In vivo bypass of hemophilia A coagulation defect by factor XIIa implant

Hemophilia A and B coagulation defects, which are caused by deficiencies of Factor VIII and Factor IX, respectively, can be bypassed by administration of recombinant Factor VIIa. However, the short half-life of recombinant Factor VIIa in vivo negates its routine clinical use. We report here an in vivo method for the continuous generation of Factor VIIa. The method depends on the implantation of a porous chamber that contains Factor Xa or XIIa, and continuously generates Factor VIIa bypass activity from the subject's own Factor VII, which enters the chamber by diffusion. Once inside, the Factor VII is cleaved to Factor VIIa by the immobilized Factor Xa or XIIa. The newly created Factor VIIa diffuses out of the chamber and back into the circulation, where it can bypass the deficient Factors VIII or IX, and enable coagulation to occur. In vitro, this method generates sufficient Factor VIIa to substantially correct Factor VIII-deficient plasma when assessed by the classical aPTT coagulation assay. In vivo, a Factor XIIa peritoneal implant generates bypass activity for up to one month when tested in rhesus monkeys. Implantation of such a chamber in a patient with hemophilia A or B could eventually provide a viable alternative to replacement therapies using exogenous coagulation factors.     

Inhibition of platelet-surface-bound proteins during coagulation under flow I: TFPI

Blood coagulation is a self-repair process regulated by activated platelet surfaces, clotting factors, and inhibitors. Tissue factor pathway inhibitor (TFPI) is one such inhibitor, well known for its inhibitory action on the active enzyme complex comprising tissue factor (TF) and activated clotting factor VII. This complex forms when TF embedded in the blood vessel wall is exposed by injury and initiates coagulation. A different role for TFPI, independent of TF:VIIa, has recently been discovered whereby TFPI binds a partially cleaved form of clotting factor V (FV-h) and impedes thrombin generation on activated platelet surfaces. We hypothesized that this TF-independent inhibitory mechanism on platelet surfaces would be a more effective platform for TFPI than the TF-dependent one. We examined the effects of this mechanism on thrombin generation by including the relevant biochemical reactions into our previously validated mathematical model. Additionally, we included the ability of TFPI to bind directly to and inhibit platelet-bound FXa. The new model was sensitive to TFPI levels and, under some conditions, TFPI could completely shut down thrombin generation. This sensitivity was due entirely to the surface-mediated inhibitory reactions. The addition of the new TFPI reactions increased the threshold level of TF needed to elicit a strong thrombin response under flow, but the concentration of thrombin achieved, if there was a response, was unchanged. Interestingly, we found that direct binding of TFPI to platelet-bound FXa had a greater anticoagulant effect than did TFPI binding to FV-h alone, but that the greatest effects occurred if both reactions were at play. The model includes activated platelets’ release of FV species, and we explored the impact of varying the FV/FV-h composition of the releasate. We found that reducing the zymogen FV fraction of this pool, and thus increasing the fraction that is FV-h, led to acceleration of thrombin generation.     

Sulfated polysaccharide purified from <Emphasis Type="BoldItalic">Ecklonia cava</Emphasis> accelerates antithrombin III-mediated plasma proteinase inhibition

Surface plasmon resonance is an important technique for studying molecular interactions and was used to investigate the molecular interaction of anticoagulant sulfated polysaccharides purified from an enzymatic hydrolysate of the brown alga Ecklonia cava (ECA) with blood coagulation factors. In a direct binding assay, binding affinity between ECA/antithrombin III (ATIII) and activated blood coagulation factors was in the order: factor VIIa (FVIIa) > factor Xa (FXa) > thrombin (FIIa); kinetic analysis determined K _D values of ECA for FVIIa, FXa, and FIIa of 15.1, 45.0 and 65.0 nM, respectively. Therefore, ECA strongly and selectively (FVII, FX, and FII) enhanced ATIII-mediated coagulation factor inhibition in both the extrinsic and common coagulation pathways. This may contribute to its high anticoagulant activity in vitro. The low cytotoxicity of ECA to venous endothelial cell line (ECV-304) also expands its value in future in vivo studies. However, to utilize it as a model for novel anticoagulant agents, its possible interference with other anticoagulant mechanisms must be addressed.     

