CHEK1 and breast cancer: In this study, we examined the overall hypothesis that Chk1 inhibitors such as PD407824 and PF477736 can suppress mammary tumor growth and osteolytic lesions by regulating pathways associated with the ATR-Chk1 axis, eIF2α and stress to the endoplasmic reticulum, as well as bone remodeling-linked genes such as NFATc1, and ATF4.