['Breast cancer resistance protein (BCRP) was overexpressed in topotecan (TPT)-selected human ovarian cancer cell line A2780/TPT, strongly suggesting BCRP to be responsible for the drug-resistance of ovarian cancer. The current study was designed to investigate the reversal effect of BCRP antisense oligonucleotide (ASODN) on topotecan- resistant A2780/TPT cells.', 'The antisense-phosphorothioate oligonucleotide including the translation initiation site of BCRP mRNA was artificially synthesized, and the sense oligonucleotide (SODN) corresponding to the ASODN was also synthesized as control. Lipofect-2000 (LF) was used for the transfer of either ASODN or SODN into A2780/TPT cells. The changes of BCRP mRNA expression, intracellular fluorescence intensity of rhodamine and resistance index to topotecan of in vitro transfected A2780/TPT cells were detected respectively by reverse transcription-polymerase chain reaction (RT-PCR),flow cytometry (FCM),and methyl thiazolyl tetrazolium (MTT) assay.', 'The transfer of ASODN/LF into A2780/TPT cells resulted in:(1)a 59.42% reduction of BCRP mRNA level (P< 0.05); (2)an obviously increased intracellular rhodamine fluorescence intensity from 5.42 to 16.63(P< 0.05); (3)a decreased resistance index to topotecan from 25 to 5 indicating sensitivity to topotecan in A2780/TPT cells recovered, as compared with non-transfected cell. But after transfecting SODN, no significant change could be measured.'] Does [ Antisense oligonucleotide reverse topotecan-resistant ovarian cancer cells ]?