Biomedical subjects
Publications and source records attributed to D W Robertson.
Injuries of the ankle and foot in athletes are quite common. They range from the extremely simple sprain to the difficult stress fracture, and may result in long-term disability. In all cases, the athlete is best treated after an accurate diagnosis is achieved.
1-Methyl-4-(2-thienyl)-1,2,3,6-tetrahydropyridine (2-MTTP) and 1-methyl-4-(3-thienyl)-1,2,3,6-tetrahydropyridine were compared with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) with respect to their interactions with MAO (monoamine oxidase) in vitro and their ability to produce persistent depletion of striatal dopamine and its metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid, in mice. Both 2-MTTP and 1-methyl-4-(3-thienyl)-1,2,3,6-tetrahydropyridine were like MPTP in being potent, competitive inhibitors of MAO-A (MAO type A) and weak, noncompetitive inhibitors of MAO-B (MAO type B) in vitro. 2-MTTP resulted in persistent depletion of striatal dopamine, 3,4-dihydroxyphenylacetic acid and homovanillic acid 1 week after the last of four daily injections to mice although 2-MTTP was less than one-fourth as potent as MPTP. The other isomer, 1-methyl-4-(3-thienyl)-1,2,3,6-tetrahydropyridine, failed to deplete dopamine or its metabolites in mouse striatum. Dopamine and its metabolites were also depleted in mouse nucleus accumbens by 2-MTTP and by MPTP; however, norepinephrine in frontal cortex was depleted by MPTP but not by 2-MTTP. The depletion of dopamine, 3,4-dihydroxyphenylacetic acid and homovanillic acid by 2-MTTP was prevented by pretreatment with deprenyl, a selective inhibitor of MAO-B, or with EXP 561, a dopamine uptake inhibitor, just as the depletion by MPTP was prevented. Mouse brain MAO oxidized 2-MTTP in vitro less rapidly than it oxidized MPTP; deprenyl was a potent inhibitor of the oxidation of both substrates, suggesting that MAO-B oxidizes both 2-MTTP and MPTP.(ABSTRACT TRUNCATED AT 250 WORDS)
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We have prepared two analogs of the antiestrogen tamoxifen that incorporate known DNA-crosslinking functions, a chloroethyl nitrosourea and a nitrosocarbamate moiety, and we have tested their bioactivities in cultures of human breast cancer cells. Both compounds bind to the estrogen receptor from MCF-7 cells, with relative binding affinities of 0.18% for the nitrosocarbamate derivative and 0.35% for the nitrosourea derivative, while the affinity of tamoxifen is 1.8%, and that of estradiol is set at 100%. The tamoxifen-nitrosocarbamate compound demonstrated a dose-related cytotoxicity by the colony formation and cell proliferation assays that was not blocked by estradiol in either estrogen receptor-positive MCF-7 cells or estrogen receptor-negative MDA-MB-231 cells, and thus, was not studied further. Tamoxifen-nitrosourea (TAM-NU) showed dose-related cytotoxicity in MCF-7 cells that was blocked by estradiol, whereas its activity in MDA-MB-231 cells was unaffected by estradiol. N-2-(4-t-butylphenoxy)ethyl-N'-chloroethyl-N'-nitrosourea (BPE-NU), a control compound which contains the nitrosourea moiety but does not bind to the estrogen receptor, had no effect on cell proliferation or colony formation in MCF-7 cells, but was very inhibitory in the receptor-negative MDA-MB-231 cells. In contrast, TAM-NU was more active in the receptor-positive MCF-7 cells than in the MDA-MB-231 line. Thus, because TAM-NU appears to be active selectively against the receptor-positive cell line, and because this activity is suppressible by estradiol, its cytotoxic effect seems to be mediated via the estrogen receptor. However, since TAM-NU is active only in prolonged treatment protocols, it appears likely that its cytotoxic activity results from the hormone antagonistic effect of the hydrolysis product of TAM-NU (bis-desmethyltamoxifen), rather than from a direct receptor-mediated, DNA-directed cytotoxic action of TAM-NU itself. This study stresses the need for the use of appropriate control compounds and cell systems in order to assess whether the toxic activity displayed by hormone-cytotoxic conjugates is mediated by receptor interactions and whether it operates through the intended toxic mechanism.
