Abstract
Quinacrine, a drug with antimalarial and anticancer activities that inhibits NF-κB and activates p53, has progressed into phase II clinical trials in cancer. To further elucidate its mechanism of action and identify pathways of drug resistance, we used an unbiased method for validation-based insertional mutagenesis to isolate a quinacrine-resistant cell line in which an inserted CMV promoter drives overexpression of the FER tyrosine kinase (FER). Overexpression of FER from a cDNA confers quinacrine resistance to several different types of cancer cell lines. We show that quinacrine kills cancer cells primarily by inhibiting the activation of NF-κB and that increased activation of NF-κB through FER overexpression mediates resistance. EGF activates NF-κB and stimulates phosphorylation of FER, EGF receptor (EGFR), and ERK p42/p44, and decreased expression of FER or inhibition of ERK phosphorylation inhibits the EGF-induced activation of NF-κB. FER binds to EGFR, and overexpression of FER in cells untreated with EGF increases this association, leading to increased phosphorylation of EGFR and ERK. We conclude that FER is on a pathway connecting EGFR to NF-κB activation and that this function is responsible for FER-dependent resistance to quinacrine.