Pharmacologic rescue of an enzyme-trafficking defect in primary hyperoxaluria 1

Significance The lethal disorder, primary hyperoxaluria 1 (PH1), is caused by mutations in peroxisomal-localized alanine:glyoxylate aminotransferase (AGT). AGT contains a C-terminal peroxisomal targeting sequence, but mutations generate a strong N-terminal mitochondrial targeting sequence that directs AGT to mitochondria. Although mutant AGT is functional, the enzyme must be in the peroxisome to detoxify glyoxylate and prevent oxalate accumulation. We have identified a Food and Drug Administration-approved drug, dequalinium chloride (DECA), from a chemical genetic screen to identify probes that attenuate mitochondrial protein import. DECA treatment restores trafficking of mutant AGT from mitochondria to peroxisomes with a subsequent reduction in oxalate levels. Thus, repurposing DECA has potential in therapeutic strategies for PH1 because current clinical trials have not produced an effective treatment, short of organ transplant. Primary hyperoxaluria 1 (PH1; Online Mendelian Inheritance in Man no. 259900), a typically lethal biochemical disorder, may be caused by the AGT ᴾ¹¹ᴸᴳ¹⁷⁰ᴿ allele in which the alanine:glyoxylate aminotransferase (AGT) enzyme is mistargeted from peroxisomes to mitochondria. AGT contains a C-terminal peroxisomal targeting sequence, but mutations generate an N-terminal mitochondrial targeting sequence that directs AGT from peroxisomes to mitochondria. Although AGT ᴾ¹¹ᴸᴳ¹⁷⁰ᴿ is functional, the enzyme must be in the peroxisome to detoxify glyoxylate by conversion to alanine; in disease, amassed glyoxylate in the peroxisome is transported to the cytosol and converted to oxalate by lactate dehydrogenase, leading to kidney failure. From a chemical genetic screen, we have identified small molecules that inhibit mitochondrial protein import. We tested whether one promising candidate, Food and Drug Administration (FDA)-approved dequalinium chloride (DECA), could restore proper peroxisomal trafficking of AGT ᴾ¹¹ᴸᴳ¹⁷⁰ᴿ. Indeed, treatment with DECA inhibited AGT ᴾ¹¹ᴸᴳ¹⁷⁰ᴿ translocation into mitochondria and subsequently restored trafficking to peroxisomes. Previous studies have suggested that a mitochondrial uncoupler might work in a similar manner. Although the uncoupler carbonyl cyanide m-chlorophenyl hydrazone inhibited AGT ᴾ¹¹ᴸᴳ¹⁷⁰ᴿ import into mitochondria, AGT ᴾ¹¹ᴸᴳ¹⁷⁰ᴿ aggregated in the cytosol, and cells subsequently died. In a cellular model system that recapitulated oxalate accumulation, exposure to DECA reduced oxalate accumulation, s