A new, triglycyl peptide linker for antibody-drug conjugates (ADCs) with improved targeted killing of cancer cells
2016
A triglycyl peptide linker (CX) was designed for use in antibody-drug conjugates (ADCs), aiming to provide efficient release and lysosomal efflux of cytotoxic catabolites within targeted cancer cells. ADCs comprising anti-epithelial cell adhesion molecule (anti-EpCAM) and anti-epidermal growth factor receptor (anti-EGFR) antibodies with maytansinoid payloads were prepared using CX or a non-cleavable SMCC linker (CX and SMCC ADCs). The in vitro cytotoxic activities of CX and SMCC ADCs were similar for several cancer cell lines, however the CX ADC was more active (5-100 fold lower IC50) than the SMCC ADC in other cell lines including a multi-drug resistant line. Both CX and SMCC ADCs showed comparable maximum tolerated doses and pharmacokinetics in CD-1 mice. In Calu-3 tumor xenografts, antitumor efficacy was observed with the anti-EpCAM CX ADC at a five-fold lower dose than the corresponding SMCC ADC in vivo. Similarly, the anti-EGFR CX ADC showed improved antitumor activity over the respective SMCC conjugate in HSC-2 and H1975 tumor models, however both exhibited similar activity against FaDu xenografts. Mechanistically, in contrast to the charged lysine-linked catabolite of SMCC ADC, a significant fraction of the carboxylic acid catabolite of CX ADC could be uncharged in the acidic lysosomes and thus diffuse out readily into the cytosol. Upon release from tumor cells, CX catabolites are charged at extracellular pH and do not penetrate and kill neighboring cells, similar to the SMCC catabolite. Overall, these data suggest that CX represents a promising linker option for the development of ADCs with improved therapeutic properties.
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