has received US FDA Fast Track Designation for PX578 (搜索), a central nervous system-penetrant small molecule activator of mitochondrial DNA polymerase gamma (POLG (搜索)), for the treatment of POLG-mediated primary mitochondrial disorders (搜索) (POLG disease). The Waltham, Massachusetts-based clinical-stage company announced the designation on September 22, 2026. No approved disease-modifying therapy currently exists for the condition.
"Receiving Fast Track Designation is an important regulatory milestone for PX578 (搜索) and further underscores the urgent need for new treatment options for people living with POLG (搜索) disease," said Ashish Dugar, Chief Development Officer of Pretzel Therapeutics (搜索). "As we prepare to initiate the POLARIS study in patients, we remain focused on generating the clinical evidence needed to advance PX578 and bring a potentially disease-modifying therapy to individuals impacted by this progressive and debilitating disease."
Regulatory Path Builds on IND Clearance and Phase 1 Data
The Fast Track Designation follows FDA clearance in August 2026 of Pretzel's Investigational New Drug application to begin the first-in-patient trial of PX578 (搜索). That clearance was predicated on a completed Phase 1 healthy volunteer study, a randomized, double-blind, placebo-controlled single and multiple ascending dose trial conducted in New Zealand. According to the company, the study met all pre-specified safety, tolerability, and pharmacokinetic objectives.
Fast Track designation provides opportunities for more frequent FDA interactions during development and potentially expedites review of PX578 (搜索), supporting Pretzel's ongoing engagement with the agency as the program advances toward Phase 2 initiation.
Mechanism Targets the Underlying Cause of Disease
PX578 (搜索) is designed to directly activate mutant POLG (搜索) enzyme, increasing mitochondrial DNA (mtDNA) levels to address the underlying cause of disease. Preclinical studies across multiple in vitro and in vivo models demonstrated increased mtDNA levels, improved cellular respiration and energy production, increased survival, and improved markers of liver health.
The mechanistic basis was further supported by a Nature publication (Valenzuela et al., DOI: 10.1038/s41586-025-08856-9) showing that small molecule POLG (搜索) activators restore enzymatic function and increase mtDNA levels in patient-derived cells carrying POLG mutations. Pretzel said PX578 (搜索) has demonstrated activity across all POLG mutations tested to date, including the four most common mutations found in approximately 70% of patients.
POLARIS Trial Design and Population
The Phase 2 POLARIS (POLg (搜索) Activation and Recovery In Subjects) study is a randomized, double-blind, placebo-controlled trial designed to evaluate safety, tolerability, pharmacokinetics, pharmacodynamics, and clinical efficacy of PX578 (搜索) in adults with POLG disease. Pretzel said initiation is planned for late 2026.
Disease Burden and Unmet Need
POLG-mediated primary mitochondrial disorders (搜索) are progressive, multisystem conditions caused by impaired cellular energy production due to mitochondrial DNA depletion. The condition represents one of the most common forms of mitochondrial DNA depletion syndromes (搜索) yet remains considerably underdiagnosed or misdiagnosed.
The disease affects individuals across all ages, with presentation and prognosis largely determined by age of onset. Childhood-onset, prior to age 12, is severe and rapidly progressive, characterized by liver involvement, seizures, and cognitive regression. Juvenile and adult-onset, between ages 12 and 40, often presents with ataxia, peripheral neuropathy, and seizures. Late-onset, at ages 40 and older, is typically more slowly progressive, characterized by ophthalmoplegia, ptosis, and myopathy. Across all forms, POLG (搜索) disease is highly debilitating and associated with substantial morbidity and early mortality.
While the FDA approved UCB (搜索)'s Kygevvi (搜索) (doxecitine and doxribtimine) in November 2025 for thymidine kinase 2 deficiency (搜索), another inherited disorder affecting mitochondrial DNA maintenance, PX578 (搜索) is designed specifically to address impaired POLG (搜索) activity and would represent a distinct mechanism if successfully developed.