SMI-4a is a potent and selective Pim protein kinase inhibitor, which blocks the growth of precursor T-cell lymphoblastic leukemia/lymphoma. SMI-4a was found to induce phosphorylation of extracellular signal-related kinase1/2 (ERK1/2), and the combination of SMI-4a and a mitogen-activated protein kinase kinase 1/2 (MEK1/2) inhibitor was highly synergistic in killing pre-T-LBL cells. SMI-4a may be developed as a therapeutic strategy for the treatment of pre-T-LBL.