Abstract

Background: Mucopolysaccharidosis type IIIB (MPSIIIB, Sanfilippo syndrome type B) is a rare lysosomal storage disease caused by deficiency of alpha-N-acetylglucosaminidase (NAGLU) enzyme, leading to progressive accumulation of heparan sulfate and severe neurological decline. MPSIIIB’s significant genetic heterogeneity presents a major barrier to developing broadly effective treatments and suggests a need for personalized therapeutic strategies. Methods: We established a personalized drug repurposing platform using high-content imaging with lysotracker dye as an indirect functional readout of lysosomal dysfunction to screen compounds that correct lysosomal defects in patient-derived fibroblasts. We screened 2807 compounds on cells from an MPSIIIB patient with a homozygous NAGLU p.Arg297Ter mutation. Hits that reduced lysosomal accumulation by at least 25% with minimal cytotoxicity were validated and subsequently tested for efficacy in fibroblasts from a second patient with a different, compound heterozygous NAGLU genotype. Results: The primary screen yielded 72 hits (2.6% hit rate), with 10 confirmed in dose–response assays. Notably, four clinically approved drugs—baclofen, dextrose, epalrestat and moxifloxacin—reduced lysosomal accumulation in the index patient’s cells. However, none of these four drugs were effective in the second patient’s cells, demonstrating a profound patient-specific effect. Only one non-clinical compound, 6-chlorothymol, showed a trend toward activity in both cell lines. Conclusions: Our study demonstrates a feasible framework for conducting rapid, N-of-1 drug repurposing screens for rare diseases. While we identified four promising candidates for the index patient, the lack of efficacy in a second patient cell line underscores that genetic heterogeneity may preclude a “one-size-fits-all” approach for MPSIIIB. These findings support the integration of individualized drug screening as a potential precision-medicine strategy, offering a potential path toward patient-specific therapies for rare diseases rather than traditional drug development.

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