Pharmacokinetic-pharmacodynamic modelling in the early development phase of anti-psychotics: a comparison of the effects of clozapine, S 16924 and S 18327 in the EEG model in rats

Optimizing transcardial perfusion of small molecules and biologics for brain penetration and biodistribution studies in rodents

Efficiently removing blood from the brain vasculature is critical to evaluate accurately the brain penetration and biodistribution of drug candidates, especially for biologics as their blood concentrations are substantially higher than the brain concentrations. Transcardial perfusion has been used widely to remove residual blood in the brain; however, the perfusion conditions (such as the perfusion rate and time) reported in the literature are quite varied, and the performance of these methods on blood removal has not been investigated thoroughly. In this study, the effectiveness of the perfusion conditions was assessed by measuring brain hemoglobin levels. Sodium nitrite (NaNO₂ ) as an additive in the perfusate was evaluated at different concentrations. Blood removal was significantly improved with 2% NaNO₂ over a 20 min perfusion in mouse without disrupting the integrity of the blood-brain barrier (BBB). In mice, the optimized perfusion method significantly lowered the measured brain-to-plasma ratio (K_p,brain ) for monoclonal antibodies due to the removal of blood contamination and small molecules with a moderate-to-high BBB permeability and with a high brain-unbound-fraction (f_u,brain ) presumably due to flux out of the brain during perfusion. Perfusion with or without NaNO₂ clearly removed the residual blood in rat brain but with no difference observed in K_p,brain between the perfusion groups with or without 2% NaNO₂ . In conclusion, a perfusion method was successfully developed to evaluate the brain penetration of small molecules and biologics in rodents for the first time. The transcardial perfusion with 2% NaNO₂ effectively removed the residual blood in the brain and significantly improved the assessment of brain penetration of biologics. For small molecules, however, transcardial perfusion may not be performed, as small molecule compounds could be washed away from the brain by the perfusion procedure.

Dopamine D2 receptor occupancy as a predictor of catalepsy in rats: a pharmacokinetic-pharmacodynamic modeling approach

OBJECTIVES

Dopamine D2 receptor occupancy (D2RO) is the major determinant of efficacy and safety in schizophrenia drug therapy. Excessive D2RO (>80%) is known to cause catalepsy (CAT) in rats and extrapyramidal side effects (EPS) in human. The objective of this study was to use pharmacokinetic and pharmacodynamic modeling tools to relate CAT with D2RO in rats and to compare that with the relationship between D2RO and EPS in humans.

METHODS

Severity of CAT was assessed in rats at hourly intervals over a period of 8 h after antipsychotic drug treatment. An indirect response model with and without Markov elements was used to explain the relationship of D2RO and CAT.

RESULTS

Both models explained the CAT data well for olanzapine, paliperidone and risperidone. However, only the model with the Markov elements predicted the CAT severity well for clozapine and haloperidol. The relationship between CAT scores in rat and EPS scores in humans was implemented in a quantitative manner. Risk of EPS not exceeding 10% over placebo correlates with less than 86% D2RO and less than 30% probability of CAT events in rats.

CONCLUSION

A quantitative relationship between rat CAT and human EPS was elucidated and may be used in drug discovery to predict the risk of EPS in humans from D2RO and CAT scores measured in rats.

Differences between Physostigmine- and Yohimbine-induced States Are Visualized in Canonical Space Constructed from EEG during Natural Sleep-wake Cycle in Rats

