Multiple Synthetic Routes to the Mini-Protein Omomyc and Coiled-Coil Domain Truncations
2019
Brown, Zachary Z. | Mapelli, Claudio | Farasat, Iman | Shoultz, Alycia V. | Johnson, Scott A. | Orvieto, Federica | Santoprete, Alessia | Bianchi, Elisabetta | McCracken, Amy Bittner | Chen, Kuanchang | Zhu, Xiaohong | Demma, Mark J. | Lacey, Brian M. | Canada, Keith A. | Garbaccio, Robert M. | O’Neil, Jennifer | Walji, Abbas
The Myc transcription factor represents an “undruggable” target of high biological interest due to its central role in various cancers. An abbreviated form of the c-Myc protein, called Omomyc, consists of the Myc DNA-binding domain and a coiled-coil region to facilitate dimerization of the 90 amino acid polypeptide. Here we present our results to evaluate the synthesis of Omomyc using three complementary strategies: linear Fmoc solid-phase peptide synthesis (SPPS) using several advancements for difficult sequences, native chemical ligation from smaller peptide fragments, and a high-throughput bacterial expression and assay platform for rapid mutagenesis. This multifaceted approach allowed access to up to gram quantities of the mini-protein and permitted in vitro and in vivo SAR exploration of this modality. DNA-binding results and cellular activity confirm that Omomyc and analogues presented here, are potent binders of the E-box DNA engaged by Myc for transcriptional activation and that this 90-amino acid mini-protein is cell permeable and can inhibit proliferation of Myc-dependent cell lines. We also present additional results on covalent homodimerization through disulfide formation of the full-length mini-protein and show the coiled-coil region can be truncated while preserving both DNA binding and cellular activity. Altogether, our results highlight the ability of advanced peptide synthesis to achieve SAR tractability in a challenging synthetic modality.
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