Daunorubicin coupled to monoclonal antibodies via a cis-aconitic anhydride linker: biochemical and cytotoxic properties revisited.

Daunorubicin (DNR) was coupled to monoclonal antibodies (Mab) reactive to breast tumor cells using the acid-labile linking agents cis-asonitic anhydride and two other non acid-labile analogs, glutaric anhydride and citraconic anhydride. The acid derivatives of DNR formed by reaction with the anhydrides were converted to their N-hydroxysuccinimide (NHS) active esters for coupling to MAb. The molar input of drug NHS ester to MAb ranged from 1:1 to 100:1. The resulting MAb-DNR conjugates were purified by gel filtration and analyzed by high performance liquid chromatography. Monomeric conjugates contained 0.2 to 11.0 moles of DNR/mole of MAb. No evidence of cell killing was observed up to a concentration of 10 micrograms/ml DNR bound to MAb, while DNR exhibited 50% killing of the breast tumor cell line MCF-7 at a concentration of 1 microgram/ml.