Characteristics And Significance Of Cyclooxygenase-2 (COX-2) And Vascular Endothelial Growth Factor (VEGF) Expression In Chronic Myeloid Leukemia

Background: Angiogenesis is a fundamental process in cancer development, which is regulated by a delicate balance between local proangiogenic and antiangiogenic factors. COX-2 and VEGF are both proved potent factors favoring tumor angiogenesis. They have not only the abilities to promote the mitosis of endothelial cells, to increase the permeability of tumor vessels, but also the effects on tumor cells proliferation, anti-apoptosis and drug-resistance.Cyclooxygenase (COX) is the most important time-limiting enzyme in PGs synthesis, which has two isoforms. COX-1 is always expressed in normal cells constantly, maintaining the physical function of bodies; while COX-2 is often expressed inductively, especially during the pathogenesis of malignant tumors. COX-2 has been proved overexpressing in many solid tumors, and related with the occurrence, progression or prognosis of malignances. Inhibition of COX-2 could depress tumor angiogenesis, induce tumor cell apoptosis and increase the sensitivity of tumor cells for chemical drugs.Vascular endothelial growth factor (VEGF) is a memenber of the growth factor family. In physical condition, VEGF expresses in low level, regulates the endothelial cells growth by paracrining. Malignant cells could synthese and exocrine large amount of VEGF, which play an important role in tumor development by promoting vessels increase, stimulating tumor cell proliferation and depressing apoptosis.Many factors influence the expression levels of VEGF. In vitro, COX-2 has showed the ability to modulate the synthesis and excetion of VEGF by its arachidonic acid metabolic product -PGE₂. There is obvious revalence between COX-2 and VEGF expression. COX-2 inhibition, PGE2 decrease, or specific VEGF inhibitors could effectively depress VEGF expression level, which at the same time decrease endothelial cells mitosis or tumor cells proliferation, induce apoptosis and increase the sensitivity of malignant cells for drugs.Chronic myeloid leukemia (CML) is a clonal stem cell disorder. With the growth in our understanding of the role of BCR-ABL chimeric protein in oncogenesis of CML, Gleevec is used in CML treatment and has made obvious improvement for chemotherapy. However, its long-term effect is not optimistic. It is a challenge for us nowadays to know more deeply about this disease, to look for new molecular targets and to find out a better way for its treatment. Recently, there are reports about the expression disturbance of COX-2 or VEGF in CML, while the conclusion lack convictive data on their characteristics during the disease. On the other hand, little is done about the association between COX-2 or VEGF expression and CML clinical parameters; the relevence between COX-2 and VEGF and their possible acting mechanisms in CML pathogenesis are remaining unknown. In our research, we used flow-cytometry, western-blot, real time-PCR and enzyme activity kit to observe the characteristics of COX-2 expression in the bone marrow mononuclear cells (BMMCs) from 60 CML patients; we detected the mRNA and protein level of VEGF in BMMCs of these patients quantitatively; we also compared the difference of COX-2 or VEGF in different phases of CML, and analyzed the possible relationship between COX-2 and VEGF in the pathogenesis of CML.Part I the characteristics and clinic significance of COX-2 gene/protein/activity expression in CML BMMCsObjective: to observe the characteristics of COX-2 expression in CML patients of different phases on gene and protein levels; to seek out the correlation between COX-2 expression and patients' clinical parameters. Methods: COX-2 expression was measured in BMMCs samples from 60 CML patients and 15 normal controls by flowcytometry, real-time PCR, Western-blot and COX-2 activity assay. COX-2 levels were compared between CML patients and normal controls; correlation was sought between COX-2 levels and many clinical parameters. Results: (1) Compared with normal control, COX-2 gene/protein/activity levels are all quite higher in CML patients (P<0.05); (2) there is no difference of COX-2 expression among different phases of CML; (3) COX-2 expression levels correlated with bigger spleen size (P=0.028), higher white blood cell count (P=0.017), and younger age (P=0.008). (4) The chronic phase lasting time is significantly shorter in the patients with higher COX-2 levels. Conclusion: COX-2 is overexpressed in BMMCs of CML patients and its level correlated with some clinical parameters. High expression level of COX-2 acts as a predictor of poor outcome.Part II Characteristics and significance of VEGF mRNA and protein expression in BMMCs of CML patientsObjective: to observe the characteristics of VEGF expression in BMMCs of CML patients; to seek out the correlation between VEGF expression and patients' clinical parameters. Methods: VEGF expression levels were measured in 60 CML patients and 15 normal controls by flowcytometry and real-time PCR. The mean expression levels of VEGF were compared between patients and normal controls; correlation was sought between VEGF levels and many clinical parameters. Results: (1) Compared with normal control, VEGF gene/protein levels are both higher in CML patients (P<0.05); (2) there is no difference of VEGF expression among different phases of CML; (3) VEGF levels correlated with bigger spleen size (P=0.008), higher white blood cell count (P=0.000), higher G/E ratio (P=0.012) and younger age (P=0.002). (4) The chronic phase lasting time is significantly shorter in the patients with higher VEGF expression. Conclusion: VEGF is overexpressed in BMMCs of CML patients and its level correlated with some clinical parameters. High expression level of VEGF also acts as a predictor of poor outcome in CML.Part III Correlation between COX-2 and VEGF expression in BMMCs of CMLObjective: (1) to reveal the characteristics and clinical significance of VEGF or COX-2 expression in different phases of CML; (2) to investigate the correlation between COX-2 and VEGF, discuss their possible mechanisms in CML pathogenesis. Methods: VEGF and COX-2 expression were measured at the same time in 60 CML patients and 15 control patients by flowcytometry and real-time RT-PCR. COX-2 or VEGF mRNA/protein expression levels were compared among patients from different phases; correlation was sought between COX-2 and VEGF expression levels. Results: (1) There is no significant difference of COX-2 or VEGF expression levels among patients in chronic, late chronic, accelerated or blastic phase. (2) The expression of VEGF correlated with the expression of COX-2 significantly. Conclusion: VEGF and COX-2 overexpress during the whole couse of CML. There exits possible mutual reaction between VEGF and COX-2 in CML pathogenesis.