Regulation of Multidrug Resistance with Antisense DNA

The ability of tumor cells to become resistant to a variety of chemotherapeutic agents is a major unsolved problem in clinical oncology. Research in this area has provided strong evidence that the overexpression of a single gene (MDR1), which encodes a membrane-bound glycoprotein, contributes to the resistance of a large proportion of drug-resistant tumors present in the clinic. This glycoprotein (Pgp) actively transports a variety of chemotherapeu- tic agents out of the cell; thereby, this activity conveys resistance. We will regulate the expression of the MDR1 gene using antisense oligodeoxynucleotides (later phosphorothioates) targeted to MDR1 mRNA. We will initially employ a transgenic cell system wherein the cloned human MDR1 gene is overexpressed in NIH3T3 cells. Restora- tion of drug sensitivity in these cells provides a rapid and effective screen for specific inhibitors of MDR1 gene expression and the gene product. We will confirm the effectiveness of anti sense sequences identified using this screen by characterizing their effects on Pgp activity at a functional and molecular level. Lastly, we will determine the ability of antisense sequences to sensitize human tumor cells resistant to chemotherapeutic agents. The results of these studies will contribute to the development of new treatment modalities effective in overcoming multidrug resistance in human cancer.