Figure 1.

Generation of CDK4/6 inhibitor-resistant cells. A. Relative cell viability of MCF-7 and MCF-7pR cells after being treated with indicated concentrations of palbociclib for 48 hours was analyzed by cell viability assay. IC₅₀ of the indicated drug in MCF-7 and MCF-7pR cells were shown. *P < 0.05. B. Western blot determined the MDR-1 expression level in MCF-7 and MCF-7pR cells. C. MCF-7 and MCF-7pR cells were treated with or without palbociclib (4 µM) for 48 hours and measured by a flow cytometer. Results were reported as mean percent cell cycle distribution with standard errors. *P < 0.05, or **P < 0.01 or ***P < 0.001. D. Respective images of colony-formation results in MCF-7 and MCF-7pR with the treatment of palbociclib or with no treatment. E. MCF-7 and MCF-7pR cells were treated with 4 µM palbociclib and collected at indicated times. Immunoblots were performed with the indicated antibodies.