Effect of feeding Yucca schidigera extract and a live yeast on the rumen microbiome and performance of dairy cows fed a diet excess in rumen degradable nitrogen

Nitrogen (N) loss from livestock agriculture via ammonia and nitrous oxide can reduce feed efficiency, production and negatively affect the environment. One option to reduce N loss is to add dietary supplements such as Yucca schidigera extract which has ammonia-binding properties and contains antimicrobial steroidal saponins, or Saccharomyces cerevisiae yeast, which can stabilise rumen pH and promote fibre degradation, increasing microbial growth and demand for degradable N. To determine the effect of Yucca schidigera extract when fed alone or in combination with a live yeast on the performance, rumen metabolism, microbiome and N balance, six rumen cannulated dairy cows were fed a mixed ration (C), mixed ration with Y. schidigera extract (De-Odorase®, Alltech®; 5 g/cow/day; D), or mixed ration with Y. schidigera extract (5 g/day) and Saccharomyces cerevisiae (Yea-Sacc®, Alltech®, 1 g/cow per day; DY), in a 3 × 3 Latin rectangle design study with three periods of 49-day duration. Digesta samples were collected via the ruminal cannula during the final week of each period and separated into liquid (LPD) and solid (SPD) phases for microbiome analysis using 16S rRNA amplicon sequencing. DM intake was 0.8 kg/d lower (P < 0.05) in cows fed DY than C or D, with milk protein concentration 1.7 g/kg higher in C than D or DY. There was a beta diversity (Bray Curtis) clustering of the LPD in cows fed D or DY compared to C (P < 0.05), driven by an increase in Prevotella ruminicola-related operational taxonomic units (OTUs), and a decrease in P. brevis and P. bryantii OTUs. A methanogen OTU, Methanobrevibacter olleyae, was decreased in cows fed D or DY and an unclassified species of Gammaproteobacteria was increased in DY (LDA > 2.0, P < 0.05) compared to C. Rumen pH, ammonia and total VFA concentration were not affected by treatment (P > 0.05) but the concentration of propionate and iso-butyrate were lower at 1700 and 2000 h in cows fed DY compared to C (P < 0.05). Measurements of N balance were unaffected by supplementation with D or DY, and there was no effect of treatment on slurry pH. In conclusion, supplementing with an extract of Yucca schidigera either alone or in combination with a live yeast had only a small effect on performance, with Yucca schidigera altering species associated with carbohydrate and protein metabolism, and reduced Methanobrevibacter olleyae which is involved in methanogenesis.

Subgroup analysis of phase 2 study of ceftolozane/tazobactam in neonates and young infants with pyelonephritis

Ceftolozane/tazobactam is approved for the treatment of patients from birth to <18 y old with complicated urinary tract infections (cUTI). This post hoc analysis evaluated the safety, efficacy, and pharmacokinetics (PK) of ceftolozane/tazobactam compared with meropenem in neonates and young infants. NCT03230838 was a phase 2, randomized, active comparator-controlled, double-blind study of patients from birth to <18 y of age with cUTI, including pyelonephritis, given ceftolozane/tazobactam or meropenem in a 3:1 ratio. This subset analysis included only neonates and young infants < 3 mo of age. The microbiologic modified intent-to-treat population (mMITT) included 20 patients (ceftolozane/tazobactam, n = 14; meropenem, n = 6). All patients had pyelonephritis at baseline; two patients in each treatment group had bacteremia (overall 4/20, 20%). Escherichia coli was the most common baseline pathogen (overall 16/20, 80%). Safety and efficacy results were similar between treatment groups and consistent with the overall pediatric population. There were no serious drug-related adverse events (AEs), no discontinuations due to AEs, and no AEs leading to death in either treatment group. For the ceftolozane/tazobactam and meropenem treatment groups, clinical cure rates in the mMITT population were 92.9% and 100%, respectively. The population PK analysis of neonates and young infants demonstrated similar ceftolozane and tazobactam exposures to those of adults, achieving pharmacodynamic targets associated with clinical and microbiologic cure. Ceftolozane/tazobactam has a favorable safety profile and achieves high clinical cure and microbiologic eradication rates in neonates and young infants < 3 mo of age with cUTI and pyelonephritis. IMPORTANCE Extrapolation of antibacterial agent pharmacokinetics from adults to newborns and young infants may not be appropriate; similarly, the clinical manifestations of infectious diseases and outcomes following antibacterial treatment may not be similar. Ceftolozane/tazobactam is an antibacterial drug combination active against Pseudomonas aeruginosa and other multidrug-resistant gram-negative bacteria. A clinical study led to the approval for ceftolozane/tazobactam in patients from birth to 18 y of age who have complicated urinary tract infections, including those with serious kidney infections. Based on data collected during that clinical study, we compared newborns and young infants who were treated with ceftolozane/tazobactam (14 patients) and those who were treated with meropenem (6 patients). We found that ceftolozane/tazobactam treatment of newborns and young infants up to 3 mo of age who have complicated urinary tract infections demonstrated a favorable safety profile and high clinical cure and microbiologic eradication rates, similar to meropenem.

Safety and Efficacy of Ceftolozane/Tazobactam Plus Metronidazole Versus Meropenem From a Phase 2, Randomized Clinical Trial in Pediatric Participants With Complicated Intra-abdominal Infection

BACKGROUND

Ceftolozane/tazobactam, a cephalosporin-β-lactamase inhibitor combination, is approved for the treatment of complicated urinary tract infections and complicated intra-abdominal infections (cIAI). The safety and efficacy of ceftolozane/tazobactam in pediatric participants with cIAI were assessed.

METHODS

This phase 2 study (NCT03217136) randomized participants to either ceftolozane/tazobactam+metronidazole or meropenem for treatment of cIAI in pediatric participants (<18 years). The primary objective was to assess the safety and tolerability of intravenous ceftolozane/tazobactam+metronidazole. Clinical cure at end of treatment (EOT) and test of cure (TOC) visits were secondary end points.

RESULTS

The modified intent-to-treat (MITT) population included 91 participants (ceftolozane/tazobactam+metronidazole, n = 70; meropenem, n = 21). Complicated appendicitis was the most common diagnosis (93.4%); Escherichia coli was the most common pathogen (65.9%). Adverse events (AEs) occurred in 80.0% and 61.9% of participants receiving ceftolozane/tazobactam+metronidazole and meropenem, drug-related AEs occurred in 18.6% and 14.3% and serious AEs occurred in 11.4% and 0% of participants receiving ceftolozane/tazobactam+metronidazole and meropenem, respectively. No drug-related serious AEs or discontinuations due to drug-related AEs occurred. Rates of the clinical cure for ceftolozane/tazobactam+metronidazole and meropenem at EOT were 80.0% and 95.2% (difference: -14.3; 95% confidence interval: -26.67 to 4.93) and at TOC were 80.0% and 100.0% (difference: -19.1; 95% confidence interval: -30.18 to -2.89), respectively; 6 of the 14 clinical failures for ceftolozane/tazobactam+metronidazole at TOC were indeterminate responses imputed as failures per protocol.

CONCLUSION

Ceftolozane/tazobactam+metronidazole was well tolerated in pediatric participants with cIAI and had a safety profile similar to the established safety profile in adults. In this descriptive efficacy analysis, ceftolozane/tazobactam+metronidazole appeared efficacious.

Safety and Efficacy of Ceftolozane/Tazobactam Versus Meropenem in Neonates and Children With Complicated Urinary Tract Infection, Including Pyelonephritis: A Phase 2, Randomized Clinical Trial

BACKGROUND

Ceftolozane/tazobactam, a cephalosporin-β-lactamase inhibitor combination, active against multidrug-resistant Gram-negative pathogens, is approved for treatment of adults with complicated urinary tract infections (cUTI). Safety and efficacy of ceftolozane/tazobactam in pediatric participants with cUTI, including pyelonephritis, were assessed.

METHODS

This phase 2 study (NCT03230838) compared ceftolozane/tazobactam with meropenem for treatment of cUTI in participants from birth to <18 years of age. The primary objective was safety and tolerability. Key secondary end points included clinical cure and per-participant microbiologic response rates at end of treatment (EOT) and test of cure (TOC) visits.

RESULTS

The microbiologic modified intent-to-treat (mMITT) population included 95 participants (ceftolozane/tazobactam, n = 71; meropenem, n = 24). The most common diagnosis and pathogen were pyelonephritis (ceftolozane/tazobactam, 84.5%; meropenem, 79.2%) and Escherichia coli (ceftolozane/tazobactam, 74.6%; meropenem, 87.5%); 5.7% (ceftolozane/tazobactam) and 4.8% (meropenem) of E. coli isolates were extended-spectrum β-lactamase-producers. Rates of adverse events were similar between treatment groups (any: ceftolozane/tazobactam, 59.0% vs. meropenem, 60.6%; drug-related: ceftolozane/tazobactam, 14.0% vs. meropenem, 15.2%; serious: ceftolozane/tazobactam, 3.0% vs. meropenem, 6.1%). Rates of clinical cure for ceftolozane/tazobactam and meropenem at EOT were 94.4% and 100% and at TOC were 88.7% and 95.8%, respectively. Rates of microbiologic eradication for ceftolozane/tazobactam and meropenem at EOT were 93.0% and 95.8%, and at TOC were 84.5% and 87.5%, respectively.

CONCLUSIONS

Ceftolozane/tazobactam had a favorable safety profile in pediatric participants with cUTI; rates of clinical cure and microbiologic eradication were high and similar to meropenem. Ceftolozane/tazobactam is a safe and effective new treatment option for children with cUTI, especially due to antibacterial-resistant Gram-negative pathogens.

Outcomes in participants with ventilated nosocomial pneumonia and organ failure treated with ceftolozane/tazobactam versus meropenem: a subset analysis of the phase 3, randomized, controlled ASPECT-NP trial

BACKGROUND

The pivotal ASPECT-NP trial showed ceftolozane/tazobactam was non-inferior to meropenem for the treatment of ventilated hospital-acquired/ventilator-associated bacterial pneumonia (vHABP/VABP). Here, we evaluated treatment outcomes by degree of respiratory or cardiovascular dysfunction.

METHODS

This was a subset analysis of data from ASPECT-NP, a randomized, double-blind, non-inferiority trial (ClinicalTrials.gov NCT02070757). Adults with vHABP/VABP were randomized 1:1 to 3 g ceftolozane/tazobactam or 1 g meropenem every 8 h for 8-14 days. Outcomes in participants with a baseline respiratory component of the Sequential Organ Failure Assessment (SOFA) score (R-SOFA) ≥ 2 (indicative of severe respiratory failure), cardiovascular component of the SOFA score (CV-SOFA) ≥ 2 (indicative of shock), or R-SOFA ≥ 2 plus CV-SOFA ≥ 2 were compared by treatment arm. The efficacy endpoint of primary interest was 28-day all-cause mortality. Clinical response, time to death, and microbiologic response were also evaluated.

