Interspecies scaling and comparisons in drug development and toxicokinetics

Impact of humanized vancomycin infusion on kidney function and kidney injury in a translational rat model

Allometric dose scaling aims to create isometric exposures between animals and humans and is often employed in preclinical pharmacokinetic/pharmacodynamic models. Bolus-administration with allometric scaling is the most simple and commonly used strategy in pre-clinical kidney injury studies; however, it is possible to humanize drug exposures. Currently, it is unknown if dose-matched, bolus-administration with allometric scaling results in similar outcomes compared to humanized infusions in the vancomycin induced kidney injury model. We utilized a preclinical Sprague-Dawley rat model to compare traditional allometrically-scaled, dose-matched, bolus-administration of vancomycin to an infusion-pump controlled, humanized infusion scheme to assess for differences in iohexol-measured kidney function and urinary kidney injury biomarkers. Following 24 h of vancomycin administration, rats in the humanized infusion group had equivalent area under the curve exposures to animals in the dose-matched bolus group (93.7 mg·h/L [IQR 90.2-97.2] vs. 99.5 mg·h/L [IQR 95.1-104.0], P = 0.07). No significant differences in iohexol-measured kidney function nor meaningful differences in urinary kidney injury biomarkers, kidney injury molecule-1, clusterin, and osteopontin, were detected. Administration of intravenous vancomycin as either a humanized infusion or dose-matched bolus resulted in similar vancomycin exposures. No differences in iohexol-measured GFR nor meaningful differences in urinary kidney injury biomarkers were observed among male Sprague-Dawley rats.

Therapeutic effect of phycocyanin on chronic obstructive pulmonary disease in mice

INTRODUCTION

The prevention and treatment of chronic obstructive pulmonary disease (COPD) is closely tied to antioxidation and anti-inflammation. Phycocyanin (PC) has numerous pharmacological effects, such as antioxidation and anti-inflammation. However, it remains unclear whether PC can play a therapeutic role in COPD.

OBJECTIVE

As inflammation and oxidative stress can aggravate COPD, this study is to explore the effect of PC on COPD mice and its mechanisms.

METHODS

The COPD mice model was established by exposing them to lipopolysaccharide (LPS) and cigarette smoke (CS); PC was administrated in a concentration of 50 mg/kg for 30 days. On the last day, lung function was measured, and bronchoalveolar lavage fluid (BALF) was obtained and classified for cells. Lung tissue pathological change was analyzed, and organ indices statistics were measured. Based on molecular docking, the mechanism was explored with Western blotting, immunohistochemical, and immunofluorescence in vivo and in vitro.

RESULTS

PC significantly ameliorated the pulmonary function of COPD mice and reduced inflammation of the lung (p < 0.05), and hematoxylin and eosin (H&E) staining showed PC depressed lung inflammatory cell accumulation and emphysema. Periodic acid Schiff (PAS) and Masson staining revealed that PC retarded goblet cells metaplasia and collagen deposition (p < 0.05). In addition, in vivo PC regulated Heme oxygenase 1 (HO-1) (p < 0.05) and NAD(P)H dehydrogenase quinone 1 (NQO1) level (p < 0.01) in the lung, as well as NOX2 level in pulmonary macrophages. Molecular docking results indicate that phycocyanobilin (PCB) in PC had a good binding site in Keap1 and NOX2 proteins; the phycocyanobilin-bound phycocyanin peptide (PCB-PC-peptide) was obtained for further studies. In vitro, PCB-PC-peptide could depress the phospho-NF-E2-related factor 2 (p-Nrf2) and NQO1 protein expression in RAW264.7 cells induced by cigarette smoke extract (CSE) (p < 0.05).

CONCLUSION

PC exerts beneficial effects on COPD via anti-inflammatory and antioxidative stress, which may be achieved through PCB.

Modelling the biodistribution of inhaled gold nanoparticles in rats with interspecies extrapolation to humans

The increasing intentional and non-intentional exposure to nanoparticles (NPs) has raised the interest concerning their fate and biodistribution in the body of animals and humans after inhalation. In this context, Physiologically Based (pharmaco)Kinetic (PBK) modelling has emerged as an in silico approach that simulates the biodistribution kinetics of NPs in the body using mathematical equations. Due to restrictions in data availability, such models are first developed for rats or mice. In this work, we present the interspecies extrapolation of a PBK model initially developed for rats, in order to estimate the biodistribution of inhaled gold NPs (AuNPs) in humans. The extrapolation framework is validated by comparing the model results with experimental data from a clinical study performed on humans for inhaled AuNPs of two different sizes, namely 34 nm and 4 nm. The novelty of this work lies in the extrapolation of a PBK model for inhaled AuNPs to humans and comparison with clinical data. The extrapolated model is in good agreement with the experimental data, and provides insights for the mechanisms of inhaled AuNP translocation to the blood circulation, after inhalation. Finally, the biodistribution of the two sizes of AuNPs in the human body after 28 days post-exposure is estimated by the model and discussed.

Novel In Vivo and In Vitro Pharmacokinetic/Pharmacodynamic-Based Human Starting Dose Selection for Glofitamab

We present a novel approach for first-in-human (FIH) dose selection of the CD20xCD3 bispecific antibody, glofitamab, based on pharmacokinetic/pharmacodynamic (PKPD) assessment in cynomolgus monkeys to select a high, safe starting dose, with cytokine release (CR) as the PD endpoint. Glofitamab pharmacokinetics were studied in mice and cynomolgus monkeys; PKPD of IL-6, TNF-α and interferon-γ release following glofitamab, with/without obinutuzumab pretreatment (Gpt) was studied in cynomolgus monkeys. Potency differences for CR between cynomolgus monkeys and humans were determined by glofitamab incubation in whole blood of both species. The PKPD model for CR was translated to humans to project a starting dose that did not induce CR exceeding a clinically-predefined threshold. In cynomolgus monkeys, glofitamab showed a species-specific atypical high clearance, with and without B-cell debulking by Gpt. CR was related to glofitamab serum levels and B-cell counts. B-cell reduction by Gpt led to a marked decrease in CR. FIH starting dose (5 µg) was selected based on IL-6 release considering the markedly higher glofitamab in vitro potency in human vs monkey blood. This is a novel PKPD-based approach for selection of FIH starting dose for a CD20xCD3 bispecific antibody in B-cell lymphoma, evidenced in the glofitamab study, NP30179 (NCT03075696).

