Reversing an agonist into an inhibitor: Development of mTOR degraders

Targeted protein degradation using proteolysis-targeting chimeras (PROTACs) has emerged as a powerful strategy for modulating protein function. In this study, we developed mTOR-targeting PROTACs by conjugating the mTOR agonist MHY-1485 to the Cereblon (CRBN) ligand pomalidomide, demonstrating that even activators can serve as effective warheads for targeted protein degradation. Through systematic screening, we identified PD-M6 as a potent bifunctional molecule capable of degrading mTOR (DC₅₀ = 4.8 microM), reversing the proliferative effects of MHY-1485, and inhibiting cell proliferation (IC₅₀ = 11.3 microM) while inducing autophagy, akin to the mTOR known inhibitor rapamycin. Proteomic analysis further revealed that PD-M6 downregulated key proteins in the mTOR signaling pathway, including LAMTOR1, MAPKAP1, and CASTOR1, which are involved in proteasome-mediated degradation, cell division, apoptosis, and lysosomal signaling. Notably, PD-M6 specifically induced the degradation of LAMTOR1. These findings highlight a novel approach for designing PROTACs from agonists, broadening the scope of targeted protein degradation strategies for therapeutic applications.