Over 100,000 people in the US suffer from primary open-angle glaucoma (POAG) caused by mutations in the MYOC gene. This form of POAG results from optic nerve damage caused by the death of a protective cell network called the trabecular meshwork (TM). TM cell death occurs in these cases because mutant myocilin abnormally accumulates into toxic aggregates. This mechanism is reminiscent of neurodegenerative diseases, such as Alzheimer's, Huntington's and Parkinson's, where abnormal proteins accumulate in neurons and lead to cell death. In fact, TM cells are long-lived just like neurons. Moreover, mutations that cause earlier POAG onset also make myocilin aggregate more readily, similar to proteins associated with neurodegenerative diseases. Thus, both types of diseases can be considered proteostasis disorders, meaning that long-lived cells (neurons and TM) progressively lose their ability to prevent the toxic accumulation of mutant proteins with age. Thus, strategies aimed at restoring proteostasis in TM cells could be beneficial for glaucoma, just as they have proven for neurodegenerative disease. Through a series of studies, we determined that the Grp94 chaperone (an Hsp90 isoform) that resides in the endoplasmic reticulum, mistakenly preserves mutant myocilin in cells. Importantly, Grp94 only affects misfolded myocilin: Properly folded and functioning myocilin is unaffected by Grp94 manipulation. Grp94 recognizes only myocilin that is misfolded due to either mutations or impaired glycosylation: But Grp94 is unable to clear this misfolded myocilin, and instead, preserves it, causing its toxic accumulation. Thus, myocilin misfolding disrupts proteostasis by mistakenly engaging the Grp94 chaperone. We have shown that the clearance of toxic myocilin can be accelerated simply by inhibiting Grp94! Our team has developed the first isoform selective Grp94 inhibitor termed BnIm. Because the list of Grp94-dependent substrates is small, compared to other Hsp90 isoforms, the toxicity profile for this Grp94 inhibitor also appears low. Therefore, we propose to validate and improve upon this Grp94 inhibitor for the treatment of myocilin-associated POAG by establishing structure-activity relationships of Grp94 inhibitors to elucidate mechanisms of misfolded myocilin triage. We will also evaluate the biological efficacy of Grp94 inhibitors towards mutant myocilin in disease relevant systems and then work to develop Grp94 inhibitors with greater efficacy and biological activity towards misfolded myocilin. These studies will result in a new suite of Grp94 modulators and demonstrate that Grp94 is a novel clinical target to treat glaucoma caused by misfolded myocilin. In addition, mechanisms identified herein that clarify how Grp94 regulates myocilin triage could provide new insights for other proteostasis diseases.

Public Health Relevance

Glaucoma is the leading cause of vision impairment and blindness in the world. Mutations in the myocilin gene cause glaucoma in ~100,000 United States citizens alone. These mutations cause myocilin to accumulate in the eye and cause cell death resulting in glaucoma. We have discovered that a drug targeting a protein called Grp94 can eliminate myocilin. We will improve these inhibitors and test their effectiveness for treating glaucoma using cell and animal models.

Agency
National Institute of Health (NIH)
Institute
National Eye Institute (NEI)
Type
Research Project (R01)
Project #
5R01EY024232-03
Application #
9129703
Study Section
Special Emphasis Panel (ZRG1)
Program Officer
Liberman, Ellen S
Project Start
2014-09-30
Project End
2018-08-31
Budget Start
2016-09-01
Budget End
2017-08-31
Support Year
3
Fiscal Year
2016
Total Cost
Indirect Cost
Name
University of South Florida
Department
Biochemistry
Type
Schools of Medicine
DUNS #
069687242
City
Tampa
State
FL
Country
United States
Zip Code
33612
Huard, Dustin J E; Crowley, Vincent M; Du, Yuhong et al. (2018) Trifunctional High-Throughput Screen Identifies Promising Scaffold To Inhibit Grp94 and Treat Myocilin-Associated Glaucoma. ACS Chem Biol 13:933-941
Que, Nanette L S; Crowley, Vincent M; Duerfeldt, Adam S et al. (2018) Structure Based Design of a Grp94-Selective Inhibitor: Exploiting a Key Residue in Grp94 To Optimize Paralog-Selective Binding. J Med Chem 61:2793-2805
Mishra, Sanket J; Ghosh, Suman; Stothert, Andrew R et al. (2017) Transformation of the Non-Selective Aminocyclohexanol-Based Hsp90 Inhibitor into a Grp94-Seletive Scaffold. ACS Chem Biol 12:244-253
Khandelwal, Anuj; Crowley, Vincent M; Blagg, Brian S J (2017) Resorcinol-Based Grp94-Selective Inhibitors. ACS Med Chem Lett 8:1013-1018
Crowley, Vincent M; Huard, Dustin J E; Lieberman, Raquel L et al. (2017) Second Generation Grp94-Selective Inhibitors Provide Opportunities for the Inhibition of Metastatic Cancer. Chemistry 23:15775-15782
Stothert, Andrew R; Fontaine, Sarah N; Sabbagh, Jonathan J et al. (2016) Targeting the ER-autophagy system in the trabecular meshwork to treat glaucoma. Exp Eye Res 144:38-45
Crowley, Vincent M; Khandelwal, Anuj; Mishra, Sanket et al. (2016) Development of Glucose Regulated Protein 94-Selective Inhibitors Based on the BnIm and Radamide Scaffold. J Med Chem 59:3471-88
Zhao, Huiping; Garg, Gaurav; Zhao, Jinbo et al. (2015) Design, synthesis and biological evaluation of biphenylamide derivatives as Hsp90 C-terminal inhibitors. Eur J Med Chem 89:442-66
Orwig, Susan D; Chi, Pamela V; Du, Yuhong et al. (2014) Ligands for glaucoma-associated myocilin discovered by a generic binding assay. ACS Chem Biol 9:517-25
Stothert, Andrew R; Suntharalingam, Amirthaa; Huard, Dustin J E et al. (2014) Exploiting the interaction between Grp94 and aggregated myocilin to treat glaucoma. Hum Mol Genet 23:6470-80

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