Antiestrogen agents are commonly used to treat patients with estrogen receptor (ER)-positive breast cancer. Tamoxifen has been the mainstay of endocrine treatment for patients with early and advanced breast cancer for many years. Following tamoxifen treatment failure, however, there are still limited options for subsequent hormonal therapy. We discovered a novel compound, NK150460, that inhibits 17β-estradiol (E2)-dependent transcription without affecting binding of E2 to ER. Against our expectations, NK150460 inhibited growth of not only most ER-positive, but also some ER-negative breast cancer cell lines, while never inhibiting growth of non-breast cancer cell lines. Cell-based screening using a random shRNA library, identified aryl hydrocarbon receptor nuclear translocator (ARNT) as a key gene involved in NK150460's antitumor mechanism. siRNAs against not only ARNT but also its counterpart aryl hydrocarbon receptor (AhR) and their target protein, CYP1A1, dramatically abrogated NK150460's growth-inhibitory activity. This suggests that the molecular cascade of AhR/ARNT plays an essential role in NK150460's antitumor mechanism. Expression of ERα was decreased by NK150460 treatment, and this was inhibited by an AhR antagonist. Unlike two other AhR agonists now undergoing clinical developmental stage, NK150460 did not induce histone H2AX phosphorylation or p53 expression, suggesting that it did not induce a DNA damage response in treated cells. Cell lines expressing epithelial markers were more sensitive to NK150460 than mesenchymal marker-expressing cells. These data indicate that NK150460 is a novel AhR agonist with selective antitumor activity against breast cancer cell lines, and its features differ from those of the other two AhR agonists.

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Background: Standard second-line chemotherapy against advanced non-small-cell lung cancer (NSCLC) is a single agent such as docetaxel, pemetrexed, or erlotinib (Erl). We recently reported that the combination of amrubicin (AMR) and Erl was clinically safe and effective for previously treated NSCLC patients. The purpose of this research is to confirm the experimental effectiveness of the combination and to investigate mechanism of the action. Methods: We perform to evaluate the NSCLC cell lines proliferation inhibition by using XTT assay and to make two-dimension isobolograms for assessment of the combination effect. Flowcytemetry analysis (FACS) and Western blot analysis (WB) is also done in vitro. In vivo growth inhibition assay using subcutaneous model on SCID mice is performed. In addition, we measure intracellular concentration of amrubicinol(AMR-OH) which is converted as active metabolite from AMR in both cells treated with AMR alone and the combination. Results: The combination of AMR and Erl had significant synergistic effect on EGFR wild type NSCLC cell line A549, while additive effect on EGFR mutant cell line PC-9. Sub G0-G1 population on FACS was significantly increased in A549 cells treated with combination. The combination activated apoptosis related proteins in WB. The strong growth inhibition of subcutaneous tumors on SCID mice was observed in the combination cohort. Intracellular concentration of AMR-OH was significantly increased in the combination than in AMR monotherapy. Conclusion: The combination of AMR and Erl is synergistically induced apoptosis and growth inhibition on A549 cells via increasing intracellular concentration of AMR-OH. This combination may be a promising therapeutic option against advanced NSCLC with wild type EGFR. Citation Format: Sakiko Otani, Jiichiro Sasaki, Kuniko Masuda, Kazuya Okamoto, Akiko Namubu, Toshihide Matsumoto, Masumi Tanaka, Mikiko Ishihara, Yoshiro Nakahara, Tomoya Fukui, Satoshi Igawa, Noriyuki Masuda. Synergistic anti-tumor effect of the combination of amrubicin and erlotinib in non-small cell lung cancer with wild type EGFR. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2284.