Phenazopyridine is a widely used
drug against urinary tract
pain. The compound has also been shown to enhance neural differentiation of pluripotent stem cells. However, its mechanism of action is not understood. Based on its chemical structure, we hypothesized that
phenazopyridine could be a
kinase inhibitor.
Phenazopyridine was investigated in the following experimental systems: 1) activity of
kinases in pluripotent stem cells; 2) binding to recombinant
kinases, and 3) functional impact on pluripotent stem cells. Upon addition to pluripotent stem cells,
phenazopyridine induced changes in
kinase activities, particularly involving
Mitogen-Activated Protein Kinases,
Cyclin-Dependent Kinases, and AKT pathway
kinases. To identify the primary targets of
phenazopyridine, we screened its interactions with 401 human
kinases. Dose-inhibition curves showed that three of these
kinases interacted with
phenazopyridine with sub-micromolar binding affinities:
cyclin-G-associated
kinase, and the two
phosphatidylinositol kinases PI4KB and PIP4K2C, the latter being known for participating in
pain induction. Docking revealed that
phenazopyridine forms strong H-bonds with the hinge region of the
ATP-binding pocket of these
kinases. As previous studies suggested increased autophagy upon inhibition of the
phosphatidyl-inositol/AKT pathway, we also investigated the impact of
phenazopyridine on this pathway and found an upregulation. In conclusion, our study demonstrates for the first time that
phenazopyridine is a
kinase inhibitor, impacting notably
phosphatidylinositol kinases involved in nociception.