Expression of the multidrug resistance gene in human tumors.

The expression of MDR1 gene was investigated in human solid tumors with respect to adriamycin resistance. Forty fresh human surgical specimens were analyzed by RNA dot blot assay for their expression of the human MDR1 gene and by immunohistological staining using a monoclonal antibody against P-glycoprotein (MDR1 gene product). The MDR1 mRNA level was increased in 11 cases of 40 cancer patients, including three rectal cancers, two breast cancers, two gastric cancers, one colon cancer, one renal cell carcinoma, one gall bladder cancer and one malignant lymphoma of stomach. However, considerable variation of the MDR1 mRNA level was noted among cancers of a specific type. Immunohistochemical studies with the monoclonal antibody were shown to be positive in 18 tumors. In all tumors tested, the MDR1 mRNA level and the immunohistochemical analysis showed a significant correlation. However, two of five tumors which resisted adriamycin treatment were found to be negative in MDR1 transcript, but positive in immunohistological analysis. These results indicate that immunohistochemical analysis would be more sensitive for detecting P-glycoprotein-expression, and that resistance to adriamycin, being multifactorial, can be associated at least, in part with the increased amount of MDR1 gene product.