RESULTS

There were 726 participants in the intention-to-treat population; 633 with R-SOFA ≥ 2 (312 ceftolozane/tazobactam, 321 meropenem), 183 with CV-SOFA ≥ 2 (84 ceftolozane/tazobactam, 99 meropenem), and 160 with R-SOFA ≥ 2 plus CV-SOFA ≥ 2 (69 ceftolozane/tazobactam, 91 meropenem). Baseline characteristics, including causative pathogens, were generally similar in participants with R-SOFA ≥ 2 or CV-SOFA ≥ 2 across treatment arms. The 28-day all-cause mortality rate was 23.7% and 24.0% [difference: 0.3%, 95% confidence interval (CI) - 6.4, 6.9] for R-SOFA ≥ 2, 33.3% and 30.3% (difference: - 3.0%, 95% CI - 16.4, 10.3) for CV-SOFA ≥ 2, and 34.8% and 30.8% (difference: - 4.0%, 95% CI - 18.6, 10.3), respectively, for R-SOFA ≥ 2 plus CV-SOFA ≥ 2. Clinical cure rates were as follows: 55.8% and 54.2% (difference: 1.6%, 95% CI - 6.2, 9.3) for R-SOFA ≥ 2, 53.6% and 55.6% (difference: - 2.0%, 95% CI - 16.1, 12.2) for CV-SOFA ≥ 2, and 53.6% and 56.0% (difference: - 2.4%, 95% CI - 17.6, 12.8), respectively, for R-SOFA ≥ 2 plus CV-SOFA ≥ 2. Time to death was comparable in all SOFA groups across both treatment arms. A higher rate of microbiologic eradication/presumed eradication was observed for CV-SOFA ≥ 2 and R-SOFA ≥ 2 plus CV-SOFA ≥ 2 with ceftolozane/tazobactam compared to meropenem.

CONCLUSIONS

The presence of severe respiratory failure or shock did not affect the relative efficacy of ceftolozane/tazobactam versus meropenem; either agent may be used to treat critically ill patients with vHABP/VABP.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02070757. Registered 25 February 2014, https://clinicaltrials.gov/ct2/show/NCT02070757.

A Phase 3, Multicenter, Double-blind, Randomized Clinical Trial to Evaluate the Efficacy and Safety of Ceftolozane/Tazobactam Plus Metronidazole Versus Meropenem in Chinese Participants With Complicated Intra-abdominal Infections

OBJECTIVE

To evaluate the efficacy and safety of ceftolozane/tazobactam plus metronidazole vs meropenem plus placebo for the treatment of complicated intra-abdominal infection (cIAI) in Chinese adult participants.

METHODS

In this phase 3 clinical trial (NCT03830333), Chinese adult participants with cIAI were randomized 1:1 to receive ceftolozane/tazobactam plus metronidazole or meropenem plus placebo. The primary objective was to assess ceftolozane/tazobactam plus metronidazole for noninferiority vs meropenem for clinical response rate at the test of cure (TOC; 28 ± 2 days after study start) visit in the clinically evaluable (CE) population. Secondary end points included clinical and microbiologic responses at the TOC and end of treatment (EOT; ≤24 hours after last dose) visits and adverse event rates.

RESULTS

Clinical cure at the TOC visit in the CE population was 95.2% and 93.1% for ceftolozane/tazobactam plus metronidazole and meropenem, respectively (between-treatment difference: 2.1% [95% CI: -4.7%, 8.8%); thus, noninferiority was met. Clinical responses at the TOC and EOT visits and microbiologic responses at the TOC visit were consistent with the primary efficacy end point. Safety was comparable between study treatment groups.

CONCLUSION

In Chinese adult participants with cIAI, ceftolozane/tazobactam plus metronidazole was noninferior to meropenem, with comparable safety.

Ceftolozane/tazobactam for hospital-acquired/ventilator-associated bacterial pneumonia due to ESBL-producing Enterobacterales: a subgroup analysis of the ASPECT-NP clinical trial

BACKGROUND

After the MERINO trial with piperacillin/tazobactam, the efficacy of β-lactam/tazobactam combinations in serious infections involving extended-spectrum β-lactamase (ESBL)-producing pathogens merits special evaluation.

OBJECTIVES

To further confirm the efficacy of ceftolozane/tazobactam in treating hospital-acquired/ventilator-associated bacterial pneumonia (HABP/VABP) involving ESBL-positive and/or AmpC-producing Enterobacterales.

METHODS

Retrospective subgroup analysis of the ASPECT-NP trial comparing ceftolozane/tazobactam with meropenem for treating HABP/VABP in mechanically ventilated adults (ClinicalTrials.gov NCT02070757). ESBLs were identified using whole genome sequencing. Chromosomal AmpC production was quantified employing a high-sensitivity mRNA transcription assay.

RESULTS

Overall, 61/726 (8.4%) participants had all baseline lower respiratory tract (LRT) isolates susceptible to both study treatments and ≥1 baseline ESBL-positive/AmpC-overproducing Enterobacterales isolate. In this subgroup (ceftolozane/tazobactam n = 30, meropenem n = 31), baseline characteristics were generally comparable between treatment arms. The most frequent ESBL-positive and/or AmpC-overproducing Enterobacterales isolates (ceftolozane/tazobactam n = 31, meropenem n = 35) overall were Klebsiella pneumoniae (50.0%), Escherichia coli (22.7%), and Proteus mirabilis (7.6%). The most prevalent ESBLs were CTX-M-15 (75.8%), other CTX-M (19.7%), and SHV (4.5%); 10.6% of isolates overproduced chromosomal AmpC. Overall, 28 day all-cause mortality was 6.7% (2/30) with ceftolozane/tazobactam and 32.3% (10/31) with meropenem (25.6% difference, 95% CI: 5.54 to 43.84). Clinical cure rate at test-of-cure, 7-14 days after end of therapy, was 73.3% (22/30) with ceftolozane/tazobactam and 61.3% (19/31) with meropenem (12.0% difference, 95% CI: -11.21 to +33.51). Per-isolate microbiological response at test-of-cure was 64.5% (20/31) with ceftolozane/tazobactam and 74.3% (26/35) with meropenem (-9.8% difference, 95% CI: -30.80 to +12.00).

CONCLUSIONS

These data confirm ceftolozane/tazobactam as an effective treatment option for HABP/VABP involving ceftolozane/tazobactam-susceptible ESBL-positive and/or AmpC-producing Enterobacterales.

Clinical and microbiological outcomes, by causative pathogen, in the ASPECT-NP randomized, controlled, Phase 3 trial comparing ceftolozane/tazobactam and meropenem for treatment of hospital-acquired/ventilator-associated bacterial pneumonia

OBJECTIVES

In the ASPECT-NP trial, ceftolozane/tazobactam was non-inferior to meropenem for treating nosocomial pneumonia; efficacy outcomes by causative pathogen were to be evaluated.

METHODS

Mechanically ventilated participants with hospital-acquired/ventilator-associated bacterial pneumonia were randomized to 3 g ceftolozane/tazobactam (2 g ceftolozane/1 g tazobactam) q8h or 1 g meropenem q8h. Lower respiratory tract (LRT) cultures were obtained ≤36 h before first dose; pathogen identification and susceptibility were confirmed at a central laboratory. Prospective secondary per-pathogen endpoints included 28 day all-cause mortality (ACM), and clinical and microbiological response at test of cure (7-14 days after the end of therapy) in the microbiological ITT (mITT) population.

RESULTS

The mITT population comprised 511 participants (264 ceftolozane/tazobactam, 247 meropenem). Baseline LRT pathogens included Klebsiella pneumoniae (34.6%), Pseudomonas aeruginosa (25.0%) and Escherichia coli (18.2%). Among baseline Enterobacterales isolates, 171/456 (37.5%) were ESBL positive. For Gram-negative baseline LRT pathogens, susceptibility rates were 87.0% for ceftolozane/tazobactam and 93.3% for meropenem. For Gram-negative pathogens, 28 day ACM [52/259 (20.1%) and 62/240 (25.8%)], clinical cure rates [157/259 (60.6%) and 137/240 (57.1%)] and microbiological eradication rates [189/259 (73.0%) and 163/240 (67.9%)] were comparable with ceftolozane/tazobactam and meropenem, respectively. Per-pathogen microbiological eradication for Enterobacterales [145/195 (74.4%) and 129/185 (69.7%); 95% CI: -4.37 to 13.58], ESBL-producing Enterobacterales [56/84 (66.7%) and 52/73 (71.2%); 95% CI: -18.56 to 9.93] and P. aeruginosa [47/63 (74.6%) and 41/65 (63.1%); 95% CI: -4.51 to 19.38], respectively, were also comparable.

CONCLUSIONS

In mechanically ventilated participants with nosocomial pneumonia owing to Gram-negative pathogens, ceftolozane/tazobactam was comparable with meropenem for per-pathogen 28 day ACM and clinical and microbiological response.

110. A Phase 3, Multicenter, Double-blind, Randomized Clinical Trial to Evaluate the Efficacy and Safety of Ceftolozane/Tazobactam Plus Metronidazole Versus Meropenem in Chinese Participants With Complicated Intra-abdominal Infections

Background

In China, the prevalence of infections due to multidrug-resistant gram-negative bacteria is high and additional treatment options for complicated intra-abdominal infections (cIAI) are needed. This study compared the efficacy and safety of ceftolozane/tazobactam (C/T) + metronidazole (MTZ) versus meropenem (MEM) + placebo (pbo) for the treatment of cIAI in adult Chinese participants.

Methods

This was a phase 3, double-blind study conducted at 21 centers in China (NCT03830333). Participants aged 18-75 years with cIAI requiring surgical intervention within 24 hours of study drug administration were stratified by site of infection and randomized 1:1 to receive 1.5 g C/T (1 g ceftolozane and 0.5 g tazobactam) + 0.5 g MTZ administered intravenously (IV) every 8 hours (q8h) or 1 g MEM + pbo administered IV q8h for 4-14 days. The primary endpoint was clinical cure at test of cure (TOC) in the clinically evaluable (CE) population. Secondary endpoints included rates of clinical cure, per-participant microbiologic response, per-pathogen microbiologic response, and adverse events (AE). Non-inferiority for clinical cure at TOC in the CE population was confirmed if the lower bound of the 2-sided 95% CI for the between-treatment difference in the clinical cure rate was larger than −12.5%.

Results

A total of 134 participants were randomized to each treatment group. Demographics and baseline characteristics were generally well balanced between treatment groups (Table 1). The median (range) age in the ITT population was 50 (18-75) years and 61% were men. The most frequent sites of infection were the appendix (C/T + MTZ, 50.0%; MEM + pbo, 49.3%) and gallbladder (C/T + MTZ, 27.6%; MEM + pbo, 29.1%). Overall, the most frequently isolated pathogens were Escherichia coli (61.4%) and Klebsiella pneumoniae (17.3%); few anaerobes were isolated (Table 1). C/T + MTZ was non-inferior to MEM + pbo for clinical cure in the CE population (C/T + MTZ, 95.2%; MEM + pbo, 93.1%; difference, 2.1% [95% CI, −4.7% to 8.8%]). Results for key secondary endpoints were comparable between treatment groups (Table 2). Rates of AEs were generally similar between treatment groups (Table 3).

Conclusion

C/T + MTZ was non-inferior to MEM + pbo in the treatment of adult Chinese participants with cIAI and demonstrated a favorable safety profile.

