Kinase Assay: Inhibitory potency of GSK2656157 is measured using recombinant GST-PERK (536–1116 amino acids) with 6-His-full-length human eIF2a as a substrate. Kinase selectivity is evaluated using 27 kinases at GSK as well as a panel of 300 kinases.

Cell Assay: human tumor cell lines, primary human microvascular endothelial cells; ~3 μM; 3 days; Antiproliferative activity of GSK2656157 against multiple human tumor cell lines as well as primary human microvascular endothelial cells is evaluated in a 3-day proliferation assay using standard culture medium. In the absence of exogeneous UPR inducers, GSK2656157 has no significant effect on the growth of any of these cells with IC50 range of 6–25 mM.

Pretreatment of cells with GSK2656157 results in inhibition of PERK activation as well as decreases in the downstream substrates, phospho-eIF2a, ATF4, and CHOP with an IC50 in the range of 10-30 nM. Cells that are exposed to 1 mM GSK2656157 before UPR induction are able to block this effect on de novo protein synthesis. Five of 84 UPR-related genes (DDIT3, HERPUD1, PPP1R15A, C/EBP-beta, and ERN1) are down regulated more than 4-fold by GSK2656157. In the absence of exogeneous UPR inducers, GSK2656157 has no significant effect on the growth of any of these cells with IC50 range of 6–25 mM. Thus, GSK2656157 can be used to evaluate the biologic function of PERK in various biologic contexts.