Neutralizing Antibody Validation Testing and Reporting Harmonization.

Evolving immunogenicity assay performance expectations and a lack of harmonized neutralizing antibody validation testing and reporting tools have resulted in significant time spent by health authorities and sponsors on resolving filing queries. A team of experts within the American Association of Pharmaceutical Scientists' Therapeutic Product Immunogenicity Community across industry and the Food and Drug Administration addressed challenges unique to cell-based and non-cell-based neutralizing antibody assays. Harmonization of validation expectations and data reporting will facilitate filings to health authorities and are described in this manuscript. This team provides validation testing and reporting strategies and tools for the following assessments: (1) format selection; (2) cut point; (3) assay acceptance criteria; (4) control precision; (5) sensitivity including positive control selection and performance tracking; (6) negative control selection; (7) selectivity/specificity including matrix interference, hemolysis, lipemia, bilirubin, concomitant medications, and structurally similar analytes; (8) drug tolerance; (9) target tolerance; (10) sample stability; and (11) assay robustness.

Anti-drug Antibody Sample Testing and Reporting Harmonization.

A clear scientific and operational need exists for harmonized bioanalytical immunogenicity study reporting to facilitate communication of immunogenicity findings and expedient review by industry and health authorities. To address these key bioanalytical reporting gaps and provide a report structure for documenting immunogenicity results, this cross-industry group was formed to establish harmonized recommendations and a develop a submission template to facilitate agency filings. Provided here are recommendations for reporting clinical anti-drug antibody (ADA) assay results using ligand-binding assay technologies. This publication describes the essential bioanalytical report (BAR) elements such as the method, critical reagents and equipment, study samples, results, and data analysis, and provides a template for a suggested structure for the ADA BAR. This publication focuses on the content and presentation of the bioanalytical ADA sample analysis report. The interpretation of immunogenicity data, including the evaluation of the impact of ADA on safety, exposure, and efficacy, is out of scope of this publication.

Anti-drug Antibody Validation Testing and Reporting Harmonization.

Evolving immunogenicity assay performance expectations and a lack of harmonized anti-drug antibody validation testing and reporting tools have resulted in significant time spent by health authorities and sponsors on resolving filing queries. Following debate at the American Association of Pharmaceutical Sciences National Biotechnology Conference, a group was formed to address these gaps. Over the last 3 years, 44 members from 29 organizations (including 5 members from Europe and 10 members from FDA) discussed gaps in understanding immunogenicity assay requirements and have developed harmonization tools for use by industry scientists to facilitate filings to health authorities. Herein, this team provides testing and reporting strategies and tools for the following assessments: (1) pre-study validation cut point; (2) in-study cut points, including procedures for applying cut points to mixed populations; (3) system suitability control criteria for in-study plate acceptance; (4) assay sensitivity, including the selection of an appropriate low positive control; (5) specificity, including drug and target tolerance; (6) sample stability that reflects sample storage and handling conditions; (7) assay selectivity to matrix components, including hemolytic, lipemic, and disease state matrices; (8) domain specificity for multi-domain therapeutics; (9) and minimum required dilution and extraction-based sample processing for titer reporting.

Renin inhibitors for the treatment of hypertension: design and optimization of a novel series of tertiary alcohol-bearing piperidines.

The design and optimization of a novel series of renin inhibitor is described herein. Strategically, by committing the necessary resources to the development of synthetic sequences and scaffolds that were most amenable for late stage structural diversification, even as the focus of the SAR campaign moved from one end of the molecule to another, highly potent renin inhibitors could be rapidly identified and profiled.

Renin inhibitors for the treatment of hypertension: design and optimization of a novel series of pyridone-substituted piperidines.

An SAR campaign aimed at decreasing the overall lipophilicity of renin inhibitors such as 1 is described herein. It was found that replacement of the northern appendage in 1 with an N-methyl pyridone and subsequent re-optimization of the benzyl amide handle afforded compounds with in vitro and in vivo profiles suitable for further profiling. An unexpected CV toxicity in dogs observed with compound 20 led to the employment of a time and resource sparing rodent model for in vivo screening of key compounds. This culminated in the identification of compound 31 as an optimized renin inhibitor.

Characterization of a stable, hypertensive rat model suitable for the consecutive evaluation of human renin inhibitors.

