The
HIV protease inhibitor nelfinavir is currently being analyzed for repurposing as an anticancer drug for many different
cancers because it exerts manifold off-target
protein interactions, finally resulting in
cancer cell death. Xenosensing
pregnane X receptor (PXR), which also participates in the control of
cancer cell proliferation and apoptosis, was previously shown to be activated by
nelfinavir; however, the exact molecular mechanism is still unknown. The present study addresses the effects of
nelfinavir and its major and pharmacologically active metabolite
nelfinavir hydroxy-tert-butylamide (M8) on PXR to elucidate the underlying molecular mechanism. Molecular docking suggested direct binding to the PXR
ligand-binding domain, which was confirmed experimentally by limited proteolytic digestion and competitive
ligand-binding assays. Concentration-response analyses using cellular transactivation assays identified
nelfinavir and M8 as partial agonists with EC50 values of 0.9 and 7.3 µM and competitive antagonists of
rifampin-dependent induction with IC50 values of 7.5 and 25.3 µM, respectively. Antagonism exclusively resulted from binding into the PXR
ligand-binding pocket. Impaired coactivator recruitment by
nelfinavir as compared with the full agonist
rifampin proved to be the underlying mechanism of both effects on PXR. Physiologic relevance of
nelfinavir-dependent modulation of PXR activity was investigated in respectively treated primary human hepatocytes, which showed differential induction of PXR target genes and antagonism of
rifampin-induced ABCB1 and
CYP3A4 gene expression. In conclusion, we elucidate here the molecular mechanism of
nelfinavir interaction with PXR. It is hypothesized that modulation of PXR activity may impact the anticancer effects of
nelfinavir. SIGNIFICANCE STATEMENT:
Nelfinavir, which is being investigated for repurposing as an anticancer medication, is shown here to directly bind to human
pregnane X receptor (PXR) and thereby act as a partial agonist and competitive antagonist. Its major metabolite
nelfinavir hydroxy-tert-butylamide exerts the same effects, which are based on impaired coactivator recruitment.
Nelfinavir anticancer activity may involve modulation of PXR, which itself is discussed as a therapeutic target in
cancer therapy and for the reversal of chemoresistance.