Disclosures

Xiaofei Chen, n/a, MSD, China (Employee) Xiaoling Du, n/a, MSD, China (Employee) Ye Wang, n/a, MSD, China (Employee) Hui Wang, n/a, MSD, China (Employee) Fang Sun, n/a, MSD, China (Employee) Matthew G. Johnson, MD, Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA (Employee) Mekki Bensaci, PhD, Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA (Employee) Jennifer A. Huntington, PharmD, Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA (Employee) Christopher Bruno, MD, Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA (Employee)

1154. Safety and Efficacy of Ceftolozane/Tazobactam Plus Metronidazole Versus Meropenem in Pediatric Participants With Complicated Intra-abdominal Infection: A Phase 2, Randomized Clinical Trial

Background

Ceftolozane/tazobactam (C/T), a cephalosporin–β-lactamase inhibitor combination, is approved for treatment of complicated urinary tract infections, complicated intra-abdominal infections (cIAI), and nosocomial pneumonia in adults. Safety and efficacy of C/T in pediatric participants with cIAI was assessed.

Methods

This phase 2 study (NCT03217136) compared C/T + metronidazole (MTZ) with meropenem (MEM) for treatment of cIAI. Age- and weight-adjusted dosing is summarized in Table 1. The primary objective was to evaluate the safety and tolerability of C/T + MTZ compared with MEM. A key secondary endpoint was clinical cure at end of treatment (EOT) and test of cure (TOC).

Table 1. Summary of Dosing and Pharmacokinetic Sampling Schedule by Age Cohort

Results

A total of 94 participants were randomized 3:1; 91 were treated with C/T + MTZ (n=70) or MEM (n=21) comprising the modified intent-to-treat (MITT) population. The clinically evaluable population included 78 participants at EOT (C/T + MTZ, n=59; MEM, n=19) and 77 participants at TOC (C/T + MTZ, n=58; MEM, n=19). The most common diagnosis and pathogen in the MITT population were complicated appendicitis (C/T + MTZ, 91.4%; MEM, 100%) and Escherichia coli (C/T + MTZ, 67.1%; MEM, 61.9%). The mean (SD) intravenous therapy/overall treatment duration was 6.4 (2.8)/9.3 (3.6) days and 5.8 (1.8)/9.0 (3.2) days for C/T + MTZ and MEM, respectively. In total, ≥1 adverse events (AE) occurred in 80.0% and 61.9% of participants receiving C/T + MTZ and MEM, respectively (Table 2), of which 18.6% and 14.3% were considered drug related. Serious AE occurred in 11.4% (8/70) and 0% (0/21) of participants receiving C/T + MTZ and MEM, respectively; none were considered drug related. No drug-related study drug discontinuations occurred. In the MITT population, rates of clinical cure for C/T + MTZ and MEM at EOT were 80.0% and 95.2%, and at TOC were 80.0% and 100%, respectively (Figure 1); 6 of the 14 failures for C/T + MTZ were indeterminate responses scored as endpoint failures per protocol. In the clinically evaluable (CE) population, rates of clinical cure for C/T + MTZ and MEM were 89.8% and 100% at EOT, and 89.7% and 100% at TOC, respectively (Figure 1).

Conclusion

C/T + MTZ was well tolerated in pediatric participants with cIAI, and rates of clinical success were high with C/T treatment. C/T is a promising new treatment option for children with cIAI.

Disclosures

Carl-Christian A. Jackson, MD, Merck & Co. Inc. (Shareholder) Julia Lonchar, MSc, Merck Sharp & Dohme Corp. (Employee, Shareholder) Feng-Hsiu Su, MPH, MBA, Merck Sharp & Dohme Corp. (Employee, Shareholder) Jennifer A. Huntington, PharmD, Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA (Employee) Mekki Bensaci, PhD, Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA (Employee) Myra W. Popejoy, PharmD, Merck Sharp & Dohme Corp. (Employee) Matthew G. Johnson, MD, Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA (Employee) Carisa S. De Anda, PharmD, Merck Sharp & Dohme Corp. (Employee, Shareholder) Elizabeth G. Rhee, MD, Merck Sharp & Dohme Corp (Employee, Shareholder) Christopher Bruno, MD, Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA (Employee)

1143. Safety and Efficacy of Ceftolozane/Tazobactam Versus Meropenem in Neonatal and Pediatric Participants With Complicated Urinary Tract Infection, Including Pyelonephritis: A Phase 2, Randomized, Clinical Trial

Background

Ceftolozane/tazobactam (C/T) is a cephalosporin–β-lactamase inhibitor combination approved to treat complicated urinary tract infections (cUTI), complicated intra-abdominal infections, and nosocomial pneumonia in adults. Safety and efficacy of C/T in neonatal and pediatric participants with cUTI was assessed.

Methods

This phase 2, randomized, double-blind study (NCT03230838) compared C/T with meropenem (MEM) for treatment of cUTI, including pyelonephritis in participants from birth to 18 years of age. Treatment duration was 7-14 days. After 3 days of intravenous therapy, optional oral step-down therapy was allowed. Participants were stratified and dosed by age group (Table 1). The primary objective was to evaluate the safety and tolerability of C/T compared with MEM, and key secondary end points included clinical response and per-participant microbiologic response at end of treatment (EOT) and test of cure (TOC).

Results

Participants were randomized 3:1 and treated with C/T (n=100) or MEM (n=33). The microbiologic modified intent-to-treat population (mMITT) included 95 participants in the C/T (n=71) and MEM (n=24) arms; the most common reason for mMITT exclusion was lack of a qualifying baseline uropathogen (28.4%). Pyelonephritis was the most common baseline diagnosis (83.2%), and Escherichia coli was the most common qualifying baseline uropathogen (77.9%). Overall mean treatment duration was comparable in both arms (C/T, 10.2 days; MEM, 10.7); a total of 50 (70.4%) and 20 (83.3%) participants switched to optional oral step-down therapy in the C/T and MEM arms, respectively, both for a mean of approximately 6 days. The overall incidence of adverse events (AE; all and drug related), serious AE (SAE), and AE leading to discontinuation was comparable between C/T and MEM arms. There were no AE leading to death, drug-related SAE, or discontinuations due to drug-related AE or SAE (Table 2). For C/T and MEM, rates of clinical cure and microbiologic eradication at EOT and TOC were high (Figure).

Conclusion

In this study, C/T was well tolerated with a safety profile comparable to MEM and to the previously reported safety profile for C/T in adults with cUTI. C/T achieved high clinical cure and microbiologic eradication rates and is a potential new treatment option for children with cUTI.

Disclosures

Emmanuel Roilides, MD, PhD, FIDSA, FAAM, FESCMID, Merck Sharp & Dohme Corp. (Consultant, Grant/Research Support) Negar Ashouri, MD, Merck Sharp & Dohme Corp. (Grant/Research Support) Matthew G. Johnson, MD, Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA (Employee) Julia Lonchar, MSc, Merck Sharp & Dohme Corp. (Employee, Shareholder) Feng-Hsiu Su, MPH, MBA, Merck Sharp & Dohme Corp. (Employee, Shareholder) Jennifer A. Huntington, PharmD, Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA (Employee) Myra W. Popejoy, PharmD, Merck Sharp & Dohme Corp. (Employee) Mekki Bensaci, PhD, Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA (Employee) Carisa S. De Anda, PharmD, Merck Sharp & Dohme Corp. (Employee, Shareholder) Elizabeth G. Rhee, MD, Merck Sharp & Dohme Corp (Employee, Shareholder) Christopher Bruno, MD, Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA (Employee)

Ceftolozane/tazobactam probability of target attainment and outcomes in participants with augmented renal clearance from the randomized phase 3 ASPECT-NP trial

Background

The randomized, double-blind, phase 3 ASPECT-NP trial evaluated the efficacy of 3 g of ceftolozane/tazobactam (C/T) versus 1 g of meropenem infused every 8 h for 8 to 14 days for treatment of adults with hospital-acquired bacterial pneumonia (HABP) or ventilator-associated bacterial pneumonia (VABP). We assessed the probability of target attainment and compared efficacy outcomes from ASPECT-NP in participants with augmented renal clearance (ARC) versus those with normal renal function.

Methods

Baseline renal function was categorized as normal renal function (creatinine clearance 80–130 mL/min) or ARC (creatinine clearance > 130 mL/min). Population pharmacokinetic models informed Monte Carlo simulations to assess probability of target attainment in plasma and pulmonary epithelial lining fluid. Outcomes included 28-day all-cause mortality and clinical cure and per-participant microbiologic cure rates at the test-of-cure visit.

Results

A > 99% and > 80% probability of target attainment was demonstrated for ceftolozane and tazobactam, respectively, in simulated plasma and epithelial lining fluid. Within treatment arms, 28-day all-cause mortality rates in participants with normal renal function (C/T, n = 131; meropenem, n = 123) and ARC (C/T, n = 96; meropenem, n = 113) were comparable (data comparisons presented as rate; treatment difference [95% CI]) (C/T: normal renal function, 17.6%; ARC, 17.7%; 0.2 [− 9.6 to 10.6]; meropenem: normal renal function, 20.3%; ARC, 17.7%; − 2.6 [− 12.6 to 7.5]). Clinical cure rates at test-of-cure were also comparable across renal function groups within treatment arms (C/T: normal renal function, 57.3%; ARC, 59.4%; − 2.1 [− 14.8 to 10.8]; meropenem: normal renal function, 59.3%; ARC, 57.5%; 1.8 [− 10.6 to 14.2]). Per-participant microbiologic cure rates at test-of-cure were consistent across renal function groups within treatment arms (C/T: normal renal function, 72.2% [n/N = 70/97]; ARC, 71.4% [n/N = 55/77]; 0.7 [− 12.4 to 14.2]; meropenem: normal renal function, 75.0% [n/N = 66/88]; ARC, 70.0% [n/N = 49/70]; 5.0 [− 8.7 to 19.0]).

Conclusions

C/T and meropenem resulted in 28-day all-cause mortality, clinical cure, and microbiologic cure rates that were comparable between participants with ARC or normal renal function. In conjunction with high probability of target attainment, these results confirm that C/T (3 g) every 8 h is appropriate in patients with HABP/VABP and ARC.

Trial registration ClinicalTrials.gov identifier: NCT02070757, registered February 25, 2014; EudraCT: 2012-002862-11.

Ceftolozane/tazobactam versus meropenem in patients with ventilated hospital-acquired bacterial pneumonia: subset analysis of the ASPECT-NP randomized, controlled phase 3 trial

Background

Ceftolozane/tazobactam is approved for treatment of hospital-acquired/ventilator-associated bacterial pneumonia (HABP/VABP) at double the dose approved for other infection sites. Among nosocomial pneumonia subtypes, ventilated HABP (vHABP) is associated with the lowest survival. In the ASPECT-NP randomized, controlled trial, participants with vHABP treated with ceftolozane/tazobactam had lower 28-day all-cause mortality (ACM) than those receiving meropenem. We conducted a series of post hoc analyses to explore the clinical significance of this finding.

