Abstract 4041: Lipofection of the designed plasmid expressing microRNA-7 has antitumor effect in gefitinib-resistant lung adenocarcinoma in vivo

Abstract

Abstract Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) is strikingly effective in tumors harboring activating EGFR mutations since the tumor cells depend on “oncogene addiction” to EGFR signaling that is inhibited effectively by a change in the affinity of ATP and EGFR-TKI to ATP binding site of mutated EGFR. Unfortunately, approximately 50% of patients who responded to EGFR-TKI acquired the resistance to EGFR-TKI due to additional mutation T790M in EGFR. Since T790M mutation restores the affinity of ATP to the ATP binding site of mutated EGFR, the oncogene addiction by EGFR pathway is presumed to sustain in the gefitinib-resistant cells harboring T790M mutation. MicroRNA-7 (miR-7) is predicted to suppress EGFR expression by targeting three sites in the 3′-untranslated region (UTR) of EGFR mRNA in silico. It was proved to be a potential tumor suppressor in EGFR-TKI-resistant lung adenocarcinoma cells by targeting the 3′-UTR of EGFR mRNA (#1396: Annual AACR meeting, 2009). The object of this experiment is to elucidate whether the miR-7 is effective or not in vivo. We established gefitinib-resistant lung adenocarcinoma cell line (RPC-9) carrying a secondary mutation T790M (Cancer Res 67: 7807-14, 2007) from gefitinib-sensitive EGFR mutated (delE746-A750 in exon 19) PC-9 cell line. RPC-9 cells (2 × 106) were injected s.c. into the backs of the female athymic mice at 7 week of age. At 1 week after injection, the mice were randomly assigned into one of three groups (five mice per group) that received either 3 μg/body of miR-7 expressing plasmid, control plasmid or mock using cationic liposome by direct injection. Marked tumor regression was observed within 2 weeks, and 60% of xenograft tumors disappeared. The immunostaining of residual tumor showed the suppression of EGFR expression on the tumor cells. To our knowledge, this is the first report to show the dramatic effect of miR-7 against EGFR-TKI resistant lung cancer model in vivo.Tumor size after treatment with miR-7 Day 1Day 5Day 11Day 18miR-710094.9445.7914.62*Control100144.0103.3242.6*tumor size(%), *p=0.00253, tumor diminished macroscopically in miR-7 group(3/5) Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4041.