Unnatural Amino Acids in Novel Antibody Conjugates

Abstract

Antibody-drug conjugates are an important and emerging drug class for the treatment of cancer. Recent evidence strongly suggests that site-specific drug conjugation results in a homogenous population of molecules with more favorable activity and pharmacokinetic properties than randomly conjugated antibodies. Unnatural amino acids (uAAs) can be incorporated in recombinant proteins to enable unique orthogonal chemistries in comparison to the side chains of the natural 20 amino acids. Thus, uAAs present a novel platform for which to create next-generation antibody-drug conjugates. Furthermore, site-specific conjugation through uAAs can also enpower unique small molecule, bispecific, multispecific and other conjugates that could be important constructs for therapeutics, diagnostics and research reagents. Here, we review the progress in uAA incorporation and conjugate construction through both cell-based and -free approaches.

Emerging formats for next-generation antibody drug conjugates

“…Genetic incorporation by-passes the need for potentially expensive downstream processing, but requires engineered cell lines with modified protein translation machinery, that is, tRNAs and tRNA synthases. It is claimed that > 70 NNAA types have been incorporated [60] and some key uses are described below. Production systems can be cellbased using organisms such as Escherichia coli, yeast and CHO cells or cell-free using essentially reaction 'soups' that can be used for rapid screening.…”

Silicon amino acids

“…These untypical compounds (e.g., d ‐amino acids, β‐amino acids, as well as α‐amino acids with modified side chains) are particularly used in the synthesis of modified peptides (such modifications result in the higher resistance toward biodegradation, the altered conformational flexibility, and changes in the higher‐order structure of the peptide chains) . Due to their usefulness, the designing and synthesis of novel unnatural amino acids remain interesting research targets …”

Site-selective orientated immobilization of antibodies and conjugates for immunodiagnostics development

“…Therefore, orientated protein immobilization could be expected via unique chemistries brought by unnatural amino acid. [199,200] As mentioned before, a 3-amino- L -tyrosine was incorporated to proteins for D-A reactions. [103,104] Introduction of a reactive azido group into the protein can be achieved by several aminoacid derivatives, such as azidohomoalanine,[114,120] p -azido- L -phenylalanine,[201] p -propargyloxyphenylalanine,[115] and others.…”