Abstract 2714: Inhibiting Myc using heterofunctional polymeric degrading chimeras (HYDRACs): a novel class of compounds capable of targeted protein degradation
Authors: Wang Max M. , Truica Mihai I. , Gattis Brayley , Zhang Xiaoyu , Abdulkadir Sarki , Gianneschi Nathan C. 
Published: April 2023

Abstract
Background: The proto-oncogene Myc is known to play critical roles in tumorigenesis, being dysregulated in &gt;70% of human cancers. Development of small molecule Myc drugs has been hampered due to the lack of suitable binding pockets. Myc inhibitory peptides H1, derived from the bHLH-LZ region, have been explored to address this. However, poor pharmacokinetic profiles have precluded clinical translation. Here, we use a novel modular platform technology referred to as the HYDRAC for the development of dual-functional Myc inhibitors/degraders.
Methods: HYDRACs were generated using ROMP resulting in dense brush polymers where peptides occupy every side chain. Heterofunctional constructs were designed incorporating synergistic secondary sequences in addition to Myc-targeting H1. Specifically, a RRRG degron sequence was added to engage endogenous cellular machinery for targeted Myc degradation. Immunofluorescence and confocal microscopy were used to assess cellular penetration; cellular viability assays coupled with both cellular (isogenic pairs, Myc-dependent and independent lines) and biochemical (scrambled H1, monomeric peptides, etc) controls were used to assess anti-proliferative and Myc-specific responses. Myc engagement was assessed via biophysical assays and protein degradation monitored by Western blot. A CRISPR E3 ligase knockdown library and mass spec was used to identify pathways responsible for HYDRAC-induced protein degradation.
Results: A library of HYDRACs with low PDI and predetermined DPs were generated. These compounds were shown to be cell-penetrating with antiproliferative effects at sub-micromolar IC50 values in a formulation- and Myc-dependent manner. HYDRAC treatment resulted in significant decreases in Myc protein levels, rescued by proteasomal inhibition with MG132. RNAseq showed selective overexpression of Myc pathway genes. Biophysical analysis showed strong HYDRAC-Myc interactions, in addtion to Myc protein present following pull-down of biotin-terminated HYDRACs. Selectivity studies revealed that HYDRAC activity requires an intact H1 targeting sequence. Identification of E3 ligases implicated in the degradation pathway are ongoing. Mice bearing transplanted Myc-CaP tumors showed delayed tumor growth following IP administration of Myc-degrading HYDRACs, with studies exploring the biodistribution and pharmacokinetic profile of the compound ongoing.
Conclusion: We present a novel platform technology that addresses the challenges inherent to peptide delivery approaches. The presented work demonstrates the feasibility of HYDRACs for targeted Myc inhibition and degradation. This first-in-class compound also opens the door for the development of HYDRACs targeting other proteins of interest and multiplexing different E3 ligase recruiters for tissue or disease-specific activity.
Citation Format: Max M. Wang, Mihai I. Truica, Brayley Gattis, Xiaoyu Zhang, Sarki Abdulkadir, Nathan C. Gianneschi. Inhibiting Myc using heterofunctional polymeric degrading chimeras (HYDRACs): a novel class of compounds capable of targeted protein degradation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2714.