Inhibition of tumor growth by a novel engineered chimeric toxin that cleaves activated mutant and wild-type RAS

Abstract

Despite nearly four decades of effort, broad inhibition of oncogenic RAS using small molecule approaches has proven to be a major challenge. Here we describe the development of a novel pan-RAS biologic inhibitor comprised of the RAS-RAP1-specific endopeptidase fused to the protein delivery machinery of diphtheria toxin. We show that this engineered chimeric toxin irreversibly cleaves and inactivates intracellular RAS at low picomolar concentrations terminating downstream signaling in receptor-bearing cells. Further, we demonstrate in vivo target engagement and reduction of tumor burden in three mouse xenograft models driven by either wild-type or mutant RAS. Intracellular delivery of a potent anti-RAS biologic through a receptor-mediated mechanism represents a promising new approach to developing RAS therapeutics against a broad array of cancers. SignificanceRAS oncoproteins have long been considered among the most elusive drug targets in cancer research. At issue is the lack of accessible drug binding sites and the extreme affinity for its GTP substrate. Covalent inhibitors against the KRAS G12C mutant have shown early clinical promise, however, targeting the other oncogenic RAS mutants across three RAS isoforms has proven challenging. Inhibition of activated wild-type RAS in the absence of canonical RAS mutations is also highly desirable in certain tumors. Here, we demonstrate delivery of an extremely potent pan-RAS and RAP1 cleaving enzyme in therapeutic quantities to specific receptor-bearing cells in vitro and in vivo. We aim to advance this approach to engineer the first targeted pan-RAS inhibitor for cancer therapy. One Sentence SummaryEngineered chimeric toxin halts tumor growth in vivo via RAS cleavage