In vitro activity: LGK974 effectively displaces [3H]-GNF-1331 with IC50 of 1 nM in the PORCN radioligand binding assay, and shows no major cytotoxicity in cells up to 20 μM. LGK974 shows comparable inhibitory activities against all tested Wnts with IC50 ranging from 0.05 to 2.4 nM, which is consistent with the genetic loss of PORCN phenotype. LGK974 specifically inhibits the growth of three RNF43-mutant cell lines, HPAF-II, PaTu 8988S, and Capan-2.

Kinase Assay: Radioligand binding assay: using the aforementioned membrane preps, filtration binding assays are performed. To reduce nonspecific binding, 96-well filtration plates are precoated as suggested by the manufacturer with 0.1% BSA and then washed four times with 0.1% BSA. Membrane preps (50 μg total protein) are incubated in polypropylene 96-well plates with 6.6 nM 3H-GNF-1331 in the presence or absence of a testing compound in binding buffer (50 mM Tris, pH 7.5, 5 mM MgCl2, 1 mM EDTA, 0.1% BSA) plus EDTA-free protease inhibitor mixture in a final volume of 150 μL for 3 h at room temperature. Binding reaction mixtures are then transferred to the precoated 96-well filtration plates, filtered, and washed using a 96-pin FilterMate Harvester. Radioactive signals are obtained using a Microplate Scintillation Counter TopCount. Curve fitting is performed using Prism.

Cell Assay: Cells are plated in growth medium in a 96-well plate at a density of 6,000–12,000 cells per well and treated with DMSO or 1 μM LGK974. After 3 d, the cells are treated with fresh growth medium containing 20 μM EdU, which is included in the Click-iT EdU Alexa Fluor 488 HCS assay kit, and the plate was incubated for 2 h at 37 °C in a humidified atmosphere containing 5% CO2. Cells are fixed with final 4% (mass/vol) paraformaldehyde for 30 min, washed with PBS, permeabilized, and stained with 50 μg/mL Hoechst in PBS for 30 min. After wash, the cells are proceeded to EdU detection according to the instruction of Click-iT EdU assay kit. Triplet wells are performed for each condition.