Antibody-Drug Conjugates of NLRP3 Agonists: How Overcoming Lysosomal Accumulation Necessitated Noncanonical Linker Attachments

An initial series of NLRP3 agonist antibody-drug conjugates (ADCs) failed to induce IL-1β in vitro due to lysosomal trapping of the payload. To address this, we developed assays and computational tools to identify a new payload that could diffuse out of the lysosomes. ADCs derived from this payload were active, emphasizing the need to avoid payload lysosomal accumulation for nonlysosomal targets. Two active ADCs necessitated attaching a cleavable valine-citrulline recognition element to the payload via a noncanonical ester linkage, rather than a canonical carbamate one, since the payload did not contain a basic amine. The citrulline stereocenter configuration was found to affect the payload release and in vitro activity. The ADC with the (L)-Val-(L)-Cit ester configuration showed superior in vitro activity, high stability in mouse serum, and rapid cleavage in human liver lysosomes. These properties suggest that this noncanonical (L)-Val-(L)-Cit ester attachment may be valuable to the ADC community moving forward.