Repurposing calcium-sensing receptor agonist cinacalcet for treatment of CFTR-mediated secretory diarrheas.

Apurva A Oak,Alan S Verkman,Amber Rivera,Parth D Chhetri,Onur Cil

doi:10.1172/jci.insight.146823

Abstract

Diarrhea is a major cause of global mortality, and outbreaks of secretory diarrhea such as cholera remain an important problem in the developing world. Current treatment of secretory diarrhea primarily involves supportive measures, such as fluid replacement. The calcium-sensing receptor (CaSR) regulates multiple biological activities in response to changes in extracellular Ca2+. The FDA-approved drug cinacalcet is an allosteric activator of CaSR used for treatment of hyperparathyroidism. Here, we found by short-circuit current measurements in human colonic T84 cells that CaSR activation by cinacalcet reduced forskolin-induced Cl– secretion by greater than 80%. Cinacalcet also reduced Cl– secretion induced by cholera toxin, heat-stable E. coli enterotoxin, and vasoactive intestinal peptide (VIP). The cinacalcet effect primarily involved indirect inhibition of cystic fibrosis transmembrane conductance regulator–mediated (CFTR-mediated) Cl– secretion following activation of CaSR and downstream phospholipase C and phosphodiesterases. In mice, cinacalcet reduced fluid accumulation by more than 60% in intestinal closed loop models of cholera and traveler’s diarrhea. The cinacalcet effect involved both inhibition of CFTR-mediated secretion and stimulation of sodium-hydrogen exchanger 3–mediated absorption. These findings support the therapeutic utility of the safe and commonly used drug cinacalcet in CFTR-dependent secretory diarrheas, including cholera, traveler’s diarrhea, and VIPoma.

Highlights

Diarrhea is a major cause of morbidity worldwide and of mortality in the developing world
R-568 appeared to be more potent than cinacalcet in T84 cells with approximately 70% reduction in ISC at 10 μM, which is consistent with its greater reported in vitro potency for calcium-sensing receptor (CaSR) activation compared with cinacalcet [12]
We showed that CaSR regulates CFTR-mediated Cl– secretion in human T84 cells, and the FDAapproved CaSR activator cinacalcet prevents intestinal fluid accumulation in mouse models of cholera and traveler’s diarrhea

Summary

Introduction

Diarrhea is a major cause of morbidity worldwide and of mortality in the developing world. Secretory diarrhea is a common type of diarrhea with diverse etiologies including certain bacterial and viral infections, intestinal inflammation, drugs, tumors, and genetic disorders [2]. In secretory diarrhea activation of Cl– channels at the luminal membrane of intestinal epithelial cells (enterocytes), including cystic fibrosis transmembrane conductance regulator (CFTR) and Ca2+-activated Cl– channels (CaCCs), increases fluid secretion [2]. Cholera and traveler’s diarrhea are major secretory diarrheas caused by the bacterial enterotoxins cholera toxin and heat-stable E. coli enterotoxin, respectively, whose mechanism involves activation of enterocyte CFTR by phosphorylation following elevation of intracellular cyclic nucleotides [4]. Despite ORS, cholera was responsible for more than 100,000 deaths in 2016 [1], and cholera outbreaks can sometimes last for many years due to lack of sanitation infrastructure and access to safe water, which may be logistically challenging in war and disaster zones [5]. There is an unmet need for simple, safe, and effective drug treatments for secretory diarrheas

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