Peter van Mourik

41 Potentiator synergy in rectal organoids INTRODUCTION Cystic fibrosis (CF) is the most common autosomal recessive, life-shortening disorder in the Caucasian population caused by mutations in the cystic fibrosis transmembrane conductance regulator ( CFTR ) gene leading to defective CFTR- mediated epithelial ion transport 1,2 . The nearly 2000 CFTR mutations that have been identified (www.genet.sickkids.on.ca ) so far are categorized into six classes according to their effect on CFTR expression and function 3,4 . The most common mutant CFTR-F508del, expressed by ~90% of all CF individuals, has defects in protein folding and trafficking (class II) and channel gating (class III), and has thermal instability at the apical cell surface (class VI) 5,6 . Classical class III mutations (e.g. G551D and S1251N) affect ~5% of CF subjects and lead to normal apical CFTR processing but severe functional impairment 3 (www.genet.sickkids.on.ca ). Novel therapeutic strategies that target mutation-specific defects of the CFTR protein include repair of CFTR mistrafficking by correctors and defective CFTR channel gating by potentiators 7-10 . The potentiator VX-770 (ivacaftor, KALYDECO TM ) dramatically improved pulmonary function in subjects with G551D, S1251N or 8 other mutations for which the drug has now been US Food and Drug Administration (FDA)- and European Medicines Agency (EMA)-approved 11-14 . More recently, VX-770 combined with the corrector VX-809/lumacaftor (combination is termed ORKAMBI) showed modest but significant effects on lung function and was FDA-approved for F508del homozygous subjects (approximately 45-50% of all subjects) 15,16 . These studies demonstrate that mutation-specific drug targeting is feasible, but also support the need for more effective treatments, as these treatment do not normalize CFTR- dependent biomarkers for most patients 11-17 . Aside VX-770, many other compounds are able to potentiate CFTR, including the natural food components genistein, an isoflavonoid found in high concentrations in soy 18-20 , and curcumin, a major constituent of turmeric 21-23 . Studies have indicated that both VX-770 and curcumin activate CFTR channels in the absence of adenosinetriphosphate (ATP) 21,22,24,25 , while genistein is known to promote ATP- dependent CFTR gating 20,26,27 . In line with their different mode of CFTR potentiation, recent patch clamp studies showed additive or even synergistic effects of curcumin and genistein on the gating of G551D-CFTR channels 27,28 . These findings suggest that potentiators with a different mode of action may likewise enhance clinical VX-770 effectiveness. 3