Gefitinib (Iressa) is an orally active epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor that has been shown to be clinically effective in a subpopulation of non small cell lung cancer (NSCLC) patients. Despite initial responses to gefitinib in some NSCLC patients, cancer eventually progresses by unknown mechanisms of acquired resistance. We explored the use of the novel tumor suppressor FUS1 to enhance the chemotherapeutic potency of gefitinib and overcome gefitinib resistance in NSCLC. We found that reactivation of wild-type FUS1 by FUS1 nanoparticle-mediated gene transfer into FUS1-deficient and gefitinib-resistant NSCLC H1299, H322, H358, and H460 cells significantly (P < 0.001) sensitized their response to gefitinib treatment and synergistically induced apoptosis in vitro and in an H322 orthotopic lung cancer mouse model. To understand the mechanism of gefitinib-induced resistance, we established a gefitinib-resistant HCC827GR NSCLC cell line (IC50 = 16 μM) by selecting against gefitinib from the parental HCC827 cells that contain an activating deletion mutation of the EGFR gene and are extremely sensitive to gefitinib treatment (IC50 = 0.016 μM). We found no secondary mutations in the EGFR gene in the HCC827GR cells, but these cells registered a significantly elevated level of phosphorylated AKT protein. Combination treatment with FUS1 nanoparticles and gefitinib at a dose level of IC10 significantly re-sensitized the cells to gefitinib, as demonstrated by synergistically enhanced growth inhibition and apoptosis. FUS1 nanoparticle treatment alone or with gefitinib markedly inactivated EGFR and AKT, as demonstrated by decreased phosphorylation levels of both proteins on Western blots, compared with either agent alone. Cleavage of caspase-3, caspase-9, and PARP was also significantly induced by the combination of FUS1 and gefitinib in HCC872GR and other gefitinib-resistant NSCLC cells. Our results suggest that a combination treatment of FUS1 nanoparticles and gefitinib could overcome drug-induced resistance by simultaneously inactivating EGFR and the AKT signaling pathway and by facilitating apoptosis. This abstract is supported by grants from NCI (SPORE P50CA70907) and DOD (TARGET, DAMD17002-1-0706).

[Proc Amer Assoc Cancer Res, Volume 47, 2006]