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Background. As is well known, cytotoxic mechanism of antitumor agent, i.e. catalytic system “teraphtal + ascorbic acid” (“TF+AA”), is associated with production of reactive oxygen species (ROS) and induction of oxidative stress in it. The “heme oxygenase-1/ferritin” (HO-1/Ft) system contributes to antioxidant defense. Aim. To analyze HO-1/Ft value in protection of leukemia cells from toxicity induced by antitumor agent “TF+AA”. Materials &amp; Methods. The study was based on human leukemia cell lines K562 and U937. HO-1/Ft basal and drug-induced expression on mRNA and protein levels was analyzed by real-time RT-PCR and Western blot, ROS concentration in cells was determined by flow cytometry, and drug cytotoxicity was measured by MTT assay. Results. Our data showed constitutively active HO-1 in U937 myelomonoblasts whereas in K562 erythroblasts the expression of this protein was blocked on the mRNA level. Hemin, HO-1 agonist, induces HO-1 and Ft co-expression in U937 cells on the mRNA and protein levels. HO-1/Ft activation by hemin in U937 cells does not affect their “TF+AA” sensitivity and doubles, for example, the cytarabine sensitivity. “TF+AA” appeared to cause up-regulation of HO-1/ Ft genes, the expression of which quadruples or increases by half, respectively, compared with basal level. Preincubation of U937 myelomonoblasts with deferoxamine, iron chelator, results in doubling of their “TF+AA” resistance. However, the use of iron-containing TF analogs leads to its doubled cytotoxicity. Conclusion. In leukemia cell line U937 with constitutively active НО-1/Ft the heme-dependent activation of it does not considerably contribute to protection of cells from “TF+AA” toxicity. The system “TF+AA” is НО-1 and Ft expression inducer in U937 myelomonoblasts. Cytotoxic mechanism of “TF+AA” involves intracellular pool of “labile” non-heme iron, the level of which affects the drug sensibility of leukemia cells.

Heme Oxygenase-1/Ferritin in Protection of Leukemia Cells from Oxidative Stress Induced by Catalytic System “Teraphtal + Ascorbic Acid”