Inhibition of PIP4Kγ ameliorates the pathological effects of mutant huntingtin protein

Abstract

The discovery of the causative gene for Huntington’s disease (HD) has promoted numerous efforts to uncover cellular pathways that lower levels of mutant huntingtin protein (mHtt) and potentially forestall the appearance of HD-related neurological defects. Using a cell-based model of pathogenic huntingtin expression, we identified a class of compounds that protect cells through selective inhibition of a lipid kinase, PIP4Kγ. Pharmacological inhibition or knock-down of PIP4Kγ modulates the equilibrium between phosphatidylinositide (PI) species within the cell and increases basal autophagy, reducing the total amount of mHtt protein in human patient fibroblasts and aggregates in neurons. In two Drosophila models of Huntington’s disease, genetic knockdown of PIP4K ameliorated neuronal dysfunction and degeneration as assessed using motor performance and retinal degeneration assays respectively. Together, these results suggest that PIP4Kγ is a druggable target whose inhibition enhances productive autophagy and mHtt proteolysis, revealing a useful pharmacological point of intervention for the treatment of Huntington’s disease, and potentially for other neurodegenerative disorders.

Phosphoinositides in autophagy: current roles and future insights

“…PI5P4Ks seem to play an important role in keeping metabolic homeostasis but the full extent of the mechanisms they employ to fulfill this function is still largely uncharacterized. Small molecules that target PI5P4Ks are being developed and tested (Table ) , and some showed positive results in a mouse model for diabetes . Interestingly, a specific PI5P4Kγ inhibitor (NCT‐504) has been shown to increase autophagic flux and delay symptoms in a Drosophila model for Huntington’s disease .…”

Targeting the PI5P4K lipid kinase family in cancer using novel covalent inhibitors

“…Deletion of PIP4K2C in mice resulted in an increase of proinflammatory cytokines and T-helpercells, as well as a decrease in regulatory T-cells via hyperactivation of mTORC1 signaling (Shim et al, 2016). Pharmacological inhibition or knockdown of PI5P4Kγ reduced mutant huntingtin protein in human patient fibroblasts and aggregates in neurons, and relieved neuronal degeneration in Drosophila models of Huntington's disease (Al-Ramahi et al, 2017). The critical role of the PI5P4Ks in mediating autophagy may explain their induced essentiality in various disease pathologies Vicinanza et al, 2015;Al-Ramahi et al, 2017;Lundquist et al, 2018).…”

“…Pharmacological inhibition or knockdown of PI5P4Kγ reduced mutant huntingtin protein in human patient fibroblasts and aggregates in neurons, and relieved neuronal degeneration in Drosophila models of Huntington's disease (Al-Ramahi et al, 2017). The critical role of the PI5P4Ks in mediating autophagy may explain their induced essentiality in various disease pathologies Vicinanza et al, 2015;Al-Ramahi et al, 2017;Lundquist et al, 2018). Collectively, these studies suggest that the PI5P4Ks represent a novel lipid kinase family whose underlying biology is important to numerous cellular processes and warrants further investigation of their therapeutic potential across a range of disease states.…”

“…The relevance of PI5P4K in a wide range of diseases has motivated efforts to develop PI5P4K inhibitors. Reported pan-PI5P4K inhibitors (Kitagawa et al, 2017) and isoform-specific inhibitors of PI5P4Kα (Davis et al, 2013), PI5P4Kβ (Voss et al, 2014) and PI5P4Kγ Al-Ramahi et al, 2017) have laid the foundation for evidence of PI5P4K druggability and motivated a need for inhibitors with further improved pharmacological properties. Here we present the identification of a novel potent, covalent PI5P4K inhibitor, THZ-P1-2, and characterize its cellular pharmacology in the contexts of autophagy and cancer.…”

“…We show that THZ-P1-2 exhibits a reasonable selectivity profile across the kinome, with an S-score S(10) of 0.02 (Karaman et al, 2008, Davis et al, 2011 and inhibits cell proliferation at micromolar concentrations in a panel of leukemia cell lines in a manner dependent on covalent targeting. Finally, further investigation of the mechanism of action of THZ-P1-2 led us to the observation that THZ-P1-2 causes lysosomal disruption and defects in the clearance of autophagosomes, halting autophagy and phenocopying the effects of genetic deletion of PI5P4K// (Al-Ramahi et al, 2017;Lundquist et al, 2018). These studies provide evidence that irreversible inhibition of PI5P4K by THZ-P1-2 compromises autophagy, an essential alternative energy source during periods of metabolic stress which cancer cells depend on to maintain cellular homeostasis and prolonged cell viability, further suggesting PI5P4K as a potentially important target in cancer metabolism and other autophagy-dependent diseases.…”