WNK1 kinase and its partners Akt, SGK1 and NBC-family Na+/HCO3− cotransporters are potential therapeutic targets for glioblastoma stem-like cells linked to Bisacodyl signaling

Abstract

Glioblastoma is a highly heterogeneous brain tumor. The presence of cancer cells with stem-like and tumor initiation/propagation properties contributes to poor prognosis. Glioblastoma cancer stem-like cells (GSC) reside in hypoxic and acidic niches favoring cell quiescence and drug resistance. A high throughput screening recently identified the laxative Bisacodyl as a cytotoxic compound targeting quiescent GSC placed in acidic microenvironments. Bisacodyl activity requires its hydrolysis into DDPM, its pharmacologically active derivative. Bisacodyl was further shown to induce tumor shrinking and increase survival in in vivo glioblastoma models. Here we explored the cellular mechanism underlying Bisacodyl cytotoxic effects using quiescent GSC in an acidic microenvironment and GSC-derived 3D macro-spheres. These spheres mimic many aspects of glioblastoma tumors in vivo, including hypoxic/acidic areas containing quiescent cells. Phosphokinase protein arrays combined with pharmacological and genetic modulation of signaling pathways point to the WNK1 serine/threonine protein kinase as a mediator of Bisacodyl cytotoxic effect in both cell models. WNK1 partners including the Akt and SGK1 protein kinases and NBC-family Na+/HCO3− cotransporters were shown to participate in the compound’s effect on GSC. Overall, our findings uncover novel potential therapeutic targets for combatting glioblastoma which is presently an incurable disease.

Research progress on therapeutic targeting of quiescent cancer cells

“…Further reports have shown that bisacodyl/ DDPM triggers necrosis in quiescent GSCs by inhibiting InsP3-induced Ca 2þ release [66]. Moreover, DDPM endows cytotoxic effects by suppressing the activity of a kinase cascade composed of WNK1 and its upstream regulators, AKT and SGK1, triggering a subsequent increase in NBC family Na þ /HCO3cotransporter activity [67]. These findings support the utility of DDPM as a potential therapeutic agent for specifically targeting resistant quiescent cancer stem-like cells.…”

“…Accumulating evidence indicates that DDPM, the active metabolite of bisacodyl, induces necrosis of quiescent human glioblastoma stem-like cells (GSCs) in vivo and in vitro without exerting deleterious effects on non-cancer neural cells [5,66]. In particular, microenvironment acidification of cultured GSCs induces cell cycle arrest and sensitization to DDPM [66,67]. Further reports have shown that bisacodyl/ DDPM triggers necrosis in quiescent GSCs by inhibiting InsP3-induced Ca 2þ release [66].…”

<strong>Antimicrobial and anticancer activities of bisacodyl and it&rsquo;s deacetylated metabolite DDPM </strong>

“…The best compounds exhibited anti-inflammatory activities at 10 µM using zebrafish model. Recently, Zeniou and co-workers described the potentialities of bisacodyl and its desacetylated metabolite DDPM to target glioblastoma cancer stem-like cells in their quiescent, more resistant state [8][9]. Taking into account the literature data concerning the new therapeutic applications of bisacodyl, we report herein the antibacterial activity of bisacodyl and its deacetylated metabolite DDPM using new pathogens strains.…”

“…intestinal to the vascular side leading to the development of diarrhea [5]. Bisacodyl has been also described for its antibacterial, [6] anti-inflammatory [7] and anticancer activities [8][9] In 2015 Sylla and coworkers described for the first time the antibacterial activity of bisacodyl against Grampositive and Gram-negative pathogenic strains [6]. Bisacodyl showed an excellent antimicrobial activity (MIC values of 6.25-12.5 µg/mL; 3.125-12.5 µg/mL and 6.25-12.5 µg/mL against Grampositive strains Micrococcus, Staphylococcus and Listeria respectively.…”

Cell-Type Dependent Regulation of the Electrogenic Na+/HCO3− Cotransporter 1 (NBCe1) by Hypoxia and Acidosis in Glioblastoma

“…Slc4a4, the gene that encodes NBCe1, is regulated by hypoxia in several epithelial cancer cell lines, but not in glioblastoma cell lines [ 12 ]. In quiescent glioblastoma cancer stem-like cells maintained in an acidic environment, WNK1-dependent NBC phosphorylation has been proposed to be linked to their response to treatment approaches [ 13 ]. However, the adaptation of pH regulatory proteins (specifically NBCs) in well-characterised tumour cell subpopulations, to changes in the tumour microenvironment has not yet been addressed.…”