David M. Ritchie

Identification and structure-activity relationships of chromene-derived selective estrogen receptor modulators for treatment of postmenopausal symptoms.

As part of a program aimed at the development of selective estrogen receptor modulators (SERMs), novel chromene scaffolds, benzopyranobenzoxapanes, were discovered. Many compounds showed binding affinity as low as 1.6-200 nM, displayed antagonist behaviors in the MCF-7 human breast adenocarcinoma cell line as well in Ishikawa cell line with IC(50) values in the range 0.2-360 nM. On the basis of the side chain substitution, various compounds demonstrated strong inhibitory activity in anti-uterotropic assay. Compound 7-(R) and its major metabolites 5-(R) and 6-(R) were evaluated in several in vivo models of estrogen action. Relative to a full estrogen agonist (ethynyl estradiol) and the SERM raloxifene, 7-(R) was found to be a potent SERM that behaved as antagonist in the uterus and exhibited estrogen agonistic activity on bone, plasma lipids, hot flush, and vagina. The overall pharmacokinetic profile and stability were significantly improved compared to those of the phase 2 development compound 9-(R).

N-Hydroxyurea and hydroxamic acid inhibitors of cyclooxygenase and 5-lipoxygenase

Two series of compounds (1 and 2) having structural features of the dual COX/5-LO inhibitor tepoxalin and the 5-LO inhibitor ABT-761 were prepared. Many of these hybrid compounds are potent COX and 5-LO inhibitors; two compounds (1a and 2t) inhibit eicosanoid biosynthesis in an ex vivo assay.

N-(5-substituted) thiophene-2-alkylsulfonamides as potent inhibitors of 5-lipoxygenase

Compound 4k N-[5-(4-fluoro)phenoxythien-2-yl]methanesulfonamide is representative of a new class of potent inhibitors of 5-lipoxygenase (5-LO). These versatile compounds exhibit dose-dependent inhibition of 5-LO with IC50s ranging from 20-100 nM in the rat basophilic leukemia (RBL-1) cell homogenate assay and submicromolar IC50s in both the RBL-1 and human peripheral blood leukocyte (PBL) whole cell assays. Compound 4k also showed significant anti-inflammatory activity in the adjuvant arthritic rat at an oral dose of 3 mg/kg.

Cytokine-modulating activity of tepoxalin, a new potential antirheumatic.

Tepoxalin is a new dual cyclooxygenase/5-lipoxygenase anti-inflammatory compound currently under clinical investigation. It has been shown to possess anti-inflammatory activity in a variety of animal models and more recently to inhibit IL-2 induced signal transduction. The current study was conducted to evaluate the cytokine modulating activity of tepoxalin and the role of iron in these effects. In human peripheral blood mononuclear cells (PBMC) stimulated with OKT3/PMA, tepoxalin inhibited lymphocyte proliferation with an IC50 of 6 microM. Additionally, it inhibited the production of LTB4 (IC50 = 0.5 microM) and the cytokines IL-2, IL-6 and TNF alpha (IC50 = 10-12 microM). Cytotoxicity was not demonstrated at these concentrations. Add-back experiments with either cytokines (IL-2 or IL-6), LTB4 or conditioned media failed to restore the proliferative response in the presence of tepoxalin. However, the concurrent addition of iron (in the form of ferrous or ferric chloride and other iron salts) reversed the inhibition of proliferation caused by tepoxalin. Tepoxalin also inhibits the activation of NF kappa B, a transcription factor which acts on several cytokine genes. Tepoxalins effect on NF kappa B is also reversed by the addition of iron salts. These data suggest that the action of tepoxalin to inhibit proliferation in PBMC may be at least in part due to its ability to reduce the amount of available iron resulting in decreased activation of NF kappa B and subsequent inhibition of cytokine production.

Robotic assay of sphingomyelinase activity for high throughput screening.

