Background and aims: Chemoresistance is a major problem limiting the utility of doxorubicin in the treatment for liver cancer. Liver cancer stem cells (LCSCs) are considered to play a key role in tumor initiation, propagation, recurrence and chemoresistance. It is well established that human ATP-binding cassette (ABC) transporter ABCB1 is expressed in most of liver cancer tissues whose level of expression is inversely related to the response of patients to doxorubicin chemotherapy. However, the association between ABCB1 and chemoresistance in LCSCs remains uncertain. We hypothesized that knockdown of ABCB1 could sensitize LCSCs to doxorubicin treatment.
Methods: LCSCs were enriched from liver cancer cells in non-adherent spheres. ABCB1 siRNA was employed to inhibit MDR1 expression in LCSCs. The knockdown of ABCB1 was verified at RNA and protein levels. The ability of siRNA to enhance intracellular accumulation of doxorubicin and chemosensitivity to doxorubicin was assessed by high performance liquid chromatography and tumorsphere formation assay with limiting dilution analysis respectively. Doxorubicin-induced cell apoptosis was determined by TUNEL assay.
Results: ABCB1 siRNA efficiently decreased the expression ABCB1 at both mRNA and protein levels. Knockdown of ABCB1 lead to increased intracellular concentration of doxorubicin and enhanced chemosensitivity to doxorubicin in LCSCs. Combination of siRNA and doxorubicin caused increased cell apoptosis.
Conclusion: These finding indicate that knockdown of ABCB1 may reverse the chemoresistance of LCSCs to doxorubicin, suggesting ABCB1 as a potential therapeutic target for liver cancer treatment.