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Hemophilia is a bleeding disorder caused by deficiency in factors VIII or IX, the two components of the intrinsic Xase complex. Treatment with replacement factor can lead to the development of inhibitory antibodies, requiring the use of bypassing agents such as factor VIIa and factor concentrates. An alternative approach to bypass the Xase complex is to inhibit endogenous anticoagulant activities. Activated protein C (APC) breaks down the complex that produces thrombin by proteolytically inactivating factor Va. Defects in this mechanism (eg, factor V Leiden) are associated with thrombosis but result in less severe bleeding when co-inherited with hemophilia. Selective inhibition of APC might therefore be effective for the treatment of hemophilia. The endogenous inhibitors of APC are members of the serpin family: protein C inhibitor (PCI) and α1-antitrypsin (α1AT); however, both exhibit poor reactivity and selectivity for APC. We mutated residues in and around the scissile P1-P1' bond in PCI and α1AT, resulting in serpins with the desired specificity profile. The lead candidate was shown to promote thrombin generation in vitro and to restore fibrin and platelet deposition in an intravital laser injury model in hemophilia B mice. The power of targeting APC was further demonstrated by the complete normalization of bleeding after a severe tail clip injury in these mice. These results demonstrate that the protein C anticoagulant system can be successfully targeted by engineered serpins and that administration of such agents is effective at restoring hemostasis in vivo.

AB002 is a recombinant thrombin analog that generates endogenous activated protein C (APC) on intravascular surfaces in a thrombomodulin-dependent manner but does not promote thrombosis. Endogenously generated APC downregulates thrombin generation, thereby reducing pathological clot formation. During hemodialysis (HD), thrombi can form within the dialyzer filter and circuit, reducing dialyzer efficiency, and increasing blood loss. Heparin administration reduces clotting within the filter and circuit, but increases bleeding risk and is not tolerated in all patients. Since end-stage renal disease (ESRD) patients undergoing HD are at higher risk of both thromboembolism and bleeding, a safe, short-term and self-limiting anticoagulant alternative to heparin is currently an unmet need for this population. This is a phase 2, randomized, double-blind, placebo-controlled, single-dose study designed to evaluate the safety and efficacy of AB002 at two dose levels when administered to ESRD patients during heparin-free HD. A total of 36 adult patients are planned to be enrolled into two cohorts and dosed sequentially. Within each cohort, patients will be randomized to active drug (12) or placebo (6). Dose levels (1.5 µg/kg or 3 µg/kg; iv infusion) were based on safety data from a completed phase 1 study performed in healthy adult subjects (NCT03453060), which demonstrated that a single dose of AB002 was well tolerated, as well as based on preclinical efficacy studies performed in a baboon vascular thrombosis model. The primary objective of this phase 2 proof-of-concept study is safety and tolerability assessed as the number and severity of adverse events (AE), changes in baseline physical and lab parameters and immunogenicity of AB002. The number and severity of AE will be tabulated and summary statistics evaluated. The secondary objectives are to assess 1) pharmacodynamics using activated protein C/protein C inhibitor complexes in plasma as a surrogate marker for drug exposure, and 2) efficacy via pre-post dialyzer pressures, visual inspection of thrombus accumulation in the HD filter and dialysis efficiency based on urea kinetics. The study population includes ESRD patients on a stable outpatient HD regimen at least 3 times per week and excludes patients with history of acute vaso-occlusive thrombotic events, concomitant use of anticoagulant/antiplatelet agents immediately prior to and during the study, active cancer and bleeding disorders. This study is currently recruiting participants at one study site (Orlando Clinical Research Center) in Orlando, FL and is estimated to complete in October 2020 (NCT03963895). Disclosures Verbout: Aronora, Inc.: Employment, Equity Ownership. Lorentz:Aronora, Inc.: Employment. Markway:Aronora, Inc.: Employment. Shatzel:Aronora, Inc.: Consultancy. Tucker:Aronora, Inc.: Employment, Equity Ownership. Gruber:Aronora, Inc.: Employment, Equity Ownership.

Heparin-induced thrombocytopenia (HIT) is caused by antibodies that recognize complexes between platelet factor 4 (PF4) and heparin or glycosaminoglycan side chains. These antibodies can lead to a limb- and life-threatening prothrombotic state. We now show that HIT antibodies are able to inhibit generation of activated protein C (aPC) by thrombin/thrombomodulin (IIa/TM) in the presence of PF4. Tetrameric PF4 potentiates aPC generation by formation of complexes with chondroitin sulfate (CS) on TM. Formation of these complexes occurs at a specific molar ratio of PF4 to glycosaminoglycan. This observation and the finding that the effect of heparin on aPC generation depends on the concentration of PF4 suggest similarity between PF4/CS complexes and those that bind HIT antibodies. HIT antibodies reduced the ability of PF4 to augment aPC formation. Cationic protamine sulfate, which forms similar complexes with heparin, also enhanced aPC generation, but its activity was not blocked by HIT antibodies. Our studies provide evidence that complexes formed between PF4 and TM's CS may play a physiologic role in potentiating aPC generation. Recognition of these complexes by HIT antibodies reverses the PF4-dependent enhancement in aPC generation and may contribute to the prothrombotic nature of HIT.

Introduction: Direct oral anticoagulants are as effective as vitamin K antagonists for the treatment of venous thromboembolism and are associated with less bleeding. We have reported that a direct oral factor Xa inhibitor edoxaban exerts a thrombus resolution effect in a rat model of venous thrombosis and enhances tissue plasminogen activator (t-PA)-induced clot lysis in human plasma. However, the mechanism underlying the thrombus resolution effect and fibrinolysis enhancement by edoxaban remains to be determined. Purposes: To evaluate the effect of edoxaban on plasmin generation during clot lysis in human plasma in vitro. To determine the role of thrombin-activatable fibrinolysis inhibitor (TAFI) in the enhancement of fibrinolysis by edoxaban. Methods: Pooled human normal plasma or TAFI-deficient plasma (both containing 180 ng/mL t-PA and 0.1 nM thrombomodulin) was mixed with edoxaban, an activated TAFI (TAFIa) inhibitor (a fibrinolysis enhancer) potato tuber carboxypeptidase inhibitor (PCI), or vehicle. Clot was induced by adding 2.5 pM tissue factor and 4 µM phospholipids. To monitor the clot formation and lysis, the absorbance of plasma at 405 nm was measured every 30 sec. Clot lysis time was defined as the interval between the time of the midpoint of the clear to maximum turbidity transition and the midpoint of the maximum turbidity to clear transition. Plasmin-α2 antiplasmin complex (PAP) concentration was measured by ELISA as an indicator of plasmin generation. Results: In normal plasma, PCI accelerated clot lysis and increased plasma PAP concentration. There was a correlation between plasma PAP concentration and percent of clot lysis, indicating that plasma PAP concentration is an appropriate marker of fibrinolysis. Edoxaban at clinically relevant concentrations (75, 150, and 300 ng/mL) significantly shortened clot lysis time and elevated plasma PAP concentration. The additive combined effect of edoxaban and PCI was observed. In TAFI-deficient plasma, clot lysis time was shortened and plasma PAP concentration increased compared with normal plasma. In these samples, the effects of edoxaban and PCI on clot lysis and plasma PAP concentration were markedly diminished as compared with normal plasma. Conclusions: Edoxaban at clinically relevant concentrations enhanced t-PA-induced clot lysis with increasing plasma PAP concentration in human plasma. The effects of edoxaban on clot lysis and plasmin generation were diminished in TAFI-deficient plasma. A TAFIa inhibitor PCI exerted similar effects. These data suggest that edoxaban enhanced fibrinolysis via inhibition of TAFI activation and enhancement of plasmin generation. Disclosures Morishima: Daiichi Sankyo Co., Ltd.: Employment. Honda:Daiichi Sankyo Co., Ltd.: Employment. Furugohri:Daiichi Sankyo Co., Ltd.: Employment.

