To elucidate the role of Bcl-XL and MCL-1 in 20(S)-PPD-induced apoptosis, overexpression of Bcl-XL or MCL-1, coupled with the application of selective inhibitors targeting MCL-1 or Bcl-2, provided direct evidence that 20(S)-PPD induces apoptosis in AML cells by inhibiting Bcl-XL and MCL-1 proteins (Figure 3). The gene discussed is MCL1; the disease is acute myeloid leukemia.