Common arterial trunk in a cat: a high-resolution morphological analysis with micro-computed tomography.

A 6-month-old female cat presented with respiratory distress. Physical examination showed a grade 5/6 holosystolic murmur with prominent precordial impulse over the left cranial chest wall. Echocardiography revealed bilateral hypertrophy of the ventricular walls, a dilated ascending aorta overriding the interventricular septum, a membranous ventricular septal defect and no obvious pulmonary trunk or pulmonary artery branches. Turbulent blood flow was detected around the ventricular septal defect and ascending aorta. Follow-up assessment, 12 months later, revealed marked and progressive biatrial dilation and biventricular hypertrophy. Four months after that, the cat died of severe congestive heart failure. To make a definitive postmortem diagnosis, we performed contrast enhanced micro-computed tomography (CT) on the ex vivo heart with micron-scale spatial resolution imaging and three-dimensional reconstruction. Micro-computed tomography analysis confirmed a common arterial trunk that bifurcated into the left pulmonary artery and aorta 5-mm distally from the truncal valve. The pulmonary trunk was absent. Slightly distal to the first branching, the common arterial trunk further branched into the right pulmonary artery and ascending aorta, indicating the aortic dominant form. Although CT angiography would be a preferred imaging modality for living animals, micro-computed tomography is a valuable tool for the ex vivo diagnosis of complex cardiac anomaly, such as presented in this cat.

Measuring Biomarker Progress.

A biomarker has been defined as "a characteristic that is objectively measured and evaluated as an indicator of normal biologic processes, pathogenic process, or pharmacologic responses to a therapeutic intervention." This comprehensive definition of biomarkers arose from the April 1999 US Food and Drug Administration (FDA)/National Institutes of Health consensus conference on "Biomarkers and Surrogate Endpoints: Advancing Clinical Research and Applications," and emphasized that biomarkers are medical measurements, including physiological measurements, blood tests, molecular analyses of biopsies, genetic or metabolic data, and measurements from images. Research on biomarkers-organized and propelled by this definition-has skyrocketed, with over 200,000 PubMed citations in the last five years.

Mitochondrial pharmacology: its future is now.

Mitochondrial medicine is an evolving discipline whose importance derives from the central function of mitochondria in adenosine triphosphate (ATP) production, generation of reactive oxygen species, and cell death by necrosis or apoptosis. Consequently, mitochondrial dysfunction plays an important role in the progression of aging and the pathophysiology of many common diseases and off-target drug effects. This provides an impetus for the development of mitochondrial pharmacology, and some promising therapeutic targets for mitochondrial protective therapy have been identified.

In search of physiologically based distribution volume estimates for macromolecules.

In their semimechanistic analysis of trastuzumab emtansine (T-DM1) pharmacokinetics, Chudasama et al., as reported in this issue, modeled the process of T-DM1 deconjugation with a series of transit compartments representing plasma volume and a single peripheral compartment. The implausibility of the two-compartment distribution model used in this study as well as in other recent attempts to analyze the distribution kinetics of trastuzumab and other macromolecules reflects the fact that this modeling has been guided primarily by statistical rather than physiological considerations.

Models of physiology and physiologically based models in clinical pharmacology.

As science matures, it becomes more mathematical, progressing from enumeration to the use of equations to the formulation of models. Clinical pharmacology has developed to the stage where models play an increasingly important role in predicting and analyzing drug pharmacokinetics and pharmacodynamics, and even in characterizing disease progression and therapeutic response. Useful models have two characteristics that are in ostensible conflict: (i) they must accurately represent the essential features of the underlying system and (ii) the representation must be sufficiently simplified to enable its salient features to be identified and investigated through further experimentation.

Pharmacokinetic studies in hemodialysis patients.

Intermittent hemodialysis is the primary supportive therapy for patients with end-stage renal disease, who commonly receive several drugs to treat both their underlying disease and the conditions that arise during long-term hemodialysis therapy. Many of these drugs are dialyzable, and their hemodialytic removal may compromise therapeutic efficacy if appropriate supplementary doses are not given. Emergency hemodialysis may also be life-saving for patients who have received drug overdoses or have ingested toxic substances. Optimal therapy in both these clinical settings is critically dependent on the availability of reliable information from well-designed pharmacokinetic studies.

Assessment of the impact of renal impairment on systemic exposure of new molecular entities: evaluation of recent new drug applications.

The US Food and Drug Administration (FDA) is currently developing a guidance for industry to replace a previous guidance, "Pharmacokinetics in Patients With Impaired Renal Function--Study Design, Data Analysis, and Impact on Dosing and Labeling" (renal guidance) issued in May 1998. The impact of the 1998 renal guidance was assessed following a survey of 94 new drug applications (NDAs) for small-molecule new molecular entities (NMEs) approved over the past 5 years (2003-2007). The survey results indicate that 57% of these NDAs included renal impairment study data, that 44% of those with renal data included evaluation in patients on hemodialysis, and that 41% of those with renal data resulted in recommendation of dose adjustment in renal impairment. In addition, the survey results provided evidence that renal impairment can affect the pharmacokinetics of drugs that are predominantly eliminated by nonrenal processes such as metabolism and/or active transport. The latter finding supports our updated recommendation to evaluate pharmacokinetic/pharmacodynamic alterations in renal impairment for those drugs that are mainly eliminated by nonrenal processes, in addition to those that are mainly excreted unchanged by the kidney.

