Abstract: The invention provides methods and compositions for modulating the sensitivity of cells to cytotoxic compounds and other active agents. In accordance with the invention, compositions are provided comprising combinations of ectophosphatase inhibitors and active agents. Active agents include antibiotics, fungicides, herbicides, insecticides, chemotherapeutic agents, and plant growth regulators. By increasing the efficacy of active agents, the invention allows use of compositions with lowered concentrations of active ingredients.

Abstract: The present invention relates to methods for modulating the resistance of cells to foreign compounds, i.e. drugs, antibiotics, etc by altering the ATP gradient across biological membranes. The altering of the ATP gradient across biological membranes is achieved through the manipulation of ecto-phosphatase activity and ABC transporter molecule activity which may be useful to confer herbicide resistance to plants, confer antibiotic resistance to bacteria, confer drug resistance to yeast cells, or to reduce resistance in cells to facilitate chemotherapeutic treatments, and to reduce resistance in bacteria and yeast. The present invention is also directed to the methods for identifying ecto-phosphatase inhibitors and uses thereof.