Peter van Mourik

146 Chapter 7 RESULTS To evaluate the relation between drug response in in vitro cultured organoids and therapeutic effect in vivo , we studied 37 paired in vitro-in vivo responses to three CFTR modulating treatments in 24 subjects with CF (baseline characteristics are provided in Table 1). Fifteen patients with the ivacaftor-responsive S1251N mutation received ivacaftor 9 . Thirteen of these patients first received a combination of the possible CFTR potentiating food supplements genistein and curcumin before receiving ivacaftor 7 . The other 9 patients carried at least one rare CFTR mutation with unknown clinical response and were selected for off-label treatment based on the organoid response to either ivacaftor or ivacaftor plus lumacaftor. Apart from the CFTR genotype there were no relevant differences in the baseline clinical characteristics (such as ppFEV 1 or SCC values) between patients that received one or two treatments. We quantified CFTR modulator responses in vitro by assessment of FIS of patient- derived rectal organoids that were previously cultured and stored in a biobank (Fig. 1a and 1b show an example, individual measurements for all patients are provided in supplemental Fig. S1). Organoid swelling was assessed after adding various concentrations of forskolin to facilitate optimal detection of drug response across the cohort for the various drugs 15 . We used two outcome parameters to evaluate the in vivo clinical effect of a treatment: change in ppFEV 1 and change in SCC. Pearson’s correlations between organoid response and pulmonary response were analyzed in a subgroup of patients who had a ppFEV 1 ≥40% and ≤90% before the start of treatment, to limit non-response of this endpoint (ceiling effects at >90% or irreversible lung damage at <40%), as is usual in clinical trials 9,11,29–32 . The organoid FIS positively correlated with both the pulmonary response (change in ppFEV 1 ; n=21, r=0.610, P=0.003, Fig. 1c) and the change in SCC (n=18, r=-0.762, P=<0.001, Fig. 1d). As observed in other studies with CFTR modulators, the two in vivo endpoints appeared only weakly correlated, in a statistically non-significant manner (SCC vs ppFEV 1 , n=18, r=-0.366, P=0.14, Fig. 1e). We observed no big impact on the correlation of the repeated genistein plus curcumin and ivacaftor measurements; for ppFEV 1 : n=21, r=0.624, P=<0.001 and for SCC: n=18, r=-0.716, P=<0.001(supplemental Fig. S2). In accordance with previous observations, all correlations were optimal when organoid responses at 0.128 µM forskolin were used (supplemental Table S1) 16 . Patients with a ppFEV 1 >90% or ppFEV 1 <40% before the start of the treatment did not show a clear correlation between the organoid response and change in ppFEV 1 , despite an identical correlation between organoids and SCC (Fig. 1f,g)). The data of all patients combined showed correlations of organoids with both ppFEV1 (n=35,