BACKGROUND: Tissue Factor Pathway inhibitor (TFPI) is a plasma serine protease inhibitor that modulates the initiation of coagulation by directly binding and inhibiting the Tissue Factor (TF)/Factor VIIa/Factor Xa complex. TFPI is a multi-Kunitz domain protein that directly binds to and inhibits both activated Factor Xa (FXa) and FVIIa. Blocking TFPI can act as a bypass therapy by facilitating hemostasis initiated by tissue factor/FVIIa, thereby, compensating for loss of Factor VIII or Factor IX (in hemophilia A or B). PF-06741086, a fully human antibody engineered to inhibit TFPI, exhibits broad cross reactivity to TFPI from numerous species, including mouse. PF-06741086 is being developed as a potential treatment for bleeding disorders including hemophilia A and hemophilia B with and without inhibitors. aPCC (activated Prothrombin complex concentrates or FEIBA, Factor Eight Inhibitor Bypass Agent) is a bypass agent for to control bleed in Hemophilia patients with inhibitors. Since it is a plasma-derived concentrate containing various prothrombin complex coagulation factors in their enzymatic or zymogen form, it is possible that FEIBA could potentially impact the activity of PF-06741086. AIMS: Here, we directly compare the hemostatic effect of PF-06741086 alone, and in combination with aPCC in Hemophilia A mouse model using severe tail vein transection. METHODS: Male hemophilia A mice were dosed with a single intravenous dose of PF-06741086 (0.5, 1, 2 or 6 mg/kg) 30 minutes prior to a 3mm tail clip, or aPCC (50, 100 or 200 U/kg) was administered 5 minutes before the tail clip. Mice were also treated with a combined dose of 0.5 mg/kg anti-TFPI PF-06741086 and aPCC at 50, 100 or 200 U/kg. Blood was collected for 10 minutes and quantified against a standard curve of hemoglobin as volume blood loss. RESULTS: PF-06741086 demonstrated a dose dependent response in improving hemostasis in Hemophilia A mice after tail clip. PF-06741086 was able to restore hemostasis at 1 mg/kg (49%), and higher doses further improved hemostasis at 2 mg/kg (63%), and 6 mg/kg (78%). aPCC also demonstrated a dose dependent reduction in blood loss and improved hemostasis with all tested doses of 50 U/kg (25%), 100 U/kg (23%) and 200 U/kg (66%). At a dose of 0.5 mg/kg, PF-06741086 did not show any improvement in hemostasis over vehicle control. We used this dose for all combination studies with aPCC. Combined use of low dose PF-06741086 (0.5 mg/kg) and 100 U/kg aPCC shows a trend towards improvement in hemostasis compared to either drug alone. A higher dose of aPCC (200 U/kg) combined with low dose PF-06741086 (0.5 mg/kg) significantly reduces blood loss (86%) in Hemophilia A mice in tail clip model compared to saline, TFPI or aPCC alone used at the same dose of 0.5 mg/kg or 200 U/kg respectively. CONCLUSIONS: Prophylactic administration of PF-06741086 exhibits a dose response and improves hemostasis in an injury model in Hemophilia A mice. The addition of aPCC alone restores hemostasis at 200 U/kg and this effect was enhanced in combination with PF-06741086 in this mouse model. Disclosures Barakat: Pfizer: Employment. Jasuja:Pfizer: Employment. Murphy:Pfizer: Employment. Pittman:Pfizer: Employment.

Protein C inhibitor (PCI) is a serpin with affinity for heparin and phosphatidylethanolamine (PE). We analyzed the interaction of PCI with different phospholipids and their oxidized forms. PCI bound to oxidized PE (OxPE), and oxidized and unoxidized phosphatidylserine (PS) immobilized on microtiter plates and in aqueous suspension. Binding to OxPE and PS was competed by heparin, but not by the aminophospholipid-binding protein annexin V or the PCI-binding lipid retinoic acid. PS and OxPE stimulated the inhibition of activated protein C (aPC) by PCI in a Ca++-dependent manner, indicating that binding of both, aPC (Ca++ dependent) and PCI (Ca++ independent), to phospholipids is necessary. A peptide corresponding to the heparin-binding site of PCI abolished the stimulatory effect of PS on aPC inhibition. No stimulatory effect of phospholipids on aPC inhibition was seen with a PCI mutant lacking the heparin-binding site. A heparin-like effect of phospholipids (OxPE) was not seen with antithrombin III, another heparin-binding serpin, suggesting that it is specific for PCI. PCI and annexin V were found to be endogenously colocalized in atherosclerotic plaques, supporting the hypothesis that exposure of oxidized PE and/or PS may be important for the local regulation of PCI activity in vivo.

The occurrence of protein C inhibitor (PCI) in human platelets and megakaryocytes was analyzed. As judged from enzyme-linked immunosorbent assays (ELISAs), PCI was present in platelets at a concentration of 160 ng/2 × 109 cells. Its specific activity was 5 times higher than that of plasma PCI. Consistently, mainly the 57-kD form (active PCI) and some high molecular weight (Mr) forms, but no bands corresponding to cleaved PCI, were detected when platelet lysates were immunoprecipitated with monoclonal anti-PCI-IgG and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting. The localization of PCI in platelets was studied by immunofluorescence histochemistry and immunotransmission electron microscopy: PCI was detected in  granules, in the open canalicular system, and on the plasma membrane. At these sites, colocalization with plasminogen activator inhibitor-1 was seen. Studies were performed to clarify whether platelet PCI is endogenously synthesized or taken up from plasma. Internalization of biotinylated-PCI was analyzed using platelets in suspension and gold-labeled streptavidin for visualization of incorporated biotin. Dose- and time-dependent uptake of PCI was found. PCI mRNA was detected in platelets by reverse transcriptase-polymerase chain reaction (RT-PCR) and Southern blotting, as well as in megakaryocytes by in situ hybridization of human bone marrow cryosections. We therefore conclude that platelets contain a functionally active PCI pool that is derived from both endogenous synthesis as well as internalization.