Surface-mediated control of blood coagulation: the role of binding site densities and platelet deposition

A mathematical model of the extrinsic or tissue factor (TF) pathway of blood coagulation is formulated and results from a computational study of its behavior are presented. The model takes into account plasma-phase and surface-bound enzymes and zymogens, coagulation inhibitors, and activated and unactivated platelets. It includes both plasma-phase and membrane-phase reactions, and accounts for chemical and cellular transport by flow and diffusion, albeit in a simplified manner by assuming the existence of a thin, well-mixed fluid layer, near the surface, whose thickness depends on flow. There are three main conclusions from these studies. (i) The model system responds in a threshold manner to changes in the availability of particular surface binding sites; an increase in TF binding sites, as would occur with vascular injury, changes the system's production of thrombin dramatically. (ii) The model suggests that platelets adhering to and covering the subendothelium, rather than chemical inhibitors, may play the dominant role in blocking the activity of the TF:VIIa enzyme complex. This, in turn, suggests that a role of the IXa-tenase pathway for activating factor X to Xa is to continue factor Xa production after platelets have covered the TF:VIIa complexes on the subendothelium. (iii) The model gives a kinetic explanation of the reduced thrombin production in hemophilias A and B.     

Deletion of the membrane anchoring region of tissue factor abolishes autoactivation of factor VII but not cofactor function. Analysis of a mutant with a selective deficiency in activity.

The activation of human blood coagulation factor VII can occur by the feedback activity of either factor VIIa (autoactivation) or factor Xa. Both of these reactions are known to be enhanced by the presence of tissue factor, an integral membrane protein and the cofactor for factor VIIa. We examine here the activation of 125I-factor VII by both factor VIIa and factor Xa employing a mutant soluble form of tissue factor which has had its transmembrane and cytoplasmic domains deleted (sTF1-219). This mutant soluble tissue factor retains cofactor activity toward factor VIIa in a single-stage clotting assay but shows a strong dependence on initial plasma levels of factor VIIa (from 1 to 10,000 ng/ml) when compared to wild-type tissue factor. We show that this dependence is due to a deficiency of sTF1-219 in ability to both promote autoactivation and enhance the factor Xa-catalyzed activation of 125I-factor VII. sTF1-219 does not, however, inhibit the tissue factor-independent activation of 125I-factor VII by factor Xa. The results strongly suggest that the phospholipid anchoring region of tissue factor is essential for autoactivation and beneficial for factor Xa-catalyzed activation of 125I-factor VII. In addition, when taken together with the dependence of clotting times on initial factor VIIa levels observed with sTF1-219, these results indicate that factor VII autoactivation may be of greater importance in the initiation of blood coagulation via tissue factor than has been previously realized.     

Factor VIIa/tissue factor generates a form of factor V with unchanged specific activity, resistance to activation by thrombin, and increased sensitivity to activated protein C

Factor VIIa, in complex with tissue factor (TF), is the serine protease responsible for initiating the clotting cascade. This enzyme complex (TF/VIIa) has extremely restricted substrate specificity, recognizing only three previously known macromolecular substrates (serine protease zymogens, factors VII, IX, and X). In this study, we found that TF/VIIa was able to cleave multiple peptide bonds in the coagulation cofactor, factor V. SDS-PAGE analysis and sequencing indicated the factor V was cleaved at Arg679, Arg709, Arg1018, and Arg1192, resulting in a molecule with a truncated heavy chain and an extended light chain. This product (FVTF/VIIa) had essentially unchanged activity in clotting assays when compared to the starting material. TF reconstituted into phosphatidylcholine vesicles was ineffective as a cofactor for the factor VIIa cleavage of factor V. However, incorporation of phosphatidylethanolamine in the vesicles had little effect over the presence of 20% phosphatidylserine. FVTF/VIIa was as sensitive to inactivation by activated protein C (APC) as thrombin activated factor V as measured in clotting assays or by the appearance of the expected heavy chain cleavage products. The FVTF/VIIa could be further cleaved by thrombin to release the normal light chain, albeit at a significantly slower rate than native factor V, to yield a fully functional product. These studies thus reveal an additional substrate for the TF/VIIa complex. They also indicate a new potential regulatory pathway of the coagulation cascade, i.e., the production of a form of factor V that can be destroyed by APC without the requirement for full activation of the cofactor precursor.     

