S6K1 blockade overcomes acquired resistance to EGFR-TKIs in non-small cell lung cancer

Area of Science:

• Oncology
• Molecular Biology
• Genetics

Background:

• Resistance to Epidermal Growth Factor Receptor (EGFR) Tyrosine Kinase Inhibitors (TKIs) is a major challenge in treating non-small cell lung cancer (NSCLC) with activating EGFR mutations.
• Mechanisms of resistance beyond genetic alterations, such as compensatory signaling pathway activation, require further elucidation.

Purpose of the Study:

• To identify novel bypass mechanisms contributing to EGFR-TKI resistance in NSCLC.
• To investigate the S6K1/MDM2 signaling axis as a potential therapeutic target for overcoming EGFR-TKI resistance.

Main Methods:

• Analysis of public databases and a clinical cohort to assess S6K1 expression as a biomarker.
• In vitro gain-and-loss of function studies to determine S6K1's role in TKI resistance.
• In vivo validation using subcutaneous and orthotopic mouse lung cancer models.
• Mechanistic studies involving EGFR inhibition and S6K1/MDM2 interactions.

Main Results:

• S6K1 expression was identified as a prognostic and predictive biomarker for EGFR-TKI therapy.
• Inhibition of S6K1 using PF-4708671 synergistically enhanced TKI efficacy in preclinical models without observed toxicity.
• EGFR inhibition induced nuclear translocation of S6K1, leading to binding with MDM2, a key mediator of resistance.

Conclusions:

• The S6K1/MDM2 signaling axis represents a novel bypass mechanism driving EGFR-TKI resistance in NSCLC.
• Targeting S6K1/MDM2 with small molecule antagonists offers a promising strategy to reverse TKI resistance and improve clinical outcomes in NSCLC patients.