The CDK4/6 Inhibitor Palbociclib Inhibits Estrogen-Positive and Triple Negative Breast Cancer Bone Metastasis In Vivo

Area of Science:

• Oncology
• Cancer Metastasis
• Pharmacology

Background:

• Cyclin-dependent kinase (CDK) 4/6 inhibitors improve survival in estrogen receptor-positive (ER+) breast cancer (BC).
• The efficacy of CDK 4/6 inhibitors against bone metastasis in ER+ BC and triple-negative breast cancer (TNBC) is not fully understood.

Purpose of the Study:

• To investigate the in vivo effects of the CDK 4/6 inhibitor palbociclib on breast cancer bone metastasis.
• To evaluate palbociclib's efficacy in both ER+ and TNBC models and assess potential resistance mechanisms.

Main Methods:

• Utilized in vivo models of breast cancer bone metastasis, including ER+ T47D and TNBC MDA-MB-231 cell lines.
• Administered palbociclib to assess primary tumor growth and bone metastasis.
• Investigated treatment interruption and combination therapies (zoledronic acid, CDK7 inhibitor).
• Analyzed downstream phosphoprotein changes in the MAPK pathway.

Main Results:

• Palbociclib significantly reduced primary tumor growth and bone metastasis in the ER+ T47D model.
• Continuous palbociclib treatment inhibited bone tumor growth in the TNBC MDA-MB-231 model.
• Intermittent palbociclib treatment led to resumed tumor growth, unaffected by subsequent cycles or combination therapies.
• MAPK pathway analysis revealed phosphoproteins like p38 potentially involved in drug-insensitive growth.

Conclusions:

• Palbociclib demonstrates efficacy against breast cancer bone metastasis in preclinical models.
• Drug resistance to palbociclib can develop, particularly with intermittent dosing schedules.
• Targeting alternative pathways, such as those identified in the MAPK pathway, is crucial for overcoming CDK 4/6 inhibitor resistance.