Extensive associative gene expression data has been developed showing links between the expression of key members of the ABC family of proteins and resistance to many of the most commonly used anti-cancer chemotherapeutic agents. Current methods to analyze the direct functional consequence of the expression of the multiple drug resistance (MDR) proteins has been hampered by the lack of specificity of drug inhibitors, and the probable overlapping functional effect of these proteins when tumor cells develop MDR. The Laboratory of Cell Biology, CCR has recently identified a compound that appears to specifically be cytotoxic to cells over expressing MDR-1 (ABCB1). Using fully characterized siRNAs corresponding to ABCB1 we have now shown that MDR-1 expression does modulate the sensitivity of cells to this compound. This work has now been published. We have also been involved in a study conducted by Drs. Calcagno and Ambudkar (LCB, CCR, NCI) investigating the role of ABCG2 in drug resistance. A manuscript describing this work has been submitted.