Conjunctival Melanoma Targeted Therapy: MAPK and PI3K/mTOR Pathways Inhibition

Area of Science:

• Ophthalmology
• Oncology
• Molecular Biology

Background:

• Conjunctival melanoma (CJM) is a rare malignancy with poorly understood molecular drivers.
• The mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinases/mechanistic target of rapamycin (PI3K/mTOR) pathways are crucial in melanoma development.

Purpose of the Study:

• To analyze MAPK and PI3K/mTOR pathway activity in benign and malignant conjunctival melanocytic lesions.
• To evaluate the efficacy of targeted inhibitors in suppressing conjunctival melanoma cell growth.

Main Methods:

• Immunohistochemistry was used to assess BRAF V600E mutations and pathway activation (ERK, MEK, S6, AKT) in 35 conjunctival nevi and 31 CJMs.
• Three CJM cell lines with distinct mutations (BRAF V600E, NRAS Q61L, BRAF G466E) were treated with specific inhibitors (vemurafenib, trametinib, selumetinib, pictilisib, dactolisib).
• Cell viability (WST-1 assay), protein phosphorylation (western blot), and apoptosis (cleaved caspase-3) were measured.

Main Results:

• BRAF V600E mutations were found in 42.6% of nevi and 35.5% of CJMs.
• MEK and ERK activation were significantly higher in CJM (90.3% and 96.8%) compared to nevi (62.9% and 45.7%).
• S6 activation was markedly increased in CJM (90.3%) versus nevi (20%). One cell line (CRMM1) responded to MEK and PI3K inhibitors, while another (CRMM2) showed moderate sensitivity to a PI3K inhibitor; a third (T1527A) was resistant to all tested drugs.

Conclusions:

• MAPK pathway activation in CJM is elevated beyond BRAF V600E mutation.
• Targeted therapy, particularly for BRAF-mutated CJM, holds therapeutic potential.
• NRAS-mutated conjunctival melanomas demonstrate relative resistance to current targeted agents.