Hiding Payload Inside the IgG Fc Cavity Significantly Enhances the Therapeutic Index of Antibody–Drug Conjugates

The inadequate understanding of the
structure–activity
relationship
(SAR) of glycosite-specific antibody–drug conjugates (ADCs)
hinders its design and development. Herein, we revealed the systemic
SAR and structure–toxicity relationship (STR) of gsADCs by
constructing 50 gsADC structures bearing three glycan subtypes and
diverse linker-drug combinations. According to the results, extra
hydrophilic linkers are indispensable for the intact glycan-based
gsADCs to achieve better in vivo efficacy. Meanwhile,
the gsADCs that conjugate linker-drug complexes onto the terminal
sialic acid are more stable and potent than the ones conjugated onto
the terminal galactose in vivo. Notably, the LacNAc-based
gsADCs, which shortened the spacer and located the linker-drug more
inside the immunoglobulin class G (IgG) Fc cavity, showed excellent
hydrophilicity, in vivo activity, pharmacokinetics,
and safety. Conclusively, we found that hiding the linker-toxin into
the Fc cavity can significantly enhance the therapeutic index of LacNAc-based
gsADCs, which will benefit the further design of ADCs with optimal
druggability.