【Objective】 To seek the new strategy for treating drug resistant leukemia by searching and identifying drug resistance related microRNAs in childhood acute leukemia. 【Methods】 Three multidrug resistant leukemia cell line-K562/DOX were derived from K562 /WT by cultured with different concentration adriamycin (DOX). RNA from K562/WT and K562/DOXs were extracted

and the possible drug resistance related microRNAs were searched and identified by using miRNA microarray assay and Quantitative real-time PCR assay. Bone-marrow samples of childhood acute leukemia were collected at three timepoints: before treatment

complete remission

or early relapse after treatment. The expression of selected microRNAs were detected by RT-PCR assay. 【Results】 1. The expression of miR-20a

miR-188-3p

and miR-214 were up-regulated

while miR-331-5p

miR-338-5p

miR-27a

miR-15a

and miR-455-3 were obviously down-regulated in K562/DOX cell lines. It is further confirmed by qRT-PCR

and an inverse relationship between the expression of P-gp and the expression of miR-331-5p and miR-27a. 2. Expression of miR-331-5p and miR-27a in the recurrent bone-marrow samples group (13 cases) were significantly lower than that of before treatment group (24 cases) and complete-remission group (11 cases)

demonstrating the presence of miR-331-5p and miR-27a low expression in relapse of childhood acute leukemia. 【Conclusions】 There were differential microRNAs expression in K562/DOX comparing with its wildtype. Low expression of miR-331-5p and miR-27a was found in multidrug resistant leukemia cell line and relapse of children acute leukemia bone-marrow sample

which may presumably partake the process of multidrug resistance in childhood acute leukemia.