Thomas H. Kramer

Transdermal Fentanyl: Pharmacokinetics and Preliminary Clinical Evaluation

A new transdermal drug‐delivery system that administers the synthetic opioid fentanyl through intact skin was evaluated for 24 hours postoperatively in eight patients who had undergone orthopedic surgery. Plasma samples were obtained over a 72‐hour period for pharmacokinetic analysis in five patients. The patients were also evaluated intensively for adequacy of analgesia, frequency of nausea and sedation, and occurrence of ventilatory depression. A median lag time of 2.25 hours after application of the transdermal system was observed before the appearance of fentanyl in the blood. Median peak concentration and time to peak were 1.0 ng/ml and 22 hours, respectively. The apparent elimination of fentanyl after transdermal administration is prolonged relative to previously reported values. Absorption analysis indicates zero‐order fentanyl administration, and in addition, suggests deposition of drug in an epidermal site, with the resultant prolonged absorption process giving the appearance of slow elimination. No significant toxicities were observed. Four patients required no additional analgesia. No consistent correlations among fentanyl concentration and any clinical values were observed. Transdermal administration of fentanyl appears to be a viable alternative to conventional routes of narcotic administration and warrants further study.

Small-Molecule Inhibitors of GSK-3: Structural Insights and Their Application to Alzheimer's Disease Models

The world health organization (WHO) estimated that 18 million people are struck by Alzheimers disease (AD). The USA, France, Germany, and other countries launched major programmes targeting the identification of risk factors, the improvement of caretaking, and fundamental research aiming to postpone the onset of AD. The glycogen synthase kinase 3 (GSK-3) is implicated in multiple cellular processes and has been linked to the pathogenesis of several diseases including diabetes mellitus, cancer, and AD. Inhibition of GSK-3 leads to neuroprotective effects, decreased β-amyloid production, and a reduction in tau hyperphosphorylation, which are all associated with AD. Various classes of small molecule GSK-3 inhibitors have been published in patents and original publications. Herein, we present a comprehensive summary of small molecules reported to interact with GSK-3. We illustrate the interactions of the inhibitors with the active site. Furthermore, we refer to the biological characterisation in terms of activity and selectivity for GSK-3, elucidate in vivo studies and pre-/clinical trials.

Topographically designed analogs of [cyclic] [D-Pen2,D-Pen5]enkephalin

The conformationally restricted, cyclic disulfide-containing delta opioid receptor selective enkephalin analogue [D-Pen2,D-Pen5]enkephalin (1, DPDPE) was systematically modified topographically by addition of a methyl group at either the pro-S or pro-R position of the beta carbon of an L-Phe4 or D-Phe4 residue to give [(2S,3S)-beta-MePhe4]DPDPE (2), [(2R,3R)-beta-MePhe4]DPDPE (3), [(2S,3R)-beta-MePhe4]DPDPE (4), and [(2R,3S)-beta-MePhe4]DPDPE (5). The four corresponding isomers were prepared in which the beta-methylphenylalanine residue was p-nitro substituted, that is with a beta-methyl-p-nitrophenylalanine (beta-Me-p-NO2Phe) residue, to give [(2S,3S)-beta-Me-p-NO2Phe4]DPDPE (6), [(2R,3R)-beta-Me-p-NO2Phe4]DPDPE (7), [(2S,3R)-beta-Me-p-NO2Phe4] DPDPE (8), and [(2R,3S)-beta-Me-p-NO2Phe4]DPDPE (9), respectively. The potency and selectivity (delta vs mu opioid receptor) were evaluated by radioreceptor binding assays in the rat brain using [3H]CTOP (mu ligand) and [3H]DPDPE (delta ligand) and by bioassay with mouse vas deferens (MVD, delta receptor assay) and guinea pig ileum (GPI, mu receptor assay). The eight analogues of DPDPE showed highly variable binding and bioassay activities particularly at the delta opioid receptor (4 orders of magnitude), but also at the mu opioid receptor, which led to large differences (3 orders of magnitude) in receptor selectivity. For example, [(2S,3S)-beta-MePhe4]DPDPE (2) is 1800-fold selective in binding to the delta vs mu receptor, making it one of the most selective delta opioid receptor ligands in the enkephalin series as assessed by the rat brain binding assay, whereas the corresponding (2R,3R)-beta-Me-p-NO2Phe-containing analogue 9 is only 4.5-fold selective (nonselective) in this same assay. On the other hand, in the bioassay systems, [(2S,3S)-beta-Me-p-NO2Phe4]DPDPE (5) is more potent than DPDPE and 8800-fold selective for the MVD (delta receptor) vs the GPI (mu receptor), making it the most highly selective ligand in this series for the delta opioid receptor on the basis of these bioassays. In these assay systems, the (2R,3S)-beta-MePhe4-containing analogue 5 had very weak potency and virtually no receptor selectivity (4.4-fold). These results demonstrate that topographical modification alone in a conformationally restricted peptide ligand can significantly modulate both potency and receptor selectivity of peptide ligands that have multiple sites of biological activity and suggest that this approach may have general application to peptide ligand design.

