Hypersensitivity to low level cytotoxic stress in mouse cells with high levels of DHFR gene amplification

Abstract

Low level cytotoxic stress greatly accelerates the loss of unstably amplified dihydrofolate reductase (dhfr) genes from methotrexate-resistant mouse cell lines. To understand this drug-induced loss of amplified genes, the highly methotrexate-resistant mouse R500 cell line was flow sorted into two subpopulations with higher and lower average dhfr gene dosage respectively. The subpopulation with higher levels of gene amplification was much more sensitive to low level cytotoxic stress as judged by both cloning efficiency and growth in the presence of low concentrations of cytotoxic drugs. These results suggest that high levels of gene amplification can confer hypersensitivity to cytotoxic stressors such as anticancer drugs.