Novel Treatment Strategy for Patients With Urea Cycle Disorders: Pharmacological Chaperones Enhance Enzyme Stability and Activity in Patient-Derived Liver Disease Models

Abstract

Urea cycle disorders (UCDs) are inherited diseases causing recurrent life-threatening metabolic decompensations due to impaired hepatic ammonia detoxification and decreased ureagenesis. Ornithine transcarbamylase (OTC) deficiency (OTCD) is X-linked and the most common and often fatal UCD. In male hemizygous patients, disease severity primarily depends on the pathogenic sequence variant, while in heterozygous females, disease severity also depends on the X-chromosomal inactivation (XCI) pattern. Females with unfavorable XCI predominantly expressing the mutant OTC protein may be severely affected. Here, we investigated a novel treatment strategy for OTCD since there is an unmet need for better therapies. In the first step, we performed a high throughput screening (HTS) using a diversity library with 10 000 chemical compounds to identify pharmacological chaperone (PC) candidates that stabilize purified wild-type OTC. Stratification of our HTS results revealed five potential PCs, which were selected for further experimentation in cellular systems using primary human hepatocytes (PHHs) and human induced pluripotent stem cell (hiPSC)-derived hepatocytes (hiPSC-Heps) from healthy controls and OTCD patients. Two PCs—PC1 and PC4—increased OTC protein stability and activity in control hiPSC-Heps, while PC4 in addition increased OTC activity in patient-derived PHHs from a female OTCD patient with unfavorable XCI. Finally, PC1 and PC4 both significantly increased ureagenesis in patient-derived PHHs. To conclude, we identified two PCs that stabilized wild-type OTC and enhanced enzyme activity and ureagenesis. Our work suggests that PCs could provide a novel treatment strategy for OTCD specifically in females with unfavorable XCI.