Stephen A. Williams

Biomarkers and Surrogate End Points for Fit-for-Purpose Development and Regulatory Evaluation of New Drugs

A consistent framework for the acceptance and qualification of biomarkers for regulatory use is needed to facilitate innovative and efficient research and subsequent application of biomarkers in drug development. One key activity is biomarker qualification, a graded, “fit‐for‐purpose” evidentiary process linking a biomarker with biology and clinical end points. A biomarker consortium model will distribute cost and risk, and drive efficient execution of research and ultimately regulatory acceptance of biomarkers for specific indications.

Changes in Human In vivo Serotonin and Dopamine Transporter Availabilities during Chronic Antidepressant Administration

Few studies have demonstrated in vivo alterations of human serotonin and dopamine transporters (SERTS and DATS) during antidepressant treatment. The current study measured these transporter availabilities with [123I]β-CIT single photon emission computed tomography (SPECT) during administration of selective serotonin reuptake inhibitors (SSRIs) or a non-SSRI, bupropion. A total of 17 healthy human subjects were randomly assigned to two different treatment protocols: (1) citalopram (40 mg/day) followed by augmentation with bupropion (100 mg/day) or (2) bupropion (100–200 mg/day) for 16 days. Citalopram significantly inhibited [123I]β-CIT binding to SERT in brainstem (51.4%) and diencephalon (39.4%) after 8 days of administration, which was similarly observed after 16 days. In contrast, citalopram significantly increased striatal DAT binding by 15–17% after 8 and 16 days of administration. Bupropion and its augmentation to citalopram did not have a significant effect on DAT or SERT. In 10 depressed patients who were treated with paroxetine (20 mg/day), a similar increase in DAT and inhibition of SERT were observed during 6 weeks treatment. The results demonstrated the inhibition of SERT by SSRI in human in vivo during the chronic treatment and, unexpectedly, an elevation of DAT. This apparent SSRI-induced modulation of the dopamine system may be associated with the side effects of these agents, including sexual dysfunction.

A Double‐Blind, Placebo‐Controlled Study of the Safety, Tolerability and Pharmacokinetics of CP‐101,606 in Patients with a Mild or Moderate Traumatic Brain Injury

ABSTRACT: CP‐101,606 is a postsynaptic antagonist of the glutamate‐mediated NR2B subunit of the N‐methyl‐d‐aspartate (NMDA) receptor. When administered intravenously (i.v.) at the time of injury, CP‐101,606 is neuroprotective in animal models of traumatic brain injury (TBI) and ischemia. Minimal adverse effects have been observed in normal human volunteers given i.v. doses of up to 3 mg/kg/hr for 72 hours. The objective of the present clinical trial was to assess the safety, pharmacokinetics, and tolerability of CP‐101,606 infused for various times in patients who had suffered either an acute moderate or mild TBI (Glasgow Coma Score 9‐14) or hemorrhagic stroke. Patients began receiving treatment within 12 hours of brain injury. A total of 53 subjects (45 with TBI and 8 with stroke) were randomized in a double‐blind fashion to receive CP‐101,606 or placebo (4 drug:1 placebo). Drug/placebo was administered by i.v. infusion (0.75 mg/kg/hr) for 2 hours and then stopped ( n= 25 ) or continued for 22 hours ( n= 4 ) or 70 hours ( n= 24 ) at a rate of 0.37 mg/kg/hr. Mean plasma drug concentrations were well above the predicted therapeutic concentration of 200 ng/ml within two hours of initiating treatment and were sustained as long as drug was infused. All the patients tolerated their drug/placebo treatment, and there were no clinically significant cardiovascular or hematological abnormalities in either group. A Neurobehavioral Rating Scale, used to detect personality changes and behavioral disturbances, indicated that all subjects showed an improvement from their postinjury, predosing baseline but did not significantly differ from each other with respect to type of head injury and/or treatment with drug or placebo. Modified Kurtzke Scoring also showed a similar pattern of improvement irrespective of type of head injury or drug/placebo treatment. This study suggests that CP‐101,606, infused for up to 72 hours has no psychotropic effects and is well‐tolerated in patients who have sustained a mild or moderate TBI or hemorrhagic stroke.

