Binimetinib (Mektovi): Understanding Its Mechanism, Dosing, Clinical Uses, and Role in BRAF V600–Mutated Melanoma and NSCLC

Binimetinib (Mektovi) is an oral, reversible inhibitor of MEK1 and MEK2, key components of the RAS–RAF–MEK–ERK/MAPK pathway. By suppressing MEK activity, binimetinib reduces downstream ERK phosphorylation and inhibits proliferation and survival signaling in tumors driven by MAPK-pathway activation.

In current practice, binimetinib is FDA approved only in combination with encorafenib for two settings: BRAF V600E- or V600K-mutated unresectable/metastatic melanoma and BRAF V600E-mutated metastatic NSCLC. The standard dose is 45 mg orally twice daily, approximately 12 hours apart, with or without food.

Key Facts

• Generic name: Binimetinib
• Brand name: Mektovi
• Drug class: MEK1/MEK2 inhibitor
• Route: Oral
• Initial US approval: 2018
• Primary targets: MEK1 and MEK2
• Standard dose: 45 mg orally twice daily
• Administration: Approximately 12 hours apart
• Food: With or without food
• Tablet strength: 15 mg
• Combination partner: Encorafenib
• FDA indications: BRAF V600E/K melanoma; BRAF V600E metastatic NSCLC
• First dose reduction: 30 mg twice daily
• Moderate/severe hepatic impairment: 30 mg twice daily
• Important toxicities: Cardiomyopathy, VTE, ocular toxicity, ILD/pneumonitis, hepatotoxicity, CPK elevation/rhabdomyolysis, hemorrhage, new primary malignancies
• Current US status: FDA approved.

What Is Binimetinib?

Binimetinib is a small-molecule inhibitor of:

MEK1 and MEK2

also known as:

MAP2K1 and MAP2K2.

MEK1/2 occupy a central position within the:

RAS → RAF → MEK → ERK

signaling pathway.

This pathway regulates:

• Cell proliferation
• Survival
• Differentiation
• Migration
• Gene transcription

In cancers with activating BRAF V600 mutations, abnormal BRAF activity causes persistent MEK and ERK signaling.

Binimetinib interrupts this pathway downstream of BRAF.

What Is the Mechanism of Action of Binimetinib?

1. BRAF V600 Mutation Activates MAPK Signaling

BRAF V600E or V600K mutations produce constitutively active BRAF kinase.

This continuously activates:

MEK1/2

which then activate:

ERK1/2.

2. Binimetinib Reversibly Inhibits MEK1 and MEK2

Binimetinib is a:

Reversible MEK1/2 inhibitor.

It inhibits both MEK activity and downstream ERK phosphorylation.

3. ERK Signaling Is Reduced

MEK inhibition decreases:

• ERK activation
• MAPK-dependent transcription
• Cell-cycle signaling
• Pro-survival signaling

4. Tumor Proliferation Falls

The result is:

• Reduced proliferation
• Reduced survival
• Increased apoptosis
• Reduced tumor growth

The mechanism can be summarized as:

Binimetinib → MEK1/2 inhibition → reduced ERK phosphorylation → suppression of MAPK signaling → reduced tumor-cell proliferation and survival.

Why Is Binimetinib Combined With Encorafenib?

Encorafenib inhibits:

Mutant BRAF

while binimetinib inhibits:

MEK1/2 downstream of BRAF.

This dual blockade suppresses the pathway at two levels:

BRAF → MEK → ERK.

Compared with BRAF inhibition alone, BRAF/MEK combination therapy can:

• Deepen MAPK-pathway suppression
• Delay resistance
• Improve response durability
• Improve progression-free survival
• Improve overall survival
• Reduce some paradoxical BRAF-inhibitor toxicities

The combination is established in both:

• BRAF V600-mutated melanoma
• BRAF V600E-mutated metastatic NSCLC

What Is the Dose of Binimetinib?

The recommended dose is:

45 mg orally twice daily

approximately:

12 hours apart

in combination with encorafenib.

Treatment continues until:

• Disease progression
• Unacceptable toxicity.

How Is Binimetinib Administered?

