Binding, internalization and the cytotoxicity of monoclonal antibody A7-neocarzinostatin conjugates (A7-NCS) in target cells

Challenges and Opportunities to Develop Enediyne Natural Products as Payloads for Antibody-Drug Conjugates

Calicheamicin, the payload of the antibody-drug-conjugates (ADCs) gemtuzumab ozogamicin (Mylotarg^®) and inotuzumab ozogamicin (Besponsa^®), belongs to the class of enediyne natural products. Since the isolation and structural determination of the neocarzinostatin chromophore in 1985, the enediynes have attracted considerable attention for their value as DNA damaging agents in cancer chemotherapy. Due to their non-discriminatory cytotoxicity towards both cancer and healthy cells, the clinical utilization of enediyne natural products relies on conjugation to an appropriate delivery system, such as an antibody. Here we review the current landscape of enediynes as payloads of first-generation and next-generation ADCs.

Production, binding and cytotoxicity of human/mouse chimeric monoclonal antibody-neocarzinostatin conjugate

A human/mouse chimeric Fab monoclonal antibody A7 (chFabA7) was covalently coupled to neocarzinostatin (NCS) by the SPDP method at various chFabA7:NCS substitution ratios. The antigen-binding activity of the conjugate, examined by ELISA using fixed antigen-positive colon cancer cells, was identical to that of the parent chFabA7 when one mole of NCS was conjugated, but was reduced with 2 or 3 moles of conjugated NCS. By means of a colony-forming assay, the cytocidal effect of the conjugate on antigen-positive cancer cells was found to be stronger than that of free NCS, whereas in antigen-negative cancer cells it was similar to that of free NCS. This effect was attenuated by adding an excess amount of monoclonal antibody A7. These findings indicate that the conjugate has an antigen-specific cytocidal action, and thus chFabA7-NCS is a promising tool for targeting cancer chemotherapy.