Enhanced antitumor activity of erlotinib in combination with quinacrine in EGFR WT and L858R/T790M mutant NSCLC.

e22153 Background: Non-small cell lung cancer (NSCLC) cell lines with epidermal growth factor receptor (EGFR) mutations are very sensitive to EGFR inhibitors such as erlotinib (E). However, the efficacy of E is limited in NSCLC cells harboring wild-type (WT) EGFR or second-site mutation EGFR-L858R/T790M. Various mechanisms of resistance have been described including activation of alternate signaling pathways through activation of MET, PI3K and NF-κB. Quinacrine (Q) is member of a group of small molecules called curaxins, which are 9-aminoacridine derivative and known to suppresses NF-κB activity by causing chromatin trapping of the FACT (facilitates chromatin transcription) complex. We evaluated utility of NF-κB inhibition by Q in overcoming the resistance to E in NSCLC cell lines Methods: E resistant NSCLC cell lines, A549 (EGFR WT), H1975 (EGFR-L858R/T790M) and H1993 (Met amplification) were used for drug synergy experiments. MTT assay, flow cytometry, Annexin V/PI staining, western blot and NF-κB luciferase assay were used for analyzing cell proliferation, cell cycle and NF-κB activity. Microarray analysis was performed using the Affymetrix Human Gene 2.0 ST Array. Results: In A549, H1975 and H1993 NSCLC cells, the combination of E and Q is highly synergistic, as quantified by the Chou-Talalay combination indices. Combination treatment significantly inhibited colony formation, induced cell cycle arrest and apoptosis as well as reduced xenograft tumor growth. Upon Q treatment, the FACT subunit SSRP1 disappeared from the soluble protein fraction, and NF-κB dependent luciferase activity was decreased. Knockdown of SSRP1 decreased cell viability and sensitized the cells to E treatment. Whole genome expression analysis of A549 and H1975 cells treated with E only, Q only, or both showed that Q or combination treatment significantly affected genes involved in cell cycle progression or nucleotide metabolism, and many of these genes contain binding sites for transcription factors that regulate SSRP1-enriched genes. Conclusions: We conclude that the combination of Q and E helps overcome E resistance in NSCLC, potentially by targeting FACT and suppressing cell cycle progression.