Protein C inhibitor (PCI), which was originally identified as an inhibitor of activated protein C, also efficiently inhibits coagulation factors such as factor Xa and thrombin. Recently it was found, using purified proteins, that the anticoagulant thrombin-thrombomodulin complex was also inhibited by PCI. The paradoxical inhibitory effect of PCI on both coagulant and anticoagulant proteases raised questions about the role of PCI in plasma. We studied the role of thrombomodulin (TM)-dependent inhibition of thrombin by PCI in a plasma system. Clotting was induced by addition of tissue factor to recalcified plasma in the absence or presence of TM, and clot formation was monitored using turbidimetry. In the absence of TM, PCI-deficient plasma showed a slightly shorter coagulation time compared with normal plasma. Reconstitution with a physiologic amount of PCI gave normal clotting times. Addition of PCI to normal plasma and protein C–deficient plasma resulted in a minor prolongation of the clotting time. This suggested that PCI can act as a weak coagulation inhibitor in the absence of TM. TM caused a strong anticoagulant effect in normal plasma due to thrombin scavenging and activation of the protein C anticoagulant pathway. This effect was less pronounced when protein C–deficient plasma was used, but could be restored by reconstitution with protein C. When PCI was added to protein C–deficient plasma in the presence of TM, a strong anticoagulant effect of PCI was observed. This anticoagulant effect was most likely caused by the TM-dependent thrombin inhibition by PCI. However, when PCI was added to normal plasma containing TM, a strong procoagulant effect of PCI was observed, due to the inhibition of protein C activation. PCI-deficient plasma was less coagulant in the presence of TM. A concentration-dependent increase in clotting time was observed when PCI-deficient plasma was reconstituted with PCI. The combination of these results suggest that the major function of PCI in plasma during coagulation is the inhibition of thrombin. A decreased generation of activated protein C is a procoagulant consequence of the TM-dependent thrombin inhibition by PCI. We conclude that TM alters PCI from an anticoagulant into a procoagulant during tissue factor-induced coagulation.

Mediterranean spotted fever (MSF) is a rickettsiosis that induces widespread microvascular injury. To obtain quantitative information on the in vivo activation and inactivation of the protein C system during the acute phase of endothelial damage, several components of the protein C pathway were studied in 28 MSF patients. Upon admission (day 1), patients showed clear evidence of endothelial damage as reflected by the significant decrease in the ratio VIII:C/vWF:Ag (0.36 +/- 0.14, mean +/- SD) compared with normals (0.98 +/- 0.14), and clinical and laboratory signs of hemostatic alterations such as decreased platelet count, positive fibrinogen/fibrin degradation products, and increased thrombin:antithrombin-III complex levels. Antigenic protein C (72% +/- 18%) and protein C inhibitor (PCI) (41% +/- 20%) were significantly decreased (P less than .001). Complexes of activated protein C (APC) with PCI or with alpha 1-antitrypsin (alpha 1AT) and of plasma kallikrein with PCI (KK:PCI) were measured using sandwich enzyme-linked immunosorbent assays. APC:alpha 1AT complex levels were increased in patients at day 1 (27 +/- 13 ng/mL) compared with controls (7 +/- 2 ng/mL), and APC:PCI and KK:PCI complexes, which were not detectable in any of the controls, were present in 57% and 75% of the 28 MSF patients, with mean levels of 11 +/- 5 and 46 +/- 16 ng/mL, respectively. After remission of the disease (day 30), a trend toward normal values in the majority of the parameters studied was found. This study shows that, in the course of endothelial injury, MSF patients experience a generalized activation of the protein C pathway, resulting in consumption of protein C and PCI, and in the appearance of APC:inhibitor complexes. Moreover, these data provide the evidence that KK:PCI circulating complexes occur in vivo.

In vivo complex formation of activated protein C with protein C inhibitor (APC-PCI) and with alpha 1-antitrypsin (APC-alpha 1AT) following infusion of 0.25 or 1.0 mg APC/kg in 1 hour into baboons was studied using immunoblotting and sandwich enzyme-linked immunosorbent assay (ELISA)s. Before APC infusion, detectable plasma levels (about 30 ng/mL) of APC-alpha 1AT complex were found in the baboon plasma. At the lower APC dose, APC-PCI and APC-alpha 1AT complex levels were 1.4 +/- 0.3 (mean +/- SD) and 0.8 +/- 0.1 microgram/mL after 1 hour of infusion. At the higher APC dose, the APC-PCI level was similar to the APC-alpha 1AT level during the first 30 minutes, but after 1 hour of infusion the APC-alpha 1AT level was higher than the APC-PCI level, reaching 4.1 +/- 1.2 and 2.9 +/- 1.2 microgram/mL, respectively. After 24 hours, complex levels had returned to basal conditions. During infusion of protein C (1.0 mg/kg in 1 hour), both complexes were detected in low concentrations. Following bolus injection of APC, half- lives (t1/2) for APC and APC-PCI and APC-alpha 1AT complexes of 10, 40, and 140 minutes, respectively, were observed. After 1-hour incubation with 2.5 micrograms/mL APC, baboon plasma contained 1.0 +/- 0.2 and 0.8 +/- 0.1 microgram/mL of APC-PCI and APC-alpha 1AT, respectively. Addition of 10 micrograms/mL APC to baboon plasma yielded 2.5 and 2.4 micrograms/mL APC-PCI and APC-alpha 1AT after 1 hour, respectively. Immunoblotting analysis also showed in vivo formation of complexes of APC with an auxilliary inhibitor but not in vitro in citrated plasma. These data show that both PCI and alpha 1AT are physiologic inhibitors of APC and suggest that when PCI is depleted by a high dose of APC, alpha 1AT becomes the major inhibitor of APC.

The rates of clearance and catabolism of human protein C inhibitor (PCI) and human alpha 1-antitrypsin (alpha 1-AT) and their complexes with human activated protein C (APC) were studied in the rabbit. The radioiodinated-free inhibitors had biologic half-lives of 23.4 and 62.1 hours, respectively, while the corresponding *I-labeled activated- protein C complexes were cleared with half-lives of 19.6 +/- 3.1 and 72.2 +/- 6.1 minutes. Complex clearances were linked to their catabolism as shown by a correlation between clearance and the appearance of free radioiodine in the plasma. Thus, the difference in the rates of catabolism would result in a fivefold greater amount of alpha 1-AT-APC complex than PCI-APC complex 1 hour after the formation of equal amounts of these in vivo. These results lead to the conclusion that the relative contribution of PCI and alpha 1-AT to the physiologic inhibition of APC cannot be determined only from the rates of the formation of these complexes in vitro, or from measurement of their levels in plasma. The APC-PCI complex is unstable as compared with the APC-alpha 1-AT complex, compounding the problem of estimating rates of complex formation from their levels in plasma.

