June 19, 2025
Published in Cell Chemical Biology
Significance
Enzymes that regulate oncogenic protein function through the addition of post-translational modifications (PTMs) represent promising targets for the development of cancer therapeutics. N-glycosylation is a critical PTM that occurs in the lumen of the endoplasmic reticulum (ER) and is essential for proper protein folding and trafficking. However, because synthesis and transfer of N-glycans to newly synthesized proteins is vital, blocking N-glycosylation has the potential for toxicity. Nevertheless, small molecule inhibitors of oligosaccharyltransferase (OST) —the ER membrane-embedded enzyme complex responsible for transferring glycans to newly synthesized proteins— have been shown to partially reduce N-glycosylation, indicating tolerability and the potential for in vivo application. In this study, we advance the understanding of OST inhibitors and utilize them to elucidate the mechanism that underlies partial loss of N-glycosylation, a biological effect previously considered unattainable. Through a drug development campaign aimed at enhancing potency and other pharmacokinetic properties, we demonstrate that the redundant activities of the mutually exclusive OST catalytic subunit paralogs (STT3A and STT3B) prevent complete inhibition of N-glycosylation, thereby conferring tolerability. Our results also indicate that OST inhibitor activities can be tailored to preferentially impact specific subsets of glycoproteins, providing a framework for OST drug development. In vitro studies using EGFR mutant non-small cell lung cancer (NSCLC) models show that highly N-glycosylated receptor tyrosine kinases (RTKs) are inactivated by OST inhibition, while tumor cell survival is rescued through N-glycosylation-independent EGFR signaling. The bioavailable inhibitor NGI-189 was advanced to patient-derived xenograft (PDX) and TKI-resistant lung cancer models, demonstrating tumor regression without observable toxicity in animals. Collectively, these data suggest that cellular N-glycosylation can be pharmacologically manipulated to elicit specific cellular effects and anti-tumor activity in selected cancer subtypes.
Highlights
Summary
Protein asparagine (N)-glycosylation, which promotes the folding and trafficking of cell surface receptors, has not traditionally been viewed as a viable target in oncology due to the essential and non-redundant enzymatic activities required for glycan synthesis and transfer. However, in mammals, an exception is the presence of the oligosaccharyltransferase (OST) catalytic subunit paralogs, STT3A and STT3B. In this study, we investigate the biological activity of OST inhibitors and develop a strategy for selectively inhibiting N-glycosylation that is optimized for its downstream effects on the EGFR glycoprotein. Small molecules with improved pharmacokinetic properties and selective preferences for STT3A or STT3B were synthesized, characterized in vitro, and advanced to in vivo testing. The lead compound from this series, NGI-189, induces tumor regression or growth delay in patient-derived and TKI-resistant EGFR-mutant lung cancer xenografts without causing toxicity. Collectively, these findings suggest that bioavailable OST inhibitors can be developed as therapeutic agents for oncology.
Oncology
Yale University
Harrington Scholar-Innovator