INTRODUCTION: The hypertensive double-transgenic (dTG) rat strain, expressing human renin and angiotensinogen, develops severe hypertension and organ damage and 50% of individuals die by 7 weeks of age. Here, we characterise a variation of this model in which animals present stable hypertension. MATERIALS AND METHODS: The effect of renin-angiotensin system blockers on blood pressure was determined with adult dTG rats treated with enalapril from 3 to 12 weeks of age. Tissue expression levels of renin and angiotensinogen were determined in dTG rats and rhesus monkeys by quantitative PCR. RESULTS: Upon withdrawal from enalapril, mean arterial pressure (MAP) rose to 160-180 mmHg, with 95% of the female dTG rats surviving for 6 to 12 months, In Sprague-Dawley (SD) rats and rhesus monkeys, renin mRNA was absent or weakly expressed in most tissues, except for the kidneys and adrenals. In dTG rats, human renin expression was high in many additional tissues. The expression of human angiotensinogen in dTG rats followed a similar tissue pattern to SD and rhesus monkey angiotensinogen. Oral dosing of aliskiren, enalapril or losartan provided a similar maximal reduction in MAP and duration of efficacy in telemetrised dTG rats. CONCLUSIONS: Enalapril-pretreated dTG rats are suitable for long-term MAP monitoring and sequential evaluation of human renin inhibitors.

Discovery of MK-0952, a selective PDE4 inhibitor for the treatment of long-term memory loss and mild cognitive impairment.

The structure-activity relationship of a novel series of 8-biarylnaphthyridinones acting as type 4 phosphodiesterase (PDE4) inhibitors for the treatment of long-term memory loss and mild cognitive impairment is described herein. The manuscript describes a new paradigm for the development of PDE4 inhibitor targeting CNS indications. This effort led to the discovery of the clinical candidate MK-0952, an intrinsically potent inhibitor (IC(50)=0.6 nM) displaying limited whole blood activity (IC(50)=555 nM). Supporting in vivo results in two preclinical efficacy tests and one test assessing adverse effects are also reported. The comparative profiles of MK-0952 and two other Merck compounds are described to validate the proposed hypothesis.

Pharmacological and genetic evidence that cathepsin B is not the physiological activator of rodent prorenin.

Renin is the first enzyme in the renin-angiotensin-aldosterone system which is the principal regulator of blood pressure and hydroelectrolyte balance. Previous studies suggest that cathepsin B is the activator of the prorenin zymogen. Here, we show no difference in plasma renin activity, or mean arterial blood pressure between wild-type and cathepsin B knockout mice. To account for potential gene compensation, a potent, selective, reversible cathepsin B inhibitor was developed to determine the role of cathepsin B on prorenin processing in rats. Pharmacological inhibition of cathepsin B in spontaneously hypertensive and double transgenic rats did not result in a reduction in renal mature renin protein levels or plasma renin activity. We conclude that cathepsin B does not play a significant role in this process in rodents.

The discovery and synthesis of highly potent subtype selective phosphodiesterase 4D inhibitors.

The SAR study of a series of 6-aryloxymethyl-8-aryl substituted quinolines is described. Optimization of the series led to the discovery of compound 26b, a highly potent (IC50=0.6 nM) and selective PDE4D inhibitor with a 75-fold selectivity over the A, B, and C subtypes and over 18,000-fold selectivity against other PDE family members. Rat pharmacokinetics and tissue distribution are also summarized.

Alkyl-bridged substituted 8-arylquinolines as highly potent PDE IV inhibitors.

Substituted 8-arylquinoline analogs bearing alkyl-linked side chain were identified as potent inhibitors of type 4 phophodiesterase. These compounds address the potential liabilities of the clinical candidate L-454560. The pharmacokinetic profile of the best analogs and the in vivo efficacy in an ovalbumin-induced bronchoconstriction assay in conscious guinea pigs are reported.

Development of a homogeneous immunoassay for the detection of angiotensin I in plasma using AlphaLISA acceptor beads technology.

Plasma renin activity (PRA) is a well-established biomarker for assessing the efficacy of various antihypertensive agents such as direct renin inhibitors, angiotensin receptor blockers, and angiotensin-converting enzyme inhibitors (ACEIs). PRA measurements are obtained through the detection and quantification of angiotensin I (Ang I) produced by the action of renin on its natural substrate angiotensinogen. The most accepted and reproducible method for PRA measurement uses an antibody capture Ang I methodology that employs specific antibodies that recognize and protect Ang I against angiotensinase activities contained in plasma. The amount of Ang I is then quantified by either radioimmunoassay (RIA) or enzyme immunoassay (EIA). In the current report, we describe the optimization of a novel homogeneous immunoassay based on the AlphaScreen technology for the detection and quantification of antibody-captured Ang I using AlphaLISA acceptor beads in buffer and in the plasma of various species (human, rat, and mouse). Ex vivo measurements of renin activity were performed using 10 microl or less of a reaction mixture, and concentrations as low as 1 nM Ang I were quantified. Titration curves obtained for the quantification of Ang I in buffer and plasma gave similar EC(50) values of 5.6 and 14.4 nM, respectively. Both matrices generated an equivalent dynamic range that varies from approximately 1 to 50 nM. Renin inhibitors have been successfully titrated and IC(50) values obtained correlated well with those obtained using EIA methodology (r(2)=0.80). This assay is sensitive, robust, fast, and less tedious than measurements performed using nonhomogeneous EIA. The AlphaLISA methodology is homogeneous, does not require wash steps prior to the addition of reagents, and does not generate radioactive waste.

