Development of DuoMYC: a synthetic cell penetrant miniprotein that efficiently inhibits the oncogenic transcription factor MYC

The master regulator transcription factor MYC is implicated in numerous human cancers, and its targeting is a long‐standing challenge in drug development. MYC is a typical ‘undruggable’ target, with no binding pockets on its DNA binding domain and extensive intrinsically disordered regions. Rather than trying to target MYC directly with classical modalities, here we engineer synthetic miniproteins that can bind to MYC's target DNA, the enhancer box (E‐Box), and potently inhibit MYC‐driven transcription. We crafted the miniproteins via structure‐based design and a combination of solid phase peptide synthesis and site‐specific crosslinking. Our lead variant, DuoMYC, binds to E‐Box DNA with high affinity ( K _D ~0.1 μM) and is able to enter cells and inhibit MYC‐driven transcription with submicromolar potency (IC ₅₀ =464 nM) as shown by reporter gene assay and confirmed by RNA sequencing. Notably, DuoMYC surpasses the efficacy of several other recently developed MYC inhibitors. Our results highlight the potential of engineered synthetic protein therapeutics for addressing challenging intracellular targets.