In
the fast-evolving landscape of targeted cancer therapies, the
revolutionary class of biotherapeutics known as antibody-drug conjugates
(ADCs) are taking center stage. Most clinically approved ADCs utilize
cleavable linkers to temporarily attach potent cytotoxic payloads
to antibodies, allowing selective payload release under tumor-specific
conditions. In this study, we explored the utilization of 1-(4,4-dimethyl-2,6-dioxocyclohexylidene)ethyl
(Dde), a cyclic β-diketone featuring an active alkylidene group,
to develop a novel chemically labile linker. This linker was designed
to exploit the difference in reduction potential between the intracellular
compartment and plasma. Upon reduction of an azido trigger strategically
installed neighboring the cyclic β-diketone, the resulting nucleophilic
primary amine reacts with the alkylidene group facilitated by a favorable
ring closure reaction in accordance with Baldwin’s rules. Consequently,
this reaction enables the simultaneous release of the attached cytotoxic
payload. The therapeutic utility of this novel linker strategy was
demonstrated by separate conjugation of the linker to two epidermal
growth factor receptor (EGFR)-targeting ligands to afford a peptide-drug
conjugate and an ADC. This work comprises a significant contribution
to the bioconjugation field by introducing the alkylidene cyclic β-diketone
as a tunable scaffold used for the temporary conjugation of therapeutic
agents to peptides and proteins.