Application of Physiologically Based Pharmacokinetic Modeling to Predict Pharmacokinetics in Healthy Japanese Subjects.

Pharmacokinetics (PKs) in Japanese healthy subjects were simulated for nine compounds using physiologically based PK (PBPK) models parameterized with physicochemical properties, preclinical absorption, distribution, metabolism, and excretion (ADME) data, and clinical PK data from non-Japanese subjects. For each dosing regimen, 100 virtual trials were simulated and predicted/observed ratios for peak plasma concentration (Cmax ) and area under the curve (AUC) were calculated. As qualification criteria, it was prespecified that >80% of simulated trials should demonstrate ratios to observed data ranging from 0.5-2.0. Across all compounds and dose regimens studied, 93% of simulated Cmax values in Japanese subjects fulfilled the criteria. Similarly, for AUC, 77% of single-dosing regimens and 100% of multiple-dosing regimens fulfilled the criteria. In summary, mechanistically incorporating the appropriate ADME properties into PBPK models, followed by qualification using non-Japanese clinical data, can predict PKs in the Japanese population and lead to efficient trial design and conduct of Japanese phase I studies.

Physiologically Based Pharmacokinetic Model Qualification and Reporting Procedures for Regulatory Submissions: A Consortium Perspective.

This work provides a perspective on the qualification and verification of physiologically based pharmacokinetic (PBPK) platforms/models intended for regulatory submission based on the collective experience of the Simcyp Consortium members. Examples of regulatory submission of PBPK analyses across various intended applications are presented and discussed. European Medicines Agency (EMA) and US Food and Drug Administration (FDA) recent draft guidelines regarding PBPK analyses and reporting are encouraging, and to advance the use and acceptability of PBPK analyses, more clarity and flexibility are warranted.

Lack of meaningful effect of ridaforolimus on the pharmacokinetics of midazolam in cancer patients: model prediction and clinical confirmation.

Ridaforolimus, a unique non-prodrug analog of rapamycin, is a potent inhibitor of mTOR under development for cancer treatment. In vitro data suggest ridaforolimus is a reversible and time-dependent inhibitor of CYP3A. A model-based evaluation suggested an increase in midazolam area under the curve (AUC(0- ∞)) of between 1.13- and 1.25-fold in the presence of therapeutic concentrations of ridaforolimus. The pharmacokinetic interaction between multiple oral doses of ridaforolimus and a single oral dose of midazolam was evaluated in an open-label, fixed-sequence study, in which cancer patients received a single oral dose of 2 mg midazolam followed by 5 consecutive daily single oral doses of 40 mg ridaforolimus with a single dose of 2 mg midazolam with the fifth ridaforolimus dose. Changes in midazolam exposure were minimal [geometric mean ratios and 90% confidence intervals: 1.23 (1.07, 1.40) for AUC(0-∞) and 0.92 (0.82, 1.03) for maximum concentrations (C(max)), respectively]. Consistent with model predictions, ridaforolimus had no clinically important effect on midazolam pharmacokinetics and is not anticipated to be a perpetrator of drug-drug interactions (DDIs) when coadministered with CYP3A substrates. Model-based approaches can provide reasonable estimates of DDI liability, potentially obviating the need to conduct dedicated DDI studies especially in challenging populations like cancer patients.

Clinical pharmacology profile of vorinostat, a histone deacetylase inhibitor.

PURPOSE: Vorinostat is a histone deacetylase inhibitor that has demonstrated preclinical activity in numerous cancer models. Clinical activity has been demonstrated in patients with a variety of malignancies. Vorinostat is presently indicated for the treatment of patients with advanced cutaneous T cell lymphoma (CTCL). Clinical investigation is ongoing for therapy of other solid tumors and hematological malignancies either as monotherapy or in combination with other chemotherapeutic agents. This review summarizes the pharmacokinetic properties of vorinostat. METHODS: Monotherapy pharmacokinetic data across a number of pharmacokinetic studies were reviewed, and data are presented. In addition, literature review was performed to obtain published Phase I and II pharmacokinetic combination therapy data to identify and characterize potential drug interactions with vorinostat. Pharmacokinetic data in special populations were also reviewed. RESULTS: The clinical pharmacology profile of vorinostat is favorable, exhibiting dose-proportional pharmacokinetics and modest food effect. There appear to be no major differences in the pharmacokinetics of vorinostat in special populations, including varying demographics and hepatic dysfunction. Combination therapy pharmacokinetic data indicate that vorinostat has a low propensity for drug interactions. CONCLUSIONS: Vorinostat's favorable clinical pharmacology and drug interaction profile aid in the ease of administration of vorinostat for the treatment of advanced CTCL and will be beneficial in continued assessment for other oncologic indications. Although a number of studies have been conducted to elucidate the detailed pharmacokinetic profile of vorinostat, more rigorous assessment of vorinostat pharmacokinetics, including clinical drug interaction studies, will be informative.

