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Merck
  • Short-term CDK4/6 Inhibition Radiosensitizes Estrogen Receptor-Positive Breast Cancers.

Short-term CDK4/6 Inhibition Radiosensitizes Estrogen Receptor-Positive Breast Cancers.

Clinical cancer research : an official journal of the American Association for Cancer Research (2020-09-25)
Andrea M Pesch, Nicole H Hirsh, Benjamin C Chandler, Anna R Michmerhuizen, Cassandra L Ritter, Marlie P Androsiglio, Kari Wilder-Romans, Meilan Liu, Christina L Gersch, José M Larios, Lori J Pierce, James M Rae, Corey W Speers
초록

Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors have improved progression-free survival for metastatic, estrogen receptor-positive (ER+) breast cancers, but their role in the nonmetastatic setting remains unclear. We sought to understand the effects of CDK4/6 inhibition (CDK4/6i) and radiotherapy in multiple preclinical breast cancer models. Transcriptomic and proteomic analyses were used to identify significantly altered pathways after CDK4/6i. Clonogenic assays were used to quantify the radiotherapy enhancement ratio (rER). DNA damage was quantified using γH2AX staining and the neutral comet assay. DNA repair was assessed using RAD51 foci formation and nonhomologous end joining (NHEJ) reporter assays. Orthotopic xenografts were used to assess the efficacy of combination therapy. Palbociclib significantly radiosensitized multiple ER+ cell lines at low nanomolar, sub IC50 concentrations (rER: 1.21-1.52) and led to a decrease in the surviving fraction of cells at 2 Gy (P < 0.001). Similar results were observed in ribociclib-treated (rER: 1.08-1.68) and abemaciclib-treated (rER: 1.19-2.05) cells. Combination treatment decreased RAD51 foci formation (P < 0.001), leading to a suppression of homologous recombination activity, but did not affect NHEJ efficiency (P > 0.05). Immortalized breast epithelial cells and cells with acquired resistance to CDK4/6i did not demonstrate radiosensitization (rER: 0.94-1.11) or changes in RAD51 foci. In xenograft models, concurrent palbociclib and radiotherapy led to a significant decrease in tumor growth. These studies provide preclinical rationale to test CDK4/6i and radiotherapy in women with locally advanced ER+ breast cancer at high risk for locoregional recurrence.

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Sigma-Aldrich
Anti-RAD51 Antibody, from rabbit, purified by affinity chromatography
Roche
cOmplete Protease Inhibitor Cocktail, Tablets provided in glass vials
Sigma-Aldrich
AZD-7762 hydrochloride, ≥98% (HPLC)
Sigma-Aldrich
Sodium L-lactate, ~98%
Sigma-Aldrich
Anti-phospho-Histone H2A.X (Ser139) Antibody, clone JBW301, clone JBW301, Upstate®, from mouse
Sigma-Aldrich
Staurosporine solution from Streptomyces sp., Ready Made Solution, 1 mM in DMSO (100 μg/214 μL), 0.2 μm filtered