Fig. 2
ERX-11 enhances the efficacy of palbociclib in reducing the growth of ER-MT and CDK4/6 inhibitor therapy-resistant BCa cells. ZR-75-ESR1-MT-Y537S (a) and ZR-75-ESR1-MT-D538G (b) cells were stimulated with E2 (10−8 M) for 7 days in the presence or absence of ERX-11 (0.5 μM), palbociclib (0.5 μM), or in combination, and the cell viability was measured by MTT assay. c ZR-75-ESR1-MT-Y537S and ZR-75-ESR1-MT-D538G cells were stimulated with E2 (10-8 M) for 7 days in the presence or absence of ERX-11 (31 nM), abemaciclib (31 nM), ribociclib (31 nM), or in combination, and the cell viability was measured by MTT assay. d Schematic representation of xenograft-derived explant (XDE) assay. The effect of ERX-11, palbociclib, and combination therapy on the proliferation of MCF-7/LTLT (e), ZR-75-ESR1-MT-Y537S (f), and ZR-75-ESR1-MT-D538G (g) tumors was measured by Ki-67 staining. The combination index (CI) was determined by the Chou-Talalay method, CI < 1 indicates synergism (**p < 0.01, ****p < 0.0001)