Abstract P2-05-09: Vascular mimicry in metastatic breast cancer patients: Molecular insight to vascular mimicry using in vitro and in vivo models

Background : Vascular Mimicry (VM) is an endothelium-independent matrix-embedded, blood-perfusion phenomenon exhibited by highly plastic and aggressive tumor cells in patients with solid tumors including breast. VM is characterized by PAS + de novo formations of micro-vascular networks which are essentially CD31 - and CD34 - . VM is a micro-circulatory phenomenon which perfuses rapidly growing tumors, transporting fluid from leaky vessels and/or connects with the constituent endothelial-lined vasculature. One of the hallmarks of metastasis in BC is the heterogeneity observed between primary tumors and metastases (a among metastases) ( Marino etal., 2013 ). Recently a model of BC heterogeneity revealed VM as a driver of metastasis which in turn has been associated with disease heterogeneity ( Wagenblast etal., 2015 ). Aim : Since BC is an aggressive and heterogeneous disease and VM is associated with the aggressiveness / poor outcome in BC, we sought to understand the functional relationship of VM with metastasis. Method : Tumors from our BC patients and TMAs were stained for CD31/PAS and CD34/PAS to identify VM. Genomic and proteomic data from these patients were obtained from re-biopsied (after consultation) samples (IHC for ER, PR, and HER2; FFPE samples for genomic [Foundation Medicine] and proteomic [Theralink] analyses). Result : VM was identified in metastatic tumors from ER+ and TNBC patients as CD31 - /PAS + and CD34 - /PAS + structures in contrast to the CD31 + /PAS + and CD34 + /PAS + angiogenic compartment of the individual tumor(s). Metastatic tumors exhibiting VM were characterized by pathological features like metaplastic lesions, positive lympho-vascular invasion and were found to be poorly differentiated. Predominant genetic alterations in these patients included (1) PI3K-mTOR pathway genes, (2) p53 (R273P, D281V) , (3) BRCA1 E1683* (for TNBC), (4) MYC amplification , (5) aurora kinase, (6) CCND1 a CDK4 amplifications and (7) loss of CDH1 exons1-3. Amplifications of cell surface TKIs/ligands included EGFR, FGFR and several FGFs. Proteomic data indicated an overexpression/activation of HER family (HER1/HER2/HER3), mTOR activation (p∼S2448), MEK1/2 activation (p∼S217-221) and JAK2 activation. In order study VM, we standardized VM formation both in 2D and 3D configurations in multiple BC cell lines which exhibited VM at differing times. The earliest response was observed around 2-3 hours in BT20, Hs578t and MDA-MB231. By 24 hours BT474, BT474HerR, SUM149, DKAT, MDA-MB231BR, Hs578t and MDA-MB468 cells demonstrated 2D VM. The BT20 cell line showed the most pronounced 3D-VM at 24 hours while MDA-MB468 was least sensitive to VM. Typical cord formation in HUVEC cells stained with hematoxylin and PAS were used for comparison. Using 2D and 3D models of VM we demonstrated the involvement of PI3K and Wnt-beta-catenin pathways in VM. Considering the involvement of VM in mediating the aggressive/metastatic nature of TNBC, we also tested VM in in vivo xenograft models using brain metastasic specific MDA-MB231BR cells, results of which will be presented in the meeting. Significance : To our knowledge this is the first report to identify genetic alterations and proteomic changes associated with VM in metastatic BC. Citation Format: Dey N, Carlson JH, Lin X, Sun Y, Theel S, Krie A, Sulaiman RA, Williams C, De PK, Leyland-Jones BR. Vascular mimicry in metastatic breast cancer patients: Molecular insight to vascular mimicry using in vitro and in vivo models. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-05-09.