Discovery of heterocyclic ureas as a new class of raf kinase inhibitors: identification of a second generation lead by a combinatorial chemistry approach

Heterocyclic ureas, such as N-3-thienyl N'-aryl ureas, have been identified as novel inhibitors of raf kinase, a key mediator in the ras signal transduction pathway. Structure-activity relationships were established, and the potency of the screening hit was improved 10-fold to IC(50)=1.7 microM. A combinatorial synthesis approach enabled the identification of a breakthrough lead (IC(50)=0.54 microM) for a second generation series of heterocyclic urea raf kinase inhibitors.

Adjusting dissolution specifications for the variability induced by storage conditions

The United States Pharmacopeia requires that drug products meet established dissolution specifications throughout their shelf life. Whereas chemical stability for six months at accelerated storage conditions is generally regarded as providing a two-year expiry period, stress conditions are not considered predictive of dissolution stability at controlled room temperature. This paper presents an application of response surface methodology intended to incorporate the variability induced by storage temperature and relative humidity into robust product dissolution specifications. Contour plots, depicting one-sided tolerance limits of percent released, are presented as a function of crushing strength and dissolution time.

Ionic composition of cisternal CSF in acute respiratory acidosis: lack of effect of large dose bumetanide

Sodium/chloride cotransport carrier is known to be involved in transepithelial fluid absorption and secretion in various tissues. Recent studies indicate that Na,K,2Cl cotransport carrier also exists in the choroid plexus cells and inhibition of the carrier alters ionic composition of the choroidal tissue. In this study, we report the effects of large dose intravenous bumetanide, a potent inhibitor of Na,K,2Cl carrier, on cisternal CSF ionic composition in acute respiratory acidosis in pentobarbital-anesthetized mechanically ventilated dogs. Renal pedicles were ligated to prevent bumetanide-induced diuresis. The experimental group (Group II, n = 7) received 50 mg/kg of bumetanide intravenously and Group I (the control group, n = 7) received the vehicle. Analysis of serum and choroidal plexus tissue revealed bumetanide concentration of approximately 10(-5) mol/L in Group II. During 5 h of acute respiratory acidosis in both groups, the mean PaCO2 increased approximately 25 mm Hg, with comparable changes in CSF PCO2. In both groups, CSF [HCO3-] and [H+] increased approximately 3 mEq/L and 20 nEq/L, respectively. Furthermore, changes in CSF [Na+], [K+], [Ca2+], [Mg2+], [Cl-], and [Na(+)-Cl-] were also similar and were not significantly different from each other. These data show that bumetanide, at the dose that inhibits NaCl cotransport carrier, does not significantly affect ionic composition of cisternal CSF.

Neuropeptide Y and peptide YY stimulate the growth of exocrine pancreatic carcinoma cells

Neuropeptides exert inhibitory effects on pancreatic secretion, but their role in the regulation of growth is unknown. This study was executed to evaluate the effects of PYY and NPY on cell growth and 3H-thymidine incorporation in human (MiaPaCa-2, Capan-2) and hamster (H2T) exocrine pancreatic carcinoma cells in vitro. A significant increase in the number of cells after 96 h of treatment with NPY was observed at 0.01 microM in H2T, 0.1 microM in MiaPCa-2 and at 1 microM in Capan-2 cells. PYY was less potent and did not increase significantly cell growth in MiaPaCa-2, but did at 0.1 microM in Capan-2 and at 1 microM concentration in H2T. Stimulation for 48h with NPY increased 3H-thymidine incorporation significantly at 0.01 microM in all cell lines. With PYY, stimulation of 3H-thymidine incorporation occurred in H2T cells at 0.01 microM. 3H-thymidine incorporation after PYY treatment was significantly increased at 0.1 microM in MiaPaCa-2 and at 1 microM in Capan-2 cells. Receptor studies showed low but definite specific binding of both NPY and PYY in all cell lines. The results suggest that NPY and PYY may have a role in the regulation of growth of exocrine pancreatic carcinoma cells.

Diabetes enhances growth of pancreatic carcinoma cells

Clinical studies suggest that carcinoma of the pancreas may be more common in patients with chronic diabetes mellitus. To examine the effect of diabetes on growth of pancreatic carcinoma, 5 X 10(5) cultured hamster H2T pancreatic carcinoma cells were implanted into the cheek pouches of streptozocin-diabetic and nondiabetic Syrian hamsters. Tumor size and weight and total tumor DNA content 22 days after implantation were significantly greater in animals with diabetes. Thus streptozocin diabetes appears to promote the growth of pancreatic carcinoma cells in the hamster.

Pancreatic insulin secretion in exocrine pancreatic cancer

Adenocarcinoma of the exocrine pancreas in man is associated with a high incidence of diabetes mellitus. Hyperglycemia in humans with pancreatic cancer is presumed to be caused by destruction of islets of Langerhans with a resultant impairment in pancreatic insulin secretion. This hypothesis was tested in an animal model of exocrine pancreatic cancer. Carcinoma of the pancreas was induced in male Syrian golden hamsters by weekly injection of N-nitrosobis(2-oxopropyl)amine. Using an ex vivo isolated perfused pancreas preparation, the capacity of cancer-bearing pancreata to secrete insulin in response to glucose and arginine was compared to normal animals of the same age. Animals with pancreatic cancer demonstrated a normal insulin secretory response to both glucose and arginine. Thus the hypothesis that exocrine pancreatic cancer causes diabetes by directly impairing insulin release must be questioned and alternative explanations for the association of diabetes and pancreatic cancer should be sought.

