Venous thrombosis

NMR-Based Structural Characterization of a Two-Disulfide-Bonded Analogue of the FXIIIa Inhibitor Tridegin: New Insights into Structure-Activity Relationships

The saliva of blood-sucking leeches contains a plethora of anticoagulant substances. One of these compounds derived from Haementeria ghilianii, the 66mer three-disulfide-bonded peptide tridegin, specifically inhibits the blood coagulation factor FXIIIa. Tridegin represents a potential tool for antithrombotic and thrombolytic therapy. We recently synthesized two-disulfide-bonded tridegin variants, which retained their inhibitory potential. For further lead optimization, however, structure information is required. We thus analyzed the structure of a two-disulfide-bonded tridegin isomer by solution 2D NMR spectroscopy in a combinatory approach with subsequent MD simulations. The isomer was studied using two fragments, i.e., the disulfide-bonded N-terminal (Lys1–Cys37) and the flexible C-terminal part (Arg38–Glu66), which allowed for a simplified, label-free NMR-structure elucidation of the 66mer peptide. The structural information was subsequently used in molecular modeling and docking studies to provide insights into the structure–activity relationships. The present study will prospectively support the development of anticoagulant-therapy-relevant compounds targeting FXIIIa.

Inhibitors of blood coagulation factor XIII

The blood coagulation factor XIII (FXIII) plays an essential role in the stabilization of fibrin clots. This factor, belonging to the class of transglutaminases, catalyzes the final step of secondary hemostasis, i.e. the crosslinking of fibrin polymers. These crosslinks protect the clots against premature fibrinolysis. Consequently, FXIII is an interesting target for the therapeutic treatment of cardiovascular diseases. In this context, inhibitors can influence FXIII in the activation process of the enzyme itself or in its catalytic activity. To date, there is no FXIII inhibitor in medical application, but several studies have been conducted in the past. These studies provided a better understanding of FXIII and identified new lead structures for FXIII inhibitors. Next to small molecule inhibitors, the most promising candidates for the development of clinically applicable FXIII inhibitors are the peptide inhibitors tridegin and transglutaminase-inhibiting Michael acceptors (TIMAs) due to their selectivity towards activated FXIII (FXIIIa). In this review, select FXIII inhibitors and their pharmacological potential are discussed.

Rationale and design of PROSPECT-CONKO 004: a prospective, randomized trial of simultaneous pancreatic cancer treatment with enoxaparin and chemotherapy)

Background

Advanced pancreatic cancer, in addition to its high mortality, is characterized by one of the highest rates of venous thromboembolic events (VTE) as compared to other types of cancer. Enoxaparin, a low molecular weight heparin (LMWH), has proven to be effective for the prevention and treatment of VTE in surgical and general medical patients. Results of some small studies suggest that this benefit might extend to patients with cancer, however, enoxaparin is not currently indicated for this use. This phase IIb study was designed to analyze the efficacy of enoxaparin in patients with locally advanced or metastatic pancreatic cancer undergoing systemic chemotherapy.

Methods

The aim of this prospective multicenter trial is to compare concomitant treatment with enoxaparin to no anticoagulation in 540 patients. Primary endpoint is the incidence of clinically relevant VTE (symptomatic deep venous thrombosis (DVT) of the leg and/or pelvic and/or pulmonary embolism (PE)) within the first 3 months. Secondary endpoints include the incidence of symptomatic and asymptomatic VTE after 6, 9 and 12 months as well as remission at 3, 6, 9 and 12 months, overall survival and bleeding. Trial registration: isrctn.org identifier CCT-NAPN-16752, controlled-trials.com identifier: ISRCTN02140505.

Results

An interim analysis for safety performed after inclusion of 152 patients revealed no increased risk of bleeding (5 pts vs. 6 pts, Chi²: 0.763).

Conclusion

PROSPECT is a pivotal study in elucidating the role of low molecular weight heparins in advanced pancreatic cancer. Its results will lead to a new understanding of the role of heparins in the prevention of venous thromboembolism and of their effect on survival, remission rates and toxicity of chemotherapeutic regimens.

Pancreatic cancer and thromboembolic disease

Thromboembolic disease is a common complication of pancreatic cancer and is causally associated with the generation of an intrinsic hypercoagulable state. Pancreatic-cancer cells activate platelets and express several procoagulant factors, including tissue factor and thrombin. The activation of coagulation is not simply an epiphenomenon, but might also be related to enhanced tumour growth and angiogenesis. Clinical manifestations of thromboembolic disease in pancreatic cancer include deep venous thrombosis, pulmonary embolism, disseminated intravascular coagulation, portal vein thrombosis, and arterial thromboembolism. Reported incidences of disease range from 17% to 57%. Treatment options include warfarin and low-molecular-weight heparins. Studies over the past decade suggest that long-term use of these heparins in both primary and secondary prevention of venous thromboembolic disease improves outcomes in comparison with warfarin. Further research is needed to understand better the morbidity and mortality associated with this disease in pancreatic cancer and to optimise strategies of prevention and treatment.