MCL1 and breast cancer: Compounds 4 and 5 exhibited a 12.7-fold increase in Mcl-1/Bim binding inhibition and a 27.3-fold increase in Bcl-XL/Bim binding inhibition compared to marinopyrrole A. Despite their increased anti-apoptotic Bcl-2 family inhibition, efficacy against the breast cancer cell line MDA-MB-468 was limited.