On mechanisms of drug resistance in acute myeloid leukemia

Abstract: In this thesis focus has been to increase the knowledge and understanding of some of the mechanisms responsible for drug resistance in acute myeloid leukemia, as well as identify possibilities to predict drug resistance at diagnosis.We have studied the intracellular behavior of cytostatic drugs and their main metabolites (paper I) and the cellular response to cytostatic drugs (paper III). A new flow cytometry in vitro chemosensitivity assay was developed, to enable identification of viable myeloid cells and determination of drug sensitivity (paper II). Finally, possible new markers involved in drug resistance were investigated (paper IV).In conclusion we found that idarubicin and daunorubicin are equally toxic at the same intracellular concentrations. The contribution of the main metabolites to the cytotoxic effects of idarubicin and daunorubicin, in both drug sensitive and drug resistant human myeloid leukemia cells, is low. It is most likely the pharmacokinetic properties of idarubicin and daunorubicin that confer their main cytotoxic effect. With the new flow cytometry chemosensitivity assay we selectively identified viable CD13/CD33 expressing myeloid cells and found that the cytotoxicity results correlated to clinical parameters, such as secondary AML and resistant disease. Short-term exposure of leukemia cell lines with different levels of drug resistance to ara-C revealed that Pgp mRNA and protein ex-pression levels, as well as GST? mRNA levels, were rapidly up-regulated. Clinically, this up-regulation may be of importance for the sequential scheduling of daunorubicin and ara-C during the induction treatment of AML. CRIM1 hasnever been studied in the context of drug resistance before. We show for the first time that baseline expression of CRIM1 mRNA is much higher in drug resistant leukemia cells compared to drug sensitive cells. We also found a co-variance between CRIM1 and Pgp mRNA expression levels in leukemia cell lines with different levels of drug resistance, suggesting that CRIM1 may be useful as a marker of drug resistance.