Methods to Design and Synthesize Antibody-Drug Conjugates (ADCs)

Abstract

Antibody-drug conjugates (ADCs) have become a promising targeted therapy strategy that combines the specificity, favorable pharmacokinetics and biodistributions of antibodies with the destructive potential of highly potent drugs. One of the biggest challenges in the development of ADCs is the application of suitable linkers for conjugating drugs to antibodies. Recently, the design and synthesis of linkers are making great progress. In this review, we present the methods that are currently used to synthesize antibody-drug conjugates by using thiols, amines, alcohols, aldehydes and azides.

Keywords: antibody-drug conjugates (ADCs); drugs; linkers; monoclonal antibodies (mAbs); targeted therapy.

Figure 1

Schematic representation of an antibody-drug conjugate (ADC). Reprinted with permission from Reference [2].

Scheme 1

Interchain cysteine to serine mutagenesis enables drugs to conjugate to the remaining cysteines. Adapted from reference [18].

Scheme 2

The synthesis of antibody-drug conjugates (ADCs) through the addition of thiols to maleimides. Adapted from reference [23].

Scheme 3

Preparation of antibody-taxoid conjugates via disulfide-thiol exchange. Adapted from reference [30].

Scheme 4

The conjugation of amine-drug to trastuzumab by using sodium 4-((4-(cyanoethynyl)benzoyl)oxy)-2,3,5,6-tetrafluorobenzenesulfonate (CBTF). Reprinted with permission from reference [32].

Scheme 5

Three approaches to make ADCs through disulfide re-bridging: thiobridge, dibromomaleimide and pyridazinedione. Adapted from reference [35,37,40].

Scheme 6

Amino mercapto-derivitized drug can be attached to an antibody through intein splicing. Reprinted with permission from reference [34].

Scheme 7

Human O⁶-alkylguanine-DNA alkyltransferase (hAGT) used guanine as a leaving group, forming a thioether bond to a benzyl-derivitized drug. Adapted from Reference [41].

Scheme 8

Amines of the antibodies reacted with the carboxyls that derived from the drugs in the effect of the N-hydroxysuccinimide (NHS). Adapted from reference [23].

Scheme 9

The reaction of the amine-drugs and antibodies under the influence of bacterial transglutaminase (BTG). Adapted from reference [50].

Scheme 10

The sortase-mediated conjugation of glycine-derivitized drugs and the antibodies. Adapted from reference [54].

Scheme 11

The BirA-mediated conjugation of biotin-like ketones, oxyamine-drugs and antibody. Adapted from Reference [56].

Scheme 12

The reaction of amines of the drug and hydroxyls of the linkers in the effect of phosgene or 4-nitrophenyl chloroformate. Adapted from Reference [57,58].

Scheme 13

The formation of an ether bond through the O-alkylation of aza-CBI by bromide and potassium carbonate. Adapted from reference [57].

Scheme 14

The conversion of the cysteine thiol to an aldehyde group by formylglycine-generating enzymes (FGE) enables reactions with oxyamine drugs. Adapted from reference [70].

Scheme 15

Incorporation of p-acetylphenylalanine (pAcPhe) allows for site-specific conjugation of drugs to the modified antibodies. Adapted from reference [74].

Scheme 16

The modification of glycans of trastuzumab by Gal T and Sial T leads to the incorporation of sialic acids, which were oxidated and coupled to the drugs through oxime ligation. Adapted from reference [75].

Scheme 17

The oxidation of amines to aldehyde groups which could react with oxyaminedrugs using transamination reagents pyridoxal 5′-phosphate (PLP) or N-methylpyridinium-4-carboxaldehyde benzenesulfonate salt (RS). Adapted from reference [79].

Scheme 18

The synthesis of ADCs through copper-catalyzed azide-alkyne cycloaddition (CuAAC) and strain-promoted azide-alkyne cycloaddition (SPAAC) click reactions. Adapted from reference [81].

Scheme 19

The synthesis of trastuzumab-porphyrin conjugates through N-propargyl-3,4-dibromomaleimide and a click chemistry. Reprinted with permission from Reference [87].