Drug-induced liver injury associated with elexacaftor/tezacaftor/ivacaftor: A pharmacovigilance analysis of the FDA adverse event reporting system (FAERS).

INTRODUCTION: The efficacy and safety of elexacaftor/tezacaftor/ivacaftor (ETI) have been established in prospective clinical trials. Liver function test elevations were observed in a greater proportion of patients receiving ETI compared with placebo; however, the relatively small number of patients and short duration of study preclude detection of rare but clinically significant associations with drug-induced liver injury (DILI). To address this gap, we assessed the real-world risk of DILI associated with ETI through data mining of the FDA adverse event reporting system (FAERS). METHODS: Disproportionality analyses were conducted on FAERS data from the fourth quarter of 2019 through the third quarter of 2022. Comparative patient demographics, onset time and outcomes for ETI-DILI were also obtained. RESULTS: 452 reports of DILI associated with ETI were found, representing 2.1 % of all adverse event reports for ETI. All disproportionality measures were significant for ETI-DILI at p < 0.05; the reporting odds ratio (ROR) (2.82) was comparable to that of drugs classified by FDA as "Most-DILI concern". The most notable demographic finding was a male majority (5:4 male to female ratio) for ETI-DILI compared to a female majority (4:5 male to female ratio) for non ETI-DILI. Median ETI-DILI onset time was 50.5 days, and hospitalization was the second most common complication. CONCLUSION: Using FAERS data, ETI was found to be disproportionately associated with DILI. Future research is needed to investigate the hepatotoxic mechanisms and assess potential mitigation strategies for ETI-induced hepatotoxicity.

Preliminary evidence for sustained efficacy of CFTR modulator therapy with concomitant rifabutin administration.

The concomitant use of elexacaftor/tezacaftor/ivacaftor (ETI) and strong CYP3A inducers including rifampin and rifabutin is not recommended due to the risk of drug-drug interactions (DDI). This presents a significant challenge to the treatment of non-tuberculous mycobacteria precluding the first line treatment. While rifabutin induces CYP3A activity, its effect appears to be moderate compared to rifampin. In this study, we investigated three cases in which concomitant use of rifabutin and CFTR modulators (ETI or ivacaftor monotherapy) was used, and these cases suggest that addition of rifabutin did not compromise the efficacy of ETI or ivacaftor as evidenced by pulmonary function and sweat chloride testing. A full physiologically based pharmacokinetic model predicted lung concentrations of ETI upon rifabutin coadministration to exceed the half-maximal effective concentrations (EC50) determined from chloride transport in phe508del human bronchial epithelial cells. This study provides preliminary evidence in support of the use of rifabutin in patients receiving ETI.

Application of Physiologically Based Pharmacokinetic Modeling to Predict Drug-Drug Interactions between Elexacaftor/Tezacaftor/Ivacaftor and Tacrolimus in Lung Transplant Recipients.

Elexacaftor/tezacaftor/ivacaftor (ETI) treatment has potential benefits in lung transplant recipients, including improvements in extrapulmonary manifestations, such as gastrointestinal and sinus disease; however, ivacaftor is an inhibitor of cytochrome P450 3A (CYP3A) and may, therefore, pose a risk for elevated systemic exposure to tacrolimus. The aim of this investigation is to determine the impact of ETI on tacrolimus exposure and devise an appropriate dosing regimen to manage the risk of this drug-drug interaction (DDI). The CYP3A-mediated DDI of ivacaftor-tacrolimus was evaluated using a physiologically based pharmacokinetic (PBPK) modeling approach, incorporating CYP3A4 inhibition parameters of ivacaftor and in vitro enzyme kinetic parameters of tacrolimus. To further support the findings in PBPK modeling, we present a case series of lung transplant patients who received both ETI and tacrolimus. We predicted a 2.36-fold increase in tacrolimus exposure when co-administered with ivacaftor, which would require a 50% dose reduction of tacrolimus upon initiation of ETI treatment to avoid the risk of elevated systemic exposure. Clinical cases (N = 13) indicate a median 32% (IQR: -14.30, 63.80) increase in the dose-normalized tacrolimus trough level (trough concentration/weight-normalized daily dose) after starting ETI. These results indicate that the concomitant administration of tacrolimus and ETI may lead to a clinically significant DDI, requiring the dose adjustment of tacrolimus.

