RANK Pathway Inhibition Sensitizes Triple-Negative Breast Cancer to CDK4/6 Inhibitors and Enhances Immune Response

Despite chemotherapy's limitations and toxic effects, it remains the primary treatment for most patients with triple-negative breast cancer (TNBC), with or without immune checkpoint inhibitors. Although cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) combined with endocrine therapy have revolutionized luminal breast cancer treatment, CDK4/6is alone are largely ineffective in TNBC, even with functional retinoblastoma protein (pRB). Activation of the receptor activator of nuclear factor κB (RANK) pathway has been associated with poor prognosis in TNBC and with resistance to CDK4/6is in luminal breast cancer, effects that can be reversed by RANK ligand inhibitors (RANKLi). In this study, we analyzed the effect of RANK knockdown or RANKLi in the response of pRB-proficient TNBC to CDK4/6i in vitro. RANK + patient-derived xenograft and cell line-derived xenograft models were used to assess therapeutic efficacy of CDK4/6i + RANKLi in vivo. Two syngeneic models of TNBC and luminal breast cancer were used to portrait the main therapy-induced alterations in the tumor immune microenvironment. RANK knockdown or RANKLi sensitized pRB-proficient TNBC cells to CDK4/6i in vitro. The combination of palbociclib and RANKLi regressed or prevented tumor growth and metastasis in vivo, enhancing cell cycle arrest. Both CDK4/6i and RANKLi elicited an antitumor immune response, characterized by an increase in CD4+ and CD8+ T cells and a decrease in tumor-associated macrophages infiltrating the tumor microenvironment. These findings suggest that combining CDK4/6i and RANKLi could offer a new therapeutic strategy for pRB-proficient TNBC, holding potential immunomodulatory benefits across breast cancer subtypes.