In vitro activity: In liver cells, Deltarasin inhibits the interaction of RAS with PDEδ with KD of 41 nM. Inhibition of PDEδ-KRAS interaction by Deltarasin suppresses proliferation of human pancreatic ductal adenocarcinoma cells that are dependent on oncogenic KRAS.

Kinase Assay: Kd values are measured by fluorescence polarization measurements. For direct titrations, increasing amounts of PDEδ are added to a solution containing 50-100 nM labelled small molecule in 200 μL PBS buffer. For displacement titrations, increasing amounts of the small molecules in DMSO are directly added to fluorescein-labelled atorvastatin (24 nM) and His6-tagged PDEδ (40 nM) in 200 μL PBS-buffer (containing 0.05% CHAPS, 1% DMSO), keeping the concentration of fluorescein-labelled atorvastatin, PDEδ and DMSO constant. For Kd measurements using isothermal titration calorimetry, PDEδ protein (280 μM) is titrated to small molecule (30 μM) in Tris/HCl buffer (temperature 25°C). In the Tm shift assays, protein melting points are detected by circular dichroism spectroscopy in the presence of small molecules.

Cell Assay: Within a minute, 5 mM of deltarasin completely inhibited PDEδ-KRAS interaction and released the insolubilized mCitrine-RHEB/KRAS6Q to the endomembrane system. This showed that deltarasin interfered with the binding of KRAS to PDEδ in cells and thereby inhibited its solubilization.