Tissue factor (coagulation factor III) inhibition by apolipoprotein A-II

Apolipoprotein A-II (apoA-II) has been shown to inhibit tissue factor participation in the activation of coagulation factor X by factor VIIa. The magnitude of inhibition was dependent on the concentration of the enzyme (factor VIIa) and substrate (factor X) present in the reaction. With factor VIIa at 0.86 nM, 0.41 microM apoA-II inhibited factor X activation as much as 50% at 200 nM factor X, with inhibition decreasing to 39% at 3 nM factor X. When factor X was held constant at 100 nM, 0.41 microM apoA-II inhibited its activation by 80% when factor VIIa was present at 26.7 pM, but the inhibition decreased to 47% when factor VIIa was increased to 1.75 nM. Kinetically, increasing apoA-II decreased the reaction Vmax. ApoA-II produced little effect on the apparent Km, but the apparent K1/2 for factor VIIa in the reaction increased as apoA-II concentration increased. In the presence of 0.75 pM bovine tissue factor, reconstituted with 4.31 microM phosphatidylserine-phosphatidylcholine (30:70, w/w) vesicles, and in the absence of apoA-II, the apparent Km was near 7 nM factor X when factor VIIa was present at 0.86 nM. Under the same conditions with factor X at 100 nM, the apparent K1/2 was near 56 pM factor VIIa. As apoA-II was added to 0.41 microM, the apparent K1/2 increased to about 200 pM factor VIIa. The aggregate results support a model in which apoA-II inhibits tissue factor potentiation of factor VIIa activity. Because the apparent K1/2 increases when apoA-II is added, the factor VIIa can apparently protect tissue factor from the effects of apoA-II. Thus, apoA-II appears to inhibit factor X activation by preventing the appropriate association of tissue factor with factor VIIa.     

Lipid-bound factor Xa regulates tissue factor activity

The activation of coagulation factor X by tissue factor (TF) and coagulation factor VIIa (VIIa) on a phospholipid surface is thought to be the key step in the initiation of blood coagulation. In this reaction, the product, fXa, is transiently and reversibly bound to the TF-VIIa enzyme complex. This in effect leads to a probabilistic inhibition of subsequent fX activations; a new fX substrate molecule cannot be activated until the old fXa molecule leaves. In this study, we demonstrate that benzamidine and soybean trypsin inhibitor-conjugated Sepharose beads, which bind fXa and sequester it away from the reaction, serve to enhance fX activation by the TF-VIIa complex. Thus, removal of fXa from the reactive zone, by either flow, fXa sequestration, or binding to distant lipid surfaces, can serve to enhance the levels of TF-VIIa activity. Using resonance energy transfer, we found the dissociation constants of fX and fXa for 100 nm diameter phospholipid vesicles to be on the order of 30-60 nM, consistent with previous measurements employing planar lipid surfaces. On the basis of the measurements of binding of fXa to phospholipid surfaces, we demonstrate that the rates of fX activation by the TF-VIIa complex under a variety of experimental conditions depend inversely on the amount of product (fXa) bound to the TF-phospholipid surface. These data support an inhibitory role for the reaction product, fXa, and indicate that models previously employed in understanding this initial coagulation reaction must now be re-evaluated to account for both the product occupancy of the phospholipid surface and the binding of the product to the enzyme. Moreover, the inhibitory properties of fXa can be described on the basis of the estimated surface density of fXa molecules on the TF-phospholipid surface.     

The first epidermal growth factor domain of human coagulation factor VII is essential for binding with tissue factor.