Safety of elexacaftor/tezacaftor/ivacaftor dose reduction: Mechanistic exploration through physiologically based pharmacokinetic modeling and a clinical case series.

INTRODUCTION: Elexacaftor/tezacaftor/ivacaftor (ETI) treatment is associated with significant improvement in lung function in people with cystic fibrosis (pwCF); however, some patients experience adverse effects (AEs) including hepatotoxicity. One potential strategy is dose reduction in ETI with the goal of maintaining therapeutic efficacy while resolving AEs. We report our experience of dose reduction in individuals who experienced AEs following ETI therapy. We provide mechanistic support for ETI dose reduction by exploring predicted lung exposures and underlying pharmacokinetics-pharmacodynamics (PK-PD) relationships. METHOD: Adults prescribed ETI who underwent dose reduction due to the AEs were included in this case series, and their percent predicted forced expiratory volume in 1 s (ppFEV1 ) and self-reported respiratory symptoms were collected. The full physiologically based pharmacokinetic (PBPK) models of ETI were developed incorporating physiological information and drug-dependent parameters. The models were validated against available pharmacokinetic and dose-response relationship data. The models were then used to predict lung concentrations of ETI at steady-state. RESULTS: Fifteen patients underwent dose reduction in ETI due to AEs. Clinical stability without significant changes in ppFEV1 after dose reduction was observed in all patients. Resolution or improvement of AEs occurred in 13 of the 15 cases. The model-predicted lung concentrations of reduced dose ETI exceeded the reported half maximal effective concentration (EC50 ) from measurement of in vitro chloride transport, providing a hypothesis as to why therapeutic efficacy was maintained. CONCLUSION: Albeit in a small number of patients, this study provides evidence that reduced ETI doses in pwCF who have experienced AEs may be effective. The PBPK models enable exploration of a mechanistic basis for this finding by simulating target tissue concentrations of ETI that can be compared with drug efficacy in vitro.

Physiologically-Based Pharmacokinetic-Led Guidance for Patients With Cystic Fibrosis Taking Elexacaftor-Tezacaftor-Ivacaftor With Nirmatrelvir-Ritonavir for the Treatment of COVID-19.

Cystic fibrosis transmembrane conductance regulator (CFTR) modulating therapies, including elexacaftor-tezacaftor-ivacaftor, are primarily eliminated through cytochrome P450 (CYP) 3A-mediated metabolism. This creates a therapeutic challenge to the treatment of coronavirus disease 2019 (COVID-19) with nirmatrelvir-ritonavir in people with cystic fibrosis (CF) due to the potential for significant drug-drug interactions (DDIs). However, the population with CF is more at risk of serious illness following COVID-19 infection and hence it is important to manage the DDI risk and provide treatment options. CYP3A-mediated DDI of elexacaftor-tezacaftor-ivacaftor was evaluated using a physiologically-based pharmacokinetic modeling approach. Modeling was performed incorporating physiological information and drug-dependent parameters of elexacaftor-tezacaftor-ivacaftor to predict the effect of ritonavir (the CYP3A inhibiting component of the combination) on the pharmacokinetics of elexacaftor-tezacaftor-ivacaftor. The elexacaftor-tezacaftor-ivacaftor models were verified using independent clinical pharmacokinetic and DDI data of elexacaftor-tezacaftor-ivacaftor with a range of CYP3A modulators. When ritonavir was administered on Days 1 through 5, the predicted area under the curve (AUC) ratio of ivacaftor (the most sensitive CYP3A substrate) on Day 6 was 9.31, indicating that its metabolism was strongly inhibited. Based on the predicted DDI, the dose of elexacaftor-tezacaftor-ivacaftor should be reduced when coadministered with nirmatrelvir-ritonavir to elexacaftor 200 mg-tezacaftor 100 mg-ivacaftor 150 mg on Days 1 and 5, with delayed resumption of full-dose elexacaftor-tezacaftor-ivacaftor on Day 9, considering the residual inhibitory effect of ritonavir as a mechanism-based inhibitor. The simulation predicts a regimen of elexacaftor-tezacaftor-ivacaftor administered concomitantly with nirmatrelvir-ritonavir in people with CF that will likely decrease the impact of the drug interaction.

