Pretzel Therapeutics Receives FDA Clearance to Advance PX578 Into Phase 2 Study for POLG-Mediated Mitochondrial Disease
Pretzel Therapeutics, Inc., a clinical-stage biotechnology company focused on developing a new generation of medicines designed to restore mitochondrial function, improve cellular energy production and potentially slow disease progression, announced that the U.S. Food and Drug Administration (FDA) has cleared the company’s Investigational New Drug (IND) application for PX578. The regulatory milestone enables Pretzel Therapeutics to initiate a first-in-patient clinical study of its lead therapeutic candidate in adults living with POLG-mediated primary mitochondrial disease, also known as POLG disease.
The planned Phase 2 clinical trial, named POLARIS—short for POLG Activation and Recovery In Subjects—will investigate PX578 in a patient population affected by a rare and progressive genetic disorder associated with mutations in the POLG gene. POLG disease is characterized by impaired mitochondrial DNA replication and depletion of mitochondrial DNA, ultimately leading to mitochondrial dysfunction that can affect multiple organs and systems, with neurological manifestations often playing a major role in disease burden.
There are currently no approved disease-modifying therapies specifically designed to address the underlying biological causes of POLG disease. Treatment is generally focused on managing symptoms and complications, leaving patients, families and physicians with significant unmet medical needs. The initiation of the POLARIS study therefore represents an important step in evaluating whether a therapy directed at mitochondrial biology can potentially alter the course of this devastating condition.
FDA Clearance Marks Important Clinical Milestone
The FDA’s clearance of the IND application allows Pretzel Therapeutics to transition PX578 from clinical testing in healthy volunteers into a patient population directly affected by mitochondrial disease.
Jay Parrish, Ph.D., Chairman and Chief Executive Officer of Pretzel Therapeutics, described the IND clearance as a major achievement for the company and an important development for the POLG disease community.
According to Parrish, the regulatory decision reflects the scientific and clinical foundation established for PX578 and moves the program closer to testing a therapeutic strategy intended to address the mitochondrial dysfunction underlying disease progression.
POLG disease results from mutations in the POLG gene, which encodes the catalytic subunit of mitochondrial DNA polymerase gamma, an enzyme essential for maintaining and replicating mitochondrial DNA. When POLG function is impaired, mitochondrial DNA can become depleted or damaged, compromising the ability of mitochondria to generate the energy required by cells.
Because tissues such as the brain, skeletal muscle and other organs have high energy requirements, disruption of mitochondrial function can produce a broad range of neurological and systemic symptoms.
The progressive nature of POLG disease can significantly affect patients’ daily lives and may lead to substantial disability over time. The absence of an approved disease-modifying treatment underscores the importance of developing approaches that target the biological mechanisms driving mitochondrial dysfunction rather than focusing exclusively on symptom management.
PX578 Designed to Target Mitochondrial DNA Biology
Pretzel Therapeutics is developing PX578 with the goal of addressing a fundamental component of POLG disease: impaired mitochondrial DNA replication.
The company’s scientific rationale centers on the ability of PX578 to enhance POLy processivity during mitochondrial DNA synthesis. POLy, or polymerase gamma, plays a central role in the replication and maintenance of mitochondrial DNA.
By supporting this process, PX578 is being investigated for its potential to increase mitochondrial DNA levels and improve mitochondrial function.
This approach differs from therapies that simply address individual symptoms of mitochondrial disease. Instead, Pretzel is seeking to intervene closer to the underlying biological mechanism responsible for disease progression.
The company’s preclinical research has provided encouraging evidence supporting this strategy. According to Pretzel, studies have demonstrated that PX578 can increase mitochondrial DNA levels and improve mitochondrial function.
The company believes these findings provide a mechanistic basis for evaluating the candidate in individuals with POLG disease.
Ashish Dugar, Chief Development Officer of Pretzel Therapeutics, said the company’s confidence in moving PX578 into patient testing is supported by both preclinical findings and the successful completion of a Phase 1 clinical study in healthy volunteers.
Successful Phase 1 Study Supports Further Development
Before moving into POLG disease patients, PX578 was evaluated in a Phase 1 healthy volunteer study conducted in New Zealand.
Pretzel reported that the Phase 1 study met all of its objectives, providing important information about the candidate’s clinical profile and supporting the company’s decision to advance into a patient-focused study.
Early-stage clinical studies are critical for establishing an investigational therapy’s safety and tolerability and for generating pharmacokinetic and pharmacodynamic information that can help guide subsequent clinical development.
The successful completion of the Phase 1 program provides Pretzel with a clinical foundation for POLARIS.
