Zur Resistenzentwicklung von Zellen der chronischen myeloischen Leukämie gegenüber Tyrosinkinase-Inhibitoren: Regulation und Funktion des ABC-Transporters A3

Abstract

Inhibition of the BCR-ABL tyrosine kinase activity by the specific tyrosine kinase inhibitors (TKI) imatinib, nilotinib and dasatinib leads to complete remission of the disease in most patients with chronic myeloid leukemia (CML). Cessation of CML treatment or the occurrence of resistance mediating bcr/abl gene mutations leads to relapse of the disease, initiated by a small fraction of cells that persisted during CML therapy. Those cells are CD34 positive leukemic progenitor cells with the phenotype of the "side population" and show high expression of the intracellular ABC transporter A3 (ABCA3) at the lysosomal membranes. The majority (>75 %) of imatinib in these cells was sequestrated in the lysosomal compartment. The aims of this work were the examination of the ABCA3 expression regulation and of the mechanism leading to ABCA3 mediated cellular export of TKI in leukemic cells. Overexpression and shRNA mediated suppression of ABCA3 showed that this transporter protects leukemic cells from the cytotoxic effects of imatinib, dasatinib and nilotinib. In those cells surviving the exposition to TKI, the expression of ABCA3 was highly increased in vivo and in vitro, associated with a strong increase of the transcription factor SALL4 that is able to bind to the ABCA3 promoter. Inhibition of ABCA3 or SALL4 by genetic manipulation or inhibiting substances indomethacin or rapamycin, but not gamma interferon disrupted the SALL4-dependent regulation of ABCA3 expression and restored the susceptibility of the leukemic cells towards TKI treatment. Further analysis showed that imatinib accumulated in microvesicles after lysosomal sequestration and was exported out of the cells. The results of this work may lead to the development of strategies to increase the amount of intracellular active TKI and thereby improve the treatment of CML patients.