色胺酮在抗藥性乳癌細胞株MCF-7/adr抑制多重抗藥性之機制

Abstract

Development of agents to overcome multidrug resistance (MDR) is important in cancer chemotherapy. MDR arises from transporter and non-transporter based mechanisms during cancer chemotherapy. Transporter-based MDR mechanisms are mainly caused by the transport proteins of ATP-binding cassette (ABC) family. Overexpression of glutathione S-transferase π (GSTπ) and underexpression of Topoisomerase II (Topo II) are associated with multidrug resistance (MDR) phenotype through non-transporter pathway. Up to date, few chemicals have been reported to down-regulate MDR1 gene expression. I evaluated the effect of tryptanthrin on P-glycoprotein (P-gp) mediated MDR in a breast cancer cell line MCF-7. When treated with doxorubicin, tryptanthrin at 10-6M could enhance cytotoxicity of doxorubicin leading to a 6.2-fold decrease in IC50, in MCF-7/adr cells. Tryptanthrin at 10-6M increased intracellular rhodamine 123 accumulation by 2 folds in MCF-7/adr cells, compared with the control. Using real-time PCR assay, tryptanthrin could depress overexpression of MDR1 gene. I observed reduction of P-gp protein in parallel with decreases in mRNA in MCF-7/adr cells treated with tryptanthrin. Tryptanthrin suppressed the activity of MDR1 gene promoter. Tryptanthrin also enhanced interaction of the nuclear proteins with the negatively regulatory CAAT region of MDR1 gene promoter in MCF-7/adr. It might result in suppression of MDR1 gene. In addition, tryptanthrin decreased the amount of mutant p53 protein with decreasing mutant p53 protein stability. It might contribute to negative regulation of MDR1 gene. In terms of non-transporter pathway, tryptanthrin down-regulated GSTπ expression and reduced GSTπ protein and glutathione-S transferase activity, but had no effect on Topo II expression. Less production of GSTπ decomposed the protein-protein interactions of GSTπ and c-jun NH2-terminal kinase (JNK). The resulting free form JNK underwent phosphorylation upon elevated intracellular doxorubicin accumulation and subsequently activated JNK-mediated apoptosis. Tryptanthrin reverses MDR partly via modulating GSTπ-related pathway, a non-transporter pathway, in MCF-7/adr cells. In conclusion, tryptanthrin exhibits MDR reversing effect by down-regulation of MDR1 gene and inhibition of GSTπ expression in conjuction with release of free JNK for activation of JNK/c-jun pathway. Results implicate that tryptanthrin may be a potential chemo-adjuvant agent, exhibiting MDR-reversing activity via transporter and non-transporter pathways.