Fig. 5.

Cyclin-dependent kinases 4/6 (DK4/6) inhibitor synergizes with epidermal growth factor receptor (EGFR) inhibitor to suppress triple-negative breast cancer (TNBC) proliferation. a MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay showing the inhibition of cell proliferation of TNBC cell lines treated with dimethyl sulfoxide (DMSO), lapatinib (LAP, 1 µM), abemaciclib (ABE, 0.5 µM), or Combo (LAP + ABE) for 48 h. b Drug synergism analysis showing synergism index on different FA (fraction affected) in TNBC cell lines. Dosage ratio: LAP:ABE = 4:1; LAP:RIBO (Ribociclib) = 2:1; LAP:PALBO (Palbociclib) = 1:2. c Western blots showing downstream signaling changes in TNBC cell lines after designated treatment for the indicated time. d, Left: Western blots showing cytosolic DEDD expression after lentiviral infected ΔNLS-DEDD in KTB cell lines. Right: MTT assay showing inhibition of proliferation of DEST- or ΔNLS-DEDD-expressing KTB cells treated with DMSO, LAP (0.5 µM), ABE (0.25 µM), or Combo for 48 h. e Western blots showing EGFR, Akt, and Erk signaling changes in DEST- or ΔNLS-DEDD-expressing KTB cells treated with DMSO, LAP (0.5 µM), ABE (0.25 µM), or Combo for 24 h. f, Left: MTT assay showing the inhibition of proliferation of MDA-MB-436 cells expressing or not expressing cytosolic DEDD after designated treatment. Cells were treated as in d. Right: Drug synergism analysis showing synergism index on different FA with the dosage ratio of 4:1 (LAP:ABE). g Western blots showing EGFR, Akt, and Erk signaling changes in MDA-MB-436 cells expressing or not expressing cytosolic DEDD treated with DMSO, LAP (1 µM), ABE (0.25 µM), or Combo for indicated hours. All quantitative data were generated from a minimum of three replicates. Error bars represent means ± s.e.m. For a, P values were derived from one-way analysis of variance (ANOVA) with multiple comparison test. For d, f, P values were derived from two-tailed t test. n.s., not significant