This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Urlaub, G. Articles by Chasin, L. A. Search for Related Content PubMed PubMed Citation Articles by Urlaub, G. Articles by Chasin, L. A.

Selective Killing of Methotrexate-resistant Cells Carrying Amplified Dihydrofolate Reductase Genes¹

Department of Biological Sciences, Columbia University, New York, New York 10027

A method for the selective killing of methotrexate (MTX)-resistant cells has been developed. The selection is based on the incorporation of tritiated deoxyuridine into the DNA of MTX-resistant cells but not normal MTX-sensitive cells in the presence of the drug. A Chinese hamster ovary cell mutant that overproduces dihydrofolate reductase was used as an example of a MTX-resistant cell line. In this system, a 10,000-fold enrichment for wild-type MTX-sensitive cells could be achieved after 24 hr of exposure to the drug combination. This selection technique was applied to the isolation of MTX-sensitive segregants from hybrid cells formed between the MTX-resistant mutant and wild-type cells. The loss of MTX resistance and dihydrofolate reductase overproduction was always accompanied by the loss of a homogeneously staining region on chromosome 2 of the resistant parent that contains the amplified genes specifying this enzyme. While this region is always lost, other parts of chromosome 2 are almost always retained, suggesting that deletion rather than chromosome loss underlies marker segregation in this case. When the selection was applied to the resistant mutant itself, no MTX-sensitive revertants were obtained among 10⁵ cells screened, attesting to the stability of gene amplification in this clone. It is suggested that this combination of drugs may be useful for the elimination of MTX-resistant tumor cells that develop after MTX chemotherapy.

¹ Supported by Grant NIH-GM-22629 from the National Institute of General Medical Sciences.

² To whom requests for reprints should be addressed.

Received 10/ 3/80. Accepted 1/21/81.