OST Catalytic Subunit Redundancy Enables Therapeutic Targeting of N-Glycosylation

Protein asparagine (N)-glycosylation, which promotes folding and trafficking of cell surface receptors such as the EGFR, has not been considered a viable target in oncology due to the essential and non-redundant enzymatic activities required for glycan synthesis and transfer. In mammals an exception to this rule is the presence of the oligosaccharyltransferase (OST) catalytic subunit paralogs, STT3A and STT3B. Here we delineate the chemical biology of OST inhibitors and develop an approach for limited inhibition of N-glycosylation optimized for downstream effects on EGFR. Small molecules with enhanced pharmacokinetic properties and preferences for STT3A or STT3B were synthesized, characterized in vitro, and advanced to in vivo testing. The lead from this series, NGI-189, causes tumor regression or growth delay of patient derived and TKI resistant EGFR-mutant lung cancer xenografts without toxicity. Together these results suggest that bioavailable OST inhibitors can be developed as therapeutic agents for oncology.