Abstract C111: In vitro characterization of TAS-121, a novel, highly potent, and mutant-specific EGFR-TKI.

Abstract

Abstract Background: The active mutation of epidermal growth factor receptor (EGFR), L858R or deletion in exon19, are present in patients with NSCLC and responsive to EGFR tyrosine kinase inhibitors such as gefitinib and erlotinib. Over time, most tumors develop resistance to these EGFR inhibitors by the acquiring of drug-resistant mutations including gatekeeper T790M mutation (more than 50% cases). Severe skin rash and diarrhea caused by wild-type EGFR (wtEGFR) inhibition limit EGFR TKI treatment. Therefore targeting mutant EGFR (mtEGFR) but not wtEGFR represents an attractive therapeutic strategy. In this report, we identify a small molecule EGFR inhibitor, TAS-121, that targets mtEGFR but not wtEGFR and its biological characterization in vitro. Methods: In vitro enzyme inhibition activity of TAS-121 for EGFR and its mutants was determined by using purified EGFRs and peptide substrates. Cellular phosphorylation of EGFR was assayed by immunoblot analysis. For growth inhibition assay, cells were treated with TAS-121 for 3 days, and living cells were determined by using CellTiter GloTM which measures cellular ATP. Apoptosis assay was conducted by using Caspase-GloTM and Cell Counting Kit. Results: TAS-121 was found to be a more potent mutant selective EGFR-TKI based on bioavailability characteristics compared to our proto-type compound, TAS-2913. TAS-121 inhibits kinase activity of EGFR mutants harboring T790M in a sub-nano molar range and much more potently than that of wtEGFR. TAS-121 inhibits auto-phosphorylation of EGFR and intercellular signaling pathways in NCI-H1975 (EGFR T790M / L858R) and HCC827 (EGFR del E746-A750). In a cell proliferation assay, TAS-121 also suppresses growth of NCI-H1975 and HCC827 more potently than that of a normal cell which grows in an EGF-dependent manner. Therefore, the wtEGFR / mtEGFR inhibition ratio of TAS-121 appears to be higher than those of other EGFR TKIs. Furthermore, TAS-121 induces apoptosis in NCI-H1975 but erlotinib could not. Conclusion: These results suggest that TAS-121, a potent mutant-selective EGFR inhibitor, may represent a new therapeutic strategy in the treatment of NSCLC resistant to currently available EGFR/TKIs. Further pre-clinical evaluations and development are ongoing. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C111. Citation Format: Kimihiro Ito, Kazutaka Miyadera, Yoshimi Aoyagi, Masanori Kato, Kazuhiko Yonekura, Yoshikazu Iwasawa, Teruhiro Utsugi. In vitro characterization of TAS-121, a novel, highly potent, and mutant-specific EGFR-TKI. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C111.