Design, synthesis, and biological evaluation of 8-biarylquinolines: a novel class of PDE4 inhibitors.

The structure-activity relationship of a novel series of 8-biarylquinolines acting as type 4 phosphodiesterase (PDE4) inhibitors is described herein. Prototypical compounds from this series are potent and non-selective inhibitors of the four distinct PDE4 (IC(50)<10 nM) isozymes (A-D). In a human whole blood in vitro assay, they inhibit (IC(50)<0.5 microM) the LPS-induced release of the cytokine TNF-alpha. Optimized inhibitors were evaluated in vivo for efficacy in an ovalbumin-induced bronchoconstriction model in conscious guinea pigs. Their propensity to produce an emetic response was evaluated by performing pharmacokinetic studies in squirrel monkeys. This work has led to the identification of several compounds with excellent in vitro and in vivo profiles, including a good therapeutic window of efficacy over emesis.

Nitrogen-bridged substituted 8-arylquinolines as potent PDE IV inhibitors.

Potent inhibitors of the human PDE IV enzyme are described. Substituted 8-arylquinoline analogs bearing nitrogen-linked side chain were identified as potent inhibitors based on the SAR described herein. The pharmacokinetic profile of the best analog and the in vivo efficacy in an ovalbumin-induced bronchoconstriction assay in conscious guinea pigs are reported.

Preferential inhibition of human phosphodiesterase 4 by ibudilast.

Ibudilast ophthalmic solution exhibited an improved clinical efficacy over cromoglycate in the treatment of allergic conjunctivitis. To further characterize its principal mode of action, the phosphodiesterase (PDE) inhibitory profile of ibudilast has been examined using human recombinant enzymes. Ibudilast, but not the other commonly used anti-allergic ophthalmic solutions including cromoglycate, ketotifen, tranilast and levocabastine, potently inhibits purified human PDE4A, 4B, 4C and 4D with IC50 values at 54, 65, 239 and 166 nM, respectively. Ibudilast effectively blocks lipopolysaccharide (LPS)-induced tumor necrosis factor (TNFalpha, IC50 = 6.2 microM) and N-formyl-Met-Leu-Phe (fMLP)-induced leukotriene (LT) B4 biosynthesis (IC50 = 2.5 microM) in human whole blood, which are 3 and 6-fold more potent than cilomilast, respectively. The attenuated inflammatory and allergic responses from the potent and preferential PDE4 inhibition of ibudilast may have contributed significantly to its beneficial pharmacological responses and distinguishes ibudilast from the other ophthalmic solutions in the treatment of ocular allergy.

Discovery of a substituted 8-arylquinoline series of PDE4 inhibitors: structure-activity relationship, optimization, and identification of a highly potent, well tolerated, PDE4 inhibitor.

The discovery and SAR of a new series of substituted 8-arylquinoline PDE4 inhibitors are herein described. This work has led to the identification of several compounds with excellent in vitro and in vivo profiles, including a good therapeutic window of emesis to efficacy in several animal models. Typical optimized compounds from this series are potent inhibitors of PDE4 (IC(50)<1nM) and also of LPS-induced TNF-alpha release in human whole blood (IC(50)<0.5microM). The same compounds are potent inhibitors of ovalbumin-induced bronchoconstriction in conscious guinea pigs (EC(50)<0.1mg/kg ip) but require a dose of about 10mg/kg po in the squirrel monkey to produce an emetic response. From this series of compounds, 23a (L-454,560) was identified as an optimized compound.

Dynamic activation of cystic fibrosis transmembrane conductance regulator by type 3 and type 4D phosphodiesterase inhibitors.

