PKR-IN-C16

PKR-IN-C16 is an ATP-binding site-directed small molecule that inhibits RNA-dependent protein kinase (PKR) autophosphorylation, with an IC₅₀ value of 0.21±0.04μM^[1]. PKR-IN-C16 has been widely used in the research of neuroprotection for brain injuries, as well as in the preparation of new mRNA vaccine formulations to enhance the translation and expression of mRNA^[2-3].

In vitro, PKR-IN-C16 treatment at 0.5μM for 24 hours can significantly reduce the phosphorylation of eIF2α in DYT-PRKRA lymphoblasts and inhibit cell apoptosis^[4]. PKR-IN-C16 treatment (6μM; 2.5h) significantly stimulated the integrated stress response (ISR) in HeLa cells, accompanied by the enhanced expression of PERK and GCN2 proteins^[5]. Treatment with 2μM PKR-IN-C16 for 7 days significantly inhibited the proliferation of HCT116 cells and reduced cell division^[6].

In vivo, PKR-IN-C16 treatment (300μg/kg/day; i.p.) reduced the tumor growth rate, decreased tumor volume, inhibited CD31 expression, and suppressed angiogenesis in the mouse xenograft tumor model^[7]. A day after injecting PKR-IN-C16 into the abdominal cavity at a dose of 100μg/kg, the volume of the infarct after ischemia and the apoptosis rate were notably decreased in the hypoxic-ischemic rat model^[8]. Intraperitoneal injection of 600μg/kg dose of PKR-IN-C16 within 24 hours in the model of toxic neuroinflammation in rats can prevent PKR-induced neuronal loss and reduce the inflammatory response^[9].

References:
[1] Jammi N V, Whitby L R, Beal P A. Small molecule inhibitors of the RNA-dependent protein kinase[J]. Biochemical and biophysical research communications, 2003, 308(1): 50-57.
[2] Couturier J, Paccalin M, Lafay-Chebassier C, et al. Pharmacological inhibition of PKR in APPswePS1dE9 mice transiently prevents inflammation at 12 months of age but increases Aβ42 levels in the late stages of the Alzheimer’s disease[J]. Current Alzheimer research, 2012, 9(3): 344-360.
[3] Zhang W, Liu Y, Chin J M, et al. Sustained release of PKR inhibitor C16 from mesoporous silica nanoparticles significantly enhances mRNA translation and anti-tumor vaccination[J]. European Journal of Pharmaceutics and Biopharmaceutics, 2021, 163: 179-187.
[4] Frederick K, Patel R C. Luteolin protects DYT-PRKRA cells from apoptosis by suppressing PKR activation[J]. Frontiers in Pharmacology, 2023, 14: 1118725.
[5] Szaruga M, Janssen D A, de Miguel C, et al. Activation of the integrated stress response by inhibitors of its kinases[J]. Nature communications, 2023, 14(1): 5535.
[6] Hashimoto Y, Tokumoto Y, Watanabe T, et al. C16, a PKR inhibitor, suppresses cell proliferation by regulating the cell cycle via p21 in colorectal cancer[J]. Scientific reports, 2024, 14(1): 9029.
[7] Watanabe T, Ninomiya H, Saitou T, et al. Therapeutic effects of the PKR inhibitor C16 suppressing tumor proliferation and angiogenesis in hepatocellular carcinoma in vitro and in vivo[J]. Scientific reports, 2020, 10(1): 5133.
[8] Xiao J, Tan Y, Li Y, et al. The specific protein kinase R (PKR) inhibitor C16 protects neonatal hypoxia-ischemia brain damages by inhibiting neuroinflammation in a neonatal rat model[J]. Medical science monitor: international medical journal of experimental and clinical research, 2016, 22: 5074.
[9] Tronel C, Page G, Bodard S, et al. The specific PKR inhibitor C16 prevents apoptosis and IL-1β production in an acute excitotoxic rat model with a neuroinflammatory component[J]. Neurochemistry international, 2014, 64: 73-83.