The cardiotonic drug milrinone (1,6-dihydro-2-methyl-6-oxo-[3,4'-bipyridine]-5-carbonitrile) is superior to its analogue amrinone (5-amino-[3,4'-bipyridin]-6(1H)-one) by virtue of its greater potency and reduced side effect profile. We confirmed initial reports on the potencies of milrinone and amrinone and found that after intravenous administration to phenobarbital anesthetized dogs, the drugs had cumulative inotropic ED50's of 37 and 1891 micrograms/kg, respectively; relative effects on heart rate and blood pressure were comparable. There are two structural differences between amrinone and milrinone: (1) milrinone has a pyridone 2-methyl substituent and (2) the pyridone 5-amino substituent of amrinone is replaced with a nitrile in milrinone. We confirmed structure-activity studies that indicated that the 2-methyl substituent appears to be primarily responsible for the dramatic difference in the potencies of amrinone and milrinone. A plausible explanation for the effect of the methyl substituent is an altered molecular topology resulting from its steric interaction with the 3',5'-hydrogen atoms. Consequently, we probed the three-dimensional structures of these two compounds by X-ray crystallography. The dihedral angle between the planes formed by the two aromatic rings of amrinone was 1.3 degrees. In marked contrast, the corresponding angle for milrinone was 52.2 degrees. Moreover, 1H NMR studies revealed conformational differences in solution. Whereas the 2-methyl substituent undoubtedly produces some electronic and hydrophobic perturbations in the bipyridine cardiotonic series, the most significant effect, from a global viewpoint, is the altered molecular topology.
A recently discovered and structurally distinct class of antiepileptic drugs is the (arylalkyl)imidazoles. Two independently discovered representatives of this class, denzimol (alpha-[4-(2-phenylethyl)phenyl]-1H-imidazole-1-ethanol) and nafimidone (2-(1H-imidazol-1-yl)-1-(2-naphthalenyl)ethanone), are undergoing clinical evaluation. Our structure-activity relationship (SAR) studies revealed that in addition to the naphthalenyl and phenethylphenyl aryl moieties of nafimidone and denzimol, respectively, fluorenyl, benzo[b]thienyl, and benzofuranyl aryl groups provided several highly active (arylalkyl)imidazole anticonvulsants. These structurally diverse aryl moieties, and comparable anticonvulsant activities, lend credence to the hypothesis that the pharmacophore of this class of anticonvulsants is the alkylimidazole portion of the molecule, with the lipophilic aryl portion enabling penetration of the blood-brain barrier. We focused our SAR studies on the (fluorenylalkyl)imidazole series. A representative compound from this series is 1-(9H-fluoren-2-yl)-2-(1H-imidazol-1-yl)ethanone. This agent was twice as potent as nafimidone in inhibiting maximal electroshock seizures in mice (po ED50's = 25 and 56 mg/kg, respectively) and considerably less toxic in the rat (po LD50's = 4550 and 504 mg/kg, respectively). The tertiary alcohol alpha-(9H-fluoren-2-yl)-alpha-methyl-1H-imidazole-1-ethanol was as potent as denzimol in mice (po ED50's = 10 and 12 mg/kg, respectively). This series of imidazole anticonvulsants was highly selective; while many compounds displayed potent antielectroshock activity, little or not activity was observed against pentylenetetrazole-induced clonic seizures or in the horizontal screen test for ataxia. All active compounds that we tested in this series, as well as denzimol and nafimidone, potentiated hexobarbital-induced sleeping time in mice, probably by imidazole-mediated inhibition of cytochrome P-450. The SAR's for the anticonvulsant activity and the sleeping time potentiation were similar. The propensity of these (arylalkyl)imidazole anticonvulsants to interact strongly with cytochrome P-450 and thereby impair the metabolism of other antiepileptic drugs may severely limit their clinical utility as anticonvulsants.