Binimetinib is available as:

15 mg tablets.

A 45 mg dose therefore corresponds to:

Three 15 mg tablets per dose.

It may be taken:

With or without food.

The twice-daily doses should be taken approximately:

12 hours apart. 

What If a Dose Is Missed?

If a dose is missed:

Do not take the missed dose if the next scheduled dose is due within:

6 hours.

Otherwise, take it when remembered.

If vomiting occurs after administration:

Do not take an additional dose.

Continue with the next scheduled dose.

How Are Binimetinib Dose Reductions Made?

Starting dose:

45 mg twice daily

First dose reduction:

30 mg twice daily.

If the patient cannot tolerate:

30 mg twice daily

binimetinib should generally be:

Permanently discontinued. 

If encorafenib is permanently discontinued:

Binimetinib should also be discontinued.

Dose interruption, reduction, or discontinuation may be required for:

• Cardiomyopathy
• Venous thromboembolism
• Serous retinopathy
• Uveitis
• ILD/pneumonitis
• Hepatotoxicity
• CPK elevation
• Rhabdomyolysis
• Hemorrhage
• Severe dermatologic toxicity

What Are the Important Drug Interactions With Binimetinib?

Unlike many oral targeted therapies, the current FDA prescribing information states:

No clinically important drug interactions have been observed with binimetinib. 

However, because binimetinib is given with encorafenib, the interaction profile of the full regimen must still be reviewed carefully.

This is especially important because encorafenib has clinically significant:

• CYP3A4 interactions
• Transporter interactions
• QT-related considerations

Therefore, medication review should always consider the combination regimen, not binimetinib in isolation.

Does Binimetinib Require Renal or Hepatic Dose Adjustment?

Renal Impairment

No routine starting-dose adjustment is generally required for mild-to-moderate renal impairment.

Data are more limited in severe renal dysfunction.

Hepatic Impairment

No adjustment is required for:

Mild hepatic impairment.

For:

• Moderate hepatic impairment
• Severe hepatic impairment

the recommended dose is:

30 mg orally twice daily. 

What Is the Pharmacokinetic Profile of Binimetinib?

Absorption

Binimetinib exposure is approximately dose proportional.

After twice-daily administration, steady-state accumulation is approximately:

1.5-fold.

Food Effect

Binimetinib may be taken:

With or without food.

No clinically important food restriction is required.

Protein Binding

Binimetinib is approximately:

97% plasma protein bound. 

Because of this high protein binding:

Hemodialysis is unlikely to be effective in overdose. 

QT Effect

At the approved:

45 mg twice-daily dose

no clinically meaningful QT prolongation was observed.

What Are the Clinical Uses of Binimetinib?

1. BRAF V600E/K-Mutated Unresectable or Metastatic Melanoma

Binimetinib is FDA approved:

In combination with encorafenib

for patients with unresectable or metastatic melanoma harboring:

• BRAF V600E
• BRAF V600K

mutations.

2. BRAF V600E-Mutated Metastatic NSCLC

Binimetinib is also FDA approved:

In combination with encorafenib

for adults with metastatic NSCLC harboring:

BRAF V600E. 

What Did Binimetinib Clinical Trials Show?

COLUMBUS — BRAF V600-Mutated Melanoma

The pivotal phase III COLUMBUS trial evaluated:

Encorafenib + binimetinib

versus:

Vemurafenib

and encorafenib monotherapy in advanced BRAF V600-mutated melanoma.

A total of:

577 patients

were randomized.

Among the approved-regimen comparison:

• Encorafenib + binimetinib: 192
• Vemurafenib: 191.

Median Progression-Free Survival

• Encorafenib + binimetinib: 14.9 months
• Vemurafenib: 7.3 months

Hazard ratio:

0.54

P < 0.0001.

Median Overall Survival

• 33.6 months
• 16.9 months

respectively.

Hazard ratio:

0.67. 

Objective Response Rate

• 63% with encorafenib + binimetinib
• 40% with vemurafenib

Complete responses occurred in:

• 8%
• 6%

respectively.

Median Duration of Response

• 16.6 months
• 12.3 months

respectively.

