Pharmacokinetics of Low Molecular Weight Heparin in Cancer Patients

Scientific background. The increased risk for venous thromboembolism (VTE) in cancer has long been recognized (1). Since first described by Trousseau in 1865, many aspects of this complex relationship are still obscure (2). Cancer patients have an increased risk for developing thrombosis. Similarly, patients presenting with idiopathic VTE are considered to have a higher risk of developing cancer (3). Approximately 10% of patients with idiopathic VTE harbor an underlying malignancy that can be detected by an extensive diagnostic work-up (4). Clinical data indicate that cancer alone is associated with a 4.1- fold risk of thrombosis, and chemotherapy increases the risk to 6.1- folds (5). Cancer patients develop postoperative VTE at least 2- folds more than patients without cancer undergoing the same surgical procedure (6). Treatment of VTE involves the administration of heparin, low molecular weight heparin (LMWH) or coumarin derivatives. Beside its anticoagulant effects, LMWH may also have an anti-tumoral effect (7-12). The use of LMWH relative to coumarin derivatives was associated with improved survival in patients with solid tumors who did not have metastatic disease at the time of an acute VTE (9). Moreover, addition of LMWH to chemotherapy increased survival of patients with small cell lung cancer (10).

Heparan sulfate proteoglycans (HSPGs) are ubiquitous macromolecules associated with the cell surface and extracellular matrix (ECM) of a wide range of cells of vertebrate and invertebrate tissues. Heparin is structurally related to heparan sulfate (HS), but has higher N- and O-sulfate contents (13). Mammalian endoglycosidase, capable of partially depolymerizing HS chains and commonly referred to as heparanase, has been identified in a variety of cell types and tissues, primarily cancer cells, activated cells of the immune system, platelets, and placenta (14-17). Heparanase is synthesized as a latent 65 kDa precursor whose activation involves proteolytic cleavage at two potential sites located at the N-terminal region of the molecule (Glu109 -Ser110 and Gln157 -lys158), resulting in the formation of two protein subunits that heterodimerize and form the active heparanase enzyme (18). Expression of heparanase correlates with the metastatic potential of human tumor cells (14-16, 19). Furthermore, elevated levels of heparanase were detected in the urine of some patients with aggressive metastatic disease (20). Heparin, LMWH, non-anticoagulant and chemically modified species of heparin (21, 22), as well as other polysaccharides (23, 24) which inhibit experimental metastasis, also inhibit tumor cell heparanase, while other related compounds had a small or no effect on both parameters (21-24). Recently, we demonstrated that the anticoagulant activities of heparin and LMWH can be neutralized by their pre-incubation with heparanase. Transgenic mice overexpressing heparanase, exhibited a hyper-coagulable phenotype expressed by a markedly shorter base-line APTT compared to control mice (25). These results may suggest that resistance to heparin, described in patients with malignancies (26, 27), could be attributed, in part, to high levels of heparanase often observed in cells (28, 29) and body fluids (20) of patients with an aggressive malignant disease. Degradation of heparin and LMWH by heparanase in vivo may be relevant in situations in which heparanase is over-expressed, and treatment with heparin or LMWH is needed (e.g., deep venous thrombosis in patients with pancreatic carcinoma) (29, 30). The pharmacokinetics of LMWH (i.e. the time course of absorption, distribution, metabolism, and degradation) as reflected by its effects upon factor Xa activity, was elucidated in several subgroups of patients (e.g. patients with renal failure, pregnant women…), but to the best of our knowledge was not addressed in patients with advanced solid tumors.

Objectives & expected significance. In view of the above described biological significance of the heparanase enzyme, and taking into account our recent in vitro and in vivo results (heparanase capability to cleave heparin and LMWH; and the altered coagulation profile in transgenic mice overexpressing heparanase) (25), we propose to focus on the following specific aims:

I) Measure plasma and urine heparanase levels in patients with advanced cancer suffering from VTE, and compare it to controls without cancer.

II) Elucidate the pharmacokinetics of LMWH in patients with advanced solid tumors (AST) suffering from VTE, and compare it to the pharmacokinetics of LMWH in patients with unstable angina pectoris.

III) Determine the correlation between heparanase blood levels and the pharmacokinetics of LMWH, if any.

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