 Despite similar abilities to alkylate DNA, adozelesin and bizelesin caused a decrease in HCT116 tumor cell proliferation by different pathways.Carzelesin (U-80244) is a cyclopropylpyrroloindole prodrug containing a relatively nonreactive chloromethyl precursor to the cyclopropyl function.Activation of carzelesin requires two steps, (a) hydrolysis of a phenylurethane substituent to form U-76073, followed by (b) ring closure to form the cyclopropyl-containing DNA-reactive U-76074.