The dose-limiting toxicity of chemotherapeutics, heterogeneity and drug resistance of cancer cells, and difficulties of targeted delivery to tumors all pose daunting challenges to effective cancer therapy. We report that small interfering RNA (siRNA) duplexes readily penetrate intact bacterially derived minicells previously shown to cause tumor stabilization and regression when packaged with chemotherapeutics. When targeted via antibodies to tumor-cell-surface receptors, minicells can specifically and sequentially deliver to tumor xenografts first siRNAs or short hairpin RNA (shRNA)–encoding plasmids to compromise drug resistance by knocking down a multidrug resistance protein. Subsequent administration of targeted minicells containing cytotoxic drugs eliminate formerly drug-resistant tumors. The two waves of treatment, involving minicells loaded with both types of payload, enable complete survival without toxicity in mice with tumor xenografts, while involving several thousandfold less drug, siRNA and antibody than needed for conventional systemic administration of cancer therapies.

via Sequential treatment of drug-resistant tumors with targeted minicells containing siRNA or a cytotoxic drug : Abstract : Nature Biotechnology.

Which is the formal way of describing a mechanism for delivering chemotherapy drugs by putting the drugs into minicells that target cancer cells. The treatment is in two parts; the first set of cell is prepared with siRNA or shRNA, these attach to the cancer cells and remove resistance to the chemotherapy drugs. Then a second set of cells are injected. These contain the chemotherapy drugs. The minicells again seek out the cancer cells, this time delivering the chemotherapy drug.

Apparently, in trials on mice with transplanted aggressive human tumours, the treatment resulted in reduced or halted tumour development and all the mice survived the treatment.