Study of multidrug resistance (mdr1) gene in non-small-cell lung cancer.

Non-small-cell lung cancer (NSCLC) is one of the tumors that shows intrinsic drug resistance to various chemotherapeutic agents. We investigated a possible role of the multidrug resistance (mdr1) gene amplification using a DNA slot blot analysis in 23 untreated non-small-cell lung cancer tissues and 14 corresponding adjacent normal lung tissue samples. In all instances, whether tumors or adjacent normal tissue samples, DNA amplification was not detected except in 1 adenocarcinoma and 2 squamous cell carcinomas that had a low level of amplification of mdr1 gene. In addition, 6 untreated tumors and 7 normal tissue samples were examined for mdr1 RNA expression using RNA slot blot analysis. Only low levels of mdr1 expression were observed in all cases. We conclude that mechanisms other than mdr1 amplification or expression account for the intrisic drug resistance of non-small-cell lung cancers.