The intrinsic pathway of coagulation is initiated when zymogen factor VII binds to its cell surface receptor tissue factor to form a catalytic binary complex. Both the activation of factor VIIa and the expression of serine protease activity of factor VIIa are dependent on factor VII binding to tissue factor lipoprotein. To better understand the molecular basis of these rate-limiting events, the interaction of zymogen factor VII and tissue factor was investigated using as probes both a murine monoclonal antibody and a monospecific rabbit antiserum to human factor VII. To measure factor VIIa functional activity, a two-stage chromogenic assay was used; an assay which measures the factor Xa generated by the activation of factor VII to factor VIIa. Purified immunoglobulin from murine monoclonal antibody 231-7, which was shown to be reactive with amino acid residues 51-88 of the first epidermal growth factor-like (EGF) domain of human factor VII, inhibited the activation of factor VII to factor VIIa in a dose-dependent manner. The mechanism of this inhibition was demonstrated using a novel solid-phase ELISA which quantitatively measured the binding of purified factor VII zymogen to tissue factor adsorbed onto microtiter wells. Thus, the binding of factor VII zymogen to immobilized tissue factor was inhibited by antibody 231-7, again in a dose-dependent manner. Similar results were obtained using a monospecific rabbit antiserum to human factor VII which also reacted with the beta-galactosidase fusion proteins containing amino acid residues 51-88 (exon 4) of human factor VII. We conclude therefore that the exon 4-encoded amino acids of the first EGF domain of human factor VII constitute an essential domain participating in the binding of factor VII to tissue factor.     

Tissue factor is not involved in the mitogenic activity of factor VIIa

The present study was undertaken to evaluate in vitro the importance of tissue factor in the mitogenic effect of factor VIIa for embryonic fibroblasts. For that purpose, embryonic fibroblasts were isolated from either wild-type or transgenic mice showing a single inactivation of the tissue factor gene or expressing a truncated form (lacking the cytosolic domain) of this protein. Factor VIIa stimulated in a dose-dependent manner the growth of the 3 types of fibroblasts, thus showing that TF is not involved in the mitogenic activity of factor VIIa. The mitogenic activity of factor VIIa disappeared in serum immunopurified in factor X and was almost totally inhibited by DX9065, a selective factor Xa inhibitor, showing that this effect of factor VIIa occurred via factor Xa generated during the incubation period. Hirudin did not show any significant effect on factor VIIa-induced fibroblast proliferation, thus showing that the effect observed for factor VIIa was selectively mediated by factor Xa and was not due to thrombin formation. Our results therefore represent the first evidence for the possible importance of factor Xa in the mitogenic effect of factor VIIa and show the negligible role of tissue factor in this process.     

Hemextin AB complex, a unique anticoagulant protein complex from Hemachatus haemachatus (African Ringhals cobra) venom that inhibits clot initiation and factor VIIa activity

During injury or trauma, blood coagulation is initiated by the interaction of factor VIIa (FVIIa) in the blood with freshly exposed tissue factor (TF) to form the TF.FVIIa complex. However, unwanted clot formation can lead to death and debilitation due to vascular occlusion, and hence, anticoagulants are important for the treatment of thromboembolic disorders. Here, we report the isolation and characterization of two synergistically acting anticoagulant proteins, hemextins A and B, from the venom of Hemachatus haemachatus (African Ringhals cobra). N-terminal sequences and CD spectra of the native proteins indicate that these proteins belong to the three-finger toxin family. Hemextin A (but not hemextin B) exhibits mild anticoagulant activity. However, hemextin B forms a complex (hemextin AB complex) with hemextin A and synergistically enhances its anticoagulant potency. Prothrombin time assay showed that these two proteins form a 1:1 complex. Complex formation was supported by size-exclusion chromatography. Using a "dissection approach," we determined that hemextin A and the hemextin AB complex prolong clotting by inhibiting TF.FVIIa activity. The site of anticoagulant effects was supported by their inhibitory effect on the reconstituted TF.FVIIa complex. Furthermore, we demonstrated their specificity of inhibition by studying their effects on 12 serine proteases; the hemextin AB complex potently inhibited the amidolytic activity of FVIIa in the presence and absence of soluble TF. Kinetic studies showed that the hemextin AB complex is a noncompetitive inhibitor of soluble TF.FVIIa amidolytic activity, with a Ki of 50 nm. Isothermal titration calorimetric studies showed that the hemextin AB complex binds directly to FVIIa with a binding constant of 1.62 x 10(5) m(-1). The hemextin AB complex is the first reported natural inhibitor of FVIIa that does not require a scaffold to mediate its inhibitory activity. Molecular interactions of the hemextin AB complex with FVIIa/TF.FVIIa will provide a new paradigm in the search for anticoagulants that inhibit the initiation of blood coagulation.     