Although quantitative EEG parameters, such as spectral band powers, are sensitive to centrally acting drugs in dose- and time-related manners, changes of the EEG parameters are redundant. It is desirable to reduce multiple EEG parameters to a few components that can be manageable in a real space as well as be considered as parameters representing drug effects. We calculated factor loadings from normalized values of eight relative band powers (powers of 0.5, 1.0~2.0, 2.5~4.0, 4.5~5.5, 6.0~8.0, 8.5~12.0, 12.5~24.5, and 25~49.5 Hz bands expressed as ratios of the power of 0.5-49.5 Hz band) of EEG during pre-drug periods (11:00~12:00) by factor analysis and constructed a two-dimensional canonical space (reference canonical space) by canonical correlation analysis. Eight relative band powers of EEG produced by either physostigmine or yohimbine were reduced to two canonical scores in the reference canonical space. While changes of the band powers produced by physostigmine and yohimbine were too redundant to describe the difference between two drugs, locations of two drugs in the reference canonical space represented the difference between two drug's effects on EEG. Because the distance between two locations in the canonical space (Mahalanobis distance) indicates the magnitude of difference between two different sets of EEG parameters statistically, the canonical scores and the distance may be used to quantitatively and qualitatively describe the dose-dependent and time-dependent effects and also tell similarity and dissimilarity among effects. Then, the combination of power spectral analysis and statistical analysis may help to classify actions of centrally acting drugs.

Industrialized MS-based proteomics in the search for circulating biomarkers

Proteomics is the study of the expression, structure and function of proteins under a range of cellular conditions. A rapidly evolving component of this field is clinical proteomics, which focuses on proteins involved in human disease and how they are affected by therapeutic intervention. MS is the main analytical technology for identifying and quantifying proteins whose expression is modulated across the normal to disease continuum. Applying this technology to clinical samples, however, is particularly challenging due to high biological variability in the population, a variety of disease stages, nonuniform response to therapy, multiple concomitant treatments and special requirements for handling samples from clinical trials. Given these challenges, an ‘industrialized’ approach is best suited to clinical biomarker development, with its standard operating procedures, process control and ‘chain of custody’. This review will focus, therefore, on MS-based industrialized proteomics for the discovery and verification of circulating candidate clinical protein biomarkers.

Modelling intestinal absorption of salbutamol sulphate in rats

The objective was to develop a semiphysiological population pharmacokinetic model that describes the complex salbutamol sulphate absorption in rat small intestine. In situ techniques were used to characterize the salbutamol sulphate absorption at different concentrations (range: 0.15-18 mM). Salbutamol sulphate at concentration of 0.29 mM was administered in presence of verapamil (10 and 20 mM), grapefruit juice and sodium azide (NaN3) (0.3, 3 and 6 mM). Different pharmacokinetic models were fitted to the dataset using NONMEM. Parametric and non-parametric bootstrap analyses were employed as internal model evaluation techniques. The validated model suggested instantaneous equilibrium between salbutamol sulphate concentrations in lumen and enterocyte, and the salbutamol sulphate absorption was best described by a simultaneous passive diffusion (ka = 0.636 h(-1)) and active absorption (VMax = 0.726 mM/h, Km = 0.540 mM) processes from intestinal lumen to enterocyte, together with an active capacity-limited P-gp efflux (V'max = 0.678 mM/h, K'm = 0.357 mM) from enterocyte to intestinal lumen. The extent of salbutamol sulphate absorption in rat small intestine can be improved by NaN3, grapefruit juice and verapamil.

Pharmacokinetics and tissue distribution of a new heterocyclic N-phenylpiperazine derivative (LASSBio-581) in rats

This work investigated the pharmacokinetics of a new N-phenylpiperazine derivative (LASSBio-581), active on dopaminergic system. LASSBio-581 plasma concentrations were determined in rats after bolus administration of 10mg/kg, i.v., 30 and 60 mg/kg, i.p. and p.o., by HPLC. Individual profiles were evaluated by non-compartmental and compartmental analysis using WinNonlin. Protein binding by ultrafiltration showed free fraction of 29+/-4%. The compound showed linear pharmacokinetics for the extravascular doses investigated. The oral bioavailability ( approximately 25%) was approximately half of the intra-peritoneal one ( approximately 47%). The 60 mg/kg oral dose showed an unusual profile with two peaks (1 and 6h). A two-compartment model better described all plasma profiles. The Vd (0.8+/-0.4l/kg) and the t(1/2) (1.2+/-0.4h) were smaller for i.v. than for the other routes. The CL(tot) was statistically similar for all three administration routes investigated (0.6+/-0.2l/(hkg)) (alpha=0.05). The compound distribution into different organs, evaluated in tissue homogenates after i.v. administration, showed a higher penetration in lungs (51.0%), followed by the brain (39.2%), where the half-life was three times bigger than in the other tissues (1.9h). The compound brain profile agreed with the central nervous system activity determined.

