ABT-737 directly binds to anti-apoptotic Bcl-2 protein (Bcl-2, Bcl-xL, and Bcl-w) and induces apoptosis,6, 7 but cancer cells with high expression levels of Mcl-1 have been reported to be resistant to ABT-737.8, 9 In an attempt to develop the therapeutic strategy to overcome ABT-737 resistance, we first tested whether ABT-737 differently regulate apoptosis in Caki/vector, Bcl-2-overexpressed Caki (Caki/Bcl-2), and Mcl-1-overexpressed Caki cells (Caki/Mcl-1). The gene discussed is MCL1; the disease is cancer.