Cellular stress signals activate adaptive signaling pathways of the mammalian integrated stress response (ISR), of which the unfolded protein response (UPR) is a subset. These pathways converge at the phosporylation of eIF2α.
Drug-like, potent and selective chemical inhibitors (valid chemical probes) targeting major ISR
kinases have been previously identified, with the exception of GCN2. We synthesized and evaluated a series of GCN2 inhibitors based on a triazolo[4,5-d]
pyrimidine scaffold. Several compounds potently inhibited GCN2 in vitro and displayed good selectivity over the related
kinases PERK, HRI, and IRE1. The compounds inhibited phosporylation of eIF2α in HEK293T cells with an IC50 < 150 nM, validating them as chemical probes for cellular studies. These probes were screened against the National Cancer Institute NCI-60 human
cancer cell line panel. Uniform growth inhibition was observed in the
leukemia group of cell lines. Growth inhibition in the most sensitive cell lines coincided with high GCN2
mRNA expression levels. Oncomine analysis revealed high GCN2 expression accompanied by lower
asparagine synthetase (ASNS) expression in patient-derived acute lymphoblastic
leukemias with B-Cell origins (B-ALL) as well. Notably,
asparaginase, which depletes
amino acids and triggers GCN2 activity, is a licensed, first-line B-ALL treatment. Thus, we hypothesize that
leukemias exhibiting high GCN2 expression and low ASNS expression may be susceptible to pharmacologic GCN2 inhibition.