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Imatinib is a targeted selective inhibitor of chimaeric Bcr-Abl tyrosine kinase developed for effective therapy of chronic myelogenous leukemia (CML) and acute lymphocytic leukemia (ALL) patients. Unfortunately, evidence now exists to indicate that a portion of such patients treated with imatinib acquire resistance and subsequently relapse. To understand the heterogeneous basis of imatinib resistance, we have investigated the possible mechanism(s) via which hemin, a key regulator of hematopoiesis that is converted to heme intracellularly, renders CML cells less susceptible to imatinib. Hemin at 30‐90 M protected a substantial proportion (>40%) of human Bcr-Abl(+) CML cells (K-562 and KU-812) from imatinib-induced cell killing by increasing the imatinib IC50 value, reducing DNA damage, and promoting erythroid differentiation. RT-PCR assessment of RNA transcripts encoded by human GAPDH, G-globin, Bcr-Abl, HO-2, Hpr-6, CEBPa, Bcl-2a, Bcl-2b, and Nrf2 genes revealed that hemin selectively counteracted the repression of antiapoptotic Bcl-2a, Bcl-2b, and Nrf2 genes in imatinib-treated cells. These genes are markedly repressed by imatinib alone in human K-562 CML cells. Hemin, however, had no detectable effect on the expression of the Bcr-Abl gene. Moreover, inhibition of de novo heme biosynthesis by succinyl-acetone enhanced the killing effect of imatinib. These data clearly indicate that: (a) cellular heme resulted from de novo biosynthesis and hemin uptake alters the developmental stage of human Bcr-Abl(+) CML cells and their susceptibility to imatinib; (b) cellular heme counteracts the ability of imatinib to repress Bcl-2 and Nrf2 gene expression; and (c) inhibitors of de novo biosynthesis can be developed and combined with imatinib to enhance its antileukemic activity.
Formerly: Oncology Research Incorporating Anti-Cancer Drug Design Oncology Research Featuring Preclinical and Clincal Cancer Therapeutics publishes research of the highest quality that contributes to an understanding of cancer in areas of molecular biology, cell biology, biochemistry, biophysics, genetics, biology, endocrinology, and immunology, as well as studies on the mechanism of action of carcinogens and therapeutic agents, reports dealing with cancer prevention and epidemiology, and clinical trials delineating effective new therapeutic regimens.