Background: The CFTR modulator tezacaftor/ivacaftor was efficacious and generally safe and well tolerated in Phase 3 studies in participants ≥12 years of age with cystic fibrosis (CF) homozygous for the F508del-CFTR mutation or heterozygous with a residual function-CFTR mutation (F/F or F /RF respectively). We evaluated tezacaftor/ivacaftor's efficacy and safety over 8 weeks in participants 6 through 11 years of age with these mutations. Methods: Participants were randomized 4:1 to tezacaftor/ivacaftor or a blinding group (placebo for F/F , ivacaftor for F /RF). The primary endpoint was within-group change from baseline in the lung clearance index 2 •5 (LCI 2 •5) through Week 8. Secondary endpoints were change from baseline in sweat chloride (SwCl), cystic fibrosis questionnaire-revised (CFQ-R) respiratory domain score, and safety. Results: Sixty-seven participants received at least one study drug dose. Of those, 54 received tezacaftor/ivacaftor (F/F , 42; F /RF, 12), 10 placebo, and 3 ivacaftor; 66 completed the study. The within-group change in LCI 2 •5 was significantly reduced (improved) by −0 •51 (95% CI: −0 •74, −0 •29). SwCl concentration decreased (improved) by −12 •3 mmol/L and CFQ-R respiratory domain score increased (improved, nonsignificantly) by 2 •3 points. There were no serious adverse events (AEs) or AEs leading to tezacaftor/ivacaftor discontinuation or interruption. The most common AEs (≥10%) in participants receiving tezacaftor/ivacaftor were cough, headache, and productive cough. Conclusions: Tezacaftor/ivacaftor improved lung function (assessed using LCI) and CFTR function (measured by SwCl concentration) in participants 6 through 11 years of age with F/F or F /RF genotypes. Tezacaftor/ivacaftor was safe and well tolerated; no new safety concerns were identified.

Background: Tezacaftor/ivacaftor is a new treatment option in many regions for patients aged ≥12 years who are homozygous (F/F) or heterozygous for the F508del-CFTR mutation and a residual function (F/RF) mutation. This Phase 3, 2-part, open-label study evaluated the pharmacokinetics (PK), safety, tolerability, and efficacy of tezacaftor/ivacaftor in children aged 6 through 11 years with these mutations. Methods: Part A informed weight-based tezacaftor/ivacaftor dosages for part B. The primary objective of part B was to evaluate the safety and tolerability of tezacaftor/ivacaftor through 24 weeks; the secondary objective was to evaluate efficacy based on changes from baseline in percentage predicted forced expiratory volume in 1 s (ppFEV 1 ), growth parameters, sweat chloride, and the Cystic Fibrosis Questionnaire-Revised (CFQ-R) respiratory domain score. Results: After PK analysis in part A, 70 children received ≥1 dose of tezacaftor/ivacaftor in part B; 67 children completed treatment. Exposures in children aged 6 through 11 years were within the target range for those observed in patients aged ≥12 years. The safety profile of tezacaftor/ivacaftor was generally similar to prior studies in patients aged ≥12 years. One child discontinued treatment for a serious adverse event of constipation. Tezacaftor/ ivacaftor treatment improved sweat chloride levels and CFQ-R respiratory domain scores, mean ppFEV 1 remained stable in the normal range, and growth parameters remained stable over 24 weeks. Conclusions: Tezacaftor/ivacaftor was generally safe and well tolerated, and improved CFTR function in children aged 6 through 11 years with CF with F/F and F/RF genotypes, supporting tezacaftor/ivacaftor use in this age group. NCT02953314.