Preclinical Pharmacokinetics and Safety of Intravenous RTD-1.

Severe illness caused by coronavirus disease 2019 (COVID-19) is characterized by an overexuberant inflammatory response resulting in acute respiratory distress syndrome (ARDS) and progressive respiratory failure (A. Gupta, M. V. Madhavan, K. Sehgal, N. Nair, et al., Nat Med 26:1017-1032, 2020, https://doi.org/10.1038/s41591-020-0968-3). Rhesus theta (θ) defensin-1 (RTD-1) is a macrocyclic host defense peptide exhibiting antimicrobial and immunomodulatory activities. RTD-1 treatment significantly improved survival in murine models of a severe acute respiratory syndrome (SARS-CoV-1) and endotoxin-induced acute lung injury (ALI) (C. L. Wohlford-Lenane, D. K. Meyerholz, S. Perlman, H. Zhou, et al., J Virol 83:11385-11390, 2009, https://doi.org/10.1128/JVI.01363-09; J. G. Jayne, T. J. Bensman, J. B. Schaal, A. Y. J. Park, et al., Am J Respir Cell Mol Biol 58:310-319, 2018, https://doi.org/10.1165/rcmb.2016-0428OC). This investigation aimed to characterize the preclinical pharmacokinetics (PK) and safety of intravenous (i.v.) RTD-1. Based on the lack of adverse findings, the no observed adverse effect level (NOAEL) was established at 10 mg/kg/day in rats and 15 mg/kg/day in monkeys. Analysis of single ascending dose studies in both species revealed greater-than-dose-proportional increases in the area under the curve extrapolated to infinity (AUC0-∞) (e.g., 8-fold increase from 5 mg/kg to 20 mg/kg in rats) suggestive of nonlinear PK. The volume of distribution at steady state (Vss) ranged between 550 and 1,461 mL/kg, indicating extensive tissue distribution, which was validated in a biodistribution study of [14C]RTD-1 in rats. Based on interspecies allometric scaling, the predicted human clearance and Vss are 6.48 L/h and 28.0 L, respectively, for an adult (70 kg). To achieve plasma exposures associated with therapeutic efficacy established in a murine model of ALI, the estimated human equivalent dose (HED) is between 0.36 and 0.83 mg/kg/day. The excellent safety profile demonstrated in these studies and the efficacy observed in the murine models support the clinical investigation of RTD-1 for treatment of COVID-19 or other pulmonary inflammatory diseases.

Chemical Synthesis of a Potent Antimicrobial Peptide Murepavadin Using a Tandem Native Chemical Ligation/Desulfurization Reaction.

Classical approaches for the backbone cyclization of polypeptides require conditions that may compromise the chirality of the C-terminal residue during the activation step of the cyclization reaction. Here, we describe an efficient epimerization-free approach for the Fmoc-based synthesis of murepavadin using intramolecular native chemical ligation in combination with a concomitant desulfurization reaction. Using this approach, bioactive murepavadin was produced in a good yield in two steps. The synthetic peptide antibiotic showed potent activity against different clinical isolates of P. aeruginosa. This approach can be easily adapted for the production of murepavadin analogues and other backbone-cyclized peptides.

Anti-Inflammatory Effects of RTD-1 in a Murine Model of Chronic Pseudomonas aeruginosa Lung Infection: Inhibition of NF-κB, Inflammasome Gene Expression, and Pro-IL-1ß Biosynthesis.