Methods

ASPECT-NP was a multinational, phase 3, noninferiority trial comparing ceftolozane/tazobactam with meropenem for treating vHABP and VABP; study design, efficacy, and safety results have been reported previously. The primary endpoint was 28-day ACM. The key secondary endpoint was clinical response at test-of-cure. Participants with vHABP were a prospectively defined subgroup, but subgroup analyses were not powered for noninferiority testing. We compared baseline and treatment factors, efficacy, and safety between ceftolozane/tazobactam and meropenem in participants with vHABP. We also conducted a retrospective multivariable logistic regression analysis in this subgroup to determine the impact of treatment arm on mortality when adjusted for significant prognostic factors.

Results

Overall, 99 participants in the ceftolozane/tazobactam and 108 in the meropenem arm had vHABP. 28-day ACM was 24.2% and 37.0%, respectively, in the intention-to-treat population (95% confidence interval [CI] for difference: 0.2, 24.8) and 18.2% and 36.6%, respectively, in the microbiologic intention-to-treat population (95% CI 2.5, 32.5). Clinical cure rates in the intention-to-treat population were 50.5% and 44.4%, respectively (95% CI − 7.4, 19.3). Baseline clinical, baseline microbiologic, and treatment factors were comparable between treatment arms. Multivariable regression identified concomitant vasopressor use and baseline bacteremia as significantly impacting ACM in ASPECT-NP; adjusting for these two factors, the odds of dying by day 28 were 2.3-fold greater when participants received meropenem instead of ceftolozane/tazobactam.

Conclusions

There were no underlying differences between treatment arms expected to have biased the observed survival advantage with ceftolozane/tazobactam in the vHABP subgroup. After adjusting for clinically relevant factors found to impact ACM significantly in this trial, the mortality risk in participants with vHABP was over twice as high when treated with meropenem compared with ceftolozane/tazobactam.

Trial registration

clinicaltrials.gov, NCT02070757. Registered 25 February, 2014, clinicaltrials.gov/ct2/show/NCT02070757.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-021-03694-3.

Evaluating the emergence of nonsusceptibility among Pseudomonas aeruginosa respiratory isolates from a phase-3 clinical trial for treatment of nosocomial pneumonia (ASPECT-NP)

OBJECTIVES

The emergence of nonsusceptibility to ceftolozane/tazobactam and meropenem was evaluated among Pseudomonas aeruginosa (P. aeruginosa) lower respiratory tract isolates obtained from participants in the ASPECT-NP clinical trial.

METHODS

ASPECT-NP was a phase-3, randomised, double-blind, multicentre trial that demonstrated noninferiority of 3 g ceftolozane/tazobactam q8h versus 1 g meropenem q8h for treatment of ventilated hospital-acquired/ventilator-associated bacterial pneumonia. Molecular resistance mechanisms among postbaseline nonsusceptible P. aeruginosa isolates and clinical outcomes associated with participants with emergence of nonsusceptibility were examined. Baseline susceptible and postbaseline nonsusceptible P. aeruginosa isolate pairs from the same participant underwent molecular typing.

RESULTS

Emergence of nonsusceptibility was not observed among the 59 participants with baseline susceptible P. aeruginosa isolates in the ceftolozane/tazobactam arm. Among 58 participants with baseline susceptible P. aeruginosa isolates in the meropenem arm, emergence of nonsusceptibility was observed in 13 (22.4%). Among participants who received ceftolozane/tazobactam and meropenem, 5.1% and 3.4% had a new infection with a nonsusceptible strain, respectively. None of the isolates with emergence of nonsusceptibility to meropenem developed co-resistance to ceftolozane/tazobactam. The molecular mechanisms associated with emergence of nonsusceptibility to meropenem were decreased expression or loss of OprD and overexpression of MexXY.

CONCLUSIONS

Among participants with emergence of nonsusceptibility to meropenem, clinical outcomes were similar to overall clinical outcomes in the ASPECT-NP meropenem arm. Ceftolozane/tazobactam was more stable to emergence of nonsusceptibility versus meropenem; emergence of nonsusceptibility was not observed in any participants with baseline susceptible P. aeruginosa who received ceftolozane/tazobactam in ASPECT-NP.

2227. Outcomes in Patients with Renal Impairment from a Phase 3 Clinical Trial for Ceftolozane–Tazobactam (C/T) Treatment of Nosocomial Pneumonia (ASPECT-NP)

Background

ASPECT-NP, a phase 3, randomized, double-blind study, evaluated C/T (at double the approved dose for other indications) vs. meropenem (MEM) in adults with ventilated nosocomial pneumonia. We compared safety and efficacy outcomes from this trial among patients with and without renal impairment (RI).

Methods

Patients were stratified by age and diagnosis and were randomized 1:1 to intravenous (IV) C/T 3 g every 8 h or IV MEM 1 g every 8 h. Study drug was administered for 8–14 days; doses were adjusted for moderate and severe RI. Eligible patients were mechanically ventilated; those on renal replacement therapy or with creatinine clearance (CrCL) < 15 mL/minute were excluded. Key efficacy endpoints included clinical cure rates at the test of cure (TOC) visit in the intent-to-treat (ITT) and clinically evaluable (CE) populations and Day 28 all-cause mortality (ACM) in the ITT population. In this analysis, patients were stratified based on renal function for outcome comparisons: normal renal function (CrCL ≥ 80 mL/minute); mild RI (CrCL > 50 to < 80 mL/minute); moderate RI (CrCL ≥ 30 to ≤ 50 mL/minute); and severe RI (CrCL ≥ 15 to < 30 mL/minute).

Results

A total of 726 patients were enrolled (C/T, N = 362; MEM, N = 364). Clinical cure rates at the TOC visit (CE and ITT populations) were robust across CrCL subgroups in both treatment arms and were similar based on 95% confidence intervals for treatment differences that included 0 (table). Day 28 ACM rates for patients with moderate and severe RI were numerically higher than those with mild RI in the MEM treatment arm. Rates of treatment-emergent adverse events (TEAEs) were similar in both treatment arms and across CrCL subgroups, with rates generally increasing with increasing RI severity. Rates of treatment-related TEAEs were low across treatment arms and CrCL subgroups with no treatment-related deaths reported.

Conclusion

Similar clinical cure and Day 28 ACM rates at the TOC visit were found across treatment groups for all CrCL subgroups, consistent with the overall primary and key secondary efficacy results for the ASPECT-NP study. Both drugs were well-tolerated. The results of this analysis indicate that the use of dose-adjusted C/T is appropriate in patients with nosocomial pneumonia and moderate or severe RI.

Disclosures

All authors: No reported disclosures.

624. Molecular Characterization of Baseline Enterobacteriaceae and Pseudomonas aeruginosa from a Phase 3 Nosocomial Pneumonia (ASPECT-NP) Clinical Trial

Background

ASPECT-NP, a phase 3, randomized, double-blind, multicenter trial, evaluated ceftolozane/tazobactam (C/T) 3 g q8h vs. meropenem 1 g q8h for 8–14 days in adults for treatment of ventilated nosocomial pneumonia. Baseline Gram-negative (GN) isolates from patients were tested for mechanisms of resistance.

Methods

Lower respiratory tract (LRT) isolates were sent to a central laboratory for organism identification and susceptibility. Of 664 total Enterobacteriaceae (ENT) and Pseudomonas aeruginosa (PsA) isolates, 351 (53%) were nonsusceptible to broad-spectrum cephalosporins and/or carbapenems and underwent whole-genome sequencing, quantitative RT–PCR, and western blot analysis. ENT isolates were tested for the presence of acquired β-lactamase genes and AmpC levels (selected species). PsA isolates were tested for acquired β-lactamase genes, AmpC (PDC) levels, efflux pump expression, and OprD loss.

Results

Of 262 ENT isolates, 114 (44%) were susceptible to C/T (MIC ≤2 µg/mL). An extended-spectrum β-lactamase (ESBL) gene was carried by 89 (78%) of the C/T-susceptible isolates. Of 148 C/T-nonsusceptible (C/T-NS) isolates, 87 (59%) were carbapenemase negative, and the majority 135 (91%) also carried an ESBL gene. The most common ESBL was bla_CTX-M15 with bla_OXA-1 and bla_OXA-30. Klebsiella pneumoniae often displayed higher C/T MICs compared with other species carrying the same resistance genes. Among all C/T-NS isolates, 61 (41%) were carbapenemase positive, most commonly K. pneumoniae carrying bla_OXA-48, bla_NDM-1, and bla_NDM-5. Of 89 PsA isolates, 58 (65%) were susceptible to C/T (MIC ≤4 µg/mL), despite elevated AmpC expression, efflux pumps, or loss of OprD; only 5 isolates had an acquired β-lactamase. Of the 31 C/T-NS PsA isolates, only 12 (39%) were carbapenemase positive and carried bla_VIM or bla_GES; isolates carrying bla_GES had lower C/T MICs (8–32 µg/mL) compared with bla_VIM (MIC > 128 µg/mL). PDC alleles were similar in isolates with high and low C/T MICs.

Conclusion

In baseline GN LRT isolates from ASPECT-NP, the most common ESBL detected in ENT was bla_CTX-M15; carbapenemases were uncommon. There was no correlation of ESBL phenotype to C/T susceptibility among ENT, nor of PDC allele to C/T susceptibility among PsA.

Disclosures

All authors: No reported disclosures.

2226. Impact of Prior and Concomitant Antibacterial Therapy on Outcomes in the ASPECT-NP Randomized, Controlled Trial of Ceftolozane/Tazobactam (C/T) vs. Meropenem (MEM) in Patients with Ventilated Nosocomial Pneumonia (NP)

Background

NP is a frequent healthcare-acquired infection associated with high mortality; rising resistance rates among causative Gram-negative pathogens require new treatment options. In the randomized, controlled, double-blind, phase 3 ASPECT-NP trial, C/T (at double the initially approved dose) was noninferior to MEM for ventilated NP in both primary and key secondary endpoints. Here we evaluate the impact of prior and concomitant Gram-negative antibacterial therapy on outcomes in that trial.

Methods

Mechanically ventilated patients with ventilator-associated or hospital-acquired pneumonia were randomized 1:1 to 3 g C/T or 1 g MEM, both by 1-h IV infusion every 8 hours for 8–14 days. Patients could receive ≤24 hours of active antibacterial therapy within ≤72 hours prior to first dose; longer durations were permitted in case of prior treatment failure (i.e., signs and/or symptoms of the current episode of ventilated NP persisted/worsened despite ≥48 hours of treatment). At sites with MEM-resistant Pseudomonas aeruginosa rates ≥15%, patients could optionally receive up to 72 h of adjunctive empiric aminoglycoside (amikacin was recommended) until study drug susceptibility was confirmed. Primary and key secondary endpoints, respectively, were 28-d all-cause mortality and clinical response at test of cure (TOC; 7–14 days after the end of therapy) in the intent to treat (ITT) population (all randomized patients).

Results

In the C/T arm, 285/362 (79%) ITT patients received prior systemic Gram-negative therapy and 103/362 (28%) received adjunctive aminoglycoside, compared with 288/364 (79%) and 112/364 (31%) patients, respectively, in the MEM arm. In the microbiologic ITT population, causative pathogens in patients failing prior therapy at the time of enrollment (C/T 15%, MEM 11%) were mainly Klebsiella spp (33%), P. aeruginosa (17%), Escherichia coli (14%), and Acinetobacter baumannii (8%). Mortality and cure rates were comparable between C/T and MEM regardless of receipt of prior systemic or adjunctive Gram-negative therapy (table).