Wide size dispersion and use of body composition and maturation improves the reliability of allometric exponent estimates

To evaluate study designs and the influence of dispersion of body size, body composition and maturation of clearance or reliable estimation of allometric exponents. Non-linear mixed effects modeling and parametric bootstrap were employed to assess how the study sample size, number of observations per subject, between subject variability (BSV) and dispersion of size distribution affected estimation bias and uncertainty of allometric exponents. The role of covariate model misspecification was investigated using a large data set ranging from neonates to adults. A decrease in study sample size, number of observations per subject, an increase in BSV and a decrease in dispersion of size distribution, increased the uncertainty of allometric exponent estimates. Studies conducted only in adults with drugs exhibiting normal (30%) BSV in clearance may need to include at least 1000 subjects to be able to distinguish between allometric exponents of 2/3 and 1. Nevertheless, studies including both children and adults can distinguish these exponents with only 100 subjects. A marked bias of 45% (95%CI 41-49%) in the estimate of the allometric exponent of clearance was obtained when maturation and body composition were ignored in infants. A wide dispersion of body size (e.g. infants, children and adults) is required to reliably estimate allometric exponents. Ignoring differences in body composition and maturation of clearance may bias the exponent for clearance. Therefore, pharmacometricians should avoid estimating allometric exponent parameters without suitable designs and covariate models. Instead, they are encouraged to rely on the well-developed theory and evidence that clearance and volume parameters in humans scale with theory-based exponents.

Challenges and Opportunities for Translation of Therapies to Improve Cognition in Down Syndrome

While preclinical studies have reported improvement of behavioral deficits in the Ts65Dn mouse model of Down syndrome (DS), translation to human clinical trials to improve cognition in individuals with DS has had a poor success record. Timing of the intervention, choice of animal models, strategy for drug selection, and lack of translational endpoints between animals and humans contributed to prior failures of human clinical trials. Here, we focus on in vitro cell models from humans with DS to identify the molecular mechanisms underlying the brain phenotype associated with DS. We emphasize the importance of using these cell models to screen for therapeutic molecules, followed by validating them in the most suitable animal models prior to initiating human clinical trials.

Interpretation of Non-Clinical Data for Prediction of Human Pharmacokinetic Parameters: In Vitro-In Vivo Extrapolation and Allometric Scaling

Extrapolation of pharmacokinetic (PK) parameters from in vitro or in vivo animal to human is one of the main tasks in the drug development process. Translational approaches provide evidence for go or no-go decision-making during drug discovery and the development process, and the prediction of human PKs prior to the first-in-human clinical trials. In vitro-in vivo extrapolation and allometric scaling are the choice of method for projection to human situations. Although these methods are useful tools for the estimation of PK parameters, it is a challenge to apply these methods since underlying biochemical, mathematical, physiological, and background knowledge of PKs are required. In addition, it is difficult to select an appropriate methodology depending on the data available. Therefore, this review covers the principles of PK parameters pertaining to the clearance, volume of distribution, elimination half-life, absorption rate constant, and prediction method from the original idea to recently developed models in order to introduce optimal models for the prediction of PK parameters.

Quantitative Prediction of Human Hepatic Clearance for P450 and Non-P450 Substrates from In Vivo Monkey Pharmacokinetics Study and In Vitro Metabolic Stability Tests Using Hepatocytes

Accurate prediction of human pharmacokinetics for drugs remains challenging, especially for non-cytochrome P450 (P450) substrates. Hepatocytes might be suitable for predicting hepatic intrinsic clearance (CL_int) of new chemical entities, because they can be applied to various compounds regardless of the metabolic enzymes. However, it was reported that hepatic CL_int is underestimated in hepatocytes. The purpose of the present study was to confirm the predictability of human hepatic clearance for P450 and non-P450 substrates in hepatocytes and the utility of animal scaling factors for the prediction using hepatocytes. CL_int values for 30 substrates of P450, UDP-glucuronosyltransferase, flavin-containing monooxygenase, esterases, reductases, and aldehyde oxidase in human microsomes, human S9 and human, rat, and monkey hepatocytes were estimated. Hepatocytes were incubated in serum of each species. Furthermore, CL_int values in human hepatocytes were corrected with empirical, monkey, and rat scaling factors. CL_int values in hepatocytes for most compounds were underestimated compared to observed values regardless of the metabolic enzyme, and the predictability was improved by using the scaling factors. The prediction using human hepatocytes corrected with monkey scaling factor showed the highest predictability for both P450 and non-P450 substrates among the predictions using liver microsomes, liver S9, and hepatocytes with or without scaling factors. CL_int values by this method for 80% and 90% of all compounds were within 2- and 3-fold of observed values, respectively. This method is accurate and useful for estimating new chemical entities, with no need to care about cofactors, localization of metabolic enzymes, or protein binding in plasma and incubation mixture.

Design and characterization of MP0250, a tri-specific anti-HGF/anti-VEGF DARPin® drug candidate

MP0250 is a multi-domain drug candidate currently being tested in clinical trials for the treatment of cancer. It comprises one anti-vascular endothelial growth factor-A (VEGF-A), one anti-hepatocyte growth factor (HGF), and two anti-human serum albumin (HSA) DARPin® domains within a single polypeptide chain. While there is first clinical validation of a single-domain DARPin® drug candidate, little is known about DARPin® drug candidates comprising multiple domains. Here, we show that MP0250 can be expressed at 15 g/L in soluble form in E. coli high cell-density fermentation, it is stable in soluble/frozen formulation for 2 years as assessed by reverse phase HPLC, it has picomolar potency in inhibiting VEGF-A and HGF in ELISA and cellular assays, and its domains are simultaneously active as shown by surface plasmon resonance. The inclusion of HSA-binding DARPin® domains leads to a favorable pharmacokinetic profile in mouse and cynomolgus monkey, with terminal half-lives of ∼ 30 hours in mouse and ∼ 5 days in cynomolgus monkey. MP0250 is thus a highly potent drug candidate that could be particularly useful in oncology. Beyond MP0250, the properties of MP0250 indicate that multi-domain DARPin® proteins can be valuable next-generation drug candidates.

Half-life extension using serum albumin-binding DARPin® domains

A long systemic half-life is key for therapeutic proteins. To that end we have generated serum albumin-binding designed ankyrin repeat domains. These domains bind serum albumin of different species with nanomolar affinities, and have significantly improved pharmacokinetic properties both in mouse and cynomolgus monkey compared to non-serum albumin-binding DARPin® domains. In addition, they exhibit high thermal stability and long storage stability, which is an essential feature for their use in drug development. Covalently linking a serum albumin-binding DARPin® domain to domains with other target specificities results in improvements of multiple orders of magnitude in exposure and terminal half-life, both in mouse and cynomolgus monkey. Pharmacokinetic assessment of such constructs revealed terminal half-life values ranging from 27 h to 80 h in mouse, and from 2.6 days to 20 days in cynomolgus monkey. Extrapolation by allometric scaling on these findings suggests terminal half-life values of 5-50 days in human, indicating that pharmacokinetic properties in the range of monoclonal antibodies can be achieved with DARPin® drug candidates. Such serum albumin-binding DARPin® domains are thus valuable tools for the generation of multi-functional drugs with an extended in vivo half-life.

Physiologically Based Pharmacokinetic (PBPK) Model for Biodistribution of Radiolabeled Peptides in Patients with Neuroendocrine Tumours

Objective(s):

The objectives of this work was to assess the benefits of the application of Physiologically Based Pharmacokinetic (PBPK) models in patients with different neuroendocrine tumours (NET) who were treated with Lu-177 DOTATATE. The model utilises clinical data on biodistribution of radiolabeled peptides (RLPs) obtained by whole body scintigraphy (WBS) of the patients.

