Vps34-PIK-III (VPS34-IN2), a selective inhibitor of VPS34 enzymatic activity, inhibits autophagy and results in the stabilization of autophagy substrates.

VPS34:0.018μM, PI3Kδ:1.2μM

VPS34 enzymatic function is essential for LC3 lipidation in mammalian cells and PIK-III is a robust inhibitor of autophagy and LC3 lipidation in mammalian cells. In H4 cells, PIK-III inhibits the formation of autolysosomes and increases the cytosolic signal of LC3 under basal conditions and when autophagy is induced with the mTOR inhibitor AZD8055. In a CCCP-induced mitophagy model, PIK-III inhibits the clearance of mitochondria.PIK-III treatment leads to an increase in the levels of LC3-I in H4 and PSN1 cells. In Panc10.05 cells, PIK-III increases the levels of LC3-II in parallel with LC3-I suggesting a cell type-specific response[1].

The DFX-induced NCOA4-dependent turnover of FTH1 and FTL is blocked with PIK-III which suggests an autophagy-dependent process[2].

In vitro tyrosine kinase assays.: Assay of IGF-1R-catalyzed substrate phosphorylation of pTG, using a 96-well plate tyrosine kinase assay kit, is performed. We use recombinant epidermal growth factor receptor, immunoprecipitated IR from HEPG2, immunoprecipitated IGF-1R from P6 cells, and IGF-1R immunodepleted supernatant from P6 (representing "non-IGF-1R tyrosine kinases"). After 30-min treatment of the receptors with the desired compounds in the kinase buffer [50 mM HEPES buffer (pH 7.4), 20 mM MgCl2, 0.1 MnCl2, and 0.2 Na3VO4], the kinase reaction is activated by addition of ATP. The phosphorylated polymer substrate is probed with a phosphotyrosine-specific monoclonal antibody conjugated to horseradish peroxidase, clone PT-66. Color is developed with horseradish peroxidase chromogenic substrate O-phenylenediamine dihydrochloride and quantitated by spectrophotometry (ELISA reader). IGF-1R tyrosine autophosphorylation is analyzed by a sandwich ELISA assay. Briefly, 96-well plates are coated overnight at 4°C with 1 μg/well of an antibody to IGF-1R β-subunit. The plates are blocked with 1% BSA in PBS Tween for 1 h, and then 80 μg/well of total protein lysate from the P6 cell line is added. As a negative control we use total protein lysate from the R- cell line. The investigated compounds are added in tyrosine kinase buffer without ATP at room temperature for 30 min before kinase activation with ATP. Kinase assay is performed using the Sigma kit (see above). After spectrophotometry the IC50 values of inhibitors are determined using the REGRESSION function of Statistica program.

To determine whether inhibition of VPS34 function impacts autophagy,LC3 and known autophagy substrates such as damaged mitochondria or the autophagy cargo receptor p62 are monitored. H4 cells expressing mCherry–GFP–LC3 are treated overnight with the indicated compounds, fixed, stained with Hoechst 33342 and imaged by automated acquisition. HeLa cells expressing GFP–Parkin are treated with PIK-III for 12 h followed by the addition of CCCP for 12 h, fixed, stained for endogenous Tom20 and imaged. (Only for Reference)