Vicious cycles of chronic airway obstruction, lung infections with Pseudomonas aeruginosa, and neutrophil-dominated inflammation contribute to morbidity and mortality in cystic fibrosis (CF) patients. Rhesus theta defensin-1 (RTD-1) is an antimicrobial macrocyclic peptide with immunomodulatory properties. Our objective was to investigate the anti-inflammatory effect of RTD-1 in a murine model of chronic P. aeruginosa lung infection. Mice received nebulized RTD-1 daily for 6 days. Bacterial burden, leukocyte counts, and cytokine concentrations were evaluated. Microarray analysis was performed on bronchoalveolar lavage fluid (BALF) cells and lung tissue homogenates. In vitro effects of RTD-1 in THP-1 cells were assessed using quantitative reverse transcription PCR, enzyme-linked immunosorbent assays, immunoblots, confocal microscopy, enzymatic activity assays, and NF-κB-reporter assays. RTD-1 significantly reduced lung white blood cell counts on days 3 (-54.95%; p = 0.0003) and 7 (-31.71%; p = 0.0097). Microarray analysis of lung tissue homogenates and BALF cells revealed that RTD-1 significantly reduced proinflammatory gene expression, particularly inflammasome-related genes (nod-like receptor protein 3, Mediterranean fever gene, interleukin (IL)-1α, and IL-1ß) relative to the control. In vitro studies demonstrated NF-κB activation was reduced two-fold (p ≤ 0.0001) by RTD-1 treatment. Immunoblots revealed that RTD-1 treatment inhibited proIL-1ß biosynthesis. Additionally, RTD-1 treatment was associated with a reduction in caspase-1 activation (FC = -1.79; p = 0.0052). RTD-1 exhibited potent anti-inflammatory activity in chronically infected mice. Importantly, RTD-1 inhibits inflammasome activity, which is possibly a downstream effect of NF-κB modulation. These findings support that this immunomodulatory peptide may be a promising therapeutic for CF-associated lung disease.

Engineered Cyclotides with Potent Broad in Vitro and in Vivo Antimicrobial Activity.

The search for novel antimicrobial agents to combat microbial pathogens is intensifying in response to the rapid development of drug resistance to current antibiotic therapeutics. Respiratory failure and septicemia are the leading causes of mortality among hospitalized patients. Here, the development of a novel engineered cyclotide with effective broad-spectrum antibacterial activity against several ESKAPE bacterial strains and clinical isolates is reported. The most active antibacterial cyclotide was extremely stable in serum, showed little hemolytic activity, and provided protection in vivo in a murine model of P. aeruginosa peritonitis. These results highlight the potential of the cyclotide scaffold for the development of novel antimicrobial therapeutic leads for the treatment of bacteremia.

Enhanced brain delivery and therapeutic activity of trastuzumab after blood-brain barrier opening by NEO100 in mouse models of brain-metastatic breast cancer.

BACKGROUND: The antitumor efficacy of human epidermal growth factor receptor 2 (HER2)-targeted therapies, such as humanized monoclonal antibody trastuzumab (Herceptin®, Roche), in patients with breast-to-brain cancer metastasis is hindered by the low permeability of the blood-brain barrier (BBB). NEO100 is a high-purity version of the natural monoterpene perillyl alcohol, produced under current good manufacturing practice (cGMP) regulations, that was shown previously to reversibly open the BBB in rodent models. Here we investigated whether NEO100 could enable brain entry of trastuzumab to achieve greater therapeutic activity. METHODS: An in vitro BBB, consisting of human astrocytes and brain endothelial cells, was used to determine trastuzumab penetration in the presence or absence of NEO100. For in vivo studies, we administered intravenous (IV) trastuzumab or the trastuzumab-drug conjugate ado-trastuzumab emtansine (T-DM1; Kadcyla®, Roche), to mouse models harboring intracranial HER2+ breast cancer, with or without BBB opening via IA NEO100. Brain and tumor tissues were examined for the presence of trastuzumab and infiltration of immune cells. Therapeutic impact was evaluated based on overall survival. RESULTS: NEO100 greatly increased trastuzumab penetration across an in vitro BBB. In vivo, IA NEO100-mediated BBB opening resulted in brain tumor-selective accumulation of trastuzumab, without detectable presence in normal brain tissue, along with increased presence of immune cell populations. IV delivery of trastuzumab or T-DM1 achieved significantly greater overall survival of tumor-bearing mice when combined with IA NEO100. CONCLUSION: IA NEO100 facilitates brain tumor entry of trastuzumab and T-DM1 and significantly enhances their therapeutic efficacy, along with increased antibody-dependent immune cell recruitment.

Rhesus Theta Defensin 1 Promotes Long Term Survival in Systemic Candidiasis by Host Directed Mechanisms.

