Intact regulation of G1/S transition renders esophageal squamous cell carcinoma sensitive to PI3Kα inhibitors

Area of Science:

• Oncology
• Molecular Biology
• Cancer Therapeutics

Background:

• Phosphatidylinositol 3-kinase alpha (PI3Kα) inhibitors are under investigation for esophageal squamous cell carcinoma (ESCC).
• Identifying biomarkers is crucial for predicting and monitoring PI3Kα inhibitor efficacy in ESCC to enhance clinical response rates.

Purpose of the Study:

• To investigate the sensitivity of ESCC patient-derived xenografts (PDXs) with CCND1 amplification to a novel PI3Kα-selective inhibitor, CYH33.
• To elucidate the underlying mechanisms of CYH33 sensitivity and resistance in ESCC.
• To explore combination therapies involving PI3Kα and CDK4/6 inhibitors for ESCC treatment.

Main Methods:

• Treatment of ESCC PDXs and cell lines with CYH33, a PI3Kα-selective inhibitor.
• Analysis of protein levels (cyclin D1, p21, Rb, SKP2, E2F1) and cell cycle progression (G1 arrest).
• Assessment of the effects of combined CYH33 and CDK4/6 inhibitors on resistant ESCC models.

Main Results:

• ESCC PDXs with CCND1 amplification demonstrated increased sensitivity to CYH33.
• CYH33 induced G1 phase arrest in sensitive cells, linked to elevated p21 and suppressed Rb phosphorylation.
• CDK4/6 inhibitors resensitized resistant ESCC cells and PDXs to CYH33, revealing a mechanistic link involving Rb phosphorylation and p21 stability.

Conclusions:

• CCND1 amplification serves as a predictive biomarker for PI3Kα inhibitor efficacy in ESCC.
• The combination of PI3Kα and CDK4/6 inhibitors presents a promising therapeutic strategy for specific ESCC patient populations, particularly those with CCND1 amplification and proficient Rb.