Sustained mTORC1 activity during palbociclib-induced growth arrest triggers senescence in ER+ breast cancer cells

Area of Science:

• Oncology
• Cell Biology
• Molecular Therapeutics

Background:

• Palbociclib, a CDK4/6 inhibitor, is a standard treatment for advanced ER+ breast cancer.
• CDK4/6 inhibitors typically induce reversible, incomplete senescence in ER+ breast cancer cells.
• Understanding mechanisms of differential response to CDK4/6 inhibitors is crucial for optimizing therapy.

Purpose of the Study:

• To investigate the mechanisms underlying complete senescence induction by palbociclib in a subset of ER+ breast cancer cells.
• To identify factors that differentiate reversible from irreversible responses to CDK4/6 inhibition.
• To explore potential therapeutic strategies for overcoming resistance to palbociclib.

Main Methods:

• Utilized ER+ breast cancer cell lines (CAMA1, MCF7, T47D) for preclinical studies.
• Administered palbociclib and evaluated cell cycle arrest, senescence, and mTORC1 signaling.
• Employed pharmacological inhibition (rapamycin) and genetic manipulation (Raptor, TSC2 knockdown) to modulate mTORC1 activity.

Main Results:

• Palbociclib induced irreversible, complete senescence in CAMA1 cells, unlike MCF7 and T47D cells.
• Sustained mTORC1 activity was observed in CAMA1 cells during palbociclib treatment.
• Inhibition of mTORC1 signaling blocked complete senescence induction in CAMA1 cells.
• Genetic depletion of TSC2 in MCF7 cells led to sustained mTORC1 activity and complete senescence during palbociclib treatment.

Conclusions:

• Sustained mTORC1 signaling is a key driver of complete senescence in ER+ breast cancer cells treated with palbociclib.
• Persistent mTORC1 activity during G1 arrest represents a vulnerability in ER+ breast cancer.
• Targeting mTORC1 in combination with CDK4/6 inhibitors may offer a novel therapeutic approach for advanced breast cancer.