The company has also indicated that it worked closely with regulatory authorities, patient advocacy organizations and clinical experts while developing the Phase 2 trial.
This collaboration is intended to ensure that the clinical program is appropriately designed for the characteristics and needs of people living with POLG disease.
POLARIS Study to Evaluate Multiple Measures
POLARIS will be a randomized, double-blind, placebo-controlled Phase 2 clinical trial.
The study is designed to evaluate several important aspects of PX578 treatment, including safety, tolerability, pharmacokinetics, pharmacodynamics and clinical efficacy.
A randomized and placebo-controlled design will allow investigators to compare outcomes between participants receiving PX578 and those receiving placebo.
The double-blind structure is intended to reduce potential bias by keeping both investigators and participants unaware of treatment assignments during the appropriate portions of the study.
The clinical program will also generate pharmacodynamic information that may help researchers determine whether PX578 is producing the intended biological effects in patients.
For a disease driven by mitochondrial DNA depletion, these biological measurements could be particularly important in understanding whether the treatment is affecting the disease mechanism.
Ultimately, the study is intended to determine whether the biological activity observed in preclinical research and healthy volunteers can translate into meaningful effects in people with POLG disease.
Addressing a Significant Unmet Medical Need
POLG disease represents a particularly challenging area of mitochondrial medicine.
The condition can arise from different mutations in the POLG gene, leading to a range of clinical presentations and levels of severity. Neurological and systemic manifestations can vary considerably between individuals.
Despite advances in understanding mitochondrial disorders, therapeutic options remain limited.
Current approaches often focus on managing specific symptoms and complications. While supportive care can be important, it does not directly correct the mitochondrial DNA depletion or dysfunction associated with POLG disease.
The development of a therapy capable of modifying the underlying disease process could therefore represent a significant advancement.
Kristen Clifford, President and Chief Executive Officer of the United Mitochondrial Disease Foundation, emphasized the lack of approved disease-modifying treatments for POLG disease and the potential significance of investigating a therapy designed to address its underlying biology.
The transition of PX578 into clinical development could provide researchers with an opportunity to learn more about whether restoring mitochondrial DNA biology can translate into improvements in disease outcomes.
Potential to Move Beyond Symptom Management
One of the central goals of the PX578 program is to determine whether targeting mitochondrial DNA replication can produce disease-modifying effects.
Mitochondria are often described as the energy-producing structures of cells, generating much of the energy required to support cellular activity. When mitochondrial DNA becomes depleted or mitochondrial function is impaired, cells may struggle to meet their energy demands.
Organs and tissues with high energy requirements can be particularly vulnerable to mitochondrial dysfunction.
In POLG disease, the resulting consequences can be extensive. Patients may experience neurological and systemic complications that can progress over time.
By attempting to increase mitochondrial DNA levels and improve mitochondrial function, PX578 is being developed with the goal of addressing a fundamental aspect of this disease biology.
However, the company emphasizes that substantial clinical work remains before the potential effectiveness of PX578 can be established.
The POLARIS study will be an important test of whether the mechanism observed in laboratory and preclinical research can translate into measurable biological and clinical benefits in patients.
Regulatory and Scientific Progress
The FDA’s clearance of the IND application represents a significant regulatory milestone for Pretzel Therapeutics.
IND clearance allows the company to begin clinical evaluation of PX578 in the United States under the conditions outlined in the development program.
For a clinical-stage biotechnology company, advancing a lead candidate from preclinical research through Phase 1 and into a patient-focused Phase 2 study represents an important stage in the development process.
The progression also reflects Pretzel’s broader focus on developing therapeutics that target mitochondrial biology.
Rather than developing treatments around individual symptoms or manifestations of rare diseases, the company is seeking to identify mechanisms that may influence the underlying cellular processes driving disease.
The POLG program provides an opportunity to apply this strategy to a genetic disorder in which mitochondrial DNA depletion plays a central role.
Importance of Biomarkers and Pharmacodynamic Assessment
Another important aspect of the POLARIS program will be the evaluation of pharmacodynamic responses.
In diseases involving complex mitochondrial biology, demonstrating that an investigational medicine is engaging its intended biological pathway can provide important information during development.
For PX578, evidence that treatment can influence mitochondrial DNA levels or related measures of mitochondrial function could help establish a connection between the drug’s mechanism and its potential clinical effects.
The pharmacokinetic data generated during the study will also provide information about how PX578 behaves within the body, including exposure and other characteristics relevant to dosing.
Together, pharmacokinetic and pharmacodynamic assessments can help investigators refine the development strategy and determine how biological responses correlate with clinical outcomes.