Conclusion

Prior and adjunctive Gram-negative antibacterial therapy did not affect the relative efficacy of C/T (at the 3-g dose) vs. MEM in these high-risk patients with Gram-negative ventilated NP.

Disclosures

All authors: No reported disclosures.

Influence of rate of inclusion of microalgae on the sensory characteristics and fatty acid composition of cheese and performance of dairy cows

Modification of milk and cheese fat to contain long-chain n-3 fatty acids (FA) by feeding microalgae (ALG) to dairy cows has the potential to improve human health, but the subsequent effect on the sensory attributes of dairy products is unclear. The objective was to determine the effect of feeding dairy cows different amounts of ALG that was rich in docosahexaenoic acid (DHA) on milk and cheese FA profile, cheese sensory attributes, and cow performance. Twenty Holstein dairy cows were randomly allocated to 1 of 4 dietary treatments in a 4 × 4 row and column design, with 4 periods of 28 d, with cheddar cheese production and animal performance measurements undertaken during the final 7 d of each period. Cows were fed a basal diet that was supplemented with ALG (Schizochytrium limancinum) at 4 rates: 0 (control, C), 50 (LA), 100 (MA), or 150 g (HA) of ALG per cow per day. We found that both milk and cheese fat content of DHA increased linearly with ALG feed rate and was 0.29 g/100 g FA higher in milk and cheese from cows fed HA compared with C. Supplementation with ALG linearly reduced the content of saturated FA and the ratio of n-6:n-3 FA in milk and cheese. Supplementation with ALG altered 20 out of the 32 sensory attributes, with a linear increase in cheese air holes, nutty flavor, and dry mouth aftertaste with ALG inclusion. Creaminess of cheese decreased with ALG inclusion rate and was positively correlated with saturated FA content. We also observed a quadratic effect on fruity odor, which was highest in cheese from cows fed HA and lowest in LA, and firmness and crumbliness texture, being highest in MA and lowest in HA. Supplementation with ALG had no effect on the dry matter intake, milk yield, or live weight change of the cows, with mean values of 23.1, 38.5, and 0.34 kg/d respectively, but milk fat content decreased linearly, and energy-corrected milk yield tended to decrease linearly with rate of ALG inclusion (mean values of 39.6, 38.4, 37.1, and 35.9 g/kg, and 41.3, 41.3, 40.5, and 39.4 kg/d for C, LA, MA, and HA, respectively). We conclude that feeding ALG to high-yielding dairy cows improved milk and cheese content of DHA and altered cheese taste but not cow performance, although milk fat content reduced as inclusion rate increased.

Ceftolozane-tazobactam versus meropenem for treatment of nosocomial pneumonia (ASPECT-NP): a randomised, controlled, double-blind, phase 3, non-inferiority trial

BACKGROUND

Nosocomial pneumonia due to antimicrobial-resistant pathogens is associated with high mortality. We assessed the efficacy and safety of the combination antibacterial drug ceftolozane-tazobactam versus meropenem for treatment of Gram-negative nosocomial pneumonia.

METHODS

We conducted a randomised, controlled, double-blind, non-inferiority trial at 263 hospitals in 34 countries. Eligible patients were aged 18 years or older, were undergoing mechanical ventilation, and had nosocomial pneumonia (either ventilator-associated pneumonia or ventilated hospital-acquired pneumonia). Patients were randomly assigned (1:1) with block randomisation (block size four), stratified by type of nosocomial pneumonia and age (<65 years vs ≥65 years), to receive either 3 g ceftolozane-tazobactam or 1 g meropenem intravenously every 8 h for 8-14 days. The primary endpoint was 28-day all-cause mortality (at a 10% non-inferiority margin). The key secondary endpoint was clinical response at the test-of-cure visit (7-14 days after the end of therapy; 12·5% non-inferiority margin). Both endpoints were assessed in the intention-to-treat population. Investigators, study staff, patients, and patients' representatives were masked to treatment assignment. Safety was assessed in all randomly assigned patients who received study treatment. This trial was registered with ClinicalTrials.gov, NCT02070757.

FINDINGS

Between Jan 16, 2015, and April 27, 2018, 726 patients were enrolled and randomly assigned, 362 to the ceftolozane-tazobactam group and 364 to the meropenem group. Overall, 519 (71%) patients had ventilator-associated pneumonia, 239 (33%) had Acute Physiology and Chronic Health Evaluation II scores of at least 20, and 668 (92%) were in the intensive care unit. At 28 days, 87 (24·0%) patients in the ceftolozane-tazobactam group and 92 (25·3%) in the meropenem group had died (weighted treatment difference 1·1% [95% CI -5·1 to 7·4]). At the test-of-cure visit 197 (54%) patients in the ceftolozane-tazobactam group and 194 (53%) in the meropenem group were clinically cured (weighted treatment difference 1·1% [95% CI -6·2 to 8·3]). Ceftolozane-tazobactam was thus non-inferior to meropenem in terms of both 28-day all-cause mortality and clinical cure at test of cure. Treatment-related adverse events occurred in 38 (11%) of 361 patients in the ceftolozane-tazobactam group and 27 (8%) of 359 in the meropenem group. Eight (2%) patients in the ceftolozane-tazobactam group and two (1%) in the meropenem group had serious treatment-related adverse events. There were no treatment-related deaths.

INTERPRETATION

High-dose ceftolozane-tazobactam is an efficacious and well tolerated treatment for Gram-negative nosocomial pneumonia in mechanically ventilated patients, a high-risk, critically ill population.

FUNDING

Merck & Co.

Safety, Tolerability, and Pharmacokinetics of 3 g of Ceftolozane/Tazobactam in Healthy Adults: A Randomized, Placebo-Controlled, Multiple-Dose Study

Ceftolozane/tazobactam is an antibacterial approved at 1.5 g (1g/0.5 g) every 8 hours (q8h); higher doses may provide additional benefits in difficult-to-treat infections. We conducted a phase I trial in healthy adults evaluating safety, tolerability, and pharmacokinetics of 3 g (2 g/1 g) ceftolozane/tazobactam administered q8h for 10 days. Sixteen participants were randomized (2:1:1) to 3 g ceftolozane/tazobactam, 1.5 g ceftolozane/tazobactam, or placebo. Participants underwent regular safety and plasma drug level assessments, with a follow-up safety visit 7 days after completion. No adverse events (AEs) were reported with placebo; 75% of participants in the 1.5-g and 50% in the 3-g arm experienced AEs. AE types were similar between the ceftolozane/tazobactam groups; all AEs were mild. No participants experienced clinically meaningful laboratory assessment or electrocardiogram abnormalities. Both ceftolozane and tazobactam exhibited dose-proportional pharmacokinetics without accumulation and without substantial differences in clearance and volume of distribution between groups. In the 3-g group, mean ceftolozane parameters were: peak concentration 104 μg/mL (day 1), 112 μg/mL (day 10); half-life 3 hours (day 10); area under the concentration-time curve (AUC_(0-t) ) 272 μg·h/mL (day 1), 300μg·h/mL (day 10). Mean tazobactam parameters were: peak concentration 28 μg/mL (day 1), 26 μg/mL (day 10); half-life 1 hour (day 10); AUC_(0-t) 47μg·h/mL (day 1), 41μg·h/mL (day 10). Administration of 3 g ceftolozane/tazobactam q8h for 10 days was safe and well tolerated in healthy volunteers.

Analysis of patients with diabetes and complicated intra-abdominal infection or complicated urinary tract infection in phase 3 trials of ceftolozane/tazobactam

Background

Diabetes mellitus and hyperglycemia are associated with increased susceptibility to bacterial infections and poor treatment outcomes. This post hoc evaluation of the treatment of complicated intra-abdominal infections (cIAI) and complicated urinary tract infections (cUTI) aimed to evaluate baseline characteristics, efficacy, and safety in patients with and without diabetes treated with ceftolozane/tazobactam and comparators. Ceftolozane/tazobactam is an antibacterial with potent activity against Gram-negative pathogens and is approved for the treatment of cIAI (with metronidazole) and cUTI (including pyelonephritis).

Methods

Patients from the phase 3 ASPECT studies with (n = 245) and without (n = 1802) diabetes were compared to evaluate the baseline characteristics, efficacy, and safety of ceftolozane/tazobactam and active comparators.

Results

Significantly more patients with than without diabetes were 65 years of age or older; patients with diabetes were also more likely to weigh ≥75 kg at baseline (57.1% vs 44.5%), to have renal impairment (48.5% vs 30.2%), or to have APACHE II scores ≥10 (33.8% vs 17.0%). More patients with diabetes had comorbidities and an increased incidence of complicating factors in both cIAI and cUTI. Clinical cIAI and composite cure cUTI rates across study treatments were lower in patients with than without diabetes (cIAI, 75.4% vs 86.1%, P = 0.0196; cUTI, 62.4% vs 74.7%, P = 0.1299) but were generally similar between the ceftolozane/tazobactam and active comparator treatment groups. However, significantly higher composite cure rates were reported with ceftolozane/tazobactam than with levofloxacin in patients without diabetes with cUTI (79.5% vs 69.9%; P = 0.0048). Significantly higher rates of adverse events observed in patients with diabetes were likely due to comorbidities because treatment-related adverse events were similar between groups.

Conclusions

In this post hoc analysis, patients with diabetes in general were older, heavier, and had a greater number of complicating comorbidities. Patients with diabetes had lower cure rates and a significantly higher frequency of adverse events than patients without diabetes, likely because of the higher rates of medical complications in this subgroup. Ceftolozane/tazobactam was shown to be at least as effective as comparators in treating cUTI and cIAI in this population.

Trial registration

cIAI, NCT01445665 and NCT01445678 (both trials registered prospectively on September 26, 2011); cUTI, NCT01345929 and NCT01345955 (both trials registered prospectively on April 28, 2011).

Efficacy of ceftolozane/tazobactam versus levofloxacin in the treatment of complicated urinary tract infections (cUTIs) caused by levofloxacin-resistant pathogens: results from the ASPECT-cUTI trial

OBJECTIVES

Empirical fluoroquinolone therapy is widely used in treating complicated urinary tract infections (cUTIs), even in areas of high fluoroquinolone resistance. While it is believed that high antibiotic concentrations in urine might be sufficient to overcome and effectively treat infections caused by resistant bacteria, clinical trial data validating this assumption are limited. This post hoc analysis evaluated the efficacy of ceftolozane/tazobactam versus levofloxacin in the subgroup of patients with cUTIs caused by levofloxacin-resistant pathogens in a randomized, controlled trial (NCT01345929/NCT01345955).

METHODS

Hospitalized adults with cUTI/pyelonephritis were randomized to 7 days of 1.5 g of ceftolozane/tazobactam every 8 h or 750 mg of levofloxacin once daily, before availability of culture and susceptibility data. A composite of microbiological eradication and clinical cure 5 to 9 days post-therapy was assessed in the microbiological modified ITT (mMITT; n = 800) and microbiologically evaluable (ME; n = 694) populations.