A rate-limiting role for Dickkopf-1 in bone formation and the remediation of bone loss in mouse and primate models of postmenopausal osteoporosis by an experimental therapeutic antibody.

Genetic studies have linked both osteoporotic and high bone mass phenotypes to low-density lipoprotein receptor-related proteins (LRP4, LRP5, and LRP6). LRPs are receptors for inhibitory Dickkopf-1 (DKK1) protein, and treatment modalities that modulate LRP/DKK1 binding therefore may act as stimulators of bone mass accrual. Here, we report that RH2-18, a fully human monoclonal anti-DKK1 antibody elicits systemic pharmacologic bone efficacy and new bone formation at endosteal bone surfaces in vivo in a mouse model of estrogen-deficiency-induced osteopenia. This was paralleled by partial-to-complete resolution of osteopenia (bone mineral density) at all of the skeletal sites investigated in femur and lumbar-vertebral bodies and the restoration of trabecular bone microarchitecture. More importantly, testing of RH2-18 in adult, osteopenic rhesus macaques demonstrated a rate-limiting role of DKK1 at multiple skeletal sites and responsiveness to treatment. In conclusion, this study provides pharmacologic evidence for the modulation of DKK1 bioactivity in the adult osteopenic skeleton as a viable approach to resolve osteopenia in animal models. Thus, data described here suggest that targeting DKK1 through means such as a fully human anti-DKK1-antibody provides a potential bone-anabolic treatment for postmenopausal osteoporosis.

Efficacy of caspofungin in a juvenile mouse model of central nervous system candidiasis.

Neonatal candidiasis is an increasingly common occurrence causing significant morbidity and mortality and a higher risk of dissemination to the central nervous system (CNS) than that seen with older patients. The current understanding of optimal antifungal therapy in this setting is limited. We have developed a model of disseminated candidiasis with CNS involvement in juvenile mice to assess the efficacy of the echinocandin caspofungin relative to amphotericin B (AmB). Juvenile mice were inoculated intravenously with 5.64 × 10(4) CFU of Candida albicans MY1055. Treatment with caspofungin at 1, 2, 4, and 8 mg/kg of body weight/day, AmB at 1 mg/kg/day, or a vehicle control (VC) was initiated 30 h after infection and continued for 7 days. Pharmacokinetic parameters for caspofungin were also determined. Culture and histology showed evidence of disseminated candidiasis with multifocal encephalitis at the start of antifungal therapy. Survival was 100% in all treated groups, while mortality was 100% in the VC by day 11 after infection. By day 5, all mice in the caspofungin treatment (four doses) groups showed reductions in kidney and brain burden relative to the VC, while AmB treatment reduced kidney burden but gave no reduction of brain fungal burden. Systemic levels of caspofungin were similar in infected and uninfected mice, while brain levels were higher in infected animals. In this juvenile mouse model, caspofungin demonstrated dose-dependent activity, equivalent to or better than that of AmB at 1 mg/kg, against disseminated candidiasis with CNS involvement.

Generation and selection of novel fully human monoclonal antibodies that neutralize Dickkopf-1 (DKK1) inhibitory function in vitro and increase bone mass in vivo.

Wnt/LRP5 signaling is a central regulatory component of bone formative and resorptive activities, and the pathway inhibitor DKK1 is a suppressor of bone formation and bone mass accrual in mice. In addition, augmented DKK1 levels are associated with high bone turnover in diverse low bone mass states in rodent models and disease etiologies in human. However, examination of the precise role of DKK1 in the normal skeleton and in higher species requires the development of refined DKK1-specific pharmacological tools. Here, we report the strategy resulting in isolation of a panel of fully human anti-DKK1 antibodies applicable to studies interrogating the roles of mouse, rhesus, and human DKK1. Selected anti-DKK1 antibodies bind primate and human DKK-1 with picomolar affinities yet do not appreciably bind to DKK2 or DKK4. Epitopes mapped within the DKK1 C-terminal domain necessary for interaction with LRP5/6 and consequently effectively neutralized DKK1 function in vitro. When introduced into naïve normal growing female mice, IgGs significantly improved trabecular bone volume and structure and increased both trabecular and cortical bone mineral densities in a dose-related fashion. Furthermore, fully human DKK1-IgG displayed favorable pharmacokinetic parameters in non-human primates. In summary, we demonstrate here a rate-limiting function of physiologic DKK1 levels in the regulation of bone mass in intact female mice, amendable to specific pharmacologic neutralization by newly identified DKK1-IgGs. Importantly the fully human IgGs display a profile of attributes that recommends their testing in higher species and their use in evaluating DKK1 function in relevant disease models.