We discovered that 6 (N-[4-(1,4,5,6-tetrahydro-6-oxo-3-pyridazinyl)phenyl]acetamide) is a potent positive inotrope in dogs, and we have prepared several lactam analogues of this agent. These included 16 (1,3-dihydro-5-(1,4,5,6-tetrahydro-6-oxo-3-pyridazinyl)-2H-indol-2-one), 32 (the analogous quinolin-2-one), and 37 (the analogous benzazepin-2-one). The inotropic ED50's of these compounds were 24, 3.3, and 5.2 micrograms/kg, respectively, after iv administration to pentobarbital-anesthetized dogs. Compound 20 (LY195115, 1,3-dihydro-3,3-dimethyl-5-(1,4,5,6-tetrahydro-6-oxo-3-pyridazinyl)-2H-i ndol-2- one), the geminal dimethyl analogue of 16, was 3.5-fold more potent than 16 when administered iv (ED50 = 6.8 micrograms/kg). However, the most profound effect of the geminal alkyl substitution was on oral activity. The approximate ED50's of 20 and 16 after oral administration to conscious dogs were 25 and 400 micrograms/kg, respectively. The increase in contractility produced by 25 micrograms/kg of 20 was maximally sustained in excess of 8 h. Thus, 20 is one of the most potent and long-acting oral inotropes described to date.
LY195115 selectively inhibited the peak III isozyme of cardiac cyclic nucleotide phosphodiesterase (PDE) eluted from DEAE-cellulose columns. Inhibition curves were biphasic, suggesting heterogeneity within this preparation. Since peak III PDE is reported to be derived from membranes, effects of LY195115 upon PDE associated with cardiac membranes were examined. LY195115-sensitive PDE measured in the various membrane fractions correlated well with the sarcoplasmic reticulum marker Ca2+-ATPase (r = 0.94; p less than 0.001), but not with Na+,K+-ATPase or azide-sensitive ATPase. Membrane disruption failed to reveal latent LY195115-sensitive PDE in sarcolemmal vesicles known to be primarily right side out. The results suggest that LY195115-sensitive PDE is located within sarcoplasmic reticulum membranes with a distribution similar or identical to that of Ca2+-ATPase. Accordingly, LY195115-sensitive PDE was referred to as SR-PDE. A subfraction of sarcoplasmic reticulum vesicles (free SR vesicles) was sufficiently homogeneous with respect to SR-PDE activity to carry out steady state kinetic studies. Double reciprocal plots of cAMP hydrolysis were linear, yielding Km and Vmax values of 0.46 +/- 0.03 microM and 700 +/- 90 pmol/min/mg of vesicle protein, respectively. LY195115 was a linear competitive inhibitor of SR-PDE with a Ki of 80 +/- 10 nM. -LogIC50 values for inhibition of SR-PDE by a series of structural analogues of LY195115 correlated highly with published -logED50 values for stimulation of cardiac contractility in vivo (r = 0.91, p less than 0.001). Consequently, in vivo effects of LY195115 upon the heart appear to result primarily from competitive inhibition of SR-PDE, or from binding to a site with a topography similar or identical to that of the catalytic site of SR-PDE.