Abstract 2223 Disseminated intravascular coagulation (DIC) represents a complex pathophysiologic syndrome where marked alterations in the hemostatic system are manifested. As a result several inflammatory mediators are up regulated through multiple mechanisms. The up regulation of inflammatory mediators such as anaphylatoxin C5a (C5a), procalcitonin (PCT), interleukin 6 (IL-6), interleukin 10 (IL-10), myeloperoxidase (MPO), C reactive protein (CRP), and circulating levels of hemostatic markers including protein C inhibitor (PCI), plasminogen activator inhibitor 1 (PAI-1), and protein C (Pr C) were evaluated in 758 subjects enrolled in a randomized, double-blind, placebo-controlled, Phase-2B study evaluating the safety and efficacy of recombinant thrombomodulin (ART-123) in subjects with sepsis and suspected DIC. Thirty healthy male and female volunteers served as the control group. Commercially available ELISA methods were used to measure the various mediators. Marked deviations in the circulating levels of these markers, as compared to controls, were noted as shown in the following table. Compared with controls, subjects in DIC showed an increase in the circulating levels of most inflammatory markers. The levels of PCT, IL-6 and CRP, where considerably higher in the DIC subjects whereas PCI, Pr C and AT exhibited slight decreases. Wide individual variations were present. The PAI-1 levels were also increased in the DIC subjects. These results are tabulated below. These results clearly indicate that inflammation and impairment of fibrinolysis play a key role in the pathogenesis of DIC Parameter Nomal (NHP Mean+SEM) DIC (Baseline Mean+SEM) % Change Protein C (% Ag) 82.5 ± 13.6 47.6 ± 23.7 −42.2% Functional Protein C (%) 83.4 ± 13.2 46.2 ± 29.8 −44.6% PCI (% Inhibition) 130.0 ± 24.6 79.4 ± 105.5 −38.9% PAI-1 (ng/ml) 35.4 ± 10.8 140.6 ± 165.6 297.1% CRP (ug/ml) 2.6 ± 0.4 48.0 ± 14.2 1736.9% C5a (ng/ml) 9.2 ± 3.2 17.2 ± 13.3 85.1% IL-6 (pg/ml) 9.3 ± 3.7 620.3 ± 1883.4 6583.9% IL-10 (pg/ml) 13.9 ± 13.1 130.2 ± 118.6 836.1% MPO (ng/ml) 16.0 ± 4.2 108.1 ± 68.6 574.6% PCT (ng/ml) 0.2 ± 0.13 21.9 ± 43.3 14514.5% Disclosures: Osawa: Asahi Kasei Pharma America Corporation: Employment. Kaul:Asahi Kasei Pharma America Corporation: Employment.

Abstract 772 Chromosomal inversion inv(16)(p13.1q22) is found in approximately 12% of acute myeloid leukemia (AML) patients, and leads to the fusion of the transcription factor gene CBFb and the MYH11 gene, and encodes a fusion protein CBFβ-SMMHC. Previous studies revealed that CBFβ-SMMHC is a dominant inhibitor of core-binding factor (CBF) function, and impairs hematopoietic differentiation. Expression of CBFβ-SMMHC predisposes for leukemia transformation, however, the molecular mechanism underlying the leukemogenic function of CBFβ-SMMHC remains elusive. The tumor suppressor p53 is considered the master genomic guardian that is frequently mutated in a wide variety of tumors but is rarely mutated in inv(16) AML. Thus, we examined whether CBFβ-SMMHC fusion protein might impair p53 function. We found that p53 acetylation (Ac-p53) level was reduced in the presence of CBFβ-SMMHC fusion protein in the myeloid progenitor 32D cell line as well as in primary pre-leukemic bone marrow progenitor cells isolated from our conditional Cbfb-MYH11 knock-in (Cbfb56M/+/Mx1-Cre) mice (Kuo et al, Cancer Cell 2006, 9:1,57-68). We assessed the effect of CBFβ-SMMHC on p53 transcriptional activity by quantitative RT-PCR analysis of p53 target genes including TP53 and p21 Cdkn1a, Mdm2, Bid, Bax, Stag1, LincRNA-p21, Gadd45b in 32D cells. The result showed that expression of these p53 target genes are reduced in the presence of CBFβ-SMMHC fusion protein, consistent with the impaired Ac-p53 by CBFβ-SMMHC. To understand how CBFβ-SMMHC impairs p53 function, we tested whether CBFβ-SMMHC fusion protein might interact with the p53 protein by co-immunoprecipitation (co-IP) assays. We found that CBFβ-SMMHC fusion protein interacts with p53 both in 32D cells and primary bone marrow cells. Although CBFβ-SMMHC fusion protein is detected both in the nucleus and the cytoplasm, the complex with p53 is present exclusively in the nucleus. It has been reported that CBFβ-SMMHC interacts with histone deacetylase 8 (HDAC8) through the C-terminal SMMHC region. Therefore, we assessed the interaction between CBFβ-SMMHC, p53 and HDAC8 in 32D cell line by co-IP and sequential co-IP. We were able to detect a multimeric protein complex containing CBFβ-SMMHC, p53, and Hdac8. To access whether HDAC8 contributes to the deacetylation of p53, we used two independent small-hairpin (sh)-RNA to knock-down Hdac8 in 32D-CBFβ-SMMHC cells. Hdac8 knock-down led to robust increase in Ac-p53 levels while total p53 levels were modestly stabilized. To test whether this effect is dependent on the deacetylase function of HDAC8, we used HDAC8 selective pharmacological inhibitors (HDAC8i including PCI-34051 and PCI-48012) directed against its catalytic sites (Balasubramanian et al Leukemia 2008, 22:5,1026-34). Treatment with HDAC8i remarkably increased Ac-p53 in both control and CBFβ-SMMHC cells. Since p53 protein levels were also increased upon HDAC8i treatment, we included Mdm2 inhibitor Nutlin-3 to stabilize p53. HDAC8i treatment alone or in combination with Nutlin-3 was able to enhance Ac-p53 compared to Nutlin-3 treatment, confirming its effect in restoring p53 acetylation. Collectively, our study shows that the CBFβ-SMMHC fusion protein forms an aberrant complex with p53 and HDAC8, leading to the aberrant deacetylation and impaired activity of p53. In addition, this deacetylation of p53 conferred by CBFβ-SMMHC is mediated by HDAC8. Our study reveals a novel leukemogenic mechanism in which CBFβ-SMMHC disrupts p53 activation through aberrant protein-protein interaction and recruitment of HDAC8. Disclosures: No relevant conflicts of interest to declare.