Abstract.A scanning electron microscope (SEM) autoradiographic technique was calibrated and used to determine the site density of acetylcholine receptors within 250 ~tm of the neuromuscular junction in innervated as well as 3-and 10-d denervated sternomastoid muscle of the mouse. In all these groups sharp gradients of receptor site density are seen around the endplates in the first 2-7 ~n, continuing less sharply to between 25 and 50 Ixm. Beyond 50 ~tm (to 250 ~tm) a spatial density gradient is present 3 d after denervation, but none exist by 10 d. These results suggest that the postdenervation steady-state extrajunctional receptor site density is reached sooner near the junction than away from the junction.The usefulness of SEM autoradiography to study the expression and distribution of membrane molecules at high resolution is demonstrated.I NFORMATION on the quantitative distribution of cell surface receptors is usually obtained using light microscope or transmission electron microscope (TEM), ~ autoradiography, biochemical-binding studies, and physiological tests. These procedures are limited either by resolution or by an inability to assess variations in receptor distribution over large areas in a morphologically intact cell. In the present study we demonstrate the value of using scanning electron microscope (SEM) autoradiography for that purpose. A SEM technique, modified from that of Junger and Bachmann (1980) is described. The procedure had already been illustrated in a nonquantitative manner to study acetylcholine receptors (AChRs) on striated muscle cells in culture (Neugebauer et al., 1985;Salpeter, 1986). In the present study, we calibrated the procedure for sensitivity and chemography and used it to demonstrate gradients of AChRs around the neuromuscular junction (nmj) on innervated and denervated mouse sternomastoid muscle. The results are consistent with, and extend those previously derived using other techniques.We conclude that SEM autoradiography can be a reproducible quantitative procedure, with sensitivities comparable to those of TEM and light microscope autoradiography and with the potential of answering questions regarding the distribution of surface receptors on a fine structural scale.1. Abbreviations used in this paper: AChR, acetylcholine receptor; nmj, neuromuscular junction; SEM, scanning electron microscope; TEM, transmission electron microscope. Materials and Methods Labeling the ReceptorsThe acetylcholine receptors in the mouse sternomastoid muscle were saturated in vivo by topically applying ~25I-¢t-bungarotoxin onto the surgically exposed muscle in anesthetized mice (10% Nembutal in 10% ethanol, 0.1 cc/10 g body wt) as previously described (Fertuck et al., 1975). Innervated muscles, or muscles denervated either 3 or 10 d previously from adult female mice (25-35 g) were used. Once the receptors on a muscle were saturated, the wound was sutured and the animal allowed to recover for ,o3 h. (We have found that nonspecific binding is more effectively removed in active animals than by ...

ABSIRACI The distribution and turnover rate of acetylcholine receptors labeled with t2Sl-~x-bungarotoxin were examined in innervated mouse sternomastoid muscle by electron microscope autoradiography using the "mask" analysis procedure. We compared the total population of receptors with receptors newly inserted at the junction 2 d after inactivation with nonradioactive cz-bungarotoxin, both at the top {thickened) region of the postjunctional folds (pjm) and the nonthickened bottom folds. We found that the receptor site density was -10 times greater on the thickened pjm than on the nonthickened bottom folds for both total and newly inserted receptors. This ratio does not change significantly during a 6-d period after labeling the new receptors. Furthermore, calculated values for turnover time of receptors show that both total and newly inserted receptors at both regions of the junctional folds have half-lives for degradation within the range given in the literature for slow junctional receptors. These data exclude a simple migration model whereby receptors are preferentially inserted in the nonthickened region of the junctional folds and then migrate into the thickened membrane at a rate equal to the turnover-rate of the receptors.The postsynaptic folds of the vertebrate neuromuscular junction are heterogeneous in terms of both receptor distribution and morphology. The top ~2,000 A of postjunctional membrane (pjm) has a distinct electron density, a cytoplasmic filamentous substructure (4) and is rich in intramembrane particles (13,26,28). This thickened region has a high density of receptors (~10,000-20,000 sites/#m 2) (2,15,16, 19,23,27). At the bottom of the folds, the membrane is morphologically indistinguishable from that at extrajunctional regions, and the receptor site density is considerably reduced (~ 1,000 sites//.tm 2, or ~5-10% the site density at the top of the folds). This site density is equivalent to that seen in the perijunctional region, 0.5-1 #m immediately surrounding each axonal end bouton (16).The reason for the heterogeneity in the organization of the pjm has not yet been established. Much is known about the properties of extrajunctional and junctional receptors both during development and after denervation (for review see references 10, 14). However, nothing is known about the properties of the acetylcholine receptor (AChR) at the bottom, nonthickened region of the pjm. In the present study, we asked two questions: (a) Do the AChRs in the nonthickened bottom folds resemble extrajunctional or embryonic receptors in having a fast turnover rate, and (b) do the nonthickened bottom folds provide a region for the insertion of AChRs that subsequently migrate to the thickened pjm7 We used innervated mouse sternomastoid muscle to examine both the localization and turnover rate of junctional receptors at the top thickened pjm and at the bottom nonthickened membrane. We did this for the total population of receptors as well as for receptors newly inserted at the junction during a 2-d period. We found t...

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