RESULTS

In the mMITT population, there were 212 patients (26.5%) with at least one baseline uropathogen that was resistant to levofloxacin. The majority of uropathogens in this subgroup were Enterobacteriaceae (n = 186) that were susceptible to ceftolozane/tazobactam [MIC ≤2 mg/L, 88.7% (165/186)]. Among patients with levofloxacin-resistant pathogens, ceftolozane/tazobactam demonstrated significantly higher composite cure rates than levofloxacin in both the mMITT [60.0% (60/100) versus 39.3% (44/112); 95% CI for the treatment difference, 7.2%-33.2%] and ME [64.0% (57/89) versus 43.4% (43/99); 95% CI for the treatment difference, 6.3%-33.7%] populations, respectively.

CONCLUSIONS

High urinary levels of levofloxacin did not reliably cure cUTIs. Seven day treatment with ceftolozane/tazobactam was more effective than high-dose levofloxacin treatment in patients with cUTI caused by levofloxacin-resistant bacteria, and it may be an alternative treatment in settings of increased fluoroquinolone resistance.

Discovery and characterization of an antibody directed against exosite I of thrombin

ESSENTIALS: An IgA paraprotein with anti-thrombin activity was not associated with a severe bleeding phenotype. This observation challenges the paradigm that anticoagulant therapy necessarily increases bleeding risk. Characterization of the antibody showed that it specifically binds to thrombin exosite I. A therapeutic drug with the properties of this antibody might be an antithrombotic that doesn't cause bleeding.

BACKGROUND

We report the case of a 54-year-old female who presented with a traumatic subdural hemorrhage. Coagulation tests were markedly prolonged due to the presence of an anti-thrombin IgA paraprotein at 3 g L(-1) . The patient made a complete recovery and has had no abnormal bleeding during a 7-year follow-up, despite the persistence of the paraprotein.

OBJECTIVES

To determine how the paraprotein prolonged clotting tests by defining its target and its epitope.

METHODS

The paraprotein was purified and added to normal pooled plasma for in vitro clotting assays. Binding studies were conducted to determine the affinity of the IgA for thrombin. The Fab was isolated and crystallized with thrombin.

RESULTS

The purified IgA was sufficient to confer the patient's in vitro coagulation profile in normal pooled plasma, and was found to bind specifically and with high affinity to thrombin. A crystal structure of the Fab fragment in complex with thrombin revealed an exosite I interaction involving CDRH3 of the antibody.

CONCLUSIONS

Although the patient originally presented with a subdural bleed, the hematoma resolved without intervention, and no other bleeding event occurred during the subsequent 7 years. During this period, the patient's IgA paraprotein levels have remained constant at 3 g L(-1) , suggesting that the presence of a high-affinity, exosite I-directed antibody is consistent with normal hemostasis. A therapeutic derivative of this antibody might therefore permit antithrombotic dose escalation without an associated increase in the risk of bleeding.

Ceftolozane/tazobactam pharmacokinetic/pharmacodynamic-derived dose justification for phase 3 studies in patients with nosocomial pneumonia

Ceftolozane/tazobactam is an antipseudomonal antibacterial approved for the treatment of complicated urinary tract infections (cUTIs) and complicated intra‐abdominal infections (cIAIs) and in phase 3 clinical development for treatment of nosocomial pneumonia. A population pharmacokinetic (PK) model with the plasma‐to‐epithelial lining fluid (ELF) kinetics of ceftolozane/tazobactam was used to justify dosing regimens for patients with nosocomial pneumonia in phase 3 studies. Monte Carlo simulations were performed to determine ceftolozane/tazobactam dosing regimens with a >90% probability of target attainment (PTA) for a range of pharmacokinetic/pharmacodynamic targets at relevant minimum inhibitory concentrations (MICs) for key pathogens in nosocomial pneumonia. With a plasma‐to‐ELF penetration ratio of approximately 50%, as observed from an ELF PK study, a doubling of the current dose regimens for different renal functions that are approved for cUTIs and cIAIs is needed to achieve >90% PTA for nosocomial pneumonia. For example, a 3‐g dose of ceftolozane/tazobactam for nosocomial pneumonia patients with normal renal function is needed to achieve a >90% PTA (actual 98%) for the 1‐log kill target against pathogens with an MIC of ≤8 mg/L in ELF, compared with the 1.5‐g dose approved for cIAIs and cUTIs.

Thrombin inhibition by the serpins

Thrombin is the central protease in the blood coagulation network. It has multiple substrates and cofactors, and it appears that four serpins are responsible for inhibiting the thrombin produced in haemostasis and thrombosis. Structural studies conducted over the last 10 years have resolved how thrombin recognises these serpins with the aid of cofactors. Although antithrombin (AT), protein C inhibitor (PCI), heparin cofactor II (HCII) and protease nexin-1 (PN1) all share a common fold and mechanism of protease inhibition, they have evolved radically different mechanisms for cofactor-assisted thrombin recognition. This is likely to be due to the varied environments in which thrombin is found. In this review, I discuss the unusual structural features of thrombin that are involved in substrate and cofactor recognition, the serpin mechanism of protease inhibition and the fate of thrombin in the complex, and how the four thrombin-specific serpins exploit the special features of thrombin to accelerate complex formation.

Type II antithrombin deficiency caused by a large in-frame insertion: structural, functional and pathological relevance

BACKGROUND

The metastable native conformation of serpins is required for their protease inhibition mechanism, but also renders them vulnerable to missense mutations that promote protein misfolding with pathological consequences.

OBJECTIVE

To characterize the first antithrombin deficiency caused by a large in-frame insertion.

PATIENTS/METHODS

Functional, biochemical and molecular analysis of the proband and relatives was performed. Recombinant antithrombin was expressed in HEK-EBNA cells. Plasma and recombinant antithrombins were purified and sequenced by Edman degradation. The stability was evaluated by calorimetry. Reactive centre loop (RCL) exposure was determined by thrombin cleavage. Mutant antithrombin was crystallized as a dimer with latent plasma antithrombin.

RESULTS

The patient, with a spontaneous pulmonary embolism, belongs to a family with significant thrombotic history. We identified a complex heterozygous in-frame insertion of 24 bp in SERPINC1, affecting strand 3 of β-sheet A, a region highly conserved in serpins. Surprisingly, the insertion resulted in a type II antithrombin deficiency with heparin binding defect. The mutant antithrombin, with a molecular weight of 59 kDa, had a proteolytic cleavage at W49 but maintained the N-terminal disulphide bonds, and was conformationally sensitive. The variant was non-inhibitory. Analysis of the crystal structure of the hyperstable recombinant protein showed that the inserted sequence annealed into β-sheet A as the fourth strand, and maintained a native RCL.

CONCLUSIONS

This is the first case of a large in frame-insertion that allows correct folding, glycosylation, and secretion of a serpin, resulting in a conformationally sensitive non-inhibitory variant, which acquires a hyperstable conformation with a native RCL.

Intrapulmonary penetration of ceftolozane/tazobactam and piperacillin/tazobactam in healthy adult subjects

OBJECTIVES

Appropriate antibiotic exposure at the site of infection is important for clinically effective therapy. This study compared the epithelial lining fluid (ELF) penetration of ceftolozane/tazobactam, which has potent in vitro activity against many Gram-negative pathogens causing nosocomial pneumonia, with that of piperacillin/tazobactam in healthy adult volunteers.

METHODS

In this Phase 1, open-label trial, 51 healthy adult subjects were randomized to receive three doses of either ceftolozane/tazobactam 1.5 g administered every 8 h via a 60 min infusion or piperacillin/tazobactam 4.5 g administered every 6 h via a 30 min infusion. Serial blood samples were obtained for determination of plasma drug concentrations. Bronchoscopy and bronchoalveolar lavage were performed at pre-specified timepoints in five subjects per timepoint in each treatment group to determine the ELF drug concentration. The penetration of individual analytes into the ELF was determined from the ratio of the area under the plasma concentration-time curve in ELF to that in plasma (AUC(ELF)/AUC(plasma)).

RESULTS

Plasma and ELF concentrations of ceftolozane, piperacillin and tazobactam increased rapidly, reaching maximal concentrations at the end of the infusion. Mean maximum concentration and AUC from time 0 to the end of the dosing interval (AUC(0-τ)) for ceftolozane in ELF were 21.8 mg/L and 75.1 mg·h/L, respectively. Corresponding values for piperacillin were 58.8 mg/L and 94.5 mg·h/L. The ELF/plasma AUC ratio for ceftolozane was 0.48 compared with 0.26 for piperacillin.

CONCLUSION

This study demonstrated that ceftolozane penetrated well into the ELF following parenteral administration of ceftolozane/tazobactam.

Daptomycin therapy for osteomyelitis: a retrospective study

BACKGROUND

Daptomycin is a rapidly bactericidal agent with broad coverage against Gram-positive organisms, including Staphylococcus aureus, the most frequent cause of osteomyelitis. The objective of this study was to describe the clinical outcome of patients with non-hardware associated osteomyelitis, and the safety profile of daptomycin in the treatment of these infections.

METHODS

All patients with osteomyelitis, excluding concurrent orthopedic foreign body infections, treated with daptomycin and identified between 2007-2008 in a retrospective, multicenter, observational registry, were included. Investigators assessed patient outcome (cured, improved, failed, non-evaluable) at the end of daptomycin therapy. Patients with a successful outcome at the end of daptomycin therapy were reassessed in 2009. All patients were included in the safety analysis; evaluable patients were included in the efficacy analysis. Data was assessed using descriptive statistics. A Kaplan Meier analysis was used to assess time to clinical failure.

RESULTS

Two-hundred and nine osteomyelitis patients successfully completed daptomycin therapy in 2007-2008, 71 of which (34%) had a follow-up visit in 2009 and had an evaluable clinical outcome. The median (min, max) daptomycin dose and duration were 6 mg/kg (4, 10) and 42 days (1, 88), respectively. Of the 52 patients with a documented pathogen, S. aureus was the most common (42%); primarily methicillin-resistant S. aureus. All patients were included in the safety analysis; evaluable patients were included in the efficacy analysis. Clinical resolution was reported in 94% (CI - 86.2%, 98.44%) of patients. A Kaplan Meier analysis of time to clinical failure showed that approximately 85% (CI - 64%, 95%) of patients had a continued successful outcome at the time of re-evaluation. Eighteen patients (25%) in the safety population experienced an adverse event; 13 patients (18%) had an adverse event that was possibly-related to daptomycin treatment.

CONCLUSIONS

Daptomycin appears to be an effective therapeutic choice with an acceptable safety profile in the management of osteomyelitis that does not involve hardware.

Serpin structure, function and dysfunction

Serpins have been studied as a distinct protein superfamily since the early 80s. In spite of the poor sequence homology between family members, serpins share a highly conserved core structure that is critical for their functioning as serine protease inhibitors. Therefore, discoveries made about one serpin can be related to the others. In this short review, I introduce the serpin structure and general mechanism of protease inhibition, and illustrate, using recent crystallographic and biochemical data on antithrombin (AT), how serpin activity can be modulated by cofactors. The ability of the serpins to undergo conformational change is critical for their function, but it also renders them uniquely susceptible to mutations that perturb their folding, leading to deficiency and disease. A recent crystal structure of an AT dimer revealed that serpins can participate in large-scale domain-swaps to form stable polymers, and that such a mechanism may explain the accumulation of misfolded serpins within secretory cells. Serpins play important roles in haemostasis and fibrinolysis, and although each will have some elements specifically tailored for its individual function, the mechanisms described here provide a general conceptual framework.