Abstract 3656 Disseminated intravascular coagulation (DIC) represents a complex polypathologic syndrome where marked alterations in the hemostatic system are manifested. As a result several inflammatory mediators are upregulated through multiple mechanisms. The upregulation of inflammatory mediators such as anaphylatoxin C5a (C5a), procalcitonin (PCT), interleukin 6 (IL-6), interleukin 10 (IL-10), myeloperoxidase (MPO) and c reactive protein (CRP), and circulating levels of hemostatic markers including protein C inhibitor (PCI), plasminogen activator inhibitor 1 (PAI-1), prothrombin fragment1.2 (F1.2), thrombin antithrombin complex (TAT), antithrombin (AT), activated protein C (APC) and protein C (Pr C) were evaluated in the baseline samples of an initial cohort of provisionally diagnosed DIC and sepsis patients enrolled in an ongoing clinical trial designed to assess the safety and efficacy of r-thrombomodulin (ART-123) (n=100). The control group consisted of normal male and female volunteers (n=30). Commercially available ELISA methods were used to measure the various mediators. Marked deviations in the circulating levels of these markers, as compared to controls, were noted as shown in the following table. Compared with normal volunteers, patients showed a 5–10 fold increase in the circulating level of most inflammatory markers, with the exception of PCT, IL-6 and CRP, where the increase was over 50 fold. PCI, Pr C and AT exhibited slight decreases. Wide individual variations were obvious. These results clearly indicate that inflammation, thrombin generation, impairment of fibrinolysis and impairment of endogenous anticoagulants play a key role in the pathogenesis of DIC. Marker Normal Human Volunteers (n=30) DIC with Sepsis Patients (n=100) Fold Change PCT (ng/ml) 0.1 ± 0.04 (0.01) 18.7 ± 31.2 (3.1) 187× Increase C5a (ng/ml) 6.7 ± 1.7 (0.5) 15.5.7 ± 14.9 (1.5) 2× Increase PCI (% NHP) 138.9 ± 71.1 (8.8) 106.9 ± 33.4 (7.1) 1.3× Decrease IL-6 (pg/ml) 2.5 ± 1.2 (0.3) 522.5 ± 881.5 (88.2) 210× Increase IL-10 (pg/ml) 9.8 ± 5.23 (1.7) 46.9 ± 73.3 (8.8) 5× Increase MPO (ng/ml) 15.1 ± 10.1 (2.7) 111.4 ± 74.9 (7.5) 7× Increase PAI-1 (ng/ml) 31.7 ± 8.9 (3.1) 130.2 ± 178.1 (22.1) 4× Increase F1.2 (pM) 108.6 ± 46.2 (12.3) 473.7 ± 320.2 (32.0) 4× Increase TAT (ng/ml) 4.4 ± 1.1 (0.3) 17.0 ± 30.8 (3.1) 5× Increase AT (% NHP) 94.2 ± 10.3 (2.7) 80.4 ± 30.7 (3.1) 1.2× Decrease APC (ratio) 2.23 ± 0.3 (0.1) 2.48 ± 0.4 (0.04) 1.1× Increase CRP (ug/ml) 0.5 ± 1.1 (0.3) 38.4 ± 3.9 (0.4) 76× Increase Pr. C (% NHP) 78.3 ± 13.3 (3.6) 41.3 ± 17.4 (1.7) 2× Decrease Disclosures: Kaul: Artisan Pharma: Employment.

To the editor: Protein C inhibitor in platelets? In a recent article, Prendes et al[1][1] described the presence and localization of protein C inhibitor (PCI) in blood platelets. The concentration of PCI antigen that was determined in platelet lysates was 160 ng/2 × 109 platelets. Although this

Abstract 3167 Poster Board III-107 Introduction Thrombin (IIa), when bound to thrombomodulin (TM), readily converts protein C (PC) into activated PC (APC). APC functions as an anticoagulant by inactivating activated factors V (FVa) and VIII (FVIIIa), and indirectly reduces IIa generation. Once formed, APC activity is controlled through inhibition by PC inhibitor (PCI), a reaction that is catalyzed by heparin (H). Chan et al. developed a covalent antithrombin-heparin (ATH) complex with increased anticoagulant activity compared to H. The current investigation looked at the role and mechanism by which ATH affects the inhibition of APC by PCI. Methods Discontinous second order rate constant inhibition assays of APC+PCI, in the presence of ATH or unfractionated H (UFH), were performed. These experiments were repeated in the presence of low molecular weight H (LMWH) or ATH (LMWATH), or a high molecular weight ATH (HMWATH). The affinity of ATH or UFH for APC or PCI was assessed using native electrophoresis and APC or PCI immobilized onto agarose beads. Results Second order rate experiments revealed that, at peak values, ATH (k2=2.0 × 107 ± 1.2 × 106) was a significantly slower catalyst of APC inhibition by PCI than UFH (k2= 3.0 × 107 ± 2.0 × 106; p=0.005). The peak reaction rate value for UFH occurred at a higher catalyst concentration (300nM) compared to ATH (60nM). LMWH was a poor catalyst of APC inhibition by PCI (k2= 4.2 × 105 ± 8.2 × 104). However, both LMWATH and HMWATH had high catalytic function (k2= 4.1 × 107 ± 2.1 × 106 and k2= 2.7 × 107 ± 4.8 × 105, respectively). Although UFH and ATH were able to bind to either APC or PCI at a pH of 7.3, increasing the pH to 8.8 eliminated all binding affinity, except that of ATH for APC. Conclusion UFH functions mechanistically through a template-mediated effect by bridging APC with PCI. The catalytic function of UFH is dependent upon H chain length, as LMWH was ineffective at enhancing APC inhibition by PCI. On the other hand, ATH may act mainly through conformational APC activation. There was no H chain length dependence for ATH, as LMWATH was able to significantly catalyze PCI inhibition of APC. We speculate that ATH's AT moiety may assist interaction with APC but prevents the H component of ATH from bridging the enzyme with the inhibitor. Compared to UFH, ATH is a more potent inhibitor of IIa, but is less effective at inhibiting APC and thereby decreasing IIa generation. These results add to the growing evidence that ATH is a superior anticoagulant to UFH. Disclosures No relevant conflicts of interest to declare.

Abstract 2122 Poster Board II-99 Protein C Inhibitor (PCI, SERPINA5, PAI3) is a non-specific, secreted serine protease inhibitor (serpin) which circulates at low levels (5μg/mL or 90nM) in blood plasma (review: Geiger 2007, Suzuki 2008). First described as an inhibitor of activated protein C (APC) an anticoagulant serine protease in human plasma, it has been shown that PCI inactivates a variety of other proteases and has a wide tissue distribution. Some compounds like glycosaminoglycans (e.g. heparin, heparan sulfate) and certain phospholipids can modify PCI activity. Recently it was shown that single-stranded DNA aptamers stimulates the inhibitory activity of PCI towards APC in a glycosaminoglycan-like fashion (Müller 2009). In 2007 Malleier et al. analyzed the interaction of PCI with phosphatidylserine (PS), oxidized PS (OxPS) and oxidized phosphatidylethanolamin (OxPE). PS, OxPS and OxPE bind to PCI and enhance the stimulation of APC-inhibition 130 to 190-fold. In addition, PE supports the internalization of PCI by cells, and internalized PCI promotes phagocytosis of bacteria (Baumgärtner et al. 2007). JFC1 (synaptotagmin-like protein 1) was identified by our group as a new intracellular interaction partner of PCI and colocalization of PCI and CSN6, a subunit of the COP9 signalosome could be observed in lymphocytes. Here, we analyzed the interaction of PCI with phosphatidic acid (PA), phosphatidylglycerol (PG), cardiolipin (CL), phosphoinositides and derived second messengers like inositol-1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). To identify lipid-regions which are important for PCI binding we were focusing on differences in fatty acid composition and headgroup phosphorylation. The binding was studied by native PAGE, protein overlay assays (dot blot analysis) or ELISA. The stimulation of PCI activity towards APC was analyzed in functional assays using a low molecular weight substrate (S-2366). IP3 and inositol-1,3,4,5-tetrakisphosphate (IP4) did neither interact with PCI nor stimulate its activity towards APC. PCI bound to saturated, unsaturated and oxidized PA. The oxidized form of 1-palmitoyl-2-arachidonoyl-phosphatidic acid (OxPAPA) exhibited lower binding to PCI, but higher stimulatory activity on APC inhibition, as compared to unoxidized PAPA. Saturated dipalmitoyl-PA did not modulate PCI activity. From all studied lipids 1-palmitoyl-2-arachidonoyl-PG (PAPG) had the strongest stimulatory effect on APC-inhibition similar to 0.1μM low molecular weight heparin. Oxidation of PAPG led to a slight decrease and saturation to a complete loss in stimulatory activity. Also tetra-oleoyl-CL bound to PCI with high affinity and had a similar effect as oxidized PAPG and OxPAPA. All mono- and diphosphorylated phosphoinositides as well as phosphatidylinositol-3,4,5-triphosphate (PI3,4,5P3) bound to PCI as judged from binding assays. A mobility shift of PCI antigen on native PAGE was observed when PCI was incubated with phosphatidylinositol-3,5-diphosphate and phosphatidylinositol-4,5-diphosphate (PI4,5P2). Therefore different phospholipids modulate the activity of PCI, but on the other hand PCI may as well effect lipid signaling. As PI4,5P2 plays an important role as substrate for PI3-kinase we will take a closer look at the effect of PCI on the PI3K/PTEN system and on the activation of AKT (PKB) by PDK1. We will also study the influence of PCI on the generation of IP3 and DAG and its possible role in calcium signaling and protein kinase activation. So far we conclude that phosphoinositides and other glycerophospholipids may function as additional intracellular interaction partners of PCI. Disclosures: No relevant conflicts of interest to declare.

