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, in vitro cytotoxic activity, plasma stability, and in vivo 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 in vitro and in vivo 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 in vitro 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.

The AUTOTAC chemical biology platform for targeted protein degradation via the autophagy-lysosome system

“…exhibit sustained efficacy, it remains to be seen whether AUTOTACs act catalytically and/or escape the lysosome, not unlike the cytotoxic drug moieties of antibody-drug conjugates 41 . Additionally, the off-target and selectivity issues of the AUTO-TAC platform have yet to be fully investigated and should be addressed in follow-up studies.…”

Antibody–drug conjugates: Recent advances in linker chemistry

“… 24 and Salomon et al. 25 both indicated that ADCs containing an ( l , l ) dipeptide linker showed higher antitumor activity in vitro and in vivo than other amino acid configurations.…”

Advances and Limitations of Antibody Drug Conjugates for Cancer

“…In addition to this valine-alanine (Val-Ala), phenylalanine-lysine (Phe-Lys) has been used in some ADCs including SGN-CD70A and labetuzumab-SN-38 [ 58 , 61 ]. Other dipeptide linkers used in ADCs include L-Alanyl-L-alanine (Ala-Ala) [ 60 ].…”