What Are the Newest MEK Inhibitors for NF1?

Yes, there are new medications available and in development for Neurofibromatosis type 1 (NF1) beyond selumetinib. The most significant recent advancement is mirdametinib, a new MEK inhibitor that has been FDA-approved for both pediatric and adult patients with inoperable plexiform neurofibromas ^[1]. Researchers continue to look for drugs that offer broader age approvals, more convenient dosing schedules, and different side effect profiles.

Mirdametinib and the ReNeu Trial

Mirdametinib was studied in a major clinical trial called the ReNeu trial, which included both children and adults with NF1-associated plexiform neurofibromas ^[1]. The results showed that the medication was highly effective at shrinking tumors in both age groups.

• Tumor Shrinkage: The trial found a confirmed objective response rate (meaning the tumor shrank significantly, typically defined as a 20% or greater reduction in tumor volume) of 41% in adults and 52% in children ^[1]. It is important to note that this approval and these results apply specifically to plexiform neurofibromas, not the typical cutaneous (surface skin) neurofibromas.
• Quality of Life: Beyond just shrinking tumors, patients in both the adult and pediatric groups reported early and sustained improvements in pain severity, pain interference, and overall health-related quality of life ^[1].

How Mirdametinib Differs from Selumetinib

While both selumetinib and mirdametinib belong to the same class of drugs called MEK inhibitors (medications that block a specific protein pathway that causes tumors to grow), mirdametinib introduces several practical advantages for patients:

• Broader Age Approval: While selumetinib is primarily approved for children aged 2 and older, mirdametinib is approved for both children (aged 2 and older) and adults ^[2].
• Different Dosing Schedule: Mirdametinib is taken on an intermittent schedule—specifically, three weeks of taking the medication followed by one week off ^[1]. This break is intended to give the body time to recover and help manage potential side effects and drug toxicity.
• No Fasting Required: Unlike some other medications, mirdametinib does not require fasting and can be taken with or without food ^[1].
• Easier to Swallow: It is available as both a standard capsule and a tablet designed for oral suspension (which dissolves in liquid), making it much easier for young children or patients with tumors in their head or neck that make swallowing difficult ^[1].

Side Effects of MEK Inhibitors

Because mirdametinib is a MEK inhibitor, it shares many of the same potential side effects as selumetinib. The most commonly reported side effects include:

• Dermatitis acneiform: An acne-like skin rash, which affected 78% of adults and 43% of children in the ReNeu trial ^[1]. While these numbers are high, these rashes are generally manageable with specialized topical creams and proactive dermatological care, rather than requiring patients to stop the medication.
• Gastrointestinal issues: Diarrhea and nausea were also common ^[1].
• Paronychia: Inflammation or infection of the tissue surrounding the fingernails or toenails, particularly seen in children ^[1].

There are also rare but serious risks associated with this class of drugs, such as retinal vein occlusion (a blockage of the small veins that carry blood away from the retina in the eye) ^[1]. Patients taking MEK inhibitors need regular monitoring by an eye specialist and should seek immediate emergency care if they experience acute warning signs like sudden blurred vision, vision loss, or dark spots.

The Future of NF1 Treatments

Research is ongoing to find even more effective treatments. Scientists are currently exploring combination therapies, which involve taking a MEK inhibitor alongside other targeted drugs, like RAF inhibitors, to block tumor growth from multiple angles ^[3].

While plexiform neurofibromas are typically benign, a small percentage can become cancerous. New drugs are being tested specifically for these more aggressive NF1-associated tumors, known as Malignant Peripheral Nerve Sheath Tumors (MPNSTs). Medications like anlotinib and mebendazole are currently being investigated in preclinical studies and clinical trials to see if they can effectively target these malignant tumors ^[4][5].

Remember, this information is meant to help you understand the emerging landscape of NF1 treatments. It is not medical advice. Always discuss with your care team to determine if a new treatment is right for you.