Cheryl Li

Comparative gene expression profiles of ABC transporters in brain microvessel endothelial cells and brain in five species including human

While P-glycoprotein (PGP, ABCB1) is known to play an important role in drug exclusion at the blood brain barrier (BBB), less is known about the contribution of other members in the ATP-binding cassette (ABC) transporter family to BBB drug efflux, or whether these transporters are expressed differently in humans and in mammalian species of pharmacological interest. We used quantitative real-time PCR to determine mRNA expression levels for the majority of ABC family members in brain and in isolated brain microvessel endothelial capillary cells (BMEC) from human, rat, mouse, pig and cow. We confirmed BBB expression of several well-characterized ABC family members that are implicated in xenobiotic exclusion from the brain, including ABCB1 (PGP), ABCG2 (BCRP), ABCC1 (MRP1), ABCC4 (MRP4), and ABCC5 (MRP5). In addition, we detected high expression and enrichment in BMEC of several less well-characterized ABC transporters in one or more species, including ABCA2-4, ABCB4, ABCB6-8, ABCB10, ABCC3, ABCC6, ABCC10, and ABCE1. We also uncovered species differences in the expression of a number of transporters, including ABCG2 and ABCC4. This study identifies several additional ABC family members that may contribute to xenobiotic efflux at the human BBB, and compares the expression of a broad array of efflux transporters between human and four other species relevant to pharmacological research.

How Modeling and Simulation Have Enhanced Decision Making in New Drug Development

The idea of model-based drug development championed by Lewis Sheiner, in which pharmacostatistical models of drug efficacy and safety are developed from preclinical and available clinical data, offers a quantitative approach to improving drug development and development decision-making. Examples are presented that support this paradigm. The first example describes a preclinical model of behavioral activity to predict potency and time-course of response in humans and assess the potential for differentiation between compounds. This example illustrates how modeling procedures expounded by Lewis Sheiner provided the means to differentiate potency and the lag time between drug exposure and response and allow for rapid decision making and dose selection. The second example involves planning a Phase 2a dose-ranging and proof of concept trial in Alzheimer’s disease (AD). The issue was how to proceed with the study and what criteria to use for a go/no go decision. The combined knowledge of AD disease progression, and preclinical and clinical information about the drug were used to simulate various clinical trial scenarios to identify an efficient and effective Phase 2 study. A design was selected and carried out resulting in a number of important learning experiences as well as extensive financial savings. The motivation for this case in point was the “Learn-Confirm” paradigm described by Lewis Sheiner. The final example describes the use of Pharmacokinetic and Pharmacodynamic (PK/PD) modeling and simulation to confirm efficacy across doses. In the New Drug Application for gabapentin, data from two adequate and well-controlled clinical trials was submitted to the Food and Drug Administration (FDA) in support of the approval of the indication for the treatment of post-herpetic neuralgia. The clinical trial data was not replicated for each of the sought dose levels in the drug application presenting a regulatory dilemma. Exposure response analysis submitted in the New Drug Application was applied to confirm the evidence of efficacy across these dose levels. Modeling and simulation analyses showed that the two studies corroborate each other with respect to the pain relief profiles. The use of PK/PD information confirmed evidence of efficacy across the three studied doses, eliminating the need for additional clinical trials and thus supporting the approval of the product. It can be speculated that the work by Lewis Sheiner reflected in the FDA document titled “Innovation or Stagnation: Challenge and Opportunity on the Critical Path to New Medical Products” made this scientific approach to the drug approval process possible.

Modulation of NMDA receptor function by inhibition of d-amino acid oxidase in rodent brain

Observations that N-Methyl-D-Aspartate (NMDA) antagonists produce symptoms in humans that are similar to those seen in schizophrenia have led to the current hypothesis that schizophrenia might result from NMDA receptor hypofunction. Inhibition of D-amino acid oxidase (DAAO), the enzyme responsible for degradation of D-serine, should lead to increased levels of this co-agonist at the NMDA receptor, and thereby provide a therapeutic approach to schizophrenia. We have profiled some of the preclinical biochemical, electrophysiological, and behavioral consequences of administering potent and selective inhibitors of DAAO to rodents to begin to test this hypothesis. Inhibition of DAAO activity resulted in a significant dose and time dependent increase in D-serine only in the cerebellum, although a time delay was observed between peak plasma or brain drug concentration and cerebellum D-serine response. Pharmacokinetic/pharmacodynamic (PK/PD) modeling employing a mechanism-based indirect response model was used to characterize the correlation between free brain drug concentration and D-serine accumulation. DAAO inhibitors had little or no activity in rodent models considered predictive for antipsychotic activity. The inhibitors did, however, affect cortical activity in the Mescaline-Induced Scratching model, produced a modest but significant increase in NMDA receptor-mediated synaptic currents in primary neuronal cultures from rat hippocampus, and resulted in a significant increase in evoked hippocampal theta rhythm, an in vivo electrophysiological model of hippocampal activity. These findings demonstrate that although DAAO inhibition did not cause a measurable increase in D-serine in forebrain, it did affect hippocampal and cortical activity, possibly through augmentation of NMDA receptor-mediated currents.

