PROxAb Shuttle: A non-covalent plug-and-play platform for the rapid generation of tumor-targeting antibody-PROTAC conjugates

Proteolysis-targeting chimeras (PROTACs) have evolved in recent years from an academic idea to a therapeutic modality with more than 25 active clinical programs. However, achieving oral bioavailability and cell-type specificity remains a challenge, especially for PROTACs recruiting the von Hippel-Lindau (VHL) E3 ligase. Herein, we present an unprecedented, plug- and-play platform for VHL-recruiting PROTACs to overcome these limitations. Our platform allows for the generation of non-covalent antibody-PROTAC complexes within minutes and obviates the need for prior PROTAC modification, antibody-drug linker chemistry optimization or bioconjugation. Our technology relies on camelid-derived antibody domains (VHHs) which can easily be engineered into existing therapeutic antibody scaffolds. The resulting targeted, bispecific fusion proteins can be complexed with PROTACs at defined PROTAC-to-antibody ratios and have been termed PROxAb Shuttles. PROxAb Shuttles can prolong the half-life of PROTACs from hours to days, demonstrate anti-tumor efficacy in vivo and have the potential for reloading in vivo to further boost efficacy. ### Competing Interest Statement HS, MR, SJ, DK, NR, CS and AE are employees of Merck KGaA, Darmstadt, Germany and inventors on a patent application covering the PROxAb Shuttle technology (WO2023275394A1). PROxAb ShuttleTM is a registered trademark.