Idasanutlin (Ro 5503781) (RG-7388) is an effective and specific p53-MDM2 inhibitor (IC50: 6 nM).

Idasanutlin inhibits cell proliferation with IC50 of 30 nM, and induces dose-dependent p53 stabilization, cell cycle arrest, as well as cell apoptosis in cancer cells expressing wild-type p53. [1]

In a mouse SJSA human osteosarcoma xenograft model, Idasanutlin (25 mg/kg p.o.) causes tumor growth inhibition and regression. [1] In a SJSA xenograft model, Idasanutlin results in induction of apoptosis and antiproliferation. [2]

Biochemical Binding Affinity – HTRF Assay: The p53-MDM2 HTRF assay is performed in buffer containing 50 mM Tris-HCl, pH 7.4, 100 mM NaCl, 1 mM DTT, 0.02 or 0.2 mg/ml BSA. Small-molecule inhibitors are stored in aliquots as 10 mM stock solutions in DMSO at 4°C in 96-deep-well plates. It is thawed and mixed immediately prior to testing. The compound is incubated with GST-MDM2 and a biotinylated p53 peptide for one hour at 37°C. Phycolink goat anti-GST (Type 1) allophycocyanin and Eu-8044-streptavidin are then added and followed by one hour incubation at room temperature. Plates are read using the Envision fluorescence reader. IC50 values are determined from inter-plate duplicate or triplicate sets of data. Data are analyzed by XLfit4 (Microsoft) using a 4 Parameter Logistic Model (Sigmoidal Dose-Response Model) and the equation Y= (A+ ((B-A)/ (1+ ((C/x)^D)))), where A and B are enzyme activity in the absence or presence of infinite inhibitor compound, respectively, C is the IC50 and D is the Hill coefficient.

Cell proliferation is evaluated by the tetrazolium dye assay. The concentration at which 50% inhibition (IC50) or 90% inhibition (IC90) of cell proliferation is determined from the linear regression of a plot of the logarithm of the concentration versus percent inhibition. (Only for Reference)