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Biomedical subjects

D J Pinto

Publications and source records attributed to D J Pinto.

At least 19 recordsLinked to original sources
PubMed2001

Discovery of 1-[3-(aminomethyl)phenyl]-N-3-fluoro-2'-(methylsulfonyl)-[1,1'-biphenyl]-4-yl]-3-(trifluoromethyl)-1H-pyrazole-5-carboxamide (DPC423), a highly potent, selective, and orally bioavailable inhibitor of blood coagulation factor Xa.

Factor Xa (fXa) plays a critical role in the coagulation cascade, serving as the point of convergence of the intrinsic and extrinsic pathways. Together with nonenzymatic cofactor Va and Ca2+ on the phospholipid surface of platelets or endothelial cells, factor Xa forms the prothrombinase complex, which is responsible for the proteolysis of prothrombin to catalytically active thrombin. Thrombin, in turn, catalyzes the cleavage of fibrinogen to fibrin, thus initiating a process that ultimately leads to clot formation. Recently, we reported on a series of isoxazoline and isoxazole monobasic noncovalent inhibitors of factor Xa which show good potency in animal models of thrombosis. In this paper, we wish to report on the optimization of the heterocyclic core, which ultimately led to the discovery of a novel pyrazole SN429 (2b; fXa K(i) = 13 pM). We also report on our efforts to improve the oral bioavailability and pharmacokinetic profile of this series while maintaining subnanomolar potency and in vitro selectivity. This was achieved by replacing the highly basic benzamidine P1 with a less basic benzylamine moiety. Further optimization of the pyrazole core substitution and the biphenyl P4 culminated in the discovery of DPC423 (17h), a highly potent, selective, and orally active factor Xa inhibitor which was chosen for clinical development.

Administration, Oral↗
PubMed2001

Processing in layer 4 of the neocortical circuit: new insights from visual and somatosensory cortex.

Recent experimental and theoretical results in cat primary visual cortex and in the whisker-barrel fields of rodent primary somatosensory cortex suggest common organizing principles for layer 4, the primary recipient of sensory input from the thalamus. Response tuning of layer 4 cells is largely determined by a local interplay of feed-forward excitation (directly from the thalamus) and inhibition (from layer 4 inhibitory interneurons driven by the thalamus). Feed-forward inhibition dominates excitation, inherits its tuning from the thalamic input, and sharpens the tuning of excitatory cells. Recurrent excitation enhances responses to effective stimuli.

Action Potentials↗
PubMed2000

Isoxazolines and isoxazoles as factor Xa inhibitors.

3,4,5-Trisubstituted isoxazolines (2) and isoxazoles (3) were prepared and evaluated for their in vitro and in vivo antithrombotic efficacy. They were compared to 3,5,5-trisubstituted isoxazolines (1) for Factor Xa selectivity and potency. They were also compared in an arterio-venous (A-V) shunt model of thrombosis.

Animals↗
PubMed2000

Circuit dynamics and coding strategies in rodent somatosensory cortex.

Previous experimental studies of both cortical barrel and thalamic barreloid neuron responses in rodent somatosensory cortex have indicated an active role for barrel circuitry in processing thalamic signals. Previous modeling studies of the same system have suggested that a major function of the barrel circuit is to render the response magnitude of barrel neurons particularly sensitive to the temporal distribution of thalamic input. Specifically, thalamic inputs that are initially synchronous strongly engage recurrent excitatory connections in the barrel and generate a response that briefly withstands the strong damping effects of inhibitory circuitry. To test this experimentally, we recorded responses from 40 cortical barrel neurons and 63 thalamic barreloid neurons evoked by whisker deflections varying in velocity and amplitude. This stimulus evoked thalamic response profiles that varied in terms of both their magnitude and timing. The magnitude of the thalamic population response, measured as the average number of evoked spikes per stimulus, increased with both deflection velocity and amplitude. On the other hand, the degree of initial synchrony, measured from population peristimulus time histograms, was highly correlated with the velocity of whisker deflection, deflection amplitude having little or no effect on thalamic synchrony. Consistent with the predictions of the model, the cortical population response was determined largely by whisker velocity and was highly correlated with the degree of initial synchrony among thalamic neurons (R(2) = 0.91), as compared with the average number of evoked thalamic spikes (R(2) = 0.38). Individually, the response of nearly all cortical cells displayed a positive correlation with deflection velocity; this homogeneity is consistent with the dependence of the cortical response on local circuit interactions as proposed by the model. By contrast, the response of individual thalamic neurons varied widely. These findings validate the predictions of the modeling studies and, more importantly, demonstrate that the mechanism by which the cortex processes an afferent signal is inextricably linked with, and in fact determines, the saliency of neural codes embedded in the thalamic response.

