Allosteric modulation of glucocerebrosidase for the purpose of Parkinson’s disease modification involves two distinct classes of small molecules: non-inhibitory pharmacological chaperones and enzymatic activators

Authors

• TC Chen
• LM Glasstetter
• D Williams
• TT Jong
• AN Hogan
• JJ Marugan
• MJ Henderson
• Y Chen
• E Sidransky

Abstract

Gaucher disease (GD) is a lysosomal storage disorder caused by loss-of-function mutations in GBA1, which encodes glucocerebrosidase (GCase). Since GCase deficiency is also a significant contributor to Parkinson’s disease (PD), small-molecule strategies to ameliorate GCase dysfunction are being intensively explored. There are two classes of direct-binding, small-molecule modulators of GCase: pharmacological chaperones (PCs) and enzymatic activators. PCs, tailored for GCase stabilization, offer protection against ER-associated degradation and enable productive enzyme trafficking to the lysosome. In contrast, enzymatic activators increase the affinity of the active site for the transition state, reducing the activation energy of the reaction. It is unclear which pharmacological profile is best suited for correction of GCase insufficiency in PD, although several activators are in clinical trials. Here, we show that our recently-discovered non-inhibitory PC, NCGC326, stabilizes GCase protein levels in engineered H4 cell lines expressing wild-type or mutant GCase, promotes lysosomal translocation of GCase, and reverses substrate accumulation. Protein levels were assessed by Western blot or a pro-luminescent reporter tag fused to GCase. Chaperone effects of NCGC326 were dramatically elevated when used synergistically in combination with proteostasis regulator trans-ISRIB. Conversely, the clinical trial candidate LTI-291 does not exhibit chaperone behavior, except at very high concentrations (100 μM). We show using recombinant GCase, lysates of H4 cells and patient-derived fibroblasts, and tissue samples that, unlike NCGC326, LTI-291 functions as a strong activator of the cleavage of a synthetic GCase substrate. Our results provide a clear separation of two modes of action converging on GCase enhancement.

Scientific Focus Area: Molecular Pharmacology

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