Abstract 5218: γ-secretase inhibitor PF-03084014 impairs Notch signaling and induces antiangiogenic and antitumor effects in breast cancer models
Authors: Zhang Cathy , Zhang Qin , Painter Cory , Yan Zhengming , Li Wendy , Buckman Dana , Zheng Xianxian , Kuszpit Kyle , Wong Anthony , Affolter Timothy , Lappin Patrick B. , Lee Nathan V. , Wei Ping , Qiu Ming , Randolph Sophia , Smeal Tod , Christensen James G. 
Published: February 2011

Abstract
PF-03084014, a small molecule γ-secretase inhibitor (GSI), has previously been shown to inhibit Notch signaling and demonstrated antitumor efficacy. The aim of this report is to gain insights into the mechanism PF-03084014-induced activity. The cell-based evaluation of PF-03084014 across 30 breast cancer (BC) cell lines indicated significant growth inhibition in only a subset of cell lines (3/30). In contrast, PF-03084014 demonstrated cell cycle arrest and induction of apoptosis by FACS analysis across the majority of a panel of T-acute lymphoblastic leukemia (T-ALL) cell lines. In vivo BrdU uptake of tumor and [18F]FLT-PET imaging studies demonstrated that PF-03084014 at an efficacious dose (120 mg/kg) caused cell cycle arrest in Sup T1 tumors but not in MDA-MB-231 xenografts, although PF-03084014 suppressed the expression of Notch target genes and tumor growth in both models. These results suggest that the primary mechanism(s) for PF-03084014-induced efficacy in T-ALL and BC models may be different, possibly because the tumor-host microenvironment in the BC model plays an important role during Notch signaling activation. IHC analysis in a panel of solid tumors demonstrated that Notch ligands including jagged 1, 2 and Dll4 were predominately expressed in the host vasculature and stromal cells. To investigate the potential antiangiogenic activity of PF-03084014, an in vitro endothelial cell/fibroblast co-culture tube formation assay was utilized. PF-03084014 disrupted the multicellular lumen-like structures at 100 nM, indicating defective differentiation of endothelial cells in early stage angiogenesis. Ultrasound imaging was utilized to further investigate the antiangiogenic properties of PF-03084014 including both the quantitative measurement of the total tumor vessel volume using 3-D scanning methods and an assessment tumor blood vessel function by measuring blood flow after iv injection of microbubble contrast agents. When MDA-MB-231 tumor bearing mice were administered with an efficacious dose of PF-03084014 consecutively for 4 days, ultrasound imaging revealed a significant (p&lt; 0.05) decrease of total tumor vessel volume and function compared to the vehicle treatment. A subsequent FITC-lectin vascular perfusion assay was performed to confirm the reduction in functional microvasculature by PF-03084014. In addition to the antiangiogenic effect, we also observed treatment-induced caspase 3 activation and Ki67 suppression in the MDA-MB-231 tumor model (2 days after treatment), suggest the GSI also induces apoptosis and cytoreductive activity. Collectively, our data provide insights that activation of Notch signaling requires the interaction of tumor cells with their host environment in solid tumors, and impairing Notch signaling by PF-03084014 results in significant antitumor efficacy in the breast cancer xenografts.
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 5218.