Paul Knöbl

Caplacizumab for Acquired Thrombotic Thrombocytopenic Purpura

BACKGROUND Acquired thrombotic thrombocytopenic purpura (TTP) is caused by aggregation of platelets on ultralarge von Willebrand factor multimers. This microvascular thrombosis causes multiorgan ischemia with potentially life-threatening complications. Daily plasma exchange and immunosuppressive therapies induce remission, but mortality and morbidity due to microthrombosis remain high. METHODS Caplacizumab, an anti-von Willebrand factor humanized single-variable-domain immunoglobulin (Nanobody), inhibits the interaction between ultralarge von Willebrand factor multimers and platelets. In this phase 2, controlled study, we randomly assigned patients with acquired TTP to subcutaneous caplacizumab (10 mg daily) or placebo during plasma exchange and for 30 days afterward. The primary end point was the time to a response, defined as confirmed normalization of the platelet count. Major secondary end points included exacerbations and relapses. RESULTS Seventy-five patients underwent randomization (36 were assigned to receive caplacizumab, and 39 to receive placebo). The time to a response was significantly reduced with caplacizumab as compared with placebo (39% reduction in median time, P=0.005). Three patients in the caplacizumab group had an exacerbation, as compared with 11 patients in the placebo group. Eight patients in the caplacizumab group had a relapse in the first month after stopping the study drug, of whom 7 had ADAMTS13 activity that remained below 10%, suggesting unresolved autoimmune activity. Bleeding-related adverse events, most of which were mild to moderate in severity, were more common with caplacizumab than with placebo (54% of patients vs. 38%). The frequencies of other adverse events were similar in the two groups. Two patients in the placebo group died, as compared with none in the caplacizumab group. CONCLUSIONS Caplacizumab induced a faster resolution of the acute TTP episode than did placebo. The platelet-protective effect of caplacizumab was maintained during the treatment period. Caplacizumab was associated with an increased tendency toward bleeding, as compared with placebo. (Funded by Ablynx; ClinicalTrials.gov number, NCT01151423.).

Changes in ADAMTS13 (von-Willebrand-factor-cleaving protease) activity after induced release of von Willebrand factor during acute systemic inflammation

Von Willebrand factor (VWF) is synthesized in endothelial cells, stored in the form of high molecular weight multimers and released after stimulation. After release, the multimers are cleaved by ADAMTS13 (von-Willebrand-factor-cleaving protease). We studied healthy volunteers in a double-blind, placebo controlled inflammation model. Ten male volunteers received 2 ng/kg endotoxin intravenously, and 5 volunteers placebo. Endotoxin infusion induced systemic inflammation and coagulation activation. After 4 hours the observed increase in neutrophils reached a maximum (273+/-34% of baseline; mean+/-SEM) and the platelet count dropped (81+/-2%). These parameters returned to baseline values after 24 hours. VWF antigen increased to 259+/-16% of baseline after 4 hours, remained elevated (192+/-15%) after 24 hours and returned to baseline after 7 days. Unusually large VWF multimers occurred in the plasma 4 hours after endotoxin infusion. ADAMTS13 activity (measured with a collagen-binding assay) decreased to 64+/-5% of baseline (P<0.001) after 4 hours, was still reduced after 24 hours (86+/- %; P=0.008) and returned to normal after 7 days. VWF multimer analysis showed pronounced satellite bands in the 4-hour samples, indicating cleavage of VWF by ADAMTS13. No apparent changes of the analyzed parameters were observed in the placebo group. The reciprocal course of ADAMTS13 and VWF after short-term VWF release induced by systemic inflammation is similar to that observed after induction of VWF release by desmopressin.

Inhibition of von Willebrand factor by ARC1779 in patients with acute thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) can cause severe organ damage due to enhanced platelet aggregation by ultra-large von Willebrand factor (VWF) multimers. Thus inhibition of VWF by the anti-VWF ARC1779 might potentially be beneficial for TTP patients. This prospective trial tested the safety, pharmacokinetics and pharmacodynamics of the anti-VWF aptamer ARC1779 added to plasma exchange therapy (PEX) in patients with acute TTP. Seven patients received bolus primed continuous i.v. infusions of ARC1779 (1-2 μg/kg/min) in addition to PEX until remission of TTP was induced or for 14 days. Mean steady state ARC1779 plasma concentrations of 9.9 μg/ml reduced VWF activity to 5% (mean baseline activity was 125% in TTP patients compared to a reference plasma). PEX reduced ARC1779 levels by 50%, but steady state concentrations were restored rapidly with a mini-bolus. After discontinuation of PEX, ARC1779 alone further increased platelet counts in one patient. Stopping ARC1779 was associated with an immediate drop of platelet counts in this patient. This suggests that ARC1779 can block the progression of TTP in patients with severe ADAMTS13 is deficiency. ARC1779 was generally well tolerated without any signs of bleeding. Pharmacokinetics and pharmacodynamics of ARC1779 were well predictable and in agreement with those observed in a previous trial with healthy volunteers. Based on its mechanism of action and the observed effect on platelet counts, ARC1779 used as an adjunctive to PEX may help accelerate recovery from organ dysfunction.

