The Cell Surface Nadh Oxidase Enox2 Is Highly Expressed In Chronic Myeloid Leukemia (Cml): A Redox Protein As A Secreted Surrogate Biomarker And Druggable Target

Ecto-nicotinamide Adenine Dinucleotide Oxidase 2 (ENOX2) or Tumor-Associated Nicotinamide Adenine Dinucleotide Oxidase (tNOX), plays a major role as a membrane hydroxyquinone oxidase catalyzing the conversion of reduced NADH to the oxidized NAD+ .Cellular NAD+/NADH ratio plays a major role in the regulation of several metabolic pathways such cell cycle and apoptosis. The membrane NAD+/NADH ratio has been shown to be involved membrane lipid and sphingomyelin metabolism. Several lines of experimental data indicate that ENOX2, as compared to ENOX1 isoform, is preferentially expressed in cancer cells and ENOX2 is also secreted in the serum of patients with cancer and representing a surrogate marker for cancer progression as well as a drug target. The expression of ENOX2 in CML has not been studied so far. To this end, we have analyzed the expression of ENOX2 by Western blots in 40 patients with CML at diagnosis and compared this expression to that of control cells from healthy donors (n= 30). ENOX2 expression was found to be highly increased ( x 6.6 fold) in primary leukemic cells and this was highly significant ( p= 0.0081). To determine if ENOX2 expression is related directly to BCR-ABL expression, we have analyzed the expression of ENOX2 in UT7 cell line and its BCR-ABL-expressing counterparts UT7-11. As compared to parental UT7, ENOX2 expression was highly increased in UT7 cells expressing either native or T315I-mutated BCR-ABL. This increase was also documented in DOX- inducible cell line BaF/p210 sin1.55 in which activation of BCR-ABL expression correlated with ENOX2 expression. The expression of ENOX2 in CML cells was a tyrosine kinase-dependent event as demonstrated by Western blot experiments showing that ENOX2 expression was reduced UT7/11 cell line treated with Imatinib mesylate (1 microM) for 6, 18 and 24 hours whereas there was no change in ENOX2 expression in similarly treated parental UT7 cell line. As ENOX2 is a protein secreted from tumor cells, we have analyzed the levels of ENOX2 in the plasma of CML patients at diagnosis as compared to controls. A series of 41 patients with CML as compared to plasma from 28 healthy donors were analyzed by ELISA. This analysis showed a highly significant increase of ENOX2 protein levels in the plasma of patients with CML (mean levels of 800 pg/ml in CML versus 500 pg/ml, Mann-Whitney U-Test, p Disclosures No relevant conflicts of interest to declare.