Disposition of vorinostat, a novel histone deacetylase inhibitor and anticancer agent, in preclinical species.

The disposition of vorinostat, an anticancer agent, was investigated in rats and dogs. Vorinostat possessed high serum clearance, a short elimination half-life and low oral bioavailability in both species. The renal route played an important role in the elimination of drug-related material and vorinostat was eliminated primarily by metabolic biotransformation.

Hepatic uptake of the novel antifungal agent caspofungin.

Caspofungin (CANCIDAS, a registered trademark of Merck & Co., Inc.) is a novel echinocandin antifungal agent used in the treatment of esophageal and invasive candidiases, invasive aspergillosis, and neutropenia. Available data suggest that the liver is a key organ responsible for caspofungin elimination in rodents and humans. Caspofungin is primarily eliminated by metabolic transformation; however, the rate of metabolism is slow. Accordingly, it was hypothesized that drug uptake transporters expressed on the basolateral domain of hepatocytes could significantly influence the extent of caspofungin uptake and subsequent elimination. In this study, experiments ranging from perfused rat livers to heterologous expression of individual hepatic uptake transporters were utilized to identify the transporter(s) responsible for the observed liver-specific uptake of this compound. Data from perfused rat liver studies were consistent with the presence of carrier-mediated caspofungin hepatic uptake, although this process appeared to be slow. To identify a relevant hepatic uptake transporter, we developed novel Tet-on HeLa cells expressing OATP1B1 (OATP-C, SLC21A6) and OATP1B3 (OATP8, SLC21A8), whose target gene can be overexpressed by the addition of doxycycline. A modest but statistically significant uptake of caspofungin was observed in cells overexpressing OATP1B1, but not OATP1B3. Taken together, these findings suggest that OATP1B1-mediated hepatic uptake may contribute to the overall elimination of this drug from the body.

Evaluation of microdosing strategies for studies in preclinical drug development: demonstration of linear pharmacokinetics in dogs of a nucleoside analog over a 50-fold dose range.

The technique of accelerator mass spectrometry (AMS) was validated successfully and used to study the pharmacokinetics and disposition in dogs of a preclinical drug candidate (7-deaza-2'-C-methyl-adenosine; Compound A), after oral and intravenous administration. The primary objective of this study was to examine whether Compound A displayed linear kinetics across subpharmacological (microdose) and pharmacological dose ranges in an animal model, before initiation of a human microdose study. The AMS-derived disposition properties of Compound A were comparable to data obtained via conventional techniques such as liquid chromatography-tandem mass spectrometry and liquid scintillation counting analyses. Compound A displayed multiphasic kinetics and exhibited low plasma clearance (5.8 ml/min/kg), a long terminal elimination half-life (17.5 h), and high oral bioavailability (103%). Currently, there are no published comparisons of the kinetics of a pharmaceutical compound at pharmacological versus subpharmacological doses using microdosing strategies. The present study thus provides the first description of the full pharmacokinetic profile of a drug candidate assessed under these two dosing regimens. The data demonstrated that the pharmacokinetic properties of Compound A following dosing at 0.02 mg/kg were similar to those at 1 mg/kg, indicating that in the case of Compound A, the pharmacokinetics in the dog appear to be linear across this 50-fold dose range. Moreover, the exceptional sensitivity of AMS provided a pharmacokinetic profile of Compound A, even after a microdose, which revealed aspects of the disposition of this agent that were inaccessible by conventional techniques.

Disposition of caspofungin, a novel antifungal agent, in mice, rats, rabbits, and monkeys.

The metabolism, excretion, and pharmacokinetics of caspofungin (Cancidas; Merck & Co., Inc.) were investigated after administration of a single intravenous dose to mice, rats, rabbits, and monkeys. Caspofungin had a low plasma clearance (0.29 to 1.05 ml/min/kg) and a long terminal elimination half-life (11.7 h to 59.7 h) in all preclinical species. The elimination kinetics of caspofungin were multiphasic and displayed an initial distribution phase followed by a dominant beta-elimination phase. The presence of low levels of prolonged radioactivity in plasma was observed and was partially attributable to the chemical degradation product M0. Excretion studies with [(3)H]caspofungin indicated that the hepatic and renal routes play an important role in the elimination of caspofungin, as a large percentage of the radiolabeled dose was recovered in urine and feces. Excretion of radioactivity in all species studied was slow, and low levels of radioactivity were detected in daily urine and fecal samples throughout a prolonged collection period. Although urinary profiles indicated the presence of several metabolites (M0, M1, M2, M3, M4, M5, and M6), the majority of the total radioactivity was associated with the polar metabolites M1 [4(S)-hydroxy-4-(4-hydroxyphenyl)-L-threonine] and M2 [N-acetyl-4(S)-hydroxy-4-(4-hydroxyphenyl)-L-threonine]. Caspofungin was thus primarily eliminated by metabolic transformation; however, the rate of metabolism was slow. These results suggest that distribution plays a prominent role in determining the plasma pharmacokinetics and disposition of caspofungin, as very little excretion or biotransformation occurred during the early days after dose administration, a period during which concentrations in plasma fell substantially. The disposition of caspofungin in preclinical species was similar to that reported previously in humans.