Molecular basis of thrombomodulin activation of slow thrombin

BACKGROUND

Coagulation is a highly regulated process where the ability to prevent blood loss after injury is balanced against the maintenance of blood fluidity. Thrombin is at the center of this balancing act. It is the critical enzyme for producing and stabilizing a clot, but when complexed with thrombomodulin (TM) it is converted to a powerful anticoagulant. Another cofactor that may play a role in determining thrombin function is the monovalent cation Na(+). Its apparent affinity suggests that half of the thrombin generated is in a Na(+)-free 'slow' state and half is in a Na(+)-coordinated 'fast' state. While slow thrombin is a poor procoagulant enzyme, when complexed to TM it is an effective anticoagulant.

METHODS

To better understand this molecular transformation we solved a 2.4 A structure of thrombin complexed with EGF domains 4-6 of TM in the absence of Na(+) and other cofactors or inhibitors.

RESULTS

We find that TM binds as previously observed, and that the thrombin component resembles structures of the fast form. The Na(+) binding loop is observed in a conformation identical to the Na(+)-bound form, with conserved water molecules compensating for the missing ion. Using the fluorescent probe p-aminobenzamidine we show that activation of slow thrombin by TM principally involves the opening of the primary specificity pocket.

CONCLUSIONS

These data show that TM binding alters the conformation of thrombin in a similar manner as Na(+) coordination, resulting in an ordering of the Na(+) binding loop and an opening of the adjacent S1 pocket. We conclude that other, more subtle subsite changes are unlikely to influence thrombin specificity toward macromolecular substrates.

Slow thrombin is zymogen-like

Blood coagulation is the result of a cascade of zymogen activation events; however, its initiation is allosteric. Factor VIIa circulates in a zymogen-like state and is allosterically activated by binding to tissue factor. Thrombin, the final protease generated in the blood coagulation cascade, has also been shown to exist in a low activity state in the absence of cofactors, and the structural features of this 'slow' form have been studied for many years. In this manuscript, I will review the general features that render zymogens inactive and how proteolytic cleavage results in activation, but I will also show how this distinction is blurred by zymogens that have activity (protease-like zymogens) and proteases with low activity (zymogen-like proteases). This will then be applied in the analysis of slow thrombin to reveal how allosteric activation of thrombin simply reflects the conversion from a zymogen-like enzyme to an active serine protease.

Immunologic and structural analysis of eight novel domain-deletion beta3 integrin peptides designed for detection of HPA-1 antibodies

BACKGROUND

The single-nucleotide polymorphism (SNP) rs5918 in the ITGB3 gene defines the human platelet antigen-1 (HPA-1) system encoding a Leu (HPA-1a) or Pro (HPA-1b) at position 33. HPA-1 antibodies are clinically the most relevant in the Caucasoid population, but detection currently requires alpha(IIb)beta3 integrin from the platelets of HPA-genotyped donors.

OBJECTIVES

We set out to define the beta3 integrin domains required for HPA-1a antibody binding and produce recombinant soluble beta3 peptides for HPA-1 antibody detection.

METHODS

We designed two sets (1a and 1b) of four soluble beta3 domain-deletion peptides (deltaSDL, deltabetaA, PSIHybrid, PSI), informed by crystallography studies and computer modeling. The footprints of three human HPA-1a-specific phage antibodies were defined by analyzing binding patterns to the beta3 peptides and canine platelets, and models of antibody-antigen interfaces were derived. Specificity and sensitivity for HPA-1a detection were assessed using sera from 140 cases of fetomaternal alloimmune thrombocytopenia (FMAIT).

RESULTS

Fusion of recombinant proteins to calmodulin resulted in high-level expression in Drosophila S2 cells of all eight beta3 peptides. Testing of FMAIT samples indicated that deltabetaA-Leu33 is the superior peptide for HPA-1a antibody detection, with 96% sensitivity and 95% specificity. The existence of type I and II categories of HPA-1a antibodies was confirmed by the study of HPA-1a phage antibody footprints and the reactivity pattern of clinical samples with the four beta3-Leu33 peptides, but there was no correlation between antibody category and clinical severity of FMAIT.

CONCLUSIONS

Soluble recombinant beta3 peptides can be used for detection of clinical HPA-1a antibodies.

Immunologic and structural analysis of eight novel domain-deletion beta3 integrin peptides designed for detection of HPA-1 antibodies

BACKGROUND

The single-nucleotide polymorphism (SNP) rs5918 in the ITGB3 gene defines the human platelet antigen-1 (HPA-1) system encoding a Leu (HPA-1a) or Pro (HPA-1b) at position 33. HPA-1 antibodies are clinically the most relevant in the Caucasoid population, but detection currently requires alpha(IIb)beta3 integrin from the platelets of HPA-genotyped donors.

OBJECTIVES

We set out to define the beta3 integrin domains required for HPA-1a antibody binding and produce recombinant soluble beta3 peptides for HPA-1 antibody detection.

METHODS

We designed two sets (1a and 1b) of four soluble beta3 domain-deletion peptides (deltaSDL, deltabetaA, PSIHybrid, PSI), informed by crystallography studies and computer modeling. The footprints of three human HPA-1a-specific phage antibodies were defined by analyzing binding patterns to the beta3 peptides and canine platelets, and models of antibody-antigen interfaces were derived. Specificity and sensitivity for HPA-1a detection were assessed using sera from 140 cases of fetomaternal alloimmune thrombocytopenia (FMAIT).

RESULTS

Fusion of recombinant proteins to calmodulin resulted in high-level expression in Drosophila S2 cells of all eight beta3 peptides. Testing of FMAIT samples indicated that deltabetaA-Leu33 is the superior peptide for HPA-1a antibody detection, with 96% sensitivity and 95% specificity. The existence of type I and II categories of HPA-1a antibodies was confirmed by the study of HPA-1a phage antibody footprints and the reactivity pattern of clinical samples with the four beta3-Leu33 peptides, but there was no correlation between antibody category and clinical severity of FMAIT.

CONCLUSIONS

Soluble recombinant beta3 peptides can be used for detection of clinical HPA-1a antibodies.

Serpins in thrombosis, hemostasis and fibrinolysis

Hemostasis and fibrinolysis, the biological processes that maintain proper blood flow, are the consequence of a complex series of cascading enzymatic reactions. Serine proteases involved in these processes are regulated by feedback loops, local cofactor molecules, and serine protease inhibitors (serpins). The delicate balance between proteolytic and inhibitory reactions in hemostasis and fibrinolysis, described by the coagulation, protein C and fibrinolytic pathways, can be disrupted, resulting in the pathological conditions of thrombosis or abnormal bleeding. Medicine capitalizes on the importance of serpins, using therapeutics to manipulate the serpin-protease reactions for the treatment and prevention of thrombosis and hemorrhage. Therefore, investigation of serpins, their cofactors, and their structure-function relationships is imperative for the development of state-of-the-art pharmaceuticals for the selective fine-tuning of hemostasis and fibrinolysis. This review describes key serpins important in the regulation of these pathways: antithrombin, heparin cofactor II, protein Z-dependent protease inhibitor, alpha(1)-protease inhibitor, protein C inhibitor, alpha(2)-antiplasmin and plasminogen activator inhibitor-1. We focus on the biological function, the important structural elements, their known non-hemostatic roles, the pathologies related to deficiencies or dysfunction, and the therapeutic roles of specific serpins.

Molecular recognition mechanisms of thrombin

Thrombin is the final protease generated in the blood coagulation cascade, and is the only factor capable of cleaving fibrinogen to create a fibrin clot. Unlike every other coagulation protease, thrombin is composed solely of its serine protease domain, so that once formed it can diffuse freely to encounter a large number of potential substrates. Thus thrombin serves many functions in hemostasis through the specific cleavage of at least a dozen substrates. The solution of the crystal structure of thrombin some 15 years ago revealed a deep active site cleft and two adjacent basic exosites, and it was clear that thrombin must utilize these unique features in recognizing its substrates. Just how this occurs is still being investigated, but recent data from thrombin mutant libraries and crystal structures combine to paint the clearest picture to date of the molecular determinants of substrate recognition by thrombin. In almost all cases, both thrombin exosites are involved, either through direct interaction with the substrate protein or through indirect interaction with a third cofactor molecule. The purpose of this article is to summarize recent biochemical and structural data in order to provide insight into the thrombin molecular recognition events at the heart of hemostasis.

Mutations in the shutter region of antithrombin result in formation of disulfide-linked dimers and severe venous thrombosis

BACKGROUND

Missense mutations causing conformational alterations in serpins can be responsible for protein deficiency associated with human diseases. However, there are few data about conformational consequences of mutations affecting antithrombin, the main hemostatic serpin.

OBJECTIVES

To investigate the conformational and clinical effect of mutations affecting the shutter region of antithrombin.

PATIENTS AND METHODS

We identified two families with significant reduction of circulating antithrombin displaying early and severe venous thrombosis, frequently associated with pregnancy or infection. Mutations were determined by standard molecular methods. Biochemical studies were performed on plasma samples. One variant (P80S) was purified by heparin-affinity chromatography and gel filtration, and evaluated by proteomic analysis. Finally, we modelled the structure of the mutant dimer.

RESULTS

We identified two missense mutations affecting the shutter region of antithrombin: P80S and G424R. Carriers of both mutations presented traces of a similar abnormal antithrombin, supporting inefficiently expressed rather than non-expressed variants. The abnormal antithrombin purified from P80S carriers is an inactive disulfide-linked dimer of mutant antithrombin whose properties are consistent with head-to-head insertion of the reactive loop.

CONCLUSIONS

Our data support the conclusion that missense mutations affecting the shutter region of serpins have specific conformational effects resulting in the formation of mutant oligomers. The consequent inefficiency of secretion explains the accompanying deficiency and loss of function, but the severity of thrombosis associated with these mutations suggests that the oligomers also have new and undefined pathological properties that could be exacerbated by pregnancy or infection.

Mechanisms of glycosaminoglycan activation of the serpins in hemostasis

Serpins are the predominant protease inhibitors in the higher organisms and are responsible, in humans, for the control of many highly regulated processes including blood coagulation and fibrinolysis. The serpin inhibitory mechanism has recently been revealed by the solution of a crystallographic structure of the final serpin-protease complex. The serpin mechanism, in contrast to the classical lock-and-key mechanism, involves dramatic conformational change in both the inhibitor and the inhibited protein. The final result is a stable covalent complex in which the properties of each component are altered so as to allow clearance from the circulation. Several serpins are involved in hemostasis: antithrombin (AT) inhibits many coagulation proteases, most importantly factor Xa and thrombin; heparin cofactor II (HCII) inhibits thrombin; protein C inhibitor (PCI) inhibits activated protein C and thrombin bound to thrombomodulin; plasminogen activator inhibitor 1 inhibits tissue plasminogen activator; and alpha2-antiplasmin inhibits plasmin. Nearly all of these reactions are accelerated through interactions with glycosaminoglycans (GAGs) such as heparin or heparan sulfate. Recent structures of AT, HCII and PCI have revealed how in each case the serpin mechanism has been fine-tuned by evolution to bring about high levels of regulatory control, and how seemingly disparate mechanisms of GAG binding and activation can share critical elements. By considering the serpins involved in hemostasis together it is possible to develop a deeper understanding of their complex individual roles.