Invasive candidiasis is an increasingly frequent cause of serious and often fatal infections in hospitalized and immunosuppressed patients. Mortality rates associated with these infections have risen sharply due to the emergence of multidrug resistant (MDR) strains of C. albicans and other Candida spp., highlighting the urgent need of new antifungal therapies. Rhesus theta (θ) defensin-1 (RTD-1), a natural macrocyclic antimicrobial peptide, was recently shown to be rapidly fungicidal against clinical isolates of MDR C. albicans in vitro. Here we found that RTD-1 was rapidly fungicidal against blastospores of fluconazole/caspofungin resistant C. albicans strains, and was active against established C. albicans biofilms in vitro. In vivo, systemic administration of RTD-1, initiated at the time of infection or 24 h post-infection, promoted long term survival in candidemic mice whether infected with drug-sensitive or MDR strains of C. albicans. RTD-1 induced an early (4 h post treatment) increase in neutrophils in naive and infected mice. In vivo efficacy was associated with fungal clearance, restoration of dysregulated inflammatory cytokines including TNF-α, IL-1ß, IL-6, IL-10, and IL-17, and homeostatic reduction in numbers of circulating neutrophils and monocytes. Because these effects occurred using peptide doses that produced maximal plasma concentrations (Cmax) of less than 1% of RTD-1 levels required for in vitro antifungal activity in 50% mouse serum, while inducing a transient neutrophilia, we suggest that RTD-1 mediates its antifungal effects in vivo by host directed mechanisms rather than direct fungicidal activity. Results of this study suggest that θ-defensins represent a new class of host-directed compounds for treatment of disseminated candidiasis.

The Potential for QT Interval Prolongation with Chronic Azithromycin Therapy in Adult Cystic Fibrosis Patients.

INTRODUCTION: Oral azithromycin (AZM) has been shown to reduce airway inflammation and disrupt biofilm formation. However, chronic AZM therapy may result in QT interval (QTc) prolongation. OBJECTIVES: The goals of this study were twofold: (i) to characterize the risk of QTc prolongation in adult patients with cystic fibrosis (CF) receiving AZM and other potential QTc-prolonging agents, and (ii) to describe and capture the number of potential QTc-prolonging agents patients with CF are prescribed. METHODS: A retrospective study was conducted over a 3-year period in an adult CF center. QTc values were recorded from electrocardiograms. Univariate and multivariate analyses were conducted. Standard QTc prolongation definitions (males ≥ 450 msec, females ≥ 470 msec) were used. RESULTS: A total of 89 adult CF patient's records were reviewed. Sixty-eight patients received chronic AZM therapy. Two male patients had prolonged QTc, but only 1 received chronic AZM therapy. The median QTc interval between patients receiving and not receiving AZM was not significantly different (405 [interquartile range, IQR: 388-425] vs 394 [IQR: 384-413] msec, respectively, p=0.14). Also, the QTc interval for patients taking chronic AZM 500 mg Monday/Wednesday/Friday or 250 mg daily was not significantly different (401 [IQR: 383-419] vs 409 [IQR: 394-427] msec, respectively, p=0.48). When stratified by the number of QTc-prolonging medications (AZM vs no AZM), there was no significant difference in median QTc values between patients receiving zero to ≥ 5 QTc-prolonging medications. CONCLUSION: An association between chronic AZM therapy and longer QTc intervals or significant QTc prolongation was not shown.

Pharmacokinetics of Tedizolid in Plasma and Sputum of Adults with Cystic Fibrosis.

Over the past decade, the prevalence of infections involving methicillin-resistant Staphylococcus aureus (MRSA) in patients with cystic fibrosis (CF) has increased significantly. Tedizolid (TZD) demonstrates excellent activity against MRSA and a favorable safety profile. The pharmacokinetics of several antibiotics have been shown to be altered in CF patients. The purpose of this study was to characterize the pharmacokinetics of tedizolid in this population. Eleven patients with CF were randomized to receive tedizolid phosphate at 200 mg orally or intravenously once daily for 3 doses with a minimum 2-day washout, followed by crossover to the remaining dosage form. Plasma and expectorated sputum were collected following the third dose of each dosage form for analysis. Population pharmacokinetic analysis was performed using the maximum likelihood expectation maximization method, and the disposition of TZD was described by a two-compartment model. The sputum concentrations exceeded the unbound plasma concentrations with an estimated mean sputum-to-unbound plasma penetration ratio of 2.88 (coefficient of variation, 50.3%). The estimated population mean ± standard deviation of total clearance, central volume of distribution, and bioavailability were 9.72 ± 1.62 liters/h, 61.6 ± 6.94 liters, and 1.04 ± 0.232, respectively. The total clearance was higher in CF patients than in healthy volunteers; however, it was similar to published data for patients with complicated skin and skin structure infections (cSSSIs). This study demonstrates that the oral bioavailability of tedizolid is excellent in patients with CF and that the plasma pharmacokinetics are similar to those reported for patients with cSSSIs.

