Design, synthesis, and biological evaluation of novel benzimidazolyl isoxazole derivatives as potential c-Myc G4 stabilizers to suppress c-Myc transcription and myeloma growth

The c-Myc oncogene is one of the most frequently deregulated driver genes in human cancer, and its rearrangement is closely associated with the development of multiple myeloma (MM). However, c-Myc is a disordered protein that lacks adequate binding pockets on its surface and has a half-life of only 20 to 30 minutes, so it is challenging to design small-molecule inhibitors. The guanine-rich nuclease hypersensitive element III1 (NHEIII1) upstream of the P1 promoter of the c-Myc gene can form intramolecular parallel G-quadruplexes (G4) structures. It has been established that c-Myc G4 controls 85-90% of the transcriptional activation of the c-Myc, which represents one of the most sought-after drug targets in cancer. Therefore, targeting c-Myc G4 to inhibit c-Myc protein would be a potential strategy for the treatment of MM. Herein, a series of benzimidazolyl isoxazole derivatives (EP1-EP19) were designed and synthesized. Among them, compound EP12 exhibited better RPMI-8226 cell inhibition activity (IC50 = 6.16 µM). Moreover, compound EP12 induced apoptosis and inhibited the expression of c-Myc mRNA and c-Myc protein at 5 µM. Circular dichroism (CD) and molecular dynamics (MD) simulation studies indicated that compound EP12 could firmly stabilize c-Myc G4. Accordingly, compound EP12 displayed potent anti-MM activities in vitro and might be a potential c-Myc G4 small molecular stabilizer to warrant further investigation.