Stromal senescence following treatment with the CDK4/6 inhibitor palbociclib increases mammary cancer metastasis

One potential resistance mechanism to CDK4/6 inhibitors in breast cancer could be induction of cellular senescence in normal host tissues. The aim of our study was to identify CDK4/6 inhibition-induced changes to host tissues that impact metastasis. Using mouse models, we found that pre-treatment with palbociclib can increase metastatic seeding of mouse mammary cancer cells in the lungs and that this can be mitigated by eliminating senescent host cells. We describe palbociclib-induced gene expression changes in lungs that correlate with this effect and reveal altered intra-lung immune populations. Senescent endothelial cells are identifiable within lung metastases of mice pre-treated with palbociclib. Using in vitro models, we show that palbociclib treatment increases endothelial cell senescence and affects macrophage invasion and migration. These studies describe how CDK4/6 inhibition-induced cellular senescence in host tissues affects metastasis and disease progression in breast cancer, which remain key obstacles to achieving long-term survival. mRNA profiles of p16-INK-ATTAC mouse lungs treated with palbociclib and/or AP20187 and HUVEC cells treated with palbociclib