5-Bromotetrandrine enhances the sensitivity of doxorubicin-induced apoptosis in intrinsic resistant human hepatic cancer Bel7402 cells

5-Bromotetrandrine (BrTet) was shown to overcome multi-drug resistance (MDR) in vitro and in vivo by inhibiting the overexpression and efflux function of P-glycoprotein in our previous study. The purpose of the present study was to evaluate the effect of BrTet on the sensitivity of doxorubicin (Dox) induced apoptosis in intrinsic resistant human hepatic cancer Bel7402 cells. The cells were treated with non-toxic concentrations of BrTet (1 μM, 2 μM, 4 μM) or the positive control drug verapamil (Vrp) (10 μM) for 24 h followed by a low dose Dox (3 μM) for 24 h. The results showed that BrTet pretreatment followed by Dox led to typical apoptotic characters as indicated by morphologic changes, DNA fragmentation and changes in cell cycle, while the same dose of BrTet, Vrp and Dox alone did not induce apoptosis in Bel7402 cells. In addition, the pretreatment of BrTet or Vrp followed by Dox induced activation of caspase-3, release of cytochrome c and AIF from mitochondria into cytosol, loss of mitochondrial transmembrane potential (ΔΨm) and elevation of Bax/Bcl-2 ratio, with no effect on activation of caspase-8 and the expression of Fas/FasL. In conclusion, BrTet pretreatment enhanced the sensitivity of Dox to induce apoptosis by causing loss of ΔΨm and elevating the ratio of Bax/Bcl-2, eventually activated mitochondrial apoptotic pathway. These findings further support the potential of BrTet to be used in clinical trail of cancer treatment.