Heterofunctional polymeric degrading chimeras (HYDRAC) for targeted protein degradation.

Abstract

e15106 Background: Here we utilize a novel proteomimetic polymer platform technology which packages peptide side chains as globular structures with benificial emergent properties for the development of compounds capable of targeted protein degradation. We refer to this class of compounds as Heterofunctional polYmeric DegRAding Chimeras (HYDRACs) and demonstrate the selective degradation of the oncoprotein Myc as a proof-of-concept. Methods: HYDRACs were generated using ring-opening metathesis polymerization (ROMP), resulting in structures highly resistant to proteolysis. Heterofunctional constructs were designed incorporating secondary sequences in addition to Myc-targeting H1. The degron sequence (RRRG) was incorporated to engage endogenous cellular machinery for targeted protein degradation. Immunofluorescence/confocal microscopy were used to assess cellular penetration; cellular viability assays coupled with use of both cellular (isogenic pairs, Myc-dependent and independent lines) and biochemical (scrambled H1 sequence, homopolymers, monomeric peptides) controls were used to assess tumor antiproliferative effects and Myc-specific responses. Myc target engagement was assessed via immunoprecipitation assays, NMR, circular dichroism, and fluorescence polarization with protein degradation monitored by Western blot. A CRISPR knockdown library screen of all known E3 ligases and mass spec was used to identify pathways responsible for HYDRAC-induced protein degradation. Results: A library of HYDRACs with narrow polydispersity and predetermined degrees of polymerization were generated. These compounds are cell-penetrating with antiproliferative effects at micromolar IC50s. HYDRAC treatment resulted in significant decreases in Myc protein levels, which was rescued by inhibition with MG132 and MLN4924. RNAseq showed selective overexpression of Myc pathway genes. Biophysical analysis showed strong HYDRAC-Myc interactions, supported by the presence of Myc protein following pull-down of biotin-terminated HYDRACs. Identification of E3 ligases implicated in the degradation pathway using a combination of a CRISPR knock down library and mass spectrometry are ongoing. Mice bearing Myc-CaP tumors showed delayed tumor growth following treatment with Myc-degrading HYDRACs. Studies on biodistribution and pharmacokinetic profile of the compound, as well as the ability to degrade other proteins of interest using combinations of degron sequences are ongoing. Conclusions: The presented work demonstrates the feasibility of HYDRACs for targeted protein degradation of Myc, providing rationale for further studies in Myc-driven tumor models. This successful demonstration of this first-in-class compound also opens the door for the development of HYDRACs targeting other proteins of interest and incorporation of different E3 ligase recruiters for tissue or disease-specific activity.