Rhesus θ-Defensin-1 Attenuates Endotoxin-induced Acute Lung Injury by Inhibiting Proinflammatory Cytokines and Neutrophil Recruitment.

Acute lung injury (ALI) is a clinical syndrome characterized by acute respiratory failure and is associated with substantial morbidity and mortality. Rhesus θ-defensin (RTD)-1 is an antimicrobial peptide with immunomodulatory activity. As airway inflammation and neutrophil recruitment and activation are hallmarks of ALI, we evaluated the therapeutic efficacy of RTD-1 in preclinical models of the disease. We investigated the effect of RTD-1 on neutrophil chemotaxis and macrophage-driven pulmonary inflammation with human peripheral neutrophils and LPS-stimulated murine alveolar macrophage (denoted MH-S) cells. Treatment and prophylactic single escalating doses were administered subcutaneously in a well-established murine model of direct endotoxin-induced ALI. We assessed lung injury by histopathology, pulmonary edema, inflammatory cell recruitment, and inflammatory cytokines/chemokines in the BAL fluid. In vitro studies demonstrated that RTD-1 suppressed CXCL8-induced neutrophil chemotaxis, TNF-mediated neutrophil-endothelial cell adhesion, and proinflammatory cytokine release in activated murine alveolar immortalized macrophages (MH-S) cells. Treatment with RTD-1 significantly inhibited in vivo LPS-induced ALI by reducing pulmonary edema and histopathological changes. Treatment was associated with dose- and time-dependent inhibition of proinflammatory cytokines (TNF, IL-1ß, and IL-6), peroxidase activity, and neutrophil recruitment into the airways. Antiinflammatory effects were demonstrated in animals receiving RTD-1 up to 12 hours after LPS challenge. Notably, subcutaneously administered RTD-1 demonstrates good peptide stability as demonstrated by the long in vivo half-life. Taken together, these studies demonstrate that RTD-1 is efficacious in an experimental model of ALI through inhibition of neutrophil chemotaxis and adhesion, and the attenuation of proinflammatory cytokines and gene expression from alveolar macrophages.

Pharmacokinetic-Pharmacodynamic Target Attainment Analyses To Determine Optimal Dosing of Ceftazidime-Avibactam for the Treatment of Acute Pulmonary Exacerbations in Patients with Cystic Fibrosis.

Acute pulmonary exacerbations (APE) involving Pseudomonas aeruginosa are associated with increased morbidity and mortality in cystic fibrosis (CF) patients. Drug resistance is a significant challenge to treatment. Ceftazidime-avibactam (CZA) demonstrates excellent in vitro activity against isolates recovered from CF patients, including drug-resistant strains. Altered pharmacokinetics (PK) of several beta-lactam antibiotics have been reported in CF patients. Therefore, this study sought to characterize the PK of CZA and perform target attainment analyses to determine the optimal treatment regimen. The PK of CZA in 12 adult CF patients administered 3 intravenous doses of 2.5 g every 8 h infused over 2 h were determined. Population modeling utilized the maximum likelihood expectation method. Monte Carlo simulations determined the probability of target attainment (PTA). An exposure target consisting of the cumulative percentage of a 24-h period that the free drug concentration exceeds the MIC under steady-state pharmacokinetic conditions (fT>MIC) was evaluated for ceftazidime (CAZ), and an exposure target consisting of the cumulative percentage of a 24-h period that the free drug concentration exceeds a 1-mg/liter threshold concentration (fT>1 mg/liter) was evaluated for avibactam (AVI). Published CAZ and CZA MIC distributions were incorporated to evaluate cumulative response probabilities. CAZ and AVI were best described by one-compartment models. The values of total body clearance (CL; CAZ CL, 7.53 ± 1.28 liters/h; AVI CL, 12.30 ± 1.96 liters/h) and volume of distribution (V; CAZ V, 18.80 ± 6.54 liters; AVI V, 25.30 ± 4.43 liters) were broadly similar to published values for healthy adults. CZA achieved a PTA (fT>MIC, 50%) of >0.9 for MICs of ≤16 mg/liter. The overall likelihood of a treatment response was 0.82 for CZA, whereas it was 0.42 for CAZ. These data demonstrate improved pharmacodynamics of CZA in comparison with those of CAZ and provide guidance on the optimal dosing of CZA for future studies. (This study has been registered at ClinicalTrials.gov under registration no. NCT02504827.).