Animals↗
PubMed1999

Orally active isoxazoline glycoprotein IIb/IIIa antagonists with extended duration of action.

Modification of the alpha-carbamate substituent of isoxazoline GPIIb/IIIa (alphaIIb beta3) antagonist DMP 754 (7) led to a series of alpha-sulfonamide and alpha-sulfamide diaminopropionate isoxazolinylacetamides which were found to be potent inhibitors of in vitro platelet aggregation. Aryl- and heteroaryl-alpha-sulfonamide groups, in conjunction with (5R)-isoxazoline (2S)-diaminopropionate stereochemistry, were found to impart a pronounced duration of antiplatelet effect in dogs, potentially due to high affinity for unactivated platelets. Isoxazolylsulfonamide 34b (DMP 802), a highly selective GPIIb/IIIa antagonist, demonstrated a prolonged duration of action after iv and po dosing and high affinity for resting and activated platelets. The prolonged antiplatelet profile of DMP 802 in dogs and the high affinity of DMP 802 for human platelets may be predictive of clinical utility as a once-daily antiplatelet agent.

Administration, Oral↗
PubMed1999

Cortical columnar processing in the rat whisker-to-barrel system.

Controlled whisker stimulation and single-unit recordings were used to elucidate response transformations that occur during the processing of tactile information from ventral posterior medial thalamus (VPM) through cortical columns in the rat whisker/barrel cortex. Whiskers were either deflected alone, using punctate ramp-and-hold stimuli, or in combination with a random noise vibration applied simultaneously to two or more neighboring whiskers. Quantitative data were obtained from five anatomically defined groups of neurons based on their being located in: VPM, layer IV barrels, layer IV septa, supragranular laminae, and infragranular laminae. Neurons in each of these populations displayed characteristic properties related to their response latency and time course, relative magnitudes of responses evoked by stimulus onset versus offset, strength of excitatory responses evoked by the noise stimulus, and/or the degree to which the noise stimulus, when applied to neighboring whiskers, suppressed or facilitated responses evoked by the columnar whisker. Results indicate that within layer IV itself there are at least two anatomically distinct networks, barrel and septum, that independently process afferent information, transforming thalamic input in similar but quantitatively distinguishable ways. Transformed signals are passed on to circuits in supragranular and infragranular laminae. In the case of supragranular neurons, evidence suggests that circuits there function in a qualitatively different fashion from those in layer IV, diminishing response differentials between weak and strong inputs, rather than enhancing them. Compared to layer IV, the greater heterogeneity of receptive field properties in nongranular layers suggests the existence of multiple, operationally distinct local circuits in the output layers of the cortical column.

Animals↗
PubMed1997

Discovery of an orally active series of isoxazoline glycoprotein IIb/IIIa antagonists.

Using isoxazoline XR299 (1a) as a starting point for the design of highly potent, long-duration GPIIb/IIIa antagonists, the effect of placing lipophilic substituents at positions alpha and beta to the carboxylate moiety was evaluated. Of the compounds studied, it was found that the n-butyl carbamate 24u exhibited superior potency and duration of ex vivo antiplatelet effects in dogs. Replacement of the benzamidin-4-yl moiety with alternative basic groups, elimination of the isoxazoline stereocenter, and reversal of the orientation of the isoxazoline ring resulted in lowered potency and/or duration of action.

Administration, Oral↗
PubMed1997

Discovery of potent isoxazoline glycoprotein IIb/IIIa receptor antagonists.

Using the isoxazoline as a common structural feature, three series of glycoprotein IIb/IIIa receptor antagonists were evaluated, culminating in the discovery of XR299 (30). In an in vitro assay of platelet inhibition, XR299 had an IC50 of 0.24 microM and was a potent antiplatelet agent when dosed intravenously in a canine model. It was shown through X-ray studies of the cinchonidine salt 49 that the receptor required the 5(R)-stereochemistry for high potency. The ethyl ester prodrug of XR299, XR300 (29), was orally active in the dog.

Animals↗
PubMed1996

A quantitative population model of whisker barrels: re-examining the Wilson-Cowan equations.

Beginning from a biologically based integrate and fire model of a rat whisker barrel, we employ semirigorous techniques to reduce the system to a simple set of equations, similar to the Wilson-Cowan equations, while retaining the ability for both qualitative and quantitative comparisons with the biological system. This is made possible through the clarification of three distinct measures of population activity: voltage, firing rate, and a new term called synaptic drive. The model is activated by prerecorded neural activity obtained from thalamic "barreloid" neurons in response to whisker stimuli. Output is produced in the form of population PSTHs, one each corresponding to activity of spiny (excitatory) and smooth (inhibitory) barrel neurons, which is quantitatively comparable to PSTHs from electrophysiologically studied regular-spike and fast-spike neurons. Through further analysis, the model yields novel physiological predictions not readily apparent from the full model or from experimental studies.

