In vitro activity: ML346 is a novel activator of Hsp70, with EC50 of 4600 nM in HeLa cells. ML346 at 10 μM restores proteostasis, restores CFTR-mediated iodide conductance, and enhances the correct folding of proteins expressed in two different cellular compartments. ML346 (Compound F1) induces multiple responses and strongly induces Hsp70, the oxidative stress response genes (HO1 and GCLM), and a 2.5-fold upregulation of BiP in WT MEF cells. ML346 (0.5-25 μM) exhibits cytoprotective effects in cells after a 35 min severe heat shock, and also causes a two-fold protection from H2O2-induced apoptosis.

Kinase Assay: HeLa cells are incubated with either DMSO as negative control, or the positive controls MG132 (10 μM) and lactacystin (6 μM) or the PRs A1, A3 and ML346 (F1) for 3 and 6 hours and then harvested. Cells are lysed in homogenization buffer (50 mM Tris-HCl, pH7.5, 250 mM sucrose, 5 mM MgCl2, 2 mM ATP, 1 mM DTT, 0.5 mM EDTA, 0.025% digitonin) for 5 min on ice, and total protein concentration of whole cell extract is determined. 3 μg of whole cell extracts are combined with assay buffer (50 mM Tris-HCl, pH 7.5, 40 mM KCl, 5 mM MgCl2, 0.5 mM ATP, 1 mM DTT, 0.05 mg/mL BSA) in a black 96-well plate and the reaction is initiated by the addition of a 2× (200 μM) fluorogenic peptide substrate Suc-LLVY-AMC. Fluorescence is measured every 10 min using a Synergy H4 multi-mode microplate reader.

Cell Assay: HeLa cells are plated in black 96-well plates (10,000 cells per well) in 100 μL of DMEM supplemented with 10% FBS and 1% Pen/Strep/Neo. Plates are incubated for 16 hours at 37°C, 5% CO2 and 95% relative humidity before compound addition. 1 μL of hit compounds (ML346) in DMSO or DMSO alone are added to the sample or control wells, respectively. Plates are then placed back in the incubator for 24 hours. After incubation, cells are washed 2× with 200 μL of PBS and 200 μL of a solution of 1 μg/mL of calcein AM is added to each well. Cells are then incubated for 45 min at 37°C, 5% CO2 before fluorescence measurement using an Analyst GT multimode reader. Percent cytotoxicity is expressed relative to wells containing cells treated with DMSO only (100%).