Reversal Effects Of Toosendanin On Doxorubicin-resistance Of Breast Cancer Cells And The Underlying Mechanisms

Multidrug resistance(MDR)is an important biological mechanism of tumor chemotherapy failure.Overexpression of P-glycoproein(P-gp)in tumor cells is one of the central causes of MDR.P-gp,an ATP-dependent drug transport membrane protein,is capable of reducing the effective drug concentrations in the cells through hydrolyzing ATP to pump the intracellular drugs out of the cells,resulting in a typical MDR phenotype of tumor cells.In recent years,the mechanisms and the reversal strategies of drug resistance have become the hotspot in research fields.In addition to P-gp overexpression,the relationship between MDR and cell signaling transduction has been becoming a new bright spot in the study of mechanisms and reversal strategies of MDR.PI3K/AKT signaling pathway is one of the important pathways in mammalian cells,which is involved in the regulation of several major physiological functions such as cell survival,proliferation and differentiation,as well as metabolism and angiogenesis.Recently,the relationship between PI3K/AKT signaling pathway and tumor growth,tumor cell multidrug resistance has been concerned.PI3K/AKT signaling pathway has been an important target for breast cancer therapy.It was reported that some small moleculars,which act as inhibitors of PI3K/AKT signaling pathway,have entered the clinical research stage as antitumor drugs.Thus this pathway is an important research target of breast cancer therapy.Adriamycin resistance is a huge obstacle to clinical breast cancer treatment.In this study,we found toosendanin(TSN),an extract of traditional Chinese medicine,was able to reverse the resistance of human breast cancer cells to doxorubicin successfully.MCR-7/ADM is a breast cancer cell line resistant to doxorubin,in which we found that combined treatment with non-toxic dosage of TSN and doxorubicin significantly reversed the resistance of MCF-7/ADM to doxorubicin.TSN treatment notably promoted the pro-apoptotic effects of doxorubicin to MCF-7/ADM.In order to explore the underlying mechanisms,we measured the concentration of doxorubicin in MCF-7/ADM and several other breast cancer cells using fluorescence spectrophotometry and high performance liquid chromatography after treatment with TSN,which showed increased accumulation of doxorubicin in the breast cancer cells,especially in the nuclei.Futher study showed that TSN obviously downregulated the protein expression of P-gp,while had no effect on mRNA level of MDR1.It is noteworthy that PI3K/AKT signaling pathway was over-activated in MCF-7/ADM cell lines,when TSN showed notable inhibitory effects on AKT phosphorylation.The role of TSN on PI3K/AKT pathway was associated with its selective downregulation effects on catalytic subunit(P1 10α and P110 β)of PI3K,while had no effect on P110 expression in normal cells,demonstrating that TSN was able to reverse drug resistance of cancer cells by selectively inhibiting PBK/AKT pathway.In conclusion,it is shown that TSN was able to reverse the tolerance of breast cancer cells to doxorubicin,which was associated with the effects of TSN on inhibiting the over-activation of PI3K in cancer cells and promoting the accumulation of doxorubicin in the nuclei of drug resistance cancer cells,thus it is worthy to further explore the strategy of combined usage of TSN and doxorubicin for breast cancer treatment.