OBJECTIVETo explore the role of X-linked inhibitor of apoptosis protein (XIAP) in the fibronectin (Fn)-adhesion mediated drug resistance of HL-60 cells.

METHODSCulture plates were coated with Fn and bovine serum albumin (BSA) (as control), respectively. Colorimetric CCK-8 assay was used to determine the effects of Fn on the cytotoxicity of DNR to HL-60 cells. Intracellular DNR accumulation was assayed with flow cytometry. Reverse transcription-PCR and Western blot were used to examine the mRNA expression and XIAP, bcl-2, MRP and mdr1 proteins, respectively. HL-60 cells were added to Fn coated Culture plates. The fully phosphorothioate antisense oligonucleotide (AS-ODNs) and the control ODNs of XIAP were delivered into HL-60 cells in the form of liposome-ODN complexes. IC(50) was calculated by linear regression of survival percent versus drug concentration.

RESULTSHL-60 cells adhered to Fn-coated plates had a significant survival advantage over those grown on BSA coated plates and in suspension when exposed to DNR, the IC(50) of Fn group being significantly higher than that of BSA group and suspension group (0.526 micromol/L vs 0.132 micromol/L, 0.123 micromol/L, respectively, P < 0.05). XIAP was up-regulated significantly in Fn group compared with BSA group and suspension group (P < 0.05), whereas there was no difference in the expressions of bcl-2, MRP and mdr1 among the three groups (P > 0.05). The intracellular concentration of DNR in Fn-adhered HL-60 cells was similar to that in BSA group and suspension group (P < 0.05). AS-ODNs of XIAP down-regulated the XIAP expression in Fn-adhered HL-60 cells. In addition, AS-ODNs sensitized HL-60 cells to the cytotoxic effects of DNR.

CONCLUSIONThe increased XIAP protein level contributes to the drug resistance induced by adhesion to Fn. AS-ODNs of XIAP might reverse the drug resistance.