Glycosylation Blockade Targets Receptor Tyrosine Kinase–Driven Tumors

The secretory pathway processes proteins for secretion into the extracellular environment or for localization to the cell surface. N-linked glycosylation, which is a mechanism of secondary protein processing that involves the attachment of a glycan to a protein, is crucial for determining the function, stability, and trafficking of glycoproteins such as receptor tyrosine kinases (RTK). To determine whether disrupting N-linked glycosylation could effectively target RTKs, Lopez-Sambrooks and colleagues designed and performed a gain-of-function high-throughput screening (HTS) approach to identify inhibitors of N-linked glycosylation. The HTS strategy identified a small-molecule chemical probe, N-linked glycosylation inhibitor 1 (NGI1), as the most efficacious glycosylation inhibitor out of the >350,000 small-molecule compounds interrogated. In vitro, NGI1 inhibited both isoforms (STT3A and STT3B) of the catalytic subunit of the oligosaccharyltransferase (OST) enzymatic complex, which catalyzes the transfer of the glycan precursor lipid-linked oligosaccharides (LLO) to recipient glycoproteins. Further, NGI1 completely ablated STT3B-dependent, but not STT3A-dependent, glycosylation sites, suggesting that NGI1 has higher specificity for STT3B than for STT3A. In lung cancer cells, NGI1 prevented EGFR N-linked glycosylation, which resulted in the sequestration of hypoglycosylated EGFR in the secretory pathway and loss of EGFR localization to the cell surface, while inhibition of integrin B1 glycosylation with NGI1 did not affect integrin B1 trafficking to the cell surface. Moreover, NGI1 exhibited greater inhibition of proliferation of EGFR-dependent lung cancer cells compared to non–EGFR-dependent lung cancer cells. Consistent with these findings, NGI1 induced G1 cell-cycle arrest and senescence in EGFR-dependent lung cancer cell lines. Taken together, these findings identify a small-molecule inhibitor of glycosylation and show that targeting the co- and post-translational modification of RTKs may be efficacious against RTK-driven cancers.

Lopez-Sambrooks C, Shrimal S, Khodier C, Flaherty DP, Rinis N, Charest JC, et al. Oligosaccharyltransferase inhibition induces senescence in RTK-driven tumor cells. Nat Chem Biol 2016 Oct 3 [Epub ahead of print].