PF-4708671

PF-4708671, is a novel cell-permeable inhibitor of S6K1, specifically inhibits the S6K1 isoform with a Ki of 20 nM and IC50 of 160 nM. ^[1].

PF-4708671 prevents the S6K1-mediated phosphorylation of S6 protein in response to IGF-1 (insulin-like growth factor 1), PF-4708671 was also found to induce phosphorylation of the T-loop and hydrophobic motif of S6K1, an effect that is dependent upon mTORC1 (mTOR complex 1) ^[1]. RSK1, RSK2 and MSK1 were the other kinases inhibited by PF-4708671 (IC50 = 4.7 µM, 9.2 µM and 0.95 µM, respectively). PF-4708671 decreased phosphorylation of ribosomal protein S6 in HEK-293 cells. PF-4708671 has been used as the standard S6K1 inhibitor for the investigation of the role of S6K1 in several cancers. PF-4708671 in combination with tamoxifen was shown to be highly effective against ER+ MCF7 cells that had overexpression of S6K1 ^[2] and enhanced cell death in glucose-starved MCF7 cells via downregulation of anti-apoptotic proteins Mcl-1 and survivin ^[3].

PF-4708671 inhibite the AKT/mTOR/S6K1 pathway led to the inhibition of cell migration in triple-negative MDA-MB-231 cells and inhibition of local relapse in mice models ^[4]. Moreover, PF-4708671 improved glucose tolerance in high-fat -fed obese mice by restoring Akt S473 phosphorylation in metabolic tissues ^[5]. PF-4708671 has protective effects against NMDA-induced retinal neurotoxicity in rats ^[6].

References:
[1]. Pearce, L. R. et al. Characterization of PF-4708671, a novel and highly specific inhibitor of p70 ribosomal S6 kinase (S6K1). Biochem. J. 431, 245-255 (2010).
[2]. Hong SE, Kim EK, Jin HO, Kim HA, Lee JK, Koh JS, et al. S6K1 inhibition enhances tamoxifen-induced cell death in MCF-7 cells through translational inhibition of Mcl-1 and survivin. Cell Biol Toxicol. 2013;29(4):273-82.
[3]. Choi HN, Jin HO, Kim JH, Hong SE, Kim HA, Kim EK, et al. Inhibition of S6K1 enhances glucose deprivation-induced cell death via downregulation of anti-apoptotic proteins in MCF-7 breast cancer cells. Biochem Biophys Res Commun. 2013;432(1):123-8.
[4]. Segatto I, Berton S, Sonego M, Massarut S, D'Andrea S, Perin T, et al. Inhibition of breast cancer local relapse by targeting p70S6 kinase activity. J Mol Cell Biol. 2013;5(6):428-31.
[5]. M. Shum, K. Bellmann, P. St-Pierre, A. Marette. Pharmacological inhibition of S6K1 increases glucose metabolism and Akt signalling in vitro and in diet-induced obese mice .Diabetologia, 59 (2016), pp. 592-603
[6]. Hayashi, I.; Aoki, Y.; Ushikubo, H.; Asano, D.; Mori, A.; Sakamoto, K.; Nakahara, T.; Ishii, K. Protective effects of PF-4708671 againstN-methyl-d-aspartic acid-induced retinal damage in rats. Fundam. Clin. Pharmacol. 2016, 30, 529-536.