Angiopoietins Modulate Survival, Migration, and the Components of the Ang-Tie2 Pathway of Chronic Lymphocytic Leukaemia (CLL) Cells In Vitro.

In actuality, chronic lymphocytic leukaemia (CLL) remains an incurable haematopoietic malignancy of high prevalence amongst elderly populations in the West. Malignant CLL cells characteristically accumulate in the peripheral blood, bone marrow, lymph nodes, and spleen of CLL patients. There is evidence that CLL cells express Ang2 and Tie1, two central components of the Ang-Tie2 pro-angiogenic pathway. Central to blood vessel development and maintenance, at present it remains unclear how the Ang-Tie2 pathway modulates CLL pathophysiology. Here we evaluate the status of the Ang-Tie2 pathway in CLL cells and assess Ang1 levels in plasma/cell medium from CLL samples. To understand how angiopoietins in the microenvironment regulate the components of Ang-Tie2 pathway, survival, migration, and metabolic fitness of CLL cells, we exposed CLL cells to recombinant angiopoietins. CLL plasma and CLL cells in culture present significant lower levels of Ang1. CLL cells simultaneously express Ang1, Ang2, and Tie1 mRNA, but lack that of Tie2 and its regulator, VE-PTP. Exposure to Ang1 confers survival advantage in the long-term, whereas Ang2 and trebananib, an angiopoietin blocker, proved detrimental. Angiopoietins differentially modulate expression of Ang1, Ang2, and Tie1 transcripts. Ang2, but not Ang1, induces the concomitant and transient expression of Tie2 and VE-PTP mRNA. Both angiopoietins, particularly Ang2, increase CLL-Tie1 expression and Ang1 clearly induces chemotaxis and transendothelial-like migration of CLL cells. Besides, changes in caspase and ATP content corroborate the sensitivity of CLL cells to angiopoietin exposure. Altogether, this work shows that angiopoietins regulate the fate of CLL cells in a Tie2-independent manner and highlights the potential of the Ang-Tie2 pathway as a therapeutic target in CLL research.

Angiogenic factors in chronic lymphocytic leukaemia (CLL): Where do we stand?

The role of angiogenesis in haematological malignancies such as chronic lymphocytic leukaemia (CLL) is difficult to envision, because leukaemia cells are not dependent on a network of blood vessels to support basic physiological requirements. Regardless, CLL cells secrete high levels of major angiogenic factors, such as vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and platelet derived growth factor (PDGF). Nonetheless, it remains unclear how most angiogenic factors regulate accumulation and delayed apoptosis of CLL cells. Angiogenic factors such as leptin, granulocyte colony-stimulating factor (G-CSF), follistatin, angiopoietin-1 (Ang1), angiogenin (ANG), midkine (MK), pleiotrophin (PTN), progranulin (PGRN), proliferin (PLF), placental growth factor (PIGF), and endothelial locus-1 (Del-1), represent novel therapeutic targets of future CLL research but have remained widely overlooked. This review aims to outline our current understanding of angiogenic growth factors and their relationship with CLL, a still uncured haematopoietic malignancy.