After treatment with nanoparticles loaded with low concentrations of MDR1 siRNA, drug resistant osteosarcoma cell lines are re-sensitized to doxorubicin as demonstrated by the results of MTT assay and by a higher intracellular accumulation of the drug in the nucleus; demonstrating an uptake and distribution pattern that is comparable to drug sensitive cells. The gene discussed is ABCB1; the disease is osteosarcoma.