Mirdametinib (MEK 1/2 Inhibitor)

Mirdametinib (formerly PD-0325901) is an investigational oral, small molecule, selective inhibitor of MEK1 and MEK2, which are proteins that play key roles in the MAPK signaling pathway. The MAPK pathway is critical for cell survival and proliferation, and inappropriate activation of this pathway, as is the case when certain mutations occur in the NF1 gene, has been shown to help enable tumor growth. Mirdametinib has demonstrated an ability to block the activity of the MAPK pathway, which may help arrest uncontrolled cellular growth.

Results of a Phase 2 investigator-sponsored study in NF1-PN demonstrated tumor shrinkage in 42 percent of adolescents and adults (n=19). In this study, mirdametinib given at 2mg/m2 on a 3-week on, 1-week off schedule was generally well-tolerated. The most commonly reported treatment-emergent grade 2 or higher AEs were acneiform rash in 53% (10/19), fatigue in 26% (5/19) and nausea in 21% (4/19) of patients. Five patients required a dose reduction, but no patients discontinued therapy due to adverse events. There were no grade 4 or higher toxicities and historical ocular events seen with the compound and class were not seen at this dose and schedule.

The U.S. Food and Drug Administration (FDA) and the European Commission granted Orphan Drug designation for mirdametinib for the treatment of NF1, and the FDA granted Fast Track designation for the treatment of patients ≥ 2 years of age with NF1-associated inoperable plexiform neurofibromas that are progressing or causing significant morbidity.

SpringWorks is preparing to initiate a Phase 2b clinical trial evaluating mirdametinib as a monotherapy for the treatment of patients with NF1-PN, a rare and devastating condition for which there are currently no approved therapies.

How it is Designed to Work

MEK1 and MEK2 occupy pivotal positions in the MAPK pathway (RAS-RAF-MEK-ERK), a critical signaling network regulating cell growth and survival. The NF1 gene encodes a protein called neurofibromin, which acts as a negative repressor of RAS activation. NF1 mutations can result in the loss of neurofibromin activity, which leads to MAPK pathway overactivation, uncontrolled cellular growth, and tumor formation.

MEK 1/2 Inhibitor (PD-0325901) MOA



Key Publications


MEK Inhibitor Combinations in Cancer

MEK inhibitors represent a promising backbone for targeted combination therapies in cancer, given the critical role that the MAPK pathway plays in the growth and proliferation of a large number of tumor types (including lung cancer, pancreatic cancer, colorectal cancer, and others). A Phase 1b clinical trial, being conducted under a global clinical collaboration agreement between SpringWorks Therapeutics and BeiGene, is enrolling patients to evaluate mirdametinib in combination with lifirafenib, a RAF dimer inhibitor, in patients with a range of solid tumor types that harbor mutations in MAPK pathway genes (such as RAS and RAF).

SpringWorks is also actively pursuing additional collaborations and partnerships to evaluate mirdametinib in combination with other rational anti-cancer agents across a range of tumor types.