MCL1 and cancer: In a study of cancer cells, where a small molecule library was used to identify compounds inhibiting Mcl-1, Bcl-XL was identified as the only marker predicting sensitivity to Mcl-1-inhibiting compounds, and these small molecules induced apoptosis via Bak not Bax.20 In the non-transformed cells we used here only the simultaneous removal of Bcl-XL and Mcl-1 but not either on its own (or in combination with any other Bcl-2-like protein) induced apoptosis.