Publisher Summary Neutral sphingomyelinase is an integral membrane protein that hydrolyzes membrane sphingomyelin (SM) to yield ceramide and phosphocholine. Sphingomyelinase activity can be measured by several methods; however, the simplest involves an extraction assay using radiolabeled sphingomyelin, with a 14 C label on the phosphocholine, as substrate for the enzyme. After incubation of the substrate with enzyme, the labeled phosphocholine can be separated from the remaining, unhydrolyzed sphingomyelin by extraction with a mixture of chloroform and methanol. The intact sphingomyelin and ceramide are captured in the solvent phase, whereas the labeled product, phosphocholine, partitions to the upper aqueous phase. Radioactivity in an aliquot of the upper phase can be counted in a liquid scintillation counter as a relative measure of sphingomyelin hydrolysis. Because this manual assay was not amenable to high throughput screening, a robotic method for an extraction assay in a 96-well format was developed that allows for the high throughput screening of inhibitor compounds of neutral sphingomyelinase. This assay retains the sensitivity and reproducibility of the manual extraction assay while providing the ability to perform the assay in a microplate.

Reticulocyte measurements as a bioassay for erythropoietin

The possibility of using reticulocyte counts in peripheral blood to assay erythropoietic activity of recombinant human erythropoietin (r-HuEPO) was evaluated in normal mice. Mice were injected subcutaneously with r-HuEPO on days 0, 1 and 2 and bled on day 4 for reticulocyte count determinations, using an automated counting system with thiazole orange fluorescent staining and flow cytometric analysis. Reticulocyte counts increased in a dose-dependent fashion upon administration of r-HuEPO. The reticulocyte count was unaffected by asialylated EPO as well as other substances tested (interleukin-1, interleukin-3, dexamethasone, human chorionic gonadotropin). These data demonstrate the usefulness of employing reticulocyte counts as a rapid, specific and reproducible assay for in vivo erythropoietic activity of r-HuEPO.

The use of the suicide CYP450 inhibitor ABT for distinguishing absorption and metabolism processes in in-vivo pharmacokinetic screens

SummarySince drug candidates with low oral systemic exposure may be due to either or both absorption and metabolism factors, determining what factors limit the oral systemic exposure is not always obvious in a singlein-vivo pharmacokinetic (PK) assay. A rapid ratin-vivo PK screen where the oxidative drug metabolism has been attenuated using the suicide CYP450 inhibitor aminobenzotriazole (ABT) is described. We have shown that the roles of absorption and metabolism for drug candidates with low oral systemic exposure can be determined by comparing the PK parameters of drug candidates orally administered to non-treated and ABT-treated rats. Propranolol, metoprolol and climetidine are used as model drugs. Propranolol and metoprolol have low oral systemic exposures in rats primarily due to metabolism factors while the oral systemic exposure of climetidine is high in rats. For propranolol and metoprolol, large increases in the systemic exposure of these drugs were observed between non-treated and ABT-treated rats. ABT appeared not to increase or decrease significantly the rate and extent of absorption or metabolism of Cimetidine since that oral systemic exposure of non-treated and ABT-treated rats did not significantly change.These experiments suggest that for drug candidates with low systemic exposures in rats an observation of no change in the oral systemic exposure in ABT-treated rats when compared to the non-treated rats imply that absorption (or formulation) factors limit the systemic exposure of the drug while an increase in the systemic exposure in ABT-treated rats imply that metabolism factors limit the systemic exposure. Due to the ease of preparing and interpreting PK data from ABT-treated rats, is suggested that this assay could be used as an alternative toin vivo cannulation assays. Please send reprint requests to: Dr G. W. Caldwell,

Applied Pharmacokinetics in Drug Development

The process of discovering, developing, and marketing new drugs has changed considerably in the last decade; however, the cost associated with this process remains staggeringly high. Although there are many reasons for this high cost, one reason appears to be the continuing high attrition rates of drugs during costly early- and late-stage human clinical trials. To address this problem, drug discovery organizations are striving to rapidly identify high-potential drug candidates and eliminate as early as possible those with inferior potency, poor pharmacokinetic properties, and toxicity problems, so that these deficient drug candidates do not incur the high costs of clinical trials. During the last 5 years, a decision-making go/no-go strategy has been introduced into the drug discovery process, using pharmacokinetic principles to minimize the risks and maximize the benefits of selecting superior drug candidates.Pharmacological deficiencies are related in part to pharmacokinetic properties. To understand this process, a brief review of pharmacokinetic properties including oral bioavailability, half-life, absorption, clearance, and volume of distribution is presented. We examine in vitro — in vivo (human) and/or in vivo (animals) — in vivo (human) correlations for several of these pharmacokinetic properties, followed by a discussion of how this preclinical information is collected and used in drug discovery at the various stages to select drug candidates. Finally, we summarize how these methods are used to make go/no-go decisions in each step of the drug discovery process.