Recombinant Human Soluble Thrombomodulin Enhances the Anti-Fibrinolytic and Anti-Leukemia Effects of All-Trans Retinoic Acid In Acute Promyelocytic Leukemia Cells.

Abstract 1079

Recombinant human soluble thrombomodulin (rTM) is composed of the active, extracellular domain of thrombomodulin, and inactivates coagulation by binding to thrombin. In addition, the thrombin-rTM complex activates protein C to produce activated protein C (APC), which in the presence of protein S, inactivates factors VIIIa and Va, thereby inhibiting further thrombin formation. Use of rTM for treatment of disseminated intravascular coagulation (DIC) associated with haematological malignancies or infections has been approved in Japan, although its effects on hyperfibrinolysis caused by acute promyelocytic leukemia (APL), as well as all-trans retinoic acid (ATRA)-mediated anti-fibrinolytic activity, remain to be fully elucidated. This study examined the effects of rTM on the plasmin activity in APL NB4 cells in vitro and found that rTM (100 nM, 48 h) alone inhibited the plasmin activity by approximately 35% when compared to the control diluent-treated NB4 cells. ATRA (100 nM, 48 h) also inhibited the plasmin activity by 40%, and when ATRA (100 nM, 48 h) was combined with rTM (100 nM, 48 h), the plasmin activity was inhibited by 60%. In further studies, neither anti-proliferative nor pro-differentiative activity was noted in NB4 cells after exposure to rTM (3-100 nM, 48 h). However, rTM significantly enhanced the ability of ATRA to induce growth arrest, differentiation and apoptosis in NB4 cells, as measured by colony forming assay, quantification of CD11b cell surface antigens and nitroblue tetrazolium reduction test, respectively. Western blot analyses showed that ATRA (30 or 100 nM, 48 h) increased nuclear levels of CCAAT/enhancer binding protein e in NB4 cells, a critical transcription factor for myeloid differentiation, which was further increased in the presence of rTM (3-100 nM, 48 h). Furthermore, we treated individuals with DIC caused by APL (n=4) with rTM (380 U/kg) in combination with ATRA (45 mg/m²) and chemotherapy (idarbicine and cytarabine), and compared their clinical outcomes with historical control patients (n=6) treated with ATRA and/or chemotherapy (idarbicine and cytarabine). Notably, treatment with rTM rescued patients from DIC earlier than historical controls (8.3 ± 4.5 days vs 12.5 ± 5.2 days in historical controls) and significantly reduced the transfusion of fresh frozen plasma to maintain plasma levels of fibrinogen at more that 150 mg/dl (0.13 ± 0.25 U/day vs 3.93 ± 1.18 U/day in historical control, p=0.0131). Taken together, the present results suggest that administration of rTM be considered in the treatment of individuals with DIC associated with APL.