A Gold-PROTAC Degrades the Oncogenic Tyrosine Kinase MERTK: Insights into the Degradome from a Steady-State System

Proteolysis targeting chimeras (PROTACs) are bifunctional molecules designed to induce the degradation of specific proteins within a cell. While most PROTACs are noncovalent interactors, covalent PROTACs may benefit from improved selectivity and pharmacodynamics, yet remain largely understudied. Here, a covalent gold-based PROTAC (AuPROTAC) was synthesized, featuring a Au(III)-warhead, known to induce cysteine-arylation in a gold-templated two-step mechanism, linked to a cereblon binding moiety. The degradome of the AuPROTAC was characterized by establishing a cycloheximide chase assay in a nonproliferative steady-state HL-60 cell culture, enabling the identification of PROTAC degradation targets uncoupled from confounding effects originating from cell-cycle-dependent translational patterns. The method was verified using the known SMARCA2 and PBRM1-degrader ACBI2. AuPROTAC could degrade the oncogenic tyrosine kinase MERTK and the thioredoxin-like 1 protein TXNL1. Their degradation was successfully rescued by proteasome inhibition. Proteome-wide degradation selectivity was further characterized by ranking the degraded targets according to the reduction extent of their protein half-lives. Interestingly, the AuPROTAC degraded a relatively limited number of proteins (95) when compared to ACBI2 (221).