A selective high affinity MYC-binding compound inhibits MYC:MAX interaction and MYC-dependent tumor cell proliferation

Abstract

MYC is a key player in tumor development, but unfortunately no specific MYC-targeting drugs are clinically available. MYC is strictly dependent on heterodimerization with MAX for transcription activation. Aiming at targeting this interaction, we identified MYCMI-6 in a cell-based protein interaction screen for small inhibitory molecules. MYCMI-6 exhibits strong selective inhibition of MYC:MAX interaction in cells and in vitro at single-digit micromolar concentrations, as validated by split Gaussia luciferase, in situ proximity ligation, microscale thermophoresis and surface plasmon resonance (SPR) assays. Further, MYCMI-6 blocks MYC-driven transcription and binds selectively to the MYC bHLHZip domain with a KD of 1.6 ± 0.5 μM as demonstrated by SPR. MYCMI-6 inhibits tumor cell growth in a MYC-dependent manner with IC50 concentrations as low as 0.5 μM, while sparing normal cells. The response to MYCMI-6 correlates with MYC expression based on data from 60 human tumor cell lines and is abrogated by MYC depletion. Further, it inhibits MYC:MAX interaction, reduces proliferation and induces massive apoptosis in tumor tissue from a MYC-driven xenograft tumor model without severe side effects. Since MYCMI-6 does not affect MYC expression, it is a unique molecular tool to specifically target MYC:MAX pharmacologically and it has good potential for drug development.

Recent advances in the development of protein–protein interactions modulators: mechanisms and clinical trials

“…126 Therefore, inhibiting the PPI between the c-Myc and Max may inhibit the activation or transcription of oncogenes, indicating an antitumor effect. 127,128 Castell et al 129 used the cell-based bimolecular fluorescence complementation (BiFC) to screen small molecules that interfere with c-Myc/Max interaction. Three compounds with good potential were identified from a library of 1990 compounds: MYCMI-6, MYCMI-11 and MYCMI-14 ( Fig.…”

“…Castell et al 129 used the cell-based bimolecular fluorescence complementation (BiFC) to screen small molecules that interfere with c-Myc/Max interaction. Three compounds with good potential were identified from a library of 1990 compounds: MYCMI-6, MYCMI-11 and MYCMI-14 (Fig.…”

Lytic Induction Therapy against Epstein–Barr Virus-Associated Malignancies: Past, Present, and Future

“…Upon initiation of lytic cycle by transfection of BZLF1 in HEK/EBV cells and incubation with CDK2/CDK9 inhibitor or alsterpaullone 2-cyanoethyl (A2CE), only the expression of late lytic proteins, but not the early lytic proteins was reduced [ 148 ]. Other compounds that target the DNA binding domain of the MYC–MAX complex such as KSI-3716 [ 149 ], MYCi975 [ 150 ], sAJM589 [ 151 ], and 10074-G5 [ 152 , 153 ] were found to have anti-tumor effects in multiple tumor cell types. New compounds such as PKUMDL-YC-1202-1205 [ 154 ], 7594-0035 [ 155 ], VPC70063 [ 156 ], and JKY-2-169 [ 157 ] have also been developed.…”

Therapeutic Inhibition of Myc in Cancer. Structural Bases and Computer-Aided Drug Discovery Approaches

“…In one of the most recent reports, Castell et al [118] (2018) aimed at targeting the Myc-Max PPI and identified a novel small molecule inhibitor, MYCMI-6 (NSC354961), from a library of 1990 compounds from NCI/DTP Open Chemical Repository using a cell-based Bimolecular Fluorescence Complementation (BiFC) assay (Figure 7). MYCMI-6 exhibited strong selective inhibition of both c-Myc-Max and N-Myc-Max PPI in vitro at single-digit micromolar concentrations.…”

“…Furthermore, MYCMI-6 inhibited tumor cell growth in a Myc-dependent manner at an IC 50 concentration as low as 0.5 μM, but it was not cytotoxic to normal human cells. Perhaps, the greatest merit of the Castell et al [118] study is the demonstration of the effects of MYCMI-6 administration by daily intraperitoneal injection at a dose of 20 mg/kg in vivo, where MYCMI-6 induced massive apoptosis and reduced tumor cell proliferation, tumor microvasculature density, and N-Myc-Max interaction in an N-Myc-dependent mouse xenograft tumor model based on human N-Myc amplified SK-N-DZ neuroblastoma cells, without causing severe side effects. MYCMI-6 treatment was well tolerated in mice with only slight and temporal effects on body weight.…”