Pharmacokinetic-Pharmacodynamic Modeling of the D2 and 5-HT2A Receptor Occupancy of Risperidone and Paliperidone in Rats

ABSTRACTPurposeA pharmacokinetic-pharmacodynamic (PK-PD) model was developed to describe the time course of brain concentration and dopamine D2 and serotonin 5-HT2A receptor occupancy (RO) of the atypical antipsychotic drugs risperidone and paliperidone in rats.MethodsA population approach was utilized to describe the PK-PD of risperidone and paliperidone using plasma and brain concentrations and D2 and 5-HT2A RO data. A previously published physiology- and mechanism-based (PBPKPD) model describing brain concentrations and D2 receptor binding in the striatum was expanded to include metabolite kinetics, active efflux from brain, and binding to 5-HT2A receptors in the frontal cortex.ResultsA two-compartment model best fit to the plasma PK profile of risperidone and paliperidone. The expanded PBPKPD model described brain concentrations and D2 and 5-HT2A RO well. Inclusion of binding to 5-HT2A receptors was necessary to describe observed brain-to-plasma ratios accurately. Simulations showed that receptor affinity strongly influences brain-to-plasma ratio pattern.ConclusionBinding to both D2 and 5-HT2A receptors influences brain distribution of risperidone and paliperidone. This may stem from their high affinity for D2 and 5-HT2A receptors. Receptor affinities and brain-to-plasma ratios may need to be considered before choosing the best PK-PD model for centrally active drugs.

Efficacy and safety of an interleukin 6 monoclonal antibody for the treatment of systemic lupus erythematosus: a phase II dose-ranging randomised controlled trial

Objectives This phase II trial evaluated the efficacy and safety of an interleukin (IL) 6 monoclonal antibody for systemic lupus erythematosus (SLE). Methods Patients with active disease were randomised to placebo or PF-04236921 10 mg, 50 mg or 200 mg, subcutaneously, every 8 weeks with stable background therapy. SLE Responder Index (SRI-4; primary end point) and British Isles Lupus Assessment Group-based Composite Lupus Assessment (BICLA) were assessed at week 24. Post hoc analysis identified an enriched population based upon planned univariate analyses. Results 183 patients received treatment (placebo, n=45; 10 mg, n=45; 50 mg, n=47; 200 mg, n=46). The 200 mg dose was discontinued due to safety findings and not included in the primary efficacy analysis. The SRI-4 response rates were not significant for any dose compared with placebo; however, the BICLA response rate was significant for 10 mg (p=0.026). The incidence of severe flares was significantly reduced with 10 mg (n=0) and 50 mg (n=2) combined versus placebo (n=8; p<0.01). In patients with greater baseline disease activity (enriched population), the SRI-4 (p=0.004) and BICLA (p=0.012) response rates were significantly different with 10 mg versus placebo. Four deaths (200 mg, n=3; 10 mg, n=1) occurred. The most frequently reported adverse events included headache, nausea and diarrhoea. Conclusions PF-04236921 was not significantly different from placebo for the primary efficacy end point in patients with SLE. Evidence of an effect with 10 mg was seen in a post hoc analysis. Safety was acceptable for doses up to 50 mg as the 200 mg dose was discontinued due to safety findings. Trial registration number NCT01405196; Pre-results.

Identification and SAR around N-{2-[4-(2,3-dihydro-benzo[1,4]dioxin-2-ylmethyl)-[1,4]diazepan-1-yl]-ethyl}-2-phenoxy-nicotinamide, a selective α2C adrenergic receptor antagonist

The discovery of the CNS-penetrant and selective alpha(2C) adrenergic receptor antagonist N-{2-[4-(2,3-dihydro-benzo[1,4]dioxin-2-ylmethyl)-[1,4]diazepan-1-yl]-ethyl}-2-phenoxy-nicotinamide, 13 is described. Structure-activity studies demonstrate the structural requirements for binding affinity, functional activity, and selectivity over other alpha(2)-AR subtypes.

