Fig. 1: Expression of CDK-Rb-E2F pathway modulators predicts CDK2i single-agent sensitivity in breast cancer cell lines.

a BLU-222 and palbociclib proliferative GI₅₀ determined by CyQUANT direct proliferation assay, 5-day compound treatment. BLU-222 responder threshold was set at 200 nM as previously described¹⁸. Dashed lines connect the BLU-222 and palbociclib IC₅₀s from an individual cell line. P-value determined by paired t-test. b Volcano plot assessing differential gene expression in BLU-222 responders versus palbociclib responders from cell lines in (a). Points above the horizontal dashed line have an adjusted P < 0.05. The left vertical dashed line and the right vertical dashed line represent log₂(FC) = -1.5 and log₂(FC) = 1.5, respectively. c Kinome-selectivity of CDK2 inhibitors, as measured by KINOMEscan at 3 μM compound. S(10) is the number of kinases inhibited at <10% of control, divided by the total number of human wild-type kinases. Kinome illustrations reproduced courtesy of Cell Signaling Technology, Inc. (www.cellsignal.com) (CSTI). The foregoing website is maintained by CSTI, and Blueprint Medicines is not responsible for its content. d Antiproliferative response to CDK2 inhibitors in breast cancer cell lines as in (a). Cell lines were categorized by RB1 (Rb) expression (+: intact, −: <25th percentile expression with copy number loss or mutation), CDKN2A (p16) expression (+: >75th percentile of mRNA expression, -: ≤25th percentile of mRNA expression), and CCNE1 (cyclin E1) expression (overexpression defined as above the 75th percentile of mRNA expression). CCNE1 copy number status is noted by symbol color. Statistical significance was evaluated using the Wilcoxon rank sum test. e–l CyQuant, 5-day compound treatment, in T-47D isogenic cell lines overexpressing CCNE1, CDKN2A, or both. Mean and standard error of the mean (SEM) of two biological replicates are plotted. m Cell cycle distribution in T-47D isogenic cell lines in response to 24-h treatment BLU-222 (100 nM) or palbociclib (250 nM), ±siRB1. Mean and standard deviation (SD) of two biological replicates are plotted. n Antitumor activity of BLU-222 (60 mg/kg twice a day [BID]), ribociclib (50 mg/kg once a day [QD]), and BLU-222+ribociclib (60 mg/kg BID + 50 mg/kg QD) in BCX.022, a TNBC PDX model. 2-way ANOVA statistical deviation in tumor volume at study end is noted, *P < 0.05, **P < 0.01. Mean tumor volume and SEM are plotted, n = 6 per group.