In this study, we combine taxol chemotherapy and miR-21 inhibitor treatment via polyamidoamine (PAMAM) dendrimers vector to evaluate the effects of combination therapy on suppression of breast cancer cells. The 50% inhibitory concentration (IC50) values for taxol were significantly decreased to a greater extent in the cells transfected with miR-21 inhibitor compared with cells treated with taxol alone. Taxol treatment also increased the percentage of apoptotic breast cancer cells in miR-21 inhibitor transfected cells compared with control cells. Furthermore, treatment of the miR-21 inhibitor-transfected cells with the anti-cancer drugs taxol resulted in significantly reduced cell viability and invasiveness compared with control cells. These results indicated that the miR-21 plays an import…