GSK2656157 is a highly specific and ATP-competitive PERK inhibitor (IC50: 0.9 nM) in a cell-free assay. The selectivty is 500-fold higher against a panel of 300 kinases.

GSK2656157 inhibits the growth of various human xenograft tumors in mice. Administered at a dose of 50 mg/kg orally, GSK2656157 completely suppresses phospho-PERK Thr980 after 8 hours. Furthermore, with dosages of 50/150 mg/kg administered twice daily, GSK2656157 exhibits a dose-dependent suppression of tumor growth in four different mouse cancer models, achieving a 54-114% inhibition of tumor growth at 150 mg/kg.

GSK2656157 (1 mM) can induce the unfolded protein response (UPR) and inhibit de novo protein synthesis. It downregulates 6% of UPR-related genes (PPP1R15A, HERPUD1, DDIT3, C/EBP-β, and ERN1), with a reduction exceeding fourfold for these targets. Pre-treatment with GSK2656157 inhibits PERK activation and decreases downstream substrates, including phospho-eIF2a, ATF4, and CHOP (IC50: 10-30 nM). In the absence of exogenous UPR inducers, GSK2656157 does not affect cell growth (IC50: 6-25 mM).

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.

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. (Only for Reference)