Fig. 6

Neratinib enhances the efficacy of CDK4/6 inhibitor combined with endocrine therapy by reducing HER2 mRNA stability through the interaction of HER2’s 3’-UTR region with hsa-miR-23a-5p. (A,B) After knockdown of HER2, the effect of the triple combination of neratinib, CDK4/6 inhibitor, and endocrine therapy on HR⁺/HER2-low breast cancer cell proliferation was assessed by the CCK-8 and colony formation assays. (C,D) In cell cycle analysis and western blot, neratinib was shown to promote G1 phase arrest through the HER2 pathway, to downregulate Cyclin D1 and CDK4, and to improve the effect of CDK4/6 inhibitor combined with endocrine therapy in HR⁺/HER2-low breast cancer. (E) Effects of CDK4/6 inhibitor + endocrine therapy and triple combination treatment (neratinib, CDK4/6 inhibitor and endocrine therapy) on HER2 mRNA stability. MicroRNA sequencing (F) revealed the effect of neratinib on miRNA changes, and compared with CDK4/6 inhibitor + endocrine therapy group, the triple combination treatment group administered neratinib, CDK4/6 inhibitor, and endocrine therapy had significantly upregulated hsa-miR-23a-5p (G), which highly interacted with HER2’s 3’-UTR region (H), and significantly lowered HER2 mRNA stability (I) and downregulated HER2 and EGFR protein expression (J). *P < 0.05; **P < 0.01; ***P < 0.001; n = 3. ET endocrine therapy, CDK4/6i CDK4/6 inhibitor, Ner neratinib.