Animals↗
PubMed1996

Spatial gradients and inhibitory summation in the rat whisker barrel system.

1. Extracellular single-unit recordings and controlled whisker stimuli were used to compare response properties of cells in the barreloids of the ventral posterior medial nucleus of the thalamus and the barrels in the rat primary somatosensory cortex. Whiskers were deflected alone or in combinations involving up to four immediately adjacent whiskers to assess their relative inhibitory and excitatory contributions to individual receptive fields. Quantitative data were obtained from 51 thalamocortical units (TCUs), 79 "regular-spiking" barrel neurons (RSUs), and 5 "fast-spiking" barrel neurons (FSUs) in 28 normal female adult rats. 2. A random-noise generator was used to produce small, continuously varying whisker movements that were applied to one to four adjacent whiskers while the principal (columnar) whisker was displaced with the use of a ramp-and-hold deflection. RSUs displayed adjacent whisker-evoked inhibition that increased as the number of adjacent whiskers stimulated was incremented. Asymptotic levels of inhibition were reached with the application of the noise stimulus to two or three adjacent whiskers depending on which particular combinations were deflected. By contrast, TCUs and FSUs showed weak, or no, surround inhibition. 3. As the number of adjacent whiskers stimulated increased, the background (prestimulus) activity in TCUs and FSUs increased, whereas displayed background activity in RSUs was relatively unaffected. The increase in background activity observed in the FSUs is hypothesized to mediate adjacent whisker-evoked inhibition in the RSUs. 4. A spatial gradient of adjacent whisker inhibition was observed in RSUs. The caudally adjacent whisker evoked more inhibition than the rostrally adjacent whisker, and the ventral more than the dorsal. A cortical origin for the gradient is suggested by the finding that TCUs did not show a spatial inhibitory gradient. 5. As the noise stimulus was applied to an increasing number of adjacent whiskers, RSUs became more sharply tuned for deflection angles. Neither TCUs nor FSUs showed increases in angular tuning. 6. Inhibition worked disproportionately in RSUs to inhibit those responses that were initially the least robust. For example, inhibition was most effective at reducing responses to nonpreferred versus preferred whisker deflection angles. 7. To assess the principal whisker's effect on adjacent whisker excitatory responses, the noise stimulus was applied to the principal whisker. In RSUs, principal whisker-evoked inhibition was more potent than adjacent whisker-evoked inhibition. FSUs were excited to a greater extent by the application of the noise stimulus to the principal whisker than to adjacent whiskers. TCUs did not display principal whisker-evoked inhibition. 8. Inhibition within the barrel serves as a contrast enhancement mechanism to differentiate small versus large magnitude responses. Less vigorous responses, such as those associated with perturbations of noncolumnar whiskers and inputs from nonoptimal deflection angles, are more strongly suppressed. During active touch, when many whiskers simultaneously palpate an object, these inhibitory interactions could effectively increase the "principal whiskerness" of the cortical column.

Animals↗
PubMed1995

Metabolism resistant isothiazolone inhibitors of cartilage breakdown.

A series of 2-(arylmethyl)pyridoisothiazolones is reported that inhibit the IL-1 beta induced breakdown of bovine nasal septum cartilage in an organ culture assay. The synthesis and preliminary SAR of these compounds are described. These compounds represent a novel, non-peptide lead series approach to the mediation of the chronic cartilage breakdown associated with arthritic disease. These compounds are relatively resistant to reductive metabolism by liver microsomal preparations and appear to inhibit cartilage breakdown by interfering with the proteolytic activation of matrix metalloproteinases.

Animals↗
PubMed1992

Synthesis, chemical, and biological properties of vinylogous hydroxamic acids: dual inhibitors of 5-lipoxygenase and IL-1 biosynthesis.

Vinylogous hydroxamic acids (3-(N-hydroxy-N-alkylamino)-2-propen-1-ones, VHA) were prepared as antiinflammatory agents. The synthesis, chemical properties, and in vitro biological activities of these relatively unexplored compounds are described. The VHAs were prepared by condensation of the appropriate N-substituted hydroxylamine with any of the three reagents: a 1,3-dicarbonyl compound (method A); a vinylogous amide (method B); or an alkynone (method C). The VHAs exist as one or more tautomers in solution with the relative proportions of each being dependent upon the structure of the VHA, solvent, and pH. VHAs undergo some of the typical reactions of hydroxamic acids as well as those of vinylogous amides. VHAs are active as inhibitors of 5-lipoxygenase and of IL-1 biosynthesis in vitro, which do not inhibit other enzymes of the arachidonic acid cascade. They have been shown by ESR studies to bring about inhibition of soybean type 1 15-lipoxygenase by reduction of the active site iron.

Animals↗