Reversal of Doxorubicin Resistance in Human Breast Adenocarcinoma (MCF-7) Cells by Liposomal Monensin

Abstract

Abstract : The purpose of the present study was to overcome the doxorubicin resistance in human breast adenomacarcinom (MCF-7/dox) cells by the delivery of monensin in long-circulating (stealth) liposomes (SML). We have previously shown that SML could enhance the cytotoxicity of anticancer drugs. In order to increase the entrapment of monensin in SML we modified our previous method by using pH-gradient method. In the present study, we studied the potential of SML (prepared by pH-gradient method) for their effect on the in vitro cytotoxicity of anticancer drugs (doxorubicin, etoposide, paclitaxel) against both sensitive and resistant MCF-7 cells by crystal violet dye uptake assay. Further, the induction of apoptosis in resistant MCF-7 cells by the combination of doxorubicin with SML was also assessed by acridine orange staining and caspase-3 assay. Our results show that SML (10x10-8 M) enhance the in-vitro cytotoxicity of doxorubicin, etoposide and paclitaxel against sensitive MCF-7 cells by a factor of 5, 261 and 90, respectively. in case of resistant MCF-7 cells, there was 16.5, 5.6 and 2.8- fold potentiaiton of the cytotoxicity of doxorubicin, etoposide and paclitaxel, respectively by monensin liposomes (20x10-8 M). There was an enhanced apoptotic response (30%) in resistant MCF-7 cells treated with doxorubicin at 0.5 meg/nil (1/50 th 1C50 concentration for doxorubicin) with nontoxic concentration of monensin liposomes (20xl 0-8 M) in comparison to less than 10% apoptotic response observed in control, doxorubicin and liposomal monensin treated cells. The specific activity of caspase-3 in resistant MCF-7 cells treated with doxorubicin (2.5 meg/ml) and monensin liposomes (20x10-8 M) was two times more than that of the cells treated with doxorubicin alone. The results indicate that it is possible to overcome the doxorubicin resistance in MCF-7 cells with liposomal monensin, which may be further explored in-vivo in nude mice with human breast tumor xenografts.