Designer Frankenproteins that Halt the Proliferation of Myc-driven Cancer Cells

Overexpression of the Myc transcription factor is involved in >70% of cancers. Notably, younger women and Black women show higher rates of Myc-driven breast cancers, with 97% of breast tumors from Black women showing elevated levels of Myc. Myc partners with transcription factor Max to bind to the E-box DNA response element (CACGTG). We engineered frankenproteins MEF and MEF/C93, based on the basic region/helix-loop-helix/leucine zipper (bHLHZ) motif, that comprise modules from different protein familes. In bacterial one-hybrid assays and quantitative EMSA, both proteins bound the E-box with Kd values 8-10 nM, which rival native transcription factors. Western blot confirmed high Myc expression in Myc-dependent MDA-MB-231 triple-negative breast cancer cells. MEF and MEF/C93 disrupted the Myc/Max/E-box network in cellulo: cell viability assays revealed IC50 values 1-2 µM in MDA-MB-231 cells vs. ~25 µM IC50 values in Myc-independent MCF-7 breast cancer cells. Furthermore, qPCR showed that our proteins significantly reduced expression of Myc-target genes in MDA-MB-231, but not MCF-7 cells. These findings demonstrate that MEF-based proteins selectively inhibit the Myc/Max/E-box network in Myc-dependent cancer cells, thus offering a promising protein-based therapeutic approach for treating Myc-driven cancers.