Dual Role of Cx43 in Enhancing CDK4/6 Inhibitor Response and Promoting the Elimination of Therapy-Induced Senescent Tumor Cells

Breast cancer has become the most prevalent malignancy worldwide. A key clinical advance has been the introduction of cyclin-dependent kinase 4/6 inhibitors (CDK4/6i), that in combination with endocrine therapy has been a major advance for the treatment of luminal (ER⁺/HER2⁻) breast cancer. CDK4/6i induce cell cycle arrest in G1 and cellular senescence improving clinical outputs. However, limited efficacy and therapeutic resistance remain major challenges due to incomplete effects or the failure to eliminate the accumulated tumor senescent cells. Here, we identify connexin 43 (Cx43), a membrane channel protein involved in cell-to-cell communication, identified as a novel target in luminal breast cancer that potentiates the effects of CDK4/6 inhibitors. We found that Cx43 not only reduces tumor cell proliferation by enhancing senescence but also reshapes the Senescence-Associated Secretory Phenotype (SASP) profile. We also demonstrate that, in combination with CDK4/6i, Cx43 reinforces G1 arrest via transcriptional downregulation of E2F targets including CDK4 and CDK6, and through interaction with p21/p27, deepens the senescent state. Importantly, the Cx43-associated senescent phenotype sensitizes tumor cells accumulated under CDK4/6i treatment to the senolytic agent Navitoclax. Our results demonstrate that upregulation of Cx43 in breast cancer reduces proliferation and enhances the clearance of therapy-induced senescent cells. The triple-drug strategy comprising CDK4/6i, Cx43 delivery, and a senolytic drug such as Navitoclax holds great promise for overcoming CDK4/6i resistance and improving clinical outcomes in ER⁺/HER2⁻ breast cancer and may also be applicable to other cancer types that respond to CDK4/6i or other pro-senescence antitumoral drugs.