TORC1 suppression predicts responsiveness to RAF and MEK inhibition in BRAF-mutant melanoma

Area of Science:

• Oncology
• Molecular Biology
• Cancer Research

Background:

• RAF and MEK inhibitors show efficacy in BRAF-mutant melanoma but often yield partial, short-lived responses.
• Mechanisms of resistance and predictive biomarkers for treatment response remain critical challenges.

Purpose of the Study:

• To investigate the role of TORC1 signaling in melanoma response to RAF/MEK inhibitors.
• To identify predictive biomarkers for treatment efficacy and patient survival.

Main Methods:

• Assessed TORC1 activity via phosphorylation of ribosomal protein S6 (P-S6) in melanoma cell lines and patient biopsies.
• Utilized in vivo mouse models to evaluate the necessity of TORC1 suppression for apoptosis and tumor response.
• Correlated P-S6 suppression with progression-free survival in patients receiving RAF inhibitor therapy.

Main Results:

• Decreased P-S6 levels predicted cell death induction in BRAF-mutant melanoma cell lines.
• Resistant melanomas maintained TORC1 activity despite MAPK pathway inhibition.
• TORC1 suppression post-MAPK inhibition was essential for apoptosis and tumor response in mouse models.
• P-S6 suppression in patient biopsies correlated with significantly improved progression-free survival.

Conclusions:

• TORC1 activity, monitored by P-S6, is a critical determinant of response to RAF/MEK inhibitors in BRAF-mutant melanoma.
• Quantitation of P-S6 via fine-needle aspiration biopsies can serve as a real-time biomarker to guide treatment strategies.
• Targeting TORC1 or utilizing P-S6 as a biomarker may enhance therapeutic outcomes for melanoma patients.