Efficacy of Rhesus Theta-Defensin-1 in Experimental Models of Pseudomonas aeruginosa Lung Infection and Inflammation.

Chronic airway infection and inflammation contribute to the progressive loss of lung function and shortened survival of patients with cystic fibrosis (CF). Rhesus theta defensin-1 (RTD-1) is a macrocyclic host defense peptide with antimicrobial and immunomodulatory activities. Combined with favorable preclinical safety and peptide stability data, RTD-1 warrants investigation to determine its therapeutic potential for treatment of CF lung disease. We sought to evaluate the therapeutic potential of RTD-1 for CF airway infection and inflammation using in vitro, ex vivo, and in vivo models. We evaluated RTD-1's effects on basal and Pseudomonas aeruginosa-induced inflammation in CF sputum leukocytes and CF bronchial epithelial cells. Peptide stability was evaluated by incubation with CF sputum. Airway pharmacokinetics, safety, and tolerance studies were performed in naive mice. Aerosolized RTD-1 treatment effects were assessed by analyzing lung bacterial burdens and airway inflammation using an established model of chronic P. aeruginosa endobronchial infection in CF (ΔF508) mice. RTD-1 directly reduces metalloprotease activity, as well as inflammatory cytokine secretion from CF airway leukocyte and bronchial epithelial cells. Intrapulmonary safety, tolerability, and stability data support the aerosol administration route. RTD-1 reduced the bacterial lung burden, airway neutrophils, and inflammatory cytokines in CF mice with chronic P. aeruginosa lung infection. Collectively, these studies support further development of RTD-1 for treatment of CF airway disease.

Rhesus θ-defensin-1 (RTD-1) exhibits in vitro and in vivo activity against cystic fibrosis strains of Pseudomonas aeruginosa.

OBJECTIVES: Chronic endobronchial infections with Pseudomonas aeruginosa contribute to bronchiectasis and progressive loss of lung function in patients with cystic fibrosis. This study aimed to evaluate the therapeutic potential of a novel macrocyclic peptide, rhesus θ-defensin-1 (RTD-1), by characterizing its in vitro antipseudomonal activity and in vivo efficacy in a murine model of chronic Pseudomonas lung infection. METHODS: Antibacterial testing of RTD-1 was performed on 41 clinical isolates of P. aeruginosa obtained from cystic fibrosis patients. MIC, MBC, time-kill and post-antibiotic effects were evaluated following CLSI-recommended methodology, but using anion-depleted Mueller-Hinton broth. RTD-1 was nebulized daily for 7 days to cystic fibrosis transmembrane conductance regulator (CFTR) F508del-homozygous mice infected using the agar bead model of chronic P. aeruginosa lung infection. In vivo activity was evaluated by change in lung bacterial burden, airway leucocytes and body weight. RESULTS: RTD-1 exhibited potent in vitro bactericidal activity against mucoid and non-mucoid strains of P. aeruginosa (MIC90 = 8 mg/L). Cross-resistance was not observed when tested against MDR and colistin-resistant isolates. Time-kill studies indicated very rapid, concentration-dependent bactericidal activity of RTD-1 with ≥3 log10 cfu/mL reductions at concentrations ≥4× MIC. No post-antibiotic effect was observed. In vivo, nebulized treatment with RTD-1 significantly decreased lung P. aeruginosa burden (mean difference of -1.30 log10 cfu; P = 0.0061), airway leucocytes (mean difference of -0.37 log10; P = 0.0012) and weight loss (mean difference of -12.62% at day 7; P < 0.05) when compared with controls. CONCLUSIONS: This study suggests that RTD-1 is a promising potential therapeutic agent for cystic fibrosis airway disease.