Disposition of caspofungin: role of distribution in determining pharmacokinetics in plasma.

The disposition of caspofungin, a parenteral antifungal drug, was investigated. Following a single, 1-h, intravenous infusion of 70 mg (200 microCi) of [(3)H]caspofungin to healthy men, plasma, urine, and feces were collected over 27 days in study A (n = 6) and plasma was collected over 26 weeks in study B (n = 7). Supportive data were obtained from a single-dose [(3)H]caspofungin tissue distribution study in rats (n = 3 animals/time point). Over 27 days in humans, 75.4% of radioactivity was recovered in urine (40.7%) and feces (34.4%). A long terminal phase (t(1/2) = 14.6 days) characterized much of the plasma drug profile of radioactivity, which remained quantifiable to 22.3 weeks. Mass balance calculations indicated that radioactivity in tissues peaked at 1.5 to 2 days at approximately 92% of the dose, and the rate of radioactivity excretion peaked at 6 to 7 days. Metabolism and excretion of caspofungin were very slow processes, and very little excretion or biotransformation occurred in the first 24 to 30 h postdose. Most of the area under the concentration-time curve of caspofungin was accounted for during this period, consistent with distribution-controlled clearance. The apparent distribution volume during this period indicated that this distribution process is uptake into tissue cells. Radioactivity was widely distributed in rats, with the highest concentrations in liver, kidney, lung, and spleen. Liver exhibited an extended uptake phase, peaking at 24 h with 35% of total dose in liver. The plasma profile of caspofungin is determined primarily by the rate of distribution of caspofungin from plasma into tissues.

Benzodiazepines as potent and selective bradykinin B1 antagonists.

Antagonism of the bradykinin B(1) receptor was demonstrated to be a potential treatment for chronic pain and inflammation. Novel benzodiazepines were designed that display subnanomolar affinity for the bradykinin B(1) receptor (K(i) = 0.59 nM) and high selectivity against the bradykinin B(2) receptor (K(i) > 10 microM). In vivo efficacy, comparable to morphine, was demonstrated for lead compounds in a rodent hyperalgesia model.

Nonpeptide tachykinin receptor antagonists. III. SB 235375, a low central nervous system-penetrant, potent and selective neurokinin-3 receptor antagonist, inhibits citric acid-induced cough and airways hyper-reactivity in guinea pigs.

In this report the in vitro and in vivo pharmacological and pharmacokinetic profile of (-)-(S)-N-(alpha-ethylbenzyl)-3-(carboxymethoxy)-2-phenylquinoline-4-carboxamide (SB 235375), a low central nervous system (CNS)-penetrant, human neurokinin-3 (NK-3) receptor (hNK-3R) antagonist, is described. SB 235375 inhibited (125)I-[MePhe(7)]-neurokinin B (NKB) binding to membranes of Chinese hamster ovary (CHO) cells expressing the hNK-3R (CHO-hNK-3R) with a K(i) = 2.2 nM and antagonized competitively NKB-induced Ca(2+) mobilization in human embryonic kidney (HEK) 293 cells expressing the hNK-3R (HEK 293-hNK-3R) with a K(b) = 12 nM. SB 235375 antagonized senktide (NK-3R)-induced contractions in rabbit isolated iris sphincter (pA(2) = 8.1) and guinea pig ileal circular smooth muscles (pA(2) = 8.3). SB 235375 was selective for the hNK-3R compared with hNK-1 (K(i) > 100,000 nM) and hNK-2 receptors (K(i) = 209 nM), and was without effect, at 1 microM, in 68 other receptor, enzyme, and ion channel assays. Intravenous SB 235375 produced a dose-related inhibition of miosis induced by i.v. senktide in the rabbit (ED(50) of 0.56 mg/kg). Intraperitoneal SB 235375 (10-30 mg/kg) inhibited citric acid-induced cough and airways hyper-reactivity in guinea pigs. In mice oral SB 235375 (3-30 mg/kg) was without significant effect on the behavioral responses induced by intracerebral ventricular administration of senktide. Pharmacokinetic evaluation in the mouse and rat revealed that oral SB 235375 was well absorbed systemically but did not effectively cross the blood-brain barrier. The preclinical profile of SB 235375, encompassing high affinity, selectivity, oral activity, and low CNS penetration, suggests that it is an appropriate tool compound to define the pathophysiological roles of the NK-3Rs in the peripheral nervous system.