Defective Cyclin B1 Induction in Trastuzumab-emtansine (T-DM1) Acquired Resistance in HER2-positive Breast Cancer

Area of Science:

• Oncology
• Molecular Biology
• Pharmacology

Background:

• Trastuzumab-emtansine (T-DM1) is a key treatment for advanced HER2-positive breast cancer.
• Acquired resistance to T-DM1 is a significant clinical challenge, limiting treatment efficacy.
• Understanding the molecular mechanisms of T-DM1 resistance is crucial for developing new therapeutic strategies.

Purpose of the Study:

• To investigate the mechanisms underlying acquired resistance to T-DM1 in HER2-positive breast cancer.
• To identify potential biomarkers for predicting T-DM1 response and resistance.

Main Methods:

• Established T-DM1-resistant HER2-positive breast cancer cell lines (HCC1954, HCC1419, SKBR3).
• Assessed HER2 expression, T-DM1 binding, and intracellular uptake in parental and resistant cells.
• Analyzed CDK1 kinase activity, cyclin B1 expression, proliferation, and apoptosis.
• Utilized siRNA to modulate cyclin B1 levels and genetic modification (cdc20 silencing) in resistant cells.
• Evaluated T-DM1 effects on cyclin B1, proliferation, and apoptosis in HER2-positive breast cancer explants.

Main Results:

• Resistant cell lines maintained HER2 amplification, T-DM1 binding, and uptake.
• T-DM1 treatment induced cyclin B1 accumulation in sensitive cells but not in resistant cells.
• Cyclin B1 knockdown conferred T-DM1 resistance, while increased cyclin B1 partially sensitized resistant cells.
• In patient explants, T-DM1's impact on proliferation and apoptosis correlated with cyclin B1 induction.

Conclusions:

• Defective induction of cyclin B1 by T-DM1 is a key mechanism mediating acquired resistance in HER2-positive breast cancer.
• Cyclin B1 induction serves as a potential pharmacodynamic biomarker for T-DM1 treatment efficacy.
• These findings suggest targeting cyclin B1 pathways or using it as a predictive marker in T-DM1 therapy.