The benchmarking and application of tag-degraders in vivo to validate therapeutic targets

Transitioning a candidate therapeutic target from bench to bedside requires significant time and financial investment, yet clinical success remains low often due to poor on-target toxicity assessment during preclinical validation. Tag-degraders provide a tool to improve target validation by enabling degradation of any protein of interest via a degron-tag. This drug-based, reversible, and dose-dependent method of protein removal can mimic degrader-based drug treatments and assess the implications of target protein depletion in vivo. However, each degrader has a distinct pharmacokinetic profile that will influence its effectiveness across tissues. To create a resource to enable the most appropriate choice of tag-degrader, we benchmark the dTAG, HaloPROTAC, and NanoTAC systems in vivo by employing a transgenic mouse expressing a reporter protein targetable by these tag-degraders. Through various treatment regimes, we characterise each degrader profile across a panel of 20 tissues and organs, highlighting the superior degradation by dTAG molecules, and identify differences between degradation in whole tissues versus single cell populations. Using an FKBPF36V knock-in mouse expressing 65K-FKBPF36V, we reveal target specific degradation kinetics, and a critical requirement for 65K in mice. Together, this resource will assist researchers in choosing the right degrader and tag for their own applications. Targeted protein degradation offers a way to test drug targets before costly drug development begins. Here, the authors benchmark tag-degrader systems in mice, identify dTAG as the most effective approach, and show that this strategy can inform early assessment of target safety.