COLUMBUS — 5-Year Outcomes

At 5 years:

Progression-Free Survival

• 23% with encorafenib + binimetinib
• 10% with vemurafenib

Overall Survival

• 35%
• 21%

respectively.

Among patients with normal LDH at baseline:

• 5-year PFS: 31%
• 5-year OS: 45%.

These results support durable long-term benefit from dual BRAF/MEK blockade.

PHAROS — BRAF V600E-Mutated Metastatic NSCLC

The phase II PHAROS study evaluated:

Encorafenib 450 mg once daily + binimetinib 45 mg twice daily

in patients with BRAF V600E-mutated metastatic NSCLC.

The efficacy population included:

• 59 treatment-naïve patients
• 39 previously treated patients.

PHAROS — Treatment-Naïve Patients

Objective Response Rate
75%.

Complete response:

15%.

Partial response:

59%. 

Duration of Response

Among responders:

• 64% had DoR ≥12 months
• 43% had DoR ≥24 months.

With longer follow-up:

Median Duration of Response
40.0 months.

Median Progression-Free Survival
30.2 months.

Median Overall Survival
Updated analysis:

47.6 months.

4-Year Overall Survival Probability
49%.

PHAROS — Previously Treated Patients

Objective Response Rate
46%.

Complete response:

10%.

Partial response:

36%.

With longer follow-up:

Median Duration of Response
16.7 months.

Median Progression-Free Survival
9.3 months.

Median Overall Survival
22.7 months.

4-Year Overall Survival Probability
31%.

What About Brain Metastases?

In COLUMBUS:

Approximately:

3%

of patients had baseline brain metastases.

In PHAROS:

Approximately:

8%

had brain metastases at baseline.

These trials were not dedicated intracranial-efficacy studies, so the evidence base for CNS-specific activity is smaller than for some modern EGFR or ALK inhibitors.

Nevertheless, encorafenib plus binimetinib is used as systemic targeted therapy in BRAF V600-driven melanoma and NSCLC, including selected patients with CNS disease.

What About NRAS-Mutant Melanoma?

Binimetinib was also studied as monotherapy in:

NRAS-mutated advanced melanoma

in the phase III:

NEMO trial.

A total of:

402 patients

were randomized to:

• Binimetinib 45 mg twice daily
• Dacarbazine.

Median PFS

• 2.8 months with binimetinib
• 1.5 months with dacarbazine

Hazard ratio:

0.62

P < 0.001.

However, the benefit was modest and did not establish binimetinib monotherapy as an FDA-approved treatment for NRAS-mutant melanoma.

Therefore:

NRAS-mutant melanoma is not a current FDA-approved indication for binimetinib.

Is Binimetinib FDA Approved?

Yes.

Binimetinib received its initial US approval in:

2018.

Its FDA-approved uses are:

Melanoma

With encorafenib for BRAF V600E/K-mutated unresectable or metastatic melanoma.

NSCLC

With encorafenib for BRAF V600E-mutated metastatic NSCLC.

What Is the Current Clinical Role of Binimetinib?

Melanoma

Binimetinib is used as part of:

Encorafenib + binimetinib

for BRAF V600E/K-mutated advanced melanoma.

The combination is one of several established BRAF/MEK regimens, alongside:

• Dabrafenib + trametinib
• Vemurafenib + cobimetinib

Treatment selection depends on:

• Prior immunotherapy
• Disease burden
• CNS disease
• LDH
• Toxicity profile
• Need for rapid disease control
• Patient preference and access

NSCLC

Binimetinib now has an important role in:

BRAF V600E-mutated metastatic NSCLC

through the:

Encorafenib + binimetinib

combination.

PHAROS demonstrated particularly durable outcomes in treatment-naïve patients, with updated median PFS of:

30.2 months

and median OS of:

47.6 months.

Read more: OncoDaily’s coverage of the updated overall survival results from the PHAROS study, evaluating encorafenib + binimetinib in BRAF V600E-mutant metastatic NSCLC.

Watch more: Explore OncoDaily’s discussion on BRAF V600E-mutated NSCLC and the evolving role of targeted therapy with BRAF/MEK inhibition.

