RUNX2 and breast cancer: However, little difference was observed in cells that express high levels of RUNX2 (T47D-RUNX2, MCF7-RUNX2 and MDA-231), implying that a negative feedback mechanism suppressing further S451 phosphorylation might be activated to balance the higher levels of RUNX2 by CADD522 or that BC cells might have different biological response to CADD522, which might be related to cellular levels of RUNX2.