Methods:

The blood flow restricted (perfusion rate limited) type of the PBPK model for biodistribution of radiolabeled peptides (RLPs) in individual human organs is based on the multi-compartment approach, which takes into account the main physiological processes in the organism: absorption, distribution, metabolism and excretion (ADME). The approach calibrates the PBPK model for each patient in order to increase the accuracy of the dose estimation. Datasets obtained using WBS in four patients have been used to obtain the unknown model parameters. The scintigraphic data were acquired using a double head gamma camera in patients with different neuroendocrine tumours who were treated with Lu-177 DOTATATE. The activity administered to each patient was 7400 MBq.

Results:

Satisfactory agreement of the model predictions with the data obtained from the WBS for each patient has been achieved.

Conclusion:

The study indicates that the PBPK model can be used for more accurate calculation of biodistribution and absorbed doses in patients. This approach is the first attempt of utilizing scintigraphic data in PBPK models, which was obtained during Lu-177 peptide therapy of patients with NET.

Comparative Pharmacokinetics of Racivir®, (±)-β-2′,3′-Dideoxy-5-Fluoro-3′-Thiacytidine in Rats, Rabbits, Dogs, Monkeys and HIV-Infected Humans

Racivir® is a 50:50 racemic mixture of the (–)- and (+)-β-enantiomers of 2′-deoxy-3′-thia-5-fluorocytosine (FTC), which is being developed for the treatment of HIV and hepatitis B virus (HBV). The (+)-enantiomer of FTC is approximately 10–20-fold less potent than (–)-FTC, but it selects for a different HIV mutation in human lymphocytes. Plasma concentrations from a group of 54 rats, 12 pregnant rabbits and 60 dogs enrolled in large toxicity studies using a wide variety of oral doses, were compared using non-compartment pharmacokinetic modelling versus dose, treatment duration, species and gender. The pharmacokinetics of Racivir® were also compared with those of a previously published pharmacokinetic study in rhesus monkeys and with data from HIV-infected human male volunteers. The (+)-FTC, but not the (–)-enantiomer, can be deaminated to the non-toxic inactive metabolite (+)-FTU. Therefore, the plasma exposure to (+)-FTU was also determined. The order of relative plasma exposure to (+)-FTU was rhesus monkeys > humans > pregnant rabbits > dogs > rats. Allometric scaling was performed to relate systemic clearance/fraction of drug absorbed (Cl/F) and terminal phase volume of distribution (Vβ/F) versus species body weights. No individual animal species mimicked the Cl/F values in humans. However, allometric scaling using a combination of rats, pregnant rabbits and monkeys predicted the mean human Cl/F value better than a combination of rats and rabbits only (within 0.24 and SD of mean vs 0.81 SD of the observed mean value). Similarly, human Vβ/F values were best predicted using a combination of rat and monkey data (within 0.64 SD of mean value). Species demonstrating greater deamination to (+)-FTU tended to have greater than predicted Cl/F values. The Cmax values of dogs were the closest to humans, but were statistically different. This study highlights the importance of selecting animal species that demonstrate similar cytidine deaminase activity to humans when performing preclinical dosing studies on Racivir® other antiviral agents that are substrates for mammalian cytidine deaminases.

Interspecies allometric scaling of antimalarial drugs and potential application to pediatric dosing

Pharmacopeial recommendations for administration of antimalarial drugs are the same weight-based (mg/kg of body weight) doses for children and adults. However, linear calculations are known to underestimate pediatric doses; therefore, interspecies allometric scaling data may have a role in predicting doses in children. We investigated the allometric scaling relationships of antimalarial drugs using data from pharmacokinetic studies in mammalian species. Simple allometry (Y = a × W(b)) was utilized and compared to maximum life span potential (MLP) correction. All drugs showed a strong correlation with clearance (CL) in healthy controls. Insufficient data from malaria-infected species other than humans were available for allometric scaling. The allometric exponents (b) for CL of artesunate, dihydroartemisinin (from intravenous artesunate), artemether, artemisinin, clindamycin, piperaquine, mefloquine, and quinine were 0.71, 0.85, 0.66, 0.83, 0.62, 0.96, 0.52, and 0.40, respectively. Clearance was significantly lower in malaria infection than in healthy (adult) humans for quinine (0.07 versus 0.17 liter/h/kg; P = 0.0002) and dihydroartemisinin (0.81 versus 1.11 liters/h/kg; P = 0.04; power = 0.6). Interpolation of simple allometry provided better estimates of CL for children than MLP correction, which generally underestimated CL values. Pediatric dose calculations based on simple allometric exponents were 10 to 70% higher than pharmacopeial (mg/kg) recommendations. Interpolation of interspecies allometric scaling could provide better estimates than linear scaling of adult to pediatric doses of antimalarial drugs; however, the use of a fixed exponent for CL was not supported in the present study. The variability in allometric exponents for antimalarial drugs also has implications for scaling of fixed-dose combinations.

Thymoquinone induces cell death in human squamous carcinoma cells via caspase activation-dependent apoptosis and LC3-II activation-dependent autophagy

BACKGROUND

Thymoquinone (TQ), an active component of Nigella sativa or black cumin, elicits cytotoxic effects on various cancer cell lines. However, the anti-cancer effects of TQ on head and neck squamous cell carcinoma (HNSCC) remain unclear.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, TQ elicited a strong cytotoxic effect on SASVO3, a highly malignant HNSCC cell line. The mechanisms of this cytotoxic effect were concentration dependent. TQ also induced apoptotic cell death in SASVO3 cells as indicated by an increase in Bax expression and caspase-9 activation. Apoptosis was possibly caspase-9 dependent because the exposure of cells to a caspase-9 inhibitor partially prevented cell death. The exposed cells also showed increased levels of autophagic vacuoles and LC3-II proteins, which are specific autophagy markers. Cell viability assay results further revealed that bafilomycin-A1, an autophagy inhibitor, enhanced TQ cytotoxicity; by comparison, Annexin V and propidium-iodide staining assay results showed that this inhibitor did not promote apoptosis. TQ treatment also increased the accumulation of autophagosomes. Using a lentivirus-shRNA system for LC3 silencing, we found that cell viability was eradicated in autophagy-defective cells. An in vivo BALB/c nude mouse xenograft model further showed that TQ administered by oral gavage reduced tumor growth via induced autophagy and apoptosis.

CONCLUSIONS

These findings indicated that TQ induced cell death in oral cancer cells via two distinct anti-neoplastic activities that can induce apoptosis and autophagy. Therefore, TQ is a promising candidate in phytochemical-based, mechanistic, and pathway-targeted cancer prevention strategies.

