Optimizing Lysosomal Activation of Antibody–Drug Conjugates (ADCs) by Incorporation of Novel Cleavable Dipeptide Linkers

Abstract

Although peptide linkers are used in multiple clinical-stage ADCs, there are only few reports on optimizing peptide linkers for efficient lysosomal proteolysis and for stability in circulation. We screened multiple dipeptide linkers for efficiency of proteolysis and compared them to the dipeptide linkers currently being evaluated in the clinic: Val-Cit, Val-Ala, and Ala-Ala. Lead dipeptide linkers selected from the initial screen were incorporated into ADCs with indolinobenzodiazepine dimer (IGN) payloads to evaluate cellular processing, <i>in vitro</i> cytotoxic activity, plasma stability, and <i>in vivo</i> efficacy. ADCs with several dipeptide linkers bearing l-amino acids showed faster lysosomal processing in target cancer cells compared to the l-Ala-l-Ala linked ADC. These variances in linker processing rates did not result in different <i>in vitro</i> and <i>in vivo</i> activities among peptide linker ADCs, presumably due to accumulation of threshold cytotoxic catabolite levels for ADCs of several peptide linkers in the cell lines and xenografts tested. ADCs with l-amino acid dipeptide linkers exhibited superior <i>in vitro</i> cytotoxic potencies in multiple cell lines compared to an ADC with a d-Ala-d-Ala dipeptide linker and an ADC with a noncleavable linker. This work adds to the toolbox of stable, lysosomally cleavable peptide linkers for ADCs.