Glucosylceramide Synthase-IN-4 (compound 12) is a highly potent GCS inhibitor (IC50 = 6.8 nM) with favorable pharmacokinetics, metabolic stability, CNS penetration, and PXR selectivity. It is a valuable research tool for investigating Gaucher disease, lysosomal storage disorders, and related neurodegenerative pathways in both cellular and animal models.