Protein C inhibitor (PCI) is a plasma serine protease inhibitor (serpin) that inhibits several proteases in blood coagulation including thrombin, thrombin-thromobomodulin and activated protein C. Although PCI has been shown to inhibit these key blood coagulation proteases, a clearly defined hemostatic role for PCI remains to be elucidated. Preliminary results from our laboratory show that exogenously added PCI prolongs venous thrombus formation upon blood vessel injury in a murine model of vascular injury. These results suggest that PCI may be responsible for inhibiting other proteases in blood coagulation, possibly including factor VIIa. Blood coagulation is initiated when factor VIIa binds to TF on cell surfaces. We investigated the ability of PCI to inhibit factor VIIa, both in the presence and absence of TF in vitro, and in a cellular environment. It has been shown previously and we have confirmed that the serpin antithrombin (AT) inhibits both factor VIIa and factor VIIa/TF; however, the ability of PCI to inhibit this protease has not been fully investigated. PCI and AT inhibit factor VIIa in the presence of TF and heparin (AT: k2=1.1 × 104 M−1 s−1; PCI: k2=7.2 × 103 M−1s−1). In the absence of heparin the inhibition of factor VIIa/TF by PCI is reduced 10-fold. Interestingly, PCI is unable to inhibit VIIa in the absence of TF with or without heparin. Furthermore, both PCI and AT form SDS-stable complexes with factor VIIa (in the presence of TF). We also investigated whether PCI is able to inhibit VIIa-mediated cell migration of the breast cancer cell line MDA-MB-231 that constitutively expresses TF. AT and PCI are able to inhibit cell surface derived factor VIIa/TF. Interestingly, the rate of factor VIIa inhibition on MDA-MB-231 cells is 1.2 and 0.4 × 103 M−1s−1 for PCI and AT, respectively. The factor VIIa-mediated cell migration of MD-MB-231 cells is attenuated in the presence of PCI, but not in the presence of the PCI inactive mutant (T341R). Given that both AT and PCI are able to inhibit factor VIIa/TF both in vitro and in a cellular environment, suggests that more potent derivatives (prepared by site-directed mutagenesis) of these serpins may be useful alternatives as novel therapeutics anticoagulants that target the initial step in the coagulation pathway.

〈Background and Methods〉: High-grade fever prior to engraftment without any apparent signs of infection, mimicking hyperacute GVHD or engraftment syndrome, is often observed in patients who undergo cord blood transplantation (CBT). This “pre-engraftment immune reaction (PIR)” peaks at around day 9 of CBT, and is often accompanied by high-grade fever, skin rash and weight gain. Although PIR responds well to corticosteroid therapy, the prolonged use of steroid often causes an increased incidence of infectious complications, leading to significant treatment-related mortality, particularly in the elderly. It has been speculated that cytokines induced by the initial immune/inflammation reaction are the primary cause of PIR, but no confirming data are available. To clarify this point, we evaluated the protein expression profile of serum in CBT recipients using a surface-enhanced laser desorption/ionization time-of-flight mass spectroscopy (SELDI-TOF MS) system and found marker candidates in PIR after CBT. 〈Results〉: Thirty-eight blood samples were taken from 13 CBT recipients at 3 different occasions, i.e. afebrile period prior to PIR onset, onset of fever and resolution of fever, to compare the relative protein expression levels. Samples were analyzed in 56 spectra by changing the elution conditions with 4 kinds of chips (IMAC30, CM10, H50, Q10), 5 different rinse conditions and 3 kinds of energy absorption molecules. Six candidate protein peaks that commonly increase at the time of PIR with molecular masses of 8611Da, 8642Da, 11452Da, 11512Da, 11539Da and 11669Da were identified. The 11kDa protein peaks that bind to a Q10-anion exchange chip were selected for further analysis. Two 11kDa protein peaks were eluted at pH9 and pH4, but since the proteins eluted at pH4 included albumin which overlapped the candidate protein peak, the elution fraction at pH9 was used for purification and identification. Proteins eluted at pH9 were separated by SDS-PAGE. After in-gel digestion of the 11kDa band by trypsin, the digested peaks were analyzed by PCI Qstar MSMS and the protein was determined using the ProFound database. The results revealed that the 11kDa protein was an N-terminal portion of serum amyloid A (SAA). The SAA level was measured by ELISA in the same sample that was assessed by SELDI-TOF MS. The mean SAA level prior to fever onset was 14 (3–51) μg/mL, and this increased to 883 (40–2470) μg/mL at the time of PIR and decreased to 45 (8–126) μg/mL after resolution of the fever. 〈Conclusion〉: A specific marker for PIR after CBT was identified by an SELDI-TOF MS system. SAA increased by 10- to 100-fold at the time of PIR, and thus may become a useful tool for the diagnosis of PIR. Figure Figure