Randomised trial and open-label extension study of an anti-interleukin-6 antibody in Crohn's disease (ANDANTE I and II)

Objective Neutralising pro-inflammatory interleukin-6 (IL-6) may effectively treat Crohn’s disease (CD). Effects of PF-04236921, an anti-IL-6 antibody, in adults with CD are reported. Design Parallel-group, dose-ranging, double-blind trial with 4-week screening and 12-week treatment periods. After induction, patients entered 28-week follow-up or 48-week open-label extension (OLE) with 28-week follow-up. Adults with confirmed CD and inadequate response to anti-tumour necrosis factor (TNF) therapy were included. Induction study: 249 patients randomised 1:1:1:1 to placebo, PF-04236921 10, 50 or 200 mg by subcutaneous injection on days 1 and 28. OLE study: PF-04236921 50 mg every 8 weeks up to six doses followed by 28-week follow-up. Results 247 patients were randomised and received treatment in the induction study. The 200 mg dose was discontinued due to safety findings in another study (NCT01405196) and was not included in the primary efficacy analysis. Crohn’s Disease Activity Index (CDAI)-70 response rates with PF-04236921 50 mg were significantly greater than placebo at weeks 8 (49.3% vs 30.6%, P<0.05) and 12 (47.4% vs 28.6%, P<0.05) and met the primary end point. Week 12 CDAI remission rates with PF-04236921 50 mg and placebo were 27.4% and 10.9%, respectively (16.5% difference; P<0.05). 191 subjects received treatment in the OLE. Common treatment-emergent and serious adverse events in both studies included worsening CD, abdominal pain and nasopharyngitis. Conclusions PF-04236921 50 mg induced clinical response and remission in refractory patients with moderate-to-severe CD following failure of anti-TNF therapy. GI abscess and perforation were observed, a specific focus of attention during future clinical development. Trial registration number NCT01287897 and NCT01345318.

Mechanism-Based Pharmacokinetic/Pharmacodynamic Modeling of Rat Prefrontal Cortical Dopamine Response to Dual Acting Norepinephrine Reuptake Inhibitor and 5-HT1A Partial Agonist

Evidence suggests that compounds possessing both norepinephrine reuptake inhibition and 5-HT1A partial agonism (NRI/5-HT1A) activities may have a greater efficacy in treating neuropsychiatric disorders than compounds possessing either activity alone. The objectives of the present study were first to characterize the pharmacokinetic/pharmacodynamic (PK/PD) relationship of the plasma concentrations of atomoxetine (NRI) and buspirone (5-HT1A partial agonist), administered alone and in combination, on the prefrontal cortex dopamine levels in rats, and second to use the model developed to characterize the PK/PD relationship of novel NRI/5-HT1A compounds, PF-04269339 and PF-03529936, in a NRI/5-HT1A drug discovery program. Maximal dopamine elevation was twofold higher after administration of atomoxetine and buspirone in combination, PF-04269339, or PF-03529936 than after administration of atomoxetine or buspirone alone. A mechanism-based extended indirect response model characterized the time profiles of the prefrontal cortex dopamine response to atomoxetine and buspirone, administered alone or in combination. After fixing three mechanism-specific pharmacodynamic parameters (Imax and γ2 for NRI and γ1 for 5-HT1A) based on the model for atomoxetine and/or buspirone, the model fitted the exposure–response profiles of PF-04269339 and PF-03529936 well. Good in vitro-to-in vivo correlation was demonstrated with the compound-specific pharmacodynamic parameters (IC50 for NRI and SC50 and Smax for 5-HT1A) across the compounds. In summary, a piecewise modeling approach was used successfully for the characterization of the PK/PD relationship of novel NRI/5-HT1A compounds on prefrontal cortex dopamine levels in rats. The application and value of the mechanism-based modeling in the dual pharmacology drug discovery program are also discussed.

OP0185 Significant Clinical Improvement and Reduction of Severe Flares Following Administration of an IL-6 Monoclonal Antibody in Systemic Lupus Erythematosus (SLE) Subjects with High Disease Activity

