Context-dependent translation inhibition as a novel oncology therapeutic modality
Inhibitors of protein synthesis, including anisomycin, homoharringtonine, and other natural products bind in the peptidyl-transferase center (PTC) of the eukaryotic ribosome to inhibit translation. Recent work has demonstrated that some PTC-binding antibiotics act in a sequence-selective manner, inhibiting translation elongation at specific amino acids while the polypeptide is engaged in the PTC. However, this phenomenon has yet to be documented for compounds that inhibit translation by the human ribosome. Here we use structure-based design to guide synthesis of molecules called interdictors that bind to the human ribosome PTC and act in a context-selective manner to inhibit translation elongation. Using ribosome profiling, in combination with in vitro biochemistry and cryo-electron microscopy, we characterize the context selectivity of unique analogues and observe their preferred interactions with nascent chain residues with complementary properties. Furthermore, we present a structure for an interdictor bound to a portion of the MYC protein at [~] 1.9 [A] resolution and identify resulting structural rearrangements in both the nascent chain and ribosomal RNA. In cells, we document how these compounds differentially impact the ribotoxic stress response pathway which monitors ribosome collisions and can trigger apoptosis. Finally, we confirm their tumor growth inhibition activity after oral dosing in cell line derived xenografts in mice using the MDA-MB-231 model for triple-negative breast cancer. Together, our data establish sequence-selective inhibition of translation as a novel small-molecule therapeutic modality for historically difficult to address cancers by targeting translation of oncogenic dependency factors in the human ribosome PTC.