Abstract-Akt is a central regulator of cardiomyocyte survival after ischemic injury in vitro and in vivo, but the mechanisms regulating Akt activity in the postischemic cardiomyocyte are not known. Furthermore, although much is known about the detrimental role that the c-Jun N-terminal kinases (JNKs) play in promoting death of cells exposed to various stresses, little is known of the molecular mechanisms by which JNK activation can be protective. We report that JNKs are necessary for the reactivation of Akt after ischemic injury. We identified Thr450 of Akt as a residue that is phosphorylated by JNKs, and the phosphorylation status of Thr450 regulates reactivation of Akt after hypoxia, apparently by priming Akt for subsequent phosphorylation by 3-phosphoinositide-dependent protein kinase. The reduction in Akt activity that is induced by JNK inhibition may have significant biological consequences, as we find that JNKs, acting via Akt, are critical determinants of survival in posthypoxic cardiomyocytes in culture. Furthermore, in contrast to selective p38 -mitogen-activated protein kinase inhibition, which was cardioprotective in vivo, concurrent inhibition of both JNKs and p38 -mitogen-activated protein kinases increased ischemia/reperfusion injury in the heart of the intact rat. These studies demonstrate that reactivation of Akt after resolution of hypoxia and ischemia is regulated by JNKs and suggest that this is likely a central mechanism of the myocyte protective effect of JNKs. (Circ Res. 2006;98:111-118.)Key Words: Akt Ⅲ apoptosis Ⅲ c-Jun NH2-terminal kinase Ⅲ hypoxia Ⅲ ischemia Ⅲ signal transduction T he families of stress-activated protein kinases (SAPKs) consist of the c-Jun N-terminal kinase (JNK) family and the p38 -mitogen-activated protein kinase (MAPK) family. 1 They are potently activated by a number of cellular stresses and produce a number of biological responses that vary by the stimulus and the cell type. These kinases are activated by ischemia (especially p38-MAPKs 2 ) and by reperfusion of ischemic tissues (JNKs and to a lesser extent p38-MAPKs 3 ).Recently, a potent and relatively selective inhibitor of the ␣ and ␤ p38-MAPK isoforms has demonstrated reductions in ischemic injury in animal models of myocardial infarction and stroke. 4,5 In addition, overexpression of dominant negative mutants of components of the p38-MAPK pathway in transgenic mice protected hearts from ischemia/reperfusion (I/R) injury. 6 However, the roles played by the JNKs in ischemic injury are much less clear than those of p38-MAPKs. This is due in large part to the fact that potent and selective inhibitors of the JNKs have only very recently been developed, are not widely available, and, to our knowledge, have not been used to study I/R injury either in vivo or in cultured cardiomyocytes.In support of a deleterious role for JNKs in ischemic injury, studies in mice in which the JNK3 gene has been deleted and studies with a peptide inhibitor of JNKs demonstrated markedly reduced ischemic injury and excitotoxicity in th...

Panitumumab is a fully human monoclonal antibody targeted to the extracellular domain of human epidermal growth factor receptor (EGFR). A comprehensive population pharmacokinetic model of panitumumab was developed using nonlinear mixed-effects modeling of 1200 patients with advanced solid tumors in 14 clinical studies. The disposition of panitumumab was best described with a 2-compartment model with parallel linear and nonlinear (Michaelis-Menten) elimination pathways. For a typical male patient with colorectal cancer (80 kg, 60 years old), the estimates for the linear clearance (CL), the maximum nonlinear clearance (V(max)/K(m)), the central volume of distribution (V(1)), the peripheral volume of distribution (V(2)), and the Michaelis-Menten constant (K(m)) are 0.273 L/d, 28.4 L/d, 3.95 L, 2.59 L, and 0.426 mcg/mL, respectively. Baseline covariates such as body weight, cancer type, age, sex, and race were studied for their influence on panitumumab pharmacokinetics. Body weight was found to be the most influential covariate on panitumumab exposure, affecting CL, V(max), and V(1). The administration of concomitant chemotherapy (IFL, FOLFIRI, or paclitaxel/carboplatin) or intensity of baseline tumor EGFR expression did not alter the pharmacokinetics of panitumumab. The presence of antipanitumumab antibodies in patients (immunogenicity rate 3.4%) did not appear to affect panitumumab exposure substantially (AUC difference 8%). In support of a new drug application in Japan, the model was used to assess panitumumab pharmacokinetics in Japanese patients compared to other racial groups; there were no significant differences in model-predicted steady-state panitumumab AUC, C(max), or C(min) after accounting for the effect of body weight.

