CD44-fibrinogen binding promotes bleeding in acute promyelocytic leukemia by in situ fibrin(ogen) deposition

Fibrinogen and tumors

Elevated plasma fibrinogen (Fg) levels consistently correlate with an unfavorable prognosis in various tumor patient cohorts. Within the tumor microenvironment, aberrant deposition and expression of Fg have been consistently observed, interacting with multiple cellular receptors and thereby accentuating its role as a regulator of inflammatory processes. Specifically, Fg serves to stimulate and recruit immune cells and pro-inflammatory cytokines, thereby contributing to the promotion of tumor progression. Additionally, Fg and its fragments exhibit dichotomous effects on tumor angiogenesis. Notably, Fg also facilitates tumor migration through both platelet-dependent and platelet-independent mechanisms. Recent studies have illuminated several tumor-related signaling pathways influenced by Fg. This review provides a comprehensive summary of the intricate involvement of Fg in tumor biology, elucidating its multifaceted role and the underlying mechanisms.

Tissue factor activates the coagulation cascade in mouse models of acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is associated with a high risk of bleeding and thrombosis. APL patients have an activated coagulation system, hyperfibrinolysis, and thrombocytopenia. APL cells express tissue factor (TF), a receptor and cofactor for factor VII/VIIa. This study had 2 goals. Firstly, we measured biomarkers of coagulation and fibrinolysis activation as well as platelet counts and bleeding in both mouse xenograft and allograft models of APL. Secondly, we determined the effect of inhibiting TF on the activation of coagulation in these models. We observed increased levels of plasma thrombin-antithrombin complexes (TAT), D-dimer, and plasmin-antiplasmin complexes, reduced platelet counts, and increased tail bleeding in both mouse models of APL. Fibrinogen levels decreased in the xenograft model but not in the allograft model. In contrast, the red blood cell count decreased in the allograft model but not in the xenograft model. Inhibition of APL-derived human TF with an anti-human TF monoclonal antibody reduced the level of TAT, increased platelet count, and normalized tail bleeding in a xenograft model. Inhibition of all sources of TF (APL cells and host cells) in the allograft model with a rat anti-mouse TF monoclonal antibody decreased the levels of TAT but did not affect the platelet count. Our study demonstrates that TF plays a central role in the activation of coagulation in both the xenograft and allograft mouse models of APL. These APL mouse models can be used to investigate the mechanisms of coagulopathy and thrombocytopenia in APL.

The Coagulopathy of Acute Promyelocytic Leukemia: An Updated Review of Pathophysiology, Risk Stratification, and Clinical Management

Acute promyelocytic leukemia (APL) has a well-established mechanism and a long-term prognosis that exceeds that of any other acute leukemia. These improving outcomes are due, in part, to all-trans retinoic acid (ATRA) and arsenic trioxide (ATO), two targeted and highly active agents in this disease. However, there remains a considerable morbidity and mortality risk in APL secondary to clinically significant hemorrhagic and/or thrombotic events. Prevention and treatment of these coagulopathic complications remain significant impediments to further progress in optimizing outcomes for patients with APL. Moreover, the relative rarity of APL hinders adequately powered randomized controlled trials for evaluating APL coagulopathy management strategies. This review draws from peer-reviewed works falling between initial descriptions of APL in 1957 and work published prior to January 2023 and provides an updated overview of the pathophysiology of hemorrhagic and thrombotic complications in APL, outlines risk stratification parameters, and compiles current clinical best practices. An improved understanding of the pathophysiologic mechanisms driving hemorrhage and thrombosis along with the completion of well-designed trials of management strategies will assist clinicians in developing interventions that mitigate these devastating complications in an otherwise largely curable disease.

Platelet-Acute Leukemia Interactions

Acute leukemia (AL) is a hematological malignancy with high morbidity and mortality that is caused by abnormal hematopoietic stem cells. AL can change the parameters, quality, and function of platelets through numerous mechanisms, resulting in bleeding and even death in AL patients. Hence, AL patients are often clinically treated using normal platelet transfusion. However, studies have found that platelets can also affect AL cells. This review discusses the changes occurring in platelet count, mean platelet volume, platelet distribution width, reticulated platelets, platelet membrane glycoprotein, platelet aggregation, and activation in AL patients, the causes of these changes, and the possible significance of these changes for patient prognosis. The effects of platelets on the proliferation and drug resistance of AL cells are also discussed.

Coagulation Abnormalities and Risk Assessment in Acute Promyelocytic Leukemia: An Experience From a Resource-Constraint Country

Introduction

The objective of the study was to assess the impact of coagulopathy in risk-stratified acute promyelocytic leukemia (APML) patients irrespective of bleeding manifestation.

Patients and methods

This was a cross-sectional study design conducted at the National Institute of Blood Diseases and Bone Marrow Transplantation (NIBD & BMT) from November 2019 to December 2021. A total of 62 patients between three years to 74 years of age of either gender and treatment-naive cases of APML were included in the study. Morphological diagnosis was made on bone marrow samples, and confirmation was done by karyotyping/fluorescence in situ hybridization (FISH) and/or polymerase chain reaction (PCR). Complete blood count (CBC), prothrombin time (PT), activated partial thromboplastin time (APTT), D-dimer, and fibrinogen levels were done for bleeding risk assessment. Cases other than APML and cases on treatment were excluded from the study.

Results

A total of 85 APML patients were registered at our institute. Among them, 62 (73%) were included in the analysis as per the inclusion criteria of the study. The median age was 32 (3-74) years, with a male predominance of 34 (55%). According to the Sanz score, 18 (29%) patients were noted to have low risk; however, 22 (35.4%) patients were found to have an intermediate-risk disease and 22 (35.4%) patients had high-risk disease. There was positive bleeding history among 44 (71%) patients, followed by fever in 28 (45%) patients. Raised PT, APTT, and D-dimer were found in 46 (74%), 38 (61%), and 52(83.8%) patients, respectively. Low fibrinogen levels were observed among 16 (26%) patients. The association of risk stratification and bleeding history with CBC and coagulation parameters was observed. Platelet count and total leucocyte count were noted to be significantly associated with risk stratification. However, there was no association observed between the rest of the parameters with risk stratification and bleeding.

Conclusion

The results of our study suggest that regardless of bleeding symptoms, coagulation parameters must be investigated at the time of diagnosis in patients with suspected APML, and in addition to all-trans-retinoic acid (ATRA), transfusion of fresh frozen plasma should be done. It has clinical value, and adding it to the algorithm of treatment would be beneficial to the patients in the developing world, where resources are already meager.