Mechanism of Action of Binimetinib
1. Binimetinib is a reversible inhibitor of MEK1 and MEK2 activation.
2. MEK proteins are upstream regulators of the extracellular signal‑related kinase (ERK) pathway, which promotes cell proliferation.
3. Approximately 40–60% of cutaneous melanomas harbor BRAF mutations. Substitution of valine by glutamic acid at codon 600 in exon 15 (BRAF V600E) is the most common BRAF mutation; substitution of valine by lysine at the same codon (BRAF V600K) occurs less frequently.
4. BRAF V600 mutations result in activation of the BRAF pathway, which includes MEK1 and MEK2.
5. BRAF V600E mutation activates the mitogen‑activated protein kinase (MAPK) and ERK signaling pathway, thereby enhancing cell proliferation and tumor progression (e.g., metastasis).
6. Combination therapy with BRAF inhibitors (i.e., dabrafenib, encorafenib, vemurafenib) and MEK inhibitors (i.e., binimetinib, cobimetinib, trametinib) completely inhibits the MAPK/ERK pathway.
7. In BRAF V600 mutation‑positive cell lines, the combination of binimetinib and encorafenib shows greater antiproliferative activity than either agent alone.
8. In mouse melanoma xenograft models harboring BRAF V600E mutations, the combination of binimetinib and encorafenib inhibits tumor growth and delays the emergence of resistance more effectively than either agent alone.
Important Safety Information
1. If a dose of binimetinib is missed by more than 6 hours or if vomiting occurs after dosing, the patient should take the next dose at the regularly scheduled time. The missed dose should not be made up.
2. Bleeding risk: If signs and/or symptoms of abnormal bleeding (e.g., headache, dizziness, weakness, blood in stool, coughing up blood, vomiting blood) occur, patients should immediately contact their clinician and seek emergency medical attention.
p> 3. Venous thromboembolism (VTE) risk: If sudden dyspnea, chest pain, or leg pain or swelling occurs, patients should immediately contact their clinician and seek emergency medical attention.
4. Cardiomyopathy risk: If manifestations of heart failure (e.g., tachycardia, dyspnea, peripheral edema, dizziness) occur, patients should immediately contact their clinician.
5. Serous retinopathy or retinal vein occlusion risk: If eye pain, swelling, redness, visual changes, or blurred vision occurs, patients should immediately contact their clinician.
6. Interstitial lung disease risk: If new or worsening pulmonary symptoms (e.g., cough, dyspnea) occur, patients should contact their clinician.
7. Hepatotoxicity risk: The importance of monitoring liver function tests before and during binimetinib treatment. Instruct patients to report any possible manifestations of hepatotoxicity (e.g., jaundice, dark or tea‑colored urine, nausea, vomiting, fatigue, loss of appetite, easy bruising, bleeding).
8. Rhabdomyolysis risk: The importance of monitoring creatine kinase (CK) levels before and during binimetinib treatment. Instruct patients to immediately report any possible manifestations of rhabdomyolysis (e.g., dark or red urine, muscle pain, unusual or new onset weakness).
9. Risk of new primary malignancies: If any new skin lesions, changes to existing skin lesions, or signs and symptoms of other malignancies occur, patients should immediately contact their clinician.
10. Fetal risk: Females of reproductive potential should use effective contraception during treatment and for at least 30 days after the last dose. Advise females to inform their clinician if they are pregnant or plan to become pregnant. Inform patients that use of this drug during pregnancy may cause fetal harm.
11. Females should avoid breastfeeding during treatment with binimetinib and for 3 days after the last dose.
12. Inform their clinician of any other concomitant medications they are taking or plan to take, including prescription drugs, over‑the‑counter drugs, and herbal supplements, as well as any concomitant diseases.
