Inhibition of human recombinant puritin-His-tagged IRE-1 RNase expressed in SF21 cells using XBP-1 RNA stem loop as substrate incubated for 30 mins prior to substrate addition measured after 2 hrs by FRET-suppression assay
In Vitro Enzyme Assays: IRE-1 alpha, T1 RNase, and RNase A assays carried out in vitro with several o-vanillin derivatives to demonstrate selectivity of the derivatives for IRE-1 alpha. T1 RNase was assayed as follows. Five ul of a reaction mixture comprising 1x reaction buffer (5x reaction buffer is 100 mM Hepes pH 7.5, 250 mM KOAc, 2.5 mM MgCl2), 3 mM DTT, and 0.4% polyethylene glycol water were added to each well of 384 well plates. Twenty-five nanoliters of a 1 mM test compound solution were added to test wells. Three ul of a 1/48,000 dilution of an approximately 200,000 U/ml RNase T1 (Worthington) preparation were added to each test well and to positive control wells (final concentration 49.5 pg/well). Negative control wells contained only reaction mixture and test compound. After spinning the plates at 1200 rpm for 30 seconds, 3 ul of the mini-XBP-1 mRNA stem-loop substrate described in Example 1 were added to each well of a control plate.
Inhibition Assay: A fusion protein comprising glutathione S transferase (GST) and human IRE-1alpha (GST-IRE-1alpha) obtained from a 500 ml baculovirus-infected insect cell culture can be used to measure IRE-1alpha activity in vitro. Five ul of a reaction mixture comprising IX reaction buffer (5x reaction buffer is 100 mM Hepes pH 7.5, 250 mM KOAc, 2.5 mM MgCl2), 3 mM DTT, and 0.4% polyethylene glycol water is added to each well of 384 well plates. Twenty-five nanoliters of a 1 mM test compound solution are added to test wells. Three ul of a 128 ng/ml IRE-1alpha preparation are added to each test well and to positive control wells (final concentration 5.82 ng/well). Negative control wells contain only reaction mixture and test compound.After spinning the plates at 1200 rpm for 30 seconds, 3 ul of an IRE-1alpha human mini-XBP-1 mRNA stem-loop substrate 5'-CAGUCCGCAGCACUG-3' (SEQ ID NO:1), labeled with the fluorescent dye Cy5 at the 5' end and Black Hole Quencher 2.
In Vitro Enzyme Assay: A fusion protein comprising glutathione S transferase (GST) and human IRE-1α (GST-IRE-1α) was obtained from a 500 ml baculovirus-infected insect cell culture and used to measure IRE-1α activity in vitro. Five μl of a reaction mixture comprising 1× reaction buffer (5× reaction buffer is 100 mM Hepes pH 7.5, 250 mM KOAc, 2.5 mM MgCl2), 3 mM DTT, and 0.4% polyethylene glycol water were added to each well of 384 well plates. Twenty-five nanoliters of a 1 mM test compound solution were added to test wells. Three μl of a 128 ng/ml IRE-1α preparation were added to each test well and to positive control wells (final concentration 5.82 ng/well). Negative control wells contained only reaction mixture and test compound.After spinning the plates at 1200 rpm for 30 seconds, 3 μl of an IRE-1α human mini-XBP-1 mRNA stem-loop substrate 5′-CAGUCCGCAGCACUG-3′ (SEQ ID NO:1), labeled with the fluorescent dye Cy5 at the 5′ end and Black Hole Quench
Cell-Based Assay: Initial cell-based XBP-1 mRNA splicing assays confirmed IRE-1α inhibition with several potent 5-bromo and 6 bromo o-vanillins. HEK293 cells were incubated with compound either overnight or for 2 hours prior to IRE-1α activation with the UPR inducing reagent thapsigargin. IRE-1α mediated XBP-1 splicing was measured by RT-PCR using XBP-1 specific primers flanking the 26 bp intron excised by IRE-1α. The results are shown in FIG. 1. It can be observed that at the higher concentrations, there is relatively more of the unspliced XBP-1 (upper band: substrate) compared to the spliced form (lower band: product).