Efavirenz and efavirenz-like compounds activate human, murine, and macaque hepatic IRE1a-XBP1

Efavirenz (EFV), a widely used antiretroviral drug, is associated with idiosyncratic hepatotoxicity and dyslipidemia. Here we demonstrate that EFV stimulates the activation in primary hepatocytes of key cell stress regulators: inositol-requiring 1a (IRE1a) and X-box binding protein 1 (XBP1). Following EFV exposure, XBP1 splicing (indicating activation) was increased 35.7-fold in primary human hepatocytes. In parallel, XBP1 splicing and IRE1a phosphorylation (p-IRE1a, active IRE1a) were elevated 36.4-fold and 4.9-fold, respectively, in primary mouse hepatocytes. Of note, with EFV treatment, 47.2% of mouse hepatocytes were apoptotic; which was decreased to 23.9% in the presence of STF 083010, an inhibitor of XBP1 splicing. Experiments performed using pregnane X receptor (PXR)-null mouse hepatocytes revealed that EFV-mediated XBP1 splicing and hepatocyte death were not dependent on PXR, which is a nuclear receptor transcription factor that plays a crucial role in the cellular response to xenobiotics. Interestingly, incubation with the primary metabolite of EFV, 8-hydroxyefavirenz (8-OHEFV), only resulted in 10.3- and 2.9-fold increased XBP1 splicing in human and mouse hepatocytes and no change in levels of p-IRE1a in mouse hepatocytes. To further probe the structure-activity relationship of IRE1a-XBP1 activation by EFV, 16 EFV analogs were employed. Of these, an analog in which the EFV alkyne is replaced with an alkene and an analog in which the oxazinone oxygen is replaced by a carbon stimulated XBP1 splicing in human, mouse, and macaque hepatocytes. These data demonstrate that EFV and compounds sharing the EFV scaffold can activate IRE1a-XBP1 across human, mouse, and macaque species.