The diseases of cystic fibrosis, chronic obstructive pulmonary disease (COPD), and chronic bronchitis are characterized by mucus-congested and inflamed airways. Anti-inflammatory agents that can simultaneously restore or enhance mucociliary clearance through cystic fibrosis transmembrane conductance regulator (CFTR) activation may represent new therapeutics in their treatment. Herein, we report the activation of CFTR-mediated chloride secretion by phosphodiesterase (PDE) 4 inhibitors in T84 monolayer using (125)I anion as tracer. In the absence of forskolin, the iodide secretion was insensitive to PDE4 inhibitor L-826,141 [4-[2-(3,4-bis-difluoromethoxyphenyl)-2-[4-(1,1,1,3,3,3-hexafluoro-2-hydroxypropan-2-yl)phenyl]-ethyl]-3-methylpyridine-1-oxide], roflumilast, or to PDE3 inhibitor trequinsin. However, these inhibitors potently augmented iodide secretion after forskolin stimulation, with efficacy coupled to the activation states of adenylyl cyclase. The iodide secretion from PDE3 or PDE4 inhibition was characterized at first by a prolonged efflux duration, followed by progressively elevated peak efflux rates at higher inhibitor concentrations. Paralleled with an increased phosphor-cAMP response element-binding protein formation, the CFTR activation dissociated from a global cAMP elevation and was blocked by H89 [N-[2-((p-bromocinnamyl)amino)ethyl]-5-isoquinolinesulfonamide]. 2-(4-Fluorophenoxy)-N-[(1S)-1-(4-methoxyphenyl)ethyl]nicotinamide, a stereoselective PDE4D inhibitor, augmented iodide efflux more efficiently than its less potent (R)-isomer. The peak efflux from maximal PDE4 and PDE3 inhibition matched that from full adenylyl cyclase activation. These data suggest that PDE3 and PDE4 (mainly PDE4D) form the major cAMP diffusion barrier in T84 cells to ensure a compartmentalized CFTR signaling. Together with their potent anti-inflammatory properties, the potentially enhanced airway mucociliary clearance from CFTR activation may have contributed to the efficacy of PDE4 inhibitors in COPD and asthmatic patients. PDE4 inhibitors may represent new opportunities to combat cystic fibrosis and other respiratory diseases in future.

Deletion of phosphodiesterase 4D in mice shortens alpha(2)-adrenoceptor-mediated anesthesia, a behavioral correlate of emesis.

A combination of pharmacological and genetic approaches was used to determine the role of type 4 cAMP-specific cyclic nucleotide phosphodiesterase 4 (PDE4) in reversing alpha(2)-adrenoceptor-mediated anesthesia, a behavioral correlate of emesis in non-vomiting species. Among the family-specific PDE inhibitors, PDE4 inhibitors reduced the duration of xylazine/ketamine-induced anesthesia in mice, with no effect on pentobarbital-induced anesthesia. The rank order of the PDE4 inhibitors tested was 6-(4-pyridylmethyl)-8-(3-nitrophenyl)quinoline (PMNPQ) > (R)-rolipram > (S)-rolipram >> (R)-N-[4-[1-(3-cyclopentyloxy-4-methoxyphenyl)-2-(4-pyridyl)ethyl]phenyl]N'-ethylurea (CT-2450). The specific roles of PDE4B and PDE4D in this model were studied using mice deficient in either subtype. PDE4D-deficient mice, but not PDE4B-deficient mice, had a shorter sleeping time than their wild-type littermates under xylazine/ketamine-induced anesthesia, but not under that induced with pentobarbital. Concomitantly, rolipram-sensitive PDE activity in the brain stem was decreased only in PDE4D-deficient mice compared with their wild-type littermates. While PMNPQ significantly reduced the xylazine/ketamine-induced anesthesia period in wild-type mice and in PDE4B-null mice, it had no effect in PDE4D-deficient mice. These findings strongly support the hypothesis that inhibition of PDE4D is pivotal to the anesthesia-reversing effect of PMNPQ and is likely responsible for emesis induced by PDE4 inhibitors.

In vitro PKA phosphorylation-mediated human PDE4A4 activation.

The PDE4 catalytic machinery comprises, in part, two divalent cations in a binuclear motif. Here we report that PDE4A4 expressed in Sf9 cells exhibits a biphasic Mg(2+) dose-response (EC(50) of 0.15 and >10 mM) in catalyzing cAMP hydrolysis. In vitro phosphorylation of PDE4A4 by the PKA-catalytic subunit increases the enzyme's sensitivity to Mg(2+), leading to 4-fold increased cAMP hydrolysis without affecting its K(m). The phosphorylation also increases the potencies of (R)- and (S)-rolipram without affecting CDP-840 and SB-207499. The results support that modulating the cofactor binding affinity of PDE4 represents a mechanism for regulating its activity.