Discovery of Methyl 4′-Methyl-5-(7-nitrobenzoc125oxadiazol-4-yl)-11′-biphenyl-3-carboxylate an Improved Small-Molecule Inhibitor of c-Myc–Max Dimerization

摘要

c-Myc is a bHLH-ZIP transcription factor that is responsible for the transcription of a wide range of target genes involved in many cancer-related cellular processes, such as proliferation, differentiation, apoptosis and metabolism. Over-expression of c-Myc has been observed in, and directly contributes to, a variety of human cancers including those of the hematopoietic system, lung, prostate and colon. To become transcriptionally active, c-Myc must first dimerize with Max via its own bHLH-ZIP domain. A proven strategy towards the inhibition of c-Myc oncogenic activity is to interfere with the structural integrity of the c-Myc–Max heterodimer. The small-molecule 10074-G5 is an inhibitor of c-Myc–Max dimerization (IC50 = 146 μM) that operates by binding and stabilizing c-Myc in its monomeric form. Herein, we report on our on-going efforts to optimize the c-Myc–Max inhibitory activity of 10074-G5-related molecules in vitro and in cancer cells that over-express c-Myc. Specifically, we have identified a congener of 10074-G5, termed 3jc48-3, that is about five times as potent (IC50 = 34 μM) at inhibiting c-Myc–Max dimerization as the parent compound. In addition, 3jc48-3 exhibited an approximate two-fold selectivity for c-Myc–Max heterodimers over Max–Max dimers, suggesting that, like its predecessor, its mode of action is through binding c-Myc. 3jc48-3 inhibited the proliferation of c-Myc-over-expressing HL60 and Daudi cells with single-digit micromolar IC50 values by causing growth arrest at the G0/G1 phase. Furthermore, co-immunoprecipitation studies indicated that 3jc48-3 inhibits c-Myc–Max dimerization in cells, which was further substantiated by the specific silencing of a c-Myc-driven luciferase reporter gene. Finally, unlike previously described 10074-G5 analogues, which are rapidly released and/or metabolized by cells following their uptake, 3jc48-3’s intracellular half-life was >17 h. Collectively, these data demonstrate 3jc48-3 to be one of the most potent cellularly active c-Myc inhibitors reported to date.