Supplementation of a high-fat diet with chlorogenic acid is associated with insulin resistance and hepatic lipid accumulation in mice

The increasing prevalence of the metabolic syndrome requires a greater need for therapeutic and prevention strategies. Higher coffee consumption is consistently associated with a lower risk of type 2 diabetes in population studies. Dietary polyphenols have been linked to benefits on several features of the metabolic syndrome. Chlorogenic acid (CGA), a major component of coffee, is one of the most consumed polyphenols in the diet. In our study, we conducted a controlled dietary intervention over 12 weeks in male mice. There were three dietary groups: (i) normal diet, (ii) high-fat diet, and (iii) high-fat diet + CGA. We assessed the effect of CGA at a physiologically obtainable dose (1 g/kg of diet) on high-fat-diet-induced obesity, glucose intolerance, insulin resistance, and also fatty acid oxidation and insulin signaling in C57BL/6 male mice. Supplementation of CGA in the high-fat diet did not reduce body weight compared to mice fed the high-fat diet alone (p = 0.32). CGA resulted in increased insulin resistance compared to mice fed a high-fat diet only (p < 0.05). CGA resulted in decreased phosphorylation of AMP-activated protein kinase (AMPK) (p < 0.001) and acetyl carboxylase β (ACCβ), a downstream target of AMPK (p < 0.05), in liver. The liver of mice fed a high-fat diet supplemented with CGA had a higher lipid content (p < 0.05) and more steatosis relative to mice fed a high-fat diet only, indicating impaired fatty acid oxidation. This study suggests that CGA supplementation in a high-fat diet does not protect against features of the metabolic syndrome in diet-induced obese mice.

Pharmacokinetics and interspecies allometric scaling of ST-246, an oral antiviral therapeutic for treatment of orthopoxvirus infection

Plasma pharmacokinetics of ST-246, smallpox therapeutic, was evaluated in mice, rabbits, monkeys and dogs following repeat oral administrations by gavage. The dog showed the lowest T_max of 0.83 h and the monkey, the highest value of 3.25 h. A 2- to 4-fold greater dose-normalized C_max was observed for the dog compared to the other species. The mouse showed the highest dose-normalized AUC, which was 2-fold greater than that for the rabbit and monkey both of which by approximation, recorded the lowest value. The Cl/F increased across species from 0.05 L/h for mouse to 42.52 L/h for dog. The mouse showed the lowest V_D/F of 0.41 L and the monkey, the highest V_D/F of 392.95 L. The calculated extraction ratios were 0.104, 0.363, 0.231 and 0.591 for mouse, rabbit, monkey and dog, respectively. The dog showed the lowest terminal half-life of 3.10 h and the monkey, the highest value of 9.94 h. The simple allometric human V_D/F and MLP-corrected Cl/F were 2311.51 L and 51.35 L/h, respectively, with calculated human extraction ratio of 0.153 and terminal half-life of 31.20 h. Overall, a species-specific difference was observed for Cl/F with this parameter increasing across species from mouse to dog. The human MLP-corrected Cl/F, terminal half-life, extraction ratios were in close proximity to the observed estimates. In addition, the first-in-humans (FIH) dose of 485 mg, determined from the MLP-corrected allometry Cl/F, was well within the dose range of 400 mg and 600 mg administered in healthy adult human volunteers.

The mastermind approach to CNS drug therapy: translational prediction of human brain distribution, target site kinetics, and therapeutic effects

Despite enormous advances in CNS research, CNS disorders remain the world's leading cause of disability. This accounts for more hospitalizations and prolonged care than almost all other diseases combined, and indicates a high unmet need for good CNS drugs and drug therapies.Following dosing, not only the chemical properties of the drug and blood-brain barrier (BBB) transport, but also many other processes will ultimately determine brain target site kinetics and consequently the CNS effects. The rate and extent of all these processes are regulated dynamically, and thus condition dependent. Therefore, heterogenious conditions such as species, gender, genetic background, tissue, age, diet, disease, drug treatment etc., result in considerable inter-individual and intra-individual variation, often encountered in CNS drug therapy.For effective therapy, drugs should access the CNS "at the right place, at the right time, and at the right concentration". To improve CNS therapies and drug development, details of inter-species and inter-condition variations are needed to enable target site pharmacokinetics and associated CNS effects to be translated between species and between disease states. Specifically, such studies need to include information about unbound drug concentrations which drive the effects. To date the only technique that can obtain unbound drug concentrations in brain is microdialysis. This (minimally) invasive technique cannot be readily applied to humans, and we need to rely on translational approaches to predict human brain distribution, target site kinetics, and therapeutic effects of CNS drugs.In this review the term "Mastermind approach" is introduced, for strategic and systematic CNS drug research using advanced preclinical experimental designs and mathematical modeling. In this way, knowledge can be obtained about the contributions and variability of individual processes on the causal path between drug dosing and CNS effect in animals that can be translated to the human situation. On the basis of a few advanced preclinical microdialysis based investigations it will be shown that the "Mastermind approach" has a high potential for the prediction of human CNS drug effects.

Therapeutic targeting of angiotensin II receptor type 1 to regulate androgen receptor in prostate cancer

BACKGROUND

With the limited strategies for curative treatment of castration-resistant prostate cancer (CRPC), public interest has focused on the potential prevention of prostate cancer. Recent studies have demonstrated that an angiotensin II receptor blocker (ARB) has the potential to decrease serum prostate-specific antigen (PSA) level and improve performance status in CRPC patients. These facts prompted us to investigate the direct effects of ARBs on prostate cancer growth and progression.

METHODS

Transgenic rat for adenocarcinoma of prostate (TRAP) model established in our laboratory was used. TRAP rats of 3 weeks of age received ARB (telmisartan or candesartan) at the concentration of 2 or 10 mg/kg/day in drinking water for 12 weeks. In vitro analyses for cell growth, ubiquitylation or reporter gene assay were performed using LNCaP cells.

RESULTS

We found that both telmisartan and candesartan attenuated prostate carcinogenesis in TRAP rats by augmentation of apoptosis resulting from activation of caspases, inactivation of p38 MAPK and down-regulation of the androgen receptor (AR). Further, microarray analysis demonstrated up-regulation of estrogen receptor β (ERβ) by ARB treatment. In both parental and androgen-independent LNCaP cells, ARB inhibited both cell growth and AR-mediated transcriptional activity. ARB also exerted a mild additional effect on AR-mediated transcriptional activation by the ERβ up-regulation. An intervention study revealed that PSA progression was prolonged in prostate cancer patients given an ARB compared with placebo control.

CONCLUSION

These data provide a new concept that ARBs are promising potential chemopreventive and chemotherapeutic agents for prostate cancer.

Prediction of a potentially effective dose in humans for BAY 60-5521, a potent inhibitor of cholesteryl ester transfer protein (CETP) by allometric species scaling and combined pharmacodynamic and physiologically-based pharmacokinetic modelling

AIMS

The purpose of this work was to support the prediction of a potentially effective dose for the CETP-inhibitor, BAY 60-5521, in humans.

METHODS

A combination of allometric scaling of the pharmacokinetics of the CETP-inhibitor BAY 60-5521 with pharmacodynamic studies in CETP-transgenic mice and in human plasma with physiologically-based pharmacokinetic (PBPK) modelling was used to support the selection of the first-in-man dose.

RESULTS

The PBPK approach predicts a greater extent of distribution for BAY 60-5521 in humans compared with the allometric scaling method as reflected by a larger predicted volume of distribution and longer elimination half-life. The combined approach led to an estimate of a potentially effective dose for BAY 60-5521 of 51 mg in humans.

