Antiangiogenic kringles derived from human plasminogen and apolipoprotein(a) inhibit fibrinolysis through a mechanism that requires a functional lysine-binding site.

Many proteins in the fibrinolysis pathway contain antiangiogenic kringle domains. Owing to the high degree of homology between kringle domains, there has been a safety concern that antiangiogenic kringles could interact with common kringle proteins during fibrinolysis leading to adverse effects in vivo. To address this issue, we investigated the effects of several antiangiogenic kringle proteins including angiostatin, apolipoprotein(a) kringles IV(9)-IV(10)-V (LK68), apolipoprotein(a) kringle V (rhLK8) and a derivative of rhLK8 mutated to produce a functional lysine-binding site (Lys-rhLK8) on the entire fibrinolytic process in vitro and analyzed the role of lysine binding. Angiostatin, LK68 and Lys-rhLK8 increased clot lysis time in a dose-dependent manner, inhibited tissue-type plasminogen activator-mediated plasminogen activation on a thrombin-modified fibrinogen (TMF) surface, showed binding to TMF and significantly decreased the amount of plasminogen bound to TMF. The inhibition of fibrinolysis by these proteins appears to be dependent on their functional lysine-binding sites. However, rhLK8 had no effect on these processes owing to an inability to bind lysine. Collectively, these results indicate that antiangiogenic kringles without lysine binding sites might be safer with respect to physiological fibrinolysis than lysine-binding antiangiogenic kringles. However, the clinical significance of these findings will require further validation in vivo.

Thrombophilic-type placental pathologies and skeletal growth delay following maternal administration of angiostatin4.5 in mice.

During placentation, the concentration of fibrinous deposits on the surfaces of maternal vasculature plays a role in villous development and has been strongly implicated in the pathophysiology of human fetal growth restriction (FGR). Fibrinous deposits are conspicuous sites of platelet aggregation where there is local activation of the hemostatic cascade. During activation of the hemostatic cascade, a number of pro- and antiangiogenic agents may be generated at the cell surface, and an imbalance in these factors may contribute to the placental pathology characteristic of FGR. We tested the hypothesis that angiostatin(4.5) (AS(4.5)), a cleavage fragment of plasminogen liberated at the cell surface, is capable of causing FGR in mice. Increased maternal levels of AS(4.5) in vivo result in reproducible placental pathology, including an altered vascular compartment (both in decidual and labyrinthine layers) and increased apoptosis throughout the placenta. In addition, there is significant skeletal growth delay and conspicuous edema in fetuses from mothers that received AS(4.5). Maternally generated AS(4.5), therefore, can access maternal placental vasculature and have a severe effect on placental architecture and inhibit fetal development in vivo. These findings strongly support the hypothesis that maternal AS(4.5) levels can influence placental development, possibly by directly influencing trophoblast turnover in the placenta, and contribute to fetal growth delay in mice.

Recombinant human angiostatin by twice-daily subcutaneous injection in advanced cancer: a pharmacokinetic and long-term safety study.

PURPOSE: A clinical study was performed to evaluate the pharmacokinetics (PK) and toxicity of three dose levels of the angiogenesis inhibitor recombinant human (rh) angiostatin when administered twice daily by s.c. injection. EXPERIMENTAL DESIGN: Eligible patients had cancer not amenable to standard treatments. Three groups of 8 patients received 7.5, 15, or 30 mg/m(2)/day divided in two s.c. injections for 28 consecutive days followed by a 7-day washout period. PK assessment was done at days 1 and 28. Thereafter, in absence of toxicity or a 100% increase in tumor size, treatment was continued without interruption. RESULTS: Median age was 53 years (range, 43-75), male:female ratio 10:14, Eastern Cooperative Oncology Group performance 0-1. At the range of doses evaluated, serum PK of all 24 of the patients showed linear relation between dose and area under the curve (0- infinity) and C(max) (reached after 2 h). Thirteen of 24 patients developed erythema at injection sites (11 patients, CTC grade 1; 2 patients, CTC grade 2) without pain or itching, spontaneously resolving within 2-3 weeks of treatment. Two patients went off study after developing hemorrhage in brain metastases, and 2 patients developed deep venous thrombosis. No other relevant treatment-related toxicities were seen, even during prolonged treatment. A panel of coagulation parameters was not influenced by rhAngiostatin treatment. Long-term (>6 months) stable disease (<25% growth of measurable uni- or bidimensional tumor size) was observed in 6 of 24 patients. Five patients received rhAngiostatin treatment for >1 year (overall median time on treatment 99 days). CONCLUSIONS: Long-term twice-daily s.c. treatment with rhAngiostatin is well tolerated and feasible at the selected doses, and merits additional evaluation. Systemic exposure to rhAngiostatin is within the range of drug exposure that has biological activity in preclinical models.