Background PF-04236921 is a fully human monoclonal antibody (mAb) that binds to circulating IL-6 and neutralizes its activity. This may be beneficial in reducing the disease manifestations of active SLE. Objectives To assess the efficacy, safety, and tolerability of PF-04236921 in subjects with active SLE. Methods 183 subjects with active SLE (SLEDAI ≥6 and ≥1 BILAG 2004 A or ≥2 Bs) received 3 doses of PF-04236921 (10, 50, or 200mg) or placebo given subcutaneously every 8 wks. The primary endpoint was the proportion of SLE Responder Index 4 (SRI-4) responders at Wk 24 using a generalized linear mixed model. The BILAG-based Combined Lupus Assessment (BICLA), frequency of severe flares, and SF-36 were also evaluated. Results The majority of subjects were female (91.8%), mean age 40.4, with musculoskeletal and mucocutaneous organ system involvement. Baseline demographics were similar across groups. At Wk 24, there were more responders in the 10mg group vs placebo for the SRI (p=0.076) and BICLA (p=0.026). Improvement in the SF-36 PCS domain was also noted for the 10mg group vs placebo (p=0.092). For the 50mg group there were no significant differences vs placebo for the SRI (p=0.528) or BICLA (p=0.1). A post-hoc subgroup analysis was completed in subjects with high baseline disease activity [SLEDAI ≥10, detectable anti-dsDNA, low complement, or prednisone >7.5 mg/day (enriched population)]. In this subgroup, a significant effect size was observed for the SRI, BICLA, and SF-36 PCS domain for the 10mg group vs placebo. There was also a significant reduction in the frequency of severe SELENA-SLEDAI Flare Index (SFI) flares for the combined 10 and 50mg groups vs placebo for both the broad (p=0.004) and enriched populations (p=0.004). Adverse events (AEs), infectious AEs, and discontinuations due to AEs were comparable across groups. The rate of SAEs was highest in the placebo and 200mg groups and the rate of serious infections was highest in the 200mg group. There were 4 deaths; 3 in 200mg [cardiorespiratory arrest, urosepsis with pulmonary embolism (PE), and disseminated tuberculosis] and 1 in 10mg (suspected PE); further dosing of 200mg was subsequently terminated. Conclusions An efficacy signal was apparent in the broad population following administration of an IL-6 mAb notably with regard to severe flare reduction. Greater efficacy was observed across several key parameters for the 10mg group in the enriched population compared to the broad population. The safety profile with 10 and 50mg doses appeared acceptable for both the broad and enriched population; dosing with 200mg was terminated due to safety concerns. Disclosure of Interest J. Smolen Grant/research support from: Abbvie, Janssen, MSD, Pfizer Inc, Roche, UCB, Consultant for: Abbvie, Amgen, Astra-Zeneca, Astro, Celgene, GSK, Janssen, Eli-Lilly, Medimmune, MSD, Novartis-Sandoz, Novo-Nordisk, Pfizer Inc, Roche, Samsung, Sanofi-Aventis, UCB, S. Popa: None declared, I. Szombati: None declared, D. Wallace: None declared, M. Petri Consultant for: Pfizer Inc., P. Lipsky Consultant for: Pfizer Inc., J. Merrill Consultant for: Pfizer Inc., V. Strand Consultant for: Abbvie, Amgen, Anthera, Astra-Zeneca, Biogen Idec, Bristol-Myers Squibb, Genentech, GSK, Janssen, Merck Serono, Novartis, Pfizer Inc, Sanofi-Aventis, Takeda, UCB, P. Healey Employee of: Pfizer Inc., C. Li Employee of: Pfizer Inc., J. Christensen Employee of: Pfizer Inc., A. Diehl Employee of: Pfizer Inc., J. Beebe Employee of: Pfizer Inc., M. Vincent Employee of: Pfizer Inc., J. Wajdula Employee of: Pfizer Inc., S. Sridharan Employee of: Pfizer Inc.

Quantitative Translational Analysis of Brain Kynurenic Acid Modulation via Irreversible Kynurenine Aminotransferase II Inhibition

Kynurenic acid (KYNA) plays a significant role in maintaining normal brain function, and abnormalities in KYNA levels have been associated with various central nervous system disorders. Confirmation of its causality in human diseases requires safe and effective modulation of central KYNA levels in the clinic. The kynurenine aminotransferases (KAT) II enzyme represents an attractive target for pharmacologic modulation of central KYNA levels; however, KAT II and KYNA turnover kinetics, which could contribute to the duration of pharmacologic effect, have not been reported. In this study, the kinetics of central KYNA-lowering effect in rats and nonhuman primates (NHPs, Cynomolgus macaques) was investigated using multiple KAT II irreversible inhibitors as pharmacologic probes. Mechanistic pharmacokinetic-pharmacodynamic analysis of in vivo responses to irreversible inhibition quantitatively revealed that 1) KAT II turnover is relatively slow [16–76 hours’ half-life (t1/2)], whereas KYNA is cleared more rapidly from the brain (<1 hour t1/2) in both rats and NHPs, 2) KAT II turnover is slower in NHPs than in rats (76 hours vs. 16 hours t1/2, respectively), and 3) the percent contribution of KAT II to KYNA formation is constant (∼80%) across rats and NHPs. Additionally, modeling results enabled establishment of in vitro-in vivo correlation for both enzyme turnover rates and drug potencies. In summary, quantitative translational analysis confirmed the feasibility of central KYNA modulation in humans. Model-based analysis, where system-specific properties and drug-specific properties are mechanistically separated from in vivo responses, enabled quantitative understanding of the KAT II-KYNA pathway, as well as assisted development of promising candidates to test KYNA hypothesis in humans.