CONCLUSION

The approach described in this paper supported the prediction of a potentially effective dose for the CETP-inhibitor BAY 60-5521 in humans. Confirmation of the dose estimate was obtained in a first-in-man study.

Physiologically based pharmacokinetic modeling for nanoparticle toxicity study

This chapter introduces the principles and development procedures for physiologically based pharmacokinetic (PBPK) models, and their application for nanoparticle toxicity studies. PBPK models describe the concentration-time or mass-time profiles of chemicals or nanoparticles in individual tissues and organs within the body. They have been used mostly for toxicology and pharmacology studies of small molecules, and their application for nanoparticles are in the early stages. Due to the biodistribution differences between nanoparticles and small molecules, modification may be necessary to build PBPK models for nanoparticles. PBPK models for nanoparticles may be applied to biodistribution predictions, data extrapolation, and property-biodistribution relationships, and, thus, can be a powerful tool in toxicity evaluation.

Methylenedioxymethamphetamine (MDMA, 'Ecstasy'): Neurodegeneration versus Neuromodulation

The amphetamine analogue 3,4-methylenedioxymethamphetamine (MDMA, ‘ecstasy’) is widely abused as a recreational drug due to its unique psychological effects. Of interest, MDMA causes long-lasting deficits in neurochemical and histological markers of the serotonergic neurons in the brain of different animal species. Such deficits include the decline in the activity of tryptophan hydroxylase in parallel with the loss of 5-HT and its main metabolite 5-hydoxyindoleacetic acid (5-HIAA) along with a lower binding of specific ligands to the 5-HT transporters (SERT). Of concern, reduced 5-HIAA levels in the CSF and SERT density have also been reported in human ecstasy users, what has been interpreted to reflect the loss of serotonergic fibers and terminals. The neurotoxic potential of MDMA has been questioned in recent years based on studies that failed to show the loss of the SERT protein by western blot or the lack of reactive astrogliosis after MDMA exposure. In addition, MDMA produces a long-lasting down-regulation of SERT gene expression; which, on the whole, has been used to invoke neuromodulatory mechanisms as an explanation to MDMA-induced 5-HT deficits. While decreased protein levels do not necessarily reflect neurodegeneration, the opposite is also true, that is, neuroregulatory mechanisms do not preclude the existence of 5-HT terminal degeneration.

Analytic theories of allometric scaling

During the 13 years since it was first advanced, the fractal network theory (FNT), an analytic theory of allometric scaling, has been subjected to a wide range of methodological, mathematical and empirical criticisms, not all of which have been answered satisfactorily. FNT presumes a two-variable power-law relationship between metabolic rate and body mass. This assumption has been widely accepted in the past, but a growing body of evidence during the past quarter century has raised questions about its general validity. There is now a need for alternative theories of metabolic scaling that are consistent with empirical observations over a broad range of biological applications. In this article, we briefly review the limitations of FNT, examine the evidence that the two-variable power-law assumption is invalid, and outline alternative perspectives. In particular, we discuss quantum metabolism (QM), an analytic theory based on molecular-cellular processes. QM predicts the large variations in scaling exponent that are found empirically and also predicts the temperature dependence of the proportionality constant, issues that have eluded models such as FNT that are based on macroscopic and network properties of organisms.

Preclinical prediction of human brain target site concentrations: considerations in extrapolating to the clinical setting

The development of drugs for central nervous system (CNS) disorders has encountered high failure rates. In part, this has been due to the sole focus on blood-brain barrier permeability of drugs, without taking into account all other processes that determine drug concentrations at the brain target site. This review deals with an overview of the processes that determine the drug distribution into and within the CNS, followed by a description of in vivo techniques that can be used to provide information on CNS drug distribution. A plea follows for the need for more mechanistic understanding of the mechanisms involved in brain target site distribution, and the condition-dependent contributions of these mechanisms to ultimate drug effect. As future direction, such can be achieved by performing integrative cross-compare designed studies, in which mechanisms are systematically influenced (e.g., inhibition of an efflux transporter or induction of pathological state). With the use of advanced mathematical modeling procedures, we may dissect contributions of individual mechanisms in animals as links to the human situation.

Circulation and metabolic rates in a natural hibernator: an integrative physiological model

Small hibernating mammals show regular oscillations in their heart rate and body temperature throughout the winter. Long periods of torpor are abruptly interrupted by arousals with heart rates that rapidly increase from 5 beats/min to over 400 beats/min and body temperatures that increase by ∼30°C only to drop back into the hypothermic torpid state within hours. Surgically implanted transmitters were used to obtain high-resolution electrocardiogram and body temperature data from hibernating thirteen-lined ground squirrels (Spermophilus tridecemlineatus). These data were used to construct a model of the circulatory system to gain greater understanding of these rapid and extreme changes in physiology. Our model provides estimates of metabolic rates during the torpor-arousal cycles in different model compartments that would be difficult to measure directly. In the compartment that models the more metabolically active tissues and organs (heart, brain, liver, and brown adipose tissue) the peak metabolic rate occurs at a core body temperature of 19°C approximately midway through an arousal. The peak metabolic rate of the active tissues is nine times the normothermic rate after the arousal is complete. For the overall metabolic rate in all tissues, the peak-to-resting ratio is five. This value is high for a rodent, which provides evidence for the hypothesis that the arousal from torpor is limited by the capabilities of the cardiovascular system.

Physiologically based pharmacokinetic modeling of nanoparticles

Rapid expansion of nanoparticle research demands new technologies that will enable better interpretation of experimental data and assistance in the rational design of future nanoparticles. The use of physiologically based pharmacokinetic (PBPK) models may serve as powerful tools to meet these needs. PBPK models have been successfully applied for the study of the absorption, distribution, metabolism, and excretion (ADME) of small molecules, such as drugs. Preliminary application of PBPK models to nanoparticles illustrated their potential usefulness for nanoparticle ADME research. However, due to the differences between nanoparticles and small molecules, modifications are needed to build appropriate PBPK models for nanoparticles. This review is divided into two sections, with the first discussing nanoparticle ADME research, emphasizing the interaction of nanoparticles with living systems, including transportation kinetics across biobarriers. In the second section, the basic principles of PBPK model development are introduced, and research pertaining to PBPK models of nanoparticles is reviewed. Factors that need to be considered for developing PBPK models for nanoparticles are also discussed. Finally, perspective applications of nanoparticle PBPK models are summarized.

Specific Dietary Polyphenols Attenuate Atherosclerosis in Apolipoprotein E–Knockout Mice by Alleviating Inflammation and Endothelial Dysfunction

Objective— Animal and clinical studies have suggested that polyphenols in fruits, red wine, and tea may delay the development of atherosclerosis through their antioxidant and anti-inflammatory properties. We investigated whether individual dietary polyphenols representing different polyphenolic classes, namely quercetin (flavonol), (−)-epicatechin (flavan-3-ol), theaflavin (dimeric catechin), sesamin (lignan), or chlorogenic acid (phenolic acid), reduce atherosclerotic lesion formation in the apolipoprotein E (ApoE) −/− gene–knockout mouse.