ORAL CONTRACEPTIVES ENHANCE THE RISK OF CLINICAL MANIFESTATION OF VENOUS THROMBOSIS AT A YOUNG AGE IN FEMALES HOMOZYGOUS FOR FACTOR V LEIDEN

In 29 patients (17 females) homozygous Arg 506 Gln mutation (FV Leiden) was identified. 25 had been investigated because of venous thromboembolism (VTE); four asymptomatic patients were found during family studies.

A dose ranging phase I/II trial of the von Willebrand factor inhibiting aptamer ARC1779 in patients with congenital thrombotic thrombocytopenic purpura

Congenital thrombotic thrombocytopenic purpura (TTP) is a very rare but potentially life-threatening disorder. This phase I/II trial compared the pharmacokinetics and pharmacodynamics and safety of three different administration modes of the anti-von Willebrand factor (VWF) aptamer ARC1779. This was a prospective clinical trial with a partial cross-over design: three periods comprised subcutaneous injections of 50 mg of ARC1779 on seven subsequent days, a low-dose infusion of ARC1779 (0.002 mg/kg/min) for 24-72 hours and a high-dose infusion (0.004-0.006 mg/kg/min) up to 72 hours. ARC1779 concentrations were determined with high performance liquid chromatography, VWF inhibition was measured with enzyme immunoassay and platelet function was determined with the platelet function analyser (PFA-100) and impedance aggregometry. ARC1779 was well tolerated without any bleeding at concentrations spanning over three orders of magnitude. The daily s.c. injection yielded plasma levels (0.5 μg/ml) of the drug that were too low to sufficiently suppress VWF. The low-dose i.v. infusion increased platelet counts in one patient, whereas the high i.v. dose increased plasma concentrations up to 69 μg/ml, completely blocked free A1 domains, VWF-dependent platelet plug formation and enhanced platelet counts in 2/3 patients. In conclusion, infusion of ARC1779 dose-dependently inhibits VWF-dependent platelet function and during infusion ARC1779 increases or stabilises platelet counts in congenital TTP. However, the tested doses, particularly the daily s.c. injections, did not correct all clinical or laboratory features of TTP.

A randomised pilot trial of the anti-von Willebrand factor aptamer ARC1779 in patients with type 2b von Willebrand disease

Desmopressin aggravates thrombocytopenia in type 2B von Willebrand disease (VWF type 2B) by release of large and hyper-adhesive von Willebrand Factor (VWF) multimers. This pilot study investigated whether the anti-VWF aptamer ARC1779 can prevent desmopressin-induced thrombocytopenia and interferes with the excessive VWF turnover in patients with VWF type 2B. Concentration effect curves of ARC1779 were established for five patients in vitro and two patients with VWF type 2B were treated by infusion of ARC1779, desmopressin, or their combination in a randomised, controlled, double-blind design. ARC1779 concentrations in the range of 1-3 microg/ml blocked free A1 domain binding sites by 90% in vitro. In vivo, desmopressin alone induced a profound (-90%) drop in platelet counts in one of the patients. ARC1779 (4-5 microg/ml) completely inhibited VWF A1 domains and prevented this desmopressin-induced platelet drop. Desmopressin alone increased VWF antigen two- to three-fold, accompanied by concordant changes in VWF Ristocetin cofactor activity (RCo) and coagulation factor VIII activity. ARC1779 substantially enhanced the desmopressin-induced maximal increase in these parameters, and improved multimer patterns. No treatment related adverse events were observed and no bleeding occurred despite marked thrombocytopenia. These data provide first proof of concept in humans and evidence that ARC1779 is a potent inhibitor of VWF. ARC1779 prevented the rapid consumption of VWF multimers together with agglutinated platelets that occurred in response to desmopressin challenge in patients with VWD type 2B.

Anti–von Willebrand factor aptamer ARC1779 for refractory thrombotic thrombocytopenic purpura

BACKGROUND: Plasma exchange is the main therapy for thrombotic thrombocytopenic purpura (TTP). No treatments other than plasma exchange have been documented to be effective nor are approved for treatment of TTP. The anti–von Willebrand factor (VWF) aptamer ARC1779 effectively inhibits VWF activity in plasma samples of TTP patients and thus shear‐dependent platelet (PLT) function as measured by the PLT function analyzer PFA‐100 (Dade Behring). It was hypothesized that ARC1779 would offer a potentially effective treatment option for a critically ill patient, refractory to standard care.

