Abstract 3492: γ-secretase inhibitor PF-03084014 diminishes the tumor-initiating cells and demonstrates synergy with docetaxel in breast cancer xenograft models

Abstract

Abstract Notch signaling is known to be a survival pathway for tumor-initiating cells. In this report, we demonstrate that the γ-secretase inhibitor PF-03084014 significantly enhances the antitumor activity of docetaxel in multiple xenograft models of triple-negative breast cancer. Mechanistic evaluation revealed that PF-03084014 perturbs the Notch signaling pathway and suppresses the function of tumor initiating cells (TIC). In MDA-MB-231Luc model, treatment of docetaxel led to a significant increase of CD133+/CD44+ and ALDH+ subpopulations by FACS analysis. In combination with PF-03084014, these two unique cell subpopulations were significantly diminished. Correspondingly, the functional analyses by tumor re-implant and mammosphere-forming efficiency assays revealed that docetaxel-therapy promoted the tumor initiating capability of the remaining cells, in which an increased stem cell property and Notch pathway activation were observed through gene signature changes. In contrast, PF-03084014 co-treatment with docetaxel substantially hampered the self-renewal ability of these cells. Notch target gene analysis demonstrated the biological relevance of PF-03084014-induced activity. To characterize the function of CD133+/CD44+ subpopulation, MDA-MB-231Luc tumors were de-bulked by the treatment with docetaxel. Subsequently, the CD133+/CD44+ and CD133-/CD44- subpopulatons were isolated and re-implanted in SCID-bg mice using a limiting dilution approach. The results showed that CD133+/CD44+ cells gave rise to tumors with a 100 % take rate (10/10), whereas CD133-/CD44- cells were not tumorgenic (0/10). In addition, CD133+/CD44+ cells exhibited much higher tumorigenicity compared with the respective adherent parental cell line. PF-03084014 treatment caused a significant delay of CD133+/CD44+ tumor growth. The ability of PF-03084014 to suppress TICs was also observed in other breast cancer xenografts, including patient derived models. This data suggests that anti-TIC is one of the contributing mechanisms for the synergistic activities of PF-03084014 in combination with docetaxel. Our work provides potential therapeutic opportunities for PF-03084014 to improve conventional cytotoxic therapy by inhibiting Notch signaling in tumor-initiating cells and other bulk tumor cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3492. doi:1538-7445.AM2012-3492