MDR1 gene expression in lung cancer.

The MDR1 gene (also known as PGY1) is frequently overexpressed in multidrug-resistant cell lines. We investigated the role of MDR1 gene expression in lung cancer by performing RNA slot blot analysis in samples from a panel of 24 lung cancers, 10 corresponding nontumorous lung tissues, and 67 tumor cell lines of several histologic types. Almost all of the tumors, nontumorous lung tissues, and cell lines expressed low levels of MDR1 RNA. Relatively higher levels were found in only one type of lung cancer, a subgroup of non-small cell lung cancers expressing neuroendocrine markers. No evidence of MDR1 gene amplification or rearrangements was detected. We found no correlation between MDR1 gene expression in cell lines and (a) in vitro chemosensitivity of the cells, (b) prior therapy status of the patients, or (c) clinical response to therapy. We conclude that the clinical multidrug resistance of many lung cancers cannot be explained solely on the basis of expression of the MDR1 gene.