Fig. 4: p16 and cyclin D1 overexpression attenuate the response to ribociclib in ER+ BC cell lines. | Nature Communications

Fig. 4: p16 and cyclin D1 overexpression attenuate the response to ribociclib in ER+ BC cell lines.

From: High p16 expression and heterozygous RB1 loss are biomarkers for CDK4/6 inhibitor resistance in ER+ breast cancer

Fig. 4

A Half-maximal inhibitory concentration (IC50) and IC50 fold-change (fc) values for ribociclib, fulvestrant and the combination of drugs in T47D and MCF7 cells overexpressing p16 compared to control cells (MOCK), treated for 6 days and evaluated as shown underneath. Data are presented as mean values ± SEM of at least three independent experiments. B Immunoblot of the indicated proteins in MOCK and p16 overexpressing T47D and MCF7 cells untreated or treated with ribociclib for 5 days at the indicated concentrations. C Immunoblot of the indicated proteins in a cell competition assay. Cells were treated with vehicle or ribociclib 1 µM for the indicated days. D Comparison of structural models for the complexes of p16 bound to P18IN003 and p16 bound to CDK4. Gray cartoon is p16, orange spheres represent P18IN003, cyan cartoon is CDK4; zoomed view are the binding pocket with p16 shown as gray surface and highlighting the residues in the binding pocket of p16 as sticks and the hydrogen bonds made between P18IN003 and p16 shown as black dashed lines. E Relative spheroid area of PDC191 and PDC313 after treatment with 1 µM ribociclib, 20 nM P18IN003 and the combination for 7 days. Data are presented as mean values of three independent experiments ± SEM. Two-tailed p-values are based on the one-way ANOVA test with Tukey’s method correction compared with the vehicle (black line). Dashed line indicates the optimal cut-off established in Fig. 3E. p16 and pRb scores of each PDC are indicated. F IC50 and IC50 fc values for ribociclib, fulvestrant and the combination of drugs in T47D and MCF7 cells overexpressing cyclin D1, compared to control cells (MOCK), treated for 6 days and evaluated as shown underneath. Data are presented as mean values ± SEM from at least three independent experiments. G Immunoblot of indicated proteins in control (MOCK) and cyclin D1-overexpressing T47D and MCF7 cells untreated or treated with 0.5 µM ribociclib for 48 h. H Immunoblot as indicated for panel (C). Source data are provided as a Source Data file.

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