Preparation and anticoagulation activity of sodium cellulose sulfate

Semi-synthesis of cellulose sulfate sodium (Na-MCS) was carried out by sulfation of microcrystalline cellulose (MCC) with chlorosulfonic acid-dimethylformamide complex as sulfating agent. As shown by FT-IR, NMR spectroscopy, and elemental analysis, the sulfation occurred mainly at C6, partially at C2, and no substitution at C3. The substitution degree ranged from 1.10 to 1.70 and the average molecular weight is between 1.1 and 3.5 x 10(4)Da. The anticoagulant efficacy and its possible mechanism were investigated using in vitro, in vivo coagulation assays and amidolytic tests in comparison with heparin. Results indicated that Na-MCS exhibited higher anticoagulation activity based on activated partial thromboplastin time (APTT) assay and prolonged the thrombin time (TT) to a lesser extent than heparin. No effect was detected on the prothrombin time (PT). Subcutaneous administration of Na-MCS to mice increased the clotting time (CT) in a moderate dose-dependent manner with a longer duration. Na-MCS exhibited anticoagulation activity mainly by accelerating the inhibition of antithrombin III (AT-III) on coagulation factors FIIa and FXa in plasma.     

Probing the structural changes in the light chain of human coagulation factor VIIa due to tissue factor association.

The crystallographic structure of human coagulation factor VIIa/tissue factor complex bound with calcium ions was used to model the solution structure of the light chain of factor VIIa (residues 1-142) in the absence of tissue factor. The Amber force field in conjunction with the particle mesh Ewald summation method to accommodate long-range electrostatic interactions was used in the trajectory calculations. The estimated TF-free solution structure was then compared with the crystal structure of factor VIIa/tissue factor complex to estimate the restructuring of factor VIIa due to tissue factor binding. The solution structure of the light chain of factor VIIa in the absence of tissue factor is predicted to be an extended domain structure similar to that of the tissue factor-bound crystal. Removal of the EGF1-bound calcium ion is shown by simulation to lead to minor structural changes within the EGF1 domain, but also leads to substantial relative reorientation of the Gla and EGF1 domains.     

Relations between factor VIIa binding and expression of factor VIIa/tissue factor catalytic activity on cell surfaces.

The kinetics of the binding of rVIIa to cell surface tissue factor (TF) and the resultant expression of VIIa/TF activity were studied. Binding of 125I-rVIIa (10 nM) to cell surface TF required 30-60 min for saturation, whereas VIIa/TF activity was fully expressed toward factor X (F X) on intact monolayers after only 1 min of incubation. At the time only 10-20% of the total VIIa TF complexes present at saturation had formed. Freeze-thawing the monolayers before assay increased VIIa/TF activity up to 30-fold, and the time course of its expression was similar to that of TF-specific binding of VIIa to the monolayers. Equilibrium binding revealed a single high affinity binding class of TF sites on intact monolayers for rVIIa with a Kd of 1.6 nM. Experiments with active-site inhibited rVIIa yielded evidence for two populations of VIIa. TF complexes on intact monolayers: (1) a minor population (less than 20%) that formed within 1 min of incubation and accounted for all VIIa/TF activity toward F X present on the intact monolayers, and (2) a major population that was inactive toward F X on intact monolayers but which was fully active after the monolayers were lysed. Tissue factor pathway inhibitor (TFPI).F Xa complexes inhibited the VIIa/TF activity of the first population, i.e. of the complexes active on intact monolayers, half maximally at a concentration of 0.2 nM TFPI. TFPI/Xa also bound to the second population of VIIa.TF complexes on intact monolayers and inhibited their expression of VIIa/TF activity following cell lysis with a half-maximal inhibitory concentration of 2.0 nM. The potential physiologic implications of these findings are discussed.     

