Structure-guided design of a methyltransferase-like 3 (METTL3) proteolysis targeting chimera (PROTAC) incorporating an indole–nicotinamide chemotype†

Methyltransferase-like 3 (METTL3) is the main catalytic subunit of the m⁶A methyltransferase complex (MTC) and plays an essential role in various disease indications, including acute myeloid leukemia (AML). Here, we describe the structure-guided design and evaluation of METTL3 proteolysis-targeting chimeras (PROTACs), starting from the potent small-molecule inhibitor STM2457. Across four design generations, we highlight key considerations, particularly regarding the exit vector, linker mechanics, and METTL3-binding chemotype composition. Our most effective PROTAC, AF151, forms a stable complex between the E3 ligase von Hippel–Lindau (VHL) and the target-of-interest METTL3, demonstrating efficient METTL3 degradation (DC₅₀ = 430 nM) in the AML cell line MOLM-13. This molecule candidate exhibits more pronounced effects on viability inhibition (IC₅₀ = 0.45 μM) and more significant m⁶A level reduction in cancer cells than its non-PRTOAC parent compounds. By incorporating the indole-nicotinamide chemotype as the METTL3-binding recruiter, this PROTAC is structurally distinct from recently published METTL3 PROTACs, expanding the design options for future METTL3 degrader development.