Methods and Results— Quercetin and theaflavin (64-mg/kg body mass daily) significantly attenuated atherosclerotic lesion size in the aortic sinus and thoracic aorta ( P <0.05 versus ApoE −/− control mice). Quercetin significantly reduced aortic F 2 -isoprostane, vascular superoxide, vascular leukotriene B 4 , and plasma-sP-selectin concentrations; and augmented vascular endothelial NO synthase activity, heme oxygenase-1 protein, and urinary nitrate excretion ( P <0.05 versus control ApoE −/− mice). Theaflavin showed similar, although less extensive, significant effects. Although (−)-epicatechin significantly reduced F 2 -isoprostane, superoxide, and endothelin-1 production ( P <0.05 versus control ApoE −/− mice), it had no significant effect on lesion size. Sesamin and chlorogenic acid treatments exerted no significant effects. Quercetin, but not (−)-epicatechin, significantly increased the expression of heme oxygenase-1 protein in lesions versus ApoE −/− controls.

Conclusion— Specific dietary polyphenols, in particular quercetin and theaflavin, may attenuate atherosclerosis in ApoE −/− gene–knockout mice by alleviating inflammation, improving NO bioavailability, and inducing heme oxygenase-1. These data suggest that the cardiovascular protection associated with diets rich in fruits, vegetables, and some beverages may in part be the result of flavonoids, such as quercetin.

Prediction of human pharmacokinetics—evaluation of methods for prediction of hepatic metabolic clearance

Methods for prediction of hepatic clearance (CLH) in man have been evaluated. A physiologically-based in-vitro to in-vivo (PB-IVIV) method with human unbound fraction in blood (fu,bl) and hepatocyte intrinsic clearance (CLint)-data has a good rationale and appears to give the best predictions (maximum ∼2-fold errors; &lt; 25% errors for half of CL-predictions; appropriate ranking). Inclusion of an empirical scaling factor is, however, needed, and reasons include the use of cryopreserved hepatocytes with low activity, and inappropriate CLint- and fu,bl-estimation methods. Thus, an improvement of this methodology is possible and required. Neglect of fu,bl or incorporation of incubation binding does not seem appropriate. When microsome CLint-data are used with this approach, the CLH is underpredicted by 5- to 9-fold on average, and a 106-fold underprediction (attrition potential) has been observed. The poor performance could probably be related to permeation, binding and low metabolic activity. Inclusion of scaling factors and neglect of fu,bl for basic and neutral compounds improve microsome predictions. The performance is, however, still not satisfactory. Allometry incorrectly assumes that the determinants for CLH relate to body weight and overpredicts human liver blood flow rate. Consequently, allometric methods have poor predictability. Simple allometry has an average overprediction potential, &gt; 2-fold errors for ∼1/3 of predictions, and 140-fold underprediction to 5800-fold overprediction (potential safety risk) range. In-silico methodologies are available, but these need further development. Acceptable prediction errors for compounds with low and high CLH should be ∼50 and ∼10%, respectively. In conclusion, it is recommended that PB-IVIV with human hepatocyte CLint and fu,bl is applied and improved, limits for acceptable errors are decreased, and that animal CLH-studies and allometry are avoided.

The species differences of intestinal drug absorption and first-pass metabolism between cynomolgus monkeys and humans

In order to elucidate the causes of the species differences in the oral bioavailability (BA) between cynomolgus monkeys and humans, the contributions of first-pass metabolism and intestinal absorption were investigated. Typical substrates of cytochrome P450 enzymes, UDP-glucuronosyltransferase enzymes and efflux transporters were selected, and the BA, the hepatic availability (Fh) and the fraction dose absorbed from gastro-intestinal tract (Fa*Fg) were calculated from pharmacokinetic analysis after oral and intravenous administration in cynomolgus monkeys. In addition, in vitro metabolism was investigated using liver and intestinal microsomes to evaluate the relationship between in vivo and in vitro results. The BA of cynomolgus monkeys was low compared with that in humans with most of the drugs tested, and not only Fh but also Fa*Fg contributed significantly to the low BA in cynomolgus monkeys. When Fh was evaluated in in vitro experiments, it correlated well with the in vivo Fh. However, although the metabolic activities of CYP3A4 substrates were high in cynomolgus monkey intestinal microsomes, those of the other substrates were low or not detected. These findings suggested that the species differences and low BA in cynomolgus monkeys could be mostly attributed not only to hepatic first-pass metabolism but also to the intestinal absorption process.

Interspecies scaling of oleanolic acid in mice, rats, rabbits and dogs and prediction of human pharmacokinetics

This study was conducted to predict the pharmacokinetics of oleanolic acid in humans based on animal data by allometry and several species-invariant time methods. Oleanolic acid was injected intravenously to mice, rats, rabbit and dogs (dose 1 mg/kg). The serum concentration-time profiles of oleanolic acid were best described by bi-exponential equation in all animal species. The average Cl, V ( ss ) and t ( 1/2 ) were 0.065 L/h, 0.019 L and 28.7 min in mice, 0.47 +/- 0.06 L/h, 0.117 +/- 0.029 L and 29.7 +/- 12.2 min in rats, 2.77 +/- 0.88 L/h, 1.83 +/- 0.60 L and 84.4 +/- 16.9 min in rabbits and 14.0 +/- 0.7 L/h, 9.2 +/- 10.1 L and 54.5 +/- 57.2 min in dogs, respectively. Based on animal data, human pharmacokinetic parameters of Cl, V ( ss ) and t (1/2) were predicted by simple allometry. In addition, actual concentration-time profiles obtained from animals were transformed to human profiles by species-invariant times of kallynochron, apolysichron and dienetichron. The predicted human pharmacokinetic parameters of Cl, V ( ss ) and t (1/2) by using simple allometry and species-invariant time transformation method ranged from 48.3-97.2 L/h, 49.1-92.9 L and 45.6-187.2 min, respectively. Those predicted parameters of oleanolic acid may be useful in designing dosing schedules of oleanolic acid in future clinical studies.

Comparative evaluation of oral systemic exposure of 56 xenobiotics in rat, dog, monkey and human

The prediction of human pharmacokinetics is often based on in vivo preclinical pharmacokinetic data. However, to date, no clear guidance has been available about the relative ability of the major preclinical species to estimate human oral exposure. The study was conducted to survey the literature on oral pharmacokinetic parameters in rat, dog, monkey and human, and to compare various methods for prediction of oral exposure in humans. Fifty-six non-peptide xenobiotics were identified with oral pharmacokinetic data in rat, dog, monkey and human, and comparison of the data from each species to humans was conducted along with an evaluation of the molecular features of these compounds. Monkey liver blood flow-based oral exposure was qualitatively and quantitatively more predictive of human oral exposure than rat or dog. Furthermore, generation of data in three versus two preclinical species did not always improve human predictivity. The use of molecular properties did not substantially improve the prediction of human oral exposure compared with the prediction from monkey alone. These observations confirm the continued importance of non-human primates in preclinical pharmacokinetics, and also have implications for pharmacokinetic lead optimization and for prediction of human pharmacokinetic parameters from in vivo preclinical data.

