Study Of The Drugs On Overcoming Multidrug Resistance In Tumor Cells And Their Mechanisms

The multidrug resistance(MDR) in tumor cells often leads to failure of tumor chemotherapy as they overexpress the proteins on cell membrane,such as P-glycoprotein(P-gp) encoded by mdr-1 gene,which can pump out of antitumor drugs from the cells.In this dissertation,several novel natural products being investigated in our institute were selected to study their characteristics of overcoming MDR in human breast cancer doxorubicin-resistant MCF7/DOX cells.The effect of histone acetylation on mdr-1 gene and P-gp expression was also researched to further understand the mechanism of overcoming MDR in tumor cells.In the strategy of inhibiting MDR gene expression via epigenetic modification, histone deacetylase(HDAC) was selected to investigate how to overcome and regulate MDR by different kinds of HDAC inhibitors.The results showed that Nicotinamide(NAM) and Sirtinol,two SIRT1 deacetylase inhibitors,exhibited no cross resistance to MCF-7/DOX cells via inducing apoptosis.This kind of inhibitors can not reverse MDR in MCF-7/DOX cells but exhibited synergistic effect on MCF-7 sensitive cells.Further investigation discovered that P-gp expression in MCF-7 cells can be induced by both increase of SIRT1 expression caused by doxorubicin and increase of SIRT1 deacetylase activity caused by resveratrol.TSA and VAS,typeâ… andâ…¡HDAC inhibitors,also showed no cross resistance to MCF-7/DOX cells while the cells were more sensitive to TSA.Combined use of VAS,taxol and doxorubicin exhibited synergistic effect on MCF-7 cells but failure on MCF-7/DOX cells.TSA can induce both P-gp expression in MCF-7 cells and increase of P-gp expression in MCF-7/DOX cells.In the research on Kanglemycin C,we discovered that Kanglemycin C can inhibit tumor cell proliferation and induce apoptosis via mitochondrial pathway in different kinds of tumor cell lines.The apoptotic hallmarks of chromatin condensation and DNA fragmentation,and 74.4%,94.4%of Annexin V positive staining cells were observed after Kanglemycin C(1,2μg/ml) treatment for 24 h in human hepatoma HepG2 cells.In the undergoing apoptosis,robust increment of P53 expression, activation of caspase-3,-7,-9,cleavage of PARP,and the phosphorylation of P38 and JNK,were detected by immunoblotting.Moreover,G₂/M cycle arrest was detected in HepG2 cells after Kanglemycin C treatment.Further investigation revealed that obvious increase of reactive oxygen species and disruption of mitochondrial membrane potential are the early apoptotic events after different concentrations of Kanglemycin C treatment for 4h.Likewise,Kanglemycin C showed no cross resistance to MCF-7/DOX cells and induced MCF-7/DOX cell apoptosis,but lag of Caspase acivation and absence of MAPK signal pathway activation.In the study on natural product PBC,we found that PBC compounds and PBC-b monomer increased the accumulation of rhodamine123 in both MCF-7/DOX drug-resistant cells and HR-20 drug-resistant cells.Moreover,the synergistic effect of combined use of PBC and doxorubicin indicated the reversal activity of MDR. Interestingly,the effect of PBC compound was stronger than PBC-b monomer, suggesting that other components existed in PBC compounds can also reverse MDR.In conclusion,the results indicated:1.SIRT1 deacetylase inhibitors exhibited no cross resistance to MCF-7/DOX cells via inducing apoptosis.This kind of agents showed synergistic effect on MCF-7 sensitive cells and was worth while developing neotype antitumor drugs;2.The antitumor effect of Kanglemycin C was mediated by activation of mitochondrial apoptotic pathway in tumor cells.Likewise,Kanglemycin C exhibited no cross resistance to MCF-7/DOX drug-resistant cells by induction of apoptosis.In this study,the prospect was thoroughly displayed to develop drugs without cross-drug resistance for overcoming MDR.