Enhanced tumor cell selectivity of adriamycin-monoclonal antibody conjugate via a poly(ethylene glycol)-based...

A novel linker consisting of poly(ethylene glycol) (PEG) and dipeptide was used for conjugation of adriamycin with tumor-specific monoclonal antibody, NL-1, to confirm that the linker can be cleaved selectively with the tumor specific enzyme to express cytotoxicity of the anti-tumor agent. Initially, adriamycin-conjugated PEG linkers through different amino acid compositions, alanyl-valine (Ala-Val), alanyl-proline (Ala-Pro), and glycyl-proline (Gly-Pro) sequences, were prepared to confirm selective digestion with model enzymes. Adriamycin was released by particular model endoproteases, thermolysin and proline endopeptidase, from the linkers with different efficiency. When conjugates were prepared using these adriamycin-bound linkers, conjugates had no loss of binding affinity and specificity for common acute lymphoblastic leukemia antigen (CALLA) expressed on the Daudi cell surfaces as the target of NL-1 antibody. In addition, adriamycin release from the conjugates was also confirmed by incubating them with specific proteases. Tumor cell growth was inhibited dose-dependently for the conjugates carrying Ala-Val and Gly-Pro linkers, whereas significant inhibitory effect was abolished for the conjugate carrying Ala-Pro linker, indicating that cytotoxic effect can be controlled by specificity of antibody and composition of linker peptide. IC(50) for Ala-Val linked conjugate was approximately 3.5 microg/ml and that for Gly-Pro linked conjugate was 5.2 microg/ml. PEG-dipeptidyl linker demonstrated here will be an effective tool for the preparation of immunoconjugate, especially specific activation of anti-tumor agents at desired tumor tissues.