MMAF shows in vitro cytotoxicity against a panel of cell lines. The IC50 values for Karpas 299, H3396, 786-O and Caki-1 are 119, 105, 257, and 200 nM, respectively. Targeted MMAF is much more potent than the free drug, and that cAC10 conjugates of MMAF display pronounced activities. On a molar basis, the cAC10-L1-MMAF4 is an average of over 2200-fold more potent than free MMAF and is active on all the CD30-positive cell lines tested.