Pharmacokinetics of florfenicol and its metabolite, florfenicol amine, in dogs

A study on the bioavailability and pharmacokinetics of florfenicol was conducted in six healthy dogs following a single intravenous (i.v.) or oral (p.o.) dose of 20 mg kg(-1) body weight (b.w.). Florfenicol concentrations in serum were determined by a high-performance liquid chromatography/mass spectrometry. Plasma concentration-time data after p.o. or i.v. administration were analyzed by a non-compartmental analysis. Following i.v. injection, the total body clearance was 1.03 (0.49) L kg(-1)h(-1) and the volume of distribution at steady-state was 1.45 (0.82) L kg(-1). Florfenicol was rapidly distributed and eliminated following i.v. injection with 1.11 (0.94)h of the elimination half-life. After oral administration, the calculated mean C(max) values (6.18 microg ml(-1)) were reached at 0.94 h in dogs. The elimination half-life of florfenicol was 1.24 (0.64) h and the absolute bioavailability (F) was achieved 95.43 (11.60)% after oral administration of florfenicol. Florfenicol amine, the major metabolite of florfenicol, was detected in all dogs after i.v. and p.o. administrations.

Deriving a data-based interspecies assessment factor using the NOAEL and the benchmark dose approach

In deriving human health-based exposure limits from animal data, differences in sensitivity to a compound between animals and humans must be taken into account. These interspecies differences can be caused by differences in toxicokinetics and or toxicodynamics. Apart from that, species differ in body size, and this is usually accounted for by scaling doses to body weight (i.e., expressed as mg/kg body weight1.0/day). Adefault assessmentfactor (AF) of 10 is commonly applied to this dose metric to account for potential toxicokinetic and toxicodynamic differences. However, both proportional body weight (BW)scalingand the defaultAFas often applied are not directly based on empirical findings. Attempts have been made to derive data-based assessment factors and allometric scaling powers using various toxicological values such as no-observedadverse-effect-levels (NOAELs). In thisstudy both the NOAEL approach and the benchmark dose (BMD) approach are applied to deriveNOAEL ratios and BMD ratios from mouse and rat studies and, based on that information, toestimate an allometric scaling power and an interspecies AF. To account for interspecies differences in body size, our results confirm earlier findings that allometric body weight scaling with a power of around 0.7 is appropriate. The factor needed to rescale the dose in terms of mg/kgBWto the allometric dose scale ranges from around 1.7 (for dogs) to 10(for mice), similar to other findings. The additional factor required for taking into account interspecies toxicokinetic and toxicodynamic differences, when based on the 95th percentile of the relevant ratio distribution, would be 3.1 for a lower Confidence limit of theBMD (BMDL), and 8.3 for a NOAEL (to be applied to the allometrically scaled dose). These results indicate that the generally used defaultAFof 10 may not cover potential interspecies differences, in particular when applied to results from smaller test species. Therefore, using the default AF of 10 could lead to human exposure limits that are insufficiently protective. Further, our results show that a data-based AF that would be needed for interspecies extrapolation is smaller when the point of departure is aBMDLrather than a NOAEL. In the context of a probabilistic hazard characterization, our results indicate that the (geometric) SD of the interspecies AF distribution should be around 2.0 when the BMDL (or BMD uncertainty distribution) is used, and around 3.4 when the NOAEL is used as a point of departure for further risk assessment.

Preclinical pharmacokinetics and interspecies scaling of ragaglitazar, a novel biliary excreted PPAR dual activator

Allometric scaling has been used as an effective tool for the prediction of human pharmacokinetic parameters. Allometry has been a useful approach for the analysis of compounds that are eliminated unchanged in the urine and/or exhibit similar metabolic patterns across species. However, it has been a challenging issue to correctly predict human pharmacokinetic parameters for drugs that are eliminated intact and/or as conjugates in the bile. Ragaglitazar is a novel, non-thiazolidinedione peroxisome proliferator-activated receptor (PPAR) alpha- and gamma-agonist. In our investigation, preclinical pharmacokinetic data on ragaglitazar were gathered for several animal species (mice, rats, rabbits and dogs). Ragaglitazar when administered orally has shown a low clearance rate (Cl/F; < 5% of hepatic blood flow) in mice, rats and rabbits and a moderately high Cl/F in dogs (> 15% of hepatic blood flow). A qualitative estimation of rat bile has unequivocally confirmed the elimination of ragaglitazar in the bile. The human pharmacokinetic data are also indicative of the involvement of enterohepatic biliary recycling. In order to predict key parameters such as Cl/F and volume of distribution (V/F), simple allometry was the approach adopted at the onset. Although V/F scaled adequately, it failed to accurately predict human Cl/F. Therefore, standard correction factors such as maximum life span potential (MLP) and brain weight were also included. Although such modifications improved the linearity (r2 > 0.9), they failed to predict the investigated values. Further incorporation of correction factors particularly relevant to biliary excreted drugs improved the prediction of these values. Interestingly, the exclusion of dog data from the interspecies scaling considerably improved the prediction of both Cl/F and V/F.

Evaluation of a basic physiologically based pharmacokinetic model for simulating the first-time-in-animal study

The objective of this study was to evaluate a physiologically based pharmacokinetic (PBPK) approach for predicting the plasma concentration-time curves expected after intravenous administration of candidate drugs to rodents. The predictions were based on a small number of properties that were either calculated based on the structure of the candidate drug (octanol:water partition coefficient, ionization constant(s)) or obtained from the typical high-throughput screens implemented in the early drug discovery phases (fraction unbound in plasma and hepatic intrinsic clearance). The model was tested comparing the predicted and the observed pharmacokinetics of 45 molecules. This dataset included six known drugs and 39 drug candidates from different discovery programs, so that the performance of the model could be evaluated in a real discovery case scenario. The plasma concentration-time curves were predicted with good accuracy, the pharmacokinetic parameters being on average two- to three-fold of actual values. Multivariate analysis was used for identifying the candidate properties which were likely associated to biased predictions. The application of this approach was found useful for the prioritization of the in vivo pharmacokinetics screens and the design of the first-time-in-animal studies.

Efficacy of hydroxocobalamin for the treatment of acute cyanide poisoning in adult beagle dogs

INTRODUCTION

The efficacy of hydroxocobalamin for acute cyanide poisoning was compared with that of saline vehicle in dogs.

METHODS

Anesthetized adult beagle dogs were administered potassium cyanide (0.4 mg/kg/min, IV) until 3 min after the onset of apnea. Hydroxocobalamin (75 mg/kg [n = 19] or 150 mg/kg [n = 18], IV) or saline vehicle [n = 17] was then infused over 7.5 min while animals were ventilated with 100% oxygen, which was stopped after 15 min.