NTF2 monomer-dimer equilibrium

Nuclear transport factor 2 (NTF2) mediates nuclear import of RanGDP, a central component of many nuclear trafficking pathways. NTF2 is a homodimer and each chain has independent binding sites for RanGDP and nuclear pore proteins (nucleoporins) that contain FxFG sequence repeats. We show here that the monomer-dimer dissociation constant for NTF2 obtained by sedimentation equilibrium ultracentrifugation is in the micromolar range, indicating that a substantial proportion of cellular NTF2 may be monomeric. To investigate the functional significance of NTF2 dimerization, we engineered a series of point mutations at the dimerization interface and one of these (M118E) remained monomeric below concentrations of 150 microM. CD spectra and X-ray crystallography showed that M118E-NTF2 preserved the wild-type NTF2 fold, although its thermal stability was 20 deg. C lower than that of the wild-type. M118E-NTF2 bound both RanGDP and FxFG nucleoporins less strongly, suggesting that dissociation of the NTF2 dimer could facilitate RanGDP release and thus nucleotide exchange after it had been transported into the nucleus. Moreover, colloidal gold coated with M118E-NTF2 showed reduced binding to Xenopus oocyte nuclear pores. Overall, our results indicate that dimer formation is important for NTF2 function and give insight into the formation of heterodimers by mRNA export factors such as TAP1 and NXT1 that contain NTF2-homology domains.

The serpin inhibitory mechanism is critically dependent on the length of the reactive center loop

The recent crystallographic structure of a serpin-protease complex revealed that protease inactivation results from a disruption of the catalytic site architecture caused by the displacement of the catalytic serine. We hypothesize that inhibition depends on the length of the N-terminal portion of the reactive center loop, to which the active serine is covalently attached. To test this, alpha(1)-antitrypsin Pittsburgh variants were prepared with lengthened and shortened reactive center loops. The rates of inhibition of factor Xa and of complex dissociation were measured. The addition of one residue reduced the stability of the complex more than 200,000-fold, and the addition of two residues reduced it by more than 1,000,000-fold, whereas the deletion of one or two residues lowered the efficiency of inhibition and increased the stability of the complex (2-fold). The deletion of more than two residues completely converted the serpin into a substrate. Similar results were obtained for the alpha(1)-antitrypsin variants with thrombin and for PAI-1 and PAI-2 with their common target tissue plasminogen activator. We conclude that the length of the serpin reactive center loop is critical for its mechanism of inhibition and is precisely regulated to balance the efficiency of inhibition and stability of the final complex.

The conformational basis of thrombosis

Antithrombin readily undergoes a spontaneous transition from its active five-stranded form to a six-stranded inactive latent form. The recognition of this change in plasma has been obscured by the immediate linkage of newly formed latent antithrombin to a molecule of active antithrombin to give a dimer with an electrophoretic mobility readily confused with that of native active antithrombin. A new micromethod now allows unequivocal identification of latent antithrombin in whole plasma. This shows that at 37 degrees C some 10% of plasma antithrombin is converted to the latent form in 24 h. The rate of conversion is greatly accelerated at increased temperatures, as occurs in the pasteurisation of plasma concentrates that should now be checked for efficacy. But increased transition also occurs in the plasma at the slightly increased temperatures that accompany incidental infections. This is of particular significance if there is a conformationally unstable variant of antithrombin; here fever can provoke a sudden transition with the onset of a characteristically severe episode of thromboembolism. Such variants are not rare and include those previously classified as pleiotropic. The precise structural pathway, now known with antithrombin, provides a model of the changes occurring in other conformational diseases, including Alzheimer's and the prion dementias.

Structure and properties of ovalbumin

Ovalbumin is a protein of unknown function found in large quantities in avian egg-white. Surprisingly, ovalbumin belongs to the serpin family although it lacks any protease inhibitory activity. We review here what is known about the amino acid sequence, post-translational modifications and tertiary structure of ovalbumin. The properties of ovalbumin are discussed in relation to their possible functional significance. These include reasons for failure of ovalbumin to undergo a typical serpin conformational change involving the reactive centre loop, which explains why ovalbumin is not a protease inhibitor, and also the natural conversion of ovalbumin to the more stable "S" form.

The serpins: nature's molecular mousetraps

A special family of inhibitors, known as the serpins, has evolved an extraordinary mechanism to enable the control of the proteolytic pathways essential to life. The serpins undergo a profound change in conformation to entrap their target protease in an irreversible complex. The solving of the structure of this complex now completes a video depiction of the changes involved. The serpin, just like a mousetrap, is seen to change with a spring-like movement from an initial metastable state to a final hyperstable form. The structure shows how this conformational shift not only inhibits the protease but also destroys it. A bonus from these structural insights is the realisation that a number of diseases, as diverse as thrombosis, cirrhosis and dementia, all share a common mechanism arising from similar mutations of different serpins.

Structure of a serpin-protease complex shows inhibition by deformation

The serpins have evolved to be the predominant family of serine-protease inhibitors in man. Their unique mechanism of inhibition involves a profound change in conformation, although the nature and significance of this change has been controversial. Here we report the crystallographic structure of a typical serpin-protease complex and show the mechanism of inhibition. The conformational change is initiated by reaction of the active serine of the protease with the reactive centre of the serpin. This cleaves the reactive centre, which then moves 71 A to the opposite pole of the serpin, taking the tethered protease with it. The tight linkage of the two molecules and resulting overlap of their structures does not affect the hyperstable serpin, but causes a surprising 37% loss of structure in the protease. This is induced by the plucking of the serine from its active site, together with breakage of interactions formed during zymogen activation. The disruption of the catalytic site prevents the release of the protease from the complex, and the structural disorder allows its proteolytic destruction. It is this ability of the conformational mechanism to crush as well as inhibit proteases that provides the serpins with their selective advantage.

The conformational activation of antithrombin. A 2.85-A structure of a fluorescein derivative reveals an electrostatic link between the hinge and heparin binding regions

Antithrombin is unique among the serpins in that it circulates in a native conformation that is kinetically inactive toward its target proteinase, factor Xa. Activation occurs upon binding of a specific pentasaccharide sequence found in heparin that results in a rearrangement of the reactive center loop removing constraints on the active center P1 residue. We determined the crystal structure of an activated antithrombin variant, N135Q S380C-fluorescein (P14-fluorescein), in order to see how full activation is achieved in the absence of heparin and how the structural effects of the substitution in the hinge region are translated to the heparin binding region. The crystal structure resembles native antithrombin except in the hinge and heparin binding regions. The absence of global conformational change allows for identification of specific interactions, centered on Glu(381) (P13), that are responsible for maintenance of the solution equilibrium between the native and activated forms and establishes the existence of an electrostatic link between the hinge region and the heparin binding region. A revised model for the mechanism of the allosteric activation of antithrombin is proposed.

The effect of a reducing-end extension on pentasaccharide binding by antithrombin

Antithrombin requires heparin for efficient inhibition of the final two proteinases of the blood coagulation cascade, factor Xa and thrombin. Antithrombin binds heparin via a specific pentasaccharide domain in a two-step mechanism whereby initial weak binding is followed by a conformational change and subsequent tight binding. The goal of this study is to investigate the role of a reducing-end extension in the binding of the longer oligosaccharides that contain the cognate pentasaccharide sequence. We determined the antithrombin binding properties of a synthetic heptasaccharide containing the natural pentasaccharide sequence (DEFGH) and an additional reducing-end disaccharide (DEFGHG'H'). Binding at low ionic strength is unaffected by the disaccharide addition, but at ionic strengths >/=0.2 the mode of heptasaccharide binding changes resulting in a 2-fold increase in affinity due to a decrease in the off-rate caused by a greater nonionic contribution to binding. Molecular modeling of possible binding modes for the heptasaccharide at high ionic strength indicates a possible shift in position of the pentasaccharide domain to occupy the extended heparin-binding site. This conclusion supports the likely presence of a range of sequences that can bind to and activate antithrombin in the natural heparan sulfates that line the vascular endothelium.

Formation of the antithrombin heterodimer in vivo and the onset of thrombosis

Antithrombin is shown to undergo a slow spontaneous conversion to its inactive latent conformation with readily discernible amounts present in plasma on incubation at 37 degrees C for 72 hours. More rapid conversion occurs on incubation of isolated antithrombin at 41 degrees C or 50 degrees C, but the appearance on electrophoresis of free latent antithrombin is preceded by the formation, in reciprocal proportions, of a new slow band. This slow component is shown to be a heterodimer of active and latent antithrombin. It can be isolated as a single stable band either by incubation of antithrombin or by mixing equimolar proportions of active and latent antithrombin under the same conditions that give overnight crystallization of the active/latent antithrombin heterodimer. Similarly, equimolar addition of latent antithrombin to plasma results electrophoretically in a quantitative shift to the slower heterodimer mobility. Clinically, the presence of latent antithrombin is potentially deleterious, because its linkage to form the heterodimer results in inactivation of the otherwise normal molecule linked to the latent antithrombin. In the case of alpha-antithrombin, because the dimer readily dissociates, there is only a 11% additive loss of activity, but with beta-antithrombin the dimer appears more stable, with the additive loss of activity from the normal beta component being 21%, increasing to 33% on stabilization of the dimer with heparin. This linked and selective loss of activity of beta-antithrombin provides an explanation for the unexpected severity of thrombotic episodes in heterozygotes with conformationally unstable antithrombins.

A 2.6 A structure of a serpin polymer and implications for conformational disease

The function of the serpins as proteinase inhibitors depends on their ability to insert the cleaved reactive centre loop as the fourth strand in the main A beta-sheet of the molecule upon proteolytic attack at the reactive centre, P1-P1'. This mechanism is vulnerable to mutations which result in inappropriate intra- or intermolecular loop insertion in the absence of cleavage. Intermolecular loop insertion is known as serpin polymerisation and results in a variety of diseases, most notably liver cirrhosis resulting from mutations of the prototypical serpin alpha1-antitrypsin. We present here the 2.6 A structure of a polymer of alpha1-antitrypsin cleaved six residues N-terminal to the reactive centre, P7-P6 (Phe352-Leu353). After self insertion of P14 to P7, intermolecular linkage is affected by insertion of the P6-P3 residues of one molecule into the partially occupied beta-sheet A of another. This results in an infinite, linear polymer which propagates in the crystal along a 2-fold screw axis. These findings provide a framework for understanding the uncleaved alpha1-antitrypsin polymer and fibrillar and amyloid deposition of proteins seen in other conformational diseases, with the ordered array of polymers in the crystal resulting from slow accretion of the cleaved serpin over the period of a year.