Biomarkers in drug discovery and development: from target identification through drug marketing

Biomarkers of disease play an important role in medicine and have begun to assume a greater role in drug discovery and development. The challenge for biomarkers is to allow earlier, more robust drug safety and efficacy measurements. Their role in drug development will continue to grow for the foreseeable future. For biomarkers to assume their rightful role, greater understanding of the mechanism of disease progression and therapeutic intervention is needed. In addition, greater understanding of the requirements for biomarker selection and validation, biomarker assay method validation and application, and clinical endpoint validation and application is needed. Biomarkers need to be taken into account while the therapeutic target is still being identified and the concept is being formulated. Biomarkers need to be incorporated into a continuous cycle that takes what is learned from the discovery and development of one series of biomarkers and translates it into the next series of biomarkers. Optimum biomarker development and application will require a team approach because of the multifaceted nature of biomarker selection, validation, and application, using such techniques as pharmacoepidemiology, pharmacogenetics, pharmacogenomics, and functional proteomics; bioanalytical method development and validation; disease process and therapeutic intervention assessments; and pharmacokinetic/pharmacodynamic modeling and simulation to improve and refine drug development. The potential for biomarkers in medicine and drug development will be limited by the least effective component of the processes. The team approach will minimize the potential for the least effective component to be fatal to the rest of the process. As scientific/regulatory foundations for biomarkers in medicine and drug development begin to be established, successes and applications will need to be effectively communicated with all of the stakeholders, including not only internal and external drug developers and regulators but also the medical community, to ensure that biomarkers are totally integrated into drug discovery and development as well as the practice of medicine.

Effects of phencyclidine (PCP) and MK 801 on the EEGq in the prefrontal cortex of conscious rats; antagonism by clozapine, and antagonists of AMPA-, alpha(1)- and 5-HT(2A)-receptors

1. The electroencephalographic (EEG) effects of the propsychotic agent phencyclidine (PCP), were studied in conscious rats using power spectra (0 - 30 Hz), from the prefrontal cortex or sensorimotor cortex. PCP (0.1 - 3 mg kg(-1) s.c.) caused a marked dose-dependent increase in EEG power in the frontal cortex at 1 - 3 Hz with decreases in power at higher frequencies (9 - 30 Hz). At high doses (3 mg kg(-1) s.c.) the entire spectrum shifted to more positive values, indicating an increase in cortical synchronization. MK 801 (0.05 - 0.1 mg kg(-1) i.p.) caused similar effects but with lesser changes in power. 2. In contrast, the non-competitive AMPA antagonists GYKI 52466 and GYKI 53655 increased EEG power over the whole power spectrum (1 - 10 mg kg(-1) i.p.). The atypical antipsychotic clozapine (0.2 mg kg(-1) s.c.) synchronized the EEG (peak 8 Hz). The 5-HT(2A)-antagonist, M100907, specifically increased EEG power at 2 - 3 Hz at low doses (10 and 50 microg kg(-1) s.c.), whereas at higher doses (0.1 mg kg(-1) s.c.) the profile resembled that of clozapine. 3. Clozapine (0.2 mg kg(-1) s.c. ), GYKI 53655 (5 mg kg(-1) i.p.), prazosin (0.05 and 0.1 mg kg(-1) i.p.), and M100907 (0.01 and 0.05 mg kg(-1) s.c.) antagonized the decrease in power between 5 and 30 Hz caused by PCP (1 mg kg(-1) s.c.), but not the increase in power at 1 - 3 Hz in prefrontal cortex.