Frequent development of lupus anticoagulants in critically ill patients treated under intensive care conditions.

Objective To investigate how often a prolongation of the activated partial thromboplastin time in critically ill patients is caused by lupus anticoagulants and to identify possible triggering events. Design Prospective study. Setting Internal medicine intensive care unit (University Hospital of Vienna, Vienna, Austria). Patients Fifty-one critically ill patients without severe coagulopathy, hepatopathy, or anticoagulant treatment (35 male, 16 female, median age 60 yrs, range: 22–85 yrs). Interventions All patients were screened daily for lupus anticoagulants with the activated partial thromboplastin time STA assay. Measurements and Main Results Diluted Russell’s viper venom time, plasma mixing studies, and confirmation assays were used to identify lupus anticoagulants at the time of an unexplained prolongation of the activated partial thromboplastin time. The influence of heparin was excluded by determination of thrombin clotting time and anti-Xa activity. In 27 of 51 patients (52.9 %) lupus anticoagulants were found after a median stay of 13 days. None of the patients had concomitant immune thrombocytopenia, hypoprothrombinemia, bleeding, or thromboembolic complications. Sepsis (p = .006) and/or catecholamine treatment (p = .002) were significantly associated with the development of lupus anticoagulants. Extracorporeal circulation, transfusion of blood products, or surgery did not increase this risk. Lupus anticoagulants resolved spontaneously in 63% of the patients after a median stay of 17 days. Conclusions Lupus anticoagulants are frequent in critically ill patients and associated with sepsis syndrome and/or catecholamine treatment. The prolonged activated partial thromboplastin time does not warrant the administration of coagulation factors or the cessation of anticoagulant therapy or prophylaxis, inasmuch as this phenomenon is not associated with bleeding or thromboembolic complications.

Closed Suctioning System Reduces Cross-Contamination Between Bronchial System and Gastric Juices

In this prospective, randomized study, we evaluated whether a closed suctioning (CS) system (TrachCare) influences crossover contamination between bronchial system and gastric juices when compared with an open suctioning system (OS). The secondary aims were an analysis of the frequency of ventilator-associated pneumonia (VAP) and an analysis of alteration in gas exchange. Antibiograms were performed from tracheal secretions and gastric juice aspirates on Days 1 and 3 of intubation in 24 patients in a medical intensive care unit. Five cross-contaminations were observed in the OS group on Day 3 versus Day 1; the 5 strains shared common genotypes as determined by random amplification of polymorphic DNA. No cross-contaminations were seen in the CS group (P = 0.037). VAP occurred in 5 patients of the OS group but in none of the CS group patients (P = 0.037). Spao(2) decreased significantly in the OS group compared with presuctioning values--the opposite of the CS group. Whereas presuctioning values were comparable between groups, postsuctioning Spao(2) was significantly higher in the CS group. CS significantly reduced cross-contamination between bronchial system and gastric juices and reduced the incidence of VAP when compared with OS. Hypoxic phases can be reduced by the help of CS.

Prognostic factors for remission of and survival in acquired hemophilia A (AHA): results from the GTH-AH 01/2010 study

Acquired hemophilia A (AHA) is caused by autoantibodies against factor VIII (FVIII). Immunosuppressive treatment (IST) results in remission of disease in 60% to 80% of patients over a period of days to months. IST is associated with frequent adverse events, including infections as a leading cause of death. Predictors of time to remission could help guide IST intensity but have not been established. We analyzed prognostic factors in 102 prospectively enrolled patients treated with a uniform IST protocol. Partial remission (PR; defined as no active bleeding, FVIII restored >50 IU/dL, hemostatic treatment stopped >24 hours) was achieved by 83% of patients after a median of 31 days (range 7-362). Patients with baseline FVIII <1 IU/dL achieved PR less often and later (77%, 43 days) than patients with ≥1 IU/dL (89%, 24 days). After adjustment for other baseline characteristics, low FVIII remained associated with a lower rate of PR (hazard ratio 0.52, 95% confidence interval 0.33-0.81, P < .01). In contrast, PR achieved on steroids alone within ≤21 days was more common in patients with FVIII ≥1 IU/dL and inhibitor concentration <20 BU/mL (odds ratio 11.2, P < .0001). Low FVIII was also associated with a lower rate of complete remission and decreased survival. In conclusion, presenting FVIII and inhibitor concentration are potentially useful to tailor IST in AHA.