Hepcidin is a key regulator responsible for systemic iron homeostasis. A semi-mechanistic PK model for hepcidin and a fully human anti-hepcidin monoclonal antibody (Ab 12B9m) was developed to describe their total (free + bound) serum concentration-time data after single and multiple weekly intravenous or subcutaneous doses of Ab 12B9m. The model was based on target mediated drug disposition and the IgG-FcRn interaction concepts published previously. Both total Ab 12B9m and total hepcidin exhibited nonlinear kinetics due to saturable Fc-FcRn interaction. Ab 12B9m showed a limited volume of distribution and negligible linear elimination from serum. The nonlinear elimination of Ab 12B9m was attributed to the endosomal degradation of Ab 12B9m that was not bound to the FcRn receptor. The terminal half-life, assumed to be the same for free and total serum Ab 12B9m, was estimated to be 16.5 days. The subcutaneous absorption of Ab 12B9m was described with a first-order absorption rate constant k(a) of 0.0278 h⁻¹, with 86% bioavailability. The model suggested a rapid hepcidin clearance of approximately 800 mL h⁻¹ kg⁻¹. Only the highest-tested Ab 12B9m dose of 300 mg kg⁻¹ week⁻¹ was able to maintain free hepcidin level below the baseline during the dosing intervals. Free Ab 12B9m and free hepcidin concentrations were simulated, and their PK profiles were nonlinear as affected by their binding to each other. Additionally, the total amount of FcRn receptor involved in Ab 12B9m recycling at a given time was calculated empirically, and the temporal changes in the free FcRn levels upon Ab 12B9m administration were inferred.

Abstract. Immunogenicity assessment is important for biological products due to potential impacts of immunogenicity on safety and efficacy. We reviewed the prescribing information and the FDA's clinical pharmacology review of 121 approved biological products for evaluating and reporting of immunogenicity data. Of the 121 products, 89% (n = 108) reported the incidence of immunogenicity and 49% (n = 59) reported immunogenicity impact on efficacy. However, only 26% (n = 31) reported whether the immunogenicity affected pharmacokinetics. A subset of 16 products reported effects of anti-drug antibodies (ADA) on both systemic clearance and efficacy; 8 of 16 products had increased systemic clearance coinciding with reduced efficacy, and 6 of 16 products had no changes in either clearance or efficacy. Factors contributing to infrequent reporting of the ADA effect on exposure and methods for determining the effect of ADA on exposure are summarized. Measuring ADA and drug concentrations concurrently over time enables the evaluation of ADA impact on pharmacokinetics. Within-subject comparison of concentration data (before vs. after ADA formation) is a useful alternative to betweensubject (ADA+ vs. ADA−) comparison when sample size is limited or when the majority of subjects developed ADA. The biological complexity of immune responses presents challenges to quantifying the ADA impact on pharmacokinetics using model-based methods. Our findings support that pharmacokinetic exposure is more sensitive than efficacy endpoints for evaluating ADA effects. A decrease in drug concentration due to formation of ADA during treatment can serve as an early indicator for potential reduced efficacy occurring at a later time.KEY WORDS: clinical pharmacology assessment; immunogenicity data for approved biological products; impact on clinical pharmacokinetics and efficacy; incidence of anti-drug antibodies and neutralizing antibodies.

Abstract. The objective of this study was to characterize the pharmacokinetics and pharmacodynamics (PK-PD) of romiplostim after single-dose administration in healthy subjects. The mean serum romiplostim concentrations (PK data) and mean platelet counts (PD data) collected from 32 subjects receiving a single intravenous (0.3, 1 and 10 μg/kg) or subcutaneous (0.1, 0.3, 1, and 2 μg/kg) dose were fitted simultaneously to a mechanistic PK-PD model based on pharmacodynamics-mediated drug disposition (PDMDD) and a precursor pool lifespan concept. The two-compartment PK model incorporated receptor-mediated endocytosis and linear mechanisms as parallel elimination pathways. The maximal concentration of receptors (assumed to be proportional to the platelet count), the equilibrium dissociation constant, and the first-order internalization rate constant for endocytosis of the drug-receptor complex were 0.022 fg/platelet, 0.131 ng/mL, and 0.173 h −1 , respectively. Romiplostim concentration stimulates the production of platelet precursors via the Hill function, where the SC 50 was 0.052 ng/mL and S max was 11.2. The estimated precursor cell and platelet lifespans were 5.9 and 10.5 days, respectively. Model-based simulations revealed that the romiplostim exposure and the platelet response are both dependent on the dose administered and the baseline platelet counts. Also, weekly dosing produced a sustained PD response while dosing intervals ≥2 weeks resulted in fluctuating platelet counts. Thus, the mechanistic PK-PD model was suitable for describing the romiplostim PK-PD interplay (PDMDD), the dose-dependent platelet stimulation, and the lifespans of thrombopoietic cell populations.

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A 96-hour infusion of VX-710 at 120 mg/m(2)/h plus doxorubicin 45 mg/m(2) has acceptable toxicity in patients with refractory malignancies. The safety and pharmacokinetics of VX-710 plus doxorubicin warrant efficacy trials in malignancies expressing P-gp and/or MRP1.

LETTER' ASSOCIATED CONTENT b S Supporting Information. Full experimental details for representative compounds synthesized, HRMS results, description of assays, animal efficacy studies, and X-ray crystallographic data. This material is available free of charge via the Internet at http://pubs.acs.org.