BI-D1870

BI-D1870 is a cell-permeable inhibitor of the p90 RSK isoforms with IC50 values of 31nM, 24nM, 18nM and 15nM for RSK1, RSK2, RSK3 and RSK4 respectively [1].

BI-D1870 is a derivative of dihydropteridinone and found to be a remarkably specific inhibitor of RSK isoforms. It is an ATP-competitive inhibitor. When the concentrations of ATP are 10μM and 100μM, the IC50 values of BI-D1870 against RSK1 and RSK2 are 5nM, 10nM and 10nM, 20nM, respectively. BI-D1870 also inhibits RSK3 and RSK4 with IC50 values of 18nM and 15nM respectively, when ATP is 100μM. The inhibition activity of BI-D1870 against RSK is more than 500-fold greater than some other AGC kinases suggesting BI-D1870 as a specific inhibitor of RSK. In addition, BI-D1870 is reported to induce the phosphorylation of ERK1/ERK2 and the subsequent phosphorylation of CREB in Rat-2 cells [1].

References:
[1] Sapkota G, Cummings L, Newell F, et al. BI-D1870 is a specific inhibitor of the p90 RSK (ribosomal S6 kinase) isoforms in vitro and in vivo. Biochem. J, 2007, 401: 29-38.

Two widely used RSK inhibitors, BI-D1870 and SL0101, alter mTORC1 signaling in a RSK-independent manner.[Pubmed:25889895]

Cell Signal. 2015 Aug;27(8):1630-42.

The 90 kDa ribosomal S6 kinases (RSK) are effectors of the Ras-ERK1/2 signaling pathway. RSK signaling controls proliferation and protein synthesis, and is altered in several types of tumors. BI-D1870 and SL0101 are two widely used inhibitors of RSK. After revision of the literature, discrepancies in the effects of the inhibitors were identified. Herein we report that while SL0101 inhibited mTORC1-p70S6K signaling, BI-D1870 increased p70S6K activation. Both effects were independent of ERK1/2 and RSK, and thus nonspecific. We also demonstrated how these opposite nonspecific effects mislead the identification of the RSK-dependent phosphorylation of rpS6 (S235/236), a known RSK and p70S6K substrate. Phosphorylation of tuberin at S1798 by RSK was proposed to mediate ERK1/2-dependent activation of mTORC1-p70S6K signaling. In glioblastoma-derived cells, phosphorylation of tuberin was abolished after RSK depletion or ERK1/2 inhibition, suggesting that RSK is its main kinase. However, RSK depletion did not reduce PMA-dependent p70S6K phosphorylation, which suggests that tuberin phosphorylation at S1798 is not the main mediator of ERK1/2-dependent activation of mTORC1. Remarkably, tuberin phosphorylation (S1798) followed the activation status of RSK in different cells and experimental conditions, suggesting that phosphorylation of that residue could be used as readout for RSK activation in cells. We confirmed the difference in the effects of SL0101 and BI-D1870 in cellular proliferation assays. Rapamycin potentiated the inhibition of proliferation induced by BI-D1870, but not by SL0101. We thus conclude that SL0101 and BI-D1870 induce distinct off-target effects in mTORC1-p70S6K signaling, and thus, the functions previously ascribed to RSK based on these inhibitors should be reassessed.

A combination of SILAC and nucleotide acyl phosphate labelling reveals unexpected targets of the Rsk inhibitor BI-D1870.[Pubmed:27919044]

Biosci Rep. 2014 Feb 1;34(1). pii: BSR20130094.

Protein kinase inhibitors frequently have interesting effects that cannot be fully ascribed to the intended target kinase(s) but identifying additional targets that might explain the effects is not straightforward. By comparing two different inhibitors of the Rsk (p90 ribosomal S6 kinase) kinases, we found that the increasingly used compound BI-D1870 had biological effects in murine DCs (dendritic cells) that could not be solely ascribed to Rsk or other documented targets. We assessed the ability of BI-D1870 and a second Rsk inhibitor, BIX 02565 to protect enzyme active sites from reaction with biotinylated nucleotide acyl phosphates. Using SILAC (stable isotope labelling by amino acids in cell culture)-labelled DC lysates as a source of enzyme targets, we identify several kinases that interact with BI-D1870 but not with BIX 02565. We confirmed that these kinases, including Slk, Lok and Mst1, are inhibited by BI-D1870 but to a much lesser extent by BIX 02565 and that phosphorylation of some of their substrates is blocked by BI-D1870 in living cells. Our results suggest that the BI-D1870 inhibitor should be used with caution. The SILAC-based methodology we used should be useful for further comparative unbiased profiling of the target spectrum of kinase inhibitors with interesting biological effects under conditions that closely mimic those found in cells.

The ribosomal S6 kinase inhibitor BI-D1870 ameliorated experimental autoimmune encephalomyelitis in mice.[Pubmed:26386981]

Immunobiology. 2016 Feb;221(2):188-92.

Multiple sclerosis (MS) is an autoimmune demyelinating disease of the central nervous system (CNS) caused by the infiltration of TH1 and TH17 cells into the CNS. Ribosomal S6 kinase 2 (RSK2; RPS6KA3) regulates TH17 differentiation by attenuating RORgammat transcriptional activities and IL-17A production. The pan-RSK inhibitor BI-D1870 also inhibits TH17 differentiation, but the effect of BI-D1870 in vivo remains unclear. Here, we generated mice with experimental autoimmune encephalomyelitis (EAE) and treated them with BI-D1870. BI-D1870 administration protected mice from EAE by reducing the infiltration of TH1 and TH17 cells into the CNS and decreasing mRNA levels of Ccr6 in TH17 cells. These results suggest that RSK inhibition is a promising strategy for the treatment of MS.

BI-D1870 is an ATP-competitive, cell permeable inhibitor of RSK isoforms, with IC50s of 31 nM/24 nM/18 nM/15 nM for RSK1/RSK2/RSK3/RSK4, respectively.

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