| Summary: | Gaucher disease is a lysosomal storage disorder in which the activity of the
enzyme glucocerebrosidase (GCase) is deficient. As a result, the substrate of GCase,
glucosylceramide, accumulates in lysosomes of Gaucher patients, causing enlargement of
the spleen and liver, bone deformity and neurodegeneration. Deficient GCase activity
results from point mutations in the gene encoding for GCase, which cause the protein to
be misfolded. The misfolded mutant form of GCase, although catalytically competent, is
identified and degraded by the endoplasmic reticulum-associated degradation (ERAD)
pathway; thereby never reaching the lysosome or its substrate, resulting in accumulation.
A threshold GCase activity level of 11-15% is all that is needed in order to be
asymptomatic, with most Gaucher patients retaining between 5-20% of GCase activity
levels. Therefore, therapeutic treatment of Gaucher disease only needs to impart modest
increases in GCase activity in order to see large clinical improvements.
An emerging therapy for Gaucher disease uses competitive enzyme inhibitors as
pharmacological chaperones (PCs), which act to increase GCase levels in the lysosome.
The PC binds and stabilizes the native, folded form of GCase, thereby allowing the
enzyme to escape ERAD and resume proper trafficking to the lysosome. Once the
mutant GCase/PC complex is delivered to the lysosome, the relatively high concentration
of accumulated glucosylceramide will compete for the active site of GCase, thereby
displacing the PC as normal glycolipid degradation activity resumes.
Isofagomine (IFG), a known competitive inhibitor of GCase, was synthesized
along with five other C6-alkyl IFG derivatives; of which four lEG derivatives were novel
compounds. All six compounds were shown to be potent competitive inhibitors of GCase
with measured K, values ranging from 0.2 nM to 610 nM. As a strategy to suppress any
inhibitory effects of the PCs after GCase reaches the lysosome, a potentially pH-labile
acetal moiety was incorporated into IFG. Unfortunately, the synthesized acetal is very
stable and unlikely to cleave under physiological conditions. All molecules synthesized,have been, or will be, sent to our collaborators, Dr. Mike Tropak and Dr. Don Mahuran at
the Hospital for Sick Children in Toronto for PC activity testing in Gaucher cell lines.
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