Abstract #4630: EZN-3920, an LNA antisense oligonucleotide RNA antagonist, down modulates HER3 expression and PI3K/Akt signaling pathway and enhances antiproliferative effect of Gefitinib in tumor cells

Introduction: The ErbB family consists of four tyrosine kinase receptors designated as ErbB1 (EGFR), HER2, HER3 and HER4. Inhibition of HER3 is likely to have antitumor effects since HER3 (1) heterodimerizes with HER2 and EGFR, (2) is a key link to the PI3K pro-survival signaling pathway, and (3) is activated in cells resistant to EGFR or HER2 targeting therapeutics. This study aimed at evaluating the activities of EZN3920, an HER3 locked nucleic acid (LNA) antisense oligonucleotide (ON), in various tumor cells. The regulation on downstream PI3K/Akt pathway and combination with EGFR inhibitor were also explored. Experimental Procedures: In vitro: the target knockdown, phospho-Akt inhibition, growth inhibition, apoptosis induction effects of EZN-3920 (Santaris Pharma) were evaluated by qRT-PCR, western blot analysis, MTS assay, caspase3/7 activity assay, respectively, in 14 cancer (prostate, liver, lung, colon, stomach, ovarian, breast, and epidermoid) cell lines two days after transfection with lipofectamine-2000. The combined antiproliferative effects of EZN3920 with gefitinib (EGFR inhibitor) were also examined in 8 ErbB inhibitor-sensitive and -insensitive tumor cell lines. In vivo: HER3 knockdown efficacy in liver and human tumors from 15PC-3 (prostate), A549 (lung) and N87 (gastric) nude mice xenograft models were examined after intravenous administration. Phospho-Akt (p-Akt) level was also monitored following the treatment. Scrambled LNA-ASONs and Molt-4 leukemia cell line served as negative controls. Results:In vitro, EZN3920 potently inhibited HER3 mRNA and protein levels in various tumor cells (IC50 Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 4630.