Small Molecule Kinase Inhibitors for LRRK2 and Their Application to Parkinson's Disease Models

Parkinsons disease (PD) is the second most common neurodegenerative disorder. Several single gene mutations have been linked to this disease. Mutations in the gene encoding leucine-rich repeat kinase 2 (LRRK2) indicate LRRK2 as promising therapeutic target for the treatment of PD. LRRK2 mutations were observed in sporadic as well as familial PD patients and have been investigated intensively. LRRK2 is a large and complex protein, with multiple enzymatic and protein-interaction domains, each of which is effected by mutations. The most common mutation in PD patients is G2019S. Several LRRK2 inhibitors have been reported already, although the crystal structure of LRRK2 has not yet been determined. This review provides a summary of known LRRK2 inhibitors and will discuss recent in vitro and in vivo results of these inhibitors.

Identification of Glycogen Synthase Kinase-3 Inhibitors with a Selective Sting for Glycogen Synthase Kinase-3α

The glycogen synthase kinase-3 (GSK-3) has been linked to the pathogenesis of colorectal cancer, diabetes, cardiovascular disease, acute myeloid leukemia (AML), and Alzheimers disease (AD). The debate on the respective contributions of GSK-3α and GSK-3β to AD pathology and AML is ongoing. Thus, the identification of potent GSK-3α-selective inhibitors, endowed with favorable pharmacokinetic properties, may elucidate the effect of GSK-3α inhibition in AD and AML models. The analysis of all available crystallized GSK-3 structures provided a simplified scheme of the relevant hot spots responsible for ligand binding and potency. This resulted in the identification of novel scorpion shaped GSK-3 inhibitors. It is noteworthy, compounds 14d and 15b showed the highest GSK-3α selectivity reported so far. In addition, compound 14d did not display significant inhibition of 48 out of 50 kinases in the test panel. The GSK-3 inhibitors were further profiled for efficacy and toxicity in the wild-type (wt) zebrafish embryo assay.

The effect of esmolol given during cardiopulmonary bypass.

beta-Adrenergic antagonism decreases the size of myocardial infarction and provides myocardial protection during hypothermic arrest for cardiac surgery. However, concern regarding the negative inotropic and chronotropic effects of beta-adrenergic antagonism persisting after cardiopulmonary bypass (CPB) has impeded the use of esmolol for this purpose during cardiac surgery. This is a randomized, double-blind prospective study of the effects of esmolol infused during CPB and the effects of hypothermic CPB on esmolol. Patients scheduled for CPB were randomized to receive intravenous esmolol (300 centered dot micro gram centered dot kg-1 centered dot min-1 during CPB after a bolus of 2 mg/kg prior to CPB) or placebo. Infusion was stopped at 10 min after release of aortic cross-clamp. Hemodynamics were measured, as well as serum esmolol, catecholamines, lactate, and potassium. Postoperative variables measured included electrocardiographic changes, creatine kinase (CK)-MB fractions, post-CPB dysrhythmias and drugs, hospitalization time and cost, and mortality. Esmolol was administered to 16 patients and placebo to 14. Esmolol levels reached a high of 10.5 +/- 0.9 micro gram/mL during CPB, but decreased to 0.1 +/- 0.02 micro gram/mL within 30 min after stopping infusion. Cardiac indices (cardiac index, stroke volume index, left cardiac work index, left ventricular stroke work index, right cardiac work index, and right ventricular stroke work index) were higher in the esmolol group for the first hour post-CPB (P < 0.05). Systemic arterial lactate and coronary sinus lactate were lower in the esmolol group after CPB (P < 0.05), but myocardial lactate extraction was not significantly different between groups. After CPB, hemoglobin was lower in the esmolol group (P < 0.05) due to longer CPB and aortic cross-clamp time (P < 0.05), but oxygen consumption was less than in the control group (P < 0.05). Post-CPB serum potassium was higher in the esmolol group (P < 0.05). Results are confounded by more chronically beta-adrenergically blocked patients randomized to the esmolol group (P < 0.05). Esmolol infused during CPB in this series of patients was associated with high concentrations during CPB but did not result in any adverse clinical effects after CPB. (Anesth Analg 1995;80:28-40)

