Abstract
The HIV protease inhibitor nelfinavir is currently being analyzed for repurposing as an anticancer drug for many different cancers, as 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 µM and 7.3 µM, and competitive antagonists of rifampin-dependent induction with IC50 values of 7.5 µM and 25.3 µM, respectively. Antagonism exclusively resulted from binding into the PXR ligand binding pocket. Impaired co-activator recruitment by nelfinavir, as compared to the full agonist rifampin, proved to be the underlying mechanism of both effects on PXR. Physiological 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 elucidated here the molecular mechanism of nelfinavir interaction with PXR. It is hypothesized that modulation of PXR activity may impact on 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 PXR and thereby act as a partial agonist and competitive antagonist. Its major metabolite M8 exerts the same effects, which are based on impaired co-activator recruitment. Nelfinavir anticancer activity may partially rely on modulation of PXR, which itself is discussed as a therapeutic target in cancer therapy and for the reversal of chemoresistance.
- © 2020 The Authors. This is an open access article under the terms of the Creative Commons Attribution Non-Commercial License, which permits use, distribution, and reproduction in any medium, provided that the original work is properly cited and is not used for commercial purposes.