P-glycoprotein plays an important role in highly drug resistant cells. But its high expression cannot be acheived by chemotherapy. In order to study the effect of P-glycoprotein on clinical tumors

we established a low ADM resistant colon cancer cell line HR/ADM and determined the amplification and expression of mdr-1 gene. The GLC/ADM showed a resistant pattern similar to classical MDR and the transcription of mdr-1 gene determined by RT-PCR increased. The immunocytochemical analysis showed strong positive staining with monoclonal antibody. The gene amplification of mdr-1 was clearly demonstrated by southernblot. Our results suggested that moderate expression of P-glycoprotein might be enough for a high resistantpattern.