The contractile state of cat papillary muscles was increased by isomazole in a concentration-dependent manner; inotropic effects of the drug were not altered by either prazosin, propranolol or cimetidine. Isomazole inhibited the peak III isozyme of dog heart phosphodiesterase with an IC50 of 100 microM; effects on isozymes I and II were less pronounced. In cat papillary muscles, carbachol (10(-5) M) shifted the relationship between contractility and concentration of isomazole to the right. These data suggest cyclic AMP (cAMP) is involved in the actions of isomazole. In order to assess the relative effects of isomazole on intracellular cAMP and Ca++, cAMP-dependent protein kinase and glycogen phosphorylase, respectively, were used as reporters of these two second messengers. The source of enzymes was either cultured cardiomyocytes or right ventricular biopsies obtained from anesthetized dogs. In the latter case, biopsies were obtained after i.v. administration of isomazole; the pure beta agonist, isoproterenol, was included for comparative purposes. A submaximal inotropic dose of isomazole (0.1 mg/kg i.v.) in dogs resulted in a pronounced increase in contractility that was associated with a 3-fold increase in phosphorylase activity (0.15 +/- 0.01 to 0.46 +/- 0.06, -5'-AMP: +5'-AMP, P less than .05); the activation state of protein kinase was not altered. By contrast, a comparably effective inotropic dose of isoproterenol (0.1 microgram/kg) caused less than a 2-fold increase in phosphorylase activity (0.15 +/- 0.01 to 0.26 +/- 0.02, -5'-AMP: +5'-AMP, P less than .05) and this was associated with a significant increase in the protein kinase activity ratio (0.36 +/- 0.01 to 0.51 +/- 0.04, -cAMP: +cAMP, P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)
Imidazo[4,5-b]pyridines, such as AR-L57, AR-L100 and AR-L115 (Vardax), have been of interest as inotropic agents for the management of congestive heart failure. Although it has been presumed that their activities derive from inhibition of phosphodiesterase, it is now apparent that similar structural analogs possess surprisingly diverse pharmacologies and mechanisms of action. AR-L100 increased the contractile state of cat papillary muscles in a concentration-dependent manner; these effects were not blocked by either alpha, beta or H2-receptor antagonists. To determine whether the contractile responses resulted from intracellular cyclic AMP accumulation, the cardiotonic actions of AR-L100 were assessed in the presence of carbachol. Muscarinic receptor stimulation did not alter inotropic responses to AR-L100; in addition, AR-L100 did not potentiate the inotropic actions of isoproterenol. These results imply that cyclic AMP is not involved in the cardiac responses to this agent. AR-L100 inhibited Na+,K+-adenosine triphosphatase activity of either canine kidney or cardiac sarcolemmal vesicles. Inhibition of this enzyme paralleled inotropic responses in vitro; that is, in papillary muscle, the EC50 for contractility was 11.5 microM compared with an IC50 for inhibition of Na+,K+-adenosine triphosphatase of 8 microM. By contrast, the IC50 for inhibition of phosphodiesterase (isozyme III) was 280 microM. AR-L100 also inhibited sodium pump activity in intact cat papillary muscles. Concentrations of 30 and 100 microM AR-L100 resulted in 13 and 45% decreases in ouabain-sensitive 86Rb+ uptake determined at 3 Hz. In anesthetized dogs, AR-L100 increased contractility but did not alter either heart rate or mean arterial blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)
Recently several noncatecholamine, nonglycoside cardiotonic drugs have been discovered that possess both inotropic and vasodilator activities in experimental animals and man. Prototypical compounds include amrinone, sulmazole, and fenoximone. We investigated the structural requirements necessary for optimal inotropic activity in a series of molecules containing a heterocyclic ring fused to 2-phenylimidazole and discovered that 2-phenylimidazo[4,5-c]pyridines were generally 5-10-fold more potent than analogous 2-phenylimidazo[4,5-b]pyridines (e.g., sulmazole) or 8-phenylpurines. Furthermore, all imidazo[4,5-c]pyridine analogues we tested were orally active; in contrast, only one of the imidazo[4,5-b]pyridine derivatives, sulmazole, was significantly active. One of several highly active compounds in the [4,5-c] series was 50 (LY175326, 2-[2-methoxy-4-(methylsulfinyl)phenyl]-1H-imidazo[4,5-c]pyridine hydrochloride). The structure-activity relationship of this series is presented and compared to that of the imidazo[4,5-b]pyridine and purine series.