Clinical pharmacology education and training at the National Institutes of Health.

In 1965, the National Institute of General Medical Sciences (NIGMS) established the intramural Pharmacology Research Associate Training (PRAT) program with the primary goals of providing postdoctoral training in pharmacology for individuals with or without previous pharmacology graduate training, and allowing individuals with doctoral degrees in pharmacology to obtain advanced training in other areas of science at the National Institutes of Health (NIH). The program utilized research preceptors drawn from laboratories that were conducting pharmacology-related research at the NIH campus. Although primary emphasis was placed on training laboratory scientists, a number of PRAT fellows obtained training that enabled them to pursue successful careers in clinical pharmacology. A partial listing of these individuals is shown in Table 1. Eventually, a clinical pharmacology training option was formalized within the PRAT program by the appointment of a Clinical Pharmacology Program Director, but this was subsequently suspended when this individual left NIH for a position in the pharmaceutical industry.

Use of biomarkers and surrogate endpoints in drug development and regulatory decision making: criteria, validation, strategies.

In the future, biomarkers will play an increasingly important role in all phases of drug development, including regulatory review. However, only a few of these biomarkers will become established well enough to serve in regulatory decision making as surrogate endpoints, thereby substituting for traditional clinical endpoints. Even generally accepted surrogate endpoints are unlikely to capture all the therapeutic benefits and potential adverse effects a drug will have in a diverse patient population. Accordingly, combinations of biomarkers probably will be needed to provide a more complete characterization of the spectrum of pharmacologic response. In the future, pharmacogenomic approaches, including those based on differential expression of gene arrays, will provide panels of relevant biomarkers that can be expected to transform the drug development process.

Oral administration of a corticotropin-releasing hormone receptor antagonist significantly attenuates behavioral, neuroendocrine, and autonomic responses to stress in primates.

We evaluated the effects of the lipophilic nonpeptide corticotropin-releasing hormone (CRH) type 1 receptor antagonist antalarmin on the behavioral, neuroendocrine, and autonomic components of the stress response in adult male rhesus macaques. After oral administration, significant antalarmin concentrations were detected in the systemic circulation and the cerebrospinal fluid by a mass spectrometry-gas chromatography assay developed specifically for this purpose. Pharmacokinetic and dose-response studies suggested that an oral dose of 20 mg/kg was optimal for behavioral and endocrine effects. We then administered this dose in a double-blind, placebo-controlled fashion to monkeys exposed to an intense social stressor: namely, placement of two unfamiliar males in adjacent cages separated only by a transparent Plexiglas screen. Antalarmin significantly inhibited a repertoire of behaviors associated with anxiety and fear such as body tremors, grimacing, teeth gnashing, urination, and defecation. In contrast, antalarmin increased exploratory and sexual behaviors that are normally suppressed during stress. Moreover, antalarmin significantly diminished the increases in cerebrospinal fluid CRH as well as the pituitary-adrenal, sympathetic, and adrenal medullary responses to stress. We conclude that CRH plays a broad role in the physiological responses to psychological stress in primates and that a CRH type 1 receptor antagonist may be of therapeutic value in human psychiatric, reproductive, and cardiovascular disorders associated with CRH system hyperactivity.

Decreased intracellular compartmentalization of doxorubicin in cell lines expressing P-glycoprotein.

After initial rapid [14C]doxorubicin distribution into drug-sensitive HL-60 and SU-4 cells, slow uptake continues for more than 4 hr, accounting for up to 80% of the total intracellular drug. In contrast, in P-glycoprotein-expressing drug-resistant HL-60R and SU-4R cells, doxorubicin distribution rapidly approaches equilibrium. The simplest kinetic model of this behavior consists of rapid diffusion from extracellular fluid into the cell, followed by uptake into a nonexchangeable intracellular pool. At 3.4 microM doxorubicin, transmembrane diffusion clearance was similar for all cell lines (0.78-0.98 microliter sec-1). There was no decrease in the normalized apparent volume of distribution in the P-glycoprotein-expressing cell lines, as would be expected if an active, unidirectional efflux were present. However, in resistant cells, doxorubicin accumulation in the nonexchangeable pool was up to 15-fold slower than in sensitive cells (0.004 vs. 0.050 microliter sec-1 in HL-60R vs. HL-60; 0.004 vs. 0.058 microliter sec-1 in SU-4R vs. SU-4). No pool inflow could be detected in either SU-4 or SU-4R cells exposed to doxorubicin at 0 degrees C, indicating that the nonexchangeable accumulation requires energy. The process preventing accumulation began to saturate in SU-4R cells at 20 microM doxorubicin, whereas no evidence of saturation was seen with HL-60R, which is more highly resistant than SU4R. We propose that alteration in compartmentalization is primarily responsible for the doxorubicin resistance observed in these cell lines.