What Are the Major Side Effects of Binimetinib?

Common adverse effects when combined with encorafenib include:

Melanoma

• Fatigue
• Nausea
• Diarrhea
• Vomiting
• Abdominal pain.

NSCLC

Common adverse reactions include:

• Fatigue
• Nausea
• Diarrhea
• Musculoskeletal pain
• Vomiting
• Abdominal pain
• Visual impairment
• Constipation
• Dyspnea
• Rash
  Cough.

Cardiomyopathy

Binimetinib can cause:

Left ventricular dysfunction and cardiomyopathy.

In COLUMBUS:

Cardiomyopathy occurred in approximately:

7%.

In PHAROS:

Approximately:

11%. 

LVEF should be assessed:

• Before treatment
• After approximately 1 month
• Every 2–3 months thereafter. 

Venous Thromboembolism

Binimetinib plus encorafenib can cause:

• Deep-vein thrombosis
• Pulmonary embolism

VTE occurred in:

• 6% in COLUMBUS
• 7% in PHAROS.

Patients should be evaluated urgently for:

• Leg swelling
• Leg pain
• Sudden dyspnea
• Chest pain

Ocular Toxicity

MEK inhibitors can cause characteristic retinal toxicity.

Important events include:

• Serous retinopathy
• Retinal detachment
• Macular edema
• Retinal vein occlusion
• Uveitis

In COLUMBUS:

Serous retinopathy occurred in approximately:

20%. 

Patients should be assessed for visual symptoms:

At each visit.

Ophthalmologic examination is recommended:

• At regular intervals
• For new visual symptoms
• For persistent abnormalities.

Documented retinal vein occlusion requires:

Permanent discontinuation. 

Interstitial Lung Disease/Pneumonitis

ILD/pneumonitis is uncommon but potentially serious.

Patients should be assessed for:

• New cough
• Dyspnea
• Hypoxia
• New pulmonary findings

Grade 3 or 4 ILD generally requires:

Permanent discontinuation. 

Hepatotoxicity

Binimetinib can cause elevations in:

• ALT
• AST
• Alkaline phosphatase
• Bilirubin

Liver function tests should be checked:

• Before treatment
• Monthly during treatment
• As clinically indicated.

Rhabdomyolysis and CPK Elevation

CPK elevation is relatively common.

In COLUMBUS:

58%

had elevated CPK.

In PHAROS:

41%

had elevated CK.

Monitoring should include:

• CPK
• Creatinine
• Muscle symptoms

before therapy and periodically during treatment.

Hemorrhage

Hemorrhagic events may occur with the combination.

In COLUMBUS:

• Any-grade hemorrhage: 19%
• Grade ≥3 hemorrhage: 3.2%.

In PHAROS:

• Hemorrhage: 12%
• Grade 3–4 hemorrhage: 4.1%.

Patients should be monitored for:

• GI bleeding
• Intracranial bleeding
• Other clinically significant hemorrhage

New Primary Malignancies

New cutaneous and noncutaneous malignancies can occur when binimetinib is administered with encorafenib.

Patients should be monitored:

• Before therapy
• During therapy
• After treatment discontinuation.

Embryo-Fetal Toxicity

Binimetinib can cause fetal harm.

Females of reproductive potential should use:

Effective contraception

during treatment and for:

30 days after the final dose.

Breastfeeding is not recommended:

• During treatment
• For 3 days after the last dose.

What Monitoring Is Required?

Monitoring during binimetinib therapy should include:

• Confirm BRAF mutation before treatment
• LVEF before treatment
• LVEF after 1 month
• LVEF every 2–3 months
• Signs of DVT/PE
• Visual symptoms at each visit
• Ophthalmologic evaluation
• Respiratory symptoms
• ALT
• AST
• Bilirubin
• Liver tests monthly
• CPK
• Creatinine
• Muscle symptoms
• Signs of hemorrhage
• Skin and other new malignancies
• Pregnancy counseling
• Particular attention should be given to:

Cardiac function, retinal toxicity, VTE, pulmonary symptoms, liver function, muscle toxicity, and bleeding.