A Fusion Protein of the p53 Transaction Domain and the p53-Binding Domain of the Oncoprotein MdmX as an Efficient System for High-Throughput Screening of MdmX Inhibitors

In nearly half of cancers, the Anticancer activity of p53 protein is often impaired by the overexpressed oncoprotein MDM2 and its homologue, MdmX, demanding efficient therapeutics to disrupt the aberrant p53-MdmX/MDM2 interactions to restore the p53 activity. While many potent Mdm2-specific inhibitors have already undergone clinical investigations, searching for MdmX-specific inhibitors has become very attractive, requiring a more efficient screening strategy for evaluating potential scaffolds or leads. In this work, considering that the intrinsic fluorescence residue Trp23 in the p53 transaction domain (p53p) plays an important role in determining the p53-MdmX/MDM2 interactions, we constructed a fusion protein to utilize this intrinsic fluorescence signal to monitor high-throughput screening of a compound library. The fusion protein was composed of the p53p followed by the N-terminal domain of MdmX (N-MdmX) through a flexible amino acid linker, while the whole fusion protein contained a sole intrinsic fluorescence probe. The fusion protein was then evaluated using fluorescence spectroscopy against model compounds. Our results revealed that the variation of the fluorescence signal was highly correlated with the concentration of the ligand within 65 μM. The fusion protein was further evaluated with respect to its feasibility for use in high-throughput screening using a model compound library, including controls. We found that the imidazo-indole scaffold was a bona fide scaffold for template-based design of MdmX inhibitors. Thus, the p53p-N-MdmX fusion protein we designed provides a convenient and efficient tool for high-throughput screening of new MdmX inhibitors. The strategy described in this work should be applicable for other protein targets to accelerate drug discovery.