Provided herein are trioxacarcin-antibody drug conjugates of Formula (A): and pharmaceutically acceptable salts thereof, comprising at least one instance of the group -L1-(A-L2)a-B attached thereto, wherein a is an integer between 1 and 10, inclusive, L1 is absent or is a linking group, A is a moiety formed from the reaction of two complimentary groups (X and Y), L2 is absent or is another linking group, and B is an antibody or antibody fragment. Also provided are methods of preparing these antibody-drug conjugates, pharmaceutically acceptable compositions thereof, and methods of their use and treatment. Further provided are precursors to the trioxacarcin-antibody drug conjugates, novel trioxacarcins without an antibody conjugated thereto, pharmaceutical compositions thereof, and methods of their use and treatment.