Ex-vivo isolated perfusion of the pancreas in the Syrian golden hamster

The technique of ex-vivo isolated pancreatic perfusion has been a valuable method for investigation of the physiology of the exocrine and endocrine pancreas. We have adapted the technique of isolated pancreatic perfusion for use in the Syrian golden hamster, an animal used widely in studies of pancreatic carcinogenesis. The technique involves surgical harvest of the pancreas with its aortic and portal venous blood supply intact and perfusion of the pancreas with a modified Krebs buffer at 37 degrees C. Physiological function of the perfused pancreas system was examined in 27 Syrian hamsters. In tests of endocrine function, the perfused pancreas responded by increasing insulin secretion within 1 min of elevating perfusate glucose concentration, and also secreted insulin promptly in response to 10 mM arginine. In exocrine studies, the flow of pancreatic juice was stimulated by the addition of 0.8 X 10(-9) M secretin to the perfusate, and amylase output was significantly increased by the addition of 0.2 X 10(-9) M cholecystokinin (CCK-8). The ex-vivo isolated perfused pancreas in the hamster thus appears to respond appropriately to physiological stimuli and is a valuable additional tool for studies of the hamster pancreas.

Detergent-solubilization, purification, and characterization of membrane-bound 3-hydroxy-3-methylglutaryl-coenzyme A reductase from radish seedlings

3-Hydroxy-3-methylglutaryl-CoA reductase (NADPH) was solubilized with polyoxyethylene ether (Brij) W-1 from a heavy-membrane fraction, sedimented at 16000 X g from a cell-free homogenate of four-day-old, dark-grown radish seedlings (Raphanus sativus L.). Approximately 350-fold purification of the solubilized enzyme activity was achieved by (NH4)2SO4 precipitation followed by column chromatography on DEAE-Sephadex A-50, blue-dextran-agarose and HMG-CoA-hexane-agarose. The presence of detergent, which was required at all times to maintain activity, did not interfere with the chromatographic procedures used. Sucrose density centrifugation suggested an apparent molecular mass of 180 kDa with subunits of 45 kDa (polyacrylamide gel electrophoresis in the presence of sodium dodecylsulphate). The enzyme was stable at 67.5 degrees C for 30 min in the presence of glycerol, dithioerythritol and detergent. Studies of enzyme stability and activation indicate that the enzyme is a hydrophobic protein with free thiol groups that are essential for full activity. The activation energy was estimated to be 92 kJ (Arrhenius plot). Antibodies raised against rat liver and yeast hydroxymethylglutaryl-CoA (HMG-CoA) reductase failed to bind or inactivate the radish enzyme. When both HMG-CoA and NADPH concentrations were varied, intersecting patterns were obtained with double-reciprocal plots. The apparent Km values determined in this way are 1.5 microM [(S)-HMG-CoA], and 27 microM (NADPH). Concentrations of NADPH greater than 150 microM caused substrate inhibition at low HMG-CoA concentrations resulting in deviations from linearity in secondary plots. Analysis of these data and the product inhibition pattern suggest a sequential mechanism for the reduction of HMG-CoA to mevalonic acid with HMG-CoA being the first substrate binding to the enzyme, followed by NADPH.

Circadian variation of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in swine liver and ileum

The temporal variation of HMG-CoA reductase activity in the liver and intestine of swine was investigated. The thin-layer chromatographic method widely used in the assay of the reductase was successfully applied to the porcine enzymes. Parallel circadian rhythms were demonstrated in both hepatic and ileal reductases from mash-fed animals. Peak activity occurred approximately 6 hr after feeding, 2.7-fold over the basal level in the liver, and 1.6-fold in the ileum. A milk-cholesterol diet caused a marked depression of both rhythms (90% in liver, 50% in ileum); however, the hourly variation in activity persisted in both organs. Cholestyramine was found to elevate hepatic activity (2.7-fold throughout the rhythm) without affecting that of the intestine. Clofibrate had no effect on either enzyme at any time during the cycle despite a 34% reduction in serum cholesterol concentrations.

Distribution of 3-hydroxy-3-methylglutaryl coenzyme A reductase and alkaline phosphatase activities in isolated ileal epithelial cells of fed, fasted, cholestyramine-fed, and 4-aminopyrazolo[3,4-d]pyrimidine-treated rats

3-Hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase, E.C. 1.1.1.34), the major rate-limiting enzyme of the sterol biosynthetic pathway, was studied in ileal epithelial cells isolated in a villus-to-crypt gradient according to Weiser (Weiser, M. M. 1973. J. Biol. Chem, 248:2536-2541). Alkaline phosphatase (E.C. 3.1.3.1) served as a marker for the mature villus cells. Protease effects on activity determinations were negligible. The intracellular location of HMG-CoA reductase could not be precisely determined. The activity of ileal reductase was predominantly associated with the less differentiated lower villus and crypt cells, while the reverse gradient occurred with alkaline phosphatase. This distribution of enzymes persisted in both fed and fasted rats injected with control saline-phosphate, although fasting decreased total reductase units in the ileum by 86% in 72 hr. Treatment with cholestyramine and with 4-aminopyrazolo[3,4-d]pyrimidine (APP) enhanced reductase activity in ileal cells. The percent stimulation in both cases was higher in the upper villus cells than in the crypt cells, leading to abolition of the gradient in enzyme activity. However, APP treatment caused a 98% loss in total alkaline phosphatase units and a 55% loss in total epithelial cell protein in 72 hr. Thus, there was no increase in total reductase units. These data show that APP affects ileal cell metabolism directly. Furthermore, it appears that the regulation of sterol synthesis in the intestinal mucosa, via HMG-CoA reductase, involves a complex interplay of the effects exerted by the level of alimentation, the enterohepatic circulation of bile, and the levels of plasma lipoproteins.