1-Methyl-4-(p-chlorophenyl)-1,2,3,6-tetrahydropyridine (PC-MPTP) failed to mimic the effects of MPTP in producing persistent depletion of striatal dopamine and its metabolites in mice one week after the last of four daily doses. MPTP was given at 20 mg/kg, whereas PC-MPTP was given at doses up to 80 mg/kg. In rats, p-chloroamphetamine (PCA) given in a single dose of 0.1 mmole/kg (20.6 mg/kg) i.p. caused marked depletion of hypothalamic serotonin and 5-hydroxyindoleacetic acid (5HIAA) concentration at 6 hrs, and the depletion persisted at 1 day and at 1 week. In contrast, PC-MPTP given at an equimolar dose failed to affect either serotonin or 5HIAA concentration at these times. Apparently the addition of a p-chloro substituent to MPTP eliminates its neurotoxicity to striatal dopamine neurons, and replacement of the aminoisopropyl side chain of PCA with a 1-methyl-1,2,3,6-tetrahydropyridin-4-yl group eliminates its neurotoxicity to brain serotonin neurons.
Compound LY175326 is one of a series of novel cardiovascular agents with both inotropic and vasodilator activities. In cat papillary muscles, LY175326 increased contractility in a concentration-dependent manner; these actions were not blocked by prazosin, propranolol or cimetidine. Inotropic responses were observed in unpaced, perfused guinea-pig hearts and these effects were associated with modest increases in heart rate and coronary flow. An i.v. dose of 0.1 mg/kg of LY175326 caused 54 and 95% increases in contractility in either the anesthetized cat or dog, respectively; corresponding heart rates were increased by less than 10%. Oral administration of 0.5 mg/kg to dogs was associated with an inotropic response that was maximal between 60 and 90 min and lasted in excess of 3 hr. These effects were not accompanied by increases in heart rate, gross behavioral changes or emesis. The pharmacology of LY175326 was evaluated in a propranolol-induced heart failure model using anesthetized beagle dogs. A bolus injection of 0.15 mg/kg of LY175326 followed by an infusion of 0.4 mg/kg/hr reversed the hemodynamic symptoms of heart failure by increasing left ventricular dP/dt60, cardiac output and stroke volume and reducing left atrial filling pressure and vascular resistance; heart rate was unchanged and calculated myocardial oxygen consumption was reduced. This balance of inotropic:vasodilator activities may provide a means of improving cardiac function while maintaining the myocardial oxygen supply:demand.
Single motor-unit (SMU) control was compared for three ambulatory cerebral-palsied and three neurologically unimpaired subjects. Both groups were similar in their abilities to produce a discrete whole muscle contraction, to isolate and maintain firing of a single motor unit, and to turn a unit on at a visual signal. Unit inter-spike intervals were very similar for both groups. However, the cerebral-palsied subjects showed a consistent inability to inhibit single motor-unit (or whole muscle) activity if the isolated unit had been firing for some time; normal subjects did not show a similar inability.
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A series of N-substituted (Z)-1,2-diphenyl-1-[4-(2-aminoethoxy)phenyl]-1-butenes, analogues of the antiestrogen tamoxifen (Nolvadex), in which the side-chain basicity is varied over a wide range, has been prepared to probe the importance of basicity in evoking estrogen antagonism. All of the compounds, except the pyrrole analogue 14, were found to possess significant antiestrogenic activity in the rat, as measured by their ability to inhibit estrogen-induced uterine growth. This implies that in the tamoxifen series the level of side-chain basicity, at least in the Lowry-Brønsted sense, is not a determining factor in the estrogen antagonist potencies of these compounds.