Topographical requirements for delta opioid ligands: presence of a carboxyl group in position 4 is not critical for deltorphin high delta receptor affinity and analgesic activity.

To investigate the role of the carboxyl group in deltorphin molecules, we have synthesized three new analogues in which the acidic amino acid residues in position 4 of the deltorphins were replaced by non-acidic but hydrophilic amino acids residues. The three analogues, [Ser4]-, [Gln4]-, and [Cys4]-deltorphin, all are as potent or more potent than either deltorphin I or II at delta opioid receptors and possess good delta selectivities. The excellent correlation between their in vitro delta receptor potencies and their intrathecal antinociception activity forms a strong argument for involvement of those receptors in spinal nociceptive modulation in the rats.

Structure-based optimization of oxadiazole-based GSK-3 inhibitors

Inhibition of glycogen synthase kinase-3 (GSK-3) induces neuroprotective effects, e.g. decreases β-amyloid production and reduces tau hyperphosphorylation, which are both associated with Alzheimers disease (AD). The two isoforms of GSK-3 in mammalians are GSK-3α and β, which share 98% homology in their catalytic domains. We investigated GSK-3 inhibitors based on 2 different scaffolds in order to elucidate the demands of the ATP-binding pocket [1]. Particularly, the oxadiazole scaffold provided potent and selective GSK-3 inhibitors. For example, the most potent inhibitor of the present series, the acetamide 26d, is characterized by an IC50 of 2 nM for GSK-3α and 17 nM for GSK-3β. In addition, the benzodioxane 8g showed up to 27-fold selectivity for GSK-3α over GSK-3β, with an IC50 of 35 nM for GSK-3α. Two GSK-3 inhibitors were further profiled for efficacy and toxicity in the wild-type (wt) zebrafish embryo assay to evaluate simultaneously permeability and safety.

A new approach to enhance bioavailability of biologically active peptides: conjugation of a δ opioid agonist to β-cyclodextrin

Abstract The cyclic δ opioid against [p-I-Phe4]DPDPE, 1, was conjugated to mono-6-amino-permethyl-β-cyclodextrin at the C-terminus to improve the bioavailability of 1. In the rat brain building assay, the conjugate 8 showed an IC50 = 134 nM vs. a δ ligand and IC50 > 10 μM at the μ receptor, making it less potent and selective than 1. However, 8 shows antinociceptive properties (i.v.) in the mouse tail flick test and prolonged activity.

Synthesis and biological evaluation of glycogen synthase kinase 3 (GSK-3) inhibitors: an fast and atom efficient access to 1-aryl-3-benzylureas.

The glycogen synthase kinase 3 (GSK-3) is implicated in multiple cellular processes and has been linked to the pathogenesis of Alzheimers disease (AD). In the course of our research topic we synthesized a library of potent GSK-3 inhibitors. We utilized the urea scaffold present in the potent and highly selective GSK-3 inhibitor AR-A014418 (AstraZeneca). This moiety suits both (a) a convergent approach utilizing readily accessible building blocks and (b) a divergent approach based on a microwave heating assisted Suzuki coupling. We established a chromatography-free purification method to generate products with sufficient purity for the biological assays. The structure-activity relationship of the library provided the rationale for the synthesis of the benzothiazolylurea 66 (IC(50)=140 nM) and the pyridylurea 62 (IC(50)=98 nM), which displayed two to threefold enhanced activity versus the reference compound 18 (AR-A014418: IC(50)=330 nM) in our assays.