Trifunctional High-Throughput Screen Identifies Promising Scaffold To Inhibit Grp94 and Treat Myocilin-Associated Glaucoma

ACS Chem Biol. 2018 Apr 20;13(4):933-941. doi: 10.1021/acschembio.7b01083. Epub 2018 Feb 20.

Abstract

Gain-of-function mutations within the olfactomedin (OLF) domain of myocilin result in its toxic intracellular accumulation and hasten the onset of open-angle glaucoma. The absence of myocilin does not cause disease; therefore, strategies aimed at eliminating myocilin could lead to a successful glaucoma treatment. The endoplasmic reticulum Hsp90 paralog Grp94 accelerates OLF aggregation. Knockdown or pharmacological inhibition of Grp94 in cells facilitates clearance of mutant myocilin via a non-proteasomal pathway. Here, we expanded our support for targeting Grp94 over cytosolic paralogs Hsp90α and Hsp90β. We then developed a high-throughput screening assay to identify new chemical matter capable of disrupting the Grp94/OLF interaction. When applied to a blind, focused library of 17 Hsp90 inhibitors, our miniaturized single-read in vitro thioflavin T -based kinetics aggregation assay exclusively identified compounds that target the chaperone N-terminal nucleotide binding site. In follow up studies, one compound (2) decreased the extent of co-aggregation of Grp94 with OLF in a dose-dependent manner in vitro, and enabled clearance of the aggregation-prone full-length myocilin variant I477N in cells without inducing the heat shock response or causing cytotoxicity. Comparison of the co-crystal structure of compound 2 and another non-selective hit in complex with the N-terminal domain of Grp94 reveals a docking mode tailored to Grp94 and explains its selectivity. A new lead compound has been identified, supporting a targeted chemical biology assay approach to develop a protein degradation-based therapy for myocilin-associated glaucoma by selectively inhibiting Grp94.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Crystallography, X-Ray
  • Cytoskeletal Proteins
  • Extracellular Matrix Proteins / genetics
  • Extracellular Matrix Proteins / metabolism*
  • Eye Proteins
  • Glaucoma / drug therapy*
  • Glycoproteins / genetics
  • Glycoproteins / metabolism*
  • HSP90 Heat-Shock Proteins / antagonists & inhibitors
  • High-Throughput Screening Assays / methods*
  • Humans
  • Membrane Glycoproteins / antagonists & inhibitors*
  • Molecular Docking Simulation

Substances

  • Cytoskeletal Proteins
  • Extracellular Matrix Proteins
  • Eye Proteins
  • Glycoproteins
  • HSP90 Heat-Shock Proteins
  • Membrane Glycoproteins
  • endoplasmin
  • olfactomedin
  • trabecular meshwork-induced glucocorticoid response protein