Development of investigational product MT1621

Deoxynucleoside combination therapy to restore mitochondrial function

Our science is based on discoveries by our academic collaborators that deoxynucleoside combination therapy can restore cellular function in a subset of mitochondrial diseases – mitochondrial DNA (mtDNA) depletion disorders. Data from preclinical disease models and initial clinical studies suggest that this approach may reverse or slow disease progression in TK2 deficiency.

Preclinical proof-of-concept data demonstrates treatment addresses underlying molecular pathophysiology of disease

Initial clinical data suggest meaningful treatment benefit relative to data from recently published natural history studies

Accelerated development path possible for ultra-orphan products with encouraging efficacy and safety data

How MT1621 works

MT1621 is a therapy that targets the underlying pathophysiology of TK2d by restoring mitochondrial DNA replication fidelity. The drug candidate consists of a combination of deoxynucleosides (the building blocks of mtDNA) given orally as a dissolved solution. Deoxynucleoside combination therapy improves nucleotide balance, increases mtDNA copy number, improves cell function, and prolongs life in preclinical models of TK2d.

MT-1621 graphic

Advancing MT1621 development

MT1621 has been granted orphan drug designation by both the FDA and EMA, and Modis is advancing discussions with health authorities on the regulatory path to approval. During initial clinical studies, there were no unexpected safety issues with deoxynucleoside combination therapy, and Modis anticipates upcoming studies to confirm a safety profile that is generally well tolerated by patients with TK2 deficiency. Data from initial clinical studies suggest that this therapy may meaningfully alter the course of disease in patients with TK2 deficiency. The company is planning to conduct additional clinical studies with the goal of obtaining regulatory approval to make MT1621 available to patients globally. If approved, MT1621 would represent the first commercial therapy for TK2d or any MDD.

Next generation therapies

Insights and knowledge gleaned from development of MT1621 position Modis to leverage the increasing understanding and genetic characterization of mitochondrial diseases to develop targeted high impact therapies for these underserved diseases. Modis is actively developing a pipeline of next generation therapeutic products for TK2d and other MDDs.

Expanded Access Policy

Modis is committed to developing MT1621 for patients with thymidine kinase 2 deficiency (TK2d.)  Well designed clinical trials are the best way to determine the safety and efficacy of an investigational therapy. Currently, participation in clinical trials is the only way for patients to gain access to MT1621. As more clinical data on the safety and efficacy of MT1621 become available, we will review and update our policy on Expanded Access. You can find more information on clinical trials at or about TK2d on We will update the TK2d community with new information about TK2d and Modis Therapeutics clinical trials. Registration on is available to patients, families or physicians.