RUNX1-PDGFBB-AKT pathway mediated CDK4/6 inhibitor resistance in HR+/HER2- breast cancer

Cyclin-dependent kinases 4 and 6 (CDK4/6) are essential drivers of the cell cycle and are also critical for the initiation and progression of diverse malignancies. Pharmacological inhibitors targeting CDK4/6 have demonstrated significant activity against various tumor types such as breast cancer. However, resistance to CDK4/6 inhibitors (CDK4/6i) (such as palbociclib) remain an immense obstacle in clinical and the underlying mechanisms have not been fully understood. Using Conditional medium co-culture, quantitative high-throughput combinational screen (qHTCS), and genomic sequencing, we report that the RUNX1-PDGFBB-AKt pathway was significantly elevated in palbociclib-resistance cells. Inhibition of this axis can enhance the therapeutic efficacy of Palbociclib and surmount Palbociclib resistance both in vitro and in vivo. Mechanistically, we found that O-GlcNAc transferase (OGT) modifies RUNX1 with O-GlcNAcylation at Serine 252 (Ser252), thereby stabilizing RUNX1 protein expression, which is crucial in regulating PDGFBB expression. Significantly, clinical studies also confirm that RUNX1-PDGFBB-Akt pahtway was elevated in palbociclib-resistance patients. Collectively, these results reveal a previously unrecognized mechanism by which RUNX1-PDGFBB mediated palbociclib resistance, and provide valuable insights for the development of innovative therapeutic strategies in future clinical contexts.