Three structurally different fucoidans from the brown seaweeds Saccharina latissima (SL), Fucus vesiculosus (FV), and Cladosiphon okamuranus (CO), two chemically modified fucoidans with a higher degree of sulfation (SL-S, CO-S), and a synthetic totally sulfated octasaccharide (OS), related to fucoidans, were assessed on anticoagulant and antithrombotic activities in different in vitro experiments. The effects were shown to depend on the structural features of the compounds tested. Native fucoidan SL with a degree of sulfation (DS) of 1.3 was found to be the most active sample, fucoidan FV (DS 0.9) demonstrated moderate activity, while the polysaccharide CO (DS 0.4) was inactive in all performed experiments, even at high concentrations. Additional introduction of sulfate groups into fucoidan SL slightly decreased the anticoagulant effect of SL-S, while sulfation of CO, giving rise to the preparation CO-S, increased the activity dramatically. The high level of anticoagulant activity of polysaccharides SL, SL-S, and CO-S was explained by their ability to form ternary complexes with ATIII-Xa and ATIII-IIa, as well as to bind directly to thrombin. Synthetic per-O-sulfated octasaccharide OS showed moderate anticoagulant effect, determined mainly by the interaction of OS with the factor Xa in the presence of ATIII. Comparable tendencies were observed in the antithrombotic properties of the compounds tested.

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The purpose of the review is to highlight the current possibilities for the prevention and treatment of venous thrombotic complications in patients with cancer.The data of 52 scientific sources published in the Russian and foreign press in 1997–2020 are considered.Cancer patients are at high risk of thrombotic complications, which worsen the outcome of anticancer treatment and are one of the leading causes of death. Thrombosis in an oncological patient increases the risk of death by 30 times, which is associated with fatal thromboembolism and a more aggressive course of the disease. The leading role in the pathogenesis of thrombotic complications is played by disorders in the hemostasis system caused both by the tumor itself and by therapy. Low molecular weight heparins are considered the basis for specific prophylaxis of thromboembolic complications in cancer patients. The use of low molecular weight heparins after surgery and during chemotherapy effectively reduces the incidence of venous thrombosis. Direct oral anticoagulants are promising drugs for oral administration and are indicated as one of the treatment options for patients with tumor-associated thrombosis with a low risk of bleeding and no drug interactions with ongoing systemic chemotherapy.