Collaboration With the POLG Community
Pretzel has emphasized collaboration with patients, families, healthcare professionals, regulators and scientific experts as the program moves into clinical development.
Patient involvement can be particularly valuable in rare diseases, where the number of individuals affected by a condition may be relatively small and the clinical manifestations can vary widely.
Working with the patient community can help researchers understand the most meaningful outcomes and challenges faced by individuals living with the disease.
The company’s engagement with the United Mitochondrial Disease Foundation and other stakeholders reflects an effort to maintain communication with the broader mitochondrial disease community as the program advances.
With FDA clearance now secured, Pretzel Therapeutics plans to initiate the POLARIS Phase 2 study and begin evaluating PX578 in adults with POLG-mediated primary mitochondrial disease.
The study represents a critical next step for a program that has progressed from preclinical research through successful testing in healthy volunteers.
The potential significance of PX578 lies in its disease-modifying objective. Rather than simply treating individual manifestations of POLG disease, the candidate is designed to address impaired mitochondrial DNA replication and depletion, which are central features of the disease mechanism.
The company’s preclinical findings showing increases in mitochondrial DNA levels and improvements in mitochondrial function provide the scientific rationale for taking the therapy into patients.
However, the clinical study will ultimately determine whether those effects translate into meaningful benefits for people living with POLG disease.
The POLARIS trial is therefore expected to provide important information about the safety, tolerability, pharmacokinetics, pharmacodynamics and potential clinical efficacy of PX578.
A Potential New Direction for POLG Disease
The advancement of PX578 into Phase 2 represents a meaningful development in the search for disease-modifying treatments for POLG disease.
For patients and families currently facing a progressive disorder with no approved therapy addressing its underlying cause, clinical investigation of a targeted mitochondrial approach offers an important opportunity.
Pretzel Therapeutics’ strategy is based on the premise that improving mitochondrial DNA replication and restoring mitochondrial function could potentially address a fundamental driver of disease progression.
The FDA’s IND clearance now enables that hypothesis to be tested in patients.
As POLARIS begins, the mitochondrial disease community will have an opportunity to learn more about whether PX578 can safely produce the biological effects demonstrated in preclinical research and whether those effects could ultimately translate into clinical improvements.
While significant development work remains, the transition into Phase 2 marks an important milestone for Pretzel Therapeutics and for research into POLG-mediated mitochondrial disease. The company’s continued focus on mitochondrial biology, combined with the clinical experience generated through Phase 1, provides the foundation for the next stage of development.
If successful, PX578 could potentially contribute to a new generation of therapies aimed not merely at managing the symptoms of mitochondrial disease but at addressing the underlying cellular dysfunction responsible for disease progression. For the POLG community, the initiation of the POLARIS trial represents an important step toward determining whether this therapeutic strategy can deliver meaningful and durable benefits to patients living with this rare and debilitating condition.
About POLG-mediated Primary Mitochondrial Disease
POLG-mediated primary mitochondrial disease (POLG disease) is a progressive, multisystem disorder caused by impaired cellular energy production due to mitochondrial DNA (mtDNA) depletion. It represents one of the most common forms of mitochondrial DNA depletion syndromes (MDDS) 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 (ages 12-40) often presents with ataxia, peripheral neuropathy, and seizures; and late-onset (ages 40+) is typically more slowly progressive, characterized by ophthalmoplegia, ptosis, and myopathy.
Across all forms, POLG disease is highly debilitating and associated with substantial morbidity and early mortality. There are currently no disease-modifying therapies, underscoring a critical and urgent need for treatments that address the underlying mitochondrial dysfunction.
About PX578
PX578 is a first-in-class, CNS penetrant small molecule activator of the mitochondrial polymerase POLG designed to increase mitochondrial DNA (mtDNA) levels, enhance mitochondrial function and improve quality of life by halting or reversing disease progression across mitochondrial disorders, including POLG-mediated primary mitochondrial disease, a rare and often devastating condition for which no approved disease-modifying therapies currently exist. Preclinical studies across multiple in vitro and in vivo models, as well as a recently completed Phase 1 healthy volunteers study, support the disease-modifying potential of PX578 and its advancement into Phase 2 clinical evaluation in patients with POLG disease.
About Pretzel Therapeutics
Pretzel Therapeutics, a clinical-stage biotechnology company building a deep, first-in-class pipeline of novel medicines designed to restore mitochondrial function, improve cellular energetics and impede disease progression across a range of neurological and rare diseases. The Company’s lead therapeutic candidate, PX578, is expected to enter Phase 2 clinical study for individuals with POLG disease in late 2026. The company is headquartered in Waltham, MA, and has research facilities in Mölndal, Sweden. For more information, visit www.pretzeltx.com.