engleski

Differentiation of leukemia cell induced by combination of ATRA and rapamycin

Acute promyelocytic leukemia, AML-M3 in FAB classification, is characterized by translocation t(15:17). It results in PML-RARalpha fusion protein and inhibition of differentiation. All-trans retinoic acid (ATRA) relieves the differentiation blockade and this is an unprecented example of differentiative therapy of leukemia. Despite its success in induction of remission, many patients have relapses and develop resistance to ATRA. Rapamycin, an inhibitor of mTOR kinase, has been recently suggested in therapy of hematologic malignancies. The aim of this study is to test for the possible enhancing effect of rapamycin in ATRA-mediated differentiation of two leukemia cell lines. NB4 is a typical AML-M3 cell line with t(15:17) while HL-60 is an AML-M2 cell line that lacks t(15:17) but is responsive to ATRA. HL-60 and NB4 cells were incubated with ATRA, rapamycin and their combination. At the end of incubation, an aliquot of cells were stained with propidium iodide and the rest of the sample was labeled by FITC-conjugated antibodies to CD11b (marker of differentiation) or isotypic control. The expression of DNA content and CD11b were determined by flow cytometry. As expected, ATRA induced a significant increase in the expression of CD11b in both leukemia cell lines. Rapamycin alone had no significant effects on the expression of CD11b in control cells. However, the level of CD11b in cells treated with combination of rapamycin and ATRA was significantly higher than the level in cells treated with ATRA alone. In conclusion, mTOR inhibitor rapamycin enhances differentiation of HL-60 and NB4 leukemia cell lines induced by ATRA.

leukemia; ATRA; rapamycin

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