IOWH-032

Target: CFTR

IC50: 1.01 μM

IOWH-032 is a potent and synthetic extracellular cystic fibrosis transmembrane conductance regulator (CFTR) inhibitor with IC50 value of 1.01 μM in T84 and CHO-CFTR cell based assays [1]. The CFTR chloride channel is the most attractive because it is the primary driver of secretion in cases of diarrhea caused by enterotoxigenic bacteria. CFTR plays an important role in transepithelial fluid homeostasis through controlling the flow of chloride ions and thus the movement of water in and out of cells [1].

In vitro: IOWH032 inhibited CFTR activity with IC50 value of 6.87 μM in T84-CFTR cell based assays [1]. IOWH-032 rapidly blocked and potentiated hCFTR activity in a concentration-dependent manner with apparent Kd value of 6.1 nM and 0.64 nM, respectively. However, IOWH-032 did not potentiate and only blocked mCFTR with an apparent Kd value of 42.9 μM [2].

In vivo: IOWH032 significantly inhibited cholera toxin (CTX)-induced secretion in a mouse closed-loop model. Moreover, IOWH032 (5 mg/kg, po dose) decreased the fecal output index by apparent 70% compared to vehicle (cholera toxin) in a cecetomized rat model. IOWH032 inhibited CFTR activity with IC50 value of 6.87 μM in T84-CFTR cell based assays [1].

References:
1.  Doyle K, et al. Inhibitors Of The CFTR Chloride Ion Channel As Potential Treatment For Acute Secretory Diarrhea: Development Of 5-membered Heterocycles Suitable For Pre-clinical Evaluation.
1.  de Hostos EL, Choy RK, Nguyen T. Developing novel antisecretory drugs to treat infectious diarrhea. Future Med Chem. 2011;3(10):1317-25.
2.  Cui G, Khazanov N, Stauffer B, Infield DT, Imhoff BR, Senderowitz H, et al. Potentiators exert distinct effects on human, murine, and Xenopus CFTR. Am J Physiol Lung Cell Mol Physiol. 2016:ajplung 00056 2016.

Potentiators exert distinct effects on human, murine, and Xenopus CFTR.[Pubmed:27288484]

Am J Physiol Lung Cell Mol Physiol. 2016 Aug 1;311(2):L192-207.

VX-770 (Ivacaftor) has been approved for clinical usage in cystic fibrosis patients with several CFTR mutations. Yet the binding site(s) on CFTR for this compound and other small molecule potentiators are unknown. We hypothesize that insight into this question could be gained by comparing the effect of potentiators on CFTR channels from different origins, e.g., human, mouse, and Xenopus (frog). In the present study, we combined this comparative molecular pharmacology approach with that of computer-aided drug discovery to identify and characterize new potentiators of CFTR and to explore possible mechanism of action. Our results demonstrate that 1) VX-770, NPPB, GlyH-101, P1, P2, and P3 all exhibited ortholog-specific behavior in that they potentiated hCFTR, mCFTR, and xCFTR with different efficacies; 2) P1, P2, and P3 potentiated hCFTR in excised macropatches in a manner dependent on the degree of PKA-mediated stimulation; 3) P1 and P2 did not have additive effects, suggesting that these compounds might share binding sites. Also 4) using a pharmacophore modeling approach, we identified three new potentiators (IOWH-032, OSSK-2, and OSSK-3) that have structures similar to GlyH-101 and that also exhibit ortholog-specific potentiation of CFTR. These could potentially serve as lead compounds for development of new drugs for the treatment of cystic fibrosis. The ortholog-specific behavior of these compounds suggest that a comparative pharmacology approach, using cross-ortholog chimeras, may be useful for identification of binding sites on human CFTR.