Pharmacodynamic evaluation of novel antiplatelet agents in clinical trials has traditionally proven problematic due to the inaccessibility of assays to measure the effects on platelet thrombosis in human blood. The present study utilized real-time perfusion chamber technology (RTTP) to compare the antithrombotic activities of PRT128, an orally available, direct-acting, reversible P2Y12 antagonist, to those achieved by chronic dosing of humans with clopidogrel (C, 75 mg/day, ± aspirin (A)). PRT128 was added in vitro to blood collected from healthy volunteers (n=20) at baseline (no treatment) and following A treatment, allowing comparison to C (±A) treatments. Blood samples were monitored using the RTTP assay, where thrombus formation was initiated by a combination of a collagen-coated surface and physiologic shear. 1.25 mM PRT128 provided equivalent inhibition of the thrombotic process achieved by chronic dosing of C (75 mg/d, 14 d)(±A, 325 mg/d, 7 d): higher concentrations (2.5, 5 mM) of PRT128 provided superior inhibition. Although neither P2Y12 antagonist alone affected the initial rate of thrombus formation, both destabilized growing thrombi, to a greater extent in the presence of aspirin, with larger effects achieved by the direct P2Y12 antagonist. Light transmittance platelet aggregation (PA) assays using platelet rich plasma (initiated by ADP (10 mM) or collagen (4 mg/ml)) indicated that the concentration of PRT128 which provided similar inhibition to C (±A) was 0.5–3 mM, while higher concentrations achieved greater inhibition. The RTTP assay was also used to determine the levels of inhibition of thrombosis achieved by C plus A treatment in 5 diabetic patients undergoing stent-placement. Interestingly, 2 of the 5 patients displayed a profile typical of a non-responder (i.e., no observed thrombus destabilization). However, when 2.5 or 5 mM PRT128 was added in vitro to blood from these patients, a clear antithrombotic effect was observed, indicating that the lack of benefit of C plus A therapy in these patients was due to C nonresponsiveness which could be circumvented by the direct-acting antagonist PRT128. Finally, a unique feature of a direct-acting P2Y12 antagonist was revealed using the RTTP assay. Thrombi formed by the perfusion of untreated whole blood for 3 minutes through the perfusion chamber were subsequently exposed to a perfusion of blood treated with PRT128. The second perfusion destabilized thrombi, illustrating the role of ADP acting on P2Y12 in maintaining thrombus stability. In summary, through use of novel perfusion chamber technology, we demonstrate that (1) PRT128, a direct-acting P2Y12 antagonist, can provide superior levels of platelet inhibition than achieved by C (±A), (2) PRT128 can overcome the limitations of C in diabetic patients undergoing PCI who appeared to be C non-responders, (3) direct-acting P2Y12 antagonism can induce destabilization of existing thrombi, and (4) the RTTP assay provides a unique tool for dose selection and evaluation of clinical indications for the further development of PRT128 and other novel antiplatelet agents.

Protein C Inhibitor (PCI) is a non-specific serine protease inhibitor (serpin), which inhibits many proteases of the coagulation and fibrinolytic systems. PCI binds to heparin, and heparin enhances the interaction of PCI with most proteases. It has been shown by Nishioka et al. (1998) that PCI also binds to phosphatidylethanolamine (PE), a major phospholipid of the inner leaflet of cell membranes, and that PCI inhibits phospholipid-bound activated protein C (APC) efficiently. These data suggest a biological role of PE exposed on the surface of activated platelets and microvesicles for the regulation of PCI activity in vivo. To further analyze to which extent phospholipids could play a role for the regulation of PCI activity, we studied the interaction of PCI with different phospholipids and their oxidized forms. We investigated binding of PCI to phospholipids [PE, phosphatidylserine (PS), and phosphatidylcholine (PC) and their oxidized forms] immobilized on microtiter plates. To control for specificity of the binding, studies were performed in the absence and presence of varying concentrations of different phospholipids and heparin in the fluid phase. These studies revealed specific binding of PCI to oxidized and to unoxidized PS, and to oxidized but not to unoxidized PE. No binding was seen with oxidized or unoxidized PC. Binding to ox-PE and PS was confirmed by a mobility shift of PCI in native PAGE. Binding of PCI to oxidized PE and PS was competed by heparin. Furthermore, PCI, in which the heparin-binding site (Lys276-Lys277-Arg278) in the H-helix was mutated to Ala-Ala-Gly, no longer bound to ox-PE or PS. We also investigated the effect of phospholipids on the interaction of PCI with its target proteases APC and urokinase (uPA) by analyzing inhibition of amidolytic activity and complex formation on SDS-PAGE. PS (oxidized as well as unoxidized) and oxidized PE stimulated the inhibition of APC and uPA by PCI and enhanced complex formation of PCI with these proteases. No stimulatory effect of phospholipids was seen with the PCI mutant lacking the heparin-binding site. The effect of oxidized PE and PS on the interaction of PCI with APC was strongly dependent on the presence of Ca++. In the absence of Ca++ oxidized PE and PS interfered in a dose-dependent manner with the interaction of APC with PCI; and this effect was antagonized by heparin. Therefore, binding of both, APC (Ca++-dependent) as well as PCI (Ca++-independent), to PS or oxidized PE are required for the stimulating effect of these phospholipids on APC-inhibition by PCI. The stimulatory effect of PS and oxidized PE seems to be specific for PCI since it was not seen with antithrombin III, another heparin-binding serpin. In conclusion, our data indicate that in addition to heparin and glycosaminoglycans also certain phospholipids (oxidized PE and PS) can stimulate the activity of the non-specific serpin PCI. Binding to these phospholipids seems to involve the heparin-binding site of PCI. Exposure of oxidized PE and /or PS may therefore be important for the regulation of PCI-activity in vivo. This may play a role at sites of inflammation and/or apoptosis (e.g. on atherosclerotic plaques) or other sites where ox-PE or PS are exposed (e.g. in myotube fusion). In fact, in mouse embryos PCI antigen seems to co-localize with PS at sites of cell fusion and apoptosis.

Earlier we showed high heritability for the variation in levels of activated protein C-protein C inhibitor complex in a large kindred with type I protein C deficiency (Vossen et al. 2004). To identify genomic regions, which might harbour a gene with a mutation that accounts for a difference in the levels of activated protein C-protein C inhibitor complex, we performed a variance component linkage analysis. Family members were genotyped for 375 autosomal markers at the Marshfield Medical Research Foundation with an average marker spacing of 9.4 cM (range 0–18 cM) and an average marker heterozygosity of 75% (range 42–89%). Levels of activated protein C-protein C inhibitor complex were measured using commercial paired antibody sets from Affinity Biologicals Inc. (Ancaster, Ontario, Canada). We estimated the probability of Identity By Descent (IBD) using the multipoint IBD method in Simwalk2 (Sobel & Lange 1996), in which the proportion of alleles shared identical by descent at marker loci is used to estimate IBD sharing at arbitrary points along the chromosome for each relative pair. Then, variance component linkage analysis was performed using SOLAR (Almasy & Blangero 1998) to test whether a proportion of the genetic variance in the levels of activated protein C-protein C inhibitor complex could be attributed to specific genomic locations. The levels of activated protein C-protein C inhibitor were log-transformed to reduce skewness (from 3.0 to 0.2) and kurtosis (from 11.6 to 0.4) and were assumed to distribute as a multivariate normal density with correlation =h2K + c2H + q2B + e2I, where matrix K contains the kinship coefficients, H contains 1 for pairs from the same household and 0 otherwise, B contains the IBD probabilities, and I represents the identity matrix. The parameters for heritability (h2), household effect (c2), and heritability contributed to a specific genomic location (q2) as well as the effects of the covariates were estimated simultaneously using maximum likelihood analysis. Lod scores were computed as the log10 likelihood for q2 estimated to q2=0. A lod score of 3.3 was used as cut-off point for statistical evidence for significant linkage (as suggested by Lander and Kruglyak 1995), and a lod score above 1.9 but below 3.3 for suggestive linkage evidence. We found suggestive linkage evidence for levels of activated protein C in complex with protein C inhibitor in 121 tested family members (without a history of venous thrombosis) for a region on chromosome 11 (marker D11S969, 146 cM) with a LOD-score of 2.6, with age added to the model. As no obvious candidate genes were available under the peak, and because the linkage region is too wide to be certain of linkage, we are currently finemapping the peak by adding microsatellite markers to the genome scan to narrow the region on chromosome 11.