An Open‐Label Study of CP‐101,606 in Subjects with a Severe Traumatic Head Injury or Spontaneous Intracerebral Hemorrhage

ABSTRACT: CP‐101,606 is a postsynaptic antagonist of N‐methyl‐d‐aspartate (NMDA) receptors bearing the NR2B subunit. When administered intravenously (i.v.), it decreases the effects of traumatic brain injury (TBI) and focal ischemia in animal models. Therapeutic plasma concentrations (200 ng/ml) in animals, have been well tolerated in healthy human volunteers. The purpose of the present dose escalation study was to assess the safety, tolerability, and pharmacokinetics of CP‐101,606 in subjects who had suffered either an acute severe TBI (Glasgow Coma Scale 3–8) or spontaneous intracerebral hemorrhage. Thirty patients, 20 with a TBI and 10 with a stroke, were enrolled in the trial and began receiving an i.v. infusion of CP‐101,606 for 2 hours, 24 hours, or 72 hours within 12 hours of brain injury. For the first two hours, the drug was given a rate of 0.75 mg/kg/hr and then stopped ( n= 17 ) or continued for 22 ( n= 2 ) or 70 hours ( n= 11 ) at 0.37 mg/kg/hr. Plasma and cerebrospinal fluid (CSF) were collected at serial times during and after treatment. There were no consistent changes in blood pressure or pulse nor any clinically significant hematological or electrocardiogram (ECG) abnormalities attributable to CP‐101,606. No adverse events or behavioral changes were considered to be related to the drug. Plasma concentrations of CP‐101,606 over 200 ng/ml were rapidly achieved in the blood and CSF within two hours and were sustained there as long as the drug was infused. CSF concentrations were slightly higher than that in plasma by the end of infusion suggesting good penetration of CP‐101,606 into the CSF. Outcome in the severe TBI patients, as measured by the Glasgow Outcome Score at six months, suggested that a two‐hour infusion yielded a range of scores similar to contemporary patients with a severe TBI treated at our hospital while the outcomes of the patients treated with either a 24‐ or 72‐hour infusion were better on average. Thus, these results indicate that CP‐101,606 infused for up to 72 hours is well tolerated, penetrates the CSF and brain, and may improve outcome in the brain‐injured patient.

CP-101,606: An NR2B-Selective NMDA Receptor Antagonist

Glutamate and aspartate play dual roles in the central nervous system as essential amino acids and the principal excitatory neurotransmitters. The theory of excitotoxicity presents the paradoxical view that these excitatory amino acids may also become endogenous neurotoxins any time the brain’s energy homeostasis is compromised (16,23,42,59). Cerebral ischemia and traumatic brain injury result in acute energy depletion and cellular depolarization. This triggers a dramatic increase in extracellular glutamate levels (10,11) due to presynaptic glutamate release and/or reversal of neuronal and glial glutamate transporters (63,64). The result is a prolonged overactivation of glutamate receptors which, through an incompletely understood cascade of events, leads to neuron death. Glutamate receptor activity is also hypothesized to play a role in the neuron death associated with chronic neurodegenerative conditions such as Alzheimer’s disease and Parkinson’s disease. In these latter conditions, subtle but chronic deregulation in neuronal energy metabolism renders neurons susceptible to excitotoxicity from physiological glutamate receptor activity (1,23,36). Given the premise of excitotoxicity as a central event in neuron loss associated with both acute and chronic neurodegenerative conditions, glutamate-receptor inhibition has been an aggressively pursued therapeutic strategy to treat these conditions. There are four major classes of glutamate receptors: N-methyl-D-aspartate (NMDA), α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), kainate, and metabotropic (2). Of these, NMDA receptors appears to be especially important to the excitotoxic process. The NMDA receptor is an ion channel gated by synaptically released glutamate in the presence of the coagonist glycine (29,32) and concomitant depolarization (38). The NMDA receptor is permeable to Na and Ca; it is Ca influx through the receptor that

Proteomic approaches in drug discovery and development.

Publisher Summary This chapter describes the proteomic approaches in drug discovery and development. Proteomics represents the effort to establish the identities, quantities, structures, and biochemical and cellular functions of all proteins in an organism, organ, or organelle and how these properties vary in space, time, or physiological state. The proteome is more complex than the genome, because the inherent biochemical nature of proteins depends on more complicated building blocks. Intracellular localization, proteolytic processing, post-translational modification, and protein-protein interactions add greatly to protein complexity. The chapter provides an overview of the existing technologies, and presents a case study that shows how two-dimensional gel electrophoresis (2DE)-mass spectroscopy (MS) profiling approaches can be applied to one type of issue central to drug discovery and development. From a drug discovery and development perspective, the greatest challenge is translating the information garnered from proteomic initiatives into quantitative, sensitive, and specific assays capable of delivering information about a drugs effect on the target, and if the drug can effectively alter the disease in a clinically beneficial manner. Although proteomics may provide information about new targets, one of the major hurdles in early drug discovery is to demonstrate that the drug has bound specifically to target and produced a biological, meaningful activity both in vitro and in vivo . Despite the existing challenges, proteomic technologies offer powerful tools for difficult scientific questions, and are certainly a path to the future for more efficient drug discovery and development.