Interestingly, treatment with ATO in combination with two MEK1 (mitogen-activated protein kinase kinase 1) inhibitors (PD98059 and PD184352) greatly enhanced apoptosis of primary cells from APL patients, as well as immortalized APL and eritroleukemia cell lines [149, 150, 168]. Here, MAP4K1 is linked to acute promyelocytic leukemia.