Abstract 1298: Mechanisms of endothelial trophic support of genitourinary tumors

Abstract

Abstract Background: Classically, principal roles of the vascular endothelium have been considered to be support of oxygenation, nutrient delivery, waste product removal, and cellular trafficking. But the endothelium may also release paracrine signals to neighboring cells. Targeting such interactions could lower the threshold for sensitivity to conventional therapies, if pro-survival signals are blocked. We hypothesize that a subset of tumor cells are protected by endothelial-derived NF-kappa B (NF-KB)-mediated trophic signals that enhance tumor growth. Due to the confounding effects of circulating signals, it has been difficult to address these hypotheses using animal models. In contrast, in vitro models are limited by the requirement of primary endothelial cells (PECs) for serum and/or growth factors (GFs), complicating efforts to identify novel secreted factors. We employed a strategy to maintain PECs without serum by expressing the non-transforming adenoviral E4ORF1 gene. Under these conditions, E4ORF1-expressing (E4) PECs retain features of native tumor endothelium, including responsiveness to endothelial GFs and the ability to form functional vessels in vivo. Using solid tumor cell lines, including testicular germ cell tumor (GCT) and prostate cancer (PC) lines, we tested the ability of E4 PECs to support solid tumor progression. Methods: Constitutive expression of E4ORF1 in primary human umbilical vein endothelial cells (HUVECs) was achieved using lentivirus. Co-culture assays in serum-free media were used to test the effect of E4 PECs on cancer cell survival, proliferation and clonagenicity. Xenografts were performed by delivering cancer cells subcutaneously in the presence or absence of E4 PECs. Results: We first identified minimal media in which significant cancer cell proliferation was not observed in the absence of feeders. Under these conditions, we observed massive expansion of cell numbers for certain lines (e.g., 27×1) in the presence of E4 PECs (62.6+/-3.1 fold [mean+/-s.d.] for 27×1) vs. feeder-free control (2.2+/-0.1 fold) over 4 days. Changes in expression of stem cell-related genes in tumor cells during exposure to E4 PECs were examined to determine the frequency of stem-like cells in the culture. Results of co-inoculation studies using tumor cells in NOD-SCID mice will be discussed. Interventions to address the role of endothelial inside-out NF-KB signaling are on-going. Conclusions: Under stressful microenvironmental conditions, some but not all solid tumor cell lines require endothelial-derived growth and survival signals. Targeting these signals may lead to alternate strategies for eliminating residual tumor present after optimal therapy. 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 1298.