Malignant hematologic disorders may be associated with coagulopathy causing bleeding or thromboembolic complications. Severe infections as well as chemotherapy may augment this risk by the action of inflammatory mediators and the release of proteases. We evaluated the hemostatic process in 10 patients with acute myeloid leukemia (no acute promyelocytic leukemia) before the start of induction therapy with IDA-C and daily during the following two weeks of treatment. Various hemostatic parameters were studied, including the complex between activated protein C and the protein C inhibitor (APC-PCI) with a newly developed method, thrombin generation, protein C, prothrombin fragment 1+2 (F1+2), antithrombin and factor VIII. The APC-PCI concentration was relatively high in all patients at start of treatment (mean 0.81 ± SEM 0.27 μg/L; normal range 0.07–0.26 μg/L) reflecting an activation of the coagulation system, and further increased during the initial phase of chemotherapy reaching the highest level on Day 3 to 5 of 1.67±0.53 μg/L (p=0.0047). The concentration of the complex then declined during the following 10 days to 0.10±0.03 μg/L on Day 14, i.e. to a concentration significantly lower than that at start of treatment (p=0.005). The concentration of F1+2 varied in a similar way with a concentration of 2.17±0.51 nM at start of treatment and an increase on Day 3–5 to 4.17±0.93 nM (p=0.005) followed by a decline to 1.09±0.22 nM on Day 14. Thrombin generation was relatively high in the initial phase of chemotherapy (319.0±44.5 nM) and then declined to 154.6±17.2 nM on Day 14 (p=0.008). The protein C activity was relatively low at start (0.70±0.05 IU/mL) indicating a state of consumption, but showed a trend towards normalization during treatment reaching an average level of 0.78±0.05 IU/mL for all patients on Day 14 (p=0.103). The factor VIII level was high and relatively stable during the two weeks of treatment with a range of 1.73±0.16 to 1.89±0.17 IU/mL, indicating a reactive state. The level of antithrombin was normal at start of treatment (1.00±0.05 IU/mL) and throughout the study period. Our data show that acute myeloid leukemia may be associated with a significant coagulopathy and that the activity in the coagulation process is increased during the initial phase of chemotherapy. This should be considered in patients at start of treatment, in particular, in patients with septicemia and/or signs of disseminated intravascular coagulation.

This study was undertaken to determine the levels of protein C antigen and activity and protein C inhibitor in sequential plasma samples of disseminated intravascular coagulation (DIC) patients. Our normal range for both protein C antigen and activity is 70 to 130 U/dL, and protein C inhibitor is 65 to 135 U/dL. A decreased level of protein C activity was found in 96% of the plasma samples from individuals with DIC; the protein C antigen was decreased in 73%. The inhibitor of protein C was decreased in all samples. Analysis of serial samples from patients with DIC reveals that protein C activity and antigen and protein C inhibitor decrease progressively during the initial stages of DIC and remain at a low level for 24 to 48 hours before gradually returning toward normal in nonfatal cases. The protein C activity decreases in parallel with protein C inhibitor and is lower than protein C antigen. In a fatal case of DIC, protein C activity and protein C inhibitor rapidly decreased to undetectable levels; however, protein C antigen was gradually decreasing but still detectable at time of death. In DIC, a discrepancy initially occurs between the activity and antigen of protein C, suggesting a complex with the inhibitor or other inactive forms of protein C. Protein C appears to play a major role in the control of DIC.

We found a new thrombophilic tendency in a family with protein S deficiency. The propositus, a 38-year-old Japanese man, is an offspring of consanguineous marriage and suffered from recurrent episodes of thromboembolism. Hemostatic studies, including platelet counts, platelet aggregation, assays of coagulation factors, and plasminogen activity were all within normal limits. The levels of antithrombin III, alpha 2-macroglobulin, protein C, and protein C inhibitor were also normal. However, functional protein S activity in plasma was markedly decreased (9%) in the propositus. The family study revealed that the reduced levels of functional protein S, less than 5% to 29% of normal (normal range: mean +/- 2 SD of 15 normal adults were 44 to 180%), were found in 11 members of this family over three generations. Six of 11 members had severe protein S deficiency (less than 5%), whereas five had partial deficiency. Four of eight adults with protein S deficiency had recurrent episodes of thrombosis. Immunologic levels of protein S antigen were variable in this family and did not correlate closely with the functional levels. These results suggest that the recurrent thrombotic disease in this family appears to be associated with an inherited deficiency of functional protein S.

Activated protein C (APC) is inhibited by two major plasma inhibitors (PCIs). To find evidence for in vivo complexation of APC, immunoblotting studies were performed on plasmas of 85 patients with suspected disseminated intravascular coagulation (DIC). Samples from 62 of these patients contained 5% to 35% of protein C antigen in APC:inhibitor complexes, indicating that protein C activation and inhibition had occurred. In 24 normal plasmas, no detectable APC:PCI complexes were observed (less than 5%). Patients with higher levels of complexes had more abnormal coagulation test data for DIC. The major band of APC complexes detected by anti-protein C antibodies did not react with antibodies to the heparin-dependent protein C inhibitor (PCI- 1) previously described. Rather, APC was complexed with another recently described plasma protein C inhibitor, PCI-2. Immunoblotting studies for protein S, the cofactor for APC, revealed that the majority of the DIC patient plasmas contained a higher than normal proportion of protein S in cleaved form, suggesting that protein S may have been proteolytically inactivated. Protein S total antigen levels were also found to be low in DIC patients, excluding those with malignancy. These studies support the hypothesis that the protein C pathway is activated during DIC.

Monoclonal antibodies specific for protein C inhibitor (PCI) partially blocked the inactivation of activated protein C (APC) in plasma, whereas in a purified system, the PCI activity could be completely blocked. The inactivation of APC in normal and in PCI-depleted plasma was similar in the absence of heparin. The addition of heparin did not change the rate of inactivation of APC in PCI-depleted plasma, whereas in normal plasma a rapid phase of inhibition of APC was followed by a slower phase of inhibition. The slower phase was identical to the rate of inhibition of APC in the absence of heparin. After incubation of normal plasma with a monoclonal antibody specific for PCI that blocked its activity, there was no difference in heparin-dependent or heparin- independent inhibition of APC. These results indicate that in the absence of heparin PCI is unable to inactivate APC in a plasma environment.