RESULTS

In vehicle-treated animals cyanide produced deterioration that culminated in a moribund state requiring euthanasia within 4 h in 10 of 17 animals and in neurological deficits necessitating euthanasia within 2-4 d in an additional 4 animals (mortality rate 82%). Survival through 14 d was observed in 15 of 19 animals administered hydroxocobalamin 75 mg/kg (mortality rate 21%), and 18 of 18 administered hydroxocobalamin 150 mg/kg (mortality rate 0%).

CONCLUSION

Hydroxocobalamin reversed cyanide toxicity and reduced mortality in a canine model.

Preclinical pharmacokinetics, pharmacodynamics, and activity of a humanized anti-CD40 antibody (SGN-40) in rodents and non-human primates

1. Cell-surface expression of CD40 in B-cell malignancies and multiple solid tumors has raised interest in its potential use as a target for antibody-based cancer therapy. SGN-40, a humanized monoclonal anti-CD40 antibody, mediates antibody-dependent cytotoxicity and inhibits B-cell tumor growth in vitro, properties of interest for the treatment of cancers, and is currently in Phase I clinical trials for B-cell malignancies. In this study, we determined in vivo activity and pharmacokinetics properties of SGN-40. 2. Effect of SGN-40 in xenograft model of CD40-expressing B-cell lymphoma in severe-combined immune deficiency mice and its in vivo pharmacokinetics properties in normal mice, rats and cynomolgus monkeys were studied. 3. Treatment with SGN-40 significantly increased the survival of mice xenografted with human B-cell lymphoma cell line. SGN-40 exhibited nearly 100% bioavailability in mice and it cleared faster when given at a low dose. In monkeys, clearance of SGN-40 was also much faster at low dose, suggesting nonlinear pharmacokinetics in these species. In rats, however, SGN-40 clearance at all tested doses was similar, suggesting that pharmacokinetics were linear in this dose range in rats. Administration of SGN-40 to monkeys also produced marked, dose-dependent, and persistent depletion of peripheral CD20(+) B lymphocytes. 4. Data presented in this report suggest that SGN-40 is active in in vivo, and based upon interspecies scaling, SGN-40 clearance in humans is predicted to be similar to observed SGN-40 clearance in monkeys. These data suggest that SGN-40 has appropriate pharmacokinetic properties that support its clinical use.

EXTRAPOLATION OF PRECLINICAL PHARMACOKINETICS AND MOLECULAR FEATURE ANALYSIS OF “DISCOVERY-LIKE” MOLECULES TO PREDICT HUMAN PHARMACOKINETICS

The prediction of human pharmacokinetics from preclinical species is an integral component of drug discovery. Recent studies with a 103-compound dataset suggested that scaling from monkey pharmacokinetic data tended to be the most accurate method for predicting human clearance. Additionally, interrogation of the two-dimensional molecular properties of these molecules produced a set of associations which predict the likely extrapolative outcome (success or failure) of preclinical data to project human pharmacokinetics. However, a limitation of the previous analyses was the relative paucity of data for typical "discovery-like" molecules (molecular weight >300 and/or clogP >3). The objective of this investigation was to generate preclinical data required for extension of this dataset for additional discovery-like molecules and determine whether the aforementioned findings continue to apply for these molecules. In vivo nonrodent intravenous pharmacokinetic data were generated for 13 molecules, and data for 8 additional molecules were obtained from the literature. Additionally, the various scaling methodologies and molecular features analysis were applied to this new dataset to predict human pharmacokinetics. Whereas the predictive accuracies demonstrated across all of the various methodologies were lower for this higher clearance compound dataset, scaling from monkey liver blood flow continued to be an accurate methodology, and human volume of distribution was similarly well predicted regardless of scaling methodology. Lastly, application of the molecular feature associations, particularly data-dependent associations, afforded an improved predictivity compared with the liver blood flow scaling approaches, and provides insight into the extrapolation of high clearance compounds in the preclinical species to human.

Pharmacokinetic profile of single and repeated oral doses of MDMA in squirrel monkeys: relationship to lasting effects on brain serotonin neurons

A large body of data indicates that (+/-)3,4-methylenedioxymethamphetamine (MDMA, 'ecstasy') can damage brain serotonin neurons in animals. However, the relevance of these preclinical data to humans is uncertain, because doses and routes of administration used in animals have generally differed from those used by humans. Here, we examined the pharmacokinetic profile of MDMA in squirrel monkeys after different routes of administration, and explored the relationship between acute plasma MDMA concentrations after repeated oral dosing and subsequent brain serotonin deficits. Oral MDMA administration engendered a plasma profile of MDMA in squirrel monkeys resembling that seen in humans, although the half-life of MDMA in monkeys is shorter (3 vs 6-9 h). MDMA was biotransformed into MDA, and the plasma ratio of MDA to MDMA was 3-5 / 100, similar to that in humans. MDMA accumulation in squirrel monkeys was nonlinear, and plasma levels were highly correlated with regional brain serotonin deficits observed 2 weeks later. The present results indicate that plasma concentrations of MDMA shown here to produce lasting serotonergic deficits in squirrel monkeys overlap those reported by other laboratories in some recreational 'ecstasy' consumers, and are two to three times higher than those found in humans administered a single 100-150 mg dose of MDMA in a controlled setting. Additional studies are needed on the relative sensitivity of brain serotonin neurons to MDMA toxicity in humans and non-human primates, the pharmacokinetic parameter(s) of MDMA most closely linked to the neurotoxic process, and metabolites other than MDA that may play a role.

Allometric relationships between the pharmacokinetics of propofol in rats, children and adults

AIMS

Allometric equations have proven useful for the extrapolation of animal data to determine pharmacokinetic parameters in man. It has been proposed that these equations are also applicable over the human size range including the paediatric population. The aim of this work was to study the relationship between various pharmacokinetic parameters for propofol and body weight using data from rats, children and adults. Furthermore, the utility of allometric scaling is evaluated by the prediction of propofol concentrations in humans based on data obtained in the rat.

METHODS

The relationship between the pharmacokinetic parameters of propofol obtained in rats, children and adults was analyzed by plotting the logarithmically transformed parameters against the corresponding logarithmically transformed body weights. In addition, based on allometric equations, pharmacokinetic parameters obtained in rats were scaled to humans. These parameters were used to simulate propofol concentrations in long-term sedated critically ill patients using NONMEM. Simulated concentrations were then compared with actually observed concentrations in humans.

RESULTS

The relationship between pharmacokinetic parameters of propofol from rats, children and adults was in good agreement with those from the literature on allometric modelling. For clearance, intercompartmental clearance, central volume of distribution and peripheral volume of distribution, the power parameters were 0.78, 0.73, 0.98 and 1.1, respectively, and r2 values for the linear correlations were 0.990, 0.983, 0.977 and 0.994, respectively. On the basis of data obtained after a single bolus injection in the rat, adequate predictions of propofol concentrations in critically ill patients can be made using allometric equations, despite the long-term nature of the use of the drug, the large number of infusion changes per day and/or differences in state of health and age.

CONCLUSIONS

For propofol, allometric scaling has proved to be valuable for cross species extrapolation. Furthermore, the use of the allometric equation between adults and children seems to be an adequate tool for the development of rational dosing schemes for children of varying body weights, and requires further study.