Search

Hydroxyurea (HU) is a nonalkylating antineoplastic agent used in the treatment of hematological malignancies. HU is a DNA replication stress inducer, and as such, it may induce a premature senescence‐like cell phenotype; however, its repercussion on bystander cell proliferation has not been revealed so far. Our results indicate that HU strongly inhibited peripheral blood mesenchymal stromal cells (PBMSC) proliferation by cell cycle arrest in S phase, and that, consequently, PBMSC acquire senescence‐related phenotypical changes. HU‐treated PBMSC display increased senescence‐associated β‐galactosidase levels and p16INK4 expression, as well as DNA damage response and genotoxic effects, evidenced by expression of γH2A.X and micronuclei. Moreover, HU‐induced PBMSC senescence is mediated by increased reactive oxygen species (ROS) levels, as demonstrated by the inhibition of senescence markers in the presence of ROS scavenger N‐acetylcysteine and NADPH oxidase inhibitor Apocynin. To determine the HU‐induced bystander effect, we used the JAK2V617F‐positive human erythroleukemia 92.1.7 (HEL) cells. Co‐culture with HU‐induced senescent PBMSC (HU‐S‐PBMSC) strongly inhibited bystander HEL cell proliferation, and this effect is mediated by both ROS and transforming growth factor (TGF)‐β expression. Besides induction of premature senescence, HU educates PBMSC toward an inhibitory phenotype of HEL cell proliferation. Finally, our study contributes to the understanding of the role of HU‐induced PBMSC senescence as a potential adjuvant in hematological malignancy therapies. [ABSTRACT FROM AUTHOR]

Hydroxyurea (HU) causes nitric oxide (NO) bioactivation, acting as both a NO donor and a stimulator of NO synthase (NOS). To examine whether HU effects are NO mediated by chemical degradation or enzymatic induction, we studied human and mouse erythroid cells during proliferation, apoptosis, and differentiation. The HU and NO donor demonstrated persisted versus temporary inhibition of erythroid cell growth during differentiation, as observed by γ- and β-globin gene expression. HU decreased the percentage of erythroleukemic K562 cells in the G2/M phase that was reversed by N-nitro l-arginine methyl ester hydrochloride (L-NAME). Besides activation of endothelial NOS, HU significantly increased apoptosis of K562 cells, again demonstrating NOS dependence. Administration of HU to mice significantly inhibited colony-forming unit-erythroid (CFU-E), mediated by NOS. Moreover, burst-forming-units-erythroid (BFU-E) and CFU-E ex vivo growth was inhibited by the administration of nitrate or nitrite to mice. Chronic in vivo NOS inhibition with L-NAME protected the bone marrow cellularity despite HU treatment of mice. NO metabolites and HU reduced the frequency of NOS-positive cells from CFU-E and BFU-E colonies that was reverted by NOS inhibition. HU regulation of the G2/M phase, apoptosis, differentiation, cellularity, and NOS immunoreactive cells was NOS dependent. Inhalation of NO therapy as well as strategies to increase endogenous NO production could replace or enhance HU activity. [ABSTRACT FROM AUTHOR]