摘要：

A great deal of interest has surrounded the use of monoclonal antibodies (mAbs) for the selective delivery of cytotoxic agents to tumor cells. We have previously demonstrated that mAb-auristatin conjugates are highly active, leading to cures and regressions of established tumors in nude mice. These antibody-drug conjugates (ADCs) contain a dipeptide valine-citrulline-p-aminobenzylcarbamate (vc-PABC) linker used to join the antimitotic drugs monomethylauristatin E or F (MMAE, MMAF) to a series of antitumor mAbs. This linker was selected for plasma stability and cleavage by lysosomal enzymes such as cathepsin B. Here, we describe several other dipeptide sequences, many of which are not cathepsin B substrates, for the attachment of auristatins to mAb carriers. More than 20 mAb-dipeptide-PABC-MMAF ADCs were prepared, all of which were active in vitro and in vivo independent of peptide sequence. There was no apparent improvement over the vc-PABC linker, since the PABC group facilitated lysosomal drug release. In contrast, a new series of mAb-MMAF conjugates was prepared in which the dipeptide linkers were directly attached to the C-terminal phenylalanine on the drug without using an intervening PABC spacer. Many of the dipeptide sequences contained unnatural amino acids in order to increase the stringency of drug release. Peptide sequences were identified within the new conjugates that led to both greater tolerability and higher potency compared to corresponding vc-PABC ADCs. The new linkers play an important role in ADC activity and tolerability, and mAb-auristatin conjugates derived from them are candidates for future development.

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