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).