Abstract A06: The role of the epidermal growth factor receptor (EGFR) in primary tumor cell escape and development of an intravasation-sustaining vasculature

Metastasis of malignant cells is regarded as the leading cause of cancer-related deaths. Metastasis is a complex process whereby a subset or individual cancer cells disseminate from the primary tumor to distant/secondary sites. Intravasation, which is the entry of escaping tumor cells into the vasculature, is a critical and rate-limiting early event in the metastatic cascade. The complex process of intravasation is difficult to model and quantify in vivo, and therefore it remains the least studied step of the metastatic cascade. To study intravasation, we employ the chick embryo model involving grafting of human cancer cells on the chorioallantoic membrane (CAM), the highly vascularized tissue capable of supporting primary tumor growth and development of angiogenic vasculature. The epidermal growth factor receptor (EGFR) is known to play an important role in cancer progression and EGFR-induced signaling has been associated with tumor invasion and metastasis. In this study, we investigated the specific roles of EGFR in the early steps of tumor metastasis such as escape of cancer cells from the primary tumor and development of angiogenic vasculature, the two critical events required for tumor cell intravasation. For this purpose we employed the EGFR-overexpressing highly disseminating variant of human fibrosarcoma HT-1080 cell line, HT-hi/diss, in several independent in vivo CAM models. In the spontaneous metastasis model, siRNA silencing of EGFR significantly reduced the levels of HT-hi/diss intravasation, suggesting a role of EGFR overexpression in tumor cell escape and/or development of intravasation-sustaining vasculature. We have demonstrated that EGFR silencing prevented HT-hi/diss cell escape from the primary microtumors in the intramesodermal model, linking EGFR-regulated cell motility to tumor cell intravasation. We further investigated the role of EGFR in development of tumor-associated vasculature. By using our newly developed topical microtumor model, we have demonstrated that both control and EGFR-silenced cells attract comparable numbers of angiogenic vessels converging to developing primary microtumors. However, epifluorescence microscopy revealed dramatic difference in the microarchitecture of blood vessels within the two types of microtumors. Whereas control microtumors exhibited well-developed networks of intratumoral blood vessels with lumen diameter of 15-30 µm, EGFR-silenced microtumors contained only thin blood vessels with lumen diameter less than 15 µm. This lack of appropriately dilated intratumoral vasculature in EGFR-silenced tumors directly correlated with a significant decrease in vascular permeability concomitant with the suppression of tumor cell intravasation. These data highlight a specific aspect of EGFR functionality that is different from its well-established role in transcriptional regulation of genes required for tumor growth and suggest a novel mechanism whereby tumor cell EGFR regulates microenvironmental cues for induction, development, and functionality of an intravasation-sustaining vasculature. Citation Format: Petra Minder, Elena I. Deryugina, James P. Quigley. The role of the epidermal growth factor receptor (EGFR) in primary tumor cell escape and development of an intravasation-sustaining vasculature. [abstract]. In: Abstracts: AACR Special Conference on Cellular Heterogeneity in the Tumor Microenvironment; 2014 Feb 26-Mar 1; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2015;75(1 Suppl):Abstract nr A06. doi:10.1158/1538-7445.CHTME14-A06