Residue Met(156) contributes to the labile enzyme conformation of coagulation factor VIIa

Serine protease activation is typically controlled by proteolytic cleavage of the scissile bond, resulting in spontaneous formation of the activating Ile(16)-Asp(194) salt bridge. The initiating coagulation protease factor VIIa (VIIa) differs by remaining in a zymogen-like conformation that confers the control of catalytic activity to the obligatory cofactor and receptor tissue factor (TF). This study demonstrates that the unusual hydrophobic Met(156) residue contributes to the propensity of the VIIa protease domain to remain in a zymogen-like conformation. Mutation of Met(156) to Gln, which is found in the same position of the highly homologous factor IX, had no influence on the amidolytic and proteolytic activity of TF-bound VIIa. Furthermore, the mutation did not appreciably stabilize the labile Ile(16)-Asp(194) salt bridge in the absence of cofactor. VIIa(Gln156) had increased affinity for TF, consistent with a long range conformational effect that stabilized the cofactor binding site in the VIIa protease domain. Notably, in the absence of cofactor, amidolytic and proteolytic function of VIIa(Gln156) were enhanced 3- and 9-fold, respectively, compared with wild-type VIIa. The mutation thus selectively influenced the catalytic activity of free VIIa, identifying the Met(156) residue position as a determinant for the zymogen-like properties of free VIIa.     

Crystallographic analysis at 3.0-A resolution of the binding to human thrombin of four active site-directed inhibitors

The mode of binding of four active-site directed inhibitors to human thrombin has been determined by x-ray crystallographic analysis. The inhibitors studied are benzamidine, PPACK, NAPAP, and MD-805, of which the last three are compounds evolved specifically to inhibit thrombin. Crystal structures were determined in the presence of both the inhibitor and the undecapeptide [des-amino Asp55]hirudin(55-65) which binds distant from the active site. Despite having significantly different chemical structures, NAPAP and MD-805 bind to thrombin in a very similar "inhibitor binding mode" which is not that expected by direct analogy with the binding of substrate. Both inhibitors bind to thrombin in a similar way as to trypsin, but thrombin has an extra loop, the "Tyr-Pro-Pro-Trp loop," not present in trypsin, which gives further binding interactions and is seen to move somewhat to accommodate binding of the different inhibitors. The fact that NAPAP and MD-805 require different stereochemistry for potent inhibition is demonstrated, and its structural basis clarified. The wealth of data on analogs and variants of these lead compounds is shown to be compatible with this inhibitor binding mode.     

Sphingosine inhibits monocyte tissue factor-initiated coagulation by altering factor VII binding

Tissue factor is a lipoprotein, expressed on the surface of cells, which binds coagulation Factor VII or VIIa, leading to activation of Factors X and IX with subsequent fibrin generation. Cellular tissue factor activity is important in pathophysiologic processes such as inflammation and disseminated intravascular coagulation. In this study, the long-chain base sphingosine inhibited coagulation initiated by lipopolysaccharide-stimulated intact human monocytes. Sphingosine (5-100 microM) also profoundly inhibited thromboplastin-initiated coagulation (greater than 90% decrease in thromboplastin activity). This inhibition was dose- and time-dependent. Sphingosine inhibited neither the intrinsic pathway of coagulation nor thrombin generation of fibrin. The sphingosine analogues sphingomyelin, ceramide, or N-acetylsphingosine did not affect thromboplastin activity, suggesting that the polar head of sphingosine was necessary for interaction of the molecule with the coagulation system. Investigation of the biochemical mechanism revealed that sphingosine (5-50 microM), but neither sphingomyelin nor ceramide, inhibited specific binding of radiolabeled Factor VII to lipopolysaccharide-stimulated intact monocytes. The results suggest that sphingosine may regulate monocyte tissue factor-initiated coagulation by modulating Factor VII binding to tissue factor. Sphingosine may represent a new class of inhibitors of hemostasis.     

