Stabilizers of the Max Homodimer Identified in Virtual Ligand Screening Inhibit Myc Function

Abstract

Many human cancers show constitutive or amplified expression of the transcriptional regulator and oncoprotein Myc, making Myc a potential target for therapeutic intervention. Here we report the down-regulation of Myc activity by reducing the availability of Max, the essential dimerization partner of Myc. Max is expressed constitutively and can form unstable homodimers. We have isolated stabilizers of the Max homodimer by applying virtual ligand screening (VLS) to identify specific binding pockets for small molecule interactors. Candidate compounds found by VLS were screened by fluorescence resonance energy transfer, and from these screens emerged a potent, specific stabilizer of the Max homodimer. In vitro binding assays demonstrated that the stabilizer enhances the formation of the Max-Max homodimer and interferes with the heterodimerization of Myc and Max in a dose-dependent manner. Furthermore, this compound interferes with Myc-induced oncogenic transformation, Myc-dependent cell growth, and Myc-mediated transcriptional activation. The Max-Max stabilizer can be considered a lead compound for the development of inhibitors of the Myc network.

Small-molecule inhibitors of the Myc oncoprotein

“…Jiang et al (200) have identified a unique group of indirect Myc inhibitors by capitalizing on the unique interaction profiles of Myc and Max. This is based on the fact that Myc homodimers do not form under physiologic conditions whereas Myc-Max heterodimers and Max homodimers form quite readily with the latter being the less stable (33,54).…”

“…This is based on the fact that Myc homodimers do not form under physiologic conditions whereas Myc-Max heterodimers and Max homodimers form quite readily with the latter being the less stable (33,54). Jiang et al (200) used the AutoDock program (201) to screen the 1,700 chemical members of the NCI ChemDiv set for potential ligands for the Max homodimer. Several such compounds with low docking energies were identified and subsequent FRET analysis (129,132,200) indicated that they stabilized the Max homdomer, thereby potentially restricting its ability to provide a ready source of Myc partners.…”

“…Jiang et al (200) used the AutoDock program (201) to screen the 1,700 chemical members of the NCI ChemDiv set for potential ligands for the Max homodimer. Several such compounds with low docking energies were identified and subsequent FRET analysis (129,132,200) indicated that they stabilized the Max homdomer, thereby potentially restricting its ability to provide a ready source of Myc partners. One compound in particular, termed NSC13728 (Fig.…”

Intrinsically disordered proteins are potential drug targets

“…Given the range of structures demonstrated to bind to Myc, it would have been surprising if natural products with similar activity were not found. Several groups have also isolated molecules that interfered with Myc activity but did not disrupt dimerization [43-45]. …”

Functional genomics identifies therapeutic targets for MYC-driven cancer

“…Recently, systemic inhibition of MYC using a transgenic mouse model has demonstrated the efficacy of a dominant negative MYC in mediating tumor regression (8). However, MYC family members encode a basic helix loop helix type of transcription factors without obvious druggable domains (9), rendering the identification of small-molecule inhibitors a challenge (10). In addition, as MYC oncoproteins carry out essential functions in proliferative tissues (11), prolonged inhibition of MYC function could cause severe toxicity.…”