Computer simulation of brainstem respiratory activity.

A mathematical model of the medullary respiratory oscillator, composed of two mutually inhibiting populations (inspiratory and expiratory) of computer-simulated neurons, is presented. Each population consists of randomly interconnected subpopulations of excitatory and inhibitory neurons, is presented. Each population consists of randomly interconnected subpopulations of excitatory and inhibitory neurons. Neuronal coupling is such that either the inspiratory or expiratory population alone is capable of cyclic activity. Weak inhibitory connections between inspiratory and expiratory populations provide satisfactory reciprocating activity independent of the natural frequency of either population alone. Initiation and persistence of rhythmic activity is dependent on a diffused noncyclic excitatory input. Vagal discharge, simulated by phasic inhibition of inspiratory neurons, results in increased respiratory frequency with decreased inspiratory activity. In the absence of simulated vagal discharge, uniform facilitation of synaptic connections increases averaged activities of inspiratory and expiratory populations, with minor effect on frequency. In the presence of simulated vagal discharge, facilitation of synaptic connections increases both frequency and amplitude. The simulated effects of synaptic facilitation, with and without vagal discharge, mimic the physiological response to CO2 in the intact and vagotimized animal.     

Synthesis, biological evaluation, and molecular docking studies of 1,3,4-thiadiazol-2-amide derivatives as novel anticancer agents

A series of 1,3,4-thiadiazol-2-amide derivatives (5a-5y) have been designed and synthesized, and their biological activities were also evaluated as potential antiproliferation and FAK inhibitors. Among all the compounds, 5h showed the most potent activity in vitro, which inhibited the growth of MCF-7 and B16-F10 cell lines with IC(50) values of 0.45 and 0.31 μM, respectively. Compound 5h also exhibited significant FAK inhibitory activity (IC(50)=5.32 μM). Docking simulation was performed to position compound 5h into the FAK structure active site to determine the probable binding model. The results of antiproliferative and Western-blot assay demonstrated that compound 5h possessed good antiproliferative activity. Therefore, compound 5h with potent FAK inhibitory activity may be a potential anticancer agent.     

Modeling Intracerebral Hemorrhage Growth and Response to Anticoagulation

The mechanism for hemorrhage enlargement in the brain, a key determinant of patient outcome following hemorrhagic stroke, is unknown. We performed computer-based stochastic simulation of one proposed mechanism, in which hemorrhages grow in “domino” fashion via secondary shearing of neighboring vessel segments. Hemorrhages were simulated by creating an initial site of primary bleeding and an associated risk of secondary rupture at adjacent sites that decayed over time. Under particular combinations of parameters for likelihood of secondary rupture and time-dependent decay, a subset of lesions expanded, creating a bimodal distribution of microbleeds and macrobleeds. Systematic variation of the model to simulate anticoagulation yielded increases in both macrobleed occurrence (26.9%, 53.2%, and 70.0% of all hemorrhagic events under conditions simulating no, low-level, and high-level anticoagulation) and final hemorrhage size (median volumes 111, 276, and 412 under the same three conditions), consistent with data from patients with anticoagulant-related brain hemorrhages. Reversal from simulated high-level anticoagulation to normal coagulation was able to reduce final hemorrhage size only if applied relatively early in the course of hemorrhage expansion. These findings suggest that a model based on a secondary shearing mechanism can account for some of the clinically observed properties of intracerebral hemorrhage, including the bimodal distribution of volumes and the enhanced hemorrhage growth seen with anticoagulation. Future iterations of this model may be useful for elucidating the effects of hemorrhage growth of factors related to secondary shearing (such as small vessel pathology) or time-dependent decay (such as hemostatic agents).